SMTA announces AIMS Harsh Environment Electronics Symposium call for papers

EMSNow: "The SMTA and Auburn University are pleased to announce that the AIMS (Automotive, Industrial, Military and Space) Harsh Environment Electronics Symposium will be held October 5-6, 2009. Dr. John Evans, Conference Chairman and the program technical committee invite you to submit an abstract to participate in this exciting program. The symposium will once again focus on harsh environments with an emphasis on military and space."

Including lead-free implementation

IPC market research library available at no charge to members

EMSNow: "IPC members will have full access to the Executive Forum library through the IPC Members Only Web site, www.ipc.org/membersonly. The library includes market research reports, proceedings from the Forum's conferences and Supply Chain Tracker, a compendium of key current findings from the quarterly and monthly studies that IPC conducts for members."

NASA Aviation Lead-Free Approach

TEERM Presentation November 2008:

NASA plans for lead-free implementation. Mention ELFNET roadmap...

The 'other' mixed technology

Circuits Assembly: "Surface mount industry has used of Pb-free assembly processes for miniature components and is increasingly utilizing various of solder paste printing processes. 

Broadband printing includes meeting the solder Pastes need of larger and smaller components on the same board using existing or new material deposition techniques. Various approaches to printing include step stencil, overprint of selected components, two-step printing passes, and augmented stencil printing. The limitation of step stencils is the keep-out distance as outlined by IPC-7525 standard. Solder paste overprinting for through hole reflow include an oversized aperture for pads that need more solder paste relative to the rest of the board. In the two-step stencil process, the first printing step uses a thinner stencil to deliver paste for miniature components and the second step uses a thicker stencil with relief etch pockets on the contact side of the stencil for miniature components."

P. Mohanty, Speedline Technologies

Effects of small amounts of Ni/P/Ce element additions on the microstructure and prope

Scopus: "The purpose of this study is to investigate the effects of small amounts of Ni, P and Ce element additions on the microstructure and properties of Sn3.0Ag0.5Cu solder alloy."

The results indicate that adding trace amounts of Ni, P or Ce element has little influence on the melting temperature of Sn3.0Ag0.5Cu solder alloy. Adding Ni or Ce element cannot improve the wettability and anti-oxidization of the Sn3.0Ag0.5Cu solder alloy, but it can depress the interfacial intermetallic compounds growth due to the high temperature aging and then improves the shear strength of the solder joint. In addition, the P element addition not only significantly increases the maximum wetting force and decreases the wetting time of the solder, but also improves the anti-oxidation property of the Sn3.0Ag0.5Cu solder. At the same time, adding P element also increases the hot cracking sensitivity of the solder surface in the solidification. However, it is noted that adding Ni or Ce element can depress the formation of the hot carking. The reason may be related to the modification of the microstructure of the solder alloys due to trace amounts of Ce or Ni elements additions. The adding elements change the microstructure of Sn3.0Ag0.5Cu solder alloy. 

Benjing University of Technology, China

Effects of ZrO2 nanoparticles on the mechanical properties of Sn-Zn solder joints on Au/Ni/Cu pads

Scopus : "The shear strength of Sn-9Zn and Sn-9Zn-ZrO2 solder balls on electrodeposited Ni/Au BGA joints after multiple reflows was investigated by shear tests and microstructural observations."

ZrO2 nanoparticles in the solder balls improved the shear strength and the reliability of solder joints after multiple reflows significantly. They embedded in the solder matrix to obstruct the motion of dislocations by pinning and also pinned grain boundaries so as to improve the shear strength of the solder matrix. At the same time, due to the strong adsorption effect of Zn atoms, the ZrO2 nanoparticles absorbed Zn atoms on their surfaces so as to impede them from gathering on the surfaces of the Ni-Zn IMC layers to give excessive growth, and, as a result, this improved the reliability of solder joints significantly

Shen. J, City University of Hong Kong

EVS launches new Solder Dross Recovery Solutions

EMSNow: "The EVS7000 offers a capacity of 10 kg/20 lb, with the EVS 9000 providing up to 20 kg/44 lb. The EVS 9000 also has the ability for single operation de-drossing of even the largest wave soldering machines. Its large integrated hopper makes rapid transfer of dross both simpler and safer, and speeds de-drossing times by up to 75 percent. This provides a cleaner wave with less maintenance, less downtime and a reduction in shorts and bridging, as well as the potential to discontinue the use of messy wave oils and/or dross reduction powders.

The process uses heat and pressure inside a magnetized cylinder to separate and return pure solder into an ingot tray. The remainder of the material is automatically ejected down a sealed chute into a dross bucket. Hundreds of solder assays prove that the recovered pure solder is exactly the same specification as the solder in the WSM pot. This has been authenticated by the solder manufacturers and confirmed by the International Tin Research Institute."

IPC happy with proposed ROHS revisions, are you?

EDN: "The IPC this week sighed with relief in respect to the proposed ROHS revisions, saying 'there is finally good news on the environmental regulation front' and applauding the lack of additional banned substances.

Why? Well, these directives, as many won't admit, aren't always based on hard, scientific tests and results. Far from being based on whims, there was lack of adequate testing done as to long-term impact of removing the six targeted materials (lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls, and polybrominated-diphenyl ether) from electronics design when ROHS was first pushed upon the electronics supply chain in 2006. And, for an industry driven by fact and figure loving engineers, that can be hard to swallow, not to mention to design around."

SJ BIST (solder joint built-in-self-test)

Factiva: "This paper presents test results and specifications for SJ BIST (solder joint built-in-self-test), an innovative sensing method for detecting faults ill solder-joint networks that belong to the I/O ports of field programmable gate arrays (FPGAs), especially in ball grid array packages. 

It is well known that fractured solder joints typically maintain Sufficient electrical contact to operate correctly for long periods of time.'"

SJ BIST detects faults at least as low as 100 Omega with zero false alarms: minimum detectable fault period is one-half the period of the FPGA clock - guaranteed detection is two clock periods. SJ BIST correctly detects and reports instances of high-resistance with no false alarms: test results are shown in this paper," wrote N. Roth and colleagues.

Effect of crystallography anisotropy of β-tin grains on thermal fatigue properties of SAC alloys

Scopus: "One of the reasons Sn-3Ag-0.5Cu had longer thermal fatigue life than Sn-1 Ag-0.5Cu can be the number of the single crystal-like or the fine grain type microstructures in Sn-3Ag-0.5Cu were larger."

Mechanical properties versus temperature relation of individual phases in Sn-3.0Ag-0.5Cu lead-free solder alloy

Scopus: "The non-homogeneous Sn-3.0Ag-0.5Cu (SAC305) lead-free solder alloy consists of Sn-rich (β-Sn) and eutectic phases. The mechanical properties of these individual phases were demonstrated to be a function of the temperature. 

The nanoindentation methodology was utilized to examine the mechanical properties at 60 'C, 80'C, 110 'C, 130 'C, and 150 'C, respectively. It was found that for both Sn-rich phase and eutectic phase, the hardness and Young's modulus exhibited the dependence on the temperature. Moreover, the creep deformation which occurred at the dwell time of sustained loading was quite sensitive to the prescribed temperature."

The recrystallization of microelectronic lead-free solders

Scopus: "In Sn-2 mass%Ag-0.5 mass%Cu solder alloy, recrystallization was induced by thermal cycles and the homogenized effect of thermal aging promoted the vibration resistance."

Effects of rare earth Ce on microstructures, solderability of Sn-Ag-Cu and Sn-Cu-Ni solders as well as mecha

Scopus: "In order to improve the properties of Sn-3.8Ag-0.7Cu and Sn-0.5Cu-0.05Ni solders, 0-0.1 wt.% of rare earth Ce was added to the base alloys, and the microstructures were studied."

optimal Ce content is in the range of 0.05-0.07 wt.% for Sn-0.5Cu-0.05Ni-xCe solders. The results also indicate that the mechanical properties of soldered joints are improved with increasing Ce addition, with peak mechanical properties at Sn-3.8Ag-0.7Cu-0.03Ce and Sn-0.5Cu-0.05Ni-0.05Ce. The grain sizes of solder alloys are refined due to the addition of Ce, thus the mechanical properties of soldered joints are improved simultaneously.

Nanjing University of Aeronautics and Astronautics, China

Chine Electronics Technology Group Corporation, China

Harbin Welding Institute, China

Alloy design of Zn-Al-Cu solder for ultra high temperatures

Scopus: "Zn-based solders were developed for ultra high temperature applications with the alloying elements: (4-6) wt.% Al and (1-5) wt.% Cu. 

The solder was designed to have a liquidus temperature between 655 and 675 K. The Al content improved the spreadability and electrical resistivity, but the Cu content had insignificant influence on the characteristics. The alloying contents increased hardness and tensile strength with the α-η eutectic/eutectoid."

