TGV (Thru-Glass Via) Metallization by Direct Cu Plating on Glass

Conformal coating or solid-filling metallization on TGV glass with the highly conductive thick Cu is desired to enhance the performance for high-frequency electronic devices in the IoT era due to the outstanding RF properties of the glass and high-Q nature of thick Cu metallization on glass. Previously, metallization on the glass with sputtering and printing technology has been demonstrated. However, there are some concerns in terms of throughput and mechanical integrity of sputter seed layer for Cu metallization on TGV sidewalls and the smooth glass surfaces. This study reports our novel metallization technology to obtain good adhesion without degrading the RF performance associated with glass properties and Cu conductivity. Metal circuits including high-Q RF inductors were created by wet direct plating process with semi-additive process, achieved without any roughening the surface of glass substrate or TGV sidewall. Surface cleaning is critical to obtain good adhesion. In this experiment, glass surface was cleaned by the irradiation of UV light and alkaline degreasing with complex agent. UV light and alkaline degreasing make the surface of the glass clean and Cu adhesion to glass improves with minimal stress to the glass itself. Through this work, Cu to glass adhesion strength of 0.35kN/m has been achieved. Using this method, we have successfully demonstrated direct cupper plating on TGV holes and glass surfaces with semi-additive processing (SAP) and conformal plating for RF front end filters with better performance. This technology further optimized for high-performance RF standalone passive network and RF interposers with the capability of thick (15um) Cu plating directly on TGV glass for the first time in 8 inch diameter x 0.35mm thick wafer format. This direct plating technology is scalable to panel sizes, targeting low-cost and high-throughput TGV metallization.