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 50µm 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 20-30µm. Thanks to the very low thickness of the chip, polyimide layers and metal, a total thickness down to 50µm 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).
Details on the process flow
The base substrate is a 20µm-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 5µm 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°C, the chip is fixed on the polyimide layer. A covering polyimide layer is spin-coated on the fixed die with a thickness of 20µm. 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 20µm can be realized.
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. Finally, the whole package is released from the rigid carrier.
IMEC is a world-leading independent research center in nanoelectronics and nanotechnology. Its research focuses on the next generations of chips and systems, and on the enabling technologies for ambient intelligence. IMEC’s research bridges the gap between fundamental research at universities and technology development in industry. Its unique balance of processing and system know-how, intellectual property portfolio, state-of-the-art infrastructure and its strong network of companies, universities and research institutes worldwide position IMEC as a key partner for shaping technologies for future systems.
As an expansion of its wireless autonomous microsystems research, IMEC has created a legal entity in the Netherlands. Stichting IMEC Nederland runs activities at the Holst Centre, an independent R&D institute that develops generic technologies and technology platforms for autonomous wireless transducer solutions and systems-in-foil.
IMEC is headquartered in Leuven, Belgium, and has representatives in the US, China and Japan. Its staff of about 1400 people includes close to 500 industrial residents and guest researchers. In 2005, its revenues are estimated to be close to EUR 200 million. Further information on IMEC can be found at www.imec.be.