Dry adhesive joining of layers of electronic devices

Abstract

There is disclosed an efficient, cost effective production method to bond layers of electronic devices into an integral stack, or for joining electronic devices to other devices or substrates with use of an adhesive material, preferably an appropriate polyimide, to provide, in effect, a two-stage bonding process. In the first stage, the electronic device is coated, preferably at the wafer level, with a liquid solution of the adhesive material, the coated device is heated to remove solvent, forming a dry adhesive coating of sufficient thickness to fill all spaces between metal traces on the electronic device. Coated wafers can be stacked and bonded, or preferably diced to yield individual chips, which are cut and stacked in a suitable fixture, and heat and pressure are applied in a second stage, to cause viscous flow of the adhesive, filling all voids, and to cure the adhesive, creating an integral, adhesively bonded stack. The adhesive selected for use in the process is one which can be dried to a solvent free layer, which has good B stage properties, exhibits viscous flow at temperatures below its curing temperature, and which is substantially free of volatile release during curing to form a substantially void-free adhesive bond having high film strength, high adhesion, chemical resistance and good dielectric properties.