Category Archives: Packaging, Handling and Storage
Most people are aware of the dangers ElectroStatic Discharge (ESD) can pose on a Printed Circuit Board (PCB). A standard bare PCB (meaning that it has no semiconductor components installed) should not be susceptible to ESD damage. However, as soon as you stuff it with electronic (semiconductor) devices, it becomes susceptible according to each of the individual’s susceptibility.
However, there is another risk factor many operators forget: moisture.
So, today’s blog post is going to address both issues and will explain how you can protect your PCBs from both when storing them.
The problem with moisture
By now you will be well aware of the problems ESD damage can cause.
Moisture, on the other hand, may be a new issue to you. Surface Mounted Devices (SMDs), for example, absorb moisture and then during solder re-flow operations, the rapid rise in temperature causes the moisture to expand and the delaminating of internal package interfaces, also known as “pop corning.” The result is either a circuit board assembly that will fail testing or can prematurely fail in the field.
Moisture from air diffuses inside the plastic body & collects in spaces between body & circuit, lead frame and wires. Expanding vapour can crack (popcorn) the plastic body or cause delamination.
All PCBs should be stored in a moisture barrier bag (MBB) that’s vacuum sealed. In addition to the bags, Desiccant Packs and Humidity Indicator Cards must be used for proper moisture protection. This ‘package’ is also known as a dry package.
Most manufacturers of the Moisture Sensitive Devices (MSD) will dictate how their product should be stored, shipped, etc. However, the IPC/JEDEC J-STD-033B standard describes the standardised levels of floor life exposure for moisture/reflow-sensitive SMD packages along with the handling, packing and shipping requirements necessary to avoid moisture/reflow-related failures. The ESD Handbook ESD TR20.20 mentions the importance of moisture barrier bags in section 220.127.116.11.2 Temperature: “While only specialized materials and structures can control the interior temperature of a package, it is important to take possible temperature exposure into account when shipping electronic parts. It is particularly important to consider what happens to the interior of a package if the environment has high humidity. If the temperature varies across the dew point of the established interior environment of the package, condensation may occur. The interior of a package should either contain desiccant or the air should be evacuated from the package during the sealing process. The package itself should have a low WVTR.”
Components of a dry package
A dry package has four parts:
1. Moisture Barrier Bag (MBB)
3. Humidity Indicator Card (HIC)
4. Moisture Sensitive Label (MSL)
Moisture Barrier Bags (MBB) work by enclosing a device with a metal or plastic shield that keep moisture vapour from getting inside the bag. They have specialised layers of film that control the Moisture Vapour Transfer Rate (MVTR). The bag also provides static shielding protection.
Desiccant is a drying agent which is packaged inside a porous pouch so that the moisture can get through the pouch and be absorb by the desiccant. Desiccant absorbs moisture vapour (humidity) from the air left inside the barrier bag after it has been sealed. Moisture that penetrates the bag will also be absorbed. Desiccant remains dry to the touch even when it is fully saturated with moisture vapour. The recommended amount of desiccant is dependent on the interior surface area of the bag to be used. Use this desiccant calculator to determine the minimum amounts of desiccant to be used with Moisture Barrier Bags.
Humidity Indicator Cards (HICs) are printed with moisture sensitive spots which respond to various levels of humidity with a visible colour change from blue to pink. The humidity inside barrier bags can be monitored by the HIC inside. Examining the card when you open the bag will indicate the humidity level the components are experiencing so the user can determine if baking the devices is required.
The Moisture Sensitive Level (MSL) label tells you how long the devices can stay outside the bag before they should be soldered onto the board. This label is applied to the outside of the bag. If the “level” box is blank, look on the barcode label nearby.
Creating a dry package
Now that you know the components of a dry package, you’re probably wondering: but how do I put it all together? Not to worry – we’ve got you covered! If you follow these steps, you will create a secure dry package and your PCBs will be protected – against ElectroStatic Discharge and moisture.
Place the desiccant and HIC onto the tray stack. Trays carry the devices. Remember to store desiccant in an air tight container until it used.
Place the MSL label on the bag and note the proper level on the label.
