We thought today we could focus on ESD during storage and transport. If you have read our recent post on Tips to Fight ESD, you will remember how important it is to protect your ESD sensitive items when leaving an EPA. Yet, too often we see customers who have the perfect EPA, but when it comes to transporting and storing their precious components, it’s all falling apart.
1. Packaging required for transporting and storing ESD sensitive items
During storage and transportation outside of an EPA, we recommend that ESD sensitive components and assemblies are enclosed in packaging that possesses the ESD control property of shielding.
- In ‘shielding’ we utilise the fact that electrostatic charges and discharges take the path of least resistance.
- The charge will be either positive or negative; otherwise the charge will balance out and there will be no charge.
- Charges repel so electrostatic charges will reside on the outer surface.
2. The Faraday Cage effect
A Faraday Cage effect can protect ESD sensitive items in a shielding bag or other container with a shielding layer. To complete the enclosure, make sure to place lids on boxes or containers and close shielding bags.
Cover must be in place to create Faraday Cage and shield contents.
3. Types of shielding packaging
The below list gives a few examples of what types of shielding packaging is available on the market. This list is by no means complete; there are many different options out there – just make sure the specifications state “shielding” properties.
- Metal-In Shielding Bags
ESD bags which protect ESD sensitive items. The ESD shielding limits energy penetration from electrostatic charges and discharge. They offer good see-through clarity. Available with and without dissipative zipper.
- Metal-Out Shielding Bags
Integral antistatic and low tribocharging bags which will not electrostatically charge contents during movement. Bags have an aluminium metal outer layer of laminated film. Available with and without dissipative zipper.
- Moisture Barrier Bags
Offer ESD and moisture protection and can be used to pack SMD reels or trays. Check out this post for more information on MBB and ESD Control.
- Bubble Shielding Bags
These bags combine the “Faraday Cage” and mechanical protection. They shield about twice as well as normal shielding bags of equivalent size.
- Component/Circuit Boards Shippers
These boxes offer an efficient way of shipping or storing ESD sensitive circuit boards and other items. They provide ESD shielding with the lid closed. The foam cushioning reduces stress from physical shock.
- In-Plant Handlers/Storage Containers
Shield ESD sensitive items from charge and electrostatic discharges (with lid in place). They provide ESD and physical protection for ESD sensitive circuit boards.
4. Additional options for storing ESD sensitive items
Do you have the following in place?
- ESD flooring
- Grounded personnel (using foot grounders). Read this post for more information on how to ground moving personnel.
- Grounded racking
Operator wearing foot grounders
IF (and this is a BIIIG IF) the above requirements are fulfilled, you can use conductive bags or containers to store your ESD sensitive items. Conductive materials have a low electrical resistance so electrons flow easily across the surface. Charges will go to ground if bags or containers are handled by a grounded operator or are stored on a grounded surface.
Conductive materials come in many different shapes and forms:
- Conductive Black Bags
Tough and puncture resistant bags which are made of linear polyethylene with carbon added. The bags are heat sealable.
- Rigid Conductive Boxes
Provide good ESD and mechanical protection. Boxes are supplied with or without high density foam for insertion of component leads or low density foam which acts as a cushioning material.
- PCB Containers
Are flat based and can be stacked. They are made of injection moulded conductive polypropylene.
Again, there are many more options available on the market so make sure you do your research.
Note: we do not recommend using conductive packaging to transport ESD sensitive devices. Also, pink antistatic and pink antistatic bubble bags are not suited for storing or transporting ESD sensitive components.
5. Final thoughts
Packaging with holes, tears or gaps should not be used as the contents may be able to extend outside the enclosure and lose their shielding as well as mechanical protection.
Also, do not staple ESD bags shut. The metal staple provides a conductive path from the outside of the ESD bag to the inside. The use of a metal staple would undermine the effectiveness of the ESD bag making a conductive path for charges outside the bag to charge or discharge to ESD sensitive components inside the bag. To close an ESD bag, it is recommended to heat seal or use ESD tape or labels after the opening of the bag has been folded over. Alternatively, you can use ESD bags with a zipper.
