Wafer level package integrated circuit incorporating solder balls containing an organic plastic-core

US8035226: An integrated circuit including solder balls containing an elastic or resilient material core, a hard or rigid shell substantially enclosing the core, and an electrical contact layer substantially enclosing the shell.

The elastic or resilient core serves as a stress buffer layer in a wafer level package (WLP) integrated circuit. The elastic or resilient material core may include an organic plastic material, such as a Divinilbenzene cross-linked co-polymer of relatively high resistance. This material has a relatively good elongation property so that it can effectively absorb forces exerted upon the integrated circuit by, for example, the flexing of a printed circuit board (PCB) or other structure to which the integrated circuit is attached.

The hard or rigid shell serves to contain the elastic or resilient core and may include copper. The electrical contact layer serve to provide a good adhesive electrical contact to an under bump metallization (UBM) layer, may include a lead free, Tin-Gold (SnAg) material.

Seeking Consensus for Lead-Free

Real Time With... SMTAI 2011 Dr. Ron Lasky of Indium discusses the status of lead-free. He is working on compiling a consensus of the challenges and successes of lead-free processes. If you're interested in contributing, he is gathering data on lead-free in his blog.

Video

Hitachi's Pb-Free Solder Retains Bond Strength at 200C -- Nikkei Electronics Asia -- March 2008 - Tech-On!

Nikkei Electronics Asia!: The new Pb-free solder, on the other hand, is an Sn-Cu based material without expensive Ag, containing about 3wt% to 10wt% Cu with respect to Sn. When this solder is used on a Ni-plated connector, a Cu-Sn compound (Cu6Sn5) is formed on top of the Ni plate, and the remainder of the phase is relatively uniform Sn-Cu eutectic solder (Sn-0.7Cu), as shown in Fig 2.

This Cu-Sn compound film is a protective film preventing solder Sn from coming into direct contact with Ni plate, and therefore preventing the deterioration it causes. Further, as a source at Hitachi added, reaction between Ni and Sn is minimized, because "The Cu-Sn compound does not include Ni, so the migration speed of Ni from the plating into the compound is extremely slow." Researchers at the firm have experimentally verified that bond strength remains at the initial level of about 20MPa even after 1,000 hours at 200*C (Fig 3). Hitachi explained that the thickness of the Ni plate on the connector is also unchanged.

The melting point of the solder is about 260*C, for a 5wt% to 7wt% Cu content. Hitachi says that a higher Cu content will increase the heat resistance, but also raise the melting point. Researchers are working now on optimizing Cu content, and plan a detailed investigation of the technology in preparation for a planned commercial launch in about 2010.

Coarsening mechanisms, texture evolution and size distribution of Cu6Sn5 between Cu and Sn-based solders

Scopus: During the reflowing procedure, the Cu concentration in the solder affects the coarsening mechanisms of intermetallic compound (IMC) grains. For the Sn3Cu solder, the mean radius of the IMC grains was proportional to the cube root of the reflowing time; while it follows the square root relation with the reflowing time for the SnAgCu and Sn solders.

It is proposed that the flux from the substrate was only consumed to coarsen the IMC grains for Sn3Cu solder, while it was separated into two fluxes for the SnAgCu and Sn solders at the reflowing initial procedure. For the Sn3.8Ag0.7Cu/Cu and Sn/Cu couples, the size distribution of the IMC grains well agrees with the modified flux driven ripening (FDR) model when the value of r/〈r〉 is above 1; while it would closely match with Marqusee and Ross analysis when the value of r/〈r〉 is below 1.

For Sn3Cu/Cu couple, the size distribution of IMC grains shows good agreement with the FDR model. However, for SnPb/poly-Cu, during the solid-state aging procedure, the mean radius of the IMC grains was proportional to the cube root of the aging time. And the size distribution of IMC grains is well consistent with the FDR model

Localized Recrystallization Induced by Subgrain Rotation in Sn-3.0Ag-0.5Cu Ball Grid Array Solder Interconnects During Thermal Cycling

Scopus: The evolution of microstructures and grain orientations of a Pb-free solder interconnect during thermal cycling significantly affects its mechanical properties and failure modes. Thus, Sn-3.0Ag-0.5Cu ball grid array assemblies were subjected to thermal cycling to study the thermomechanical responses of the solder interconnects.

Thus, Sn-3.0Ag-0.5Cu ball grid array assemblies were subjected to thermal cycling to study the thermomechanical responses of the solder interconnects.

The orientations and microstructures of the solder interconnects were studied by optical microscopy with cross-polarized light and scanning electron microscopy with an electron backscattered diffraction analysis system.

Localized recrystallization behavior was observed in Pb-free solder interconnects during thermal cycling.

Closer examination of the very early stage of recrystallization in the same solder interconnect revealed that the subgrains appeared before the formation of the recrystallized grains, and the orientations of the small recrystallized grains separated by high-angle grain boundaries evolved from the initial orientations by subgrain rotation. The localized recrystallization produced fine-grained microstructures during thermal cycling, providing an additional deformation mechanism for the solder interconnects, i.e., grain boundary sliding, which would have been impossible prior to recrystallization.

The grain orientation has a strong effect on damage generation and the subsequent failure mode; initiation and propagation of cracks could be facilitated by the intrinsic anisotropic thermomechanical responses of the differently oriented grains, leading to a change in the crack propagation path and corresponding failure mode

Improved strength of boron-doped Sn-1.0Ag-0.5Cu solder joints under aging conditions

Scopus: The mechanical properties of new lead-free Sn-Ag-Cu solder alloys containing 0.05-0.1 wt.% boron were investigated under a range of isothermal aging and reflow conditions.

The boron-doped solder joints showed higher ball pull strength than the baseline Sn-1.0Ag-0.5Cu solder joint under all isothermal aging and reflow conditions examined.

In particular, the high-speed ball pull strength of the 0.05 wt.% B-doped solder joint was approximately 2.5 times greater than that of the baseline Sn-1.0Ag-0.5Cu solder joint aged at 150 C for 200 h, which is attributed mainly to the reduced rate of grain growth in the intermetallic compound (IMC) layers of B-doped solder joints under aging conditions

Influence of trace alloying elements on the ball impact test reliability of SnAgCu solder joints

Scopus: In this work, we present ball impact test (BIT) responses and fracture modes obtained at an impact velocity of 0.8 m/s on SAC (Sn-Ag-Cu) package-level solder joints with a trace amount of Mn or RE (rare earth) additions, which were bonded with substrates of OSP Cu and electroplated Ni/Au surface finishes respectively.

With respect to the as-mounted conditions, the Ni/Au joints possessed better impact fracture resistance than those with Cu substrate. Subsequent to aging at 150 C for 800 h, multi-layered intermetallic compounds emerged at the interface of the Ni/Au joints and gave rise to degradation of the BIT properties.

This can be prevented by RE doping, which is able to inhibit the growth of interfacial IMCs during aging.

As for aged Cu joints, the Mn-doped samples showed the best performance in impact force and toughness. This was related to the hardened Sn matrix, and most importantly, a greater Cu3Sn/Cu6Sn5 thickness ratio at the interface.

Compared to Cu6Sn5, Cu3Sn with a similar hardness but greater elastic modulus possessed better plastic ability, which was beneficial to the reliability of solder joints suffering high strain rate deformation if no excess Kirkendall voids formed.

Grain Orientation Evolution and Deformation Behaviors in Pb-Free Solder Interconnects Under Mechanical Stresses

Scopus: n this study, the effect of mechanical stresses on the recrystallization behavior of Sn-3.0Ag-0.5Cu Pb-free solder interconnects was studied by four-point cyclic bending, shear tests, and tensile tests. Scanning electronic microscopy with electron backscattered diffraction was used to characterize the microstructure and crystallographic orientation of the solder interconnects.

The results show that recrystallization occurs under the different mechanical stresses in these tests at room temperature, and that recrystallized grains evolve from subgrains by rotation. Microhardness measurements after shear tests show that the hardness of the recrystallized microstructure was decreased by 15% and 41%, respectively, compared with that of the nonrecrystallized and as-solidified microstructures.

Furthermore, the fine-grained microstructure produced after recrystallization facilitated grain boundary sliding. Therefore, the deformation and cracking behaviors were localized in the degraded recrystallized microstructures once recrystallization occurred, accelerating failure of the solder interconnects

Reliability of the lead-free system part 3: Grid array solder joint reliability

Scopus Over the last 10 years, I have received bountiful questions about best practices when a PCB comprises lead-free packages, tin-lead packages using lead-free solder paste or leadfree solder paste. Concerns often arise regarding the resulting performance and reliability level in each scenario.

Hwang, J.S.

H-Technologies Group, United States:

Solder Volume Effects on the Microstructure Evolution and Shear Fracture Behavior of Ball Grid Array Structure Sn-3.0Ag-0.5Cu Solder Interconnects

Scopus: The standoff height of ball grid array (BGA) structure solder joints has a significant influence on the formation and growth of interfacial intermetallic compounds (IMC).

