Ask the Experts
January 17, 2023 - Updated
September 11, 2012 - Originally Posted

Zip-lock Bags vs. Heat Sealed Bags

Are zip-lock bags vs. heat sealed bags an acceptable option for storage of moisture sensitive components?


Expert Panel Responses

No. Zip lockbags are made from polyethylene, which moisture and other gases can transpire.

Rick Perkins
Chem Logic
Rick Perkins is a chemical engineer with more than 33 years of Materials & Processes experience. He has worked with Honeywell Aerospace in high-reliability manufacturing, as well as with several oil-field manufacturing companies. He also has a good understanding of environmental, health, and safety regulations.

The correct answer would be no.

From the fact that air cannot be fully evacuated from a zip lock ESD compliant bag the contents would be subject to moisture absorption.

The proper method for storage is to evacuate the bag of all air via a dry N2 purge & then vacuum seal the bag. The placement of a desiccant pack & indicator card in the bag is also recommended.

Now that the"proper method" is outlined the other answer is you could use a ziplock bag if the purpose was to transfer the component from stores to the production line for usage within a relatively short period of time. I would still utilize a desiccant in the zip bag as an added safety.

A comment on "heat sealed" bag. The proper bag for usage is an MVB (moisture vapor barrier)bag. This is manufactured using a thicker & more durable film than the standard shielding bag.

Jerry Karp
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.

In a word, no. When the components are placed in the Moisture Barrier Bag (MBB) we'll assume they are dry. We then rely on the desiccant and the bag to keep the environment within the bag very dry. The effectiveness of the bag in keeping moisture out depends on two things:
  1. The permeability of the bag itself
  2. The effectiveness of the seal
On both counts,"Ziploc" type bags are vastly inferior to a good MBB. A good MBB will meet the requirements of J-STD-033 with respect to permeability, and will retain a dry environment for as long as 3 years. The permeability of the bag is improved(reduced) by the metallization; it's much harder to diffuse water through a metal film than through a plastic one. The metal film is not present across the seal, so the thickness of the seal (the distance the moisture needs to travel) is important. A Ziploc-type bag has an extremely poor seal, as well as high permeability.

Fritz Byle
Process Engineer
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.

Both vacuum & heat - sealed ESD bags would actually be a perfect solution for storage purposes, client could pass Nitrogen (inert gas) prior to the sealing process.

Umut Tosun
Application Technology Manager
Zestron America
Mr. Tosun has published numerous technical articles. As an active member of the SMTA and IPC organizations, Mr. Tosun has presented a variety of papers and studies on topics such as "Lead-Free Cleaning" and "Climatic Reliability".

The question of the quality of the seal in somewhat mute once you open a sealed component bag.

Once a sealed bag from the manufacture is opened, moisture enters and begins its intrusion into the moisture sensitive components. The only real reason to keep the parts in a bag after it has been opened is to keep them safe from ESD,assuming it's an ESD protective bag, and to keep them labeled and gathered together for storage.

Unless you actively take measures to draw out the moisture from the resealed bag, you might as well leave it open. You can drop in a new "desiccant" pack or "pill"and reseal. The only problem with this is it is sometimes hard to tell if the desiccant is exhausted or not.

The best way to keep moisture sensitive components "dry" once the factory sealed bag is opened is to keep them in a controlled and monitored dry cabinet below 10% rH. This will "pull" the moisture out of the air and out of the parts. Then the quality of the bag's seal is no longer an issue. All it need do is keep the components from escaping. In fact, if the seal is too good, it will trap the moisture in the bag and your dry components will absorb it rather than the dry cabinet removing it from the air.

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.

First - Both are not acceptable provided bag is not vacuum sealed. Usually zip-lock type doesn't get vacuum sealing whereas Heat sealing type will able to get vacuum sealing.

Second - MSD part need to be sealed in moisture barrier bag not any usual bags on account of ESD through a validated vacuum sealing machine.

Subrat Prajapati
Supplier Quality Leader
Ge Healthcare
Subrat has 10 year of extensive experience in PCB assembly process optimizing for quality, process includes screen printing, wave, reflow. He has a copyright in stencil design published in Apex Expo2010 at Las Vegas US.

Reader Comment
To add to all the good comments, the Cabinet is the must efficient but expensive way to keep dry the components, especially when you have a lot of material in your warehouse, the cabinet take production space also.

zip is just on a shilding bag with out MTV material and is perfect to re-use the bag (just few time -Without mistreating the bag). for MVT the best film material is with foil and this do not use zip, at all, because the aluminum Is very thin and breaks in the zipper area, losing the vacuum.
Matias Aliseda, EXTRUPAC

Reader Comment
J-STD-033 requires the MBB be heat-sealable. There is no allowance for "zip lock"-style MBBs. Therefore, the answer has to be "no".
Rick Wyman, Benchmark Electronics

Reader Comment
I suspect the original question intended "zipper" style ESD bags, and not the SC Johnson brand, "Ziploc."

Obviously clear, polyethylene "sandwich bags" are not acceptable for anything but lunchtime. Many manufacturers of ESD static dissipative bags offer the smaller sizes with a zipper "seal." One is ESD safe, but neither are suitable for moisture control.
Alan Couchman, Process Sciences, Inc.

No, zip-loc bags should not be used for storing MSDs, for the reasons the experts say, but also I am adding two other notes: 1. Polyethylene zip-lock bags generate between 500VDC to as much as 2kVDC when zipped open (triboelectric charge from the plastic zip liner and when separating the layer of one side of the non-dissipative bag from the other).

Note 2. The statement "it is sometimes hard to tell if the desiccant is exhausted or not. The best way to keep moisture sensitive components "dry" once the factory sealed bag is opened is to keep them in a controlled and monitored dry cabinet below 10% rH. This will "pull" the moisture out of the air and out of the parts." is not entirely true. J-STD-033 does state that the original MSD bag CAN be opened, parts removed for the job at hand, and then the parts CAN be re-sealed in the original bag WITH fresh desiccant AND A NEW MOISTURE INDICATOR CARD. The new MIC will provide the status of the parts upon each opening.

True ESD bags can be opened and resealed as long as there is enough bag material to provide a good heat seal and there are no holes, as indicated by the inability to provide a good vacuum. It does not have to be a very strong vacuum, as this can both damage parts and is somewhat counter-effective because it will pull in outside moisture faster. The use of a drybox is not absolutely required if a good drypak is used but is highly recommended for a double-redundancy standpoint.

Dry-boxes are not that expensive; the ones I have been using for 20 years cost around 6K (today) for a medium size benchtop and even after that the only maintenance they need is a period replacement of the desiccant which is easily accessible and can be swapped out right in your factory at a very low cost. Nitrogen is not required to keep the RH at 5% or less.

For very long-term Legacy Program part storage the requirements are completely different from those described in J-STD-033; you DO want to use nitrogen as well as keep the parts at -40 degrees C or F, use the double bag method, getters as well as desi-pouches, etc., etc.

Richard D. Stadem
Advanced Engineer/Scientist
General Dynamics
Richard D. Stadem is an advanced engineer/scientist for General Dynamics and is also a consulting engineer for other companies. He has 38 years of engineering experience having worked for Honeywell, ADC, Pemstar (now Benchmark), Analog Technologies, and General Dynamics.
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