Pre-Cure Modification of Electrically Conductive Adhesive for Low Temperature Interconnection

Abstract

The temperature sensitivity of CZT medical imaging devices precludes the use of traditional solder attach technologies for package interconnection. Continued advancement in electrically conductive adhesives (ECAs) has resulted in commercially available ultra-low temperature (<60°C) cure candidates that would be compatible with CZT device assembly. However, inherent to their low cure temperature is a rapid onset of room temperature polymerization and associated increase in viscosity. This quickly degrades printability and thereby manufacturing pot life. Conversely, ECA's with a longer pot life typically cure at an unacceptably higher temperature and have lower viscosities that are not compatible with screen printing. To address this dichotomy, we propose an approach that enables low temperature interconnection by initiating the cure process prior to material printing in the assembly process. The approach uses a short time, high temperature pre-heat of a high pot life material to initiate polymerization in a controlled fashion before it is interconnected to the temperature sensitive device then cured at an ultra-low temperature. The results demonstrate that the pre-treatment not only serves to shift the particular material's viscosity to a more acceptable range for screen printing, it also improves low temperature cure resistivity values from 21KΩ-cm to less than 1 mΩ-cm. At the same time, the pre-treatment maintains the long pot life of the material that favors its use in a volume-manufacturing environment. This approach opens the door for exploring a larger portfolio of electrical conductive adhesives to be used in low temperature interconnection applications.