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A Faraday cage or Faraday shield is an enclosure formed by conducting material or by a mesh of such 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 to be in a thunderstorm.
ESD control products that provide a Faraday Cage or shielding include Statshield® Metal-In and Metal-Out Shielding Bags, Protektive Pak™ impregnated corrugated with shielding layer when using a lid, and Conductive Totes. Statshield® ESD Smocks creates a Faraday Cage effect around the torso and arms of the operator and shields charges from the operator’s clothing from damaging ESD sensitive devices. (Technically, suppressing the electrical field from clothing worn underneath).
There are standard tests measuring the energy penetration of electrostatic discharges to the interior. The Shielding test method per Packaging standard ANSI/ESD S541 is ANSI/ESD STM11.31 and the required limit is less than 50 nanoJoules of energy.
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 section 6.2 Outside an EPA “Transportation of sensitive products outside of an EPA shall require packaging that provides:
- Low charge generation.
- Dissipative or conductive materials for intimate contact.
- A structure that provides electrostatic discharge shielding.”
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.”
Note: the ESD Association sells most documents, however, the Packaging standard ANSI/ESD S541 and the Glossary ESD ADV1.0 are free downloads from www.ESDA.org (click Standards and then Documents, scroll down to find documents that can be downloaded at no charge).
A company with an ANSI/ESD S20.20 ESD control program needs to document the program and define ESD protective packaging for ESD sensitive (ESDS) items. Packaging is to be defined for all material movement within the EPA and for outside the EPA. Best practice is to define the required packaging or material handling item on a product’s bill of materials. The ESD packaging is as important as a component part.
Customer contract packaging can take precedence, but otherwise “the organization shall define ESD protective packaging requirements, both inside and outside the EPA per ANSI/ESD S541.” [ANSI/ESD S20.20 section 8.4]
The ESD Association sells most of their documents. However, both ANSI/ESD S20.20 and ANSI/ESD S541 are available as complimentary downloads from www.ESDA.org.
The fundamentals of ESD control include grounding all conductors in the EPA. ESD packaging will have special material composition to lower the resistance so that when grounded, electrostatic charges will be removed to ground.
This is the Summary of ESD Protective Properties ANSI/ESD S541 Table 2:
|Low charging (antistatic)||Materials that have reduced amounts of charge accumulation as compared with standard packaging materials.|
|Dissipative or Conductive Resistance||Provides an electrical path for charge to dissipate from the package.|
|Discharge Shielding||Protects packaged items from the effects of static discharge that are external to the package.|
ANSI/ESD Table 3 lists Test Methods for Electrostatic Protective Packaging:
|Material Property||Test Method||Method Description||Limits|
|Low Charging (Antistatic)||ESD ADV11.2||Tribocharging of tubes, planar materials, bags, unit packs (vibration)||User defined|
|Conductive||ANSI/ESD STM11.11||Surface resistance of planar materials||< 104 ohms|
|ANSI/ESD STM11.12||Volume resistance of planar materials||< 104 ohms|
|Dissipative||ANSI/ESD STM11.11||Surface resistance of planar materials||> 104 to < 1011 ohms|
|ANSI/ESD STM11.12||Volume resistance of planar materials||> 104 to < 1011 ohms|
|ANSI/ESD STM11.13||Surface resistance 2-point electrode||> 104 to < 1011 ohms|
|Shielding||ANSI/ESD STM11.31||ESD Shielding of Bags||< 50 nanojoules|
Note that the unit of measurement for conductive and for dissipative is surface or volume resistance in ohms; not resistivity.
Statshield® bag film construction includes a metalized shielding layer. Shielding bags are designed to dissipate electrostatic charges over their surface, protecting ESDS contents from electrostatic fields and from ElectroStatic Discharge (ESD). Their surface resistance is dissipative, which is recommended when packaging in contact with the ESDS; per ANSI/ESD S541 section A.3 “Dissipative Material for Intimate Contact, to avoid rapid discharge to sensitive items, dissipative materials should be used as the layer of packaging that contacts the item.”
