Packaging of GaAs Chips for Use in RF MCM Products

摘要

Incorporation of GaAs devices in a multi-chip module (MCM) process in which the chips are put down first, followed by buildup of their interconnect structure, presents several problems. First, GaAs devices are much thinner than the silicon chips and passive components that are typically used. Second, a low impedance electrical connection to the backside of the GaAs device is usually required. And third, it is desirable to surround the chip with a metal shield structure. All three of these issues have been addressed with a chip scale package fabricated from sheet copper stock. This package is fabricated by etching cavities through the sheet to form the die cavity. Next, Kapton film is bonded to one side of the sheet, to form the package bottom. Then, the entire chip cavity is metalized with gold. The metallized sheet is then mounted to a thermal release tape so that the individual carriers can be diced from the substrate. The device is bonded to the bottom of the carrier with conductive adhesive. The fully assembled package is then removed from the thermal released tape after the curing the conductive material. The package has proven to be robust, fully compatible with the MCM assembly process, and also offers some benefits with respect to thermal management.