Welcome back to “A Minute with Miranda.” This week we will be covering how the Ground Master Monitor provides continuous monitoring of the path-to-ground impedance and electromagnetic integrity of eight metal ground connections of process tools in your SMT assembly work area.
The Ground Master Monitor
continuously monitors eight metal tools for electromagnetic interference (EMI).
EMI can cause equipment lockups and malfunction. The Ground Master Monitor will
alarm if EMI is detected. The Ground Master will also alarm if the grounded
metal tools have a high-frequency noise that can cause electrical overstress
(EOS) damage. The Ground Master Monitor provides both a visual and audible
alarm for the monitored ground connections. The Ground Master Monitor meets the
Continuous Monitor requirements of ANSI/ESD S20.20 in accordance with ESD TR53.
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.”
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 220.127.116.11.4 “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 18.104.22.168.4 “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.”
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.
When the tip of a soldering iron comes into direct electrical contact with the pins of a sensitive component, there is a danger of voltage and/or current signal transfer between:
the grounded iron tip and the grounded PC board,
the ungrounded iron tip and the grounded PC board,
the grounded iron tip and the ungrounded PC board.
This can cause Electrical Overstress (EOS) and Electrostatic Discharge (ESD).
What is Electrical Overstress (EOS) and why is it important to detect?
EOS is the exposure of a component or PCB board to a current and/or voltage outside its operational range. This absolute maximum rating (AMR) differs from one device to the next and needs to be provided by the manufacturer of each component used during the soldering process. EOS can cause damage, malfunction or accelerated aging in sensitive devices.
ESD can be generated if a component and a board have different potentials and the voltage transfers from one to the other. When such an event happens, the component goes through EOS. ESD can influence EOS, but EOS can also be influenced by other signals.
Many people are familiar with Electrostatic Discharge (ESD) which is caused by the spontaneous discharge between two materials that are at different levels of ElectroStatic potential. Once electrostatic potential between the two materials is balanced, the ESD event will stop.
An EOS event on the other hand is created by voltage and/or current spikes when operating equipment; it can therefore last “as long as the originating signal exists”. [Source] The potentially never-ending stimulus of EOS is what makes it such a big concern in the electronics industry. Even though the voltage levels are generally much lower compared to an ESD event, applying this smaller voltage combined with a larger peak current over a long period of time will cause significant damage.
The high temperatures during an EOS event (created by the high current) can lead to visible EOS damage.
For more information on EOS and the differences to ESD, check-out this post.
Sources of EOS during the Soldering Process
When soldering components, it’s the tip of the soldering iron that comes into contact with the potentially sensitive device. Therefore, many people assume the soldering tip is the cause of ESD/EOS. However, the soldering iron and its tip are just some of the components used at a workbench. Other components on the bench like tweezers, wiring, test equipment, etc. can also be sources of ESD/EOS as they come into contact with the component or board.
There are many sources of EOS during the soldering process, which can include:
Loss of Ground The tip of an ungrounded soldering iron can accumulate a voltage of up to ½ of the iron’s supply voltage. It can be caused within the soldering iron itself or in power outlets.
Noise on Ground If a noise signal exists on ground, the tip of the solder iron will carry noise, too. These high-frequency signals, or electromagnetic interference (EMI), are disturbances that affect an electrical circuit, due to either electromagnetic induction or electromagnetic radiation emitted from an external source.
Noise on Power Lines Noise not only generates via ground but in power lines, too. Transformers and power supplies that convert voltages to 24V are the main culprit. They regularly carry high-frequency spikes which end up on the tip of the soldering iron.
Power Tools Although not technically related to the soldering process itself, it’s worth mentioning that the tips of power tools (e.g. electric screwdrivers) may not be properly grounded during rotation. This can result in high voltage on the tip itself.
Missing/Inadequate ESD Protection ESD can be a cause of EOS damage. Therefore, it is essential to have proper ESD Protection in place. A voltage on the operator or the PCB board can otherwise lead to an ESD Event and expose the components on the PCB to EOS.
Detecting EOS during the Soldering Process
EOS/ESD events can be detected, measured, and monitored during the soldering process using a variety of diagnostic tools.
SCS CTM051 Ground Pro Meter The SCS CTM051 Ground Pro Meter is a comprehensive instrument that measures ground impedance, AC and DC voltage on the ground as well as the presence of high-frequency noise or electromagnetic interference (EMI) voltage on the ground. It will alert if the soldering iron tip has lost its ground or has EMI voltage induced into the tip from an internal source on the soldering iron or from an EMI noisy ground or power lines.
SCS CTM048 EM Eye – ESD Event Meter The SCS CTM048 EM Eye – ESD Event Meter paired with the SCS CTC028 EM Field Sensor is a diagnostic tool for the detection and analysis of ESD events and electromagnetic fields and can identify sources of harmful ESD Events and electromagnetic interference (EMI).