Place the tray stack (with desiccant and HIC) into the moisture barrier bag.
Using a vacuum sealer, remove some of the air from the bag, and heat seal the bag closed. It is not good to take all the air out of the bag. Only slight evaluation is needed to allow the bag to fit inside a box.
Now your devices are safe from moisture and ESD.
Do you use moisture barrier bags in your facility? What are your experiences? We’d love to hear from you in the comments!
And that’s a wrap! Just to let everyone know that we will be taking a little summer break over the next few weeks so there won’t be any new posts going up until the end of September. Don’t miss us too much…
If your company has an ESD Control Programme per EN 61340-5-1 in place, you need to define ESD protective packaging for ESD sensitive items (ESDs). But where do you start? Don’t panic – we’re here to help!
What is ESD Protective Packaging?
ESD Protective Packaging comprises all “items and materials that provide intimate protection for ESDS parts during all phases of handling, shipping and storage”. [EN 61340-5-2 User Guide clause 4.8.1 Introduction and purpose]
You don’t need to worry about secondary or exterior packaging unless it’s used for ESD protection purposes.
Example of ESD Protective Packaging – Protektive Pak Inplant Handlers
Why do you need ESD Protective Packaging?
The fundamentals of ESD control include grounding all conductors in the EPA. ESD packaging will have special material composition to lower the resistance so that when grounded, electrostatic charges will be removed to ground thus protecting your ESD sensitive devices inside.
“An ESD protective packing system’s basic function is to make up the difference between the ESD sensitivity of the product and the level of threat that exists in the distribution environment. For example, if the product has a human body model sensitivity of 100 V and the people that will be handling the package are known to have a maximum of 1 000 V on their bodies, then a package shall be selected that will make up the difference between the product’s ESD sensitivity and the distribution environment.” [EN 61340-5-2 User Guide clause 4.8.3 Selecting/designing the right package]
Packaging is to be determined for all material movements inside and outside of the ESD Protected Area (EPA). Best practice is to define the required packaging or material handling item on the product’s bill of materials. Remember: the ESD packaging is just as important as a component part.
Customer contract packaging can take precedence, but otherwise “the organization shall define ESD protective packaging requirements for ESDS within the plan based on IEC 61340-5-3. Packaging, when required, shall be defined for all material movement within EPAs, between EPAs, between job sites, field service operations and to the customer.” [EN 61340-5-1 clause 5.3.5 Packaging]
Choosing your ESD Protective Packaging
A number of factors need to be taken into consideration when choosing your ESD protective packaging including “the ESD sensitivity of the product as well as the expected distribution environment hazards.” [EN 61340-5-2 User Guide clause 4.8.3 Selecting/designing the right package]
Example of ESD Protective Packaging – Protektive Pak Circuit Board Shippers
The User Guide EN 61340-5-2 recommends the following steps to implement your ESD Protective Packaging:
1. Understand the product sensitivity
You can gather information about the ESD sensitivity of an item by either measuring it in-house, contacting the manufacturer of the product or by analysing published ESD sensitivity data.
2. Determine the distribution environment for the packaged product
Knowing the environment in which the product is shipped and how it will be handled is extremely important. Humidity and temperature are the main factors to consider when it comes to choosing the right type of packaging for your ESD sensitive items. If items are susceptible to moisture, barrier material should be chosen to prevent excessive humidity exposure. On the other hand, condensation may occur inside the packaging if temperatures vary around the dew point of the established interior conditions. In those instances, desiccant should be put inside of the package or the air should be evacuated from the package before shipment.
3. Determine the type of packaging system that is best suited for the intended application
The first step is to choose low charging or static dissipative materials when in contact with ESD sensitive devices. Many companies also require the packaging to protect the contents from a direct discharge or exposure to electric fields. In addition to these requirements, there are further questions that need to be asked:
- Returnable or reusable packaging?
- Disposable or one-time only packaging?
- Aesthetic requirements for packaging?
4. Select and test packaging materials
Test methods are explained in EN 61340-5-1 and will classify packaging materials as conductive, static dissipative or insulative.
