Arc commands in raster polygon data (G36/G37) become sectorized on import into CAM350. This sectorization can affect the quality of the data. It can alter DRC check results in extreme cases.
But you can control the level of sectorization that occurs. Using the “Precise Arc Approximation” which can be found under File | Setup | Preferences
Here is what a 50 mil void looks like with precise arc approximation OFF.
If this had a pad in the center of it, it may well fail a Track to Pad test based on the areas filled in by the sectorization.
Here is what a 50 mil void looks like with precise arc approximation ON.
Obviously this is much better as the arc is smooth. This would not cause any false DRC errors.
But when the scale gets smaller, problems may start appearing again. Take the example of a 5 mil void with precise arc approximation on
We are starting to see a little sectoring again. As the scale gets smaller, the problem will get worse. For boards done in small scale or with very tight DRC standards, this can be a problem.
But we can increase the Precise Arc settings with a modification to camnt95.ini.
To do this:
Locate and open your camnt95.ini file in notepad. Typically this is in
C:\Documents and Settings\ <login>\Application Data\DownStream Technologies\CAM350 9.5
Note that Application Data is often a hidden folder. So you may need to adjust your view settings to access the folder.
Add or Modify the following line to your [Preferences] section
Precise_Arc_Deviation=.000001
Default value is .00001. Numbers smaller than .000001 are not valid.
Here is is the 5 mil void again, imported with Precise_Arc_Deviation=.000001.
Arcs are smooth again.
And just for completeness sake. Here is the 5 mil circle void with precise arc approximation off.
So turn on and leave your precise arc approximation option. It is not a burden to any modern system and the risks of bad data imports are increased without it. As of Cam350 9.5 we have made this a default setting. But if your defaults has been checked you can select
File | New
File | Setup | Preferences
Check the “precise arc approximation” box.
OK
File | Setup | Save Defaults
Is there any downside to increasing arc precision?
Yes. Increased arc precision means more data points on the exported Gerber file. This could increase the plot time noticeably on some databases. It really depends on the number of arcs and their size.