Interfacial Intermetallic Compounds Research Articles

A data-driven framework to predict the morphology of interfacial Cu6Sn5 IMC in SAC/Cu system during laser soldering

A data-driven approach combining together the experimental laser soldering, finite element analysis and machine learning, has been utilized to predict the morphology of interfacial intermetallic compound (IMC) in Sn-xAg-yCu/Cu (SAC/Cu) system. Six types of SAC solders with varying weight proportion of Ag and Cu, have been processed with fiber laser at different magnitudes of power (30−50 W) and scan speed (10−240 mm/min), and the resultant IMC morphologies characterized through scanning electron microscope are categorized as prismatic and scalloped ones. For the different alloy composition and laser parameters, finite element method (FEM) is employed to compute the transient distribution of temperature at the interface of solder and substrates. The FEM-generated datasets are supplied to a neural network that predicts the IMC morphology through the quantified values of temperature dependent Jackson parameter (αJ). The numerical value of αJ predicted from neural network is validated with experimental IMC morphologies. The critical scan speed for the morphology transition between prismatic and scalloped IMC is estimated for each solder composition at a given power. Sn-0.7Cu having the largest critical scan speed at 30 W and Sn-3.5Ag alloy having the largest critical scan speed at input power values of 40 W and 50 W, thus possessing the greatest likelihood of forming prismatic interfacial IMC during laser soldering, can be inferred as most suitable SAC solders in applications exposed to shear loads.

Effect of nano-Ag3Sn additions on wettability, interfacial intermetallic growth and mechanical properties of Zn–30Sn–1Ge solders on Cu substrates

The influences of different addition (0, 0.2, 0.4, 0.6, 0.8, and 1.0 wt%) of Ag3Sn on the wettability, the morphology of interfacial intermetallic compounds (IMCs), and the mechanical properties of Zn30Sn1Ge (ZSG) solder on Cu substrate were investigated. The Ag3Sn nanoparticles with an average particle size of approximately 30–45 nm were dispersed in the α-Zn phase and IMC layer. The added Ag3Sn nanoparticles can remarkably improve the wettability of ZSG solder and inhibit the formation and growth of the interfacial IMCs between the nanocomposite solders and Cu substrates. The enhancement of wettability and inhibition of interfacial IMC increased with the increase of nano-Ag3Sn addition amount under low concentration. However, the excessive addition of Ag3Sn nanoparticles in ZSG solder will degrade the wettability and inhibition of interfacial IMCs. When the amount of Ag3Sn nanoparticles is 0.6 wt%, the ZSG–0.6Ag3Sn solders possess the best wettability. In addition, the ZSG–0.4Ag3Sn solder exhibits the most prominent effect in retarding the formation and growth of interfacial IMCs. Meanwhile, the addition of Ag3Sn nanoparticles increases the shear strength and Vickers hardness of the solder joint. When the amount of Ag3Sn nanoparticles is 0.4 wt%, the shear strength of the welded joint is increased by 13.3%. Moreover, the macroscopic hardness of ZSG–0.6Ag3Sn solder is 49.507 HV, which is 57.5% higher than that of the solder without added nanoparticles (31.38 HV). Results show that the addition of Ag3Sn nanoparticles plays an important role in the interfacial reaction and mechanical properties between the ZSG solder and Cu substrate.

Effect of doping Ni nanoparticles on microstructure evolution and shear behavior of Sn–3.0Ag–0.5Cu(SAC305)/Cu–2.0Be solder joints during reflowing

