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Now is the Time for ESD Control Programs to be Improved

Originally Published by InCompliance Magazine- September 2012
“By Fred Tenzer and Gene Felder”

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 particularly with electronic devices operating faster. Thus the semiconductor circuitry is getting smaller. For example Intel began selling its 32 nm processors in 2010 that would be 0.032 micrometer equal to 0.000032 millimeter or 0.00000128 inch.

For more information on ESD and the direction of electronics manufacturing, see the articles listed below.

Evaluation Engineering Magazine November 2001 article “ESD Control Program Development” “As the drive for miniaturization has reduced the width of electronic device structures to as small as 0.10 micrometer (equal to 0.0001 millimeter or 0.000004 inch), electronic components are being manufactured with increased ElectroStatic Discharge (ESD) susceptibility.”

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 are:

“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 and CDM 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.”

InCompliance Magazine 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 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.”

Charleswater

For additonal technical information Click Here

To read the rest of the article go to Now is the Time for ESD Control Programs to be Improved

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Tips for Addressing Charged Device Model Failures


CHARGED DEVICE MODEL

It may seem to some that CDM has newly arrived as a problem for ESD control programs. However, the ESD Association first published ANSI/ESD STM5.3.1 in 1999 – ESD Association Standard for Electrostatic Discharge Sensitivity Testing – Charged Device Model (CDM) – Component Level. Basically, CDM testing has to do with “testing, evaluating and classifying the electrostatic discharge (ESD) sensitivity of components to the defined charged device model (CDM)” … “to allow for accurate comparisons of component CDM ESD sensitivity levels.”

JESD22-C101C Field-Induced Charged-Device Model Test Method for Electrostatic-Discharge-Withstand Thresholds of Microelectronic Components Table 3
Devices shall be classified as follows:
CLASS I <200 volts
CLASS II 200 to <500 volts
CLASS III 500 to 1000 volts
CLASS IV >1000 volts

The importance of CDM came about primarily because of the increased use of automated component handling systems. The Foreword of ANSI/ESD STM5.3.1 states “In the CDM a component itself becomes charged (e.g., by sliding on a surface (tribocharging) or by electric field induction) and is rapidly discharged (by an ESD event) as it closely approaches a conductive object.”

In November 2002, Roger Peirce published an article entitled “The Most Common Causes of ESD Damage”. There were actually 23 causes. As the founder and president of ESD Technical Services, Roger had investigated hundreds of companies for over eight years. All 23 causes were CDM failure modes. So CDM is really not so new, it has just received a lot of attention in the last few years.


TACKLING CDM

So, what are the things companies should look at to improve their ESD control program regarding CDM? It would seem to be easy: don’t slide ESDS devices and assemblies unless grounded at all times, keep insulators at least 12” away from ESDS, and don’t allow ESDS items to make contact with a conductive surface. Seems simple, but in actual application . . . not so easy.

If the ESD control program has not used ionization that should be considered. If the ESDS items becomes charged, ionization will help neutralize the charge. The primary function of ionizers with regard to ESDS items are:

  • To remove / neutralize charges from process necessary insulators, which can charge ESDS items, thus creating the potential for a damaging CDM event
  • Remember that the PCB substrate is a process necessary insulator and can become charged during automated handling processes
  • To remove / neutralize charges from a charged, isolated/floating conductor, which, when grounded can result in a potentially damaging CDM event
  • Remember that during automated handling processes, the ESDS devices on the PCB are isolated or floating conductors

Use an Overhead Ionizer to neutralize charges at your workstation.

The ESD Standards Committee has a Working Group (WG-17) which is currently involved with developing a Standard for Process Assessment to help the electronics community assess their manufacturing and handling processes to determine what levels of devices their process can handle. Once one fully understands where their process is with regards to ESDS devices and assemblies, they will have a clearer picture on what actions need to be taken to further improve the ESD Control Program.

