Plasma Treatment for Robust Interface Adhesion of Wafer Level Packaging

Wafer level chip scale packaging (WLCSP) has numerical advantages, such as smaller form factor, high electrical performance, and lower manufacturing cost. And the flip chip package need plating bump as the interconnection to substrate or lead-frame. In order to re-route the electrical signal or facilitate a balanced metal bumps, the additional metal redistribution (RDL) layer would be necessary. The redistribution layer technologies require polymer/re-passivation as insulator to serve the rerouting purpose. Hence, the adhesion between metal and polymer/re-passivation or polymer/re-passivation and polymer/re-passivation will be a critical issue, which will impact to the package reliability performance. This paper illustrates the methodology to improve adhesion at the interface with specific index of metal or re-passivation bump shear. Two different main atmospheric plasma of surface treatment, nitrogen atmospheric and oxygen atmospheric were investigated from the point of view of adhesion for polyimide-on-polyimide and polyimide-on-plated Cu. Also, the general high temp polyimide and low temp polyimide present different surface morphology with variance adhesion performance under plasma surface treatment. By applying the mechanical shear force as the representation of adhesion, it will be easier to judge the interface bonding energy. The result indicate that surface plasma treatment is the recommended process for enhancing interface adhesion, and different atmospheric should apply for different pattern design based on the ratio of Cu to polyimide.