Conformity Magazine - March 2009 - (Page 39) additives, such as metal fibers or carbon black. Carbon black solutions can therefore cause problems with hard discharge, especially if grounding cannot be fully guaranteed, such as during inter-plant and intra-plant transportation, and may be responsible for a significant portion of the annual $84 billion cost due to ESD damage. Table 1 shows that permanent antistatic agents provide a controlled, soft discharge or “air bag” solution that forgives any missing links of grounding over the entire process line of electronics manufacturing. Relationship of Surface Resistivity to Charge Decay Time Figure 1 shows the correlation between surface resistivity and charge decay time. The blue points are measured, while the red points must be calculated because the charge decay values become too small to measure effectively. Figure 1 highlights that surface resistivity above 1012 passes beyond the two second limit of charge decay time as defined in the norms, so that the linear correlation falls apart and the damage potential from uncontrolled discharge increases significantly. Surface resistivity below 107 gets into the range that charge decay time is effectively close to zero, leading to the potential dangers of instantaneous discharge. The graph shows that the optimal regime of surface resistivity falls between 109 to 1011. This gives a charge decay range of 0.01 seconds up to 0.2 seconds, allowing a safe controlled discharge. Conductive Materials Have Greater Potential for Damage What ultimately accounts for damage is the amount and density of the total electric energy potential that is discharged. Figure 2 shows examples of charge transfer over time for conductive and dissipative materials. Standard & Custom Board Level Shielding Photoetching process improves design flexibility enabling complex shapes without expensive tooling for standard single-piece, standard two-piece, and custom designs. No tooling charges for standard designs! 1-Piece Standard Designs with depth-etch bend lines save time and money. Interactive PDF sales drawings are available to download from the website. 2-Piece Standard Designs are comprised of a fence and cover, plus multiple mounting options. Interactive PDF sales drawings are available at the website. Custom Designs offer unlimited possibilities for materials and shapes. Product engineers can help you develop the best design for your application. Never an additional cost for slots, holes and logos, since photoetching allows the engineer complete flexibility when designing board level shielding. No limitation on shape or size welded seams Prototypes in as few as 5 days Made in USA See Complete Board Level Shielding Specs at www.tech-etch.com/shield ISO 9001:2000 REGISTERED TECH-ETCH, INC., marCh 2009 Conformity 39 http://www.tech-etch.com/shield http://www.tech-etch.com/shield
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