gEDA-user: Ok, who moved pin 4?

[DJ Delorie <dj@xxxxxxxxxxx>]

Spent the day building two r8c-based boards, thought I'd give a quick
status, since I did some new things with this.

First off, I've got a board that has a USB chip (FTDI232R) connected
to an R8C/20, connected to a bunch of headers.  In other words, it's a
programmable USB GPIO port.  The only design flaw so far is that the
mini-B connector has an extra pin, and ground is on pin 5 instead of
pin 4 like all other USB connectors.  Fortunately, pin 4 is not
connected on the device end, so I just shorted pins 4 and 5, and it
worked just fine.  Haven't talked with the R8C yet, I need to adapt my
R8C programmer to the FTDI driver.  This board also used the global
puller, as I was able to coerce it to give me useful results.

Second, I've got an R8C/27 (TQFP-32) adapter (files are at
http://www.delorie.com/pcb/r8c-27-adapter/).  Along with being a TQFP
to DIP converter, it includes some pullups and the oscillator, so
aside from programming you shouldn't need any support parts.  This
board takes advantage of the ability to rotate parts 45 degrees.

Now, for the new things...

The DIP adapter is a two-layer board.  However, I did it using two
separate SS boards, taped together.  This lets me line up the two
etched boards after etching, instead of before etching.  The clad is
16 mil (1/64") with 1 oz copper, resulting in a 36 mil board.  The
tape is 3M 7953 laminate adhesive, about 4 mil thick.

The USB board is a home-etched four layer board.  Yes, four.  The core
is a 32 mil DS board, where I lined up the resist before etching.
What I did here is iron on one side, drill out the alignment holes,
and use those to line up the resist for the other side.  This core
held the ground and power planes.  Then I taped the outer layers to
it.  Those were 8 mil 1/2oz SS, and are pretty much transparent, so
easy to line up and tape on.

The tricky part is the vias.  What I ended up doing is drilling big
holes in the outer layers before taping them on, then drilling small
holes through the full stack.  That left some of the inner layer
copper exposed through the holes in the outer layers.  For signal
vias, I only did the small holes, like a 2 layer board.  If I do more
of these, I'm going to have to add some support to PCB for it, because
I mis-drilled a lot of the holes.  For example, to connect a top
signal (layer 1) to power (layer 3), I had to drill a big (35-45 mil)
hole in layer 4, and no hole in layer 1, then a 14 mil hole through
the stack.  To connect it to ground instead, I drill a 22 mil hole in
layer one and no other holes.  To connect both sides to an inner layer
means drilling a 22, a 25, and a 14 mil hole.  Plus, it would have
gone better if I could have had different size copper (or no copper)
on different layers based on connectivity.

I had to print each layer separately, because PCB wouldn't let me
paste two boards into one layout and flip one, which would have let me
etch both sides on one board then cut them apart and tape them
together.

I also tried using glossy magazine paper instead of my usual coated TT
paper.  I wanted to use some of my 64 mil (1/16") clad that won't fit
through the laminator, too, so I ended up ironing it on.  The paper
rubbed off like "they" said, but I was back to the original problem of
getting the toner to stick completely, without getting so hot it
smears.  I think the paper might work in the laminator though, and I
have more clad than coated paper at the moment.


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