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December 2001

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Subject:
From:
"Sauer, Steven T." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 11 Dec 2001 09:10:09 -0500
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Good morning Peter,
I'm sure Dave Hillman will provide the most accurate response (IMHO) but
until he comes around later in the day, I'll give my $.02.
The first thing is to determine if the components are solderable upon
receipt (reference J-STD-002) by performing a solderability test.  If the
leads/terminations pass the solderability test and no additional
conditioning is performed, the components should be used within 120 days
(guidance information developed under MIL-STD-2000 and predecessors).
Longer storage can occur based on packaging, temperature, humidity and air
particulates (i.e. dust, sulphur dioxide, chloride, ammonia).  Previous
guidance suggested that storage could be extended if storage conditions do
not exceed 25°C and 50% RH, and sealed containers/bags are used.  One note
of caution is to ensure the storage containers/bags do not introduce
contaminates (silicones, sulphur, polysulphides, etc.,) to the components
that could degrade the solderability.
As you mentioned, nitrogen storage is a good option, as it will minimize
oxidation formation dependent on the purity and temp/humidity control, but
this option comes with a cost.
To summarize:
        - impose a solderability (coating durability) requirement on
suppliers; component packaging requirements
        - verify solderability upon receipt or obtain certificate of
compliance
        - develop FIFO material control
        - prepare for storage (repackage if necessary; original supplier
packaging is usually suitable)
        - control environment
        - periodically perform solderability tests to determine adequacy of
methods employed above.

Good Luck!

Steve Sauer
Mfg Engineer
Xetron Corporation

-----Original Message-----
In general, what is the standard shelf life for the normal PTH and SMD
components like DIP IC's, SOIC's, PLCC's?

Assuming that they are non-MSD critical, what would be the proper
storage method to ensure good solderability is being preserved (such as
nitrogen storage chamber)?

How significant is the impact of storage conditions (e.g. humidity,
expose to ambient) and shelf life have on the solderability of component
leads?


Rgds,
Peter


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