Sn Intermetallic Compounds Research Articles

Ni mesh-reinforced ultrasonic-assisted Cu/Sn58Bi/Cu joint performance: Experiments and first-principles calculations

The Ni mesh was incorporated into the Cu/Sn58Bi/Cu bonding as a reinforcing skeleton to achieve an enhancement effect analogous to steel reinforcement in concrete. Ultrasonic-assisted soldering (UAS) improved the metallurgical bond among the solder, Ni mesh, and substrate. It facilitated the formation of (Cu, Ni)6Sn5 intermetallic compounds (IMCs) layers, increasing the joint strength. Observations indicated that ultrasonic treatment effectively refined the (Cu, Ni)6Sn5 grains and induced a uniform preferred orientation of β-Sn and Bi grains in the joint matrix adjacent to the Ni mesh. The shear strength of the joint reached 72.23 MPa when the ultrasonic application was sustained for 15 s, achieving the fabrication of a high-strength point with low energy consumption. First-principles calculations have confirmed that changes in the Ni content within (Cu, Ni)6Sn5 IMCs improved the stability of the crystal structure. Furthermore, the variations in content could potentially improve the mechanical and electrical properties of the (Cu, Ni)6Sn5. Enhancements in ultrasonic efficiency and the reinforcement of IMC structures offer new avenues for research in green and high-performance electronic packaging material joining technologies.

Solid-phase transient soldering method based on Au/Ni–W multilayer thin-film-modified copper-based structures

The copper crystal cone-shaped micro-nanostructure is used as the substrate, and the Ni–W alloy layer and Au nanolayer are plated sequentially. Instantaneous soldering with lead-free solder is realized under ultrasonic assistance at room temperature. This solves the residual stress and thermal damage caused by high melting point lead-free solder on thin chips and thermal components, and ensures the safety and reliability of electronic components. Copper-based microstructures are deposited by electrochemical methods. An amorphous Ni–W alloy layer with a thickness of 180 nm is deposited on the Cu-based microstructures by adjusting the atomic ratio of the plating solution. The Ni–W layer is further coated with a 50 nm Au layer to prevent oxidation. Solid-phase transient soldering is realized by combining the Au/Ni–W multilayer thin-film-modified Cu substructures with commercial solder (SAC305) for a holding time of 3 s at a soldering pressure of 10,000 gf (20 MPa) while ultrasonically assisted. The soldered samples are aged at 180 °C for 10 min, 30 min, and 60 min, respectively. Copper substructures with different surface modifications are subjected to destructive shear experiments with solder balls. Scanning electron microscope and X-ray fluorescence thickness gauge are used to study the microstructure, intermetallic compound (IMC) composition thickness and properties of the soldered interface and section. The cone height of the Cu-based structure is 2–4 μm, and the diameter of the bottom is 800 nm–1200 nm, which has a sharp tip and an excellent L/D ratio. The interface between the Au/Ni–W modified Cu substructure and the solder ball is almost free of holes. The average shear strength at the soldering interface is about 43.06 MPa. The fracture surface after the shear experiment basically occurs inside the solder ball matrix, which belongs to the pure toughness fracture. The interface between the Au/Ni–W-modified Cu-based structure and the solder ball is subjected to long aging treatment at 180 °C. The soldering interface showed a “bright layer”. New phases are generated on the solder side above the “bright layer”, while no new phases appear on the Cu substructure side below the “bright layer”. The copper-based microstructure is inserted into the inside of the solder ball to form an inlay and produce mechanical interlocking. Au/Ni–W alloy modification layer can effectively improve the surface hardness of copper-based structures. This creates a large hardness difference with soft solder and enables the formation of fewer holes in the insertion solder. Amorphous Ni–W alloys are prone to form dense oxide films during ultrasonication. The Au film modification prevents oxide generation and increases the average shear strength of the soldering interface. The Ni–W alloy layer retards the interdiffusion between Cu–Sn, blocks the excessive growth of Cu–Sn IMCs, and reduces the reliability problems caused by interface failure.

