So we’ve talked about various components in an EPA before (e.g. wrist straps, bags, tape and so on). But there is one important part we have not covered yet: ESD protective working surfaces. So let’s change that right now!
Definition of an ESD protective working surface
ESD protective working surfaces aid in the prevention of damage to ESD sensitive items (ESDS) and assemblies from electrostatic discharge.
ESD working surfaces, such as mats, are typically an integral part of the ESD workstation, particularly in areas where hand assembly occurs. The purpose of the ESD working surface is two-fold.
- To provide a surface with little to no charge on it.
- To provide a surface that will remove ElectroStatic charges from conductors (including ESDS devices and assemblies) that are placed on the surface.
Types of ESD protective working surface
When deciding to invest in ESD protective working surface, you have the choice of ESD matting (laid-out on a standard non-ESD bench) or ESD benches. Performance-wise there is no difference so what option you go for depends solely on your personal preference.
Examples of ESD protective working surface matting – for more details click here
Generally speaking, ESD matting offers a lower initial investment and is easier to replace. On the other hand, some people prefer the robust and consistent approach of ESD benches.
Grounding your ESD protective working surface
Whatever your choice, your ESD protective working surface needs to be grounded.
A ground wire from the surface should connect to the common point ground which is connected to ground, preferably equipment ground. For electronics manufacturing a working surface resistance to ground (Rg) of 1 x 104 to less than 1 x 109 ohms is recommended. Best practice is that ground connections use firm fitting connecting devices such as metallic crimps, snaps and banana plugs to connect to designated ground points. The use of alligator clips is not recommended.
Example of an ESD Protective Working Surface – click here for more grounding products
Using a current limiting resistor in the ground cord is the user’s choice. However, the resistor is not for ESD control purposes. The ESD Association standard for grounding is ANSI/ESD S6.1 which recommends a hard ground (no resistor) but allows the use of a current limiting resistor in the mat’s ground cord. “The grounding conductors (wires) from wrist straps, working surfaces, flooring or floor mats, tools, fixtures, storage units, carts, chairs, garments and other ESD technical elements may or may not contain added resistance. Where added resistance is not present, a direct connection from the ESD technical element to the common point ground or common connection point is acceptable and recommended.
Note: Manufacturers may add resistance to the grounding conductors for purposes other than ESD (e.g. current limiting). Added resistance is acceptable for the purposes of controlling ESD provided electrostatic accumulation does not exceed specific EPA requirements. The typical added resistance in grounding conductors is 1 megohm, although other values may be specified.” [ANSI/ESD S6.1 section 5.3.3 ESD Technical Element Conductors]
Working at an ESD protective working surface
Operators should ensure that the working surface is organised to perform work and that all unnecessary insulators and personal items are removed. Regular plastics, polystyrene foam drink cups and packaging materials etc. are typically high charging and have no place at an ESD protective workstation.
An operator installing an ESD protective working surface mat
Insulators can be a considerable threat to your products. Remember that an insulator cannot be grounded so it will retain its charge for a long time. Removing all non-essential insulators from the ESD protective workstation is an important rule. If not, your company’s investment in the grounded ESD working surface may be wasted.
“The biggest threat is Field Induced Discharges, which can occur even at a properly grounded ESD working surface. If an ESDS is grounded in the presence of an ElectroStatic charge, instead of the ESDS having charges removed from it, the ESDS may become charged with a voltage induced on it. Then, when placed on the grounded ESD work surface, a discharge occurs. If the ESDS is removed from the presence of the ElectroStatic charge and grounded again, a second discharge may occur.“ (Ref. ESD Handbook, ESD TR20.20, section 2.7.5).
Maintaining your ESD protective working surface
The ESD working surface must be maintained and should be cleaned with an ESD cleaner. Regular cleaners typically contain silicone and should never be used on an ESD working surface.
Example of an ESD cleaner – click here for more information
The ESD control plan should require testing of the resistance to ground periodically. For more information on testing your ESD working surface, check this post. However, the operator should be on guard every day and check visually that the ground wire is attached.
So you’ve identified ESD sensitive items in your factory and you realise that you need to implement ESD Control measures. But where do you start? There is so much information out there and it can be completely overwhelming. Don’t panic – today’s blog post will provide you with a step-by-step guide on how to set-up a suitable ESD Control Plan.
“The Organization shall prepare an ESD Control Program Plan that addresses each of the requirements of the Program. Those requirements include:
• compliance verification
• grounding / equipotential bonding systems
• personnel grounding
• EPA requirements
• packaging systems
• marking” [EN 61340-5-1 Edition 1.0 2007-08 clause 5.2.1 ESD control program plan]
“Each company has different processes, and so will require a different blend of ESD prevention measures for an optimum ESD control program. It is vital that these measures are selected, based on technical necessity and carefully documented in an ESD control program plan, so that all concerned can be sure of the program requirements.” [EN 61340-5-1 Edition 1.0 2007-08 Introduction]
1. Define what you are trying to protect
A prerequisite of ESD control is the accurate and consistent identification of ESD susceptible items. Some companies assume that all electronic components are ESD susceptible. However, others write their ESD control plan based on the device and item susceptibility or withstand voltage of the most sensitive components used in the facility. A general rule is to treat any device or component that is received in ESD packaging as an ESD susceptible item.
