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Solder Question

Posted: Thu Aug 22, 2019 2:58 pm
by Peakoverload
A bit of a random question and not directly Pi related but thought someone here might know as I know next to nothing about it. Where I work we have boxes and boxes of solder and nobody knows why, where it came from or how long it's been there. We have absolutely no use for it and we were considering seeing if a local school/college (UK) could make use of it. However when trying to google the solder I can't really seem to find any info about it and wondered if this is because it's now discontinued because of it's lead content and if that therefore means it would not be suitable for schools etc or even if it can still be used by anyone.

The solder is made by Multicore and comes on 2.5Kg reels. The label says that it is Solid Solder Wire and that it's 20/80 BS219 Grade V with a diameter of 20swg 0.9mm. We also have identical reels with a diameter of 18swg 1.2mm

The only other info on the reel is that underneath where it lists the diameter it says 957.

The tiny amount of soldering I've done I've either used lead free solder or 60/40 and never even heard of 20/80 before.

Is this suitable for electronics work or does it require much higher heat due to the lead content? Can it still even be used, I seem to have a very vague memory that some law had been passed to reduce or ban the use of lead completely within the EU?

Re: Solder Question

Posted: Thu Aug 22, 2019 3:21 pm
by pica200
Lead free is only needed to meet RoHs conformity which i don't think is needed in schools (unless they want to sell stuff built with it). I don't know if they banned it outside of this requirement so still not sure. I guess you can ask them if they need some and are allowed to take leaded solder.

That alloy you got there is pretty unusual. Most common is 60/40 and 63/37 and minor variants of them with copper in the mix. Maybe that stuff you have is for stained glass (windows)?

Re: Solder Question

Posted: Thu Aug 22, 2019 3:26 pm
by drgeoff

Re: Solder Question

Posted: Thu Aug 22, 2019 6:39 pm
by Heater
According to this document Multicore 20/80 solder has a higher melting point than regular electronics solder and is recommended for "lamps".

Are you working in an old light bulb factory?

Probably not much use for electronics, high temps damage components. Schools might not like it for it's lead content, I don't know.

I'd be tempted to fire up the soldering iron an try try out...

Re: Solder Question

Posted: Thu Aug 22, 2019 9:57 pm
by Imperf3kt
Judging from the information provided, I'd second the idea that it isn't electrical solder, but rather for old leadlight windows.

Re: Solder Question

Posted: Thu Aug 22, 2019 10:13 pm
by Andyroo
That’s way too thin for classic stained glass work. Locally they use I-beam style strips (63/37) up to 2cm wide and the irons have to be heated in a brazier :o

OK - I hang around with restoration teams and archaeologists :lol:

It sounds about the right size but most are lead free now.

Re: Solder Question

Posted: Fri Aug 23, 2019 9:16 am
by Burngate
Traditional electronic solder has several cores of rosin (or similar) flux to aid wetting and removing oxides.
Although the company is called "Multicore", this solder is solid - no cores.

Not knowing where you work, I have no idea what your company (or someone in it) was thinking about doing, but ...

Would it be worth asking at your local college if they have a metal-working school? The Tech College I went to had one, last century.

Re: Solder Question

Posted: Fri Aug 23, 2019 5:59 pm
by Peakoverload
Thanks all for the replies. The mystery continues. I work in a recording studio and when I first saw the reels thought it was left over from when we moved in and all our equipment and patchbays had to be wired up. But when I saw it was 20/80 I thought that couldn't be the case. We have absolutely no idea why we have it, we are 99.9% sure it must have been left by a contractor but other than electrical wiring/telecommunications and air conditioning no other contractors come in.

Looking up prices of reels of 60/40 that are this size, I realise that each reel is possibly worth £80-£120 which is a lot more than I thought and makes me want to ensure someone gets some use from it. We don't really have the means to sell it and we'd rather not chuck it hence wanting to give it to an organisation that would benefit from it.

I've got a list of colleges in our area and will contact them to see if it's something they could use.

Thanks again for the help.

