I’m new to this forum and ESD concept I’m looking to improve my understanding of ESD safety practices and procedures. I have a few questions and would greatly appreciate your insights:
In an EPA, if a staff member is not using certain safety measures, could this be considered a violation? For example, they are wearing ESD safe shoes and ESD safe T-shirts but are not using a wrist strap. Would this be classified as a compliance issue?
Datasheets for pink antistatic bags mention they are not entirely resistant to external influences. Does this mean external contact can affect the interior contents? If so, what precautions should be taken?
If there is a power outage, are devices connected to ground points still operational, or does grounding only ensure safety without affecting functionality?
Can you recommend any resources or references for understanding ESD effects at different levels, such as system-level and chip-level?
Glad to Welcome you to the ESDA Forum and good luck .
Well my first suggestion would be to visit ESD Association site @ www.esda.org and down load the ANSI.ESD S20.20.2021 , ANSI/ESD TR 53-01-2022 and ANSI /ESD 541-2019 which are all available on Complimentary basis under the Standards heading and, you will get answers and detailed information pertaining to point 1 -3 and from news room column you will find some white papers which can perhaps answer your point 4 plus many more.
You may go through the membeship details and if you decide to become a member many of the Technical reports are also available on Complimentary basis to the members.
As far as your thrid point on power outage is concerned , to the best of my knowledge the ESD facility grounding connected to your equipment earth is basically for ESD control aids /devices /equipments you are using for ESD safety and has nothing to do with your power outage.
Our ESDA experts Mr. JohnK and Mr. Andy and others would perhaps throw more light on your topic because their experience in the field is very vast and benefiting all of us in the forum every time.
Question 1:
This depends on the specific EPA requirements for your facility. In your example a wrist strap may only be required for seated operations but the footwear/flooring is okay for standing operations. If your operator is never seated, a wrist strap would be optional.
Question 2:
This means that the bags do not have static shielding which is only typical in the silver shielded bags. This would mean that an ESD event outside the bag could affect the ESD sensitive materials inside because they do not have static shielding properties. The pink antistatic bags may have a conductive/dissipative resistance and may be low charging, but they will not be able to shield its contents from an actual ESD event. That is why the pink antistatic bags are only acceptable inside an EPA. Anything leaving an EPA needs to have the discharge shielding property.
Question 3:
Grounding is independent of power being on as the ground wire should connect to an earth ground
I have two specific cases related to ESD safety practices, and I would greatly appreciate your expertise to clarify these issues:
Case 1:
In our ESD-safe environment, the flooring is compliant with ESD standards, and our staff wear ESD-safe clothing, smocks, and footwear. However, during PCB handling, they directly touch the PCBs with their hands instead of using a handling tool or carrier. My question is: does this constitute an ESD violation, or is it acceptable under these conditions?
Additionally, I am trying to understand how ESD footwear alone provides sufficient protection for standing operations. For instance, I tested a wrist strap by touching it to my smock, and the continuity tester indicated it was not grounding properly. This raised questions for me: if a wrist strap can fail due to layers like smocks, socks, and footwear, how does footwear effectively maintain a grounding path for standing operations?
Case 2:
To evaluate how ESD violations might contribute to PCB failures, I started counting instances of potential ESD non-compliance by our staff. Although I understand this method may not yield perfectly reliable data, I aim to identify possible correlations between ESD violations and PCB failures.
For example, when staff transfer PCBs between workstations by hand (even while wearing ESD-compliant smocks and footwear), I count this as a violation. Similarly, I monitor seated operations where wrist straps are not used. My question is: should such instances (like hand-carrying PCBs) be considered ESD violations, or are they acceptable under certain conditions?
Your insights on these practices will help me refine our procedures and better understand ESD risk management.
First, a little background on footwear and flooring to make sure we are on the same page, then I will answer your questions. Both the footwear and flooring should be qualified separately per ANSI/ESD STM9.1 (footwear) and ANSI/ESD STM7.1 (flooring). They also need to each be verified on a periodic basis per ESD TR53 (typically daily for footwear and monthly or quarterly for flooring). The resistance limits for both footwear and flooring are less than 10^9 ohms per ANSI/ESD S20.20.
Sometimes a given footwear and flooring option do not work well together even though each may pass the resistance tests above. To ensure the footwear and flooring system work well together, both ANSI/ESD STM97.1 (resistance) and ANSI/ESD STM97.2 (walking voltage) should be used to qualify the footwear/flooring system. Each different footwear option (for example, brand of shoe) used should be tested on a given floor. The limits for these tests per ANSI/ESD S20.20 is less than 10^9 ohms and less than 100 volts.
If all this has been done, your footwear/flooring system should be acceptable for operators to handle/transfer ESD sensitive items by hand as they are grounded through their shoes and then to the flooring.
You also asked how footwear effectively transfers charge through the socks and shoes when a wrist strap will not do this if it is placed over clothing. The answer is that socks develop moisture in them as they are used and the charge is able to pass through this moisture layer and then into the shoe. Sometimes, after putting on the footwear, it will not pass the resistance test right away because not enough moisture has accumulated to create a good path for charge transfer. After walking around a while, this clears up and the footwear passes the resistance test. This would not happen with a wrist strap over clothing as a moisture layer would not typically develop in the clothing
You also mentioned observing seated operations without using a wrist strap. This would not be acceptable per ANSI/ESD S20.20 as the operator may lift their feet off the floor and remove the path to ground. If a wrist strap is not a good option for seated operation, you could also use the groundable static control garment system (basically a garment with a strap attached at the waist) to free the operator’s wrist
Hope this helps. Feel free to ask any other questions. You may also find it helpful to go through some of the training material on the ESDA website.
I’m looking to improve my understanding of ESD safety practices and procedures. I have a few questions and would greatly appreciate your insights:
