Charging Station of a Planar Miniature Thermal Ground Plane

Thermal ground planes (TGPs) are flat thin (less than 1 mm thick) heat pipes that can be used as a thermal spreader in a variety of microelectronic cooling applications. Like conventional heat pipes, TGP’s utilize two-phase cooling. Major advantages, include the ability to integrate directly with the microelectronic substrate for a wide range of applications; and the ability to operate in an adverse gravity environment of up to 20g. Other advantages include a very high thermal conductivity, reliability, no moving parts, electrodes, or need for external power. A key factor in the design of the TGP is evacuation prior to filling and introduction of the proper amount of working fluid (water) into the device. The major challenge of this work is to fill heat pipes with a total liquid volume of less than 1 ml, without being able to see into the device. The current filling station is an improvement over the current state of the art as it allows for accurate filling of micro liter sized volumes. Tests were performed to validate performance of the system and to verify that little to no non-condensable gasses were introduced to the system. Careful calibration of the amount of liquid introduced is essential. Therefore, calibration of the burettes utilized for a liquid fill range of 0.1 ml to 100ml was important. The magnitude of the pressure inside the TGP envelope is also an important factor. Calibration curves for the burettes and error characterization curves for a range of liquid charging volumes will be presented and discussed.