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Recently, interest in power modules is increasing in eco-friendly mobility such as electric vehicles (EVs) and fuel cell electric vehicles (FCEVs). The power module is a key component of the eco-friendly mobility that drives a motor by converting direct current (DC) supplied from the battery into alternating current (AC). However, a lot of heat is generated in the power module during its operation. To ensure the reliability of power modules, it is essential to form a joint suitable for high-temperature operation. Many pieces of research have been published on various bonding methods such as soldering, Ag sintering, Cu-Cu direct bonding, and transient liquid phase (TLP) bonding. The TLP bonding has many advantages, such as significantly less cost and a high melting temperature joint. In this review paper, various TLP bonding technologies with different materials and methods have been introduced and compared.

A comparison study of the interfacial reactions and mechanical shear strengths of normal and thin electroless-nickel electroless-palladium immersion gold (ENEPIG) with Sn–3.0Ag–0.5Cu (SAC305) solder during isothermal aging at 150 °C is presented. The thicknesses of the Ni layers of the normal and thin ENEPIG were 6 and 0.1 μm, respectively. In the normal ENEPIG substrate, small and thin needle-shaped (Cu,Ni)6Sn5 intermetallic compounds (IMCs) were formed at the interface after reflowing, and a relatively thin IMC layer remained despite a long aging period of 1000 h. On the other hand, in the thin ENEPIG substrate, the thin Ni layer as well as the Au and Pd layers were completely reacted, and a relatively thick (Cu,Ni)6Sn5 IMC was formed at the interface after reflowing. In addition, the interfacial IMC layer grew continuously with increasing aging time. During aging at 150 °C, the interfacial IMC layers at the thin ENEPIG joints were consistently thicker than those at the normal ENEPIG joints. During a low-speed shear test, the shear strength did not significantly change depending on the aging time and surface finish, and all the fractures occurred in the ductile mode. On the other hand, in the high-speed shear test, the thick (Cu,Ni)6Sn5 IMC layer significantly deteriorated the shear strength of the thin ENEPIG joints. The thin ENEPIG joints showed inferior mechanical reliability (especially, high impact reliability) than the normal ENEPIG joints during solid-state isothermal aging at 150 °C.

The feasibility of transient liquid phase (TLP) bonding technology for high-temperature endurable power electronics packaging has been evaluated in this study. An Ag-Sn3.0Ag0.5Cu hybrid solder paste was fabricated and used as a bonding material. The bonding reactions between chip/substrate and hybrid solder paste and die shear strengths of the TLP-bonded joints were evaluated during conventional soldering and vacuum soldering processes. Compared to the conventional soldering, the vacuum-soldered joints had fewer voids and relatively good metallurgical microstructures. After TLP bonding, (Cu,Ni)6Sn5, Ag3Sn, and Cu6Sn5 intermetallic compounds formed at the chip interface, in the middle of the joint, and at the bottom interface, respectively. It was confirmed that the vacuum soldering process could create good interfacial uniformity with minimal voids in the Si chip/ceramic substrate joints. The formation of voids during TLP bonding significantly affected the mechanical shear strength of the TLP-bonded joints. The vacuum-soldered joints had high shear strength values of approximately 40 MPa. To ensure the high joint strength and long-term reliability of Sn-based TLP-bonded joints, critical void control in the joints is needed.

