Adhesive based flip chip technology for assembly on polyimide flex substrates

This paper describes research conducted to develop and evaluate isotropically conductive adhesive preforms for the assembly of die onto polyimide flex circuit based MCMs and single chip packages. The preforms are fabricated by screen printing complimentary dielectric and silver filled epoxy patterns corresponding to the die I/O pattern. The dielectric pattern provides a built-in underfill, eliminating the need for a post die placement underfill process. The silver filled epoxy dots provide the electrical connections. The preforms are produced in volume as a multi-up array printed on a release film. In the assembly process, the preform is first aligned and adhered to the die surface. Next the die and preform are aligned to the corresponding flex substrate pattern and bonded. The epoxy is then cured to complete the process. High temperature storage and thermal cycling results are presented