Choosing solder: 63/37 vs 60/40 - any practical difference?

[e-pirate]

Hi folks.

Recently I did a bunch of XT60 connectors for my outdoor solar panel extender cable and found that my decade old 250g 0.8 ПОС61 solder spool is coming to en end.

ПОС61 is a Soviet/Russian naming for Припой Оловянно-Свинцовый which literally mean nothing more then "tin lead solder with lead content of 61%". Everyone who started doing electronics in Soviet or early post-Soviet era is 100% familiar with this stuff - no exceptions. It is often made to standard by unknown manufacturer (at least the most vintage ones), the old one come in 2-3 mm diameter "wires" and some times in 8mm bars with no flux added. This thing just does the job and this is all to be said about ПОС61 solder even now days. It melts at expected temperatures of about 190-200 C, spreads in controlled way, gives you some blurry solder joint and that's it. Just add some ethanol (no, vodka will not do!) dissolved rosin as a flux and you're good to go. Characteristics will vary slightly from sample to sample: not the lowest melting temperature, not the best wetting, not the most perfect shiny joint, but it cheap (in most cases free), always work and never fail in any way regardless if it is half century old noname spiral you got from your father's wooden box they days trees were taller and skies were blue or a new spool you got from marketplace delivered to the nearest pick point next day (or on the second day if you're unlucky).

I use my 0.8mm ПОС61 with rosin core for my general work. I also have Asahi 0.25mm spool for SMD, but it looks like that 0.25 will last me a lifetime as I tend to.. be lazy and use 0.8mm even for 0102.

Things changed when I got Quick 202d inductive soldering station really cheap for black Friday sale. I also got "knife" and "microwave" tips for it and that changed my soldering experience so much that I was thinking of selling my old and trusty Goot RX-711AS with a bunch of chisel tips (no, I'll keep it). Suddenly I realized that I don't need to keep iron tip at 340-360C any more - the 90W (it is actually 100W) induction heated thermocouple controlled tip pumps heat into the tip and reacts to temperature changes so fast, that I'm in most cases good at 300C or even less for leaded stuff. No overheating to compensate for low power and slow reaction of ceramic element with sensor deep inside is needed. The short finger-to-tip distance is another thing I like about Quick 202d. There some (many!) disadvantages, but this is another story.

OK, now I have a better control of my iron tip and can keep it at a lower temperatures because of different heating technique and more power involved. This brought me to idea I should try some potentially better solder as my current one is almost over and it may be a good point I can improve my soldering even more.

So, I started searching for one to fulfill my requirements. Nothing special, actually: I need leaded solder with flux for a general PCB work. I always use additional flux for my work (for general stuff I prefer rosin-based RusFlux Souze-Apollon that is unexpectedly good for the money and for BGA I have a decade old EFD FluxPlus 412).

For sure we have all sorts of ПОС61 still available and according to youtube comments good manufacturers are known. But what I found is that many reputable import (as well as some local) manufacturers produce two common types of solder at the same time (among "special" ones): this are 63/37 and 60/40. Asahi does this, Kester does this, Cynel does this, Kaina does this. Pretty sure others do as well, but my manufacturers list is limited to what I know and can get locally.

So, let put Soviet 61/39 aside and now my question is what is the reason for manufactures to produce 63/37 and 60/40 solders simultaneously and what is a real practical differences?

The second (optional) question is: why "special" solders have some 1-2% silver or copper added and is it worth paying extra for such solders?

[Someone]

my question is what is the reason for manufactures to produce 63/37 and 60/40 solders simultaneously and what is a real practical differences?

The only reason left is to hit the right keywords for people who have always used 60/40 (it used to be cheaper as it was less precisely alloyed/mixed ?) so it will show up in searches.

The second (optional) question is: why "special" solders have some 1-2% silver or copper added and is it worth paying extra for such solders?

There are some useful additional elements for specific applications, see PDF below. Worth paying extra over 63/37? probably not much.

For most electronics work the flux is far more important which you seem to have organised/decided already.

[TimFox]

Sn63, or 63-37 is the "binary eutectic" alloy of Sn and Pb, and goes directly from solid-to-liquid and back again, in both directions.
60-40 is often considered "close enough":  the temperature region where the state is uncertain is relatively narrow.
40-60 Sn-Pb is normally a cheap solder (less Sn) that has a higher melting point:  only useful when the higher melting point is needed.  The excess lead is essentially in solution with the binary eutectic.  Can be "mushy".