Mechanical Bonding Properties of Solderable Anisotropic Polymer Composite containing Low-Melting-Point and High-Melting-Point Solder Fillers

In this papers, to enhance the mechanical bonding properties of solderable anisotropic polymer composites (SAPCs) containing low-melting-point solder filler only, a new low-melting-point solder and high-melting-point solder mixed filler filled SAPCs (LH-SAPCs) was proposed, and the influence of the high-melting-point solder filler on the conduction path formation and mechanical bonding properties of the LH-SAPC were investigated. Two types of LH-SAPC were synthesized by adding high-melting-point solder within the low-melting-point solder/high-melting-point solder mixed filler at mixing ratios of 0 and 50 vol% (the volume fraction of low-melting-point solder/high-melting-point solder mixed filler in the polymer composite was 20%), and a bonding test was conducted using QFP. The results exhibited that the LH-SAPC containing high-melting-point solder formed a wide and stable conduction path due to the proper selective conduction path formation behavior by the interaction between molten low-melting-point solder and solid-state high-melting-point solder fillers within the polymer composite with low viscosity condition. Furthermore, the mechanical bonding properties of the LH-SAPC joints containing high-melting-point solder were enhanced compared to that of LH-SAPC containing low-melting-point solder only owing to the precipitation hardening and dispersion strengthening effects due to the increase of fine Bi-rich, Cu<sub>6</sub>Sn<sub>5</sub>, and Ag<sub>3</sub>Sn intermetallic compound particles inside the conduction path.

Investigating the impact of cobalt incorporation on the transformation of Cu6Sn5 layer to (Cu, Co)6Sn5: Microstructural and mechanical insights

In this study, cobalt (Co) particles were incorporated as reinforcing agents into the Sn58Bi solder. The solderability of the solder and the strength of the solder joints were investigated. The results indicated that adding Co particles did not alter the low melting point characteristics of the Sn58Bi solder, yet its undercooling was reduced, and the wettability was enhanced. In the Sn58Bi/Cu solder joint, adding Co led to forming free (Cu, Co)6Sn5 intermetallic compound (IMC) and generating the CoSn2 phase through microalloying. The interfacial IMC was gradually transformed from a fan-shaped Cu6Sn5 to a flatter layer-like (Cu, Co)6Sn5 IMC, eventually exhibiting a coral-like structure with increased Co content. Adding Co particles increased the thickness of the IMC layer, but at low levels, the Co could refine the IMC grains. Simultaneously, implementing grain refinement and Orowan strengthening resulted in heightened microhardness and shear strength. In the shear test, the fracture of solder joints predominantly transpired within the solder matrix. Excessive Co particles were prone to aggregating within the solder, forming irregular block-shaped (Cu, Co)6Sn5. Concurrently, the coral-like IMC at the interface led to a decline in the mechanical performance of the solder joints, with some interfacial IMC being exposed in the fracture region.

Applications of Ni and Ag metallizations at the solder/Cu interfaces in advanced high-power automobile interconnects: An electromigration study

