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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]

Cu pillar bumps were mechanically enhanced using electroless Ni plating for fine-pitch electronic packaging applications. The interfacial reaction and mechanical properties of the Ni-plated Cu pillar bump joints were evaluated. After reflowing, the plated Ni layer dissolved into the Sn-Ag solder caps. The Ni was incorporated into the interfacial reactions, forming a (Cu,Ni) 6 Sn 5 intermetallic compound on the Cu pillar bumps. Adding Ni to the Cu pillar bumps significantly affected the mechanical properties of the joint and increased the bump shear strength of the solder cap. [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: The interfacial reactions and ball shear properties of ball grid array (BGA) solder joints aged at 170°C for up to 21 days were investigated with different displacement rates. Two different kinds of solders, Sn–37Pb and Sn–3.5Ag (all wt.%), and an electroplated Ni/Au BGA substrate were employed in this work. A continuous Ni3Sn4 intermetallic compound (IMC) layer was formed at the interfaces between both the Sn–37Pb and Sn–3.5Ag solders and the substrate during reflow. After aging, two different reaction layers, consisting of (Au x Ni1−x )Sn4 IMC and Pb-rich phase, were additionally observed between the Sn–37Pb solder and the Ni3Sn4 IMC layer. The thicknesses of these interfacial reaction layers increased with increasing aging time. After reflow, all the fractures occurred inside the bulk solder. The fracture location of the Sn–37Pb solder joints was shifted toward the solder/Ni interface with increasing aging time and displacement rate, whereas the fracture of the Sn–3.5Ag solder joints mainly occurred inside the bulk solder, irrespective of the aging time and displacement rate. Consequently, the shear properties of the Sn–37Pb solder joints significantly decreased with increasing aging time, whereas those of the Sn–3.5Ag solder joints slightly decreased. The tendency toward brittle fracture of the Sn–37Pb solder joints was intensified with increasing displacement rate. The shear properties of the ductile solder joints increased with increasing displacement rate, while the displacement until fracture, deformation energy and displacement rate sensitivity of the brittle solder joints significantly decreased with increasing displacement rate. [Copyright &y& Elsevier]

Abstract: The microstructural evolution and interfacial reactions of Au/Sn/Au/Au/Ni/Kovar joint were investigated during aging at 180 and 250°C for up to 1000h. The Au/Sn combination formed a rapid diffusion system. Even in non-annealed joint, three phases such as AuSn, AuSn2 and AuSn4 were formed. After initial aging at 180°C, the AuSn, AuSn2, AuSn4, Au and Sn phases, which were formed after plating, were fully transformed into ζ-phase and δ-phase, and (Ni,Au)3Sn2 intermetallic compound (IMC) layer was observed between the ζ-phase and Kovar. As a whole, the microstructure of the joint was stable during aging at 180°C. On the other hand, the solid-state interfacial reaction was much faster at 250°C than at 180°C. During aging at 250°C, the Ni layer on the Kovar reacted primarily with the δ-phase in the solder, resulting in the formation and growth of the (Au,Ni)Sn IMC layer at the interface. After aging for 48h, the Fe–Co–Ni–Au–Sn phase was formed underneath the (Au,Ni)Sn IMC layer. Furthermore, cracks were observed inside the interfacial layers after complete consumption of the Ni layer. The study results clearly demonstrate the need for either a thicker Ni layer or an alternative surface finish on Ni, in order to ensure the high temperature reliability of the Au/Sn/Au/Au/Ni/Kovar joint above 250°C. [Copyright &y& Elsevier]

Abstract: Thermo-mechanical reliability of flip chip packages employing anisotropic conductive film (ACF) was investigated in terms of the effect of bonding forces on the failure mode of the packages. Conventional reflow process was conducted to evaluate the reliability of the package. Two kinds of failure modes were detected in this study. The first one is formation of a conduction gap between conductive particle and Ni/Au plated Cu pad, while the second one is delamination of the adhesive matrix from the plated Cu pad on flexible substrate. The determination of the failure mode was mainly affected by the variation of the bonding force. In case of the ACF joints with lower bonding forces, a conduction gap was the main failure mode of the reflowed joints, while the delamination of the adhesive matrix was frequently observed in case of the joints with higher bonding forces. The difference in failure mode was discussed in the main text. [Copyright &y& Elsevier]