5. Design a packaging system
Once the ESD sensitivity and distribution environment have been evaluated and available materials have been selected, the design of the packaging system can begin. Per the User Guide, the following general rules apply:
- “If the package is primarily used to transport product in an ESD protected environment then a low charging, static dissipative package may suffice.
- If the product is moving between ESD protected areas (uncontrolled environment) a low charging, discharge shielding package may be required.
- When the package is shipped into a totally uncontrolled environment a low charging discharge shielding package is recommended.”
In addition to these guidelines, there may be additional factors that should be considered, e.g.:
- Cost/value relationship: The cost of the packaging compared to the total value of the contents is important. Some companies choose less expensive packaging for less valuable parts.
- Handling: If rigorous handling is expected, cushioned packaging may need to be considered.
6. Test the final packaging design for effectiveness
It is highly recommended to subject packages to the type of hazards that can be expected during shipments. These tests can, for example, involve the following:
- High voltage discharges to the exterior of the packaging
- Simulated over the road vibration
- Drop tests
- Environmental exposure
Final thoughts on ESD Protective Packaging
Now that you have an understanding of the factors to consider when choosing your ESD Protective Packaging, you’re ready to implement the above guidelines. ESD packaging comes in all sorts of shapes and forms so bear in mind to not just look at bags when deciding what type of packaging to choose. If you want to learn more about the different types of options, we recommend reading this post.
Also, remember that ESD packaging should be marked. This post will help you finding the correct symbol for your application.
Example of ESD Protective Packaging – ESD Bags
Do you currently use ESD Protective Packaging? Do you use bags or boxes or something else? How did you choose your ESD Protective Packaging?
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.
Today’s post concludes our 2-part series on periodic verifcation. If you have missed the first part, you can catch-up on it here. As a reminder, it is recommended to regularely check all ESD Protected Area (EPA) products to ensure they are working correctly. After covering working surface matting and wrist straps in last week’s post, we’ll jump right in to discuss the remaining components in your EPA.
A flooring / footwear system is an alternative for personnel grounding for standing or mobile workers. Foot grounders quickly and effectively drain the static charges which collect on personnel during normal, everyday activities. Foot grounders should be used in conjunction with floor surfaces which have a surface resistance of less than 1010 ohms.
As ESD floors get dirty, their resistance increases. For optimum electrical performance, floor matting must be cleaned regularly using an ESD mat cleaner, such as Reztore™ Surface & Mat Cleaner. Do not use cleaners with silicone as silicone build-up will create an insulative film on the surface.
Dissipative floor finish can be used to reduce floor resistance. Periodic verification will identify how often the floor finish needs to be applied. As the layer(s) of dissipative floor finish wear, the resistance measurements will increase. So, after some amount of data collection, a cost effective maintenance schedule can be established.
Testing floor matting
Floor matting can be checked using a resistance meter. Surface resistance meters are designed to measure resistance point-to-point (Rp-p) or surface to ground (Rg) in accordance with EN 61340-5-1 Electrostatics and its test method IEC 61340-2-3.
ESD Shoes or Foot Grounders play an essential part in the flooring/footwear system. For more information on how to ground moving personnel effectively, check this post.
Before handling ESD sensitive devices, visually inspect your ESD footwear for any damage. Just like wrist straps, footwear should be checked while being worn using a wrist strap/footwear tester.
Checking foot grounders using 222567
Records of each test should be kept. Analysis and corrective action should take place when a footwear tester indicates a failure. Footwear needs to be checked daily.
Re-using shielding bags is acceptable as long as there is no damage to the shielding layer. Shielding bags with holes, tears or excessive wrinkles should be discarded.
Make sure your ESD shielding bags are un-damaged
It is up to the user to determine if a shielding bag is suitable for re-use or not. The testing of every bag before re-use is not practical. Many companies will discard the shielding bag once used and replace it with a new one. Others will use a system of labels to identify when the bag has gone through five handling cycles:
- Non-reusable labels are used that require the label be broken to open the bag.
- The bag is then resealed with a new label.
- When there are five broken labels, the bag is discarded.
The same principle applies to other ESD packaging, e.g. component shippers.
