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Conductors & Insulators

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We’ve previously published a post that explains when you need ionisation. However, following this post, we got a number of questions that prompted us to dive a bit deeper into the whole subject of ionisers. Basically with this post we’re starting right at the beginning so stay tuned…
Before talking about ionisers in more detail, we need to have a little chat about the types of materials that can be found in an EPA – conductors and insulators:

Conductors

• Electrical current flows easily
• Can be grounded

Materials that easily transfer electrons (or charge) are called conductors and are said to have “free” electrons. Some examples of conductors are metals, carbon and the human body’s sweat layer. Grounding works effectively to remove electrostatic charges from conductors to ground. However, the item grounded must be conductive.
The other term often used in ESD control is dissipative which is 1 x 104 to less than 1 x 1011 ohms and is sufficiently conductive to remove electrostatic charges when grounded.

ConductorWhen a conductor is charged, the ability to transfer electrons gives it the ability to be grounded.

Insulators

• Electrical current does not flow easily
• Cannot be grounded

Materials that do not easily transfer electrons are called insulators and are by definition non-conductors. Some well known insulators are common plastics and glass. An insulator will hold the charge and cannot be grounded and “conduct” the charge away.
Both conductors and insulators may become charged with static electricity and discharge. Grounding is a very effective ESD control tool; however, only conductors (conductive or dissipative) can be grounded.

InsulatorInsulators like this plastic cup will hold the charge and cannot be grounded and “conduct” the charge away.

Insulators, by definition, are non-conductors and therefore cannot be grounded. Insulators can be controlled by doing the following within an EPA:
• Keep insulators a minimum of 31cm from ESDS items at all times or
• Replace regular insulative items with an ESD protective version or
• Periodically apply a coat of topical antistat

“Process essential” Insulators

When none of the above is possible, the insulator is termed “process essential” and therefore neutralisation using an ioniser should become a necessary part of the ESD control programme.

Examples of some common process essential insulators are a PC board substrate, insulative test fixtures and product plastic housings.
An example of isolated conductors can be conductive traces or components loaded on a PC board that is not in contact with the ESD worksurface.
Reduction of charges on insulators does occur naturally by a process called neutralisation. Ions are charged particles that are normally present in the air and as opposite charges attract, charges will be neutralised over time.
A common example is a balloon rubbed against clothing and “stuck” on a wall by static charge. The balloon will eventually drop. After a day or so natural ions of the opposite charge that are in the air will be attracted to the balloon and will eventually neutralise the charge. An ioniser greatly speeds up this process.

BalloonA balloon “stuck” on a wall by static charge.

What is an ioniser?

An ioniser creates great numbers of positively and negatively charged ions. Fans help the ions flow over the work area. Ionisation can neutralise static charges on an insulator in a matter of seconds, thereby reducing their potential to cause ESD damage.

IoniserAn ioniser creates positively and negatively charged ions.

Note: Ionisers require periodic cleaning of emitter pins and the offset voltage must be kept in balance. Otherwise, instead of neutralising charges, if it is producing primarily positive or negative ions, the ioniser will place an electrostatic charge on items that are not grounded.

Summary

This citation from the ESD handbook provides an excellent summary:
The primary method of static charge control is direct connection to ground for conductors, static dissipative materials, and personnel. A complete static control program must also deal with isolated conductors that cannot be grounded, insulating materials (e.g., most common plastics), and moving personnel who cannot use wrist or heel straps or ESD control flooring and footwear. Air ionization is not a replacement for grounding methods. It is one component of a complete static control program.
Ionizers are used when it is not possible to properly ground everything and as backup to other static control methods. In clean rooms, air ionization may be one of the few methods of static control available.” (ESD Handbook ESD TR20.20 Ionization, section 5.3.6.1 Introduction and Purpose / General Information)

Now that you know what conductors and insulators are, how to treat them in an EPA and when to use ionisation, the next step is to learn about the different types of ionisers available. However, as this post is already quite long, we will save that part for next week so stay tuned…. Click here to read the follow-up post.

Storage and Transport of ESD Sensitive Items

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We thought today we could focus on ESD during storage and transport. If you have read our recent post on Tips to Fight ESD, you will remember how important it is to protect your ESD sensitive items when leaving an EPA. Yet, too often we see customers who have the perfect EPA, but when it comes to transporting and storing their precious components, it’s all falling apart.

