Flipchip bonding of ultrahin Si dies onto PEN/PET substrates with low cost circuitry

All-printed, cost effective, smart electronic products are expected to be used in a wide range of applications and in large quantities in our society. The substrate material for these applications will be low cost materials like PEN or PET foils. For the functionality of the printed electronics product it often will still be required to integrate a Si chip. To keep the flexibility of the package and not to add too much to the thickness, the chip needs to be integrated into the product as a bare, thinned die. Because of the low temperature stability of the PEN and PET and the use of printed conductors it is necessary to interconnect the chip using an adhesive. The current paper specifically addresses the challenges associated with this. Research efforts will be discussed on the flip chip bonding of ultrathin (i.e. thickness 20 µm) bare chips on printed circuitry on both PEN and PET foils using a typical anisotropic conductive adhesive (ACA). Based on the results it can be concluded that a reproducible, low contact resistance and a good lifetime and flexural durability can be achieved over a wide range of bonding forces and temperatures.