Ultra-low-modulus Positive-type Photosensitive Polyimides (4). Improvement of Adhesion Strength with Copper Foil

Abstract

Amide- and triazine-containing diamines were incorporated by copolymerization into a siloxane-containing ultra-low-modulus polyimide (PI) as a novel cover layer material to solve some serious problems in the plating process such as interpenetration of an acidic plating solution into the interface between the S-side of electro-deposited copper foil and the cover layer. Our previous approach, a physical roughness modification of the S-side was effective to inhibit the interpenetration of the plating solution. This result suggests that the Cu/cover layer adhesion strength can be an important factor in the present case. The present work describes our chemical approach to increase the adhesion strength by using some heterocyclic monomers expected as adhesion promoters. The modified siloxane-containing PI possessed significant film toughness in spite of their low inherent viscosities. Unfortunately, the use of the amide- and triazine-containing diamines with minor contents (5?20 mol %) did not enhance the peel strength, however, the initial peel strength was almost maintained at 5 mol% without curling in the copper clad laminates (CCL), although the value significantly decreased at higher contents (10?20 mol%) with a prompt increase in the tensile modulus of the PI films and concomitant CCL curling. The results suggest that the decreased peel strength is closely related to the increased modulus of the PIs. Other properties (thermal and electrical properties, resistance to plating solutions, and photosensitivity etc.) of the modified siloxane-containing PIs will be also discussed in this work.