I prefer Sn62, which is 62 Sn, 36 Pb, 2 Ag (the "ternary eutectic"):  it is more expensive (due to Ag), a bit stronger mechanically, and shinier.
The alloys with added Cu ("Sav-Bit") were made to extend the life of copper tips on soldering irons:  otherwise, Cu from the tip would leach out into the molten solder.
Tektronix used ceramic terminal strips with Ag metallization, and Ag-bearing solder was necessary to avoid damage to the metallized ceramic.

They will take Sn62 away from my cold, dead hands.

[RoGeorge]

Recently I did a bunch of XT60 connectors for my outdoor solar panel extender cable and found that my decade old 250g 0.8 ПОС61 solder spool is coming to en end.

Yep, that feeling:

it’s a spool of wire…
Cindy Thomas and Dan Burrell

https://knowyourmeme.com/memes/spool-of-wire-guy

 

[shapirus]

I prefer Sn62, which is 62 Sn, 36 Pb, 2 Ag (the "ternary eutectic"):  it is more expensive (due to Ag), a bit stronger mechanically, and shinier.
The alloys with added Cu ("Sav-Bit") were made to extend the life of copper tips on soldering irons:  otherwise, Cu from the tip would leach out into the molten solder.
Tektronix used ceramic terminal strips with Ag metallization, and Ag-bearing solder was necessary to avoid damage to the metallized ceramic.

They will take Sn62 away from my cold, dead hands.

Absolutely. A pleasure to work with and the joints look great. Not that I really need a silver-containing solder, but it's so good that it became my default choice. One problem though is that I can't get it locally in diameters less than 1 mm, unfortunately. For that I've got some 0.3 mm thick 63/37, but it's a Chinese brand (Mechanic), so who knows what its real composition is.

[mariush]

I use Multicore (now Harimatec) 63/37 0.56mm with no-clean flux (C502) : https://www.digikey.co.uk/en/products/detail/harimatec-inc/386851/2498927

 - bought a 500g spool from Digikey for around $50 a few years ago, will last me another decade, probably.

I prefer 63/37 due to being euctetic - snaps from liquid to solid at 183c - it can be a useful feature if you're working in an environment with vibrations, but also in general, it's nice to see the solder harden almost instantly after you raise the iron tip.

Regular 60/40 has a region around 180 degrees Celsius where it transitions from liquid to solid, and if you disturb the joint during that cooldown you can get a bad solder joint (by moving the lead during solder cooldown, vibrations shaking the board/component being soldered etc)

Yeah, 62/36/2 (extra Silver) would probably be even better but not worth the price bump (almost 2x the price of regular 63/37)

Even with this solder wire having 2.2% flux (3% for smaller diameters), I still like to use extra flux - I like to buy a Polish made no clean rosin based flux , Topnik TK83 ... 100 ml bottle is 6 euro : https://www.tme.eu/ro/en/details/flux-tk_100/fluxes/ag-termopasty/art-agt-045/  and 500ml bottle is less than 20 eur ... even the 100ml bottle would last you months.

or if they don't sell you the flux due to shipping restrictions, you can make your own flux by combining purified colophonium with isopropyl alcohol

500 grams of colophonium is 6 euro : https://www.tme.eu/ro/en/details/kalafonia-500/fluxes/ag-termopasty/art-agt-094/

Isopropyl alcohol (97% or better) you can buy locally, if not at chemical stores, veterinarians and pharmacies may have it.

The Topnik TK83 above is made out of 20-25% colophonium, less than 80% isopropyl alcohol, and it's mildly activated with benzoic acid (<5%) and adipic acid (<3%) ... basically a few drops in a 100ml bottle ... these can be bought as food grade additives in stores. But just mixing colophonium with isopropyl alcohol and mixing until the colophonium is fully dissolved is enough.

[SiliconWizard]

For hand soldering and if there's no constraint to be lead-free, I mostly use 63/37 SnPb.
For hand soldering of fine-pitch SMD, I almost only use 96SC though (which is SAC387).

[e-pirate]

For that I've got some 0.3 mm thick 63/37, but it's a Chinese brand (Mechanic), so who knows what its real composition is.

I've seen a lot of reviews on youtube (most of them in Russian) with clear proofs showing Mechanic XT100 solder is not a good choice for many reasons. 63/37 Kaina on a blue (not orange) spool is way better and priced about the same. HiClass (they often sell themself as Asahi) is another good choice. Both available on AliExpress and Kaina is my favorite to buy right now if I decide not to get +2% Ag solder as I found many people suggest it.

[EC8010]

They will take Sn62 away from my cold, dead hands.

Absolutely. I'm halfway through a Tektronix 500g reel and have another (unopened) reel. That should see me through. It produces beautiful joints, so if you've done something wrong, you see it instantly. Not like the horrible lead-free stuff where everything looks like a dry joint. I was not aware that there was such a thing as a ternary (tertiary?) eutectic, please do expand.

