Abstract
Wafer-to-wafer bonding methods provide hermetic packages for hundreds of devices in a single processing step. Once the wafers have been bonded, most defects are no longer visible to the naked eye but may be responsible for die failures. Detection of internal defects in bonded wafer pairs is vital to achieving anticipated yield and long-term device reliability of packaged MEMS devices. Acoustic micro imaging provides a nondestructive technique for detecting and analyzing these defects and is an essential component of process development and root cause analysis. In this paper, we discuss and analyze acoustic imaging results of wafer pairs bonded using various bonding techniques such as silicon direct, eutectic, glass-frit, and thermal compression bonding.