Improved thermal fatigue reliability for flip chip assemblies using redistribution techniques

The bond pad design on a chip can be reconfigured to a new pad design using a redistribution layer, based on multichip module-deposited (MCM-D) techno logy. The new pad configuration can be used for flip chip mounting. The the rmo-mechanical reliability of these redistributed flip chip structures is i n particular determined by the visco-plastic deformations of the solder joi nts and by the stresses in the photosensitive BCB redistribution layers. In this paper, the influence of this redistribution layer on the solder joi nt reliability will be investigated. Also the induced stresses in this redi stribution layer may not exceed the ultimate stress level. Three different redistribution processes are considered. Finite element simulations and Cof fin-Manson based reliability models are used to compare the thermal cycling reliability of redistributed and standard flip chip assemblies. The existence of a photosensitive BCB redistribution layer on the chip infl uences the thermal fatigue of solder joints. The largest reliability improv ement using redistributed chips is achieved by moving the solder joints fro m the perimeter to the interior of the die resulting in an area array flip chip.