Line Neckdown (Size)

Reports lines that are joined so that the width at the narrowest point is less than nominal line width.

Internal ERF Name	<Area>:neckdown
Measurement Shape Measurement Value Measurement ID	Segment Size Line
Layers Displayed	Signal layer
Graphic
Purpose	A line neckdown can be a dangerous defect. The indentation of copper at the connection point may become an acid trap and cause over etching of the copper. This forms a nick and a potential cut.
Function	Reports lines that are joined so that the width at the narrowest point is less than nominal line width. Measurements are segments representing the minimal line width.
ERF Parameters	pp_layer
ERF Variables	max_line_width
Constraint	Feature Spacing
Limitations	Neckdowns are not reported if the difference between the wider section and the narrower section is less than 0.5 mil. Neckdowns are always reported, except when max_line_width is less than 1000my (default value is 12mil=304.8my), if the difference is greater than 0.6mil. See Fig. A. Differences between 0.5mil and 0.6mil are sometimes reported (0.1mil accuracy). If the wider section is greater than max_line_width, the line is replaced by a virtual line of the same coordinates with width equal to max_line_width. The narrower part is reported if less than [max_line_width - 0.6mil]. See Fig. B.