Ionisers are intended to neutralise static charges on insulators thereby reducing their potential to cause ESD damage. However, poorly maintained ionisers with dirty emitter pins and out-of-balance ionisers can put a charge on ungrounded items.
Remember to clean ioniser emitter pins and filters regularly. You can now even purchase ionisers that will alarm when emitter pins need to be cleaned or the ioniser is out of balance.
Checking ionisers using 50598
The EMIT Ionisation Test Kit 50598 allows the Digital Static Field Meter 50597 to be used to measure the offset voltage (balance) and charge decay of ionisation equipment. The Test Kit also includes a Charger used to place a ±1000V charge on the 50567 Conductive Plate, making it possible to measure the discharge times of air ionisation equipment per ANSI/ESD SP3.3 Periodic Verification of Air Ionizers.
Wrist Strap/Footwear and Resistance Testers etc.
So you check your wrist straps and/or footwear and bench and/or floor matting regularly. But have you remembered the testers themselves? What good do all the checks do, if the testers you use are out-of-spec and show you incorrect results?
Yearly calibration is recommended – many manufacturers offer a calibration service or alternatively you can purchase calibration units from them and perform the calibration yourself.
So there you have it – a list of the most commonly used products in your ESD Protected Area (EPA) that you should check on a regular basis.
Questions for you: Do you have a verfication plan in place? If so, how often do you check your ESD protection products?
We recently received a question regarding brushes in ESD protected areas (EPAs) so we thought this would be a great opportunity to share the information with all of you guys.
Problems with using regular brushes in an EPA
When a regular brush is being held by an operator and they wipe it upon a product or assembly, tribocharging occurs due to the contact and separation of the brush bristles on the product. Per the ESD Handbook ESD TR20.20 section 2.4 Sources of Static Electricity includes “Brushes (camel/pig hair and synthetic bristles).” Even if the operator is grounded, the electrostatic charge will remain on the brush fibres and/or handle. It is therefore a threat to discharge possibly damaging ESD sensitive products. All portions of the ESD brush are to be conductive or dissipative.”
Most man-made synthetic materials are high charging and generate a substantial electrostatic charge. Per the ESD Handbook ESD TR20.20 section 2.4 “It should be understood that any object, item, material or person could be a source of static electricity in the work environment. Removal of unnecessary nonconductors, replacing nonconductive materials with dissipative or conductive materials and grounding all conductors are the principle methods of controlling static electricity in the workplace, regardless of the activity.” Brushes whose job is intimate contact with products may be critical and it is recommended to change from high charging insulative materials to conductive and/or dissipative materials.
Often in an EPA, products are cleaned off by brushing or by blowing using a compressed gas. For any hand tool used in the EPA, the handle of the tool cannot be made from an insulative material as that will block the path-to-ground to the hand of the grounded operator. Charges on the tool can discharge and possibly caused damage to ESD sensitive products. There have been numerous examples in the industry where brushing a circuit board after soldering with insulative nylon brushes have caused product failures.
Types of brushes to use in an EPA
ESD control advises removing all insulators (non-conductors) and grounding all conductors in an ESD protected area (EPA). This can be accomplished by switching from regular brushes to ESD protective brushes.
Examples of Conductive Brushes
In an ESD protected area (EPA) an operator should use dissipative or conductive brushes when working on ESD sensitive products or assemblies. All portions of the brush need to be conductive or dissipative – so that includes both handle and bristles.
For ESD control purposes, conductive is less than 1 x 104 ohms (10,000 ohms) and static dissipative is 1 x 104 to less than 1 x 1011 ohms (10,000 to less than 100,000,000,000 ohms). This resistance range is able to remove electrostatic charges to ground when grounded.
Dissipative bristles (instead of conductive bristles) should be selected if the product or assembly may be holding a charge and Charged Device Model (CDM) failures are a concern.
Examples of Dissipative Brushes
An ESD brush is grounded by being held by the grounded operator. Also, the ESD brush will be grounded when in contact with a grounded working surface or bench mat.
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.
ESD brushes come in many sizes, shapes and hardness – all serving different applications. For more information, check our website.
