TN1250
Mounting the
module to a heat sink
DocID030935 Rev 1
9/16
4
Mounting the module to a heat sink
The heat produced by a module must be dissipated to avoid overheating and consequent
damage. The thermal performance of a module in combination with a heat sink can be
characterized by the sum of all thermal resistances along the thermal path: junction-to-
case, case-to-heatsink,and heatsink-to-ambient, as shown in the figure below.
Figure 9: Dissipation mechanism
Proper contact between the module substrate and the surface of the heat sink is crucial for
managing the overall thermal efficiency of the system. Thermal Interface Materials (TIMs)
are thermally conductive materials used to allow proper matching of the two surfaces and
improve heat transfer.
4.1
Requirements for a heat sink
In order to maximize heat transfer efficiency, the heat sink contact surface must be flat and
clean. The required heat sink surface qualities to achieve good thermal conductivity must
be according to DIN 4768-1. Roughness (Rz) should be 10
μm or less and flatness, based
on a length of 100 mm, should be 50 μm or less. In particular, the flatness must be less
than above value in the module mounting area, including the two clamp screws.
Furthermore, the interface surface of the heat sink must be free of particles and
contamination.
4.2
Application of thermal paste
Thermal paste thickness strongly affects the thermal resistivity between the module and the
heat sink. An even layer of 80 μm is recommended. Thermal grease quantity is sufficient if
a small amount of it can be seen out of the module after the heat sink mounting process.
4.3
Heatsink mounting
Heatsink mounting on the modules requires aligning the clamp screw holes of the module
with the two thread holes on the heatsink.