The results show that the thickness of the IMC layer at the solder/Cu interface of BGA structure Cu/Sn-3.0Ag-0.5Cu/Cu joints increases with decreasing standoff height after reflowing. The growth behavior of the total IMC layer is controlled by a diffusion process with the growth rate increasing with standoff height.

Both the standoff height and isothermal aging time greatly influence the shear behavior of joints, the shear strength of which shows a parabolic trend with increasing standoff height, while the nominal shear strain decreases monotonically with increasing standoff height.

The fracture location of BGA structure joints changed from the middle of the solder matrix to near the interface when the standoff height was increased.

After undergoing isothermal aging at 125C, the fracture mechanism of solder joints changed from ductile fracture to the mixed mode of brittle and ductile fracture with increasing standoff height

Shock impact reliability characterization of a handheld product in accelerated tests and use environment

Scopus: The effect of mechanical shock impacts is a key factor in the reliability of modern handheld products. Due to differences in product enclosures, impact orientations, strike surfaces and mountings of component boards, the loading conditions induced in a true product drop differ from those encountered in standardized board-level tests.

In order to better understand the correlation between board-level drop testing and actual drops of a complete device, series of board and product-level drop tests were conducted using specialized test boards. The mechanical shock impact response of the commercial handheld device component board was characterized with the help of acoustic excitation laser vibrometry and finite element analysis. The results were used to design the mechanically compatible specialized test board for both 4-point supported board-level and unsupported product-level drop tests. Special care was taken to ensure that the vibration behavior of the test board accurately represented the vibration behavior of the commercial component board. Additional board-level drop tests were conducted using a JEDEC JESD22-B111 compliant component board for comparison.

The drop test results showed that, even though the test board design and supporting method have a marked influence on the strain conditions and lifetime of solder interconnections, the primary failure mode and mechanism under the product-level drop tests is comparable to that typically encountered in the standard JEDEC JESD22-B111 board-level drop tests.

More detailed analyses suggest that the comparability of the shock impact loading conditions affecting solder interconnections can be characterized using three metrics: (1) the maximum component board strain rate, (2) the maximum board strain amplitude and (3) the damping of the component board.

Effect of intermetallic compounds on fracture behaviors of Sn3.0Ag0.5Cu lead-free solder joints during in situ tensile test

Scopus: In this paper, in situ tensile tests under various amounts of deformation were performed on Sn3.0Ag0.5Cu lead-free solder joints subjected to multi-reflow and isothermal aging processes by using a scanning electron microscope.

Microstructure evolution and deformation behavior of the solder joints were observed. Effects of the intermetallic compound (IMC) Cu6Sn5 on fracture behaviors of the solder joints were investigated. Results showed that the Sn3.0Ag0.5Cu lead-free solder joints contained only a few Sn grains, and the sequence and degree of plastic deformation varied for the different grains in the same solder joint due to the strong anisotropic properties of Sn grains. Further experiments revealed that plastic deformation occured primarily in the form of slip bands in the solder joints during the in situ tensile test.

Various fracture modes including intergranular and phase boundary fractures were observed. The fracture behaviors of solder joints were significantly affected by morphologies and distributions of the Cu6Sn5 IMCs.

It was found that Cu6Sn5 particles located at the grain boundaries are apt to become crack sources, and that the long rod shaped Cu6Sn5 were easily broken. However, spherical Cu6Sn5 hardly deformed during the tensile test, resulting in dynamic recrystallization. In this case, fracture occured at the sub-grain boundaries

In Situ Synchrotron Characterization of Melting, Dissolution, and Resolidification in Lead-Free Solders

Scopus: Melting and solidification of SAC 305 lead-free solder joints in a wafer-level chip-scale package were examined in situ with synchrotron x-ray diffraction. The chips with balls attached (but not assembled to a circuit board) were reflowed one to three times using a temperature and time history similar to an industrial reflow process.

Diffraction patterns from the same joint were collected every 0.5s during the melting and solidification process. The solidification of the Sn phase in the solder joint occurred between 0.5s and 1s. During melting, most of the Sn melted in about 0.5s, but in some cases took 2-5s for the Sn peak to completely disappear. In one instance, the Sn peak persisted for 30s. The Ag3Sn peaks dissolved in about 1-2s, but the Cu6Sn5 peaks from the interface were persistent and did not change throughout the melting and solidification process. Completely different Sn crystal orientations were always developed upon resolidification

Investigation preparation method and soldering behaviors of Sn-58Bi lead-free solder with carbon nanotubes

Scopus: Varying weight fraction of multi-walled carbon nanotubes were incorporated into Sn-58Bi soler alloy by ball-milling and low temperature melting methods, the morphologies of carbon nanotubes in solder alloy and the influences of carbon nanotubes on the pull-off strength were investigated by SEM, EDS, and DSC.

The experimental results indicate that part of carbon nanotubes are incorporated into Sn-58Bi soler alloy after ball-milling and low temperature melting; 0.03% CNTs can improve the wettability; the melting point of Sn-58Bi-CNTs solder does not change much; the dispersive distribution of carbon nanotubes could refine the microstructure of Sn-58Bi-CNTs joints and the reliability of solder joints also is improved by the influences of CNTs on the fracture mechanism of solder joints


He, P.a , An, J.b , Ma, X.c , Chen, S.c , Qian, Y.b , Lin, T.a  
a  State Key Lab of Advanced Welding Production Technology, Harbin Institute of Technology, Harbin 150001, China
b  Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, China
c  Yik Shing Tat Industrial Co., Ltd, Shenzhen 518101, China

IPC releases PCB industry results for September 2011

EMSNow: "Sales and orders were both under last year's levels in September," said IPC President & CEO Denny McGuirk. "Bookings have been especially sluggish and that has caused a drop in the book-to-bill ratio … although it is still very near parity, which suggests that flat sales is the likely near-term scenario."

The Quest for Standardized Lead-Free Solder Data

Real Time With... SMTAI 2011 Karl Seelig, VP of technology for AIM Solder and chairman of the IPC Solder Product Values Council, discusses his group's drive to create standardized test data for alternative lead-free solders.

Video interview

Alternative Lead-Free Alloys

SMTONLINE : While SnAgCu (SAC) alloys still dominate lead-free selection in North America, especially Sn3.0Ag0.5Cu (SAC305), alternative material systems are available. For any OEM concerned about the high reflow temperatures of SAC, or relying on ODM, it is important to be aware of the most popular alternative lead-free alloys and any potential concerns regarding quality and reliability.

The most popular alternative lead-free alloys, currently, are:

SnAgCuBi;
SnAgCuIn;

SnAgBiIn; and
SnNiCu.

This discussion on the reliability on these alloy systems will provide general trends in terms of performance, but all four systems share a lack of sufficient test data that would allow for the derivation of test-to-field correlation for thermal cycling and vibration.

Reliability of Lead-Free System: Part II, The Role of Creep

SMTONLINE : Like other materials, solder joints do wear out during their service life. This degradation process is unavoidable. The objective of solder joint reliability is to make sure that solder joints do not degrade to the level that loses its required functionality--be it electrical, thermal or mechanical--under a designated service life and anticipated service environments.

Barring other extraneous causes, this solder joint intrinsic degradation process engages two scientific phenomena--fatigue and creep. (For the purpose of this discussion, other extraneous causes include the improperly formed solder joints due to wetting problem, inadequate process issue, surface finish-induced problem at or near the interface, such as Au-embrittlement, and other intermetallic issues, etc.)

Effects of adding 0.05% (La+Ce) on intermetallic compounds at Sn-X-Cu-Ni/Cu interface

Scopus: The microstructure evolution and the behavior of the formation and growth of intermetallic compound (IMC) layer at the interface between Sn-4.1X-1.5Cu-Ni solder and Cu substrate after isothermal aging were studied.

The results show that the thickness of IMC layers in Sn-4.1X-1.5Cu-Ni/Cu system and Sn-4.1X-1.5Cu-Ni-0.05 (La Ce)/Cu system increases with the increase of the aging time, and their growth is mainly controlled by diffusion mechanism. The addition of 0.05% (mass fraction) (La Ce) into the Sn-X-Cu-Ni solder alloy effectively inhibits the formation and growth of IMC during the isothermal aging, which develops solder alloy with a high reliability.

Intermetallic growth rate constant for Sn-4.1X-1.5Cu-Ni/Cu and Sn-4.1X-1.5Cu-Ni-0.05 (La Ce)/Cu is 2.95 10-17m2/s and 2.51 10-17m2/s, respectively.

Chen, H.-Y.a , Jie, X.-H.a , Zhang, H.-Y.a , Guo, L.b

a Faculty of Materials and Energy, Guangdong University of Technology, Guangzhou 510006, China

b GAOXIN Stannum Industry Co., Ltd, Huizhou 516123, Guangdong, China

Dependence of Sn Grain Morphology of Sn-Ag-Cu Solder on Solidification Temperature

Scopus: Near-eutectic Sn-Ag-Cu samples were produced in different sizes and geometries, with different solidification temperatures.