This is also true for enclosed Protektive Pak impregnated dissipative corrugated containers, either closed or with lid in place. The impregnated corrugated has a buried shielding layer that provides the shielding ESD control property so that ESD sensitive items can be stored or transported outside an ESD protected area.
Protektive Pak offers a number of ESD control packaging solutions, including Protektive Pak® Impregnated Dissipative Corrugated Products, Statshield Shielding Bags, Moisture Barrier Bags, Pink Poly Bags, and Labels for use within an ESD protected area (EPA) and for shipping outside an EPA. Protektive Pak products are designed to meet ANSI/ESD S20.20 and the ESD Association Packaging standard ANSI/ESD S541; they provide a great value balancing cost and durability.
ANSI/ESD S541 for the Protection of Electrostatic Discharge Susceptible Items Packaging Materials for ESD Sensitive Items
Protektive Pak’s Dissipative Impregnated Corrugated material features a unique characteristic, a buried shielding layer. This provides a better value because unlike dissipative or conductive painted material, the buried shielding layer will not rub/scratch off or lose its ESD properties. This translates into a superior, longer lasting ESD safe package.
Third party testing has been performed on Protektive Pak’s Impregnated Corrugated material demonstrating that the buried shielding layer in our corrugated material provides a better value than dissipative or conductive coated (or painted) material.
- Protektive Pak impregnated corrugated material has a buried shielding layer
- Protektive Pak impregnated corrugated material equals or exceeds the discharge shielding capabilities of a coated box
- Protektive Pak impregnated corrugated material has discharge shielding capabilities equal to a metal-out shielding bag
- Protektive Pak Dissipative Corrugated Material meets the ANSI/ESD S541 recommendation, avoiding rapid discharge when contacting ESD sensitive items –
conductive coated boxes DO NOT!
Protektive Pak Dissipative Impregnated Corrugated Material meets ANSI/ESD S20.20 and Packaging standard ANSI/ESD S541 tested per ANSI/ESD STM11.11 and modified ANSI/ESD STM11.31
For complete third party test results, click HERE.
Watch our Material Test video:
ESD Control Program Periodic Verification
Fred Tenzer and Gene Felder, Desco Industries, Inc.
Want to accomplish something important? A familiar formula is write a plan, select the speciﬁcations, and then periodically test to verify that the plan is being implemented according to the test results. This is basically the requirements of an ESD control program, per the ESD Association standard, ANSI/ESD S20.20. This important standard, entitled Development of an Electrostatic Discharge Control Program, covers the requirements necessary to design, establish, implement, and maintain an ESD control program to protect electrical or electronic parts, assemblies and equipment susceptible to ESD damage.
S20.20 is a process document, and provides ESD control plan guidance; one of its requirements is having a “compliance veriﬁcation plan” as a component of the ESD control plan. Per S20.20, paragraph 6.1.3., Compliance Veriﬁcation Plan:
To view more information on ESD Control Program Periodic Veriﬁcation CLICK HERE
What is Desiccant?
Desiccant is a drying agent that is used to absorb moisture from the air inside moisture barrier bags. Desiccant absorbs moisture vapor (humidity) from the air left inside that barrier bag after is has been sealed. Any moisture that penetrates the bag will also be absorbed. Desiccant remains dry to the touch even when it is fully saturated with moisture vapor.
Why are Electronics Moisture Sensitive?
Certain kinds of electronic devices called “Surface Mount Devices” or SMD’s are mounted on a circuit card by high temperature soldering. The body of the SMD is made from plastic that absorbs moisture from the air. When the case is heated during soldering, the moisture inside turns to steam and may break the device as the steam escapes. Keeping SMD’s dry before soldering means that the devices will not be damaged.
How is Desiccant Purchased?
