On Mon, 2007-10-15 at 19:06 +0200, Bernd Jendrissek wrote: > On 10/15/07, Peter Clifton <[EMAIL PROTECTED]> wrote: > > With square + rounded, the misalignment is not allowed to be as big in > > both directions at the same time. (Eg.. if the registration is out both > > in the X and Y directions at once, it might mean mask covers the corner > > of the pad whilst the X and Y registrations are otherwise in tolerance. > > (It seems likely to me that the X and Y registrations are independent > > error terms, not some "distance" offset error in registration. > > IF your X and Y errors are normally distributed, then exactly because > they are independent variables, you can indeed do a coordinate > transform into (r, theta) and take advantage of the rotational > symmetry of the error distribution: your X and Y error limits would > then be equivalent to a limit on "distance" error.
I wasn't assuming the errors were normally distributed, but I take you're point. Anyone friendly with a fab house enough to find out how these registration errors work for real? > OTOH, if the fab house achieves its tolerances only by grepping out > the out-of-error-band machine settings, then you'd need a > square+square pattern to survive their out-of-control process with its > rectangular error distribution. Peter _______________________________________________ geda-dev mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-dev