The Cu–2.0Be alloy is widely used as the substrate in aircraft electronic device, which has a potential trend to replace the pure Cu substrate. However, few studies have investigated the influence of the doped Ni nanoparticles on interfacial reaction between Cu–2.0Be substrate and the SAC305 solder during reflowing. In this study, the effect of Ni nanoparticles on wettability, microstructure evolution and mechanical behavior of SAC305/Cu–2.0Be solder joint was investigated. The results showed that a certain amount of Ni nanoparticles could increase the spreading area and mechanical property of the SAC305/Cu–2.0Be solder joint. The interfacial intermetallic compound (IMC) layer thickness could be reduced significantly by adding Ni nanoparticles. Moreover, the interfacial IMC layer thickness of SAC305/Cu–2.0Be solder joint was obviously thicker than that of SAC305-0.1Ni/Cu–2.0Be solder joint after different soldering times, which meant that a certain amount of Ni nanoparticles could hinder the IMC growth during soldering process. The growth kinetic of interfacial IMC layer after adding 0.1 wt% Ni nanoparticles showed that the growth coefficient of interfacial IMC layer changed from 1.21 µm/s0.28 to 1.82 µm/s0.32. In addition, the value of the shear strength of SAC305-0.1Ni/Cu–2.0Be solder joint was larger than that of SAC305/Cu–2.0Be solder joint with a typical mixture ductile and brittle fracture mode, which contributed to increasing the shear strength. Therefore, SAC305-0.1Ni solder alloy is a promising potential solder alloy in aircraft electronic device.

Dynamic Observation of Interfacial IMC Evolution and Fracture Mechanism of Sn2.5Ag0.7Cu0.1RE/Cu Lead-Free Solder Joints during Isothermal Aging.

Dynamic observation of the microstructure evolution of Sn2.5Ag0.7Cu0.1RE/Cu solder joints and the relationship between the interfacial intermetallic compound (IMC) and the mechanical properties of the solder joints were investigated during isothermal aging. The results showed that the original single scallop-type Cu6Sn5 IMC gradually evolved into a planar double-layer IMC consisting of Cu6Sn5 and Cu3Sn IMCs with isothermal aging. In particular, the Cu3Sn IMC grew towards the Cu substrate and the solder seam sides; growth toward the Cu substrate side was dominant during the isothermal aging process. The growth of Cu3Sn IMC depended on the accumulated time at a certain temperature, where the growth rate of Cu3Sn was higher than that of Cu6Sn5. Additionally, the growth of the interfacial IMC was mainly controlled by bulk diffusion mechanism, where the activation energies of Cu6Sn5 and Cu3Sn were 74.7 and 86.6 kJ/mol, respectively. The growth rate of Cu3Sn was slightly faster than that of Cu6Sn5 during isothermal aging. With increasing isothermal aging time, the shear strength of the solder joints decreased and showed a linear relationship with the thickness of Cu3Sn. The fracture mechanism of the solder joints changed from ductile fracture to brittle fracture, and the fracture pathway transferred from the solder seam to the interfacial IMC layer.

Intermetallics evolution and its reliability effects on micro-joints in flip chip assemblies

PurposeThis paper aims to assess precise correlations between intermetallic compounds (IMCs) microstructure evolutions and the reliability of micro-joints with a Cu/SAC305solder/Ni structure using thermal shock (TS) tests.Design/methodology/approachThis paper uses 200-µm pitch silicon flip chips with nickel (Ni) pads and stand-off height of approximately 60 µm, assembled on substrates with copper (Cu) pads. After assembly, the samples were subjected to air-to-air thermal shock testing from 55 to 125 per cent. The transfer time was less than 5 s, and the dwell time at each temperature extreme was 15 min. To investigate the microstructure evolution and crack growth, two samples were removed from the thermal shock chamber at 0, 400, 1,200, 2,000, 5,800 and 7,000 cycles.FindingsThe results showed that one (Cu, Ni)6Sn5/(Ni, Cu)3Sn4 dual-layer structure formed at the Ni pad interface of chip side dominates the micro-joints failure. This is because substantial (Ni, Cu)3Sn4 grain boundaries provide a preferential pathway for the catastrophic crack growth. Other IMCs microstructure evolutions that cause the prevalent joints failure as previously reported, i.e. thickened interfacial (Cu, Ni)6Sn5 and Ni3P layer, and coarsened IMCs inside the solder matrix, only contributed to the occurrence of fine cracks. Moreover, the typical interfacial IMCs spalling triggered by thermally induced stress did not take place in this study, showing a positive impact in the micro-joint reliability.Originality/valueAs sustained trends toward multi-functionality and miniaturization of microelectronic devices, the joints size is required to be constantly scaled down in advanced packages. This arises a fact that the reliability of small-size joints is more sensitive to the IMCs because of their high volume proportion and greatly complicated microstructure evolutions. This paper evaluated precise correlations between IMCs microstructure evolutions and the reliability of micro-joints with a Cu/SAC305solder/Ni structure using TS tests. It found that one (Cu, Ni)6Sn5/(Ni, Cu)3Sn4 dual-layer structure formed at the Ni pad interface dominate the micro-joints failure, whereas other IMCs microstructure evolutions that cause the prevalent joints failure exhibited nearly negligible effects.

