Static Control

Welcome back to “A Minute with Miranda.” This week we will be covering how the EM Aware Monitor provides continuous monitoring to detect and measure ESD Events in your STM machine.

The SCS EM Aware Monitor is a continuous monitor for three key parameters that allow you to verify your ESD process in an automated insertion machine; ESD events, change in static voltage field, and ionizer balance. The thresholds for all three of these parameters are fully adjustable by the user. The EM Aware Monitor is a miniature radio receiver tuned to detect and measure the unique waveform generated by an ESD event. The EM Aware Monitor meets the Continuous Monitor requirements of ANSI/ESD S20.20 in accordance with ESD TR1.0-01 and ANSI/ESD STM3.1. It meets the recommendations of ESD Handbook ESD TR20.20 which includes “if the products that are being produced are of such value that the knowledge of a continuous, reliable ground is needed, then continuous monitoring should be considered or even required.”

View the full range of SCS EM Aware Monitors here

Welcome back to “A Minute with Miranda.” This week we will be covering how the WS Aware provides continuous monitoring for an operator at an SMT line.

The SCS WS Aware Monitor is a continuous monitor for operators, ESD Worksurfaces and metal tools. It will continuously monitor the path-to-ground integrity and body voltage of two operators. It also monitors the path-to-ground integrity of two metal tools. In addition, it continuously monitors for electromagnetic interference (EMI) on two metal tools, which may cause electrical overstress (EOS) damage. The WS Aware Monitor eliminates the need for periodic testing and record keeping of wrist straps.

Per ESD Handbook ESD TR 20.20 section 5.3.2.4.4 “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 knowledge of a continuous, reliable ground is needed, then continuous monitoring should be considered or even required.”

View the full range of SCS WS Aware Monitors here.

Welcome back to “A Minute with Miranda.” This week we will be covering how the WS Aware Monitor provides for continuous monitoring of an ESD Workstation setup.

The SCS WS Aware Monitor is a dual workstation continuous monitor for operators, ESD Worksurfaces and metal tools. It will continuously monitor the path-to-ground integrity and body voltage of two operators. It also monitors the path-to-ground integrity for two conductive or dissipative worksurfaces and two metal tools. It also continuously monitors for electromagnetic interference (EMI) on two metal tools which may cause electrical overstress (EOS) damage. The WS Aware Monitor eliminates the need for periodic testing and record keeping of wrist straps.

Per the ESD Handbook ESD TR20.20 section 18.4.2 “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. However, the monitor will not detect insulative contamination on the worksurface.”

View the full range of SCS WS Aware Monitors here.

Welcome back to “A Minute with Miranda.” This week we will be covering how to use the WS Aware Monitor for continuous monitoring of SCS wrist straps when at an ESD Workstation.

The SCS WS Aware Monitor is a dual workstation continuous monitor for operators, ESD Worksurfaces and metal tools. It will continuously monitor the path-to-ground integrity and body voltage of two operators. The WS Aware Monitor eliminates the need for periodic testing and record keeping of wrist straps. The WS Aware Monitor features operator body voltage detection. It will alarm if the operator generates or comes into contact with voltage that would be dangerous to an ESD susceptible item. Per the ESD Handbook ESD TR20.20 section 5.3.2.4.4 “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 knowledge of continuous, reliable ground is needed, then continuous monitoring should be considered or even required.”

View the full range of SCS WS Aware Monitors: https://staticcontrol.descoindustries…

Welcome back to “A Minute with Miranda.” This week we will be covering how to properly clean an ESD Worksurface Mat.

For optimum electrical performance, the ESD worksurface mat surface should be cleaned regularly using a recommended ESD mat cleaner. Per the ESD Handbook ESD TR20.20, “Ensure that cleaners that are used do not leave an electrically insulative residue common with some household cleaners.”
We recommend using Reztore ESD Surface and Mat Cleaner. Reztore is alcohol free and does not contain silicone or other substances that will leave an insulative residue or inhibit the performance of the ESD worksurface mats.

After cleaning the ESD worksurface mat with Reztore it is recommended to test the surface to ensure that all insulative contaminates such as dirt and grime have been removed from the mat.
SCS worksurface mats meet the ANSI/ESD STM4.1 and 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. View the range of Reztore Alcohol Free products here.

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.

Have you ever walked across a car park on a bright cold winter’s day only to get zapped by your car’s door handle? It’s commonly known that these ‘zaps’ are much more common in cold dry weather. It begs the question: if there are less ‘zap, will using air humidifiers in a manufacturing environment prevent ESD damage of sensitive components? Let’s find out!

