Towards a predictive behavior of non-conductive adhesive interconnects in moisture environment

Flip chip on flex interconnections with non-conductive adhesive paste are taken as test vehicles to study the behavior of adhesive interconnects in a moisture environment. A dedicated test structure is used to enable a proper four-wire resistance measurement of single interconnects. A new and very powerful approach is used, focusing on the response of the contact resistance of the interconnect to humidity. Two types of accelerated tests have been performed with on-line measurement of the contact resistance with high measuring resolution. The first test aims at the durability of the interconnects and the second is a step stress-type test which shows that the relative response of the contact resistance to humidity is much larger at high relative humidity levels, compared to the response at low relative humidity levels. Combining the results of both types of experiments allows the definition of a simple transform for non-conductive adhesive interconnects in a changing humidity environment. Failure analysis is performed to understand the physical behavior of the interconnects during the accelerated tests.