Heat Pipes Protect Against Thermal Failure in Embedded Electronics

Embedded computing systems are important in the military of today. A given mission uses the critical functionality for data processing and significant computing power. The systems’ electronics are extremely expensive. Often the thermal management solution is overlooked. Electronics intensify thermal challenges. Trends lean toward packaging with less volume and weight and higher heat fluxes.

Multiple electronics cards that are inserted into a chassis or rack are embedded into computing systems. They are sealed to assure no small particles or liquid comes in contact with the electronics. Mechanical retainer clamps hold the cards in the chassis. Heat is conducted to the edge of the card, through the clamp, along the chassis until it is rejected through pumped liquid or convection.

The most economical and easiest approach to improving thermal performance is the reduction of thermal gradients caused by conduction. Embedded heat pipes are the best method to achieve the reduction. Heatpipes offer passive, efficient heat transfer.

Utilizing heat pipes is a two-phase process of transferring heat. The vaporization of a fluid’s latent heat is used to an advantage. The closed loop system is made up of a small amount of liquid, an internal wick structure, and a sealed envelope or tube. During the process, there is no air in the tubes, which allows heatpipes to maintain vapor and liquid phases over a wide range of temperatures. 

Waste heat enters the heat pipes near the evaporator, which is a heat generating component. As the heat vaporizes the liquids, an internal pressure gradient is formed. Vapor is forced to the condenser, by the internal pressure gradient. Here the fluid loses its heat, condenses, and is returned to the evaporator through the wick structure’s capillary force.

Most common heatpipes use copper envelopes for applications involving terrestrial electronic cooling. The heat pipes also have a copper wick and the working fluid used, is water. The system provides the ultimate in power capacity within the temperature range of typical electronic operation.

For further details about heatpipes and heat pipes please visit the website.

Selecting Suitable Heat Sinks

Computer designers keep products cool by following some fundamental equations for designing heat sinks that use forced air or natural convection cooling. High current diodes, numerous power-supply regulator assemblies, and power modules and transistors generate more heat than the mass can dissipate safely. To effectively increase the surface area and mass of heat-dissipating junctions, suitable heatsinks must be securely fastened to power devices.

Heat sinks are available in a variety of surface finishes, colors, sizes, and shapes for general and specific semiconductor applications. The amount of heat generated by a power module or semiconductor depends on the applied signal shape, signal amplitude, bias level, and operation mode. The devices need heatsinks to dissipate the generated internal power.

High current diodes and silicon power transistors need heat sinks that allow maximum junction temperature. Heat-generating devices that are not connected to heatsinks that provide greater surface area and mass will barely approach the voltage and junction current specifications, before exceeding the maximum temperature of the collector junction. That is why device specification sheets list characteristics with devices mounted on heat sinks of considerable size, usually referred to as ‘infinite’ heatsinks.

The surrounding air temperature of the heat-generating devices must be considerably less than the allowable temperature of the junction for devices to cool. Heat sinks attempt to reduce the temperature of the junction to that of surrounding mediums. To be thermally perfect the heatsinks would allow the transistor junction temperature to reach the temperature of the lower ambient. 

Reaching that temperature is impossible in practice. The connections are thermally imperfect and consequently, produce temperature differentials. The variable between ambient and collector junctions are kept to a minimum with heat sinks.

For further details about heatsinks and heat sinks please visit the website.