Area array encapsulation with stencil printing and microwave curing

An alternative to the transfer molding of area array packages is the stencil printing of the encapsulant followed by a variable frequency microwave (VFM) cure process. A block of epoxy encapsulant resin was stencil printed over a square array of ICs bonded to a printed circuit board. The board circuitry included tuned microwave structures that focused curing of the edges of the encapsulant while the bulk was cured in the VFM oven at a low temperature in just a few minutes. A void free, fully cured encapsulant was produced with the same dimensions as the stencil and with satisfactory mechanical properties