NVIDIA put faulty solder in new MacBook Pros

CrunchGear : "A very thorough article at the Inquirer, based on analysis of a new MacBook Pro teardown by parties who wish to remain anonymous, shows that the solder bumps used in at least their test MBP are in fact the infamous high-lead solder that overheated and cracked without fail. 

An NVIDIA spokesperson has stated that the 9600s in MBPs use the new eutectic solder, but the tests show otherwise. There are a number of explanations for the bad solder being in the new 9600s, but none of them are good for NVIDIA or Apple. There’s no way to tell if your MBP has the bad solder, but if it starts overheating and freaking out like crazy, be assured it isn’t your fault."

Reducing and Preventing Tin Corrosion Whiskers

SMT: "On the basis of these preliminary studies, a post-dip solution was developed to reduce or prevent corrosion attack and the growth of corrosion whiskers under JEDEC test conditions. Solderability improved significantly. 

It was discovered that the degree of improvement after treatment of the samples with anti-corrosion agent also improves according to the storage time and the increase in the corrosive test parameters in direct comparison with un-treated samples. Reproducible results were achieved. These results are of significance not only for the IC/leadframe industry, but also for the plug connector industry.

After treatment, the tin coatings showed no discoloration at the surface, after 24 hours in the pressure cooker test.

It was also proven that use of an anti-corrosion solution for protection of solder beads in BGA housings also allowed significant improvements in yield and contact resistance to be achieved.

*The anti-corrosion agent developed from these findings is Protectostan LF."

Atotech, Germany

Laser soldering using lead free solder

Scopus: "In an attempt to resolve some of the manufacturing issues presented to the industry, CSIRO Manufacturing and Infrastructure Technology (CMIT) conducted a project to examine the use of a 30W diode laser to manufacture some of the soldered joints currently made using the mass reflow techniques. 

Work was conducted on both traditional lead containing solder and the new environmentally friendly lead free containing solders. The advantages perceived by using lasers included low heat input processing, improved mechanical properties due to the reduced grain size, much thinner intermetallic layers, consistent and repeatable joints, and faster cycle time than with hand soldering. This results in a potentially superior joint, being stronger and more reliable, yet formed at competitive rates."

CSIRO, Australia

Japanese Inventors Develop Solder Deposition Method

Factiva: "The present invention provides a solder deposition method that includes the step of forming a dam around an electrode on a substrate, the step of applying a solder precipitating composition to the substrate, and the step of depositing solder on the surface of the electrode while heating the solder precipitating composition applied. 

This solder deposition method is suitable for forming large bumps at fine pitches. In particular, it is capable of depositing solder in a desired height precisely and easily, and yet preventing occurrence of voids.'

The patent has been assigned to Harima Chemicals Inc., Hyogo, Japan. The inventors were issued U.S. Patent No. 7,452,797 on Nov. 25."

Henkel launches breakthrough self-filleting die attach technology

EMSNow : "Further advancing the capabilities of modern die attach technology, Henkel has developed and made commercially available a line of new Ablestik brand die attach materials known as self-filleting die attach.

The new class of die attach products offers all of the benefits of traditional die attach pastes, but takes the adhesive technology further by incorporating a self-filleting mechanism, making it a viable and much less costly alternative to die attach films."

MicroFriction Stir Welding

PCB007: "Helen Goddin of TWI reviewed trends for joining in microelectronics, referring to case studies on wire bonding, flip chip and laser welding. A recent innovation, based on a technique developed by TWI, was micro-friction stir welding. This could be used to join traditionally difficult materials like aluminium. Potential applications in electronics and photonics included package sealing and interconnection."

Copper Dissolution: A New Industry Challenge

PCB007: "But a new lead-free soldering challenge called copper dissolution is now the 'Sword of Damocles' hanging over the heads of PCB fabricators, EMS companies and OEMs. Copper dissolution is the term for the reduction in copper thickness that occurs during HASL or soldering."

With traditional lead-containing solder, the reduction in copper thickness was constant at a level of 1.5 µm for each soldering or HASL process, and this was always covered by the normal tolerances applicable to PCB fabrication and assembly processes.

However, in lead-free soldering, the reduction in copper thickness is typically 3.5 µm for each HASL or soldering process--this has been confirmed by tests on many thousands of PCBs. During testing, it was also found that on 12 to 15% of the samples, the copper dissolution was 6.5 µm for each HASL or soldering process, and in certain instances (albeit less than 1%) the copper dissolution was 10 µm for each HASL or soldering process.

E.M. Monroe and co-authors describe advances in quality technology

Factiva: "We find that the importance of selecting an experimental design exceeds the importance usually given to the selection of sample size and censoring scheme, or to the choice of a test unit allocation strategy in the context of a reliability test case study. 

D-optimal-based designs provide good performance for acceleration model validation, especially when the testing feasibility region is asymmetric. D-optimal designs offer an eightfold reduction in sample size over legacy designs for a fixed precision. Alternatively, D-optimal designs yield a 3.5x increase in parameter estimate precision over legacy designs for a fixed sample size,' wrote E.M. Monroe and colleagues."

Control of interfacial reaction layers formed in Sn-3.5Ag-0.7Cu/electroless Ni-P solder joints

Scopus: "This study investigated a method for controlling the interfacial reaction between a Sn-3.5Ag-0.7Cu (wt.%) solder and an electroless nickel-immersion gold-plated Cu substrate through heat treatment. 

The interfacial reaction layer was controlled by heat treating of the electroless Ni-P plated layer. By applying a heat treatment, the thickness of the reaction layer (intermetallic compounds, P-rich Ni layer) was observed to be reduced. The formation of Ni2SnP, which significantly affects the mechanical reliability of solder joints, was suppressed."

Sungkyunkwan University, South Korea

White paper clarifies objections to proposed RoHS expansion

Dataweek: "The IPC has announced the release of a new white paper, ‘The electronic interconnection industry supply chain’s response to the Oko-Institut recommendations for proposed revisions to the RoHS directive’.

The white paper is the culmination of presentations made during an IPC workshop on 18 June in Brussels. Industry leaders, representing key segments of the electronics supply chain, came together at the workshop to detail industry concerns with the Oko-Institut report on the proposed expansion of RoHS substance restrictions."

Simulating damage mechanics of electromigration and thermomigration

Scopus: "Electromigration (EM) and thermomigration (TM) are processes of mass transport which are critical reliability issues for next generation nanoelectronics and power electronics. The purpose of this project is to develop a computational tool for simulating damage mechanics of EM and TM and their interaction. 

In this paper, a model for EM and TM processes is proposed and has been implemented in a general purpose finite-element code. The governing equations utilized for the model include mass conservation, force equilibrium, heat transfer and electricity conduction. A damage evolution model based on thermodynamics is introduced to evaluate the degradation in solder joints subjected to high current densities and high temperature gradients. The simulation results are compared with expe]rimental data to validate the model."

State University of New York at Buffalo, US

Alloying modification of Sn-Ag-Cu solders by manganese and titanium

Scopus: "Effects of Mn and Ti additives on the microstructure and solidification behavior of Sn-1.0Ag-0.5Cu alloys (SAC105), as well as mechanical properties, were investigated in this study. 

Results show that alloying of Mn and Ti resulted in dramatically reduced undercooling, coarse eutectic structure and extended volume fraction of proeutectic Sn of which the dendritic size was refined. Those thermal and microstructural changes might be ascribed to the formation of MnSn2 and Ti2Sn3 intermetallic compounds (IMCs) which appeared respectively in the Mn-doped and Ti-doped samples. Nanoindentation tests demonstrated that the heterogeneous IMCs produced by alloying were harder and stiffer than the inherent IMCs, Ag3Sn and Cu6Sn5. Worthy of notice is that the elastic modulus of SAC105 alloys decreased with only a minor alloying addition due to the shrunken eutectic regions and coarsened eutectic microconstituents. With a larger quantity of additives, an ascending elastic modulus could be obtained because of the strengthening effect by hard heterogeneous compounds"

National Dong Hwa University, Taiwan

Advanced Semiconductor Engineering, Taiwan

Indium Corporation, US

Effect of minor addition of Pb upon interfacial reactions and mechanical properties at Sn-3.0Ag-

Scopus: "Interfacial reactions and mechanical properties between the Cu and Pb-free solders, Sn-3.0Ag-0.5Cu and Sn-58Bi with addition of 0.1 to 1.0 wt.% Pb are investigated in this study."

Experimental results indicate that the higher Pb concentration in Sn-3.0Ag-0.5Cu or Sn-58Bi solders reduces the alloy liquidus temperature and increases the thickness of the intermetallic compound. Thicker intermetallic compounds reduce the mechanical strength of the solder joint.