[TimFox]

They will take Sn62 away from my cold, dead hands.

Absolutely. I'm halfway through a Tektronix 500g reel and have another (unopened) reel. That should see me through. It produces beautiful joints, so if you've done something wrong, you see it instantly. Not like the horrible lead-free stuff where everything looks like a dry joint. I was not aware that there was such a thing as a ternary (tertiary?) eutectic, please do expand.

A binary eutectic is an alloy of two elements with the lowest melting point, and does not have an intermediate temperature range between "solidus" and "liquidus" temperatures.
A ternary (not tertiary) eutectic is an alloy of three elements with the same characteristics.
You can consider a non-eutectic alloy in its liquid state as the excess element (e.g., Pb in Sn40 Pb60 alloy) dissolved in the eutectic (e.g., Sn63 Pb37) alloy.

[Geoff-AU]

I've been a 60/40 heathen my whole life, should try eutectic sometime...    at the moment I just know to leave 60/40 undisturbed while it passes through its transition zone.

If I was doing anything critical (high vibration etc) I'd certainly use the best alloy for the job.

[TimFox]

63-37 is not much more expensive than 60-40 and you avoid the transition zone completely.

[switcher]

An excellent soldering tutorial video, by Hewlett Packard no-less, explains well different types of solder, flux, techniques, etc.

[soldar]

An excellent soldering tutorial video, by Hewlett Packard no-less, explains well different types of solder, flux, techniques, etc.
<video>
 

Contents is good but narrated very slowly. Even at 2X speed it is a bit slow. Those people in the dark ages had all the time in the world.

Image is also poor quality. Probably transferred from home video tape.

Still, good tutorial for anyone starting.

[Housedad]

I watched it.  Brought back memories of watching tutorials just like that in high school in the 70's.  The original was probably on 16mm film and transferred to VHS with a telecine machine sometime after. 

[mariush]

Speaking of tutorials / videos, Pace has a nice series

actual content starts at 2 minutes :

[andy2000]

Image is also poor quality. Probably transferred from home video tape.

Still, good tutorial for anyone starting.

I don't know why people even bother uploading at less than 480p.  Even lowly VHS is 480i, and can be deinterlaced to 480p.  240p is just useless. 

[m k]

60/40 if you're calm and steady, and no special connection requirements.
I've used it professionally during late digital through hole era without a problem, around not exactly lax quality environment.

63/37 if you have a difficult position or mass of a joint is big.

More importantly, use quality stuff.

[Canis Dirus Leidy]

The second (optional) question is: why "special" solders have some 1-2% silver or copper added and is it worth paying extra for such solders?

The addition of copper (in the solder) reduces the rate at which the copper (in the soldered parts) dissolves. So these solders are used for soldering really small items, such as thin (less than 0.2 mm in diameter) wire or copper foil. On the other hand, they (or at least ПОС-61М) are unsuitable for wave soldering or immersion soldering.

[mariush]

The second (optional) question is: why "special" solders have some 1-2% silver or copper added and is it worth paying extra for such solders?

The addition of copper (in the solder) reduces the rate at which the copper (in the soldered parts) dissolves. So these solders are used for soldering really small items, such as thin (less than 0.2 mm in diameter) wire or copper foil. On the other hand, they (or at least ПОС-61М) are unsuitable for wave soldering or immersion soldering.

I remember reading about Savbit solders, which also claimed the copper is added to extend the life of the soldering iron tips, besides the advantages for soldering very thin wires.

See https://stores.acrosales.com/content/solderwireproperties.pdf
 
MULTICORE SAVBIT ALLOY
x SAVES Copper and Iron-plated Soldering  Iron Bits
x SAVES failure of soldered joints as Savbit prevents erosion of copper wires and copper  plating
x SAVES costs and improves reliability Multicore Savbit Solder is produced especially to overcome the problem of ordinary tin/lead solders dissolving copper. It is an alloy to which a precise amount of copper has been added so that no further copper absorption should take place during soldering.

[...]

Savbit solder has been used by leading electronics manufacturers throughout the world for over forty years.
Savbit was originally used to increase the life of copper soldering iron bits. Soldering speed and efficiency are increased by keeping the iron in good condition. Ironplated bits having a longer life than plain copper tips are now commonly used but they also fail eventually (usually by cracking of the plating) and then erode rapidly unless Savbit solder is used.
It has also been proved that the use of Savbit alloy can improve the strength and reliability of soldered joints very considerably. This is because ordinary tin/lead alloys can erode thin copper wires (as used for leads of electronic components) and thin copper films (as used on printed circuit boards.) This erosion is between 50 and 100 times slower at normal soldering temperatures when Savbit alloy is used.