Hello all,
I have a doubt about thermal relief in the specific situation of power components.
Thermal relief is recommended to allow for better soldering of both thru-hole and SMD parts. Without thermal relief, the pad has a very high thermal conductivity to the plane and it is very difficult to heat, it cools down much quicker than the other pad's, creating all sorts of problems. So as I understand it, by adding thermal relief we are effectively increasing the pad's thermal resistance, solving many of these assembly problems. Up to this point everything is fine.
The problem comes when we have a heat-producing part, such as a D2-PAK or SO-8 power transistor. In these type of components, the tab or bottom pad is used to dissipate heat. We might have connected such thermal pad to a big plane to lower thermal resistance. But if we placed a thermal relief to help manufacturing, isn't the added thermal resistance of the relief making dissipation worse? Wouldn't it be better to have a direct connection of the power part to the plane?
I guess there must be some accepted compromise in this regard.
Thanks guys and gals,
Pedro