photo plotter apertures for traces

Since my CAD package pretty much handles the code generation for FLASH and DRAW I couldn't say for sure without looking in the output file, BUT I doubt it. I do know that CADStar can optimize route T's and other junctures so there isn't an overshoot bulge on the far side. Kinda' does a little pull back on the gerber data.

Jim

Where does that "overshoot bulge" come from?

If I draw a T with 3 lines using the same dia round pen, it comes out clean. I'm drawing the lines so they all meet at the same point which is the middle of each line.

The circle from the left matches the circle from the right. At the junction, there is a circle that gets painted twice.

If I bring the bottom line up to the exact same point, it doesn't overshoot at all. The circle at the end point overpaints the same circle that was already painted twice. The new line adds a pair of small sections to the area that gets painted twice. They are the corners from the circle SW and SE to the edges of the lines.

I only use round traces for tracks.

Clearly pads can be round, square, rectangular or numerous other shapes.

I only use round traces for tracks.

Clearly pads can be round, square, rectangular or numerous other shapes.

Actually there are 5 types of apertures circular, rectangular, oblong, diamond and drawn. all except the drawn can be used for traces. only the round one will give you the same width in all directions and gurantee no overshoot from the traces.

Bob

Cadstar specifies an annular ring to draw traces. Apparently the idea was to prevent overexposure by the overlap of a solid circle.

Geo

PCB film exposure is an all or nothing process. It is either fully exposed to light, or not exposed at all. There is no chemical difference in the emulsion between fully exposed, and fully-fully-fully exposed. The only way to overexpose PCB photographic film is to burn a hole in it, which isn't going to happen.

-Chuck

There is but little in Cadstar that isn't targeted at those who know little about the electronic design and manufacture processes.

If all the routes are of the same diameter then yes, no bulge, but not all intersections are from the same DRAW code. You, obviously, don't need to optimize out a bulge that isn't there. You can also get a bulge when a DRAW and a FLASH overlap/end on each other. Big DRAW aperture onto a smaller rectangular FLASH and you get a little overshoot.

Jim