Polygon Related Problems - Mask to PADS
After we finished the first pass of MSK2PADS using the PADS documentation as a reference for the data sheet we ran into some serious problems when importing the ascii file into PowerPCB 1.5.
Re-entrant Polygon not Supported by PowerPCB
A re-entrant polygon is one which folds back on itself and actually touches itself. It must follow the "winding" rule - i.e. it winds around only in one direction, either CW or CCW.
This type of polygon can be output by Agilent's layout program-unfortunately when this is converted into a PADS polygon, Power PCB does not display nor fill it correctly.
Ideally the MSK2PADS translator would automatically detect and convert such polygons into either multiple polygons or filled and empty polygons. A robust routine to do this no matter how complex the re-entrant polygon is not simple. One must also consider that although we have shown the boundary to be composed of straight lines it may in fact contain arc sections.
Hence MSK2PADS only detects the re-entrant polygon and issues a warning in the log file (supplying x,y coordinates....)
Limited Number of Vertices per Polygon
Microwave designers often create very complex polygons since the exact polygon shape affects the microwave signal. It is not uncommon to find meandering serpentine or spirals with thousands of vertices. Agilent does not explicitly define the maximum number of allowable vertices per polygon but we have in practice seen circuits with 5000-7000 vertices.
PADS is limited to 100 vertices in 1.5/2.0 but appears to have
a very high limit in version 2.1 - this means that
many RF and microwave designs will not be able to pass every polygon into PADS. The MSK2PADS translator detects such polygons (easy) but cannot break it into a number of smaller polygons.
It can however issue a warning and break the polygon into a series of lines, each of whose
vertex count does not exceed either 100 (for 1.5/2.0) or 5000 for 2.1.