Rosin-free wire solder

Dataweek: "Indium has adapted its solder paste technology for use in a cored wire solder to develop CW-501, a product that contains no rosin, a known allergen. CW-501 comes in a variety of alloys and wire diameters, and provides excellent wetting and solder spread with minimal smoking and low odour. It solders comparably to no-clean or RMA rosin-containing cored wires, and is compatible with Indium’s latest line of no-clean products, including wave fluxes and the award-winning Indium8.9."

Nihon Superior Envisages Doubling in Thai Sales of Lead-free Solder

Factiva: "Nihon Superior plans to double by 2010 the annual sales of lead-free solder at its Thai operations Nihon Superior (Thailand) Co., seizing upon a revival in popularity of its products, which are mainly made of tin, copper and nickel, since prices for precious metals like silver began to skyrocket.

The Osaka-based company intends to step up its marketing to Western-affiliated and Taiwanese-affiliated electronic manufacturing services companies in Thailand, since the EMS industry is active in the country. It also has established several local warehouses, weaving an efficient supply network that can quickly deliver products to customers within 12 hours.

'This is a golden opportunity to expand our business,' says Tsuyoshi Yamanaka, managing director of Nihon Superior (Thailand) Co. The Thai base, which chiefly supplies its parent company's silver-free SN100C lead-free solder to end-users in the country for electronics applications, reports that the market is once again positively rating its products amid the soaring prices for precious metals."

Lead free Test - ROHS resource for pb-free pcb

Lead free Test: "The creation of www.lead-freetest.com was to help customers with gathering lead-free /RoHS data, paper/articles, events, resources, etc. This website is a compilation of what is happening in lead-free in the industry and is a great resource for customers of all types. This valuable resource is available as a free service to our valued customers and to others with an interest in lead-free."

Heraeus Announces Two Appointments to Assembly Materials Business Unit

EMSNow: "Frank Murch and Roy Baumer have recently joined the Assembly Materials Business Unit of the Heraeus Contact Materials Division (CMD) located in West Conshohocken, PA. Murch has been appointed to the position of sales and marketing director, while Baumer has been selected to fill the position of operations manager. The appointments were announced by Erik Bergum, manager of the Assembly Materials Business Unit."

Research advances in nano-composite solders

Scopus: "Recently, nano-composite solders have been developed in the electronic packaging materials industry to improve the creep and thermo-mechanical fatigue resistance of solder joints to be used in service at high temperatures and under thermo-mechanical fatigue conditions. This paper reviews the driving force for the development of nano-composite solders in the electronic packaging industry and the research advances of the composite solders developed."

The rationale for the preparation of nano-composite solders are presented at first. Examples of two nano-composite solder fabrication methods, a mechanical mixing method and an in-situ method, are explained in detail. The achievements and enhancements in the nano-composite prepared solders are summarized. The difficulties and problems existing in the fabrication of nano-composite solders are discussed. Finally, a novel nano-structure composite solder, which attempts to solve the problems encountered in the fabrication of nano-composite solders, is introduced in detail. Guidelines for the development of nano-composite solders are then provided

City University of Hong Kong, China

Preparation of glue joints and bridges between Ag nanowires and their metallization. A possible method for na

Scopus: "Bridges between Ag nanowires and glue joints were made for the first time in water."

The method developed might provide a new means to join two metal nanowires

An investigation on wetting characteristics of solder particle for solderable electrically conductive adhesives (ECA)

Scopus: "A novel electrically conductive adhesives (ECAs) with solder particle have been developed."

The wetting characteristic of two solders on two kinds of metals were investigated using an optical microscope. It was found that developed resin material showed good fluxing capacity against Sn-Bi solder on Ni/Au and the wetting angles was about 24°.

Effects of isothermal aging on the microstructure and tensile behavior of Sn-3.0Ag-0.5Cu-0.2Co solder

Scopus: "Effects of isothermal aging on the microstructure and tensile behavior of Sn-3.0Ag-0.5Cu-0.2Co (SAC305-0.2Co) solder was explored, and compared with the standard Sn-3.0Ag-0.5Cu (SAC305) solder. The addition of Co resulted in the formation of CoSn2 phase in SAC305-0.2Co solder matrix."

After aging, the UTS of SAC305 was obviously decreased, whereas the elongation hardly changed. For the SAC305-0.2Co, the tensile behavior showed two trends: one was the decrease of the UTS, which was similar to that of SAC305; the other was the notable increase of elongation. The examination of the fracture surfaces indicated that isothermal aging could alter the fracture pattern of SAC305-0.2Co solder from brittle to ductile.

Osaka University, Japan

Tianjin University, China

Micromechanical responses of Sn-3.5Ag-xCo lead-free solders by nanoindentation

Scopus: "The lead-free casting solders Sn-3.5Ag-xCo (x = 0, 0.1, 0.5 and 1.0 mass%, respectively) were subjected to isothermal aging at 150'C for 0, 1008 and 2016 h, respectively. The nanoindentation methodology was employed herein to assess the mechanical properties."

Basically, there is no remarkable tendency of the variation of Young's modulus after aging, while to some extent, the hardness of the alloys drops. The strain rate sensitivity index value continues to decrease with the prolonged aging time. The solder grain growth and the coarsening of the intermetallics namely, Ag3Sn and CoSn 2, are responsible for the mechanical evolution of the alloys. The 1.0% (mass%) Co additive improved the hardness of the solder alloy, and caused the decrease of the strain rate sensitivity value.

Osaka University, Japan

Effect of laser parameter on the bond characteristics of Sn-3.5%Ag solder ball

Scopus: "Pulsed Nd;YAG laser was applied to investigate the bond characteristics of Sn-3.5wt%Ag (hereafter, Sn-3.5Ag) solder ball."

The IMC (Intermetallic Compound) of Ag 3Sn in the solder changed from acicular to rod type with increasing laser pulses. Ni3Sn4 was produced between the solder and the UBM, and its thickness increased from 0.65 to 1.80μm with increasing number of pulse from 2 to 4. These are thinner than those of general air reflow. Shear strength of the laser soldered ball with output energy of 1 J showed 652.3 gf, and it was similar value compared to the result from hot plate soldering, 654.5 gf

Interfacial reaction of electroless Ni-P plating with Sn-3.5Ag (-Co) solder

Scopus: "The reaction between Sn-Ag (-Co) solder and electroless Ni-P plating was investigated in order to clarify the effect of the addition of Co to Sn-Ag solder on the formation of intermetallic compound (IMC) at the interface and the joint strength at the interface."

The results show that there is little effect of the addition of Co to the Sn-Ag solder on the IMC formation and the thickness of the IMC at the interface. For the pull strength of the solder bump joint, the addition of Co to the solder didn't strongly affect the pull strength of the solder joints, but it affected the fracture mode of the solder joints.

Osaka University, Japan

Solder ball attachment using laser soldering

Scopus: "Reballing BGAs due to rework and conversion from RoHS-compliant solders to SnPb (or vice versa) typically requires the component be subjected to additional reflow cycles beyond the component manufacturer's recommendations. Laser attachment or laser reballing in an oxygen-free bath eliminates two additional temperature excursions and provides improved component reliability by facilitating the use of standard assembly reflow temperatures without mixed alloys."

Reaction properties and interfacial intermetallics for Sn-xAg-0.5Cu solders as a function of Ag content

Scopus: "Wetting and interfacial reactions were investigated for Sn-xAg-0.5Cu alloys, in which the Ag content had a variation from x = 1.0 to x = 4.0"

Low Ag contents increased the melting temperature ranges and deteriorated the wetting properties

The extent of undercooling increased and the thickness of intermetallic compounds (IMC) decreased as the Ag content decreased.As the Ag content decreased, the initial IMC thickness decreased due to the large undercooling and, during the solid aging at 170 °C, the IMC growth slightly decelerated 

For the application of good drop shock reliability, Sn-Ag-Cu solder of low Ag content should be beneficial due to the restraint of the IMC growth (Cu6Sn5 and Cu3Sn) and of the coarse plate-like IMC (Ag3Sn).

Seoul National University of Technology, Korea

Korea Institute of Industrial Technology, Korea

Inha University, Korea

Pussan National University, Korea

Effect of indium on wettability of Sn-Ag-Cu solders

Scopus: "The density and surface tension measurements of the Sn3.13Ag0.74Cu liquid alloys with 2, 3, 4, 15, 30, 50 and 75 at.% In additions were conducted in the temperature range from 431 K up to 1209'K"

The improvement of wettability in liquid alloys containing different In additions was confirmed

IMIM PAS, Poland

Control of interfacial reaction layers formed in Sn-3.5Ag-0.7Cu/electroless Ni-P solder joints

Scopus: "This study investigated a method for controlling the interfacial reaction between a Sn-3.5Ag-0.7Cu (wt.%) solder and an electroless nickel-immersion gold-plated Cu substrate through heat treatment. The interfacial reaction layer was controlled by heat treating of the electroless Ni-P plated layer. By applying a heat treatment, the thickness of the reaction layer (intermetallic compounds, P-rich Ni layer) was observed to be reduced"

Sungkyunkwan University, South Korea

Medical devices must go lead-free

EETimes.com: "But designers must learn to do so, because within the next year or so the European Union's Restriction of Hazardous Substances (RoHS) lead-free directive is expected to incorporate medical electronics. Hence, medical device designers must start now to incorporate new design considerations and understand the adverse effects previous lead-based design techniques can have on lead-free electronics assemblies.