1. Packaging required for transporting and storing ESD sensitive items

During storage and transportation outside of an EPA, we recommend that ESD sensitive components and assemblies are enclosed in packaging that possesses the ESD control property of shielding.

Remember:

  • In ‘shielding’ we utilise the fact that electrostatic charges and discharges take the path of least resistance.
  • The charge will be either positive or negative; otherwise the charge will balance out and there will be no charge.
  • Charges repel so electrostatic charges will reside on the outer surface.


2. The Faraday Cage effect

A Faraday Cage effect can protect ESD sensitive items in a shielding bag or other container with a shielding layer. To complete the enclosure, make sure to place lids on boxes or containers and close shielding bags.

ESDPackaging
Cover must be in place to create Faraday Cage and shield contents.

3. Types of shielding packaging

The below list gives a few examples of what types of shielding packaging is available on the market. This list is by no means complete; there are many different options out there – just make sure the specifications state “shielding” properties.

  • Metal-In Shielding Bags
    ESD bags which protect ESD sensitive items. The ESD shielding limits energy penetration from electrostatic charges and discharge. They offer good see-through clarity. Available with and without dissipative zipper.
  • Metal-Out Shielding Bags
    Integral antistatic and low tribocharging bags which will not electrostatically charge contents during movement. Bags have an aluminium metal outer layer of laminated film. Available with and without dissipative zipper.
  • Moisture Barrier Bags
    Offer ESD and moisture protection and can be used to pack SMD reels or trays. Check out this post for more information on MBB and ESD Control.
  • Bubble Shielding Bags
    These bags combine the “Faraday Cage” and mechanical protection. They shield about twice as well as normal shielding bags of equivalent size.
  • Component/Circuit Boards Shippers
    These boxes offer an efficient way of shipping or storing ESD sensitive circuit boards and other items. They provide ESD shielding with the lid closed. The foam cushioning reduces stress from physical shock.
  • In-Plant Handlers/Storage Containers
    Shield ESD sensitive items from charge and electrostatic discharges (with lid in place). They provide ESD and physical protection for ESD sensitive circuit boards.


4. Additional options for storing ESD sensitive items

Do you have the following in place?

  • ESD flooring
  • Grounded personnel (using foot grounders). Read this post for more information on how to ground moving personnel.
  • Grounded racking

TEAMOperator wearing foot grounders

IF (and this is a BIIIG IF) the above requirements are fulfilled, you can use conductive bags or containers to store your ESD sensitive items. Conductive materials have a low electrical resistance so electrons flow easily across the surface. Charges will go to ground if bags or containers are handled by a grounded operator or are stored on a grounded surface.
Conductive materials come in many different shapes and forms:

  • Conductive Black Bags
    Tough and puncture resistant bags which are made of linear polyethylene with carbon added. The bags are heat sealable.
  • Rigid Conductive Boxes
    Provide good ESD and mechanical protection. Boxes are supplied with or without high density foam for insertion of component leads or low density foam which acts as a cushioning material.
  • PCB Containers
    Are flat based and can be stacked. They are made of injection moulded conductive polypropylene.

Again, there are many more options available on the market so make sure you do your research.

Note: we do not recommend using conductive packaging to transport ESD sensitive devices. Also, pink antistatic and pink antistatic bubble bags are not suited for storing or transporting ESD sensitive components.

5. Final thoughts

Packaging with holes, tears or gaps should not be used as the contents may be able to extend outside the enclosure and lose their shielding as well as mechanical protection.
Also, do not staple ESD bags shut. The metal staple provides a conductive path from the outside of the ESD bag to the inside. The use of a metal staple would undermine the effectiveness of the ESD bag making a conductive path for charges outside the bag to charge or discharge to ESD sensitive components inside the bag. To close an ESD bag, it is recommended to heat seal or use ESD tape or labels after the opening of the bag has been folded over. Alternatively, you can use ESD bags with a zipper.

