How Electrical Overstress damage is caused

What is EOS? Electrical Overstress, or EOS, is a failure state wherein the device is subjected to undesirable voltage, current, or power. EOS can destroy a component in many ways, resulting in observable signs of damage or failure attributes.  These signs may include burns, excessive heat generation of components, shorts and open circuitry.

How is EOS damage caused?  

  1. Connecting a data cable incorrectly while the PCB is powered up can cause a short between two or more pins. 
  2. Incorrect power source, orientation or voltage can cause a surge that the PCB is unable to handle.  For example, applying voltage in excess of 3.3VDC to a OEMV-1 or OEMV-2 card will cause EOS damage.  Furthermore, applying more than 18VDC to a OEMV-3 card will cause EOS damage. 
  3. Handling the PCB without proper ESD (Electro Static Discharge) precautions can lead to electrical degradation.   For example, wearing a wool sweater in close proximity to the unshielded or improperly grounded device.
  4. Contact with conductive surfaces via an outside source such as jewelry can cause shorts.  Examples of jewelry may be rings, watches, bracelets or necklaces.
  5. Excessive moisture.  Moisture such as spilt water can be conductive which can result in shorts.

Often the EOS damage is greatest in the sensitive devices; however, stronger cases may cause unrepairable damage often in between the layers of the PCB. 

How can you reduce the chances of EOS damage?  

  1. Ensure proper ESD measures are met. Use an ESD station and wear ESD equipment.
  2. Ensure all power systems are properly set up before connecting it to electronic devices. 
  3. Connect all data cables prior to powering up the device.  Also ensure that the pins are matched when connecting the cables.
  4. Ensure the area is clear of loose conductive surfaces.
  5. Ensure no liquids are near the exposed device.