Component suppliers report that most major medical electronics OEMs are moving toward RoHS compliance. Yet, there are many small and midsized medical electronics manufacturers operating under a cloud of confusion over a variety of lead-free issues and technologies.

Many OEM designers buttonhole themselves into their own engineering departments, refusing to consult with outside experts. This is not a good idea,"

IPC delivers comments on Consumer Product Safety Improvement Act

EMSNow: "Most significantly for the electronics industry, the regulations enacted August 14, 2008, include new requirements limiting the use of phthalates and lead in products intended for children. The new CPSIA regulations also require manufacturers to certify compliance with every consumer product shipment beginning November 12, 2008. The CPSIA affects more than 15,000 consumer products used in and around the home, and in sports, recreation and schools.

In its response to the CPSC, IPC noted that most electronic devices should not be considered children's products."

Modelling of SAC alloy behaviours

Factiva: "'Constitutive models for SnAgCu solder alloys are of great interest at the present. Commonly, constitutive models that have been successfully used in the past for Sn-Pb solders are used to describe the behavior of SnAgCu solder alloys.'"

n this study all of the above issues are addressed in developing constitutive models of Sn3.8Ag0.7Cu and Sn1.0Ag0.5Cu solder alloys, which represent the extremes of Ag composition that have been mooted at the present time. The results of monotonic testing are reported for strain rates ranging from 4.02E-6 to 2.40E-3 s(-1). The creep behavior at stress levels ranging from 7.8 to 52 MPa is also described. Both types of tests were performed at temperatures of 25 degrees C, 75 degrees C and 125 degrees C. The popular Anand model and the classical time-hardening creep model are fit to the data, and the experimentally obtained model parameters are reported

Effect of Ni, Co, Zn on interfacial reactions of SAC solder and CuNi(P) substrates

Factiva: "The effect of minor transition metal (TM) additives of Ni, Co, or Zn on the interfacial reactions of the solder joints between Sn-Ag-Cu (SAC) solder and the Cu/Ni(P)/Au substrate was investigated, especially subsequent to multi-reflowing. (Cu,Ni)(6)Sn-5 formed at the interface of all the joints except that of SAC-Ni, of which the interfacial compound was (Ni,Cu)(6)Sn-5. The interfacial compounds of the SAC-Co and SAC-Zn contained a small amount of alloying elements of less than 3 at.%,"

National Dwong Ha University, Taiwan

Electroplated Sn-rich soft solder for fluxless hermetic MEMS capping

Factiva: "A new fluxless hermetic sealing technique using electroplated Sn-rich soft solder is reported. Specific glass (SCG72) is chosen as lid material to seal alumina packages,' investigators in the United States report.

'It has nominal coefficient of thermal expansion of 7 ppm/degrees C, close to that of alumina. Alternatively, sapphire can also be used as the lid material. A thick Sn layer is plated over the Cr/Au patterned glass wafer, followed immediately by thin An layer. This outer An layer prevents the inner Sn from oxidation. In bonding, the glass lid is placed over the package rim which has a metallization structure of W/Ni/Au. The fluxless sealing process is performed in vacuum (50 millitorrs) to suppress tin oxidation."

Effect of La doping on SnAg creep and fatigue

Factiva: "In this paper, extensive testing was conducted to study the effects of Lanthanum (La) doping on the creep and fatigue behavior of SnAg lead free solder alloys. Variables considered in this paper include doping amount, aging temperature, and aging time,' researchers in the United States report.

'The experimental data show that rare earth element (RE) doping increases SnAg solders creep resistance by about 15%. Meanwhile, RE doping does not affect thermal aging behavior of the solder alloy. A microstructure dependent Anand viscoplastic model is proposed to capture the RE doping effect on the creep behavior. Good agreement between the model predictions and experimental data are obtained. In addition, fatigue tests were performed with bulk specimen. It is found that La doping increases the fatigue life by about five times,' wrote M. Pei and colleagues.

The researchers concluded: 'The optimal doping level for better fatigue performance is around 0.1%.'"

Georgia Institute Technology, US

Effect of La doping on SnAg creep and fatigue

Factiva: "In this paper, extensive testing was conducted to study the effects of Lanthanum (La) doping on the creep and fatigue behavior of SnAg lead free solder alloys. Variables considered in this paper include doping amount, aging temperature, and aging time,' researchers in the United States report.

'The experimental data show that rare earth element (RE) doping increases SnAg solders creep resistance by about 15%. Meanwhile, RE doping does not affect thermal aging behavior of the solder alloy. A microstructure dependent Anand viscoplastic model is proposed to capture the RE doping effect on the creep behavior. Good agreement between the model predictions and experimental data are obtained. In addition, fatigue tests were performed with bulk specimen. It is found that La doping increases the fatigue life by about five times,' wrote M. Pei and colleagues.

The researchers concluded: 'The optimal doping level for better fatigue performance is around 0.1%.'"

Georgia Institute Technology, US

Effect of joint thickness on resistivity and creep

Factiva: "Single shear lap creep specimens with a 1 mm(2) cross sectional area between thin copper strips, were developed and fabricated using a lead-free solder (Sn-3.5Ag) to quantify their electrical resistance. The electrical-resistance strain of solder joints with different thicknesses (0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.40, 0.50 mm) were measured by a tailor-made in situ micro-electrical-resistance measurement,' investigators in Changsha, People's Republic of China report.

'The results showed that the solder joints with 0.25 mm thickness yielded a minimum electrical-resistance strain and the longest creep life."

Effect of La on intermetallic compounds of Sn-Ag-Cu lead-free alloy solder

Scopus: "The effects of minor La on the formation and growth behaviors of intermetallic compounds at Sn-3.0Ag-0.5Cu lead-free solder alloy/copper substrate interface and inside the solders during soldering and aging were investigated. The results show that Cu6Sn5 layer formed at the interface exhibits a continuous scallop-shaped structure after soldering, the thickness of Cu6Sn5 layer decreases with increasing La content."

Central South University, China

Issues with Bismuth in High Temperature Solders

There are a number of possible problems. In general, any potential bismuth alloy would tend to be very heavily bismuth rich (the tin-bismuth system is quite uncommon in that the second element, tin, forms a eutectic at ~43%). This means that the a-bismuth dominates the microstructure. This is doubly so as differences in nucleation and growth rates seem to favour bismuth during non-equilibrium solidification. The problem with this is that the bismuth phase is rhombohedral and that it tends to grow in large angular crystals. This forms an inherently brittle microstructure with poor mechanical properties. There may also be problems with the thermal expansion behaviour. Bismuth expands during solidification which might cause manufacturing problems e.g. component push off. There might also be unusual thermal cycling behaviour due to anisotropic expansion/contraction during thermal cycling.

The thermal characteristics other that the nominal melting points of many candidate bismuth alloys might cause problems, either because of the solder composition or because of substrate reactions. Many, like copper and nickel, have sharply rising liquidi on the hyper-eutectic side of the reaction. This makes compositional control critical, which isn’t always easy or possible due to dissolution from the substrate materials. It is also possible that small amounts of substrate dissolution will cause a dramatic rise in “melting temperature” such that the joint solidifies too quickly, which could result in cold joints or incomplete spreading and wetting. This in combination with the expansion of freezing could also increase the incidence of differential solidification defects such as opens, cracked joints and hot-tearing.

That said, it may still be possible to develop a usable solder alloy. I don’t think it will be easy though and industry would require a lot of convincing.

Nick Hoo

Simulation of migration effects in solder bumps

Scopus: "Due to miniaturization, the width of interconnects, as well as the dimensions of solder bumps, decreases. As a result of the finer pitch, the density of solder bumps in flip-chip designs increases. This allows the usage of small 3-D assembly technologies like package-on-package in compact applications. The reduction of the geometrical dimensions leads to an increase of the carried current density in the solder bumps."

Under high dc current density conditions, electromigration in the solder joint is known as a reliability concern for high-density flip-chip packaging and power packaging. This paper will give an overview of thermal-electrical and mechanical finite-element simulations of migration effects in solder bumps and related assembly technologies. The effects will be illustrated by some simulation examples.

