We modeled flexible microelectronic systems, in which a thinned silicon die is flip-chip bonded to a flexible substrate, and analyzed the stress and strain distribution generated during twisting deformation. Because of the presence of the rigid silicon die, the strain distribution of the system model was significantly different from that of the substrate model. Unlike the substrate model, there is no significant difference in the von Mises strain according to the position in both the molding layer and the substrate in the system model. Therefore, the results of modeling or testing only flexible substrate cannot be directly applied to predict the behavior of flexible microelectronic systems. The copper bumps revealed stress above the ultimate strength as well as the yield strength. Therefore, the copper bump would be the most mechanically weak component in the operation of the face-down flexible microelectronic system during twisting. By replacing copper bumps with polymer bumps, the maximum stress in the bumps can be significantly reduced from 282 to 47 MPa, and the maximum mechanically safe twisting angle was also improved from approximately 40° to 80°. Therefore, in flexible electronic systems where twisting deformation is applied, polymer bumps are a better bonding method than the conventional copper bumps.

中文翻译：

---

扭转应力作用下柔性微电子系统的力学分析

我们模拟了柔性微电子系统，其中减薄的硅芯片倒装芯片键合到柔性基板上，并分析了扭曲变形过程中产生的应力和应变分布。由于刚性硅芯片的存在，系统模型的应变分布与衬底模型的应变分布有显着差异。与衬底模型不同，根据系统模型中模制层和衬底的位置，von Mises 应变没有显着差异。因此，仅对柔性基板进行建模或测试的结果不能直接应用于预测柔性微电子系统的行为。铜凸点显示出高于极限强度和屈服强度的应力。所以，在扭转期间，在面向下柔性微电子系统的操作中，铜凸点将是机械上最弱的部件。通过用聚合物凸点代替铜凸点，凸点中的最大应力可以从 282 MPa 显着降低到 47 MPa，并且最大机械安全扭转角也从大约 40° 提高到 80°。因此，在应用扭曲变形的柔性电子系统中，聚合物凸点是比传统铜凸点更好的键合方法。