ESD Sensitivity Symbol

Happy Friday to everyone! Are you ready for another round of ESD updates? We’ve got a real gem for you today so let’s jump right in.
We’ve so far learned what ESD is and why ESD Protected Areas are so important. In today’s post, we want to arm you with 3 simple tactics to protect your ESD sensitive items. It’s easier than you think!

ESD Protection is a Requirement!
As electronic technology advances, electronic circuitry gets progressively smaller. As the size of components is reduced, so is the microscopic spacing of insulators and circuits within them, increasing their sensitivity to ESD. Industry experts estimate that average electronics product losses due to static discharge range from 8 to 33%. Others estimate the actual cost of ESD damage to the electronics industry as running into the billions of dollars annually. It is therefore critical to be aware of the most sensitive items being handled in your factory as the need for proper ESD protection increases every day.
Per ESD Handbook ESD TR20.20-2008 section 2.2: “Electronic items continued to become smaller, faster and their susceptibility to static damage increased…all electronic devices required some form of electrostatic control to assure continued operation and product reliability.”

Below you will find 3 simple tips to get ahead of the game.

1. Establish your ESD Protected Area
As a reminder, an ESD Protected Area (EPA) is a defined space within which all surfaces, objects, people and ESD Sensitive Devices (ESDs) are kept at the same potential. That means:

• All surfaces, products and people are linked to ground.
• Moveable items, such as containers and tools, are bonded by standing on a grounded surface or being held by a grounded operator.
• Everything that does not readily dissipate a charge must be excluded from the EPA.

In our last post we talked in detail about how to set-up an ESD Protected Area so if you’re unsure where to start, catch-up with the post here.

Remember that it’s just as important to mark your ESD Protected Area as it is to have it set-up correctly in the first place. If your EPA is not clearly identified, operators will not realize that special pre-cautions are required when entering. You really don’t want an unprotected person wandering over and touching things on the ESD workbench. All your hard work, time and money could be wasted. Make sure you use signs and tape to distinguish your EPA from the rest of your workshop.

Some take-away points for you:

• The ESD Protected Area (EPA) should have signage to clearly identify where it is.
• All conductors including personnel must be grounded. Operators must either wear wrist straps or footwear in combination with an ESD floor. ESD working surfaces (e.g. mats) are to be grounded.
• Wristbands are to be worn snug; the grounding tab of foot grounders must be placed under the foot in the shoe; ESD smocks need to cover all clothing on the torso.
• Wrist straps and footwear are to be tested daily. For wrist straps a continuous monitor can be used instead.
• Remove all non-essential insulators or neutralize essential insulators with ionizers.
• Use packaging with shielding properties to store or transport ESDS outside the EPA.
• Only handle unpackaged ESDs in an EPA when grounded.
• Periodic checks of installed products (e.g. ESD working surfaces, ESD flooring etc.) are required.
• Only trained or escorted people are to be allowed in the EPA.

2. Determine your ESD sensitive items
It is critical to be aware of the most sensitive item being handled in your factory. As with any type of control, there are several levels of protection. The method for choosing the necessary degree of ESD protection starts with defining your static sensitivity for electronic components. The ESD Association defines different classes of sensitivity for the HBM (Human Body Model) and CDM (Charged Device Model).

How can you determine the class of sensitivity of the devices within your facility? Look at your product flow through your facility, start at receiving and walk the components or products through until they are at dispatch ready to ship. Chances are, you have several different product flows through your facility. Each flow or loop will have specific components that enter or travel the loop. Make a list of all the sensitive components in each loop and determine the static voltage sensitivity or rating from each of the manufacturers. The lowest voltage sensitivity will dictate the sensitivity class of each loop. The philosophy here is “the chain is only as strong as the weakest link”. Each loop should have the required ESD protection for the most sensitive components that will travel this loop. This will define what class of protection is needed for each loop. You can have different class loops as long as the loops are closed, not allowing other components in. The objective here is to define a static control program to safeguard your most sensitive component.

Per ESD Handbook ESD TR20.20-2008 section 4.1.1 Determining Part ESD Sensitivity “The first step in developing an ESD Control Program plan is to determine the part, assembly or equipment sensitivity level under which the plan is to be developed. The organization can use one of several methods to determine the ESD sensitivity of the products that are to be handled. Some of the various methods are: 1) Assumption that all ESD products have a HBM sensitivity of 100 volts; 2) Actual testing of products using accepted test methods.”
Any ESD sensitive item should be identified with the ESD sensitivity symbol, either on itself or its container. The ESD Sensitivity Symbol (also called Susceptibility or Warning Symbol) identifies items that can be damaged by ESD and should ONLY be unpackaged and handled while grounded at an ESD protected workstation.

3. Train, train train!
No, we’re not talking about railway cars here. What we are referring to is teaching your employees. “Initial and recurrent ESD awareness and prevention training shall be provided to all personnel who handle or otherwise come into contact with any ESDS [ESD sensitive] items. Initial training shall be provided before personnel handle ESDS items. The type and frequency of ESD training for personnel shall be defined in the Training Plan. The Training Plan shall include a requirement for maintaining employee training records and shall document where the records are stored. Training methods and the use of specific techniques are at the Organization’s discretion. The training plan shall include the methods used by the Organization to verify trainee comprehension and training adequacy.” [ANSI/ESD S20.20-2007 section 7.2]

Perhaps the most important factor in a successful static control program is developing an awareness of the “unseen” problem. People are often a major factor in the generation of static charges. Studies have shown that personnel in a manufacturing environment frequently develop 5000 volts or more just by walking across the floor. Again, this is “tribocharging” produced by the separation of their shoes and the flooring as they walk.
A technician seated at a non-ESD workbench could easily have a 400-500 volt charge on his or her body caused not only by friction or tribocharging but additionally by the constant change in body capacitance that occurs from natural movements. The simple act of lifting both feet off the floor can raise the measured voltage on a person as much as 500-1000 volts.
Educating your personnel is therefore an essential basic ingredient in any effective static control program. A high level of static awareness must be created and maintained in and around the protected area. Once personnel understand the potential problem, it might help to reinforce this understanding by hanging up a few static control posters in strategic locations. The technician doesn’t need an unprotected person wandering over and touching things on the service bench.