Hi Werner,
        Thanks for taking the time to respond to my query.  Let me expand on
the rational behind our plan.

        Our product is planned to sit in a controlled environment for up to 20
years before being activated.  We found an article that addresses a similar
storage condition for plastic encapsulated microcircuits.  But, the product we
manufacture has more components than just PEMs (i.e. chip caps and laminate
substrate).  The article gives an acceleration model that represents the
influence of temperature and humidity and sample test condition of 130 C and
85 %RH.   We wanted to avoid a 130 C temperature due to the Tg of the base
laminate...getting too close for comfort.  That's when we looked at lowering
the temperature to 120 and increasing the humidity to maintain the
acceleration.  It sounds like you're suggesting 98 %RH may be too hard to
control.  Maybe we should look at lowering it to 85 %RH.

        So, I guess I'm looking for any objection to following the same test
methodology for this more complex package.  Now with a condition of 120 C and
85 %RH

Thanks again for any input.

Glenn Pelkey
Quality/Reliability Engineer


Ref:  IEEE Transactions on Reliability, Vol. 45 No. 1, 1996 March.  "The
Appropriateness of Plastic Encapsulated Microcircuits in a Specific
Wooden-Round Application," John R. Gardner.

[log in to unmask] Wrote:
|
| Hi Glenn,
| A couple of comments:
| (1) there is now way I know of that any HAST of the type
| you describe can be
| related to 20 years of operation,
| (2) the water vapor pressure at 120C, 98%RH is huge and is
| likely to cause
| all kinds of things to happen to your PWAs that would not
| happen in realistic
| conditions,
| (3) you must have an incredibly well controlled humidity
| chamber in order not
| to get condensation somewhere in the chamber--and then of
| course all bets are
| off anyway,
| (4) a HAST really is designed to serve a totally different
| purpose than an
| accelerated reliability test; HAST is designed to be used
| on prototypes to
| make a design more robust, while accelerated reliability
| tests are designed
| to cause damage by the same damage mechanism expected in
| operation or storage
| on an accelerated basis WITHOUT the introduction of any
| extraneous damage
| mechanism(s).
|
| Werner Engelmaier
| Engelmaier Associates, Inc.
| Electronic Packaging, Interconnection and Reliability
| Consulting
| 23 Gunther Street
| Mendham, NJ  07945  USA
| Phone & Fax: 973-543-2747
| E-mail: [log in to unmask]
|