Picture5Sealing ESD Bags the correct way

One final word of warning:
When ESD sensitive items are unpackaged from shielding bags or other containers, they should be handled by a grounded operator at an ESD workstation

 

 

What you need to set-up an ESD Protected Area

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An ESD Protected Area (EPA) is a defined space within which all surfaces, objects, people and ESD Sensitive Devices (ESDs) are kept at the same potential. This is achieved by simply using only ‘groundable’ materials, i.e. materials with an electrical resistance typically of less than 109 ohms, for covering of surfaces and for the manufacture of containers and tools. All surfaces, products and people are bonded to Ground. Bonding means linking, usually through a resistance of between 1 and 10 megohms. Movable items, such as containers and tools, are bonded by virtue of standing on a bonded surface or being held by a bonded person. Everything that does not readily dissipate charge must be excluded from the EPA.

Example of an EPA Area:

EPA Area

1. Bench Top Ionisers 8. Ground Cords 15. Floor Mats
2. Packaging Containers 9. Overhead Ionisers 16. Wrist Straps
3. Earth Bonding Point Bar 10. Shielding Bags 17. Foot Grounders
4. Testers and Monitors 11. Data Acquisition 18. Lab Coats
5. ESD Tape 12. PCB Storage 19. Floor Maintenance
6. Worksurface Mats 13. Signs and Labels 20. Waste Bins and Liners
7. Surface Resistance Meters 14. Floor Marking Tape 21. Document Handling

Vermason Continuous Monitors and ESD Control

Vermason Continuous or Constant Monitors pay for themselves by improving quality, productivity, eliminating wrist strap daily testing and test result logging. EN 61340-5-1 specifies wrist strap standard ANSI/ESD S1.1 which states “The wrist strap system should be tested daily to ensure proper electrical resistance. … Daily testing may be omitted if continuous monitors are used.“(1)

Companies manufacturing products containing ESD sensitive items need to ask themselves “how important is the reliability of our products”?
Because wrist straps have a finite life, it is important to develop a test frequency that will guarantee integrity of the system. Typical test programs recommend that wrist straps that are used daily should be tested daily. However, if the products that are being produced are of such value that a guarantee of a continuous, reliable ground is needed then continuous monitoring should be considered or even required.“(2)

The wrist band will normally be worn for several hours at a time so it needs to be comfortable while making good contact with the skin. It is a good idea to check the wrist strap every time it is applied. Constant on line monitors can be used so that any breaks will be immediately found.“(2)

The ESD Association produced the ESD TR 12-01 technical report which is entitled “Survey of Constant (Continuous) Monitors for Wrist Straps”(3). It contains useful information:
Since people are one of the greatest sources of static electricity and ESD, proper grounding is paramount. One of the most common ways to ground people is with a wrist strap. Ensuring that wrist straps are functional and are connected to people and ground is a continuous task.” “While effective at the time of testing, wrist strap checker use is periodic. The failure of a wrist strap between checks may expose products to damage from electrostatic charge. If the wrist strap system is checked at the beginning of a shift and subsequently fails, then an entire shift’s work could be suspect.

Wrist strap checkers are usually placed in a central location for all to use. Wrist straps are stressed and flexed to their limits at a workstation. While a wrist strap is being checked, it is not stressed, as it would be under working conditions. Opens in the wire at the coiled cord’s strain relief are sometimes only detected under stress.

The goal remains consistent; electrical connections are tested between the ground point, coiled cord, wrist band, and body while the wearer performs operations on static sensitive items.

In many EPAs [ESD protected areas] constant monitor wrist straps are used. These fall into two categories, dual wrist band and single wrist band. The dual wrist strap type using a split band is used with a two core cord. The dual wrist strap type normally works using the resistance bridge method. The single wrist strap type uses a single strap for both grounding and monitor purposes and has an a.c. signal injected which is used for monitoring purposes. This type has the advantage of using the simpler single wrist strap.“(4)

Impedance (or single wire) constant monitors:
The impedance monitor uses a detection circuit designed to reduce false alarms and eliminate adjustments. [It] use[s] the phase difference between current and voltage to detect changes in impedance of the cord, band and person. A very low AC voltage is used for constant sensing. Any standard [single wire] wristband and coiled cord can be used.

Impedance Wave Distortion Technology used in Vermason Single Wire Continuous Monitors utilises AC analysis to determine if the correct conditions exist. A steady state 1 volt AC signal is sent out and the impedance (combination of resistance and capacitance) of the system will distort the signal wave. The acceptable distorted wave consists of a 1 megohm resistor and the impedance ranging from a 90 lb., 5 foot tall person on the low end and a 250 lb., 6 foot, 5 inch tall person on the high end. If the 1-megohm resistor is not there, the alarm will sound. If the resistive component of the path to ground exceeds 18 megohms, the alarm will sound. Vermason has never received a skin irritation complaint using impedance wave distortion technology Continuous Monitors.

