At 05:55 PM 3/15/01 -0800, Brad Velander wrote:
>Abd-ul Rahman,
>         Not that it warrants arguing over but you and I just have different
>views. You say a single layer pad is a SMT pad. I say a single layer pad is
>the most ancient of all pads and originally in it's concept had a drill even
>though it is a single layer pad, it was a single sided PCB design the
>predecessor of all else. You can call a single-layer pad SMT all you want
>but you won't convince me because the single layer pad predated both of our
>births, long before SMT was even a glint in anyone's eyes.

When I was born, printed wiring, I think, had been used but it was not 
common. Radios had masses of wiring in them.

SMT predates CAD systems. I worked with flatpacks in 1975, and they were 
not new.

The first pads had holes associated with them. When CAD programs were 
developed, we had pad definitions, and these initially consisted of pads on 
both sides of the board with a hole. Surface pads, per se, came later. I've 
done a lot of single-sided design and, when I have used a CAD system to do 
it, I never used "surface pads." It didn't even occur to me that I might 
want to do that.

The present surface pad option on a primitive was designed for SMT parts. 
Period. That is the history, and the programmers -- or at least one of them 
as just reported -- agree. Calling it a "single layer pad" and connecting 
it with single-sided PC design is a red herring.

>         On your note about undocumented features you are leaving yourself a
>little open there consider Protel's lacking documentation.

Leaving myself open for what? I'm not trying to make a case that Protel is 
perfect! It isn't! (But the 99SE manual is much better than the 99 manual.)

>  A lot of what we
>all do day in and day out is undocumented or it is just mentioned without
>further explanation or qualification of the limitations.

What we do every day, especially what most of us do every day, is not what 
I was writing about. "Surface pads" with holes do not fall into this 
category. Protel was designed to use through holes with variable pads for 
mounting components and for other uses, and to use surface pads for 
mounting SMT parts and a few other uses such as fiducials. As proof, 
consider paste masks. Protel assumes that a surface pad has paste mask 
geometry associated with it.

I'll say this again. There are several bugs here. A big one is the 
discrepancy between drill drawing and drill file when someone has used a 
surface pad with a hole. Another is that Protel allows surface pads to have 
holes at all. Some have chimed in with objections that they use surface 
pads all the time with holes and they need such structures. I'm not talking 
about PCB structures, per se, but about how these structures are 
represented in the database and user interface. The way to make "single 
layer pads" with holes in Protel is to use a multilayer padstack with 
appropriate pad sizes. Essentially, if it has a hole, it *must* be a 
multilayer pad because a hole is always multilayer (even if it is a blind 
via, it is on more than one layer). You might get away with using a surface 
pad in some applications, but I'm not sure that all aspects used to work 
even with Protel 98. We'd have to look at ground plane blowouts, copper 
pours, clearance DRCs on inner layers, paste masks, etc., etc.

>         Have a good evening, I am sure we will talk tomorrow.

I may not talk much; I'll be out and about, most of tomorrow, and I do need 
to do some, uh, work once in a while.

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

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