Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

----- Original Message -----
From: "Stefan Trethan" <stefan_trethan@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Wednesday, August 04, 2004 9:35 AM
Subject: [Homebrew_PCBs] advanced routing


> Hi,
>
> i was wondering if there is a tutorial for advanced routing.
> I mean as soon as you have two layers and more than 100components
> it starts to get more difficult.
> If there is no tutorial we could maybe exchange some tricks.

I've looked and I don't think there is one.

Here are a few 'rules of thumb' I've come across which I find very useful:

>
> How do you start?

Start placement with the largest parts.

> How do you decide which parts are on which side?

> (i put the SMD ones on top which can be connected to throughhole without
> adding a via, and i aim for the same population density top and bottom.)

For low-cost manufacture it's best to put all the SMDs on the top. If you
put them on top and bottom your technique seems OK.

>
> Often it is required to rotate and rearrange parts to get a good layout,
> but at a certain number of parts it is very hard to keep track of things.

Try to keep the components in functional blocks, like in the schematic. An
autorouter can be useful, even if you are routing manually, to show where
there are going to be problems. If you are using an autorouter, here are
some tips:

http://www.connecteda.com/doc/Autorouting%20Techniques.pdf

They are applicable to any autorouter. BTW, that Electra autorouter is
∗very∗ good, it's now supplied with the Pulsonix software I use.

>
> Do you start routing with special nets, like supply?

Critical nets like power and ground, and clocks, etc. should always be
routed first.

>
> You see, the methods i used for years on smaller circuits seem very, very
> hard
> to apply to bigger circuits, and i believe there must be some tricks i
> don't
> know yet.
> Maybe if everyone throws in a few ideas we can all learn something.

Placement is the important thing, once that is optimised the actual routing
should be quite easy, until you get to the last few tracks - they will take
as long as all the others put together. 8-)

Always start by routing the shortest tracks, working up to the longest. That
is probably the most important rule.


> I always use different color "rubber bands" for GND and VCC which helps a
> bit.

That can help a lot. The software I use highlights an entire net when it is
selected. I can use different colours for different nets, as well.

Leon
--
Leon Heller, G1HSM
http://www.geocities.com/leon_heller