SCS’s upcoming webinar will review various ESD Bag test methods. With our in-house equipment, we will demonstrate how to test your bags per the most current ANSI/ESD and Mil-Spec standards.
Date: Thursday July 30th, 2020 at 10 AM PDT
Register at www.StaticControl.com
Have you been questioned by your quality manager about shelf life on ESD bags? Maybe it’s an internal quality procedure that is being written and you would like to know where the manufacturer stands on the shelf life of ESD packaging. Well today we will address the topic of ESD Static Control bag storage and the expected shelf life.
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 so I will address only the items that I convert here at SCS. In our process, I 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, I use a topical anti-stat solution. 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.
How does all this pertain to shelf-life you ask? SCS provides a Static Control Bag Storage document with a 1 year warranty from the date of purchase. I have witnessed SCS ESD bags stored in a controlled climate, well-ventilated area that have maintained passing surface resistance results after 5 yrs. on the shelf. Some customers have relied on our Moisture Barrier products to archive various critical products for as long as 20 yrs. They found through extensive testing that SCS had the highest quality and most repeatable results to trust with their archived product.
End users cannot always provide a climate and humidity-controlled atmosphere for our raw material, so it is recommended that you test your bags periodically per the S541 standard and dispose of any materials that are found to be questionable. As a best practice, you can log your products by purchase date or lot number and create an annual spot check audit to assure that your 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 take away are this:
Thank you,
Kevin Cleary
ESD Packaging Specialist – Sales
Direct Line: (919) 903-1724
A Desco Industries Brand
StaticControl.com
In a previous post we learnt how to select the correct ESD bag for your application, we want to focus on the next step: how to correctly use your ESD bag. We’ll use shielding bags as an example as they are the most commonly used ESD bags. However, the below can be applied to all types of ESD bags.
There are a few “dos and do-nots” you should keep in mind to ensure you get the most from your ESD bags. Nothing is worse than investing in all the right equipment and then using it incorrectly rendering all your efforts void. So, on that note, we have comprised a list of 5 tips for you on how to most efficiently use your shielding bags.
Shielding bags should be large enough to enclose the entire product within. The shielding bag should be closed with a label or tape. Alternatively, you can use a zipper-style shielding bag. Following this advice ensures a continuous Faraday Cage is created which provides electrostatic shielding. This is the only way to ensure ESD sensitive devices placed inside the shielding bag are protected. If you are unfamiliar with the term “Faraday Cage”, scroll to the bottom of this page – we’ve included a more detailed explanation at the end of the post.
Please do not staple your shielding bag. The staple punctures the shielding layers and will provide a conductive path from the outside of the shielding bag to the inside. Charges outside the shielding bag could potentially charge or discharge to ESD sensitive components inside the shielding bag.
If you’re unsure as to what the correct size is for your application, catch-up on this post which will provide all the required information.
When receiving an ESD sensitive device enclosed in a shielding bag, make sure you place the closed shielding bag on an ESD worksurface before removing the product. This will eliminate any charge that might have accumulated on the surface of the shielding bag.
Re-using shielding bags is acceptable as long as there is no damage to the shielding layer. Shielding bags with holes, tears or excessive wrinkles should be discarded.
Do not use a shielding bag as an ESD worksurface. Although a shielding bag is safe to use around ESD susceptible products, it is not intended to be a worksurface for product. When working on ESD sensitive devices, do so using ESD worksurfaces that are grounded correctly.
Do not use a shielding bag as an “ESD potholder” or “ESD glove”. This type of use offers no ESD protection to the product.
If you need to handle ESD sensitive devices, make sure you are properly grounded using wrist straps or heel grounders.
Some of you may have read through this post and have stumbled across the term “Faraday Cage” as you have not come across it before. We’ve also mentioned it before when talking about storing and transporting ESD sensitive items. However, we’ve never actually explained what a Faraday Cage is – so let’s rectify that!
A Faraday Cage or Faraday shield is an enclosure formed by conducting material or by a mesh of conductive material. Such an enclosure blocks external static and non-static electric fields. Faraday Cages are named after the English scientist Michael Faraday, who invented them in 1836.