University of Hannover, Germany

IEEE Transactions on Device and Materials Reliability Volume 8, Issue 3, September 2008, Article number 4595633, Pages 442-448

Improvement of Thermal Fatigue Properties of Sn-Ag-Cu Lead-Free Solder Interconnects on Casio's Wafer-Level

Scopus: "Thermal fatigue properties of commercial LF35 (Sn-1.2Ag-0.5Cu-0.05Ni), SAC105 (Sn-1Ag-0.5Cu), and SAC305 (Sn-3Ag-0.5Cu) solders on Casio's wafer-level packages are discussed from the viewpoints of both morphology and grain boundary character. Orientation imaging microscopy revealed that both LF35 and SAC305 resisted the coarsening of tin grains during thermal fatigue as compared with SAC105, correlating with their greater fraction of coincidence site lattice boundaries. 

This seems to explain why LF35 has superior thermal fatigue life in spite of its lower silver content."

Development of high strength Sn-Cu solder using copper particles at nanolength scale

Scopus : "In this study, varying amounts of nanolength scale copper particles were incorporated into tin by microwave sintering assisted powder metallurgy route."

Results of tensile testing revealed that with the addition of 0.35 vol.% (∼0.43 wt.%) of Cu in pure Sn, a significant improvement in yield strength (∼233%) and ultimate tensile strength (∼159%) is realized, when compared with that of commercially available Sn-0.7 wt.% Cu solder.

National University of Singapore, Singapore

Nanoparticles of the Lead-free Solder Alloy Sn-3.0Ag-0.5Cu with Large Melting Temperature Depression

Scopus: "The nanoparticles were manufactured using the self-developed consumable-electrode direct current arc (CDCA) technique. The melting temperature of the nanoparticles, with an average size of 30nm, was found to be 213.9'C, which is approximately 10'C lower than that of the bulk alloy. The developed CDCA technique is therefore a promising method to manufacture nanometer-sized solder alloy particles with lower melting temperature compared with the bulk alloy."

Shanghai University, China

Chalmers University, Sweden

Kirkendall voids formation in the reaction between Ni-doped SnAg lead-free solders and different Cu substrates

Scopus: "The Ni additions made the Cu3Sn layer thinner. For the case of the electroplated Cu substrates, the amount of Kirkendall voids decreased correspondingly with the Ni additions."

Effect of aluminum concentration on the interfacial reactions of Sn-3.0Ag-xAl solders with copper and ENIG

Scopus: "Aluminum was added into Sn-3.0Ag (wt.%) solder to investigate the effect of aluminum concentration on the interfacial reaction of Sn-3.0Ag-xAl solders with copper or electroless nickel immersion gold (ENIG) metallizations."

The aluminum additive in Sn-Ag solder inhibited the growth of IMCs in the reaction with copper or ENIG metallizations, which was favorable for the reliability of solder joints. 

Correlation between accelerated ageing tests and FE Modelling for BGA

Scopus: "his paper describes a methodology using experiments and FE simulations that allow us to assess acceleration coefficients (ACs) and to predict assembly lifetimes. Two accelerated ageing tests have been conducted on lead-free ball grid array (BGA) assemblies."

Then, the correlation between the experimentations and the simulations has allowed us to assess the ACs of two different kinds of thermal cycles and, thus, the cycles-to-failure for another test.

ENSEIRB, France

High Heat-resistant Lead-free Solder Uses Nanoparticles

Factiva: "Nintac aims to develop markets for its newly developed lead-free solder, composed of silver nanoparticles and copper powder, which enables soldering at about 180 C and, once applied, can withstand temperatures of 500 C or more.

The Tokyo-based startup company, which specializes in creating industrial applications for nanoparticles, says that its solder, priced about Yen 300 ($3.08)/g, is suitable for joining metals or plastics, mainly in the manufacture of automobiles and heavy electrical equipment that need to operate under high-temperature conditions and currently require the use of high heat-resistant solders.

It adds that the solder, has a sea-island structure in which silver nanoparticles 5 nanometers in diameter act as binder and surround copper powder with particle size of 50 nm."

Worldwide product innovation despite varying standards

EDN: "However prepared companies might be, the IPC paper contends that a ban on TBBPA would have significant side effects. Although halogen-free alternatives are available, quantities are limited, and their inclusion would dramatically raise manufacturing costs. Cost aside, these materials have not undergone the rigorous risk assessments of TBBPA, and the phosphorus and other elements that they contain may turn out to be dramatically more toxic than the bromide that they are intended to replace. Some products would not tolerate the substitution at all. According to the paper, the following would be the most significant consequences of such a ban:"

IPC Publish REACH Guidebook

IPC: IPC, in conjunction with ERA Technology Limited, has developed REACH and the Electronics Industry Supply Chain: The Basics, the Impact, and How to Survive to provide you with all of the information you need. 

The guidebook includes:

- An overview of the REACH regulation, including a timetable of activities and better knowledge of which substances are considered hazardous ….these substances may be present in your materials and may need to be eliminated! 

- An explanation of electronics manufacturer obligations under the regulation and the ramifications of non-compliance 

 

- Insight into the pre-registration and registration process 

 

- Specific details on the REACH implications, including analysis of how each segment of the supply chain will be impacted. 

The Guidebook can be downloaded at www.ipc.org/ReachGuidebook for $50 ($25 for IPC members). 

Solder-free contact-making of dielectrically impeded discharge lamps

Delphion: Use of mechanical contact method in discharge lamps instad of soldering processes, sacing time, energy.

US Patent 7,446,463, Nov 2008

Since the Armed Forces are exempt from RoHS, this directive has especially impacted the Mil/Aero market.

Factiva: "Let’s face it. RoHS isn’t going away, regardless of the added stresses this regulation has put on military and defense systems, especially. So, where will the greatest impact on military and defense systems really be? It’s not necessarily going to be on the formation of tin whiskers, a subsystem’s reduced operating temperature, the proliferation of counterfeit components or potentially lowered reliability, but rather on the information flow between the customer and the manufacturer.

who supplies parts, the better the resulting subsystems will be. Processes that facilitate information exchange must be developed and adhered to or reliability of military and defense systems may begin to decline."

Characterization of low-temperature nanosilver pastes

Scopus: "As the electronics industry continues to integrate more functions in smaller packages, the electrical, thermal and mechanical properties of the existing die-attach materials such as solders and conductive epoxies will fail to meet more demanding requirements for performance and reliability. To address this problem, we developed low-temperature sintered nanosilver as a new die-attaching material. Experimental results of the electrical, thermal, and mechanical properties of the sintered silver die-attachment are presented in this paper. The nanoscale silver paste was made by dispersing 30-nm silver powder under ultrasonic agitation in an organic binder system."

These results demonstrate that the nanoscale silver paste sintered at low temperature is an excellent alternative to solders or epoxies for die attachment.

Virginia Polytechnic, US

Preparation of Sn-3.5Ag nano-solder by supernatant process

Scopus: "The nano-scaled Sn-3.5Ag solder was prepared successfully by a supernatant process in the present study. The morphology of the nano-particle was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. It was found from the SEM micrographs that the average diameter of the particle was 137 nm with a standard deviation of 5 nm."

National Cheng Kung University, Taiwan

Chien-Kuo Institute of Technology, Taiwan

Murdoch University, Australia

It's all about VME

Embedded.com: "Since July of 2006, the world's electronics markets have been plagued by low-quality products that fail early in their useful lives because of the mandated RoHS legislation (Restriction of Hazardous Substances), originally begun in Europe. This legislation banned lead-based solders used to fabricate printed circuit boards. The entire electronics industry shifted to brittle high-temp lead-free solders, which spurred the highest failure rates in electronics devices in the history of the electron, and the largest increase in new landfill development. Tin whiskers, cracked solder balls in ball grid arrays, and separated via plating resulted from the untested but mandated use of those RoHS-compliant solders, rendering all compliant equipment worthless. The VME community refused to use these unproven solders in critical embedded systems bound for military and industrial applications and maintained their use of tin/lead solders as outlined in the VITA52 Lead-free practices document completed in 2009. Most VME-based products have a mean time between failure (MTBF) of 10–15 years (as calculated with the VITA51 Reliability Prediction guidelines). Despite the tremendous investment and research into RoHS failures and solutions by the electronics industry and governments for the past two decades, the MTBFs for RoHS-compliant products are still measured in months."

Study on wettability of Sn-Ag-Cu-Ce solder and mechanical properties of soldered joints

Scopus: "The wettability of Sn-Ag-Cu-Ce solders on Cu substrate was determined by the wetting balance method, the mechanical properties of Sn-Ag-Cu-Ce joints were investigated, and the fracture morphologies of joints were also studied. 

It is found that the wetting times, and wetting angles of Sn-Ag-Cu-Ce solder are decreased with the increase of Ce content, and good wettability of Sn-Ag-Cu-Ce is obtained with around 0.03%-0.05% (mass fraction) Ce. The mechanical properties of soldered joints are enhanced with the addition of Ce, and the soldered joints possess the peak values of pull forces as well as improved ductility with obvious dimples when the Ce addition is about 0.03% in Sn-Ag-Cu-Ce joint."

