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I'm designing a PCB for the first time and I'm using NI's Ultiboard software to do so.

I tried uploading my Gerbers to a few cheap fabrication services, but I've noticed one discrepancy: I don't understand how these services are determining the width and height of my board. I designed my board to be 50.8mm by 52.6288mm - the size of the board outline in my design. These services are all detecting my board as being sized 82mm by 66mm. The height discrepancy is small, but why is the width discrepancy so large?

I suppose that the most general question is this: what can I do to limit or estimate the actual size of a PCB before I upload it to a site to be fabricated?

This is my board as it is being interpreted by one such service: Board layout

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    \$\begingroup\$ You design your boards to 100 nm precise?? \$\endgroup\$
    – stevenvh
    Commented Aug 27, 2012 at 18:38
  • \$\begingroup\$ Heh, I suppose not- I did specify the 50.8mm (2in) width, but the 52.6288mm height was just the result of dragging the box to the appropriate point and then later reading the value and writing it here. \$\endgroup\$
    – TheNoonMoose
    Commented Aug 27, 2012 at 18:52
  • \$\begingroup\$ I personally have a mechanical layer that contains only the board outline, and then when I send my files I include in a readme.txt which mech layer is the board outline. I've also started including a separate mech layer that has just dimensions. I realize your question deals with automated services, but these uploads usually get reviewed by humans before the board gets built, and these tips can help catch potential errors during that review. \$\endgroup\$
    – ajs410
    Commented Aug 27, 2012 at 19:31
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    \$\begingroup\$ Don't forget mounting holes! Also, make sure there's enough physical clearance between the 0.1" pitch headers at the top and those capacitors to actually place the connector in the finished product. It's those types of things that make you want to kick yourself in the head. Try to visualize yourself populating and installing the board step-by-step to try to catch those in advance. \$\endgroup\$
    – Scott Seidman
    Commented Aug 27, 2012 at 21:09
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    \$\begingroup\$ Regarding Scott's visualization tip, one thing I have done in the past when I'm unsure about clearance is to actual print a copy of the PCB to scale and populate the printout to make sure there's enough room. You can even poke holes in the paper for thru-hole stuff. \$\endgroup\$
    – ajs410
    Commented Aug 28, 2012 at 15:58

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Ultiboard appears to be exporting extra fiducials (those circular marks at the top left, bottom left and bottom right of the image you posted) which are being interpreted by OSH Park, and other online PCB fab house previews, as part of your design.

For example, I use Eagle and also use OSH Park (which is what you appear to be using) and when OSH Park previews my designs, the images are essentially zoomed in on my board outline. The preview picture will contain everything present in the gerbers... and since my board outline is the biggest thing, that's what is present in the preview.

You need to figure out how to configure Ultiboard to not export those fiducials into the final gerbers.

EDIT: I found the user manual for Ultiboard and it appears you can disable the automatic addition of fiducials on gerber export. Read the manual here and go down to page 1-19 to see instructions for how to get to the setting.

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    \$\begingroup\$ You know, I had already found that option in the settings- it's the only fiducial-related option in Ultiboard- but I didn't think that not including fiducials was an option. This did seem to work as expected though, so thank you! \$\endgroup\$
    – TheNoonMoose
    Commented Aug 27, 2012 at 19:10
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    \$\begingroup\$ Fiducials are typically a physical thing - used for machine vision systems or even human-related alignment tasks. It doesn't make much sense, to me at least, for having it in Gerbers for layer alignment. Usually, the program exports them all aligned and the reader assumes they will be aligned.... which is the only behavior I've ever seen. As such, this is why OSH Park and others will process your Gerbers properly without them. :) \$\endgroup\$
    – Toby Lawrence
    Commented Aug 27, 2012 at 19:14

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