An operator handling an ESD susceptible item
2. Become familiar with the industry standards for ESD control
A copy of EN 61340-5-1:2007 can be purchased from British Standards: “BS EN 61340-5-1:2007 applies to activities that: manufacture, process, assemble, install, package, label, service, test, inspect, transport or otherwise handle electrical or electronic parts, assemblies and equipment susceptible to damage by electrostatic discharges greater than or equal to 100 V human body model (HBM). BS EN 61340-5-1 provides the requirements for an ESD control program. The user should refer to IEC 61340-5-2 for guidance on the implementation of this standard.
3. Select a grounding / equipotential bonding system
The elimination of differences in potential “can be achieved in three different ways:
- grounding using protective earth:
the first and preferred ESD ground is protective earth if available. In this case, the ESD control elements and grounded personnel are connected to protective earth;
- grounding using functional ground:
the second acceptable ESD ground is achieved through the use of a functional ground. This conductor can be a ground rod or stake that is used for grounding the ESD control items in use at a facility. In order to eliminate differences in potential between protective earth and the functional ground system it is highly recommended that the two systems be electrically bonded together;
- equipotential bonding:
in the event that a ground facility is not available, ESD protection can be achieved by connecting all of the ESD control items together at a common connection point.” [EN 61340-5-1 Edition 1.0 2007-08 clause 5.3.1 Grounding/equipotential bonding systems]
Example of a grounding/equipotential bonding system
4. Determine the grounding method for operators (Personnel Grounding)
The two options for grounding an operator are:
- a wrist strap or
- foot grounders/footwear.
In some cases, both (wrist strap and foot grounders) will be used.
5. Establish and identify your ESD Protected Area (EPA)
ESD Control Plans must evolve to keep pace with costs, device sensitivities and the way devices are manufactured. Define the departments and areas to be considered part of the ESD Protected Area. Consider if customers and/or subcontractors should be included. Implement access control devices, signs and floor marking tape to identify and control access to the ESD Protected Area.
Example of an ESD Protected Area including signs and floor marking tape
6. Select ESD control items to be used in the EPA based on your manufacturing process
Elements that should be considered include: working surfaces, flooring, seating, ionisation, shelving, mobile equipment (carts) and garments. Check-out this post for more information.
7. Develop a Packaging (Materials Handling & Storage) Plan
When moving ESD susceptible devices outside an ESD protected area, it is necessary for the product to be packaged in an enclosed ESD Shielding Packaging.
8. Use proper markings for ESD susceptible items, system or packaging
From EN 61340-5-1 Edition 1.0 2007-08 clause 5.2.1: “The Organization shall prepare an ESD Control Program Plan that addresses each of the requirements of the Program. Those requirements include: …marking”.
If you are handling ESD sensitive devices, there are 3 symbols you need to know.
The ESD Susceptibility (left) and ESD Protective Symbol (right)
9. Implement a Compliance Verification Plan
Developing and implementing an ESD control programme is only the first step. The second step is to continually review, verify, analyse, evaluate and improve your ESD programme.
“Process monitoring (measurements) shall be conducted in accordance with a compliance verification plan that identifies the technical requirements to be verified, the measurement limits and the frequency at which those verifications must occur. The compliance verification plan must document the test methods used for process monitoring and measurements… 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 2007-08 clause 5.2.3 Compliance verification plan]
Regular programme compliance verification and auditing is a key part of a successful ESD control programme.
10. Develop a Training Plan
“The training plan shall define all personnel that are required to have ESD awareness and prevention training. At a minimum, initial and recurrent ESD awareness and prevention training shall be provided to all personnel who handle or otherwise come into contact with any ESDS [ESD sensitive] items. Initial training shall be provided before personnel handle ESD sensitive devices. The type and frequency of ESD training for personnel shall be defined in the training plan. The training plan shall include a requirement for maintaining employee training records and shall document where the records are stored. Training methods and the use of specific techniques are at the organization’s discretion. The training plan shall include methods used by the organization to ensure trainee comprehension and training adequacy.” [EN 61340-5-1 Edition 1.0 2007-08 clause 5.2.2 Training Plan]
11. Make the ESD Control Plan part of your internal quality system requirements
A written ESD Control Plan provides the “rules and regulations”, the technical requirements for your ESD Control Programme. This should be a controlled document, approved by upper management initially and over time when revisions are made. The written plan should include following:
- Qualified Products List (QPL): a list of EPA ESD control items is used in the ESD control Plan
- Compliance Verification Plan: includes periodic checking of EPA ESD control items and calibration of test equipment per manufacturer and industry recommendations.