An advanced Pb-free solder interconnect, Cu line/Cu pillar/Ni/Sn1.8Ag/Ag/Cu lead frame/Sn3Ag0.5Cu/Au/Ni(P)/Cu trace, using the flip-chip quad flat no‑lead (FCQFN) packaging technology was designed for high-power automobile applications. An electromigration study revealing the Ni and Ag metallization effects on the interfacial reaction was investigated. Current stressing was conducted at a 2 A direct current at 160 °C until the defined 200 %-electrical-resistance-rise failure occurrence. Electromigration induced a two-stage electrical resistance increase mode in the advanced automobile test vehicle with a mechanism transition time of 585 h, as evidenced by the in situ resistance monitoring. Phase transformation from the constituent phases into the predominant (Cu,Ni)6Sn5 and Cu3Sn intermetallic compounds (IMCs) at the interfaces was proposed to explain the rapid resistance rise in the early-stage electromigration. Void formation and coalescence due to the Kirkendall effect and volume shrinkage during the phase transformation were proposed to explain the following steady resistance increase after the critical current stressing time. Furthermore, the phase transformation and growth of the IMCs behaved divergently at different interfaces and electron flow directions. The rapid phase transformation occurred in the downstream Sn1.8Ag solder interconnect due to the accelerated Ni metallization dissolution and formed a complete IMC joint. The anisotropic diffusion driven by the competitive or synergetic effect between the electron wind force and chemical potential gradient was proposed to explain the asymmetric microstructures after the electromigration experiment. The application of Ag metallization benefited the flip-chip soldering process, and the layer-type Ag3Sn IMC served as a diffusion barrier against Sn/Cu interdiffusion at the solder/Cu lead frame interface during the solid-state electromigration. In contrast, the Ni metallization was designed as a diffusion barrier to hinder interdiffusion and the undesirable Cu3Sn growth at the solder/Cu interface. The findings presented in this study could benefit the solder interconnect design with an appropriate metallization combination against undesirable electromigration failure.

Efficient and robust ultrathin porous carbon encapsulated Ni–Sn intermetallic compounds derived from metal–organic frameworks for in-situ aqueous phase deoxygenation of fatty acid methyl esters

Deoxygenation of fatty acid esters in aqueous phase using in-situ generated H2 has emerged as a promising approach to producing sustainable diesel-like hydrocarbons. In this study, we employed a solvothermal method to synthesize novel Ni–Sn metal–organic frameworks (MOFs) with a homogeneous distribution of Ni and Sn elements. Subsequently, various Ni–Sn intermetallic compounds (IMCs) encapsulated with a porous carbon layer (<3 nm) (Ni–Sn IMC@C) were prepared through the facile pyrolysis of metal–organic frameworks under a controlled N2 atmosphere. Applying methyl palmitate as model reactant and methanol as hydrogen donor, Ni3Sn2 IMC@C gives approximately 100% conversion and 93% yield towards n-C15 and n-C16 alkanes at 330 °C, without significant deactivation during the recycling for five times. The deoxygenation pathway is dominated by decarbonylation (DeCO) on Ni–Sn IMCs. In Ni–Sn IMCs, the oxophilic nature of Sn, along with its charge transfer with Ni, enhances the adsorption of an η2(C, O)-aldehyde configuration. The strategic isolation of adjacent Ni by Sn effectively inhibits methanation and C–C bond hydrolysis, reducing H2 consumption and increasing carbon yield. Moreover, the ultrathin porous carbon encapsulation not only prevents the loss and sintering of Ni3Sn2 IMC under harsh hydrothermal condition but also mitigates mass transfer limitation. Surface oxidation of Ni3Sn2 IMC, particularly the formation of SnO2, is detrimental to deoxygenation. Additionally, Ni3Sn2 IMC@C exhibits high hydrocarbon yields (>89.6%) in in-situ aqueous phase deoxygenation of methyl laurate, methyl stearate and methyl oleate. These findings highlight the remarkable potential of MOF-derived catalysts for hydrothermal deoxygenation.

Effects of electrodeposited Co–W and Co–Fe–W diffusion barrier layers on the evolution of Sn/Cu interface

In 3D IC, a high-efficiency diffusion barrier layer is urgently required for Sn/Cu micro-bumps, to inhibit the formation of Cu–Sn intermetallic compounds (IMCs). In this work, the barrier performance of electrodeposited Ni, Co–9W, Co–20W, Co–20Fe–10W and Co–36Fe–17W were studied. After aging at 150 °C for 672 h, the thicknesses of the IMCs formed between Sn and these barriers were determined. Among the five barriers studied, Co–36Fe–17W exhibited the best barrier effect, with a thickness of 0.61 μm. At the Sn/Co–W interface, CoSn3 IMC and Co–W–Sn were formed, while at the Sn/Co–Fe–W interface, CoSn3 IMC, FeSn2 IMC, and Co–Fe–W–Sn were observed. The layered CoSn3 IMC gradually evolved into an isolated island structure as the Fe and W concentration rose at the Sn/Co–Fe–W samples. The growth of CoSn3 in the Sn/Co–W and Sn/Co–Fe–W samples involved a competition between diffusion control and interfacial reaction control. The presence of W atoms effectively inhibited Co diffusion, while the FeSn2 IMC layer acted as a barrier, suppressing the nucleation of CoSn3. The synergistic effect of these factors contributed to the excellent barrier properties of the Co–Fe–W layer. This research establishes a scientific basis for selecting barriers that exhibit superiority in advanced packaging.

