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We investigated the interfacial reactions and mechanical reliabilities of different Ni layer thicknesses and P-containing Pd layers in thin electroless-Ni electroless-Pd immersion gold (thin-Au/Pd(P)/Ni(P)) surface-finished printed circuit board (PCBs) with Sn-3.0Ag-0.5Cu (SAC 305) solder joints. To analyze the optimal Ni layer thickness in the thin-Au/Pd(P)/Ni(P) for aging, we evaluated 0.3- to 1.0-μm Ni layers in thin-Au/Pd(P)/Ni(P) PCBs with SAC 305 solder joints aged at 75, 100, 125, and 150 °C for 1000 h. A scallop-type (Cu,Ni) 6 Sn 5 intermetallic compound (IMC) dominantly formed at the bottom and top sides of the interfaces of all Ni joints under all aging conditions. Furthermore, a P-rich Ni layer formed at the interface between the (Cu,Ni) 6 Sn 5 IMC and Cu substrate during aging regardless of Ni layer thickness. The (Cu,Ni) 6 Sn 5 IMCs of the joints with 0.3- and 0.5-μm Ni layers aged at 125 and 150 °C for 1000 h were thicker than those of 0.7- and 1.0-μm Ni layers. In high-speed shear tests, the shear strength reduction rates of the joints with 0.3-μm Ni layer aged at 125 and 150 °C were higher than those of the 0.7- and 1.0-μm Ni layers. The brittle fracture rates of the joints with 0.3- and 0.5-μm Ni layers aged at 150 °C for 1000 h were higher than those of the 0.7- and 1.0-μm Ni layers. We determined that these trends arose from the diffusion barrier role of the relatively thick P-rich Ni layers maintained at the interfaces of the joints with 0.7- and 1.0-μm Ni layers for all aging temperatures and times. In low-speed shear tests, the shear strengths of the joints with 0.3-μm Ni layer were slightly lower than those of the 0.5- to 1.0-μm Ni layers. The low- and high-speed shear strengths of the joint with 0.7-μm Ni layer were similar to those of the 1.0-μm Ni layers for each condition. Therefore, Ni joint thicknesses of over 0.7 μm are expected to provide high reliability for aging. • Different Ni layer thicknesses and aging temperatures affected joint reliability. • Thicker P-rich interfacial Ni layers act as a barrier to diffusion. • Ni layer thicknesses over 0.7 μm are recommended for reliable joints. [ABSTRACT FROM AUTHOR]

Abstract: This study investigated the interfacial reaction between eutectic Sn–9wt.% Zn solder and Au/Ni electroplated Cu BGA substrate during aging at temperatures between 70 and 180°C, as well as the shear strength of the resulting joints. After reflowing, the intermetallic compound (IMC) formed at the interface was AuZn3. The formed AuZn3 layer became detached from the interface during reflowing. In the case of aging at 70°C, only an AuZn3 IMC layer was observed, whereas after aging for 2400h at 100 and 120°C, the Ni5Zn21 IMC was also observed on the Ni substrate. In the cases of aging at 150 and 180°C, AuZn3 and Ni5Zn21 IMCs were observed at all the interfaces. The thickness of the detached AuZn3 layer did not change with increasing aging temperature and time, whereas that of the Ni5Zn21 IMC layer formed on the Ni layer increased with increasing aging temperature and time. After aging at 150 and 180°C, the detached AuZn3 IMC layers were separated into AuZn3 and (Au, Ni)Zn3. After aging at 180°C for 2400h, the Ni5Zn21 IMC grew more extensively near both edges of the substrate and the entire Ni layer was completely consumed. In addition, the Cu5Zn8 phase was formed between the Ni5Zn21 IMC and Cu substrate. The shear strength of the aged Sn–9Zn/Au/Ni/Cu joint was significantly related to the detachment of the AuZn3 IMC layer and all fracturing occurred on the detached AuZn3 IMC layer. Therefore, this detachment of the AuZn3 layer must be prevented to ensure the reliability of the Sn–Zn/Au/Ni/Cu joint. [Copyright &y& Elsevier]

Abstract: Sn–9Zn (in wt.%) solder ball was bonded to Cu pad, and the effect of aging on shear reliability was investigated. After reflow, the intermetallic compound (IMC) phase formed at the interface was Cu5Zn8, and the as-reflowed Sn–9Zn/Cu joint had sufficient shear strength. In the isothermal aging test, only Cu5Zn8 IMC was observed in the samples aged at temperatures between 70 and 120°C. On the other hand, after aging at 150°C for 250h, Cu6Sn5 phase was observed at the interface between the interfacial Cu5Zn8 IMC layer and the Cu substrate. And, the layer-type Cu5Zn8 IMC layer was disrupted locally at the interface. In the ball shear test conducted after aging treatment, the shear strength significantly decreased after aging at all temperatures for initial 100h, and then remained constant by further prolonged aging. The fracture mainly occurred at the interface between the solder and Cu5Zn8 IMC layer. The aged Sn–9Zn/Cu solder joint had an inferior joint reliability. [Copyright &y& Elsevier]

