[hpsdr] Fwd: Munin heat sink and spreader

[Tom McDermott]

My heat sink was also warped.  Initial gap between the spreader bar and the heatsink was about 0.009 inches.
I opened up a vice about 1 inch less than the length of the spreader bar, and placed the spreader bar across the vice opening. Then carefully banged at it with a hammer until the spreader bar was warped to match the heatsink. This closed the gap to the point where it was not possible to get a 0.0015 feeler gauge between the two, and it was hard to see light between them. 
 
Then using the heatsink compound, I placed a thin film between the two and rubbed them together. Without any screws, it was most difficult to remove the spreader bar from the heatsink due to the film adhesion. Good enough for me. Then screwed the bar in place.  The 8 or 9 thousandths of induced deflection of the bar did not present any problems with mounting the transistors to the PCB.
 
-- Tom, N5EG
 
 



On Thursday, October 10, 2013 7:19 AM, Phil Crosno <n6as at mac.com> wrote:
  
I used sandpaper and a lot of elbow grease on both the heat sink and copper spreader....

Phil
N6AS



Begin forwarded message:

From: Mike Culver <mculver at extencia.com>
>
>Subject: Re: [hpsdr] Munin heat sink and spreader
>
>Date: October 9, 2013 7:42:45 PM PDT
>
>To: HPSDR <hpsdr at openhpsdr.org>
>
>
>***** High Performance Software Defined Radio Discussion List *****
>
>Not 100%, but isn't Penetrox for aluminum wire joints? It's a great anti-oxidant but not a great heat transfer agent.
>
>I'd vote for filing in order to address the concave issue.
>
>Mike
>WA9QHP
>
>-----Original Message-----
>From: hpsdr-bounces at lists.openhpsdr.org [mailto:hpsdr-bounces at lists.openhpsdr.org] On Behalf Of AA8K73 GMail
>Sent: Wednesday, October 9, 2013 7:36 PM
>To: HPSDR
>Subject: [hpsdr] Munin heat sink and spreader
>
>***** High Performance Software Defined Radio Discussion List *****
>
>
>Has anyone else noticed a concave surface in the heat sink in the latest Munin kit?
>
>When I hold the copper spreader against the heat sink, it touches on the ends, but the middle portion is about 1 mm away. 
> I could:
>
>
>1. File the copper spreader and/or aluminum heat sink to get a 
>closer fit.
>
>2. Put the copper spreader in my arbor press and bend it to 
>conform to the heat sink.  But then it wouldn't be flat for the 
>transistors.
>
>3. Fill the gap with something to provide a better heat transfer 
>than air.
>
>4. Not worry and just screw it together.
>
>
>What do you think?
>
>
>Also, what about using Penetrox (zinc particles in petroleum) in 
>place of ordinary heat sink compound (ceramic particles in 
>silicon, I think) for the spreader/sink interface?  I've used 
>Penetrox frequently in industrial electrical work when joining 
>aluminum with copper.
>
>
>Mike - AA8K
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