If ionizers are already in use, the company should consider reducing the ionizer offset voltage limit of ±50 volts (the required limit in ANSI/ESD S20.20) to ±25 volts and maybe less, depending on the application and device sensitivity. Discharge times are user defined and should be considered for reducing the time required to neutralize a ± 1,000 volt charge to ± 100 volts.

The required limit for worksurfaces per ANSI/ESD S20.20 is less than 1 x 10^9 ohms with no lower limit. Most companies handling electronics should be following the recommendation of Worksurface standard ANSI/ESD S4.1 that the lower limit be 1 x 10^6 ohms. To combat CDM failures, all surfaces that might come into contact with ESDS items should be dissipative at the 1 x 10^6 to less than 1 x 10^9 ohms range used for worksurfaces where possible. Items such as Static Shielding bags will have a higher resistance on the interior & exterior surfaces, but it still must be less than 1 x 10^11 ohms.

Use a Statfree Dissipative Mat on your workstation.

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

Images of ESD Damage

Seeing ElectroStatic Discharge (ESD) damage is basically impossible. Damage to semiconductor device structure is NOT visible at ordinary magnifications of an optical microscope. If the microscope is capable of 1000X-1500X magnifications, you just might be able to “see” something. The method used, only occasionally as there is considerable expense, is by delayering and etch enhancement producing high magnification photographs using a scanning electron micrograph (SEM). See Images of ESD Damage, photos of Human Body Model (HBM) ESD damage provided by Hi-Rel Laboratories, Inc. at 6116 N Freya, Spokane, Washington 99217 (509-325-5800 or www.hrlabs.com). Used with their permission.

Ground Trolleys in Series With Cords Having 1 Megohm Resistor

Question:
I am confused on ESD connections. I understand that you cannot clip a cord from a wrist strap to the edge of an ESD protective mat. I know that the cord for wrist straps has 1 megohm of resistance and that the point to connect the wrist strap cord should have less than 1 ohm to ground.

I have people using 2 meter high metal rolling trolleys. I believe the preferred method is to connect each trolley directly to a common ground point. Can several trolleys, say 3 to 5 be connected in series with 1 megohm cords with the final cord connected to a ground point or earth bonding point? From what I have read this would only mean about 5 megohms to ground at the furthest cart. I read somewhere something about staying under 35 megohms to ground. Now I cannot find that.

Answer:
The compliance verification limit per EN 61340-5-1 for wrist strap system is less than 3,5 x 10^7 ohms listed in Personnel grounding requirements Table 2. The required limit per ANSI/ESD S20.20 for both working surfaces and mobile equipment (trolleys) is less than 1 x 10^9 ohms resistance to ground listed in EPA requirements Table 3.

It does not do much good to have an operator test their wrist strap using an integrated wrist strap tester as describe in IEC 61340-5-1 Clause A.1, but then work where the matting resistance is added resistance in the path-to-ground.

Although not recommended you could attach the cord for the wrist band to the matting material, and daisy chain the mats and/or trolleys if you could demonstrate that you reliably meet the required limits.

Per CLC/TR 61340-5-2:2008 User guide Wrist Strap subclause 4.7.2.2.2 “NOTE Many wrist strap users have been observed to clip the wrist cord to the edge of an ESD protective mat. This process is not recommended as it can increase the total system resistance to ground to over the 3.5 x 10^7 ohms limit required by IEC 61340-5-1.”

Regarding daisy-chaining “All working surfaces need to be capable of being grounded. EPA grounding of instruments or surfaces by chaining, or by placing items in series should not be used, since in the event of a broken connection the risk of floating items and ESD damage will be unnecessarily increased.” [EN 61340-5-2 clause 5.2.2 Working surfaces and storage racks] Note that both of these recommendations are not requirements.

Regarding ground cords, 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 ground point or common connection point is acceptable and recommended.

However, “A nominal 1 megohm resistor is commonly used in wrist straps and to ground work surfaces. In the event of an operator touching an energized conductor, for the normal mains electricity supplies this resistor will limit the current flowing through the person to less than 0,5 mA.” [User Guide IEC 61340-5-2-1999 subclause 5.1.1]

Charleswater sells ground cords with and without current limiting resistors – Click Here

ESD Control Programs Should be Improved

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 particularly with electronic devices operating faster. Thus the semiconductor circuitry is getting smaller.

