White Paper: Semiconductors & ICs
Epoxies and Glass Transition Temperature
SPONSORED BY: ![]()
Gain a better understanding about glass transition temperature (Tg) and why it is one of many factors to consider for bonding, sealing, coating and encapsulation applications. In this paper, we explore how temperature impacts the performance of polymers, why glass transition temperature is significant, and how it is measured. Tg can be an extremely useful yardstick for determining the reliability of epoxies as it pertains to temperature.
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Overview
The white paper from Master Bond Inc. discusses the critical role of glass transition temperature (Tg) in the performance of epoxies and thermosetting polymers. Tg is the temperature range where a cured epoxy transitions from a rigid, glassy state to a more pliable, rubbery state. This transition significantly affects the material's physical properties, including tensile strength, thermal expansion, and heat capacity.
The paper emphasizes that while a higher Tg generally indicates better heat resistance, it is not the sole factor to consider when selecting an epoxy for specific applications. For instance, lower Tg epoxies may be more suitable for applications involving rigorous thermal cycling with short dwell times above Tg, as they tend to be more flexible. Conversely, for sustained high-temperature applications, a higher Tg is essential.
The document outlines the methods used to determine Tg, including Differential Scanning Calorimetry (DSC), Thermo Mechanical Analysis (TMA), and Dynamic Mechanical Analysis (DMA). DSC measures changes in heat capacity as temperature rises, while TMA observes dimensional changes in the material to identify Tg. TMA is noted for its accuracy and reliability, making it a preferred method for measuring Tg, especially in filled systems. DMA, while the most precise, is more complex and involved.
The paper also highlights the importance of understanding the coefficient of thermal expansion (CTE), which quantifies how much a material expands or contracts with temperature changes. As a material passes through the Tg range, its CTE can increase dramatically, affecting its performance in applications.
Additionally, the white paper discusses exceptions to the general rule regarding Tg and temperature resistance, particularly with silicones, which have low Tg values but can perform well at high temperatures. It concludes by stressing the importance of testing epoxies in the specific context of their intended applications, as relying solely on Tg can be misleading.
Overall, the white paper serves as a comprehensive guide for design engineers, providing insights into the significance of Tg in epoxy selection and the various factors that influence material performance under temperature variations.