The Shocking Truth (and Lies) about ESD

Paul McNamara’s recent post titled ‘The Shocking Truth (and Lies) about ESD” on the Network World‘s documents some stories of damage caused by ESD.

One notes:

I once zapped my home’s thermostat when I was attempting to change the temperature setting. The LCD went blank and refused to come back on. I ended up replacing the unit.

While the damage caused by ESD can seem like a mystery, the basic practices of controlling ESD when handling ESD susceptible items are pretty straight forward.

  • Establish an ESD Protected Area. It can be one bench or a whole facility.
  • Ground all conductors including operators.
  • Use a dissipative grounded surface for ESD susceptible products to be placed on if needed.
  • Remove all non-process essential insulators from the ESD Protected Area. Use ionization to control charges on process essential insulators.
  • If an ESD susceptible item needs to be removed from the ESD Protected Area, place it in a shielding bag or storage container that forms a faraday cage.

Desco has been making products to be used in an ESD Protected Area for over 30 years.

Questions about ESD Control?

Question: 1) In the scope, 200 volts CDM & 35 volts on isolated conductors are added. What is the intention to add them? Why are both of them determined on the value of 200 volts and 35 volts, respectively? 

Question: 2) As defined in clause 8.3.1, “If the field measured on the process required insulator is greater than 125 volts/inch and the process required insulator is less than 2.5 cm (1 inch) from the ESDS item, steps shall be taken to either A)… or B)…”, is there any relation between 125 volts/inch in here and 200V CDM in scope? If there is ESDS items whose sensitivity level is lower than CDM 200 volts (e.g., 100 volts) to be handled, which additional control elements or adjusted limits should be required? 

For answers to these questions and more answers about ESD control see the ESDA’s Threshold March/April edition HERE.

Busy day at CA1

Visit Desco at the IPC Apex Expo in San Diego, CA – February 24-26 Booth#318

Stop by the Desco Industries Inc booth to see new products including our:

The exhibitions area is open Tue 2/24 – 10AM to 6PM, Wed 2/25 – 10AM to 6PM,and Thur 2/26 10AM to 2PM.

For more info see the IPC Apex Expo website HERE

ESD Flooring – To Be or Not to Be

The following is based on a recent process analysis regarding the benefits of an ESD floor at a particular end user.  The end user currently has ESD Flooring and they are adding an additional production area.  Upper management questioned the cost of the ESD Floor and asked the ESD Coordinator and Production Manager to evaluate the process changes needed if there was no ESD Floor.  Below is the analysis of the burn-in processes.  The end user prefers to remain anonymous.

Process steps during the burn-in – oven process with ESD flooring:

1) Operator places burn-in board on ESD cart

2) Operator rolls ESD cart to the burn-in oven

3) Operator removes the burn-in board from the ESD cart and places in the oven

Process steps during the burn-in board – oven process with no ESD flooring:

1) Operator connects their wrist strap ground cord to ground

2) Operator connects the cart ground cord to ground

3) Operator places a container having discharge shielding on the cart

4) Operator loads the board into the container

5) Operator covers the container with lid

6) Operator disconnects wrist strap from ground

7) Operator disconnects the cart ground cord from ground

8) Operator rolls the cart to the burn-in oven

9) Operator connects their wrist strap ground cord to ground

10) Operator connects the cart ground cord to ground

11) Operator uncovers the container

12) Operator removes the burn-in board from the container and places in the oven

13) Operator disconnects the cart ground cord from ground

14) Operator disconnects wrist strap from ground

25 personnel who work in this area would now have some level of static voltage on their body when not wearing a grounded wrist strap.  If anyone reaches out and mistakenly touches a part, defects and product scrap is possible.  Use of ground cords may also cause dropped product / scrap.

36 ESD carts are used in this area.  Many are used for transporting unprotected product.  With no ESD floor to ground these carts via conductive casters or by the Operator grounding the cart while moving it  every cart will have some static charge on them and all product would now need to be transported in a covered container having the discharge shielding ESD control property..  If someone mistakenly placed an unprotected part on a cart, product defects and scrap are possible.

The most significant process challenge (product safety/throughput) with a no ESD floor scenario is the burn-in process.  Populated burn-in boards will need to be transported in covered discharge shielding containers as a functioning Faraday Cage.  Burn-in board carts will need to be modified for these new containers and will carry less burn-in boards after the modification.  More handling (packing / unpacking) will increase the possibility of dropped product.

Summary

The ESD floor is used in every process, by every product builder, technician, and support engineer.  Each added step is an added risk to the product from both ESD and the added handling is an opportunity for dropped product.  If the ESD floor was not added to the new production area, every production and production maintenance process step would somehow change, and the ESD control culture in this area could shift dramatically.

