Test voltage for ESD resistance measurements & grounding of ESD mats

Technical Questions
#1

There are surface resistance meters available with only 10 V activation for range 10^3 ohms TO 10^12 ohms . But the recommended one as per ESD norms is 10-100v .

  1. why can’t the dissipative range too be measured with 10v activation only ?

  2. And at the same time why can’t be measured at higher to 100v ?

  3. what should be resistance of the conductive rubber pad used below the SS probes of 5 lbs each ?

  4. In a 3 layer mat the bottom is basically a cushion layer to top two layers. Conductive is in between . Here no sense in using conductive adhesive as bottom is an insulate layer. and, in that case even with a very close matrix of the copper mesh if the cross over junctions are not connected to the mat with rivets how can it be effective for a proper dissipation when the bottom layer is an insulator / adhesive used is an insulator except for copper foil that alone is a conductor. ? Even if the extra lengths of copper foil taken out below the mat are connected to a proper ground , how does the in between area of the floor mat gets ground connectivity just with copper foil running below without any connectivity to the mat ? This is the procedure being adopted by many floor laying people … But when I get a floor installed, I stand in person to ensure a grid of 1.5 mt x 1.5 mt and get the grounding buttons put at all junction points on the floor towards all four walls and get the small SS rivets put in between on the mat surface to connect at all alternative copper foil junction points to ensure full connectivity of the mat. Is this okay or wrong ?

Further, I do not advise my customers 2 layer for flooring as conductive bottom is a brittle material and, likely to develop cracks in dry weather and, may loose the conductivity in between and being brittle the ware and tear too may be fast due to more load on floor in comparison to work tops. But mainly for tables tops only 2 layer I recommend. However, I use copper foil network in both the cases for flooring and tables too, if the table atop area is more than 1 sq. mtr max. or 3 ‘x 3’ . Many people use normal rubber adhesive only which is an insulator . Is this okay or wrong ?

I recommend each work top grounding separately but not in series. Is this okay or wrong ?

#2

Hello esdtekniks, I apologize for taking so long to reply. As far as your questions;

  1. As part of any standard that the ESD Association writes, the results must be repeatable and reproducible. When writing the first standards it was shown that once the resistance of a material is above 10*6, the current used by the measurement instrument is so low that it will be influenced by any noise or outside fields. The voltage was raised to 100 v the current used to measure allows for the measurement to be repeatable. You can use 10 v but the results may not be repeatable.

  2. Other voltages have been used, such as 500 v and 1000 v and the results have been different. Some materials, such as multilayer mats have shown that at a higher voltage the current is sufficient that the material burns through to the mesh below and gives a false result.

  3. The probe definition is "The resistance between two electrodes shall be less than 1.0 x 103 ohms when measured on a metallic surface." The probe pads need to be less than 103 to meet this requirement. For more information, please see ANSI/ESD STM 4.1.

  4. I really can’t comment on the floor grounding system as there are many different type of products that meet requirements of ANSI/ESD S20.20. If the system you recommend meets the requirements for personal grounding than is meets the requirements. Simple as that.

Again, I cannot make a recommendation or say what your are doing is right or wrong. As I tell everyone, looks at the standards and if it meets the requirements it is ok.

As far a gounding in series or individually, if it meets requirements it is ok. As far as best practice, grounding each mat individually is considered the best practic.

#3

Sir,
Thank you for your valuable reply .
Look forward to further interaction on ESD issues