LM4780 insulators?

[head_spaz]

The large TO_220 is an unusually large die.
The generic one-size-fits-all insulators are not ideal.
Q-Pad materials are carbon fiber based, and are electrically conductive.

So what's the alternative? .... silpad in sheets?

What are you using for LM4780 insulators?
Part numbers?
Suppliers?
Bulk materials?

Anyone have some extra stock laying around?

 

[VLSI]

I use Mica washers for the MT-200 package (used for 2SA1216/2SC2922 etc.) it’s not perfect, as the whole spacing should be 1mm wider.
I have mounted about 8 LM4780 devices so far and have had no trouble with them (yet)
Use the best thermal conducting paste you can find, Try the silver loaded stuff for a computer CPU.
Also you could try mounting the LM4780 directly to a good size chunk of thick copper (with paste) and then insulate that from the heatsink.

 

[Nordic]

Its a shame the sinks are made of aluminium otherwise you'd love Coollaboratory Liquid Pro

An externally hosted image should be here but it was not working when we last tested it.

Sadly this stuff will eat regular heatsinks for breakfast.

"Coollaboratory liquid metal" consists of a liquid metal alloy at a 100%. It does not contain any non-metallic additives like silicone, oxides etc. It does not include any solid components either. Due to this composition, which is completely new for heat conducting pastes, it surpasses the best previously existing heat conducting pastes in the heat conductivity value by the factor 9-10, more simple heat conducting pastes by the factor 100. "Coollaboratory liquid metal" is optimised in its composition for the application with high-quality copper coolers, and can also be used with gold and silver plated coolers (such as some waterblocks).

 

[CarlosT]

Wakefield kapton washers 175-6-280P...perfect for LM3875 and other similar .8" x .8" TO220s.

http://www.wakefield.com/pdf/accessories.pdf

 

[Minion]

I have tried Pieces of tempered Glass with heatsink compound on either side and Have gotten fair results.....

The hard part was drilling the Screw hole through the Glass without breaking it but once I got that figured out it actually worked pretty well....


Cheers

 

[BrianDonegan]

For LM3886 and 3875 you can use Bergquist pads. Digikey# BER118-ND is a kapton-based pad (K10). Highly recommend.

 

[traw]

shoot, can not find the baggie with the part number. it was from digikey. search the catalog pages i guess.

 

[traw]

i can mail you this sheet of 4 if you like

 

[BrianDonegan]

Digikey BER117-ND

 

[CarlosT]

The Wakefield stuff is cheaper...well like by about the cost of a small cup'o'joe

 

[BrianDonegan]

Cheaper, but not as good.

 

[CarlosT]

I'm sorry...not as good how? Both are kapton...right? Both are about the same size, thickness, etc.? Berquist has the je ne sais quoi of kaptoniness?

Expand...or retract...

 

[BrianDonegan]

Actually, I was thinking about the standard Wakefield pads, not the Kapton. However, the Bergquist pads do have better specs: higher thermal conductivity ( 1.3 vs 1.2) and lower thermal resistance* (0.24 vs 0.40).

http://www.wakefield.com/pdf/accessories.pdf

http://www.bergquistcompany.com/objects/data_sheets/PDS_SPK10_0305E.pdf

Expanded

* Note that the Wakefield datasheet does not list at which pressure this number is achieved, so we must assume it is at the recommended pressure of 350lb/in2. Bergquist achieves it's number at 200lb/in2. This would seem to indicate that less mounting pressure is required with the Bergquist pad.

 

[CarlosT]

Interesting...I'll have to look at that again. Short of a Kapton Shootout, it's hard to kow who's tweaking the numbers to make their stuff look good.

Related question...if you have a nekkid LM4780, besides the obvious kapton/sillyputty/mica pads, is there such a thing as a little bushing that goes inside the mounting tab hole to keep the screw threads from making contact?

 

[chipco3434]

Mouser has stuff...

http://www.mouser.com/catalog/628/1610.PDF

 

[BrianDonegan]

Kapton Shootout

Yeah. If I had paid attention and realized you were talking about the Kapton stuff in the first place, I would not have even brought it up. I think either pad would do a fine job.

there such a thing as a little bushing that goes inside the mounting tab hole to keep the screw threads from making contact?

You could use a shoulder washer as mentioned, but I have never used one with the 4780. I didn't think the metal was exposed to the hole, though. I should look again. I thik I just used 6-32 cap screws with washers.

 

[head_spaz]

Kapton Film - good deal on e-bay

Thanks for everyone's input.

This is what I ended up with.

Polymide Kapton MT Film 2 mil thick insulator
(Dupont 200MT). - Dirt cheap on e-bay

Item number: 180028543577
5.5"W x 72"L (that's six feet long !)
Buy it now price is : US $8.99
US Postal Service First Class Mail is : US $2.25
Shows Qty = 13 in stock.

For you bulk buyers, the same vendor has:
Item number: 180028544664
5.5"W x 144"L (that's 12 feet long)
Buy it now price is : US $16.49
US Postal Service First Class Mail is : US $3.00
Shows Qty = 8 in stock.

An externally hosted image should be here but it was not working when we last tested it.

P.S. I'm not affiliated with this vendor, just thought I'd pass
the info to you'se guys. Is this a bargain or what???

 

[CarlosT]

Interesting...that's significantly thinner than the Wakefield stuff so it should transfer heat nicely. I've heard that it's tough to cut. Let us know...

In the same vein of thought...has anyone considered making their own heatsink adhesive? The two-part epoxy stuff is awful expensive and comes in Lilliputian quantities with dubious shelf lives.

I was thinking about taking some regular silicone sealant and mixing in metal powder for conductivity.

 

[BrianDonegan]

Adding metal powder will make it electricly conductive as well, so be cautious of shorts.

 

[CarlosT]

So are there any thermally conductive silicone adhesives available to mere mortals...like at the Home Depot or something? Are we relegated to boutique adhesives at $35 per 1/2 ounce?