Influence of energy ratio on dual–spot laser welded–brazed Al/steel butt joint

Al/steel butt joints were successfully obtained using a dual–spot laser welding–brazing process with different R (R = E Fe :E Al = 4:6, 5:5, and 6:4; E Fe and E Al represented the energy ratios of the laser near steel and Al, respectively). The molten filler metals wet and spread well along the front and back surfaces of the steel when R was 5:5 and 6:4, whereas an undercut occurred when R was 4:6. The interfacial intermetallic compound (IMC) along the brazing interface consisted of only thin–layered τ 5 –Fe 1.8 Al 7.2 Si when R was 5:5 and 4:6. The IMC had a greater thickness when R was 5:5 owing to its higher peak temperatures than when R was 4:6. A mixed IMC (θ–Fe(Al,Si) 3 +τ 5 –Fe 1.8 Al 7.2 Si) was newly formed in the top region of the brazing interface when R was 6:4. TEM observations revealed that two types of grains existed in θ–Fe(Al,Si) 3 : normal and twinned. Numerical simulations for the thermal cycles along the brazing interface indicated that the IMC thickness was determined by the interfacial peak temperature, while the IMC homogeneity was determined by the temperature gradient. The results of an experiment involving the tensile properties indicated that the highest average joint strength (193 MPa) and largest average fracture displacement (0.64 mm) when R was 5:5, owing to its satisfactory weld formation and reasonable IMC distribution.

Suppression of (Cu,Ni)6Sn5 Intermetallic Compound in Sn-0.7Cu-0.05Ni+1wt.TiO2 Solder Paste Composite Subjected to Isothermal Aging

This paper investigated the intermetallic compound (IMC) layer that formed in Sn-0.7Cu-0.05Ni+1wt.% TiO2 (SCNT) composite solder paste added with reinforcement (TiO2) particles. Besides, the growth of the IMC layer during subsequent aging at temperature of 75 °C, 125 °C and 150 °C also being studied. Scanning electron microscopy was used to observe the IMC growth and to measure the thickness of IMC layer. The interfacial IMC layer has been suppressed whereas the activation energy value of the composite solder paste was high (37.35 kJ/mol) which in turn improved the thermal stability of the IMC layer. Results also show the IMC formed at bulk solder microstructure of SCNT solder paste composite was refined. The presence of TiO2 particles has become the obstacle for the Cu atom diffusion from the substrate to the solder and Sn atom from the solder, thus, successful for the suppression of the IMC layer.

Development of Geopolymer Ceramic as a Potential Reinforcing Material in Solder Alloy: Short review

Nowadays, the consumption of lead-free solder has been widely used around the world since the utilization of SnPb solder has been banned and restricted by European Union. Variety of studies have been conducted by the researchers to find an alternative to replace the usage of SnPb such as SnCu, SAC, SnAg and etc. However, the development of plain lead-free solder was declared to provide low mechanical, thermal, and electrical properties in terms of interfacial intermetallic compound and wettability towards its solder joint compare to the traditionally monolithic SnPb solder alloy. Mostly, previous studies stated that addition of some additives such as ceramic particles (Si 3 N 4, TiO 2, SiC, NiO and etc) may improves the solder joint reliability. At the same time, no major studies were done using geopolymer ceramic as reinforcing agent in plain matrix alloy. Therefore, this paper reviews the fabrication process of multiple geopolymer-based ceramic such as fly ash, kaolin, and slag as reinforcement in solder alloy. The development process includes the processing method of geopolymer ceramic and the characterization of geopolymer ceramic as reinforcing material consist of; i) chemical composition, and ii) phase identification.

