What is the Expected Shelf Life of ESD Control Bags?
There are many ways to manufacture an ESD shielding bag with low charging properties on the inner and outer layers. This is the first factor to consider. Some processes achieve shielding values via a buried metal layer. The metal layer is laminated between two layers of polyethylene. This process makes a very robust and long-lasting product in terms of shielding values as per ANSI/ESD S541-2018, the electronic industry’s most recognized standard for ESD packaging. Still, the metal layer is exposed to oxidization if not stored properly and subject to extreme climate or moisture.
To achieve the outer and inner low-charging properties, a topical anti-stat solution is sometimes used. This provides the outer and inner resistance readings of >/= 1 x 10^4 to < 1 x 10^11 ohms as called out in ANSI/ESD S541-2018 packaging standard. This property is the most vulnerable to change and should be tested frequently.
End users cannot always provide a climate and humidity-controlled atmosphere, so it is recommended that bags be tested periodically per the S541 standard and dispose of any materials that are found to be questionable. As a best practice, products can be logged by purchase date or lot number and an annual spot check audit created to assure that bags are still in compliance. Using a FIFO (First In First Out) process is critical in keeping your inventory fresh. You can imagine that there are 1000’s of variations to consider when we discuss shelf life. Heat, storage rack conditions, travel method and local climate to name a few, so the points to remember are:
- Avoid extremes
– Hot, Cold, sunlight, moisture
– Add controls when possible
- In a controlled environment, ESD bags can have 5 years of proven shelf life
- Follow the FIFO process as a best practice for inventory
- An audit should be performed annually or prior to use as a best practice to ensure that your devices are getting the best protection
- If the bags are questionable, recycle the product at your local recycler and order and new lot
In conclusion, for best results, bag inventory and reusable bags should periodically tested for surface resistance and added to your Compliance Verification Plan It is recommended that bags be stored in their original packaging. The user must determine the suitability for use of an ESD bag for their particular application. Bags should be stored in a dry, well ventilated room with a reasonably consistent temperature of 68°F (20°C) and be protected from exposure to direct sunlight. Bags should not be stored in ultraviolet sunlight, moisture, or heat because the aluminum shielding layer could oxidize if exposed to these conditions. Bags should be evaluated by the user to determine acceptability for the user’s application. Mishandling or improper storage may render an ESD Bag unusable to perform its function. ESD Bags that are ripped, torn, or scratched should be discarded.