Thermal Relief doesn't work for Power palnes

If you are going to use negative planes, you will have to define flash symbols (.fsm) for each different thru-hole padstack in your design.  The flash symbol then needs to be called out in each thru-hole padstack.  In Pad Designer you will see a field for inputing the flash symbol name for the internal layers.

Since it doesn't appear that this was done at the beginning, you will have to do a bit of work to bring your board up to date.  First, after updating the padstacks, the updated padstacks will then need to be refreshed in all your footprints, and then your board will need to have all the footprints refreshed in order to bring in the updated padstacks.   

That is why most are getting away from negative planes because of the extra work involved, at least in Allegro.

Chad

What are the benefits of using Negative or Positive Layers?!. We used to define Negative Layers for power planes in Altium PCB and here  I just followed my provious experience. I would really appreciate if you could tell me fundamentals of Negative & Positive layers in Allegro PCB. Can I safely convert them all to positive or not?

Thanks,

Hossein

I am speaking only from an Allegro background, so your experience may be different.

From my experience, negative planes were commonly used because of the resulting large file size that positive shapes created.  Back in the day when we used floppy disks to transfer information, file size was of utmost importance.  Now days, it really doesn't matter how big the files are.

Positive shapes are more suited to WYSIWYG.  You can easliy control the thermal connections thru contraint manager or even on individual pins and vias themselves.  As I alluded to in my earlier post, negative planes require a bit more work.

Converting them is as simple as unchecking the negative plane in your stack-up.  I usually set up unique constraints for my power/ground nets, since they usually require heavier traces and possibly greater spacing than other nets.

The end results are the same, no matter which you use.  I used negative shapes until the late 1990's and have been using positive ever since. 

Chad

Thank you very much for your wise words Chad. You gave me enough information to change the power planes to Positive.Especially, when I hear from a veteran, I also come to the conclusion that by Positive layers I would have less trouble than Negative ones. However, I am curious to know why some shapes were drawn regarding DRC rules while others did not obey rules? Would you please take a look at the last picture in this post? just click on it to see what I am asking.

Thanks,

Hossein

Like I said, it's been a few years since I worked with negative planes.  Not having the actual board to look at, I would have to guess that since the pin in question has less than 50% off the pin outside of being totally enclosed by the one shape,  The other shape recognises your DRC spacing rule.  I think I do remember that pins that fell in to plane splits were handled differently.

Sorry, but I am sure this isn't much help.

Chad