Lead-free soldering and related matters in 2019

[mcovington]

This is a mix of observations and queries... Having started to build electronic toys for my grandchildren, I've gotten serious about lead-free solder.  Here's what I've experienced and what I'm wondering about.

(1) I don't like SAC (SnAgCu) solder -- the solder joint always *looks* bad, whether or not it's good internally -- but SnCu (99C) is serving me well, especially Kester K100LD, which is Sn, Cu, and tiny amounts of nickel and bismuth.

(2) There has to be plenty of flux.  Newer lead-free solders are 3% flux and work a lot better than older ones, which didn't have enough flux.  Small-diameter solder, so that you feed it slowly, also helps.

(3) The purpose of the iron temperature is to activate the flux, not just melt the solder.  Kester recommends 750 F (400 C) for lead-free solder and for leaded "no-clean" solder; 700 F for leaded solder with conventional flux.

And this accords with my experience.  Many times over the years I've found that some kind of solder was finicky and hard to work with, and it turned out my iron wasn't hot enough.  (One soldering station was 50 F out of calibration.) 

Conversely, an iron that is too hot can burn up the flux before it works.  Beware when the flux is leaving brown marks.

(4) Beware the wet sponge.  Wiping the iron with a wet sponge can lower it 50 to 100 F for as much as half a minute afterward.  Back in the day, when irons were unregulated and always too hot, this practice got the iron *down* to a good working temperature, and it's a habit I stuck with until I made some temperature measurements just recently.  A ball of brass wool is much better.

OK, those are the observations.  Some will disagree vehemently with any and all.  Here are my queries:

(a) Who sells Multicore in the USA?  Availability seems to be very spotty.  I liked Multicore leaded solder very much back in the 1970s (I got some in England; the USA had it) but couldn't get any more in the USA after 1982 or so.  Now I see that it's back.

(b) Has anyone compared Multicore 99C with Kester K100LD?  (Both are SnCu solders.)  I see that Dave has a roll of Multicore 99C, but also that Dave generally doesn't like lead-free solder, unless he has changed his opinion recently.

By the way, I agree that lead-free solder is dreadful -- if it is SnAgCu, and if it doesn't have enough flux, and the first generation of lead-free solder had both of those faults!

[Someone]

(a) Who sells Multicore in the USA?  Availability seems to be very spotty.  I liked Multicore leaded solder very much back in the 1970s (I got some in England; the USA had it) but couldn't get any more in the USA after 1982 or so.  Now I see that it's back.

https://www.newark.com/w/search/prl/results?brand=multicore-loctite
99C 309 flux

[mcovington]

I got exactly one hit from that query, and it's solder 1 mm in diameter, a bit big for the purpose.  And it mentions "UK stock."  Maybe the stuff isn't actually marketed in the US at all?

[Someone]

Newark parametric search and descriptions are poor enough to be almost useless, so you are better off finding the part numbers from the manufacturer and working from there. They have a range of different sizes and fluxes but don't make the effort to advertise/categorise them. Even if its UK stock you only pay for local delivery (usually free), how quickly do you really need a roll of top quality solder delivered?

[mcovington]

No hurry.  If I could find the manufacturer's master list of stock numbers, I'd have a much easier time figuring out what various suppliers have.

[scatterandfocus]

I know very little about lead-free soldering, but I'm interested in knowing more about it and using it.  Obviously manufacturers are using it with reliable results, but do the results of their materials and processes translate well to hand soldering?  Is lead-free solder whiskers still a problem today?  I have repaired some lead-free solder joints over the years using lead solder, because that is what I have always kept around due to having good results with it for hand soldering, even with a crappy cheapo iron that should be in the trash.  How forgiving is hand lead-free soldering using current solders and fluxes?

[tooki]

No hurry.  If I could find the manufacturer's master list of stock numbers, I'd have a much easier time figuring out what various suppliers have.

You're probably focused on the Multicore brand name, not realizing that its current owner, Henkel, is in the process of phasing out that name in favor of the Loctite brand. So when you look at Digi-Key, etc, look for both names.

Here’s the product page: https://www.henkel-adhesives.com/us/en/products/solder-material/solder-wires.html

(And for completeness’ sake, in Europe, Henkel mostly markets it under the Stannol brand.)

[tooki]

I know very little about lead-free soldering, but I'm interested in knowing more about it and using it.  Obviously manufacturers are using it with reliable results, but do the results of their materials and processes translate well to hand soldering?  Is lead-free solder whiskers still a problem today?  I have repaired some lead-free solder joints over the years using lead solder, because that is what I have always kept around due to having good results with it for hand soldering, even with a crappy cheapo iron that should be in the trash.  How forgiving is hand lead-free soldering using current solders and fluxes?

I don’t have any insight on tin whiskers, etc., but in terms of handling, I think people are making a huge fuss about nothing when it comes to lead-free. Quality lead-free solder works just fine, it just needs a higher temperature than leaded solder. I’m able to achieve excellent results with either, using a decent soldering station. Regardless of solder type, I like to apply some extra flux with a flux pen.