Desiccant is sold by the “Unit” or fractional Unit. One unit of desiccant will absorb a specific amount of moisture. A unit weighs about 28 grams or 1 ounce. The pouches of desiccant are placed into metal pails to keep the desiccant dry during shipping and storage.
How is Desiccant Packaged?
Desiccant is packaged in small sealed pouches made from a white plastic called “Tyvek”, or brown “Kraft” paper. Tyvek pouches are very clean and sulfur free. Kraft pouches are economical.
How Much Desiccant Do I Need?
Method 1 (per MIL-P-116)
1. Formula: Unit = 0.011 x bag area in square inches
2. Example: 10″ x 20″ barrier bag
3. Find Bag Area: 10″ x 20″ x 2″ sides = 400 sqin
4. Apply Formula: Units = 0.011 x 400 sqin = 4.4
Use 4.5 Units of desiccant
Method 2 (per EIA 583. This formula allows you to tailor the desiccant to your specific needs)
What do you need to know?
Bag area, Bag MVTR, Months of Storage, Maximum Interior Humidity (MIH)
Units = 0.231 x Bag Area x Bag MVTR x Months divided by Moisture Capacity
For a 10″ x 20″ bag with a 0.02 MVTR, a 12 month storage time and a MIH of 20%
Apply formula Units =
0.231 x 400 sqin x 0.02 MVTR x 12 divided by 4.8g / unit = 4.6
Use 4.5 Units of Desiccant
10% MIH: 3.0 g/unit
20 MIH: 4.8 g/unit
30% MIH: 5.8 g/unit
40% MIH: 6.2/unit
For more information on desiccant packs and moisture barrier bags, visit ProtektivePak.com
“Returnable Packaging,” as defined by Returnable Packaging Association (RPA), is packaging which includes “…reusable pallets, racks, bulk containers, hand-held containers and dunnage that move product efficiently and safely throughout the supply chain. Reusable packaging is typically used by manufacturers/processors and their suppliers/customers in a well-organized supply chain, with very tightly managed shipping loops.”
So what does this mean? Returnable packaging is manufactured of durable materials and is specifically designed for multiple trips and extended life.
When a vehicle leaves a facility to drop off product and then returns to pick up more product, you have what is called a “milk run”. Milk runs are perfect for returnable packaging.
Utilizing returnable packaging cuts down on material costs as well as total cost. There is much less need for repeated purchasing of disposable containers. The money saved will now go towards your profit line! In addition, returnable packaging cuts down on waste by re-using packaging rather than just using it once and throwing it away. No more dumpsters full of unneeded waste!
Protektive Pak In-Plant Handlers are a great choice for reusable packaging. Made to protect ESD sensitive components, the boxes are constructed with double thick sides and double or triple thick ends and are extremely durable. They withstand the abuse of transporting. After transporting product to another facility, the boxes can be reused to ship more product or collapsed and stored for future use.
ElectroStatic Discharge (ESD) is silent, quick and potentially lethal to electronic parts. When electronic parts are not properly handled during manufacturing, assembly, storage, or shipping, damage from ESD can reach into the millions of dollars each year.
For an ESD control container to be effective against ElectroStatic Discharge, it must possess certain electrical characteristics:
- Surface resistance <1 x 1011 ohms per ANSI/ESD STM11.11
- Energy penetration <50 nanoJoules per ANSI/ESD STM11.31
Non-shielding containers might be cheaper, but they are not less costly when it comes to handling ESD sensitive items. Anytime ESD sensitive parts and assemblies are handled, regular containers are not a sound option, even part of the time, as the risk of ESD damage is always lingering. As a result, costs will be incurred, either via ESD damage or as an additional investment in discharge shielding packaging and material handling containers.
The disadvantages of cross-using shielding and non-shielding containers include:
- Increased cost
- Risk from ESD damage
- Handling inconvenience
The cost of a discharge shielding container is far less than the cost associated with damaged parts or extra handling that result with a “less expensive” non-shielding container.