Electroless and Electrolytic Copper Plating of Glass Interposer Combined with Metal Oxide Adhesion Layer for Manufacturing 3D RF Devices

Abstract

High performance radio frequency (RF) front end filters were fabricated using glass interposer and 3D packaging technologies, especially through glass vias (TGV) and direct Cu metallization on the glass. Major challenges for the use of TGV in RF and electronics applications are the cost competitiveness, high throughput and reliable metallization of both TGV and flat glass surface with an excellent adhesion. In this study, a thin metal oxide adhesion promotion layer (about 8-9 nm) called VitroCoat layer is dip-coated by a modified sol-gel process followed by sintering which creates chemical bonds to the glass. Sol-gel dip coating process has good coating uniformity on both TGV and top surface under optimized coating conditions. Uniform coating can be achieved on minimum 30 µm diameter TGVs on a 300 µm thick and 200 mm diameter glass wafers. The thin adhesive layer enables electroless and electrolytic copper plating directly onto glass substrates without impacting high frequency performance. Excellent adhesion of electroless plated copper seed layer on glass can be achieved by using the adhesive layer and annealing technology. The thin adhesive layer is non-conductive and can be easily removed from the area between circuit traces during electroless copper seed layer etching. We have successfully integrated the adhesion layer and electroless and electrolytic copper plating technologies into semi-additive process (SAP) and built up a 3D RF front end filter devices on 400 µm thick 200mm diameter glass wafers as well as 300mm x 300mm glass panels with 80 µm diameter holes.