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. 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. _______________________________________________ geda-dev mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-dev