The effect of Ag on the growth of intermetallics at the interface of Sn5Zn/Cu interconnects

The reliability of electronic packages is primarily affected by the growth of the intermetallic compound (IMC) between the solder and the copper interconnection. It is therefore necessary to study the effect of element addition on the growth of the IMC interface with respect to an improvement in the package reliability. In this study, the influence of Ag on the growth of intermetallic compounds in the Sn5Zn solder/copper interconnection interface was investigated. The results revealed that in comparison with Sn5Zn/Cu, the interfacial IMC thickness decreased initially and then increased in accordance with an increase in the doping amount of alloying elements in the solder. Further, it was observed that the doping of the alloying element (Ag) can significantly reduce the IMC growth rate at the interface. Compared with the Cu5Zn8 unit cell formation energy (-0.632eV), one dopant atom and two dopant atoms of Ag can reduce the formation energy of a Cu5Zn8-based unit cell to the minimum values of -0.636 eV and –0.640 eV, respectively; consequently, the stability is increased. The maximum diffusion activation energies of Cu atoms and Zn atoms in a Cu5Zn8-based unit cell are 3.419 eV and 1.692 eV, which increase to 3.512 eV and 1.971 eV, respectively, after doping with Ag.

Inhibition of intermetallic compounds growth at Sn–58Bi/Cu interface bearing CuZnAl memory particles (2–6 μm)

In total, 0.5 wt% CuZnAl memory particles with the diameters (2–6 μm) were added into Sn–58Bi solder in order to enhance the properties of solder joints in electronic packaging. The interface reaction and the growth kinetics of intermetallic compounds at Sn–58Bi/Cu interface and Sn–58Bi–0.5CuZnAl/Cu interface were studied systematically at 250 °C, 230 °C and 210 °C, the results indicate that the growth rate of intermetallic compounds (IMC) at both interfaces at 250 °C was higher than that at 230 °C, the addition of CuZnAl memory particles can reduce the diffusion coefficient of interfacial IMC, and however, at 210 °C the inhibition effect of CuZnAl particles was so small. Based on the transient liquid phase bonding, it is demonstrated that Cu/Sn–58Bi–0.5CuZnAl/Cu-bonded joints can achieve the chip stacking in 3D packaging with 10 μm thickness with obvious superiority.

Microstructure-based modeling of IMC layer thickness effect on tensile behavior of Cu/Al clad strip

A microstructure-based model is proposed for quantitative estimation of tensile mechanical property of Cu/Al clad strips. In the proposed model, the fracture criterion for matrix Cu and Al, interface intermetallic compounds (IMCs) and interface between matrix and IMCs are established and incorporated. The effect of IMCs thickness and strip thickness on tensile behavior of Cu/Al strip was studied quantitatively using the proposed model. And a new dimensionless parameter w/t is also proposed to be a control index for tensile mechanical property of Cu/Al clad strips. And a critical value of w/t which is defined to be 0.025 in this study is found to be important in controlling mechanical property of Cu/Al strip with a thickness less than 0.5 mm. The potential application of the proposed model and parameter is also discussed for annealing process optimization and mechanical property control of 0.12 mm thick Cu/Al clad strips.