To analyze the effects of Ni(P) layer thickness and Pd layer composition on interfacial reactions and the mechanical reliabilities of Sn–58Bi solder joints, we evaluated a phosphorous-contained Ni (Ni(P)) layer thicknesses ranging from 0.3 to 1.0 μm with Au/Pd/Ni(P) or a phosphorous-contained Pd [Au/Pd(P)/Ni(P)] layer in thin-electroless-nickel electroless-palladium immersion gold (ENEPIG) with Sn–58Bi solder joint after aging test. (Pd, Au)Sn4 and Ni3Sn4 intermetallic compounds (IMCs) were dominantly formed at the interfaces of the 0.3 µm to 1.0 μm Ni(P) layers in the thin-Au/Pd/Ni(P) or thin-Au/Pd(P)/Ni(P) joints after aging at 85 °C and 95 °C for 100 h. However, the Ni3Sn4 IMC layer changed to the (Cu, Ni)6Sn5 IMC layer in the 0.3 μm Ni(P) layer contained the Au/Pd/Ni(P) joint after aging at 85 °C for 300 h, because the Cu elements in a Cu pad penetrated through the P-rich Ni layer. Otherwise, the Ni3Sn4 IMC of the 0.3 μm Ni(P) layer in the Au/Pd(P)/Ni(P) joint changed to (Ni, Cu)3Sn4 IMC after aging at 105 °C and 115 °C for 1000 h, due to the P in the Pd layer, which affects the IMC growth rate. The 0.7 µm and 1.0 μm Ni(P) layers in the Au/Pd/Ni(P) or Au/Pd(P)/Ni(P) joints were attributed to the Ni3Sn4 IMC layer for whole aging conditions because the thick P-rich Ni layer suppress Sn and Cu diffusion during aging. In a high-speed shear tests, the shear strength of the 0.3 μm Ni(P) layer in the Au/Pd/Ni(P) joints was relatively low than that of the Au/Pd(P)/Ni(P) joints after aging at 105 °C and 115 °C for 100 h. Ni3Sn4 IMC was observed at the fracture surfaces of the 0.3 μm Ni(P) layer in the Au/Pd(P)/Ni(P) joints after aging at 115 °C for 1000 h, whereas the fracture surface of the Au/Pd/Ni(P) joint was Cu substrate. Therefore, Ni(P) layer thicknesses in excess of 0.7 μm and the P-contain Pd layer in the thin-ENEPIG surface finish with Sn–58Bi solder joints are expected to be highly reliable after long-term aging treatment.

The suitability of Ni–Sn combination paste as a transient liquid phase sintering (TLPS) bonding material for applications in high-temperature power electronic technologies was investigated. The microstructure and mechanical properties of joints bonded through TLPS with a Sn-30 wt% Ni paste were investigated at varying bonding temperatures (250, 270, 300, and 350 °C) and times using field-emission scanning electron microscopy, field-emission transmission electron microscopy, electron probe micro-analyzer, differential scanning calorimetry, and X-ray diffraction analyses. The results indicated that Ni and Sn reacted and bonded quickly to form Ni–Sn intermetallic compounds, which primarily consisted of Ni3Sn4 and residual Ni particles. The mechanical strength analysis results show that the shear strength values of the joints tended to increase as the bonding temperature increased. As Ni3Sn4 reacted with Ni particles, the joints achieved a stable and dense microstructure. The shear strength values were determined to be 47.9 MPa (300 °C) and 41.4 MPa (350 °C) for 15 and 5 min, respectively. Furthermore, the shear strength value saturated at a bonding temperature of 350 °C for a bonding duration of 5 min.

The microelectronics packaging industry, although rapidly growing, faces several challenges including 3-D integration, issues with multifunctional capability, and fluctuating input/output (I/O) density, among others. Better-performing microelectronics assemblies for mitigating these challenges require alloys with superior solderability and minimal metallization layer thickness. To this end, in this study, we investigated two kinds of electroless-nickel electroless-palladium immersion gold (ENEPIG) with 0.3 μm Ni, 0.1 μm pure Pd or Pd-phosphorous (Pd(P)), and 0.1 μm Au layers plated on a printed circuit board (PCB) substrate. To analyze the effects of the pure Pd and Pd(P) layers in the thin ENEPIG, we evaluated the interfacial reactions and mechanical properties of the SAC305 solder with a pure Pd or Pd(P) layer in the thin ENEPIG joints after aging at 150 °C. Needle-type and chunky-type (Cu,Ni)6Sn5 IMCs were formed at the interfaces of the pure Pd and Pd(P) joints, respectively. The (Cu,Ni)6Sn5 IMC of the pure Pd joint was thinner than that of the Pd(P) joint after reflowing and aging for 100 h. However, the total IMC of the Pd(P) joint was thinner than that of the pure Pd joint from 250 to 1000 h. In a low-speed shear test, the shear strength of the Pd(P) joint was higher than that of the pure Pd joint for the entire aging time. Most fractures occurred at the Sn-rich surface with a ductile mode, regardless of the different substrates and aging times. After high-speed shear testing, the shear strength of the pure Pd joint was higher than that of the Pd(P) joint until aging for 100 h. After aging for 250 h, the shear strength of the Pd(P) joint was higher than that of the pure Pd joint. The results for brittle fracture rate were similar to those for high-speed shear strength. Hence, Pd(P) joints are expected to demonstrate higher reliabilities than pure Pd joints after long aging treatment.

