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Old 16th Jan 2020, 6:59 pm   #1
ahankinson
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Default Brown substance on Solder Joints

I’m working on an Advance signal generator, and all of the solder joints in it are covered in a brown substance. I’m wondering if someone could tell me what it is, and how problematic it will be if it goes under the soldering iron. Tips on how to remove it pre-soldering would also be appreciated.
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Old 16th Jan 2020, 7:17 pm   #2
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Default Re: Brown substance on Solder Joints

I'll be interested too. Encountered this before and just ploughed on through, cant recall it giving me any major problems
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Old 16th Jan 2020, 7:39 pm   #3
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Default Re: Brown substance on Solder Joints

It doesn't look like flux-residue. In times-past on 'professional/military' gear it was quite normal for soldered joints to be inspected after soldering [by someone other than the solderer, obviously] and a lacquer or paint was applied to each joint to confirm it had been inspected. I've not come across brown lacquer being used for this, but a small red paint-dot on each joint was quite commonplace in WWII-and-subsequent military equipment.

As to what to do about it - I wouldn't worry - just solder through it.
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Old 16th Jan 2020, 7:53 pm   #4
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Default Re: Brown substance on Solder Joints

Yep, inspectors at Thorn where I worked had to mark every soldered joint with a felt tip marker pen to show that it had been inspected. This was also done on PCBs. It's just marker pen ink, not a problem to resolder, remover solder, whatever.
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Old 16th Jan 2020, 7:53 pm   #5
ChristianFletcher
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Default Re: Brown substance on Solder Joints

I was going to say QC marks. Those Advance signal generators are very good.

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Old 16th Jan 2020, 8:13 pm   #6
Dave Moll
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Default Re: Brown substance on Solder Joints

Is it possibly shellac?
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Old 17th Jan 2020, 12:16 am   #7
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Default Re: Brown substance on Solder Joints

I have seen this in red and also brown, and think that it is some sort of varnish or shellac. It certainly seems to preserve the solder in a shiny state (and does not seem to cause a problem when re-soldering) If attacked with a screwdriver or similar i should think it will crack off in flakes.

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Old 17th Jan 2020, 1:26 am   #8
ahankinson
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Default Re: Brown substance on Solder Joints

It certainly seems to give off a lot of smoke. I got a good whiff of it by accident the other day (I have an exhaust fan, but stood over the joint for a better angle) so knowing what it is would be nice. I had heard about the QC marking before, but this seems to be an actual deliberate coat, rather than a small dab.

I think I’ll try washing the joint with IPA and see if it does anything. If it’s shellac it should dissolve with alcohol.
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Old 17th Jan 2020, 9:16 am   #9
Craig Sawyers
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Default Re: Brown substance on Solder Joints

If it is shellac, meths is the solvent (or ethyl alcohol). Not sure if IPA will work.
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Old 17th Jan 2020, 10:29 am   #10
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Default Re: Brown substance on Solder Joints

My father's two emi group radios were what was called back in 1937 "tropicalised"

This appeared as a brown coating which in hindsight i am sure was shellac. It was certainly on the transformers and chokes and their solder terminals but cannot remember if it was on the other components. I have recently dismantled a Grampian PA amp for spares. It is early 1950' I think and the transformers and joints had a similar brown coating. There was no problem in de-soldering.
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Old 17th Jan 2020, 10:33 am   #11
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Default Re: Brown substance on Solder Joints

Very interesting this, I've often thought that it was aged solder flux, you never stop learning.
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Old 17th Jan 2020, 11:06 am   #12
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Default Re: Brown substance on Solder Joints

Yes, shellac was commonly applied - not just to soldered joints but often found on nuts & bolts.
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Old 17th Jan 2020, 11:46 am   #13
barrymagrec
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Default Re: Brown substance on Solder Joints

When I was at Leevers Rich in 1969 the inspector always put a dab of red varnish on each joint to show it had been inspected - I began to doubt the efficacy of this procedure when I found a joint which had not been soldered at all but nevertheless had its dab of red varnish.....
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Old 17th Jan 2020, 2:29 pm   #14
duncanlowe
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Default Re: Brown substance on Solder Joints

Quote:
Originally Posted by barrymagrec View Post
When I was at Leevers Rich in 1969 the inspector always put a dab of red varnish on each joint to show it had been inspected - I began to doubt the efficacy of this procedure when I found a joint which had not been soldered at all but nevertheless had its dab of red varnish.....
That reminds me of a similar thing I heard about. In an assembly process, after a nut was torqued, it was dabbed with paint to confirm it had been properly torqued. One day it was spotted that there were a whole stack of nuts on the operators bench, with the paint dab already applied, because it was easier to do them all at the same time.
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Old 17th Jan 2020, 4:42 pm   #15
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Default Re: Brown substance on Solder Joints

Workers will always find ways 'navigate' around procedures that take time.

At Thorn we also did work for the military. For such contracts and equipments, mechanical wire strippers were not allowed because of the risk of weakening the copper conductors and the chance of them severing as a result of vibration, shock etc in battle. So, hot wire strippers were designated for use of. I won't comment on whether or not I ever saw mechanical strippers being used.
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