Sn Intermetallic Compounds Research Articles

Microstructural and shear strength properties of GNSs-reinforced Sn-1.0Ag-0.5Cu (SAC105) composite solder interconnects on plain Cu and ENIAg surface finish

In this study, the combined effect of GNSs (graphene nanosheets) and ENIAg (Electroless Nickel Immersion Silver) surface finish on the formation of intermetallic compounds (IMCs) and shear strength of the Sn-1.0Ag-0.5Cu (SAC105) solder system was studied. Both plain and composite solder systems (SAC105-xGNS; x = 0, 0.01, 0.05 and 0.1 wt%) were successfully prepared using the powder metallurgy technique and thereafter soldered on the plain Cu and ENIAg surface finish substrates. From the microstructural analysis, the Cu6Sn5 IMC was observed at the solder/substrate interface of the SAC105-xGNS/Cu solder joints. Moreover, the Ni3Sn4 and (Cu,Ni)6Sn5 IMC phases were observed at the solder/substrate interface of the SAC105-xGNS/ENIAg counterparts. The GNSs and ENIAg surface finish provided huge barrier for Sn and Cu atoms diffusion required for IMC formation. The interfacial IMC layer thickness decreased with increasing addition of GNSs for both sample grades. The SAC105-xGNS/ENIAg demonstrated lower IMC thicknesses that ranged between 2.98 and 2.53 μm relative to the 5.23–3.35 μm exhibited by the SAC105-xGNS/Cu. In general, the strengthening potential of the GNSs was well marked in both sample grades, with the SAC105-0.01GNS/Cu and SAC105-0.01GNS/ENIAg demonstrating the highest shear strengths of 11.2 MPa and 12.1 MPa, respectively.

Investigation on Cu–Sn intermetallic compounds growth and signal transmission loss of the diverse copper lines after soldering in printed circuit board

Investigation on Cu–Sn intermetallic compounds growth and signal transmission loss of the diverse copper lines after soldering in printed circuit board

Microstructure and Optical Properties of Nanostructural Thin Films Fabricated through Oxidation of Au-Sn Intermetallic Compounds.

AuSn and AuSn2 thin films (5 nm) were used as precursors during the formation of semiconducting metal oxide nanostructures on a silicon substrate. The nanoparticles were produced in the processes of annealing and oxidation of gold–tin intermetallic compounds under ultra-high vacuum conditions. The formation process and morphology of a mixture of SnO2 and Au@SnOx (the core–shell structure) nanoparticles or Au nanocrystalites were carefully examined by means of spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) combined with energy-dispersive X-ray spectroscopy (EDX). The annealing and oxidation of the thin film of the AuSn intermetallic compound led to the formation of uniformly distributed structures with a size of ∼20–30 nm. All of the synthesized nanoparticles exhibited a strong absorption band at 520–530 nm, which is typical for pure metallic or metal oxide systems.

Microstructure, thermal behavior and joint strength of Sn-0.7Cu-1.5Bi/electroless nickel immersion gold (ENIG)

This paper details an investigation into the microstructure, thermal behaviors and joint strength of Sn-0.7Cu-1.5Bi solder alloy on electroless nickel immersion gold (ENIG) surface finish. Besides conventional techniques, the real-time synchrotron imaging was used to analyze the microstructure evolution in Sn-0.7Cu-1.5Bi/ENIG. This research investigated the growth behavior of the primary (Cu,Ni)6Sn5 intermetallic compounds (IMCs) in the solder joint with the Bi alloying. The elemental distribution analysis showed the Ni diffused from the ENIG surface finish and dissolved into the bulk solder during solidification and that the size of the primary (Cu,Ni)6Sn5 IMCs decreased due to the addition of 1.5 wt% Bi. The average kinetic growth rate of the primary (Cu,Ni)6Sn5 IMCs in Sn-0.7Cu-1.5Bi/ENIG was lower than that of the Sn-0.7Cu/ENIG. The thermal analysis revealed that the pasty range slightly increased and the undercooling degree decreased due to the addition of 1.5 wt% Bi for free-standing solder and soldering on ENIG surface finish. The shear strength of the Sn-0.7Cu-1.5Bi/ENIG was determined using a high-speed bond tester, and it increased by ~12% at bulk solder fracture of ~15% within the solder joint interfacial fracture due to the addition of 1.5 wt% Bi into the Sn-0.7Cu. These occurrences can be attributed to the solid solution strengthening effect at the bulk solder and the formation of finer interfacial (Cu,Ni)6Sn5 IMCs within the solder joints. The results indicated that the microstructural changes, especially the size reduction of IMCs, in Sn-0.7Cu-1.5Bi/ENIG impacted the joint strength.