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: 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 of 185 and 200°C for aging times of up to 60days. After reflow, the IMC formed at the interface was (Cu,Ni)6Sn5. After aging at 185°C for 3days and at 200°C for 1day, two IMCs of (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 were observed. The growth of the (Ni,Cu)3Sn4 IMC consumed the (Cu,Ni)6Sn5 IMC at an aging temperature of 200°C due to the restriction of supply of Cu atoms from the solder to interface. After aging at 200°C for 60days, the Ni layer of the substrate was completely consumed in many parts of the sample, at which point a Cu3Sn IMC was formed. In the ball shear test, the shear strength decreased with increasing aging temperature and time. Until the aging at 185°C for 15days and at 200°C for 3days, fractures occurred in the bulk solder. After prolonged aging treatment, fractures partially occurred at the (Cu,Ni)6Sn5 +Au/solder interface for aging at 185°C and at the (Ni,Cu)3Sn4/Ni interface for aging at 200°C, respectively. Consequently, thick IMC layer and thermal loading history significantly affected the integrity of the Sn–0.7Cu/Ni BGA joints. [Copyright &y& Elsevier]

Abstract: The interfacial reaction between the Sn–0.4 wt.% Cu solder and two different kinds of substrates (Cu and ENIG (electroless nickel-immersion gold)) during isothermal aging at 150 °C were studied. In case of the Cu substrate, two IMCs (intermetallic compounds) of Cu6Sn5 and Cu3Sn formed at the interface after aging for 250 h. After aging at 150 °C for 1000 h, crack occurred along the interface between the Cu3Sn IMC and Cu substrate. In case of the ENIG substrate, the solder/electroless Ni–P interface exhibited a duplex structure of (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 after aging at 150 °C for 24 h. Many discontinuous (Cu,Ni)6Sn5 IMCs formed on (Ni,Cu)3Sn4 IMC layer. The presence of P in the electroless Ni–P layer caused complicated interfacial reactions such as formation of a P-rich Ni (Ni3P) and Ni–Sn–P layers. The growth of the Cu–Sn IMC layer formed on the Cu substrate was much faster than that of the Cu–Ni–Sn IMC ((Cu,Ni)6Sn5 and (Ni,Cu)3Sn4) layer formed on the ENIG substrate. In addition, the formation of the Cu–Ni–Sn IMC layer retards the consumption of the Ni from the electroless Ni–P layer. Results of this study showed that the ENIG plating layer acts as a good diffusion barrier for the Sn–0.4Cu solder. [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 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 microstructural evolutions and shear properties of the Sn–3.5Ag (in wt%) BGA solder joints were investigated in terms of the effects of various substrate metallization methods with multiple reflows. A continuous scallop-shaped Cu6Sn5 intermetallic compound (IMC) layer was formed at the solder/Cu interface, whereas a reaction layer between the solder and electrolytic Ni/Au substrate was analyzed to be a continuous Ni3Sn4 IMC layer. The thickness of the IMC layers increased with the number of reflows. The reaction products between the solder and electroless Ni/immersion Au (ENIG) substrate were three distinctive layers consisting of Ni3Sn4, Ni–Sn–P and Ni3P. The spalling of the Ni3Sn4 IMC and the growth of Ni–Sn–P and Ni3P layers were observed with the number of reflows. The shear properties of the Sn–3.5Ag/Cu solder joints were nearly consistent with the multiple reflows. The electrolytic Ni/Au substrate provided the excellent mechanical properties of the Sn–3.5Ag BGA solder joints. The shear properties of the Sn–3.5Ag/ENIG solder joints significantly decreased with the multiple reflows. [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]

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]

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]

