Via-First Process to Enable Copper Metallization of Glass Interposers With High-Aspect-Ratio, Fine-Pitch Through-Package-Vias

A via-first process for metallizing copper on glass substrates is presented using a thin, patternable polymer film, electroless copper deposition, and semiadditive processing. A procedure for partially precuring the polymer was developed in order to achieve a tented via structure after dry-film lamination and curing. The flexibility of the process is demonstrated by the use of plasma etching, CO2, and UV laser ablation as patterning technologies. Metallization by electroless copper deposition and semiadditive processing is shown to be conformal, continuous, and without defects on the surface and in the vias as demonstrated by cross-sectional analysis. Glass of 100 mu m thickness with vias of 10-20 mu m diameter and 40 mu m pitch was metallized to demonstrate the dimensional capability of the process. Thermomechanical reliability was validated by copper peel testing after highly accelerated stress testing and daisy-chain resistance measurements taken throughout thermal cycle testing.