ESD Protection Cont'd

Packaging/Handling:

1) Suitable packaging:

• Antistatic tubes, bins, conductive foams

• Plastics with conductive material 

• Place PCB in static-shielding bag before/after use

  • Avoid using torn or punctured static-shielding bags

2) Cover unused connectors with antistatic materials when not in use 
3) Clothing/Area:

• Antistatic footwear

• Grounded table, floor mats 

• Antistatic wristbands 

  • Portable Field Service Grounding Kit, like 3M Kit #8501 or #8507 consists of portable mat and wristband https://www.itm.com/product/scs-8501-static-dissipative-field-service-kit-standard-0-021

4) Things to avoid during handling:

• Tools with plastic handles, since handle can get charged due to triboelectric effect 

• Letting boards/components come in contact with clothing, since static charges on fabrics can’t be dissipated with normal grounding

• Moving PCBs unnecessarily 

• Coming into contact with the connectors and components 

• Letting chargeable plastics, like binders, within 0.6m of unshielded PCBs

• Letting PCBs come within 0.3m of a computer monitor

5) Use a soldering iron with a tip that has proper ground connection:

• Prevents chance of potential differences between pins of the device during handling

6) Humid atmosphere:

• Discharges atmospheric floating charges to ground 

• Provides protection against static electricity build up due to dry air

• Maintain a relative humidity level between 20% and 80% non-condensing 

PCB Design: 

1) Clean and low impedance ground:

• Allows electrostatic discharge currents to flow to ground easily 

• Create a clean ground using a mixture of analog and digital circuits 

• Unused areas in PCB should be converted to a ground plane 

2) Avoiding long leads and PCB traces: 

• Have parasitic inductance 

• Cause voltage overshoots and ringing issues if an ESD transient gets into the circuit

3) Reduce loop areas:

• If board routing encloses large loop areas -> conducting paths enclose more magnetic flux -> loop currents cause interfering fields -> affects circuit components 

• Route supply and ground lines close together

• Signal lines should have ground lines running close by 

4) Trace all around PCB edge: 

• Acts as a guard trace to be connected to ground

• Discharges static due to human contact

• Ensure large spacing between adjacent traces on the board

5) EMI Suppression Filters:

• These can eliminate noise using capacitors (to inhibit direct current) and inductors (to hold energy in a magnetic field as current passes through it). 

• E.g. LC 3rd Order Low Pass Filter https://www.digikey.ca/en/products/detail/murata-electronics/DSS1NB32A103Q91A/5018364?utm_adgroup=EMI%2FRFI%20Filters%20%28LC%2C%20RC%20Networks%29&utm_source=google&utm_medium=cpc&utm_campaign=Shopping_Product_Filters_NEW&utm_term=&productid=5018364&gclid=Cj0KCQjws4aKBhDPARIsAIWH0JW0KNZwbyTH6V0F7VDo5jdbQ9Xt89J_Vz47rjsTV9cWBku2yWSrJt4aAq8YEALw_wcB  

6) Transient-suppressor diodes:

• These are connected at critical points in the circuit, between input and output pins to ground

• Kept close to terminals

• Clamp voltage to a safe value based on the rating  

• To suppress ESD transients, place a ferrite bead on the input lead and connect a low value capacitor from the input lead to ground. LC at input filters the energy in the ESD transient to ground.

References

https://www.murata.com/en-us/products/emc

https://www.eetimes.com/design-techniques-to-control-electrostatic-discharge-damage-in-electronic-devices/#

https://docs.novatel.com/OEM7/Content/Appendix/ESD_Practices.htm?TocPath=Maintenance%7C_____8