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.