底部填充式BGA封装热机械可靠性浅析

Simple Analysis for Thermomechanical Reliability of Underfilled BGA Packages

探讨了在超级球阵列封装(SBGA)中,底部填充对各种热机械可靠性问题的影响;针对加工诱发的各种残余应力,研讨有底部填充和没有底部填充的非线性有限元模型;把焊料作为时间和相关温度建模,其他材料酌情按照温度和相关方向建模,分析由于热循环在封装中出现的应力/应变状况;对于焊料球中有关时间的塑性应变、蠕变应变和整个非弹性应变的大小和位置,分析底部填充的影响和铜芯对焊料球应变的影响;凭借定性的界面应力分析,探讨插件与底部填充界面以及基板与底部填充界面处发生剥离的可能性;有关SBGA封装结果表明,底部填充并不总是提高BGA可靠性,底部填充的特性,在BGA封装整体可靠性方面,效果是显著的;与现有试验数据相比,焊点疲劳热循环的预测数量类似于没有底部填充的BGA封装。

The effect of underfill on various thermo-mechanical reliability issues in super ball grid array（SBGA） packages is studied in this paper.Nonlinear finite element models with underfill and no underfill are developed taking into consideration the process-induced residual stresses.In this study,the solder is modeled as time and temperature-dependent,while other materials are modeled temperature and direction-dependent,as appropriate.The stress/strain variations in the package due to thermal cycling are analyzed.The effect of underfill is studied with respect to magnitude and location of time-independent plastic strain,time-dependent creep strain and total inelastic strain in solder balls.The effect of copper core on the solder ball strains is presented.The possibility of delamination at the interposer-underfill interface as well as substrate-underfill interface is studied with the help of qualitative interfacial stress analysis.Results on SBGA packages indicate that the underfill does not always enhance BGA reliability,and that the properties of the underfill have a significant role in the overall reliability of the BGA packages.The predicted number of thermal cycles to solder joint fatigue are compared with the existing experimental data on similar nonunderfilled BGA packages.