ESD Information

Welcome back to “A Minute with Miranda.” This week we will be discussing how to store and ship your static sensitive assemblies within and outside of an ESD Protected Area using an In-Plant Handler.

ANSI/ESD S20.20 requires that ESD protective packaging is necessary to store, transport and protect ESD sensitive electronic items during all phases of production and shipment. Beyond the static protection, packaging also provides protection from physical damage, moisture, dust and other contaminates. Per the ANSI/ESD S541 Packaging Standard packaging that is used inside and outside of an EPA shall be low charge generating, constructed from dissipative or conductive material for intimate contact with ESD items and provide electrostatic discharge shielding.

The Protektive Pak In-Plant Handlers are constructed from an impregnated dissipative corrugated material that has a surface resistance range of 1 x 106 to less than 1 x 109 ohms per ANSI/ESD STM11.11. This minimizes the potential of rapid discharge or sparking. The in-plant handlers will shield ESD sensitive items from charge and electrostatic discharges with the lid in place. The partition sets are constructed from the same impregnated dissipative material and are available in over 300 cell size configurations to suit your specific packaging needs.

View the full range of Protektive Pak In-Plant Handlers here.

Welcome back to “A Minute with Miranda.” This week we will be discussing how to test the point-to-point resistance (Rtt) and the resistance-to-ground (Rtg) of a Conductive ESD Floor.

ANSI/ESD S20.20 requires initial and periodic verification of an ESD Flooring System. ANSI/ESD STM7.1 outlines the test methods applicable for the Conductive flooring material. For the Point-to-Point resistance (Rtt) test the flooring will be tested with a resistance measurement meter and
2 x 5lbs cylindrical electrodes positioned 36” apart. The value for the test should be less than or equal to 1 x 106 ohms.

The Resistance Point-to-Ground (Rtg) test should be conducted with a resistance measurement meter and 1 x 5lbs cylindrical electrode. One lead from the meter should be connected to the ground point and the other lead will be connected to the electrode. The test value should be less than or equal to 1 x 106 ohms.

View the full range of SCS Surface Resistance Testers here.

Welcome back to “A Minute with Miranda.” This week we will be discussing how to test the point-to-point resistance (or Rpp) of an ESD Smock.

ANSI/ESD S20.20 requires initial and periodic verification of ESD Control items – this includes ESD Smocks. ANSI/ESD STM2.1 outlines the test method applicable for ESD Smocks: the ESD Smock is to be placed on an insulative surface and 2 x 5lbs cylindrical electrodes are to be positioned on each cuff before taking the measurement. The Resistance Point-to-Point Rpp of the groundable smock needs to be less than 1 x 109 ohms.

View the full range of SCS ESD Smocks here.

Welcome back to “A Minute with Miranda.” This week we will be covering how to properly wear a wrist strap.

ANSI/ESD S20.20 requires seated personnel to be connected to the grounding / equipotential bonding system via a wrist strap. The total resistance of the Wrist Strap System needs to be less than 3.5 x 10^7 ohms. The key to a wrist strap is the intimate contact of the band to the skin and that the coil cord is connected to ground. Wrist straps need to be tested at least daily before handling any ESD sensitive devices.

Operators can choose between elastic and metal wristbands. Elastic wristbands are comfortable to wear and easy to adjust. Metal wristbands generally last longer and are easier to clean. View the full range of SCS Wrist Straps here.

Welcome back to “A Minute with Miranda.” This week we will be covering how to perform the Rtt and Rtg test on an ESD Worksurface Mat.

Before using a worksurface mat in an EPA environment, you need to verify that the mat will meet the ANSI/ESD S20.20 Worksurface Requirements.
For both the Rtt and Rtg test the worksurface should test between 1 x 106 to less than 1 x 109 ohms. The test should be performed in accordance to the ANSI/ESD S4.1 Standards.

SCS worksurface mats meet the ANSI/ESD STM4.1 and ANSI/ESD S20.20 required limit of 1 x 10^6 to less than 1 x 10^9 ohms for Rtt and Rtg and the recommendations of ANSI/ESD S4.1.

View our complete SCS Static Worksurface mat offering here.

Welcome back to “A Minute with Miranda.” This week we will be covering how to launder your ESD Smocks.

