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April 26, 2021

Moisture Barrier Bag Calculation

For calculating the life of moisture barrier bags used for long-term storage, I need to give the initial volume of the "vacuum-sealed" moisture barrier bag as input to one of my calculations.

After vacuum sealing the MBB, it occupies the shape of whatever object was sealed inside in such a way that the thickness becomes near zero. So, how do I calculate the volume of vacuum-sealed bag?

S.R.

Expert Panel Responses

We solved a very similar issue by immersing the irregular shaped sample in a measured volume water. The volume of water displaced is the volume of the object.

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Mitch Holtzer
Director of Reclaim Business
Alpha Assembly Solutions
I've been in the soldering materials/applications industry for 25 years. Since joining Alpha, Ive been the global product manager for preforms, wave soldering flux, solder paste and more recently the Director of the soldering materials reclaim business.

Please use J-STD-033 for calculations. The calculations is not based on the collapsed bag, but the bag volume regardless of sealed or unsealed.

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David Cormier
Engineering Manager
Circuit Technology Center, Inc.
Manufacturing Engineer of 20+ years. Involved in Industries relating to all sectors of defense, Commercial product Industries, RF - Microwave and Semiconductor industries. Vast knowledge and experience relating Mil-STD’s, IPC-STD’s, EAI-STD’s, GEIA-STD’s, J-STD’s and MIL-PRF-STD’s.

The most common way to find the volume of an irregular shape is to submerse it in water and note its displacement. This seems a bit counterintuitive since the goal is to keep the parts dry, but if the MBB is sealed, it should not matter to give it a quick dip.

However, I'm sure a good estimate of length x width x height (even if only a few mm) would be good enough for your calculations.

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Paul Austen
Senior Project Engineer
Electronic Controls Design Inc
Paul been with Electronic Controls Design Inc. (ECD) in Milwaukie, Oregon for over 39 years as a Senior Project Engineer. He has seen and worked with the electronic manufacturing industry from many points of view, including: technician, engineer, manufacture, and customer. His focus has been the design and application of measurement tools used to improve manufacturing thermal processes and well as moisture sensitive component storage solutions.

Take the largest assembly that fits inside the bag and then vacuum-seal it.

Second, change everything to mils, for example a 6 X 8 inch bag now is 6000 X 8000.

Third, measure the bag thickness including component. Let's say is 25 mils.

Fourth, multiply 6000 X 8000 X 25 = 1200000000 cubic mils.

Fifth, convert to cubic inch = 1.2 cubic inches. You can then convert the result to other volume measurements.

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Edithel Marietti
Senior Manufacturing Engineer
Northrop Grumman
Edithel is a chemical engineer with 20 year experience in manufacturing & process development for electronic contract manufacturers in US as well as some major OEM's. Involved in SMT, Reflow, Wave and other assembly operations entailing conformal coating and robotics.

I'm not sure of what he is referring to when he states "volume of vacuum-sealed bag?" It's nebulous. Without knowing what he is seeking I can't answer the question.

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Jerry Karp
President
JSK Associates
Based in. Northern California since 1971. Founded JSK Associates in 1979. Actively involved in soldering, cleaning, chemistries. 30 years experience in EOS/ESD control.

We solved a very similar issue by immersing the irregular shaped sample in a measured volume water. The volume of water displaced is the volume of the object.

image
Mitch Holtzer
Director of Reclaim Business
Alpha Assembly Solutions
I've been in the soldering materials/applications industry for 25 years. Since joining Alpha, Ive been the global product manager for preforms, wave soldering flux, solder paste and more recently the Director of the soldering materials reclaim business.

Reader Comment
Vacuum sealing is to keep moisture in products. (think freezer burn in food) Do NOT vacuum seal electronics because you want to do the opposite, you want to remove moisture. If you vacuum seal then the moisture has no path to get to the desiccant. Also the vacuum can draw moisture through the moisture barrier bag and poke holes at sharp corners. Lightly evacuate the air, and then seal. If the bag conforms to the contents then you have taken out too much air.
Stephen Olan, Stim Canada

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