Thermally conductive, electrical insulating material? 1

[KevinH673]

I'm interested if there is a material I can use in a 1/2" thick piece I have, that will dissipate heat (it is up against a cold plate), yet will electrically insulate. Can anyone recommend anything?

Am I better off posting in the composite forum? I found a polymer composite with boron nitride coated carbon flakes, but this requires a mold. This piece must be tapped for bolts! I have attached a picture of the part, and where it is mounted, if this helps...

Thank you all.
-Kevin

 

[NickE]

I dont know about 1/2" thick, but TO-3 Power transistors use mica sheet to insulate, while still conducting heat to the sink.

 

[btrueblood]

One of the higher conductivity ceramics is alumina (Al2O3), it has heat conductivity close to that of titanium. You need high-density (pressed/sintered) material to get it. Diamond is even better...but kinda spendy at 1/2" thick.

 

[IRstuff]

Mica sheets are usually thinner than paper, though.

You can do a websearch: machinable ceramic thermally conductive

resulting in:

http://www.precision-ceramics.co.uk/shapal.htm

supposedly drillable.

TTFN

FAQ731-376

 

[KevinH673]

Thanks for the help.

I believe it will be okay to machine the part from aluminum, and put some kind of coating on it. In this event, the mica sheets may be okay, assuming that a thing sheet of mica will be enough to electrically insulate the piece. I will keep searching though. Thanks again.

 

[ornerynorsk]

Anodized aluminum is actually non-conductive to a degree. What kind of voltage/amperage do you need to insulate against, and in what kind of environment?

 

[unclesyd]

Could you work in coating for Aluminum similar to those used on cookware. I used this type for a development project by buying a case of cookie sheets and making the part from them. Most of these coatings have very good dielectric strength and will take pretty high heat. Most of these are Fluorocarbon with or without additives and are extremely tough.
There are some ceramic type coating for Al but at present are very expensive and are limited in size.

http://www.whitfordww.com/design/electrical.html

http://www.enduracoatings.com/prod100_a.asp

Can you come back with your actual requirements as to temperature and dielectric strength

 

[KevinH673]

Thank you for the replies.

I asked the electrical engineer, as far as electrical properties, it is dealing with (estimating) 9 V, 1/2 A, 4~5 W. He did not know the temperature, but the aluminum part is not too hot to touch. Without it, the heat sink on the boards it's attached to get too hot to touch, though (sorry so vague).

Upon further thought, I'm not sure I can use pieces like the mica sheets on the ends, as there are bolts attached to the electrical boards on this piece, and other bolts that attach to the base. The bolts would carry current, unless there is some coating I could spray in the threads. Thoughts?

IRStuff - I have emailed that company you posted the link to and will look into getting a quote from there, thanks.

 

[IRstuff]

Are these bolts highly torqued? People have used non-conductive washers and sleeves for electrical isolation in the past.

TTFN

FAQ731-376

 

[unclesyd]

While cooking my wife's and I's breakfaast on an electric range top a thought struck me.
As you are leaning toward Mica and bolting it on I think you should look at alternatives to Mica such as the ceramic glasses like Pyroceram that will fill your needs. Here is just one of many suppliers of these materials. If you look at the Whitford site in my previous post you will find a coating "Xylan" that is one of the better dielectric coatings for fasteners available. You might be able to find machine screws off the shelve coated with Xylan.

http://www.fireviewglass.com/index.asp

Another thought is that it may be possible to anchor what ever type material is used by using posts with a ceramic adhesive or potting compound.

 

[KevinH673]

Thanks unclesyd, I will look into it (I appreciate that you were considering my problem outside of when you first read it, as well).

 

[KevinH673]

I'm going to find out pricing on Xyland coated bolts today now that I'm back in the office. Will the material work as an electric insulator for the numbers I mentioned?

(Estimating) 9 V, 1/2 A, 4~5 W.

Thanks in advance (and for the help).

 

[KevinH673]

It looks as though the properties are 1,000 V/25 micron of Xylan electrical insulating, so that should be plenty fine as long as the 25 microns is what is applied to the fastners. Will it also be a concern that the Xylan may come off when the bolt is tightened?

 

[KevinH673]

I was given a quote back from precision-ceramics, though I'm not sure if we will be going that route or not. Should we be looking for a cheaper solution, what do you all think of covering the outside of the aluminum block with a Mica sheet (it currently has a Silpad, which I believe is a Mica sheet with some added coating), and cutting out piece of the Mica for the holes. Then, using nylon bolts, along with nylon/plastic washers for standoffs. This seems to be a pretty basic/cheap fix for this problem, should another material not be in the budget.

 

[unclesyd]

There is always a cheaper or better solution to problem such as yours but there comes a time you have to do something or you will burnout. I'll guarantee that the minute you attach whatever you choose to do the the job you will find or someone will suggest a neater way of doing it.
I would try this approach as starting point.

A little warning, Mica is not the easiest thing to get a neat hole in. Another thing give you self a little leeway in the design for expansion of the Al and be aware that Mica thermal expansion is very low.

For your Nylon Fasteners take a look at Micro Plastics as they have about anything you need in the Nylon line.

https://secure.microplastics.com/category.aspx?fam=10&sec=᷎鱤띝鬼鍮唛뭀爘

Just thought of another possible solution. Take a look at Glyptal Insulating Paint for you Al plate and fastener heads. This is one tough paint that been around for a long time as an electrical insulator and heat conductor.
I've used it in some pretty tough conditions, both temperature wise and chemical exposure. It will easily take the 135C temperature mention in the description.

http://www.caswellplating.com/aids/glyptal.html

 

[KevinH673]

Syd, that paint seems interesting, but will painting it on the Aluminum work well enough to be the sole electrical insulator? Or are you suggesting it in addition to the Mica sheet?

 

[unclesyd]

The Glyptal 1201 coating should be good enough alone. It was/is used for years in all types of industrial electrical apparatus many times as the only form of electrical insulation. I have also used the Glyptal 1202 material as a masking for electrochemical milling up to 100 VDC @ 400 amps.

It might take a little experimentation to get an even coat.
For maximum durability you may need to bake it. If you have any questions the Glyptal people have always been very helpful.

http://www.glyptal.com/Glyptal_Product_Data_Sheets.htm

 

[SnTMan]

KevinH673, for what little it's worth I have found that if you can leave your hand on a hot object for any time at all, its probably not over about 150 F.

Regards,

Mike

 

[hendersdc]

Try using Sarcon thermal interface material from Fujipoly. It can be die cut and adhesive backed. Good thermal conductivity and electrical insulation.

http://www.fujipoly.com/products/genProductLine.asp?ProductLine=Sarcon_Thermal_Interface_Materials

 

[mighoser]

I'd use Sil-Pad or Gap-Pad products from this manuf.

http://www.bergquistcompany.com/thermal_materials.cfm