- Training Plan: an ESD Programme is only as good as the use of the products by personnel. When personnel understand the concepts of ESD, the importance to the company of the ESD control programme and the proper use of ESD products, they will implement a better ESD control programme improving quality, productivity and reliability.
A video making the rounds on Social Media this week highlights a very common problem in ESD Protection: dry air.
The report shows energy minister Simon Bridges walking around his office spraying the floor with water, applying tape to door handles and using an antistatic mat at his desk. The reason? Simple: a new carpet which was installed at the Beehive and the “little tickles” ministers are getting as a result.
Simon Bridges spraying the floor in his office with water (Source)
Jim Robb who is in charge of maintaining the parliament building provides the following explanation: “We’re in the middle of winter, we’ve got cold polar air, there’s no moisture in it and it’s a very common problem, I’ve been dealing with this for thirty years.”
While the ministers at the Beehive seem to have figured out solutions to avoid the “zap”, we want to show you how you can solve the issue of dry air in your EPA.
Impact of relative humidity on ESD
Just like the ministers in the above report, many people will notice a difference in the ability to generate static electricity when the air gets dryer (the % RH decreases).
Relative humidity (RH) directly affects the ability of a surface to store an electrostatic charge. As RH increases, the time a surface will hold a charge will decrease and the dissipation rate will increase.
An example: walking across a carpet can yield a charge of 35kV at 10% RH (very dry air) but will drop significantly to 7.5kV at 55% RH. In an electronics manufacturing environment lower humidity may result in lower output from production due to an increase in ESD events during manufacturing processes.
A normal range for humidity in an electronics manufacturing environment is be between 30% RH and 70% RH. Some facilities try to maintain a constant moderate RH (~50%), whereas other environments may want lower % RH due to corrosion susceptibility to humidity sensitive parts.
The recommended humidity range is usually determined by the specifications of the devices and components being assembled. Increasing the humidity in an electronics manufacturing facility can help to reduce ESD events but increased humidity can lead to other unwanted quality issues in sn electronics manufacturing environment such as corrosion, soldering defects and the popcorn effect on moisture sensitive devices.
The popcorn effect (Source)
Dealing with dry air in an EPA
While not a replacement for grounding, shielding or ESD working surfaces, ionisation can mitigate ESD events in areas where dry air is normal. For more information on ionisation and the different types of ionisers, we recommend reading these two posts:
In summary, worksurface ionisers (Bench Top and Overhead Ionisers) produce positively and negatively charged ions that are moved to the controlled area with fan driven airflow. Point-of-use air ionisers use compressed gas to combat electrostatic attraction neutralising charges on particles causing contamination or visual defects on products.
Using a point-of-use air ioniser
The ESD Standard on Relative Humidity
The ESDA’s TR20.20-2008 discusses RH in a few different places. Some significant statements are listed below.
ESD Handbook ESD TR20.20-2008 section 2.3 Nature of Static Electricity:
“The moisture level in the air, or relative humidity in the environment, are important considerations in the liberation and accumulation of static electricity. It is well known that static electricity in the form of static cling and static shocks are more prevalent when the air is dry. Heating interior air in the winter months dries out the already dry air in the higher latitudes. Static charge accumulation is easier on dry materials since moisture on surfaces tends to allow charges to slowly dissipate or recombine.
However, it is impractical to use humidity control alone to provide static control since static charges are developed even at relative humidity levels of 90% and greater. For most situations, 30 to 70% RH is considered the appropriate range. Special areas, such as wafer fabrication, may require lower humidity control for processes that are affected by moisture (e.g., photoresist application). Soldering is known to be affected by high relative humidity conditions (>70%). For areas that have low ambient humidity, ionization is an important consideration to aid in reducing charge accumulation levels and provide neutralization of charges after they are developed but before they can cause difficulties.”
ESD Handbook ESD TR20.20-2008 section 5.3.16 Humidity:
“Humidity is beneficial in all ESD control program plans. Contact and separation of dry materials generates greater electrostatic charges than moist materials because moisture provides conductivity that helps to dissipate charge. For this reason, ESD effects are most noticeable in the winter since heating systems reduce building environment moisture. Geographic location (desert vs. coastland) is also a major contributor to ambient conditions inside buildings. Any circumstance that results in a low relative humidity will permit a greater accumulation of electrostatic charges. Relative humidity above 30% in ESD protective areas is desirable as long as other adverse conditions are not created as a result of humidity levels. Generally speaking an upper limit of 70% is desirable to prevent corrosive effects on the metal portions of electronic devices and assemblies.
Besides the increasing propensity to generate electrostatic charges on dry materials in general, performance of many ESD protective materials degrade. In fact, when exposed to low humidity conditions, some ESD protective materials become totally ineffective or become sources of electrostatic charges. Therefore, evaluation of ESD control materials should include performance testing in controlled environments at the lowest expected operating relative humidity level. Manufacturers of ESD protective materials should be able to provide performance data in regards to relative humidity. Likewise, materials should be tested in moderate humidity conditions as well to ensure they do not become “too conductive” and present a potential safety hazard to personnel working with substantial voltages. See the Personnel Safety section of this handbook for further guidance in this area.
