Ok, I am scratching my head on this one....but I have been on an extended vacation and might not be seeing this clearly (but I doubt it), so I thought I would post it for your comments. A company here in the Philippines is doing final assy on a circuit board built in Thailand which consists of adding an anodized aluminum slug beneath a previously soldered TO-220. The design calls for the "sandwich" to be mounted flush to the PWB using a screw and nut. My assumption is that it is intended to have the generated heat be dissipated into the PWB as opposed to being mounted on heat sink fins and dissipating into the air. Not the best design but not uncommon. A thin layer of thermally conductive adhesive or gasket is typically used. When I watch the actual assembly, I realize that the designer has added one more twist to the sandwich......a piece of 0.14 mm thick Mica sheet between the aluminum slug and the PWB. The only thermal compound is a small dot between the slug and the Mica (basically adhering the slug and Mica alignment). One thing to keep in mind that this is a "high volume" product and the cost of thermal compound far outweighs the cost of the slug, and increasing cost (complete layer of thermal grease between all layers of the sandwich) is not an option. Mica is an electrical requirement but I am questioning the use of the anodized aluminum slug in this design. I am suggesting that we run a test with the slug removed entirely. As I mentioned, I really haven't had much cerebral challenge over the past year and a half, so all comments are appreciated. Phil ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------