We're doing a prototype run of boards for which awareness of Moisture
Control and Moisture Sensitive components came quite late on. Components'
packaging was opened and left opened in an uncontrolled environment, so I
also insist that all MSD's are baked out at 125 deg C for 48 hours prior to
assembly and stored in a dry cabinet (5% RH and 25 deg C).
Ideally though, they should be baked out and immediatey re-sealed in their
original packaging as you describe. J-STD's 20 and 33 should give you the
info you need on this. The moisture classification really only indicates
the sensitivity to moisture absorbtion - how quickly the component reaches
it moisture limit before bake-out is required. Bake-out time and
temperature is standard, I believe, as stated above. I always prefer to
have the minimum number of thermal excursions of any kind for anything to
do with board assemblies to maximise longevity and reliability, and
continually pre-baking components that are not properly sealed in their
original packaging is anathema to me.
Peter Duncan
Grant Emandien
<gemandien@TEL To: [log in to unmask]
LUMAT.COM> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST
Sent by: Aero/ST Group)
TechNet Subject: [TN] Handling of moisture sensitive
<[log in to unmask] devices
RG>
11/15/01 05:15
PM
Please respond
to "TechNet
E-Mail Forum."
Hi All,
I am seeking advice on handling methods of moisture sensitive devices from
reception/storage to use. Components have varying baking requirements after
the packaging has been opened - is baking performed as per. manufacturer's
instructions?
One of our customers is insistent on us, as an assembler to bake
(customer-supplied) components just prior to assembly - this approach
however does impose some impracticalities on production. Our initial
counter
proposal is to receive only components in original OEM wrapping indicating
the moisture instructions and class/level and to then return bake and
reseal
(vacuum/nitrogen) excess opened material to stores - the package would also
include a humidity indicator. Our proposal is more amenable to production,
but is it sufficient to ensure device integrity? Any insights on the
approach of assemblers?
TIA
Grant
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