Resistance (or Dual Wire) constant monitors:
This type of monitor is used with a two wire (dual) wrist strap. When a person is wearing a wrist strap, the monitor observes the resistance of the loop, consisting of a wire, a person, a wristband, and a second wire. If any part of the loop should open (become disconnected or have out of limit resistance), the circuit will go into the alarm state.” “While the continuity of the loop is monitored, the connection of the wrist strap to ground is not monitored.” “There are two types of signals used by resistance based constant monitors; steady state DC and pulsed DC. Pulsed DC signals were developed because of concerns about skin irritation. However, pulse DC units introduce periods of off time (seconds) when the system is not being monitored.“(3)

Vermason Dual Wire Continuous Monitors utilise a steady state DC signal and never have received a skin irritation complaint. Vermason Dual Wire Wrist Straps passed the ANSI/ESD S1.1 flex test at over 1,000,000 cycles vs. the 16,000 requirement while the top competitor has touted their dual wire wrist strap life at only 200,000 cycles. Some brand dual wire wrist straps do not meet the ANSI/ESD S1.1 Breakaway Force requirement of less than five pounds but greater than one pound force.

Resistance Dual Wire continuous monitors, using the same technology as on demand touch testers, is easily understood. An important feature of the Dual Wire Wrist Strap is that even if one conductor is severed, the operator has reliable path-to-ground with other wire. The electrical signal does place that amount of charge on the operator. Vermason Zero Volt Monitor utilises a steady state DC dual polarity signal, with a plus signal sent via one wire and a minus signal sent via the other wire balancing and leaving virtually zero voltage on the operator. A Programmer is available to quickly and accurately set the upper and lower resistance levels to be monitored while the Continuous Monitor is installed at the workstation.

Working surface monitors:
An option available with some continuous or constant monitors is the ability to monitor working surface ground connections. “Some continuous monitors can monitor worksurface ground connections. A test signal is passed through the worksurface and ground connections. Discontinuity or over limit resistance changes cause the monitor to alarm. Worksurface monitors test the electrical connection between the monitor, the worksurface, and the ground point. The monitor however, will not detect insulative contamination on the worksurface.“(3)

Most Vermason Continuous Monitors do monitor the working surface ground. Note: the working surface must have a conductive layer such as Dual Layer Rubber or Dissipative 3-Layer Vinyl or Micastat® Dissipative Laminate with conductive buried layers. Vermason Continuous Monitors are not recommended for use with homogeneous matting.

Selection Considerations:
When considering constant monitors, the equipment cost including the wrist strap, maintenance and training cost, labor time for performing wrist strap tests, and the potential failures due to non-functional wrist straps should be considered. A broken wrist strap may expose products to ESD over an entire shift if it is checked only at shift change with wrist strap checker. Constant monitors may reduce the time people spend testing wrist straps before each shift.“(3)

(1) ANSI/ESD S1.1 Annex A3 Frequency of System Testing
(2) User guide CLC/TR 61340-5-2 Wrist Strap clause 4.7.2.4.4 Test frequency
(3) ESD TR 12-01 Technical Report Survey of Constant (Continuous) Monitors for Wrist Straps

(4) IEC 61340-5-1 Electrostatics – Part 5-1: Protection of electronic devices from electrostatic phenomena – General requirements

ESD Control – Other Considerations

Application Photo of Surface Resistance Test Kit

OTHER CONSIDERATIONS
Discipline
A significant increase in the discipline of implementing the fundamentals of ESD control noted in ANSI/ESD S20.20 Foreword, calls for:

  • Ground all conductors in the EPA including people
  • Remove all insulators from the EPA or use ionizers for process necessary insulators
  • Package ESD sensitive items going outside the EPA in packaging that provides electrostatic discharge shielding

Insulators
We encourage developing a hatred for insulators. The alternatives are:

    Remove the insulative item from the EPA

  • Substitute the item with an ESD protective version (such as tape, document holders, material handling containers, plastic bottles, etc.)
  • Periodically treat insulative surface with a topical antistat
  • Neutralize electrostatic charges using ionization

Other ESD Control Items
Other EPA ESD control items to add to the ESD control program might include shelving, mobile equipment (carts), gloves, and/or seating.