Formation and nanomechanical properties of intermetallic compounds in electrodeposited Cu–Sn–Co multilayers

The properties of the intermetallic compounds (IMCs) formed at the interface between the solder and the Under Bump Metallization (UBM) are crucial for the reliability of solder joints. Cobalt (Co) is a potential candidate for UBM since it can act as a diffusion barrier and hence can improve the performance of tin-based solder joints. Growth kinetics, mechanism of formation, and properties of IMC in the copper-tin-cobalt (Cu–Sn–Co) system that is encountered with Co UBM are presented in this paper. Cu–Sn–Co systems were prepared by electrodeposition of Cu, Sn and Co multilayers on Cu substrates followed by reflow at 250 °C for varying durations (1–30 min). Microscopic observation revealed the formation of defect-free (Co,Cu)Sn3, crack-containing (Cu,Co)6Sn5 and thin irregular Cu3Sn IMCs after 1 min reflow. As reflow duration increased, (Co,Cu)Sn3 and Cu3Sn grew at the expense of (Cu, Co)6Sn5. The consumption of the entire Sn layer after 1 min and the calculated effective interdiffusion coefficient of (Co,Cu)Sn3 suggested that the growth of (Co,Cu)Sn3 after 1 min is controlled by solid-state diffusion of Sn. The average Young’s Modulus values of (Co,Cu)Sn3, (Cu,Co)6Sn5 and Cu3Sn are 99.5 ± 3.2 GPa, 110.8 ± 7.3 GPa and 109.4 ± 0.3 GPa, respectively, while the nanohardness values are 4.15 ± 0.34 GPa, 6.74 ± 0.62 GPa and 4.96 ± 1.09 GPa, respectively. Increasing the reflow duration in the Cu–Sn–Co system is expected to improve the performance of the solder joint, through the replacement of the crack-containing (Cu,Co)6Sn5 by the defect-free (Co,Cu)Sn3.

Effect of Ni on the Suppression of Sn Whisker Formation in Sn-0.7Cu Solder Joint.

The evolution of internal compressive stress from the intermetallic compound (IMC) Cu6Sn5 growth is commonly acknowledged as the key inducement initiating the nucleation and growth of tin (Sn) whisker. This study investigates the effect of Sn-0.7Cu-0.05Ni on the nucleation and growth of Sn whisker under continuous mechanical stress induced. The Sn-0.7Cu-0.05Ni solder joint has a noticeable effect of suppression by diminishing the susceptibility of nucleation and growth of Sn whisker. By using a synchrotron micro X-ray fluorescence (µ-XRF) spectroscopy, it was found that a small amount of Ni alters the microstructure of Cu6Sn5 to form a (Cu,Ni)6Sn5 intermetallic layer. The morphology structure of the (Cu,Ni)6Sn5 interfacial intermetallic layer and Sn whisker growth were investigated by scanning electron microscope (SEM) in secondary and backscattered electron imaging mode, which showed that there is a strong correlation between the formation of Sn whisker and the composition of solder alloy. The thickness of the (Cu,Ni)6Sn5 IMC interfacial layer was relatively thinner and more refined, with a continuous fine scallop-shaped IMC interfacial layer, and consequently enhanced a greater incubation period for the nucleation and growth of the Sn whisker. These verification outcomes proposes a scientifically foundation to mitigate Sn whisker growth in lead-free solder joint.

A low-temperature sealing method for metal-supported oxide fuel cell applications: Ni–Sn transient liquid phase bonding

A low-temperature sealing approach, transient liquid phase bonding with Ni–Sn system, was employed to seal metal-supported solid oxide fuel cell (MS-SOFC) components in this study. The Ni layer was prefabricated on the ferritic stainless steels by electroplating firstly, and then were vacuum annealed to enhance the bonding between the Ni coating and the steel substrate. Afterward, the Ni coated steels were transient liquid phase bonded using a thin interlayer of pure Sn. Effects of bonding temperature (250–400 °C) and holding time (10–60 min) on the interface of joints were investigated. The interfacial microstructure of joints was observed by the scanning electron microscope and the transmission electron microscope. A joint with full intermetallic compounds (IMCs) of Ni3Sn4 and Ni3Sn2 were formed at 400 °C/60 min. These Ni–Sn IMCs were all stable up to 794.5 °C, ensuring that the joint with full IMCs microstructure can be performed at the operating temperature of ∼600 °C for MS-SOFC. Furthermore, the residual Ni coating can also be served as a protective layer for the stack.

