Storage and Transport of ESD Sensitive Items

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.

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, should be combined with Desiccant to absorb moisture and Humidity Indicator Cards to measure the level of relative humidity in the packaging.
• 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).
• Grounded racking

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. When charged device model (CDM) damage is a concern, it is recommended that the material be of dissipative resistance. 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.

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 or placed on a protective ESD work surface.