[sdiy] SMD layout tips

[ChristianH]

I gave up on "tidy" when trying to combine inch and mm grids.

Now I stick to the usual inch grid (50 or 25 mils), drawing a trace from
the metric TQFP pads and let it snap to the nearest inch grid position. 
If it looks too awquard I correct the nearest position by completely
releasing the grid ("finest" in Eagle), but mostly I just accept that it
looks a bit kinky around metric packages.

What really p***es me off is that some of Eagle's SMD library packages
with e.g. 16 pins are defined with their local origin at the exact
center - meaning that all the pads are off grid when the component is
placed on a 50 mil grid position. And there aren't even millimeters
involved...

Chris



On Mon, 10 Sep 2012 10:46:08 +0100 Tom Wiltshire <tom at electricdruid.net>
wrote:

> Having sorted out my problems with tight-pitch TQFP uPs and got lots of suggestions for places that could easily produce such a board, I'm now looking for layout tips.
> 
> The processor has legs on 0.5mm pitch - e.g. metric. Many of the connectors are on 0.1" pitch - e.g. non-metric.
> 
> I'm having trouble getting anything that looks even reasonably tidy, since I'm having to jump back and forth between metric and non-metric grids, and things that line up in one don't line up in the other, etc etc. Particularly difficult are tracks where one end is on a metric grid and the other end is on a non-metric grid. Add extra complexities if the track needs to go from very thin at the uP (0.29mm) up to some more reasonable size.
> It seems to go like this:
> Select thin track, start at uP, do short length, change track size, do short length, change track size, do short length, change track size, change grid size, change grid units, do final track to connector.
> All this to do one simple track from one pin to another, less than an inch long! Is this what's required?! It takes an age!
> 
> Many of you must have dealt with these problems already. Any tips for good SMD layout would be much appreciated.
> 
> Thanks,
> Tom
> 
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy