Adhesion Enabling Technology for Reliable Metallization and Patterning of Glass Interposers

Abstract

In this study a thin-film adhesive metal oxide layer is described that forms chemical bonds with glass, and mechanically anchors to copper to create strong, reliable adhesion between the glass substrate and the deposited metal. A modified sol-gel deposition process followed by sintering was used to create the thin, transparent film that then enables electroless, and electrolytic copper plating directly onto glass. With this new approach, a copper film thickness of over 50μm can be applied without delamination from the smooth glass. Adhesion at 15μm Cu thickness as measured by 90° peel strength tests can achieve values of ≥5 N/cm. This is compared in the study to mechanical roughening and a control with no adhesion promoter applied. Thermal stress tests using lead free reflow conditions and Highly Accelerated Stress Testing (HAST) were carried out without significant adhesion loss. Through hole adhesion was demonstrated inside the Through Glass Vias (TGV's) without issues of blistering or delamination from the walls. The study also looks at filling of the TGV's with electrolytic copper. Photolithography of fine-lines as small as 5/5 μm was feasible, with very small undercut observed. Electro migration and high frequency tests were also conducted to test material compatibility for RDL patterning, showing no loss in surface insulation or signal integrity.