John,
The solder you want is
and the flux is
When it comes to soldering decoders and in particular your SMT LED's you will get no better advice than to read the "how to sheets" here
All the above advice has been sound but one alarm bell went off loudly with the words from David Woodcock above due to his response being off topic
DON'T USE POWERFLOW FLUX ON YOUR DECODERS? -?? bye bye warranty.
Don't get me wrong, its great stuff and I use it for nearly all my brass and nickel silver soldering. However, the context here was soldering electronics and, in particular, decoders. PowerFlow is an agressive and corrosive flux and not suited to electronics work. If you soldered your decoders with it you'd have to wash them under the hot tap ( not great for electronics) and fully dry them or, if you don't get it off, you'll have a hideous and midly conducting crust on your decoder terminals.
John - if you see this thursday morning and want some solder and flux and let me know before midday I can stick some in the post as I leave for Wales. I'll catch up with you next week for payment
Paul Martin
EDM Models
Paul Martin