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
The patented* SmartLog V5™ system is designed for fast, frequent and accurate testing of ESD personnel grounding items. The SmartLog V5™ records ESD test data and exports it to a central PC or server in real-time where it can be managed and reported using TEAM5 Software.
- Single-wire and Dual-wire Wrist Strap Compatible
- Embedded CCD Barcode Scanner
- Ethernet Communication
- Adjustable Resistance Limits
- Programmable Test Requirements
- Compatible with Proximity Readers
- Embedded relay terminal for use with electronic
TEAM5 is the most powerful and accurate ESD Test Acquisition Software on the market. Use TEAM5 to automate and manage the ESD test data collected by the SmartLog V5™.
Click here to learn more.
|50762||Smartlog V5™, Europe, w/o Software||£2,294.72|
|50763||SmartLog V5™, Euro, 10MM Adapter, w/o Software||£2,294.72|
|50764||Reader Only, SmartLog V5™, HID ProxPoint Plus||£ 370.28|
|50765||Reader Only, SmartLog V5™, HID iClass||£ 383.04|
|50491||TEAM5 Enterprise Software with 1 Year Service||£3,886.16|
|50493||TEAM5 Software with 1 Year Service||£ 623.36|
“Compliance verification records shall be established and maintained to provide evidence of conformity to the technical requirements. The test equipment selected shall be capable of making the measurements defined in the compliance verification plan.” [EN 61340-5-1 Edition 1.0 2007-08 clause 5.2.3 Compliance verification plan]
When working with voltages over 250 VAC, ESD personnel grounding should not be used, rather ionization may be required to neutralize electrostatic charges. “Wrist straps should not be worn by personnel where they could come into contact with voltage over 250 V.” [CLC/TR 61340-5-2:2008 User guide wrist strap clause 188.8.131.52]
Per CLC/TR 61340-5-2:2008 User guide wrist strap clause 184.108.40.206 “For personnel safety, wrist straps incorporating a 1.0 x 10^6 ohm resistor should not be used in situations where there is an exposed electrical circuit of 250 V or higher. Some additional options for high voltage operations are as follows:
- Select a wrist strap system that utilizes a higher value resistor
- Intentionally isolate the operator from ground through the use of high resistance floor mats or gloves.
NOTE: Several publications exist that provide varying limits of allowable current for personnel safety. For example, most power supplies are current limited to 5 mA. For this reason, the user should check with local safety personnel to determine requirements for their particular area.”
Per CLC TR 61340-5-2 2008 Ionization clause 220.127.116.11 “The primary method of static charge control is direct connection to ground for conductors, static dissipative materials and personnel. However, a complete static control programme must also deal with isolated conductors that cannot be grounded as well as insulating materials (e.g., most common plastics). … Air ionization can neutralize the static charge on insulated and isolated objects by charging the molecules of the gases of the surrounding air. Whatever static charge is present on objects in the work environment, this will be neutralized by attracting opposite polarity charges from the air.”
As important as ESD control is, it is of secondary importance compared to employee safety. Questions regarding safety should be answered by the facility’s safety officer. The safety officer and ESD Coordinator should be aware of this information
EN 61340-5-1 clause 4 “Personnel safety, The procedures and equipment described in this standard may expose personnel to hazardous electrical conditions. Users of this standard are responsible for selecting equipment that complies with applicable laws, regulatory codes and both external and internal policy. Users are cautioned that this standard cannot replace or supersede any requirements for personnel safety.
Electrical hazard reduction practices should be exercised and proper grounding instructions for equipment must be followed.”
Per EN 61340-5-1 wrist strap product qualification is to be tested per ANSI/ESD S1.1 which includes “Current-Limiting Resistance, A resistance value incorporated in series with the wrist strap’s electrical path to ground. This resistance limits electrical current that could pass through the ground cord in the event of inadvertent user contact with electrical potential.” [Section 3 Definition of terms]
When equipment voltage exceeds 250 volts, guidance should be obtained from the appropriate Safety Officer if inadvertent user contact is possible. If so, Wrist Straps and ESD footwear, as well as Static Control Garments, should not be used. If the Safety Officer determines that the high voltage is adequately insulated and isolated, then personnel grounding, which is more effective and less expensive, can be used.
Vermason Wrist Straps [and many Foot Grounders] include a 1 megohm current limiting resistor (or resistance). At 250 volts, a 1 megohm [1,000,000 ohms] resistor limits current to 0.25 milliamp. These products are not recommended for use on equipment with operating voltage exceeding 250 volts. Do not remove the resistor. If it becomes damaged, replace the product immediately.
These products are for ElectroStatic control. They will not reduce or increase your risk of receiving electrical shock when using or working on electrical equipment. Follow the same precautions you would use without ESD grounding devices, including:
- Make certain that equipment having a grounding type plug is properly grounded.
- Make certain that you are not in contact with grounded objects other than through the ESD grounding device.
Per CLC/TR 61340-5-2:2008 User guide garment clause 18.104.22.168 Other considerations “Personnel safety should be considered before allowing static control garments to be worn where there is exposure to high voltage.”
To continue reading Click Here
To see other Articles Click Here
As important as ESD control is, it is of secondary importance compared to employee safety.
When working with voltages over 250 VAC, ESD personnel grounding should not be used including Wrist Straps, ESD Footwear & Garments.
Ground fault circuit interrupters (GFCI) and other safety protection should be considered wherever personnel might come into contact with electrical sources.
The written ESD Control Plan should be in accordance with IEC 61340-5-1:5.1.1
ESD training should be repeated as specified in the company’s written ESD Control Plan.
For an introduction to ESD and to see how you can prevent your products being damaged watch our ESD Basics Presentation.