why 60-40 solder?

It costs a bit more.

If you're asking why 60-40 still exists, I'd chalk it up to residual demand from when it *was* the universal standard. I suppose there are companies around who still have that formulation in their process specifications and it's easier to keep buying it than to rewrite the documentation.

Because you can't sell it in the EU if it's got lead in it.

You better hide under the sheets, now. The Non-Sequitur police are coming to get you.

Uh... 63-37 has lead in it.

The 63 is tin, the 37 lead. Traditionally, tin has been more expensive than lead, so eutectic solder cost more than 60-40.

Not true at all. There are plenty of organisations that are still legally allowed to use 60/40..... Schools colleges/military/telecoms/space etc. Plus many more who don't care about lead free....

Plus lead helps prevent the formation of 'tin whiskers'.

--
If there is a no_junk in my address, please REMOVE it before replying!
All junk mail senders will be prosecuted to the fullest extent of the 
law!!
http://home.att.net/~andyross

I don't think you'll find that to be true these days (i.e., last twenty years or so) because solder prices are driven more by volume than the commodity values of tin and lead. As a WAG, maybe 100 times as much

63/37 as 60/40 is sold, so I believe the premium is on the less common formulation. If you can show me a cite to the contrary, I *might* be willing to stand corrected. It has been many years since I priced 60/40.

Because sometimes you want mush.

Eutectic is either solid, or liquid.

Formulations off eutectic have a range of mushiness, which can be of use.

And they have higher melting points, which can be of use in multipart assemblies, where you might use 50-50, 60-40 and 63-37 to assemble and solder a series of parts.

--
Cats, coffee, chocolate...vices to live by

Interesting. I've not heard of this before. Do you speak from:

1> experience 2> rumor 3> speculation

Not wanting to be confrontational, just curious. Wikipedia lists melting points as:

63/37: melts between 180-185°C 60/40: melts between 183-190°C 50/50: melts between 185-215°C

I'm not aware of any soldering process that is able to control temperature so closely as to not melt one, while melting another of those formulations. Can you elaborate?

Smitty Two wrote in news: snipped-for-privacy@news.phx.highwinds-media.com:

When I worked as a process engineer for Sprague Electric Co, in the early

70's, making capacitors and resistors, we used 95/5 solder, I think it was tin/lead with a small amount of silver, to assemble the capacitors and resistors.

One reason for that choice was so that the parts would withstand normal

60/40 soldering when boards were assembled.

Like you, I have some doubts about the kind of close control that would be needed to use mixes as close as the ones given.

--
bz    	73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an 
infinite set.

bz+ser@ch100-5.chem.lsu.edu   remove ch100-5 to avoid spam trap

bz wrote in news:Xns9A07DE839DD08WQAHBGMXSZHVspammote@130.39.198.139:

I doubt it can be that accurately done. I use various indium based solders for making small assemblies of optics and electronics when I want to get different melting points, and you need well defined narrow ranges for ech solder, with at least 10 degrees apart between each rangem ideally, because an assembly might easily see several degrees variation unless you're prepared to control the conditions with expensive rigour and to wait a long time for equlibrium to settle each time you change the temperature. Two solders wth overlapping ranges for melting would be useless.

Not true, most if not all UK wholesalers still sell 60/40 leaded solder.

Ron(UK)

...

It's not whether you can melt it, it's how it hardens. Eutectic solder hardens very suddenly. 60/40 solder goes through a fleeting stage of being viscous but not yet completely hard. I'd like to hear more about this, but I'm told some people prefer the "feel" of one vs. the other.

If you're going to quote me, I'd appreciate it if you wouldn't snip all contextual relevance out of the discussion. As it is, your post might appear to the casual observer as bearing some relevance to the topic at hand. It may be a response to the OP, but it certainly isn't relevant to the sub-topic of sequential soldering using a variety of formulations.

I am indeed trying to discuss the original topic of the thread. The original poster's question interested me, an nobody has responded to it.

dances_with snipped-for-privacy@yahoo.com wrote in news:a232ec67-c9bd-42ad-99f3- snipped-for-privacy@t1g2000pra.googlegroups.com:

Probably because the gradual solidification makes dry joints less likely. I'm not even sure it it does make them less likely, but I bet it does because you're not relying only on ductility of a solid to maintain good structure during thermal contraction. If the two metals in the alloy don't solidify together, one can flow to fill pores that might form in the other, or between the solder and the parts joined with it.

If by "dry joints" you mean what I was taught as "cold solder" -- where the solder crystallizes and looks like the dull side of a sheet of aluminum foil, then you've got it backwards.

63/37 solder passes from liquid to solid so fast that there's almost no chance for the solder to crystallize (which is usually caused by movement during the cooling phase) and so has _less_ chance of forming cold joints. 63/37 also has a lower melting point than 60/40 which means that theoretically it puts less heat stress on the component being soldered.

In practice I don't think the difference in melting points makes much difference, at least for hand soldering, since the iron's tip temperature isn't controlled that tightly. But I can definitely say from personal experience that cold solder joints are much less frequent with 63/37 than 60/40. Not impossible, though.

--
Gordon S. Hlavenka           http://www.crashelectronics.com
               It's bad luck to be superstitious

From my days at Mullard in the early 1960's, I seem to remember that thermostatically controlled irons were not used, there were horrible large things like an ice pick!

Multicore set the standard in the UK for many years and what they suggested/supplied was what industry used. As everything was hand soldered then, it had to be a solder and flux with as wide an operating temperature range as possible.

Peter

-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk