Heat Sink-Transistor Insulating Tape?

[The Heater]

Hi, all:

Can someone tell me where I can buy replacement tape that goes between the power transistors and the heat sink (and the aluminum hold down bar) in a car audio amplifier? And what is it called?

I have an Orion 4100gx and although I have not pulled the bar yet, some of the insulating tape under the bar appears to have been burned through.

Thanks.

 

[Perry Babin]

It's Kapton (polyimide is the generic name). The most commonly used thickness is 1mil (0.001").

 

[The Heater]

Well, looking on Digikey, here is one search result I have. Are any of these products suitable? There is a column listing the thermal conductivity, and some are a lot more than others in this search result.

Fans, Thermal Management | Thermal - Pads, Sheets | DigiKey

 

[The Heater]

And I did some searching on this web forum, and apparently I have to use a thermal grease (where exactly I am still uncertain but thinking it would be between the transistor surface and what it touches). Here is the search result on Digikey for that stuff. Any narrowing of these results that can help me out here is appreciated.

Fans, Thermal Management | Thermal - Adhesives, Epoxies, Greases, Pastes | DigiKey

 

[Perry Babin]

345-1007-ND If you're going to do more repairs, buy a tube of Dow Corning 340 from eBay.

You can get the tape from ebay.

 

[JonSnell Electronic]

Using Heatsink Paste with these pads will destroy the properties of the pads. Heatsink compound is for mica washers!

 

[1moreamp]

Hi, all:

Can someone tell me where I can buy replacement tape that goes between the power transistors and the heat sink (and the aluminum hold down bar) in a car audio amplifier? And what is it called?

I have an Orion 4100gx and although I have not pulled the bar yet, some of the insulating tape under the bar appears to have been burned through.

Thanks.

Since your working with a Orion car amp which uses a high pressure aluminum bar clamping system you will not need silicon paste when using sil-pad like materials. Sil-pad materials require large pressures to operate properly and the Orion clamping system will do that nicely.
If on the other hand you should use Kapton tape or Mica insulators then you will need some silicon paste. Orion used kapton tape in early models before Sil-pads were in wide use.
The Sil-pad system uses the high pressures to force compliance of the sil-pad materials to perform the same purpose that silicon paste does...Fill the voids between the two surfaces so heat transfer is as high as possible.
On dry hard surfaces like mica and kapton the voids can only be filled with heatsink compound as no amount of pressure you can realistically apply can deform those surfaces enough to fill the voids completely, so the grease does that in those circumstances.... hope this helps some.

 

[The Heater]

Hi, 1moreamp:

What product(s) from the web link for Digikey (for thermal tapes/sheets), above, are you suggesting for the Orion amps (I have others besides this one)?

And how wide does the strip have to be? (I was estimating 1 inch.)

I will take a look and use your language to see if I can find something but if you can tell me which part number like what Perry stated that would be appreciated. It looks like there is some difference in thickness between those tapes/sheets and the Kapton tape mentioned, which is 1-2 mil. Is "sil-pad" referring to the adhesive on the thermal tape/sheet?

(There is some kind of white paste used to attach some small components on the board to the side of the aluminum hold down bar on the transistors (not on the transistors). I did remove the board from one of my HCCA 250 amps and you are right, there is no paste of any sort between the transistors and the heat sinks.)

 

[1moreamp]

Hi, 1moreamp:

What product(s) from the web link for Digikey (for thermal tapes/sheets), above, are you suggesting for the Orion amps (I have others besides this one)?

And how wide does the strip have to be? (I was estimating 1 inch.)

I will take a look and use your language to see if I can find something but if you can tell me which part number like what Perry stated that would be appreciated. It looks like there is some difference in thickness between those tapes/sheets and the Kapton tape mentioned, which is 1-2 mil. Is "sil-pad" referring to the adhesive on the thermal tape/sheet?

(There is some kind of white paste used to attach some small components on the board to the side of the aluminum hold down bar on the transistors (not on the transistors). I did remove the board from one of my HCCA 250 amps and you are right, there is no paste of any sort between the transistors and the heat sinks.)

Sil-pad is Brand name used to describe silicon based pads. Which are used by many manufacturers of car amps. I use the term loosely to describe typically what you find in car amps. Pads can be silicon based, Graphite based, etc...typically you will see silicon based products in car amps due to cost reasons mostly.

