Purpose |
When an annular ring around a plated through hole is too small, the hole may shift during drilling and cause insufficient plating later. |
Function |
Reports for PTHs (or vias) embedded in copper the shortest distance between drill and laminate, if the distance is less than the pp_d2c action parameter. The measurement takes into account both negative and positive data. Measurements are spacing segments representing the shortest distance from the drill to laminate. An option is available to allow breakouts by specifying the breakout angle (as defined by the ERF parameters pth_breakout_angle and via_breakout_angle ). Range of breakout angle values = 0-180 where 0 means No Breakouts Allowed. For more info , see below |
Activation |
After selecting the Drill test, set the ERF variable classify_pad_ar to No
. |
Known Limitations |
If no single pad gives the drill the same annular ring
value as the value calculated for all copper elements, then no pad will be
associated with the measurement and an r0
will be inserted instead (a drawn surface, for instance). |
This section describes the possible modifications of annular ring
measurements in cases where breakouts are allowed by the designer of the board.
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 will clarify:
The following example describes an annular ring with a 90 0 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.