We performed 30Ni–70Sn (wt%) transient liquid phase sintering (TLPS) bonding with micro-sized Ni and Sn powders for high-temperature power applications. A Ni–Sn paste was fabricated and TLPS bonding was performed. We investigated the interfacial reactions, transformations into Ni3Sn4 intermetallic compound (IMC) phases, and joint strength in this study. The Ni–Sn TLPS bonding was an easy and simple process under a relatively low bonding temperature and short bonding time. After TLPS bonding, low melting point Sn element was completely consumed, and the bonded joint was composed of Ni3Sn4 IMCs and the remaining Ni particles. The Ni3Sn4 IMC joint formed with remaining Ni particles was very stable. All the Ni–Sn TLPS samples had high shear strengths of over 70 MPa, and the shear strength was approximately 32% higher than that of the conventional Sn–3.0Ag–0.5Cu solder joint. The Ni–Sn TLPS bonded joints in the present study were not brittle and exhibited superior adhesion strength. This suggests high applicability of the Ni–Sn TLPS bonding for high-temperature power electronic applications in future EV/HEV systems.

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)6Sn5 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)6Sn5 IMC and Cu substrate during aging regardless of Ni layer thickness. The (Cu,Ni)6Sn5 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.

The effects of the thickness of the Ni layer in thin electroless-nickel electroless-palladium immersion gold (thin-ENEPIG) surface-finished printed circuit boards (PCB) with Sn-3.0Ag–0.5Cu (SAC305) solder joints during aging treatment were investigated. We evaluated the interfacial reactions and mechanical properties of 0.3–1.0 µm thick Ni layers in thin-ENEPIG PCBs with SAC305 solder joints at aging temperatures of 75, 100, 125, and 150 °C for 1000 h. A needle-type (Cu,aNi)6Sn5 intermetallic compound (IMC) layer formed at the interface of the SAC solder and Cu substrate. In addition, P-rich Ni layers were formed at the interface of the (Cu,Ni)6Sn5 IMC and Cu substrate for the 0.5–1.0 µm thick Ni joints. The thicknesses of the (Cu,Ni)6Sn5 IMCs with 0.3 and 0.5 µm Ni joints were strongly affected by the aging time and temperature. In contrast, the IMC growth rates of the 0.7 and 1.0 µm thick Ni joints were significantly lower than that of the 0.3 µm thick Ni joint. The reason for this behavior is that the P-rich Ni layer acts as a barrier for Sn and Cu diffusion at the joint and was maintained at the IMC/Cu interface after aging. In high-speed shear tests, the shear strengths of all Ni joints aged at 75 °C were similar. However, the rate of reduction in shear strength decreased with increasing Ni layer thickness as the aging time and temperature increased, but the shear strength of the 0.3 µm Ni joint rapidly decreased with increasing aging temperature and time. In contrast, the shear strengths of the 0.7 and 1.0 µm Ni joints slightly decreased with increasing aging temperature and time. The brittle fracture rates of the joints decreased with increasing Ni thickness, and we determined that this occurred because of the remaining P-rich Ni layer, which acts as a diffusion barrier during aging, at the interface of the 0.7 and 1.0 µm Ni joints. In low-speed shear tests, the shear strengths of the 0.7 and 1.0 µm Ni joints were slightly higher than those of the 0.3 and 0.5 µm Ni joints after aging at 125 and 150 °C for the entire aging period. Most fractures occurred via a ductile mode regardless of the Ni layer thickness. Therefore, a Ni layer thickness of more than 0.7 µm in thin-ENEPIG finished PCB with SAC305 solder joints is expected to yield high reliability on aging.

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 Ag2In IMC. On the other hand, the Au/In/Au TLP joint was composed of three Au In IMCs of Au7In3, AuIn, and AuIn2.

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 Ni3Sn4 phases were transformed into the Ni3Sn2. With increasing aging treatments, the reactions between Ni3Sn4 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.

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.

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 Au7In3 IMC. During TLP bonding, the In solder was sequentially transformed in the following order: I (Au7In3, AuIn, and AuIn2), II (Au7In3 and AuIn), and III (Au7In3). We effectively fabricated the Au/In/Au TLP-bonded joint under moderate bonding pressures of 5 and 10 MPa for a short bonding time.