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 objective of this work was to demonstrate the feasibility of friction stir welding (FSW) for joining of copper. Defect free weld were produced on 4 mm thick copper plate at travel speed of 61 mm/min and tool rotation speed of 1250 rpm using a general tool steel as the welding tool. The stir zone showed the very fine and equaxied grain structure compared to the base metal which had a elongated grain and its size is approximately 100 μm. The heat-affected zone (HAZ) which lies beside the stir zone had a near-equaxied and larger grain structure than that of the base metal due to annealing effect. Slight softening region was formed in the weld zone due to lower density of dislocation relative to the base metal. Transverse tensile strength of FSW copper joint reached about 87% of that of the base metal and showed slight higher value than that of the EBW copper joint. [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]

• We investigated solid-state growth of Cu-Sn intermetallics in composite Sn/Cu/Sn preform. • Aged Sn/Cu/Sn preforms compensated for drawback of long bonding time. • As the aging time elapsed, the thickness of Cu decreased. • The Cu 3 Sn adjacent to Cu core layer increased, whereas the Cu 6 Sn 5 gradually decreased. This paper presents the interfacial reaction and growth rate of Cu-Sn intermetallic compounds (IMCs) for various aging times in a composite preform for a die-attach material at high temperature. The feasibility of the composite preform we fabricated for power electronic applications to reduce the long bonding time of transient liquid phase (TLP) bonding was evaluated in this work. After the plating process, the composite preform was composed of Sn layers at both sides of the Cu core layer and the Cu layer. In terms of the aging treatment, the IMC layer was formed rapidly at the Cu-Sn interface in the composite preform by consuming the Sn layers, and the reduction and growth rates of Cu and Cu 3 Sn were calculated, respectively. We performed the TLP bonding process at 270 °C using various aged composite preforms. The Cu-Sn IMC was formed rapidly on both sides adjacent to the Cu core layer. The thickness of Cu decreased as the aging time elapsed. Therefore, the amount of Cu 3 Sn adjacent to the Cu core layer increased and the amount of Cu 6 Sn 5 rapidly increased, simultaneously. We investigated the thicknesses and variations of the phase of the joint in the composite preform during the aging treatment process and sequential TLP bonding process for various times. We fabricated pre-annealed Sn/Cu/Sn preforms and performed fast Cu-Sn TLP bonding for high temperature power electronic applications. [ABSTRACT FROM AUTHOR]

• Interfacial reactions at Sn-3.0Ag-0.5Cu/thin-Au/Pd/Ni(P) solder joints were probed. • Effects of Pd layer structure on these reactions probed for various reflow times. • P in the Pd layer strongly affected interfacial reactions during reflow. • Pd layer structure affected interfacial reactions and microstructure evolution. Herein, we investigated the interfacial reactions of crystalline Pd (pure Pd) and amorphous Pd (Pd(P)) layers in thin electroless-Ni electroless-Pd immersion-Au (thin-ENEPIG) surface-finished printed circuit board with Sn-3.0Ag-0.5Cu (SAC305) solder joints reflowed at 260 °C for 10–180 s. After 20 s reflow, a thick (Pd,Au)Sn 4 IMC was formed at the interface of the pure Pd joint, while thick AuSn 4 and thin (Pd,Au)Sn 4 IMCs were formed at the interface of the Pd(P) joint. After 30 s reflow, needle-type (Cu,Ni) 6 Sn 5 IMC was mainly formed at the top-side interface of the pure Pd joint, while scallop-type (Cu,Ni) 6 Sn 5 IMC was formed at the top-side interface of Pd(P) joints. Finally, the top-side (Cu,Ni) 6 Sn 5 IMC of the pure Pd and the top- and bottom-side (Cu,Ni) 6 Sn 5 IMCs of the Pd(P) joints coarsened with increasing reflow time up to 180 s. In the results of top-view SEM micrographs, the (Cu,Ni) 6 Sn 5 IMCs on the Pd(P) joint were larger than those on the pure Pd joint for reflow times of 30–180 s. Therefore, P in the Pd layer was concluded to significantly affect the interfacial reactions and IMC morphology of the SAC 305 solder with ENEPIG joints during reflow reactions. [ABSTRACT FROM AUTHOR]

