A GUIDE TO CORRECT USE OF ANTISTATIC FOAMS

History

Pink ESD foam has been a standard in the ESD packaging world since its creation in the seventies. It is a wonderful product and solves many needs for many uses. Commonly used to cushion a package or work surface, pink foam became a "fix” for many shortcomings. That said, there is confusion about the anti-static properties and how long they last. Pink anti-static foams have a shelf life. Once that shelf life is gone, pink foam can become quite dangerous sensitive components and the manufacturing environment. When inspecting an EPA (ESD Protected Area), the most common broken standard ESD practices is the misuse of these foams.

ANSI/ESD S541 tells us in 6.1 and 6.2 as it relates to ANSI/ESD S20.20 that packaging (pink foam) used inside and outside an EPA has 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 direct or "intimate" contact of sensitive products, packaging shall be dissipative or conductive according to S541. For most applications, the thing making "intimate contact" is foam. Which is why it's so crucial to understand what makes Pink ESD foam static dissipative and why it has a shelf life. After that shelf life has been expired, all you have is 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 gives great padding to protect contents from physical damage. The problem with regular foam is that it is very high on the triboelectric scale for producing a static charge. FYI, all materials, even conductors, can be tribo-electrically charged. The extent of the charge is impacted by material type, speed of contact and separation, humidity and several other factors. As a result, regular (non ESD) foam is cannot be used in an EPA (ESD Protected Area) environment. Remember, once the ESD properties disappear from the Pink ESD Foam, you are left with regular foam.

Pink Anti Static Foam

Considering its chemical composition and high surface area, flexible foam is ideal for static charge accumulation. This property is fixed by the addition of anti-static chemical additives or anti-static surfactants. These additives are most commonly added to the foam during manufacturing. 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 often based on amides or amines. Surfactants are mobile (blooming) surface modifiers that temporarily change the coefficient of friction between mating surfaces (tribo charging). This is a pretty big statement. Now, let's investigate further to better understand it. The surfactant molecules are unsaturated in their initial state.

The unsaturated bonds in these molecules want to absorb moisture. In this unsaturated state, they work well to lower the friction rate of the foam which helps its Antistatic properties. The challenge of unsaturated molecules is their main goal in life is to become saturated. Once a molecule is saturated, their antistatic properties are no longer present. How much time does it take for these molecules to become saturated? That varies depending on several factors. Humidity plays a vital role. The environment plays a vital role.

Handling the foam also plays a vital role. The truth is, there isn't any real guideline for how long it will take. Many experts in the industry consider one year as the critical date to begin testing while others test earlier and some later. It boils down to your understanding and your procedures. What works for some may not work for everyone.

Shelf Life

So now we know why foam has a shelf life. Once its shelf life has passed, foam will not seem any different, but its ESD protective properties will be gone. We also know that, based on many factors, shelf life can vary. So what to do?

Luckily, the ESD Association has given us a guideline 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 (in this case pink foam) used inside and outside an EPA has to have certain characteristics. One of these characteristics is that materials must be low charge generating. It also states that for intimate contact of sensitive products, it must be dissipative or conductive.

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

And now we have a problem. We've identified 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 do you do? Lucky for us, we again 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 will degrade over time, it also tells us that we must develop a verification process to ensure the properties are still valid. Another reference to validate this is ESD TR53-01-06. This document addresses compliance verification of ESD protective equipment and materials.

Package Compliance Verification

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

FOD (Foreign Object Debris)

One final consideration when using 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 are much better than others, but all foams will produce some FOD. If you’re wondering about FOD when handling devices, use other options to prevent contact with foam.

Summary

So we've done it. We’ve identified that you may have a problem if you're using Pink ESD Foam.

• Pink ESD Foam has a shelf life
• The shelf life of that foam is variable
• When it loses its ESD properties, it is unacceptable in, and potentially out, of an EPA
• If you are 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 is a potential solution to the issue of limited shelf life. Compliance verification can make an antistatic foam viable. Without compliance verification, or if it's not practical, then other more permanent options should be considered.