SCS Static Control Smocks should be laundered periodically for proper operation. Smocks should be washed by hand or with a standard household washing machine using cold or warm water with a non-ionic liquid detergent. Avoid using bleach, fabric softeners or dry detergents as these can contaminate the conductive fibers and make the garment insulative .

After washing the smocks they should either be hung dry or tumbled dry at low heat. High heat can degrade the conductive fibers within the garment and degrade the ESD properties.

With normal wearing and washing conditions, SCS Static Control Smocks will maintain their ESD properties for a minimum of 100 washings.

SCS Smocks meet the requirement for Groundable Static Control Garment System per ANSI/ESD S20.20 required limit of less than 3.5 x 107 ohm Rtg tested per ANSI/ESD STM2.1 and ESD TR53.

To learn more about SCS Smocks, click here.

Welcome back to “A Minute with Miranda.” This week we will be covering ESD Worksurface Mats.

SCS worksurface mats serve two purposes for an ESD worksurface in an EPA:

  • they provide a surface that does not generate a static charge and
  • they remove charges from all charged conductors, which include ESD susceptible devices and assemblies, that are placed on the surface.

SCS worksurface mats are constructed from either dissipative 2 layer rubber or 3 layer vinyl material and are available in both rolls and mat kits.

We can also quote custom sizes SCS worksurface mats meet ANSI/ESD STM4.1 ANSI/ESD S20.20 required limit of 1 x 106 to less than 1 x 109 ohms for Rtt and Rtg and the recommendations of ANSI/ESD S4.1

For more information on SCS Worksurface matting, check out our Selection Guide here.

SCS is excited to announce a brand new video series discussing real-life ESD problems and solutions.  This is a great educational resource for anybody new to ESD or just wanting to learn more about best practices.

Each episode will focus on one issue commonly found in an ESD Protected Area – at the same time we will present solutions so you know how to tackle the problem should you ever face it in your own factory.

A new episode will be published each week so make sure you subscribe to our YouTube channel to get notified when a new video is available. Episodes 1 and 2 are now live so don’t waste a second longer and catch-up now:

The best way to keep electrostatic sensitive devices (ESDs) from damage is to ground all conductive objects and remove insulators from your ESD Protected Area (EPA). This is not always possible because some insulators are “process-essential” and are necessary to build or assemble the finished product. The only way to control charges on these necessary non-conductive items is the use of ionization systems.

However, if an ionizer is out of balance, instead of neutralizing charges, it will produce primarily positive or negative ions. This results in placing an electrostatic charge on items that are not grounded, potentially discharging and causing ESD damage to nearby sensitive items.

It is therefore essential to regularly clean your ionizers and verify they function correctly. Below we have put together a list of tasks you need to perform with your ionizers on a regular basis.

Maintenance

All ionization devices will require periodic maintenance for proper operation. Maintenance intervals for ionizers vary widely depending on the type of ionization equipment and use environment. Critical clean room uses will generally require more frequent attention. It is important to set-up a routine schedule for ionizer service. Routine service is typically required to meet quality audit requirements.” (ESD Handbook TR20.20 section 5.3.6.7 Maintenance / Cleaning)

EIA-625, recommends checking ionizers every 6 months, but this may not be suitable for many programs particularly since an out-of-balance may exist for months before it is checked again. ANSI/ESD S20.20 section 6.1.3.1 Compliance Verification Plan Requirement states: “Test equipment shall be selected to make measurements of appropriate properties of the technical requirements that are incorporated into the ESD program plan.

Under normal conditions, an ionizer will attract dirt and dust (especially on the emitter points). To maintain optimum neutralization efficiency and operation, cleaning should be performed on a regular basis.

1. Case

Wipe the case with a soft cloth and deionized water. Fully squeeze the wiping cloth or sponge to remove any excess liquid. If a stronger cleaning solution is required, dab a soft cloth with mixture of isopropyl alcohol and deionized water (70% IPA and 30% DI water).

2. Emitter Points

The emitter points should be cleaned using specific emitter point cleaners or a swab dampened with Isopropyl alcohol. Below are general instructions on how to clean emitter points. However, each unit is slightly different so always refer to the ionizer’s manual.