Interfacial Reactions and Mechanical Properties of Sn-58Bi Solder Joints with Ag Nanoparticles Prepared Using Ultra-Fast Laser Bonding.

The effects of Ag nanoparticle (Ag NP) addition on interfacial reaction and mechanical properties of Sn–58Bi solder joints using ultra-fast laser soldering were investigated. Laser-assisted low-temperature bonding was used to solder Sn–58Bi based pastes, with different Ag NP contents, onto organic surface preservative-finished Cu pads of printed circuit boards. The solder joints after laser bonding were examined to determine the effects of Ag NPs on interfacial reactions and intermetallic compounds (IMCs) and high-temperature storage tests performed to investigate its effects on the long-term reliabilities of solder joints. Their mechanical properties were also assessed using shear tests. Although the bonding time of the laser process was shorter than that of a conventional reflow process, Cu–Sn IMCs, such as Cu6Sn5 and Cu3Sn, were well formed at the interface of the solder joint. The addition of Ag NPs also improved the mechanical properties of the solder joints by reducing brittle fracture and suppressing IMC growth. However, excessive addition of Ag NPs degraded the mechanical properties due to coarsened Ag3Sn IMCs. Thus, this research predicts that the laser bonding process can be applied to low-temperature bonding to reduce thermal damage and improve the mechanical properties of Sn–58Bi solders, whose microstructure and related mechanical properties can be improved by adding optimal amounts of Ag NPs.

Influence of Cu–Sn Intermetallic Compound Surface Form on Contact Resistance Behavior of Fretting Corrosion of Tin Plating

Influence of Cu–Sn Intermetallic Compound Surface Form on Contact Resistance Behavior of Fretting Corrosion of Tin Plating

Growth of intermetallic compounds and brittle fracture behavior of Sn-Ag-Cu/ENIG joint with columnar Ni-P layer

A growth of intermetallic compounds (IMCs) at the interface between electroless Ni/immersion Au (ENIG) and Sn-3.0Ag-0.5Cu (SAC305) solder and related brittle fracture behavior of solder joint with microstructure changes of electroless Ni-P was investigated. An amorphous columnar Ni-P and an amorphous structureless Ni-P surface finishes were used for the comparison. The (Cu,Ni)6Sn5 IMC layers with a similar thickness were formed between solder and ENIG interface at the as-reflowed stage for both Ni-P surface finishes. During thermal aging, the interfacial IMC thicknesses for columnar Ni-P and structureless Ni-P increased up to 400 and 800 h, respectively, and then decreased with thermal aging time. This decrease of IMC thickness with thermal aging was due to spalling. The spalling rate of the columnar Ni-P sample was higher than that of the structureless sample. The shear strength decrease with aging time was lower for the columnar Ni-P sample than the structureless Ni-P sample. Brittle fracture for the columnar Ni-P sample was lower than for the structureless Ni-P sample.

Performance of Cu–Ag Thin Films as Diffusion Barrier Layer

It is well-known that Cu–Sn intermetallic compounds are easily produced during reflow process and result in poor reliability of solder bump. Recently, amorphous metallic films have been considered to be the most effective barrier layer because of the absence of grain boundaries and immiscibility with copper. Since Cu–Ag alloys are characterized by their lower electrical resistivity and superior glass-forming ability, they are appropriate to be used as the diffusion barrier layers. In this study, molecular dynamics simulation was performed to investigate the effects of composition ratio and quenching rate on the internal microstructure, diffusion properties, and the strength of the interface between polycrystalline Cu and Cu–Ag barrier layers. The results showed that Cu40Ag60 and Cu60Ag40 present more than 95% of the amorphous at quenching rate between 0.25 and 25 K/ps, indicating a good glass-forming ability. Diffusion simulation showed that a better barrier performance can be achieved with higher amorphous ratio. For the sample of Cu20Ag80 with quenching rate of 25 K/ps, a void is initially generated in amorphous Cu–Ag layer during the tensile test. This indicates the strength of amorphous Cu–Ag is weaker than Cu–Ag/Cu interface and the polycrystalline Cu layer.

