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October 2009

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Subject:
From:
"McGee, Michael" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, McGee, Michael
Date:
Wed, 14 Oct 2009 13:28:21 -0400
Content-Type:
text/plain
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text/plain (112 lines)
Leif,
A long time ago I did a similar experiment on a smaller board. I used a
laboratory balance accurate to 4 places. 
I saw a max of .1% weight gain.  
Bev is right, you need a good anti-draft shelter.

-Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Wednesday, October 14, 2009 12:06 PM
To: [log in to unmask]
Subject: Re: [TN] Weighing PCBs

Leif,
You either need to:
1) Use a smaller board
2) A cut down portion of your board 
3) Build an anti-draft shelter for a top-loading balance. 

Now the latter (top loaders) are usually good to 0.001 grams. 

You also need to consider electrostatic effects if you are going to have
board edges near the plastic containment walls of a four figure balance.


Regards,
Bev
RIM

----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Wed Oct 14 12:44:54 2009
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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