Nanjing Univerity of Aeronautics and Astronautics, China

China Electronics Technology Group Corporation, China

Harbin Welding Institute, China 

Study on wettability and spreadability of lead-free solder with diode laser soldering pro

Scopus: "Wettability and spreadability of Sn-Ag-Cu lead-free solder on Cu substrate were tested by diode laser soldering system, influence of different soldering parameters on wettability and spread-ability of Sn-Ag-Cu lead-free solder was studied. The results indicate that, as the laser output power increases, the spreading area of lead-free solder increases and the wetting angle decreases, the optimal wettability and spreadability is obtained while the laser output power increase to a certain range."

Nanjing University of Aeronautics and Astronautics, China

China Electronics Technology Group Corporation, China 

Effect of Cu content on microstructure and interfacial reactions of Sn

Scopus: "Two kinds of lead-free solders, Sn-xCu(x = 0.7%, 2%) and Sn-9Zn-xCu(x = 0, 2%, 10%) were chosen. The microstructure as well as interfacial reactions between the selected lead-free solders and Cu substrate within short soldering time was studied. 

The intermetallic compounds (IMC) are coarsened into nubbly Cu6Sn5 phase by adding excessive Cu into Sn-Cu solder alloy. For Sn-9Zn-xCu solder alloys, the long needle-like Zn rich phase which is the mainly existing form of Zn in Sn-Zn solders is transformed into Cu6Zn8 phase and fine Zn rich phase by the addition of 2% Cu, while CuZn phase and Cu6Sn5 phase are formed in Sn-9Zn-10Cu bulk alloy. 

When soldering within short time under 260'C, the ripening and growth of IMC at Sn-xCu/Cu interface are accelerated with increasing Cu content in Sn-Cu solders."

Dalian University, China

The Silver Debate: Sn/Cu-based Solder Explained

SMT: "Lead-free solder alloys with micro-additions like nickel and germanium are finding increased acceptance globally, entering the mainstream for high-reliability PCBAs. Thoroughly understanding solder paste and flux materials is key to maximizing print and reflow performance."

There are compelling reasons to study the relationship between the higher liquidus of the Sn/Cu-based alloy and the topography of its solder powder, as early developments with paste revealed that some of these materials not only showed a lower wetting potential, but also an inferior mobility when compared to traditional solder paste.

Using the data from TGA, we are able to adjust the retention time of our solvent system and modify our resin, activator, and synergist system to remove the paste/flux constituents that cause negative anomalies and replace them with other, more effective systems. In modern lead-free Sn/Cu-based solder, the developed flux system displays exceptional reflow soldering ability as well as strict compliance with global reliability criteria. With advanced rheology, concurrent development of high-speed properties in ultra-fine-pitch applications and long stencil life are a reality.

SN100e lead free solder alloy from Qualitek

EMSNow: "This unique patented alloy has been developed as a lead free alternative for those now using costly SAC alloys and for those switching from lead containing Sn63/Pb37 alloys to the lead free process.

SN100e is manufactured from tin, copper, and cobalt to create solder so pure it far exceeds the most common specification requirements. The lead-free solder alloy is RoHS compliant and reduces copper dissolution. This alloy provides brighter, shinier, less grainy solder joints when compared to other lead free alloys such as SAC305 and is much less expensive."

SN100e contains 0% nickel and upto 0.05% cobalt. Other known alloys contain nickel and 0% cobalt. The ratio of nickel commonly used in comparison to cobalt requires more frequent monitoring due to the increased depletion of the nickel in comparison to cobalt during process resulting in an increased cost for those using the nickel containing alternative alloys.

Qualitek Have Glow-in-the-Dark Green Paste

Qualitek: Qualitek have a Green Paste product that is not only coloured green but also glows in the dark under UV light. This enables operators to distinguish it from leaded pastes and avoid crossovwe contamination in assembly operations. 

MBO Takeover Radiel Fondam

Electronique: MBO have acquired Radiel Fondam.

La société MBO a le plaisir de vous faire part de la reprise de la totalité des actifs et de personnel de la société Radiel Fondam dont l'ensemble des formules et procédés de fabrication des produits Radiel Fondam.

La société MBO, qui fabrique toute la gamme de produits de brasage tendre depuis plus de 60 ans, va ainsi étendre sa gamme de produits et notamment les flux de brasage et les crèmes à braser.

La société MBO dispose de sites de fabrications et de filiales de commercialisation en Pologne, en Chine, en Angleterre et au Brésil de façon à pouvoir répondre aux besoins de ses clients en alliages, fils pleins, fils avec décapants, préformes, flux de brasage, crèmes à braser, produits de masquage. 

New PoP Paste from Alpha

Cookson Alpha: Cookson Electronics is launching new ALPHA® POP-959 Lead-Free, no-clean solder paste specifically designed to deliver highly repeatable paste volumes for challenging PoP assembly, thus increasing throughput and yield while minimizing expensive rework and scrap.

To meet the demand of high-density and memory/logic options for sophisticated electronic

devices, many assemblers are evaluating package on package (PoP) technology. PoP

assemblies allow for higher electronic functionality per unit circuit board area, and allow low cost

product memory customization, and highly flexible manufacturing.

Research Updates on PCBs, RoHS, Economy, and PCs

SMT : "The Nikkei Business Daily reports that PCB manufacturers face a tough road ahead amid growing uncertain about demand. 

Ken Murakoshi, senior analyst at the equities research division of Mizuho Securities Co., explains that new demand for PCBs does not match that seen in recent years, and that even those PCB fabricators that are doing well now face uncertainty about demand resulting from the Christmas shopping season and beyond. Rising labor costs in China and soaring materials prices are exacerbating conditions. Some manufacturers may begin lowering prices to win orders, Murakoshi adds. Value-added products such build-up circuit boards that were immune to price declines could end up being subject to competitive pricing. The demand outlook from January 2009 is still up in the air, and it's impossible to come up with any specific numbers. The previous model under which finished-product manufacturers paved the way for growth at PCB manufacturers no longer applies, he asserts. A sharp recovery within fiscal 2009 is not likely. Nikkei reports that Murakoshi detailed a lacking investment in capital equipment from PCB makers and a focus on high-value-added products to overcome economic challenges. The downturn in share prices is conducive for corporate acquisitions, added Murakoshi."

Electrical and mechanical characterization Conductive adhesive with a low melting point solder

Scopus: "For the highly reliable interconnection in a micro-packaging technology requiring an excellent electrical and mechanical performance, the new anisotropic conductive adhesive (ACA) system with a low melting point solder was designed and characterized. An optimum flip-chip bonding cycle considering the chemo-rheological properties of a polymer matrix and solder was proposed."

Microstructure, defects, and reliability of mixed Pb free / SnPb assemblies

Scopus: "The results of an intensive reliability study on Pb free BGA / SnPb solder assemblies as well as some lessons learnt dealing with mixed assembly production at Celestica are described in this paper. In the reliability study, four types of Pb free ball grid array components were assembled on test vehicles using the SnPb eutectic solder and typical SnPb reflow profiles with 205-220'C peak temperatures. Accelerated thermal cycling was conducted at 0 to 100'C The influence of the microstructure on Weibull plot parameters and failure mode will be shown. Interconnect defects such as non-uniform phase distribution, low melting structure accumulation, and void formation are discussed. Recommendations on mixed assembly and rework parameters are given"

Effect of Ag, Fe, Au and Ni on the growth kinetics of Sn-Cu intermetallic compound layers

Scopus: "The effect of Ag, Fe, Au and Ni on the interfacial reactions between Sn-based solder and Cu substrate has been investigated in this paper. Based on the solubility of the alloying elements in the Sn-Cu intermetallic compound (IMC) layers these elements can be divided into two categories: (i) alloying elements that do not dissolve significantly in either Cu6Sn5 or Cu3Sn and (ii) elements that exhibit significant solubility in Cu6Sn5 and also to Cu3Sn. It is shown that the latter group of elements have stronger effect on the growth behaviour of IMC's in the Sn-Cu system than those belonging to the first group. Of the investigated elements Ni had the most prominent effect on the growth kinetics. It reduced greatly the thickness of Cu3Sn and consequently also the total IMC layer thickness"

SMART Group to Participate in EKTN Event

PCB007: "SMART Group is delighted to be involved in the fifth year of the prestigious event Trade & Investment TechnologyWorld08, November 17-18, 2008 at the Ricoh Arena in Coventry, UK.

SMART Group will support the Electronics Knowledge Transfer Network (EKTN) to organize the Seminar Programme entitled 'Breakthroughs - Bending the Design Rules!'  Breakthrough technologies to be covered during the seminars include: Energy Harvesting, Solder Free Electronic Assemblies, Design and Product Responsibility, Heat Dissipation in Electronic Design, Flexible Interconnection Markets andSystem in Package.

