The viability of anisotropic conductive film as a flip chip interconnect technology for MEMS devices

The use of anisotropic conductive film (ACF) and stud bumping to form interconnects between die and substrates is one variation of current flip chip technologies with potential applications to MEMS devices. The key concerns associated with ACF are its long-term mechanical stability and consistent electrical performance. During this study a process methodology was developed for using ACF interconnections on MEMS devices by investigating key electrical parameters, and a practical example was investigated by packaging a pressure sensor using ACF flip chip techniques. Results of process development and contact resistance measurements using glass substrates and the anisotropic conductive film Sony FP1526 are discussed and analyzed. All required processing steps, such as stud bumping, application of ACF and thermocompression bonding of the die and substrate, were carried out using a digital wire bonder and a bench-top flip chip system. FP1526 yielded an average contact resistance of 10.23 m Omega, a stray capacitance measurement of 10 femtofarad and less than 0.1% change in contact resistance after being encapsulated in parylene C and being immersed in DI water for 72 h. Finally, the performance of an ACF-packaged MEMS piezoresistive pressure sensor was compared to that of a conventional wire-bonded device and showed a significant improvement in temperature stability (< 0.34% deviation in offset voltage) with essentially no change in sensitivity.