A new multilayer metallization, electroless-nickel electroless-palladium immersion gold (ENEPIG) with a thin 0.1-μm-thick Ni(P) layer (thin-ENEPIG), was plated onto a Cu printed circuit board substrate for fine-pitch package applications. We evaluated the interfacial reactions and mechanical strengths of Sn–3.0Ag–0.5Cu (SAC305) solder on thin ENEPIG-coated substrates over various reflow times and compared them to those of a conventional ENEPIG-coated substrate with a 6-μm-thick Ni(P) layer. Thin Au, Pd, and Ni layers on the thin ENEPIG substrates were exhausted during the initial reflow time, which brought the underlying Cu layer in direct contact with the molten SAC305 solder, resulting in the formation of scallop-shaped (Cu,Ni)6Sn5 intermetallic compounds (IMCs) at the interface. The interfacial IMC layer for the thin ENEPIG substrate was thicker than that for the normal ENEPIG substrate due to the direct contact between the SAC305 solder and the Cu layer. In the low-speed shear test, all the fractures occurred in the bulk solder regardless of the different substrates and reflow times. In the high-speed shear test, the fracture mode was changed from ductile to brittle on increasing the reflow time. The P-rich Ni layer and thick Cu–Sn IMC formation deteriorated the shear strengths of the normal and thin ENEPIG joints, respectively. The thin ENEPIG joints showed better mechanical strength in the solder joint than the normal ENEPIG joints, despite the thick interfacial IMCs.

Cu-Sn solid–liquid interdiffusion (SLID) bonded joints were fabricated using a Sn-Cu solder paste and Cu for high-temperature power electronics applications. The interfacial reaction behaviors and the mechanical properties of Cu6Sn5 and Cu3Sn SLID-bonded joints were compared. The intermetallic compounds formed at the interfaces in the Cu-Sn SLID-bonded joints significantly affected the die shear strength of the joint. In terms of thermal and mechanical properties, the Cu3Sn SLID-bonded joint was superior to the conventional solder and the Cu6Sn5 SLID-bonded joints.

The sintering reactions and mechanical reliability of Ag sinter paste with three different surface finishes, Cu, Ag, and electroless nickel-immersion gold, were evaluated during the sintering process. We compare the sintering reaction behaviors of the three sintered joints and identify the relationship between the sintering behavior and the sintered Ag/substrate compatibility. Inter-diffusion behaviors result in of good metallurgical bonding during the Ag sintering process in the three sintered joints. The shear strength increases on increasing the bonding pressure, irrespective of the surface finish. The surface finish material of the substrate strongly affects the shear strength of the Ag sintered joints. The Ag finished joint exhibits superior interfacial stability and shear strength compared to the Cu and Au finished joints.

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.

The mechanical strength of Sn-3.0Ag-0.5Cu (SAC305) and Au-20Sn solder joints and their interfacial reaction with a Ni-plated ceramic substrate were evaluated to assess their suitability for use as die attach materials in power module applications. The compatibility between the two solder alloys and the Ni substrate was assessed during isothermal long-term aging, while the mechanical strength of the two solder joints was measured by die shear testing. A higher intermetallic compound (IMC) growth rate and Ni consumption rate was observed in the SAC305 solder joint, with the formation of a thick IMC layer and weak interface resulting in brittle fracture. The Au-20Sn solder joint, on the other hand was found to exhibit superior high temperature interfacial stability and joint strength.

Power electronics modules in electric vehicles and hybrid electric vehicles, particularly those containing next-generation power semiconductor devices such as silicon carbide and gallium nitride are operated at high temperatures exceeding 200 °C. Consequently, the reliability requirements for such modules have become highly stringent and new packaging materials and technologies are required to meet the demands of power electronic modules. Some good candidates for high temperature applications include high-temperature solders such as Au–20Sn, Ag or Cu sinter pastes, and transient liquid phase (TLP) bonding materials. In particular, the TLP bonding technology is suitable for use in high temperature environments owing to its low cost and simplicity of the bonding process. In this study, the feasibility of Cu–Sn and Ni–Sn TLP bonding technologies as die-attach methods for power electronics packaging applications is examined. The results of the study indicate that the Cu–Sn and Ni–Sn TLP bonding processes transform the joints fully into Cu6Sn5/Cu3Sn and Ni3Sn4 intermetallic compounds (IMCs), respectively. Further, the mechanical strength and reliability of the two TLP bonding joints are reduced owing to the formation of brittle IMCs.

