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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