Abstract: The shear test for flip chip solder bump was investigated in terms of effects of test parameters, i.e., shear height and shear speed, with an experimental and non-linear 3-dimensional finite element analysis for evaluating the solder joint integrity of area array packages. A representative Pb-free, Sn–3.0Ag–0.5Cu, was examined in this study. It could be observed that increasing shear height, at fixed shear speed, has the effect of decreasing shear force, while the shear force increased with increasing shear speed at fixed shear height. Relatively high shear height exceeding about 20% of the solder bump height could cause some unfavorable effects on the test results such as unexpected high standard deviation values or shear tip sliding from the solder bump surface. The low shear height conditions were favorable for screening the type of premature brittle interfacial fractures or the degraded layers in the interfaces. The increase in shear force with the shear speed is highly related with the stress values of the von Mises stress contours within the solder bump. [Copyright &y& Elsevier]

Abstract: The ball shear tests were investigated in terms of effects of test parameters, i.e. shear height and shear speed, with an experimental and non-linear finite element analysis for evaluating the solder joint integrity of area array packages. A representative low melting point solder, In–48Sn, was examined in this work. The substrate was a common solder mask defined (SMD) type with solder bond pad openings of 460μm in diameter. The microstructural investigations were carried out using scanning electron microscopy (SEM), and the intermetallic compounds (IMCs) were identified with energy dispersive spectrometer (EDS) and electron probe micro analyzer (EPMA). Shear tests were conducted with the two varying test parameters. It could be observed that increasing shear height, at fixed shear speed, has the effect of decreasing shear force, while the shear force increased with increasing shear speed at fixed shear height. Too high shear height could cause some bad effects on the test results such as unexpected high standard deviation values or shear tip sliding from the solder ball surface. The low shear height conditions were favorable for screening the type of brittle interfacial fractures or the degraded layers in the interfaces. The sensitivity of shear speed in In–48Sn solder is largely higher than those of Sn-based solders. [Copyright &y& Elsevier]

An experimental investigation was combined with a non-linear finite element analysis using an elastic–viscoplastic constitutive model to study the effect of ball shear speed on the shear forces of BGA solder joints. Two solder compositions were examined in this work: Sn–3.5Ag and Sn–3.5Ag–0.75Cu. The Cu substrates had been surface finished electrolytically with a 7 μm thick Ni diffusion barrier followed by an 0.5 μm thick Au layer to enhance solderability. Ag3Sn and a few AuSn4 intermetallic compound (IMC) particles were found inside the two solders. Only a continuous Ni3Sn4 layer was observed at the interface between the Au/Ni plated layer and the Sn–3.5Ag, while a continuous (Ni1−xCux)3Sn4 layer and a small amount of discontinuous (Cu1−yNiy)6Sn5 particles were formed at the interface between the substrate and the Sn–3.5Ag–0.75Cu. The IMC was identified using energy dispersive spectrometer (EDS) and electron probe micro analysis (EPMA). Shear tests were carried out over a shear speed range from 10 to 700 μm/s at a shear ram height of 50 μm. The shear force was observed to linearly increase with shear speed and reach a maximum value at the highest shear speed in both the experimental and the computational results. All test specimens fractured in a ductile mode. The failure mechanisms were discussed in terms of von Mises stresses and plastic strain energy density distributions. [Copyright &y& Elsevier]

