A bit more on Thermal Mass
My post from a few days ago discussed a problem that can potentially make some RoHS parts not work in a RoHS application. I forgot to mention, that since this is a prototype, we solved the problem by hand soldering the parts. You could never afford to have that done in a volume production environment, but for a prototype, it worked. Still, the best solution is to change to a more robust part or re-layout the board to give more spacing between components with above average thermal mass.