Hello my fellow nsolder freaks. In manufacturing you must (?) be lead free. Those of us occasional users still have leaded solder. suck the fumes away! it is the flux. Not sure if any lead is in the flux fumes, we melt the solder, not vaporize it.
I prefer to use solder with some silver in it. It works a lot better for me. Leaded or lead free.
There is a thread where Led4Power said that he uses lead free solder for everything he does and that it has better properties than leaded we mostly use here.
I think someone could do solder joint tests for our flashlight modding purpose: Lead vs Lead free solder strength test… Someone like Djozz with “touch” for doing experiments. 
Sounds good for a test. Way back, I wound two solenoids (springs) from solder, leaded and silver tin lead. Pulling the leaded solder, it stayed pulled, no strength. The silver / lead / tin “spring” had resilancey, it went most of the way back to original. I also find it to tack better. And someone may comment, don’t use the solder to hold the connection, it needs to be mechanically attached first. This goes back to chassis wiring, point to point. Now surface mount, it is the mechanical attachment also. Will be interested in the test results.
Not a test, per se, but some of those pertinent qualities are listed here: [Reference] Physical and Mechanical Properties of Solder Alloys
I’m in agreement about source of irritation being the flux rather than the lead. Active fume reduction/movement is pretty much standard at pro benches and you can get decent cheaper units these days for $45 to $80 without going all in on a commercial unit ($$:money_mouth_face:. It’s been a long time since I’ve done enough soldering for a length of time to really bother me, but it used to get me a little with sinuses and a headache…most of that was acid core and non-electronics rosin core, though.
It also has terrible thermal conductivity which may be an issue for LEDs. That’s why Clemence uses indium for his low temp Nichia reflows.
[Reference] Physical and Mechanical Properties of Solder Alloys , although not all are listed here for example the one I use is Sn60Pb39Cu1 which could be similar to Sn60Pb40 which has melting point 183 / 191 °C, solidus / liquidus and 535 kgf/cm² of Tensile Strength at Break which is one of the best from the table.
Also the one that thefreeman mentioned Sn42/Bi57.6/Ag0.4 could be similar to Bi58Sn42 from mentioned table which has lower melting point 138 / 138 °C solidus / liquidus and 565 kgf/cm² Tensile Strength at Break which seems like the best properties for our modding job if we look the table - very low melting point and excellent tensile strength! But lower thermal conductivity…
The question is: Should we use Bi58Sn42 instead Sn60Pb40? Bi58 has very bad thermal conductivity at 19 W/m⋅K while Sn60 has 49!
So real question: Is thermal conductivity more important than lower melting point and Tensile strength properties? If that is not so important than Bi58Sn42 is winner here?!
Yes. This certainly is an issue if we repair over existing setup but it should not be an issue if we do build from scratch?
True but he uses BiSn for the wires IIRC, his MCPCB are so good that when using high temp solder for the wires, or even SnPb, it can reflow the indium. I also use indium for the non DTP LEDs but I’m not sure it matters that much vs SnPb or SAC.
It shouldn’t, all the drivers I’ve made where soldered with BiSnAg (paste and wire)
Shouldn’t matter for things that don’t produce a lot of heat.
I do need to check if it has an effect on dc/dc regulators with integrated switches on my drivers, which also produce heat (not as much as an LED), on one of my driver the regulator I used went into thermal protection at high current, I’ll need to test if it does the same with SnPB or SAC. (It’s possible it was also inadequate thermal design).
There are many lead free solder alloys. I don't know what Led4Power uses but, in my experience, Sn99.3Cu0.7 just sucks.
Sn63Pb37 has always been the golden standard for electronics work, and for me it continues to be so. Right now I am using Sn60Pb40 I got from AliExpress, which is veery close but not quite.
I currently find little to no reason to do away with leaded solders, at least for our usage. As far as I know it all started with RoHS, which excluded :!!!: batteries; so at least in this respect I don't give a damn about it.
Concerning the above solders, no one noticed Sn91Zn09? Its resistance is lower than that of Sn63Pb37 or Sn60Pb40, so higher conductance, while its thermal conductivity is also better (22%/24.49% higher). It also is a good alloy for soldering over aluminium, according to this Kester's 2600 aluminum soldering flux document.
