Infrared Curing of Flip Chip Electrically Conductive Adhesive (ECA) Interconnections

A novel approach to achieving low temperature electrically conductive adhesive (ECA) flip chip interconnections of CZT device is proposed. This approach exploits CZT transparency to certain IR radiation wavelengths and the non-thermal effects imparted upon epoxies by such IR radiation. We determine appropriate conditions, such as wavelength, source temperature and exposure time of an IR radiation source. A series of experiments examine the extent of CZT transparency, including the impact of the CZT contact pads. These results are used to determine appropriate cure schedules for selected ECA candidates as characterized by degree of polymerization and volume resistivity. The detailed results presented in this paper demonstrate the ability to maintain CZT temperature significantly lower (by as much as 50°C) than the ECA cure temperature. Further, non-thermal effects, previously documented for IR curing of non-conductive epoxies, are demonstrated for ECA materials, thereby providing important reductions in ECA cure times (as compared to convection curing) while ensuring a high degree of polymerization (>95%) and low volume resistivity (< 5 mΩ.cm). In fact, improved volume resistivity was observed at low temperatures as compared to convection curing; a hypothesis for this improvement is postulated and preliminary validation experiments discussed.