Category Archives: Working Surface Mats
The purpose of an ESD protective working surface is to aid in the prevention of damage to ESD sensitive items (ESDS) and assemblies from electrostatic discharge. An ESD protective working surface provides protection in the following two ways:
- Providing a low charging (antistatic) working surface area that will limit static electricity to be generated below potentially damaging levels.
- Removing the electrostatic charge from conductive objects placed on the working surface.
1. Types of ESD working surfaces
ESD protective working surfaces are categorised into two general categories: conductive and dissipative.
A conductive working surface is defined by most documents as a material that has a surface resistance of less than 1 x 104 ohms. Conductive materials are the quickest to ground a charge but they can also cause damage by discharging too rapidly. Conductive materials are usually used as floor mats or flooring products.
A dissipative working surface is defined as being materials having a surface resistance of at least 1 x 104, but less than 1 x 109 ohms. Dissipative materials will dissipate a charge slower and are recommended for handling electronic components. Dissipative materials are usually the preferred choice for bench top working surfaces.
Most people in the industry consider working surfaces to be the second most important part of an ESD Control Programme, with personnel grounding being most important.
2. Grounding Methods for working surfaces
Method 1: Grounding via ground cords
- Vermason recommends using an earth bonding point cord when grounding via ground cords. Most earth bonding point cords will ground an ESD protective working surface and provide banana jacks for two wrist strap grounds.
Earth Bonding Point for each workstation
- An earth bonding point should be installed at each workstation and should be connected directly to a verified electrical system ground or to a verified grounding bus which is connected to the protective earth ground. Only one groundable point should be installed on a working surface.
- Wrist straps should never be grounded through a working surface, as the added resistance of the working surface material will prevent the wrist strap from operating properly.
Proper Grounding of Wrist Straps
Method 2: Grounding via a grounded conductive surface
- This alternate form of grounding should only be employed when using a homogeneous dissipative material with a volume resistance of less than 1 x 108
- The dissipative working surface may be placed on a properly grounded laminate, metal or other conductive surface. The working surface will electrically couple to the grounded surface and may not require a separate ground cord.
- When using this type of grounding method be sure to test that the working surface Rg is less than 1 x 109 ohms, tested per IEC 61340-2-3. Also consider increasing Compliance Verification test frequency.
Alternate Grounding Method via a Grounded Conductive Surface
3. Groundable Point Installation
Before installing a groundable point on your work surface you must first determine whether you will need a male stud or female socket, the type of snap hardware and the desired location.
There are generally 3 types of groundable points available for working surface mats: screw-on snap kits, push & clinch snaps (with prongs) or stud & posts sets (requiring installation using a punch and an anvil).
Snap Kits and Tools
- Determine the position of the grounding snap (one only per mat). Punch a hole through the material with a small Phillips screwdriver or awl.
- Insert the screw through the bottom on the snap fastener, the washer and the material. Affix the assembly with the conical nut supplied with the kit and tighten down the screws.
Installing a screw-on Mat Grounding Snap
Push & clinch snaps:
This snap is designed for use with any type of soft mat material: dissipative, conductive or multi-layered. It is recommended for use with three-layered material, because it provides better contact with the internal conductive layer. It is recommended that before inserting this snap, the mat be punctured with a sharp tool where the snap will be placed.
Centre the prongs on the snap assembly. Apply pressure to the snap until the prongs come through the back of the mat, then clinch over prongs making flat to the mat’s bottom side to secure snap as shown in the below picture.
Installing Push & Clinch Mat Grounding Snap
Stud & post sets:
This type of groundable point must be riveted through bench and floor mats to connect ground cords. A punch and anvil are simple but effective tools to achieve a neat finish with firm materials no more than 4mm thick.
- Punch a 5mm diameter hole at the desired location of the mat.
- Insert the post from underneath and apply the stud over the protruding post on the top side.
- Fit the anvil under the post and place the punch inside the stud and hammer the post (or use an arbor press) until it rolls and a tight assembly is achieved.
Using a Punch and Anvil to install Stud & Post Sets
4. Selection of Common Point & Floor Mat Grounding Systems
- Determine the type of common point grounding system you will use: barrier strip, bus bar, grounding block or common point ground cord. Vermason recommends the use of common point ground cords and earth bonding bars.
- If you determine that you will use ground cords, you must now determine the type of ground cord you will use for your workstation grounds. It is the user’s preference to use a ground cord with or without a current limiting 1 megohm resistor to ground working surfaces or floor mats. Selection of the ground cord is determined by user needs and specifications; the resistor is not for ESD control.
