Changing Line Width of a Trace in a Net without DRC Errors

You can also use the "NECK" rule so that you can limit how long a branch or segment can be shrunk down.  If you use the MIN_LINE_WIDTH rule then all real checking gets thrown out as long as the line is MIN width wide.  Try both methods and see which works best for you.

Hi Excellon1/Redwire,

Thanks for your suggestions, very much appreciated.

In this design, this net is one of the DC power inputs at approx. 4.3V/3A that feeds various voltage regulators at several locations apart. Instead of 8mil as Min width in constraints manager, I use 100 mils as Min (as well as 100 mils neck width) to force the trace to 100 mils (designed for ~4.75A for extra headroom). This is to make sure I do not have any bottlenecks on main traces to the regulators.

As mentioned in the previous message, I have branches coming off from this for circuits that are 6-8" away from this area. These do not require 100mils but 8mils width is good (and needed for tight areas). These are the ones giving me L><W errors when I change their width to 8mils.

After my first posting, I've managed to clear the errors: left click on a trace segment, right click and select Net - Property edit. The Edit Property window pops up. In there, I select Min_Line_Width and enter 8 in the Value box. This clears all L><W errors on that trace. The strange thing is that this Value box does not retain the entered value (just blank) so you would not know. If I enter 10, errors come back (as expected) so some guessing is needed. The next issue that I have is that when I slide this 8mil trace segment to tidy it up, that segment turns back to 100mils. It is a hassle and not sure how to handle this yet. Any help for this would be great. 

At this time I am still learning how to use this software and just wonder if there is any documentation available that explains the topology used, especially the constraints manager and how various properties that users can set outside of constraints manager come into play, their dependencies and so on. Diagrams would be very helpful as well.

Thanks.

TC 

HI TC.

So you can assign net properties via the CM or via net properties in the editor. The properties available in the CM are the same as whats available via using a right click "Edit Properties"

In the CM you had 100Mil as the minimum trace width so Allegro will check the net to see if it is indeed meeting this constraint. Because you had traces that were less than 100 Mil cutting into that branch Allegro flagged you because it saw those 8 mil traces. Allegro is just checking the whole net in this regards.

When you changed the net properties in the editor by right click you actually changed that whole net to have a minimum width of 8 mils. This is why the DRC errors went away. If you open the CM you should see that the actual min net width is really 8Mil and not 100.

To get around what you are wanting to do there is a way and Red pointed it out. The trick is to also use the "Neck Width and also the Neck Length" constraint in conjunction with your minimum line width.

In the CM make Min Line width = 100, Min Neck Width = 8, Min Neck Length "However long it needs to be" for the 8 mil line.

There is one additional constraint via right click on the net called branches. I was looking for some info in the help on this but couldn't find anything. As a wild guess this may pertain to the max number of branches that net will go to. Kind of unsure.. Maybe someone else knows about that ?.

I know what you mean about the "Net Properties Window" It has been that way for along time in that it does not show the actual values entered. The values do show on another pop up window but is it kind of archaic how this method was implemented. "Not Intuitive"

To know what you have entered when the properties dialog box has been closed out you can select the net and click the "Show Element" icon or hit the F4 key. A window pops up to display the properties. In that window everything will be displayed. Also you will notice that the location of the nets are shown. If you click the x,y location "There in blue" Allegro will jump to the actual location. This is very handy for moving around and jumping to the location. One thing on this. If you are just dealing with nets verify that your find filter has the net box checked "Only"

The easiest way to get the info you need is to simply check the items in the find filter first. Maybe things like Nets, Clines, cline Segs, Nets etc.

With your mouse hover over the trace until it highlights. You can use the TAB Key to cycle through what was selected in the find filter. You can then right click and select show element.

All the best.

Hi Excellon1,

I thought changes to the Edit Property window in the editor are local changes that overwrite the global settings in the constraints manager for the selected object only. In my case they cleared the errors with 8mils for that trace but 100mils setting is still in the constraints manager. This is why a document explaining the inter-working relationships of all these settings would be great.

I will try the necked routing as you and Redwire suggested and see how that goes.

Once again, thanks for your help. You guys are great. 

TC

Hi Excellon1,

I thought changes to the Edit Property window in the editor are local changes that overwrite the global settings in the constraints manager for the selected object only. In my case they cleared the errors with 8mils for that trace but 100mils setting is still in the constraints manager. This is why a document explaining the inter-working relationships of all these settings would be great.

I will try the necked routing as you and Redwire suggested and see how that goes.

Once again, thanks for your help. You guys are great. 

TC