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EOS (Electrostatic Overstress) EOS vs ESD ESD or EOS Damage? What is Electrical Overstress (EOS)? • Electrical Over Stress is exactly what it says…. A device is electrically stressed over it’s specified limits in terms of voltage, current, and/or power/energy • Unlike ESD events, EOS is the result of "long" duration stress events (millisecond duration or longer) – Excessive energy from turning off inductive loads – Load Dump – Extended operation at junction temperatures > 150degC – Repetitive excessive thermal cycling – Excessive/extended EMC exposure, etc. • EOS often results in large scorch marks, discoloration of metal, melted metallization and/or bond wires, and massive destruction of the semiconductor component What is Electrical Overstress (EOS)? • Failures from EOS can result in the following: – Hard failure: failure is immediate and results in a complete non-operational device – Soft failure: EOS results in a marginal failure or a shift in parametric performance of the device – Latent failure: At first the EOS results in a non-catastrophic damage but after a period of time further degradation occurs resulting in a hard or soft failure What is Electrical Overstress (EOS)? EOS damage can at times be seen as visual damage to the device. This damage is the result of the high temperatures experienced during the EOS event. External (visible to the naked eye or with low power microscope) – – – – Visible bulge in mold compound Physical hole in mold compound Burnt/discolored mold compound Cracked package Internal (visible after decapsulation with high power microscope) – – – – Melted or burnt metal Carbonized mold compound Signs of heat damage to metal lines Melted or vaporized bond wires EOS External Damage EOS Internal Damage What is Electrical Overstress (EOS)? • What indicates EOS? Degradation/recrystalisation of metal (≥400ºC) ---also repetitive fast transients<100ºC Scorched/Melted metal (≥650ºC) Melted silicon (≥1200ºC) EOS: Failure signature from repetitive thermal cycling combined with high current Severely degraded recrystalized metal Possible Causes of EOS • Uncontrolled voltage surge on the power supply. • Voltage spikes due to internal PCB switching. • Voltage spikes due to an external connection –capacitive charge on an external cable, antenna pick-up of external switching noise, inductive loads. • Poor grounding resulting in excessive noise on the ground plane. • Overshoot or undershoot during IO switching. • EMI (electromagnetic interference) due to poor shielding in an electrically noisy environment. • ESD events that trigger a larger EOS event or cause damage that weaken the device making it more susceptible to future EOS events. • Latch-up events may result in EOS damage if the current is high or if it persists for an extended time period. How to Electrically Over Stress Components • Put components in/out of sockets while power already applied (hot plug) • Applying electrical signals which exceeds a component’s ratings • Apply an input signal to a device before applying supply voltage and/or ground • Apply an input signal to a device output • Use an inexpensive power supply (supply overshoot) • Provide insufficient noise filtering on the board’s input line(s) • Use a poor ground with high resistance and inductance EOS Summary • Electrical over stress refers to a condition when a device is electrically stressed over its specified limits • EOS often catastrophically damages devices by degrading or melting of metallization and bond wires • Operation of devices within the specified Safe Operating Area will eliminate electrical over stress damage ESD (Electrostatic Discharge) • Electrostatic discharge occurs when excessive static charge on an object builds up to a very high voltage (thousands of volts) and causes device damage during contact and subsequent discharge (current flow) with another object • The very fast (HBM=nsecs / CDM=psecs) ESD pulses have low energy and result in VERY small physical damage signatures • Static voltage are generated through triboelectrification, induction charging or ionic charging and is greatly dependent on object’s Q (charge) and C (capacitance). • Composed of different models suchs as HBM, MM and CDM. HBM ESD Gate Shorted to Source Very small damage area due to low energy of ESD pulses, normally cannot be seen with “naked eye” HBM ESD Gate Shorted to Source This device had a G-S short and you can see the burn mark is right at the boundary region of gate poly and source metal which is common since this is the area of highest E field strength Gate contact metal Gate Polysilicon Source contact metal What is the difference between EOS and ESD? ESD, or electrostatic discharge, is the charge that flows through a spark between two bodies at different electrostatic potentials as they approach each other (for example, when a person who is or has been walking touches someone and ignites a spark). EOS, on the other hand, refers to the exposure of an item to a current or voltage beyond the item's maximum ratings. EOS, or electrical overstress, can occur when a part is placed on a board and the board is subject to electrical current that exceeds the chip's capacity. What is the difference between EOS and ESD? ESD and EOS are related types of over stress events but at opposite ends of a continuum of current/voltage/time stress conditions. – ESD is a very high voltage (generally >500V) and moderate peak current (~1A to 10A) event that occurs in a short time frame (generally <1µs). – EOS is a lower voltage (<100V) and large peak current (>10A) event that occurs over longer time frame (generally >1ms). What is the difference between EOS Distinguishing between ESD and and EOS failures has always been of interest to failure ESD? analysts. Sometimes it is easy to do - gross metallization burn-outs will always be attributed to EOS, while a point rupture at the interface between an input thin-film resistor and a metal line is always indicatve of ESD damage. But what if the attributes exhibited by the device falls in between those of EOS and ESD? Since ESD and EOS failure attributes depends on the following: – – – – nature of the electrical stress circuit design die lay-out, and fab process used With this, it would be difficult (if not impossible) to come up with a catch-all manual that will tell one how to distinguish between EOS and ESD failures. A more practical approach therefore is to generate an in-house compilation of EOS/ESD photos instead involving your own devices. This compilation must be generated by a highlycontrolled process for simulating the EOS/ESD failures. EOS FAQs… What is EOS? • EOS is thermally induced damage to a component induce by an overvoltage condition. How is EOS different from ESD? • EOS and ESD are related voltage overstress conditions but they differ in the total energy and time span of the event. EOS has higher energy and a longer time span. How do I prevent EOS? • A careful review of the power supply variations and input signals to look for possible conditions that exceed the product specifications.