Examples of Grounding Cords
- Earth bonding point bars allow the grounding of multiple operators at one common ground point. They also mount easily under the front edge of a workstation benchtop.
Earth Bonding Point Installation
5. Mat Installation
- For best results, allow the mats to lay flat for about four hours at room temperature before installing. This will give the material time to flatten out from being rolled for shipment.
- Test all workstation grounds for proper resistance to ground.
- Lay the mat in position and snap the ground cord to it. Bring the other end of the ground cord to the common ground point (or earth bonding bar) and attach it using the ring terminal (or other termination device). The electrical systems junction box and connecting conduit should also connect to earth protective ground. Tie the ground wire to the bench to keep it out of the way and neat. You may cut and strip the ground wire to a shorter length and attach it with an extra ring terminal if required.
Note: DO NOT DAISY CHAIN. Because of the high resistances inherent to many types of protective surfaces, daisy chaining of these materials can cause the overall resistance to exceed the required limit of EN 61340-5-1.
ESD working surface should never be grounded in series, i.e. daisy chained
- If your kit includes a floor mat, you should duplicate step 2 and attach the floor mat ground to the same ground point as the working surface ground.
- Measure the resistance from the ground snap on the mat to the common ground point. It should read 1 megohm ±20 percent if you are using a ground cord with a resistor, and less than 10 ohms if you are using a ground cord without a resistor.
- If you have a surface resistance or resistance to ground tester available, you may wish to test the resistance to ground from the mat surface. Note: depending upon the accuracy of the instrument you are using, you may get a wide range of results in resistance to ground tests. In order to get the electrical readings specified per EN 61340-2-3, two 2.2kg electrodes are to be used. This will require a megohmmeter with 100 volt open test circuit voltage and two 2.2kg electrodes.
- If you are using a mat kit that includes the wrist strap, install the wrist strap directly to the common point mat ground cord. Again, test the resistance from the backplate of the wrist strap to the common ground point. It should read 1 megohm ± 20 percent.
Adding a Wrist Strap
- Your completed installation of an ESD workstation should comply with one of the electrical diagrams illustrated below.
Proper wiring diagrams for conductive and dissipative ESD workstations
6. Maintenance and Cleaning
For optimum performance, periodic cleaning is required following the manufacturer’s recommendations.
BE SURE YOU TEST ALL GROUNDS AND THE WRIST STRAP FREQUENTLY
Today we want to talk about a subject many users forget about when it comes to ESD protection: periodic verification.
Whilst many people understand the basic concepts of ESD and as a result insist on a properly equipped ESD Protected Area (EPA), they then forget all about it. They use the same products day-in, day-out, year after year, without knowing if their products are actually still working properly.
So today we want to look at the most common products in your EPA that you should be checking on a regular basis. And because there are quite a few product groups to discuss, we have split this post in 2 parts – we don’t want to scare you away with a never-ending blog post…
Why periodic verification?
Each component in an ESD protected area (EPA) plays a vital part in the fight against electrostatic discharge (ESD). If just one component is not performing correctly, you could damage your ESD sensitive devices potentially costing your company money. The problem with many ESD protection products (think wrist straps!) is that you can’t always see the damage. Just by looking at a coiled cord that has no visibly damage to the insulation you would not know if the conductor on the inside is damaged. That’s where periodic verification comes into play.
ESD protected area (EPA) products should be tested:
- Prior to installation to qualify product for listing in user’s ESD control plan.
- During initial installation.
- For periodic checks of installed products as part of IEC 61340-5-1 Edition 1 2007-08 clause 5.2.3 Compliance verification plan.
It’s #3 we will be focusing on in this 2-part series.
The purpose of ESD bench matting is to ensure that when charged conductors (conductive or dissipative) are placed upon the surface, a controlled discharge occurs and electrostatic charges are removed to ground. However, this only occurs if the ESD work surface is actually connected to ground. If the matting is out-of-spec, not grounded at all, the stud on the mat has become loose or the ground cord has become disconnected, charges cannot be removed.
Many companies use a daily checklist, which includes the operator having to verify that ground cords are firmly connected.
Remember to regularly clean your bench matting to maintain proper electrical function (e.g. Reztore Surface and Mat Cleaner). Do not use cleaners with silicone as silicone build-up will create an insulative film on the surface.
The company’s compliance verification plan should also include periodic checks of work surfaces measuring:
- Resistance Point-to-Point (Rp-p) and
- Resistance-to-ground (Rg).
Testing a working surface using 222643
Surface resistance testers can be used to perform these tests in accordance with EN 61340-5-1 Electrostatics and its test method IEC 61340-2-3; if these measurements are within acceptable ranges, the worksurface matting and its connections are good.
