Re: PCB Layout Designers

On Wed, 23 May 2007 11:26:42 -0700, John Larkin
<jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

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

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 operate in different worlds, John { ;) >

(snip)

We never autoroute

I wonder how many do autoroute at both your level and down here at the base
where I operate. The tools are there, but I don't think it is ego that stops
most layout people lwetting the autorouter have a go.

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.

I'm surprised that you don't accommodate gate swapping. Assigning a gate from a
package at schematic time is an arbitrary thing, and can't second-guess which
gate will provide the best layout.
.

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