Those are good points, and I'm glad you responded.
The original question was "what is a proper value
for..." and the answers you and others gave were all
"proper values" (acceptable) for what he was asking.

My intention was to try and provide some kind of
foundation to build on. If you understand where
numbers come from, it much easier to adjust them when
the need arises. I guess I'm just fanatical about
starting at some kind of logical basis and building
from there, instead from a random number that someone
assures me will work.

"Give a man a fish and he eats for a day,
teach a man to fish and he eats for a lifetime."

Didn't mean to sound harsh (or offend the old farts
who have been designing successfully for decades)

onward thru the fog...
Jack



--- Chris Robertson <[log in to unmask]>
wrote:
>
> 2221's AR specifications are..how to say this
> with out offending... not very good for soldered
> pads.
>
> Talking with old fart that teaches Design, I was
> given a value that I've heard for years regarding
> a SOLDERED pad. Not a via or mounting hole, but a
> Soldered pad. The value of 2 over the hole size
> was given.
>
> The Min AR specification in IPC spec wasn't designed
> to provide a solderable pad, but only to say "this
> is the bottom line". Our industry has a history of
> providing limits but not working values. This is due
> to the fact that many working values are APPLICATION
> SPECIFIC and what worked for one doesn't work for
> others.
>
> The values in IPC will actually solder ok, but the
> some assembly (not all) people will not like it and
> the
> chances of component replacement are low. Thicker
> board
> are more apt to re-soldering since there is enough
> in the
> hole to keep the plating from ripping out.
>
> These are the questions to ask...
> *Could the component be replaced - or would the
> board just
> be discarded.
> *Is space in demand on this board.
>
>
> CR
>


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