A GUIDE TO CORRECT USE OF ANTISTATIC FOAMS

History

Pink ESD foam has been a staple in ESD packaging since its creation in the 1970's. It is a fantastic product that solves many requirements in many situations. Commonly used as padding for a package or work surface, pink foam has become an "answer” for many shortcomings. There has been some confusion regarding the life span of the anti-static properties. Pink anti-static foams have a shelf life. Once that shelf life is gone, the foam can be very dangerous manufacturing sensitive components. When inspecting an EPA (ESD Protected Area), the most common violation of standard ESD practices is the use, or misuse of these foams.

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 both inside and outside an EPA must 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. It also points out that for "intimate" or immediate contact of sensitive products, packaging must be dissipative or conductive. For most applications, foam is often used for “intimate contact”. That is why it's so important to understand how pink ESD foam is static dissipative and why it has a shelf life. When 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

Regular foam provides wonderful padding to protect items from physical impact. The challenge with regular foam is that it is very high on the triboelectric scale for producing a static charge. In fact, all materials, including conductors, can be tribo-electrically charged. The extent of the charge is affected by material type, velocity of contact and separation, humidity and several additional factors. Thus, regular (non ESD) foam is unacceptable 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

By the nature of its chemical composition and high surface area, flexible foam is prone to the acumulation of static charges. This characteristic is fixed by adding anti-static chemical additives or anti-static surfactants. These additives are typically applied to the foam during the manufacturing process. Pink is just the color the industry chose to help identify the foam belonging to “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 which temporarily change the coefficient of friction between mating surfaces (tribo charging). That is a pretty bold statement. Now, let's investigate further to help understand it better. The molecules (in surfactants) in their initial state are unsaturated.

These unsaturated molecular bonds want to absorb moisture. In their unsaturated state, they help lower the friction rate of the foam and help in its Antistatic properties. The challenge of unsaturated molecules is their main goal in life is to become saturated. Once a molecule is saturated, the game is up and their antistatic properties are no longer present. How much time for these molecules to become saturated? That can change depending on a few factors. Humidity plays a vital role. The environment plays a vital role.

The handling of the foam plays a vital role. In reality, there is little real guideline for how long it will take. Many experts in the industry determine one year as the critical date to begin testing and others recommend testing earlier and some later. It comes down to your understanding and your procedures. What works for some will not always work for all.

Shelf Life

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

Fortunately, the ESD Association has provided us guidelines to help navigate this problem. As it relates to ANSI/ESD S20.20, 6.1 and 6.2 of ANSI/ESD S541 tells us that packaging (in this case pink foam) used inside and outside an EPA has to meet certain characteristics. One of these 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 regularly used for intimate contact of sensitive products. You see it lining racks and shelves, in bottom of drawers, in boxes and as separators between stacks of circuit boards or assemblies. This is pretty self-explanatory. We can't have any charge generating packaging material in an EPA or in some circumstances outside of an EPA.

Now we have a problem. We have documented and explained why these foams may or may not be static safe. If the foam still meets its material specifications, we're all set. If the properties of pink foam are gone, what do you do? Conveniently 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 an important statement. Not only does it validate that material will degrade over time, it also says that we must create a verification process to assure the properties are still good to go. ESD TR53-01-06 is another reference that validates thos. ESD TR53-01-06 covers 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). Considering the wide variety of packaging materials in use, the users should create their own packaging compliance verification plan.

FOD (Foreign Object Debris)

One final consideration in the use of foam for intimate contact with electronics is concerns about foreign object debris (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 foam will generate some FOD. If you are concerned about FOD when handling devices, use alternate options to avoid contact with foam.

Summary

So here we are. We’ve learned 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's 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, we have a potential solution to the issue 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.