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.