Failed pot removal from PC Board

Thread Starter

briceelectric

Joined May 28, 2023
15
A 20 turn 5K ohm trimmer pot has failed on a 4 layer PC board. Attempts to unsolder it using a solder sucker and braided copper de soldering wire were unsuccessful, The body of the trim pot was forcibly removed. Two of its leads were successfully removed by heating the underside of the PC board with a soldering iron and pulling them out of the top side with pliers.

The third lead remains in the PC board. The exposed ends are too short to grasp. I would appreciate any suggestions as to how to remove the remaining lead. The other concern is whether the board's internal power and ground layers could have been damaged. The lead that remains in the board is connected to the ground layer.
 

JWHassler

Joined Sep 25, 2013
306
A 20 turn 5K ohm trimmer pot has failed on a 4 layer PC board. Attempts to unsolder it using a solder sucker and braided copper de soldering wire were unsuccessful, The body of the trim pot was forcibly removed. Two of its leads were successfully removed by heating the underside of the PC board with a soldering iron and pulling them out of the top side with pliers.

The third lead remains in the PC board. The exposed ends are too short to grasp. I would appreciate any suggestions as to how to remove the remaining lead. The other concern is whether the board's internal power and ground layers could have been damaged. The lead that remains in the board is connected to the ground layer.
There are two ways: a lot of solder, piled up until it can hold enough heat to let the pin wiggle, OR less solder: wicked away until the pin isn't surrounded. In either case, find a way to hold the PCB and rap it sharply against, say, the table edge , when heat is at max, to eject the offending part.
It can get a little messy, but beats surgery.
 

Thread Starter

briceelectric

Joined May 28, 2023
15
There are two ways: a lot of solder, piled up until it can hold enough heat to let the pin wiggle, OR less solder: wicked away until the pin isn't surrounded. In either case, find a way to hold the PCB and rap it sharply against, say, the table edge , when heat is at max, to eject the offending part.
It can get a little messy, but beats surgery.
JWHassler
Thanks for the solder tip. Hopefully This will be resolved soon.
Sam
 

Ya’akov

Joined Jan 27, 2019
9,101
Welcome to AAC.

This post has something that might help. It‘s a low-melting point alloy that makes the solder stay liquid at very low temperatures allowing parts to be easily pulled out even if they have a high pin count. In fact, they often just fall out.

1688123443975.gif

A couple of important things I didn’t mention in that post.

First, use very little of the alloy—I find that about a millimeter of it will work for 8 pin packages easily if you can get it distributed. To give you time to spread it around, you can turn down your iron temperature and avoid overheating the part.

Second, do a really good job of removing the low temperate alloy and existing solder mix from both the PCB and your iron’s tip. If there is residue, it will interfere with good joints for the replacement part. This is why you should use the smallest amount possible (also because it is not cheap though it goes a long way, much more than solder itself), and be careful to avoid nearby pads.

You don’t need flux, and you can carry the alloy on the iron’s tip if you get it to wet. It helps if you put a little leaded solder on first. By the way, adding 63Sn/37Pb eutectic alloy solder to a lead free pad will greatly assist in desoldering as well, even without the desoldering alloy. Of course if you must persevere a RoHS certification, that’s not going to work.
 

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Thread Starter

briceelectric

Joined May 28, 2023
15
Welcome to AAC.

This post has something that might help. It‘s a low-melting point alloy that makes the solder stay liquid at very low temperatures allowing parts to be easily pulled out even if they have a high pin count. In fact, they often just fall out.


A couple of important things I didn’t mention in that post.

First, use very little of the alloy—I find that about a millimeter of it will work for 8 pin packages easily if you can get it distributed. To give you time to spread it around, you can turn down your iron temperature and avoid overheating the part.

Second, do a really good job of removing the low temperate alloy and existing solder mix from both the PCB and your iron’s tip. If there is residue, it will interfere with good joints for the replacement part. This is why you should use the smallest amount possible (also because it is not cheap though it goes a long way, much more than solder itself), and be careful to avoid nearby pads.

You don’t need flux, and you can carry the alloy on the iron’s tip if you get it too wet. It helps if you put a little leaded solder on first. By the way, adding 63Sn/37Pb eutectic alloy solder to a lead free pad will greatly assist in desoldering as well, even without the desoldering alloy. Of course if you must persevere a RoHS certification, that’s not going to work.
Ya'akov
Thanks for the tip. That is good to know for future use as well.
Sam
 

Thread Starter

briceelectric

Joined May 28, 2023
15
BobTPH said:

Heat the bottom and push it through using a needle?
BobTPH
The needle trick worked. After several failed tries using a straight pin, I started moving it in a circle. It took about 5 minutes of constant rotation and pressure to remove the failed lead, but it finally pushed through. Your suggestion saved a complex PCboard and a whole lot of work.
Thank you.
Sam
 
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