Re: The correct solder type for Feeder Wire and Rail joints
First a few words on soldering joiners:
Electrically, you do not need to solder both feeders to every piece of
rail and solder the joiners. You only need to do one or the other.
Mechanically, if you solder every rail joiner, your track may buckle
as your room temperature changes. Modelers do like to solder the
joiners of flex track to keep from getting a kink in the joint.
Regarding your use of solder:
Solder that is 96% tin and 4% silver and has a rosin core will
definitely work. However, for easiest solderability, I suggest you
use solder that contains 37-40% lead. I have found that solder with
4% silver and/or no lead takes more heat to solder than solder
containing only .4% or 0% silver and 37-40% lead. I like the high
(4%) silver content lead for soldering G-scale track - which is able
to take the additional heat a little easier. But for HO track, you
are likely to melt ties.
While rosin core solder on HO track definitely works, I suggest you
use a solid solder that has no rosin core and use liquid flux. With
rosin core, you have to apply heat to melt the rosin. With liquid
flux, you don't need to apply this additional heat since the flux is
laready liquid. So with liquid flux, you run a slightly lesser risk
of melting ties.
For more on soldering, see my webpage on soldering: