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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.

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 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.

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.

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.

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.

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)Sn4 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)6Sn5 IMCs formed at the interface between the (Pd,Au)Sn4 IMC and partially destroyed P-rich Ni layer of the pure Pd joints. In contrast, a Ni3Sn4 IMC formed at the interface between the (Pd,Au)Sn4 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 Ni3Sn4 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.

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&ndash, 300 &deg, 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 &deg, C) and 60 min (at 225 and 250 &deg, 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.

The exemption of Pb-bearing automobile electronics in the End of Life Vehicle (ELV) directive has recently expired, bring an urgent need to find Pb-free alloys that can maintain good performance under high-temperature and vibration conditions for automobile application. In this study, a new lead-free solder, Sn-0.7Cu-0.2Cr (wt.%) alloy, was developed. To evaluate the thermomechanical reliability of the new solder alloy in automobile electronics, a thermal shock test was performed. The results show that the presence of Cr in solder inhibits the growth of interfacial Cu3Sn layer and the formation of Kirkendall voids, which effectively improves the joint reliability under intense thermal shock condition compared with the commercial SAC305 and SC07 solders. Specifically, the shear strength of the Sn-0.7Cu-0.2Cr/Cu solder joints was higher by 23% and 44% than that of SAC305 and SC07 solder joints after 2000 cycles of thermal shock at 1 m/s shear speed.

The electromigration behavior of low-melting temperature Sn-58Bi (in wt%) solder joints was investigated with a high current density between 3 and 4.5 × 103 A/cm2 between 80 and 110 °C. In order to analyze the impact of various substrate metallizations on the electromigration performance of the Sn-58Bi joint, we used representative substrate metallizations including electroless nickel immersion gold (ENIG), electroless nickel electroless palladium immersion gold (ENEPIG), and organic solderability preservatives (OSP). As the applied current density increased, the time to failure (TTF) for electromigration decreased regardless of the temperature or substrate metallizations. In addition, the TTF slightly decreased with increasing temperature. The substrate metallization significantly affected the TTF for the electromigration behavior of the Sn-58Bi solder joints. The substrate metallizations for electromigration performance of the Sn-58Bi solder are ranked in the following order: OSP-Cu, ENEPIG, and ENIG. Due to the polarity effect, current stressing enhanced the fast growth of intermetallic compounds (IMCs) at the anode interface. Cracks occurred at the Ni3Sn4 + Ni3P IMC/Cu interfaces on the cathode sides in the Sn-58Bi/ENIG joint and the Sn-58Bi/ENEPIG joint; this was caused by the complete consumption of the Ni(P) layer. Alternatively, failure occurred via deformation of the bulk solder in the Sn-58Bi/OSP-Cu joint. The experimental results confirmed that the electromigration reliability of the Sn-58Bi/OSP-Cu joint was superior to those of the Sn-58Bi/ENIG or Sn-58Bi/ENEPIG joints.

In this paper, we introduce recent cloud system security technologies categorizing them according to Reliability, Availability, Serviceability, Integrity, and Security (RASIS), terms that evaluate robustness of the computer system. Then we describe examples of security attacks and corresponding security technologies for each of them. We introduce security technologies based on Software Defined Network (SDN) for Reliability, security technologies based on hypervisor and virtualization for Availability, disaster restoration systems for Serviceability, authorization and access control technologies for Integrity, and encryption algorithms for Security. We believe that this paper provide wise view and necessary information for recent cloud system security technologies.

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.

