Use ferrules to join wires, and on your board either solder directly (it doesn't matter what solder you use because it's not going to get hot if your wires are gauged properly). Or use soft copper wires and clamping terminals without the wires being tinned or risk a fire hazard.
Tinning makes the surface harder which makes for less contact area. If it deforms from heat , it can come loose and cause arcs, which is where the fire hazard comes from.