Even with the best intent on your part to justifiably "raise the bar",
this is a potentially false perception due to your supply chain
implementing a "lowering of the floor" strategy.
This is on a par with me trying to explain how clever and witty
"Deweyisms" are to someone when English is not their native language.
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brooks, Bill
Sent: Monday, May 02, 2011 9:52 AM
To: [log in to unmask]
Subject: Re: [TN] "The Curse of IPC-A-610 and IPC-J-STD-001" - opinion
piece by James Smith
I have been 'listening' to this thread and it kind of struck a nerve.
'Designing to minimums' or to 'just meet a spec'. Not just meeting
minimums on the low side of the 'bell curve'... but DESIGNING to the
minimums... I have seen this happen a number of times where someone
reads a MIN. requirement spec and then designs to it. WRONG! Only
inexperienced folks who don't understand tolerances' do this sort of
thing.
When we train PCB designers we drill it into their heads... don't forget
the tolerances. Worst case means WORST case....even after everything
else has gone to the extreme limits... If you want reliability you need
to design in some 'de-rating' into your tolerance calculations... give
yourself some 'head room' for things to go wrong... a good design will
still fly even if everything else has failed... by design. It doesn't
happen by accident.
I believe board manufacturers use the IPC standards as a way to commonly
agree what minimum acceptance they can 'get away with' process-wise...
but if their customers aren't designing their products to achieve the
results needed then they are going to just make a lot of scrap.
Tolerances statistically will get you every time!
Maybe what this guy James Smith was 'trying' to say is, (even though he
did it badly), that he needs to 'raise the bar' of the design higher
because he is seeing the quality of the boards coming in and they aren't
acceptable to him or his company... even though they are meeting the IPC
standards. Maybe he needs to hold his vendors to a 'higher standard' or
or rather a higher design requirement... ??? Typically when the min
requirements stated in an IPC standard are not acceptable to us for our
product, we put an exclusion or acception in the notes of the drawing to
say how our requirements differ from the spec. IPC specs are a
baseline... from there you can design in the higher quality through your
DESIGN requirements. DON'T design to the minimums... BAD DOG... TIME
OUT... NO COOKIE...
Frankly, James is blaming the wrong guys... it's not the IPC
standards... it the design and quality teams not setting the
requirements high enough for his product.
Imho :)
Best regards,
Bill Brooks | Datron World Communications, Inc.
PCB Designer/Engineer | Office: 760-602-7004| Fax: 760-597-3777 |
[log in to unmask]
3055 Enterprise Court, Vista, CA 92081 | www.dtwc.com
Performance You Require. Value You ExpectTM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Woolley, Mark D.
(Mark)
Sent: Monday, May 02, 2011 7:16 AM
To: [log in to unmask]
Subject: Re: [TN] "The Curse of IPC-A-610 and IPC-J-STD-001" - opinion
piece by James Smith
Sorry, Let me try again. (I don't know what happened the last time.)
Being a slave to "Standards" is not where we should be as an industry.
The "standards" are, in reality, minimum acceptable criteria. I often
hear manufacturers state that they build to a standard or their product
meets the "standards."
However, as I inspect these products per the same standards (mostly
IPC-A-600 and IPC-A-610), I see that while the product might meet the
"Standards" it was manufactured along the minimum edge of acceptability
per the standard.
An example: Visible, opaque particulates embedded in the solder mask
might meet the IPC-A-610 standard if they do not encroach on certain
areas of the PWB. But what does finding multiple occurrences of
particulates in the solder mask mean in terms of the PWB manufacturing
quality? Unless you are dealing with military classes, in mass
production a close visual inspection can only be performed on a limited
number of units. If those units barely meet the standard what does that
indicate about the remainder? (How many particulates might be embedded
within the PWB layers where they are not readily visible? And of these
how many could eventually cause a short?)
Meeting the Standards is not sufficient to build a reliable product.
The standards must always remain as the minimum acceptable criteria not
as the expected mean or median product.
The IPC committees put long hours into each specification to clarify
points and make the items as understandable as possible. IPC-A-610E
(and later revisions) is a great asset. Pictures showing both the good
and the bad are presented. But never is it stated in the specification
(that I have read) that a process that consistently produces products at
the edge of acceptability (per the standard) is acceptable to industry.
Having said that I must agree with Brian's statement:
"In short, Standards, used appropriately, can help, as far as possible,
to perfect reliability for a given application. Used inappropriately,
they can drive up costs dramatically ..."
There needs to be common sense in the application of the standards, both
from a user and a manufacturer point of view. Customers' don't want
manufacturers to hide behind the "Standards' Wall" when confronted with
issues with their products. And the products should be manufactured in
a manner that places only the smallest percentage, (ideally none) of
products below these limits.
mark
Mark Woolley |PTRL Laboratory | Avaya | 1300 West 120th Ave |
Westminster, CO 80234 USA |
Voice (Lab): (303) 538-2166 | email: [log in to unmask] |
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