Ultrasonic spot welding of Al/Mg alloys: A state-of-the-art review

Lightweight materials like aluminum (Al) and magnesium (Mg) alloys are extensively used in automotive industries. The welding between these dissimilar alloys is inevitably essential to produce high-quality and reliable joints. High power ultrasonic metal welding (USMW) technology, which mimics the properties of solid-state bonding, offers a potential solution in welding of these difficult-to-weld materials. The superior characteristics of this welding process, such as low heat input, less weld time, and high production efficiency, reduce the tendency to form brittle intermetallic compounds (IMCs) and enhance the joint strength of Al/Mg dissimilar joints. The current study is focused on obtaining favorable performance measures during the USMW of dissimilar Al/Mg alloys through controlling the dominant input factors. The tensile shear (TS) and T-peel (TP) failure load firstly increased up to a specific limit and decreased further with the rise in weld energy. The compared fatigue strength results of Al/Mg dissimilar joints with other bonding techniques provides an insight into the fatigue failure mechanism. The mechanism behind the weld formation is discussed based on the fracture surface and interface morphologies, microstructure evolution, and IMC formation along the weld interface. At higher weld energy, the elevated interfacial temperature promoted the formation of Mg17Al12, Al3Mg2 IMCs and accelerated the elemental diffusion at the weld interface. Mechanical interlocking and dynamic recrystallization at the periphery of the weld interface due to severe shear deformation results in refining the grain structure. However, this detrimental interfacial reaction can be reduced by introducing a coating on the Mg surface. Thus, the process engineers can now adopt this technique to get best combinations of input parameters in USMW problems, and there is no need to depend on the manufacturer’s handbook.

Effect of Aging Temperature on the Microstructure and Shear Strength of SAC0307-0.1Ni Lead-Free Solders in Copper Joints

This paper presents an investigation of the effects of aging temperature on the microstructure and shear strength of SAC0307-0.1Ni/Cu solder joints. Single-overlap shear solder joints were aged for 1 h at 80, 130, and 180°C. The microstructure of the interface between the solder and the Cu substrate contained phase of the intermetallic compounds (IMCs) (Cu,Ni)6Sn5 formed along the interface. The shape of scallop-like (Cu,Ni)6Sn5 IMCs changed to the long dendrite and grew larger at the interface of solder joints after increased aging temperature. In addition, a phase of particle-like Ag3Sn IMCs was formed in the solder matrix. The growth of the interfacial IMC layer in the solder joints increased with increasing the aging temperature. The thickness of this layer was controlled by diffusion mechanism. The shear strength of the as-reflowed solder joints was greater than that of the aged solder joints, and the shear strength of all the aged solder joints decreased with increasing the aging temperatures. Therefore, the aging temperature mainly affected the thickness of the interfacial layer of IMCs and the shear strength of the solder joints.

Influence of Interfacial Inter-metallic Compounds on the Electrical Characterization of Cu/Al Joints Produced by Flash Welding and Diffusion Brazing

Abstract The aim of this study was to clarify the influence of inter-metallic compounds (IMCs) on the electrical conductivity of Cu/Al joint. The longitudinal resistance and the lateral current distribution at flash welded and diffusion brazed Cu/Al joint interfaces were investigated using four-point method and conductive atomic force microscopy, respectively. A 2μm Cu9Al4/CuAl2 layer was formed in both joints. The IMCs layer was homogenous and the current distribution interface was planar at diffusion brazed joint. However, the IMCs layer was discontinuous and the current distribution interface was non-planar at flash welded joint. After heat treatment at 350°C for 500h, the thickness of interfacial layer was increased to 50μm. CuAl and a short crack were newly formed in the diffusion brazed joint. CuAl, (Cu,Al)xOy and a long crack were newly formed in the flash welded joint. A multilayer current distribution was found at both heat treated joints. The resistivity of all Cu/Al joints was higher than that of copper and lower than that of aluminum. The resistivity of diffusion brazed joint was the lowest, which was lower than the theoretical value. The resistivity of the heat treated flash welded joint was the highest among all the joints.