The effects of Ni(P) layer thickness (5 μm and 0.7 μm) on the microstructural behavior and electrical reliability of electroless-nickel electroless-palladium immersion gold (ENEPIG) (substrate-side) surface-finished printed circuit boards (PCBs) with Sn–3.0Ag–0.5Cu (SAC305) solder joints under current stressing of 9000 A/cm2 have been investigated. An organic solderability preservative (OSP) surface finish was applied on the chip-side. (Cu,Ni) 6 Sn 5 and Cu 6 Sn 5 intermetallic compound (IMC) layers were formed on the chip-side (the interface between SAC305 and the OSP surface finish) and substrate-side (the interface between the ENEPIG surface finish and SAC305) solder joints after reflow. The thicknesses of the (Cu,Ni) 6 Sn 5 and Cu 6 Sn 5 IMC layers of the chip- and substrate-side of the normal- and thin-ENEPIG/SAC305/OSP solder joints increased with increasing current stressing time, regardless of the nickel phosphorous (Ni(P)) layer thickness. The total IMC thicknesses of normal-ENEPIG/SAC305/OSP solder joints were relatively thinner than those of thin-ENEPIG/SAC305/OSP solder joints under current stressing for 50–120 h. This is the reason why only a P-rich Ni layer was formed at the interface between SAC305 solder and the Cu pad in the thin-ENEPIG/SAC305 solder joints under current stressing. Otherwise, the P-rich Ni and Ni(P) layers remained at the interface of the normal-ENEPIG/SAC305 solder joint under current stressing. The Ni(P) layer of the ENEPIG surface finish played an important diffusion barrier role by suppressing IMC growth and movement toward the SAC305 solder under current stressing. In the electrical evaluation, the time to failure at the normal-ENEPIG solder joint was relatively longer (approximately 2.2 times) than that of the thin-ENEPIG solder joint. Therefore, the relatively thick Ni(P) layer contained in the ENEPIG/SAC305/OSP solder joint is expected to attain higher electrical reliability under the electromigration test. • Effect of Ni(P) layer thickness in ENIPIG joint with Sn–3.5Ag-0.5Cu solder examined. • Interfacial reactions and electrical properties considered at varying current stressing times. • Ni(P) layer in the ENEPIG acts diffusion barrier role and suppress interfacial reactions. • Thick Ni(P) layer contained ENEPIG should improve the electrical reliability of the joint for use in PCBs. [ABSTRACT FROM AUTHOR]

Abstract: This study utilized a solder ball shear test to evaluate the mechanical behavior of Sn–3.0Ag–0.5Cu/Cu and Sn–3.0Ag–0.5Cu/electroless Ni-immersion Au solder joints under high speed loading and hence the drop reliability. The combination of the force–displacement graphs captured from the shear tests and the fracture morphology analysis discloses three fracture modes active in our samples, which include a ductile fracture occurring through the solder (Mode I), a brittle fracture along the interface with intermetallic compound (IMC) layer after some plastic deformation in the solder (Mode II), and a brittle fracture through the IMC layer with almost no plastic deformation (Mode III). Identifying a fracture mode dominant in the samples for different solder joints and shear speeds leads us to conclude that the drop reliability of solder joints is highly related to the morphology of the IMC formed at the interface and the strain rate applied to the joints. These results underscore the utility of the experimental methodology adopted in this study to evaluate the drop reliability of solder joints. [Copyright &y& Elsevier]

Abstract: In this study, we investigated the effect of the Cu content on the interfacial reactions between the Sn–Ag–xCu solders and Cu substrate. In addition, we evaluated the effects of adding Cu or Ni to Sn–Ag solder on the interfacial reactions of the Sn–Ag–Cu (or Ni)/ENIG joints. The formation and growth of interfacial intermetallic compounds (IMCs) between the Ni-containing Sn–Ag–Ni solder and ENIG substrate were studied and the results were compared to the Sn–Ag–Cu/ENIG system. Increasing the amount of Cu added to the Sn–Ag solder significantly reduced the thickness of the Cu3Sn IMC, while increasing that of the total Cu–Sn and Cu6Sn5 IMCs. (Ni,Cu)3Sn4 and Ni3Sn4 IMCs formed at the Sn–3.0Ag–0.5Cu/ENIG and Sn–3.0Ag–0.5Ni/ENIG interfaces, respectively. These two IMCs grew during isothermal aging and similar interfacial microstructures were found in the Sn–3.0Ag–0.5Cu (or Ni)/ENIG joints. Comparing the Sn–3.0Ag–0.5Cu/Cu and Sn–3.0Ag–0.5Cu/ENIG joints, the growth rate of the IMC layer for the Cu substrate was about 3.3 times faster than that for the ENIG substrate. [ABSTRACT FROM AUTHOR]

Abstract: A comparative study was undertaken of the interfacial reactions of the Ni–P layer with four kinds of solder, Sn-37Pb, Sn-3.5Ag, Sn-3.5Ag-0.75Cu, and Sn-3Ag-6Bi-2In (wt.%), by performing isothermal aging at 150°C for up to 2400h. The formation and growth of the interfacial compound phases were investigated. The ball shear strength was also measured to investigate the effect of the microstructures and interfacial reactions on the reliabilities of these solder joints. The study results confirmed that the Sn-Ag based Pb-free solders are mechanically more reliable than the Sn-Pb solder. [Copyright &y& Elsevier]

