Abnormal Shear Performance of Microscale Ball Grid Array Structure Cu/Sn–3.0Ag–0.5Cu/Cu Solder Joints with Increasing Current Density

The shear performance and fracture behavior of microscale ball grid array structure Cu/Sn–3.0Ag–0.5Cu/Cu solder joints with increasing electric current density (from 1.0 × 103 to 6.0 × 103 A/cm2) at various test temperatures (25 °C, 55 °C, 85 °C, 115 °C, 145 °C, and 175 °C) were investigated systematically. Shear strength increases initially, then decreases with increasing current density at a test temperature of no more than 85 °C; the enhancement effect of current stressing on shear strength decreases and finally diminishes with increasing test temperatures. These changes are mainly due to the counteraction of the athermal effect of current stressing and Joule heating. After decoupling and quantifying the contribution of the athermal effect to the shear strength of solder joints, the results show that the influence of the athermal effect presents a transition from an enhancement state to a deterioration state with increasing current density, and the critical current density for the transition decreases with increasing test temperatures. Joule heating is always in a deterioration state on the shear strength of solder joints, which gradually becomes the dominant factor with increasing test temperatures and current density. In addition, the fracture location changes from the solder matrix to the interface between the solder matrix and the intermetallic compound (IMC) layer (the solder/IMC layer interface) with increasing current density, showing a ductile-to-brittle transition. The interfacial fracture is triggered by current crowding at the groove of the IMC layer and driven by mismatch strain at the solder/IMC layer interface, and the critical current density for the occurrence of interfacial fracture decreases with increasing test temperatures.

Effects of Isothermal Aging on Interfacial Microstructure and Shear Properties of Sn-4.5Sb-3.5Bi-0.1Ag Soldering with ENIG and ENEPIG Substrates

Sn–Sb system solders and ENIG/ENEPIG surface finish layers are commonly used in electronic products. To illustrate the thermal reliability evaluation of such solder joints, we studied the interfacial microstructure and shear properties of Sn-4.5Sb-3.5Bi-0.1Ag/ENIG and Sn-4.5Sb-3.5Bi-0.1Ag/ENEPIG solder joints after aging at 150 °C for 250, 500 and 1000 h. The results show that the intermetallic compound of Sn-4.5Sb-3.5Bi-0.1Ag/ENIG interface was more continuous and uniform compared with that of Sn-4.5Sb-3.5Bi-0.1Ag/ENEPIG interface after reflow. The thickness of the interfacial intermetallic compounds of the former was significantly thinner than that of the latter before and after aging. With extension of aging time, the former interface was stable, while obvious voids appeared at the interface of the latter after 500 h aging and significant fracture occurred after 1000 h aging. The shear tests proved that shear strength of solder joints decreased with increasing aging time. For the Sn-4.5Sb-3.5Bi-0.1Ag/ENEPIG joint after 1000 h aging, the fracture mode is ductile-brittle mixed type, which means fracture could occur at the solder matrix or the solder/IMC interface. For other samples of these two types of joints, ductile fracture occurred inside of the solder. The Sn-4.5Sb-3.5Bi-0.1Ag/ENIG solder joint was thermally more reliable than Sn-4.5Sb-3.5Bi-0.1Ag/ENEPIG.

Ultrasound-Assisted Surface Modifications on Ceramic Reinforcement for Lead-Free Composite Solders : Short Review

The purpose of this paper is to review and examine the effect of ultrasound-assisted surface modifications of ceramic reinforcements on the properties of lead-free solders. The discussion will highlight the fundamental understanding, main parameters, configurations, and recent surface-modified ceramic reinforced composite lead-free solder developments. The review also identified and summarized the advantages, current trends, and significant findings in this field. The ultrasound-assisted surface modification was found to provide a crucial improvement on the wettability properties of molten solders as the matrix phase on the ceramic reinforcement. Further, the excellent distribution of ceramic reinforcement in solder matrix was also seen after the surface modification process. This has led to significant improvements in mechanical properties such as hardness and strength. The pinning of dislocation movement was seen as the reason for improving the mechanical properties. This positive impact in enhancing the ceramic reinforcement-solder interfacial reaction allows more explicit future research directions and opportunities for composite solder applications.

