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Solder issues...

hnash53

hnash53

Super Member
This is weird. I'm replacing a radial electrolytic cap in a vintage receiver and having trouble soldering one of the leads. One lead solders in place like the hundreds of others I've done. But the other is giving me fits.

The leads are less than 1/4" apart. The one I'm having trouble with the solder is not sticking to the trace nor wicking up the lead at all. The melted solder is clinging to the iron. I've scraped & sanded around the lead hole repeatedly to no avail. I've made sure my iron is clean and all that.

It's not the soldering iron, and it's not the solder. Like I mentioned, the other lead solders in place just like it oughta... and it's less than 1/4" away from the other.

I've not run into this ever after soldering in scores and scores of caps.

Wazzup... and what can I try?

Thanks!
 
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Hi Hnash53, A couple of questions, 1) Is it a small pad or a large pad you are soldering to? 2) Are you using additional flux on the joint? 3) Sometimes the lead of the part doesn't want to take solder due to oxidation/ lead material. I have had to flux the joint to get the solder to flow. Sometimes a large pad will soak up the heat from the iron but you don't want to put too much heat in damaging the pad lifting it from the PCB. Have had to scrape a lead to get it to take solder. 34 yrs electronic tech. Leaded and lead free soldering exp.
 
OK... a few terms I am unfamiliar with... pads? If you are talking of the "bubble" around the lead hole... it looks like it's still there... is there supposed to be a bulge upward?

If I sound like a novice... I am. I have replaced numerous (not every single one) caps in two different quad receivers. In one of them I had to install a wire jumper where the PCB had lifted up and broken off... so am I right about the bubble being what you are calling the pad?

As for the leads of the cap, I've got a whole bag of the identical caps left over from an earlier project. The caps are new, leads are good. And no, I've not fluxed the joint. Learning curve goin' up. Thanks. I'll chase these for awhile and get back. Appreciate the comments... and more, if anything I said above warrants more comments.
 
Use a Q-Tip and acetone or alcohol to clean off the solder pad and assess its condition.
 
You should be able to see shinny copper if you scrape at the pad as it is a thin layer of copper basically "glued" to the board (not to hard though) just enough to get rid of oxidation.

Do the same with wires and try to tin them after along with the solder pad. You can buy flux for electronic soldering in some hardware stores.
 
If the board in question is double sided: The lead is connected to a copper ground plane inside the PCB. It absorbs all the heat, so you'll need a very powerful iron to deal with that.
 
In a vintage receiver, a multi-layer PCB, I doubt it.

Much more likely to be contamination of the track with something, capacitor glue, epoxy from a previous track repair, a build up of spent flux etc. What has been suggested up to now should get the job done.
 
Are you using a soldering station with temperature display? What temperature are you using - 350degrees C or thereabouts?

I've had this issue a few times and it was tracked to a loose soldering tip. On my soldering station (a locally made Magnum with digital temp display) - there's a thermocouple going into the hollow part of the tip. If the tip becomes loose, it doesn't make proper contact with the thermocouple and you get a false reading on the station's display. Eg if the station's display shows 350 degrees C, the actual tip temperature can be as low as 200 degrees C.

tri_pod
 
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On the delicate pads the Hakko can suck not only the solder but the critical part as well. It can happen when I use the large tip on the thin legs.
I hate when it does that.
 
I've encountered solder in some 1930s/40s units and some later import units which seem to have a lot of tin and possibly silver. They have been a problem. The best solution I've found for these is to clean off contamination, add paste flux, allow some NEW solder to the joint (60/40) to alter the alloy, and after cooling go back at it with the sucker. They usually comply after that treatment.
 
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