Soldering issues

[Levente]

Hey Guys, i hope I am in the right thread for this but something is happening during soldering on a particular PCB which never happened to me before. I need to change the tantalum drop cap's as many of them are out so here is what is happening:

1. PCB is from a 1974 Lexicon delay unit, very well built
2. Surface prepared the new capacitor to be slodered in
3. One drop of Weller flux
4. Solder is Stannol HS10

As soon as I touch the soldering tip with the solder on to the surface with the Weller flux on it to solder the component in, does not reacting at all. It's like the solder goes frozen cold. As soon as I remove back my soldering iron, the solder at the tip again get's melted.

What am I doing wrong? Only happened with this PCB. Works fine on others.

Something is special on this PCB in terms of what soldering material were used?

Also, the original solder on the pcb and my solder I am using can not be mixed. They don't react.

Any suggestion would be greatly appreciated.

Cheers!

[Sideband]

Maybe you are trying to use unleaded solder? Back in 1974 it would have been standard 60/40 leaded solder. You should just use ordinary leaded solder.

Modern unleaded solder has a higher melting point than leaded solder and shouldn't be mixed with leaded solder. I don't know what the effect is when using unleaded solder with flux. Usually the flux is built in to the solder so why use separate flux?

[Beardyman]

Hello Levente,

From your description it sounds like your soldering iron isn't putting enough heat into the joint.
Look at the size of the joint on both sides of the PCB. If there is a large area of copper on either side it will act as a heat sink & draw the heat out of the iron tip, until the copper is up to the melting point of the solder it will remain solid. If your iron is a small bench type (15W or so) then it will struggle.
It is possible you are mixing lead free & leaded solder, this can cause some very odd things to happen, one of which is a joint that looks very grey or granular.
I suspect it is simply your iron cannot put enough heat into the joint.

Hope that is of some help.

[Jon_G4MDC]

All the above but also it can be that the soldering iron bit has bad contact with the heating element - due to being a loose fit or some corrosion happening in the joint.

Causes very strange effects.

[Levente]

Thank you guys for the help and responses.

I have this Stannor solder the HS10

https://www.soselectronic.com/a_info...f/ine/hs10.pdf

Yes, on the pcb i was soldering there was actually a massive junction point like 2 inches wide in diameter copper on it so that acted as a heat sink i guess?

..also, tried the same on my built in 1947 amplifier... now that was also a struggle. The old and new solder did not mix and became a white-grey ish powder substance... interesting.

So for old gear I should go with old types of leaded solders...and perhaps changing my desktop soldering iron to a better one... hmmm..

This is the first time I came across this issue.. and I was not aware of these at all...

[Herald1360]

Sounds like HS10 is a generic code for a wide range of leaded and unleaded solders.

From those listed, the Sn60 Pb40 would be the one to use for vintage kit, though the slightly lower melting point Sn62 Pb36 Ag2 might be handy ( if costlier) for fine work.

If you use lead free, one of the silver containing mixes will be easier to use for hand soldering. And more expensive

Odd factoid- lead free solder needs a bigger reel for the same weight (tin is less dense than lead).

[Levente]

Thanks Herald,

The reel i am using says Sn99,3/ Cu 0,7 is that the reason why isn't working ?

[Skywave]

"The reel i am using says Sn99,3/ Cu 0,7".
That sounds like lead-free solder: hence the problem. You need tin / lead solder.

Al.

[John10b]

That seems a strange mix Sn 99.3 / Cu 0.7 ? What would it be best suited for?
Cheers
John

[Jon_G4MDC]

Fixing up the plating on a tin bath!
My coat is on..

[davidw]

Its Lead free ..... https://www.amazon.co.uk/Solder-Ag0-.../dp/B06XKSSQDF

[cmjones01]

Originally Posted by Levente

The reel i am using says Sn99,3/ Cu 0,7 is that the reason why isn't working ?

Yes. That solder, which is almost pure tin, melts at quite a high temperature and has a very narrow 'plastic region': it goes solid very quickly as soon as it cools down. That makes it very difficult to work with. It's cheap but not worth the trouble. Get some 60/40 tin/lead and everything gets easier.

The other issue, as other people have mentioned, is large areas of copper on the PCB drawing the heat away from the joint. The PCB may even have internal planes (though it's unlikely in a product from 1974) which absorb even more heat.

The solution is to use better solder and get a more powerful (and maybe a bit hotter - I favour around 370C) iron. And be patient - it can take 10 seconds or more to get the track and component lead hot enough to melt solder and make a good joint on a PCB with a large copper area.

Chris

[ITAM805]

Hi Levente, yes wrong solder type for the job. There's lots of choice on eBay but I recommend this brand

[David Simpson]

It may help some folk when purchasing solder to know what the abbreviations mean :- Sn = Stanium = Latin for 'Tin'
Pb = Plumbium = Latin for 'Lead'
Cu = Cuprium = Latin for 'Copper'
So good old 60%/40% solder would = Sn 0.6/ Pb 0.4 on modern technical info & labels.
Likewise, many chemical elements used for transistors/diodes/etc are shown in technical documentation using Latin abbreviations.
I'm not trying to be a smarty pants, its just that I've actually visited the Roman world's oldest ancient copper mine in Cyprus. Cyprus = Kypros = ancient Greco-Roman for 'Copper'. Small world, eh.
Back to soldering - if you are using flux-cored 60/40 for vintage radio pursuits & you are using a soldering station with inter-changeable bits(recommended these days) - set the temp at approx. 340 - 350 degrees for basic joints. A tad more for thick tags etc., and a tad less for small semi-conductor circuitry. Last week I had to set mine at 400 degrees - to remove some components from a 'lead free' soldered scrap pcb.
Advice - use scrap circuitry & components to practice soldering techniques, working temperatures, and bit sizes. And, as the A said to the B - keep your tip well-wiped & clean. Some folk advocate a wet sponge, me - I used cheapo kitchen roll sheets.

Regards, David

[barretter]

To be strictly accurate that should be "plumbum" for lead, "stannum" for tin and "cuprum" for copper. There is no "i" in "stylus" either!

[David Simpson]

Thanks barretter for the spelling correction. Me thinks that next time I meet our local village plumber(big Jock McGraw) in the pub, I'd be wise to not mention the correct Latin spelling/pronunciation for lead. He has a reputation of being able to shove 22 & 28mm cuprum pipes into the most awkward of places.

Regards, David

[ms660]

That's where the name of the mineral Stannite was derived from and in a historical sense the Stannary Parliament.

The main ore of tin where I worked was Cassiterite...The Cassiterides...lost in time.

Lawrence.

[broadgage]

Originally Posted by John10b

That seems a strange mix Sn 99.3 / Cu 0.7 ? What would it be best suited for?
Cheers
John

Used for heavy electrical connections, rather than electronics.
Connecting magnet wire to commutators in DC motors and in Dynamos.
Sometimes used for jointing large cables.
Higher melting point reduces risk of failure under fault or overload conditions.
Can be used with a suitably high temperature electric soldering iron, but a micro-flame gas torch is sometimes preferred.

I used this solder when re-building a resistance starter for a large DC motor, being fearful that ordinary "electronic" solder might fail due to heat.
I used a German made propane gas torch that produced a small but very hot flame.

[Oldcodger]

Another use would be as a high melt point solder on the tuning coils in high powered transmitters. e.g. Clansman 353 , and even then you'd need more than the standard 45w Weller.

[John10b]

Thank you both for that interesting reply. I wonder if that solder would be suitable for soldering “dropper “resistors which get very hot?
Cheers
John