TO-3P Insulators

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EchoWars

EchoWars

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Joined 2003
Does anyone make a Mica insulator for a TO-3P package? All I can find is the silicone pads from Parts Express.

In another thread Kapton tape was discussed, but the price is outragous, and 33m is waayyyy more than I'll ever need. Even if the price was acceptable, the only width I can find is .75" (Digikey), which isn't wide enough for a TO-3P device.

I'm getting pretty frustrated...why is a plain-old Mica insulator impossible to find? Should I just give up and order the silicone pad from Parts Express and hope it's good enough?
 
EchoWars

EchoWars

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Joined 2003
Nelson Pass

Nelson Pass

The one and only
Joined 2001
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EchoWars said:
Does anyone make a Mica insulator for a TO-3P package? All I can find is the silicone pads from Parts Express.

In another thread Kapton tape was discussed, but the price is outragous, and 33m is waayyyy more than I'll ever need. Even if the price was acceptable, the only width I can find is .75" (Digikey), which isn't wide enough for a TO-3P device.

I'm getting pretty frustrated...why is a plain-old Mica insulator impossible to find? Should I just give up and order the silicone pad from Parts Express and hope it's good enough?
Click to expand...

They are available - I think Digikey has them. If the application
is critical and high power, use the micas and grease. If the heat
sink is bead blasted or otherwise frosted finish and you have
high power, use micas and grease. Otherwise the silicone
products are fine.

Kapton? Never used it.
 
EchoWars

EchoWars

Member
Joined 2003
Hi Nelson!

Digikey sells the sil-pads and variations of, but seemingly not for TO-3P's. They do not have mica for anything other than TO-220 and TO-3, and perhaps one or two others, but not TO-3P. Bummer.

electron...

I may do that. I just sent a request for samples from Aavid, and if I get them I think I'll be the only one on the planet using mica for TO-3P. If I can't get them, I guess I'll settle for Parts Express sil-pads. :xeye:
 
BrianGT

BrianGT

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chipamp.com
EchoWars

EchoWars

Member
Joined 2003
BrianGT said:
Mouser does indeed carry an insulator that should work fine:
mouser link to 4180 Aavid Aluminum Oxide pad
"1,030 Ships Immediately"

They are noticibly bigger than the 4170 insulators.

Aavid's site:
http://www.aavidthermalloy.com/products/standard/access/insulate.shtml
They say: "For TO-218, TO-247, and TO-3P"

They are not listed on Mouser as insulators, so they are more difficult to find, unless you search for the 4180 part number.

--
Brian
Click to expand...
Yikes! 2mm thick! I think I might have room for 'em. Nice research though Brian!!

I thought that these oxide washers/spacers were fragile...? Never used 'em, so anyone else have firsthand experiance?

Still hoping that Aavid will send me freebies...:santa2:
 
BrianGT

BrianGT

Retired diyAudio Moderator
Joined 2002
chipamp.com
EchoWars said:
Yikes! 2mm thick! I think I might have room for 'em. Nice research though Brian!!

I thought that these oxide washers/spacers were fragile...? Never used 'em, so anyone else have firsthand experiance?

Still hoping that Aavid will send me freebies...:santa2:
Click to expand...

I have used the 4170 them for both the TO-3P (TO-264) and the TO-247 devices. The 4180 is bigger. As you can see, the 4170 works fine, since it is thicker and seperates the package from the heatsink. For the TO-264, most of the contact area on the package is covered with the 4170. I couldn't find the 4180 at the time, but it is a better choice.

TO-247:
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TO-264:
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As for getting the insulators, just buy them from Mouser, as shipping is cheap, and there is no minimum order. You might be waiting for a long time for the samples. I put a request in over 2 years ago, and still haven't received anything.

--
Brian
 
EchoWars

EchoWars

Member
Joined 2003
I got two responses from Aavid this morning...one wanting to know how many I needed, and another giving me links to two places that supposedly carry them..

Bisco Industries

...and another link at Heilind Industries which does not appear to work. Maybe the guy who wanted to know how many I could use will come through...

Still, the sources you gave Brian are appreciated. If I can't get the mica, I'll go with the others...
 
H

hughmon

Member
Joined 2004
If anyone should be interested in Kapton tape for whatever reason, McMaster-Carr sells it in a wide variety of widths, thickness's, and a couple of different lengths. Type in "Kapton Tape" in their search window. They also sell lead tape, as well as other materials suitable for damping mechanical resonances in chassis and turntables.

http://www.mcmaster.com

And I'm curious, why the high desire for the mica insulators?? About 10 years ago I looked for them for the TO-3P, and reluctantly ended up trying the silicone insulators. I've used the silicone ones ever since without a single incidence of failure (ok, I'm real careful about burrs, and in applications where there isn't much power I sometimes double them up). I'm aware that the mica/grease is a bit better up front in terms of thermal resistance, but when the grease starts drying out on the mica, things get a bit more problematic. Is there an issue of voltage stand-off (I wouldn't think that'd come into play until several hundred volts were reached)??
 
S

Sheldon

Member
Joined 2003
Call me nuts, but I've used plain old polyester film. It's tough, can tolerate modestly high temperatures (generally up to about 150 C) and is readily available from many sources. If it weren't a reasonable dielectric it wouldn't be used in caps. It's heat transfer characteristics aren't as good as the other materials, but that's a function of thickness. If thin enough it should be fine for moderately demanding applications. I wouldn't think, used with thermal grease, it could be worse than the layer on insulated chips. If you're worried about burrs or sharp edges, polish the part with a little fine wet and dry paper.

Sheldon
 
BrianGT

BrianGT

Retired diyAudio Moderator
Joined 2002
chipamp.com
niconoise said:
as an aside, note that some of the newer transistors like mjl21193 come in a package to-3pbl (to-264) which is larger than to-3p. the aavid to-3p pads are too small for those. i am still looking for to-264 insulators.
Click to expand...

If you get the Aluminum Oxide ones, they work fine, since they have the extra thickness. In the above picture, I am using Aavid 4170 TO-220 insulators for the TO-264 (TO-3P) MJL1302A devices, with the same size package as teh MJL21193.

I later picked up some of the 4180 Aavid pads from mouser, and they fit the output devices very nicely. I wouldn't worry about having them too small. The TO-220 ones work fine even, as they cover almost all the metal surface on the back.

--
Brian
 
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