Processability and electrical characteristics of glass substrates for RF wafer-level chip-scale packages

Abstract

Various types of glass substrates have been compared with respect to their suitability as a low-loss substrate in waferlevel chipscale packaging for RF applications. Processability has been evaluated by fabrication of shallow and deep recesses using wet etching in HF (iHjP04) solutions. Electrical characteristics (dielectric constant and attenuation) have been extracted from measurements on coplanar wave guides (CPWs) up to 10 GHz. Results show that Coming Pyrex #7740 glass provides optical quality of wet-etched deep recesses, but exhibit about 2 times higher electrical attenuation than Hoya SD-2. Pyrex #7740 and SD-2 are thermally matched to silicon and due to some alkali content, they are suitable for anodic bonding. The relatively high content of A120j (-20%) in SD-2 is favorable for its electrical properties, but makes wet etching of deep recesses more difficult. The non-alkaline AF45, with C'IE almost 2 times of Si (CTEm45=4.5x106 K'), is suitable for adhesive bonding and is difficult to pattern using wet etching. Its electrical attenuation is close to that of SD-2. The measured dielectric constants (at 6 GHz) for SD-2, F'yrex #7740 and AF45 are 4.7,5.9 and 6.1, respectively. Introdnetion