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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]

• Microstructural and mechanical stabilities of 30Ni-70Sn TLPS joints are analyzed. • The microstructures of Ni 3 Sn 4 intermetallics around Ni particles are dense and stable during aging. • The initial strengths maintained even after aging for 1000 h at 150 and 200 °C. • Ni-Sn paste is effective as a die attach material for power electronic devices. In this study, the feasibility and high-temperature stability of Ni-Sn bonded joints fabricated by transient liquid phase sintering (TLPS) were investigated for high-temperature power electronics applications. A 30Ni-70Sn (wt%) TLPS paste was fabricated with micro-sized pure Ni and Sn powders, and chip bonding was performed on a direct bonded copper (DBC) substrate. During TLPS bonding, Sn particles melted and reacted with Ni particles, which resulting in the formation of stable Ni-Sn TLPS intermetallic joints. During aging treatments at 150 and 200 °C, the formed Ni 3 Sn 4 phases were transformed into the Ni 3 Sn 2. With increasing aging treatments, the reactions between Ni 3 Sn 4 intermetallics and remaining Ni particles increased, which resulted in the formation of the Ni-rich Ni-Sn intermetallics. Even after 1000 h at an aging temperature of 200 °C, there is no significant difference in the stable and dense microstructure of Ni-Sn TLPS joints. In addition, their mechanical strengths did not vary significantly even after long-term treatment for 1000 h at 150 and 200 °C. This means that the Ni-Sn TLPS joints have a good long-term microstructural stability and mechanical reliability at high temperatures up to 200 °C. Therefore, we conclude that the Ni-Sn paste is a promising candidate as a die-attach material for high-temperature electronic assemblies. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we investigated the interfacial reaction and joint reliability of immersion Ag-plated Cu substrate with the most promising Sn–3.5Ag–0.7Cu solder. We first evaluated the interfacial reactions of the solder joint and also successfully revealed a connection between the interfacial reaction behavior and mechanical reliability. During reflow, the Ag plating layer was dissolved completely into the molten Sn–Ag–Cu solder and some of the Cu layer was also dissolved into the molten solder. The dissolved Ag and Cu were precipitated as Ag3Sn and Cu6Sn5 IMCs in the solder matrix. Upon reflow, the Sn–Ag–Cu solder exhibits an off-eutectic reaction to produce the eutectic phase and precipitate (Cu6Sn5 and Ag3Sn). The Cu–Sn IMC layer was formed at the solder/Cu interface after reflow and the IMC layer grew during aging treatment. During the shear tests, the failure mode switched from a bulk-related failure to an interface-related failure. After aging for 500h, the joint failed partially at the solder/Cu6Sn5 interface. The brittle fracture was linked to the formation of thick Cu–Sn IMC layer. [Copyright &y& Elsevier]

Abstract: The interaction between Cu/Sn–Ag–Cu and Sn–Ag–Cu/Cu(ENIG) interfacial reactions has been studied during isothermal aging at 150°C for up to 1000h using a Cu/Sn–3.5Ag–0.7Cu/Cu(ENIG) sandwich solder joints. A typical scallop-type Cu–Sn intermetallic compound (IMC) layer was formed at the upper Sn–Ag–Cu/Cu interface after reflow. On the other hand, a (Cu,Ni)6Sn5 IMC layer was observed at the Sn–Ag–Cu/ENIG interface. The Cu in the (Cu,Ni)6Sn5 IMC layer formed on the Ni side has to be contributed from the dissolution of the opposite Cu metal pad or Cu–Sn IMC layer and the original Cu atom in the Sn–Ag–Cu solder. When the Cu arrived at the interface of the Ni pad, the (Cu,Ni)6Sn5 IMC layer was formed on the Ni interface, preventing the Ni pad from reacting with the solder. Although a long isothermal aging treatment at 150°C was performed, any Ni was not detected in the Cu–Sn IMC layer formed on the upper Cu side. Compared to the single Sn–Ag–Cu/ENIG solder joint, the formation of the (Cu,Ni)6Sn5 IMC layer at the lower Sn–Ag–Cu/ENIG interface of the Cu/Sn–Ag–Cu/ENIG sandwich joint retarded effectively the consumption of the Ni from the electroless Ni–P layer, resulting in the formation of the very thin Ni3P layer. The coupling effect of the Cu/Sn–Ag–Cu/ENIG sandwich joint is helpful to prevent the excessive consumption of Ni substrate and the formation of the brittle Ni3P and Ni2SnP layers. [Copyright &y& Elsevier]

