Additional information
19 of 31
Revision 4.0
2021-10-11
Recommendations for board assembly of Infineon transistor outline
type packages
Mounting of through-hole devices
4.2
Component placement of THD
THDs are inserted either with special automatic equipment or manually. During this insertion, special care has
to be taken that excessive deformation or violent bending is avoided. The diameter of the drill holes in the PCB
has to be appropriate for the tolerances of component leads, drill hole position placement accuracy, and
properties of the solder alloy used.
4.3
Heat sink mounting
For special packages with high power dissipation, heat sinks can be mounted before or after soldering the
leads.
Insulating material
Commonly used insulating materials are mica and rubber. Mica is much harder than rubber. For softer
materials, the mounting torque in particular needs to be controlled very carefully in order to avoid high
mechanical stress and damage to the package as shown in
Figure 12
Schematic view of the influence of the insulating material (left mica, right rubber) on the
generation of mechanical stress.
Thermal grease
A specific amount of grease must be applied. The amount should be determined during customer process
evaluation. When the amount is correct, a very small amount of grease should appear around the perimeter of
each surface as the assembly is slowly torqued to the recommended value. Examination of a demounted
assembly should reveal even wetting across each surface.
Heat sink requirements
The contact areas of the package and the heat sink must be free of any particles and damage as well as any
other contamination. The following surface conditions are recommended:
Heat sink roughness
R
Z
≤ 10 µm
Heat sink flatness
≤ 10 µm (reference length 15 mm)
Attachment holes
Drill holes for heat sink screw mounting should be as small as possible. Using drill holes that are too big will
reduce the effectiveness of the heat sink.
The flatness and effectiveness of the heat sink will also be reduced by intrusions and/or burrs around the hole.
These are caused by the punching or drilling process and should be less than the specified heat sink roughness
and flatness.
If intrusions or large drill holes are unavoidable, a fitting square washer should be used to get a good and flat
contact between heat sink and package.
