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

Abstract: 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 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: 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 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: 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]

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]

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]

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

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

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

Abstract: The 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: The interfacial microstructure of Sn–3.0Ag–0.5Cu solder with electroless Ni/immersion Au (ENIG) was studied using SEM, EPMA and TEM. (Cu,Ni)6Sn5 intermetallic compound layer was formed at the interface between the solder and Ni–P UBM upon reflow. However, after isothermal aging the AuSn4, with a certain amount of Ni dissolved in it, i.e. (Au,Ni)Sn4 appeared above the (Cu,Ni)6Sn5 layer. Two distinctive layers, P-rich and Ni–Sn–P, were additionally found from the TEM observation. The analytical studies using EDS in TEM revealed that the averaged composition of the P-rich layer is 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. Shear force of the flip chip solder joints decreased during aging at various temperatures. The decrease in shear force was mainly caused by the coarsening of microstructure within the solder and increase of the interfacial intermetallic compound thickness. Nearly all of the test specimens showed ductile failure mode and this could be well explained with the results of FEM analyses. [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: In this study, we investigated the effect of the current density on the interfacial reaction and mechanical reliability of an electroless Ni/immersion Au (ENIG) substrate with Sn–3.5Ag solder. We first evaluated the interfacial reactions of the solder joint under aging for up to 800h and current stressing with current densities of 3×102 A/cm2 and 5×103 A/cm2. Also, we successfully revealed the correlation between the interfacial reaction behavior and mechanical reliability under current stressing. With increasing aging time, the thickness of the Ni3Sn4 layer increased. At both low and high current densities, the thickness of the Ni3Sn4 layer increased up to 400h and decreased thereafter at the cathode, while that of the IMC increased up to 800h at the anode. After the die shear test, the ductile fracture was observed in the as-reflowed joint without current stressing. The fracture mode changed from ductile fracture to brittle fracture when thermal aging and current flow were simultaneously applied. The combination of the current stressing and isothermal aging at high temperature significantly deteriorated the mechanical reliability of the solder joint. [Copyright &y& Elsevier]

Abstract: The effect of displacement rate and intermetallic compound (IMC) growth on the shear strength of electroplated Sn–2.5Ag (in wt.%) flip chip solder with Cu under-bump metallization (UBM) were investigated after multiple reflows. Cu6Sn5 IMC was formed at the interface after one reflow. After five reflows, two different IMC layers, consisting of a scallop-shaped Cu6Sn5 phase and a planar Cu3Sn phase, and their thicknesses increased with increasing reflow number up to 10. The shear strengths peaked after four reflows, and then decreased with increasing reflow number. Increasing displacement rate increased the shear force. The tendency toward brittle fracture characteristics was intensified with increasing displacement rate and reflow number. [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 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 effect of displacement rate and intermetallic compound growth on the shear properties of the electroplated Sn–37Pb (wt.%) flip-chip solder bumps with Cu under-bump metallization (UBM) were investigated after multiple reflows. The compounds Cu6Sn5 and Cu3Sn were formed at the interface after one reflow, and their thicknesses increased with increasing reflow number up to 10. The shear properties peaked after four reflows, and then decreased with increasing reflow number. Increasing displacement rate increased the shear force, but decreased the displacement until fracture. The tendency toward the brittle fracture characteristics was intensified with increasing displacement rate and reflow number. [Copyright &y& Elsevier]

Abstract: This study focused on the feasibility of using Ni flip chip bumps with a Sn–2.5Ag (wt.%) solder encapsulation. The interfacial reaction and die shear property of the Ni flip chip bump with a Sn–Ag solder cap bonded on the electroplated Cu/Sn–Ag substrate were investigated with increasing bonding time. After bonding for 1s (Cu x Ni1−x )6Sn5 and Cu6Sn5 intermetallic compound (IMC) layers were formed at the upper and lower interfaces, respectively, with the former IMC being the predominant phase during bonding. The transformation of the solder cap into the (Cu x Ni1−x )6Sn5 IMC depleted the solder after bonding for 30s, and then the Ni concentration in the IMC gradually decreased with increasing bonding time. The shear property peaked after 30s, and then decreased with increasing bonding time. The fractures occurred at the solder/Cu6Sn5 interface and inside the (Cu x Ni1−x )6Sn5 IMC after bonding for 1s and 30s, respectively, after which the fracture location shifted toward the (Ni x Cu1−x )3Sn4/(Cu x Ni1−x )6Sn5 interface with increasing bonding time. [Copyright &y& Elsevier]

Abstract: This study was focused on the formation and reliability evaluation of solder joints with different diameters and pitches for flip chip applications. We investigated the interfacial reaction and shear strength between two different solders (Sn–37Pb and Sn–3.0Ag–0.5Cu, in wt.%) and ENIG (Electroless Nickel Immersion Gold) UBM (Under Bump Metallurgy) during multiple reflow. Firstly, we formed the flip chip solder bumps on the Ti/Cu/ENIG metallized Si wafer using a stencil printing method. After reflow, the average solder bump diameters were about 130, 160 and 190μm, respectively. After multiple reflows, Ni3Sn4 intermetallic compound (IMC) layer formed at the Sn–37Pb solder/ENIG UBM interface. On the other hand, in the case of Sn–3.0Ag–0.5Cu solder, (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 IMCs were formed at the interface. The shear force of the Pb-free Sn–3.0Ag–0.5Cu flip chip solder bump was higher than that of the conventional Sn–37Pb flip chip solder bump. [Copyright &y& Elsevier]

Abstract: The surface morphology, electrical property and reaction with solder alloy of two electroless nickel-phosphorus (EN–P) deposits (Ni–7wt.%P and Ni–10wt.%P) were investigated in this study. The P content of the EN–P layer decreased with increasing pH value. The EN–P plating layers had an amorphous structure and the electrical resistivity of the layer increased with increasing P content. Reaction layers of Ni3Sn4, Ni2SnP and Ni3P formed at the interfaces between the Sn–3.5Ag solder and the two EN–P deposit layers. The thickness of the interfacial Ni3Sn4 intermetallic compound (IMC) layer in the Sn–3.5Ag/Ni–7wt.%P joint was thicker than that in the Sn–3.5Ag/Ni–10wt.%P joint, whereas the thickness of the Ni3P layer increased with increasing P content. These study results confirmed that the interfacial reaction between solder and the EN–P layer is significantly affected by the composition (P content) of the EN–P layer. [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]