Fairly regularly we are seeing low charging or antistatic Pink Poly bags being used for the wrong application. These bags are made from a tinted polyethylene material with an antistatic coating that can wear away. This turns the bag insulative and high charging over time, making it noncompliant to ANSI/ESD S541 recommendations.
They also lack discharge shielding protection which makes components within the bag susceptible to ESD event damage. It is this distinction that is most important – as Pink Poly bags don’t provide shielding, they should not be used to carry ESD Susceptible (ESDS) items outside the EPA, i.e. when the sensitive item isn’t grounded. Per ANSI/ESD S541-2018, Table 1. ESD Protective Packaging Requirements by Location, Discharge Shielding is Required for Outside the EPA (UPA).
SCS Metallized Shielding bags are constructed from a metalized polyester film and a low charging polyethylene laminate. This provides the bags with a shielding layer that creates a Faraday cage protecting the ESD sensitive components within the bag from possible ESD event damage. The low charging inner layer and outer layer of the bag prevent tribocharging from occurring, minimizing the build-up of ESD charges when handling components. This low charging layer is longer lasting than a pink antistatic bag.
Per ANSI/ESD S541-2018 – Table2. Summary of ESD Protective Properties
“Protects packaged items from the effects of static discharge that are external to the package and limits current flow through package”
Per ANSI/ESD S541-2018 – Per 7.3.1 Electrostatic Discharge Shielding
“Electrostatic discharge shielding materials are capable of attenuating an electrostatic discharge when formed into a container such as a bag”
Watch our video for a simple demonstration on how pink poly bags differ from static shielding bags:
Implementing ESD control measures can be very simple, particularly if you are starting with one or two workbenches. Each workbench would be an individual ESD Protected Area (EPA) and when ESD Sensitive (ESDS) devices are not at the ESD workbench they should be in a closed ESD shielding container or bag. In today’s blog we provide a basic set up for a start-up workbench EPA.
Single-Wire Wrist Straps
Adjustable Wrist Strap, Blue, with 6′ Coil Cord
One size fits all adjustable wrist band with coil cord is used to ground a stationary operator.
Tests Digital Compliance Verification Surface Resistance Meter Kit – Measures resistance point-to-point (Rtt) and resistance-to-ground (Rtg) of worksurfaces, flooring systems, garments, packaging, and other materials in accordance with ESD Association documents: ESD TR53, ANSI/ESD S4.1, ANSI/ESD S7.1, ANSI/ESD STM97.1 and others
Internal Memory – Stores and recalls up to 100 measurements. Captures resistance, temperature, humidity and test voltage.
Whilst this guide provides a high quality but manageable avenue into ESD Control, not all ESD Programs are created equal, every company has different processes. So, get in touch with your requirements or complete our Checklist and SCS will support with a custom qualified parts list based on your application.
There are all kinds of variations and combinations of ESD Laminate and Continuous Monitors used by companies with ESD Programs.. There are some key factors that you need to be aware of if you intend to use ESD Laminate together with a continuous monitor that will monitor the worksurface connections.
It’s important to note that continuous monitors don’t monitor the status/condition of the outer surface of an ESD workstation. The continuous monitor monitors the connection between groundable points on the worksurface (often snaps), not the Resistance to Ground (RTG) of the surface itself. The RTG measurement must be taken separately, per ANSI/ESD TR53-01-18 – Compliance Verification of ESD Protective Equipment and Materials (Pages 6 and 7).
The basic technology is that the monitor applies a low test voltage to the scrim layer in the worksurface. Because the test voltage is so low, the resistance of the scrim layer of the mat must also be low so that the test voltage can complete a circuit of the scrim layer, worksurface connections (snaps) and ground cords. Completing that circuit indicates that the worksurface is electrically connected. The goal is to have the worksurface circuit fail because of a bad connection, not because the scrim layer resistance was too high. As mentioned earlier, testing the combination of the outer layer and the scrim layer together (RTG) is a separate test.
When choosing a continuous monitor and worksurface combination that will work together it is important to consider the following:
Does the worksurface have a separate scrim layer? (vs. a homogenous mat material)
Does the continuous monitor spec sheet note the resistance limit of the scrim layer required for the monitor/worksurface alarm system to pass?
See the excerpt below from the SCS 724 Continuous Monitor Technical Bulletin – https://www.descoindustries.com/PDF/724-Workstation-Monitor-User-Guide.pdf “Red Worksurface LED (M) This indicates that a high resistance condition (> 3.7 Megohms) exists across the conductive layer of theworksurface and/or the ground connections. Check the worksurface, ground cords and their connections for continuity. Note the audible alarm may also sound if enabled.”
What this means is if the resistance of the mat scrim layer is greater than 3.7 Megohms then the continuous monitor mat alarm would alarm for a high resistance condition even if the grounding hardware connections to the worksurface were intact. There are other SCS monitors available that will monitor a scrim layer with a resistance as high as 5 x 108.
In summary, it’s critical to know both the upper limit of the “pass” condition of the continuous monitor and the construction of the worksurface material (does it have a scrim layer and if so what is the resistance of the scrim layer?)
ESD Laminate requires extra attention when being considered for use with a continuous monitor for the following reasons:
Laminate material is rigid, which makes it more difficult for grounding hardware to make a good contact with the scrim layer.
Consider abrading the outer, decorative surface to expose the scrim layer for better contact. Consider a flat bottom drill for this process.
