Re: gEDA-user: Metric, Imperial, Rounding, DRC, and board houses

[Steven Michalske <smichalske@xxxxxxxxx>]

I use mil grids, as many boards houses expect mil units, like yours.

PCB layout is engineering, engineering involves tolerances.......

I start my traces from off grid components so that the stub going from
the pin/pad is off grid byt quickly becomes on grid after the first 45
degree bend.

Steve


On Mon, Feb 21, 2011 at 2:44 PM, Stefan Salewski <mail@xxxxxxxxxxxx> wrote:
> On Mon, 2011-02-21 at 15:23 -0700, Russell Dill wrote:
>> I'm starting a new design and all my components are metric based,
>> including a few 1mm pitch BGA components. I'd really like to do the
>> layout in metric, but I'm worried about two factors. The first of
>> which is that PCB does not yet have the option to store things
>> internally in metric (at least from what I understand) so rounding may
>> occur on that end. In addition, my board house rounds everything to
>> 2.4 format (0.1 mil). I can envision several scenarios where my design
>> meets DRC in PCB, but fails when I send it to the board house.
>>
>> What is my best option?
>>
>> Just use imperial units and cope with weird grids?
>>
>> Use metric spacing, but recalculate DRC based on worst case rounding?
>>
>> Some other option?
>>
>
> Use metric grid/unit, I guess most of us use that.
> Internal resolution is 0.01 mil, which is good. Of course nm would be
> better. One problem for me was, that a few 0.01 mil garbage lines were
> generated for the layout. Not a big problem. Some not really smart
> people have tried to use a very very  fine grid, 0.01 mm or so. That is
> like using no grid at all, I call that silly. Try to use a useful basic
> grid like 0.25mm grid if most of your parts have 0.5mm pitch -- I think
> that was what I did, I am not sure. Important: Enable snap to pads/pins,
> so you can make good connections to imperial parts which are not on the
> metric grid.
>
>>my board house rounds everything to
>> 2.4 format (0.1 mil).
>
> Strange -- so pitch of metric parts may vary from pad to pad a bit. That
> was a problem in very old days of PCB, when 1mil internal units was
> used.
>
>
>
>
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