Conformity Magazine - March 2009 - (Page 40) The integral under each curve reflects the energy density, while the height of the peak indicates the maximum charge transfer. For the same energy density, the shorter charge decay time means that peak current transfer is significantly higher with conductive materials, leading to greater potential damage. Can You Salvage the Hidden Cost of Insufficient ESD Solutions? Electronic components, especially at the interconnect or chip level, are especially sensitive to dust and additive contamination. Some antistatic solutions cross-contaminate the very components they are intended to protect. Carbon black, for example, is prone to release fine particles (sloughing). Since carbon black particles are highly conductive, they can cause short circuits in electrical devices through hard discharges. Surface active (migratory) additives can also cause crosscontamination because these additives are inherently small, mobile molecules designed to work at a substrate surface. These mobile molecules can easily make the leap from packaging to part when the two come in contact. Contamination of electronic parts adds substantially to offspec rates within chip manufacturing plants, and is the hidden cost associated with some ESD solutions. Every time a component or assembly is placed in or removed from a package, whether a bag or transportation tray, it can become charged. When the component’s pins touch a conductive surface, the speed of the discharge is so fast that the damage is devastating. However, part of the trapped charge on the insulating parts of the component remains and can lead to another discharge when it is picked up or dropped into another conductive surface. With the introduction of plastic containers, it was thought that a conductive container would be the final answer to ESD control. Even so, if a component or device is already charged, contact with the conductive surface will lead to a “hard” discharge. Clearly, dissipative material to enhance ESD protection is needed. So What’s the Solution? The major current solutions include: • Choosing a ready-to-use antistatic or ESD polymer grade, such as polyamide; • Adding a conductive additive such as carbon black to conventional plastic grades; • Using inherently dissipative polymers; • Use of a permanent or temporary external antistatic coating. Inherently dissipative polymers (IDPs) are permanent antistatic agents. Because they are dispersed throughout the part, they work independent of humidity. This can allow a company to standardize ESD packaging solutions in its plants, regardless of the different environments in different regions. This becomes even more critical with global supply and assembly. In addition, standardizing solutions across all plants can save on purchasing resources, promote discounts on larger volume purchases, and reduce the number of suppliers. Since they are permanent, IDPs last throughout the lifetime of the article in use and, in many cases, even after washing and wiping. This durability provides cost savings of replacing ESD packaging over the long term, particularly for customized solutions. Reducing packaging volume and extending the service life of materials are also environmentally responsible. In contrast, surface active antistatic agents “migrate” to the surface and require humidity to absorb moisture in the air and form a conductive layer. Over time, these migratory antistats 0 Conformity marCh 2009
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