Surplus lead solder

[Lawsen]

Should I continued to use my 1 pounds (2.2 kg) of Kester lead tin 60%/40% solder? The silver based lead free solder are becoming more available. I still have a pound of lead solder that I inherited and the solder dates back to the 1950s. These are for my electronics hobby stuff like op amps and 555.

[Nusa]

I'd guess that most things that end up in space fall under one RoHS exemption or other. Assuming it was ever subject to it: unique space experiment packages typically are not commercial products.

[CatalinaWOW]

Unfortunately those one of a kind space packages almost always have to be built with commercially available parts.  Which means re-balling, or re-tinning or whatever.   It is getting harder and harder to buy leaded parts.  But still easy to buy a PbO battery for your automobile.  Whatever.

Reliability may not be as critical for hobby applications as it is for a mission to Jupiter where a failure may mean a billion dollars down the drain, but it still does matter.  It is very easy to build up enough equipment that you are constantly fixing the failures rather than using it for the intended purpose.

[Ian.M]

At that vintage R and RMA flux core would be natural rosin based and had virtually indefinite shelf life. RA core would probably already be falling apart from internal corrosion and was never suitable for general PCB work anyway.  Worst case, the end few inches might sputter a lot due to moisture penetrating the core.

The only issue would be oxide buildup on the outside if the solder, which if fairly light can easily be removed by pulling it through a folded coarse paper towel.  However this does fractionally increase your risk of lead exposure, so if the solder is crusty enough to need more drastic cleaning it would be a good idea to buy new solder and give the really old solder to someone who casts their own bullets, who will be glad to have some known composition high tin alloy to adjust their casting alloy composition with.

Personally I mostly use 60/40, but keep small quantities of 4% silver lead free solder for repair work on ROHS era boards - mixing SnPb and Pb-free alloys in a joint is known to cause reliability problems and its a lot of extra work to get a joint clean enough of one type of alloy to swap to the other if you are just touching up dry joints.

[mariush]

You could repurpose that solder for a soldering pot, to tin wires with it or to help you remove components from various boards:





For such applications the flux quality won't matter, as you basically evaporate the flux when you get all that solder melted in a pot. Just move dross aside, shove the wire inside, tin it and you're done.

As for oxides on the surface of the solder wire, I suppose you could get some microfiber cloth and some isopropyl alcohol and drag the solder wire through microfiber to wipe the surface and potentially clean the oxides off the wire. It could be done fast, just take it from one spool and spin the wire into another spool.
Solder from the 50s would probably have not so great flux inside it, but I doubt it would be downright "bad".. after all it should be just rosin

 

[thm_w]

As long as the flux is still working (which I highly doubt), I see no reason why is can't work.
However, I am a lead free guy. Since all my soldering gears are designed for lead free, I don't see much benefits from using leaded solder anymore.
Some say lead free solder uses higher temperature, hence more toxic flux fumes, but since I use a non-adjustable soldering iron, it works at same temp regardless leaded or lead-free, so it doesn't matter.
Leaded solder has reliability advantages, but I guess for hobby use, it doesn't matter anyway, unless your hobby project makes its way to ISS.

It does use higher temperature, and hence more fumes, that's correct.

but since I use a non-adjustable soldering iron, it works at same temp regardless leaded or lead-free, so it doesn't matter.

Well yes, but that was your choice to select the temperature wasn't it? 
Use a good fan with carbon filter or extractor and you will be ok.