Design, development and manufacturing engineers will have a unique opportunity to look into the future of electronic design, components, printed circuit technology and environmental breakthroughs. However, for some this is not the future--it is now. A group of world-class presenters will illustrate existing and current technology developments overcoming functional and reliability concerns now and for the future."

Delegates will also be able to register for a free copy of Joe Fjelstad's latest book covering the principles and applications of the Occam Process

Balver Zinn appoints Holders Technology to Support PCB Fabrication Business in India

evertiq.com: "Balver Zinn, provider of solders in various alloys, anodes, solder wire, fluxes and pastes, has appointed Holders Technology as distributor for their PCB Fabrication business in India.

This appointment will provide customers in India with local access to Balver Zinn’s range of solder for PCB applications, including bar, billet, pellets and plate for galvanic and hot air levelling processes. Business Development Manager, Paul Salmon, explains: 'Balver Zinn reached verbal agreement with Holders Technology at the Electronica show in Bangalore on the 2nd September. Their leading position in this field, spanning thirty five years, creates another important step in constructing a global distribution network for our products.'"

Laser soldering vs IR reflow for fine pitch joints

Scopus : "Soldering experiments of fine pitch devices were carried out using diode-laser soldering system and IR reflow soldering with SnPb, SnAgCu, SnAg, and the tensile strengths of soldered joints were measured by Micro-joints Tester. The results indicate that mechanical properties of fine pitch devices soldered joints with laser soldering system is better than that of fine pitch devices soldered joints with IR reflow soldering method, especially for SnAg soldered joints,"

Effect of germanium on shearing strength and fracture surface of SnAgCu/Cu solder

Scopus : "A little element Ge was added into lead-free solder Sn2.5Ag0.7 Cu (0.25, 0.5, 0.75, 1.0 wt%), and the shear test specimens were designed and welded. The joint shearing strengths were measured and fracture surfaces were analyzed by scanning electron microscope and energy dispersive X-ray analysis method. The result indicates that the shearing strength of the joint increases obviously. The joint fracture forms of the Sn-Ag-Cu-Ge lead-free solder are mainly ductile fracture, and most of them have secondary cracks. Lots of dimples formed on the fracture surface when adding element Ge, and IMC Cu6Sn5 play a part on the dimple forming."

Harbin University, China

IMR Chinese Academy, China

Anhui University, China

Effect of heating rate on microstructure and mechanical properties of composite solders

Scopus: "The current study was to research the morphology of the IMC formed around the metallic Cu reinforced particulates incorporated in the Sn-3.5Ag solder by mechanically, and the mechanical property of composite solder joints. Experimental results indicated that the different heating rate have no influence on the morphology of the IMCs formed around Cu reinforced particulate, but just have effect on the thickness of the IMCs and mechanical property of composite solder joints. The relationship between dimension of IMCs and mechanical property in different processing condition was established."

Beijing University, China

Changes in the microstructure of materials and their impact on reliability

Scopus: "Several types of microstructural changes in microelectronic solder materials are briefly discussed, namely the formation of intermetallics, Kirkendall voiding, spinodal decomposition, and coarsening. Moreover, a theoretical framework, based on the entropy principle, is developed by means of which constitutive equations can be derived that are necessary to understand and simulate such processes. The resulting equations are specialized to binary alloys and then investigated numerically. Finally, simulations of spinodal decomposition and coarsening are performed for the eutectic solder AgCu. The theoretical predictions are compared with experiments"

Institut fur Mechanik, Germany

ThyssenKrupp Steel, Germany

Modeling of interfacial intermetallic compounds in the application of very fine lead-free solder interconnections

Scopus : "This paper reviews the modeling techniques in the literature for both the growth kinetics and morphology of the interfacial IMCs, under the context of lead-free soldering in very fine interconnections. The advantages and disadvantages of each method are discussed. Possible solutions to include the geometrical features of micro solder joints in the modeling of growth kinetics of interfacial IMC are presented."

Loughborough University, UK

Max-Plank Institut, Germany

Pohang University, Korea

A simple method for testing the electromigration resistance of solders

Scopus: "The present paper proposes a simple method to test the electromigration resistance of Pb-free solders. One of the key points of the present method is the fabrication of a simple solder sample that can produce sufficient current density to cause electromigration. Moreover, the actual local temperature of a small area subjected to electromigration in the sample was measured by a direct method. A right-angled diamond-shaped hole was introduced in a thin film of solder using a focused-ion-beam system. A direct current was supplied to the film far from the hole, perpendicular to the diagonal of the hole. In this way, the current density was concentrated near to the corner of the hole, and the value of this was obtained through a theoretical analysis."

Tohoku University, Japan

Fuji Electric, Japan

Senju Metal Industry to Expand China Solder Operations

Factiva: "Tokyo based major solder maker, Senju Metal Industry expands Chinese operation. The firm expands the integrated operation output capacity from solder alloy to finished products at Huizhou and Beijing in 3 years. The firm also improves the optimization of the production in Chinese operations including paste operations in Shanghai and Hong Kong."

Isotropic conductive adhesives on immersion silver printed-circuit boards

Scopus: "This paper presents the electrical properties of Ag epoxy composite ICAs materials on Cu-finished and immersion-Ag finished PWBs, as solder replacements for SMT or flip chip technologies."

J. Lee, J.E. Morris, Portland State University, US

C.S. Cho, Kyungpook National University, South Korea

IPC Voices Concerns Over RoHS Revision Developments

PCB007: "On the heels of a recent news report that Tetrabromobisphenol A (TBBPA) is on a draft list of substances for priority examination under the European Union's (EU) Restriction of Hazardous Substances (RoHS), IPC President Denny McGuirk dispatched a letter to EU commissioners expressing the organization's concerns for the inclusion of TBBPA."

Nihon Superior patent for precipitating Cu from wave solder baths

Precipitation of copper in lead-free soldering of copper lead wires used for mounting components on printed wiring board, involves adding tin to copper eluted in lead-free soldering and precipitating copper-tin complex.

The purpose of the present invention is to separate excess coppers leached out in a lead-free solder bath and recover tin with high efficiency. An element X (Ni, Co, Fe) for forming a (CuX)6Sn5 compound between copper and tin in molten lead-free solders is added to separate out a (CuX)6Sn5 compound. Tin is recovered by binding the (CuX)6Sn5 compound by passing thereof through a multi-perforated plate, further generating swirling currents to precipitate and separate the bound (CuX)6Sn5 compounds and removing thereof. 

US20080216605, Sept 2008

Indiana Skunkworks Wants to Eliminate Solder

PCB007: "Defense electronics' 20-year reliability requirements rule out the use of l-f solder. Tin whiskers, copper dissolution from printed circuit pads, copper migration into l-f solder, voids, and poor wetting are just some items on the list of l-f hazards that result in shorted or open circuits, even without the help of vibration or shock. The higher melting temperature for l-f solder stresses components and printed circuits, making them less reliable as well. L-f tosses another curve at defense electronics. Use of lower-cost 'commercial off-the shelf' components is constrained because l-f finishes and tin-lead solder are not compatible."

Well-meaning European environmentalists, with help from the tin industry and other self-interest seekers, forced l-f solder on a divided, fragmented, leaderless electronics industry after 1998.

The great irony is that in 2008 problematic l-f solder has inspired a better, cheaper assembly system alternative that eliminates all PCB assembly solder: the Occam Process. If Occam had been universally used in 2008, 9 trillion solder joints would have been replaced by reliable true 3-D blind via interconnects, copper plated, to join component leads to traces. The following discussion will place the new manufacturing structural change in a historical context and discuss the many economic improvements, reliability increases, and environmental benefits.              

Harvey Miller                

International Conference on Lead-Free Electronics to be held December 8–10, 2008

Global SMT & Packaging magazine: "IPC - Association Connecting Electronics Industries and JEDEC Solid State Technology Association today announce an International Conference on Lead-Free Electronics. To be held December 8–10, 2008 at the Fairmont Hotel in Dallas, Texas, the event will feature a full-day technical conference with an outstanding roster of speakers, as well as two full days of informative half-day workshops."

Intel Patent InX Reactive Solder

Intel have patented the use of In with 2% of 'active' rare earth elements such as hafnium, cerium, titanium and lutetium, transition elements such as nickel, copper, iron, and cobalt, and other elements such as magnesium, strontium and cadmium.

 

The solder is for typical use as a solder-based conductive adhesive in die bonding to thermal management devices.  It does not have to use a flux and can bond to non-metallic surfaces.
The patent also mentions SnAg and 'other conventional thermal conductive solder types', although the claims are for indium.

Melting point of In is 156'C so it is not a high temperature option.

Patent

Plans to extend RoHS law out from the shadows

ENDS: Details of legislative plans to extend the EU's 2002 restriction of hazardous substances (RoHS) directive have emerged.  A draft proposal seen by ENDS confirms plans put to public consultation earlier this year.

