A GUIDE TO CORRECT USE OF ANTISTATIC FOAMS

History

Pink ESD foam has been ubiquitous in ESD packaging since it was developed in the 1970's. It's a fantastic product that meets many needs for many uses. Regularly used as padding for a package or work surface, pink foam became a “solution” for many ills. That said, there has been a misconception of the life span of the anti-static properties. Pink anti-static foams have a shelf life. Once the shelf life has expired, the foam can be very dangerous to the manufacturing environment and sensitive components. Looking closer at an EPA (ESD Protected Area), the the use, or misuse of these foams is the most commoninfraction of standard ESD practices.

As it relates to ANSI/ESD S20.20, 6.1 and 6.2 of ANSI/ESD S541 tells us that packaging (pink foam) used both inside and outside an EPA is required to meet 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.

Low charge generation is one of those characteristics of the materials. S541 also specifies that for "intimate" or immediate contact of sensitive products, it has to be dissipative or conductive. Foam is used for "intimate contact" in most applications. This is why it is so critical to understand what is ESD static dissipative about pink foam and why it has a shelf life. Once that shelf life is reached, 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

Regular foam offers great padding to protect contents from physical impact. The concern with regular foam is that it sits very high on the triboelectric scale for producing 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, relative humidity and several additional factors. Thus, regular (non ESD) foam is is not valid to use in an EPA (ESD Protected Area) environment. Remember, after the ESD properties dissipate from Pink ESD Foam, you're left with regular foam.

Pink Anti Static Foam

Because of its chemical composition and high surface area, flexible foam is prone to the build-up of static charges. This characteristic is overcome with the addition of anti-static chemical additives or anti-static surfactants. These additives are most commonly applied to the foam during manufacture. The color pink is just the color the industry chose 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 that temporarily change the coefficient of friction between mating surfaces (tribo charging). That’s a pretty big statement. Now, let's investigate further to help understand it better. The molecules (in surfactants) in their initial state are unsaturated.

The unsaturated bonds in these molecules want to absorb moisture. In their unsaturated state, they help lower the friction rate of the foam helping its Antistatic properties. The challenge of unsaturated molecules is they are made to become saturated. Once a molecule is saturated, their antistatic properties are done. How much time does it take for these molecules to become saturated? That can change depending on many factors. Humidity and the environment play a vital role.

How the foam is handled also plays a vital role. Sadly, there is little actual guideline for how long it will take. Most industry experts determine one year as the magic date to begin testing and others suggest earlier and some later. It boils down to your understanding and your procedures. What works for some may not work for all.

Shelf Life

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

Fortunately, the ESD Association gives us guidelines to help navigate this problem. 6.1 and 6.2 of ANSI/ESD S541 tells us, as it relates to ANSI/ESD S20.20, that packaging (pink foam) used inside and outside an EPA has to have certain characteristics. One of those 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 usually used for intimate contact of sensitive products. You see foam lining racks and shelves, in bottom of drawers, inside containers and as separators between stacks of circuit boards or assemblies. This makes sense. We cannot have any charge generating packaging material in an EPA or in certain scenarios outside of an EPA.

And now we have an issue. We have documented and explained how these foams might or might not be static safe. If the foam still meets its material specifications, we’re all good to go. If the ESD of pink foam have expired, what should you do? Luckily for us, we can turn to the ESD Association for guidance. Specificially, 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 a vital statement. It not only validates that material can deteriorate over time, it also states that we must develop a verification process to ensure the properties are still valid. ESD TR53-01-06 is another refernce to validate this. ESD TR53-01-06 discusses compliance verification of ESD protective equipment and materials.

Package Compliance Verification

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

FOD (Foreign Object Debris)

One last thing to consider when using foam for intimate contact with electronics is concerns of foreign object debris or FOD. All foams, standard non-ESD foams, antistatic foams, and conductive foams will shed particulates to varying degrees. Some foams are much better than others, but all foams will produce some FOD. If you are concerned about FOD when handling devices, use alternate options to prevent contact with foam.

Summary

So there it is. We have discovered that you may have a problem if you are using Pink ESD Foam.

• Pink ESD Foam has a shelf life
• The shelf life of that foam is unknown
• When it loses its ESD properties, it is unacceptable in, and potentially out, of an EPA
• If you're using 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's a potential solution to the problem of limited shelf life. Compliance verification can make an antistatic foam viable. If you don't have compliance verification, or if it isn't practical, then other more permanent options should be chosen.