Path: ...!weretis.net!feeder6.news.weretis.net!usenet.blueworldhosting.com!diablo1.usenet.blueworldhosting.com!feeder.usenetexpress.com!tr3.iad1.usenetexpress.com!69.80.99.23.MISMATCH!local-2.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Sat, 06 Apr 2024 15:40:45 +0000 From: John Larkin Newsgroups: sci.electronics.design Subject: Re: silicone grease Date: Sat, 06 Apr 2024 08:39:04 -0700 Organization: Highland Tech Reply-To: xx@yy.com Message-ID: References: <050658@dontemail.com> <29ej0j5staom8amnb5lkfde7uc94m99hsf@4ax.com> <3vll0j9f1qj64k1m1pd6ae58iqtri27ldl@4ax.com> X-Newsreader: Forte Agent 3.1/32.783 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 34 X-Trace: sv3-ASFp/oG7/kZkTD261r1vuOy1wgKA4uLAfblZiVaqxjDDsZqK5PEXAFid8y6uA+D52ihlo6vaA99jKgU!P55EGP4s4jxk6lfA6nEfd78ldMSM85b1u8xofVvDlVI1G6+grcdUQL3oXbKSY+XjFDPTZR0leSD9!5y7+Yg== X-Complaints-To: www.supernews.com/docs/abuse.html X-DMCA-Complaints-To: www.supernews.com/docs/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Bytes: 2752 On Sat, 6 Apr 2024 11:53:25 -0000 (UTC), Jasen Betts wrote: >On 2024-04-01, john larkin wrote: >> On Mon, 01 Apr 2024 09:12:38 -0700, John Larkin >> wrote: >> >> The Bergquist pads I was looking at are theortetically 1.8 W/mK >> material, but the actual TO-220 theta suggests about half that in real >> life. >> >> T-global makes pads that are rated 5 W/mK. > >Honeywell does 8.5 with PTM7950 etc. > >It's a phase change material I need reliable electrical insulation, so phase-change or graphite won't do. That's another reason not to use mica... it's fragile. All the gap-pads that we have tested have been awful, numbers like 5 degc/watt for our TO-220. None come within a factor of three of the theta that we calculate based on their specified material thermal conductivity. Bummer. What really works is an AlN insulator with grease, like 0.35 K/W for the TO-220. The silicon itself is 0.74 j-c. I guess we'll do that, messy but effective. At 40 watts/fet, Tj = 80 (= cooler temp) * 40 * (0.74 + 0.35) = 124c We can't anodize the copper cooler. Hard anodize and phase change could be another option.