Abstract In this article, the effect of voids on thermomechanically-induced failure in the lead-free solder interconnections of power amplifier (PA) modules is investigated. The interconnection of interest is between the module's flange and substrate (baseplate) initially having a large contact area, and whose cracking has strong detrimental effects on the RF performance and reliability of the PA. PA modules were attached onto baseplates with lead-free SAC305 solder and put to a thermal cycling test (TCT) in the 15 °C to 95 °C range. X-ray imaging was used to characterize the number of voids in interconnections after reflow soldering. The cross-sections of the pristine reflow-soldered and tested interconnections were inspected with cross-polarized light microscopy to reveal the shapes of the voids and crack paths. It was noted that the voids forming in interconnections during the final stages of the reflow process take an elliptical shape, leaning towards the module's outer edge, due to differences in the thermal expansions of the module and baseplate. During the TCT, high thermomechanical stresses caused localized recrystallization of the as-soldered SAC matrix in the vicinity of the elliptical voids. Finally, creep related intergranular cracks formed in these recrystallized areas. Anand's viscoplastic model was used to model the void formation and the effect of the formed voids on crack evolution in solder. Simulations of the high creep energy of the elliptical, tilted voids and their correlation with the recrystallization behavior of the SAC305 interconnections were consistent with the observed creep related failures. Confirmed by simulations, these voids are detrimental to the reliability of solder interconnection because the creep strain is strongly localized to the sharp curvatures of the elliptic void.

中文翻译：

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空洞对功率模块无铅Sn3Ag0.5Cu互连热机械开裂的影响

摘要 在本文中，研究了空洞对功率放大器 (PA) 模块无铅焊接互连中热机械引起的故障的影响。感兴趣的互连是模块的法兰和基板（基板）之间最初具有较大的接触面积，其开裂对 PA 的 RF 性能和可靠性有很大的不利影响。PA 模块使用无铅 SAC305 焊料连接到基板上，并在 15 °C 至 95 °C 范围内进行热循环测试 (TCT)。X 射线成像用于表征回流焊接后互连中的空隙数量。使用交叉偏振光显微镜检查原始回流焊接和测试互连的横截面，以揭示空隙和裂纹路径的形状。值得注意的是，由于模块和基板的热膨胀差异，在回流工艺的最后阶段，互连中形成的空隙呈椭圆形，倾向于模块的外边缘。在 TCT 期间，高热机械应力导致在椭圆空洞附近焊接时的 SAC 基体发生局部再结晶。最后，在这些再结晶区域形成蠕变相关的晶间裂纹。Anand 的粘塑性模型用于模拟空洞的形成以及所形成的空洞对焊料裂纹演变的影响。椭圆形倾斜空隙的高蠕变能量及其与 SAC305 互连再结晶行为的相关性的模拟与观察到的蠕变相关故障一致。经仿真证实，