Abstract: Ball shear tests were investigated in terms of the 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. Two representative Pb-free solders were examined in this work: Sn–3.5Ag and Sn–3.5Ag–0.75Cu. 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 spectrometry (EDS). Shear tests were conducted with the two varying test parameters. It was observed that increasing shear height at a fixed shear speed has the effect of decreasing shear force for both Sn–3.5Ag and Sn–3.5Ag–0.75Cu solder joints, while the shear force increased with increasing shear speed at fixed shear height. Shear heights that were too high had some negative effects on the test results such as unexpectedly high standard deviation values or shear tip sliding from the solder ball. Low shear height conditions were favorable for screening the type of brittle interfacial fractures or the degraded layers in the interfaces. [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 interfacial reaction and morphology change of intermetallic compound (IMC) between the Sn–0.4wt.% Cu solder and two different kinds of substrates (Cu and electroless nickel-immersion gold (ENIG)) during reflow at 255°C for up to 60min were studied. Until the reaction time of 1min, only Cu6Sn5 IMC was formed on the Cu substrate. After reflow for 5min, the solder/Cu interface exhibited a duplex structure of Cu6Sn5 and Cu3Sn. According to the top view observation, the Cu6Sn5 IMC formed on the Cu substrate had a well-known morphology of a round or scallop shape. In the case of the ENIG substrate, the reaction between molten Sn–0.4Cu solder and electroless Ni–P layer resulted in the formation of a (Ni,Cu)3Sn4 layer at the interface. Until the reaction time of 10min (Ni,Cu)3Sn4 IMC layer was formed and attached well on the electroless Ni substrate. And, the Cu content in the (Ni,Cu)3Sn4 IMC layer increased with increasing reaction time. From the top view micrograph of the interface, it was known that three types (needle-type, boomerang-type and chunk-type) of (Ni,Cu)3Sn4 IMC were formed. Also, P-rich Ni (Ni3P) and Ni–Sn–P layers were observed between IMC layer and electroless Ni–P layer. On the other hand, the reaction for 60min resulted in the formation of two IMCs, a relatively thin and continuous (Ni,Cu)3Sn4 and a relatively big discontinuous (Cu,Ni)6Sn5, at the interface. After reflow for 60min, the electroless Ni–P layer in some parts of the sample was completely consumed by reaction between molten solder and substrate. [Copyright &y& Elsevier]

The growth kinetics of intermetallic compound layer formed between In–48Sn solder and bare Cu substrate were investigated at temperatures between 70 and 100 °C for 0–60 days. In the solder joint between the In–48Sn solder and bare Cu substrate, the intermetallic compound layer was composed of two phases: Cu(In,Sn)2 adjacent to the solder and Cu6(In,Sn)5 which was the dominant phase. A quantitative analysis of the intermetallic compound layer thickness as a function of time and temperature was performed. Additionally, the thickness of these intermetallic compounds increased with increasing aging temperature and time. The layer growth of the intermetallic compound in the couple of the In–48Sn/Cu system satisfied a parabolic law in the given temperature range. As a whole, because the values of time exponent (n) is approximately equal to 0.5, the layer growth of the intermetallic compound was mainly controlled by a diffusion mechanism in the temperature range studied. The apparent activation energies calculated for the growth of the total of intermetallic compounds [Cu(In,Sn)2 + Cu6(In,Sn)5] and for Cu6(In,Sn)5 were 95.11 and 97.63 kJ/mol, respectively. [Copyright &y& Elsevier]

Interfacial reactions and growth kinetics of intermetallic compound (IMC) layers formed between Sn–3.5Ag solder and electroless Ni–P substrate were investigated at temperature between 100 and 170 °C for up to 60 days. The IMC formed at the interface was mainly Ni3Sn4. Also, a P-rich Ni (Ni3P) layer was observed as a by-product of the Ni–Sn reaction. The Ni3P layer was between the Ni3Sn4 IMC and the electroless Ni–P deposit layer. The thickness results fitted a power-law relationship with exponent of 0.4 for the Ni3Sn4 layer. The interface between electroless Ni–P and Ni3P was planar and the thickness of the Ni3P layer also was found to increase linearly with the square root of aging time. The thickness of the Ni3Sn4 and Ni3P layer reached about 3 and 2 μm after 60 days of aging at 170 °C, respectively. The activation energy for the growth of the Ni3Sn4 IMC equals 49 kJ/mol. [Copyright &y& Elsevier]

The growth kinetics of intermetallic compound layers formed between Sn–5Bi solder and Cu substrate by solid state isothermal aging were examined at temperatures between 343 and 473 K for 0–30 days. In the solder joints between the Sn–5Bi solder and Cu substrate, the intermetallic compound layer was composed of two phases: Cu6Sn5 (η-phase) adjacent to the solder and Cu3Sn (ϵ-phase) adjacent to the copper. As a whole, because the values of the time exponent (n) are approximately 0.5, the layer growth of the intermetallic compound was mainly controlled by a diffusion-controlled mechanism over the temperature range studied. The intermetallic compound layer thickness reached 2.16 μm after 30 days of aging at 393 K. The apparent activation energies for growth of total Cu–Sn (Cu6Sn5+Cu3Sn), Cu6Sn5 and Cu3Sn intermetallic compound layers were 107.1, 98.35 and 90.5 kJ/mol, respectively. [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]

