Therma-Base Heat Sink
Today's Challenge: More Power in Smaller Packages
Therma-Base is a vapor spreader used as the base of a heat sink.
As electronic devices decrease in size and increase in power, the required heat sinks have grown to be larger than the devices. Heat sinks are most efficient when there is a uniform heat flux applied over the entire base. "Spreading resistance"1 occurs when a heat sink with a large baseplate area is attached to a heat source of a smaller footprint area. The higher the power, the smaller the source, and the farther the source is off-center, the greater the thermal spreading resistance as shown below.
The brute force approach to overcoming spreading resistance is to increase the size of the heat sink, increase the thickness of the base, increase the airflow, or decrease the incoming air temperature. These steps increase weight, noise, system complexity, and expense. When a solution cannot be achieved, the impact can be much greater: lost profits due to reduced electronics' performance, decreased reliability due to high operating temperatures and fan speeds, and delays in new product introductions while thermal issues get resolved.
Thermacore Therma-Base Heat Sinks
Thermacore's Therma-Base heat sinks deliver higher performance by alleviating spreading resistance. They operate in the same way conventional heat pipe heat sinks do, through a two-phase heat transfer process.
The base of a Therma-Base heat sink is a vapor chamber, a vacuum vessel with a saturated wick structure lining the inside walls. As heat is applied to the base, the working fluid at that location immediately vaporizes, and the vapor rushes to fill the vacuum. Wherever the vapor comes into contact with a cooler wall surface it will condense, releasing its latent heat of vaporization. The condensed fluid returns to the heat source via capillary action in the wick structure. It is this capillary action that enables the Therma-Base heat sink to work in any orientation with respect to gravity. As in a heat pipe, the thermal resistance associated with the vapor spreading is negligible, providing an effective means of spreading the heat from a concentrated source to a large surface.
Internal structure of a Therma-Base Heat Sink
The thermodynamic attributes of water make it an order of magnitude better than any other working fluid for the majority of electronics cooling applications2 including Therma-Base heat sinks. Water's high latent heat of vaporization spreads more heat with less fluid flow. Its high surface tension, when used in combination with Thermacore's proprietary sintered powder wick, generates a large capillary force that allows operation in any orientation. Water's high thermal conductivity minimizes the DT associated with conduction through the wick. High flux applications benefit most from Thermacore's unique internal wick architecture, which enables Therma-Base heat sinks to handle heat fluxes over 80 W/cm2 in standard products. In addition, custom wick structures are available that substantially increase flux capabilities without increasing thermal resistance, providing a seamless growth path for the future.
Thermacore International, Inc., 780 Eden Road, Lancaster, PA 17601. Tel: 717-569-6551; Fax: 717-569-8424.