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April 2003

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Subject:
From:
Francois Monette <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 28 Apr 2003 13:31:14 -0400
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As you can tell the question of shelf life and storage conditions for
electronic components and assemblies is a very complex issue.

One of the criteria to consider is the fact that most ICs are classified as
moisture-sensitive devices (MSD). This means that the components are shipped
from the manufacturer in a sealed dry bag with desiccant and a warning
label. The label includes two important pieces of information relative to
the safe storage of these components. First the seal bag date provides an
indication of the actual shelf life of the sealed bag itself. Since a
Moisture Barrier Bag is never perfectly hermetic, it will absorb some
moisture from the ambient air and eventually the desiccant will saturate and
moisture will exceed the safe level for the components. By definition, the
packaging guidelines included in the joint IPC/JEDEC standard J-STD-033A
guarantee a shelf life of at least 12 months at conditions of less than
40C/90%RH. This is conditional upon using the proper type of dry bag (Water
Vapor Transmission Rate WVTR is less or equal to 0.002 gm/100in2 in 24 hres
ar 40C) and the proper amount of desiccant (Ref. J-STD-033A, section
3.3.2.2).

The second important information is the maximum floor life of the components
once they are removed from the sealed bag, prior to reflow. This can vary
from a few hours to a few months. An important consideration is the fact
that if you are re-sealing components that have previoulsy been exposed to
ambient conditions, the moisture gradient that was previoulsy absorbed will
continue to diffuse towards the die interface and may eventually exceed the
critical limit. In other words, re-sealing MSDs in a dry pack does not
necessarily stop the floor life clock and your components may expire while
they are stored in a re-sealed bag. This would be applicable in the case of
assembled PCBs being placed in re-sealed dry bags for example. Of course it
is always possible to re-set the floor life clock by completely baking the
components and boards prior to re-sealing them in dry bags. Once again the
guidelines for baking components and boards are included in J-STD-033A.

On the subject of vacuum, this is not required for dry storage of MSDs. A
simple heat seal with the proper quantity of desiccant will provide the
protection required.

I suggest that you familiarize yourself with J-STD-033A since the
Moisture-sensitive components will most likely be your most critical
components. This document is a free download at www.jedec.org. Once you
define a process that meets the requirements for MSDs, everything else
should be much simpler.

I hope this information is helpful, do not hesitate to call or e-mail if you
have any questions on the above.

Francois Monette
Cogiscan Inc.
Tel : 450-534-2644
[log in to unmask]
www.cogiscan.com


------------------------------

Date:    Sun, 27 Apr 2003 10:27:35 +0300
From:    Reuven ROKAH <[log in to unmask]>
Subject: Expiry time in vacuum package

Hello Technet forum,

Pls reply how long Active component of assembled PCB / system can be stored
in sealed / vacuum package before use / operating the system / component.


Best  Regards

ROKAH Reuven

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