Effects of lead bonding process on reliability of chip scalepackage

摘要

An integrated circuit (IC) package has become smaller and itsprofile becomes lower as new chip scale packaging (CSP) designs havebeen introduced. A new design of packages demands new materials andoptimization of manufacturing processes to enhance reliability of thepackage. A compliant layer in Tessera's μ-BGA(R) package is a crucialcomponent to increase solder ball reliability in the board levelassembly. The compliant layer can reduce damage to the solder balls,which is induced by mismatch of the coefficient of thermal expansion(CTE) between Si die and the printed circuit board (PCB). Siliconeelastomer is one of the best candidate for the compliant layer due toits low modulus and low moisture absorption. While the colder ballreliability in the μ-BGA package is significantly improved due to itsunique design and optimal materials set, fatigue damage can be imposedon beam leads inside of the package during thermal cycling. To reducethe damage in the package, an optimal lead (or beam lead) bondingprocess becomes critical for flex circuit interposer type of CSP designsincluding μ-BGA. Three dimensional (3D) Finite Element Analysis (FEA)of the lead bonding and subsequent thermal cycling, is conducted to showeffects of designs of the lead (dimensions and shapes) as well as thelead bonding process parameters. Several different loci of a bond toolmotion are numerically simulated to determine optimal lead bondingparameters based on the calculated damage accumulated in the deformedshape of leads during the lead bonding process followed by the thermalcyclings