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At 04:15 PM 10/3/01 -0400, Jeff Adolphs wrote:
>1. Since I am using a small via to make routing SMT easier. Small via
>having a 10 mil dia. annular ring (pad of 31_21).

Ah, the confusion of it! "Annular ring" in the industry means the radial 
difference between the hole wall and the outside edge of the pad. Protel, 
somewhere back there, got it completely wrong. They have fixed it in some 
places and not in others. The described via has a 5 mil annular ring.

This is not an uncommon situation for vias. One might expect to pay a 
premium, but not much.

>  Am I free to reduce
>the annular ring on other parts without any harm. Specificly, reducing a
>Pad of 75 with a drill of 43, to a Pad of 61 with a drill of 43? A pad
>of 61_43 would make a connector much easier to route.

60/40 is a very common pad/hole size, it works for 25 mil square posts. The 
hole size which should be used in Protel is the *finished size*. With a 10 
mil annular ring, this is standard production. I don't recommend going 
below 10 mil ring for soldered components, i.e., 20 mil diametric oversize.

>Board info:  So far I'm trying to keep the PCB at space 9 mil minimum,
>trace of 9 mil minimum.

This is overkill. 8/8 has been standard production for a long time, I've 
been told that 7/7 is also no problem, things start to get dicier at 6/6 
but that is still common. Below that things get more difficult for the 
fabricator. 4/4 is pretty much the finest I've seen advertised for normal 
production materials.

>2. Will I save money by using a Via of 31_21 only when necessary and
>using a Via of 50_28 everywhere else.

Maybe, maybe not. By the way, you might be able to use a via of 25/15 if 
you need it. I've seen plenty of boards with this small a hole and via. A 
15 mil hole is drilled oversize at 18 mils and comes back to 15 with the 
plating (just like a 40 mil nominal hole is drilled 43 mils nominal).
[EMAIL PROTECTED]
Abdulrahman Lomax
Easthampton, Massachusetts USA


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