Effects of laser power on the interfacial intermetallic compounds and mechanical properties of dual-spot laser welded–brazed Ti/Al butt joint

A sound Ti/Al butt joint was successfully obtained by dual-spot laser welding–brazing with a Al-12Si wire as the filler. The influence of laser power on the weld appearance, microstructure of the interfacial intermetallic compounds (IMC), and tensile strength of joints was investigated. With an increase in laser power, the thickness of IMC layer also increased and the morphology of IMC layer changed from a cellular-shape to a serrated-shape, and finally to a club-shape. The microstructure of the interface IMC comprised a brazed zone in which Ti(Al, Si)3 was dominant and the microstructure at the Ti/Ti(Al, Si)3 interface was composed of nano-sized granular Ti5Si3, and Ti7Al5Si12. The highest tensile strength of the joints could reach up 75% of that of the Al base metal. The inhomogeneous IMC layer at the brazing interface caused a decrease in the tensile strength of joints and induced a deflection of fracture path during the tensile process.

Effect of interfacial intermetallic compounds evolution on the mechanical response and fracture of layered Ti/Cu/Ti clad materials

Three-layered Ti/Cu/Ti clad materials fabricated by cold roll-bonding process and in the following underwent heat treatment cycles. Microstructure evolution and mechanical properties of as-rolled and annealed samples studied by SEM, XRD, microhardness and tensile examinations. According to the results, as-rolled and treated samples contained several IMCs at their Ti/Cu interfaces while thickness of the reaction layer enhanced noticeably by annealing. Examined average IMC layers' thickness were 1.34, 1.61, 2.39 and 5.39 μm, for as-rolled, 300, 500 and 700 °C annealed specimens, respectively, consisting four different phases of CuTi2, CuTi, Cu3Ti2, and Cu4Ti. However, continuity, uniformity and thickness variation as well as the growth rate during treating for each layer was distinct. From SEM and XRD results that acquired from separated surfaces, major debonding occurred at CuTi2/CuTi and CuTi/Cu3Ti2 interfaces suggesting that bonding strength for these IMC layers were weaker than those for the other IMC/IMC interfaces and the parent-metal/IMCs. The stress-strain curves demonstrated that the strength decreased and subsequently ductility improved by annealing up to 700 °C. Meanwhile, SEM analyses revealed that cracks within IMC layers during tensile deformation emerged only in specimen annealed at 700 °C; however, it did not lead debonding or layer separation similar to other clad metals reported in literature. By fractography, it is indicated that dimples formed in the whole fracture surface of as-rolled and annealed specimens at 300 and 500 °C. For the 700 °C annealed specimen, however fracture mode was ductile, dimples hardly noticed since the cracks propagation and extension path was along the weak IMC interfaces. In addition, this sample unlike others exhibited limited necking extension before failure. According to the obtained results and as the current research's novelty, it is claimable that intermetallics formed in Ti/Cu clad materials would be more ductile comparing with other compounds reported for talented cladding metals in literature.

Comparative study on the hourglass-like joint of electroplated Sn-base solder reinforced by adding Ag3Sn nanoparticles and Ag micro-alloying elements

In this work, two types of tin (Sn)-based solder bumps reinforced by Ag3Sn nanoparticles (nano-Ag3Sn), and Ag microalloying elements were successfully deposited on copper-clad laminates (CCL) by electroplating. Hourglass-shaped Sn-based solder joints were formed by precise control of the solder volume and the joint height during the reflowing process in solder bonding. Results show that when shaping the solder joints during solder reflowing, Ag3Sn nanoparticles would uniformly disperse in the Sn-nano-Ag3Sn solder joint, while microalloying Ag preferentially binds to Sn elements enriching at Sn-Ag solder/CCL interfaces and producing large interfacial intermetallic compounds (IMCs). After the solder reflowing, the nano-Ag3Sn will redistribute in the solder joints, where the nano-Ag3Sn adjacent to the solder/CCL interface would advance and adhere to the IMC surface. Compared with the solder joints containing Ag microalloying elements, nano-Ag3Sn can aggregate on the surface IMC surfaces and hinder the interdiffusion of Sn and Cu ions across the solder/CCL interface. Mechanical shear strength tests of solder joints illustrate the enhancement of mechanical robustness of nano- Ag3Sn reinforced solder, which inherently correlates to the absorption of nano- Ag3Sn at the interfaces. Thus, we conclude that the nano-Ag3Sn will inhibit the overgrowth of the interfacial IMC, specifically Cu6Sn5, which ultimately improves the mechanical strength and interconnect reliability of the hourglass-shaped solder joints.