EOS Continuous Monitors
SCS CTC331-WW Iron Man® Plus Workstation Monitor
The SCS CTC331-WW Iron Man® Plus Workstation Monitor is a single workstation continuous monitor which continuously monitors the path-to-ground integrity of an operator and conductive/dissipative worksurface and meets ANSI/ESD S20.20.The Iron Man® Plus Workstation Monitor is an essential tool when it comes to EOS detection. The unit is capable of detecting EOS on boards and alarms if an overvoltage (±5V or less) from a tool such as a soldering iron or electric screwdriver is applied to a circuit board under assembly.
SCS Static Management Program SCS Static Management Program (SMP) continuously monitors the ESD parameters throughout all stages of manufacturing. It captures data from SCS workstation monitors, ground integrity monitors for equipment, ESD event and static voltage continuous monitors and provides real-time data of manufacturing processes.The SCS 770063 EM Aware Monitor, which is part of SMP, can help during the soldering process by monitoring ESD events and change of static voltage that may result in EOS. The EM Aware alarms (visual and audibly) locally and sends data to the database of the SMP system if any of the ESD parameters are detected to be higher than user-defined limits.
Eliminating EOS during the Soldering Process
Once the source of ESD/EOS is known, there are many things that can be done to prevent it in the first place:
1. Managing Voltage on a PCB board
PCB boards contain isolated conductors and non-conductive (insulative) components. The only way to handle voltage on a PCB board is neutralizing potential static charges through ionization. An ionizer creates great numbers of positively and negatively charged ions. Fans help the generated ions flow over the work area to neutralize static charges (or voltage) on a PCB board in a matter of seconds.
For more information on ionization and how to choose the right type of ionizer for your application, please read these posts.
2. Managing Voltage on an Operator
Static voltage on an operator can be eliminated through proper grounding using a workstation monitor, e.g. WS Aware or Iron Man Plus Monitor, and proper grounding hardware. Sitting personnel are required to wear wrist straps. A wrist strap consists of a conductive wristband which provides an electrical connection to skin of an operator, and a coil cord, which is connected to a known ground point at a workbench, a tool or a continuous monitor. While a wrist strap does not prevent generation of voltages, its purpose is to dissipate these voltages to ground as quickly as possible.
Sitting personnel can also use continuous monitors – not only is the operator grounded through the continuous monitor, but they also provides a number of additional advantages:
Immediate feedback should a wrist strap fail
Monitoring of operators and work stations
Detection of split-second failures
Elimination of periodic testing
This post provides more details on continuous monitors.
Moving or standing personnel are grounded via a flooring/footwear system. ESD Footwear (e.g. foot grounders) are designed to reliably contact grounded ESD flooring and provide a continuous path-to-ground by removing electrostatic voltages from personnel.
3. Managing Current
One solution is the “re-routing of ground connection and separation of “noisy” ground from a clean one” as “connecting soldering iron and the workbench to the “quiet” ground often result in lower level of transient signals.“. [Source]
This will greatly reduce the high-frequency noise that could cause EOS damage.
If the noise on power lines and ground cannot be reduced manually, then the use of noise filters becomes necessary to reduce the risk of EOS exposure during the soldering process. Utilizing these filters suppresses the noise on power lines and will allow the solder iron to use “clean” power only.
In his papers, Vladimir Kraz, explains the set-up of a soldering station using a noise filter in more detail.
During the soldering process, current and voltage spikes between the solder tip and PCB can cause ESD/EOS. Sources are varied and can include:
Loss of Ground
Noise on Ground
Noise on Power Lines
Missing/Inadequate ESD Protection
ESD/EOS can be identified and controlled using diagnostic tools. SCS offers a number of tools that can detect current, voltage and EMI – all potentially leading to ESD and EOS.
Once the source of ESD/EOS is known, the next step is eliminating the source:
Managing voltage on a PCB board using ionizers.
Managing voltage on an operator using workstation monitors or foot grounders.
Managing current using noise filters.
Managing voltage on materials at the work bench.
Managing ESD generation during specific processes.
For more information regarding this topic, please see below for additional references.
Do your employees handle ESD-sensitive high-end components that are expensive to replace if they failed? If so, reducing the possibility of ESD damage is an important part of an ESD control program. Today’s blog post will look at one option of protecting your critical applications: Dual-Wire Wrist Straps.
In an ESD Protected Area (EPA), all surfaces, objects, people and ESD sensitive devices (ESDs) are kept at the same electric potential. This is achieved by using only ‘groundable’ materials that are then linked to ground.
