A low-cost, flexible ball-grid-array multichip module technology

In pursuit of lower cost packaging solutions, a new type of multichip module (MCM) has been designed and fabricated on flexible polyimide films. The new technology uses a double-sided copper metallized, through-via, polyimide film with a ball-grid-array packaging solution. The enabling technology is the Interconnected Mesh Power System (IMPS) MCM topology which provides the signal wiring and power distribution using two metal layers instead of the four-layer metallization scheme as in conventional MCM topology. One side of the polyimide Nm has passivation openings where chips are wire bonded; this side is encapsulated to provide structural rigidity and environmental protection of the circuitry. The other side has solder pads where solder spheres are placed and reflowed to create a ball grid array package. The two-layer copper metallized polyimide film substrates with through-vias are obtained either by laser drilling of pre-metallized polyimide films or reactive ion etching of polyimide layers fabricated from their liquid precursor. Issues of solder joint integrity and module warp were investigated. Preliminary test data are also reported.