trace wrinkles

No. The differences in expansion just are not that big. If you do the math, you will see that the dimensional changes of the the two disimilar substances just are not that big - way too small to cause all sorts of wrinkles. At worst case, maybe *a* wrinkle would show up on a long trace. The expansion was a problem with early surface mount chip designs, however. Here the dimensional tolerances were/are tiny, so the little swings could cause breaks in the connections. This is why there is a B in BGA - the little balls raise the package above the board and act as little moment arms to flex during temperature shifts. No. It is almost all due to bureaucratic inertia. The military is funny this way - sometimes a new technology will be scooped up as soon as served, yet others they drag their feet with. And of course, in the 1950s and 60 all the contractors were making a mint, charging the government for all that hand wired work. They were not about to change to a cost saving new idea. -- Will