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Characterization of Die Attach Adhesives to Identify Contamination Source Present in MEMS Packages
Keywords: die-bonding, adhesives , offgassing
Hermetic packages are designed to prevent gas flux in and out of the package to protect internal components from premature aging resulting from oxidation, corrosion, and interactions with other reactive species. Because outgassed contaminants inside the package are sealed in, their concentration often increases with time. Many hermetic packages are die bonded with cyanate ester adhesives, claimed as quick-curing, low-outgassing, and acceptable for high-reliability military products. Recent investigations at Sandia National Laboratories found some MEMS-containing packages, bonded with these adhesives, were non-functional due to the presence of condensed outgassing products. Sandia has developed a novel tool for destructively sampling and characterizing volatile organic compounds in hermetic packages outgassed from die bond adhesives. The package is sealed in a leak tight, low-volume custom valve body, and cracked under static vacuum to release the internal gases. While breaching the package seal, the pressure is monitored to look for a pressure rise (characteristic of a hermetic package) or for no detectable pressure rise (characteristic of a “leaky” package). The gas sample is collected (for those packages exhibiting a measurable pressure rise), concentrated using a cryo-focuser, and introduced into a gas chromatograph interfaced with a mass spectrometer for analysis. In addition to volatile organic compounds, permanent gasses (e.g., nitrogen, oxygen, argon, hydrogen) can be analyzed using a residual gas analyzer. This sample collection technique has been demonstrated on packages ranging in volume from 30 nanoliters hundreds of microliters. This novel technique is very effective for determining hermeticity, characterizing gas composition, and optimizing cure processes to minimize contaminants and increase the reliability of MEMS devices. Examples of how this technique has been employed will be discussed including how it has been used to evaluate commercially packaged die (non-MEMS) to measure and understand residual cure products present in the hermetic packages after cure and lidding processes.
James M. Hochrein, Postdoctoral Appointee
Sandia National Laboratories
Albuquerque, NM

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