A GUIDE TO CORRECT USE OF ANTISTATIC FOAMS

History

Pink ESD foam has been common in the ESD packaging world since it was developed in the 1970's. It's a fantastic product that solves many needs for many uses. Pink foam has typically been used as a cushioning aspect of packaging or work surface and has become a “solution” for many ills. However, there are misconceptions about the ant-static nature of the foam and how long it lasts. Pink anti-static foams have a shelf life. Once that shelf life is gone, the foam can become extremely dangerous manufacturing sensitive components. Upon further inspection of an EPA (ESD Protected Area), the using, or misusing these foams is the most commonviolation of standard ESD practices.

6.1 and 6.2 of ANSI/ESD S541 tells us, as it relates to ANSI/ESD S20.20, that packaging (pink foam) used in- and outside an EPA has 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 these characteristics of the materials used. S541 also states that for "intimate" or direct contact of sensitive products, it shall be dissipative or conductive. Foam is used for "intimate contact" in most applications. That is why it's so vital to understand what makes Pink ESD foam static dissipative and why it has a shelf life. Once the shelf life has been reached, all you have is regular foam. So we can better understand the “shelf life,” we must look 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 cushioning to protect contents from physical impact. The challenge with regular foam is that it's very high on the triboelectric scale and can 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, relative humidity and several other factors. Therefore, regular (non ESD) foam is unacceptable in an EPA (ESD Protected Area) environment. Remember, once the ESD properties dissipate from the Pink ESD Foam, you are left with regular foam.

Pink Anti Static Foam

Considering its high surface area and chemical composition, flexible foam is ideal for static charge accumulation. This characteristic is addressed by the addition of anti-static chemical additives or anti-static surfactants. These additives are typically added to the foam during the manufacturing process. The color pink is just the color the industry chose to help identify the foam as “ESD” or “Antistatic” materials.

The surfactants used are low molecular weight fatty acids commonly based on amides or amines. Surfactants are mobile (blooming) surface modifiers that temporarily change the friction properties between mating surfaces (tribo charging). That’s a pretty big statement. Let us look closer to help understand it better. The molecules (in surfactants) are unsaturated in their initial state.

The unsaturated bonds in these molecules want to absorb moisture. In this unsaturated state, they 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, the game is up and their antistatic properties are no longer present. How much time does it take for these molecules to become saturated? That depends on many factors. Humidity and the environment play vital roles.

Handling the foam also plays a vital role. In reality, there isn't any real guideline for how long it will take. Many experts in the industry look at one year as the magic date to start testing while others recommend testing earlier and some later. It all comes down to your understanding and your procedures. What works for some will not always work for all.

Shelf Life

And now we know why foam has a shelf life. Once its shelf life has gone, foam will not seem 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 can you do?

It's a good thing that the ESD Association has given us a guideline to help address this problem. As it relates to ANSI/ESD S20.20, 6.1 and 6.2 of ANSI/ESD S541 tells us that packaging (pink foam) used inside and outside an EPA must meet 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 it lining racks and shelves, in bottom of drawers, inside containers 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.

But now we have an issue. We've outlined and explained how these foams may or may not be static safe. If the foam still meets its material specifications, we are all set. If the ESD of pink foam have expired, what can you do? Fortunately for us, we can turn again 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 a vital statement. It not only validates that material deteriorates over time, it also states that we must develop a verification process to ensure the properties are still good to go. Another reference to validate this is ESD TR53-01-06. ESD TR53-01-06 addresses compliance verification of ESD protective equipment and materials.

Package Compliance Verification

Regularly confirm packaging materials as recommended in ANSI/ESD S541 (Packaging Materials for ESD Sensitive Items). Because of the large variety of packaging materials in use, 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, standard non-ESD foams, antistatic foams, and conductive foams will shed particulates to varying degrees. Some foams are much better than others, but foam will create some FOD. If you’re worried about FOD when handling devices, use alternate options to eliminate contact with foam.

Summary

So there you have it. We’ve learned 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 it loses its ESD properties, it's unacceptable in, and potentially out, of an EPA
• If you’re 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, we have a potential solution to the issue 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 used.