Abstract Intense pulsed light sintering of printed metallic circuits on polymer substrates is an attractive technique. However it still does not yield the mechanical quality required for industrial applications. This technology must improve adhesion and flexibility to produce highly reliable flexible electronic devices. The effects of atmospheric pressure oxygen plasma and acrylic acid polymerization treatments upon the adhesion and flexibility properties were investigated. Modified polyimide surfaces were characterized by surface free energy measurements, and adhesion and flexibility properties were evaluated by means of roll-type 90° peel tests and IPC sliding tests. The strength of adhesion with oxygen-treated and acrylic acid polymerized samples increased about 17- and 20-fold compared with that of untreated samples, and the flexibility was improved by about 2 fold, respectively. The evident improvements in surface free energy, adhesion and flexibility were attributed to the creation of oxygen functional groups on the polyimide surface after atmospheric pressure plasma treatment. Graphical abstract Unlabelled Image Highlights • Our group has studied modifying surface characteristic to enhance the adhesion of photonic sintered Ag printed circuit. • An acrylic acid polymerization using APP was proposed as an effective method for modifying surface of substrate. • We suggest the surface free energy, XPS spectra contrast, and peel strength after the APP treatment. [ABSTRACT FROM AUTHOR]

Abstract A micro-sized Ag paste was fabricated with the metal content of approximately 85% as a sinter-bonding material in this study. The sintering reactions and joint strengths of Ag sintered joints with three different surface finishes of Cu, Ag, and electroless Ni-immersion Au (ENIG) were evaluated at different sinter bonding times during the sintering process. Stable interfacial microstructures and relatively dense Ag sintered layers were formed in the three Ag sintered joints, and the interdiffusion behaviors between the Ag paste and substrate metals promoted in the formation of good metallurgical bonding during the Ag sintering process, regardless of surface finish. The bonding time of 10 min was sufficient for full sintering reactions between the chip and different substrate finishes. The shear strength did not increase with increased sintering time regardless of surface finish. The substrate metals strongly affected the die shear strengths of the Ag sintered joints, and the Ag-finished joint had a more stable interfacial microstructure and superior shear strength compared to the other metal-finished joints. Graphical abstract Unlabelled Image Highlights • Ag paste with 85% metal content and 2–3 μm particles was fabricated. • Bare, Ag-coated, and ENIG-treated DBC substrates were sintered using paste. • Joint strengths of Ag-coated Si chips to metallized DBC substrates were tested. • Ag-coated DBC substrates allowed the best atomic interdiffusion and joint strength. [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]

Silver nanowire (AgNW) network is known for its low percolation threshold, high conductivity and good flexibility, therefore, considered one of the best candidates for fabrication of flexible and transparent electrodes. However, a general approach to make the AgNWs-based electrodes, an overcoating of nanowire dispersion onto a transparent polymer, should make an issue of poor mechanical stability, mainly caused by low adhesion between the nanowires and polymer. In addition, a thin insulating layer of polyvinylpyrrolidone (PVP) formed on the surface of AgNWs deteriorates the conductivity of their network, which means that a post-processing such as high temperature annealing is essentially needed. Here we employed a plasma treatment with an inert gas to remove the residual PVP layer, so that the conductivity could be enhanced without employing any high temperature processing. Interestingly, the optical transmittance in the wavelength near 400 nm was also increased, resulting in more neutral coloration of the electrode. An inverted layer processing made the nanowires to be partially buried at the surface of colorless polyimide (cPI), so that the enhancement of mechanical stability and connectivity with overlying materials were simultaneously achieved. [ABSTRACT FROM AUTHOR]

High reliability has become one of the crucial requirements for portable electronic devices, due to the high dependence of their radio frequency (RF) characteristics on the end-user's surroundings. The RF characteristics of screen-printed silver (Ag) circuits were investigated after a steady-state temperature and humidity storage test. A conductive paste containing Ag nanoparticles was screen-printed onto a silicon (Si) substrate and then sintered at 250 °C for 30 min in air. The printed Ag circuits were placed in a chamber at 85 °C/85% relative humidity (RH) for various durations: 100, 300, 500, 1000 h. The microstructural evolution and thickness profiles of the Ag circuits were observed with field emission scanning electron microscopy and α-step, respectively. The oxidation of the printed Ag circuit surface was analyzed with Auger electron spectroscopy. A network analyzer and Cascade's probe system in the frequency range of 40 MHz to 40 GHz were employed to measure the scattering parameters of the Ag circuits. The experimental results showed that the insertion losses at higher frequencies increased with increasing durations of exposure to the 85 °C/85% RH environment, due to the thicker specific layer for oxidation on the circuit surfaces. The oxide layer was the dominant factor affecting the RF characteristics of the screen-printed Ag thin circuits. Therefore, it is essential to control the oxidation of printed circuits for versatile RF applications. [ABSTRACT FROM AUTHOR]