We analyzed the effects of phosphorous (P) in a palladium (Pd) layer on the interfacial reactions and mechanical properties of Sn–58Bi solder with thin electroless-nickel electroless-palladium immersion gold (ENEPIG) joints (pure Pd and Pd(P) joints) after a high-temperature storage test. Flake-type (Pd,Au)Sn 4 intermetallic compounds (IMCs) mainly formed in the pure Pd and Pd(P) joints. After being aged at 85–115 °C for 300 h, top- and bottom-side (Cu,Ni) 6 Sn 5 IMCs formed at the interface between the (Pd,Au)Sn 4 IMC and partially destroyed P-rich Ni layer of the pure Pd joints. In contrast, a Ni 3 Sn 4 IMC formed at the interface between the (Pd,Au)Sn 4 IMC and P-rich Ni layer of the Pd(P) joints after most aging temperatures and durations. This is because the reaction rate of the Pd(P) joint was lower than that of the pure Pd joints. The unreacted Ni layer remained at the Pd(P) joints after aging. In a high-speed shear test, the shear strength of the pure Pd joints rapidly decreased after being aged at 115 °C for 100 h. In contrast, the shear strength of the Pd(P) joints slightly decreased after being aged at 115 °C for 1000 h. The shear strengths of the pure Pd and Pd(P) joints were quite different under same aging conditions because of the different diffusion rates and IMC compositions of the pure Pd and Pd(P) joints. Fracture surfaces of the pure Pd joints after being aged at 115 °C were observed on the Cu substrate, but those of the Pd(P) joints were on the Ni 3 Sn 4 IMC surface. Therefore, the Sn–58Bi solder with a Pd(P) layer in thin-ENEPIG is expected to be more reliable than that with pure Pd joints under aging treatment. • Effect of adding P to Pd layer of an ENIPIG joint with Sn–58Bi solder examined. • Interfacial reactions/mechanical properties considered at varying temperatures/ages. • Adding P reduced reaction rate at interfaces and increased shear strength. • Adding P to the Pd layer should improve the reliability of the joint for use in PCBs. [ABSTRACT FROM AUTHOR]

The mechanical properties of screen-printed silver circuit were focused by fabricating hybrid silver pastes composed of silver nanoparticles and micron-sized silver flakes with various contents of silver flakes (0, 25, 50, 75, 100 wt%). All printed hybrid silver circuits on the polyimide (PI) substrate were sintered at 250 °C for 30 min in air. Surface porosity and pore volume of hybrid silver were analyzed by SEM image analyzer and BET method, respectively. Pore volume was increased as contents of silver flake from 1.7 cm 3 /g to 3.0 cm 3 /g. The low cycle flexibility of screen-printed hybrid silver circuits was evaluated by Massachusetts Institute of Technology (MIT)-type folding endurance test to confirm the flexibility of screen-printed circuit. A roll-type 90° peel test was conducted to measure the peel strength of the hybrid silver circuits. The highest flexibility and peel strength of screen-printed silver circuit was 50 wt% of silver flake contents. Silver flake improved the peel strength and folding endurance property of the silver circuit screen-printed silver nanopastes. [ABSTRACT FROM AUTHOR]

Abstract: The present study was carried out to evaluate the microstructural and mechanical properties of a friction stir welded AZ31 with CaO Mg alloys. Friction stir welding (FSW) was performed at a tool rotation speed of 1600rpm and a traveling speed of 80mm/min. An intermetallic compound, Al2Ca, was resulted in the base metal (BM). In the stir zone (SZ), fine grains and intermetallic compound particles formed due to dynamic recrystallization and mechanical stirring. Hardness profiling showed that the SZ was harder than the BM, likely due to the presence of fine grains and thermally stable intermetallic compounds. [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: The microstructural evolution and interfacial reactions of fluxless-bonded, Au–20wt.%Sn/electroless nickel-immersion gold (ENIG) solder joint were investigated during reflow and aging. After the reflow process, only (Au,Ni)Sn intermetallic compound (IMC) was formed at the interface. After prolonged reflow reaction, the (Au,Ni)Sn IMCs that had been formed in the initial reflow stage grew into the solder and a (Ni,Au)3Sn2 IMC was formed at the interface. In the aging treatment, the solid-state interfacial reaction was much faster at 250°C than at 150°C. After aging at 250°C for 100h, a thick (Au,Ni)Sn IMC layer was formed at the interface. With increasing aging temperature and time, the δ(AuSn)-phase adjacent to the interfacial layer was gradually replaced by the ζ(Au5Sn)-phase. The interfacial (Au,Ni)Sn IMC grew with the preferential consumption of the available δ-phase in the solder. The Ni3P layer formed from the Ni(P) layer in the initial 500h of aging was subsequently further transformed into a Ni5P4 layer during further aging treatment between 500 and 1000h. The original electroless Ni(P) plating layer lost its initial role of a diffusion barrier due to its crystallization. After aging for 1000h, the Ni5P4 layer was partially destroyed, and the Au–Cu IMCs were formed below the P-rich Ni layer. [Copyright &y& Elsevier]

