Leif Erik Laerum,

Circa 1994, in a previous life, we did the same thing on various board
materials to see how much moisture they absorbed. If memory serves
correct, we baked out the boards at 125C for a few days to remove any
moisture, placed them in ambient to absorb moisture, then weighed them
with a Mettler balance.

We did one more thing that was of interest to us. After weighing, we
baked at 125C the boards and pulled board samples every 15 minutes and
weighed them to see how much moisture remained on the board. After about
1 hour, the amount of moisture on each board material was minimum. It
was the kind of thing that I wish I kept the data and wrote a paper on
because since then, that subject has come up from time to time.

Hope this helps.

Good Luck.

Lee Whiteman, PMP
Senior Member Engineering Staff
L-3 Communications East
Telephone: (856) 338-3508
FAX: (856) 338-2906
E-Mail: [log in to unmask]
 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leif Erik Laerum
Sent: Wednesday, October 14, 2009 12:45 PM
To: [log in to unmask]
Subject: [TN] Weighing PCBs

Technetters,

We would like to have the capability to weigh PCBs in order to evaluate 
moisture content. IPC-TM-650 2.6.28 (proposal inside IPC 1601 (draft) ) 
suggests I need a scale with accuracy down to 0.0001g. I have a hard 
time finding something and I was wondering if anyone has "real world" 
experience weighing PCBs and what type of scale they use.

I have a 12 layer 8" x 10" board that weighs around 4 oz. If we assume 
for sake of argument that this board has reached it's maximum moisture 
absorption level. After baking this bone dry, what percentage (ballpark)

weight reduction should we see?

Any advice is appreciated.

Thank you.

-- 
Leif Erik Laerum

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