Micro Heat Pipes for Stacked 3D Microelectronic Modules

In context of a European Commission funded project, development of a standardized multifunctional stacked 3D package was envisioned for potential applications in aviation, space and telecommunication sectors. The standardization and modularity was aimed to integrate packages from different technologies and to allow mutual slice inter-changeability. Thermal management solutions to the proposed new stacked 3D package as per the project specifications (a total of three stacked substrate slices, each slice of size 55 × 55 × 1 mm3 and total package height not exceeding 10.5 mm) are reported here. Three potential options were studied i.e. (a) module liquid cooling, (b) integration of miniature copper-water cylindrical heat pipes (OD 3.0 mm) with the 1.0 mm substrate slice and (c) development of flat plate heat pipes of 0.9 mm thickness. For options (a) and (b), initial tests have been performed taking aluminum as a representative material for AlSiC metal matrix composites which were to be employed in the final design. Further, copper based flat plate micro-structure conventional heat pipes have been developed and performance tested. Thermal interactions have been investigated with thermocouples coupled with infrared thermography. For safe operation up to 30W heating power (10W/slice), while thermal diffusion through the bare metallic substrate is sufficient for heat transfer from chip to the substrate, micro heat pipes should be employed to cool the substrate and transfer heat from it to an external cold plate. Flat plate heat pipes are advantageous for higher power levels per slice. Interlayer thermal interactions also affect the response of stacked 3D packages.