Evolution of residual-inplane stress during adhesive curing and recuring in chip-on-board packages

The residual stress induced in assembly is a common concern in electronic packaging, especially for those chips sensitive to residual stress. On chip-on-board (COB) packages, bisphenol A-type epoxy adhesive is applied to attach the chip to the substrate board. Silicon piezoresistive sensors are used to record residual stresses and stress evolution during adhesive curing. After 20-days storage in air at room temperature after curing, the residual stresses accumulate significantly in the recuring process, and after additional curing, the residual stress stabilizes at a relatively low level. Thermal analysis of the adhesive was performed to identify the incomplete cure of the adhesive after the first curing process.