 

Humidity

Humidity describes the amount of water vapor in the air. There are 3 main measurements of humidity with the most common one being the relative humidity (RH). It is expressed in percent and describes “how much humidity there is in the air, compared to how much there could be. Meteorologists often use the relative humidity as a measurement to describe the weather at various places.” [Source]

At 0% the air is completely dry; at 100% it is so moist that mist or dew can form. The optimum relative humidity level is somewhere between 40% and 60%:

  • A lower relative humidity increases charge generation as the environment is drier.
  • If the humidity level is too high, condensation can form on surfaces.

 

Charge Generation and ElectroStatic Discharge (ESD)

The simple separation of two surfaces generates an ElectroStatic charge. Examples:

  • Unwinding a roll of tape
  • Gas or liquid moving through a hose or pipe
  • A person walking across a floor with heels and soles contacting and separating from the floor

 

Walking across a floor generates ElectroStatic charges.
Walking across a floor generates ElectroStatic charges.

 

The amount of static electricity generated varies and is affected by materials, friction, area of contact and the relative humidity of the environment. A higher charge is generated at low humidity or in a dry environment.

Once an item has generated a charge, it will want to come into balance. If it is in close enough proximity to a second item, there can be a rapid, spontaneous transfer of electrostatic charge. This is called discharge or ElectroStatic Discharge (ESD).

Going back to our earlier example of getting a zap from your car’s door handle:

  1. Charge generation: you walk across the car park with your soles contacting and separating from the floor. A charge is built-up on you.
  2. ElectroStatic Discharge (ESD): you touch the door handle. Charges move from your body to your car until both are balanced out.

 

Impact of relative humidity on ESD

Many people will notice a difference in the ability to generate static electricity when the air gets dryer (relative humidity decreases). Relative humidity (RH) directly affects the ability of a surface to store an electrostatic charge. “With a humidity level of 40% RH, surface resistance is lowered on floors, carpets, table mats and other areas. … the moisture in the air forms a thin protective “film” on surfaces that serves as a natural conductor to dissipate electric charges. When humidity drops below 40% RH, this protection disappears, and normal employee activities lead to objects being charged with static electricity.” [Source]

ESD Damage on an integrated circuit. No Magnification, 400x magnification, 5,000x magnification.

In an electronics manufacturing environment lower humidity may result in lower output from production due to an increase in ESD events during manufacturing processes.

 

Air Humidification and ESD

Air humidifiers are used to add moisture to the air and are commonly used in drier environments to keep humidity at a constant (optimum) level. Given that a lower humidity level increases the risk of ESD events, the obvious questions are:

  1. Can air humidifiers replace normal ESD Control measures?
  2. Are air humidifiers required for complete ESD protection?

Let’s address both questions:

  • Let’s be very clear about one thing here: air humidifiers cannot replace ESD Control measures.

As explained further above, ESD is caused by two items that are at a different electrostatic equipotential and want to equalize their charges. Adding moisture to the air using humidifiers will not stop this discharge from happening. The only thing you may achieve is a reduction in the number of ESD events. BUT: they will still happen; just walking across a carpet will generate a charge on an operator. If they then touch an ESD sensitive component, discharge will still occur and may damage the component. No humidifier will prevent this.

The only way to control electrostatic charges on a person or object is through ESD grounding – this will ensure any charges generated dissipate to earth:

For more information on how to create a ESD workstation and how to correctly ground all elements, have a look at this post.

Wrist-Strap.jpg
Grounding of an operator using a wrist strap

  • Low air humidity can increase the number of ESD events so it may make sense to keep a factory at a higher humidity level. However, there are many other factors that come into play when choosing the ‘right’ humidity for a manufacturing environment. The recommended humidity range is usually determined by the specifications of the devices and components being assembled. Increasing the humidity in an electronics manufacturing facility can help to reduce ESD events but increased humidity can lead to other unwanted quality issues in an electronics manufacturing environment such as corrosion, soldering defects and the popcorn effect on moisture sensitive devices.

A normal range for humidity in electronics manufacturing is between 30% RH and 70% RH. Some facilities try to maintain a constant moderate RH (~50%), whereas other environments may want lower % RH due to corrosion susceptibility to humidity sensitive parts.
And remember: you will not eliminate ESD by using humidifiers and keeping humidity levels at a higher level. You need an ESD Control Program in place to avoid ESD and associated damages.

 

Conclusion

Air humidification can help reduce the number of ESD events in an electronics manufacturing environment but at the same time there are other factors (e.g. moisture sensitivity of components) that need to be considered.

A lower relative humidity level increases charge generation as the environment is drier. This will result in more ESD events which can potentially damage sensitive components. The only way to protect sensitive components from ESD damage is by having proper ESD control measures in place and connecting operators, objects and surfaces to ground. This will ensure each element is kept at the same electrical potential and any electrostatic discharge is being removed to ground.

For more information on how to get your ESD control program off the ground or improve an existing program, request a free ESD/EOS Assessment at your facility by one of our knowledgeable local representatives to evaluate your ESD program and answer any ESD questions!