Mark and Susan,

20 mils is a rule of thumb for minimum annular ring size mentioned in Darryl
Lindsey's very old book (1984) "The Design & Drafting of Printed Circuits" where
he also recommends that the hole size be at least 6 mils but not more than 20
mils larger than the lead size.  Once you have decided on these factors then the
minimum pad size is calculated.

E.g.

the lead size is 20 mils
the clearance is 6 mils (multiply by 2 to get dia of clearance hole) = 12
min annular is 20 mils (multiply by 2 to get dia of minimum annular ring) = 40

so minimum pad size = 20+12+40 = 72 mils

Try to pick as few pad sizes as possible and as few drill hole sizes as possible
that will fit as many components as possible.

Don't forget about tolerances of drilled holes and lead dia tolerances so you
don't end up with an interference fit.  (dimensional analysis)

Regards,

Bob Landman




-----Original Message-----
From: Susan Clayton <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: April 16, 1999 7:12 AM
Subject: Re: [DC] Pad sizes


>Mark,
>My rule of thumb is .020 mils larger than hole size and my hole size is .012 -
.018 larger than pin size
>depending on if it is going to be hand assembled or not.
>Susan Clayton
>Volumetrics Medical Imaging, Inc.
>
>Mark Holmes wrote:
>
>> Hello all,
>>
>> Can anyone offer me any advice on where I can get hold of some guidelines
>> regarding the size of the Pad with respect to the hole size, for through
>> hole components?
>>
>> Ideally I would like to know how best to determine the correct pad size for
>> a
>> given pin size, taking into account current requirements, whether the part
>> is to be wave soldered or hand soldered, and whether the board is double or
>> single sided.
>>
>> I would like some sort of guideline for reference, but would also like to
>> hear anyone
>> else's 'rule of thumb' methods.
>>
>> Regards,
>>
>> Mark Holmes
>>
>> [log in to unmask]
>>
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