WLCSP中微焊球结构尺寸对其热应力的影响

晶圆级芯片尺寸封装(WLCSP)微焊球结构尺寸对其热机械可靠性有重要的影响。通过二维有限元模拟筛选出对WLCSP微焊球及其凸点下金属层(UBM)中热应力影响显著的参数,采用完全因子实验和多因子方差统计分析定量评估各种因子影响的显著性,最后建立三维模型,用子模型技术研究关键尺寸因子对热应力变化的影响。研究发现,焊球半径是影响焊球热应力的最关键尺寸因子,电镀铜开口和铜焊盘厚度对焊球热应力的影响也较显著;钝化层开口和焊球半径是影响UBM热应力的最关键尺寸因子。随着焊球半径增大,焊球热应力减小。

Effect of Micro-Solder Joint Structure Parameters on Its Thermal Stress in WLCSP

The effect of micro-solder joint structure parameters on its thermal-mechanical reliability is important in wafer level chip scale packaging(WLCSP).The structure parameters which have a significant effect on thermal stress of the solder joint and under bump metal(UBM) were obtained by a 2D finite element simulation.Furthermore,full-factorial experiment and analysis of variance(ANOVA) were used to exhibit quantitative sensitivity information of structure parameters.Finally,the 3D submodel simulation was carried out to show the effect of a critical parameter on thermal stress,which eliminated the 2D assumption.The results revealed that the solder joint radius is a critical factor for thermal stress of solder joint,electroplating copper dimension and copper pad thickness have significant influence on thermal stress of solder joint;The passivation diameter and solder joint radius are critical factors for thermal stress of UBM.In addition,the thermal stress of solder joint decreased when solder joint radius increased.