Things to Consider When Joining A Heat Pipe to A Heat Sink Plate or Block

A heat pipe can be best understood as a Heat Super Highway. It has one primary function – to transport heat. If you look at our freeway and surface street infrastructures, you will notice that they are primarily designed to move the traffic. The surface streets are for gathering motor vehicle traffic; speedily moving vehicles from one city to the other via highways and freeways with the final traffic being distributed to its final destination via surface streets. A thermal assembly has a similar infrastructure as our road way systems only its primary function is to transport and dissipate heat.

A thermal assembly typically consists of several types of mechanical components including a heat sink, fins, fan, heat spreader plate, thermoelectric cooler, and/or a heat pipe. Heat is gathered by a heat collecting component, then passed to the evaporator end of a heat pipe, then onto the condensor end of the heat pipe with its final destination being dissipation to the ambient via fins or a heat sink. And just as surface streets and freeway systems need non-constricting passages to allow for efficient flow from in and out of the roadway, a heat pipe must also be thermally and mechanically joined in a way that allows the external component within the assembly to remain an effective thermal interface with full mechanical integrity. Thus, the temperature gradients along the thermal path from the heat source to the heat sink can be minimized to avoid thermal traffic “bottlenecks”.

This article will address the guidelines on how to build an effective thermal and mechanical connection between the heat pipe and the external thermal components.

Things to Consider When Joining a Heat Pipe to A Heat Sink Plate or Block

A plate or block made of aluminum or copper is typically designed to thermally connect the heat source (CPU or power electronics component) to a heat pipe.

To ensure an effective thermal and mechanical connection between your heat pipe and plate/block, there are several factors that should be kept in mind:

Do Not Design the Heat Pipe by Inserting It into A Deep Hole in A Plate or Block

When joining a heat pipe to a plate or block, please consider the following drawbacks to inserting your heat pipe into a deep hole within the heat sink plate or block:

  • A hole’s ID tolerance and a heat pipe’s OD tolerance will cause a variable gap thickness between the pipe and wall. This variable is the number one cause for high thermal resistance
  • It will be very difficult to evenly distribute the thermal grease or solder paste along the inner gap. In fact, if the thermal grease or solder paste is pre-applied to the pipe surface, once the pipe has been inserted into the hole, almost all the grease or solder paste will be scraped at the mouth.

On rare occasions, this design form is needed in order to dissipate the heat pipe from both sides of the plate or block. If this is the case for your specific application, we recommend that your design be made to split the block or plate into two symmetrical parts with grooves with the heat pipe being sandwiched in between.

With this design method, the gap between the pipe and the wall will be minimized and the solder paste, or thermal grease will be evenly applied to the surface of the groove walls before the reflowing or curing process. If the assembled parts need to be disassembled in the field for maintenance purposes, a thermal conductive grease may be used.

In most thermal management designs however, the heat is typically inputted from one side of the heat pipe.

For applications such as these, the assembly can be designed by placing the heat pipe onto an open groove on a plate or a block. Soldering or thermal conductive epoxy should then be used to secure the heat pipe within the groove.

To view our list of commonly used joining methods, please visit our Commonly Used Joining Methods blog post.

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