  1. Turn the unit OFF and unplug the power cord.
  2. Open the top screen by loosening the screw and swinging the grill to one side.
  3. Clean the emitter points using the an emitter point cleaner or a swab dampened with Isopropyl alcohol.
  4. Re-attach the top screen.
  5. Plug in the power cord and turn the unit ON.
  6. Verify the performance of the ionizer by using a charged plate monitor or ionization test kit (see below).

Cleaning of Emitter Points using SCS 9110-NO as an example

With normal handling, the emitter points should not require replacement during the life of the unit.

Verification

Per ESD TR53 section 5.3.6.7.1 “The best practice is to measure the offset voltage and discharge times, clean the unit, including emitter points and air filters if present, offset voltage to zero (if adjustable), and then repeat offset voltage and discharge time testing. If the unit does not meet offset voltage specifications or minimum established discharge time limits, further service is indicated. Manufacturers should provide details on service procedures and typical service intervals.

Most companies will assign a number or otherwise identify each ionizer and setup a Compliance Verification / Maintenance / Calibration schedule. If the ionizers all test good, the data can justify lengthening the calibration period. If ionizers require adjustment, the calibration period should be shortened. Although ESD TR53 does not advise a test frequency, JESDD625-A (Revision of EIA-625) recommends ionizers be tested semi-annually, noting to use “S3.1 except the number of measurement points and locations may be selected based on the application.

Verification should be performed in accordance with the ESD Association ionization standard ANSI/ESD STM3.1.

Below are general instructions on how to verify your ionizer’s offset voltage and discharge time. Always refer to the User Guide accompanying your Charge Plate Monitor or Ionization Test Kit for proper operation and setup.

1. Testing Ionizer Offset Voltage:

The required limit per ANSI/ ESD S20.20 is less than ± 35 volts. Check your ionizer’s operating manual or consult with the ionizer manufacturer to determine what the offset voltage should be for your ionizer.

Charge Plate Monitor (CPM)

  1. Position the ionizer and charge plate monitor as shown below.
  2. Set the CPM to Decay/Offset mode.
  3. Set the CPM to decay and offset voltage mode with a starting charge at either + or – 1 KV and a stopping charge at either + or -100 Volts.
  4. Start the decay/offset test sequence on the CPM. This will take a few seconds.
  5. Record the decay time, and offset voltage as displayed on the CPM.

Positioning your Charge Plate Monitor for Overhead and Benchtop Ionizers

Ionization Test Kit

  1. Zero the charge plate by touching it with a grounded object. This can either be the finger of a grounded person or some other item which is connected to electrical ground. In either case, zeroing the charge plate should make the display on the field meter read zero.
  2. Hold the meter approximately one foot (30.5 cm) in front of the ionizer.
  3. Monitor the display. The value displayed is the offset balance of the ionizer, which is the difference between the number of positive and negative ions being emitted.
Testing Ionizer Offset Voltage using the SCS 718A Air Ionizer Test Kit

2. Testing Ionizer Discharge Time:

The required limit per ANSI/ESD S20.20 is “user defined”. Please refer to the ionizer’s operating manual or consult with the ionizer manufacturer to determine what this discharge time should be.

Charge Plate Monitor (CPM)

  1. Set the CPM to Decay/Offset mode.
  2. Set the CPM to decay and offset voltage mode with a starting charge at either + or – 1 KV and a stopping charge at either + or -100 Volts.
  3. Start the decay/offset test sequence on the CPM. This will take a few seconds.
  4. Record the decay time, and offset voltage as displayed on the CPM.

Ionization Test Kit

  1. After charging the plate of the ionization test kit, hold the field meter approximately one foot (30.5 cm) away from the ionizer.
  2. Monitor the display of the meter to see how quickly the 1.1 kV charge is dissipated to 0.1 kV.
  3. The speed at which this occurs (the discharge time) indicates how well the ionizer is operating.
  4. Repeat this procedure for both a positively and a negatively charged plate.

Some ionizers offer adjustment options (e.g. trim pots) which allow modification of the offset voltage.

However, if your ionizer is out of balance (and cannot be adjusted) or if the discharge time is out of specification, the ionizer will require service/repair by an authorized company.

Conclusion

Ionization is one of the best methods of removing charges from insulators and as a result plays an important role in controlling ESD.