Properties and microstructure evolution of Sn–Cu–Ni/Cu joints bearing carbon nanotubes and graphene nanosheets for solar cell

In this paper, 0.5 wt% carbon nanotubes (CNTs) and 0.05 wt% graphene nanosheets (GNSs) were selected as additives to modify the properties of Sn–Cu–Ni solder joints for solar cell. The mechanical properties of Sn–Cu–Ni solder joints can be improved by 20–25%. The interface growth behavior of Cu–Sn intermetallic compounds at Sn–Cu–Ni/Cu and Sn–Cu–Ni–0.5CNTs–0.05GNSs/Cu couples after 250 °C and 260 °C soldering with 10 min and 20 min. The experimental results indicate that the growth rate of Cu6Sn5 IMC of Sn–Cu–Ni/Cu solder joints is higher than that of Sn–Cu–Ni–0.5CNTs–0.05GNSs/Cu solder joints. That is, adding 0.5 wt% CNTs and 0.05 wt% GNSs can reduce the growth rate of the Cu6Sn5 IMC layer, which can be attributed to the reduction of the element diffusion coefficient. In addition, the stress–strain of the two solder joints were calculated using finite element method, it is found that the Sn–Cu–Ni–0.5CNTs–0.05GNSs/Cu solder joints have significantly less stress–strain than Sn–Cu–Ni/Cu solder joints, due to the reduction of Cu6Sn5 layer thickness, fatigue life of solder joints can be enhanced by three times.

Effects of Ni(P) layer thickness and Pd layer type in thin-Au/Pd/Ni(P) surface finishes on interfacial reactions and mechanical strength of Sn–58Bi solder joints during aging

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.

Performance and reliability of Al2O3 nanoparticles doped multicomponent Sn-3.0Ag-0.5Cu-Ni-Ge solder alloy

The effect of Al2O3 nanoparticles addition on melting, microhardness, microstructural, and mechanical properties of multicomponent Sn-3Ag-0.5Cu-0.06Ni-0.01Ge (SACNiGe) solder alloy was investigated. The shear strength of the capacitor assemblies under varying high-temperature environments for different nanocomposites was assessed and the reliability of the joint was determined using Weibull analysis. The SACNiGe solder doped with 0.01 and 0.05 wt% Al2O3 nanoparticles to prepare nanocomposites and tested on the solder joints for their performance and reliability under different thermal conditions. Plain copper and NiP layer coated substrates were used to investigate the effect of different surface finish on the joint reliability. The addition of ceramic nanoparticles in small amounts did not affect the melting parameters of the solder. In comparison with the bare solder alloy, nanocomposites yielded about 20% increase in tin-climb height and 14% higher microhardness. The dispersion of ceramic nanoparticles in the matrix and presence of Ni and Ge elements in the solder resulted in substantial microstructure refinement and about 24% supression in intermetallic compounds (IMCs) growth at the joint interface. In comparison with the bare Cu substrate, the NiP coating on the substrate provided a strong diffusion barrier, promoted thin and complex (Cu, Ni)6Sn5 IMC layer formation at the interface, and significantly retarded the IMC growth kinetics under elevated temperature conditions. Under varying thermal conditions, nanoparticles doped solder compositions showed about 20% increase in the joint shear strength value. The reliability of joints improved appreciably with the addition of 0.05 wt% Al2O3 nanoparticles in the solder. Samples with SACNiGe+0.05Al2O3 nanocomposite reflowed on NiP coating showed about 32% higher reliability than that on the uncoated-copper substrate. The SACNiGe solder joint performance and reliability could be significantly improved by minor weight percent addition of Al2O3 nanoparticles in the presence of NiP coating on the substrate.

Effect of Ni(P) thickness in Au/Pd/Ni(P) surface finish on the electrical reliability of Sn–3.0Ag–0.5Cu solder joints during current-stressing

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.

An effective method to retard Cu–Sn intermetallic compounds formation on the sidewall of microbumps by thermal oxidation

The formation of intermetallic compound (IMC) on the sidewall of Cu-pillar microbumps brings potential reliability threats. To inhibit its formation, a thin CuO layer was fabricated on the sidewall of Cu pillars by thermal oxidation first. Then, we verified that the CuO layer effectively retarded Sn–Ag solder sidewall wetting in the reflow process and exhibited a strong inhibition effect on Cu–Sn IMCs formation on the sidewall of microbumps during aging process. Secondly, microstructural evolution of copper oxides layer during aging was discussed studied. Results showed that the initial simple CuO layer became complex as Cu2O/CuO, fully covered the whole solder cap and formed a continuous reticulation structure on the polyimide layer after 2000 h aging. Then, the formation mechanism of copper oxides layer was proposed according to its oxidation kinetics. The growth behaviors of copper oxides layer around microbumps and its inhibition ability of IMC growth on the sidewall of microbumps are of great importance to electronics reliability.

