A rigid board is glass-reinforced epoxy with copper on it. That description has not changed in fifty years and it still covers the large majority of electronics built. What has changed is what “standard” means: 100 µm lines, 0.2 mm mechanical vias and ± 10 % impedance are ordinary today and would have been advanced work not long ago.
Because the technology is settled, the differences between suppliers turn up somewhere else — in whether the copper thickness after plating is what the drawing said, whether drill registration holds across the panel, and whether the same board arrives the same way in twelve months. That is the part of a rigid board worth asking about.
