What is this Adhesive Thermal Pad?

[Harry_22]

Hi all!

I would like to clarify what kind of thermal pad this is. It looks like a flexible fiber-reinforced mat. The surface is not sticky.

The transistor was removed only by heating it on a hotplate at 200 degrees plus heating the transistor metal tab by soldering iron.
The photo shows that there are particles of molten solder left on the contact pad.

I do not quite understand what is this technology and how to attach the transistor back without much destruction.

[u666sa]

You could use this https://aliexpress.ru/item/1005005922520519.html

[coromonadalix]

in some cases its when they deteriorate they become stickier ...     unless really made like this ?

witch i only saw on old thermal pads i need to remove, and they almost ripped off parts ?

[Audiorepair]

This is pretty common really.

You can separate the transistors from the pad  by levering the legs against the heatsink, and they will pop off.
And you won't have to remove the whole heatsink plus transistors to do this.


By the time you come across this the heatsink pad is toast, you don't want to reuse it.
Simply lever off all the transistors and replace the pad with any kind of generic thermal sheet.

Or you could even ditch  the sheet altogether and use Mica washers and heatsink compound like in the old days, which would no doubt give you a far higher thermal performance, should the application need or benefit from it.

The sheet is a cost saving manufacturing choice.

[Harry_22]

Many thanks for the answers.

This sandwich is installed on completely new cutting-edge equipment. I have not seen this technology yet. 
Typically transistors on such radiators are pressed by the spring plates. But here they rely only on magic word. I couldn't tear him off by the legs when it was cold and actually desoldered it as TO-263AB/D2-PAK.
Even drops of solder remained.

Obviously it needs to be glued. Drilling a hole is inconvenient due to the ribs located behind and a closed area for working with a screwdriver. Therefore I will need to install everything assembled.

But how to glue? Right on this pad? Because if you remove it, then how to maintain the gap between transistor and radiator?
Also possible to put Al₂O₃ and glue it on both sides. This will be a real sandwich!

[Audiorepair]

Ah, OK, I assumed some kind of clamping device not shown in photo.

Not seen anything like this before is the correct answer.

[Harry_22]

The sheet is a cost saving manufacturing choice.

You are absolutely right!
It is definitely technologically simple solution, no screws, no clamping devices.
A kind of double-sided tape with glue activation. Shine it with ultraviolet light and you're done (it is my fantasy).

[Harry_22]

You could use this https://aliexpress.ru/item/1005005922520519.html

Just glued the faulty transistor to the heat-conducting pad. As soon as the glue dries, I will try to tear it off.
I am concerned about the adhesion of this glue to the surface.

[calibrationfixture]

Hi Harry_22,

A bit overdue with my response. The Colour of the Thermal Pad resembles Bergquist K10 Silpad:

https://eu.mouser.com/c/thermal-management/thermal-interface-products/?m=Bergquist%20Company&series=K-10%20%2F%20TSP%20K1300

Calibrationfixture

[Harry_22]

Hi Harry_22,

A bit overdue with my response. The Colour of the Thermal Pad resembles Bergquist K10 Silpad:

https://eu.mouser.com/c/thermal-management/thermal-interface-products/?m=Bergquist%20Company&series=K-10%20%2F%20TSP%20K1300

Calibrationfixture

Hi Calibrationfixture!

You are very on time!

 I've been waiting for the glue to dry for two days now. Today I will try to break away.
The thing is, I have a second assembly of the same kind. The Customer was purposeful and burned out the two different PCB channels in R&S NGP800 power supply. I wish we could have more such a good Customers.
So the original transistor was glued so well that I could not tear it off. To be more precise I was afraid of damaging the thermal pad. As I wrote, it turned out to “unsolder” it as if it was on PCB.
It turns out to be some kind of magic glue, moreover the gasket is soft, just like the one in your attached link.

[Harry_22]

The glued transistor withstood a load of 5 kg.
I didn't pull it any further because afraid to tear the thermal pad off the heat sink.

[keenox]

If you are going to mount the whole heatsink with the transistors attached anyways, why do you not want to use a screw?

[Audiorepair]

More to the point, why are you wearing a pair of Crocs?

[Harry_22]

More to the point, why are you wearing a pair of Crocs?

No Crocs is allowed. This is Abebas Abeba
ESD protective area.

[Harry_22]

If you are going to mount the whole heatsink with the transistors attached anyways, why do you not want to use a screw?

I apologize if I use the wrong terms.
On the reverse side there are ribs and a step. This can be seen from the first photo. Therefore, you need to drill from the back side between the ribs. In this case, it is possible that the internal reinforcement of the thermal pad will wrap around the drill. And you also need to remove the chamfer from the radiator under the thermal mat. Since the nut will not fit, you need to make the thread.
So it is not the easiest way. But I was already preparing to do this, since I was not sure of the adhesion of this glue.

[keenox]

Why drill from the ribbed side? Drill from the transistor side. You don't need a nut if you use the screw head to hold the transistor in place. Your heatsink seems thick enough to hold a screw no problems. Tapping aluminium is super easy. It might not even need tapping. The steel screw will do the self tapping.
The only problem I see with this approach is if the heatsink is connected to the ground plane on the PCB and needs to isolated from the transistor drain. Seen at least one case in the past.

[Harry_22]

Why drill from the ribbed side? Drill from the transistor side. You don't need a nut if you use the screw head to hold the transistor in place. Your heatsink seems thick enough to hold a screw no problems. Tapping aluminium is super easy. It might not even need tapping. The steel screw will do the self tapping.
The only problem I see with this approach is if the heatsink is connected to the ground plane on the PCB and needs to isolated from the transistor drain. Seen at least one case in the past.

Yes the heatsink is isolated via the themal pad.
But why start mechanic work if the transistor is held in place with glue quite well. You saw it yourself.
And the device will be in complete order, almost like it came from the factory.

PS
I am sure that the thermal resistance will not change, the main rule here is not to leave air cavities.
All that remains is to dispel doubts that it will fly off when heated, and I have these doubts.

[Harry_22]

I am very pleased with this superglue.
It holds stronger than the factory one. I could barely tear it off the thermal pad without breaking anything.