Phosphinated polyimide hybrid films with reduced melt-flow and enhanced adhesion for flexible copper clad laminates

Adhesion properties of phosphinate-contained polyimide (P-PI) hybrid films were studied to develop suitable heat resistant adhesive film with excellent hot-melt processability. The diamine, 1,1-bis(4-aminophenyl)-1-(6-oxido-6H-dibenz<1, 2> oxaphosphorin-6-yl) ethane (i.e. DMA), was introduced to synthesize a series of P-PI films with different contents of DMA. The presence of the bulky phosphinate pendant group on PI backbone increased the adhesion strength and effectively reduced the melt flow after hot-pressing to flexible copper clad laminates (FCCL) without the usage of adhesive. The P-PI film tended to produce rougher surface that facilitated the mechanical interlocking effect between P-PI hybrid film and copper. The presence of characteristic phosphinate functional groups and the formation of polyphosphate layer on P-PI film were confirmed by FTIR and XPS results. The storage modulus and glass transition temperature of P-PI films were increased because of the enhanced rigidity by phosphinate groups. The presence of bulky phosphinate pendant group also reduced the coefficient of thermal expansion and dielectric constant of PI films. Although the introduction of phosphinate in PI reduced the initial weight loss temperature, the thermal stability of P-PI films was sufficient for the following manufacturing processes. Furthermore, another interesting observation was the enhancement of transparency at 400 nm for P-PI. Those properties make P-PI films useful in FCCL application.