I just finished doing this to determine the optimum bake time after wash to ensure that any populated CCA is dry prior to test.
The time required is about 1 hour at 105 deg. C., and this varied only between 30 minutes for a simple CCA with 3 or 4 large planar components (64 pin QFPs or 15 mm square BGAs) to 1 hour for a complex CCA (40" wide, 36" high) with 19 3600-pin sockets made of FR4 that held water due to capillary action. I used a precision scale that I leased.
Nearly all CCAs will be completely dry in 1 hour. Conversely, nearly all CCAs retain some surface moisture after 30 minutes.
The key factor is how long it takes the PWB surface to heat up to 105 deg. C, which is just above the point at which the water turns to steam.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Saturday, September 11, 2010 1:54 PM
To: [log in to unmask]
Subject: [TN] Weight of water on board after rinse / blow off.

Hi,

 

 If I had a sensitive scale I would try this myself, I was wondering if
anyone out there could try this simple experiment.

 

Goal: Get an idea of how much water is left on a board after rinse and blow
off.

 

 If someone could take a board with parts on one side, rinse in water, then
make these measurements.

 

1.    Weigh a PCB with parts on one side. Record size and weight.



2.    Rinse board under water spray.



3.    Shake off free water then measure weight of board.



4.    Blow of water with air gun then measure weight.



5.    Oven dry then weigh.



 I realize there is a lot of variations in PCBs and this is controlled test
by any means. But I am curious to get a first order approximation.

I would love to see the numbers.

 

Thanks,

Bob Kondner



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