The adhesive used varies but but in kapton tapes its typically silicon based adhesives. The adhesive serves two purposes. One to hold the pad in place temporarily till the assembly has be clamped to spec. And 2 it can offer similar benefits as silicon grease does by aiding in the bonding of the surfaces so as to fill all void space to improve heat transfer.

I myself use both kapton tape and sil-pad type materials since I stock both and have both on hand at all times. I also have mica, and ceramic based AL2O3 products. I stay away from Beryllium based products for heath hazard and cost reasons.

The materials physical size can be what ever is needed to do it job. You don't need to cover any more then the mating surfaces between the transistors and the heatsink face, so using excessively larger amounts only equates to excessive costs to your pocket. Most per-cut and sized products are slightly over-sized to facilitate fast assembly. This is that small amount you see sticking outside of the transistor all around its case dimensions.

All of the insulators you have listed in the link list the "thickness" of the material. This spec varies by material and usage, and clamping pressure requirements. Your Orion clamps are more then capable of dealing with most any material you may select, barring that you do not use too thick of a insulator to begin with.
I stick to the 1 to 5 mil range of thickness unless a job specific assembly requires otherwise. I use 2 mil kapton tape but also have 1 mil on hand. In the case of car amps the 1 mil thickness variance will likely not show and negative effects to the amps operations. These are simple car audio amps, they won't be going into orbit around the earth so generally speaking its just not that critical IMHO. Stuffing your car amp inside of a hot trunk will cause more issues then the insulator spec will.

Any white greasy pasty materials you will likely find inside of a car amp is most likely silicon based heat sink compounds. The white color comes from the addition is alumina compounds in most cases. It can also come from beryllium based compounds but that is rarely used by anyone because it is lightly radioactive and it represents a inhalation health hazard if you breath the dry product into your lungs. Also try to stay away from the super compounds you see used for CPU's these contain pure copper and Silver and both are electrically conductive and can cause short circuits to the case. CPU's are isolated from there sink surfaces, always have been. Transistors and Fets are directly bonded to the metal tabs used in there cases unless spec'ed otherwise at the time of manufacture. Yes they can be ordered in isolated packing, but in most cases it reduces the devices power dissipation significantly.

Perry Babin's experience is top notch in my book. If he says you should use a particular device then I would take it as golden information. He is the only person I would send my gear to if I could not work on it myself.

 

[The Heater]

OK. So, what you are saying is I shouldn't get too focused on that column in Digikey that lists the thermal conductivity rating of the thermal material?

I noticed that some of the graphite based materials have what appears to be a much higher thermal conductivity coefficient (or whatever that value represents) than other products.

What I was wanting to do was reproduce what was already in the amplifier, and I don't think it uses Kapton tape.

 

[Perry Babin]

Kapton was used in many of the older Orion amps, including the 4100GX. Before I replied, I checked the photos of a 4100. That's why I recommended the Kapton.

Some of the insulators are electrically conductive. If you use something that's not specifically recommended, confirm that it's an electrically insulating material.

 

[The Heater]

HI, Perry:

I recently ordered a CD of your tutorial by the way. Looking forward to using it to learn a few things.

Thanks for your help on this. I did think of this issue with conductivity, since most of the materials are listed to be used with semiconductors and computers and cell phones, and I looked at the data sheet for one of the graphite products sold by one of the manufacturers (Panasonic) and I also looked at the data sheet for a fiberglass based sheet made by one of the other manufacturers.

I was unable, however, to translate the electrical conductivity rating into something I understand. I don't even know what a "low" rating of conductivity would be for the values and units of measure stated on the data sheets. I have spent all the time I am going to allow on that issue in terms of reading on the web, for now anyway.

So, that leads me back to Kapton tape. What width? One inch? Other?

 

[Perry Babin]

1" is OK on most amps. That's what I've used for the Orion amps.

 

[rrae]

Got question about kapton tape, how to do it right. Add thermal compound between kapton tape and amplifier heatsink or not? I have seen both.

 

[Perry Babin]

I don't use heatsink compound under tape with adhesive unless it can't be laid down without sliding it into place.