Abstract
The mechanical stability of Chip Scale Packages (CSP) used in surface mount technology is primary concern. The dominant issues are package warpage and solder fatigue in solder joints under cyclic loads. To address these issues, molding compound and die attach film were characterized with finite element method which employed a viscoelastic and viscoplastic constitutive model. The model was verified with experiments on package warpage, PCB warpage and solder joint reliability. After the correlation was observed, the effect of molding compound and die attach film on package warpage and solder joint reliability was investigated. It was found that package warpage tremendously affected solder joint reliability. Furthermore, a die attach film was developed based on the results of modeling. CSPs with the developed die attach film are robust and capable of withstanding the thermal stresses, humidity and high temperature encountered in typical package assembly and die attach processes. Also, lead free solder and 2P versus 3P Weibull distributions are discussed. This paper presents the viscoelastic and viscoplastic constitutive model and its verification, the optimum material properties, the experimental and simulated reliability performance results of the μBGA packages, the lead free solder creep, and the 3P Weibull distribution.
