Hi John,
Below wrist strap test limit control appear in one of our customer(semiconductor) spec.
Have you came across this type of stringent wrist strap control? If yes, how to achieve this?
I asked my customer if I can control according to ANSI standard < 35M ohms, the reply is “please follow this spec, as this is standard for all our subcontractor. Still within ANSI spec, but tighter.”
Current ESD wrist strap we use are embedded with 1M ohm. WRIST STRAP SYSTEM TEST reading I can get is more than 1M ohms. (2.0M - 3.8M ohms)
I guess my first question would be, what type of industry/processes is your company involved with? typically you find that lower resistances in wrist strap cords are called out for certain chemical/explosive types of processes. Here is an excerpt from ESD TR20.20:
Wrist strap ground cords that contain a current limiting resistor with a value other than 1 megohm will be marked in some way, generally a red color on the ground cord head. In addition, the actual resistor value may be molded into the ground cord head. Resistor values other than 1 megohm are commonly used in applications involving chemical processing, munitions, explosives, and other hazardous processes.
Second I would reach out to your customer and ask in a respectful manner for them to provide a technical justification or resource standard that calls for or promotes the tightened requirements.
I would also recommend that you obtain a copy of the wrist strap standard S1.1. It has a good deal of information on wrist straps/systems plus a brief discussion on non-standard resistances as you mentioned here.
Also I would communicate to the customer that re-tooling your wrist cord system could be potentially cost prohibitive depending on how many cords you have to replace
