Author Topic: Ratlines and Ground Planes  (Read 3746 times)

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Offline NivagSwerdna

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Ratlines and Ground Planes
« on: October 11, 2016, 09:24:41 pm »
OK so I am laying out my second ever(2-layer)  PCB... I'm planning to manually route...

This time my circuit is a bit more complex and one thing I've noticed is that the rat lines associated with a component don't seem to really follow the logic of the circuit (from my point of view) so for example my circuit has power coming in at a jumper going through a diode, past a capacitor, to a regulator, etc but the ratlines don't really reflect the flow.  Is there a way of changing the ratlines as you lay out?

Also...

Initially I have no ground plane so I get a lot of ratlines which will ultimately end up as being grounded to the plane.  How do you approach this?  Do you layout the ground plane first or layout some connections and combine them later.

Thanks in advance
 

Offline DerekG

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Re: Ratlines and Ground Planes
« Reply #1 on: October 11, 2016, 10:33:03 pm »
... for example my circuit has power coming in at a jumper going through a diode, past a capacitor, to a regulator, etc but the ratlines don't really reflect the flow.  Is there a way of changing the ratlines as you lay out?

Shift the components to where you want them on the board (& lock them there if you want them there forever), then run
VERIFICATION
COMPARE TO SCHEMATIC

The rats nesting lines will be recalculated based on which is now the shortest length to connect the components. If you placed the above components quite close to each other, the "new" rats nesting lines will show them directly connected together.

Quote
Initially I have no ground plane so I get a lot of ratlines which will ultimately end up as being grounded to the plane.  How do you approach this?  Do you layout the ground plane first or layout some connections and combine them later.

I lay down the ground plane first, then make some non ground connections. Every now and then, I regenerate the ground plane which will then be disconnected from your new (non ground) routes. Alternatively, just lay down your ground plane first, then set it to "unpoured", connect all your non ground connections, then "repour" the ground plane.

Remember that the auto-place function gives you a good head start (just lock in place the components that must be in set locations first like LEDs & switches) & the auto-router in DipTrace ver 3.0.0.2 actually works quite well.

ADDED: In fact since the latest release, I now reach for DipTrace over Altium & Proteus everytime. The latest ver 3 release has come a long way over ver 2.
« Last Edit: October 11, 2016, 10:35:36 pm by DerekG »
I also sat between Elvis & Bigfoot on the UFO.
 

Offline NivagSwerdna

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Re: Ratlines and Ground Planes
« Reply #2 on: October 12, 2016, 12:34:01 am »
Thanks.  Some great tips there!

My circuit comprises 5 sheets with signals crossing the sheets via 1 connection Ports

Maybe that introduces extra nets?

(I'm on a very recent version)
 

Offline Farley

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Re: Ratlines and Ground Planes
« Reply #3 on: October 12, 2016, 12:54:37 am »
Depending on the complexity of the PCB you can spend almost as much time placing the components as routing the traces.

As you are placing, rotating, and adjusting components you can periodically press the F12 key to recalculate the ratlines.

Another method I use (similar to DerekG's suggestion) is that once the component placement is close to final I go ahead and lay in a ground plane and connect it to whatever net is representing ground/common of the circuit. Then on the right side of the layout window I uncheck Copper Pours under the Objects tab. That will hide the ground plane but keep the connections to it so the ratlines don't reappear.  As you route, and consequently nudge components around, you may need to update the copper pour periodically. You can keep it hidden as you do this.

Adding a hotkey to update the copper pours is helpful.
 

Offline John Coloccia

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Re: Ratlines and Ground Planes
« Reply #4 on: October 12, 2016, 03:02:06 am »
Right click on the ground net and select "Hide Ratlines"....and poof, they're gone, ground plane or not.

And yes, hit F12 to clean up the ratlines. The most useful feature is when you mouse over a pad, all of the pads in that net light up. Sometimes I find that more useful than the ratlines.

There are some other useful things they could do to make it a little better, and it would be very simple, but my experience is it would be a complete waste time and energy to suggest them.
 
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