May 2006John Chubb Instrumentation Methods for measurement John Chubb John Chubb Instrumentation Ltd Unit 30, Lansdown Industrial Estate Gloucester Road CHELTENHAM, GL51 8PL, UK Website:

May 2006John Chubb Instrumentation Rationale Many different materials described in this symposium with their performance features Testing performance requires measurements Reliable measurements require: - good instrumentation - test methods appropriate to user requirements These are the topics of this paper (see JCI Website for copies of several published papers)

May 2006John Chubb Instrumentation Protection against static electricity Suitability of materials to avoid risks and problems from static electricity depends on: –voltages arising on surfaces when these are contacted or rubbed by other surfaces –ability of surfaces to drain charge away from conductors in contact –ability of materials to provide shielding against electric field transients –ability of a material to support an incendive electrostatic discharge Today I am dealing with 1st and 3rd of these

May 2006John Chubb Instrumentation Surface voltages The surface voltage created when surfaces separate depends on: Quantity of charge transferred Rate of dissipation of charge compared to time for separation of surfaces Capacitance experienced by transferred charge

May 2006John Chubb Instrumentation Surface charge Quantity of charge transferred depends on: –Materials involved –Speed and pressure of contact Quantity typically less than 50nC - but if capacitance low voltage may be many kV and energy high (U = 1/2 C V 2 ) In general - no problems from static if: –Time for charge dissipation less than 1/2 s –Effective capacitance is high

May 2006John Chubb Instrumentation Measurements Resistivity does not properly assess materials as many materials non-homogeneous Can measure dissipation of charge when surfaces tribocharged. Can do in simple way, but not easy to be quantitative - and not suitable as industrial test Corona charge decay - quick and easy measurement: -use high voltage corona discharge to deposit charge -use fast response fieldmeter to measure surface voltage created and time for voltage to decay Studies show good matching to tribocharging behaviour

May 2006John Chubb Instrumentation Instrumentation

May 2006John Chubb Instrumentation JCI 155v5 Charge Decay Test Unit Corona +2 to +10kV Initial peak voltage V Decay times 50ms - 1Ms Charge measurement In-situ analysis plus JCI-Graph Decay time: from peak V to 10% Target: 2s (better less)

May 2006John Chubb Instrumentation Charge decay example graphs

May 2006John Chubb Instrumentation Shielding To protect electrostatically sensitive devices and assemblies within uncontrolled environments Packaging for microelectronic devices Cleanroom garments against charge on undergarments Protect against electromagnetic emissions

May 2006John Chubb Instrumentation ESDA Shielding Test For assessment of electronic packaging - no information on performance below 10MHz

May 2006John Chubb Instrumentation Instrumentation Approach to measure shielding over wide frequency range

May 2006John Chubb Instrumentation Shielding performance Example variations of shielding with frequency 10Hz to 10MHz

May 2006John Chubb Instrumentation Measurement of resistivity Variation of shielding with test resistors and damp paper

May 2006John Chubb Instrumentation Conclusions Suitability of materials to avoid static problems from surface charge: –Charge decay –Capacitance loading Shielding: – ESDA test for electronic packaging – Variation of shielding with frequency gives information for wide variety of applications - relevance to ignition risks