1
\$\begingroup\$

<noob-disclaimer></noob-disclaimer>

For context, I need to solder a wire onto a pcb. However, the pad was destroyed during demounting the original component (picture 1). The plan B is to solder the wire onto the copper trace next to the pad. I am however worried that

A) soldering alone won't be sufficient for a durable bond.

B) that the piece of exposed wire/trace might interfere with something.

At the same time I have this guy lying around (picture 2) and noticed that it also has wires soldered onto the board, with some glue(?) being used for, as I understand, similar reasons. What is this substance, and would it be suitable to use in my case?

Picture 1 The pad in question

Picture 2 enter image description here I appreciate you tolerating my knowledge of electronics.

Thanks.

\$\endgroup\$
7
  • 2
    \$\begingroup\$ You might also consider repairing the PCB properly with a through-hole repair kit. Run a Google or YouTube search using keywords like "Through hole repair kit" or "PCB eyelet repair", etc. FWIW, if that's a multilayer board, you may be out of luck if the barrel has disconnected from the runs on the board's internal / sandwiched layers. \$\endgroup\$
    – Jim Fischer
    Jan 18, 2018 at 0:34
  • 3
    \$\begingroup\$ In the lower image with the blue wires, it looks to me like someone used a hot glue gun(?) or epoxy(?) to dab some glue onto the ends of the wires at the point where they are soldered onto the board, possibly for strain relief purposes. \$\endgroup\$
    – Jim Fischer
    Jan 18, 2018 at 0:38
  • \$\begingroup\$ Indeed, if the hole plating is damaged then soldering to the visible trace looks like it would connect you to nothing but the now orphaned capacitor. Likely at minimum you'll need to run the wire through the hole and solder it on both sides. \$\endgroup\$
    – Chris Stratton
    Jan 18, 2018 at 1:27
  • 2
    \$\begingroup\$ The glue is just being used for strain relief. Strain relief is a good idea, but NEVER GLUE ON TOP OF SOLDER unless you have no choice. Put the glue somewhere back from where the wires are attached. \$\endgroup\$
    – user57037
    Jan 18, 2018 at 5:42
  • 2
    \$\begingroup\$ I don't think that's glue, it looks like some really nasty rosin flux that wasn't cleaned up after board assembly. \$\endgroup\$
    – DerStrom8
    Jan 18, 2018 at 12:04

3 Answers 3

Reset to default
6
\$\begingroup\$

Carefully scrape the soldermask (the green stuff) off of the PCB trace that routes to the damaged through-hole. You can solder a wire directly onto that trace to form a good electrical connection, but it won't be a very durable mechanical connection. You need something, like glue or tape, to hold the wires in place and decouple mechanical stress from the solder joint. I typically use hot glue in this application because it's easy to work with and remove if needed.

The substance in the second image might be flux residue left from when the wires were soldered to the pads, but it's hard to tell. If you can wipe it off, it's probably flux residue.

As others have noted in the comments on your post, it appears there may be damage to the through hole. I would try to heat it up and fill it with solder. If the plated through-hole is thoroughly damaged, more serious repairs may be necessary. Through-hole repair kits are commercially available.

\$\endgroup\$
5
  • 1
    \$\begingroup\$ There is a concern about connectivity. Sometimes traces may lead away from a through hole pin on both top and bottom. It looks like the plating of the through-hole may be gone now, so the board may need real repair. There could even be mid-layer traces leading away from the through hole (unless it is a two-layer board). \$\endgroup\$
    – user57037
    Jan 18, 2018 at 5:44
  • 1
    \$\begingroup\$ @mkeith - You might be right. It's hard to tell. To me it looks like some of the annular ring was ripped off (I do that a lot), but the plated through-hole looks like it's still there. I updated my answer. \$\endgroup\$
    – vofa
    Jan 18, 2018 at 5:53
  • \$\begingroup\$ +1 for mentioning the flux. I don't believe that's glue at all. \$\endgroup\$
    – DerStrom8
    Jan 18, 2018 at 12:04
  • \$\begingroup\$ Thanks for the answer. I'll mark this as accepted since this is probably what I will end up doing. I might also try a through hole repair kit first, as suggested in the comments to my post. If you can add that option to your answer would be great. \$\endgroup\$
    – ivanibash
    Jan 18, 2018 at 12:51
  • 1
    \$\begingroup\$ @redFur - Added another sentence about repair kits. I have never managed to destroy a plated through-hole, so don't have any additional insight. \$\endgroup\$
    – vofa
    Jan 18, 2018 at 15:36
2
\$\begingroup\$

It is hot glue from a glue gun. There is a stacke exchange question dealing with the issue here

\$\endgroup\$
2
\$\begingroup\$

For permanently stabilising repairs/modifications two part epoxy (araldite or similar) works well. Just make sure your repair is electrically correct first.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.