23 Jul
2016
23 Jul
'16
3:20 p.m.
On Sat, 23 Jul 2016, Corey Cohen wrote:
My guess is that is was a test board for Apple. There
are some weird
mods to the ram timing with a variable cap and to the negative supply
that looks like they were experiments to figure out the tolerances of
the chips. The board was wave soldered. You can't fake that on an
Apple-1 because of what happens to the back of the board by the
regulators. [...]
If you mean the crinkle tin plate under the solder mask, that doesn't
happen due to wave soldering. The heavy tin plate was applied that way in
a separate process before the solder mask was applied to the board. It
used to be common to do that to all sorts of boards in the 1970s-1980s.
With modern boards, is much more common now to just leave exposed
copper/gaps in the solder mask and allow those areas to take up solder
from the wave soldering (or reflow) processes.