Assembly of multiple chips on flexible substrate using anisotropie conductive film for medical imaging applications

Flip-chip interconnection technology based on anisotropic conductive film (ACF) has been selected to assemble multiple chips (i.e. ASICs - Application-Specific Integrated Circuits) on a flexible substrate in an electro-acoustic module. The chips are relatively large with a high number of I/O pins distributed over its area (on the order of 100 mm²). In this work, the processes of bonding one single chip, two chips simultaneously and four chips simultaneously to a substrate using ACF were characterized and compared. The results show similar effect of bond force on electrical resistance of ACF interconnects for bonded samples with one single chip, two chips and four chips. High bond yield values (more than 99 %) are obtained for all groups of samples bonded with a normalized bond force varying from 50 N/chip to 500 N/chip. In general, higher bond force, hence higher bond pressure, provides better ACF interconnects in terms of lower electrical resistance and higher bond yield. This work has demonstrated the feasibility of bonding multiple chips, each of which has a relatively large area with a high number of I/O pins, to a flexible substrate using ACF.