I am currently recapping a power PCB for a TV. One cap at time.

In removing one of the caps a part of the underlying circuit has come away from the board.

What I want to try to do is to remove some of the laquer / conformal coating surrounding the damaged
part and bridge the cap to the underlying circuit to see if I can save this board.

Picture attached of the damaged pin location.

What do the members think? Feasible? Anyone else come across this kind of situation? How did you deal with it?

Thanks for your time.

Ray

 

What do the members think? Feasible?

Does the board have more than 2 layers? Repair is straightforward for 1 or 2 layers. For more layers, complexity depends on whether the plated through hole was used for connectivity on inner layers.

More information will yield better answers.

 

What are we looking at in your picture? Is that one of the holes/vias that the through-hole cap was mounted into?

 

What are we looking at in your picture? Is that one of the holes/vias that the through-hole cap was mounted into?

I think it's a ground connection for a cap that the OP tried removing before sufficient solder was removed.

 

Thanks for the responses. I will answer them all at once if I may.

I have no reason to suspect that it is multi layered. The hole is the hole that you would push the cap pin through and solder.

What happened was the cap had been worked on before and there was a liberal amount of solder on the pin. A small mole hill. So I took my snips and trimmed the top to reduce the amount of solder to melt. This solder is quite a high temp melting point. I then melted what was left, pulled the cap through and the lump of solder literally fell off when I turned the board over leaving the damage that you can see in the picture.

I have a plan. Carefully remove the coating using acetone until I rach bare circuit. Then stick the cap pin to it using and electrical adhesive. How does that sound?

 

You could carefully remove the conformal coating on the damaged trace and solder a short, bare wire from the component pin to the trace (small wire-wrap wire works well for that).
That's a common way to do such a repair.

Use a small amount of rosin flux on the trace and pin before soldering, to allow good solder adhesion.
Use low melting point tin-lead solder.
Be careful to not overheat the trace. It should only take a fraction of a second for the solder to flow.

 

I have a plan. Carefully remove the coating using acetone until I rach bare circuit. Then stick the cap pin to it using and electrical adhesive. How does that sound?

Skip the acetone and adhesives. You won't be able to control the application of the acetone and it will affect more solder mask than you intend to remove. Just use an X-acto blade to scrape away the solder mask.

You don't need any adhesive. Assuming the other terminal still has a pad, all you need to do is use a short jumper wire from the trace that you expose to the cap lead.

We're all shooting in the dark because you aren't showing us what you're talking about.

 

You could carefully remove the conformal coating on the damaged trace and solder a short, bare wire from the component pin to the trace (small wire-wrap wire works well for that).
That's a common way to do such a repair.

Use a small amount of rosin flux on the trace and pin before soldering, to allow good solder adhesion.
Use low melting point tin-lead solder.
Be careful to not overheat the trace. It should only take a fraction of a second for the solder to flow.

Sounds good. I was considering the use of electric glue rather than solder. What do you think of that idea? It's pretty delicate and I don't want to risk making it worse. The key is to expose the circuit with the acetone. Have you used acetone for this purpose?

 

The key is to expose the circuit with the acetone. Have you used acetone for this purpose?

Just use a hobby knife, like an X-acto to remove the solder resist. You'll spend the rest of your life trying to remove it with acetone.

 

Just use a hobby knife, like an X-acto to remove the solder resist. You'll spend the rest of your life trying to remove it with acetone.

Really? Gosh. That sounds a bit scary. How thick is it? The circuit layer I mean.

 

I was considering the use of electric glue rather than solder.

Depends upon its resistance.

The key is to expose the circuit with the acetone.

Not sure that will work.
Read here for some other ideas on removing the conformal coating.

 

Really? Gosh. That sounds a bit scary. How thick is it? The circuit layer I mean.

Probably 0.0015" thick and pretty tough. As long as you don't have gorilla hands, the solder resist should be easily removable.

 

Depends upon its resistance.
Not sure that will work.
Read here for some other ideas on removing the conformal coating.

Thanks

 

Here's a more detailed picture of the problem for those interested. Yellow arrow marks the spot.

 

Much better picture - thanks.

Looks like all you have to do is remove the conformal coating for a fraction of an inch or so above the trace that the (removed) solder pad connected to. Then solder one lead of the cap directly to that exposed trace, the one right next to your yellow arrow.

As to what it takes to remove the conformal coating, it all comes down to what kind it is. I know whenever we have to rework or white-wire boards, the conformal coating is removed chemically (not by scratching or scrapping). I would try some acetone on a q-tip, in order to minimize the amount of coating removed.

 

Guess what? Problem solved. I did a lot of searching on the net and I came up with a wiring diagram.

All I have to do is connect the cap directly to the neighbouring inductor on the board and I am good to go.

See the attached pic.

Thanks for your help folks. It's appreciated.