Paul,

There are several specifications out there but the
most common (today) is IPC-6012.  I could stop with
this single comment but I've never been accused of
stopping when I should.  [My wife thinks I should go
to on-and-on-anonymous because I go on and on and
on...:)]

We are faced with this problem everyday.  If you call
out IPC-6012 do you really mean it?  '6012 contains
specific requirements for cross sectioning, testing,
inspection etc.

Let me illustrate the potential problem(s) associated
with calling out something like 6012.  Let's say you
have a really cool design, you've worked with your
board house and have maximized panel layout, you are
getting the most value for the dollar by placing the
most number of boards on the suppliers panel.  Then
you toss in 6012.  Whoops, the fabricator must reduce
the number up on a panel to make room for the coupons
you are asking for.  You will lose some panel
efficiency.  Then you have to pay for the testing
(micro-sectioning) and to add insult to injury the fab
may charge you more money because they are going to
reject some of your boards that they would not have
lost if you hadn't called out '6012.  (And all you
wanted to do was reduce the number of notes called out
on the print.)

What many companies do is call out IPC-A-600.  This is
an incorrect callout because it doesn't specify
anything.  It simply states a condition and shows
acceptability, it never says I have to look at the
attribute.

If '600 gives criteria for innerlayer separation at
the post but you don't ask me to look at innerlayer
separation at the post (because '600 doesn't tell me
to) then I have met your requirement, or have I?  You
didn't ask me to look (so I didn't) but I processed
your boards as if I would have looked if you had asked
me....Confused?

What is probably happening right now is that you are
issuing a print to your supplier and they are looking
for any unusual notes you might have on the print.
(Etchback ,UL listing etc.) If they don't see anything
unusual they run the board, just like every other
board. If you wanted to test my theory submit an RFQ
to several board houses with NO NOTES, just Gerber
data.  See if anyone asks any questions? Assuming they
don't ask you the fine points like barrel thickness,
bow and twist etc. you have found an answer.  We all
(very generally speaking) make boards to the same
'general' guidelines.  (btw these are mostly tied in
some manner to IPC-XXXX)

Two final points - If your application is critical I
would pay for the coupons and the requirements stated
in IPC-6012, either class II or III.  If you are happy
with the quality you have been getting and want to
eliminate some notes, post the notes you want to
eliminate and I'm sure the board shops will tell you
what you need and don't need to call out...

I hope this helps although I'm sure after re-reading
it I will get a lot of grief over some of my points...

Pete Menuez








--- Paul Bannister <[log in to unmask]> wrote:
> I am trying to update and standardize the notes that
> appear on our printed
> circuit board fabrication (drill drawing) drawing.
> The current drawing has
> over 20 notes detailing things like hole
> registration electroplating
> thickness, wrap and twist ECT.  I would like to
> reference one specification
> that covers all aspects of the board fabrication and
> eliminate all the
> specific notes.
>
> Is there and industry standard on what needs to be
> specifically called out
> on the fabrication drawing and what is the best
> specification to reference
> (IPC-A-600?) for fabricating 4 layer commercial
> grade surface mount PCB's.
>
>
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