Author Topic: Cleaning up solder from a stubborn thruhole  (Read 12913 times)

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Offline lpc32

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Cleaning up solder from a stubborn thruhole
« on: November 12, 2014, 10:33:32 pm »
I've desoldered a capacitor, which wasn't that difficult, and am now trying to clean up the holes. One was easy enough. The other (the positive), not at all. So far it resisted: manual sucker, braid, flux, adding solder, all of the above on both sides, and temperatures at least up to 450C (I think more). It was partially unclogged after one of the cleaning attempts but after adding solder I can't even get the solder on the side opposite the iron to melt.

It's on an old low-end graphics card, I don't think there are too many layers.

Edit: Photos in a later post.
« Last Edit: November 16, 2014, 03:08:36 pm by lpc32 »
 

Offline krivx

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Re: Cleaning up solder from a stubborn thruhole
« Reply #1 on: November 12, 2014, 10:35:53 pm »
Sometimes force is the only thing that can work. A de-soldering station with vacuum pump would probably clear it. If you don't have one you could try heating it and poking out the solder with something like a toothpick before it solidifies.
 

Offline kxenos

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Re: Cleaning up solder from a stubborn thruhole
« Reply #2 on: November 12, 2014, 10:39:06 pm »
1. Take an unused resistor and while heating from one side push the lead from the other and don't stop moving the resistor until the pad gets cold
2. while heating the pad blow air with a high pressure air gun if you have one
3. Don't do anything, and when you place the new part just keep this pad melted so the new part will slide through
 

Offline Alex Eisenhut

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Offline AG6QR

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Re: Cleaning up solder from a stubborn thruhole
« Reply #4 on: November 13, 2014, 12:33:43 am »
kxenos has some very good suggestions.  I'll add one more that has worked for me.

Use that copper braid you had been using, but before you start, put some rosin flux on it.  Sometimes that will make the difference and help the braid to suck up the solder.
 

Offline BradC

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Re: Cleaning up solder from a stubborn thruhole
« Reply #5 on: November 13, 2014, 01:06:37 am »
If you take tip no 1 from kxenos above and substitute a stainless steel sewing needle for the resistor lead you'll get great results. Solder won't touch the stainless steel and it just pushes the solder out of the way. I used to do that when replacing caps on 8 layer boards with big ground planes before I bought a desoldering gun.

The tip from AG6QR about the extra flux is a winner too. Flux always makes things easier.
 


Offline Alex Eisenhut

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Re: Cleaning up solder from a stubborn thruhole
« Reply #7 on: November 13, 2014, 01:15:03 am »
http://www.ebay.com/itm/61-80-MICRO-MINI-PIN-NUMBER-WIRE-SIZES-NUMBERED-DRILL-BIT-TOOL-SET-KIT-INDEX-/320886280065?pt=LH_DefaultDomain_0&hash=item4ab6500f81

I would be careful with these - they can take out the through-hole plating

The solder is far softer than the copper. Use a bit just over the size of the cap's lead and use a hand tool. You just get a nice little spiral of solder coming out, there you go. No heat, flux, or braid.
*Except AC/DC adapters on eBay. Avoid them all!
 

Offline krivx

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Re: Cleaning up solder from a stubborn thruhole
« Reply #8 on: November 13, 2014, 01:20:45 am »
http://www.ebay.com/itm/61-80-MICRO-MINI-PIN-NUMBER-WIRE-SIZES-NUMBERED-DRILL-BIT-TOOL-SET-KIT-INDEX-/320886280065?pt=LH_DefaultDomain_0&hash=item4ab6500f81

I would be careful with these - they can take out the through-hole plating

The solder is far softer than the copper. Use a bit just over the size of the cap's lead and use a hand tool. You just get a nice little spiral of solder coming out, there you go. No heat, flux, or braid.

Yep sure, I've done it with a pin vice and that same micro drill kit. Just have to make sure the size is right.
 

Offline Rasz

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Re: Cleaning up solder from a stubborn thruhole
« Reply #9 on: November 13, 2014, 03:05:28 am »
no no nooooo
use a thin Hypodermic needle - they are made out of steel so solder wont adhere to it.

You melt the solder and quickly puncture it, stop heating it up while still moving the needle around. Done.


It also sounds like you might want to look into hot air stations.
and if you plan to do multilayer boards wit heavy ground planes more often  buy a preheater.
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Offline Dave Turner

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Re: Cleaning up solder from a stubborn thruhole
« Reply #10 on: November 13, 2014, 07:30:21 pm »
I agree with the stainless steel needle but would advise imbedding the blunt end into a cork, holding it in a pin vice or even wrapping it with insulating tape to improve handling accuracy and reduce the chance of a burn.
 

Online nfmax

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Re: Cleaning up solder from a stubborn thruhole
« Reply #11 on: November 13, 2014, 07:39:50 pm »
I use a stainless steel dental pick for this sort of job. For some reason, these used to appear regularly on the second hand tool-tat stalls that populate the market area of steam rallies round these parts. I've no idea if they still do...
 