An impressive demonstration of the Faraday Cage effect is that of an aircraft being struck by lightning. This happens frequently but does not harm the plane or passengers. The metal body of the aircraft protects the interior. For the same reason, a car may be a safe place during a thunderstorm.
In ESD Protection, the Faraday Cage effect causes charges to be conducted around the outside surface of the conductor. Since similar charges repel, charges will rest on the exterior and ESD sensitive items on the inside will be ‘safe’.
Examples of ESD control products that provide a Faraday Cage or shielding include Metal-In and Metal-Out Shielding bags.
ESD shielding packaging is to be used particularly when transporting or storing ESD sensitive items outside an ESD Protected Area.
Per Packaging Standard ANSI/ESD S541 clause 6.2 Outside an EPA “Transportation of sensitive products outside of an EPA shall require packaging that provides:
Other helpful ESD related definitions from the ESD Association Glossary ESD ADV1.0 include:
Faraday Cage: “A conductive enclosure that attenuates a stationary electrostatic field.”
Electrostatic discharge (ESD) shield: “A barrier or enclosure that limits the passage of current and attenuates an electromagnetic field resulting from an electrostatic discharge.”
Electrostatic shield: “A barrier or enclosure that limits the penetration of an electrostatic field.”
So, hopefully we’ve clarified a few things today when it comes to the “shielding” property by explaining the phenomenon of the “Faraday Cage”. Don’t forget to implement our tips when it comes to using your ESD bags!
Last time, we discussed the storage requirements of ESD sensitive items. Today we want to focus on the overall selection process for ESD bags: from choosing the correct type of material all the way through to determining the right size for your application. Sounds complicated? Honestly – it’s not and once you have the right tools (you’re welcome!), you’ll be an expert in no time. So, let’s go!
Choose the correct material for your ESD bag
Before you get started, you need to be clear about the purpose of your ESD bag and the environment it’s being used in. Make sure you have the answers to the following questions:
Once you have answers to ALL of the above questions, you can move on to the below selection chart and choose the right material for your application.
| ESD sensitive items | Moisture protection | Self-sealable | Physical protection | Inside/ Outside EPA |
|
| Metal-In | x | x | Both | ||
| Metal-Out | x | x | Both | ||
| MBB – High Barrier | x | x | x | Both | |
| MBB – Low Barrier | x | x | x | Both | |
| Bubble Shielding | x | x | Both | ||
| Conductive Black | Only if used on a grounded surface | Inside only if used with ESD sensitive items |
A few more details on the different types of materials listed in the above chart:
Calculating the correct size for your ESD bag
Once you have selected the correct type of material, it’s time to choose the right size for your ESD bag. There are different ways to determine this based on the type of material you use:
Shielding and Black Conductive Bags:
A. Bag Width = Item’s Thickness + Item’s Width + 25mm
B. Bag Length = Item’s Thickness + Item’s Length + 50mm
Moisture Barrier Bags (MBB):
A. Bag Width = Item’s Thickness + Item’s Width + 25mm
B. Bag Length = Item’s Thickness + Item’s Length + 76mm
Cushioned Bags:
A. Bag Width = Item’s Thickness + Item’s Width + 76mm
B. Bag Length = Item’s Thickness + Item’s Length + 76mm
Bonus Tip: Measuring a bag
It might seem obvious to some of you but given that we do get these types of queries on a regular basis, we thought this would be a good opportunity to include. Imagine you already have ESD bags that you use in your company. Someone has just taken the last one off the shelf and you need to order some more. How do you know what size ESD bag you have in front of you so you can place a new purchase order? No worries – we have the answer:
A. The width is measured from inside seam to inside seam. This is also your opening.
B. The length is measured from the top of the opening to the bottom of the bag.
Bonus Tip 2: Remember your ESDS items
Outside an ESD protected area, the objective of ESD protective packaging is to prevent a direct electrostatic discharge to the ESD sensitive item contained within and allow for dissipation of charge from the exterior surface. In addition, the packaging should minimize charging of the ESD sensitive item in response to an external electrostatic field and triboelectrification. If the user does not know the sensitivity of the items being used, we would always recommend static shielding packaging to be on the safe side.