ESD Tests and Standards

 

Surface Resistivity by the parallel probe method. [ohms/square] This test is done with a Megohmmeter and is used on flat more-or-less homogeneous surfaces. However the instrument is special as it must have rather higher than common voltage facilities, say 10VDC and 100VDC (the voltage to select depends of the resistivity range to be measured). Normally there is provision to do a measurement under the instrument by means of a couple of parallel  bars constructed of a conductive compound that also provides grip to avoid slippage. Test: place meter over the surface to be measured. Select lowest voltage to start, say 10V and follow the instrument provided instructions, the RH(%) and t(C) values are also to be measured as the resistivity of a surface's material changes with these two parameters.  

 

Surface Resistivity by the concentric probe method. [ohms/square] This test is done with a Megohmmeter with a special concentric probe and measures similarly to the above. Normally the value found by using this probe has to be multiplied by a factor of ten, again RH and t values need to be measured. This probe has been specified in the ANSI/ESD Standards S11.11
Surface Resistance, Test point to Test point measurement (RTT) with 5lb probe electrodes The test measures resistance in between two points of a surface, no reference earthing point is involved. To compare a measurement with some manufacturer's claim or to repeat a manufacturers test procedure use the same given distance and apply similar preparation of the surface in between the electrodes. RH and t values are also to be measured.  
Surface to Ground Resistance Test (RTG) Use a 5lb electrode in conjunction with a normal alligator clip end. Connect the alligator clip to a known earth point and place the the 5lb electrode on the surface point according to required test procedure and measure. RH and t values are also to be noted.
Summary of the ESD Association Standard ANSI/ESD S20.20-2007 "for the Development of an Electrostatic Discharge Control Program for - Protection of Electrical and Electronic Parts, Assemblies and Equipment (Excluding Electrically Initiated Explosive Devices)

(This the the final revision of the 1999 document)

 

The standard sets down guidelines for the design, establishment, implementation and maintenancion of an ESD control program. The guidelines are offered for implementation where devices may experience damage due to ESD where potentials may exist in excess of 100V, as per the Human Body Model (HBM), hence for devices susceptible to potentials of <100V HBM other stringent guidelines need to be used. Please check the new document in the  ESD Association site via the provided button link.

Summary of the ESD Association Standard.  ESD STM12.1-1997 " Seating - Resistive Measurement"

 

The Standard defines methods to test seating  (chairs and stools) which are located within an ESD controlled environment and which are part of a site's  ESD control program, the tests focus on a quantity of electrical resistance measurements from diverse specified points on the seats to each of the floor contacts, the tests must be effected in two stages within pre-defined controlled environments. There are three type of test outlined, a qualification test, an acceptance test and a periodic test, all follow a similar step-by-step structure and end up with appropriate reporting guidelines. The standard provides thresholds for measured resistance results.

 People moving in and out of seats produce charge generation due to triboelectricity which in turn adds to charges generated due to seat movements over the floor. Even when tests of seatings will show whether there is an excessive resistivity to earth in some of them and replacement may be recommended it must be understood that seats are not a main ESD control mechanism and the relevance of the results are not be compared, as for example with wrist straps.

 

Summary of the National Fire Protection Association of the USA (NFPA 77-00), recommended practice on static electricity No.77 edition 2000. Presents a new view of the problem of fires and explosions triggered by static electricity. Explains the fundamentals behind the phenomenon and recommends ways for evaluating and controlling potential hazards. It also produces recommendations for the appropriate bonding of grounds.
Summary of the current EN 61340-5-1 & 2 EU Standards The main document, EN 61340-5-1 specifies generic requirements for the installation and maintenance of an ESD controlled area or EPA (ESD Protected Area). In this area, ESDS (E SD Sensitive devices) which are susceptible to ESD events with potentials in excess  of the Human Body Model (100V) will not experience harmful discharges. Also deals with training, auditing, signs to use in the EPA demarked areas and ESD protective packaging. The EN 61340-5-2 document is a User Guide.