Historically, for semiconductors subject to standard operating temperatures--which tend not to exceed 125°C--the Tg (glass transition temperatures) of the organic packaging materials protecting the chips is usually around 175°C. Given that, when it comes to electronics operating at high temperatures—typically an environment where the ambient temperature exceeds 200°C—the use of organic materials is generally prohibited due to rapid degradation. At those elevated temperatures, the packaging materials selected are generally composed of metals and ceramics but these materials come with their own shortfalls as well as higher material and manufacturing costs. Therefore, it would be desirable if there were ‘ruggedized’ versions of the organic compounds so commonly used in semiconductor packaging but available for more extreme temperatures, both to reduce cost and package footprint.
Meanwhile, the demands from recent developments in high performance computing (HPC) and high-speed data networks means a greater need for increased power and thermal dissipation coupled with very large package body sizes to accommodate the high I/O count. The latest in server microprocessor (MPU) products can easily generate up to 300W during operation, and the heat generated must be quickly transported away from chip to prevent the threat of thermal shutdown. The thermal dissipation issue is controlled by the use of heat spreaders and heat sinks, both of which are intended to make contact with the back-side of a flipped MPU via a thermal interface material (TIM), as part of a large die, large body-size flip-chip ball grid array (FCBGA) package.
The thermal interface materials discussed here are examples of organic engineered materials that are capable of withstanding higher operating temperatures than typically seen by semiconductors encased in organic-based packaging. This paper will look at the key material and mechanical attributes for a good thermal interface material, examines the pros-and-cons of various thermal interface material formulations, and discusses the factors for reliable thermal dissipation performance.