Study of Parameter Tuning for the Curing Condition on ABF Type for Large FCBGA Package

The dielectrics material of flip-chip ball grid arrays, Ajinomoto build-up film (ABF), crack root cause and methods to prevent it were studied. The ABF crack was observed after dielectrics lamination and laser via de-smear process. An internal stress from substrate material CTE mismatch and shrinkage during cooling, which is the ABF crack root cause. The factors affecting the ABF stress were also studied, it was found that ABF thickness and residual Cu rate of substrate pattern are the key factors to the ABF stress. Strategies of decreasing the thermal stress stored and releasing the stored stress to prevent ABF crack were demonstrated through process DOE.