New concept for bendable packaged ultra-thin chips presented
IMEC and its associated laboratory INTEC of the University of Ghent jointly developed a new process flow for ultra-thin chip packages resulting in bendable packaged chips of only 50碌m thickness. The technology enables embedding packaged chips empowering smart, highly-integrated, flexible electronic systems for a wide variety of applications.
The process has been demonstrated with silicon chips thinned down to 20-30碌m. Thanks to the very low thickness of the chip, polyimide layers and metal, a total thickness down to 50碌m is achieved making the whole package bendable. The ultra-thin chip package can provide an interposer enabling testing of the chip before embedding. It offers a contact fan out with more relaxed pitches.
Thanks to its flexibility, the technology enables embedding of packaged chips in flexible boards empowering smart, highly-integrated, flexible electronic systems for 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 is a 20碌m-thick polyimide layer spin-coated on a rigid glass carrier. For the fixation and the placement of the chips on the polyimide layer a bicyclobutane of less than 5碌m is used as adhesive. Bicyclobutane is resistant to the high curing temperature of the top polyimide since its solvents evaporate during a pre-curing.
By placing the chips properly, either in vacuum or with a dispensed bicyclobutane, void-free bonds can be obtained.
Current research focuses on the optimization of the chip placement on dispensed (pre-cured) bicyclobutane and on avoiding voids by controlling the dispensed quantity. In this way, no vacuum environment will be required.
After the cure of the bicyclobutane at 350掳C, the chip is fixed on the polyimide layer. A covering polyimide layer is spin-coated on the fixed die with a thickness of 20碌m. For contacting to the chip, contact openings to the bumps of the chips are laser drilled. By using a shaped laser beam, via diameters with a top diameter down to 20碌m can be realized.
A top metal layer of 1碌m TiW/Cu is sputtered and photolithographically patterned, metallizing the contacts to the chip and providing a fan out to the contacts of the chips. Finally, the whole package is released from the rigid carrier.
Source: IMEC
