Characterization of chip scale packaging materials

The mechanical stability of Chip Scale Packages (CSP) used in surface mount technology is of primary concern. The dominant issues are package warpage and solder fatigue in solder joints under cyclic loads. To address these is sues, molding compound and die attach film were characterized with finite e lement method which employed a viscoelastic and viscoplastic constitutive m odel. The model was verified with experiments on package warpage, PCB warpa ge and solder joint reliability. After the correlation was observed, the ef fect of molding compound and die attach film on package warpage and solder joint reliability was investigated. It was found that package warpage treme ndously affected solder joint reliability. Furthermore, a die attach film w as developed based on results of the modeling. CSP with the developed die a ttach film are robust and capable of withstanding the thermal stresses, hum idity and high temperatures encountered in typical package assembly and die attach processes. Also, a lead free solder is discussed based on the resul ts of creep testing. This paper presents the viscoelastic and viscoplastic constitutive model and its verification, the optimum material properties, t he experimental and simulated reliability and performance results of the u* BGA packages, and the lead free solder creep. (C) 1999 Elsevier Science Ltd . All rights reserved.