Scott,
        I recommend you get a copy of IPC-2221, Generic Standard on Printed
Board Design. It covers this and whole host of pcb design issues. To answer
your question, use the following method:

First, find the minimum required hole size ...
Min hole size, plated through hole = (at least .006" over Max lead diameter,
but not more than .028" over min lead diameter).
Min hole size, unplated  hole = nominal lead diameter + (at least .006", but
more than .020").

Then find your maximum hole size ..
Max hole size = min hole size + hole tolerance range (there are charts for
this, but you can use .008" [ +/- .004] for most applications (lead
diameters below .063").

Land (pad) size = a + 2b + c, where:
        a = Max hole size
        b = min annular ring (again, more charts; I recommend .005" for
plated through, and .012" for unplated holes).
        c = fabrication allowance (even more charts; I recommend at least
.012").

Hope this helped.

 Michael Hiteshew
 Lockheed Martin Launching Systems
 [log in to unmask]
 (410) 682-1259


> ----------
> From:         Scott Rebman[SMTP:[log in to unmask]]
>
> I am in the process of laying out a new single layer PCB.
> I find that the Protel library supplies components with .032 holes with
> .050 pads.
> On other existing PCB's I see that the components with .032 holes have
> .077 pads.
> No one hear can tell me why.
> Does anyone know of standards for hole Vs pad sizes?
>
> Thanks
> Scott R.
>
>

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################