At 01:37 PM 5/16/2002 -0700, Brad Velander wrote:
>Abd ul-Rahman,
>         I agree with your general idea but suggest it is not practical with
>a most designs.

Depends on how one tries to use it, doesn't it?

>  The text size would have to be so small as to make it
>unreadable on anything but an E size print.
>  How many companies even have E
>size plotters left hanging around these days?

An E-size plotter is not necessary. The "biggest" problem is with small 
vias. Suppose we have a 25 mil pad with a 15 mil hole. The clearance is, 
let's say, 5 mils. So we have a 30 mil circle within which we can have text 
without any overlap. A small amount of overlap is acceptable, but I'll 
neglect that.

If we are stating hole sizes in mils, there will be no more than two digits 
for such small holes. So we must represent two digits in 30 mils. I'm not 
testing it right now, but offhand I'd say that 15 mil text would accomplish 
the deed. Too small to read? Not.

The print should be made at 2:1 at least. 30 mil text is readable if the 
resolution of the printer is good. But it would be better at 4:1 or more.

Yes, if the PCB is larger than, say, 5 x 8, a 2:1 print will be larger than 
B size. But this is already a problem for inspection. In other words, 
inspecting the plots at 1:1 is not really practical, so they must be 
inspecting them at higher magnification.

>  If the text size were not so
>small then you would have text overlapping text with equally illegible
>numbering. Most fab shops that I have dealings with would only be able to
>print B size docs and they don't typically supply CAD stations to
>inspectors.

This also assumes that a print for an inspector must be one piece of paper 
originally. That is not necessary. Prints can be taped together.

But the whole thing is a tad ridiculous. If the inspectors don't have a 
computer of any kind on which they could view a PDF or a gerber file (with 
a free viewer, if the company is really that cheap), then we have one weird 
company in this day and age.

What is a drill drawing for? Some of us don't supply them at all! Once upon 
a time, drill plots were bombsighted, hence the use of target-like symbols.

To my mind, the major remaining role for a drill drawing (which may double 
as a fab drawing) is for the designer's convenience. With it, he or she can 
quickly tell what a hole size is supposed to be. He or she will be able to 
view it at any magnification desired....

>         As for the number of drills, David's answer suggests that he has
>good reason for so many drills.

Yes, it was acknowledged that this could be true.

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