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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Brian Ellis <[log in to unmask]>
Date:
Tue, 3 May 2011 08:57:44 +0300
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text/plain
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text/plain (186 lines)
The bar seems to raise itself at times, after the sixth single malt. As 
for the floor lowering, five suffice before it moves all over the place.

Brian

On 02/05/2011 20:30, Whittaker, Dewey (EHCOE) wrote:
> 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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