Sealing ESD Bags the correct way
One final word of warning:
When ESD sensitive items are unpackaged from shielding bags or other containers, they should be handled by a grounded operator at an ESD workstation
A flooring / footwear system is an alternative for personnel grounding for standing or mobile workers. Foot grounders quickly and effectively drain the static charges which collect on personnel during normal, everyday activities.
- It is recommended that foot grounders be worn on both feet, in order to assure that a continuous path to ground is maintained.
- Contact strips should be tucked inside the shoe with as much contact area as possible to the bottom of the stockinged foot. Foot grounders rely upon the perspiration layer inside of the shoe to make contact through the stocking.
- Foot grounders should be used in conjunction with floor surfaces which have a surface resistivity of less than 1010 ohms. Wearing ESD footwear on a regular, insulative floor is a waste of time and money.
- A current limiting one or two megohm resistor in series with the contact strip is recommended but not required.
- ESD footwear should be tested independently at least daily while being worn.
Not sure what floor matting to choose? Check out our Floor Mat Selection Chart.
- Single Station Continuous Dual-Wire Monitor
Continuously monitors the ground integrity and charge generation of one operator and supervisor as well as the ground integrity for one ESD worksurface and one optional tool, eliminating the need for periodic testing and record keeping of wrist straps
- Patented* Dual Polarity Technology
Provides Real-Time Continuous Monitoring for Operator Path-to-Ground and Presence of 1 Meg Resistor True continuous monitoring (versus pulsed) instantaneously detects broken cords, intermittent faults, dry skin, loose bands and low resistance.
- Dual Polarity Technology
Steady-State DC Dual Polarity Signal yields virtually zero voltage on the operator
- Operator Charge Detection Alarm
Alarms if the operator generates or comes in contact with a voltage that would be dangerous to an ESD susceptible item
- RS-485 Communication Ports
Use with EMIT SIM Software for test data acquisition and management
- User Adjustable Features
Use the internal DIP switches to enable / disable test circuits and modify the operator test voltage, operator charge detection voltage and worksurface resistance limit
- NIST Calibrated with Certificate
Calibrated with accepted procedures and standards traceable to the National Institute of Standards and Technology. For more information on calibration of EMIT products see Calibration
|50579||ZVM Solo, Europe||£211.38|
“A properly grounded wrist strap will keep a person’s body voltage to approximately + 10 V. The main advantage to a constant [or continuous] monitor is the immediate indication that the employee receives if the wrist strap falls open. With an unmonitored system, the employee will not be aware of a wrist strap failure until the start of the next shift. This has reliability benefits for an ESD program as it might help reduce or eliminate ESD damage.
There are also other process benefits from using constant monitors such as the elimination of the need to maintain daily test logs and a reduction in the time for employees to make the daily test. For units that also monitor the connection of a work surface to protective earth, it is also possible to reduce or eliminate the checking of the work surface as part of the periodic audit of the process.
Constant monitors might be implemented by an organization due to high reliability requirements imposed by customers.” [CLC/TR 61340-5-2:2008 User guide Annex B.1.3 Constant monitors]
*US patents 6,052,053 and 6,205,408
ESD events are the cause of maddening, difficult-to-duplicate, and intermittent product malfunctions. They consume a great deal of time, annoy all involved, and are often never resolved.
Combating the invisible enemy with an effective ESD control program can produce financial benefits. But the greatest savings come from decreasing latent defects, which are extremely difficult to detect after the component is assembled into a finished product.
Any relative contact and physical separation of materials (or flow of solids, liquids, or particle-laden gases) can generate electrostatic charges. Common sources include personnel, items made from common polymeric materials, and processing equipment. ESD can damage parts by direct contact with a charged source or by electric fields emanating from charged objects that induce a charge on ungrounded sensitive items.
To view more information on how to Develop an ESD Control Program Click Here