Ask the Experts
June 15, 2018
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 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 wouldbe no.
From the fact that aircannot be fully evacuated from a zip lock ESD compliant bag the contents wouldbe subject to moisture absorption.
The proper method forstorage is to evacuate the bag of all air via a dry N2 purge & then vacuumseal the bag. The placement of a desiccant pack & indicator card in the bagis 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 theproduction line for usage within a relatively short period of time. I wouldstill utilize a desiccant in the zip bag as an added safety.
A comment on "heatsealed" bag. The proper bag for usage is an MVB (moisture vapor barrier)bag. This is manufactured using a thicker & more durable film than thestandard shielding bag.
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 MoistureBarrier Bag (MBB) we'll assume they are dry. We then rely on the desiccant andthe bag to keep the environment within the bag very dry. The effectiveness ofthe bag in keeping moisture out depends on two things:
On both counts,"Ziploc" type bags are vastly inferior to a good MBB. A good MBB will meet therequirements of J-STD-033 with respect to permeability, and will retain a dryenvironment 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 ametal film than through a plastic one. The metal film is not present across theseal, 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 highpermeability.
- The permeability of the bag itself
- The effectiveness of the seal
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.
Bothvacuum & heat - sealed ESD bags would actually be a perfect solution forstorage purposes, client could pass Nitrogen (inert gas) prior to the sealingprocess.
Application Technology Manager
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".
Thequestion of the quality of the seal in somewhat mute once you open a sealedcomponent bag.
Oncea sealed bag from the manufacture is opened, moisture enters and begins itsintrusion into the moisture sensitive components. The only real reason to keepthe 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 gatheredtogether for storage.
Unlessyou actively take measures to draw out the moisture from the resealed bag, youmight 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 thedesiccant is exhausted or not.
The best way to keepmoisture sensitive components "dry" once the factory sealed bag is opened is tokeep them in a controlled and monitored dry cabinet below 10% rH. Thiswill "pull" the moisture out of the air and out of the parts. Then the qualityof the bag's seal is no longer an issue. All it need do is keep the componentsfrom escaping. In fact, if the seal is too good, it will trap the moisture inthe bag and your dry components will absorb it rather than the dry cabinetremoving it from the air.
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 vacuumsealed. Usually zip-lock type doesn't get vacuum sealing whereas Heat sealingtype will able to get vacuum sealing.
Second - MSD part needto be sealed in moisture barrier bag not any usual bags on account of ESDthrough a validated vacuum sealing machine.
Supplier Quality Leader
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.
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
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
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 bagsoffer the smaller sizes with a zipper "seal." One is ESD safe, but neither are suitable for moisture control.
Alan Couchman, Process Sciences, Inc.