Abstract: The interfacial reactions between Sn–3.5Ag–0.7Cu solder and an electroless nickel-immersion gold (ENIG)-plated Cu substrate were investigated during aging at 200°C for up to 1000h. During aging, the Ni(P) layer was transformed partially into an Ni3P layer, and then the Ni3P layer was also transformed into an Ni–Sn–P ternary layer. After aging for 1000h, Cu6Sn5 and Cu3Sn IMCs were formed below the Ni–Sn–P layer. During aging at 200°C, the interfacial IMC was transformed sequentially into (Cu,Ni)6Sn5, (Ni,Cu)3Sn4 and finally (Cu,Ni)6Sn5. [Copyright &y& Elsevier]

Abstract: The interfacial reaction and morphology change of intermetallic compound (IMC) between eutectic Sn–Cu solder and Ni substrate under various reflow and cooling conditions were investigated. The reaction between the solder and Ni layer resulted in the formation of (Cu,Ni)6Sn5 IMC at the interface. Reflow and cooling conditions changed the morphology of the IMCs formed at the interface. At low temperatures (≤255°C), only a needle-type (Cu,Ni)6Sn5 IMC with a hexagonal cross-section was formed. On the other hand, the morphology of the (Cu,Ni)6Sn5 IMC changed from needle-type to dodecahedron-type with increasing reflow temperature and time. The morphology of the (Cu,Ni)6Sn5 IMC was also affected by cooling condition. Even though the morphology of the IMC changed with the reflow and cooling conditions, these IMCs had a similar chemical composition. [Copyright &y& Elsevier]

Abstract: Brazing between WC–Co and carbon steel using multiple layers of Cu and Ni alloys as insert metal was successfully carried out without weld defects. However, as the brazing time was increased, brittle intermediate phases and coarsening of WC grains were produced and deteriorated the joint strength. On the basis of inhibiting WC grain growth by the addition of carbides during sintering, this study focused on the improvement of the joint strength related to microstructural changes caused by various concentrations of Cr3C2 during the brazing. Increased amounts of Cr3C2 were effective to prevent the formation of η phase (Co3W3C) and the coarsening of WC grains, however, in the case of 1.0% Cr3C2 addition, deteriorated the shear strength due to the formation of brittle Cr7C3 in the insert metal layer. The highest shear strength was 370MPa under the condition of 0.5% Cr3C2 concentration in WC–8%Co, which was higher than that (310MPa) of a similar joint without Cr3C2 under same brazing condition of 1323K and 0.6ks. [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]

Abstract: The interfacial reactions and growth kinetics of intermetallic compound (IMC) layers formed between Sn–0.7Cu (wt.%) solder and Au/Ni/Cu substrate were investigated at aging temperatures between 70 and 170°C for up to 100 days. After reflow, the IMC formed at the interface was (Cu,Ni)6Sn5. In addition, only this (Cu,Ni)6Sn5 layer was observed in the samples aged at temperatures between 70 and 150°C. On the other hand, after isothermal aging at 170°C for 50 days, the solder/Ni interface exhibited a duplex structure of (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4. The time exponents (n) determined at temperatures below 150°C were about 0.2. The determined n values are presumably related to a grain boundary diffusion-controlled mechanism. In the ball-shear tests, the shear strength significantly decreased after aging for initial 1 day, after which it remained nearly unchanged through further prolonged aging. In all samples, fracture occurred in the bulk solder. [Copyright &y& Elsevier]

Abstract: Al/Cu metal joints applied for the electrical connector was joined by the friction welding method to limit the formation of intermetallic compound under optimum friction welding condition. To guarantee the reliability of the Al/Cu joints in service requirement, the effects of the intermetallic compound layer on the electrical and mechanical properties have been investigated under various annealing conditions. Two kinds of intermetallic compounds layer were formed in the joints interface and identified by AlCu and Al2Cu. The growth kinetic of these intermetallics during the annealing can be followed by volume diffusion process. The activation energy of Al2Cu, AlCu and total intermetallic compound (AlCu + Al2Cu) represented 107.5, 98.42 and 110.22kJ/mol, respectively. A thicker intermetallic compound layers could seriously degrade the electrical resistivity and tensile strength. The electrical resistivity with 21μm thickness of intermetallic compound was 45μΩcm and increased to be 85μΩcm with 107μm of intermetallic compound. Tensile strength remarkably decreased from 85MPa to near zero at the annealing condition of 773K and 129.6ks and fracture occurred through the intermetallic compound layers. [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]