Improve Compliance Verification Plan

  • Consider greater frequency of internal audits per ESD TR53
  • Use of computer data collection system for wrist straps and footwear testing, continuous monitors, and ionizers
  • Use of ground continuous monitors for worksurfaces and other ESD elements
  • Test ionizers more frequently, consider self monitoring ionizers, consider computer based data collection
  • Increased testing using static field meter to verify that automated processes (like auto insertion, tape and reel, etc) are not generating charges above acceptable limits.

Application Photo of Volt Meter and Software in Factory STM97.2 Testing Voltage Charge on Person (Photograph courtesy of TREK, INC.)

Improve Training

  • ESD awareness training for all in the EPA or who may come into the EPA including suppliers
  • Testing to verify comprehension and training adequacy
  • Training on the proper use of test equipment
  • Training on proper compliance verification test procedures

Application Photo CD-ROM ESD Training

Conclusion
Just to maintain a company’s current level of quality and reliability may require a substantial improvement in a company’s ESD control program. Now is the time for improvement as ESD sensitivity withstand voltages continue to get lower and companies may soon be handling class 0A HBM items. To combat HBM failures improved personnel grounding is required. For example, heel grounders should be replaced with full coverage foot grounders. However, most failures are CDM. To combat CDM failures, ionization should be added or improved, and conductive surfaces should be covered with dissipative material. In general, disciple should be enhanced implementing ESD control fundamentals, compliance verification testing should be increased, and training should be improved.

From published article “Now is the Time for ESD Control Programs to be Improved” by Fred Tenzer and Gene Felder. See full article at InCompliance Magazine- September 2012

What’s Happening to Electronics Device ESD Sensitivity

Factory ESD control is expected to play an ever-increasing critical role as the industry is flooded with even more HBM (Human Body Model) and CDM (Charged Device Model) sensitive
designs.

ElectroStatic Discharge (ESD) is the hidden enemy within your factory. You cannot feel or see most ESD events but they can cause electronic components to fail or cause mysterious and
annoying problems. There are two types of ESD damage: 1) catastrophic failures, and 2) latent defects. By definition, normal quality control inspections are able to identify catastrophic failures, but are not able to detect latent defects.

In general, the ESD susceptibility of modern electronics are more sensitive to ElectroStatic Discharge; that is the withstand voltages are lower. This is due to the drive for miniaturization and with electronic devices operating faster. Thus the semiconductor circuitry is getting smaller. What’s happening currently? The width of electronic device structures continues to get smaller. Intel began selling its 32nm processors in 2010 that would be 0.032 micrometer equal to 0.000032 millimeter or 0.00000128 inch.

See www.ESDA.org, the ESD Association’s latest White Paper “Electrostatic Discharge (ESD) Technology Roadmap” Revised April 2010” forecasts increased ESD sensitivities continuing the recent “trend, the ICs became even more sensitive to ESD events in the years between 2005 and 2009. Therefore, the prevailing trend is circuit performance at the expense of ESD protection levels.” The White Paper’s conclusions include:

  • With devices becoming more sensitive through 2010-2015 and beyond, it is imperative that companies begin to scrutinize the ESD capabilities of their handling processes. Factory ESD control is expected to play an ever-increasing critical role as the industry is flooded with even more HBM (Human Body Model) and CDM (Charged Device Model) sensitive designs. For people handling ESD sensitive devices, personnel grounding systems must be designed to limit body voltages to less than 100 volts.
  • To protect against metal-to-device discharges, all conductive elements that contact ESD sensitive devices must be grounded.
  • To limit the possibilities of a field induced CDM ESD event, users of ESD sensitive devices should ensure that the maximum voltage induced on their devices is kept below 50 volts.
  • To limit CDM ESD events, device pins should be contacted with static-dissipative material instead of metal wherever possible.

See May 2010 article by Dr. Terry L. Welsher The “Real” Cost of ESD Damage which includes “Recent data and experience reported by several companies and laboratories now suggest that many failures previously classified as EOS [Electrical Overstress] may instead be the result of ESD failures due to Charged Board Events (CBE). Some companies have estimated that about 50% of failures originally designated as EOS were actually CBE or CDE [Charged Device Events].”

