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To: Mani1 who wrote (21429)	12/4/2000 12:42:03 PM
From: pgerassi	Read Replies (1) \| Respond to of 275872

Dear Mani: Even using the updated numbers 5.7C against a total drop of 25C (Tj - Tamb), (Tj - Tdie@heatsink) / (Tj - Tamb) is 23% of the drop for the bulk (evenly spread heat generation distribution) wafer region. For localized hot spots, the percentage could be 2 to 3 times as high. The worst case is of course a point heat source (all of the heat is generated at a single point), which would yield drops of 684C for the die and drops in the heatsink of 40 to 50C. Bulk resistance dominates in that case (no way could all the heat be generated (55W) in an area less than .01sqmm). One problem is that the figure I used (0.8W/cmC) may be for bulk thermal conductivity at 25C or 0C. The figure goes down as temperatures rise (I do not have a reference handy with the figures for 95C (or so)) and if it changes rapidly enough, could have an amplifying effect for larger temperature drops to exacerbate the problem. Pete