Written by: Gene Felder, Corporate Product Manager
What is the ESD control requirements for battery and pneumatic powered hand tools? From ESD Handbook ESD TR20.20 section 22.214.171.124 “Battery powered and pneumatic hand tools while being held should have a resistance to ground of less than 1 x 10E12 ohms.”
If tool’s housing is conductive or dissipative, it can be grounded being held by a grounded operator. If insulative and can charge to 2,000 volts (measuring with a static field meter), it is to be kept at least 12” away from ESD sensitive items at all times. This of course would defeat most purposes of a hand tool. Otherwise, ionization should be used. Alternatively, the housing could be periodically treated with a topical antistat.
From ESD Handbook ESD TR20.20 section 126.96.36.199 Electrical Hand Tools
“All electrical tools and equipment used to process ESD sensitive devices require the three prong, grounded-type AC plug. The metal portions of the tool that touch the device should have a low resistance (<2 ohms) to the equipment ground terminal on the plug. In some cases, the user may wish to verify that the metal portions of the tool have acceptable voltage levels and leakage current. The tester defined in ESD STM13.1 provides a means of checking soldering iron tips while being used. Although the document was written to make measurements on soldering and desoldering equipment, the measurement techniques can be used for other electrical hand tools.
The working part of AC powered tools should be capable of providing a conductive path to ground. New powered hand tools such as soldering irons typically should have a tip to ground resistance of less than 1.0 ohm. NOTE: This resistance may increase with use but should be less than 20.0 ohms for verification purposes.
A low resistance ground is needed as many soldering iron controllers adjust tip temperature either by switching the iron on or off at limits, or by using high frequency effect. The result can be electric fields, and a low impedance path to ground will limit high potentials from being accumulated which can damage ESDS.
Battery powered and pneumatic hand tools while being held should have a resistance to ground of less than 1 X 10E12 ohms.
Care must be taken with double insulated tools for work on ESD sensitive devices because there is no hard connection to ground. Grounding a power (utility) tool through a person may be hazardous. Pneumatic tools should have a path from the tool tip to ground through a wire and/or through a grounded operator.”
Desco has a number of resistance measuring tools including the Desco 19781 Surface Resistance Digital Meter to measure the < 1 x 10E12 ohm requirement, and Desco 19245 Low Resistance Tester to measure the low resistance requirements.
If using ionization, you would be following ANSI/ESD S20.20. Its section 8.3 includes:
“In order to mitigate field-induced CDM [Charged Device Model] damage, the ESD program shall include a plan for the handling of process-required insulators. If the field exceeds 2,000 volts/inch, steps shall be taken to either:
A) Separate the insulator from the ESD-sensitive device by a distance of 30 cm (12 inches);
B) Use ionization or other charge mitigating techniques to neutralize the charge.”
To verify that the solution is actually accomplishing something, best practice would be to rub the item (your process-required insulator) and measure what charge can be generated on the hand tool with and without the ionizer on.
Note: the ESD Association sells the 132 page ESD Handbook ESD TR20.20 as a hardcopy or a PDF. Go to www.ESDA.org, click “Standards”, then “Documents” and then “Order Publications”. ANSI/ESD S20.20 is available as a complimentary download at no charge.