ANSI/ESD S20.20, the ESD Association document covering the development of an ESD control program, lists numerous ESD Protected Area (EPA) ESD control items. Each company can pick and choose which ones are appropriate for their program. The selection of specific ESD control procedures or materials is at the option of the ESD Control Program Plan preparer and should be based on risk assessment and the established electrostatic discharge sensitivities of parts, assemblies, and equipment.” [ANSI/ESD S20.20-2007 Annex B] “An EPA [ESD protected area] shall be established wherever ESDS [ESD Sensitive] products are handled. However, there are many different ways to establish ESD controls within an EPA. Table 3 lists some optional ESD control items which can be used to control static electricity.” [ANSI/ESD S20.20-2007 section 8.3 ESD Protected Areas (EPAs)]

There are companies with good ESD control programs who are pleased with their quality and reliability results. But to maintain that level, they would be wise to consider ESD control program improvements. Now might be a good time to do that.

From published article “Now is the Time for ESD Control Programs to be Improved” by Fred Tenzer and Gene Felder. See full article at InCompliance Magazine– September 2012

Flexibility of EN 61340-5-1 ESD Control Plans

To have an ESD control programme conform to EN 61340-5-1 does the programme have to use all the ESD protected area ESD control items listed in Table 3? These are: working surfaces, storage racks, trolleys, flooring, ionization, seating, and garments.

Answer:
No, you can decide which ESD control items to use.

Per EN 61340-5-1 clause 5.2.1 “ESD control program plan, The organization shall prepare an ESD control program plan that addresses each of the requirements of the program. Those requirements concern:

  • training,
  • compliance verification,
  • grounding/bonding systems,
  • personnel grounding,
  • EPA requirements,
  • packaging systems,
  • marking.”

Each company has flexibility designing its programme as EN 61340-5-1 Introduction states: “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.”

The ESD control programme plan is to be written. We recommend starting by reviewing Annex A of User guide CLC/TR 61340-5-2:2008 “Example ESD Control Document based on IEC 61340-5-1”. It notes “The following document demonstrates the flow and required sections for an ESD control program as defined by IEC 61340-5-1. This program is based on one of the most basic ESD programs that can be implemented. In most cases, an actual ESD program will utilize more ESD control elements. Personnel are grounded by a wrist strap. Handling operations are performed at a grounded worksurface and ESD sensitive devices are moved from operation to operation inside a metallized shielding bag.”

To ask an ESD Question Click Here

ESD Survey – 50% Off from Vermason

Book an ESD Survey for
March 7 or 8, 2012
and receive the ESD Survey
for 50% off the standard price

Do you want a FREE OF CHARGE ESD SURVEY?

You place an order for a survey at £175, if you order goods following the survey with a total value of more than £175 you get the survey at no cost.

Is your ESD Control Programme in Compliance? Is it costing
your company too much money and/or future business?


Is it compliant to your own internal standards?
Is it compliant to your customer(s) standards?
Is it compliant to industry accepted standards?

To place your ESD Survey enquiry – CLICK HERE

Request an ESD Control Survey at any of your facilities or your supplier’s facility and receive:

  • ESD Assessment verifies that your ESD products meet EN-61340-5 standards.
  • Receive a written report to help improve your productivity, quality, and customer satisfaction.
  • Typically provides 10:1 Return on Investment.

The Vermason ESD control survey written report cites applicable EN61340-5-1 and -2 citations.

Sign Up HERE | Click HERE for a typical EPA setup | See list of sales reps and distributors HERE
All items & programmes are available through your participating distributor | Submit your questions HERE

Solving The Wristband Snap Release Problem

by E. E. Bliley, Lucent Technologies

When ESD wristband snaps disconnecting from the coiled ground cords became a persistent problem for one manufacturing line, a thorough investigation revealed the culprit—the stud snap on the buckle. More specifically, a direct correlation was discovered between the breakaway force and the unintentional disconnects for formed snaps vs. machined snaps.

The solution resulted in an improved ESD process as well as a reduction in the cost of wristband and coil-cord products for Lucent Technologies in Columbus, OH. In this 2.2 million square feet facility, approximately 5,200 employees are engaged in manufacturing wireless telecommunications equipment deployed throughout the world. An estimated 3,000 ESD-protected workstations are located in 39 separate manufacturing areas.

