The difficult part of your question is the phrase
"proper value". In my opinion a good designer should
do two things:
1) determine the MINIMUM acceptable pad diameter based
on some logical scientific approach.
2) ADJUST the minimum (IF NEEDED) to match your
products to particular manufacturing needs

As for the MINIMUM, the approach that makes the most
sense to me is the one suggested in IPC-2221. since
the MINIMUM goal is to have a good plated hole with at
least a little bit of copper pad around it (no
breakout), take the drill size, and a minimum amount
of copper all around (called annular ring, at least
one mil? so add 2) and then add enough to allow your
fabrication vendor some "wiggle room" since
manufacturing processes aren't perfect (fabrication
tolerance).

As for the ADJUSTMENT, some designers need more space
so they will REDUCE the minimum but add a teardrop to
protect against breakout. Others will ADD to the
minimum to allow for rework or hand soldering. The
result is not the issue, the designer taking into
account the needs of others down the line is what is
crucial.

The tricky part is the fabrication tolerance. You may
want to speak with your fabrication/assembly partners,
but in your case I would think you are going for high
volume and cheap price (consumer products), so I would
give the vendors as much leeway as possible (add more
copper) if the boards aren't too dense.

Just don't go below the minimum unless you are
prepared to defend your decisions!
(especially if reliability problems arise or vendors
are upset with you for making their lives difficult)!

Jack

p.s. Just for the record, I believe that adding a
generic multiplier to a hole size is bogus, unless you
have studied your design needs and manufacturing
processes enough to develop your own "rule of thumb"
(and be warned that explaining a board problem by
saying "I did it that way because some old fart did it
that way" usually doesn't make you look so good)
And from my experience, pads aren't used for "heat
dissipation".

onward thru the fog...


--- Ahmed El-Sanhoury <[log in to unmask]>
wrote:
> All
> When we have a passive component used in consumer
> electronics application
> (TV application single layer),which has a hole
> diameter equals to 1.2mm,what
> is the proper value of pad diameter to satisfy
> maintenance and reliability consideration.
>
> Thanks
> A.sunhoury
>
>
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