EOS Root Causes
Since electrical overstress (EOS) is a violation of the absolute maximum ratings (AMR) of a product, the root causes of EOS are always located outside the damaged product. However, if a damage was not caused by electrical overstress, it must have been caused either by a weakness of the device or by incorrect or incomplete absolute maximum ratings (AMR*).
The root causes of electrical overstress can be divided into a) direct and b) indirect root causes. The former category includes every electrical stress, that can be attributed to mishandling and misuse of the damaged product. The latter category comprises every electrical stress, that is indirectly caused by electromagnetic interference (EMI) or uncontrolled ESD.
Damage due to Mishandling or Misuse
| Category | Root Cause |
|---|---|
| System Design | Insufficient heat dissipation |
| Saturation of inductors (ferrites) | |
| Software errors (e.g.. undefined states) | |
| Assembly | Misadjusted or misaligned (e.g. rotated) solder paste or assembled components (floating and hence undefined pins, leakage due to creepage distance violations, sparks and shorts) |
| Hot plugging (cable-discharge events, charged-board-events, charged-device-model events) | |
| Testing | Incorrect or misinterpreted standards |
| Incorrect handling of devices under test | |
| Unstable or incomplete test programs (transient overvoltage, overcurrent or overload conditions) | |
| Defective or incorrectly applied test equipment | |
| Misaligned (e.g. rotated) devices under test (floating and hence undefined pins, sparks and shorts) | |
| Hot plugging of devices under test (no leading ground pins of in-circuit bed-of-nails) | |
| Hot switching (underestimated timing tolerances, switching of charged capacitors)Kondensatoren) | |
| Application | Open or shorted supply lines (undefined or indirect supply as well as overload condiotions) |
| Wrong power supply sequencing of ICs with multiple supply pins (transient overvoltages, overcurrents or overload conditions within ICs or between different ICs) | |
| Accidental power fails (transient overvoltages, overcurrents or overload conditions) | |
| Intermittent contacts of mechanical components e.g. connectors, potentiometers (transient overvoltages, overcurrents or overload conditions) | |
| Overheating (latch-up, accelerated aging, failures due to thermal instability) | |
| Malfunction or failures of adjacent components (transient overvoltages, overcurrents or overload conditions) |
Damage due to Electromagnetic Interference
| Category | Root Cause |
|---|---|
| Slow Voltage Transients | Load dump (e.g. in automotive applications) |
| Unregulated or defective power supplies | |
| Surge Currents | Switching of charged capacitors |
| Sparks and shorts due to poor electrical isolation (e.g. of PCBs, cables and components) | |
| Fast Voltage Transients | Power up and power down of power supplies, insertion of batteries |
| Ground bounces | |
| Inductive switching (e.g. parasitic inductors due to insufficient metal routing, lack of snubber networks or insufficient snubber networks) | |
| Induction due to transient magnetic fields | |
| Reflected signals due to mismatching transmission lines | |
| RF and EMP | Insufficient PCB design (e.g. ground loops, parasitic inductors or antennas due to insufficient metal routing, wrong placement of components, reflected signals due to mismatching transmission lines) |
| Lack of filters or insufficient filters (e.g. lack of decoupling capacitors, insufficient or wrongly placed decoupling capacitors) | |
| Lack of shielding or insufficient shielding (e.g. plastic housings) | |
| Noise | Hard switching (e.g. switch-mode power supplies or motor drivers) |
| Lack of filters or insufficient filters (e.g. lack of decoupling capacitors, insufficient or wrongly placed decoupling capacitors) |
Damage due to Uncontrolled ESD
| Category | Root Cause |
|---|---|
| Electrostatic Charging | Unsuitable processes |
| Unsuitable materials (e,g, insulators) | |
| Unsuitable packing | |
| Lack of grounding or insufficient grounding | |
| Uncontrolled ESD |
Charged personnel (e.g. lack of grounding, insufficient or defective grounding) |
| Charged objects (e.g. lack of grounding, insufficient or defective grounding) | |
| Charged devices, PCBs or systems |