Abstract: The thermal fatigue properties of the solder joints with various underfills were evaluated by thermal shock test. The thermal fatigue crack initiated at the bottom edges of interface between the (Ni,Cu)3Sn4 intermetallic compounds layer and the Ni3P layer and spread to all the interfaces with increasing number of thermal shock cycles. The thermal fatigue properties of package with underfill, which has the higher glass-transition temperature (T g) and lower coefficient of thermal expansion (CTE) were better than those of the package with underfill having the lower T g and higher CTE value. [Copyright &y& Elsevier]

Abstract: The formation of Au–20wt.%Sn flip chip solder bumps using sequential electroplating method with Sn and Au was investigated. We obtained eutectic Au–20Sn solder bumps with a diameter of 100μm on the patterned Si wafer. After reflowing and aging at 150°C for up to 1000h, we investigated the interfacial reaction between the Au–20Sn solder and Ni under bump metallization (UBM). The Au–Ni–Sn, ternary, intermetallic compound (IMC) layer was formed, and the resettlement of δ-phase was confirmed during aging. The shear force was also measured to evaluate the effect of the interfacial reactions on the mechanical reliability as a function of aging time. The shear force was stable and the fracture occurred on the Ti/Cu metallization layer independent of the aging time. The results from this study confirm the mechanical robustness of the Au–20Sn/Ni flip chip solder joint. [Copyright &y& Elsevier]

Abstract: The interfacial reaction of the ENIG/Sn–3.5Ag–0.7Cu/ENIG sandwich solder joint was studied during aging at 150°C for up to 1000h. (Ni,Cu)3Sn4 intermetallic compounds (IMCs) formed at both ENIG/Sn–Ag–Cu/ENIG interfaces after reflowing. After aging for 24h, IMCs changed from (Ni,Cu)3Sn4 to (Cu,Ni)6Sn5. Until the aging for 250h, the (Cu,Ni)6Sn5 IMC layers grew thicker with increasing aging time. After aging for 500h, the IMCs changed from (Cu,Ni)6Sn5 to (Ni,Cu)3Sn4 once again. The phase transition could be significantly related to the diffusion and content of available Cu atoms from the solder to interface during aging. On the other hand, the results of the analyses of the interfacial reactions of the ENIG/Sn–Ag–Cu/ENIG and Cu/Sn–Ag–Cu/ENIG joints showed that the interfacial reaction on the lower Ni–P side was strongly affected by the interfacial reaction on the opposite pad. In the case of the Cu/Sn–Ag–Cu/ENIG joint, only a (Cu,Ni)6Sn5 IMC layer was observed at the lower Sn–Ag–Cu/ENIG interface during aging. A coupling effect occurred between Cu/Sn–Ag–Cu and Sn–Ag–Cu/ENIG interfaces of the Cu/Sn–Ag–Cu/ENIG joint. [Copyright &y& Elsevier]

Abstract: The microstructural investigation and thermo-mechanical reliability evaluation of the Sn–3.0Ag–0.5Cu solder bumped flip chip package were carried out during the thermal shock test of the package. In the initial reaction, the reaction products between the solder and electroless Ni–P bump of the chip side were composed of two layers, i.e., a continuous layer of (Ni,Cu)3Sn4 and discontinuous particles of (Cu,Ni)6Sn5, while a continuous (Ni,Cu)3Sn4 IMC layer was formed between the solder and electroless Ni–P layer of the package side. It is found that the primary failure mechanism of the solder joints in this type of test was thermally activated solder fatigue failure. For the interpretation of the failure mechanism of the package, finite element analyses were also conducted. The finite element analyses revealed that the cracks were induced by the accumulation of the plastic work and creep strain. Inelastic strain accumulations are primarily affecting the crack initiation and growth time, so called the life of the solder joint in this thermal shock test condition. [Copyright &y& Elsevier]

Abstract: Shear test for flip chip solder bump was investigated in terms of shear height and shear speed with an experimental and non-linear 3-dimensional finite element analysis. It could be observed that increasing shear height, at a fixed shear speed, has the effect of decreasing shear force, while the shear force increased with increasing shear speed at a fixed shear height. From the experimental and computational results, low shear height and low shear speed could be recommended for the shear test of the flip chip solder bumps. The shear test method was applied to investigate the effect of bump geometries on the shear force of the solder joints. The shear force increased with increasing height of Cu mini bump. [Copyright &y& Elsevier]

