Improvement of epoxy adhesion to polyimide passivation

Adhesion of epoxy to polyimide passivation is very important in electronic packaging. Pyromellitic dianhydride-4,4´-oxydianiline polyimide (PMDA-ODA PI) showed lower adhesion to most epoxy formulations. Different approaches were explored to improve the adhesion of epoxy formulations to PMDA-ODA PI. Silane coupling agents did not improve the adhesion of epoxy to PMDA-ODA PI, but they improved the adhesion hydrolytic stability. Amine and sodium hydroxide were used to treat the PMDA-ODA PI surface. Sodium hydroxide treatment was more effective in improving the adhesion between PMDA-ODA PI and epoxy than the amine treatment. The hydrolytic stability of adhesion between epoxy and sodium hydroxide treated PMDA-ODA PI depends on the curing condition of the epoxy formulation. When the formulation was cured at temperature of 200°C or below, the hydrolytic stability of adhesion between epoxy and sodium hydroxide treated PI was worse than that of adhesion between epoxy and untreated PMDA-ODA PI. When epoxy formulation was cured at 250°C, the hydrolytic stability of adhesion between epoxy and sodium hydroxide treated PI did not degrade. In addition, it was discovered that epoxy cured with imidazole or its derivatives showed excellent adhesion to PMDA-ODA PI. The surface treatment of PI could not further improve the adhesion of PMDA-ODA PI passivation to epoxy cured with imidazole or its derivatives.