Insulating TO-264 packages

[mbroker]

Due to a mixup in my brain, I thought that the MJL21193/4 were TO-247 packages, not TO-3P/TO-264. It seems that proper insulators for TO-264 packages are very difficult to find. Moreover, the TO-247 packaged MJW21193/4 have extremely long lead times (over 2 months at best).

I was thinking that teflon film might be an answer to the insulation problem. McMaster Carr has some nice virgin Teflon film, .002" thick for $1.20 for a 12" x 12" square. At the price, it's certainly hard to beat! I am concerned that a 2 mil thickness would be rather flimsy -I would imagine it would rip or punch through rather easily, like Cling-Wrap. Then again, 2 mil Teflon could be rather stiff - I've never worked with it. Thermal Conductivity for Teflon is about .25W/m-K, or about .3 C/W-sq in for the 2 mil film.

Can anyone point me to some "normal" heat sink insulators for TO-3P packages? Has anyone used teflon or similar film as an insulator? Does anyone see any advantages or disadvantages to using it?

Thanks,

Mark Broker

[ThingyNess]

I can get TO-264 Mica insulators for $0.20cdn each locally here - I've never actually seen them for sale online, though.

With a proper knife, you can usually split one insulator into three or four with little difficulty.

(also, I always thought TO-3P was TO-247, and TO-264 was like the "Super" TO-3P (OnSemi refers to it as TO-3PBL)

[mbroker]

It would appear you are correct about the size.... I've never worked with flat packs before. However, OnSemi only lists TO-247 on the MJW components, not TO-247 and TO-3P. Siest la vie.

I live in poe-dunk Wisconsin. The only local electronics store is Radio Shack unless I want to drive a half hour North. But Radio Shack does have this nice 4% silver solder Fred was talking about....

I've pretty much decided that I'll buy the teflon and test it out. The very worst that happens is it doesn't work, I fry 6 free output devices, and resume the hunt for mica.


Thanks,

Mark Broker

[ThingyNess]

Best of luck. If you decide the teflon doesn't work, I could always send you some. They're $0.25cdn each after taxes. Shipping would be cheap (like a dollar) since you can fit 100 of them in a bubble envelope sandwiched between two pieces of cardboard.

[dkemppai]

Hi!

Check digikey for something called a sill pad. They are supposed to be better than the mica/silicone grease combo. I've only used then a little bit, but they seem to work well. It's nice to not have to deal with grease, but they supposedly are 50% better at conducting heat out of a device...

Example digikey part number...
BER178-ND

They are a little spendy, about $1.00 each! But worth it, Since transistors are usually more expensive!

Dan

[mbroker]

Yes, Newark also has some kapton reinforced rubber insulators for about US$.50 each.... In the wrong size, of course. I do try to stay away from Digikey whenever possible, since they really tend to screw the little guy moreso than other catalogs.

I asked a EE at work today (I am more of an ME by training and education) about local electronics shops. Apparently there's one a couple miles north of my apartment, and they carry Mallory and CDE caps Maybe they can help me

ThingyNess, thanks for the offer. Since we're trying to set this up as a future student project, I'm attempting to find long term sources for all parts. McMaster-Carr sells .004" thick mica sheets for a good price (~US$5.70 for a 4"x8" sheet). Looks rather tempting, also

Later,

Mark Broker