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March 2000

DesignerCouncil@IPC.ORG

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DesignerCouncil <[log in to unmask]>
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Abd ul-Rahman Lomax <[log in to unmask]>
Date:
Tue, 7 Mar 2000 13:19:34 -0800
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"DesignerCouncil E-Mail Forum." <[log in to unmask]>, Abd ul-Rahman Lomax <[log in to unmask]>
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At 02:13 PM 3/7/00 -0500, Ron James wrote:

>      To sum up my questions:
>      1)  Does your company use standard hole size symbols across all
>      designs?

As an independent service bureau I wouldn't be doing this. I can see the
purpose of doing it where all design is coming from a single source and is
being checked by the same engineers. But there is, in my view, a better way.

>      2)  If so, does your software accommodate this, or is it a manual
>      process for you?

I used to use Tango DOS PCB, and you could assign specific flash apertures
to drill symbols, and these definitions could be used by other designs. I
never did this; I always used the drawn drill symbols. I don't recall how
this is handled in OrCAD, but in Protel Advanced PCB 99SE, there is no
option, as far as I can tell, to use flashed symbols. However, there *is*
an option to plot the hole size numerically, and I find this far more
useful for checking than symbols or a letter code (which are the other two
options).

Drill symbols were invented for films so that they had a readily locatable
center which could be bombsighted to determine hole positions. With the
common use of CAD-generated drill files, this step is bypassed and it is no
longer necessary that the drill drawing *precisely* indicate hole position;
typically the drill drawing will be overlaid for checking with another
layer which shows position....

>      3)  If so, do your end users (design, manufacturing or process
>      engineers) find this to be valuable?

Fabricators have their own tools and I would expect that they would be
checking the drill *file*, not so much the drawing. For others who might
need to know what hole sizes are used and where, I highly recommend, if it
is available, using the hole size directly; no translation is required. I
use pretty small text, particuarly on boards with small holes close
together, but it is generally, as used, printed or plotted at 2:1 or better
for checking.



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Abdulrahman Lomax
P.O. Box 690
El Verano, CA 95433

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