April 4, 2006 – IMEC and its associated laboratory at the U. of Ghent have developed a new process flow for ultrathin chip packages resulting in bendable packaged chips. The process has been demonstrated with silicon chips thinned down to 20-30µm, with total thickness of 50µm.
The technology enables embedding packaged of chips in a wide variety of applications, such as smart textile and flexible displays. The process flow has been developed within the EU funded FP6 Integrated Project, SHIFT (Smart high-integration of flex technologies).
The base substrate used in the process is a 20µm thick polyimide layer spin-coated on a rigid glass carrier. A layer of bicyclobutane (<5µm thick), resistant to high curing temperature of the top polyimide, is used to glue the chips on the layer. Placing the chips in either a vacuum or with dispensed bicyclobutane enables void-free bonds -- current research is focusing on optimizing the chip placement on dispensed (pre-cured) bicyclobutane, and on controlling the dispensed quantity to avoid voids, to eliminate the need for a vacuum environment.
After curing the bicyclobutane at 350°C, the chip is fixed on the polyimide layer, with a 20µm covering polyimide layer spin-coated on the fixed die. Contact openings are laser drilled to the bumps of the chips; via diameters with top diameter down to 20µm are achieved by using a shaped laser beam. A top metal layer of 1µm TiW/Cu is sputtered and photolithographically patterned, metallizing the contacts to the chip and providing a fan out to the contacts of the chips.