Poor solderability of old components, solutions?
I bought a batch of opto-isolators for a project a while back but when I came to use them they won't take solder. I haven't put the leads under a microscope but they do look a bit dull to the naked eye. My guess is they haven't been stored well. They are old stock because the component has been obsolete for a while.
I managed to find a newer equivalent and build up my parts, but I'd like not to waste these parts I have and maybe use them on a next batch of parts.
I tried just using a flux pen and then tinning but no joy. So I was wondering which of these, or maybe any other suggestions, is likely to have best and or easiest results (I use four per board):
Fibreglass pencil?
Rubbing on very fine emery paper?
More active flux?
Anything else?
They are surface mount but will be hand soldered, so I need to keep the surface fairly flat prior to actually soldering to the board.
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