Die and Baseplate Warpage as Critical Factors for Thermal Interface Material Development

Considerable focus is placed by industry on development of practical thermal interface materials (TIMs) to address rapidly increasing heat flux and total power dissipation for semiconductors, used at different packaging levels for devices and modules. Warpage of baseplates and warpage of semiconductor die are two different factors that affect TIM performance in (a) power semiconductor modules, and (b) very high performance AI/GPU processors and ASICs, respectively. Current AI/GPU and CPU IC design are now in volume production that exhibit sharp increases in total power dissipation -- now in the kilowatt and higher range, similar to IGBT power semiconductors. Forecasts for AI processors, specifically, show continuing increases in die power dissipation through the next decade.Warpage for power semiconductors develops due to stresses induced (a) during soldering or sintering in assembly, and (b) during operation, due to rapid temperature cycling (caused by rapid switching during operation that equates to power cycling), leading to baseplate flexing and movement. In each circumstance, differences in coefficient of thermal expansion (CTE) between materials are primary factors leading to temperature-induced stresses and warpage.Warpage for integrated circuits packaged as C4 flip-chip devices occurs due to the CTE mismatch between the die and substrate when bonded. By contracting or expanding at different rates, a curvature or warpage will occur, thoroughly studied in thermal strains/stresses literature. Rapid external ambient temperature change may also be present, depending on application and physical environment.These different causes and types of warpage of critical components, the material contact surfaces involved, and the operational aspects and reliability requirements in differing environments all are factors that impact rapidly changing industry demands for significantly improved forms of TIMs. These differing performance demands are not simple and must be evaluated and understood by TIM developers – and simplistic targets such as a single bulk thermal conductivity or thermal resistance value alone cannot be used to set requirements for new material development programs.Separating out the two major industry sectors, power semiconductors and integrated circuits, is critical for identification and understanding of TIM development requirements, operational and reliability requirements, and which material types may or may not be suitable for specific application parameters. Experience in one sector is now increasingly applicable as industry learning to the second sector, including rapidly-developing innovations with metallic and other newer TIM types. This includes the increasing challenges of thermal management hardware technologies, specifically single- and two-phase liquid immersion.Many descriptions are available in academic and industry manuscripts of characterization methods of thermal resistance, resistance across interfaces, and including detailed examples of development of primarily polymeric TIM types [1–5]. Development of industry-standard test methodologies is continuing and many TIM developers and manufacturers have implemented these methods [6–8].The following is intended to identify principal differences between power and IC industry sectors and how requirements impact TIM material developments, how specific development challenges are intensifying, and new requirements are developing in an era of highly specialized thermal materials.