Why does 60/40 solder exist?

[JackOfDiamonds]

I only use 37% lead / 63% tin solder, because that's what my forefathers taught me. I happen to know that 37% lead solder has the lowest melting point of all mixtures.

When I go to the hardware store and look for solder, leaving aside lead-free solders, I often see mostly 60% lead solder. I have to specially shop for 37% lead solder. 60/40 seems to be the "norm", and 37/63 seems to be special. So why is 60/40 so popular? Is it just cheaper (I would think lead costs more than tin, but maybe not). Does it have a property that makes it easier to use than 37/63?

 

[welder4956]

 

[bwringer]

From the chart, it would appear that the 60% lead is easiest to work with. "Long melting range" and "fill larger gaps".

But I'm no solderologist. I expect one will be along shortly.

 

[The Cobbler]

I was always taught that 50/50 is (was) best for plumbing .but that was long before the lead ban for potable water

 

[micromind]

I've soldered a lot of stuff, if I were to solder something with 63/37 and a half-hour later solder the same thing with 60/40, I seriously doubt I could tell the difference.

 

[pizza]

why have you not mentioned your application? i hope not plumbing. lol

for electronics, i have often wondered that myself. i have not noticed much too difference between eutectic and 60/40, and in fact, imo eutectic's better – it solidifies in a snappier fashion and so makes it harder to get cold joints. so why do many manufacturers offer both?

i'm not sure tbh.

Solder mixture - 60/40 67/37 - Page 1

Solder mixture - 60/40 67/37 - Page 1

www.eevblog.com

 

[isb cornbinder]

Solder containing lead is banned in Canada for use in water pipe connections.

 

[JackOfDiamonds]

I was only thinking about electronics soldering....for plumbing we can't use lead at all, and I use whatever they sell at Home Depot for that.

 

[mark-NJ]

63/37 is eutectic. That alone is enough to call it "best" for electronics.

 

[alfadan]

I'm gonna guess.....money.

I also wouldn't be surprised if 60/40 or 63/37 could be anywhere from 55/45 to 70/30!

 

[cowades206]

If you do a lot of soldering with 63/37 and then use some 60/40 you will notice a difference. It will be a little harder to get a nice looking joint. I've used a lot of both for electronics work and I've never had bad solder joints with either one; the 60/40 doesn't always look as good. If I had both at hand I would always use the 63/37.
I'd also guess cost money is the reason. Don't know why one would be cheaper though.

 

[dscheidt]

I only use 37% lead / 63% tin solder, because that's what my forefathers taught me. I happen to know that 37% lead solder has the lowest melting point of all mixtures.

When I go to the hardware store and look for solder, leaving aside lead-free solders, I often see mostly 60% lead solder. I have to specially shop for 37% lead solder. 60/40 seems to be the "norm", and 37/63 seems to be special. So why is 60/40 so popular? Is it just cheaper (I would think lead costs more than tin, but maybe not). Does it have a property that makes it easier to use than 37/63?

60/40 wets better, so it sticks to things a little bit better, especially when it's less than perfectly clean. It's also used in some multi step operations. because it melts at higher temperature, it can be used to solder stuff, and then eutectic solder on later components, without disturbing the 60/40 joints.

Also: tin is more expensive than lead. today's tin price was about $14/lb. Lead is about $1/lb. that adds up fast if you're using a lot of solder.

 

[pizza]

yeah, 60/40 is slightly cheaper...
but imo none of the theories in this thread explain this to my satisfaction:

why, especially in 2024, would a company offer electronic solder in both 63/37 and 60/40?
i think it's fair to assume that chipquick leaded solder wire is mostly being sold to hobbyists and to certain professionals repairing vintage equipment. in any event, it's for hand soldering. and the difference in price between them is like $2 ($41 vs $39) for a 1lb spool. seriously, what supports the business decision to offer 60/40?

Chip Quik - Leaded No-Clean (33)

edit: you know what, i'll just ask them.

 

[welder4956]

I have done some electrical soldering with 60/40 but not 63/37. From the chart above, the 63/37 appears to have an advantage for electrical solder because the melting and solidification temp are eutectic, so as soon as the heat is removed the connection is not subject to damage if moved slightly. That said, either would work fine for a home user. I believe 60/40 is easier to make and cheaper only because the composition does not have to be controlled to the same degree as 63/37 during manufacturing.

 

[danielbuck]

my GF uses 60/40 fairly often for stained glass soldering. along with a few other blends. We don't buy it from the local home stores though.

 

[Hohn]

I'm pretty ********* into electronics soldering for a home gamer. I have two stations and a separate iron on my bench with 13 different solder varieties (almost all SN63 eutectic) from which to choose (mostly variable in diameter, flux type and flux concentration).


Frankly, this question has always bothered me. Especially when I was less skilled, the Eutectic SN63 seemed like magic. But as I got better and refined my technique, I realize that 60/40 didn't really hold me back at all because I was working with small things that would fly through the narrow temperature range where it mattered.

As an aside for those who may not know, "eutectic" alloys means that it has one set solidus and liquidus temperature. The whole thing melts and solidifies at the same temperature. For SN63, this is 183C or about 361F.


SN60 with a 60/40 blend is not eutectic. So the melting isn't a single point, but rather a range with starting and ending temperatures. For 60/40, it starts melting at 183C but doesn't finish until 192C. So there's this 9C window of temperature where it's partially melted, partially still a solid. If the joint is disturbed while it's in this transition phase during solidification, you can get a bad solder joint.

That's all well and good, but it only makes the question more puzzling-- given the obvious advantages of SN63, why SN60?

I can only speculate:
1) 60/40 discovered first and tradition and human nature took over after that?
2) Tiny bit more ductility with SN60?
3) Tiny bit higher shear strength with SN60?
4) SN60 has about 10% higher thermal conductivity so it might provide more margin in high-heat applications?

I think SN60 persisted so long largely because it's what people grew up with and once you get your skills and tools dialed in, SN63 and SN60 are functionally interchangeable.

I personally like buying old SN60 rolls that are "expired" from ebay (joke's on them-- solder lasts almost forever) and use them for tip tinning and other "wasteful" activities.

 

[Shoreline_]

I have an old roll of 50/50 for when I am up against the wall or close to a wood beam.

 

[pizza]

FAQ | Kester

Sn60 vs. Sn63: When is the use of one of these two alloys more appropriate than the other?

The Sn60Pb40 has a plastic range and puts down a slightly thicker coating of solder. Sn60 is often preferred for lead tinning and other solder coating applications. Sn63Pb37 is eutectic and as such has no plastic range. Generally it flows better than the Sn60 and is the preferred alloy for wave soldering and surface mount applications.

 

[Hohn]

FAQ | Kester

That's a bit hilarious because I've been using SN60 for that very purpose and yet had no idea why, having never read that guidance. I tin wires, pads, and terminals with SN60 mostly because I wanted to use it up. Ironic?

 

[pizza]

yes, funny that you were using it by accident for its intended purpose