I have dessicated components such as these by leaving them in McDry
dessicators for about two weeks (at room temp). The dryboxs will
eventually remove the moisture to a content less than 15%. You can
verify this by renting a precision scale, soak a few of the parts in a
humidity chamber, then weighing these parts individually to establish
the saturated average weight, then drying them in an oven for 24 hours
@105 C to get their average dry weight. Then leave the balance in the
drybox for at least a week and take them out and weigh a sample. If the
average weight is close to the previously established dry weight, you
have verified their dry condition. For most component types, if you get
the moisture content below 20% or so you have removed any probability of
popcorning during reflow. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Collins
Sent: Thursday, December 01, 2005 8:04 AM
To: [log in to unmask]
Subject: [TN] moisture bake-out of ICs in tubes

Hello Technet!
I've got a pile of ICs received in tubes, that are MSL 3 and have been
exposed to ambient conditions.  Thus, the parts need to be baked out.
My question is this: if I want to bake them in the tubes (not take them
out of the tubes), what lowered temperature / longer time can I use?
The quantity means it would be very painful to take them out of the
tubes, and I know the tubes won't withstand 90C / 2 days, but the 40C /
28 days alternative per J-STD-033 (body <= 2mm, per table 4-1) is not
great either.  How can I calculate a happy medium between these two
time/temp combinations?

I do know this has come up on Technet before, but I can't find it in the
archive.

Thanks!

regards,

Graham Collins
Process Engineer,
L-3 Communications Electronic Systems Inc.
Halifax
(902) 873-2000 ext 6215

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