Heatsink mounting large devices

[trwh]

Hi

What electrical insulators do people use when mounting larger devices, such as power opamps (the LM3886 in my case) onto heatsinks?

In the past I have simply used a row of mica washers cut for TO220 devices, but since this new project is for a higher power application I'd like to avoid this 'bodge'. Some of the holes in the TO220 washers were sandwiched between the metal tab and the heatsink; this concerned me since although there was no physical contact, I'm not sure how good an electrical insulator thermal compound is.

Thanks!
TRWH.

 

[annex666]

You're right about heatsink compound - most good thermal conductors also tend to be good electrical conductors too.

As for thermal interface materials try reading Rod's heatsink article;

http://sound.westhost.com/heatsinks.htm

 

[roddyama]

Hi TRWH,

Take a look at this thread. It provides a few sources for insulator material.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=5446

Stay Cool
Rodd Yamas***a

 

[trwh]

Thanks for the replies!

I had seen some large uncut insulator sheets for sale, but as someone says in the thread Rod linked to, they are very expensive. I wonder why insulators for larger packages aren't easier to find - they must be frequently used in commercial gear.

Thanks,
Tim.

 

[Zapped]

I have a very large sheet (several feet by about 1 foot, as I remember) of electrically insulating material that I got as a free sample from Thermalloy. The stuff is dark amber color and fairly transparent. I have seen TO-3 device insulators that resemble it. I have no idea what thermal transfer characteristics it has (no doubt grease or Aavid's paraffin-like stick compound would be required as well on it) but electrically it is suitable. With a little research, we could look up the precise insulation characteristics, if you need exactitude. If you tell me what size strips you need, I will cut off some and send it to you. No cost to me, so no cost to you. (The word "prototype" must make those account exec's go all warm inside.)

Larry Wright
Seattle area

 

[trwh]

Larry,

Thanks for your kind offer, but another forum member has already agreed to send me some.

"The word "prototype" must make those account exec's go all warm inside."

Hehe, good job for us, too!

Thanks again,
Tim.

 

[kec]

Larry,

Sounds like you have kapton. Rod (ESP) states that the thermal resistance is 0.9 - 1.5.

http://sound.westhost.com/heatsinks.htm

-Ken