Re: gEDA-user: How do I get the router to go where I want it to?

[Gabriel Paubert <paubert@xxxxxxx>]

On Tue, Feb 16, 2010 at 10:50:11PM +0100, Maciej Pijanka wrote:
> On Tue, 16 Feb 2010, Jim Lynch wrote:
> 
> >    I have a board I'm developing (maybe) that is a backplane.  It has 9
> >    edge connectors mounted on it and when I went to autoroute it Oh Lord!
> >    I've never seen such a mess!  Traces all over, a million or so vias,
> >    etc.  You'd think it would be a simple set of parallel lines, but no.
> >    So I ripped it up and started autorouting them one at a time.  The
> >    first one went well, then the second row didn't.  I'm guessing that I'm
> >    trying to violate some sort of clearance rule but I don't know which
> >    one or how to fix it.  I may even have the pins too large.  Take a look
> >    at the image
> 
> Looks like pin to track clearance causes some of your problems, you may enable
> auto enforce drc and try to route track manually between pins and see if it fit at
> all, if not then change clearance lets say to 8mil, and try again. Usually
> its doable to place one track between two adjacent 0.1" spaced pins, i was told
> that one put two tracks between them, but i haven't seen that myself.

I was told that one PCB manufacturer (in Denmark at the time, it was 1985 
or 1986) was able to put up to seven tracks between DIL pads at 0.1" spacing. 
But I never saw it myself.

A bit later (1988?), when multilayer was still a very expensive proposition and 
frequencies were not what they were today, I got a board with a 680x0 processor 
(can't remember whether 12 or 16MHz) and something like 1MB of UV EPROM and 2MB 
of SRAM on which I saw up to four, very narrow, tracks between two pins at the 
standard 0.1" spacing.

Of course these were with relatively smooth transition of 74LS TTL and a few
PAL, 70-80 ns memory cycles and on a single Eurocard (100x160mm), so lines 
were never very long compared to the rise and fall time. Crosstalk, what 
is crosstalk?

However, to come back to your problem, it really depends on the pad and
hole size that you need for your connector. Many connectors really need
a much larger hole than a standard DIL package.

	Best regards,
	Gabriel


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