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The relationship between Ce content/CeSn sizes and the whiskers growth is newly reported systematically. The whiskers growth can be observed in the surface of bulk CeSn particles, the rate of whisker growth was significantly slowed with Ce content lower than 0.1 wt%. At higher concentration of Ce, whisker growth rate becomes higher and noticeable. It is thought that the higher Ce chemical potential for oxidation provides a path for the mechanism of whisker growth. With all the other benefits of Ce addition, the potential to promote whisker growth indicate that only dilute concentration of Ce can be tolerated in SnAgCu alloys without whiskering effect. The results demonstrated that the trace amount of Ce can be utilized as additive into SnAgCu solder in microelectronic industry. [ABSTRACT FROM AUTHOR]

With the addition of Zn, Co and Fe, the microstructures and properties of SnAgCu solders can be improved obviously, the constitutive response of SnAgCu solder bearing 0.8%Zn, 0.8%Co and 0.8%Fe was studied under uniaxial tension. Anand model was used to represent the inelastic deformation behavior of the lead-free solders. The material parameters of the constitutive relations for SnAgCu(Zn,Co, Fe) solders were determined from separated constitutive relations and experimental results. Combining the model, finite element analysis (FEA) was used to study the thermally induced inelastic deformation and the stress-strain response of the solder joints in wafer-level chip scale packages (WLCSP) mounted on printed circuit boards (PCB). And it is found that the addition of Zn, Co and Fe can enhance the fatigue life of SnAgCu solder joint, the superiority can be found for the addition of Fe among the three elements. [ABSTRACT FROM AUTHOR]

Growth kinetics of intermetallic compound (IMC) layers formed between SnAgCu solder for reflow soldering and Cu substrate by solid state isothermal aging were investigated at temperatures between 100 and 140 °C. For the aged samples, two distinct layers of IMCs of the type CuSn and CuSn were identified with the later adjacent to the copper substrate. In the as-soldered samples, only a single layer of interfacial CuSn type IMC was formed. Moreover, the apparent activation energies were 96.75 kJ/mol (total IMC), 85.98 kJ/mol (CuSn IMC) and 105.92 kJ/mol (CuSn IMC), respectively. [ABSTRACT FROM AUTHOR]

Abstract: With the addition of 0.03wt% rare earth Ce, in our previous works, the properties of SnAgCu solder were enhanced obviously. Based on the Garofalo–Arrhenius creep constitutive model, finite element method was used to simulate the stress–strain response during thermal cycle loading, and combined with the fatigue life prediction models, the fatigue life of SnAgCu/SnAgCuCe solder joints was calculated respectively, which can demonstrate the effect of the rare earth Ce on the fatigue life of SnAgCu solder joints. The results indicated that the maximum stress–strain can be found on the top surface of the corner solder joint, and the warpage of the PCB substrate occurred during thermal cycle loading. The trends obtained from modeling results have a good agreement with the experimental data reported in the literature for WLCSP devices. In addition, the stress–strain of SnAgCuCe solder joints is lower than that of SnAgCu solder joints. The thermal fatigue lives of solder joints calculated based on the creep model and creep strain energy density model show that the fatigue life of SnAgCuCe solder joints is higher than the SnAgCu solder joints. The fatigue life of SnAgCuCe solder joints can be enhanced significantly with the addition of Ce, is 30.2% higher than that of SnAgCu solder joints, which can be attributed to the CeSn3 particles formed resisting the motion of dislocation; moreover, the refinement of microstructure and the IMC sizes also contribute to the enhancement of fatigue life, which elucidates that SnAgCuCe solder can be utilized in electronic industry with high reliability replacing the SnAgCu solder. [Copyright &y& Elsevier]

Abstract: Lead free solder alloys for electronic assembly is being driven by environmental and health concerns regarding toxicity of lead and, more importantly, by the perceived economic advantage of marketing “green” products. Of the currently available lead free solders, SnAg has the greatest potential. In this solder, the Ag3Sn compound is distributed in a eutectic network throughout the β-Sn matrix and these results represent mechanical strength. In order to further improve the microstructures and properties of SnAg-based alloys, alloying elements such as rare earth, Zn, In, P, Cu, Ni and particles such as ZrO2, POSS are selected to meet the requirement of high reliability of high-density electronics devices. For SnAg solder bearing rare earth (Ce and La), the creep-rupture life of solder joints can be remarkably increased up to four times more than that of the original SnAg solder joints at room temperature, meanwhile, rare earths can dramatically reduce the thickness of IMCs layer at solder/pad interfaces and also refine the microstructure of the alloy which results in the enhancement of mechanical properties of the SnAg solder. Moreover, the addition of ZrO2 nanoparticles significantly refined the size of Ag3Sn due to the adsorption effect of the ZrO2 nanoparticles. This paper summarizes the effects of alloying elements and particles on the wettability, mechanical properties, creep behavior, microstructures, etc. of SnAg-based lead free solder alloys. [Copyright &y& Elsevier]