Altium track to polygon clearance a random number - bug? - Page 1
Forum section: electronics / general

author: vzoole
author_rank: Regular Contributor
timestamp: November 29, 2017, 10:07:40 pm
content: Hello,I've set 0.15mm minimum clearance for everything.It is good everywhere except one place (0.159mm) where really important the exact 0.15mm clearance.What should be wrong?Video about issue:https://youtu.be/qIV1OZ50psE

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 30, 2017, 01:36:22 am
content: Try measuring between corners of the polygon on either side of the trace, and subtract trace width?Try setting 0.01mm grid, zoom in and measure it yourself?Looks the same to me, but all I've got is a blurry video to look at.On principle, I don't like functions that compact a huge amount of data into a single result. This is such a function. Some problems that immediately come to mind:- In what location did it measure 0.159mm between?- How many locations/regions have the same measurement?- The shapes have complex geometry; how can I verify that it's picked the correct distances?- What is the exact decision tree that led to this number being given to me?I don't know if this particular function is reporting correctly or not -- I rarely use it, personally. I have no particular reason to doubt that it's reporting correctly.I also have no particular reason to doubt that the polygon is being poured correctly. My experience with polygons has been quite good, but goofs do appear from time to time, and polygons in general tend to be one of the more glitch-prone aspects of most EDA tools.In any case, you seem to be overemphasizing the criticality of this dimension -- CPW is more sensitive to trace width, for those proportions. I find it very unlikely that an "ANT" trace needs precision impedance, and you aren't going to get much better than 10% on an impedance controlled fab anyway, or 20% or worse for generic proto. I'm making a number of assumptions here, so do fill in anything I'm missing.Speaking of fabs, generic proto fabs may enhance the shape-to-polygon clearance for you. I've seen 7 to 10 mil (up to 0.25mm) clearance set by the fab.Tim

author: voltsandjolts
author_rank: Unknown
timestamp: November 30, 2017, 02:45:10 pm
content: What PCB fab are you going to use and what manufacturing tolerances do they work to?

author: tszaboo
author_rank: Super Contributor
timestamp: November 30, 2017, 02:56:18 pm
content: I have the same thing with my Altium.I dont think it is a bug. If you decrease the "Arc aproximation" "Maximum deviation from perfect" for the poligon, the distance is reduced also.So double click the poligon, reduce the value to the desired value.

author: vzoole
author_rank: Regular Contributor
timestamp: November 30, 2017, 08:41:36 pm
content: Thanks for all the answer!The distance between track and polygon was 0.159mm everywhere and I've checked in gerber too.It will produced in Eurocircuits. I don't know they tolerance, I'll ask them.Anyway it is can make 2% difference in impedance, not a big deal.Quote from: NANDBlog on November 30, 2017, 02:56:18 pmThanks for your reply, this is the solution. I have to go really down as 0.0001 to get correct value and it is make the repour very slow but good.Quote from: NANDBlog on November 30, 2017, 02:56:18 pmEventually you are right... if something is wrong in every product that is not a bug, that is a feature

author: tszaboo
author_rank: Super Contributor
timestamp: November 30, 2017, 09:19:46 pm
content: Nincs mit.I wouldnt worry about 9um