ESD “Health” Inspections

Certainly the most important part of an ESD control scheme is the earthing system, particularly if the earthing system is designed solely for ESD protection. The earth is to be checked first before proceeding ahead. Once we are satisfied that the earth is sound an robust, then we proceed to check the way bodies which are susceptible to ESD are earthed. Typically, in practice an electric conductor plus its interconnecting electrode should have less than 10Ω when measured to ground. An effective ground which is providing connection to a body with around 1MΩ should not allow accumulation of charges at all.

In some places a large body mass, which is floating or which is highly resistive to ground is used as a sinker of static charges in order to use its large storage capacitance, however this is not a sound technique and is recommended that some earthing conductors and electrodes be connected in between that floating body and earth. In time such a floating body will accumulate charges as to create a low but effective damaging potential.

Should the site be some type of manufacturing line of electronic equipment or components the mobile tray carriers, carts or trolleys used to transport these materials in between sections of the site must be ESD protected by adequate provision of some kind of sound earthing at all times eg antistatic flooring, mass connecting carbon conductive brushes, dragging chain, all wheels of conductive or antistatic material, etc… and hence be carefully checked out. Also check out strategic locations of the line as to assess whether there may be static charges accumulation and suggest use of appropriate ionisers where necessary.

Should the site be provided with some type of antistatic or conductive flooring, it must be checked and measured for effectiveness or otherwise produce adequate guidelines as to how properly maintain such a floor. Proceed to measure randomly some foot-straps (heel/toe) or antistatic shoes used by workers.

Check up relative humidity of the air and the average room temperature as to assess figures against ESD recommended values, otherwise produce fixing recommendations.

Check out personnel antistatic apparels if any are being used. Fabrics of synthetic materials are not recommended.