Friction welding characteristics between TiAl and AISI 4140 have been investigated in this study. In spite, many trials were applied to achieve the sound weld zone of direct bonding between TiAl and AISI 4140 without crack under various friction welding conditions, a micro and large crack occurred through the interface due to the brittle nature of reaction products and the martensite transformation resulted in volume expansion near the weld zone. The formation of crack resulted in a lower tensile strength of joints relative to those of other welding technique. Therefore, to prevent crack formation at the interface, pure copper was used as insert metal for stress relief buffer layer. In the view point of tensile strength, the highest tensile strength between TiAl and AISI 4140 was acquired by using pure copper as insert metal. Fracture occurred at the TiAl base metal under optimum friction welding condition. [Copyright &y& Elsevier]

Printed electronics have been used because of various advantages such as low cost, productivity, and eco-friendly processing. However, for fabricating printed electronics, the conventional sintering process conducted at high temperatures has problems such as thermal damage and long processing time. To solve these problems, low-temperature processes such as intensive pulsed light (IPL) have been widely studied. Research of composite materials has become important in supporting these low-temperature processes. We fabricated Ag-decorated, multi-walled carbon nanotubes (Ag-MWCNTs) in composite pastes and sintered printed circuits using IPL energy. We investigated the electrical resistivity, microstructure, and flexibility of the Ag-MWCNT composite circuit with various durations of IPL energy irradiation and Ag-MWCNT content (0, 1, 2, and 3 wt%). The electrical resistivity of the circuit sintered with IPL energy decreased with irradiation time, but it had an unstable microstructure from the drastic sintering process. The Ag-MWCNTs could solve this problem using the net structure of the MWCNTs. The Ag-MWCNT composite nanoparticles could be a solution to overcome the problems in the photonic sintering process using IPL energy. • Intensive pulsed light sintering process were performed for printed electronics. • The irradiation time of intensive pulsed light affects on printed Ag circuit. • Flexibility and electrical resistivity of Ag circuit improved with Ag-MWCNT. [ABSTRACT FROM AUTHOR]

Abstract Highly reliable bonding materials have attracted tremendous interest due to a growing demand for high-temperature electronics. We developed a fluxless and binder-free paste comprising Cu nanoparticles (NPs), Sn-58Bi (SnBi) particles, and polyvinylpyrrolidone (PVP) dispersing agent, which enables pressureless, low-temperature (190–250 °C) formation of robust joints (over 7 MPa) by means of transient liquid phase sintering (TLPS). Microstructural evolution of the joint was investigated under variations in PVP molecular weight (MW; 10,000, 55,000, 360,000, or 1,300,000) and bonding conditions including temperature and time. In a die-shear test, the joint formed with PVP MW 360,000 was the strongest due to its proper particle dispersion and the formation of intermetallic compounds (IMCs). Conditions of excessive PVP MW, bonding temperature, and time impeded the bonding characteristics of the TLPS joint, with formation of voids and increasing brittleness. TLPS bonding with the optimal dispersing agent enabled pressureless die attach without chip damage, demonstrating applicability as a simple, robust interconnection for high-temperature electronics. Highlights • Pressureless TLPS bonding was conducted with Cu nanoparticles and Sn-58Bi particles. • PVP MW of 360,000 assisted TLPS reactions by dispersing Cu and Sn-58Bi particles. • The process with excessively high energy degenerated strength by formation of voids. • The strength is consistent after aging time of 500 h due to completion of reactions. [ABSTRACT FROM AUTHOR]

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]

Ag circuit embedded in polydimethylsiloxane (PDMS) substrate were fabricated through photonic sintering and transfer of Ag nanoparticles (NPs) for reducing processing time, cost, damage to the substrate, and delamination caused by the low surface energy of PDMS. The photonic energy led to the microstructural evolution of a printed Ag circuit by rapid cluster formation and by removing the organics within several microseconds. Variations of surface roughness showed increasing trends at higher photonic energy conditions and drastic decrease after the embedding process. Hardness and electrical resistivity were measured before and after PDMS embedding, and after the second photonic sintering at various photonic energy conditions. The Ag circuit embedded in the PDMS substrate showed improved hardness by 207% due to the denser microstructure of the flipped surface and increased electrical resistivity increasing by 54% on average. Moreover, the effects of second sintering on the microstructure, electrical, and mechanical properties and the electrochemical reliability of the embedded Ag circuit are also studied. [ABSTRACT FROM AUTHOR]

