Yes, but the person asked if he should MAXIMIZE the pad sizes because that
is what IPC says you should do in IPC-2221 9.1.1, but I have never heard of
anyone doing that
(and thanks for the ego boost)
Jack (the talented and experienced but still somewhat humble layout guy)
-----Original Message-----
From: [log in to unmask]
[mailto:[log in to unmask]]
Jack,
First, let me correct your self perception: You are NOT
"just a lowly layout
guy"! ;-) No need to be humble here. Stand up and take
pride!!
Second, it is my understanding the IPC makes recommendations
for pad sizes which
will accomodate most every vendors' process. So, perhaps
the best thing to do
is start with that but then go to your assembly shop and ask
their opinion of
whether the pad size(s) is/are suitable as is, or if it
could be reduced to some
degree. I personally use the guidelines given by SMT Plus
as it seems to be a
tweeked basis of the IPC standards and have had no trouble
whatsoever.
Best regards,
Bill Gebhardt
Electrical Engineer/PCB Designer
Overland Data Inc.
San Diego, CA
Jack Olson <[log in to unmask]> on 09/24/99 09:16:48 AM
That is a really good question, but I don't know how much
response you will
get, because in my experience it is usually the opposite
that happens. The
assembler wants to reduce the pad size and corresponding
amount of solder
paste applied. I've never thought about how IPC says
minimum, and how that
could be interpreted to mean that you should make everything
bigger if you
can, because nobody does that! Everyone wants smaller
smaller smaller
(except maybe big pads on through-hole for high-power
components, or
something like that). So maybe you should take that "land
sizes should be
maximized" statement with a grain of salt, since I believe
the IPC
recommendations are already bigger than anyone else's out
there. (correct me
if I'm wrong you guys, I'm just a lowly layout guy)
-----Original Message-----
From: Mark Holmes
[mailto:[log in to unmask]]
Sent: Friday, September 24, 1999 1:09 AM
Subject: Pad Sizes for good solder
Joints
All the data I have regarding pad sizes
(e.g. IPC-2221
9.1.1) give examples
on how to calculate Minimum pad sizes,
usually from a PCB
fabrication
standpoint. IPC-2221 states that all lands
and annular ring
shall maximised
wherever feasible, consistent with good
design requirements
and electrical
clearance requirements.
My questions are: How do I determine the pad
size that will
give me the best
soldered joint?
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