Reliability improvement of SnAgCu interconnections under extreme temperature condition by TiO2 nanoparticles doping: Experiments and first principles calculations

Electronic components of the spacecraft during their service may endure intricate and extreme temperature environments. In this study, the interfacial microstructure evolution and reliability of Cu/Sn-3.0Ag-0.5Cu (SAC305)/Ni and Cu/Sn-3.0Ag-0.5Cu-0.05TiO2 (SAC305–0.05TiO2)/Ni interconnections under thermal shock from −196 °C to 150 °C are investigated. Short-column-type (Cu,Ni)6Sn5 intermetallic compounds (IMCs) are developed at the solder/Ni interface for both interconnections after the reflow process, and their morphology changes to long-rod type after 200 cycles. Extremely thin and discontinuous (Ni,Cu)3Sn4 phases are generated between (Cu,Ni)6Sn5 and Ni only in SAC305 interconnections after 200 cycles. The rate of interfacial IMCs growth in SAC305–0.05TiO2 interconnections is slower than that in the SAC305 interconnections. Cracks are formed in the IMC layer of the SAC305 interconnection after 200 cycles, which propagate through the whole IMC layer after 250 cycles. While for the SAC305–0.05TiO2 interconnection, no crack is observed until after 250 cycles. TiO2 nanoparticles doping could suppress the interfacial IMC growth, leading to an enhancement in the interconnection reliability under thermal shock. First-principles calculations are performed to further understand the mechanism for phase transformation of Ni-Cu-Sn IMCs and the reliability improvement of interconnections.

A first-principles study of the mechanical and physical properties of Ni3Snx intermetallic compounds for high-temperature power device packaging

Ni–Sn intermetallic compound is a highly promising high-temperature packaging material for power devices, and it is very necessary to understand and control the physical and mechanical properties of Ni–Sn intermetallic compounds(IMCs). However, the current research mainly focuses on the rapid preparation of such packaging solder joints, and there is little research on the microstructure, physical and mechanical properties of alloys. In this study, the first-principle and quasi-harmonic Debye models were used to analyze the mechanical characteristics, electronic structure, thermal conductivity, and linear expansion coefficient of three IMCs (Ni3Sn, Ni3Sn2, and Ni3Sn4) of the Ni–Sn system. The results show that Ni3Sn has the highest modulus and fracture toughness and has the best elastic match with Ni. The welded joints of Ni/Ni3Sn/Ni structures can effectively prevent the generation of microcracks under the stress field. They're all mixed-bond compounds, according to the results of electronic structure simulations, and Ni3Sn4 has the most ionic and covalent bonds, so its fracture toughness is the lowest and its anisotropy tendency is the most significant. The thermal conductivity of Ni3Sn is the highest, the linear expansion coefficients of Ni3Sn and Ni3Sn4 are not significantly different, and they match well with the linear expansion coefficients of Ni.

