Test and evaluation of chip-to-chip attachment of MEMS devices

In the IC industry, the bond layer serves as the foundation and often the weak link in the reliability of chip packages. MEMS packages are likely to have a greater number of bond layers with more stringent requirements. The additional bond layers arise from multiple interfaces inside the package. The bond layers in MEMS devices often must maintain precise component or chip alignment. In addition, the bond layers may have to withstand loading from both the macroenvironment and loading within the package. This paper presents the bond requirements for a MEMS based Safety and Arming (S&A) device. The S&A system requires precise alignment between a micromachined silicon chip, a patterned Alumina ceramic chip, and a deflection delimiter. Several candidate designs were subjected to a series of environmental tests including thermal cycling, accelerated stress tests, mechanical shock, and combinations of the above conditions. A Scanning Acoustic Microscope (SAM) is utilized to measure initial delamination and to identify incremental damage due to environmental exposure. The tests are ultimately used to rank the suitability of the bond layer material for chip-to-chip attachment with large coefficient of expansion differences. Tested bond materials include epoxy, thermoplastic, and solder.