Effects of Silane Coupling Agents on the Adhesion Strength of a Printed Cu Circuit on Polyimide

It is difficult to maintain high adhesion strength between a printed metal circuit and polymer substrate due to the weak chemical bonding of metal and organic materials. Therefore, an additional process is necessary to improve the adhesion strength. Silane coupling agents (SCAs), which are capable of forming bonds with metals and organic materials, can provide a solution. Here, SCAs were placed on polyimide (PI) substrates and coated with various functional groups to compare the effects of various functionalized SCAs on the adhesion strength between a screen-printed copper (Cu) circuit and the PI substrate, where the printed Cu patterns were fabricated on the coated PI substrate. Chemical bonding between the coated silane coupling agent and the PI substrate interface was investigated by X-ray photoelectron spectroscopy. The adhesion strength of the screen-printed Cu circuit and PI substrate interface was measured by a roll-type 90° peel test. The surface free energy was calculated using the contact angle. The failure mode was analyzed by field emission scanning electron microscopy. The silane coupling agent containing an amine functional group significantly improved the adhesion strength because it facilitates a superior bond between organic substrates and metals via chemical reactions such as copolymerization and graft copolymerization. As a result, the adhesion strength between the printed Cu pattern and PI increased about 4.26 times with the use of SCAs.