The doped Pd on the crystal calculation and intermetallic property of low-temperature soldered ENEPIG substrates

The preparation of new solder joint materials for chip packaging by designing a variety of brazing material mixes has become one of the future research directions for solder joints. They added low melting point elements to traditional solder materials to prepare low-temperature hybrid solder to meet the low-temperature packaging trend. To improve the performance of low-temperature solder, adding some alloying elements can refine the grain, change the IMC morphology and size, and improve the joint strength to a certain extent. The design of the hybrid solder joint system needs to be based on different metal pads. There are various failure modes of interconnected solder joints on different metal pads. Therefore, the interfacial response, microstructure, and mechanical properties between different hybrid solder and different metal pads need to be studied to optimize the design of the hybrid solder joint system. This paper investigated hybrid low-temperature Sn–3Ag-0.5Cu/Sn–58Bi solder joints on Au/Ni/Cu (ENIG) and Au/Pd/Ni/Cu (ENEPIG) substrates. The addition of Pd elements can change the IMC morphology of hybrid solder joints and affect the fracture failure mode of the joints under shear, with a higher average shear strength at different process parameters than ENIG welded joints. Finally, the presence form of Pd elements in the solder joints was observed under TEM and the fracture mechanism was analyzed. The results showed that Pd atoms on ENEPIG pads can replace some Cu atoms to form (Cu, Pd)6Sn5 intermetallic compounds, distorting the lattice stripe to produce distortions. And compared to ENIG pads, the IMC morphology is pin-rod-like and finer, with more complex grain boundary paths between the grains of the hybrid solder.

Transient liquid phase bonding using Cu foam and Cu–Sn paste for high-temperature applications

This study presents a new structure for transient liquid phase (TLP) bonding using Cu foam and Cu–Sn paste. Cu foam and Cu–Sn paste with large reaction surface areas were used to reduce the long bonding time, which is a disadvantage of the conventional TLP bonding process. After applying the Cu–Sn paste at an optimized ratio to the top and bottom of the Cu foam, pressure was applied to fill the pores inside the Cu foam with the paste, and a bonding process was performed at 260 °C under a pressure of 3 kgf. Bonded joints composed of only the Cu skeleton and Cu–Sn intermetallic compounds (IMCs) were confirmed within a bonding time of 5 min. In addition, the proportion of the Cu3Sn phase in the joint increased with the bonding time. After a bonding time of 40 min, the joint was mostly composed of a Cu skeleton and Cu3Sn, with a measured shear strength of approximately 39.2 MPa. After the joint analysis of the as-bonded samples, a high-temperature storage test (HTST) was conducted to evaluate their high-temperature long-term reliability. As a result of HTST, because most of the joint was converted to Cu3Sn after the bonding process, the shear strength did not decrease despite heat treatment at a high temperature of 240 °C, and a similar microstructure of the joint was maintained.

Wetting Transition of Liquid Tin on the Surfaces of Initially Oxidized Steels

Experiments were carried out to investigate the wetting behaviour of liquid tin on two different steel substrates EN1.4301 stainless steel and 42CrMo4 low-alloyed steel. The experiments were carried out in a vacuum furnace at residual pressure (10−8 bar) with the temperature raised till 1233 K (960 °C). The transition of the liquid tin droplet from a non-wetting to a wetting state was achieved on the surface of both steels after the spontaneous oxide removal. The transition temperatures in the Sn/EN1.4301 and Sn/42CrMo4 systems were nearly identical, 1140 K and 1130 K, respectively. SEM images showed the formation of the Fe–Sn intermetallic compounds at the Sn/steel interfaces above the transition temperature. Tin penetration into the grain boundaries of EN1.4301 and 42CrMo4 steels was also observed.Graphical abstract

Study on preparation and sintering properties of nano-silver-coated tin slurry

A nano-sized silver-coated tin (Sn@Ag) slurry was prepared by heterogeneous flocculation method by adjusting the pH value of solution and selecting different dispersants. The slurry improved the oxidation resistance of tin and its dispersibility in silver matrix. The sintering strength of nanometre Sn@Ag slurry increases with the increase of Sn content. When the Sn content reaches 5%, the shear strength of the joint reaches the highest 50 MPa, which is more than 10 MPa higher than that of the pure nanometre silver slurry sintered joint. The increase of shear strength is due to the fact that the equilibrium phase formed after sintering is Ag–Sn replacement solid solution and intermetallic compound Ag 3 Sn, which have the effect of replacement solution strengthening and dispersion strengthening, respectively. It is proved by experiments and analysis that the application of nano-silver paste in chip interconnection is feasible. The research of this subject provides experimental reference and theoretical basis for the application of new generation interconnect materials in power devices and promotes the development of microelectronics packaging technology.

