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Abstract A comparative study of initial interfacial reactions and kinetics of Ag In and Au In as die-attach materials for high-temperature power electronics applications was performed in this study. Sequential interfacial reactions and transformations of the In solder to intermetallic compound (IMC) phases of the Ag/In/Ag and Au/In/Au joints were investigated and compared for transient liquid phase (TLP) bonding at 190 °C for 1 min under different bonding pressures. The interfacial reaction of the Ag/In/Ag joint was faster than that of the Au/In/Au joint under same bonding conditions. In the Ag/In/Ag joints, the TLP joint was fully converted into the Ag-rich Ag 2 In IMC. On the other hand, the Au/In/Au TLP joint was composed of three Au In IMCs of Au 7 In 3 , AuIn, and AuIn 2. Graphical abstract Unlabelled Image Highlights • Ag In and Au In as die-attach materials for power applications were tested. • Ag/In/Ag and Au/In/Au transient liquid phase bonded joints were fabricated. • Two TLP joints were fully converted into Ag In and Au In IMC, respectively. • Ag In TLP reaction is faster than Au In system. [ABSTRACT FROM AUTHOR]

Sequential interfacial reactions of Sn‐3.0Ag‐0.5Cu solder on a new multilayer metallization, ENEPIG (electroless nickel‐electroless palladium‐immersion gold) with a 0.1‐μm‐thin Ni(P) layer (thin‐ENEPIG), during reflowing were evaluated in this study. After 20‐second reflow process, layer‐shaped (Au,Cu)Sn4 intermetallic compounds formed at the interface, and thin Ni and Pd layers underneath the Au layer remained unreacted on the polycrystalline Cu substrate. On the other hand, Au, Pd, and Ni tri‐layers in the thin ENEPIG layer were exhausted and (Cu,Ni)6Sn5 intermetallic compounds formed at the interface after reflowing for 30 seconds. [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 transient liquid phase (TLP) bonding of Au/In/Au as a die-attach material for high-temperature applications was studied in this work. The sequential interfacial reactions between Au and In layers and the phase transformations of an In solder to the intermetallic compound (IMC) phases of the Au/In/Au joints were investigated for TLP bonding at 190 °C for up to 30 min under different bonding pressures (0.2–10 MPa). The TLP joint was fully converted into the Au-rich Au 7 In 3 IMC. During TLP bonding, the In solder was sequentially transformed in the following order: I (Au 7 In 3 , AuIn, and AuIn 2 ), II (Au 7 In 3 and AuIn), and III (Au 7 In 3 ). We effectively fabricated the Au/In/Au TLP-bonded joint under moderate bonding pressures of 5 and 10 MPa for a short bonding time. [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]

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]