Solder alloys @ Wikipedia adds the following information about Sn91Zn09:
KappAloy9 Designed specifically for Aluminum-to-Aluminum and Aluminum-to-Copper soldering. It has good corrosion resistance and tensile strength. Lies between soft solder and silver brazing alloys, thereby avoiding damage to critical electronics and substrate deformation and segregation. Best solder for Aluminum wire to Copper busses or Copper wire to Aluminum busses or contacts.[54] UNS#: L91090
I'm using Stannol Sn95Ag4Cu1 0.8mm wire (Manuf. nr: 593410), silver makes a lot of difference, and this alloy has 4% of it. 100gr spool can last for years, so it's a very bad idea trying to save some money on solder wire/paste.
Avoid any kind of cheap no-name junk from Aliexpress etc., most of them have no silver (even if they claim they do), and contain so much impurities/junk that soldering is not possible.
Well, I believe quite differently. Since I believe that I can buy BBB stuff (bueno, bonito y barato in spanish, which translates as good, beautiful and cheap/affordable), that's what I get.
While kind of off-topic I buy stuff like this. Yes, $4.05 for a 100g roll right now. Still, the last time I bought solder wire I paid like $3 for a 100g roll 1¾ years ago, and I even got two rolls for the same money (first roll arrived late, after I had won the unsuccesful delivery dispute; I wanted to give seller his money, so I bought another roll and told him not to send me the item, but he did anyways). O:)
I can also find other solder pastes and wires with ease in AliExpress, there's plenty of good stuff you just have to find the right product and sellers (i.e. believe correctly).
Your link is for leaded solder wire, of course they are cheaper, not just because the don't have any silver in it, but they also have 63% of tin compared to 95-96% for lead-free solder wires.
Lead-free Stannol with 3-4% silver content is ~14€ per 100gram (with tax), you obviously have never tried Stannol or similar wires, so you can't compare how good or bad stuff from Aliexpress is.
And I'm talking about lead-free soldering, not leaded.
I'm sure many people who tried to switch to lead-free soldering bought some random silver-less junk from Aliexpress were disappointed with soldering results, and decided to abandon lead-free stuff.
Thanks guys for nice discussion and replying… 
So lets continue… If we compare Lead free solder Led4Power recommended to this table [Reference] Physical and Mechanical Properties of Solder Alloys we will see that Sn95.5Ag3.8Cu0.7 (which is the most similar by properties to Sn95Ag4Cu1 Led4Power recommended has highest “Tensile strength at breaking” at 600 kgf/cm² and better thermal conductivity at 60 W/m⋅K but it has low Tensile Elongation at Break of 16% while classic Sn60Pb40 has 40% if mentioned elongation at break is important for our hobby?
So I will have to try mentioned Sn95Ag4Cu1 and decide… Silver and copper in Soldering alloy can’t be bad right?
But question is can we use Sn95Ag4Cu1 as a “repair component” over lets say Sn60Pb40? I am sure there will be no problem for scratch builds but how it would behave if we merge it with leaded solder? Cause I’m sure plenty of guys here fix those Cheap(and no so cheap) flashlights for their friends etc…
Seeing you all as a group know your solder. My question is what solder flows best with repairing already existing traditional Pb/Sn base.
As Barkuti said in post #21,
WHY? Because that is the eutectic point for this mixture, that is to say that it melts from a solid to a liquid at the lowest temperature (361 F) of any other mix of the two elements.
Well this is true, I never tried any good unleaded solders.
In fact, the only unleaded solder I've ever had is a roll of Sn99.3Cu0.7 alloy which I bought many many years ago in an emergency from a local chinese market store. I could do the repair, but it sucked. The roll is still lying on my repair table, and as usual it still sucks butt. :-D
Concerning the question from luminarium iaculator and texas shooter, how about using a traditional Sn/Pb solder to fix Sn/Pb solderings? I provided a link up there, just in case.
