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Old 2nd June 2012, 05:58 AM   #1
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Default solder streak

Hi and thanks for taking the time to read this post.
The other day I was attempting to remove a capacitor from a circuit board by applying a small blob of fresh solder onto the capacitorís pad, applying heat then sucking the old solder and new solder up with a desoldering pump.
As I was busy celebrating my success I noticed some solder had oozed over onto an adjacent pad and I tried to quickly brush it back with the soldering iron tip before it cooled, this didnít work now I have a short circuit between the two pads. There is a streak of solder connecting the two pads together.
I applied more heat then the desoldering pump again but for some reason it is not lifting this solder streak. I then placed desoldering wire over the streak then the iron on top but this cannot shift it.
Finally I applied a lot of flux over the streak then the wire then the iron which did something but again did not lift the streak.
Does anyone have any experience of this and how it may be remedied.

Many thanks in advance.
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Old 2nd June 2012, 06:06 AM   #2
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Got a pic?
Did you try just the flux and the hot iron?
If nothing else, use a razor blade to cut through the "streak of solder."
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Old 3rd June 2012, 01:28 AM   #3
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Default solder streak

Yes, i did try just the flux and a hot iron it made a hissung sound as the flux evaporated. The solder wick does not seem to be picking up the solder for some reason. I purchased it from a well known auction site and is labelled High Quality Solderwick Don't think it's anygood though. Can anyone recommend a decent wick to go for Is there a good make for solderwicks.

Many thanks. Mark.
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Old 3rd June 2012, 01:34 AM   #4
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I've always found goot to be good de soldering braid. Are you sure there isn't actually a small track between the two components?

Tony.
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Old 3rd June 2012, 01:34 AM   #5
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Solder wick is just copper wire.

Does the circuit board have a mask covering the traces? If not, it's possible, if your lucky that the two parts are connected anyways. That would make it hard to break the bead.
*Use a schematic to verify.

If not, heat both sides and use compressed air to blast the solder off both pads.

I don't find solder wick particularly useful for anything.
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Old 3rd June 2012, 02:06 AM   #6
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Oh, how many times have I thought I made a nasty solder bridge, brought out every desolder tool and trick there is, only to finally get it nice an clean and lightly scrape off the remaining solder in a spot to see the original copper trace that was there all along..
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Old 3rd June 2012, 01:33 PM   #7
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There are a number of possibilities that may cause the inability to remove the streak and it could be a combination.

If the pads are connected to a large amount of copper, it will be harder to heat them up than if they are only connected to a thin trace. Copper is a good thermal conductor and a large amount might suck away the heat faster than the iron can supply it. Added to that is the wick, which increases the amount of copper to be heated up.
A tell tale sign of this is if the tip of the iron doesn't heat the wick within a couple of seconds and you end up with the wick stuck to the pad.
This may also indicate too low temperature setting or inadequate thermal capacity from the iron (a 15 W iron can't do what a 75 W solder station can; despite having same tip size and temp).

A mistake that I often see made at work is the usage of too narrow a tip. A narrow tip cannot supply the same amount of heat as a wide one, despite having the same temperature. Use the widest tip you can safely use in that location on the board.

I agree with Andrew Eckhardt. There may also be the possibility that the pads are actually connected to eachother by a short and narrow trace between them. If this is a board with the (usually) green solder resist coating on it, the trace might not be visible that easily. After rubbing with an iron and a wick the solder resist coating will most likely have been removed and the trace is bare with solder on it. It still looks very much like a short but of course this won't let itself be removed.
At work my colleages and I have been fooled by this more than once.
A magnifying glass and the schematic/trace layout will tell you more.

The wick itself might be old and oxidated. Of course a quick test would be to put the iron on the wick and add a bit of solder where tip and wick meet. The solder should immediately flow into the wick without pooling near/on the tip.

If none of the the above is the case, a trick that might help is add solder before desoldering. This may sound counter productive but the new solder will help increase the thermal contact area of the tip quite a bit. Just like thermal grease helps increase the contact area between heatsink and component (or the water in between the icecubes of a Champagne cooler).

I would probably try something like this:
Add fresh solder to actually make the short worse. Place the wick and tip on the short and, if the wick doesn't immediately start to suck up solder, add some more solder to where the tip touches the wick. Then, without applying pressure, move wick and tip sideways before lifting them off the board.

Good luck!

Last edited by jitter; 3rd June 2012 at 01:40 PM.
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Old 5th June 2012, 12:43 AM   #8
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Default solder streak

Many thanks. Will definetly give it a try.
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Old 5th June 2012, 03:31 AM   #9
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last time I did this...I burned through the board...mainly because I started STABBING it out of frustration...damn solder knomes, never around when you need them!
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Old 5th June 2012, 03:31 PM   #10
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Quote:
Originally Posted by Andrew Eckhardt View Post
Oh, how many times have I thought I made a nasty solder bridge, brought out every desolder tool and trick there is, only to finally get it nice an clean and lightly scrape off the remaining solder in a spot to see the original copper trace that was there all along..
This ^^^^^^^^^^
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