This is in line with the requirements of ANSI/ESD S20.20: “The Organization shall prepare an ESD Control Program Plan that addresses each of the requirements of the Program. Those requirements include:
– Product Qualification
– Compliance Verification
– Grounding / Equipotential Bonding Systems
– Personnel Grounding
– ESD Protected Area (EPA) Requirements
– Packaging Systems
[ANSI/ESD S20.20 clause 7.1 ESD Control Program Plan]
Wrist straps are the most common personnel grounding device and are used to link people to ground. They are required if the operator is sitting.
A wrist strap is made up of two components:
A wrist band that is worn comfortably around your wrist and
A coiled cord that connects the band to a Common Grounding Point.
Components of a Wrist Strap
Dual-Wire Wrist Straps
Dual-Wire Wrist Straps have two conductors (compared to single-wire monitors which have only one conductor inside the insulation of the coiled cord). They offer a reduced risk of damaging ESD sensitive devices because if one conductor is severed or damaged, the operator still has a reliable path-to-ground with the second conductor. For that reason, they dual-wire wrist straps are generally used in critical applications.
For maximum benefit, dual-wire wrist straps should be used together with dual-wire continuous monitors. Instead of connecting a coil cord directly to a common grounding point, the operator connects to a continuous monitor. The operator is grounded through the continuous monitor and the operator-to-ground connection is monitored.
The monitors provide operators with instant feedback on the status and functionality of their wrist strap and/or workstation. Continuous monitors detect split-second failures when the wrist strap is still in the “intermittent” stage. This is prior to a permanent “open” which could result in damage to ESD sensitive components. The “intermittent” stage is characterized by sporadic failures as the cord is not completely severed. Once the cord is fully split, the “open” stage is reached.
“Since people are one of the greatest sources of static electricity and ESD, proper grounding is paramount. One of the most common ways to ground people is with a wrist strap. Ensuring that wrist straps are functional and are connected to people and ground is a continuous task.” “While effective at the time of testing, wrist strap checker use is periodic. The failure of a wrist strap between checks may expose products to damage from electrostatic charge. If the wrist strap system is checked at the beginning of a shift and subsequently fails, then an entire shift’s work could be suspect.” “Wrist strap checkers are usually placed in a central location for all to use. Wrist straps are stressed and flexed to their limits at a workstation. While a wrist strap is being checked, it is not stressed, as it would be under working conditions. Opens in the wire at the coiled cord’s strain relief are sometimes only detected under stress.“ [ESD TR 12-01 Technical Report Survey of Constant (Continuous) Monitors for Wrist Straps]
Resistance (or dual-wire) constant monitors are “… used with a two wire (dual) wrist strap. When a person is wearing a wrist strap, the monitor observes the resistance of the loop, consisting of a wire, a person, a wristband, and a second wire. If any part of the loop should open (become disconnected or have out of limit resistance), the circuit will go into the alarm state.” “While the continuity of the loop is monitored, the connection of the wrist strap to ground is not monitored.” “There are two types of signals used by resistance based constant monitors; steady state DC and pulsed DC. Pulsed DC signals were developed because of concerns about skin irritation. However, pulse DC units introduce periods of off time (seconds) when the system is not being monitored.“ [ESD TR 12-01 Technical Report Survey of Constant (Continuous) Monitors for Wrist Straps]
Dual Polarity Technology provides true continuous monitoring of wrist strap functionality and operator safety according to accepted industry standards. Dual-wire systems are used to create redundancy. In critical applications redundancy is built-in to have a backup if the primary source fails. With dual-wire wrist straps the redundancy is there as a protection rather than an alternative. If you are monitoring your dual-wire wrist strap and one wire fails, then the unit will alarm. You will still be grounded by the other wire, so there will be a significantly reduced risk of damaging ESD sensitive components if you happen to be handling them when the wrist strap fails. The wrist strap still needs to be replaced immediately.
And there you have it: dual-wire wrist straps together with dual-wire continuous monitors offer better protection than intermittent monitoring or testing if you have a critical application.
Imagine this scenario: you come to work in the morning and test your wrist strap per your ESD program’s recommended test frequency procedure. The wrist strap passes and you start work on your ESD sensitive devices. 3 hours later, when you come back from your tea break, you test your wrist strap again before continuing work and the wrist strap fails.
What to do? It is unknown when exactly the wrist strap failed in those 3 hours after your first periodic test in the morning and it is possible the devices you worked on during that time frame have been damaged. You don’t know which products have been damaged – latent defects are not visible and failures may only occur at a later time, reducing the potential reliability of the products.
Periodic testing is commonly used in an ESD program, however using continuous monitoring while working on those sensitive devices will alert the operator as soon as their wrist strap and/or workstation path-to-ground connection fails. Today’s blog post will highlight various benefits of continuous monitoring.
