ESD

Ionizers remove static from surfaces that cannot be grounded. You will find two common types: AC or Alternating Current and DC or Direct Current. This presentation reviews the pros and cons of each technology and will help you decide which ionizer will work best for your application.

For more information, contact Transforming Technologies 419-841-9552.

This week’s ESD Q&A question:

Question: Is there really a need for an ESD wastebasket?

Answer:

It is fair to wonder why there is a need for ESD wastebaskets. If the waste basket resides underneath a workstation and stays there permanently, it is extremely unlikely that a wastebasket could present a danger to ESD sensitive devices, regardless of the field voltage that may exist on the basket.

However, there are a number of circumstances  when the wastebasket could present a significant hazard to electronic products. The following are just a few examples of potentially risky scenarios:

Work surface cleaning:   The operator lifts the wastebasket to the edge of the work station to collect the debris being removed. Should product be present on the work surface and not contained in a shielding container, there is a good opportunity for exposure to electrostatic fields that exceed safe limits.

Lead trimming/board cleaning operations:   When trimming component leads or using aerosol cleaners on PCBs (Printed Circuit Boards), some operators will hold the PCB over the wastebasket to catch the clippings or solvent run-off. Many times the PCB will be placed well into the waste container to assure catching the unwanted materials. This operation puts PCBs and ESD sensitive devices very close to potentially significant electrostatic fields.

Aisle proximity:  Some wastebaskets have been observed in close proximity to production floor aisles where product transfer carts pass or may be parked. ANSI/ESD S2020 requires items that generate 2000 volts or more (measured at 1” from the item) be kept at least 12” from ESD sensitive devices. Using ESD wastebaskets eliminates the risk of carts being parked next to static generating baskets.

Taking out the trash:  The simple action of removing trash from the ESD sensitive area could generate a dangerous amount of static. Static is caused by movement, specifically friction. So moving the trash cans to empty them or removing the plastic trash bags from the can generates voltage and they could come in close proximity to sensitive components on the way out of the area.

While company ESD policies may prohibit some of the actions mentioned above, it does not mean that they will not occur from time to time. ESD wastebaskets provided assurance that the wastebasket will never be an ESD threat to your product.

What Do ESD Standards Say?

The ANSI/ESD S20.20 standard says to remove all insulators from the ESD protected Area (EPA). There is nothing specifically mentioned in the standard about Trash Cans or Waste Baskets. But most trash cans as well as trash bags are plastic, which is an insulators that can generate significant charges. It is better to be safe than sorry when is comes to static damage which is why we developed ESD-Safe Trash Cans and Waste Baskets.

Transforming Technologies offers three ESD wastebaskets in static dissipative polypropylene :

• WBAS28 – 7 Gallon ESD Waste Basket
• WBAS90 – 22 Gallon ESD Trash Can
• WBAS180 – 44 Gallon ESD Trash Can

We also supply a stainless steel ESD waste basket for clean room operations:

• WBAS28MET – 7 Gallon Conductive Cleanroom Waste Basket

If a liner is to be used for easier maintenance, Transforming Technologies offers them in both conductive and static dissipative.

WBAS 28

• Volume: 28 Quart (7 gallon)
• Height: 15″, Opening: 10.5″ X 14.75″
• Carbon Loaded

Q:  What is “ESD”?

A: ESD is short Electrostatic Discharge.

Electrostatic Discharge, or ESD, is a single-event, rapid transfer of electrostatic charge between two objects, usually resulting when two objects at different potentials come into direct contact with each other.  ESD can also occur when a high electrostatic field develops between two objects in close proximity.  ESD is one of the major causes of device failures in the semiconductor industry.

Electrostatic charge build-up occurs as a result of an imbalance of electrons on the surface of a material.  Such a charge build-up develops an electric field that has measurable effects on other objects at a distance.  The process of electron transfer as a result of two objects coming into contact with each other and then separating is known as ‘triboelectric charging’.

This charging process results in one object gaining electrons on its surface, and therefore becoming negatively charged, and another object losing electrons from its surface, and therefore becoming positively charged. A person can get triboelectrically charged in a number of ways, even by just walking across a room.

