Provided by the ESD Association

ESD-Sensitive Products:
How to Package Them Properly

Several factors should be considered to ensure the protectiveness of packaging materials.

Q: How does one decide which type of packaging--conductive, dissipative, or antistatic--is the proper choice for ESD-sensitive products?

A: ESD protective packaging is intended to eliminate or reduce charge generation and accumulation, and to prevent discharges from reaching susceptible parts and assemblies.

Packaging materials are generally classified in one of three categories depending upon their electrical resistance. However, these definitions do not necessarily indicate a material's ability to provide static protection. Conductive materials have a surface resistance £1 x 10⁴ W per EOS/ESD standard S11.11, or volume resistivity £1 x 10⁴ W-cm per EIA standard 541. Conductive materials act as a Faraday cage, helping prevent direct discharges from reaching the components inside the package.

Shielding (electrostatic) materials have a surface resistance £1 x 10³ W per EOS/ESD standard S11.11, or a volume resistivity £1 x 10³ W-cm per EIA standard 541. Shielding attenuates electrostatic fields on the packaging material's surface to prevent a difference in electrical potential from existing inside the package. Some materials may also provide protection from a direct discharge.

Dissipative materials have a surface resistance >1 x 10⁴ W but £1 x 10¹¹ W per EOS/ESD standard S11.11 or a volume resistivity > 1 x 10⁵ W-cm but < 1 x 10¹² W-cm per EIA standard 541. These materials drain and dissipate charges across the entire surface of the packaging.

The term antistatic is no longer used to classify materials. However, it is sometimes used to describe materials that resist triboelectric charge generation caused by the material contacting and then separating from itself or from other materials. The capability of a material to resist triboelectric charge is not necessarily indicated by resistance or resistivity measurements.

Several factors influence selection of the proper package. The first step is to determine if the item being packaged is to be protected from triboelectric charge generation, direct ESD, or electrostatic fields, or any combination of the three. The ESD sensitivity of the item to be packaged should be considered and the package design determined accordingly. Most companies today utilize packaging materials that provide all three benefits. For example, conductive or shielding materials may be necessary to prevent direct discharges from reaching the product, but they may also need to be combined with a dissipative material to reduce the possibility of a charged-device-model discharge from the product.

A second consideration is the entire shipping cycle of the item, from packaging and internal handling to the actual shipment and final handling of the part by the receiver. Longer cycles and more handling increase the chances for exposure to ESD events and influence the level of protection required of the packaging material.

Reuse of the package by the manufacturer or the customer is also a factor. Will it be reused several times by the manufacturer or the purchaser? What is the shipping cycle from the time the product is packaged until the customer removes it from the package for use? Materials designed for reuse or for long life cycles must retain their ESD properties and provide physical protection for the anticipated useful life of the material.

Also for consideration is the physical protection that the item needs. Some items may require the use of foam or cushioning to protect component leads or prevent item damage. In some cases flexible bags may be suitable; in others, corrugated or thermoformed packaging may be required.

Other concerns go beyond ESD protection. These include contamination, chemical and physical compatibility of the material with the packaged product, transparency, tear strength, water or moisture vapor transmission, printability, bar code reading, and disposability and recyclability.

Finally, one must consider cost and value. Cost analysis should take into account the value attained, not simply the out-of-pocket costs.

To submit your questions to the ESD Help Desk or to browse the archives of past questions and answers, visit the ESD Help Desk. Information on the ESD Association may be found at http://www.esda.org.

Back to March/April Table of Contents