cause it's the PI and the Al slug is made from Phil's left over San
Miguel cans?

At 09:08 PM 7/15/2010, Paul Edwards wrote:
>Hey Phil,
>
>Nice to hear from you again...
>
>Here is my cents worth...
>
>Aluminum slug is acting like a
>         1) heat spreader
>         2) heat sink for impulse power dissipation because the
> readily heat     goes into the cooler Al block faster than PCB material
>         2) helps keep the screw and nut from  bowing the tab flange
> if          tightened too much
>
>Question though... Why is a slug of Al cut to size with a hole in
>it, cost less heatsink compound?  I would have thought chemical junk
>is cheaper then processed Al..
>
>Paul
>
>Paul Edwards
>Surface Art Engineering
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Phillip Bavaro
>Sent: Thursday, July 15, 2010 7:55 PM
>To: [log in to unmask]
>Subject: [TN] Mica and heat sink slug and TO-220
>
>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
>
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