A GUIDE TO CORRECT USE OF ANTISTATIC FOAMS

History

Pink ESD foam has been a standard in the world of ESD packaging since it was developed in the 1970's. It is a fantastic product and fulfills many needs for many situations. Pink foam has often been used as padding for packaging or work surface and has become a "fix” for many shortcomings. There are misconceptions about the anti-static properties and how long they last. Pink anti-static foams have a shelf life. Once that shelf life has expired, the foam can become very dangerous manufacturing sensitive components. Looking closer at an EPA (ESD Protected Area), the using, or misusing these foams is the most commonbroken standard ESD practices.

ANSI/ESD S541 tells us in 6.1 and 6.2 as it relates to ANSI/ESD S20.20 that packaging (pink foam) used both inside 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 direct or "intimate" contact of sensitive products, the packaging has to be dissipative or conductive according to S541. In most applications, foam is used for “intimate contact”. That is why it's so critical to understand what makes Pink ESD foam static dissipative and why it has a shelf life. Once the shelf life has been reached, you just have regular foam. In order to better understand the “shelf life,” we must look at regular foam in general, ESD foam, and appropriate applications of it.

Foam Is Great For Cushioning

Regular foam as a substrate gives wonderful cushion to protect items from physical damage. The challenge with regular foam is that it's 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 affected by type of material, velocity of contact and separation, humidity and several additional factors. Therefore, 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're left with regular foam.

Pink Anti Static Foam

Because of its high surface area and chemical composition, flexible foam is ideal for static charge build-up. This is fixed with the addition of anti-static chemical additives or anti-static surfactants. These additives are usually applied to the foam during manufacture. The color pink is just what the industry came up with to help identify the foam as “ESD” or “Antistatic” materials.

The surfactants used are low molecular weight fatty acids typically developed from amides or amines. Surfactants are mobile (blooming) surface modifiers that temporarily change the coefficient of friction between mating surfaces (tribo charging). That is a pretty big statement. Now, let's investigate further to better understand it. The surfactant molecules in their initial state are unsaturated.

These molecules have unsaturated bonds that want to absorb moisture. In the unsaturated state, they work well to lower the coefficient of friction of the foam and help in its Antistatic properties. The challenge of unsaturated molecules is they want to become saturated. Once a molecule is saturated, they are considered expired and their antistatic properties are no longer present. How much time for these molecules to become saturated? That varies depending on a few factors. Humidity plays a vital role. The environment plays a vital role.

Handling the foam also plays a vital role. In reality, there isn't any actual guideline for how long it will take. Many industry experts consider one year as the critical date to start testing while others suggest earlier and some later. It all comes 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 gone, foam will not 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 to do?

Fortunately, the ESD Association provides us a guideline to help handle 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 is required to have certain characteristics. One of these characteristics is that materials must be low charge generating. It also points out 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. This is pretty self-explanatory. We can't have any charge generating packaging material in an EPA or in specific circumstances outside of an EPA.

But now we have a problem. We have outlined and explained how these foams might or might not be static safe. If the foam still meets its material specifications, we are all set. If the properties of pink foam are gone, what do 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 an important statement. It not only validates that material deteriorates over time, it also says that we must develop a verification process to ensure the properties are still present. Another reference to validate this is ESD TR53-01-06. ESD TR53-01-06 covers 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). Because of the wide variety of packaging materials, users should come up with their own packaging compliance verification plan.

FOD (Foreign Object Debris)

One final consideration when using foam for intimate contact with electronics is concerns about FOD – foreign object debris. 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 are concerned about FOD when handling devices, select alternative options to prevent contact with foam.

Summary

So here we are. We have discovered that you might have a problem if you are 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 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, we have a potential solution to the problem of limited shelf life. Compliance verification can make an antistatic foam viable. In the absence of compliance verification, or if it's not practical, then other more permanent options should be chosen.