Polygon pour direct connect rule - Page 1
Forum section: electronics / general

author: Harvs
author_rank: Super Contributor
timestamp: June 03, 2020, 10:53:00 pm
content: Something I've never been able to work out properly and has always cost me time, is how to efficiently specify the pad class for pad you want direct connected to polygon pours.At the moment I'm going into the classes dialog within the PCB editor, searching for individual components and adding them to a "PowerPads" class that I have a rule setup for. This is ridiculously in-efficient, but what's worse is it gets lost when you want to re-use part of a layout in another design, which for me often is proven small dc-dc converter layout.No amount of googling has led me to a better solution, so I'm hoping someone might unlock a search term for me?Surely there has to be a way to specify the pad class on the pin the schematic?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 04, 2020, 12:06:58 am
content: Yes, since... AD17 or 18 or so? You can add schematic parameters, which are pulled into PCB and can be queried by rules. I'm not sure offhand if ClassName is one of them.Component class is certainly one (since old versions), and you can use component class, pad naming and optionally footprint naming to select relevant pads.You can also construct rules by size, which is probably a more common case anyway. My designs often have a, for example:IsPad AND (AsMils(PadXSize_AllLayers) > 60) AND (AsMils(PadYSize_AllLayers) > 60)query in them for a PolyConnect rule, and set to a modest increase in dimension, say 20 or 30 mils spokes, with 10 being the default.Keep in mind that direct connection is rarely necessary, and simply increasing the size of the thermals will do. Direct connects are a hazard for poor reflow soldering. You can calculate the conductance of a thermal spoke, and I think you will find it isn't substantial under most cases, is merely worth increasing (but not eliminating) under more demanding cases.Ed: your search for a more general rule is a worthy one, because not only are pad classes just another step you need to ensure is made, but also as component names or IDs are updated in the course of updates, class assignments can be lost, or confused accidentally. Pad classes are at least better than directly naming pads in rules (e.g. "(Name Like 'P1-13') OR ...") but still not all that reliable.Tim

author: Harvs
author_rank: Super Contributor
timestamp: June 04, 2020, 12:33:56 am
content: Ok, thanks sound like there's something promising I'm missing.Sure ClassName is definitely one I've used at component level, but that will not carry across if assigned to a pin, only a component as a whole.I guess in some ways it doesn't really matter, this could probably just be done at component level. For something like a switching converter with integrated mosfet, anything connected to a plane on that device is going to be high current, and all the other pins will just have normal tracks.I also take your point about direct connection. But I find on small dc-dc converter designs I'll normally just shape the plane entry to the pad to provide some thermal relief, I find the spokes a bit useless where the plane only partially covers the pad.