This week’s ESD Q&A question comes from StaticCare reader Paul, he asks:

Question: What measurement or measurements do I need to make when auditing an ESD worksurface?

Answer:

Hello Paul,

Thank you for taking the time to submit your question to Transforming Technologies.

There are three primary measurements for evaluating a work surface; Resistance Point to Point (RTT – also known as Resistance Top to Top), Resistance to Groundable Point (RTGP) and Resistance to Ground (RTG).

Figure 1 – Resistance To Ground (RTG)

Resistance to Ground Measurement

For general auditing purposes, the primary measurement is RTG. This measurement is made using a 5 lb electrode connected to the positive terminal of the resistance meter. The electrode is placed on the work surface in the most heavily used area. The negative lead is connected to electrical ground. This measurement assures that the mat is connected to AC Equipment Ground. ESD standard procedure says to test at 10 volts, and if the measurement exceeds 1.0 x 10⁶ ohms, switch to 100 volts. If you are certain that your worksurface material has a resistance greater than 1.0 x 10⁶ ohms, you may want to start at 100 volts to save time.

A simple and safe way to connect to AC Ground is by using a grounding plug, such as the Transforming Technologies AD22. The AD22 assures a solid connection to the third wire ground of an AC outlet, while insulating the plug from the hot and neutral wires. Always check electrical outlets for proper wiring before using grounding plugs.

If the resulting RTG measurement is within your required limits, no further work surface testing is required and you can proceed to the next work surface. Should the RTG measurement exceed your limits, clean the work surface with an approved cleaning product, check all wiring connections to make sure that they are secure and re-test. Should the measurements still exceed your limits you will then want to conduct a Resistance to Groundable Point (RTGP) measurement.

Figure 2 – Resistance Point To Groundable Point (RTGP)

Resistance to Groundable Point Measurement

This measurement is similar to the RTG measurement except that the negative lead is attached to the grounding point (snap) of the work surface. The testing is performed using 100 volts when the expected resistance is greater than 1.0 x 10⁶ ohms.

Should this measurement provide a reading that is within your requirements the problem is somewhere between the snap and AC Ground. Typically, either the ground wire became disconnected or it is faulty. Check and verify all wiring between the work surface and the AC equipment ground.

If this measurement also provides a value that exceeds your requirements, then there may be a problem with the work surface. A point-to-point resistance measurement can be done to verify the performance of the work surface material.

Figure 3 – Resistance Point To Point (RTT)

RTT – Resistance Point-to-Point

This measurement is made using two 5 lb electrodes. The electrodes are placed 10” apart on the work surface in various locations. Figure 3 is an example of a point-to-point test.

The testing is performed using 100 volts when the expected resistance is greater than 1.0 x 10⁶ ohms.

If the reading meets your requirements, there is possibly a connection problem with the groundable point. Should the reading exceed your limits the work surface is likely faulty and should be replaced.

It is important that RTG measurements be made regularly. The frequency of testing is dependent up on internal requirements and testing history. RTG testing must be performed even if constant monitoring is in place, as constant monitors verify ground connection of the worksurface, but not the performance of the worksuface.

This week’s ESD Q&A question comes from StaticCare reader Stephanie, she asks:

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

Answer:

Hello Stephanie,

Thank you for taking the time to submit your question to Transforming Technologies.

It is fair to wonder why there is a need for ESD wastebaskets. If the basket resides underneath a workstation and stays there permanently, the need may not exist. It is extremely unlikely that a wastebasket that stays underneath a workstation could present a danger to ESD sensitive devices, regardless of the field voltage that may exist on the basket.

There are a number of circumstances however, 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.

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.

Transforming Technologies offers ESD wastebaskets in static dissipative polypropylene and in stainless steel for clean room operations. 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

Transforming Technologies is proud to announce the addition of the HG9000 Series ESD Non-Marking D-Ring/Elastic Sole Grounders to our line of ESD Products.

Sole Grounders, or Foot Grounders, cover more of the shoe which allows more contact to the ESD floor during the process of a step.

The HG9000 series non-marking D-ring/elastic sole grounder provides a more complete path to ground than regular heel or toe grounders due to a wider and more consistent contact area. The HG9000 series will not mar shoes or floors – reducing maintenance costs of touching up on floors. Available in XS, S, M and L sizes.