If you’ve been handling ESD sensitive devices for a while, you’ve probably come across the different ESD symbols already. But do you know the difference(s) and when to use them? No? Read on!
Are you new to ESD protection or have just taken over responsibility for an existing ESD programme? Congratulations – you’ve come to the right place! Keep on reading!
1. ESD Susceptibility Symbol
The ESD Susceptibility Symbol is the most commonly known symbol which consists of a yellow hand in the act of reaching, deleted by a bar; all within a black triangle. It is intended to identify devices and assemblies that are susceptible to ESD.
The ESD Susceptibility Symbol
When to use the ESD Susceptibility Symbol
The ESD Susceptibility Symbol is correctly used as follows:
- on individual components and related documents to state: ‘this device is static sensitive; do not touch without appropriate precautions’
- on assemblies and related documents to state: ‘includes static sensitive components; take appropriate precautions’
- as part of a sign identifying an area where sensitive devices are handled; to warn all who approach it that precautions are required
Colour of the ESD Susceptibility Symbol
The colour is optional except “the color red shall not be used because it suggests a hazard to personnel.” The preferred colour is a yellow hand and slash on a black triangle.
2. ESD Protective Symbol
Just like the ESD Susceptibility Symbol, the ESD Protective Symbol has a reaching hand in a triangle. However, note the arc and missing slash through the triangle! Because of these differences it has a very different meaning.
This symbol should be on ESD protective products identifying a specialty product that has at least one ESD control property.
The ESD Protective Symbol is also called the ESD Packaging Symbol.
The ESD Protective Symbol
If a letter is under the triangle, it should identify the most important ESD control property:
- L = Low Charging
- D = Static Dissipative
- C = Conductive EPA (for use in the ESD Protected Area)
When to use the ESD Protective Symbol
The ESD Protective Symbol may be used to identify items that possess at least one ESD control property:
- Low Charging (formerly referred to as astatic or antistatic)
- Resistance (Conductive or Static Dissipative) able to remove electrostatic charges when grounded
- Discharge Shielding
Colour of the ESD Protective Symbol
The colour is optional except “the color red shall not be used because it suggests a hazard to personnel.” The preferred colour is a yellow hand and slash on a black triangle; the arc should be black.
3. ESD Common Ground Point and Earth Bonding Point Symbol
These two symbols identify where all ESD elements at an ESD workstation should be connected. There is a newer and older symbol; they are very different but basically have the same meaning:
- The Earth Bonding Point Symbol has the earth ground symbol and concentric circles around the ground snap, plug or jack.
- The ESD Common Ground Point Symbol has concentric circles with thick circle around the ground snap, plug or jack.
Both symbols should include text identification.
ESD Common Ground Point and Earth Bonding Point Symbol
Symbol artwork for all of the above symbols can be downloaded at no charge from the ESD Association.
Use the comments section below for any questions you may have.
Reference: EN 61340-5-1, CLC/TR 61340-5-2 ESD User guide, and Symbol standard ANSI/ESD S8.1.
Let’s talk “desiccant” and “humidity indicator cards” this week! “Desi-what” I hear you say???
Seems like we chose the right subject…!
But let’s rewind a little at this point: A few months ago we published a post on Moisture Barrier Bags (MBB) and ESD Control. The article described that Moisture Barrier Bags shield (no pun intended here!) ESD sensitive devices from 2 potential risks:
- The faraday cage created when using these bags correctly protects contents from ESD Damage.
- Specialised layers of film controlling the Moisture Vapour Transfer Rate (MVTR) also protect contents from moisture.
Moisture Barrier Bags
The blog post went on to explain that “desiccant” and “humidity indicator cards” must be used for proper moisture protection.
So what are “desiccant” and “humidity indicator cards” and how are they used? These are the questions we’d like to clarify with today’s blog post.
What is desiccant?
Desiccant is a drying agent that absorbs moisture from its surrounding area. Desiccant will stay dry to the touch even when it is fully saturated with moisture.
In a Moisture Barrier Bag it is used to ‘soak up’ moisture from the air inside the bag AFTER it has been sealed. Any moisture that gets through the bag from the outside will also be absorbed.
