Anisotropic conductive film interconnects for fine-pitch MEMS

The flip-chip interconnection technology based on anisotropic conductive films (ACFs) has recently become an attractive solution for the assembly of micro-electromechanical systems (MEMS) and application specific integrated circuits (ASIC) in MEMS packages. In the present work, we have studied the fine pitch capability of ACF interconnects for MEMS applications such as fingerprint sensors and capacitive micromachined ultrasonic transducers, in which interconnects spread around MEMS and ASIC surface. The silicon test chips and substrates with different interconnect pitch were assembled using a single layer ACF. The electrical performance of ACF interconnects with varying pitch from 110 to 200 μm was compared. Furthermore, the distribution of conductive particles and the electrical resistance of ACF interconnects at both peripheral and central parts of the chips were evaluated. Effect of thermal shock cycling test (−40 to +125 °C) on samples was investigated. The results showed insignificant difference in the electrical performance between ACF interconnects with pitch varying from 110 to 200 μm. The particle distribution and the electrical resistance of ACF interconnects at different chip regions were similar. No significant effect of the thermal shock cycling test was observed. No failures (open/short circuit) occurred, both before and after the thermal shock cycling test.