RE: [CAD_CAM_EDM_DRO] Keeping heat sinks on chips???

Danny,
What would you recommend to epoxy some circuitry for security reasons. I
would need to be non-conductive.
Thanks

www.soundlogicus.com
Plasma THC-300
Serial Spindle Speed control


-----Original Message-----
From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Danny Miller
Sent: Tuesday, April 21, 2009 1:42 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Keeping heat sinks on chips???

There are many thermal epoxies out there, Arctic Silver is the best,
Arctic Alumina is cheaper and just fine for this app. Clean the
surfaces and measure and mix carefully.

Be aware that adding heatsinks to the TOPS of chips, where there's no
thermal pad, has very limited effectiveness. The die inside is what
needs to be kept cool but the chip's case- probably plastic- strongly
insulates the die from the cooling heatsink. In this case reducing the
thermal resistance of the bond layer between the sink and the case is
beside the point when the die-to-case resistance is 100x bigger anyways.

I know you can't change the board, but any chip mfg who intended their
chip to be run at power levels exceeding the normal case/lead
dissipation either includes leads with a direct thermal connection to
the die (instead of a thin gold bondwire) or, far better, a thermal pad
on the bottom of the chip that can be soldered to a big copper pad on
the PCB to spread out the heat.

This weird stuff of gluing on heatsinks tends to mean the board designer
wants to run the chip outside its mfg specified ratings. And it often
won't end up getting the benefit expected.

Danny

Jon Elson wrote:

> Jack Mc Kie wrote:
>
>> My Mechatronics controller has heat sinks attached to the chips with

double sided tape. Sadly this doesn't want to stick and they keep falling
off. Any suggestions???

>>
>>
>>
> Either Thermalloy or Wakefield (heat sink manufacturers) used to make a
> thermally-conductive epoxy called Output.
> It was the only TC epoxy that didn't cost an arm and a leg. I don't
> know if this is still available, but there has to be something that will
> do the same job. Double-sided tape is worthless, unless it is designed
> for the purpose. Bergquist makes thermally conductive electrical
> insulating materials, and some of them come with adhesive coatings, but
> mostly those are one-side only. Check the Digi-Key catalog, they have
> an entire page of Bergquist items.
>
>
> Jon
>
>

------------------------------------

Addresses:
FAQ: http://www.ktmarketing.com/faq.html
FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
Post Messages: CAD_CAM_EDM_DRO@yahoogroups.com

Subscribe: CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
List owner: CAD_CAM_EDM_DRO-owner@yahoogroups.com, wanliker@...,
timg@...
Moderator: pentam@... indigo_red@... davemucha@...
[Moderators]
URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO

OFF Topic POSTS: General Machining
If you wish to post on unlimited OT subjects goto:
aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if
you have trouble.
http://www.metalworking.com/news_servers.html

http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
sister site to the CCED group, as many of the same members are there, for OT
subjects, that are not allowed on the CCED list.

NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
bill
List Mom
List Owner

Yahoo! Groups Links