Percolated networks of silver nanowires (AgNWs) have attracted intensive attention because of their remarkable mechanical stability, along with their excellent optical and electrical performance for the fabrication of flexible transparent electrodes. Most prior research has mainly focused on fabricating transparent electrodes that can be used in optoelectronic devices such as touch sensors, light emitting diodes, and photovoltaics. However, fabrication of transparent and flexible transmission lines designed to conduct alternating current of high frequency has not been reported so far. Herein, we developed highly transparent, mechanically stable transmission line by employing inverted layer processing (ILP) in order to embed the AgNWs just below the surface of a free-standing transparent polymer. For this, we synthesized polyvinyl butyral (PVB), which can be prepared from polyvinyl alcohol by reaction with butyraldehyde, for AgNW support. AgNWs deposited on a preliminary substrate (glass) were plasmonically sintered to significantly enhance their conductivity, and then transferred to the surface of the cured PVB film by the ILP. Measurements and simulation of specially designed coplanar waveguide circuits comprising AgNWs and PVB revealed that the fabricated electrode can simultaneously provide impressive transmission performance as well as excellent mechanical flexibility and transparency. An interesting finding was that the transmission characteristics and mechanical stability are in a trade-off relationship, which needs to be carefully considered in the design and selection of materials for the flexible transmission lines. [ABSTRACT FROM AUTHOR]

The microstructural features and mechanical properties of a B 4 C particle-reinforced Cu matrix composite prepared by friction stir welding (FSW) were investigated. For this purpose, the FSW process was carried out along a 0.6-mm-width gap, between two Cu plates, filled with boron carbide (B 4 C) particles. Microstructural observations taken in the stir zone (SZ) revealed that the presence of B 4 C particles led to the evolution of fine grains (∼2 μm). Based on the hardness measurements of the FSW-fabricated samples, the hardness values were significantly improved after the B 4 C particles were incorporated. [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]

Interfacial reactions and intermetallic compound (IMC) formation of Sn–1 wt.%Ag solder with two different surface finishes, electroless nickel–immersion gold (ENIG) and electroless nickel–electroless palladium–immersion gold (ENEPIG), were evaluated during a reflow process. We first compared the interfacial reactions of the two solder joints and identified a relationship between the interfacial reaction behavior and solder/substrate compatibility. The Sn–1Ag/ENIG joint exhibited stable IMC growth and superior interfacial stability compared with the Sn–1Ag/ENEPIG joint. The growth rate of the interfacial IMC layer and consumption rate of the Ni(P) layer were closely related to the interfacial microstructure and morphology of the IMCs. The layer-type well-attached interfacial IMCs had advantages with respect to IMC growth rate and Ni(P) consumption rate. Compared to the previous Sn–3.0Ag–0.5Cu study, ENEPIG performed very well with Sn–Ag–Cu solder alloy. On the other hand, ENEPIG proved not to be a suitable surface finish for Sn–Ag solder alloy in this study. [ABSTRACT FROM AUTHOR]

Abstract: Friction stir welds of aluminum alloy 5083 are created at tool rotation speeds of 700, 1050, and 1600 rpm, with a fixed traveling speed of 100 mm/min. Stir welded structures, together with the as-received alloy, are subjected to a sensitization heat treatment of 175 °C for 240 h, which is known to produce severe sensitization in the as-received materials. It is demonstrated that stir welding dramatically reduces the sensitization response measured by the nitric acid mass loss test (NAMLT ASTM G67-93), suggesting that stir welding can be used to mitigate sensitization damage. The microstructures produced by the stir welding are evaluated using optical microscopy (OM), scanning electron microscopy (SEM), and an electron probe micro-analyzer (EPMA) to document the variations in the distribution of beta phase precipitates, which are believed to be responsible for this outcome. [Copyright &y& Elsevier]

Abstract: The spot welding of Al plate to Mg plate was produced by friction stir spot welding using various tool rotation speed and duration time of the tool to investigate the effects of the welding parameters on the reaction of Al and Mg alloy. The interface microstructure and phase were investigated using optical microscopy, scanning electron microscopy and X-ray diffraction. The mechanical properties of the joints are evaluated using tensile test. Experimental results show that intermetallic compounds were formed in the interface of the Al and Mg alloys. The thickness of intermetallic compounds layer increases with increasing tool rotation speed and duration time, and has a significant effect on the strengths of the joints. Heavy thickness of intermetallic compounds layer seriously deteriorates the mechanical properties of the joints. The intermetallic compounds layer mainly contains Al3Mg2 and Al12Mg17 [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]

