Another point you may wish to consider: how many guys sitting in front of the CAD
screen doing the placement of components on the board have the slightest clue about
cleaning it after soldering? A poorly designed assembly may be manufactured using
perfect components and the very best modern technology, but if it cannot be cleaned,
you will never achieve hi-tech reliability. And, in my 40 year's experience of
cleaning, very few of the guys actually doing it, or their bosses, have much clue, let
alone the designers. Viva concurrent engineering with people who know what they are
doing.
Brian
joyce wrote:
> Dave,
> agree with you about the testing...in order to select a new components for
> the design, the overall components design spec shall be considered too...new
> components also has its design spec. for material selection and
> interconnect, and targeted market (intended use)..If you are lucky, you can
> package the components per your own spec...(if you have capability or you
> are a large company = standard setting type)...the grandfather clause is
> related to the product (assembly) application environment, which changes
> relatively slow (lets not talk about 15 or 20 years, shall we?) compared to
> fast spinning of new components (when was the last Intel P3 version?). I
> still use those classification for select the protection methods for product
> for following reasons:
> (1) the classification is still applied for old product (15 to 20 years life).
> (2) the environment is not changed that much (building code or out door
> environment=beside globle warming or cooling...however, the acid release
> from the plywood did has impact on the storage and other equipment packaging
> concerns). Agree that Asia and Jungle do exceed the old classification (at
> least not the old days of design consideration) in some sense, required
> modification (wait for more data come out...I believe someone did wonderful
> study of the humidity and dust conditions far east).
> (3) Trade-off for cost evaluation is necessary. If the box is completly
> sealed, and system package design take care of the temperature swing, you
> can use class 1.x for the sub-assembly. (ready to use or re-use some of the
> off-the-shelf design can cut the cost for using such an practice. Best
> example is the ruggedized computer for Harsh environment=COTS).
> (4) You are right! the classification required baseline to support its
> effectivness.(material, style of package, reliabiity test data, components
> data base, etc.). New components and new technology shall be added to the
> data base (old and obsolete one shall be eliminated)...It is on-going
> "growing" process, just like human being (my poor old soul!)...Some company
> has good data...The others are located in someone's head (sometimes just
> want to "download" their database before they retire...It is very
> difficult...I am sure someone can recall trips to retired "cheif" cottage
> for "friendly chat over the beers".
> (5) there are lot of good work being done in the 60-80s regarding the
> packaging design and reliability (some of them follow the classification).
> Most of the "new work", like flip chip, CCGA are started in 80s. My
> personal believe is, start from the basics and build up. We did send a man
> to the moon.
> Thanks for your comments.
> jk
> At 06:51 PM 1/1/00 -0700, you wrote:
> >Joyce,
> >
> >Pardo me for jumping in here ( because I started all this I feel
> >obligated ) but you
> >brought out a very critical point.
> >
> >"Environmental exposure classification for electronic packaging are well
> >defined based on my knowledge (can't remember the document name...it has
> >been used so much..almost a "grandfather" clause)."
> >
> >Electronic circuitry, components and materials are changing so rapidly
> >that these types
> >of classifications and "grandfather" clauses can and do create
> >expensive, sometimes
> >dangerous situations. The basic problem is there does not appear to be
> >any baseline information, tests, or test equipment using combined
> >environmental conditions. This
> >results in very limited testing, disputes about the relevance of the
> >testing methods,
> >diverging views of the test results, and confusion over what needs to be
> >done.
> >
> >A very poor situation at best. There needs to be a starting
> >point/testing method used as a
> >reference to build on. Otherwise the result is ever expanding chaos.
> >
> >If you have not done so please read my response to Mel Parrish (from
> >EMPF ) under
> >this "Harsh Environments?" thread.
> >
> >Thank you for your time.
> >
> >D. A. Douthit
> >
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