热冲击条件下倒装封装焊点的裂纹生长研究

Study on Crack Growth of Flip Chip Solder Joints under Thermal Shock

【目的】研究热冲击条件下倒装芯片封装焊点裂纹的萌生和扩展。【方法】采用有限元模拟法分析封装体的形变,获取累积应变能密度及应力分布与变化情况,同时结合试验结果进行验证。【结果】在热冲击条件下,裂纹会先出现在焊点的最外侧且在焊盘与焊料的交界处,此位置累积塑性应变能密度和塑性应力最大。【结论】高累积塑性应变能密度和应力会造成焊料和焊盘界面上产生应力集中,并发生形变,导致裂纹在该外侧界面上萌生,并沿着界面向内扩展,最终焊点因产生裂纹而失效。试验结果与模拟分析结果一致,进一步验证了模拟结果对裂纹生长的合理性。

[Purposes]This paper mainly studies the initiation and propagation of solder joint cracks in flip chip packaging under thermal shock.[Methods]The finite element simulation method was used to analyze the deformation of the package,obtain the distribution and change of the cumulative strain energy density and stress,and analyze the results combined with the test results.[Findings]Under the condition of thermal shock,the crack will first appear at the outermost of the solder joint and at the junction of the solder pad and the solder,where the cumulative plastic strain energy density and plastic stress are the largest.[Conclusions]The high cumulative plastic strain energy density and stress will cause stress concentration and deformation on the interface between the solder and the solder pad,which will lead to the initiation of cracks on the outer interface and the expansion of cracks along the interface.Finally,the solder joint will fail due to cracks.The test results are consistent with the simulation analysis results,which further verifies the rationality of the simulation results for crack growth.