All employees are trained in ESD control per Lucent corporate requirements. Each employee is recertified at a maximum of 24 months. Control of ESD is accomplished through wrist straps, static-dissipative work surfaces, grounded workstations, and proper handling of static-generating material.

The Problem Unfolds

In April 1999, a high-performance team on the second shift asked the ESD coordinator to help solve a functionality problem with wristbands. The team reported that the coiled ground cord was easily disconnected from the wristband. Sometimes the accidental snap release was discovered immediately, but more often it was several minutes later.

This problem puzzled the ESD coordinator who had been in his position for nearly four years. Why had this problem not surfaced earlier? After a couple of meetings with the team, the ESD coordinator decided the concern was valid and started an investigation to determine the magnitude of the problem.

Analysis

Production associates began keeping records on the frequency of accidental snap releases over a given period of time. Each of the 16 associates recorded the number of unintentional disconnects over a 21-day period. During the study period, 241 unintentional disconnects were experienced by the team members. This data yielded an average of 0.72 releases per person per day and substantiated the magnitude of the problem.

Since four employees had zero disconnects, analysis of their work patterns was conducted to determine if undue stretching of the cord and/or excessive mobility might be responsible for the accidental releases. This study showed that employees seated at test sets had the fewest releases.

A dimensional analysis was conducted to determine if the stud on the wristband might be the problem. The shank, minimum diameter, and the head, maximum diameter, were measured and the data analyzed. In many cases, the analysis noted that the difference between the two diameters was only a few thousandths of an inch. This finding convinced the ESD coordinator that a real problem existed and further investigation was warranted.

The supplier of the ground cords and wristbands was contacted to discuss the breakaway force specification. The supplier maintained that its breakaway force specification ranged between 0.5 and 5.0 lb.

This specification was compared to the ESD Association ESD-S1.1 Standard for Protection of Electrostatic Discharge Sensitive Items: Personnel Grounding Wrist Straps. It states that “at least 1 pound but not more than 5 pounds of breakaway force applied to the ground lead in the normal disconnect direction shall be required to cause separation.”

To continue reading Solving The Wristband Snap Release Problem Click Here.

Enhancing Profits With Effective ESD Control

Our thanks to Conformity Magazine Published in December 2004 issue

Accurate process evaluation provides real answers

Provided by the ESD Association
by Stephen Halperin, in collaboration with Ron Gibson

“We need to spend HOW MUCH?”
Recently, a company experienced several large losses due to electrostatic discharge (ESD) and had a very unhappy customer on their hands. The manufacturing vice president now faced a substantial expenditure for new ESD loss prevention equipment. The company’s first step had been to hire an ESD consultant who recommended the purchase of several thousands of dollars in ionization equipment and monitoring instruments for several of the company’s facilities.

The troubled VP read the report several times looking for justification of the expense. However, the report did not define how the recommended equipment would meet the VP’s specific needs. Other than describing how ionization reduced electrostatic charge after it is generated and that the instruments could confirm that a discharge occurred, the report did not identify the actual cause of the process problem. No ESD measurements were described. There were no details related to cause of product loss, device sensitivity concerns, value issues, process and handling details, examination and description of existing controls, or rationale for how the recommended tools would solve the problem in question. The report was clearly based on the consultant observing the process of a single manufacturing environment. In effect, the report made a purchasing recommendation based on a “blanket” opinion, not on facts specific to the needs of the company or their customer. Such an approach typically makes a bad situation worse. While the recommended tools may have been very useful for investigating a process or for solving defined problems, they are expensive Band Aids“ when used in undefined problem situations.

Today’s electronic manufacturing environment demands that minimal ESD controls be in place to provide fundamental protection for electrostatic discharge sensitive (ESDS) devices. When basic ESD controls are employed and losses still occur, manufacturing and quality managers face more difficult problems., In assessing the problem, companies struggle with a variety of major questions concerning a specialized technology, while having minimal information and available skills. To avoid the risk of making the wrong investment decision without solving the initial problem, management needs a way to select and implement the most effective ESD controls that fit their financial situation, solve their specific problems, and provide a respectable return on their investment.

To continue reading Enhancing Profits with Effective ESD Control Click Here

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