Highlights: [•] Screen printing enables for metallization of stretchable electronics. [•] Various circuit designs were employed for stretchable interconnects. [•] Horseshoe-type circuit shows the greatest extensibility of about 8%. [ABSTRACT FROM AUTHOR]

Highlights: [•] Formation of the clusters by interparticle necking during sintering process. [•] cluster size in the patterns increased with increasing sintering temperature and time. [•] Ag films for high sintering temperature and time had good electrical properties. [•] Ag patterns exposed to higher sintering temperature and time had higher ECM resistances. [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: 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: The adhesion strength of a Cu/Ni–Cr/polyimide flexible copper clad laminate (FCCL), was evaluated according to the thickness of the Ni–Cr (Ni:Cr=95:5 ratio) seed layer using the 90° peel test. The changes in the morphology, chemical bonding and adhesion properties were characterized by SEM, AFM and XPS. The peel strength of the FCCL increased with increasing thickness of the Ni–Cr seed layer, due to the increase in the ion bombardment caused by the higher power used in the Ni–Cr sputtering process. This increase in the FCCL peel strength was attributed to the lower proportion of C–N bonds and higher proportion of C–O bonds in the polyimide surface. The adhesion strength between the metal and polyimide was mostly attributed to the chemical interaction between the metal layer and the functional groups of the polyimide. [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: In this study, the effect of two laminating parameters, laminating pressure and holding time, on the adhesion strength of flexible copper clad laminate (FCCL) with an epoxy-type adhesive layer was evaluated. The changes in the adhesion property, fracture surface, morphology, and chemical bonding state were characterized by 90° peel test, scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The results showed that the adhesion strength of the FCCL was decreased as the laminating pressure was increased beyond the suitable level. Laminating pressure exerted the greatest influence over the FCCL adhesion strength. On the other hand, the holding time did not significantly affect the peel strength of the FCCL. The fracture of FCCL occurred at the interface between the rolled Cu and the adhesive layer. In addition, the FCCL with high adhesion strength was stable with the variation of adhesion strength after temperature and humidity test. [Copyright &y& Elsevier]

Abstract: The radio frequency (RF) and high frequency performance of the flip chip interconnects with anisotropic conductive film (ACF) and non-conductive film (NCF) was investigated and compared by measuring the scattering parameters (S-parameters) of the flip chip modules. Low cost electroless-Ni immersion-Au (ENIG) plating was employed to form the bumps for the adhesive bonding. To compare the accurate intrinsic RF performance of the ACF and NCF interconnect without lossy effect of chip and substrate, a de-embedding modeling algorithm was employed. The effects of two chip materials (Si and GaAs), the height of ENIG bumps, and the metal pattern gap between the signal line and ground plane in the coplanar waveguide (CPW) on the RF performance of the flip chip module were also investigated. The transmission properties of the GaAs were markedly improved on those of the Si chip, which was not suitable for the measurement of the S-parameters of the flip chip interconnect. Extracted impedance parameters showed that the RF performance of the flip chip interconnect with NCF was slightly better than that of the interconnect with ACF, mainly due to the capacitive component between the bump and substrate and self inductance of the conductive particle surface in the ACF interconnect. [Copyright &y& Elsevier]