Humidity control in factories or physically large areas or buildings can be difficult and expensive. In smaller rooms or areas, it may be possible to use portable humidifiers to raise the immediate area humidity. However, in large facilities and factories the environmental systems many need to include steam generation and monitoring equipment to control humidity. This type of equipment is expensive to install and purchase especially in pre-existing facilities. To reduce the total cost impact, companies should consider the need for humidification equipment when planning new facility construction.”
ESD TR20.20-2008 can be purchased directly from the ESD Association.
We have mentioned the term “Faraday Cage” many times on this blog before – for example when talking about the transport and storage of ESD sensitive items or the role of ESD lab coats in ESD Protected Areas. When discussing ESD protection, the concept of the “Faraday Cage” will always come into play. But what exactly is it? Read on to find out…
A Faraday Cage or Faraday shield is an enclosure formed by conducting material or by a mesh of conductive material. Such an enclosure blocks external static and non-static electric fields. Faraday Cages are named after the English scientist Michael Faraday, who invented them in 1836.
An impressive demonstration of the Faraday Cage effect is that of an aircraft being struck by lightning. This happens frequently but does not harm the plane or passengers. The metal body of the aircraft protects the interior. For the same reason, a car may be a safe place during a thunderstorm.
Lightning striking an airplane
In ESD Protection, the Faraday Cage effect causes charges to be conducted around the outside surface of the conductor. Since similar charges repel, charges will rest on the exterior and ESD sensitive items on the inside will be ‘safe’.
ESD control products that provide a Faraday Cage or shielding include Statshield® Metal-In and Metal-Out Shielding Bags or Protektive Pak™ impregnated corrugated boxes with shielding layer when using a lid.
ESD shielding packaging is to be used particularly when transporting or storing ESD sensitive items outside an ESD Protected Area. Per Packaging Standard EN 61340-5-3 clause 5.3 Outside an EPA “Transportation of sensitive products outside of an EPA shall require packaging that provides both:
– dissipative or conductive materials for intimate contact;
– a structure that provides electrostatic discharge shielding.“
ESD Smocks create a Faraday Cage effect around the torso and arms of the operator and shields charges from the operator’s clothing from damaging ESD sensitive devices. (Technically, suppressing the electrical field from clothing worn underneath).
There are standard tests measuring the energy penetration of electrostatic discharges to the interior. The Shielding test method per Packaging standard EN 61340-5-3 is ANSI/ESD STM11.31 and the required limit is less than 50 nanoJoules of energy.
Definitions from the ESD Association Glossary ESD ADV1.0 include: Faraday Cage “A conductive enclosure that attenuates a stationary electrostatic field.”
Electrostatic discharge (ESD) shield “A barrier or enclosure that limits the passage of current and attenuates an electromagnetic field resulting from an electrostatic discharge.”
Electrostatic shield “A barrier or enclosure that limits the penetration of an electrostatic field.”
We’re talking about Electrostatic Discharge (ESD) on this blog all the time. But what exactly does it mean and why is it so dangerous? Today’s post will answer those questions!
All matter is constructed from atoms. These atoms have negatively charged electrons circling the atom’s nucleus which includes positively charged protons. As the atom has an equal number of electrons and protons, it balances out having no charge. So far, so good!
The problem is that all materials can tribocharge or generate ElectroStatic charges. Most commonly, this happens through contact and separation – examples are:
- Unwinding a roll of tape
- Gas or liquid moving through a hose or pipe
- A person walking across a floor and soles contacting & separating from the floor.
Unwinding a roll of tap can generate an electrostatic charge
The simple separation of two surfaces can cause the transfer of electrons between surfaces resulting in one surface being positively and the other one negatively charged. With that we’ve just generated an ElectroStatic charge!
The amount generated varies and is affected by materials, friction, area of contact and the relative humidity of the environment. At lower relative humidity, charge generation will increase as the environment is drier. Common plastics generally create the greatest static charges.
ELECTROSTATIC DISCHARGE (ESD)
If two items are at the same electrostatic charge or equipotential, no discharge will occur.
However, if two items are at different levels of ElectroStatic charge (i.e. one is positively and the other one negatively charged), they will want to come into balance. If they are in close enough proximity, there can be a rapid, spontaneous transfer of electrostatic charge. This is called discharge or ElectroStatic Discharge (ESD). Examples in daily life:
- Lightning, creating lots of heat and light
- The occasional zap felt when reaching for a door knob
- The occasional zap felt when sliding out of a car and touching the door handle
Have you felt the zap before?
In a normal environment like your home, there are innumerable ESD events occurring, most of which you do not see or feel. It takes a discharge of about 2,000 volts for a person to feel the “zap”. It requires a much larger ESD event to arc and be seen (e.g. lightning). While a discharge may be a nuisance in the home, ESD is the hidden enemy in a high tech manufacturing environment. Modern electronic circuitry can be literally burned or melted from these miniature lightning bolts. ESD control is therefore necessary to reduce and limit these ESD events.
