According to section 9.1.3 the minimum antipad clearance is P+A+2B=antipad
diameter where P is your drilled pad size, A is your minimum electrical
clearance, and B is your positional tolerance based on table 9-1. As an
example
For a 50mil[1.27mm] Pad on a class 2 Board 3"[76.2mm] x 2"[50.8mm] where
minimum electrical clearance is 10mil [.25mm] the antipad needs to be:
50mil+10mil+2(10mil)=80mil dia. 1.27mm+.25mm+2(.25mm)=2.02mm dia.
Hope this helps.
Jeffrey A McGlaughlin, CID
Engineering Designer
Battelle Memorial Institute
Columbus Ohio
http://www.battelle.org
[log in to unmask]
-----Original Message-----
From: Lum Wee Mei [mailto:[log in to unmask]]
Sent: Wednesday, June 25, 2003 8:31 PM
To: [log in to unmask]
Subject: Re: [DC] Thermal Relief Calculations
Mark,
You have asked the same question I did last year. No one has attempted to
answer me. I wish you luck this time and hoping to bank on your luck,
someone will be kind enough to give us a good explanation?
Regards,
Wee Mei
Mark Holmes wrote:
>Hi all,
>
>I am looking at IPC-2222 9.1.2 regarding thermal relief pads. It
>provides a formula for the web width based on the minimum pad size.
>
>I can use this method with my current software, which allows me to
>create a thermal relief for each pad. But, I also use a system that
>only allows me to specify thermal
>relief pads for 'non-vias' in a particular plane.
>
>My questions are, what are you guys using to calculate your thermal
>relief pads? Do you calculate the web size for each pad used, Or do you
>have some other method of calculating the web width.
>
>Any advice, rules of thumb etc. would be most appreciated.
>
>Just one more thing, could anyone confirm what is meant by "Standard
>Manufacturing Allowance" in IPC-2222 Figure 9-1. Is this the same as
>IPC-2221 table 9-3 "Minimum Hole Location Tolerance, dtp"?
>
>Regards.
>
>Mark
>
>Mark Holmes PCB Designer
>Helvar Merca Ltd.
>Hawley Mill
>Hawley Road
>Dartford
>Kent DA2 7SY
>Tel: 01322 222211
>mailto:[log in to unmask]
>
>Visit our NEW updated website at:
>http://www.helvar.co.uk
>
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