Andrew

The first statement is a "%AM" statement which means "Aperture Macro". 
Within this statement, standard gerber recognises "CIRCLE", "LINE-VECTOR", 
"LINE-CENTER", "LINE-LOWER LEFT", "OUTLINE", "POLYGON", "MOIRE" and 
"THERMAL". I assume that "TH" is an abbreviation of "THERMAL". 201 is the 
macro reference number. In this case, the entire reference is THD201.

The codes on the following line mean :
7 (Thermal) 0 (X center) 0 (Y center) 1.4 (Outside diameter) 1.4 (Inside 
diameter) 0.0 (Crosshair thickness) 45 (Rotation).

I'm not sure which of these make sense. The X,Y offset of 0,0 seems to be 
OK. The outside and inside diameters of 1.4 coupled with a crosshair 
thickness of 0.0 sounds like some sort of 0-relief thermal (ie pad merges 
into plane) and 45 degree rotation in this case sounds irrelevant. The real 
question is what does it look like on screen.

The "%ADD201THD201" command assigns the THD201 macro to D-code 201 so that 
it can be selected by issuing the D201 command further down the file.

All in all, I'd say it was probably standard gerber providing that the 
inside and outside diameters / crosshair thickness are acceptable..


Doug

>I've just tried to send our latest Gerbers to our board house, and they 
>can't interpret a thermal aperature embedded in one of the files for a 
>power plane.
>
>The offending item is:
>
>%AMTHD201*
>7,0,0,1.400,1.400,0.000,45*
>%
>%ADD201THD201*%
>
>This situation throws up lots of questions:
>
>What am I seeing? A Protel bug or an inexperienced board house? I've heard 
>dark things said about Protel's Gerber generation in the past.
>
>How do I interpret the above if, say, I wanted to hack my own thermal 
>aperature? Or if I wanted to work out if a pair of parameters is impossible 
>(e.g. if one figure is an outside diameter and the other is an inner 
>diameter, then setting them both the same would give a zero width line).
>
>Does Gerber have a standard set of aperatures, and does Protel throw in 
>it's own customised ones?
>
>I have other custom thermals on the board. Why aren't these causing 
>problems?
>
>Our temporary fix is for our board house to hack the aperature, and in the 
>meantime I'll experiment with changing my custom thermals, and perhaps 
>trying Protel's default ones.
>
>Andrew Ircha


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