I check photos of de-lidded CPUs to determine the layout of cores, uncore controllers, cache, and other "hot" areas. If I'm using a thick TIM like AS5 then I heat it up a bit (let the tube sit in very hot water for a few minutes). I spread thin "rice grain" lines above the "hottest" areas and slide/scrape it evenly (about 1 mil thick, maybe) across the entire IHS with a razor blade. I sometimes also scrape a layer across the base of the heatsink, if my TIM seems runny. I let it sit and settle for some hours or a day, and of course most TIMs have a curing period (of up to a week or more) before best thermal performance is realized. I've never had any bubbles, voids, or bad temps. The idea is to use the absolute minimum possible while still getting complete coverage on the mating surfaces, too little is better than too much. I ensure all surfaces are absolutely chemically/mechanically clean, not a trace of dust, residue, or fingerprint oil. I haven't honed and lapped a CPU or heatsink in years, but some people swear it helps - beware that some CPU/heatsink geometries are deliberately designed to not be flat and sometimes this means things don't really fit properly and a "compatible" cooler will be mismatched. Gelid GC Extreme, Prolimatek PK-1, and good old Arctic Silver 5 are my TIMs of choice (depends on application, mostly). A lot of people swear by IC Diamond, Tuniq, and Thermene, but I've had decidedly mediocre experiences with them. Indigo XTreme and Coollaboratory Ultra are superior to any paste TIMs, but often require several (expensive) applications for best results, are a serious pain to scrub off, and usually aren't compatible with the sorts of big air coolers I prefer.
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