Hi Ted,
I'm not sure if you already got a response yet, but I normally use a
clearance of 0.010".  IPC-2222 section 9.1.3 suggests this clearance in
figure 9-1.  This makes the board manufacturable.  The clearance can get
smaller, but issues re: electrical clearance, mfg allowance,
manufacturablity, etc., come into play.
Wish success with your certification!
Roger M. Stoops, C.I.D., PCB Designer


Trimble
Engineering and Construction Division
5475 Kellenburger Rd.
Dayton, OH 45424-1099 USA
Ph: +01 937.233.8921 or +01 937.233.4574 ext 288
Fax: +01 937.233.7511






                    Ted Tontis
                    <ttontis@ENGA        To:     [log in to unmask]
                    GENET.COM>           cc:
                    Sent by:             Subject:     [TN] thermo relief in conductor planes
                    TechNet
                    <[log in to unmask]
                    ORG>


                    05/11/01
                    12:18 PM
                    Please
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                    "TechNet
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                    Please
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                    Ted Tontis





        I am still fairly new to PCB design and I am studying for the IPC
design cert. I cam across IPC -2222 9.1.2 Thermal relief in conductor
planes
which states the relationship between the hole size, land and web area is
critical. Typically, divided 60% of the minimum land area diameter by the
number of webs desired to obtain the width of each web in accordance with
the following example:
        I understand this with no problem but where does it state the air
gap or expansion size? Is it the same value all the way around the land
area? or does the current control the distance?

Thank you,

Ted Tontis
Engage Networks Inc.
[log in to unmask]
PH 414.273.7600 Ext. 7607    <http://www.engagenet.com>

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