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Storage and Transport of ESD Sensitive Items

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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.

Remember:

  • 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.

ESDPackaging
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

TEAMOperator 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.

Picture5Sealing 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

 

 

ESD Control – Other Considerations

Application Photo of Surface Resistance Test Kit

OTHER CONSIDERATIONS
Discipline
A significant increase in the discipline of implementing the fundamentals of ESD control noted in ANSI/ESD S20.20 Foreword, calls for:

  • Ground all conductors in the EPA including people
  • Remove all insulators from the EPA or use ionizers for process necessary insulators
  • Package ESD sensitive items going outside the EPA in packaging that provides electrostatic discharge shielding

Insulators
We encourage developing a hatred for insulators. The alternatives are:

    Remove the insulative item from the EPA

  • Substitute the item with an ESD protective version (such as tape, document holders, material handling containers, plastic bottles, etc.)
  • Periodically treat insulative surface with a topical antistat
  • Neutralize electrostatic charges using ionization

Other ESD Control Items
Other EPA ESD control items to add to the ESD control program might include shelving, mobile equipment (carts), gloves, and/or seating.

Improve Compliance Verification Plan

  • Consider greater frequency of internal audits per ESD TR53
  • Use of computer data collection system for wrist straps and footwear testing, continuous monitors, and ionizers
  • Use of ground continuous monitors for worksurfaces and other ESD elements
  • Test ionizers more frequently, consider self monitoring ionizers, consider computer based data collection
  • Increased testing using static field meter to verify that automated processes (like auto insertion, tape and reel, etc) are not generating charges above acceptable limits.

Application Photo of Volt Meter and Software in Factory STM97.2 Testing Voltage Charge on Person (Photograph courtesy of TREK, INC.)

Improve Training

  • ESD awareness training for all in the EPA or who may come into the EPA including suppliers
  • Testing to verify comprehension and training adequacy
  • Training on the proper use of test equipment
  • Training on proper compliance verification test procedures

Application Photo CD-ROM ESD Training

Conclusion
Just to maintain a company’s current level of quality and reliability may require a substantial improvement in a company’s ESD control program. Now is the time for improvement as ESD sensitivity withstand voltages continue to get lower and companies may soon be handling class 0A HBM items. To combat HBM failures improved personnel grounding is required. For example, heel grounders should be replaced with full coverage foot grounders. However, most failures are CDM. To combat CDM failures, ionization should be added or improved, and conductive surfaces should be covered with dissipative material. In general, disciple should be enhanced implementing ESD control fundamentals, compliance verification testing should be increased, and training should be improved.

From published article “Now is the Time for ESD Control Programs to be Improved” by Fred Tenzer and Gene Felder. See full article at InCompliance Magazine- September 2012

Example of an EPA – ESD Protected Area

EPA, ESD Protected Area

  1. Floor Marking Tape
  2. Floor Mats
  3. Waste Bins
  4. Meters and Probes
  5. Work Surface Mats
  6. Earth Bonding Points
  7. Ionisers
  8. Floor Finish
  9. Surface and Mat Cleaner
  10. Shelf Lining
  11. Ring Binders
  12. Dissipative Circuit Board Shippers
  13. Data Acquisition
  14. Signs
  15. Labels and ESD Tape
  16. On-Demand Wrist Strap Testers
  17. Rigid Conductive Boxes
  18. Wrist Straps and Heel Grounders
  19. Garments
  20. ESD Packaging
  21. Work Surface Grounding
  22. PCB Storage Products
  23. Antistatic Waste Bags

For a larger image Click Here

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