A GUIDE TO CORRECT USE OF ANTISTATIC FOAMS

History

Pink ESD foam has been common in ESD packaging since its creation in the 1970's. It is a wonderful product and solves many needs in many applications. Generally used as padding for a package or work surface, pink foam has become an "answer” for many shortcomings. There has been a misconception of the anti-static properties and how long they last. Pink anti-static foams have a shelf life. Once the shelf life has expired, pink foam can be very dangerous sensitive components and the manufacturing environment. Looking closer at an EPA (ESD Protected Area), the most common violation of standard ESD practices is using, or misusing these foams.

As it relates to ANSI/ESD S20.20, 6.1 and 6.2 of ANSI/ESD S541 tells us that packaging (pink foam) used in- and outside an EPA is required to have certain characteristics.

6.1 Inside an EPA

Packaging used within an EPA (that satisfies the minimum requirements of ANSI/ESD S20.20) shall be:

• Low charge generation.
• Dissipative or conductive materials for intimate contact.
• Items sensitive to < 100 volts human body model may need additional protection depending on application and program plan requirements.

6.2 Outside an EPA

Transportation of sensitive products outside of an EPA shall require packaging that provides:

• Low charge generation.
• Dissipative or conductive materials for intimate contact.
• A structure that provides electrostatic discharge shielding.

Additionally, for immediate or "intimate" contact of sensitive products, it must be dissipative or conductive according to S541. Foam is used for "intimate contact" in most applications. This is why it is so crucial to understand what makes Pink ESD foam static dissipative and why it has a shelf life. After the shelf life is expired, you're left with regular foam. So we can better understand the “shelf life,” first we need to look at at regular foam in general, ESD foam, and applications where it can and cannot be used.

Foam Is Great For Cushioning

As a substrate, regular foam provides wonderful cushion to protect products from physical harm. The challenge with regular foam is that it's very high on the triboelectric scale and has a high likelihood to produce a static charge. In fact, all materials, even conductors, can be tribo-electrically charged. The extent of the charge is impacted by type of material, speed of contact and separation, humidity and several additional factors. Therefore, regular (non ESD) foam is unacceptable in an EPA (ESD Protected Area) environment. Remember, once the ESD properties expire from the Pink ESD Foam, you just have regular foam left.

Pink Anti Static Foam

By the nature of its high surface area and chemical composition, flexible foam is prone to the acumulation of static charges. This characteristic is fixed by the addition of anti-static chemical additives or anti-static surfactants. These additives are most commonly applied to the foam during manufacture. Pink is just the color the industry decided on to help identify the foam as a category of “ESD” or “Antistatic” materials.

The surfactants used are low molecular weight fatty acids typically based on amides or amines. Surfactants are mobile (blooming) surface modifiers temporarily changing the coefficient of friction between mating surfaces (tribo charging). This is a pretty big statement. Let’s look closer to better understand it. The molecules (in surfactants) in their initial state are unsaturated.

These unsaturated molecular bonds want to absorb moisture. In the unsaturated state, they help lower the friction rate of the foam helping its Antistatic properties. The challenge of unsaturated molecules is their main goal in life is to become saturated. Once the molecule is saturated, their antistatic properties are gone. How much time does it take for these molecules to become saturated? That depends on many factors. Humidity plays a vital role. The environment plays a vital role.

How the foam is handled also plays a vital role. Sadly, there is no real guideline for how long it takes to saturate. Many people in the industry look at one year as the magic date to start testing and others test earlier and some later. It all comes down to your understanding and your procedures. What works for some will not always work for others.

Shelf Life

So now we know why foam has a shelf life. Once foam's shelf life has expired, foam won't appear any different, but the foam's ESD protective properties will be gone. We have also learned that, based on many factors, shelf life can vary. So what to do?

It's a good thing that the ESD Association provides us guidelines to help navigate this problem. As it relates to ANSI/ESD S20.20, ANSI/ESD S541 tells us in 6.1 and 6.2 that packaging (in this case pink foam) used both inside and outside an EPA has to meet certain characteristics. One of the characteristics is that materials must be low charge generating. It also says that for intimate contact of sensitive products, it must be dissipative or conductive.

Foam is often used for intimate contact of sensitive products. You see it lining racks and shelves, in bottom of drawers, inserted in totes and as separators between stacks of circuit boards or assemblies. That’s pretty self-explanatory. We can't have any charge generating packaging material in an EPA or in specific scenarios outside of an EPA.

Now we have a problem. We've documented and explained how these foams may or may not be static safe. If the foam still meets its material specifications, we are good to go. If the ESD of pink foam have expired, what do you do? Lucky for us, we again can turn to the ESD Association for guidance. More specifically, ANSI/ESD S541. In section A.6:

The static control properties of some packaging materials can deteriorate with time and use. Compliance Verification of static control packaging properties should be part of the ESD control compliance verification plan.

A6 Compliance Verification

This is an important statement. It both validates that material can deteriorate over time, it also tells us that we must develop a verification process to ensure the properties are still valid. ESD TR53-01-06 is another reference that validates thos. ESD TR53-01-06 discusses compliance verification of ESD protective equipment and materials.

Package Compliance Verification

Periodically validate packaging materials as recommended in ANSI/ESD S541 (Packaging Materials for ESD Sensitive Items). Due to the wide variety of materials used in packaging, users should develop their own plan for verification of packaging compliance.

FOD (Foreign Object Debris)

One last thing to consider in the use of foam for intimate contact with electronics is the concern about foreign object debris or FOD. All foams, regular non-ESD foams, antistatic foams, and conductive foams will shed particulates to varying degrees. Some foams are much better than others, but foams will create some FOD. If you’re wondering about FOD when handling devices, select alternate options to eliminate contact with foam.

Summary

So here we are. We have identified that you may have issues if you're using Pink ESD Foam.

• Pink ESD Foam has a shelf life
• The shelf life of that foam is unknown
• When foam loses its ESD properties, it is unacceptable in, and potentially out, of an EPA
• If you are going to use Pink ESD Foam, it should be a short term solution
• Consider the potential FOD issues with foam
• Have a quality program in place if you are going to use foam long term

Thanks to the ESD Association, there is a potential solution to the challenge of limited shelf life. Compliance verification can make an antistatic foam viable. Without compliance verification, or if it is not practical, then other more permanent options should be considered.