Steve,
        your comments are very sound and acceptable but there is another
approach which I believe would be more common. You simply assess your design
rules with the appropriate allowances for the PCB technology to be applied
to the job. IMO this will lead to less problems with component/hole issues
and allows you to consider the rule requirements while designing rules for a
particular job, not when designing different library parts for multiple
stackups, plating thicknesses, etc.

Sincerely,
Brad Velander.

Lead PCB Designer
Norsat International Inc.
Microwave Products
Tel   (604) 292-9089 (direct line)
Fax  (604) 292-9010
email: [EMAIL PROTECTED]
http://www.norsat.com

Visit us at Booth 2G2-09 at CommunicAsia 2002 in Singapore June 18-21.



> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
> Sent: Friday, May 17, 2002 10:59 AM
> To: Protel EDA Forum
> Subject: Re: [PEDA] Too many hole sizes
> 
> 
> In a message dated 5/17/2002 1:43:29 PM Eastern Daylight Time, 
> [EMAIL PROTECTED] writes:
> 
> I used to do this too, but I've found that there's a very 
> good reason to make 
> the plating allowance when you choose the hole size, and 
> consider the nominal 
> hole size to be the exact drill size. All Protel's clearance 
> checks are based 
> on the outside diameter of the barrel (the named hole size) 
> being exactly as 
> given. If you let the fabricator increase the drill size to allow for 
> plating, you don't have the clearance you think you do. Maybe 
> you get away 
> with it this time, maybe the next time too, but sooner or 
> later it's sure to 
> bite you. Thus I routinely go up a few mils on hole sizes, to 
> ensure that 
> plating plus all the worst case tolerances can't make the 
> hole smaller that 
> the pin which goes in it. That way, all the design rules are really 
> guaranteeing the clearances I asked for. And I make a point 
> of telling the 
> fabricator that my drill file is real drill sizes, that they 
> aren't permitted 
> to increase drill sizes to allow for plating.
> 
> Steve Hendrix

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