In this study, electrodes on a flexible printed circuit board (FPCB) and rigid printed circuit board (RPCB) were bonded by a thermo-compression bonding. Pb-free Sn–3.0Ag–0.5Cu solder was used as an interlayer. In order to determine the optimum bonding conditions for bonding pressure and time, a 90° peel test of the FPCB–RPCB joint was conducted. The relationships between the bonding conditions, interfacial reactions, and peel strength were investigated. The optimum bonding pressure and time were 2.04MPa and 5s at 260°C, respectively. Thin and uniform (Ni,Cu)3Sn4 intermetallic compound (IMC) layers formed at both FPCB/Sn–3.0Ag–0.5Cu/RPCB interfaces. In a high temperature storage (HTS) test of 125°C, the peel strength decreased as the aging time increased. After the HTS test, brittle interfaces formed in the PCB joints, resulting in the switching of the failure mode from a polyimide–electrode failure to a brittle IMC failure. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we investigated the phenomena of electrochemical migration (ECM) on a silicon (Si) substrate with directly printed Ag paste with epoxy binder (7wt.%) using a screen-printing method. The microstructure and electrical characteristics of the directly printed Ag patterns under different sintering conditions were estimated. In addition, the ECM characteristics of the directly patterned Ag circuits on Si substrates were evaluated according to the sintering conditions. The ECM characteristics of the Ag paste with epoxy binder were compared with the ECM characteristics of Ag paste without epoxy binder. Clusters were formed by interparticle necking during the sintering process; the cluster size in the patterns increased as the sintering temperature and time increased. Granular Ag films, which were sintered at high temperatures and for long time periods of time, had excellent electrical characteristics as a result of the formation of interparticle necking of sufficient size. The directly printed Ag patterns that were exposed to higher sintering temperatures and longer sintering times had higher resistances to ECM than those that were exposed to lower sintering temperatures and shorter sintering times. Also, the directly printed Ag pattern with epoxy binder had a higher resistance to ECM phenomenon than the pattern without epoxy binder. [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, the effect of a Ni–Cr seed layer on the adhesion strength of flexible copper clad laminate (FCCL) was evaluated after thermal treatment. The changes in the chemical composition, morphology and adhesion property were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), electron probe micro analyzer (EPMA), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and 90° peel test. The peel strength of the FCCLs was significantly affected by the thermal treatment and the FCCL with a higher peel strength had a higher thermal stability than that with a lower peel strength. The roughness of the fracture surface for the FCCLs decreased with increasing thermal treatment temperature and holding time. The thermal treatment of the FCCL increased the ratio of the C–N bonds and reduced that of the C–O and carbonyl (Cin 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 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: In this study, the bending fatigue reliability of Au bump flip chip packages with anisotropic conductive film (ACF) and non-conductive film (NCF) as adhesive materials was evaluated using a four-point bending test. Differential bending between the substrate and the Si chip was the dominant failure driver for the Au bump flip chip packages subjected to the bending test. The bending fatigue life of the NCF joint was longer than that of the ACF joint, regardless of the bending frequency. The main reason for the increased electrical resistance of the packages with ACF and NCF was the delamination between the adhesive material and the electroless Ni-immersion Au (ENIG) pad and between the Au bump and ENIG pad, respectively. For the ACF package, the bending stress was concentrated at the conductive particles between the Au bump and the ENIG pad during the bending fatigue test, resulting in a low bending fatigue strength. The delamination in the packages propagated with increasing bending fatigue cycles and frequency. The Au bump flip chip package with NCF was mechanically robust due to the higher initial strength and the larger bonding area between the Au bump and the ENIG pad. [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: This study examined the effects of isothermal aging and temperature–humidity (TH) treatment of substrate on the joint reliability of a Sn–3.0Ag–0.5Cu (wt.%)/organic solderability preservative (OSP)-finished Cu solder joint. Two types of OSP-finished chip-scale-package (CSP) substrates were used, those subjected and not subjected to the TH test. This study revealed an association between the interfacial reaction behaviors, void formation and mechanical reliability of the solder joint. Many voids were formed at the interface of the OSP-finished Cu joint subjected to the TH test. These voids were caused by the oxidation of the OSP-finished Cu substrate during the TH test. In the shear tests, the shear force of the joint with the substrate not subjected to the TH test was slightly higher than that with the TH test. The mechanical reliability of the solder joint was degraded by voids at the interface. [Copyright &y& Elsevier]

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

Abstract: 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: 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: 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 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: 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]

We studied the growth kinetics and characteristics of electroless nickel–phosphorus (EN–P) deposition layer on Cu substrate in an acid plating bath with sodium hypophosphite as the reducing agent. The individual nodules of the EN–P layer increased in size but decreased in number with increasing plating time and pH, i.e. the root-mean-square (RMS) roughness of the EN deposit decreased. In addition, the plating rate of the EN layer increased with increasing plating bath pH. X-ray diffraction (XRD) analyses revealed that the as-plated deposit was in an amorphous phase, while the heat-treated layer was composed of crystallized Ni and Ni3P compound. The solderability of the EN layer increased with decreasing P content. In addition, the wetting force increased with increasing surface roughness. The present study clearly showed that the solderability behavior of the EN layer is affected by both surface composition (P content) and morphology. [ABSTRACT FROM AUTHOR]

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: 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]

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

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 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: 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 reactions and shear strength of joints between Sn–9Zn solder and two different kinds of BGA (ball-grid-array) substrates (Cu and Au/Ni–P/Cu) were investigated for reflow conditions of 230°C up to 60min. For the Cu substrate, only Cu5Zn8 intermetallic compound was observed and other Cu–Sn IMCs were not observed. For the Au/Ni/Cu substrate, an AuZn3 IMC layer formed at the interface due to the fast reaction between Au and Zn. In addition, some of the AuZn3 IMC layer was detached from the interface after reflow. The thickness of the AuZn3 layer did not change with reflow time because the Au was consumed during the initial reflow process. After being reflowed for 60min, a Ni5Zn21 IMC formed between AuZn3 IMC and Ni substrate. Also, many voids existed inside the upper AuZn3 IMC layer. Ball shear tests for the Cu substrate showed the shear strength significantly decreased after reflow for 60min. A Cu5Zn8 IMC was also observed on the fracture surface. For the Au/Ni/Cu substrate, the shear strength value did not change much as a function of reflow time and fractures occurred within the solder. [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 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]

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]

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]

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]