Interfacial reactions and joint mechanical reliability of a representative low melting temperature Sn–58 wt%Bi solder with three different surface finishes were evaluated during a reflow process. The surface materials consisted of organic solderability preservative (OSP), electroless nickel–immersion gold (ENIG), and electroless nickel–electroless palladium–immersion gold (ENEPIG). The relationships between the interfacial reaction, surface finish, shear speed, and shear force were elucidated in this study. The interfacial intermetallic compounds (IMCs) on the ENEPIG substrate were sequentially changed during reflowing at 180 °C in the following order: (Pd,Ni)Sn4, (Pd,Ni)Sn4 + Ni3Sn4, and Ni3Sn4. Compared to the Cu6Sn5 IMC on the OSP-finished Cu substrate, the Ni3Sn4 IMCs on the ENIG and ENEPIG substrates were much thinner. The IMCs of each of the different surface finishes grew as the reflow time increased; however, the morphologies of the IMCs were different each other. Layer-type interfacial IMCs created a stable metallurgical interfacial structure during the reflow reaction, resulting in reduced rates of IMC growth and Ni–P consumption. High-speed shear tests were conducted to evaluate the effects of interfacial reactions on the mechanical properties of three Sn–58Bi solder joints. In spite of the different interfacial reactions and IMC formations, there were no large differences among shear forces in the three Sn–58Bi solder joints. Further, the type of surface finish material did not significantly affect the shear force of the Sn–58Bi solder joints under high-speed shear loading.

The shear force and failure behaviors of the Sn-58Bi epoxy solder joints with various surface finishes under the high-speed shear test were investigated. The relationships between the shear speed, shear force, and fracture mode are elucidated in this study. The shear force of the Sn-58Bi solder joints increased with increasing shear speed, mainly due to the high strain-rate sensitivity of the solder alloys. Brittle interfacial fractures were more easily achieved at higher shear speed in the high-speed shear test. This result was discussed in terms of the relationship between the strain-rate of the solder alloy, the work-hardening effect, and the resulting stress concentration in the interfacial regions. The fracture mode changed from ductile solder fracture to brittle interfacial fracture with increasing shear speed. On the other hand, the different surface finish materials did not affect the shear force and fracture mode of the Sn-58Bi solder joints under high-speed shear loading.

The performance of surface finishes as a function of the pH of the utilized plating solution was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in 3.5 wt.% NaCl solution. In addition, the surface finishes were examined by x-ray diffraction (XRD), and the contact angle of the liquid/solid interface was recorded. NiP films on copper substrates with gold coatings exhibited their highest coating performance at pH 5. This was attributed to the films having the highest protective efficiency and charge transfer resistance, lowest porosity value, and highest contact angle among those examined as a result of the strongly preferred Au(111) orientation and the improved surface wettability.

Interfacial reactions and joint reliability of Sn-3.0Ag-0.5Cu 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 also successfully revealed a connection between the interfacial reaction behavior and mechanical reliability. The Sn-Ag-Cu/ENIG joint exhibited a higher intermetallic compound (IMC) growth rate and a higher consumption rate of the Ni(P) layer than the Sn-Ag-Cu/ENEPIG joint. The presence of the Pd layer in the ENEPIG suppressed the growth of the interfacial IMC layer and the consumption of the Ni(P) layer, resulting in the superior interfacial stability of the solder joint. The shear test results show that the ENIG joint fractured along the interface, exhibiting indications of brittle failure possibly due to the brittle IMC layer. In contrast, the failure of the ENEPIG joint only went through the bulk solder, supporting the idea that the interface is mechanically reliable. The results from this study confirm that the Sn-Ag-Cu/ENEPIG solder joint is mechanically robust and, thus, the combination is a viable option for a Pb-free package system.

In this study, electrodes on a flexible printed circuit board (FPCB) and rigid PCB (RPCB) were bonded by a thermo-compression bonding. The surface finishes on the Cu electrodes of the FPCB and RPCB were organic-solderability-preservative and electroless Ni/immersion Au (ENIG), respectively. Pb-free Sn-3.0 Ag and Sn-3.0 Ag-0.5 Cu solders were used as interlayers. In order to determine the optimum bonding conditions, such as bonding force, time, and temperature, a 90° peel test of the FPCB-RPCB joint was conducted. The relationships between the bonding conditions and peel strength were investigated. We successfully accomplished the thermo-compression bonding of reliable FPCB-RPCB joints by using Sn-Ag and Sn-Ag-Cu interlayers. The thermo-compression bonding method is a stable and well-controlled process and can produce robust and reliable connections.