See November 2001 Evaluation Engineering Magazine article “ESD Control Program Development” “As the drive for miniaturization has reduced the width of electronic device structures to as small as 0.10 micrometer (equal to 0.0001 millimeter or 0.000004 inch), electronic components are being manufactured with increased ElectroStatic Discharge (ESD) susceptibility.”

What’s happening currently? Intel began selling its 32 nm 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 are:

“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 and CDM 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 InCompliance Magazine 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 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.”

Charleswater

For additonal ESD information Click Here

ESD Control Program Considerations when Dealing with Class Zero Items

ANSI/ESD S20.20 Foreword states:

  • “This standard covers … electrical or electronic parts, assemblies and equipment susceptible to damage by electrostatic discharges greater than or equal to 100 volts Human Body Model (HBM).”
  • “When handling devices susceptible to less than 100 volts HBM, more stringent ESD Control
    Program Technical Requirements may be required, including adjustment of program Technical
    Element Recommended Ranges.”

HMB Classification Class 0 is:
Per ESD-STM5.1 Human Body Model (HBM) Table 1 Class 0 has ESD Voltage Range < 250 Volts
Basically, to control the environment to decrease the probability of ESD damage in “Class Zero”
situations, involves increasing ESD protective redundancies and periodic verifications to those ESD
Control technical elements.

Improved Grounding

  • Personnel: Decrease Wrist Strap and ESD Footwear upper limit permitted (The ESD Association has test data showing charge on a person is less as the path-to-ground resistance is less) The use of continuous monitors, smocks, use / increased use of ESD flooring, sole or full coverage foot grounders (HBM & CDM)
  • Worksurfaces: Dissipative (CDM) i.e. change < 10^9 to a requirement of 10^6 to 10^8 ohms
  • Bonded grounds – Carts, shelves, equipment
  • Conductors: Minimizing isolated conductors like devices on PC Boards (CDM)

To see examples of Wrist Straps capable of dealing with class zero environments Click Here

To see examples of Grounding Cords capable of dealing with class zero environments Click Here

Minimize Charge Generation
The best form of control is to minimize charge generation. Grounding and ionization eliminate charges once generated. Shielding protects from generated charges.

  • Personnel – Low Charging floor finish
  • Surfaces – Use of low charging (anti-static) topical treatments

Insulators

  • Eliminate as best as possible all non-process necessary insulators
  • Topically treat where ever possible insulators that cannot be removed
  • Consider use of ESD Chairs or treat to reduce charge generation
  • Shield charges on clothing by using ESD Smocks

To continue reading ESD Control Program Considerations when Dealing with
Class Zero Items Click Here

About ESD Awareness

About Electrostatic Discharge

We have all seen static electricity in the form of lightning or perhaps felt the zap when reaching for a door knob. Similar types of electrical charges can have an effect on the electronic components you handle every day in your work. Unfortunately, their effect is much more hazardous and not as readily apparent.

Definition

Static electricity is an electrical charge at rest. Static electricity is most commonly created by friction and separation. Friction causes heat which excites the molecular particles of the material. When two materials are then separated, a transfer of electrons from one material to the other may take place.

As electrons transfer, the absence or surplus of electrons creates an electrical field known as static electricity. The simple separation of two materials, as when tape is pulled off a roll, can also create this same transfer of electrons between materials, generating static electrical fields.

The amount of static electricity generated depends upon the materials subjected to friction or separation, the amount of friction or separation and the relative humidity of the environment. Common plastic generally will create the greatest static charge. Low humidity conditions such as those created when air is heated during the winter will also promote the generation of significant static electrical charges.

Materials that easily transfer electrons (or charge) between atoms are called conductors and are said to have “free” electrons. Some examples of conductors are metals, carbon and the human body’s sweat layer. Materials that do not easily transfer electrons are called insulators. Some well known insulators are common plastics, glass and air. Both conductors and insulators may become “charged” with static electricity. When a conductor is charged, the free electrons give it the ability to discharge rapidly when it comes close to another conductor with a different potential.

