热循环与晶界对铜锡镀层锡须生长影响的分子动力学模拟

Molecular Dynamics Simulation of Effects of Thermal Cycling and Grain Boundaries on the Growth of Whiskers in Copper-tin Coatings

随着微电子封装全面走向无铅化,且日益趋向极小化、便携化和多功能化,锡须生长严重威胁电子产品服役的可靠性和安全性。本文以铜锡双镀层的锡须生长过程为研究对象,创建有晶界和无晶界分子动力学模型,并在多物理场(热-力)耦合下进行热循环与晶界对锡须生长过程的模拟,探究外力、不同热循环次数(0、5、10次)和晶界等因素对锡须生长的影响及部分内部应力的变化规律。结果表明:在一定范围内,热循环次数增多会促进锡须生长,且在有晶界的模型中,锡须生长速率更大;锡须底部的内应力达到最大,形成应力梯度促进锡须生长;外加载荷会增大铜锡双镀层的内部应力,内部应力积累的时间也缩短1.5 ns左右,从而加快锡须生长速率。

With the comprehensive trend of microelectronic packaging towards lead-free,it is becoming increasingly miniaturized,portable,and multifunctional.The growth of tin whiskers poses a serious threat to the reliability and safety of electronic products in service.In this study,the molecular dynamics models with and without grain boundaries were built to explore the growth process of tin whisker of copper-tin double coating.The growth process of tin whisker was simulated by thermal cycling and grain boundaries under multi-physical field(thermo-mechanical)coupling.The effects of external force,different thermal cycles(0,5,10)and grain boundaries on the growth of tin whiskers and the variation of internal stresses were investigated.The results show that in a certain range,the increase of thermal cycles will promote the growth of tin whisker,and the growth rate of tin whisker is faster in the model with grain boundary.The internal stress at the bottom of tin whisker reaches the maximum,forming a stress gradient to promote the growth of tin whisker.The external load will increase the internal stress of copper-tin double coating,and the accumulation time of internal stress will be shortened by about 1.5 ns,accelerating the growth rate of tin whiskers.