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ELECTROSTATIC PROTECTION IN ELECTRONICS

NEW STANDARDS

As a result of global co-operation, a suite of standards (IEC 61340 Parts 1-5), covering all aspects of electrostatic measurement and control has been developed. BS EN 61340-5 Part 1 now has the status of a full European standard, replacing BS EN 100015-1. BS EN 61340-5 Part 2 is the User Guide section.

The full titles of the documents are :

BS EN 61340-5-1:2001 Electrostatics - Part 5-1: Protection of electronic devices from electrostatic phenomena - General Requirements.

BS EN 61340-5-2:2001 Electrostatics - Part 5-2: Protection of electronic devices from electrostatic phenomena - User Guide.

STATIC DISSIPATIVE FLOOR COVERINGS

There is a very important change to the requirements for floors used for grounding personnel (primary grounding). The resistance limit to ground is recommended as less than 3.5 x 10^7 Ohms, including the resistance of the operative and footstraps/shoes. (BS EN 61340-5-1:2001, Clauses 5.2.3 and Table 1). This is a technically based recommendation, to ensure the protection of devices sensitive down to 100v ESD levels.

This change is based on the view that floors with leakage resistance values at the upper end of the limit set out in BS EN 100015-1 (>7.5 x 10^5 and <10^9 Ohms) provide a discharge path that is too slow to guarantee that there is no accumulation of charge above 100V on moving people and trolleys.

It is now recommended that a new floor covering be chosen, to comply with the revised recommendation, as best practice in terms of technical performance. (See page 36 of the current SSE Catalogue for more details - PDF Here)

A guarantee that the earth leakage resistance will be maintained, throughout the useful life of the floor material, should be obtained from suppliers, together with actual test results from recent installations.

Note: Most floor coverings are not manufactured to comply with the more stringent requirement detailed above . Claims that a product does comply must be qualified to a specified leakage resistance window. Consideration must also be given to the choice of footwear or grounding straps.

BS EN 61340-4-5:2004 details test methods for characterising floors in combination with a person, both for resistance to ground and body voltage parameters. The next issue of BS EN 61340-5-1 will include a choice of method for the assessment of floors, based on section 4-5.