Abstract: An experimental investigation was combined with a non-linear finite element analysis using an elastic–viscoplastic constitutive model to study the effect of ball shear speed on the shear forces of flip chip solder bumps. A solder composition used in this study was Sn–3mass%Ag–0.5mass%Cu. A low cost bumping process has been employed using electroless Ni and immersion Au followed by solder paste stencil printing. A thin layer of intermetallic compound, (Ni1−x Cu x )3Sn4, was formed by the reaction between the solder and electroless Ni with a thickness of about 1.4μm, while some discontinuous (Cu1−y Ni y )6Sn5 particles were also formed at the interface. The compositions of the resulting compounds were identified using energy dispersive spectrometer (EDS) and electron microprobe analysis (EPMA). Shear tests were carried out over a shear speed range from 20 to 400μm/s at a shear ram height of 20μm. The shear force was observed to linearly increase with shear speed and reach the maximum value at the fastest shear speed in both experimental and computational results. The optimum shear speeds for the shear test of solder bumped flip chip were recommended to be not exceeding 200μm/s. The failure mechanisms were discussed in terms of von Mises stresses and plastic strain energy density distributions. [Copyright &y& Elsevier]

Abstract: The microstructural investigation and thermo-mechanical reliability evaluation of the Sn–37Pb solder bumped flip chip package were carried out during the thermal shock test of the package. In the initial reaction, the reaction product between the solder and Cu mini bump of the chip side was Cu6Sn5 IMC layer, while a layer of Ni3Sn4 was formed between the solder and electroless Ni–P layer of the package side. The primary failure mechanism of the solder joints in this type of test method and package was confirmed to be thermally activated solder fatigue failure. The brittle interfacial failure mode was sometimes detected from the cross-sectional studies, but nearly whole of the failed packages showed the occurrence of the typical fatigue cracks. The finite element analyses were conducted to interpret the failure mechanisms of the packages. The finite element analyses revealed that the cracks were induced by the accumulation of the plastic work. [Copyright &y& Elsevier]

Abstract: The interfacial reaction, morphology of intermetallic compound (IMC) and shear strength between the Sn–3.5Ag–0.7Cu (in wt.%) solder and Ni ball grid array (BGA) substrates during reflow at 255°C for up to 20min were investigated. The reaction between the molten solder and Ni layer resulted in the formation of two IMCs such as (Cu, Ni)6Sn5 and (Ni, Cu)3Sn4 at the interface. The (Ni, Cu)3Sn4 IMCs were needle-like type, while the (Cu, Ni)6Sn5 IMCs were cylinders with a hexagonal cross-section and pointed tips. Compared to the quenched sample, the (Cu, Ni)6Sn5 IMCs nucleated heterogeneously on the (Ni, Cu)3Sn4 layer during the solidification of the solder. In the ball shear test, the shear strength value did not change much as a function of reflow time. In all samples, the fracture occurred in the bulk solder. The results of interfacial reaction and shear test in this study show that the Sn–Ag–Cu/Ni BGA solder joint has a desirable joint reliability. [Copyright &y& Elsevier]

The interfacial reaction and shear strength between the eutectic Sn–0.7 wt.% Cu solder and two different kinds of ball grid array (BGA) substrates (Cu and Au/Ni–P/Cu) during reflow at 255 °C for up to 30 min were studied. With the solder joints between the Sn–0.7Cu solder and Cu substrates, a Cu6Sn5 intermetallic compound (IMC) was formed at the interface. In the case of the electroless Ni–P substrate, the IMC formed at the interface was mainly (Cu, Ni)6Sn5. Also, a P-rich Ni (Ni3P) layer was observed as a by-product of the Cu–Ni–Sn reaction. The Ni3P layer was between the (Cu, Ni)6Sn5 IMC and the electroless Ni–P layer. The thickness of the Cu6Sn5, (Cu, Ni)6Sn5 and Ni3P layer was found to increase with the reaction time. The growth of the Cu6Sn5 IMC layer for Cu substrate was faster than that of the (Cu, Ni)6Sn5 IMC layer for electroless Ni–P substrate. The Ni content in the (Cu, Ni)6Sn5 IMC layer formed at the interface increased with increasing reaction time. In the ball shear tests, the shear strength value did not change much as a function of reflow time. In all samples, the fracture mainly occurred in the bulk solder. However, for the Sn–0.7Cu/electroless Ni–P joint reflowed for 10 min, the fracture occurred in ductile and slightly brittle mode. [Copyright &y& Elsevier]

