MOISTURE SENSING AND STRESS TEST CHIPS FOR PLASTIC PACKAGING QUALIFICATION
Author: L.T. Nguyen Company: National Semiconductor Corp. Date Published: 9/10/1996
Surface Mount International
Abstract: The protection of integrated circuits from moisture-induced failures ad failure caused by thermo-mechanical stresses has been the subject of intense study during the past twenty years. As the military moves ever closer to substituting plastic-ecapsulated microcircuits (PEMs) for ceramic hermetic packages in high reliability applications, it is vital that these failure modes in plastic are well characterized and understood. Moisture-induced failures in PEMs often take the form of wire bond/bond pad opens due to corrosion brought on by the presence of moisture and contaminants from & wafer fabrication processor or the molding compound. In addition, Al thin film interconnects can also open due to corrosion caused by moisture penetration through defects in the passivation. A unique porous silicon-based test chip, NATO1, has been developed to help characterize the potential for moisture-induced failures in specific combinations of molding compound formulations and chip passivation coatings. Results from use of this test chip during HAST and moisture uptake measurements in the DoD-funded Plastic Package Availability program (PPA) will be discussed. In the area of thermo-mechanical stress, results will be presented of experiments using the ATC04 stress measurement chip to evaluate in-plane comprehensive and shearing stresses in packages using a number of state-of-the-art molding compounds. The level of ionic getters added to inhibit corrosion for instance, affected the cure profile ad the subsequent stress magnitudes measured. These parts were subjected to increasing levels of stress through temperature and thermal shock testing. The integrity of W packages was monitored with scanning acoustic microscopy, and compared with the ensuing stress profiles recorded. Both test chips have shown their usefulness in characterizing the performance of various grades of molding compounds and coatings. When used judiciously with a comprehensive assembly level reliability program , such test chips are useful for rapid qualification of materials and processes resulting in cost-effective and faster time-to-market.