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December 18, 2017

Stainless Steel Benches and ESD

I do some contract work for a company that uses stainless steel benches in both their assembly area and test lab. I'm having trouble making the case to replace them with non-conductive surfaces and ESD mats.

Is anyone aware of any standard, or industrial best practices to help me highlight the various concerns with using stainless steel benches when handling ESD sensitive components?

T.S.

Experts Comments

I'm not sure I have an answer to this question and whether it requires additional questions for clarification.

From a dissipative perspective stainless steel is definitely a conductive surface, so perhaps the ESD mats could be used on the SS surfaces. The ESD mats should be connected to the ground connection and since they are static dissipative, that would seem to work. Measurements could be taken to verify this condition from the perspective of dissipative and conductive conditions.

Going to non-conductive benches would be an expense they may not want to undertake and are trying to make do with equipment they already have so by just adding the ESD mats to the SS benches could be the best of both worlds.
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Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.

Stainless steel benches are a risk for electronic parts, specially ESDS. Stainless steel benches or all metal surfaces provide a fasten or hard discharge, or a CDM discharge. This event can damage all ESDS. A resistance in the grounding cord is not a solution. The discharge go on direct from the ESDS to the metal surface. The true solution are table mats on the metal surface. So you achieve a resistance to ground higher as 1 x 106 Ohm. The risk for a CDM discharge is reduced. You doesn't need a non-conductive plate or surface between stainless steel bench surface and ESD mat.

The standards ANS/ESD S20.20-2014 or IEC 61340-5-1 require a minimum resistance from 1 x 104 Ohm.

For cleanroom facilities will be use stainless steel bench for cleanliness, in this case you shell be use ionizer to reduce the electrostatic voltage on the ESDS under 10 Voltage or better. The CDM discharge is mostly excluded.
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Hartmut Berndt
President
B.E.STAT group
Mr. Burndt has been in Electronics & Semiconductor Technology since 1980 and work in the area of Electrostatic (ESD) and electronic devices. He is President of the B.E.STAT group (Germany); expert in ESD audits, trainings, failure analysis and ESD control programs.
We have used benches with stainless steel tops in certain areas for years. The important thing is to make sure to properly ground the top for ESD.
Paul Dickerson
Supply Chain Engineer
Matric Group
Mr. Dickerson is an engineer with 20 years of manufacturing experience. He has worked supporting SMT, THT, cable assembly, and box build processes. He is a Certified SMT Process Engineer.
Stainless steel is a highly conductive metal not suitable for electronic work. This type of tables need a hard ground connection plus static-dissipative mats.
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Edithel Marietti
Senior Manufacturing Engineer
Northrop Grumman
Edithel is a chemical engineer with 20 year experience in manufacturing & process development for electronic contract manufacturers in US as well as some major OEM's. Involved in SMT, Reflow, Wave and other assembly operations entailing conformal coating and robotics.

The use of SS or metal benches is dangerous to your component and more so to your employees.

Stainless steel provides an almost zero resistance to ground. Any sensitive or memory component coming into contact with SS will in all probability suffer a catastrophic failure due to the rapid ( explosive ) discharge of any latent electrical charges that may be present.

Employees... Since it is common practice to ground employees with either wrist straps, heel straps or a combination of both, they are the path to ground.

Should ANY electrical charge, shorted soldering iron i.e.;, transfer to the table your operator is now the primary path to ground. The live electric current will utilize your operators connection to ground as its discharge route...therefore the electrical charge will pass through the employee.

Utilization of a dual or triple layer mat material covering the entire surface of the table is recommended. Proper grounding of this mat is essential. A dual or triple layer mat will provided a dissipative surface ( slow drain ) & a conductive layer ( fast drain ).
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Jerry Karp
President
JSK Associates
Based in. Northern California since 1971. Founded JSK Associates in 1979. Actively involved in soldering, cleaning, chemistries. 30 years experience in EOS/ESD control.

Metal benches, if grounded correctly are not an ESD hazard, in fact grounded metal is the best sort of ESD protection. Rather, metal benches as a test bench for electronic devices is more of a safety/electrocution issue. Testing electrical/electronic devices on metal benches can cause all sorts of potential hazards and short circuit problems, a little like using a hair dryer in the bath tub. It's not very safe!

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Paul Austen
Senior Project Engineer
Electronic Controls Design Inc
Paul been with Electronic Controls Design Inc. (ECD) in Milwaukie, Oregon for over 34 years as a Senior Project Engineer. He has seen and worked with the electronic manufacturing industry from many points of view, including: technician, designer, manufacture, and customer. His focus has been the design and application of thermal process measurement tools used to improve manufacturing processes like: mass reflow and wave soldering, bread baking, paint and powder curing, metal heat treatment and more.
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