The Sn grain morphologies of samples were characterized and found to be correlated with the sample solidification temperature; the lower the solidification temperature, the higher the degree of interlacing observed.

These Sn grain morphologies were observed to be consistent with a simple model that envisions the nucleus in an undercooled Sn-Ag-Cu liquid to be Sn atoms clustered around a Ag atom in a hexagonal configuration that allows Sn to grow epitaxially on each of its surfaces.

At intermediate degrees of undercooling, a mixed Sn grain morphology is observed, with the interlaced portion associated with the region closer to Sn nucleation in these samples

The Effect of Sb Addition on Sn-Based Alloys for High-Temperature Lead-Free Solders: an Investigation of the Ag-Sb-Sn System

Scopus: Today there is renewed interest in alloys belonging to the Sb-Sn-X (X=Cu, Ag, Bi) ternary systems and their phase equilibria, phase transformations, and thermodynamic properties because of their possible use as high-temperature lead-free solders in the electronics industry.

The integral mixing enthalpy of Ag-Sb-Sn liquid alloys has been measured along five different sections (Ag0.25Sn0.75, Ag0.50Sn0.50, Sb0.30Sn0.70, Sb0.50Sn0.50, and Sb0.70Sn0.30) at 530C, 600C, and 630C, using a high-temperature Calvet calorimeter by dropping pure elements (Ag or Sb) in the binary alloy liquid bath.

The ternary extrapolation models of Muggianu and Toop were used to calculate the integral enthalpy of mixing and to compare measured and extrapolated values. Selected ternary alloys have been prepared for thermal investigation by using a differential scanning calorimeter at different heating/cooling rates in order to clarify the temperature of the invariant reactions and the crystallization path.

Microstructure and tensile behavior of Sn-5Sb lead-free solder alloy containing Bi and Cu

Scopus: Tensile deformation behavior of Sn-5Sb, Sn-5Sb-1.5Bi, and Sn-5Sb-1.5Cu alloys was investigated at temperatures ranging from 298 to 400 K, and strain rates ranging from 5 10-4 to 1 10-2 s-1. Addition of Bi and Cu into the binary alloy resulted in an increase in both ultimate tensile strength (UTS) and ductility.

The improved strength of the Bi-containing alloy can be attributed to the microstructural refinement, uniform distribution of the SnSb intermetallic particles, and solid-solution hardening effect of bismuth in the β-Sn matrix.

The enhanced strength of the Cu-containing alloy was ascribed to the presence of the Cu6Sn5 intermetallic particles and structural refinement. The ductility of both ternary alloys was, however, improved by the structural refinement, caused by the addition of alloying elements.

PCB related failures in electronic assemblies

Scopus: The complexity of Printed Circuit Boards (PCBs) has increased dramatically over the last three decades with the development of surface mount technology (SMT). The typical manufacture of rigid multilayer PCB contains many process procedures, which makes manufacture and application much more challenges. This paper focuses on some typical PCB related failures. Recommendations are provided on optimizing PCB manufacture process and material application. Microvia crack, black pad, galvanic attack, pad design, conductive anodic filament and pad crater are presented in detail

Liu, P.a b , Gu, X.a , Zhao, X.b , Liu, X.a

a Zhejiang Province Key Laboratory of Soldering and Brazing Materials and Technology, Zhejiang Metallurgical Research Institute, Hangzhou 310011, China

b Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China

Vibration fatigue analysis of the solder connector

Scopus: With the increasing problems of fatigue failure of PCB in aeronautic and astronautic electronic chassis, the paper proposes a life prediction method of the solder connector based on physics of failure by simulation and physical test.

The virtual modal and random vibration response of the box should be solved by finite element method in the ANSYS software, and these results have been verified by modal test and random vibration test.

While the structure parameter and the environment stress of the box, the results of the simulation as the input of the vibration fatigue physics of failure model, the life of solder connector could be computed. There is a comparison between results from the CalcePWA software and it from physics of failure model and simulation

Guo, X., Li, C., Liu, L.

Beihang University, Beijing, 100191, China

Solder bump with inner core pillar in semiconductor package

US8039960: An electrical interconnect within a semiconductor device consists of a substrate with a plurality of active devices.

A contact pad is formed on the substrate in electrical contact with the plurality of active devices. A passivation layer, first barrier layer, adhesion layer, and seed layer are formed over the substrate. An inner core pillar including a hollow interior is centered over and formed within a footprint of the contact pad.

A second barrier layer and a wetting layer are formed over the single cylindrical inner core pillar and hollow interior.

A spherical bump is formed around the second barrier layer, wetting layer, and single cylindrical inner core pillar. A footprint of the spherical bump encompasses the footprint of the contact pad. The spherical bump is electrically connected to the contact pad

SMTA International Concludes Successfully

SMTA International Concludes Successfully: The SMTA released a summary of the SMTA International Conference and Exhibition which attracted more than 1,000 attendees from 25 countries. The event took place October 16-20 at the Fort Worth Convention Center in Fort Worth, Texas.

The technical conference was very well-received and continued the SMTAI tradition of having the strongest technical conference in the industry. Lee Smith of Amkor Technology gave a rousing opening session presentation on the future of Package-on-Package technology. The Lead-Free Symposium was once again a big draw, covering findings from the NASA-DoD Lead-Free Electronics Project. The riveting Keynote Address by Mark Medlen, Riverwood Solutions, provided an inside look at how a company can develop a supply chain that is as competitive as it is responsive.

All technical papers from the conference are available on the conference proceedings CD which can be purchased in the SMTA BookStore.

Seika Machinery’s SPR Produces Pure Solder Ingots

Seika Machinery said an independent lab has confirmed its Solder Paste Recycling machine is capable of producing pure solder ingots from solder paste.

The ingots produced by the SPR Unit are reportedly 100% pure, with no additives or impurities added to the solder paste during the recycling process. The system removes the flux from the metal and produces a flux-free ingot. There are no voids inside the solder ingots, says Seika.

A number of analyses were performed, including Fourier Transform Infrared Spectroscopy, Inductively Coupled Plasma technique, and Scanning Electron Microscopy.

The machine enables 100% of the metal content of waste solder paste to be recovered as solder bar, the firm says.

New Electronic Materials to be Debuted at Productronica 2011 in Munich

TMCnet.com: With the industrial electronics market in mind, Henkel has developed a pair of breakthrough electrically conductive adhesive (ECA) technologies that overcome many of the shortcomings of competitive materials.

ABLESTIK ICP-3535M1 is a single component ECA that enables manufacturers to incorporate lower cost tin-terminated components and thus obtain a cost-effective, lead-free, high reliability assembly. The material has excellent electrical and adhesion stability, no bleeding or wicking on miniaturized components and can be cured quickly at low temperature. For automotive applications where both high flexibility and excellent conductivity are required, Henkel has designed the first-ever high-end conductive silicone adhesive technology. In fact, ABLESTIK ICP-4000 has already been qualified and is being used for automotive sensor products where components are bonded to metal leadframes inside plastic housings.

Historically, the CTE (coefficient of thermal expansion) mismatch between the metal and the plastic has introduced damaging stress to the device. But, Henkel's conductive silicone technology is able to absorb this stress, maintain the bond and deliver the electrical interconnect between the component and the leadframe.

Relation between Kirkendall voids and intermetallic compound layers in the SnAg/Cu solder joints

Scopus: Several different kinds of intermetallic compound (IMC) layers were fabricated through adding trace elements into the Sn-3.5Ag solder, to investigate the relationship between the Kirkendall void (KV) and the IMC layers.

The results show that a considerable amount of KVs were observed at the Cu3Sn/Cu interface in the Sn-3.5Ag/Cu joint after isothermal aging. A proper amount of Zn (0.5 wt%) and Ge (0.1 and 0.3 wt%) were found to effectively suppress the formation of the Cu3Sn layer, and no obvious KVs were observed at the Cu6Sn5/Cu interface, while more Zn induced the formation of the Cu6Sn5 plus Cu-Zn mixed IMC layer, and voids (not KVs) were observed at the Cu6Sn5/Cu-Zn interface. (Cu,Ni)6Sn5 IMC layer replaced the initial Cu6Sn5 at the SnAg-Ni/Cu joints, likewise, the Cu3Sn was suppressed at the thermal aging stage.

Moreover, voids were found at the IMC/solder interface, while not at the IMC/Cu. Therefore, the formation of KVs is greatly determined by the characteristic of the IMC layer, this is consistent with the previous reports. On other hand, the KV can be suppressed by controlling the interfacial phase through adding trace elements into the solder.

Yu, C.a b , Yang, Y.a , Wang, K.a , Xu, J.a b , Chen, J.a b , Lu, H.a b

a School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China

b Shanghai Key Laboratory of Materials Laser Processing and Modification, Shanghai, 200240, China

Effect of solder joint parameter on vibration fatigue reliability of high density PCB assembly

Scopus: In order to explore the influence of solder joint parameter on vibration fatigue reliability of high density PCB assembly, a three-dimensional simulation model which was almost completely in keeping with test samples was created, and the modal parameters were obtained through modal test and finite element method respectively.

