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Making footprint out of grid

LOR75

Good morning,

I'm a beginner in PCB/footprint and I don't know what's the best way to do this task.

I have to make a footprint of a microcontroller with pitch = 0.8mm so the pads are out of grid because I normally set the grid  1mils as a standard.

I have rounded the pad coordinates in order to put them on the grid but in this way I could get an incorrect position for some pads. 

What do you suggest to me? I could put grid equal to 0.1mils in the footprint but do I have then keep this extremely low resolution even during pcb layout? If the footprint is completed with 0.1mils and then I put it on a board with 1mils of resolution does pcb editor keep the pad in the correct position or it round the coordinate to the grid of pcb.

I apologize for this silly question for experienced users but I didn't get any suggestion from the web.

Best regards.

Lorenzo

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  • excellon1

    My suggestion is when dealing with footprints that have data sheets for the part in "Metric" it is alot easier to create your new parts on a metric grid and not try convert the metric to mills. I use mills or imperial inch here at this end laying out boards but the vast majority of the smd parts are created in metric aka mm, cm etc.

    Go with creating metric parts using grid coordinates of metric in Allegro as opposed to mils and your life will be alot easier. If you do this you wont need to be rounding off the measurements to the corresponding mils.

    Also sometimes it is handy to have a cheat cheat for the mm to mils conversion in front of you.

    To begin start out by setting the grid in allegro to your desired pitch of 0.8mm for everything and go from there.

    Your question is not silly, it is a good question !

    Hope this helps you out.

  • LOR75
    in reply to excellon1

    Tanks for the answer: that's good but I have a little doubt.

    If I create the footprint in metric scale and then I use the imperial inch during board layout is the metric footprint correctly imported on the imperial grid of the board? Are the distances between pads maintained correct or they are changed? So the grid during the footprint creation and the grid during board layout are indipendent  

    Thanks

  • excellon1
    in reply to LOR75

    Yes it will because the footprint will snap to the grid. It wont be any problem.

    When you create a footprint in either metric or mils when laying out your board these units are inter-changable. This means you can design footprints in Metric but lay out the board in mils.

    Go ahead and try it out.. You will like it :)

    BTW you can also download a metric symbol online to test it.

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  • excellon1
    in reply to LOR75

    Yes it will because the footprint will snap to the grid. It wont be any problem.

    When you create a footprint in either metric or mils when laying out your board these units are inter-changable. This means you can design footprints in Metric but lay out the board in mils.

    Go ahead and try it out.. You will like it :)

    BTW you can also download a metric symbol online to test it.

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