Metallization of Polyamide-imide for High-Frequency Communication by Polyethylenimine Modification and Electroless Copper Plating

A dielectric filter utilizing polyamide-imide (PAI) as the substrate exhibits a promising application potential in the field of high-frequency microwave communication with advantages of smaller volume and lighter weight, while achieving the metallization of the PAI substrate remains a challenge. In this paper, a facile and effective method for synthesizing a high-adhesion and low-resistivity copper layer on a PAI substrate via coating modification with electroless copper plating (ECP) is demonstrated. Through the chemical etching of alkaline potassium permanganate solution, the surface of the PAI substrate was successfully coated with a polyethylenimine and glutaraldehyde chain-reaction-modified coating. The modified coating contained bonding functional groups with high chemical activity, enabling the substrate to adsorb silver ions as catalytic sites for subsequent ECP. Eventually, a dependable copper layer was deposited on the modified PAI substrate, exhibiting a low resistivity of 3.2 μΩ·cm and a high adhesion rating of 5B in ASTM D3359. Moreover, the metallized PAI substrate of the dielectric filter demonstrated exceptional reliability for high temperature and ideal filtering performance with a pass-band frequency ranging from 3.42 to 3.60 GHz. This technology provides a reliable approach for fabricating a high-performance copper layer on the PAI substrate of the dielectric filter, holding significant potential in the realm of communication electronics.