电子封装材料“爆米花”失效的弹-塑性分析

Elasto-Plastic Analysis of "Popcorn" Failur in Electronic Packages

对具有超弹性-塑性特征的neo-Hookean高聚物电子封装材料在回流焊过程中由于湿热所引发的"爆米花"式的孔穴破裂现象进行了理论研究.采用超弹性应变能函数来描述高聚物电子封装材料的的弹性本构特征,用T rescaa屈服条件来描述高聚物电子封装材料的塑性本构特征,并用有限变形理论给出了此类各向同性不可压材料在包含单一球形孔穴的条件下,孔穴的增长和吸湿产生的蒸气压力与热应力之间的解析方程组.研究结果表明:当考虑材料的弹-塑性特性时,孔穴增长规律与纯弹性分析的不同,弹-塑性分析时的极限载荷要比纯弹性分析时的小.

Popcorn failure in Hyperelastic-plastic electronic packages under thermal load and moisture was studied. Elastic constitutive relation was described by Neo-Hookean strain energy function and plastic constitutive relation was described by the Tresca yield condition. Using the theory of finite deformation, the analytical relation were obtained between void growth and the sum of the vapor pressure induced by moisture and thermal stress induced by heat mismatch. Numerical analysis show that the regularity of the unstable void growth changes when the elastic-plastic behavior of materials is considered. The critical stress of the unstable void growth in elastic-plastic analysis is much lower than the result of pure elastic analysis.