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Line to Shape spacing in Constraint Region - doesn't work!

Cleverdic

Hi,

In Allegro (I'm using  V16.5), I am seeing some curious behaviour when trying to manage the spacing between a Cline and an auto generated shape.

In summary, if a Cline crosses from the default area to a constraint area, the whole Cline line to spacing is increased to the larger size defined in either the default or constraint area. - In my opinion, this is wrong.

In this example, consider that the auto generated shape is a GND plane covering all non etch areas of the top layer.

In constraint manager, I can set up a default line to shape spacing of say 20 mils. If I then want to have a smaller line to shape spacing of say 10 mils around a BGA, I would define a constraint region around the BGA and then manage this by applying a spacing rule Cset in constraint manager and entering 10 mils for the line to shape spacing.

This combination is not controlling the spacing correctly whenever a Cline crosses from the default area into the BGA constraint region. (or vice versa).

It appears that if I draw the Cline in the default area, I get spacing 20 mils (correct) and if I draw the same Cline in the BGA constraint region I get spacing 10 mils (correct) but as soon as this Cline passes over the region boundary, the line to shape spacing of the complete Cline on both the default and BGA side then jumps to the largest size of 20 mils.  I cannot get the tool to effectively generate a spacing "step" on the boundary. Worse, it is forcing the whole Cline spacing to the largest value.

I'm advised this is correct behaviour but it doesn't look right to me.  In order to achieve what I need, I can see that I could manually identify the nets leading into the BGA, choose a smaller line to shape spacing for these nets as default AND BGA constraint region and then void the spaces in the default area by drawing and copying the voids.  It's a large amount of work where I would have expected the tool to provide what I want.  

Has anyone encountered this problem and is there a simpler solution? 

 

  • I know this is an old question but I was facing the same problem and here is the solution:

    By default, a cline crossing a region boundary will be voided to the larger of the inside/outside constraint values. Customers desire what is referred to as vectorized behavior where the line to shape spacing follows the explicit rules defined. The user preference variable “shape_void_cline_region” can be enabled to change the default behavior.

    Here is the document that helped me fix it.

    www.flowcad.de/.../flowcad-cadence-AN-allegro-tips.pdf

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