Re: PCB Layout Designers

On Wed, 23 May 2007 09:23:55 +0800, budgie <me@xxxxxxxxxxx> wrote:

On 22 May 2007 15:27:32 -0700, john@xxxxxxxxxxxxxxxxxxxxx wrote:

I've come across a number of commercial designers that still route
manually. They'll go the circuit diagram route only if the board
complexity demands it (say 20 or more packages). They say the main
reason is time saving from not having to fart about creating unique
library components and the ensuing struggle with third rate diagram
editors.

I'm a one-man band when it comes to circuit and pcb design, and I prefer manual
layout (two layers only) over importing a schematic into the pcb software. I
find that:

. package placement is easier without the ratsnest, but with the ability to
have just a selection of interconnections showing.
. the autorouter is great at achieving 85% faster than me, but often fails to
complete and I have to undo sooo much that I haven't used autorouting in the
last five years.
. I have developed a fairly thorough and successful checking process that
hasn't let a layout/connection error through in those five years.

We recently did a board that has over 1000 parts, including a uP and
two FPGAs, 8 layers, parts on both sides. Hand checking that would
probably take two people a week or so, one calling out connections and
the other tracing them. PADS will do a full connectivity check on this
board in about 2 seconds, and a full design-rule check in under 10.

We do the full schematic thing for even the tiniest boards. One nice
thing is that you can ECO a schematic and export the changes to the
PCB and keep things in sync. You can also resequence the ref
designators on the board and back-annotate the schematic. We formally
release the schematic and the PCB files together, and we have a rule
that they *must* fully cross-check.

We never autoroute, and almost always go with the pins as originally
assigned on the schematic, ie no pin or gate swapping. We also often
pass the design around from person to person. An engineer may do some
critical placement as a model, our layout guy does the real work, then
another engineer or two may have a final lick at it, checking critical
clock nets and such.

John




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