Moreover, solder joint stress and strain decreases with solder joint height decreasing and diameter increasing, but when height and diameter reaches a certain value, stress and strain will almost keep constant. Under the same conditions, the order of the strains of the joints is: lead solder joints (Sn63Pb37) > mixed solder joints (79% SAC and 21% SnPb) > lead-free solder joints (SAC305). Consequently, more PCB fixations and solder joints which have smaller height, larger diameter or have lead-free will decrease stress and strain of key positions of PCB assembly, and BGA (ball grid array) devices should be placed near the region which has more fixation positions. Finally, based on stress and strain failure criteria, it can make some references for predicting and optimizing random vibration fatigue life of solder joints, guiding BGA layout and selecting solder joints.

Qi, X.a b , Zhou, B.b , En, Y.b

a School of Electronic and Information Engineering, South China University of Technology, Guangzhou, China

b Science and Technology on Reliability Physics and Application of Electronic Component Laboratory, China Electronic Product Reliability and Environmental Testing Research Institute, Guangzhou, China

Fracture behavior of Cu-cored solder joints

Scopus: Copper-cored solder can be regarded as the next-generation solder for microelectronic semiconductors exposed to harsh operating conditions owing to its excellent sustainability under extreme thermal conditions, e.g., in microelectronic semiconductors used in transportation systems.

Cu-cored solder joints with two different coating layers, Sn-3.0Ag and Sn-1.0In, were compared with the baseline Sn-3.0Ag-0.5Cu solder. The fracture strength and failure mode were examined using the high-speed ball-pull and normal-speed shear tests. The Cu-cored solder joint with the Sn-1.0In plating layer exhibited the highest ballpull and shear strengths. In addition, it showed a much lower percentage of interface fracture between the Cu-core and plating layer than the interface fracture percentage in the Sn-3.0Ag plating layer due to the improved wettability between the Cu-core and Sn-1.0In plating layer

Kim, Y.a , Choi, H.a , Lee, H.a , Shin, D.a , Moon, J.b , Choe, H.a

a School of Advanced Materials Engineering, Kookmin University, Jeongneung-dong, Seongbuk-gu, Seoul 136-702, South Korea

b MK Electron Co., Ltd, 316-2 Geumeoh-ri, Pogok-eup, Cheoin-gu, Yongin-si, Kyeonggi-do 449-812, South Korea

Effect of adding Ce on interfacial reactions between Sn-Ag solder and Cu

Scopus: We investigated the effect of adding cerium (Ce) to low Ag content Sn-1.0wt.%Ag solder on the interfacial reactions between the Sn-1.0Ag solder and Cu substrate. The formation and growth of interfacial intermetallic compounds (IMCs) between the Sn-1.0Ag-0.3Ce solder and Cu substrate were studied and the results were compared to those obtained for the Ce-free Sn-1.0Ag/Cu and most promising Sn-3.0Ag-0.5Cu/Cu systems.

The addition of Ce to the Sn-Ag solder significantly reduced the growth of the interfacial Cu-Sn IMCs, retarded the interfacial reactions between the solder and the substrate, and prevented the IMC from spalling from the interface. The Sn-1.0Ag-0.3Ce solder alloy had a good interfacial stability with the Cu substrate during solid-state isothermal aging in the viewpoint of IMC growth.

Yoon, J.-W., Noh, B.-I., Choi, J.-H., Jung, S.-B.

School of Advanced Materials Science and Engineering, Sungkyunkwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon, Gyeonggi-do 440-746, South Korea

Effect of Bismuth on Intermetallic Compound Growth in Lead Free Solder/Cu Microelectronic Interconnect

Scopus: The intermetallic compound (IMC) growth kinetics in pure Sn/Cu and Sn10 wt%Bi/Cu solder joints was studied, respectively, after they were aged at 160-210'C for different time.

It was found that the total IMC in SnlO wt%Bi/Cu joint developed faster than it did in pure Sn/Cu solder joint, when they were aged at the same temperature. And the activation energy Qa for total IMC in Sn10 wt%Bi/Cu joint was lower than that for pure Sn/Cu interconnect. The IMC growth process was discussed. The IMC Cu6Sn5 was enhanced in compensation of reduced IMC Cu3Sn growth.

The work reveals that Bi element containing in lead free solder alloys with 10 wt% can enhance IMC growth in lead free solder/Cu joint during service

Kang, T.Y.a , Xiu, Y.Y.b , Hui, L.b , Wang, J.J.b , Tong, W.P.a , Liu, C.Z.b

a Key Laboratory of Electromagnetic Processing of Materials, Ministry of Education, Northeastern University, Shenyang 110004, China

b Shenyang Aerospace University, Shenyang 110136, China

Renesas - Cu and tin balls for high temperature soldering

(US8022551):Each of junctions formed between a semiconductor device and a substrate comprises metal balls of Cu, or other materials and compounds of Sn and the metal balls, and the metal balls are bonded together by the compounds.

A semiconductor module comprising a substrate having an electrode, a chip component mounted on said substrate and a semiconductor chip mounted on said substrate, wherein said chip component is connected to said electrode with a solder bonding material, said solder bonding material being substantially free of lead (Pb) and comprising an intermetallic compound, an amount of unreacted solder on a periphery of said intermetallic compound, and a plurality of copper (Cu) balls disposed in said intermetallic compound, said intermetallic compound having a melting point higher than that of said solder.

Soga, Tasao; Fujisawa, Japan

Shimokawa, Hanae; Yokohama, Japan

Nakatsuka, Tetsuya; Yokohama, Japan

Miura, Kazuma; Yokohama, Japan

Negishi, Mikio; Komoro, Japan

Nakajima, Hirokazu; Saku, Japan

Endoh, Tsuneo; Komoro, Japan

Assignee: Renesas Electronics Corporation, Kawasaki, Japan

Hitachi - Anti-oxidant for solder ball surface

US8020745: Solder ball for mounting e.g. chip scale package on printed wiring board, has surface coated with sorbitan fatty acid ester, vitamin or vitamin derivative containing cyclic structure and aliphatic hydrocarbon group

Ota, Ryo; Hitachi, Japan

Itabashi, Takeyuki; Hitachi, Japan

Doping of lead-free solder alloys and structures formed thereby (US20100155115A1)

US20100155115A1: Methods of forming a microelectronic structure are described. Those methods include doping a lead free solder material with nickel, wherein the nickel comprises up to about 0.2 percent by weight of the solder material, and then applying the solder material to a substrate comprising a copper pad.

Pang, Mengzhi; Phoenix, AZ, United States of America

Gurumurthy, Charan; Higley, AZ, United States of America

Assigned to Intel

Wetting and interfacial reaction characteristics of Sn-1.2Ag-0.5Cu-xIn quaternary solder alloys

Scopus: Through the use of a wetting balance technique, the wetting characteristics of Sn-1.2Ag-0.5Cu-xIn quaternary solder alloys with respect to the In content and soldering temperature were investigated to validate the applicability of compositions with a low Ag content as solder material. It was found that a small addition (0.4-0.6 wt.%) of In significantly improved the wetting properties of the Sn-1.2Ag-0.5Cu-xIn composition at soldering temperatures ranging from 230 'C to 240 'C due to the excellent wetting property of In. In an observation of the interfacial reaction, it was found that the added In element did not participate in the interfacial reaction with a Cu or Ni pad, unlike in the Sn-Ag-Cu-In case, which has a high In content. The package or boardside IMC layers in Sn-1.2Ag-0.5Cu-0.4In joints were thinner than those of Sn-3.0Ag-0.5Cu, especially after aging.

Yu, A.-M.a , Kim, M.-S.a , Lee, C.-W.b , Lee, J.-H.c

a Division of Materials Science and Engineering, Inha University, Incheon 402-020, South Korea

b Advanced Welding and Joining RandD Department, Microjoining Center, Korea Institute of Industrial Technology (KITECH), Incheon 406-840, South Korea

c Department of Materials Science and Engineering, Seoul National University of Science and Technology, Seoul 139-743, South Korea

Jasbir Bath on low silver solders

Real Time With... IPC Midwest 2011

Jasbir Bath talks with Bob Neves about the industry's reaction to the soaring cost of silver.

What does the market need to consider in the move to produce solders with a lower percentage of silver?