Every Thursday, Transforming Technologies will answer questions concerning all things ESD: static causes, threats,  ESD prevention, best practices and all things static in a feature we call ESD Q&A.  If you have ESD questions that you would like to be answered, email info@transforming-technologies.com  with Q&A in the subject line.

Q:  What is the greatest static threat to electronics and other materials?

A:  YOU!

The human body can generate the biggest charge of anything likely to come near these devices.

Charge can often build-up on people and reach levels that give uncomfortable shocks, can damage sensitive electronic parts or give fire risks when handling solvents and other flammable materials. Dry air humidity encourages static charge build-up, and under dry external conditions the atmosphere in a building can become even drier. Electrostatic charge build-up can be far worse under these conditions. For example, on a dry day, humans can generate a static field of more than 100 volts by just the slight raising of an arm.  During normal, everyday activities, it is common to generate 6,000 volts or more.

Every Thursday, Transforming Technologies will answer questions concerning all things ESD: static causes, threats,  ESD prevention, best practices and all things static in a feature we call ESD Q&A.  If you have ESD questions that you would like to be answered, email info@transforming-technologies.com  with Q&A in the subject line.

One Meg Vs Two Meg Heel Grounders

Introduction

Have you ever wondered what it means when a heel grounder described as having a “1 meg resistor”? or a 2 meg resistor?  The size of a current limiting resistor is often included in the description  of personal grounding products, but what does it mean and how concerned should I be with the size of the resistor when I am buying heel grounders?  Today we will answer these questions but first some background:

What is a Resistor?

A common resistor

A resistor is a component of an electrical circuit that resists the flow of electrical current. A resistor has two terminals across which electricity must pass, and is designed to drop the voltage of the current as it flows from one terminal to the next. A resistor is primarily used to create and maintain a known safe current . Most grounding products have a current limiting resistor and it is most commonly one megohm, rated at least 1/4 watt with a working voltage rating of 250 volts. This ensures that the flowing current will be within safe levels.

Heel Grounders and ESD Protection?
Heel grounders discharge static from a person to ground by connecting the person to a grounded walking surface. A heel grounder is made from a conductive material and is worn on each shoe.  A conductive ribbon placed inside the wearer’s shoe or sock makes electrical contact with the skin through perspiration. The ribbon is joined to a resistor which limits current should accidental exposure to electricity that may  occur. The other end of the resistor is joined to a conductive sole. This sole contacts a grounded ESD floor mat or ESD flooring system. Heel grounders should be worn on both feet to maintain ground contact while walking. UL and OSHA recommends a minimum of 1 megohm resistance to ground (RTG) in order to limit current for safety purposes.

Types of Heel Grounders?
Heel Grounders come in a variety of styles:

• Cup Style: Made with two reversible soles for longer life span.
• Foot Grounder: Provides a more complete path-to-ground due to wider contact area and heel-to-toe coverage.
• Disposable: Strip of conductive material is applied to shoe. Economical and perfect for one time use.
• Toe Grounder: Ideal for high heels when standard heel grounders won’t fit properly.

Resistors and Heel Grounders
Heel grounders come with either a 1 megohm or 2 megohm resistor. When one foot is on the ground, a 1 megohm heel grounder gives you an RTG of 1 megohm and a 2 megohm heel grounders results in 2 megohm RTG. But when both feet are on the ground, the sum of the resistors yield a RTG of 1/2 that measurement.
For example:

• When you wear two, 1 megohm heel grounders and have both feet on the floor, your RTG is only 1/2 megohm, NOT 1 megohm!
• If you wear two, 2 megohm heel grounders an have both feet on the ground, your RTG is 1 megohm.
• By wearing two heel grounders with a 2 megohm resistor you are complying with UL and OSHA at all times.

This can be sometimes confusing.  So we made a diagram to illustrate:

Conclusion

Heel grounders are an effective and popular way to ground mobile personnel in ESD areas. Heel grounders use built in resistors to limit any potential current that flows through the device to ensure operator safety.  The size of the resistor that you use depends on the standards of the specific operation,  but by wearing two heel grounders with a 2 megohm resistor you are complying with UL and OSHA at all times.

To learn more about ESD heel grounders and Resistors, visit Transforming Technologies.com