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.
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.
Turn the unit OFF and unplug the power cord.
Open the top screen by loosening the screw and swinging the grill to one side.
Clean the emitter points using the an emitter point cleaner or a swab dampened with Isopropyl alcohol.
Re-attach the top screen.
Plug in the power cord and turn the unit ON.
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.
Check out how to clean an Ionizer in A Minute with Miranda:
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)
Position the ionizer and charge plate monitor as shown below.
Set the CPM to Decay/Offset mode.
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.
Start the decay/offset test sequence on the CPM. This will take a few seconds.
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
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.
Hold the meter approximately one foot (30.5 cm) in front of the
ionizer.
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.
Zero point adjust the meter. Bring the plate into contact with a grounded body, and press the 0ADJ button.
Set the desired mode. Press the SELECT button, and the meter will scroll through the modes. To measure balance (offset voltage), use I.B mode.
Point the plate at the measurement location, the meter will measure the balance.
Watch how to test the balance using the SCS Portable Charge Plate Monitor:
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)
Set the CPM to Decay/Offset mode.
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.
Start the decay/offset test sequence on the CPM. This will take a
few seconds.
Record the decay time, and offset voltage as displayed on the CPM.
Ionization Test Kit
After charging the plate of the ionization test kit, hold the field
meter approximately one foot (30.5 cm) away from the ionizer.
Monitor the display of the meter to see how quickly the 1.1 kV
charge is dissipated to 0.1 kV.
The speed at which this occurs (the discharge time) indicates how
well the ionizer is operating.
Repeat this procedure for both a positively and a negatively charged
plate.
Portable Charge Plate Monitor
If you haven’t already, turn the meter on and zero it.
Set the desired decay range, select +Decay to measure positive discharge time. Select -Decay to measure negative discharge time.
Point the plate in the airflow of the ionizer to be measured and press the START button.
The meter will chirp and display the neutralization time when the measurement is completed.
Watch how to test the decay time using the SCS Portable Charge Plate Monitor:
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.
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.
