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July 2010

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TechNet E-Mail Forum <[log in to unmask]>, Dwight Mattix <[log in to unmask]>
Date:
Thu, 15 Jul 2010 23:20:29 -0700
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TechNet E-Mail Forum <[log in to unmask]>, Phillip Bavaro <[log in to unmask]>
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From:
Phillip Bavaro <[log in to unmask]>
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Nah, I only drink dark beer and San Miguel's dark beer (Cerveza Negra) only 
comes in bottles..........


________________________________
From: Dwight Mattix <[log in to unmask]>
To: [log in to unmask]
Sent: Fri, July 16, 2010 12:49:29 PM
Subject: Re: [TN] Mica and heat sink slug and TO-220

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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