Recently, research and development of power electronics, such as inverter systems and power modules, in electric vehicles (EV) and hybrid electric vehicles (HEV) are increasing. In the power electronic systems, the chip junction temperature is extremely high during operation. Therefore, the new bonding materials and methods are needed for operation at high temperatures for power electronic packaging. Some good candidates for high temperature die-attach applications include high-temperature solders such as Au-Sn, Ag sinter pastes, and transient liquid phase (TLP) bonding materials. Among them, a TLP bonding technology utilizes cheap metals such as Cu, Ni, and Sn. This process is also similar to the conventional soldering process and is reliable when subjected to high temperatures over long durations. TLP bonding is a die-attach technology wherein an intermetallic compound (IMC) is formed via a diffusion reaction by incorporating a low melting point metal between metals with high melting points. This paper presents the growth rate of forming Cu-Sn IMCs in the composite preform that is used as a die-attach material for a TLP bonding. To overcome the drawbacks of the TLP bonding such as a long bonding time, the composite preform was fabricated, and the feasibility for high-temperature power electronics applications was evaluated in this study. The composite preform is composed of a Cu core layer with a high-melting temperature and a low-melting temperature Sn coating at both sides of the Cu core layer. During aging treatment, the Cu-Sn IMC layer was rapidly formed by consuming the both low-melting point Sn layers. The IMC formation by the reaction between Cu and Sn is very important because it affects the thermal, electrical and mechanical reliability for electronic packaging technologies. After isothermal aging treatments at $150^{\circ}\mathrm{C}$ for various times, the thicknesses of Sn, Cu, and Cu-Sn IMC layers in the composite preform were investigated using field-emission scanning electron microscope (FE-SEM, INSPECT F, FEI, USA) equipped with an energy dispersive X-ray spectroscope (EDX) and focused ion beam (FIB, NOVA-600, FEI, USA).

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)6Sn5 and Cu6Sn5 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)6Sn5 and Cu6Sn5 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.

The wetting behavior, interfacial reactions, and mechanical reliability of Sn-Ag-Cu solder on a plasma-coated printed circuit board (PCB) substrate were evaluated under multiple heat-treatments. Conventional organic solderability preservative (OSP) finished PCBs were used as a reference. The plasma process created a dense and highly cross-linked polymer coating on the Cu substrates. The plasma finished samples had higher wetting forces and shorter zero-cross times than those with OSP surface finish. The OSP sample was degraded after sequential multiple heat treatments and reflow processes, whereas the solderability of the plasma finished sample was retained after multiple heat treatments. After the soldering process, similar microstructures were observed at the interfaces of the two solder joints, where the development of intermetallic compounds was observed. From ball shear tests, it was found that the shear force for the plasma substrate was consistently higher than that for the OSP substrate. Deterioration of the OSP surface finish was observed after multiple heat treatments. Overall, the plasma surface finish was superior to the conventional OSP finish with respect to wettability and joint reliability, indicating that it is a suitable material for the fabrication of complex electronic devices.

Objectives This study was designed to investigate whether the Cheongajihwang-Tang (CT) has an inhibitory effect association with oxidation or inflammation in RAW264.7 cells. Methods Cytotoxic activity of CT extract on RAW264.7 cells was evaluated by using 3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide (MTT) solution. Nitric oxide production was measured using Griess reagent system. The total phenolic contents and 1,1-Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity was measured to evaluate the anti-oxidative effects of CT. Dichlorofluorescin diacetate (DCFH-DA) has been used as a substrate for measuring intracellular oxidant production. Results Cheongajihwang-Tang does not impair the cell viability in tested concentration. CT showed anti-oxidative effects in vitro by decreasing electron donating ability, and also showed anti-inflammatory effects suppressing NO and ROS expression in LPS induced RAW264.7 activation. CT inhibited the generation of intracellular ROS production as dose dependant manner. Conclusions CT has anti-oxidative effects and anti-inflammatory activities. These results indicate that CT extract has an anti-inflammatory activities via anti-oxidative effects.

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.

Automotive today has been transforming to an electronic product by adopting a lot of convenience and safety features, suggesting that joining materials and their mechanical reliabilities are getting more important. In this study, a Sn-Cu-Cr-Ca solder composition having a high melting temperature (>230℃) was fabricated and its joint properties and reliability was investigated with an aim to evaluate the suitability as a joining material for electronics of engine room. Furthermore, mechanical properties change under complex environment were compared with several existing solder compositions. As a result of contact angle measurement, favorable spreadability of 84% was shown and the average shear strength manufactured with corresponding composition solder paste was 1.9kg/mm 2 . Also, thermo-mechanical reliability by thermal shock and vibration test was compared with that of the representative high temperature solder materials such as Sn-3.5Ag, Sn-0.7Cu, and Sn-5.0Sb. In order to fabricate the test module, solder balls were made in joints with ENIG-finished BGA and then the BGA chip was reflowed on the OPS-finished PCB pattern. During the environmental tests, resistance change was continuously monitored and the joint strength was examined after tests. Sn-3.5Ag alloy exhibited the biggest degradation rate in resistance and shear stress and Sn-0.7Cu resulted in a relatively stable reliability against thermo-mechanical stress coming from thermal shock and vibration.