27 Feb
2008
27 Feb
'08
8:13 a.m.
From: "David Griffith":
Whatever happened to that idea of building
mini-flipchips with
surface-mount parts?
I drew a version of the R202 (dual flip-flop) with all SMT components
that fits on a 1"x2" board, but I never went on to do all the other
boards in an 8/S. It was interesting to see what was easy and what
was hard, but it felt a bit too much like work to continue, at least
at the time :-). [For comparison, the DEC module is 2.5"x5" with
through-hole components.]
I used a 2x10 right angle header to replace the edge connector,
which wouldn't work for the Mxxx modules of the 8/L, as they need
36 connections instead of 18.
One thing I'd worry about with SMT components, is that if you pack
the stuff in there too tight you might start to have heat problems.
The designs aren't exactly low power!
One nice thing about the Rxxx series is that most of the modules used
components for which similar replacements are still plentiful, in both
through-hole and SMT packages.
The yucky thing about them is that you need so incredibly many of the
things to get anything done. (There aren't all that many different
types, though.) The R202 requires 50 diodes, 4 transistors, 20+
resistors, and some capacitors in a fairly dense circuit board assembly,
to accomplish essentially what is implemented on a 7474 chip. Hundreds
of similar modules are used to build a PDP-8/S. (That ends up being an
awful lot of soldering!)
Vince