Homebrew PCBs

"Steve Wiseman" <sjwiseman@...> writes:
> Do you have links for complex stuff?

The really interesting boards are all NDA.  I have them so I can fix
pcb bugs.  Suffice to say, one of them was the reason PCB can do more
than 16 layers.

> Then again, my first real gEDA project ought to be a toy, rather than
> a 12-layer 4-thou uBGA monstrosity, I guess :)

12@4 isn't that hard for PCB.  I think the prime factor at the moment
is how "busy" your ground/power planes are, because of how we manage
polygons.

> trace spreading, trace fattening, trace centring,

I've thought of these.  The global puller was supposed to be that, but
I discovered that the always-arc technique I used produced good
results with a lot less work.  I still want to do that, though -
something like "copper hates other copper, proportional to how close
they are, up to a point".  So, you'd say "I can do 8/8 rules, but I'd
prefer 20/20 when it fits".  You'd want automatic necking too.  I
figured out the math once, but never wrote the code.

> teardrops

Got that one.  At least, for the types of teardrops I like.  There
doesn't seem to be a "standard" for teardrops.  Mine are designed to
minimize mechanical strain between the trace and the annulus.

> and pad expansion,

That can probably be a plugin.  "expand pads to the most that our
space rules allow" would be easy.  Checking for traces between would
be harder, but not a lot so.

> solder thieving,

Which kind?

> copper balancing, etchant use minimisation,

What I do is just plop a rectangle over the whole board when I'm done,
that fills in all the big areas with copper.

> It might be easier to do it by hand, if the board's
> small... Rules-based stuff is hard, and people are clever.

I think some of those are better as house-specific plug-ins, too.
Part of our (pcb's) task is to provide the right hooks to make writing
those easier.

> For sure - teardrops are great. They can be bettered, though.

I once thought of a plug-in that fattened the traces leaving all vias
to the diameter of the via's copper, for a short distance, when the
rules allowed it.

> And, interestingly, real PCB shops don't care if they're there or
> not.  Holes are drilled before etching (to allow PTH), so the via
> pads don't break out enough to be worth protecting.

It wasn't the drilling.  I was removing a jumper block and the abuse
fractured the connection.