Typical Electrostatic Voltages

Many of the common activities you perform daily may generate charges on your body that are potentially harmful to components.

Some of these activities include:

  • Walking across a carpet, 1,500 to 35,000 volts
  • Walking over untreated vinyl floor, 250 to 12,000 volts
  • Worker at a bench, 700 to 6,000 volts
  • Vinyl envelope used for work instructions, 600 to 7,000 volts
  • Picking up a common plastic bag from a bench, 1,200 to 20,000 volts

To continue reading About Electrostatic Discharge Awareness Click Here

Use ESD Control Products Correctly Or You Can Do More Harm Than Good

A Comprehensive Program Is Required For Effective ESD Control

With most companies pressured by global competition, effective ESD control can be a key to improving productivity, quality, and customer satisfaction. It is a pity that many companies buy ESD protective products or equipment and then misuse them, often causing more harm than good.

Electronic components that are electrostatic discharge sensitive (ESDS) must be protected throughout the entire manufacturing cycle. According to ANSI/ESD S20.20, the ESD Association’s standard for the development of an Electrostatic Discharge Control Program, safeguards are required during activities that “manufacture, process, assemble, install, package, label, service, test, inspect or otherwise handle electrical or electronic parts, assemblies and equipment susceptible to damage by electrostatic discharges.”

If ESD latent defects occur during this manufacturing and product cycle, it can be most frustrating and costly. Latent defects in components by definition will not be detected so products will pass normal inspections. ESD damage is the hidden enemy; electrostatic charges cannot be seen, typically discharges less than 3,000 volts cannot be felt, and latent defects cannot be detected through normal quality control procedures.

Manufacturing facilities should be as diligent with their ESD control program as hospital operating rooms are in implementing sterilization procedures. Damage caused by invisible and undetectable events occurs in medicine where people can experience infection or even death from viruses or bacteria. In hospitals, the defense against this invisible threat is extensive contamination control procedures including sterilization.

To learn more about correct ESD product usage Click Here

Introducing Jewel® Workstation Mini Monitor

  • NEW Improved Banana Jack
    Creates a more consistent connection and helps to prevent accidental disconnects with operator’s wrist strap banana plug.
  • Replaces Item 99130
  • Can be used with any brand of single-wire wrist strap and cord
  • Single station Continuous Monitor for operator and ESD worksurface
  • Made in the United States of America
Item Description Price
99135 Jewel® Workstation Mini Monitor, 220VAC $132.09
Sign up HERE | Request a demo HERE | See list of sales reps and distributors HERE
All items & programmes are available through your participating distributor | Submit your questions HERE

ESD Control Programme Periodic Verification

by Fred Tenzer and Gene Felder, Desco Industries, Inc.

Some practical advice for implementing
ESD control periodic checks
Want to accomplish something important? A familiar formula is write a plan, select the specifications, and then periodically test to verify that the plan is being implemented according to the test
results. This is basically the requirements of an ESD control program, per the ESD Association standard, ANSI/ESD S20.20. This important standard, entitled Development of an Electrostatic Discharge Control Program, covers the requirements necessary to design, establish, implement, and maintain an ESD control program to protect electrical or electronic parts, assemblies and equipment susceptible to ESD damage.
S20.20 is a process document, and provides ESD control plan guidance; one of its requirements is having a “compliance verification plan” as a component of the ESD control plan. Per S20.20, paragraph 6.1.3., Compliance Verification Plan:
“A Compliance Verification Plan shall be established to ensure the organization’s compliance with the requirements of the Plan. Formal audits or certifications shall be conducted in accordance with a Compliance Verification Plan that identifies the requirements to be verified, and the frequency at which those verifications must occur. Test equipment shall be selected to make measurements of appropriate properties of the technical requirements that are incorporated into the ESD program plan.”
To view more information on ESD Control Program Periodic Verification CLICK HERE