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For years I have used 60/40 rosin core solder.  I like to buy it in small diameter which is more suitable for tiny electrical connections I work with on my trains.  

I have two soldering irons and one gun.  One of the soldering irons is butane fired, while the other is 110 volt house current. The soldering gun is a 260/140 degree Weller.  All three have their uses depending on the type of work I am performing.  

I'm just about out of solder and am getting ready to buy more.  I noticed some Therm-O-Flow 60/40 on Ebay.  The description says it works best between 572 and 752 degrees.  Are there any other rosin core solders that might work well at lower melting temperatures ?

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63/37 is the lowest melting temp of the Pb/Sn and is eutectic which means it transitions from liquid to solid at a lower temperature than either of its constituents or any other mixture of them. This also means that it avoids a slushy mixture during heating and cooling. It's my choice.

From wiki...

Alloys commonly used for electrical soldering are 60/40 Sn-Pb, which melts at 188 °C (370 °F), and 63/37 Sn-Pb used principally in electrical/electronic work. 63/37 is a eutectic alloy of these metals, which: has the lowest melting point (183 °C or 361 °F) of all the tin-lead alloys

gunrunnerjohn posted:

I'm with Chuck, I use 63/37 rosin core exclusively.  None of the lead-free junk for me, it doesn't work nearly as well!  Since I've survived all this time using lead based solder, I figure if it was going to kill me, it would have done so before now.

Right on. I just don't hold the solder in my teeth any more for a third hand when soldering...

gunrunnerjohn posted:

I'm with Chuck, I use 63/37 rosin core exclusively.  None of the lead-free junk for me, it doesn't work nearly as well!  Since I've survived all this time using lead based solder, I figure if it was going to kill me, it would have done so before now.

Years ago I was working on College Hall at U of P.  We were restoring the original double hung windows.  Well the original paint was lead based of course.  So we all had to be tested during the job for the amount of lead we may have absorbed.  I passed out from the test !   

Looking at Cjack's post from wikipedia, in practice, is the 9 deg F difference between melting points of 63/37 and 60/40 noticeable?  I agree that the lead-free is a bear to use. 

I have found that using the very thin 60/40 (I haven't found any 63/37 locally), permits use of one of the otherwise poor 8-watt battery irons for thin wires in out-of-the-way places.

I like the 63/37 'Leaded' as well. The lead free stuff is terrible to use, as others have said. Just don't use any type of 'leaded' solder for anything that could be used for human consumption. Nowadays, I believe that is also illegal too, but it's fine for 'non-edible' electronics. 

DigiKey has a good selection, but may cost more than ebay though? I got some small 63/37 from them a couple years ago when I was ordering some other stuff. It didn't really seem all that expensive when I ordered it? It was the size that GRJ said he used for small work, 0.020 and 0.031, but I don't remember the brand?

Dan:

As others have said go with eutectic lead tin solder 63/37. For model train stuff you want the lowest melting temp solder you can get to protect sensitive components such as LED lights. You want the low temp especially if you are soldering microelectronic components on a circuit board.

I was a microelectronics packaging engineer in my other life. During my tenure the government force all microelectronic industries to switch to non leaded solders. The next lowest temp solder was silver based. With tin lead solder max furnace temperatures were set at 200-220C. With the change to silver based solders the max temp had to be increased to 260C. The difference of just 40C was disastrous for microelectronic packages based on plastic encapsulation (the little black packages with metal leads sticking out of them). If there was just a little bit of moisture in the plastic the packages would literally explode while in the furnace. This was called the popcorn effect because that was what it sounded like. Even now the industry is still struggling to come up with a good plastic mold compound formula that can withstand what is called 260C Moisture Level 1 criteria.

Also if I remember correctly - this was reliability while I was packaging, silver based solders have yet to attain the quality lead tin has enjoyed for centuries.

Joe

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