A question regarding thermal adhesives - diyAudio
Go Back   Home > Forums > Design & Build > Parts

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 28th February 2007, 09:34 PM   #1
diyAudio Member
 
neil_kaye's Avatar
 
Join Date: Dec 2005
Location: San Francisco
Default A question regarding thermal adhesives

I am planning on using Artic Silver Thermal Adhesive to attach my Mosfets and Jfets to their appropriate heatsinks.
The chips need to be electrically isolated from the heatsinks, so i have the following questions:
1. Would a thin layer of Thermal adhesive (which is non conductive) plus the anodizing on the chassis be enough to stop the Fets from shorting?
I have silicone pads which i can use to further isolate the FETS but Artic Silver recommends against this; the theory being, why add more thermal resistance if you don't need it.

Any experience in regards to this?
  Reply With Quote
Old 28th February 2007, 09:45 PM   #2
diyAudio Member
 
Geek's Avatar
 
Join Date: Sep 2004
Default Re: A question regarding thermal adhesives

Hi,

Quote:
Originally posted by neil_kaye
1. Would a thin layer of Thermal adhesive (which is non conductive) plus the anodizing on the chassis be enough to stop the Fets from shorting?
Probably not, unless it specifies this.


Quote:
Originally posted by neil_kaye
I have silicone pads which i can use to further isolate the FETS but Artic Silver recommends against this; the theory being, why add more thermal resistance if you don't need it.
Yeah, thermal pads are crummy for higher power applications. Mixing any grease or adhesive and thermal pads is a no-no. Has to be either or.

Thin sheet of mica would be what I'd use.
  Reply With Quote
Old 1st March 2007, 12:32 AM   #3
diyAudio Member
 
neil_kaye's Avatar
 
Join Date: Dec 2005
Location: San Francisco
Thanks.
Do you have an online source for Mica?
  Reply With Quote
Old 1st March 2007, 12:34 AM   #4
diyAudio Moderator
 
pinkmouse's Avatar
 
Join Date: Apr 2002
Location: Chatham, England
Any load on the mica and it will shear. I'd stick to bolts.
__________________
Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
  Reply With Quote
Old 1st March 2007, 01:27 AM   #5
diyAudio Member
 
neil_kaye's Avatar
 
Join Date: Dec 2005
Location: San Francisco
I am going to give Artic Alumina a try: http://www.arcticsilver.com/arctic_a...l_adhesive.htm

It is completely non conductive so it should eliminate the need to additional thermal taps or pads
  Reply With Quote
Old 1st March 2007, 02:00 AM   #6
diyAudio Member
 
Pit Hinder's Avatar
 
Join Date: Nov 2006
Location: Hannover, Germany
Send a message via ICQ to Pit Hinder
Al,
mica was b****y good when nothing else was available. I'm 53 and my grandfather told me to keep away from that oldfashioned *beep* from his appreticeship days.

Pit
  Reply With Quote
Old 1st March 2007, 10:40 AM   #7
diyAudio Moderator
 
pinkmouse's Avatar
 
Join Date: Apr 2002
Location: Chatham, England
Yup. Mica is pretty good as an insulator. It's pretty strong in compression, but tension or lateral shear will delaminate it very easily. Glue on each side will lead to exactly this situation, which is why bolts, that hold it in compression, are the best bet.
__________________
Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
  Reply With Quote
Old 1st March 2007, 01:42 PM   #8
diyAudio Member
 
theAnonymous1's Avatar
 
Join Date: Feb 2004
Location: Anonymityville
www.mcmaster.com carries all kinds of mica. I bought some from them a few years ago for an amp. It can get a bit messy putting heat goop on both sides though.
  Reply With Quote
Old 1st March 2007, 09:18 PM   #9
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
mica with thermal compound on both sides performs very well and even better if you can get 0.001inch thick insulators. Many are 0.004 to 0.006inch.
A few of the self adhesive dry insulators perform better than mica but tend to be at the expensive end of the range.
The cheaper dry insulators usually perform worse than mica.
Compare the numbers/prices.

All anodise is a good insulator IF UNDAMAGED.
Some of the softer and thinner anodised surfaces scratch very easily. Be prepared for a few failures if you do not use insulators.
You can test before making the semis live. An elevated voltage between collector/drain and sink will prove it.
__________________
regards Andrew T.
  Reply With Quote
Old 2nd March 2007, 06:06 AM   #10
diyAudio Member
 
Geek's Avatar
 
Join Date: Sep 2004
Quote:
Originally posted by pinkmouse
Yup. Mica is pretty good as an insulator. It's pretty strong in compression, but tension or lateral shear will delaminate it very easily.
Yes, indeed!

Don't pick up the device by the heatsink
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Biasing/thermal compensation of Thermal Trak transistors Bob Cordell Solid State 161 8th March 2014 09:42 AM
Thermal Tracking Question Mark245 Solid State 7 27th February 2009 02:43 PM
Thermal runaway question ricsmuts Car Audio 39 22nd May 2008 04:03 PM


New To Site? Need Help?

All times are GMT. The time now is 01:52 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2