Design of thermal interfaces with embedded microchannels to control bond line formation

Abstract

Integrating microchannels at the thermal interfaces of heat sinks, spreaders, and microprocessor chips can reduce bond line thickness, assembly pressure, and overall thermal resistance. The channels help control the flow of particle-filled thermal interface materials (TIM) during the assembly squeeze but the relationship between channel geometry, material properties, and interfacial area is not fully understood. In the absence of meaningful analytical models, we develop a computational fluid dynamics approach to the non-Newtonian squeeze flow applied to rectangular 3D geometries. Experiments confirm the applicability of the models and illustrate the effect of viscoplasticity in highly loaded TIMs. Based on a first-principles thermal-fluidic model, the optimal width for a corner-to-corner channel is 608 μm for an 18x18 mm2 chip with 35 μm thick TIM bondline, or channel-to-chip size ratio of 0.068. Ongoing work will extend the technique to a general squeeze cell and multiple channel hierarchy levels for bond line optimization of high-performance thermal interface materials. ©2008 IEEE.