Sn-coated nanotubes for nanochips

Factiva "A Sn coated single multi-walled carbon nanotube (MWCNT) was connected between Cu terminals and with other MWCNTs using tin solder. HRTEM micrographs showed the interconnections between two sides as well as on one side of a Cu grid," researchers in Tainan, Taiwan report.  "MWCNTs not only formed straight connections but also bent in the middle with little damage to the graphenes of nanotubes. The process also joined a single nanotube with other nanotubes at their tips as well as in the middle, and in various modes including series and parallel. The connections were found to be stable in air and under TEM observations, and could be made by both small and large diameter MWCNTs," wrote J. Mittal and colleagues, National Cheng Kung University.  The researchers concluded: "The process uses existing Sn-based soldering technology and provides a way for the development of CNT-based nanochips

An investigation of microstructure and mechanical properties of novel Sn3.5Ag0.5Cu-XTiO2 composite solders as functions of alloy composition and cooli

Scopus: In the present study, the influence of both TiO2 nanoparticle addition and cooling rate on the melting temperature, microstructure, and mechanical behaviour of Sn3.5Ag0.5Cu (SAC) solder alloys was studied. The composite solders were prepared by mechanical mixing of TiO2 nanoparticles with SAC solder. With the addition of TiO2 nanoparticles into the eutectic SAC alloy, a novel SAC composite solder was successfully prepared. The melting temperature for the SAC composite solders was found to be only 1.56 �C higher than that of the SAC solder, indicating that the novel SAC composite solder is fit for existing soldering process. The cooling rate and TiO2 nanoparticle addition affected the solidification of the microstructure dramatically. Notably, SEM observation of the microstructure of the SAC composite solders under the rapid-cooled condition revealed fine dot-like nano-Ag3Sn IMC in the solder matrix. The ultimate tensile strength (UTS), 0.2% yield strength (0.2YS), and microhardness of the SAC composite solder increased with the increase of TiO2 nanoparticle content by 0.25-1.0 wt.% and the cooling rate, which could be attributed to the dispersion strengthening mechanisms. However, the ductility of the composite solders was found to decrease because of microporosity at the Ag3Sn network grain boundary

Tsao, L.C.

Department of Materials Engineering, National Pingtung University of Science and Technology, 1, Hseuhfu Road, Neipu, Pingtung 91201, Taiwan

Creep-fatigue crack growth behavior of Pb-contained and Pb-free solders at room and elevated temperatures

Scopus - Document details: Fatigue crack growth tests of lead-contained (Sn-37Pb) and lead-free (Sn-3.0Ag-0.5Cu) solders were conducted under frequencies ranged from 10 to 0.1 Hz and a stress ratio of 0.1 at room temperature and 70'C. J-integral range (ΔJ) and modified J-integral (C*) were used for discussing about cycle-dependent and time-dependent crack growth behavior for both the solders.

The experimental results showed that crack growth behavior of both the solders was predominantly time-dependent at lower frequency and higher temperature, while it was predominantly cycle-dependent at higher frequency and lower temperature. Under the present test condition of stress ratio of 0.1, when the frequency was higher than 0.5 Hz at room temperature and 1 Hz at 70'C for both the solders, crack growth behavior was cycle-dependent. The crack growth resistance of lead-free solder was higher than that of lead-contained solder, which was much significant in time-dependent region. From the fracture surface observations, it was found that as the frequency decreased and/or the temperature increased, the fracture surface appearance changed from transgranular to intergranular manner for both the solders

Fakpan, K.a , Otsuka, Y.b , Mutoh, Y.b , Inoue, S.c , Nagata, K.d , Kodani, K.d

a Department of materials science, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka 940-2188, Japan

b Department of system safety, Nagaoka Universty of Technology, 1603-1 Kamitomioka, Nagaoka 940-2188, Japan

c Department of Mechanical Engineering, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoga 940-2188, Japan

d Toshiba Corporation, Toshiba-cho 183-8511, Japan

Effects of different solder alloys on reliability of 3D PLUS solder joint

Scopus: Thermal cycling was applied to assess the effect of tin-lead solder 63Sn37Pb and lead-free solder 95.5Sn3.8Ag0.7Cu on the reliability of 3D PLUS solder joints. Nonlinear finite element method and viscoplastic Anand model were used to evaluate the stress and strain distribution and dangerous position of solders under the thermal cycling condition. The law of solder joints stress and plastic strain were finally obtained and showed significant cyclical changes. The stress and strain emerged the trend of accumulated enhancement with the process of time, then ultimately stabilized. Comparing two curves of equivalent stress and plastic strain obtained from lead-free and tin-lead solder, it was found that the reliability of 95.5Sn3.8Ag0.7Cu was better than that of 63Sn37Pb

Advanced Materials Research

Volume 314-316, 2011, Pages 1038-1042

Bao, N., Wang, C., Zhu, L., Song, S.

School of Mechanical Engineer and Automation, Beihang University, Beijing 100191, China

Influence of surface segregation on wetting of Sn-Ag-Cu (SAC) series and Pb-containing solder alloys

Scopus: Wetting of Sn-Ag-Cu (SAC) series solder alloys to solid substrates is strongly influenced by surface segregation of low-level bulk impurities in the alloys. We report in situ and real-time Auger electron spectroscopy measurements of SAC alloy surface compositions as a function of temperature as the alloys are taken through the melting point. A dramatic increase in the amount of surface C (and frequently O) is observed with temperature, and in some cases the alloy surface is nearly 80 at.% C at the melting point. The C originates from low-level impurities incorporated during alloy synthesis and inhibits wetting because C acts as a blocking layer to reaction between the alloy and substrate. A similar phenomenon has been observed over a wide range of (SAC and non-SAC) alloys synthesized by a variety of techniques. That solder alloy surfaces at melting have a radically different composition from the bulk uncovers a key variable that helps to explain the wide variability in contact angles reported in previous studies of wetting and adhesion

Bozack, M.J.a , Suhling, J.C.b , Zhang, Y.b , Cai, Z.b , Lall, P.b

a Department of Physics, Center for Advanced Vehicle and Extreme Environment Electronics (CAVE3), Auburn University, Auburn, AL 36849, United States

b Department of Mechanical Engineering, Center for Advanced Vehicle and Extreme Environment Electronics (CAVE3), Auburn University, Auburn, AL 36849, United State

Low-temperature joining technique as interconnection technology for power electronics

Scopus: There is a demand for higher junction temperatures in power devices, but the existing packaging technology is limiting the power cycling capability if the junction temperature is increased. Limiting factors are solder interconnections and bond wires. With Replacing the chipsubstrate soldering by low temperature joining technique, the power cycling capability of power modules can be increased widely. Replacing also the bond wires and using a double-sided low temperature joining technique, a further significant increase in the life-time of power devices is achieved

Advanced Materials Research

Volume 324, 2011, Pages 437-440

Amro, R.

Palestine Polytechnic University, Hebron, Palestine

Developments of microwave heating system for soldering fine circuits

Scopus: The microwave heating system using evanescent wave for soldering fine circuits had been proposed. The evanescent wave is useful for the microwave heating very locally. The heating system consists of a matching circuit and a resonator for enhancing the magnetic field around the mouth of a circular waveguide in which the strong evanescent waves are excited.

The experiments of heating lead-free solders have been done with the microwave at a frequency of 2.3-2.35 GHz and a power of about 200 W. The lead-free solder can be heated locally to be melted with microwave without any breakdown in the resonator.

IEEJ Transactions on Fundamentals and Materials

Volume 131, Issue 8, 2011, Pages 665-670

Saigusa, M., Shengguo, S., Takekawa, T., Sugawara, S.

Saigusa Labs., College of Engineering, Ibaraki University, 4-12-1, Nakanarusawa-chou, Hitachi-shi, Ibaraki 316-8511, Japan

iNEMI Lead Free Wave Soldering Project: An Investigation of Reliability of Through-Hole Electrical Interconnects

Printed Circuit Design & Fab Magazine Online: Previous investigations of Pb-free wave soldering, as well as standards development, focused on process optimization, material selection, through-hole fill, coverage requirements, etc.

However, few published investigations focus on the reliability of surface mount and through-hole solder joints assembled with various board finishes and thicknesses, component types and alloys. This iNEMI collaboration studied and reports on the behavior and performance of various solder alloys and solder joints after long-term thermal cycle testing.

(SMTA International, October 2011)

Authors: Denis Barbini, Quyen Chu, Denis Jean, Stuart Longgood, Keith Howell and Jian Miremadi; barbini@uic.com.

The Effect of Design Parameters on PTH Barrel Fill in High Complexity Assembly

Printed Circuit Design & Fab Magazine Online: Through-hole barrel fill, especially for high-complexity thick PCBs, is an issue in Pb-free soldering. Many experimenters have identified that inadequate hole fill can be improved by optimized preheat profiles, higher pot temperatures, and more aggressive fluxes. However, processing temperatures are limited by the thermal tolerances of the laminate and components. Even Pb-free-compliant laminates cannot withstand extended exposures to liquid solder, and flux chemistries limit preheat temperatures. The application of more aggressive fluxes with high solid contents often leads to undesirable residues that can affect AOI, pin probability at downstream testing, and a host of other problems associated with reduced cleanliness. This work explores the optimization of through-hole solder fill by design for manufacture. The focus is on investigating design factors affecting barrel fill of high-complexity thick boards (>0.120", >10 layers) populated with high-thermal-mass components. Assembly processes, test methods, analysis and selected results are discussed.