TYPES OF ESD DEVICE DAMAGE
ESD damage to electronic components can lead to:
- Catastrophic Failures
- Latent Defects
Catastrophic failure causes a failure in an ESD sensitive item that is permanent. The ESD event may have caused a metal melt, junction breakdown or oxide failure. Normal inspection is able to detect a catastrophic failure.
A latent defect can occur when an ESD sensitive item is exposed to an ESD event and is partially degraded. It may continue to perform its intended function, so may not be detected by normal inspection. However, intermittent or permanent failures may occur at a later time.
COSTLY EFFECTS OF ESD
A catastrophic failure of an electronic component can be the least costly type of ESD damage as it may be detected and repaired at an early manufacturing stage.
Latent damage caused by ESD is potentially costlier since damage occurs that cannot be felt, seen or detected through normal inspection procedures. Latent defects can be very expensive as the product passes all inspection steps and the product is completed and shipped. Latent defects can severely impact the reputation of a company’s product. Intermittent failures after shipping a product can be frustrating, particularly when the customer returns a product, reporting a problem which the factory again fails to detect. It consequently passes inspection and the product is returned to the customer with the problem unresolved.
The worst event is when the product is installed in a customer’s system, and performs for a while and then performs erratically. It can be very expensive to troubleshoot and provide repairs in this situation.
One study indicated the cost to be:
- £7 Device
- £7 Device in board – £700
- £7 Device in board and in system – £7,000
- £7 Device and system fails – £70,000
Industry experts have estimated average electronics product losses due to static discharge to range from 8 to 33%. Others estimate the actual cost of ESD damage to the electronics industry as running into the billions of dollars annually.
It is critical to be aware of the most sensitive items being handled in your factory. As electronic technology advances, electronic circuitry gets progressively smaller. As the size of components is reduced, so is the microscopic spacing of insulators and circuits within them, increasing their sensitivity to ESD. As you can predict, the need for proper ESD protection increases every day.
If you’re new to ESD and ESD Control, we suggest you read this article for more information on how to protect your ESD sensitive devices.
Last time we talked about what to look out for when using containers to transport or store ESD sensitive items. Have you implemented our 3 tips yet?
Today we thought we’d cover a topic that ties in nicely with last week’s post: Protektive Pak® Impregnated Corrugated Material. Never heard of it? Don’t panic – we’re here to help! Protektive Pak® Material is made from static dissipative impregnated corrugated material with a buried shielding layer – it provides static shielding to protect ESD sensitive items from ElectroStatic charges, and ElectroStatic Discharges [ESD].
Introduction to Protektive Pak® Material
So now you’re probably wondering what’s different about this type of material – loads of companies out there offer similar products, right? That’s true – BUT what makes Protektive Pak® Material so unique is that its ESD properties are manufactured into the liners of the material itself. Many other materials have a coating or paint applied that gives them their ESD properties. This in itself is not a problem. However, it becomes an issue if the outer layer of your ESD container is damaged.
Protektive Pak® Inplant Handler – for more information click here
Have you ever removed tape from your ESD container or accidently pierced the surface with a sharp object? If you have, chances are you’ve found the black coat give way to a lighter brown material. That’s your ESD properties gone potentially damaging your ESD sensitive devices inside the ESD container. This will not happen with Protektive Pak® Material – even if the outer layer is damaged, your ESD sensitive items are still protected. Not convinced? Check-out this video.
Protektive Pak® Circuit Board Shippers – for more information click here
4 Reasons why you should be using Protektive Pak® Material
Independent ESD tests have proven that Protektive Pak® Impregnated Corrugated Material is superior! Click here to see the full test report. The bottom line is:
- Protektive Pak® impregnated corrugated material has a buried shielding layer.
- Protektive Pak® impregnated corrugated material equals or exceeds the discharge shielding capabilities of a coated box.
- Protektive Pak® impregnated corrugated material has discharge shielding capabilities equal to a metal-out shielding bag.
- Protektive Pak® impregnated corrugated material meets the ANSI/ESD S541 recommendation, avoiding rapid discharge when contacting ESD sensitive items – coated boxes DO NOT.
Comparing Impregnated Corrugated Protektive Pak® and Coated Materials
Now that we have talked about the advantages of Protektive Pak® Material – how exactly does it compare to the more common coated materials out there on the market? The below table provides a summary:
|Impregnated vs. Coated Material|
Manufactured by one paper mill with computerized control, resulting in consistent high quality.
|Manufactured without computer controls and applied at various geographical locations, resulting in quality variations.|
Carbon is added during the paper making process. The paper is a 6-layer process. The top surface layer is static dissipative, measuring 107 to 109 ohms. The conductive layer is in the 5th layer from the surface measuring <104 ohms.