Wrist straps are considered the first line of ESD Control. They are used to link people to ground ensuring operators are kept at the same potential as surfaces, objects and ESD sensitive devices (ESDs). Before handling sensitive items, wrist straps need to be visually inspected and checked (while worn) which will alert the operator to potential faults.
Per ESD Handbook TR 20.20 paragraph 22.214.171.124.4 Test Frequency, “Because wrist straps have a finite life, it is important to develop a test frequency that will guarantee integrity of the system. 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.”
Continuous monitors come in different styles and sizes but are intended to be kept on the workstation. Some units just ‘sit’ on the bench; others are attached to the working surface matting; some can even be attached underneath the workbench so they don’t take away valuable workspace. Operators connect their wrist strap to the unit to allow for real-time continuous monitoring. If the wrist strap fails, the unit will alarm. Many continuous monitors also feature a parking snap providing a means for the operator to disconnect when leaving their workstation.
Types of Continuous Monitors
There are two different types of continuous monitors available:
Single-wire continuous monitors allow the use of any standard, single-wire wrist strap and coiled cord. The monitor / wrist strap system life-cycle costs are significantly lower compared to dual-wire systems. While they would not be suitable for the most critical applications, single-wire continuous monitors are an economical way to monitor both the operator’s wrist strap and/or workstation surface.
Dual-wire continuous monitors provides true continuous monitoring of wrist strap functionality and operator safety according to accepted industry standards. Dual-wire continuous monitors provide redundancy because even if one dual-wire wrist strap conductor is severed, the operator still has a reliable path-to-ground with the other conductor. Dual-wire technology requires the use of dual-wire wrist straps and coiled cords.
Benefits of Continuous Monitors
1. Instant Feedback
Continuous monitors provide operators with instant feedback on the status and functionality of their wrist strap. The instant an operator’s wrist strap or cord fails, the monitor will issue audible and visual (LEDs) alarms alerting the user and supervisor of the problem. The faulty wrist strap can be replaced with a new one from stock.
2. Monitoring of Operator AND Workstation
When the monitor is connected to an ESD working surface, the amount of current that flows is a function of the total resistance between the monitor and through the working surface to ground. When the resistance of the working surface is below a pre-set threshold*, the monitor will indicate good. Conversely, if the resistance level is high when compared to the monitor’s reference*, the unit will alarm. This is an integrating resistance measuring circuit, therefore it is relatively insensitive to externally induced electromagnetic fields.
*The resistance threshold limits can vary between brands and models (and can sometimes also be adjusted by the user) so make sure you do your homework before committing to a particular unit and check the limit meets your individual requirements.
“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 and test methods such as those outlined in ESD TR53 can be used to isolate this problem. ” [ESD TR20.20 Continuous Monitors Clause 18.4.2 Worksurface Ground Monitoring].
3. Detection of Initial Flex Fatigue
Unlike wrist strap testers, continuous monitors detect split-second failures when the wrist strap is still in the “intermittent” stage. This is prior to a permanent “open” which could result in damage to ESD sensitive components.
“During operation, wrist straps might be stressed and flexed to their limits at a workstation. While a wrist strap is being checked it is typically not stressed, as it would be under working conditions. Openings in the wire at the coiled cord’s strain relief are sometimes only detected under stress. Even if the wrist strap is working properly, a bad or intermittent ground connection will render the wrist strap system less than 100% effective.” [ESD TR20.20 Continuous Monitors Clause 18.2 Wrist Strap Checkers]
4. Elimination of Periodic Testing
Many customers are eliminating periodic touch testing of wrist straps and are utilizing continuous monitoring to better ensure that their products were manufactured in an ESD protected environment. Continuous monitors also eliminate the need for users to test wrist straps and log the results.
When using continuous monitoring, operators:
Don’t have to waste time queuing at a wrist strap test station before each shift.
Don’t have to remember to complete their daily test logs.
If your company manufactures products containing ESD sensitive items, you need to ask yourself “how important is the reliability of our products”? Sooner or later a wrist strap is going to fail. If your products are of such high value that you need to be 100% sure your operators are grounded at all times, then you should consider a continuous monitoring system.
Advantages of Continuous Monitors are plentiful:
Immediate feedback should a wrist strap fail
Monitoring of operators and work stations
Detection of split-second failures
Elimination of periodic testing
All of the above advantages of Continuous Monitors will lead to a reduction in overall costs.
Savings comes from:
Eliminating time/labor required in verifying a wrist strap before handling ESDs
Reducing damage to ESDs from broken wrist straps that may go unnoticed with standard wrist strap testers.
For more information and an overview of SCS Workstation Monitors, have a look at our Selection Guide.