Reliability of Thermal Interface Materials in Combined Mechanical and Thermal Stress

Emerging electronics in transportation, telecommunications, and autonomous driving require improved thermal management. Thermal interface materials (TIM) provide a thermal pathway for heat dissipation between thermal sources and sinks. These engineered materials must meet demanding targets including delivery of high performance, safe operation, and simplified design and assembly. Because of the complex needs to balance mechanical, thermal, and electrical performance, a deep understanding of the material science of TIMs has been developed. TIMs span a range of modulus to enable adhesive bonding or soft compliant gap filling. The fillers that provide thermal transport can be selected to provide a balance of cost, modulus, density, and thermal performance needed for the intended application. The TIM matrix and additive packages control rheology and ease of dispensing and assembly as well as the ability to select and ensure EHS compatibility and long-term sustainability. Thermal and mechanical cycling is critical to long term electronic device operation. Most thermal interface materials (TIM) are assessed in static thermal aging and cycling chambers. In addition to in-application performance, TIMs can experience a wide variety of environmental conditions prior to device assembly including the application process, storage of individual components, such as heat-sinks, and shipping. During assembly and use, impacts from the exposure to extreme temperature ranges and varied humidity conditions can have significant impacts on the TIMs' performance. This exposure can lead to dry-out and loss in thermal conductivity in some TIM materials. There is a need to understand material performance and define representative test methods to estimate TIM performance in realistic supply chain and application scenarios. In this paper the reliability of several commercial TIMs are assessed in combined thermal and mechanical stress to determine the impact of both mechanisms on the reliability and expected device stress.