ESD Sole Grounders (or ESD Foot Grounders) have over 20 times the surface contact of standard esd heel straps. This surface area advantage extends the life of the Sole grounder over standard heel grounders which fail over time due to even the slightest contamination, necessitating replacement or cleaning, wasting time, and costing money.

These sole grounders provide rapid and complete static dissipation due to constant contact through entire walking motion. Wearing the conductive ribbon inside the shoe or sock assures proper electrical contact with the user. A rugged 1 meg ohm buried resistor is standard. Heel grounders are worn on both feet to provide consistent grounding while in motion.

 Features

• Non-Marking
• Buried Resistor
• Full Sole Coverage Design

For price and availability on the HG9000 series soles grounders or for information on any products in Transforming Technologies full line of ESD products, please call 419-841-9552 or email info@transforming-technologies.com.

One of the requirements of any quality ESD control program is to minimize the charge (also called voltage) on operators. When operators are charged, they can transfer this charge to the product, possibly causing damage or destruction. One effective way to reduce static charging on people is to ground them through the use of a wrist strap and coil cord. When working properly, the wrist strap system (band and coil cord connected to common point ground) can control voltages on people down to 10 volts and less and limit damage.

While wrist strap systems are the most common and effective way to minimize voltage on personnel, they are also the ESD control element that is most likely to eventually fail over time. A broken wire in the coil cord, a dirty cuff interior, incorrect wearing of the strap (too loose or placed over clothing), and high skin resistance are just a few of many causes of wrist strap failure. Should any of the previous examples occur, the resistance between the operator and ground increases, and subsequently, so does voltage. Therefore, it is imperative that measures are taken to assure that the operator is properly grounded when wearing a wrist strap.

The PDT800 is a deluxe “Near-Fail” wrist strap and foot wear combination tester with a digital read out, “near-fail” LED indicator, human body noise filtration, and options to test wrist strap only, foot only, or both wrist and feet.

ESD Test Stations

One way to assure that the wrist strap system is working correctly is for the operator to use a test station. The test station assesses the resistance of the wrist strap system, including the operator, and provides a pass/fail indication. Some more advanced test stations will also provide the actual resistance measurement and may even indicate that the system is nearing the failure level. Many companies institute this type of testing system. Some companies require testing just once at the beginning of the shift. Other companies may require re-testing when the operator leaves for break, and some companies have systems that require the operator to test and pass the wrist strap system before they are allowed to enter the ESD Protected Area (EPA). Regardless of how many times an operator tests, there is a risk that at some point while handling ESD sensitive devices or assemblies, the wrist strap system will fail.

Transforming Technologies offers several testing station options that range from wrist strap monitors (WST200), wrist strap and footwear test stations (GTS600K), wrist strap and individual foot test stations (GTS900K), test stations with “near-fail” technology (PDT700K), and test stations with “near-fail” technology and digital display (PDT800K). These testing stations function with a standard wrist strap and coil cord using a banana jack connector and standard heel grounders.

Constant Monitoring

The CM410 continuously monitors any one standard wrist strap and bench, is easy to use, and easy to install.

If a wrist strap fails the test at the beginning of a shift, the question arises, “When did the failure take place and how much product was handled after the failure?” Constant monitors provide assurance that the wrist strap system is working and alarms immediately if there is any disconnect from the operator to ground. There are several benefits to constant monitor systems:

• They provide immediate notification of a problem and alert the operator to not handle the product until the problem is resolved
• They monitor the wrist strap at the work location, eliminating the possibility of a functional wrist strap but a defective ground attachment
• They eliminate the need for recording and storing test results
• Some units will also monitor the work surface to verify that it is still connected to ground

Transforming Technologies offers several constant monitor options that range from monitoring a single operator (CM400), an operator and a work surface (CM410), and two operators and a single work surface (CM420). These monitors function with a standard wrist strap and coil cord using a banana jack connector.

Wrist straps are the primary method for removing charge from operators handling ESD sensitive products. Constant monitors provide assurance that the system is working as designed and the products are being handled safely.

Stop by the Transforming Technologies booth at the 2013 ESD Symposium at the Rio All Suites in Las Vegas,

Rio All Suites Hotel in Las Vegas, Nevada

Nevada! The EOS & ESD Symposium runs from Sunday, September 8th through Friday, September 13th. During the Exhibit on September 9th-11th, we will be located at booth 111. Feel free to drop in and ask us any questions you may have about ESD or any of our products.

