Re: [N8VEM-S100:1469] S-100 board reorders

[David Riley <frave...@gmail.com>]

On Feb 25, 2013, at 1:25 AM, Crusty OMO <crus...@hotmail.com> wrote:

> -12/12 rule.  that is, 0.012" trace thickness with 0.012" spacing between traces.  I think high density boards go as low as 8/8.

High density boards definitely go smaller than that.  I've worked with ones as small as 5/5, and for the REALLY fine BGAs (.5 or .4mm ball pitch), they might even go smaller.  Note that once you get down below 8/8, boards tend to get MUCH more expensive, especially if you need controlled impedance, because it is a complex process to get photoresist/chemical etching that precise.  Your yield tends to go down as well.

> Personally, I don't use any auto trace routing, so I manually optimize my traces by hand.

On all of our commercial stuff, we route by hand as well because when you get to really high density boards with sensitive analog stuff, autorouters are basically useless (and don't save any time, because you spend so much time setting up the rules).  It's a bit of a pain, but the higher-end tools provide a lot of help for manually routing things like differential lines, especially when it comes to length matching.

Circuit board layout is definitely an art.  I've done a few (small/low-complexity) boards myself, but I prefer to leave it to the professionals because I recognize my complete lack of spatial reasoning skills when it comes to laying out the boards.  The closest I tend to get at work is determining initial component placement for mechanical constraints or bus topology; I generally leave almost everything else to the layout sorcerers. :-)



- Dave