• We prepare Sn-coated Cu particles of different diameters as a micro paste. • We use the paste to bond a dummy chip and a DBC substrate. • The bonding is carried out via transient liquid-phase sintering (TLPS) technology. • The paste affords a high shear strength value of ~40 MPa. • Our approach is suitable for power electronics packaging and allied applications. Cu paste has been considered as a promising substitute for Ag paste for high-temperature-endurable chip-bonding applications, particularly for power electronics packaging, because it is cheaper than Ag. However, the primary disadvantage of using Cu paste is its possible oxidation during the handling and bonding process. In this context, to overcome the oxidation problem of the Cu sinter paste and to exploit the advantages of transient liquid-phase sintering (TLPS) bonding technology, we prepare Sn-coated Cu micro paste in this study, and we evaluate its feasibility as a die-attach material for power electronics packaging. We first prepare various Sn-coated Cu powders under various plating conditions, and we successfully perform TLPS bonding with Sn-coated Cu paste at a relatively low bonding temperature and a short bonding time. During the TLPS bonding, Sn is completely consumed, and the resulting bonded joint is composed of the Cu–Sn intermetallic compounds and remnant Cu particles. The TLPS-bonded joints exhibit relatively high shear strength values of ~40 MPa, and all fractures mainly occur at the chip-side interfaces irrespective of the Cu particle size. We believe that our findings can contribute to the use of Sn-coated Cu paste as an alternative bonding technology for power electronics applications. [ABSTRACT FROM AUTHOR]

In this study, the feasibility of low-cost Cu-sintering technology for power electronics packaging and the effect of sintering conditions on the bonding strength of the Cu-sintered joint have been evaluated. A Cu paste with nano-sized Cu powders and a metal content of ~78% as a high-temperature bonding material was fabricated. The sinter-bonding reactions and mechanical strengths of Cu-sintered joints were evaluated at different sinter bonding pressures, temperatures, and durations during the sintering process. The shear strength of the Cu-sintered joints increased with increasing sintering pressure. Good interfacial uniformity and stable metallurgical microstructures were observed in the Cu joints sintered at a high sintering pressure of 10 MPa, irrespective of the sintering time. It was confirmed that a high-pressure-assisted sintering process could create relatively dense sintered layers and good interfacial uniformity in the Cu-sintered joints, regardless of the sintering temperatures being in the range of 225–300 °C. The influence of the sinter bonding pressure on the shear strengths of the Cu-sintered joints was more significant compared to that of the sintering temperature. Durations of 10 min (at 300 °C) and 60 min (at 225 and 250 °C) are sufficient for complete sintering reactions between the Si chip and the direct bond copper (DBC) substrate. Relatively good metallic bonding and dense sintered microstructures created by a high sintering pressure of 10 MPa resulted in high shear strength in excess of 40 MPa of the Cu-sintered joints. [ABSTRACT FROM AUTHOR]

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]

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]

A comparative study of Sn-3.0Ag-0.5Cu (SAC305) and Au-20Sn solders as die-attach materials for high-temperature power electronic applications was performed. The solid-state interfacial reactions of SAC305 and Au-20Sn solders with a Ni-plated Si chip and a direct-bonded-copper substrate, as well as the growth of interfacial intermetallic compound layers and interfacial stability, were investigated and compared during aging at 150 and 200 °C for up to 2000 h. The SAC305 solder exhibited a higher interfacial intermetallic compound growth rate and a higher consumption rate of the Ni layer than the Au-20Sn solder. The Au-20Sn solder had a superior interfacial stability for high-temperature power electronic applications. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Microelectronic devices with advanced capabilities, such as multi-functions, high input/output densities, and high capacities, have recently found extensive application in areas such as servers, big data, data centers, IoT, and supercomputing. Owing to the diverse operating conditions of these applications, the reliability of the microelectronic packaging depends on the integrity of the soldered joints at various (high) operating temperatures. In this study, the mechanical shear properties of Sn-3.0Ag-0.5Cu (SAC305) and Sn-58Bi (in wt%) solder joints were studied using a ball shear test at various temperatures on substrates with two types of surface finish: organic solderability preservative (OSP) and electroless nickel-electroless palladium-immersion gold (ENEPIG). The joint strength, force-displacement curve, and fracture energy were measured and calculated for each joint, and the correlations between solder alloys, operating temperatures, and joint mechanical behaviors were revealed. In the case of the SAC305 solder, regardless of the substrate, with increasing temperature, the shear force decreased, fracture distance increased, and the fracture energy decreased. In addition, the fracture was predominantly ductile. In the case of the Sn-58Bi solder, with increasing temperature, the shear force decreased, and the fracture distance increased slightly and then decreased (OSP substrate) and kept constant then decreased (ENEPIG substrate), and the fracture energy decreased. Although ductile fracture occurred at low temperatures, the brittle fracture proportion gradually increased as the temperature increased. Further, the microstructure significantly affected the mechanical properties and fracture behavior of the SAC305 and Sn-58Bi solder joints. • Mechanical shear properties of solder joints at various temperatures were studied. • SAC305 solder showed ductile fracture at all test temperatures. • Fracture mode in the Sn-58Bi solder shifted from ductile to brittle with increasing temperature. • Microstructure significantly affected the mechanical properties and fracture behavior of the 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 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]