The exhibit hours are:
Monday, September 9: 6:00 p.m. – 9:00 p.m.
Tuesday, September 10: 9:30 a.m. – 5:30 p.m.
Wednesday, September 11: 9:30 a.m. – 1:00 p.m.

2012 EOS & ESD Symposium

John G. Kappenman of Storm Analysis Consultants will be the Keynote speaker for the event, and he will be speaking on Geomagnetic Superstorm Events and their impacts on power grids. More information about the schedule for the event seminars, tutorials, technical sessions, workshops, and showcases can be found here.

Visit the ESDA website for information on purchasing Symposium and Tutorial passes, airfare, hotel, and meals. Their bundle form is located here.

They also have the 2013 EOS & ESD Symposium Program on their website. This program contains descriptions for each of the sessions that will be offered.

This week’s ESD Q&A question comes from StaticCare reader John, he asks:

Question: When measuring ESD Mat resistance, I have noticed that the resistance measures higher on some of my older ESD rubber mats when using 10V and will sometimes be greater than 10^9 ohms. Switching to 100V will lower the resistance into the green, passable range(less than 10^9 ohms). If the mat passes at 100V, is that sufficient to give the mat a pass? When should I use 10 volts vs. 100 volts?

Answer:

Hello John,

Thank you for submitting your question to Transforming Technologies.

Industry standards specify the test voltage required when testing or verifying ESD control items (i.e. mats).    For verification of mats, or work surfaces, you can reference the ESD Association TR53 Compliance Verification document.  This is a free download at www.esda.org.   (select the Standards tab and scroll down to TR53).

The following rule applies for resistance testing of ESD control items:

Perform the test at 10 volts.   If the resistance is < 1.0 x 106 ohms record the reading.

If the measurement at 10 volts is ≥1.0 x 106 ohms, switch to 100 volts, make your measurement and record the result.

Most ESD mat materials are designed to have a resistance greater than 1.0 x 106 ohms, so you can start your testing at 100 volts.  In the example that you stated, the mat that you tested meets the requirements.  If you are seeing the values creep higher it would be wise to test the older mats more frequently to verify that they are still under 1.0 x 109 ohms.

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.

Question:  What materials are the biggest cause ESD damage?

Answer:  Plastics and other synthetic materials cause the most trouble because they are insulators and trap charges on their surfaces.

Materials that are insulators hold an electric charge and cannot easily transfer the charge and cannot be grounded to earth by common means.  Conductors are just the opposite.  They are materials that easily transfer a charge.  Examples are metals, water, carbon and people. Understanding insulators and conductors is an important part of creating an ESD action plan.

Question:  What are common causes of ESD?

Answer: Just about any contact and separation of two materials will generate static.

Opening a common plastic bag. Removing adhesive tape from a roll or container. Walking across a floor and grabbing the door knob. Sliding circuit boards on a work bench.  You get the idea.

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.

Question: Why do I only get a static shock when I touch metal?

Answer: Shocks are usually only felt if your body is charged to over about 4000V, and you touch something conductive (like metals or water, or other people).

If the wall or door is made of wood, concrete or some other material that has low or intermediate conductivity, any static charge on your body escapes slowly and usually does not cause a shock. If you touch metal, water, or another person when your body is highly charged, the charge is discharged quickly as the material is highly conductive. In this case you may feel a shock.

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.

Question:  Does the weather affect static electricity?

Answer: You’ll often find dry weather will affect static electricity.

Shocks are worst under certain weather conditions. Static shocks will increase during the winter when the air outside is cold and dry. They may disappear in warmer damper weather.

Static charge build-up is enhanced when the weather is dry so static problems are often noticed more in dry air of the winter. The air outside can be very dry when the weather is cold. Indoors, central heating or air conditioning can give very dry conditions which promote static electricity. Heating warms the air and reduces its humidity.

Static shocks are often noticed in cold dry weather, especially when in a centrally heated environment, and may disappear when the weather gets more humid. Static shocks may also be encouraged under air conditioning in hot weather.  Many people choose to use a humidifier to increase air moister which helps dissipate static charges.

When there are ESD concerns in environments such as semiconductor or electronics manufacturing, the ANSI20.20 requires that temperature and humidity readings are taken when measuring static.  Typically a static field meter or a surface resistance meter are use to measure static and many take these readings as well as measuring static.

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.