Factors Affecting Metal/Polymer Interface Durability in Microelectronics Packaging: Chemistry and Water Uptake

Durability of metal/polymer interfaces is essential for the long-term reliability of high performance microelectronics packages. Such interfaces undergo stresses during production and in service. In this work, we report on the durability of interfaces formed between reactive metals and polyimides (PI) that have been subjected to stresses simulating both types of environment. The P1 surfaces were treated by Ar RF plasmas prior to metal deposition, and durability was determined by measuring the 90 degree peel strength as a function of environmental exposure. The durability of Cr and Ti/PMDA-ODA interfaces through processing stresses (i.e., large thermal excursions) depends on the PI surface modification and the metal reactivity. For both, we observed interfacial degradation due to oxidation of the metal–the cause is water absorbed by the polyimide. These studies, coupled with water transport measurements, suggest that the physical structure of the interface is the dominant factor. To determine the durability under service environmental stresses (e.g., temperature/humidity), we correlated peel strengths with interfacial chemistry and water uptake. In this case, Ar and O2 plasmas were used. For Ta/BPDA-PDA, the durability depends on the type of plasma treatment. Ar-treated specimens maintain strength through 500 hours T/H stressing whereas those treated by O2 plasma alone fail at 165 hours. The differences here can be explained by the interfacial chemistry–Ta/Ar-etched surfaces form a stable TaG-like structure whereas the Ta/O2-etched surfaces form a metastable, sub-oxide structure that transforms to Ta2O5 during stressing. Ta/PMDA-ODA interfaces fail readily under these conditions due to the increased water uptake of the PI.