Abstract We investigated the effect of Ag-coated multi-walled carbon nanotubes (Ag-MWCNT) on the microstructures and electromigration behaviors of a Sn58%Bi solder and organic solderability preservative (OSP) surface finished on the FR-4 printed circuit board (PCB) joint under a current stress of 3000 A/cm2 at 100 °C. Electromigration of Ag-MWCNT Sn58%Bi composite solder was investigated by daisy-chain test-kit. Reaction layers formed at the anode side and cathode side of the Sn58%Bi solder joints consisted of three microstructures; Bi-rich layer, Sn-rich layer, and intermetallic compounds (IMCs, Cu 6 Sn 5 and Cu 3 Sn). The Bi-rich layer was mainly formed at the anode side in the couple of the Sn58%Bi solder joint with various times of applying current stress. The Bi-rich layer of the Ag-MWCNT Sn58%Bi composite solder joint was approximately 2 times thinner than that of the Sn58%Bi solder joint because the Ag-MWCNT acts as a diffusion barrier. Also, the Cu 6 Sn 5 and Cu 3 Sn IMCs that formed at the interface between the Ag-MWCNT Sn58%Bi composite solder joints were thinner than those of the Sn58%Bi solder joints. The time to failure (TTF) was longest at the 0.05% Ag-MWCNT Sn58%Bi composite solder joint. Therefore, Ag MWCNT is expected to improve the reliability of electromigration in the Sn58%Bi composite solder joint. Highlights • The electromigration of the Ag-MWCNT Sn58%Bi composite solders were investigated. • Ag-coated MWCNTs were widely distributed in the Sn58%Bi solder joint. • MWCNT suppressed growths of Cu-Sn IMCs and Bi-rich layer under current stress. • TTF value of the 0.05 wt% Ag-MWCNT Sn58%Bi composite solder joint was the longest. [ABSTRACT FROM AUTHOR]

In the electronic packaging technology, lead-free solders have been widely used to replace lead-based solders because of the toxicity of lead. Among the investigated lead-free solders, the Sn–58Bi solder has been considered as a highly promising candidate because of its low-melting temperature, high tensile strength and good creep resistance. However, the Sn–58Bi solder has poor ductility and shock absorbance. To enhance the mechanical properties of the Sn–58Bi solder, epoxy resin is mixed with the Sn–58Bi solder. The advantages of the Sn–58Bi solder with epoxy are good reliability and no need of a cleaning process. This study elucidated not only the mechanical properties of the Sn–58Bi epoxy solder but also the effects of the epoxy during the reflow process by conducting a shear test and a board-level drop test. The shear strength of the Sn–58Bi epoxy solder was about 2 times higher than that of the Sn–58Bi solder. In result of the drop test, the Sn–58Bi solder specimen failed under the 10th drop. However, the number of drops of the Sn–58Bi epoxy solder was over 100 drops without failure. [ABSTRACT FROM AUTHOR]

This study examined the interfacial reaction in Sn–3.5Ag/electroless Ni(P) solder joints using in situ transmission electron microscopy (TEM). In situ TEM confirmed that the thickness of the ternary layer increased by approximately 70nm. A new interfacial reaction layer (Ni3P) formed in the P-rich Ni layer/Ni(P) interface. Several Ni–P compounds that formed in the reflow process changed into the stable Ni3P phase. This suggests that the P-rich Ni layer acts as a diffusion barrier layer between the intermetallic compounds and the Ni(P) layer during the annealing process. [ABSTRACT FROM AUTHOR]

This study examined the ternary Ni2SnP layer in Sn–3.5Ag–0.7Cu/electroless Ni (P) solder joints using in situ transmission electron microscopy (TEM). TEM confirmed the formation of an Ni2P phase underneath the ternary Ni2SnP after reflowing. We can directly observe the Sn diffused into Ni2P to form Ni2SnP during annealing in TEM. These results suggested that the ternary Ni2SnP forms through the diffusion of Sn into Ni2P. In addition, small Kirkendall voids were newly formed in the ternary Ni2SnP layer after annealing in TEM. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the effects of adding small amounts of cerium (Ce) to low Ag content Sn solder (Sn–1.0wt.%Ag) on melting temperature, microstructure, wettability and mechanical properties using differential scanning calorimeter, optical microscope, scanning electron microscope, energy dispersive X-ray spectroscopy, wetting balance tester, Vickers hardness tester and tensile tester assays. The addition of Ce had little influence on the melting behavior of Sn–1.0Ag solder, but improved its wettability, mechanical properties, and microstructure. [Copyright &y& Elsevier]

This study investigated a method for controlling the interfacial reaction between a Sn–3.5Ag–0.7Cu (wt.%) solder and an electroless nickel-immersion gold-plated Cu substrate through heat treatment. The interfacial reaction layer was controlled by heat treating of the electroless Ni–P plated layer. By applying a heat treatment, the thickness of the reaction layer (intermetallic compounds, P-rich Ni layer) was observed to be reduced. The formation of Ni2SnP, which significantly affects the mechanical reliability of solder joints, was suppressed. [Copyright &y& Elsevier]