|Material is coated or printed with carbon loaded black ink which is then coated with a clear sealer to help coating stay on. Shielding layer is very close to surface and high carbon content can bleed through. Result is very poor and inconsistent static dissipative effectiveness.|
|3||LOWER SULPHUR CONTENT
Manufactured from 100% recycled paper with consistently low sulphur content.
|Manufactured from either recycled or virgin paper or a combination of both. sulphur content may be low or high which can cause corrosion to leads and circuits.|
1,000 Times Thicker: Abrasion tests have shown no loss in particles at 100 cycles, only 1% loss for 200 cycles and 60% loss for 500 cycles.
|Tests have shown a 50% loss in particles in only 10 cycles and a 100% loss in 100 cycles.|
|5||SLOWS RAPID DISCHARGE
Burying the conductive layer under a dissipative surface reduces the potential for a rapid discharge when contacted by a charged device.
|A very conductive surface that may pose a charged device model (CDM) ESD danger to components stored in open bin boxes, in-plant handlers, shippers, totes, nesting trays, etc.|
|6||BETTER SHIELDING EFFECTIVENESS
Shielding effectiveness is equal to or greater than coated conductive materials.
|Some coated products shield poorly due to inconsistent application procedures by some manufacturers.|
More durable structure, 1,000 times thicker, which consistently shields your product from ESD, is also safer and better for the environment.
|Simple structure which can lack consistency of ESD shielding, durability and safety.|
All microscopic photos are approximately the same scale. A PDF version of the above table is available here.
Do you use containers to store or transport ESD sensitive items? If so, make sure to read on! We’ve compiled a list of 3 tips you should follow to make sure your ESD sensitive devices are fully protected. So let’s get started:
1. Use shielded containers!
ElectroStatic Discharge (ESD) is silent, quick and potentially lethal to electronic parts. When electronic parts are not properly handled during manufacturing, assembly, storage or shipping, damage from ESD can reach into the millions of dollars each year.
For an ESD control container to be effective and meet EN 61340-5-1 Edition 2.0 2016-05, the requirements are:
- Surface resistance 1 x 104 to < 1 x 1011 ohms per IEC 61340-2-3
- Discharge Shielding (energy penetration) < 50 nanoJoules per IEC 61340-4-8
We know what you’re saying now: “But non-shielding containers are so much less expensive than ESD shielding containers.” Unfortunately, it’s not as simple as that.
Non-shielding containers might be cheaper, but they are not less costly when it comes to handling ESD sensitive items. Anytime ESD sensitive parts and assemblies are handled, regular containers are not a sound option, even part of the time, as the risk of ESD damage is always lingering. As a result, costs will be incurred, either via ESD damage or as an additional investment in discharge shielding packaging and material handling containers.
The disadvantages of cross-using shielding and non-shielding containers include:
- Increased cost
- Risk from ESD damage
- Handling inconvenience
The cost of a discharge shielding container is far less than the cost associated with damaged parts or extra handling that result with a “less expensive” non-shielding container. So the bottom line is: ALWAYS go for shielded containers!
2. Put a lid on it!
A Faraday Cage effect can protect ESDS contents in a container with a shielding layer (this is what a shielding bag has). This Faraday Cage effect protects people in real life when a lightning bolt strikes an airplane or automobile with the charge residing on the outer metal fuselage or car body.
The Faraday cage effect causes charges to be conducted around the outside surface of the conductor. Since similar charges repel, charges will rest on the exterior.
To complete the enclosure, make sure to place lids on boxes or containers. 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.
|Outside an EPA||Inside an EPA|
Outside the ESD protected area (EPA), the lid needs to be in place to provide the ESD control property electrostatic discharge shielding. Per Packaging Standard EN 61340-5-3 clause 5.3 Outside an EPA: “Transportation of sensitive products outside of an EPA shall require packaging that provides both:
|Inside the EPA, it would still be a good idea to have the lid in place, but it is not a requirement. When using a shielded container, electrostatic charges and discharges take the path of least resistance. Packaging with the discharge shielding property protects ESD sensitive items from the effects of static discharge that are external to the package.|
3. Choose the right foam!
Generally speaking, there are 2 types of foam available with shielded containers: pink static dissipative and black conductive foam. Depending on your application and/or budget you should choose the one best suited for you.
There are resistance differences but the key is that the black foam resistance is inherent and longer lasting:
|Pink Static Dissipative Foam||Black Conductive Foam|
|Static dissipative polyurethane <1011 ohms||Conductive polyurethane 1 x 103 to < 1 x 105 ohms|
|Antistatic low charging – minimising electrostatic charge generation||Permanently conductive|
|Will lose electrical properties over time||Will not lose electrical properties|
|When exposed to the environment, the foam will discolour (turn yellow) over time||Foam will not discolour over time|
|Economical||Higher initial investment; better value for long term applications|
|Ideal for short term use and/or one-time shipments||Ideal for storing or transporting ESDS over a prolong period of time, and reusing the container|
|Not recommend for lead insertion applications||Not recommended in applications where Static Dissipative properties are required|
|Easy to adapt for custom uses by die-cutting, laminating, etc.|
|Non-contaminating, non-corrosive, and non-sloughing|
We hope you found this post helpful and informative – let us know if you have any requests for future blog posts.