Abstract: The effects of Cu and Ni additions on the wettability and interfacial reaction of Sn–Ag solder with Cu substrate were investigated. The wettability of the Sn–3.0Ag–0.5Cu (or Ni) solder alloy was firstly measured by a wetting balance test. The formation and growth of intermetallic compounds (IMCs) between the Sn–Ag–Ni solder and Cu substrate were evaluated, and compared the results to the Sn–Ag–Cu/Cu system. In the wetting test, the Cu and Ni additions exerted positive and negative effects, respectively, on the wettability of the Sn–Ag solder. In the solid-state reaction of the Sn–Ag–Cu/Cu solder joint, two IMC layers, Cu6Sn5 and Cu3Sn, grew with increasing aging temperature and time. The growth rate of the Cu3Sn IMC was higher than that of the Cu6Sn5 IMC at the high aging temperatures of 150 and 170°C. On the other hand, in the case of the Sn–Ag–Ni/Cu solder joint, thick (Cu,Ni)6Sn5 and thin Cu3Sn IMCs formed and grew at the interface during isothermal aging. The addition of Ni to the Sn–Ag solder effectively suppressed the growth of the Cu3Sn IMC but increased the amount of the (Cu,Ni)6Sn5 IMC at the interface. [Copyright &y& Elsevier]

Abstract: The surface morphology, electrical property, solderability and interfacial reaction with Sn–3.5wt.%Ag solder of two electroless nickel–boron (EN–B) deposits (Ni–1wt.%B and Ni–3wt.%B) were investigated. The B content of the EN–B layer decreased with increasing pH value. The crystallinity and solderability of the EN–B plating layer decreased with increasing B content, while the electrical resistivity increased. Reaction layers of Ni3Sn4 and Ni3B were formed at the interfaces between the Sn–3.5Ag solder and the two EN–B deposit layers. The thickness of the interfacial Ni3Sn4 intermetallic compound (IMC) layer decreased with increasing B content, i.e., decreasing Ni content. These study results confirmed that the interfacial reaction between solder and the EN–B layer is significantly affected by the B content of the EN–B layer. [Copyright &y& Elsevier]

Abstract: The effects of multiple reflows on the microstructural variation and joint strength of the flip chip solder joints were investigated. Conventional Sn–37Pb and a representative Pb-free Sn–3.0Ag–0.5Cu were used, and a popular low cost under bump metallurgy (UBM) of immersion Au/electroless Ni–P plating was employed. In case of Sn–37Pb, only Ni3Sn4 intermetallic compound layer was formed during multiple reflows. In case of Sn–3.0Ag–0.5Cu, (Cu,Ni)6Sn5 intermetallic compound layer was observed after a single reflow, while (Ni,Cu)3Sn4 layer was additionally settled at the interface between the (Cu,Ni)6Sn5 layer and Ni–P UBM. The thicknesses of the intermetallic compound layers increased and coarsened. The shear force of the both joints slightly decreased during the multiple reflows. The decrease of the joint strength was caused by different softening phenomena between the two cases, and that is discussed in the main text. [Copyright &y& Elsevier]

Abstract: The microstructures and wear property of friction stir welded AZ91 Mg alloy/SiC particle reinforced composite (AZ91/SiC/10p) were investigated. The initial microstructures of the AZ91/SiC/10p were composed of irregularly distributed β-phases (Al12Mg17) and agglomerated SiC particles, while the friction stir weld zone was characterized by the homogeneous distribution of SiC particles, the recrystallized grain structure and the dissolution of β-phase. Thank to the microstructural modification, an improvement in the hardness and wear property of the weld zone were observed as compared to those of the base metal. The hardness near the weld zone was a higher and more homogeneously distributed and the wear resistance within the weld zone, as evaluated by the specific wear loss, was superior, as compared with the base metal. [Copyright &y& Elsevier]

Abstract: The interfacial microstructure of Sn–37Pb solder with immersion Au/electroless Ni–P under bump metallization (UBM) was studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A Ni3Sn4 intermetallic compound (IMC) layer was formed at the interface between the solder and Ni–P UBM upon reflow. However, after isothermal aging, AuSn4 containing a certain amount of Ni dissolved in it, i.e. (Au,Ni)Sn4, appeared above the Ni3Sn4 layer. Two distinctive layers, P-rich and Ni–Sn–P, were additionally found from the TEM observation. Analytical studies using energy dispersive spectrometer (EDS) equipped in TEM revealed that the averaged composition of the P-rich layer is more close to that of a mixture of Ni3P and Ni, while that of the Ni–Sn–P layer is analogous to the P-rich layer but containing a small amount of Sn in it. The growth of the Ni3Sn4 IMC layer thickness obeyed a parabolic growth law which implies that the interfacial IMC growth is mainly controlled by volume diffusion of the elements to the reaction layer. The shear force of the joints decreased during isothermal aging at 373K. The decrease of the shear force could be mainly due to the coarsening effect of the microstructure within the solder. The failure behavior could be well explained with the results of finite element modeling (FEM) analyses. [Copyright &y& Elsevier]

