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August 2009

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Subject:
From:
Joyce Koo <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Joyce Koo <[log in to unmask]>
Date:
Fri, 14 Aug 2009 10:09:56 -0400
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Don't check, just vac bake and test reflow 100 after.  Put back in your cabinet with additional absorbert such as mitsubishi stuff. My 2 cents. 
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----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Fri Aug 14 09:52:43 2009
Subject: Re: [TN] How to check absorbed humidity in IC packages.

Checking the weight does not work because minute variance in the
material weight (solder ball volume, for example) can represent tons of
water.
Checking the weight only works for determining the rate of moisture
adsorption or removal.
Unfortunately, I don't think there is any way to tell what the moisture
content is just by weighing one unit and comparing it to one that has
been baked out.
What you can do is initially weigh a sample, say three or four from each
nitrobox, bake them for 1/2 hour at 105 C, weigh again, bake again for
another 1/2 hour, and weigh again. If there is a significant delta in
the initial reading, the second reading, and the third reading, that may
indicate significant moisture adsorption which would mean you may want
to bake everything. On the other hand, if the d/dt is constant,
indicating very little weight change over time, then the rate of
moisture removal is very small, indicating that the parts are relatively
dry. This is essentially what you are already doing, and while I
understand you don't like it, it is probably the best method. The rate
of removal indicates where the moisture content is on the curve.
By the way, perhaps you should look into getting dessicators (McDry
boxes). No plumbing required, no nitrogen required. You can move them
wherever there is 110VAC, and they will actually serve as a long term
bake process without the oxidation issues. They pay for themselves very
quickly. Not very expensive, perhaps 5K for a very large one.
Besides, I never did like putting a bunch of expensive ESD parts inside
of a Plexiglas box. Too easy to build up a charge. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
Sent: Friday, August 14, 2009 7:51 AM
To: [log in to unmask]
Subject: [TN] How to check absorbed humidity in IC packages.

We have a number of Nitrogen cabinets for all SMT components, reels,
trays, boxes etc for BGAs, FPBGAs etc...all kind of. The Nitrogen did
not flow as usual today, and flow meter did not alarm. We found a
regulator issue.  The cabinets have been without Nitrogen for a week or
more. What is a simple and reliable way to check the moisture content of
the components? What sample size do you use? We have taken some five
superBGAs, some 20 QFPs and and likewise from a number of cabinets,
measured the weight on a 3 decimal balance and placed the samples in a
oven at +125 C for the weekend to pass. And we will check weight again
on Monday. I'm not happy with this method. Anyone having better idea? To
bake out all and everything would take a long time. 
/Inge
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