Electrostatic Discharge (ESD)

Electrostatic Discharge (ESD) (Page 2 of 2)

Page 1 mentioned that ESD controls may be classified into three major categories: 1) prevention of static charge build-up; 2) safe dissipation of any charge build-up; and 3) improvements in the ESD robustness of the product. The second category is very closely related to, and may sometimes even be indistinguishable from, the first category. Safe dissipation of accumulated charge involves the provision of a suitable electrical path that will allow charges to flow to ground. No ESD control program will be successful without a sound policy on grounding. As much as possible, there should only be one common ground for the entire factory.

Everything in the production line, from equipment to work tables to cabinets and racks, must be connected to this common ground. If the factory uses conductive flooring, then this should also be connected at regular intervals to this common ground. Having a single or common ground will ensure that everything in the production floor will remain at the same potential. Any charge build-up will immediately be dissipated by a good grounding system. The use of properly grounded wrist and foot straps or conductive shoes will also fall under this category, since these will bring any charge build-up on personnel to the common ground.

Fig. 2. Examples of personnel grounding accessories:

wrist strap, sole grounder, and conductive shoes

Control of RH is also important, since the moisture in the air acts as a conductive path that can bring static charges to the common ground. Thus, a very dry environment is inviting ESD. Care must be exercised though because excessive RH might trigger corrosion.

The third category does not actually control the ESD phenomenon per se, but pertains to making devices more resistant to ESD damage. This involves incorporating ESD protection cells in the design of the IC, and the use of physically robust features that can withstand the high current brought about by an ESD event.

Proper training of personnel on ESD precautions is also a must. A good ESD control program therefore incorporates a training scheme that will ensure that everyone is aware of the company's ESD controls and SOP's. A regular audit of the manufacturing line for ESD control compliance is important. Check out our ESD audit checklist.

ESD Audit Checklist; The Triboelectric Series

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