To suppress thermomigration of Cu–Sn intermetallic compounds in flip-chip solder joints

We report here an approach to inhibit Cu–Sn intermetallic compounds (IMCs) in flip chip solder joints under thermal-gradient annealing. We reflowed two types of solders joints, Cu/SnAg/Cu and Cu/SnAg/Ni, in an oven (isothermal) and on a hot plate (with thermal-gradient) at 260 °C. During the isothermal reflow, the IMC growth rates in the top and bottom sides of the solder joint were ∼4.0 × 10−2 and 8.9 × 10−2 μm/min, respectively. However, the IMC growth rate increased to 7.8 × 10−1, 7.9 × 10−1, and 8.9 × 10−1 μm/min in the cold ends with low, medium, and high thermal gradients, respectively. Yet, the IMC thickness on the hot ends remained almost unchanged. These results indicate that the thermal gradient has facilitated the Cu–Sn IMC formation in the cold ends. But, when a Ni film was sandwiched at the cold end, the IMC growth rates in the cold end were reduced to ∼9.7 × 10−2, 1.4 × 10−1, and 1.5 × 10−1 μm/min with low, medium, and high thermal gradients, respectively, indicating that the thermomigration of IMCs was retarded by the Ni. It is speculated that the Ni layer transformed the IMCs on the hot end into stable (Cu,Ni)6Sn5 ternary IMCs, and thus the thermomigration of Cu was suppressed. A kinetic model is also proposed to address the competitive reactions of Cu-molten solder joints.

Microstructures and mechanical properties of ENIG/Sn-3.5Ag/ENIG joints formed by ultrasonic-assisted solder bonding

The effects of temperature and ultrasonic-assisted time on the microstructures and mechanical properties of the electroless nickel-immersion gold (ENIG)/Sn-3.5Ag/ENIG sandwich structure in ultrasonic chip bonding were investigated. Ultrasonic-assisted solder bonding was performed for 0.5–4 s at 25, 150, and 250 °C. The bonding was successful under all conditions. At 25 °C, Au–Sn intermetallic compounds (IMCs) were formed at the upper interface, and AuSn4 was formed on Ni–Sn IMCs at the lower interface. As the bonding time increased, spalling of AuSn4 was increasingly observed at the upper interface. At 150 °C, a trend similar to that at 25 °C was observed, but as the time increased, the thickness of the joint decreased, Au–Sn IMCs at the upper interface disappeared, and thin Ni–Sn IMCs and Cu6Sn5 were formed. The results observed at 250 °C differed from those observed at 25 and 150 °C because ultrasonic-assisted solder bonding was performed with the solder in a molten state. Ni–Sn IMCs were formed at the upper and lower interfaces, residual Sn and Au–Sn IMCs were present inside, and the thickness of the joint was very small. At 250 °C, the shear strength was high regardless of the bonding time. Observations of the top views and cross-sections of the fracture surfaces showed that, at 25 and 150 °C, the fractures initially occurred at the lower interface but moved to the upper interface as the bonding time increased. At 250 °C, the fractures did not significantly change, regardless of the ultrasonic-assisted time.