How is desiccant purchased?
Desiccant is available as a “unit” or fractional “unit”. A unit of desiccant absorbs a specific amount of moisture. One unit of desiccant weighs about 28g.
How is desiccant packaged?
Desiccant is packed in small sealed pouches made from a white plastic called “Tyvek” or brown “Kraft” paper. Tyvek pouches are very clean and sulphur free. Kraft pouches are economical.
A desiccant pouch
Pouches of desiccant are placed into metal pails – this ensures the desiccant is kept dry during transport and storage.
How much desiccant do you need?
A word of warning before we move forward – the following calculations may look a bit daunting at first sight. But honestly, once you’ve read through it all and calculated a couple of examples, you’ll be fine! Promise!!!
There are 2 different methods you can use – so let’s dive right in:
1. Method 1 per MIL-P-116
- Formula: Unit = 0.011 x bag area in square inches
- What you need: Bag area (2 times the surface area of your bag as there are 2 sides to a bag)
- Example: 10″ x 20″ MBB bag
- Apply formula: 0.011 x (10″ x 20″ x 2) = 4.4 rounded up to 4.5 units of desiccant
2. Method 2 per EIA 583 (allows you to tailor desiccant to your specific needs)
- Formula: Unit = 0.231 x Bag Area x Bag MVTR x Months divided by Moisture Capacity
- What you need: Bag area, Bag MVTR, Months of Storage, Maximum Interior Humidity (MIH), Moisture capacity table below:
10% MIH 3.0 g/unit 20% MIH 4.8 g/unit 30% MIH 5.8 g/unit 40% MIH 6.2 g/unit
- Example: 10” x 20” bag with a 0.02 MVTR, a 12 month storage time and a MIH of 20%
- Apply formula: 0.231 x (10″ x 20″ x 2) x (0.02) x (12/4.8) = 4.62 rounded down to 4.5 units of desiccant
Phew – told ya’ it wasn’t that bad! Now that we’ve covered the desiccant, we’ll take a quick look at humidity indicator cards. And I really mean “quick” because they’re much easier to explain/use….
What is a humidity indicator card?
A humidity indicator card allows for quick visual inspection of the relative humidity levels within its surrounding area. They are printed with moisture sensitive spots which respond to various levels of humidity with a visible colour change from blue to pink.
In a Moisture Barrier Bag they provide a low-cost method of verifying the effectiveness of the moisture barrier packaging. If you are using Moisture Barrier Bags, moisture will be an issue in your application so you’re obviously aiming for as little moisture as possible. However, if you happen to open your MBB and the humidity indicator card shows a relative humidity of 60%, you’ll know that the contents of your bag have been exposed to moisture and may not be safe for use anymore.
How are humidity indicator cards purchased?
Humidity indicator cards come in many shapes and forms. Some will show relative humidity from 10% – 60%; others from 5% to 15%. Depending on the sensitivity of your application to moisture, the correct type of card should be chosen.
Example of a humidity indicator card
Bear in mind that not all humidity indicator cards are reversible. Some cards will measure the relative humidity only once and then halt at that reading. These types of humidity indicator cards are NOT re-usable. This is important to know so make sure you check before purchasing!
How are humidity indicator cards packaged?
Humidity indicator cards are sold in containers. It is recommended that cards are stored in their original un-opened canister in a dry, well ventilated room with a reasonably consistent temperature of 20°C. Humidity indicator cards should not be stored in ultraviolet sunlight, moisture or heat.
How many humidity indicator cards do you need?
One humidity indicator card per MBB is needed for proper verification of relative humidity.
Moisture Barrier Bags, desiccant and humidity indicator cards all play a very unique and important role when protecting ESD sensitive devices from moisture. They should always be used together to ensure maximum protection. However, remember that all three tools need to be used correctly as otherwise all your efforts have been in vain. And don’t forget: your Moisture Barrier Bag must be heat sealed with a vacuum sealer to eliminate the amount of “moisture laden air” within the package.
Well, that’s it – that’s all we have for today! Did we answer all your questions? If not, let us know your questions in the comments below!