PCB Design Blogs

I’ve been testing Allegro® PCB design software for 20 years and every so often I test something that makes my jaw drop. This year, it’s the new Fast shape mode, and I feel like I need to talk about it because it is a game-changer in working with positive shapes when it comes to performance and the display quality of shapes.

The more etch shapes you have or the larger the database with positive shapes, the slower it has been to move a via, move a component, or edit etch when the change intrudes on the shape or void edges.

Ground fill is common on positive conductor layers and that means a lot of complex void and shape outlines exist. In the Smooth mode, editing data that causes a shape or void edge to change can cause the whole shape or large parts of it to re-generate as it checks the integrity and adjusts the segments of the shape or void. And that is what makes editing less snappy (or downright slow) when you are trying to etch edit or modify the placement in Smooth mode.

Here is the Global Dynamic Shape Parameters form (all versions up to October 2020):

And here is the changed Global Dynamic Shape Parameter form, using release 17.4-2019 QIR2 (HotFix 013), December 2020 (or later):

Notice that the Rough dynamic fill mode has been replaced by the Fast mode.

What Should You Expect from Fast Mode

For one, exponential performance gains and an overall better feel as you edit. I can (and did) measure the CPU time for edits, and depending on the database and shape complexity, I measured anywhere from .5x to 2x to 30x improved response time. It all depends on the database, shape complexity, or the number of shapes touched with an edit.

What I cannot measure is the improved feel you have while working in this mode. My edits in real-time are faster on any board with complex shapes. The mode was primarily added for large data that may leave you waiting seconds between edits, but I ‘feel’ the change on just about any data. My eyes see the shape update as I click a destination, and it feels like the system is ready for the next pick faster than my hand can move the mouse. In many large boards where I can count a couple of seconds between picks in Smooth mode, it is either instant or a fraction of a second to complete when in Fast mode. Extremely large boards that would only be editable with shapes in a disabled state are now editable in the Fast mode.

On to the Display and Shape Quality

When edits cause shape edges to require updates in this mode, instead of re-carving every segment to be in an artwork-ready state, only the area touched will update and the update will not walk through all processes needed to be “artwork ready”.  This means no more waiting for a complex 300-segment void to regenerate the entire 300 segments!  If five segments of one void are affected by sliding a line, then just five segments regenerate.

For all intents and purposes, it will display just like a Smooth shape, the webbing will be accurate, and connectivity to thermals will be correct (unlike Rough mode).

The following two examples display differences between Smooth and Fast. I slid a via in Fast mode and the updated void created with 10 segments and 6 arcs in Fast mode:

Performing the same action when in Smooth mode, the void re-generates with 10 segments and 4 arcs because it runs all smooth and trim code:

The Smooth mode void is ready for manufacturing and I’d be hard-pressed to see a difference that matters when I am working on the board.

Here is another illustration of the differences between modes. The fill will regenerate with small segments instead of the smooth arcs that you will want in your final shape. Fast is on the left and Smooth is on the right:

Again, these minor differences during a work session are an easy tradeoff to get the work done quickly.

Other Notable Differences

Every shape that updates in Fast mode will be marked Out of Date. But to be honest, who cares?  You are busy editing and you want to see a correctly outlined shape with correct thermal connectivity, right?  And that’s what you will have.

Now you are probably saying, “This looks great! Should I turn on Fast mode and never leave it?

I would advise you to set the shape parameter to Fast and start your work session. You do not need to update all shapes to Fast before working. They will convert quickly as they are touched.  

You can work all day or all week in Fast mode.

But, during a long editing session where the same area of a shape may be updated multiple times, you might see a larger piece of missing fill than the above illustration. So, what do you do?  Open the Status form and in the Shapes parameters section, click the Update All button. While the mode is set to Fast, this won’t take long to complete.

I would use Update to Smooth and run DRC periodically in the design cycle and when you are ready to output manufacturing media.

Final Thoughts

It is not a magic bullet for everything. It is meant to address performance during etch editing and placement changes. Some commands will convert shapes to smooth when executed (like Auto-Interactive Delay Tuning), so they will not run faster. Also, note that 

• DBdoctor will be accurate while shapes are in a Fast state.
• DRC will not be marked out of date by Fast shape conversions.
• Artwork, stream out, ODB++ and IPC2581 will not output with shapes Out of date, so you do not have to worry about making a mistake in the media you need for fabrication.

Finally, if you need to keep your data at a 17.2 revision, you can install release 17.4-2019 and take advantage of Fast mode performance by setting the database_compatibility_mode environment variable to a value of 17.2.

So, what are you waiting for? Try the latest 17.4 and experience the difference!