Commonly Used Joining Methods in Heat Pipe Assemblies

There are several methods that can be used when joining a heat pipe onto a heat sink plate or block and understanding the differences among each will be helpful in determining what method is the best option for your specific industry application.

Please see below for our list of commonly used joining methods when joining a heat pipe onto a plate or block as well as our recommended applications for each.

Should you have any questions about any specific method, please feel free to call or email us and we will connect you through to an engineer who can assist you.

Solder Bonding

The 58Bi42Sn solder with a eutectic at 138 oC is recommended when joining a heat pipe to a heat sink block or plate.  If the block or plate is made of aluminum, a  wettable solder surface should be plated with a protective layer such as electroless nickel coating.

There are two advantage to using 138 oC solder; lead free and creates less internal vapor pressure during the solder reflow process.  The lower internal vapor pressure is essential for allowing reflow in a flattened heat pipe.  If higher melting point solder is used for joining a flattened heat pipe, the internal vapor pressure will expand the flattened heat pipe into an oval shape.

ENERTRON_417191
ENERTRON_417192

The photos below illustrate when the join is completely floored with solder and then when the entire surface is fly cut.  This solder join method is mostly for aesthetic purposes. It’s thermal performance will not have a noticeable improvement over a non-floored join method.

ENERTRON SOLDER BONDING EXAMPLE 1
ENERTRON SOLDER BONDING EXAMPLE 2
Epoxy Bonding

If the aluminum surface cannot be plated with nickel or needs to be processed with another type of surface treatment such as anodization or chromate conversion coating then a solder bonding method is not ideal.

Under these circumstances, the thermal conductive epoxy bonding method should be considered.  Most epoxy requires an oven curing process to achieve the desired bond strength. The typical curing temperature ranges are between 100 and 160oC and the curing times vary from 30 minutes to an hour; depending on the epoxy manufacturer.

Press Fitted and Fly Cut

This method should be considered when the aluminum surface cannot be plated with nickel or when it needs to be processed with another type of surface treatment; such as anodization. This method is also used when epoxy is not an option for cost reduction purposes.

ENERTRON_PRESS FITTED AND FLY CUT METHOD

The thermal contact is formed by expanding the heat pipe against the block/plate after applying the pressure to the heat pipe. A final surface flatness can be obtained by fly cut machining.

Mechanical Fastening

If the heat pipe assembly needs to be disassembled in the field for maintenance or other purposes, then a mechanical fastening assembly method should be considered.

ENERTRON_MECHANICAL FASTENING METHOD
ENERTRON_MECHANICAL FASTENING METHOD 1
Assembled Fins

If the design objective is to dissipate heat directly to the forced air stream from a blower or fan, then a fin bank should be fabricated at the condenser end of the heat pipe.  There are two types of fabrication method commonly seen:

  • Preforming fins with flared hole(s) where:
    • Fins are press fitted onto heat pipe using a progressive stamping method. Flared section is then pressed against the heat pipe; forming the thermal contact.
  • Preforming fins with flared hole(s) where:
    • Fins are placed place onto the heat pipe(s) using solder preformed spacer(s) placed in between the two fins. Assembly is then placed into oven for solder reflowing.

More than 95% of heat pipe finned assemblies are press fitted. Solder bonding is only used for extra vibration, shock, or corrosive environments.

ENERTRON_ASSEMBLED FINS METHOD 1
ENERTRON_ASSEMBLED FINS METHOD `
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