Most importantly, perform a test on the resistance between two points on the worksurface to determine if the resistance meets the requirements of the specified monitor (for the SCS 724 that requirement is less than 3.7 Megohms – 3.7 x 106 ). We recommend using an ohm meter with a test voltage similar, if not identical to the test voltage used by the continuous monitor. We recommend performing this test before the purchase/installation of any number of continuous monitor/worksurface combinations.
Worksurface and floor mats are most commonly grounded with a dedicated wire that is connected to electrical ground. Traditionally, the connection between the mat and wire is made with a snap. Snap connections can become electrically intermittent or accidentally disconnected, causing the worksurface or floor mat (which can often become ungrounded due to carts rolling over them) to lose its connection to ground.
To improve this connection, a ground cord with threaded holes can help. Threaded connections are recommended because they are more secure than traditional snaps; they allow the ground cord to be optionally bolted to the mat. This keeps the cord from disconnecting, ensuring proper grounding. The path-to-ground integrity of a mat should be periodically verified with a surface resistance meter and/or a continuous monitor.
Watch video of the SCS’s Dome Style Ground Cord with threaded snap connection to see how it works.
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.
Sensitivity to electrostatic discharge (ESD) is an important concern in PCB assembly manufacturing. Pinpointing where ESD events are occurring on an SMT line can be difficult determine. ESD exposure can take place anywhere in the process, including PCB loading, component handling, soldering, and operator interventions. ESD events generate electromagnetic radiation. The stronger the ESD event, the stronger the electromagnetic radiation. Detecting and measuring the unique waveform generated by an ESD event can help determine where the ESD event is occurring and reduce the time it takes to identify and solve the problem. Watch this video to see how continuous ESD Event Detection monitoring can be setup on an SMT Line to monitor the processes and triangulate where static voltage and ESD events are occurring in the process.
With electronic components getting smaller and more sensitive, it’s important to make sure they are protected from ESD events like static discharge. Per ANSI/ESD S20.20, “Protective packaging is required to store, transport, and protect ESDS electronic items during all phases of production.” Per the new 2018 requirements for ANSI/ESD S541, the shielding requirement was changed that remaining discharge for the bags should be less than 20 nanojules.
One of the more common used bags is a low charging Pink Poly bag. These bags are made from a tinted polyethylene material with an antistatic coating that can wear away. This turns the bag insulative over time, making it noncompliant to ANSI/ESD S541 recommendations. They also lack discharge shielding protection which makes components within the bag susceptible to ESD event damage. Metallized Shielding bags are constructed from a metalized polyester film and a low charging polyethylene laminate. This provides the bags with a shielding layer that creates a Faraday cage protecting the ESD sensitive components within the bag from possible ESD event damage. The low charging inner layer and outer layer of the bag prevent tribocharging from occurring, minimizing the build up of ESD charges when handling components.
Watch this video on Pink Poly vs Static Shielding Bag Testing and learn why Metallized Static Shielding Bags are the best packaging solution offering full protection against ESD events.
Have you been questioned by your quality manager about shelf life on ESD bags? Maybe it’s an internal quality procedure that is being written and you would like to know where the manufacturer stands on the shelf life of ESD packaging. Well today we will address the topic of ESD Static Control bag storage and the expected shelf life.
There are many ways to manufacture an ESD shielding bag with low charging properties on the inner and outer layers. This is the first factor to consider so I will address only the items that I convert here at SCS. In our process, I achieve shielding values via a buried metal layer. The metal layer is laminated between two layers of polyethylene. This process makes a very robust and long- lasting product in terms of shielding values as per ANSI/ESD S541-2018, the electronic industry’s most recognized standard for ESD packaging. Still the metal layer is exposed to oxidization if not stored properly and subject to extreme climate or moisture.
To achieve the outer and inner low-charging properties, I use a topical anti-stat solution. This provides the outer and inner resistance readings of >/= 1 x 10^4 to < 1 x 10^11 ohms as called out in ANSI/ESD S541-2018 packaging standard. This property is the most vulnerable to change and should be tested frequently.
How does all this pertain to shelf-life you ask? SCS provides a Static Control Bag Storage document with a 1 year warranty from the date of purchase. I have witnessed SCS ESD bags stored in a controlled climate, well-ventilated area that have maintained passing surface resistance results after 5 yrs. on the shelf. Some customers have relied on our Moisture Barrier products to archive various critical products for as long as 20 yrs. They found through extensive testing that SCS had the highest quality and most repeatable results to trust with their archived product.
End users cannot always provide a climate and humidity-controlled atmosphere for our raw material, so it is recommended that you test your bags periodically per the S541 standard and dispose of any materials that are found to be questionable. As a best practice, you can log your products by purchase date or lot number and create an annual spot check audit to assure that your bags are still in compliance. Using a FIFO First In First Out process is critical in keeping your inventory fresh. You can imagine that there are 1000’s of variations to consider when we discuss shelf life. Heat, storage rack conditions, travel method and local climate to name a few, so the points to take away are this:
Hot, Cold, sunlight, moisture
Add controls when possible
In a controlled environment, SCS ESD bags have seen 5 yrs. of proven shelf life.
Follow the FIFO process as a best practice for inventory.
SCS warranties the product for a period of 1 year from the date of purchase. You need to audit annually or prior to use as a best practice and assure that your devices are getting the best protection.
If the bags are questionable, recycle the product at your local recycler and order and new lot from SCS – Static Control Solutions.
Thank you, Kevin Cleary ESD Packaging Specialist – Sales Direct Line: (919) 903-1724