(SMTA International, October 2011)

Authors: Jinda Songninluck, et al; jsongni@celestica.com.

Effect on lead-free solder joint reliability caused by solder volume - Welding International - Volume 25, Issue 11

Welding International - Volume 25, Issue 11: Welding International

Volume 25, Issue 11, 2011

Effect on lead-free solder joint reliability caused by solder volume

Mitsuharu Yamabea, Masako Fukumitsua & Yoshitoshi Fukuchia
pages 851-856

Available online: 22 Sep 2011

New method for soldering to glass

Factiva "A new variant of the anodic bonding technique (ALTSAB: Activated Liquid Tin Solder Anodic Bonding) is described, which offers a number of advantages for direct glass to metal sealing over conventional methods. It employs a tin solder alloy containing an activating metal which is anodically bonded to alkali rich glass substrates in the liquid state."

"Two different test specimens were fabricated and characterized under vacuum at a pressure of 5 x 10(-4) mbar and a bonding temperature of 300 degrees C and compared with standard Al/glass anodic bonds. The ability to fabricate dual interface bonds of good quality and high shear strength > 16 MPa by the ALTSAB method was demonstrated. With the sealant metal in the liquid state, this methodology promises superior surface adaptation and therefore joint performance when compared with the standard anodic bonding. More importantly, there is no need for premetallization or surface pretreatment of the glass substrates, and unlike in conventional anodic bonding, there is no need for mechanically loading the joining assembly. Wetting of the float glass substrates by the activated solder alloy SnAl0.6 after successful anodic bonding was confirmed by optical microscopy. The enrichment of the activating element Al at the bonding interface was confirmed by SEM and EDS element mapping," wrote M.M. Koebel and colleagues, Swiss Federal Laboratories for Materials Testing and Research.

The researchers concluded: "The methodology presented here shows great promise for various large-area sealing applications, particularly vacuum glazing, thin film and organic PV and OLED technology."

Koebel and colleagues published their study in Solar Energy Materials and Solar Cells (Anodic bonding of activated tin solder alloys in the liquid state: A novel large-area hermetic glass sealing method. Solar Energy Materials and Solar Cells, 2011;95(11):3001-3008).

Genesis analysis of common defects of reflow soldering and research for solutions

Scopus: To guarantee the quality of surface mounting electronic products, this article analyzes the process features of its four working zones, discusses some main factors which influences the soldering quality of reflow soldering, analyzes the common soldering defects and their causes according to the temperature and process features of reflow soldering during the process of reflow soldering like row-up, bridging, wicking and solder balling. By these measurements, appearance frequency of reflow soldering is effectively reduced and quality of surface mounting electronic products is also raised.

Peng, Y., Wang, W., Wang, X.

School of Information Engineering, Chongqing City Management College, Chongqing 401331, China

Influences of atomizing pressure on properties and microstructure at brazed joint of lead-free solder powder

Scopus: he effects of the atomizing pressure on the microstructures and properties of the lead-free solder powder by the supersonic atomizer method were investigated.

The microstructures of the brazed joint of solder paste were also observed. The results showed that with increasing atomizing pressures from 0.4 to 0.7 MPa, the powder particles are refined significantly and the effective atomization efficiency increases rapidly, but the oxygen content slightly rises.

When the atomizing pressures increases from 0.7 to 0.9 MPa, the effective atomization efficiency only increases slightly, meanwhile both sphericity and roughness of the powder deteriorate. The atomized powder exhibits high effective atomizing efficiency, uniform size distribution, good sphericity and smooth surface when the atomizing pressure is 0.7 MPa.

The diffusion layer brazed welded by Sn3Ag2.8Cu paste with Cu substrate is thicker and more irregular than that of by Sn37Pb paste

Xu, T.a b , Jin, H.b , Zhao, M.c , Wang, D.a

a Shool of Materials Science and Engineering, Xi'an Shiyou University, Xi'an 710065, China

b Xi'an Jiaotong University, Xi'an 710049, China

c Shool of Materials Science and Engineering, Xi'an University of Technology, Xi'an 710049, China

Interface reaction between SnAgCu/SnAgCuCe solders and Cu substrate subjected to thermal cycling and isothermal aging

Scopus: Trace amount of rare earth Ce (0.03 wt.%) was added into SnAgCu solder in order to reform the properties of the solder. In this study, interface reaction mechanism during thermal cycling and isothermal aging, was studied by studying the formation and growth of the intermetallic compound (IMC) at the solder (SnAgCu or SnAgCuCe)/Cu interface, and the growth kinetics which forming IMC in both systems (SnAgCu or SnAgCuCe) were also investigated under different aging conditions.

The results show that the morphology of IMCs formed both at SnAgCu/Cu and SnAgCuCe/Cu interfaces was gradually changed from scallop-like to planar-like, and the thickness of different IMCs evolved with the increasing of aging time.

The results also indicate that the growth rate of IMC at both interfaces during thermal cycling was higher than that during isothermal aging.

Especially, the addition of amount of rare earth Ce into the SnAgCu solder can refine the microstructures; decrease the thickness of the intermetallic compound layer of SnAgCu solder alloys

Zhang, L.a b , Xue, S.B.a , Zeng, G.a , Gao, L.L.a , Ye, H.a

a College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

b School of Mechanical and Electrical Engineering, Xuzhou Normal University, Xuzhou 221116, China

US WEEE recycling statistics

Factiva According to the International Data Corporation (IDC), a global market research provider, growth in the U. S. electronics recycling industry in the past decade shows a bright spot in an otherwise sluggish economy.

"Approximately 3.5 million tons of electronics were recycled by the recycling industry in the United States in 2010, employing more than 30, 000 workers with estimated revenue of over $5 billion," said David Daoud, IDC research director.

A recent IDC survey "shows a booming electronics recycling industry and prescribes a clear path for even more growth," said Robin Wiener, president of the Institute of Scrap Recycling Industries Inc.

"Electronics recyclers are creating American jobs, adopting an industry standard that will help sustain growth, and are recycling electronics here at home." McKernan, who has been in the electronics industry more than 40 years and with the Victor company for 12, said he is proud to be part of a positive movement.

Recycling "is our biggest environmental defense," he said.

Solder selection of lead-free reflow soldering and optimization of craft curve

Scopus: Lead-free reflow soldering craft is the most important solder craft in surface mount technology at present. However, the great reduction of crafting window brings challenges to the soldering quality and also poses higher requirement for the stability and reliability of lead-free soldering equipment. This article analyzes problems out of lead-free process, introduces the selecting principle of lead-free solder and analyzes the optimizing gist of temperature curve of lead-free reflow soldering

Wang, W., Peng, Y.

School of Information Engineering, Chongqing City Management College, Chongqing 401331, China

Inhibiting the consumption of Cu during multiple reflows of Pb-free solder on Cu

Scopus: An effective approach to inhibiting the consumption of Cu during multiple reflows of SnAg2.3 solder on Cu is reported. By depositing a very thin layer of solder on Cu, followed by a 10-min reflow, the scallop-type morphology of interfacial Cu6Sn5 intermetallic compounds (IMC) became flat, and the channels between them closed up. When additional solder was deposited on the sample and reflowed again, the consumption of Cu as well as the growth the IMC was retarded.

Hsiao, H.-Y.a , Hu, C.-C.a , Guo, M.-Y.a , Chen, C.a , Tu, K.N.b

a Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan

b Department of Materials Science and Engineering, University of California at Los Angeles, Los Angeles, CA 90095-1595, United States

Toward a Better Understanding of the Effect of Cu Electroplating Process Parameters on Cu3Sn Voiding

Scopus: "Kirkendall voiding" in the interfacial Cu3Sn intermetallic compound is often observed in solder joints made between Sn-containing alloys and Cu interconnect pads, during extended thermal aging or electromigration testing.

It is commonly believed that voids arise from the Kirkendall effect, i.e., the imbalance of diffusion fluxes of Cu and Sn atoms in Cu3Sn. However, recent studies have demonstrated that the propensity for voiding is greatly affected by the amount of organic impurities incorporated during Cu electroplating.

The level of impurities was shown to depend on various electroplating parameters, such as current density, bath temperature, bath age, etc.