Abstract: This study examined the effects of isothermal aging and temperature–humidity (TH) treatment of substrate on the joint reliability of a Sn–3.0Ag–0.5Cu (wt.%)/organic solderability preservative (OSP)-finished Cu solder joint. Two types of OSP-finished chip-scale-package (CSP) substrates were used, those subjected and not subjected to the TH test. This study revealed an association between the interfacial reaction behaviors, void formation and mechanical reliability of the solder joint. Many voids were formed at the interface of the OSP-finished Cu joint subjected to the TH test. These voids were caused by the oxidation of the OSP-finished Cu substrate during the TH test. In the shear tests, the shear force of the joint with the substrate not subjected to the TH test was slightly higher than that with the TH test. The mechanical reliability of the solder joint was degraded by voids at the interface. [Copyright &y& Elsevier]

Abstract: In this study, we evaluated the mechanical reliability of Sn-rich, Au–Sn/Ni flip chip solder bumps by using a sequential electroplating method with Sn and Au. After reflowing, the average diameter of the solder bump was approximately 80μm and only a (Ni,Au)3Sn4 intermetallic compound (IMC) layer was formed at the interface. Due to the preferential consumption of Sn atoms within the solder matrix during aging, the solder matrix was transformed sequentially in the following order: β-Sn and η-phase, η-phase, and η-phase and ε-phase. In the bump shear test, the shear force was not significantly changed despite aging at 150°C for 1000h and most of the fractures occurred at the interfaces. The interfacial fracture was significantly related to the formation of brittle IMCs at the interface. The Sn-rich, Au–Sn/Ni flip chip joint was mechanically much weaker than the Au-rich, Au–Sn/Ni flip chip joint. The study results demonstrated that the combination of Sn-rich, Au–Sn solder and Ni under bump metallization (UBM) is not a viable option for the replacement of the conventional, Au-rich, Au–20Sn solder. [Copyright &y& Elsevier]

Abstract: This study utilized a high speed lap-shear test to evaluate the mechanical behavior of Sn-37Pb/Cu under bump metallization (UBM) solder joints under high speed loading and hence the drop reliability. The samples were aged for 120h at different temperatures (150°С, 180°С) and then tested at different displacement rates in the range of 0.01mm/s to 500mm/s to examine the effects of aging on the drop reliability. The combination of the stress-strain graphs captured from the shear tests and the fracture morphology analysis discloses that the aging at high temperatures has influenced critically the deformation behavior of the solder joints and the effects appears more significant at high strain rates. This study demonstrates a unique capability of a drop reliability evaluation method that utilizes a high speed lap-shear test. [Copyright &y& Elsevier]

In this study, we fabricated Sn-rich, Au–Sn flip-chip solder bumps by using a sequential electroplating method with Sn and Au. After reflowing, only a (Ni,Au)3Sn4 intermetallic compound (IMC) layer was formed at the Au–Sn solder/Ni interface. During aging for up to 1000h at 150°C, the solder matrix was transformed sequentially in the following order: β-Sn and η-phase, η-phase, η-phase and ε-phase. The microstructure variation resulted from the preferential consumption of more Sn atoms within the solder matrix during aging. [Copyright &y& Elsevier]

High heat-endurance bonding between Cu Ni was investigated by hybrid transient liquid phase sintering bonding. By simultaneously adding Cu and Ni to SAC305, the IMC was stably formed, and the bonding strength of hybrid TLPS joint was the highest. It is expected to be used for SiC die attachment of power module packaging. [Display omitted] • Novel hybrid transient liquid phase sintering bonding is developed for Cu Ni bonding. • Fast and stable ternary (Cu,Ni)-Sn IMCs were formed by hybrid transient liquid phase sintering bonding. • Electron probe micro-analyzer was used for investigating the atomic distribution of TLPS joints. A novel approach to copper-nickel bonding was investigated by hybrid transient liquid phase sintering (TLPS) method. Hybrid bonding material containing copper, nickel, and Sn-3.0Ag-0.5Cu (SAC305) and an organic solvent was fabricated to form a fast and stable ternary Cu Ni Sn intermetallic compound (IMC) joint between Cu to Ni joint. The atomic distribution was analyzed by an electron probe micro-analyzer, showing full IMC formation of the hybrid TLPS joint. In addition, by simultaneously adding Cu and Ni to SAC305, the IMC was stably formed, and the bonding strength of hybrid TLPS joint was the highest. [ABSTRACT FROM AUTHOR]