Phase analysis and growth kinetics of intermetallic compound (IMC) layers formed between low cost Sn–Cu–Ni solder for wave soldering and Cu substrate by solid state isothermal aging were examined at temperatures between 80 and 150 °C for 0 to 60 days. The IMC layer was composed of two phases; Cu6Sn5 (also (Cu,Ni)6Sn5) adjacent to the solder, Cu3Sn adjacent to the copper. The Cu3Sn layer was absent at all time periods for the aging temperatures of 80 and 100 °C. After isothermal aging at 120 °C for 30 days and at 150 °C for all time periods, the solder/Cu interface exhibited a duplex structure of Cu6Sn5 and Cu3Sn intermetallics. From the EPMA analysis, a comparatively high Ni concentration is found between the Cu6Sn5 and Cu3Sn layer. The Ni concentration in the (Cu,Ni)6Sn5 intermetallic was about 4.3 at.%. The total IMC layer thickness was approximately 11.5 μm after 60 days of aging at 150 °C. The apparent activation energies for growth of total and Cu6Sn5 IMC layer were 76.17 and 66.35 kJ/mol, respectively. [Copyright &y& Elsevier]

• Low temperature sintering process was performed with intensive pulsed light. • The pulse condition of intensive pulsed light affected on printed Cu circuit. • Electrochemical migration behavior of Cu circuit was investigated. Problems associated with the oxidation of Cu nanopaste have been widely studied in efforts to develop a replacement for Ag nanopaste. The intensive pulsed light (IPL) sintering process has been suggested to solve the oxidation problem because it is a method with a short processing time and is conducted at room temperature. Cu nanopaste was fabricated with Cu nanoparticles and a functional organic matrix. Cu nanopaste screen-printed onto a polyethylene terephthalate substrate was subjected to various IPL sintering conditions, and the effects of pulse power and pulse width on the microstructure, electrical resistivity, and electrochemical migration behavior of the printed Cu patterns were investigated. The electrical properties of the Cu patterns improved with increasing pulse power and pulse width because organic residues were removed by the IPL energy. The electrical properties of the Cu patterns improved with increasing pulse power and pulse width because organic residues were removed by the IPL energy. The electrochemical migration behavior was varied because of leaked ethylene glycol from organic matrix. The dendrites from lower pulse condition has finer microstructure and increased nucleation. [ABSTRACT FROM AUTHOR]

Cu–Cu bonding was successfully achieved through the transient liquid phase sintering (TLPS) bonding method using Cu and an eutectic Sn–Bi alloy. The bonding process was performed for total bonding process time of 2 h under a pressureless condition in air. The bonding temperature was 220 °C considering that the Cu 6 Sn 5 intermetallic compound (IMC) and Bi react at 195.9 °C to transform into Cu 3 Sn and a liquid. The shear strength of Cu-70(Sn–58Bi) was approximately 22.06 MPa with the formation of the Cu 3 Sn. The residual eutectic Sn–Bi structure remained at Cu-90(Sn–58Bi), and the voids were largely observed at Cu-50(Sn–58Bi). In case of Cu-70(Sn–58Bi) and Cu-50(Sn–58Bi), the remelting temperature increased to 270 °C by the IMC reaction between Cu and Sn. On the other hand, the remelting temperature of Cu-90(Sn–58Bi) joint remained at 139 °C due to residual eutectic Sn–Bi structure. The salt spray test was conducted at 35 °C under the 5% NaCl condition for 24, 48, and 96 h to evaluate the bonding reliability under the salt spray condition. The corrosion behavior was evaluated using the electrochemical impedance spectroscopy measuring method. In addition, the thermal bonding reliability was investigated through a high-temperature storage test at 200 °C for 100, 500, and 1000 h. Analysis results of the experiment showed that the electrochemical and thermal bonding reliabilities were improved with the Cu 3 Sn formation owing to its high resistance properties under the salt spray and high-temperature conditions. • Pressureless transient liquid phase sintering bonding was achieved by composite paste consisted of Cu and Sn–58Bi. • TLPS joint consisted of Cu 3 Sn and Bi, was formed for high heat endurance and high reliable bonding. • Electrochemical and thermal bonding reliability was confirmed by salt spray and high-temperature storage test. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced plastic (CFRP) is increasingly considered for various industrial applications. CFRP has been applied to the automotive industry to increase fuel efficiency due to its excellent strength and lightweight. Therefore, the demand for dissimilar material joining techniques is gradually increasing. In this study, we investigated the intense pulsed light (IPL) as surface treatment for CFRP. The IPL surface treatment requires a very short processing time and can be easily automated compared with other processes such as chemical and mechanical treatments. The change in morphology and chemical composition of the CFRP-treated surfaces was analyzed using scanning electron microscopy, profiler, and X-ray photoelectron spectroscopy. The bonding strength due to varying IPL exposure time was evaluated by the lap shear test. The apparent shear strength increased by up to 159% in this study. The IPL treatment is very simple and requires short processing time to produce enhanced adhesive joints. [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]