Annular Ring Measurement

The calculation of annular ring measurements depend on whether breakouts are allowed by the designer.

The normal procedure requires two values:

RM_AR, Reliability Margin for Annular Ring as received from the customer (the implementation of the RM_AR does not allow the specification of a breakout).
DRA, Design Registration Allowance is generated by the analysis (the maximum misregistration permitted by a design while still meeting all other requirements).

For example, if the minimum annular ring width = 4, RM_AR =1, then DRA=4-1=3.

If the user specifies that the RM should allow a breakout (RM_AR=0), the measurement will be extended to the outer perimeter of the drill hole in the position of a theoretical breakout, as in the following figure:

The breakout angle is defined in the ERF parameter via_breakout_angle or pth_breakout_angle. The range is 0-180, where 0 means no breakout is allowed.

When you do specify a breakout, RM_AR must be specified as zero, and the system will automatically calculate an extended Annular Ring measurement based on the size of the AR and drill. The AR size that is reported is larger than the actual AR size by an amount that depends on the AR and drill sizes (see example below).

The system assumes a drill that is centered within the AR and an AR that is a circle. If the AR is any other shape the system will construct a circle from this shape and plan the breakout on the constructed circular AR. The following figure clarifies this:

When a negative feature shaves an AR pad, the system assumes a hold circle and positions the breakout according to this assumption.

When the feature is rectangular, the system also assumes a circular AR and positions the breakout accordingly.

This example describes an annular ring with a 900 breakout angle. Outer radius = 20, Inner radius = 10. The annular ring width = 5. In this case, since RM=0, the minimum annular ring = 5.81 and DRA = 5.81 - 0 = 5.81.