A carbon nanotube (CNT) has remarkable properties, but it has disadvantages in application because of its dispersal- and bonding-related issues. Metal–CNT composite materials are necessary in solving these problems. In this study, nickel (Ni)–multi-walled CNTs (Ni–MWCNTs) are synthesized through sequential processing, functionalizing, and electroless plating processes to deposit Ni nanoparticles on MWCNTs. The synthesized Ni–MWCNTs are used to fabricate composite solders with various contents (0, 0.05, 0.1, and 0.2 wt%). The test kit used for the 3-point bending test in this study is designed with a differential package structure to evaluate the bending reliabilities of the Ni–MWCNT composite materials with various contents. The crack initiation and propagation in the microstructure evolution solder joints are also investigated. The bending reliabilities improve with the BGA structure and indicate that the highest bending cycle fails with 0.1 wt% of Ni–MWCNTs. The chemical composition and distribution of the Ni–MWCNTs in the solder joints are investigated with electron probe microanalysis. • Test-kits for 3-point bending test were designed with differential structure. • Bending test was performed to evaluate the mechanical properties of solder joints. • Ni-MWCNTs composite solder could improve the bending reliability of Sn58Bi solder. [ABSTRACT FROM AUTHOR]

A Cu-cored solder ball (CCSB) is often used as the interconnection material for 3D package. The CCSB has a Cu core surrounded by Sn-Ag-Cu alloy. The effect of the Cu core on mechanical reliability of the CCSB was investigated using thermal shock test. Microstructure and thermal shock reliability of the CCSB with organic solderability preservative (OSP) surface finish was compared with that of Sn-3.0wt.%Ag-0.5wt.%Cu (SAC) solder. The thermal shock test was performed in the temperature range of −40 °C to 125 °C in compliance with JESD22-A104. Failure mechanism was analyzed by finite element method analysis. Average number of thermal shock cycles for the CCSB/OSP joints was 1.15 times higher than that for SAC/OSP joints. Maximum value of simulated plastic strain for the SAC/OSP joints was 1.25 times higher than that for the CCSB/OSP joints because the stand-off height of the CCSB/OSP joints could be maintained by the Cu core. • Thermal shock reliability of Cu cored solder joint was investigated. • Simulated stress and strain were reduced because stand-off height of solder ball was maintained by Cu core. • Crack of solder joint was propagated through the solder matrix that was highest simulated plastic strain regions. • Thermal shock reliability of solder joint was improved due to stand-off height. [ABSTRACT FROM AUTHOR]

The mechanical properties and microstructure of Sn-58 wt%Bi solder including various levels of Ag-decorated MWCNTs (0, 0.05, 0.1, and 0.2 wt%) were investigated for use in solder joints. The electronic industry relies on Pb-free solders because lead can have harmful effects on the environment and human health. The Sn-58 wt%Bi solder is a representative low temperature Pb-free solder with high tensile strength and good creep resistance. However, the Sn-58 wt%Bi solder has poor ductility for relieving shock impact. To address this drawback, Ag-decorated MWCNTs were used to reinforce the mechanical properties of Sn-58 wt%Bi solder. The Sn-58 wt%Bi-nanocomposite solder paste was fabricated by mechanically mixing Ag-decorated MWCNTs with solder paste. The Sn-58 wt%Bi solder pastes including Ag-decorated MWCNTs were printed on a printed circuit board (PCB), and the joints were aged in an isothermal environment. Inclusion of 0.1 wt% Ag-decorated MWCNTs increased the shear strength of the solder by about 15%. The thickness of the IMC of Sn-58 wt%Bi solder increased with age. • The Ag-decorated MWCNTs were synthesized with functionalizing process. • The Ag-decorated MWCNTs increased shear strength of Sn-58 wt%Bi solder. • Furthermore, Ag-decorated MWCNTs have an effects on microstructure of Sn-58 wt%Bi solder. [ABSTRACT FROM AUTHOR]

Abstract: The interfacial reactions between Sn–3.0wt.% Ag–0.5wt.% Cu solder and an electroless nickel–electroless palladium–immersion gold (ENEPIG) substrate were investigated. After initial reflowing, discontinuous polygonal-shape (Cu,Ni)6Sn5 intermetallic compounds (IMCs) formed at the interface. During reflowing for up to 60min, the interfacial IMCs were sequentially changed in the following order: discontinuous (Cu,Ni)6Sn5, (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4, and embedded (Cu,Ni)6Sn5 in (Ni,Cu)3Sn4. The interfacial product variation resulted from the preferential consumption of Cu atoms within the solder and continuous Ni diffusion from the Ni(P) layer. [Copyright &y& Elsevier]