Interfacial reaction between Ni particle reinforcements and liquid Sn-based eutectic solders

Purpose This paper aims to derive a model of growth kinetics of the intermetallic compound (IMC) layer formed in the reaction between liquid Sn-based solders and Ni particle reinforcements and to compare with the experimental data to verify the effects of Sn concentration and alloying element. Design/methodology/approach A composite solder was manufactured by mechanically introducing Ni particle reinforcements into a solder matrix. The effect of the non-reactive alloying elements, Ag, Pb and Bi, on the growth kinetics of the IMC formed between liquid Sn-based eutectic solders and Ni particles, reacting this composite solder at 250°C–280°C was studied. Findings Experimental results showed that only the IMC Ni3Sn4 was present as a reaction product. Using the diffusion-controlled reaction mechanism, a kinetic equation quantifying both Sn concentration and alloying element effects was derived and verified by comparing the kinetic data obtained using four different solders with different concentrations of Sn and the alloying elements. Originality/value The similarity between the activation energies of these four solders confirms that the diffusion of Sn atoms through the IMC is the rate-controlling step. Besides, the kinetic values are independent of the geometry of Ni, whether spherical particle or flat substrate.

Electrical resistivity of Sn–3.0Ag–0.5Cu solder joint with the incorporation of carbon nanotubes

The main objective of this study is to investigate the electrical properties of Sn–3.0Ag–0.5Cu solder joint with the incorporation of carbon nanotube instead of solder bulk. Sn–3.0Ag–0.5Cu solder paste with the incorporation of carbon nanotube up to 0.04 wt% was fabricated by using mechanical mixing method. Fabricated solder pastes were then soldered on printed circuit board via reflow soldering at 260°C peak temperature. Electrical resistivity of Sn–3.0Ag–0.5Cu-carbon nanotube solder joints was measured by the four-point probe method at room temperature. Microstructure properties were observed by optical microscope and field emission scanning electron microscope. Electrical resistivity of Sn–3.0Ag–0.5Cu solder joint was found to increase with the incorporation carbon nanotube up to 0.03 wt% and slightly decrease at 0.04 wt%. Incorporation of carbon nanotube in the solder matrix apparently changes the microstructure of Sn–Ag–Cu solder alloys. Microstructural observation found that electrical resistivity correlated with the distribution area of eutectic phase in the solder matrix due to the existence of carbon nanotube. It was revealed that eutectic phase area increases with the increasing of carbon nanotube wt% up to 0.03 and then slightly decreases at the incorporation of 0.04 wt% carbon nanotube as parallel with the trend of electrical resistivity values.

Effect of Cr Addition on Microstructure and Properties of AuGa Solder

In order to meet the service requirements of electronic devices working at 300 °C in the fields of energy resource prospecting and space exploration, Cr element was added to modify AuGa solder to improve its high-temperature performance. The results showed that the addition of 0.3 wt.% Cr element reduced the loss of Ga element in the smelting and casting process, and effectively improved the problem of the inhomogeneous microstructure of the solder matrix. On the basis of maintaining the good wettability of the solder, the addition of trace chromium effectively restrains the excessive flux of the solder, and the presence of chromium improves the oxidation resistance of the solder. Furthermore, Cr element optimized the interface morphology and improved the mechanical properties of the solder joint. The shear strength of the AuGa-0.3Cr/Ni joint was 87.2 MPa, which was 13.1% higher than that of the joint without Cr element. After 240 h of aging, the shear strength of the AuGa-0.3Cr joint was still the peak value at 84.1 MPa, which was 16.3% higher than that of the AuGa joint.

Shear Strength and Aging Characteristics of Sn-3.0Ag-0.5Cu/Cu Solder Joint Reinforced with ZrO2 Nanoparticles

This study investigates the shear strength and aging characteristics of Sn-3.0Ag-0.5Cu (SAC 305)/Cu joints by the addition of ZrO2 nanoparticles (NPs) having two different particle size: 5–15 nm (ZrO2A) and 70–90 nm (ZrO2B). Nanocomposite pastes were fabricated by mechanically mixing ZrO2 NPs and the solder paste. ZrO2 NPs decreased the β-Sn grain size and Ag3Sn intermetallic compound (IMC) in the matrix and reduced the Cu6Sn5 IMC thickness at the interface of lap shear SAC 305/Cu joints. The effect is pronounced for ZrO2A NPs added solder joint. The solder joints were isothermally aged at 175 °C for 24, 48, 144 and 256 h. NPs decreased the diffusion coefficient from 1.74 × 10–16 m/s to 3.83 × 10–17 m/s and 4.99 × 10–17 m/s for ZrO2A and ZrO2B NPs added SAC 305/Cu joints respectively. The shear strength of the solder joints decreased with the aging time due to an increase in the thickness of interfacial IMC and coarsening of Ag3Sn in the solder. However, higher shear strength exhibited by SAC 305-ZrO2A/Cu joints was attributed to the fine Ag3Sn IMC’s dispersed in the solder matrix. Fracture analysis of SAC 305-ZrO2A/Cu joints displayed mixed solder/IMC mode upon 256 h of aging.