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Exploring High-temperature Reliability Limits for Silicone Adhesives
July 16, 2014 |Estimated reading time: 1 minute
Abstract
The thermal stability of silicone polymers, fluids, and resins has been well documented and studied extensively. The high-temperature performance of silicone adhesives and sealants used for electronics applications has only moderately been investigated. This report documents the effects of very high-temperature exposures to electronics-grade silicone adhesives and sealants for such properties as tensile strength, elongation, tensile modulus, weight loss, shrinkage, durometer, and lap shear adhesion. The goal of the work is to determine application “life expectancies” of the products as well as an extrapolated estimate of the Underwriter’s Laboratories’ “continuous use” temperature rating--the highest temperature at which a product is expected to lose no more than 50% of its original value for whatever key property degrades the fastest.
Four different formulations of silicone adhesives and sealants were evaluated for high-temperature stability. For these products, elongation was found to be the fastest degrading property among those tested. The data was found to fit a power curve of exposure temperature vs. time to reach a 50% loss of initial tensile strength and elongation to an R-squared value of 0.99 and to a linear fit in an Arrhenius plot to the same very strong fit. These plots could be used to closely estimate the effects of heat aging on the material over a wide range of temperatures.
Introduction
Silicone is the generic name used by many to identify a family of products based on the polydimethyl siloxane (PDMS) molecule with unique characteristics. For electronics applications silicones can be used as adhesives, encapsulants, gels, protective coatings, thermal management materials, even device packaging materials and wafer-level coatings.
Silicones have a combination of properties which contribute to provide a proven long-term reliability and performance in electronics applications. These features include: Unmatched thermal stability, flexibility, moisture resistance, adhesion to many common substrates used in electronics, low ionic impurity and compatibility with common processing techniques. Among all these characteristics that are shared by the majority of silicones, one property is recognized as one of the most useful in electronics applications and that is their consistent performance over a very wide temperature range. Read the full article here.Editor's Note: This article originally appeared in the June 2014 issue of SMT Magazine.