Interfacial transfer and phase evolution between Cu and Sn solder doped with minor Cu, Ag and Ni: experimental and theoretical investigations

The effects of minor Cu (0.7%), Ag (3.5%) and Ni (0.1%) additions in Sn solder on the interfacial transfer and phase evolution were clarified in Sn/Cu solder joints. (Cu,M)6Sn5 and (Cu,M)3Sn (M = Cu, Ni) layers were observed at the Sn/Cu interface during thermal aging at 150 °C. The additions of Cu, Ag and Ni alloy elements were found to change the growth of the Cn–Sn intermetallic compounds (IMCs). The results showed that Cu, Ag and Ni additions were able to suppress the growth of (Cu,M)3Sn (M = Cu, Ni) layers, but promoted the (Cu,M)6Sn5 growth. This was because the reactions on the (Cu,M)6Sn5 side were promoted by the refined IMCs grain size, whose growth was at the expense of (Cu,M)3Sn. In addition, the interfacial transfer rate (thickness ratio, y) of (Cu,M)3Sn/(Cu,M)6Sn5 versus the thermal aging time (t) was found to be close to parabola relationship, the y increased gradually with the alloy elements from Ni, Cu to Ag. The phase evolution (η′-Cu6Sn5, η-Cu6Sn5, e-Cu3Sn, Ag3Sn, η′-(Cu,Ni)6Sn5, η-(Cu,Ni)6Sn5 and e-(Cu,Ni)3Sn) at the interface between Cu and Sn solder doped with minor Cu, Ag and Ni was also elucidated.

Fast formation of Ni–Sn intermetallic joints using Ni–Sn paste for high-temperature bonding applications

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.

A study on wettability and formation of intermetallic phase between Co–Cr–Mo alloy and Sn-Solder used as a potential under bump metallization for flip-chip packages

The wettability and formation of intermetallic compounds (IMCs) formed between a Co–Cr–Mo-based alloy and Sn-solder metal were investigated using the reflow soldering method. Soldering was conducted in an electric furnace in separate experiments at temperatures of 533, 553, 573, 623, and 673 K for 600 s. The morphology of the intermetallic layer formed at the Co–Cr–Mo-based/Sn-solder interface was characterized by scanning electron microscopy (SEM). The chemical composition and phase of the formed intermetallic layer were analyzed by electron probe microscopic analysis (EPMA) and X-ray diffraction analysis. Wettability analysis indicated that the soldering temperature influenced the wettability. With increasing soldering temperatures, the spreading factor increased, whereas the contact angle decreased. The intermetallic layers were found in triples in the intermediate zone between the solidified Sn-solder and the Co–Cr–Mo-based substrate. The thickness of the intermetallic layers increased in proportion with increasing soldering temperature. The EPMA analysis indicated only two IMCs formed at the interface of the joint at all of the investigated soldering temperatures, although three interfacial layers were observed by SEM analysis. The Sn-richer phase, Co(Cr,Mo)Sn2, formed adjacent to the Sn-solder matrix, whereas the Co(Cr,Mo)Sn was found near the Co–Cr–Mo-based substrate. The nanoindentation measurement revealed that the formed Co(Cr,Mo)Sn2 and Co(Cr,Mo)Sn IMCs possessed lower hardness values compared to the Sn–Cu intermetallic systems.

Pressureless transient liquid phase bonding using SAC305 with hybrid Ag particles and its reliability under high-temperature storage test

Transient liquid phase (TLP) bonding has attracted much attention as a high-temperature interconnection method. TLP is a bonding method that converts entire joints into heat endurable intermetallic compounds (IMCs) by solid–liquid interdiffusion between high-melting-point (high-MP) parent metals and low-MP bonding metals. However, conventional TLP bonding requires high bonding pressure and long process time because IMC reactions occur only at the interfaces between the high-MP parent metals and the low-MP bonding metals.We fabricated TLP paste using SAC305 with 10 wt% Ag particles to induce IMC reactions to take place across an entire joint simultaneously. A TLP bonding process was performed at 300 °C for 2 h in air without added pressure. SAC residue was found in the SAC305 joint, while the whole SAC305–10 wt% Ag joint was converted into Cu–Sn and Ag–Sn IMCs. The SAC305–10 wt% Ag joint also demonstrated 2.5 times higher maximum shear strength compared with the SAC305 joint. In addition, the bonding reliability was evaluated by high-temperature storage test at 200 °C for 1000 h. The SAC305–10 wt% Ag joint maintained its bonding strength, while the SAC305 joint mechanically deteriorated.