The proposal was drafted by the European commission's environment department and is currently going through inter-service consultation with other departments pending formal adoption.

The environment department proposes extending RoHS to cover medical devices from 2012.  Industrial monitoring and control instruments would become subject to the rules from 2015.  In vitro diagnostic devices and "active implantable medical devices" should be covered from 2016 and 2020 respectively.

Five new chemicals would be reviewed for possible inclusion on a list of six substances already banned from use in electrical goods under RoHS . These are the brominated flame retardants TBBP-A and HBCDD, and the phthalates DEHP, BBP and DBP.

In future the list should be reviewed in line with the EU's Reach regulation, the environment department says.  Detailed rules for how this will work in practice will be established under the EU comitology procedure, it adds.

A new annex setting out a list of products to be covered by the law is proposed.  The move is designed to more closely align RoHS with a related EU law on waste electrical and electronic equipment (Weee).  This alignment is also proposed in draft legislation to revise the Weee directive.

Other proposals include a requirement for EU member states to carry out market surveillance activities to ensure conformity with the rules.  New "maximum concentration values" for the presence of substances banned under RoHS in "homogeneous materials" are also proposed.

The Influence of an Imposed Current on the Creep of Sn-Ag-Cu Solder

Scopus: "The work reported here included preliminary tests on the influence of an imposed current on the creep rate of the Pb-free solder Sn-Ag-Cu 305 (Sn-3Ag-0.5Cu in wt.%)"

Samples were prepared with three starting microstructures: as cast, thermally aged by long-term isothermal exposure, and current aged by long-term exposure to a fixed current density. The three microstructures were then tested with and without current at two ambient temperatures. The different microstructures had very different creep rates in the absence of current but, surprisingly, imposing a current (5.5 × 103 A/cm2) increased the creep rate by very nearly the same factor (~7×) in every case. Neither of these results is well understood at this time.

University of California, US

Cisco Systems, US

EU governments looking to increase RoHS enforcement

evertiq.com: "Mr. Norlem, Esq. continues: 'EU governments are also looking at more international collaboration with local-RoHS monitoring authorities in China and the United States. Many products sold in Europe are that of companies trading worldwide, so there is scope for more collaboration internationally'. Intertek hosted a forum in which EU and Chinese, and EU and Taiwanese authorities met, respectively, in Shanghai and Taipei on November 16 and 19, 2007 to present and discuss this. A further forum is being organized for February 2009 with California’s DTSC."

Executive's Guide to Environmental Megatrends that will Shape the Future of the Electronics

Research and Markets: "This 67-page guide was written by Dr. Paul Goodman of ERA Technology, one of the world's leading consultancies on environmental trends with expertise in the electronics industry. IPC commissioned this study to help electronics executives steer their companies through the increasingly costly and complex landscape of worldwide environmental requirements. Three major environmental trends are the focus of the report. It covers future substance restrictions, including new substances that may be restricted by RoHS and the new REACH regulation restricting an estimated 30,000 chemical substances. It also forecasts the impact of energy efficiency and end-of-life recycling requirements and trends. Published September 2008."

Conductive adhesive could replace solder

EETimes.com: "Researchers have invented a nanotube-based dry adhesive that they propose using instead of solder to assemble components on circuit boards. The adhesive, which has very high electrical and thermal conductivity, models its sticking power on the foot of the gecko lizard. It works without heat or solvents, permitting use in the vacuum environments used to make chips and in space."

Limin Dai, Liangti Qu, University of Dayton, Ohio

Zhenhai Xia, University of Akron

Zhong Lin Wang, Georgia Institute of Technology

Morley Stone, Air Force Research Laboratory

See also:

ASI (Adhesives & Sealants Industry), 21/10/08

Japan Automotive to be lead-free by 2009

Kay Nimmo, ITRI, 04/05/08

The japanese automotive industry have required suppliers of electronics to be Pb-free by 2009

Market data: Potential tin use in High-Lead High Temperature Solders

Kay Nimmo, ITRI, 04/05/08

The Japanese estimate of use of high Pb solder (i.e. 95%Pb) in japan is actually a third of total Pb use (in 2000 statistics) and therefore around 11,000tpa. They think that half of this can be replaced in 2-3 years. 

Correction: Japan use 2000 = 2,500 tpa, extrapolating to 11,000 tpa Sn90Pb worldwide

Otmar Deubzer, Fraunhofer-IZM, 17/09/08

The total amount of high melting point solders in electronics is around 11,000 t per year. This refers to HMP solders with high lead content. The figures go back to a detailed interview with Senju Metals in Japan. However, the data are from 2000. I do not have more current ones, and I have never found another source indicating the amount of HMP solders used in electronics. 

I do not have the exact range of lead content in these HMP solders. 

The influence of low level doping of Ni on the microstructure and reliability of SAC solder joint

Scopus: "Both solder composition and PCB surface finish had a notable effect on the interfacial microstructare, the Ni addition can give rise to needle like NiCuSn IMC formation and reduce the grain size locally at solder/NiAu pad interface after one time reflow according to top-view interface analysis, and had no obvious effect on the IMC evolution of solder/OSP pad," It was found that the decrease of Ag concentration and Ni addition in SAC solder could significantly improve the drop test performance when NiAu pad was used. In bending test, OSP pad show better performance than Au/Ni pad. The correlation between joint microstructare and joint reliability was discussed in detail.

Samsung

Effects of Ni addition on microstructure and the shear strength of Sn-3.0Ag-0.5Cu/Cu solders joints

Scopus: "The results indicate that the addition of Ni element increases the shear strength of solder joint. When the content of Ni is 0.10 wt. %, the shear strength of solder joint is the highest by 40.28MPa which is 18% higher than that of Sn-3.0Ag-0.5Cu lead-free solder. The fracture morphology shows that the addition of Ni promotes grain refinement which leads to the increase of shear strength. The shear strength of the solder joints decrease continuously. The fracture microstructare became coarse-rained with the increase of thermal aging time."

Harbin University, China

Suppressing intermetallic compound growth in SnAgCu solder joints with addition of CNTs

Scopus: "Results revealed that after soldering, the initial interfacial IMC thickness of the unreinforced solder joint was comparable to that of the composite solder joints. However, after aging, the interfacial IMC layer of the unreinforced solder joint was observed to grow more significantly than that of the composite solder joints. Furthermore, the composite solder joints exhibited lower diffusion coefficient"

University of Singapore

Solder joint reliability of different BGAs reworked using low melting point Pb-free alloys

Scopus: "Solder joint reliability of different BGA's reworked using low melting point Pb-free alloys was investigated." The CSP 46 component was removed and a new component was placed using low-melt In-containing alloy A

Celestica

Matsushita Use Bubbles for Solder Self-Assembly

Matushita have developed a novel self-assembly technique for soldering using a bubble-generating reagent during heating to 'herd' solder particles towards electrodes, eliminating bridging and cutting process time.

The work was presented at the September 2008 IMAPS Nordic meeting in Denmark.

The SASB (Self Assembling Solder Bonding) technique disperses a solder paste containing solder particles and the reagent across the whole interconnection region between two boards or a board and component. In the heating process, the bubbles cause the solder particles to migrate to the interconnection space between opposite electrodes, where they can then be melted to form the multiple solder joints. The resin is also cured, meaning that no additional underfill operation is needed.

Matsushita have successfully used the technique for 100um pitch board-to-board connections for flexible printed circuits (FPCs), without bridging and with good reliability.

To obtain a copy of the paper, apply to the IMAPS Nordic office for the CD of proceedings.

The effect of Ni nanoparticles addition on shear behavior and microstructure

Scopus: "The result shows that adding nickel nanoparticles can improve the shear performance of the soldered joint; the shear force of the soldered joint is highest when adding 0.5wt% Ni nanoparticles at reflow 240s. The SEM observations shows that the hexagonal Cu6Sn5 IMC (intermetallic compound) in the inside solder is disappears gradually and the morphsa of the IMC that on the interface of the solder joint becomes planar after adding Ni nanoparticles into solder"

Shijiazhuang Railway Institute, China

Reliability Prediction for Different Sn-based Solders

Scopus: "Recent studies revealed that there is no simple 'drop in' solution for the lead-free replacement of SnPb joints, instead different Sn-based solders are advantageous for different use conditions, which can be dominated either by drop loading or by thermal cyclic loading in harsh use conditions. By way of high-speed shear testing reliability assessments of components during drop and shock events can be studied in a simplified manner. Dynamic 3-D finite element simulations have been performed applying explicit FEA to replicate the shear tests virtually. It was shown in this way that SAC 1305 solder outperformed SAC 387 solder. The low cycle fatigue behavior of different SAC alloys is additionally of interest."

Rainer Dudek, Fraunhofer IZM, Germany