If you mix a quality unleaded solder with a standard Sn/Pb alloy, you'll end up with some sort of solder mixture. If you care to somehow remove most or all of the original solder alloy and redo the soldering with the good unleaded one, sure there will be no problem. It may still be perfectly fine even if you mix it. I remember having redone some solderings in a connector long ago, removing and replacing pesky :-D Sn99.3Cu0.7 with standard Sn63Pb37, and all was good. The inverse procedure should be fine too.
I will report when I receive mentioned Sn95Ag4Cu1 0.8mm wire from Stannol(Germany) which is probably the best manufacturer on Europe market.
Barkuti has real BLF spirit… If it ain’t cheap I don’t wanna buy it 
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Edit: Last several hours I tried to find recommended Stannol lead free wire online without any luck so I took “Armack Lötdraht Typ26-3 Sn95Ag4Cu1” and chosen 0.8mm one from ebay.
Hope that it will come fast and that it has good properties although it is not from Stannol but from Armack?! Since I never heard for that brand it could be just OEM for some retailer by Stannol?
Well, not exactly. But of course there are reasons for it, and I have to draw up a plan to fix it. ;-)
Just out of curiosity I made a search in eBay. Now that AliExpress has gone downhill real hard, it's been a pleasure to use eBay advanced search again.
I think you found this stuff: “Typ32-3” search @ soldanshop24.
Funny to see how the title description reads Sn95Ag4Cu1 in some cases, and Sn95.5Ag3.8Cu0.7 in others. The product photographs are the same, reading Sn95Ag4Cu1, though.
Reputable seller. Price wise won't say a thing in this regard. 
I exclusively use Sn63Pb37 solder. I don’t have much experience with lead-free solder other than what comes on pre-assembled electronics, and that stuff is the worst. It’s difficult to melt and it’s got the consistency of peanut butter when it does.
Sn63Pb37 is extremely easy to work with, melts at a low temperature, sticks right to the pad/part and is eutectic which helps prevent cold joints when soldering parts that might have a chance of moving while the solder is still cooling (like LED power leads).
Lead-free solder is primarily used in manufacturing environments where workers would be exposed to MUCH higher amounts of lead than what a hobbyist with a soldering iron is going to see. I don’t know anyone that has a wave soldering rig in their garage.
I’m unconcerned with slight improvements in tensile strength and elasticity since I’ve never had a component in a flashlight fall/tear off after being soldered properly with Sn63Pb37.
Improvements in thermal conductivity are nice, but probably immeasurably miniscule. For my uses, it’s not worth the extra cost or sacrificing the ease of use of Sn63Pb37.
Sn63Pb37 is my ol’ reliable and I’ll probably keep using it forever unless I have a compelling reason to purchase something different.
Yeah… Very little difference between standard Sn60Pb40, Sn60Pb39Cu1, Sn63Pb37 etc. if they have real SnPb rating, from real deal; from real brand like Kester, Stannol etc. But if we buy same rated thing from aliexpress and compare to premium ones than difference is huge. I have about 5 x 100-250g reels of solder wire from aliexpress that I don’t use after trying premium brand like Stannol. Not only that… I just can’t believe how stupid I was using that crabp on my builds(that was in a start 13 years ago - maybe even Chinese improved from then)! I thought I will never learn soldering until i bought better and after trying better one I found out Wtf?! Omg! I know how to solder stuff 
It’s just bad solder wire that restrained me from proper job 
Only thing I do use is that “Mechanic” solder paste but I guess I could start with better one in a start since it lasts the whole eternity for my type of reflowing job.
Any alloy with silver content >3% is fine, it doesn't have to be 4%, many of "old" Stannol wires are not available anymore, there is no more 100gram spools too.
These ones should be just as good:
https://www.tme.eu/en/details/sac305k511_0.7_250/solder-wires-lead-free/stannol/810899/
https://www.tme.eu/en/details/sac305hs10_0.7_250/solder-wires-lead-free/stannol/593080/
https://www.tme.eu/en/details/sn955hs10_0.7_0.5/solder-wires-lead-free/stannol/631939/
https://www.tme.eu/en/details/sn955k511_0.7_0.5/solder-wires-lead-free/stannol/593202/
Edit: it's interesting that TME does not have any lead containing solder wire or paste anymore, only lead-free.