Last week we talked about why insulators in your ESD Protected Area (EPA) can cause problems and started creating a list of the most commonly used insulative items that you should replace with ESD safe alternatives. Missed the post? Catch-up here.
So let’s continue with our list:
If you work with solder irons or perform various cleaning tasks at your ESD workstation, you will likely be using water or some sort of cleaning agent. Where do you store those liquids? Plastic cups? If so, that’s a BIG no-no and if you’re truly committed to your ESD Control Programme, you should be switching to ESD protective bottles immediately. ESD dispensing bottles come in all sorts of sizes, colours and with different pumps or spouts. Whatever type you need for your application, you will generally be able to find an ESD alternative.
Examples of ESD safe dispensing bottles – more information
ESD dispensing bottles are dissipative and high-quality types will have no migratory additives which reduces the chance for contamination from the bottle.
Examples of dissipative and conductive brushes – more information
Summing-up the most important points in regards to using brushes in your ESD protected area (EPA):
- Use dissipative or conductive brushes in an EPA.
- All portions of the brush (handle and bristles) need to be conductive/dissipative.
- Operators need to be grounded during use.
- Choose dissipative bristles if your product/assembly may be holding a charge and Charged Device Model (CDM) failures are a concern.
Probes are ideal for opening plastic cases such as MP3 players, cell phones, laptops, etc. and for popping out batteries. They are also used for holding, probing, and manipulating wires and components during assembly and soldering. ESD safe versions are made of nylon, wood or stainless steel.
Examples of ESD safe probes – more information
The hygroscopic (readily accepts moisture) properties of Nylon will make this tool suitable for use around ESD sensitive components after a few minutes of handling the tool with bare hands. If used with gloves in a clean environment the tools must be dipped in a topical antistatic solution before use in sensitive areas. Topical treatment should be repeated at six month intervals. Without exposure to moisture or antistatic treatment, Nylon is in the insulative resistance range and charges will not be removed to ground.
Wood is considered a safe material for use in ESD sensitive areas. It is hygroscopic and has a low propensity for triboelectric charge generation under most conditions.
Any charge on a stainless steel probe can be grounded when it is placed on an ESD protected work surface.
Waste bins and bin liners
ESD safe waste bins are generally conductive and are useful in ESD Protected Areas where waste accumulates and cannot be conveniently removed except in bulk. By placing them on a grounded floor, electrostatic charges are removed to ground. They do not require separate grounding when placed on a grounded surface.
Examples of waste bins and bind liners – more information
If you’re currently using standard bin liners, replace those with non-tribocharging ESD versions. Even at low humidity they do not become charged with static electricity and are designed for use in ESD protected areas where electrostatic sensitive devices are present.
And there you have it – a list of of tools and accessories that you should be replacing with ESD protective alternatives. Can you think of any others? Let us know in the comments!
In a previous post we talked about 2 types of materials you should be aware of in an ESD Protected Area (EPA): insulators and conductors. We learned that one way to protect your ESD sensitive devices (ESDs) is to replace regular insulative items with an ESD protective version. But exactly what items can and should you replace? Well, that’s what today’s post is all about. We put together a list of the most common items used at a workstation and explain in more details why they should be replaced and what options you have.
Conductors and Insulators
Materials that easily transfer electrons (or charge) are called conductors and are said to have “free” electrons. Grounding works effectively to remove electrostatic charges from conductors to ground.
Materials that do not easily transfer electrons are called insulators or non-conductors. An insulator will hold the charge and cannot be grounded; therefore, the charge cannot dissipate in a controlled way. This could lead to static damage of nearby sensitive components as there can be a rapid, spontaneous transfer of electrostatic charge.
So how do you control static electricity in the workplace? Easy – just follow these principles:
- Remove all unnecessary non-conductors,
- Replace all non-conductive materials with dissipative or conductive materials and
- Ground all conductors.
So what insulators in your EPA can be replaced with dissipative of conductive materials? Here is a list of the most commonly used insulative items and their replacements:
Paper is everywhere in the workplace and an ESD Protected Area is no exception. The problem with regular paper is that it is insulative but tends to be low charging because it is hygroscopic (readily absorbs moisture). The primary concern with paper is placing ESD sensitive items on the paper interfering with the path-to-ground of the grounded ESD mat. Best practice is to use dissipative paper or have regular insulative paper in dissipative document holders or wallets.
Dissipative self-stick notes – more information
EN 61340-5-1 “Paperwork inside the EPA shall either be kept in containers conforming to the requirements of table 2 or shall not generate a field in excess of that specified in paragraph 5.3.5 (ESDS should not be exposed to electrostatic fields in excess of 10 kV/m).”
There are a number of products available on the market that can assist with handling documents/paper in ESD Protected Areas:
- ESD safe document holders and wallets
Document wallets and holders are designed for use within ESD Protected Areas in accordance with EN 61340-5-1. They are static dissipative which means charges are removed to ground when placed on a grounded working surface or handled by a grounded operator.