Offline AndyC_772

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Re: Cleaning up solder from a stubborn thruhole
« Reply #12 on: November 13, 2014, 07:56:25 pm »
I once resorted to a very short piece of stiff copper wire held in a drill chuck, with just a few mm poking out. The sharp edges from where the wire was cut act like the teeth of a drill bit, and the copper is hard enough to chew away the solder without damaging the plating.

Proud of what I did? Not really. Got the job done without damaging the board? Sure!

Offline krivx

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Re: Cleaning up solder from a stubborn thruhole
« Reply #13 on: November 13, 2014, 08:44:56 pm »
Hey, if it got the job done you should be proud.
 

Offline AndyC_772

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Re: Cleaning up solder from a stubborn thruhole
« Reply #14 on: November 13, 2014, 08:48:04 pm »
 :-+

Offline DmitryL

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Re: Cleaning up solder from a stubborn thruhole
« Reply #15 on: November 13, 2014, 09:33:38 pm »
I've desoldered a capacitor, which wasn't that difficult, and am now trying to clean up the holes. One was easy enough. The other (the positive), not at all. So far it resisted: manual sucker, braid, flux, adding solder, all of the above on both sides, and temperatures at least up to 450C (I think more). It was partially unclogged after one of the cleaning attempts but after adding solder I can't even get the solder on the side opposite the iron to melt.
It's on an old low-end graphics card, I don't think there are too many layers.

[sigh] put some flux into that thruhole, take a big blob of a normal _leaded_ solder on a a tip of a _proper_ temperature controlled soldering iron (it should be > 50 Watts).
Fill that hole with solder, it should be liquid, that's why you need a high power soldering iron with controlled temperature. From the opposite side stick something like a bamboo toothpick into this hole.
 

Offline German_EE

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Re: Cleaning up solder from a stubborn thruhole
« Reply #16 on: November 14, 2014, 01:20:16 pm »
I have been known to use a sharpened pencil, nothing sticks to pencil lead and the wooden shaft means that you do not burn your fingers.
Should you find yourself in a chronically leaking boat, energy devoted to changing vessels is likely to be more productive than energy devoted to patching leaks.

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Offline GreyWoolfe

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Re: Cleaning up solder from a stubborn thruhole
« Reply #17 on: November 14, 2014, 01:43:32 pm »
I use a stainless steel dental pick for this sort of job. For some reason, these used to appear regularly on the second hand tool-tat stalls that populate the market area of steam rallies round these parts. I've no idea if they still do...

On this side of the pond, you can find boxes of dental picks at the local flea markets.  I have used the dental pick method in the past.  Now I have a ZD-985 that was a Christmas gift from SWMBO ;D.
"Heaven has been described as the place that once you get there all the dogs you ever loved run up to greet you."
 

Offline lpc32

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Re: Cleaning up solder from a stubborn thruhole
« Reply #18 on: November 14, 2014, 10:21:54 pm »
Thanks everyone.

I tried what I could of the above. I can't push anything through because at no point the solder melts all the way through the hole. Tried more flux on the board, flux on the braid, another type of braid (new, but fishy), another type of solder (known good and new). The soldering iron is good. Tried up to 480C.

The best I could get is shallow depressions in both sides of the hole, but the middle remained blocked. I suspect something blocks heat transfer in the middle. Is that a common occurrence, and any idea what and why that might be?

Those drill bits, what range of mm sizes is useful for this?

BTW, in some cases when touching the iron to the hole something creaked. Maybe the board, but not sure. Common thing? A bad sign? :)
 

Offline Dave Turner

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Re: Cleaning up solder from a stubborn thruhole
« Reply #19 on: November 14, 2014, 11:43:44 pm »
Let's see some pictures
 

Offline KJDS

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Re: Cleaning up solder from a stubborn thruhole
« Reply #20 on: November 15, 2014, 06:29:27 am »
What soldering iron and bit are you using?

Offline Richard Head

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Re: Cleaning up solder from a stubborn thruhole
« Reply #21 on: November 15, 2014, 09:14:00 am »
Try using an iron with a large flat bit. Place a short length of silicone tube (silicone wire insulation) over the end of your solder sucker. This allows you to get a very good seal on the board when you suck. Then, place the iron on the side of the board with the groundplane while simultaneously placing the solder sucker over the pad on the opposite side of the board and suck. This generally works with stubborn THP holes but not always. If all else fails use the stainless steel needle method. If that fails drill the bloody thing out and use one of the inserts to repair the THP.
Dick
 


Offline DTJ

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Re: Cleaning up solder from a stubborn thruhole
« Reply #23 on: November 15, 2014, 11:39:22 am »
Something else that can be used to poke through a hole and clear solder is a stainless steel hypodermic needle. The solder doesn't stick to it. Dirt cheap at your local chemist or vet, available in lots of sizes. Perhaps not quite as nice as the Hakko desoldering gun.
 

Offline GreyWoolfe

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Re: Cleaning up solder from a stubborn thruhole
« Reply #24 on: November 15, 2014, 01:56:34 pm »
When I have had to use a dental pick, I heat the pick not the solder.  Did you try it this way?  The heat will probably soften the pick and warp it, but just keep it for opening the holes up only.
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