Effect of reflow temperature and solder size on Cu-Ni cross-interaction in the Cu/Sn/Ni micro solder joints

PurposeSolder bumps for chip interconnections are downsizing from current approximately 100 µm to the expected 1 µm in future. As a result, the Cu-Ni cross-interaction in Cu/Solder/Ni solder joints will be more complicated and then strongly influence the growth of the intermetallic compounds (IMCs). Thus, it is critical to understand the fundamental aspects of interfacial reaction in micro solder joints. This paper aims to reveal the effect mechanism of reflow temperature and solder size on the interfacial reaction in Cu/Solder/Ni solder joints.Design/methodology/approachThe Cu-Ni cross-interaction in the Cu/Sn/Ni micro solder joints with 50 and 100 µm solder sizes at 250°C and 300°C were observed, respectively. The line-type interconnects were soaked in silicone oil, and the temperature of the line-type interconnects was 250 ± 3°C and 300 ± 3°C, which were monitored by a fine K-type thermocouple, and followed by an isothermal aging process at various times. After aging, the specimens were removed from the silicone oil and cooled in the air to room temperature.FindingsThe major interfacial reaction product on both interfaces was (Cu,Ni)6Sn5, and the asymmetric growth of (Cu,Ni)6Sn5, evidenced by the thickness of (Cu,Ni)6Sn5 IMCs at the Sn/Ni interface was always larger than that at the Sn/Cu interface, resulted from the directional migration of Cu atoms toward the Sn/Ni interface under Cu concentration gradient. The morphology of (Cu,Ni)6Sn5 IMC at Sn/Cu interface was columnlike at 250°C, and which changed from columnlike to scallop with large aspect ratio at 300°C, while that at Sn/Ni interface gradually evolved from needlelike to the mixture of needlelike and layered at 250°C, and which evolved from needlelike to scallop with large aspect ratio at 300°C. The evolution of morphology of (Cu,Ni)6Sn5 is attributed to the content of Ni. Furthermore, the results indicate that the Cu-Ni cross-interaction was stronger with small solder size and relatively low temperature in the Cu/Sn/Ni micro solder joints.Originality/valueThe asymmetric growth of (Cu,Ni)6Sn5 in the Cu/Sn/Ni micro solder joints, evidenced by the thickness of (Cu,Ni)6Sn5 IMCs at the Sn/Ni interface, was always larger than that at the Sn/Cu interface. The morphology evolution of (Cu,Ni)6Sn5 IMC at both interfaces was attributed to the content of Ni. The Cu-Ni cross-interaction was stronger with small solder size and relatively low temperature in the Cu/Sn/Ni micro solder joints.

Comparative study on solid-solid interfacial reaction and bonding property of Sn-Ag-Cu/Ni-P joints by laser and reflow soldering

PurposeLaser soldering has attracted attention as an alternative soldering process for microsoldering due to its localized and noncontact heating, a rapid rise and fall in temperature, fluxless and easy automation compared to reflow soldering.Design/methodology/approachIn this study, the metallurgical and mechanical properties of the Sn3.0Ag0.5Cu/Ni-P joints after laser and reflow soldering and isothermal aging were compared and analyzed.FindingsIn the as-soldered Sn3.0Ag0.5Cu/Ni-P joints, a small granular and loose (Cu,Ni)6Sn5 intermetallic compound (IMC) structure was formed by laser soldering regardless of the laser energy, and a long and needlelike (Cu,Ni)6Sn5 IMC structure was generated by reflow soldering. During aging at 150°C, the growth rate of the IMC layer was faster by laser soldering than by reflow soldering. The shear strength of as-soldered joints for reflow soldering was similar to that of laser soldering with 7.5 mJ, which sharply decreased from 0 to 100 h for both cases and then was maintained at a similar level with increasing aging time.Originality/valueLaser soldering with certain energy is effective for reducing the thickness of IMCs, and ensuring the mechanical property of the joints was similar to reflow soldering.

