PCB News - About the unit settings of Allegro out of gerber

About the unit settings of Allegro out of gerber
Usually drawing pictures usually use mm as the unit, and when the gerber is produced, the metric system is also used as the unit, which corresponds to mm, and there is no problem. Sometimes when I encounter a board drawn in mils, some problems will occur when I use the English gerber as the unit and then transfer it to the CAM350. After thinking about it carefully, I can understand the meaning.

Allegro uses two sets of units for drawing and gerber respectively, which are not related to each other. In 15.7, the drawing unit is set at Setup-->Drawing Options; the gerber file unit is set at Manufacture-->Artwork, and the unit of Drill and Route is set at Manufacture-->NC-->NC Parameters.

Regarding the accuracy of the data, the gerber is theoretically more accurate than the drawing. For example, if you use mm for drawing and 2 decimal places, you use at least 3 decimal places for the gerber. If the unit is different, convert to the same unit and compare. For example, use mil for drawing, 1 decimal place, and use imperial system for gerber, that is, inch. To be accurate to 0.1mil, you need 4 decimals, and for gerber, you need 5 decimals. Everyone suggests to use the same unit for drawing and gerber. I think it is to avoid the possibility of inexhaustible division when converting between different units, which will affect production. The conversion of inch and mil is fine, and the conversion of mm and inch will cause some minor problems. No need to ask for trouble.

Also mention Ncroute. Ncroute needs a ncroutebits.txt file to specify the diameter of the milling cutter. The unit of the milling cutter diameter in this file must be consistent with the NC Parameters. For example: use mm for drawing, inch for gerber, and the diameter of the milling cutter is 1mm. When drawing the Route path on the Ncroute_path layer, the line width should be 1, and the milling cutter must be identified in ncroutebits.txt in inches, which is 0.0394 T0* . In this case, I find myself awkward.

Therefore, when designing the PCB board, suppose the drawing setting unit is A, and gerber, NC and ncroutebits.txt must use the same unit, set to B, then A and B are best to be the same.

The above is an introduction to the unit settings of Allegro's gerber. Ipcb also provides PCB manufacturers and PCB manufacturing technology.