Remember though: ionizers require periodic cleaning of emitter pins and verifying of the offset voltage and discharge time. Otherwise, instead of neutralizing charges, the ionizer will primarily produce positive or negative ions. The ionizer will therefore place an electrostatic charge on items that are not grounded, potentially discharging and causing ESD damage to nearby sensitive items.

Setting up an ESD-safe workstation is often more challenging than it first appears. There are many methods of controlling ElectroStatic Discharge (ESD), and typically, it requires a combination of these to curb all static problems. Unfortunately, there is no single method that will fill all requirements.

Wrist straps and work surface mats are probably the most familiar to everyone, draining charges from operators as well as from the product being worked on. But what if the static charge in question is on an insulator? Electronic products, by nature, will normally consist of conductors and insulators. Insulators at the workstation can be found on the product itself, tools being used, tapes for masking, even circuit boards. A static charge on an insulator cannot be drained by grounding, as you could with a conductive material.

Ionization

To effectively remove charges from insulators, we need to make the surrounding air more conductive. We have all seen a balloon cling to a wall because of a static charge, and we know that, after a period of time, it will drop. That is because the air is somewhat conductive and the charge eventually drains off. The problem with this concept is that it takes too long. The more conductive the air is, the faster the charge will be neutralized.


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

The method most frequently used to increase the conductivity of the air is ionization.

Ionizers are useful in preventing electrostatic charge generation, ElectroStatic Discharge, ElectroStatic Attraction, as well as preventing equipment latch-up. Per ANSI/ESD S20.20 section 6.2.3.1. Protected Areas Requirement states: “Ionization or other charge mitigating techniques shall be used at the workstation to neutralize electrostatic fields on all process essential insulators if the electrostatic field is considered a threat.”

How do Ionizers work?

Most ESD workstations will have some insulators (e.g. product plastic housing) or isolated conductors (e.g. PCB board components not in contact with ESD worksurface) that cannot be removed or replaced. These should be controlled using ionization.

Ionizers create great numbers of positively and negatively charged ions. Fans help the ions flow over the work area. If there is a static charge present on an item in the work area, it will be reduced and neutralized by attracting opposite polarity charges from the air.

Ionization can neutralize static charges on an insulator in a matter of seconds, thereby reducing their potential to cause ESD damage.


Electronic enclosures are process-essential insulators

The charged ions created by an ionizer will:

  • neutralize charges on process required insulators,
  • neutralize charges on non- essential insulators,
  • neutralize isolated conductors and
  • minimize triboelectric charging.

How does Ionization fit into an ESD Control Program?

Ionization is just one component of your ESD Control Program. Before utilizing ionization, you should follow the fundamental principles of ESD Control:

  • Ground all conductors (including people) using conventional grounding methods (e.g. wrist straps or footwear/flooring system).
  • Remove all insulators, e.g. coffee cups, food wrappers etc.

“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)

  • Ionizers can be critical to reduce induction charging caused by process necessary insulators
  • Ionizers can be critical in eliminating charges on isolated conductors like devices on PCBs
  • Ionization can reduce ElectroStatic Attraction (ESA) and charged particles clinging and contaminating products.

The SCS Ionizer 9110-NO in Use

It is recommended to use ionizers with feedback mechanisms, so you’re notified if the offset voltage is out of balance.

Ionizers should be pieces of equipment that have serial numbers and are included in the company’s maintenance and calibration schedules. This is particularly critical to ensure that the offset voltage or balance is within acceptable limits. Otherwise, instead of neutralizing charges the out of balance ionizer will charge insulators and isolated conductors. The user, depending on the value and function of their products, must determine the appropriate frequency of maintenance and calibration.

Summary

The best way to keep electrostatic sensitive devices (ESDs) from damage is to ground all conductive objects and remove insulators. This is not always possible because some insulators are “process-essential” and are necessary to build or assemble the finished product. The only way to control charges on these necessary non-conductive items is the use of ionization systems. Applications include:

  • eliminating charges on process essential insulators,
  • neutralizing workstations where ESDS are handled,
  • removing charged particulates to create a static free work area.

For more information and to select the right ionizer for your application, check out our Ionizer Selection Guide.