[sdiy] SMD layout tips

[Tim Ressel]

I use 1mm grid with 0.05mm alternate. I rely heavily on the wire bend setting to get me where I'm going. For example I'll use the one right-angle wire bend to start the trace, then switch to the other right-angle wire bend mode to finish. That way I just don't care about spacing or alignment issues. Right click on the mouse for scrolling through the wire bend modes btw. Another trick: hold CTRL key down while selecting a component with the move tool will align it to the grid. 




Tim Ressel
Circuit Abbey
503-750-9331
timr at circuitabbey.com




>________________________________
> From: ChristianH <chris at chrismusic.de>
>To: synth-diy at dropmix.xs4all.nl 
>Sent: Monday, September 10, 2012 3:38 AM
>Subject: Re: [sdiy] SMD layout tips
> 
>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
>> 
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