Epoxied transistor removal, non destructive.

[Tyso_Bl]

Hi,

This is a vertical deflection amplifier from a scope, the output transistors have an aluminium heatsink which is unsupported, so the manufacturer has chosen to solder them to the PCB, and to make sure that the solder doesn't fail has put a blob of what I think is some sort of
epoxy type resin to keep it all secure.

The question is how to I get them out? the soldering iron does nothing to the glue...

[Radio Wrangler]

Tiny scrapers and files to abrade the stuff away. A microdrill if you have one. Don't bother with stone burrs, they just clog. A tungsten carbide burr is what I use, in a Desoutter air-driven turbine tool. It's like an unburnoutable Dremel on steroids, gets colder the harder you work it. Have a good breeze blowing debris away from your breathing air.

Don't try to clear from the solder mask, just go for the solder meniscus, it doesn't matter when you touch that.

David

[Terry_VK5TM]

Edge of a sharp blade and carefully slide it under one edge of the epoxy and twist the blade up.

If you are lucky, the whole 'blob' will pop off, otherwise keep working around it with the blade.

Alternatively, depending on what it is, IPA may soften it enough to make it easier to pick off but it will be a slow process.

[Refugee]

I would carefully grind the epoxy down just enough to gain thermal access to the component leads and then add enough solder to melt all three joints so that the component can be lifted.
Then you can suck out the solder and chip the epoxy away enough to allow the component to be soldered back in again. You should end up with three holes in the blob of epoxy.

[kalee20]

Agree with Refugee, the thermal way is the way to do it.

Epoxy sticks with a very strong bond, but it weakens a lot with temperature. The loss of strength is reversible, so it's no good heating, allowing to cool, and attacking, as the former strength will be regained. You have to do all the removal while it's hot.

[Radio Wrangler]

Levering up will likely pull the pad off the board. Not a problem if the board is scrap and it's the transistor you want.

David

[Craig Sawyers]

This is something called Staking Compound, often but not always epoxy based. Generally used in aerospace applications where mechanical vibration can compromise the solder joint or the components themselves.

It is odd to see it in a commercial application. But it is intended to be tough, and stick like ordure to the proverbial blanket.

You will probably need to mechanically abrade it down to the solder joints.

Craig

[Tyso_Bl]

OK then, thanks for the advices, got some burrs, and a dremel type thing, will have a go... nothing to lose, have googled for something that might soften or dissolve whatever it is but no luck with anything available here, need to repair the board as a transistor has failed.

T

Is it for leakage reduction? If so better put some back on afterwards.

[Bazz4CQJ]

It doesn't look as though anything is being glued together there, and whatever it is flowed smoothly in to quite a thin layer. May be not epoxy, but perhaps something more like varnish? Is there any reason to put down extra insulation/protection from the elements at those places? If the transistors run hot, maybe the PCB track was more prone 'deteriorate'?

In any event, mechanical removal with a burr is probably the best way to go.
Varnish might dissolve with acetone, but putting acetone on an in-service PCB sounds a bit risky.

B

[Tyso_Bl]

The glue is to stop the trannys breaking away with the print , they are attached to a large heatsink on the other side of the board which is not supported in any other way.

T