C&H Technology PowIRtab Mounting Guidelines - Manual (Page 5)

Application Note
4.2 Contact Thermal resistance as a Function of Force
Above the Die (Clip Mounting).
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 50 100 150 200 250 300
Force / N
Thermal Resistance C/W
Dry Mounting
With Heatsink Compound
Figure 8
Figure 8 shows the contact thermal resistance as a
function of force above the die with and without heatsink.
It can be seen from the graph that when heatsink
compound is not used the contact resistance decreases
with increasing force. However there is a point beyond
which the advantage gained by increasing the force is
offset by the additional cost required to do so. The use of
heatsink compound reduces the thermal resistance by a
factor of 85% and also makes the thermal resistance less
dependent on the applied force.
This measurement was acheived using a device with
60W power applied for 100secs, on an ‘infinite’ heatsink.
Recommended force:
Without heatsink compound: 20N (4.5lbf) minimum to
give a thermal resistance, case to sink, of 1.5
o C/W.
With heatsink compound: 20N (4.5lbf) minimum to give a
thermal resistance, case to sink, of 0.23
o C/W.
5.0 Summary Table
Screw Mounting Maximum allowable torque
(Tab & lead)
Thermal mounting
Clip Mounting Maximum allowable force
Thermal mounting Without heatsink compound
With heatsink compound
250N (56.21lbf)
3Nm (2.2 lbf ft)
Without heatsink compound
With heatsink compound
1 o C/W @ 1.1Nm
0.22 o C/W @ 0.8Nm
1.5 o C/W @ 20N
0.23 o C/W @ 20N
Laminated Busbar supplier
Rogers Mektron Busbar Division
Rogers N.V.
Afrikalaan 188,9000 Gent
Belgium