Examples of ESD safe document wallets and holders – more information
- ESD safe ring binders and clipboards
Ring Binders and clipboards are designed to replace high charging insulative regular binders for use within ESD protected areas. They come in different widths with different ring sizes and 2 or 4 rings. Just like document holders/wallets they are static dissipative so charges are removed to ground when placed on a grounded working surface or handled by a grounded operator.
Examples of ESD safe ring binders and clipboards – more information
- ESD safe letter trays
Generally conductive, any electrostatic charges on letter trays are removed to ground when the tray is placed on a grounded working surface or contacted by a grounded operator. They do not require separate grounding when laid on a grounded surface.
Examples of ESD safe letter tray – more information
We all love our cup of tea or coffee in the morning and most of us have water bottles on stand-by throughout the day to stay hydrated. But do you know how much charge a foam or plastic cup generates? Well, let’s just say it’s enough to damage your precious components! The answer: ESD safe drinking cups and water bottles. There aren’t too many options out there so make sure you do your research before purchasing.
ESD safe water bottles are generally dissipative so charges are removed when placed on a grounded surface or handled by a grounded operator.
Menda drinking cup – more information
One option for a drinking cup (for hot drinks) is the MENDA insulated drinking cup. It is low charging and the stainless steel portion is grounded when picked up by a grounded operator or when placed on a grounded ESD worksurface.
Read the follow-up post here.
Most people are aware of regular high charging tape in ESD Protected Areas (EPAs) and know that these should be replaced with ESD tape. However, there is a lot of confusion out there as to what type of ESD tape should be used for what application. So we’ve put together an overview of the different types of ESD tape available and when to use them.
“All generators of electrostatic charges, such as untreated plastic films, foams, synthetic fibres, adhesive tapes, etc., must be prohibited and should be kept away from the EPA [ESD protected area].” (EN 61340-5-2 section 6)
“EPA should never have any electrostatic generative adhesive tapes or labels, as these can cause very high potentials when applied or stripped off.” (EN 61340-5-1 section 7.4)
ESD Cellulose Tape
- Colour: generally transparent; some types have a blue, red, green or yellow hue
- Film construction: cellulose
Examples of ESD Cellulose Tape – find out more
- Sealing ESD bags and other ESD packaging/containers
- General purpose ESD tape applications
- Secure (bundle) IC DIP tubes
- Prevents damage to sensitive electronic components in manufacturing
- Ideal for holding notes, work orders or instructions in offices, ESD workstations, or for general purpose
- Ideal for conformal coating or holding and sealing supplies in manufacturing
- Ideal in packaging for container sealing, static shielding bag closure and holding DIP tubes
- Use with ESD symbols for ESD awareness
ESD Conductive Shielding Grid Tape
- Colour: tan/brown with black grid pattern
- Film construction: antistatic copolymer with conductive grid layer
Examples of ESD Conductive Shielding Grid Tape – find out more
- For applications requiring EMI shielding
- Use in areas where the generation of static electricity is of concern
- Secure (bundle) IC tubes
- Cover external plugs, holes or connector pins on electronic chassis (black boxes, etc.) during transportation or storage
ESD High-Temp Masking Tape
- Colour: natural
- Film construction: crepe paper
Examples of ESD High-Temp Masking Tape – find out more
- Silk screening applications
- Masking application in spray and brush painting, non-staining
- Protective purposes in manufacturing processes, strips clean
- For securing polyethylene sheeting to walls during painting
- For OEM repair shops
- Use in applications masking PCBs gold features for wave soldering or soldering under 150°C
- Thick conductive adhesive excellent for conformability to protect critical PCB features
- Easily handles high temperatures of wave soldering without leaving significant residue
- Handles temperatures found in test and burn-in ovens
- For best results, apply to board using a rubber roller
ESD High-Temp Polyimide Tape
- Colour: brown opaque
- Film construction: polyimide
Examples of ESD High-Temp Polyimide Tape
- Ideal for masking gold leads and other components on boards populated with sensitive integrated circuits
- Thick conductive adhesive excellent for conformability to protect critical PCB features
- Masking off PCBs for IR reflow ovens or wave soldering under 300°C for ~ 10 seconds
Aisle or Floor Marking Tape
- Colour: yellow with black printing
- Film construction: PVC
Examples of Floor Marking Tape – find out more
- Use to mark off floors designating ESD Protective Areas
- Can be used as area signs
- Note: floor marking tape has no ESD control properties
- Colour: yellow with black printing
- Film construction: PVC
Example of Packaging Tape – find out more
- Suitable for sealing secondary packaging such as cartons
- Note: packaging tape has no ESD control properties
ESD tapes come in all sorts of widths and lengths so make sure you check the specifcations to ensure your chosen tape will work for your application. And once you’ve picked the right kind of ESD tape, don’t forget an ESD tape dispenser to go with it…