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Contents:
What is electrical overstress (EOS)?
What causes EOS?
Recommendations to prevent EOS
Preventative action to reduce damage
What is electrical overstress (EOS)?
- EOS is caused by an unusual spike in voltage applied to the system that causes damage at the component or board level, rendering system or component failure. The event usually lasts from microseconds to seconds (short pulses range in the nanoseconds).
- EOS damage is typically not visible because the damage is at the transistor level.
- Signs of EOS include:
- Blown metal line – Thermal Damage
- Molten damage – High Power Consumption
- Electrostatic Discharge (ESD) is a subset of EOS. The event occurs within pico to nanoseconds and is usually caused by human contact. The impact is similar with blown metal lines.
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What causes EOS?
- Hot Plugging. Any time you plug a cable or component into a running computer you are hot plugging and can cause Electrical Overstress.
- Power Supply. Power supplies can cause electrical overstress if they fail to regulate voltage and amperage properly. Power spikes can damage components.
- Inadequate Work Procedures. This includes incorrectly positioning components, not completely seating connections, or improper powerup and powerdown sequences.
- Ground Bounce. Ground bounce is a fast current switch resulting in high voltage due to insufficient grounding points and can be caused by turning on a large current device, such as a motor, or other electrical component.
- High Potential Testing. Hi-pot testing can cause EOS through surges and power spikes while testing.
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Recommendations to prevent EOS
- Check all test and assembly equipment are grounded
- Monitor electrical lines (AC) for noise
- Ensure operators are tightening loose connections to prevent intermittent events
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Preventative action to reduce damage
- Correct insertion of devices
- Post simple EOS guidelines for training and reinforcing proper techniques
- Check connections - Cable connections, add-in card insertion, memory, processor, etc.
Beware of powered insertions and removals
Never hot swap devices.
Promote awareness of stand-by power. Power can be present on the motherboard when it appears off.
Don’t add or remove devices when stand-by current is present, as it can damage devices and the motherboard.
Remove AC power when adding or removing devices to the system.
- Assembly – connect AC last
- Disassembly – disconnect AC first
Battery
- Avoid touching the battery - Shorting top (+) to board can cause EOS damage to the board
During test and debug, avoid:
- Hot swapping
- Use of incorrect test sequence
- Foreign material on board or in connectors
This applies to:
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