As discharges from people handling ESD sensitive devices cause significant ESD damage, the wrist strap is considered the first line of ESD control.
Before handling ESD sensitive items, you should visually inspect the wrist strap to see if there are any breakages etc. The wrist strap should then be tested while worn using a wrist strap tester. This ensures all three components are checked: the wrist band, the ground cord (including resistor) and the interface with the wearer’s skin. Records of each test should be kept. Wiggling the resistor strain relief portion of the coil cord during the test will help identify failures sooner. Analysis and corrective action should take place when a wrist strap tester indicates a failure.
Checking wrist straps using 222566
It is recommended that wrist straps are checked at least daily. An even better solution to daily wrist strap checks is the use of continuous monitors. They will alarm if the person or work surface is not properly grounded.
A note on worksurface matting and wrist straps: if you are using earth bonding points, earth bonding bars etc. to ground the operator and/or bench matting, remember to inspect and test those regularly as well (every 6 months for example).
Make sure you read the follow-up post here.
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 authors of a recent article in InCompliance Magazine titled Early Life Failure of Dissipative Workstation Mats have confirmed that Vermason’s Statfree™ T2 was the top performing worksurface mat (Mat ID#4 in the article) in their study. To read the rest of the article click HERE.
Vermason T2 Mats
Part of any good ESD Control Programme is periodic verification of the specifications of products being used for the ESD Control Plan. The most obvious example of periodic testing is when operators test their foot grounders or wrist straps before entering an ESD Protected Area. The ESD Association’s ESD TR53-01-15 Compliance Verification of ESD Protective Equipment and Materials describes the test methods and instrumentation that can be used to periodically verify the performance of ESD protective equipment and materials. Plexus Manufacturing Solutions in Neenah, WI noticed during periodic verification of their workstation mats, that the mats were drifting out of spec and wanted to determine what was causing the mats to fail. Through their in-house tests, they concluded that:
- A solid ESD control programme including compliance verification periodic testing with data collection provides valuable and useful information.
- Factory fluorescent lighting, likely from ultraviolet (UV) radiation, can have a measurable effect on the electrical properties of ESD dissipative mats over time.
- Different mats tolerate or resist the effects of factory fluorescent lighting.
- Since this experiment did not take into account lot-to-lot variation at the supplier for each mat P/N, future mats purchased will require lot traceability information to be stamped on the bottom of the roll, every 0.9m minimum.
- The ESD Association technical report ESD TR4.0-01-02 Worksurfaces and Grounding Survey should consider adding ultraviolet light resistance as a property to consider in the Worksurface Selection Guide.
Vermason’s Statfree™ T2 mats include Ultraviolet (UV) stabiliser additives in the mat formula to stabilise colour retention, ensure ESD performance over time and eliminate surface layer deterioration resulting in cracking when the product is flexed. Additionally, we mark lot traceability information on the bottom of the roll every 0.9m to provide tracking information for lifespan of the product and to ensure quality control.
Top 3 Benefits of Statfree™ T2 Working Surface Matting:
- Superior wear, heat and chemical resistance.
- Withstands abrasion, stretching and tearing.
- Ultraviolet (UV) additives stabalise colour retention to ensure ESD performance over time and eliminate surface layer deterioration.
Continuous Monitors provide operators with instant feedback on the status and functionality of their wrist strap and/or workstation. They detect split-second failures when the wrist strap is still in the “intermittent” stage. This is prior to a permanent “open” which could result in damage to ESD sensitive components. Continuous Monitors verify the ground integrity of both the operator and ESD workstation and eliminate the need for periodic testing (and record keeping).
Single-Wire Monitoring allows the use of any standard, single-wire wrist strap and coil cord. The monitor / wrist strap system life-cycle costs are significantly lower than dual-wire systems. While they would not be suitable for the most critical applications, Single-Wire Continuous Monitors are an economical way to monitor both the operator’s wrist strap and workstation surface.
The Multi-Mount Monitor continuously monitors:
• One operator wearing a wrist strap
• One ESD worksurface
Its small package and mounting tabs with holes make it highly suitable to install on most equipment or work bench surface.
The Jewel® Mini Monitor continuously monitors:
• One operator wearing a wrist strap
• One ESD worksurface
This unit is ideal for individual workstations for assembly, test, packaging or other applications.
The Dual-Operator Monitor continuously monitors:
• Two operators wearing a wrist strap
• Two ESD worksurfaces
This unit is ideal for workstations that are shared by two operators.
To determine the correct monitor for your application, make sure you check our Continuous Monitor Selection Chart.