"Inner" measurement vs "Outer" measurement

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"Inner" measurement vs "Outer" measurement

Postby salamander » Mon Jul 01, 2013 2:21 pm

I am currently measuring edge to edge distance between a round BGA pad and a via. The Viewmate tool indicates "inner" measurement is 5.1mil the "outer" measurement is 4.6mil.

Doing the calculation by hand given the center of each circle and the radius, I get the 5.1mil number. Why is this an "inner" measurement and what is the "outer" measurement ?

This is a problem because my pcb design tool sees 5+ mils and decides I have no clearance problems. One of the board houses I use (who probably uses Viewmate internally) uses the 4.6mil value and claims a spacing violation. I need a way to measure apple to apples between tools.
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Joined: Mon Jul 01, 2013 2:12 pm

Re: "Inner" measurement vs "Outer" measurement

Postby marius » Mon Jul 01, 2013 9:14 pm

It would be best if you pasted a screenshot of the two pads that you are measuring.
Then we can figure out what is going on.
You also have another alternative rather than worrying about measuring distances.
You can run your design through Smart DFM in VIewMate which will do a complete DFM check and report errors. The limitation is that it uses the DFM rules of our PCB fabricator partner, but they are pretty standard. You can try ordering your boards after doing the DFM check, if you decide that the price is competitive with what you currently pay. Worth a try.
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