Design and Fabrication of a Low-cost Wafer-level Packaging for RF Devices

This paper presents the structure and process technology of simple and low-cost wafer-level packaging (WLP) for thin film radio frequency (RF) devices. Low-cost practical micromachining processes were proposed as an alternative to high-cost processes, such as silicon deep reactive ion etching (DRIE) or electro-plating, in order to reduce the fabrication cost. Gold (Au)/Tin (Sn) alloy was utilized as the solder material for bonding and hermetic sealing. The small size fabricated WLP of $1.04{\times}1.04{\times}0.4mm^3$ had an average shear strength of 10.425 $kg/mm^2$, and the leakage rate of all chips was lower than $1.2{\times}10^{-5}$ atm.cc/sec. These results met Military Standards 883F (MIL-STD-883F). As the newly proposed WLP structure is simple, and its process technology is inexpensive, the fabricated WLP is a good candidate for thin film type RF devices.