Per ANSI/ESD S20.20 flooring is an optional ESD protected area ESD control item. However, per ESD Handbook ESD TR20.20 “For standing operations, personnel shall be grounded via a wrist strap system or by a flooring/footwear system.” “The use of floor materials to control personnel or equipment generated static has a number of benefits. Floor materials tend to be passive. Employees who work in areas protected with floor materials simply need to wear and test the appropriate footwear. They do not need to implement any additional actions themselves to assure that the floor material is functioning properly.” (ESD Handbook TR20.20 section 5.3.4.4)

To download a complimentary .pdf of ANSI/ESD S20.20-2014, go to the ESD Association web site www.ESDA.org

What’s New in ANSI/ESD S20.20-2014

ANSI/ESD S20.20-2014 is an update that has a number of changes, including changes to the tables, and a number of statements rewritten to better clarify the meaning. The ESDA continues to remove guidance from the ANSI/ESD S20.20-2014 and focus it on requirements for an ESD Control Plan.  Guidance is detailed in the ESD Handbook ESD TR20.20.

The JAN/FEB edition of the ESDA’s Threshold details the changes in this article – Significant Changes Made From the 2007 Version To The 2014 Version Of ANSI/ESD S20.20

To download a complimentary .pdf of ANSI/ESD S20.20-2014, go to the ESD Association web site www.ESDA.org.

Controlling ESD in the 1400s?

Electrostatic discharge (ESD) is the sudden flow of electricity between two electrically charged objects caused by contact, an electrical short, or dielectric breakdown. The natural phenomena of ESD has been occurring for as long as our planet has been around and apparently it has been a problem for much of that time.  A recent post on the Static State Technology website notes:

“ESD has been an issue across multiple industries for as long as manufacturing has been taking place. Military forts in the 1400s were using static control procedures and devices trying to prevent inadvertent electrostatic discharge ignition of gunpowder stores. By the 1860s, paper mills throughout the U.S. employed basic grounding, flame ionization techniques, and steam drums to dissipate static electricity from the paper web as it travelled through the drying process [2].

As electronic device technology has progressed, we have seen reduced voltage tolerances and lower capacity for heat dissipation. The age of electronics brought with it new problems allied to electro- static discharge. Today, ESD impacts productivity and product reliability in virtually every aspect of the global electronics environment and emphasis on minimizing electrostatic charging and ESD has become hugely important [2].”

To read the entirety of the article see: Eliminating Electrostatic discharge: Protecting Tomorrow’s Technology.

Desco started as a company in the 1950s and focused on manufacturing continuity testers and soldering aids used by operators at electronics manufactures. As the components that the electronics manufacturers used progressed in technology, the same operators that required continuity testers and soldering aids now needed ESD control products. Desco started manufacturing wrist straps for ESD control in the early 1980s. Since this time the requirements for ESD control has changed greatly to keep up with the increasing sensitivity of electronic components and the automation of electronics manufacturing.

Wireless Wrist Straps…Still Don’t Work

The ESD Association’s  Resistance-to-Ground (Rtg) requirement for an operator wearing a wrist strap is < 3.5 X 107 ohms (ANSI/ESD S20.20) .  A wireless wrist strap will never meet this requirement.

Wireless wrist straps claim to work by “making (a) body’s static electricity to discharge through discharge box.” Assuming that an operator was tribocharged to 10 KiloVolt and wearing the “wireless” wrist strap, it would take many hours (days even depending on the ambient relative humidity) to get you below 5 KiloVolt, never the less 10 Volts. Most (if not all) of the charge reduction would be due to natural recombination of the charges on your skin (and now metal casing of your “wireless” wrist strap) with the air molecules and the natural conductance of the air through water vapor content (relative humidity).

You could get the same effect of a wireless wrist strap by cutting your hair to about 1/4″ long and then putting conductive jell in your hair (The guys over at the ESD Journal have another solution too). The ends of your now conductive hair would act like corona discharge points at extremely high voltages to bleed current into the air or help to enhance the natural recombination process.  The fact that your hair would need to come in very close proximity [0.1 to 1.5 inches] to ground or any other potential with at least a 3 KiloVolt difference (due to the dielectric strength of air) or enhancing the natural conductivity of the air needs to be considered to even get you down below a few KiloVolt.

Happy Holidays from Desco

Happy Holidays

From all of us here at Desco, we would like to wish you a safe and Happy Holiday season!

We will be closed on Thursday, December 25th and Thursday, January 1st.

As always, thank you for your business and the opportunity to provide you with an ESD solution!

Desco is thankful for…

Canton, MA Facility

…your business and the opportunity to provide you with an ESD solution!

Desco will be closed for the holiday on:
Thursday, November 27th and Friday, November 28th!

Have a Happy Thanksgiving!

 

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