Effect of 0D and 1D ZnO nano additive reinforced Sn-3.0Ag-0.5Cu solder paste on InGaN LED chip/ENIG joints

Nanocomposite solder has been recognized as an excellent strategy to improve the reliability of solder joints. This study attempts to find the effects of ZnO nanoparticles (NP) and nanowires (NW), on the LED/Sn3.0Ag0.5Cu joint reliability. Varying amounts of ZnO NP and NW are dispersed into solder using a high-speed centrifugal paste mixer and LED/solder joints were assembled via paste printing and reflow technique. Until 0.2 wt %, adding NP and NW improved the spreading ratio of SAC 305 paste by 8.7 % and 11.1 %. However, due to ceramic/metal surface instability, higher addition declined the spreading ratio. Both NP and NW suppressed the (Cu, Ni)6Sn5 intermetallic compound (IMC) formed at the LED/solder joint. Dispersion strengthening provided by NP and NW improved the joint shear strength by 28.2 % and 31.1 %, respectively. The Weibull modulus and 75 % survival probability improved consistently with increasing ZnO NW addition, displaying homogeneity in shear strength and reliable LED/solder joints.

Novel and fast transient liquid phase bonding using etched Cu foam/Sn–3.0Ag–0.5Cu composite solder preform

In this study, an effective transient liquid phase (TLP) bonding structure using a composite solder preform including a Cu metal foam was formed. Cu foam has a large surface area owing to its structural characteristics, enabling a faster reaction between Cu and Sn atoms compared to that in a conventional sandwich-type structure. This facilitates the rapid formation of an intermetallic compound (IMC) at the joint. In addition, because Cu metal has high electrical and thermal conductivities, the Cu foam inserted into the joint acts as an electrical and thermal pathway. To increase the surface area of the Cu foam and improve the reaction rate with Sn, the Cu foam was etched, and the effect was analyzed and compared with non-etched conditions. A composite solder preform was fabricated by dipping the Cu foam in a molten Sn–3.0Ag–0.5Cu (SAC305) solder bath for 1–2 s. The fabricated preform comprised Cu foam and SAC305 solder filled between the network structure of the Cu foam. In the case of the etched Cu foam, after bonding at 260 °C for 40 min, the bonded joint comprised only Cu–Sn IMCs and a residual Cu skeleton and trace amounts of Ag3Sn. The shear test results showed a high shear strength under the etched and non-etched conditions, with the value being higher under the etched condition. After bonding times of 3 and 40 min, the shear strengths were approximately 57 and 42.3 MPa, respectively, under the non-etched Cu foam condition and approximately 67.4 and 53.9 MPa under the etched Cu foam condition, respectively. A fracture morphology analysis was conducted to analyze the shear strength results. With increasing bonding time, the fracture path moved from the inside of the bonded joint to around the interface between the joint and substrate.

Microstructure evolution and grain refinement of ultrasonic-assisted soldering joint by using Ni foam reinforced Sn composite solder.

In this investigation, ultrasonic-assisted soldering at 260°C in air produced high strength and high melting point Cu connections in 60s using Ni foam reinforced Sn composite solder. Systematically examined were the microstructure, grain morphology, and shear strength of connections made with various porosities of Ni foam composite solders. Results shown that Ni foams as strengthening phases could reinforce Sn solder effectively. The addition of Ni foam accelerated the metallurgical reaction due to great amount of liquid/solid interfaces, and refined the intermetallic compounds (IMCs) grains by ultrasonic cavitation. The joints had different IMCs by using Ni foam with different porosity. Layered (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 phases both existed in Cu/Ni60-Sn/Cu joint while only (Cu,Ni)6Sn5 IMCs grew in Cu/Ni98-Sn/Cu joint. As ultrasonic time increasing, Ni skeletons were dissolved and the IMCs were peeled off from substrates and broken into small particles. And then, the IMCs gradually dissociated into refined particles and distributed homogeneously in the whole soldering seam under cavitation effects. Herein, the Cu/Ni60-Sn/Cu joint ultrasonically soldered for 60s exhibited the highest shear strength of 86.9MPa, as well as a high melting point about 800℃ for the solder seam composed of Ni skeletons and Ni-Cu-Sn IMCs. The characterization indicated that the shearing failure mainly occurred in the interlayer of the soldering seam. The homogeneous distributed granular IMCs and Ni skeletons hindered the crack propagation and improved the strength of Cu alloy joints.