In this study, a general picture is proposed to provide a better understanding of the effect of electroplating process parameters on Cu3Sn voiding. The picture correlates the level of impurity incorporation to (1) the applied electroplating overpotential, and (2) the crystallographic orientation of the Cu deposit. As a first-order approximation, the picture is supported by a variety of electroplating experiments, secondary-ion mass spectroscopy (SIMS), and x-ray diffraction (XRD) analysis

Yin, L.a , Wafula, F.b , Dimitrov, N.b , Borgesen, P.c

a Universal Instruments Corporation, Conklin, 13748, United States

b Department of Chemistry, Binghamton University, Binghamton, 13902, United States

c Department of Systems Science and Industrial Engineering, Binghamton University, Binghamton, 13902, United States

Influence of temperature and strain rate on tensile properties of single walled carbon nanotubes reinforced Sn-Ag-Cu lead free solder alloy composites

Scopus: The effect of temperature and strain rate on the tensile properties of Sn-3.8Ag-0.7Cu (SAC387) alloy as well as SAC387 alloy reinforced with two different weight percentages (wt.%) of SWCNT was investigated. It was found that addition of 0.05 wt.% SWCNT to SAC387 alloy results in an increase in yield and ultimate tensile strengths without affecting the total elongation at all temperatures and strain rates studied, although the increase in strength values at 75 °C was marginal. Further increasing the SWCNT to 0.1 wt.% did not result in any significant improvements in the strengths as compared to the composite containing 0.05 wt.% SWCNT. Temperature and strain rate were observed to have a significant effect on the strengths in both SAC387 alloy as well as the composites. Both the yield and ultimate tensile strengths were observed to decrease with increase in temperature and increase with increase in strain rates in SAC387 alloy as well as the composites. This behaviour was attributed to the competing effects of work hardening and dynamic recovery processes and the effect of temperature and strain rates on these processes.

Niranjani, V.L.a , Rao, B.S.S.C.b , Singh, V.a , Kamat, S.V.a

a Defence Metallurgical Research Laboratory, Hyderabad, India

b Department of Mechanical Engineering, National University of Singapore, Singapore

Recrystallization and Precipitate Coarsening in Pb-Free Solder Joints During Thermomechanical Fatigue

Scopus: The recrystallization of β-Sn profoundly affects deformation and failure of Sn-Ag-Cu solder joints in thermomechanical fatigue (TMF) testing. The numerous grain boundaries of recrystallized β-Sn enable grain boundary sliding, which is absent in as-solidified solder joints. Fatigue cracks initiate at, and propagate along, recrystallized grain boundaries, eventually leading to intergranular fracture.

The recrystallization behavior of Sn-Ag-Cu solder joints was examined in three different TMF conditions for five different ball grid array component designs. Based on the experimental observations, a TMF damage accumulation model is proposed: (1) strain-enhanced coarsening of secondary precipitates of Ag3Sn and Cu6Sn5 starts at joint corners, eventually allowing recrystallization of the Sn grain there as well; (2) coarsening and recrystallization continue to develop into the interior of the joints, while fatigue crack growth lags behind; (3) fatigue cracks finally progress through the recrystallized region. Independent of the TMF condition, the recrystallization appeared to be essentially complete after somewhat less than 50% of the characteristic life, while it took another 50% to 75% of the lifetime for a fatigue crack to propagate through the recrystallized region.

Yin, L.a , Wentlent, L.b , Yang, L.b , Arfaei, B.b , Oasaimeh, A.b , Borgesen, P.b

a Universal Instruments Corporation, Conklin, 13748, United States

b Department of Systems Science and Industrial Engineering, Binghamton University, Binghamton, 13902, United States

Microvoid Formation at Solder-Copper Interfaces During Annealing: a Systematic Study of the Root Cause

Scopus: The electrodeposition conditions that contribute to microvoid formation during isothermal aging of Pb-free solder-electrodeposited copper were evaluated in a systematic series of processing experiments.

The results of 2K full-factorial design of experiment are presented to show the effect of prescreened electroplating parameters such as brighteners, wetting agent, bath age, and current density on the propensity for microvoiding at solder-copper interfaces after annealing at 125'C for 40 days.

It was found that the amount of microvoiding is greatly affected by bath age, wetting agent, brightener, and their interactions. Time-of-flight secondary-ion mass spectroscopy and glow discharge spectroscopy allowed us to establish a correlation between impurities incorporated in copper during electroplating and microvoiding at the solder-copper interface.

Intermetallic compound growth suppression at high temperature in SAC solders with Zn addition on Cu and Ni-P substrates

Scopu: The effect of adding 0.5-1.5 wt.% Zn to Sn-3.8Ag-0.7Cu (SAC) solder alloy during reflow and solid state ageing has been investigated.

In particular, the role of the Zn addition in suppressing interfacial Intermetallic Compound (IMC) growth on Cu and Ni-P substrates has been determined.

Solder-substrate couples were aged at 150 'C and 185 'C for 1000 h. In the case of 0.5-1.0 wt.% Zn on Cu substrate, Cu3Sn IMC was significantly suppressed and the morphology of Cu6Sn5 grains was changed, leading to suppressed Cu6Sn5 growth. In the SAC-1.5Zn/Cu substrate system a Cu5Zn8 IMC layer nucleated at the interface followed by massive spalling of the layer into the solder, forming a barrier layer limiting Cu6Sn5 growth. On Ni-P substrates the (Cu,Ni)6Sn5 IMC growth rate was suppressed, the lowest growth rate being found in the SAC-1.5Zn/Ni-P system.

In all cases the added Zn segregated to the interfacial IMCs so that Cu6Sn5 became (Cu,Zn)6Sn5 and (Cu,Ni)6Sn5 became (Ni,Cu,Zn)6Sn5. The effect of Zn concentration on undercooling, wetting angles and IMC composition changes during ageing are also tabulated, and a method of incorporating Zn into the solder during reflow without compromising solder paste reflow described.

Kotadia, H.R.a , Mokhtari, O.a , Clode, M.P.b , Green, M.A.a , Mannan, S.H.a

a Department of Physics, King's College London, Strand, London WC2R 2LS, UK

b Materials Research Group, Division of Engineering, King's College London, London WC2R 2LS, UK

Comparison of Extensive Thermal Cycling Effects on Microstructure Development in Micro-alloyed Sn-Ag-Cu Solder Joints

Scopus: Pb-free solder alloys based on the Sn-Ag-Cu (SAC) ternary eutectic have promise for widespread adoption across assembly conditions and operating environments, but enhanced microstructural control is needed. Micro-alloying with elements such as Zn was demonstrated for promoting a preferred solidification path and joint microstructure earlier in simple (Cu/Cu) solder joints studies for different cooling rates.

This beneficial behavior now has been verified in reworked ball grid array (BGA) joints, using dissimilar SAC305 (Sn-3.0Ag-0.5Cu, wt.%) solder paste. After industrial assembly, BGA components joined with Sn-3.5Ag-0.74Cu-0.21Zn solder were tested in thermal cycling (-55°C/+125°C) along with baseline SAC305 BGA joints beyond 3000 cycles with continuous failure monitoring. Weibull analysis of the results demonstrated that BGA components joined with SAC + Zn/SAC305 have less joint integrity than SAC305 joints, but their lifetime is sufficient for severe applications in consumer, defense, and avionics electronic product field environments. Failure analysis of the BGA joints revealed that cracking did not deviate from the typical top area (BGA component side) of each joint, in spite of different Ag3Sn blade content. Thus, SAC + Zn solder has not shown any advantage over SAC305 solder in these thermal cycling trials, but other characteristics of SAC + Zn solder may make it more attractive for use across the full range of harsh conditions of avionics or defense applications

Anderson, I.E.a b , Boesenberg, A.b , Harringa, J.a , Riegner, D.b , Steinmetz, A.b , Hillman, D.c

a Division of Materials Sciences and Engineering, Ames Laboratory (USDOE), Ames, United States

b Materials Science and Engineering Department, Iowa State University, Ames, United States

c Rockwell-Collins, Inc., Coralville, United States

Enhanced solder joint bonding strength of electronic packaging with electrowetting effect

Scopus: This paper reports a novel method to enhance solder ball or solder ring bonding strength by using electrowetting-on-dielectric (EWOD) effect. With a low melting point, the metal Sn has been widely used in electronic packaging technology. Since Sn will be molten into liquid when the temperature is increased above the melting point, the method for treating liquid can be herein employed. Contact angle of the molten Pb-free balls or ring structure on silicon substrate have been experimentally changed by applying electric field across the thin dielectric film between the molten solder and the conductive silicon substrate. The contact area between the solder and the substrate is enlarged due to the decrease of the contact angle. Our testing results on the EWOD enhanced packaging structures of solder balls, flip-chip and solder ring hermetic package generally show about 50% enhancement in bonding shear strength. The significantly enhanced solder link bonding strength is hopeful for improving packaging reliability and is promising to be used in high performance silicon based electronic or microelectromechanic SiP (system in package) technologies

Effects of bump size on deformation and fracture behavior of Sn3.0Ag0.5Cu/Cu solder joints during shear testing

Scopus: To elaborate deformation and fracture behavior of Sn3.0Ag0.5Cu/Cu solder joint, dynamic shear testing was designed and performed on as-reflowed and aged solder joints which contained limited numbers of grains. Polarized light microscopy (PLM) and electron backscatter diffraction (EBSD) were used to reveal the grain morphology and the grain distribution.

Scanning electron Microscopy (SEM) was applied to observe the influences of microstructures and intermetallic compounds (IMCs) on the solder joints fracture behavior. The experimental results suggested that the morphology and distribution of IMCs (Cu6Sn5 and Ag3Sn) were the main reasons for the size effect in Sn3.0Ag0.5Cu solder joints.

