A Fluxless and Low-Temperature Flip Chip Process Based on Insertion Technique

For heterogeneous materials assembly, the thermal expansion mismatch between the chip and the substrate is a roadblock for flip chip bonding of ultrafine-pitch ( les 10 mum) and large diagonal devices ( ges 20 mm). Residual strains in bumps and device warpage have been calculated to evaluate the thermomechanical limits of a conventional flip chip soldering process using micro bumping. As a solution to overcome these limits, this paper describes a new patented flip-chip technology representing a technological breakthrough compared to conventional methods such as soldering or bonding through conductive adhesives. Electrical connections are performed by the insertion of metallic micro-tips in a ductile material. As a low-temperature process and fluxless technology, this method is adapted to fine-pitch and large devices. As a proof of concept, we present the bonding results obtained on fine-pitch large arrays of daisy chains with 500 times 500 contacts and 30 -mum pitch. The electrical contact has been demonstrated and characterized in terms of resistance and yield.