Re: Solder Question

Posted: Fri Aug 23, 2019 10:55 pm
by W. H. Heydt
If the comment about 80/20 being used to do stained glass work is correct, the nearest church with such windows might be a good candidate to offer it to. If they don't do any maintenance "in house", they'd know who does. The bigger the church, the more likely to either need it or to have some local artisan who does.

Re: Solder Question

Posted: Fri Aug 23, 2019 11:49 pm
by Douglas6
There are two main techniques for stained glass; lead cames, which use solid lead-alloy 'i-beams' that are soldered at the joints, like in church windows and other windows. Then there is copper foil stained glass, mainly used by hobbyists, or for lampshades, in which the glass is wrapped in copper foil tape, and soldered together using solid core solder, a jar of liquid flux, and an electric iron. I've done both, but always used 60/40 solder. Professionals may use 80/20.

Re: Solder Question

Posted: Sat Aug 24, 2019 1:39 am
by mahjongg
80/20 probably not only has a much increased melting point, but might also be harder (AFAIK).

The higher melting point is useful for cases where the soldered joint might become extremely hot, as in high voltage high amperage joints, within a confined space, so heat cannot get away easily from the joint.

as for electronics, I would never use such solder, and using lead free solder for repairs and such the higher melting points of such solders is also problematic, and for repairs, and hobby you never need to use lead free solder (luckily).

Also 80/20 solder might not transit from solid to liquid quickly, but have a large non eutonic phase, where it is neither liquid nor solid, and that is very bad for soldering electronics reliably, as it can lead to unreliable "cold joints".

Re: Solder Question

Posted: Sat Aug 24, 2019 1:40 am
by scruss
Since this isn't flux-core solder, it'll basically last forever. Old flux-core solder often doesn't work as well and needs liberal quantities of flux pen to make nice joints. 20/80 might've found some use for soldering valve/tube mounts, if your facility has been a recording studio for a really long time.

But an 20/80 alloy is so far from the eutectic mix that it's going to have a very long cooling period where it's a pasty slush of molten tin with rapidly growing lead crystals that will just be unpleasant to work with. I think I learned to solder with 20/80 (dad was a radar tech; mention TSR2 and he'll go apoplectic still) and it was dismal. It was a great way of making dry joints. Still, watching those crystals form and having to deal with intermetallic buildup (purple! bright yellow! harder than metal files!) on the iron got me interested in materials engineering.

But really, you should be avoiding lead: lead-free all the way, don't listen to the old guys. Good on you for trying to pass it on in a responsible manner rather than dumping it.

Apart from being a great word to say, eutectics are a neat concept: an alloy of two metals that has a lower melting point than either of them. I forget how this works, but the eutectic diagram (nicked from is neat:
Pb-Sn eutectic
solder-000.jpg (29.43 KiB) Viewed 2186 times
It shows pure lead on the left melting at 327 °C and pure tin melting at 232 °C on the right. Only pure lead, pure tin and the eutectic alloy (63/37) go straight from liquid (light grey) to solid (mid grey). Every other alloy goes through a slushy phase (dark grey on the diagram) until it cools below 183 °C, where all lead/tin allows are solid. 20/80 is only fully liquid above 275 °C, and it has to cool by nearly 100 °C before it is solid. That part of the cooling curve is an increasingly sullen slurry until it finally hardens. Blecch.

Re: Solder Question

Posted: Sat Aug 24, 2019 3:26 am
by LTolledo
use what is easy for you....whether for soldering or de-soldering...

you are one that will be doing it on your project....

Re: Solder Question

Posted: Sat Aug 24, 2019 4:00 pm
by scruss
LTolledo wrote:
Sat Aug 24, 2019 3:26 am
use what is easy for you....whether for soldering or de-soldering...

you are one that will be doing it on your project....
Lead remains toxic forever, so if you can use less of it, people in the future won't have to deal with your mess. My wife used to work with people who were childhood victims of lead poisoning and it was very sad to see people left at kindergarten-level development because of an avoidable industrial ingredient.