The shear strength of as-reflowed and aged solder joints decreased with the increased joint sizes. The nano-scale particle-like Ag3Sn dispersed in the small solder joints had a strengthen effect on their mechanical property. While the dendritic and feather-like Ag3Sn brought the big solder joints the brittleness.

Furthermore, obvious plastic deformation in company with dynamic recovery and recrystallization was observed in small solder joints during dynamic shear testing. The fracture occurred in the bulk solder. While the brittle fracture occurred in big solder joints and the fracture positions were at the areas close to the soldering interface.

The cracks propagated by the way of transgranular fracture. After aging, dynamic recovery and recrystallization occurred in all solder joints. While the plasticity of big solder joint was enhanced and the transgranular fracture as well as the intergranular fracture occurred during dynamic shear testing

Tian, Y.a b , Hang, C.a b , Wang, C.a b , Yang, S.b , Lin, P.b

a State Key Lab of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001, PR China

b Department of Electronics Packaging Technology, Harbin Institute of Technology, Harbin 150001, PR China

Material and method of manufacturing of a solder joint with high thermal conductivity and high electrical conductivity (US8034195)

US8034195: A solder composition for forming a solder joint. The composition includes a powder material including a solid metal matrix material and a filler material.

The solid metal matrix material includes one or more of tin-silver-copper (Sn—Ag—Cu), tin-copper (Sn—Cu), tin-copper-nickel (Sn—Cu—Ni), tin-silver (Sn—Ag), tin-silver-bismuth (Sn—Ag—Bi), tin-bismuth-indium (Sn—Bi—In), tin-gold (Au—Sn), tin-zinc (Sn—Zn), tin-zinc-bismuth (Sn—Zn—Bi), tin-bismuth-silver (Sn—Bi—Ag), tin (Sn), tin-indium (Sn—In), indium (In), indium-silver (In—Ag), and tin-lead (Sn—Pb). The filler material includes one or more of copper (Cu), gold (Au), nickel (Ni), nickel-gold (Ni—Au), carbon, silver (Ag), aluminum (Al), molybdenum (Mo), nickel (Ni) or nickel-gold (Ni—Au) coated carbon, the platinum group metals (PGM's), and their alloys.

Schmid, Richard K.; Gerlikon, Switzerland

Doesburg, Jacobus C.; Westbury, NY, United States of America

Assignee: Sulzer Metco (US), Inc.

Nihon Superior's Keith Sweatman to Present at SMTA International 2011

EMSNow: In this presentation, Mr. Sweatman will report on a study of the thickness morphology and growth of intermetallics formed on a copper substrate by eight alloys that are representative of the range of low- and no-Ag formulations currently used or proposed as Pb-free solders for electronic assembly. In addition to the basic constituents of Sn, Cu and Ag, these alloys included additions of Ni, Bi, Ce, Ge and P. Cross-sections were examined by SEM, and the thickness and growth at 130', 140' and 150'C of both the Cu6Sn5 and Cu3Sn phases was monitored.

While Ni was found to have a strong effect on all aspects of the interfacial intermetallics, any effects of Bi were more subtle

Effects of Bi and Ni addition on shear strength of low-Ag lead-free solder joints

Scopus: The objective of this paper is to investigate the shear fracture mechanism of solder ball. The shear strength of solder joints were measured by Joint Strength Tester.

The results indicate that addition of the Ag element has a significant effect on the shear strength of Sn-Ag-Cu solder joints. The shear strength of Sn0.7Ag0.5Cu-BiNi solder joints is higher than that of Sn-0.3Ag-0.7Cu and Sn-3.0Ag-0.5Cu solder joints as -reflowed or after aging. The 3-D morphology of shear fracture shows that lots of typical dimples were distributed in the solder joints after reflow. But fracture dimples in Sn-0.7Ag-0.5Cu-BiNi solder joints were less than the other two solders and they were all composed of tiny compounds. The fractured position was much more close to the IMC.

It indicated that the Sn0.7Ag0.5Cu-BiNi solder shows the best toughness. After aged for 196 hours, the scale of IMC in the surface of shear fracture increases, dimples appear and the shear strength of solder joints decrease.

Sun, F., Zou, P., Liu, Y.

School of Material Science and Engineering, South Campus, Harbin University of Science and Technology, China

Influence of Ag, Cu and additive Bi elements on the thermal property of low-Ag SAC solder alloys

Scopus: This paper investigated the influence of Ag, Cu, and additive Bi elements on the thermal property of low-Ag SAC solder alloys.

The results indicate that the solidus is barely influenced by the content of Ag in the solders. But the liquidus and melting range decrease evidently due to the increase of Ag content; When the content of Cu increase from 0.3wt% to 0.7wt%, the liquidus of the solders decrease from 228.05'C down to 225.77'C. When the content of Cu increases to 1.0wt%, the liquidus increases to 226.66'C;

The addition of Bi significantly decreases both solidus and liquids of the low-Ag SAC solders. Compare with liquidus, the influence of Bi on solidus is more effective. As a result, when the content of Bi increased from 2.0wt% to 4.0wt%, the melting range of the solders increased from 16.7'C to 20.94'

Liu, Y., Sun, F., Zhang, H., Wang, Y.

College of Material Science and Engineering, Harbin University of Science and Technology, Harbin, China

Effect of microelements on Sn-20Bi solder

Scopus: Adding microelements Ag In Ga and Sb into Sn-20Bi solder, the changes of melting properties and microstructures of the solder were observed.

The experimental result showed that when the content of Ag was 0.7% (wt%), In was 0.1% , Ga was 0.5% and Sb was 0.5%, the melting points of the solder reduced to the bottom and the segregation of Bi obviously decreased. Sb was not suitable to add solely but when it was added together with Ag In and Ga, it can produce a good effect on reinforcement of solid solution, furthermore it can restrain the phase change of Sn.

The Sn-Bi-X solder with the best compositions of Ag In Ga and Sb has a near melting point to Sn-37Pb. The solder is close to practicality without segregation of Bi


Li, Y., Luo, Y., Chen, X. 
School of Computer, National University of Defense Technology, Changsha, 410073, China

Impact of Microstructure Evolution and Isothermal Aging on Sn-Ag-Cu Solder Interconnect Board-Level High-G Mechanical Shock Performance and Crack Prop

Scopus: The root cause of shock-induced solder joint failures in the range of 800G to 1500G is investigated. Joint stability under various shock and strain level combinations and the impact of isothermal aging on board-level shock performance were analyzed. A test vehicle was developed to obtain various combinations of shock and strain levels in a single board. Using 17mm x 17mm body-sized ball grid array packages on a shock test board, isothermal aging was applied prior to shock testing to determine the impact of different interface microstructures. Results revealed clear indications of a correlation between shock and strain and a trend of isothermal-aging-induced degradation. A shift in the failure locations was observed based on the interface intermetallic microstructure, and some preliminary evidence for the influence of Sn grain orientation was identified. The interrelated effects of isothermal aging, locally experienced shock and strain levels, and Sn grain orientation on mechanical shock performance are discussed

Lee, T.-K.a , Zhou, B.b , Bieler, T.b , Liu, K.-C.a

a Component Quality and Technology Group, Cisco Systems, Inc., San Jose, 95134, United States

b Michigan State University, East Lansing, United States

Interfacial reaction and solderability of Zn20SnxCu solder

Scopus : Zn20Sn solder with the melting point of 383.9'C and a low cost is considered as an ideal high-temperature lead-free solder. In the paper a new solder alloys were made by adding trace Cu into Zn20Sn alloy through alloying principle. Interfacial reaction and solderability of Zn20SnxCu (x=0 wt.%, 2 wt.%, 4 wt.% and 6 wt.%) solder on the copper substrate were investigated. Results showed that β′-CuZn, γ-Cu5Zn8 and ε-CuZn5 IMC layers were formed at the interface of Zn20SnxCu/Cu. The spreading areas of the Zn20SnxCu solders were reduced linearly with the increasing of the content of copper. The spreading aera of Zn20Sn solder was 52.88 mm2 while that of Zn20Sn6Cu was 50.82mm2 which was approximately 3.9% smaller than that of matrix solder. It is mainly related to the formation of ε-CuZn5 phase and the metal intermetallic compound between the solder and the substrate

Zhao, K.-L., Yan, Y.-F., Sheng, Y.-Y., Du, N., Liu, Z.-L.

Materials Science and Engineering College, Henan University of Science and Technology, Luoyang, Henan, 471003, China

Anticipating New SEC Rules, Tech Companies Shift To Conflict-Free Metals

Forbes: Now tech companies are beginning to throw their collective weight behind the new Public-Private Alliance for Responsible Minerals Trade, an alliance between private companies, the U.S. State Department, the U.S. Agency for International Development, various industry trade associations, non-governmental organizations working in the regions, and the International Conference on the Great Lakes Region (ICGLR). So far Intel, Sony, and HP have all indicated their intent to join the Alliance, which is expected to officially launch by the end of the year.