Interlayer Material Design Reducing Transient Liquid Phase Bonding Time

Power semiconductors require a large bonding area for die attachment. For this purpose, transient liquid phase bonding (TLPB) was applied using fabricated interlayers, namely Sn–3Cu and Sn–10Cu, to study the intermetallic compound (IMC) formation, and the results were compared with those obtained with a pure-Sn interlayer. The Sn–3Cu and Sn–10Cu interlayers exhibited primary IMC fraction of 0.06 and 0.24, respectively, before the TLPB. For a Cu/interlayer/Cu sandwich structure, the TLPB was applied at 250 °C over various time periods (1–4 h). A reduction in the bonding time was more significant for a Sn–10Cu interlayer with a larger amount of primary IMCs than for the Sn–3Cu interlayer. The time exponent of the IMC fraction with respect to the bonding time was approximately 0.3 for all interlayers. This implies that the IMC growth mechanism is governed by a liquid channel or wet grain boundary diffusion. The nearly constant fraction and increasing size of the primary IMCs produced during the TLPB indicate that the primary IMCs coalesced during this process. The primary IMCs preferentially coalesced with the interface IMCs produced during the TLPB when they had the same crystalline orientation.

Influence of cooling conditions on the interfacial Cu6Sn5 intermetallic compound in Sn-37Pb/Cu solder joints during reflow

Despite a shift to Pb-free solders in the majority of electronic assemblies, Pb-containing solders are still used in a variety of applications. Recent research has revealed the complexities of the intermetallic Cu6Sn5 in terms of its crystal structure and stability when present as the reaction product between Pb-free solders and common substrates. In light of these findings, the effect of multiple reflow cycles with different cooling conditions on the microstructure of the interfacial Cu6Sn5 intermetallic compound (IMC) between Sn-Pb solders and Cu substrates was re- examined. For this purpose, the Sn-37Pb (in wt.%) solder was reflowed on a Cu substrate at a temperature of around 240 °C and cooled at a rate of around 30 °C/min under each of two conditions; (i) direct-cooling to room temperature, and (ii) interrupted-cooling with extended isothermal holding periods of 30 and 180 seconds at 140 °C. This second condition was chosen to encourage the polymorphic transformation that occurs in the Cu6Sn5 (at an equilibrium temperature of 186 °C) at a temperature which minimises the stresses involved. Smaller cracks and a thinner interfacial IMC layer were observed in the solder joints that were reflowed repeatedly with the interrupted-cooling conditions. However, despite the higher number of cracks in the samples undergoing conventional reflow, the shear strength was not significantly affected.

Effect of addition of CuZnAl particle on the properties of Sn solder joint

Abstract The effects of minor addition micron of CuZnAl particles on the melting temperature, wettability, mechanical strength and interfacial reaction in Sn/Cu solder joints were investigated. The microstructure evolution of the solder joints was observed using SEM. When the CuZnAl particles were added, the melting temperature of the solder joints was slightly reduced. The wettability and shear strength were significantly enhanced. When the content of CuZnAl particles was 0.5 wt.%, the properties of the Sn solder joints were optimized. Cu/Sn-0.5CuZnAl/Cu transient liquid phase bonding was carried out by using a composite solder having a content of 0.5 wt.%. The addition of CuZnAl particles inhibited the growth of interfacial intermetallic compounds and microvoids in Cu/Sn/Cu solder joints. The grain orientation of Cu6Sn5 also became more random.