Happy that Cathar talk about that, it was the same idea as mine to make my proper die with IHS but without TIM to avoid assembly, never realized because no time... Not difficult to mill at all, some care should be take to avoid conduction secondary paths. I would to use a MOSFET because of the small size and capable to dissipate a lot of power easily and easy to control, power resistors or cartbridge are generally too big for a small and light die like that (no need to heat 500 gr of copper, too long and useless...). TIM die/IHS is only a gap in Rth, its thickness is too small to change flux repartition, so we could pull out this element and get a solid one piece die with a flat surface above. IHS and die center would be instrumented with very small TC using EDM holes (diam. <0.3mm). This kind of die would be much better than bare die for sure, nearer to reality in terms of flux spreading (always different with any WB !)
In french on attached pic but you'll understand... I think Cathar's idea is like mine if I understood well.
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