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: 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: An oxidation treatment was conducted in a rolled copper foil of 9μm in the thickness by a method of the electroless plating in the alkali liquid having sodium as the main element. The morphology of the oxidized surface was varied from patch type to grass type with increasing of oxidation time. According to the results of energy-dispersive X-ray spectrometry and X-ray photoemission spectroscopy analysis, its chemical composition was changed from Cu2O to CuO. The peel strength was steeply increased by the formation of oxides and was closely related to morphology and growing direction of oxide. [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: Polymer spheres coated with a slurry, consisting of copper(I) oxide+Zn (0–30wt.%) powders, water and polyacrilamide (PA), were sintered at temperatures ranging from 800 to 930°C under a hydrogen atmosphere to fabricate high-porous brass hollow spheres. The metallurgical and mechanical properties of the spheres were investigated with different Zn contents and sintering temperatures. Increasing sintering temperature accelerated the Zn evaporation and sphere densification. Increasing Zn content and decreasing sintering temperature increased the porosity of the spheres, but degraded their mechanical properties. [Copyright &y& Elsevier]

Abstract: This study investigates whether the electrochemical migration (ECM) is affected by factors such as the printed circuit board (PCB) surface finish, distance between the electrodes and bias voltage under water drop (WD) and polarization tests. The main element of the dendrite structure for ENIG (electroless nickel and immersion gold), electroless Ag and electroplate Sn was nickel, silver and tin, respectively. The order of speed in which the dendrite structure was formed from the cathode electrode to the anode electrode on the PCB with various surface finishes was electroless Ag, electroplate Sn and ENIG, irrespective of the distance between the electrodes and the bias voltage. The ECM rate was increased by decreasing the distance between conductors of the opposite polarity and increasing the bias voltage. The order of corrosion rate in distilled water with pH 6.5 and NaCl 1.0wt% solution was electroless Ag, electroplate Sn and ENIG. This trend was corresponded with the tendency for ECM rate. [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 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: A time–temperature–glass transition temperature diagram under a dynamic-heating condition (dynamic t–T dyn–T g diagram) was developed to analyze physicochemical transitions of a reacting polyisoimide system using 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 3,3′-diaminodiphenyl sulfone (3,3′-DDS) as a model system. Under the dynamic-heating condition, the complex electric modulus properties exhibited two transitions at high frequencies but three transitions at lower frequencies, due to the coupled phenomena of the viscoelastic glass–rubber transitions and the kinetic increment of the glass transition temperature of the isomerizing polyisoimide. The dynamic t–T dyn–T g diagram was proposed to analyze those multiple peaks to identify the material status and the transition temperatures corresponding to the initial glass transition (T g0), vitrification (T vit), and final glass transition (T g∞) temperatures. Using the developed methodology, the isomerization of polyisoimide, which is usually difficult to analyze, was successfully investigated to identify the relationships among the thermodynamic, viscoelastic, and kinetic processes. [Copyright &y& Elsevier]

Abstract: The flip chip solder bump was investigated in situ with current stressing in an ambient temperature of 423K. For the in situ investigation of the solder joints, a single flip chip package was examined during whole investigation time. Cross-sectional studies were conducted with the scanning electron microscope (SEM). Cu mini bumps were formed on a Si chip for the solder bumping and electroless Ni-immersion Au (ENIG) surface treatment was conducted on the Cu pads in substrate side. Cu6Sn5 and Ni3Sn4 intermetallic compound (IMC) layers were formed in the both interface, while a typical eutectic structure of Pb-rich and Sn-rich phases were formed within the solder region. After current stressing of 6h, separation of the Pb-rich and Sn-rich phases were occurred in the left solder bump, while a void was formed under the Cu6Sn5 IMC layer in the right side solder bump. After current stressing of 7.5h, the solder joints were catastrophically failed due to the remelting of the solder bump. [Copyright &y& Elsevier]

Abstract: Effects of reflow process on the thermo-mechanical reliability of the anisotropic conductive film (ACF) joints were investigated. Cross-sectional studies were carried out to investigate the effects using a scanning electron microscope (SEM). Swelling of ACF matrix in z-direction and formation of a conduction gap were observed in the reflowed ACF joints which were bonded in lower flip chip bonding pressures than 60N. However, a delamination as well as the formation of a conduction gap was occurred between the ACF and Cu pad on flexible printed circuits (FPC) when ACF joints bonded in higher bonding pressures than 70N were reflowed. This difference of failure mode was mainly due to the divergence of adhesive matrix thickness between the Au bump on Si chip and Cu pad on FPC. Finite element analyses were also conducted to interpret the failure behaviors of the ACF joints. [Copyright &y& Elsevier]