Transcript failure analysis

FAILURE ANALYSIS
ELECTRICAL
CHARACTERIZATION
SCHOOL OF
MICROELECTRONICS
KUKUM
Introduction
• A general approach is recommended for failure
analysis electrical testing that will help the failure
analyst to electrically characterize the device under
analysis (DUA) without causing additional damage
that may obscure or obliterate the original cause of
failure.
Introduction
• Failure Analysis is performed on a device to
determine the root cause of the failure.If, during the
analysis electrical testing causes damage to the
device or alters the device’s failure mechanism, then
wrong conclusions will be made concerning the root
cause of failure.
Introduction
• The initial electrical verification process
provides a general understanding of
how the device is failing electrically (eg.
datalog,
measured
continuity,
parametric, functional outputs of the
device from production test equipment).
Example
• Electrical leakage identified -> detailed
I-V characterization on a curve tracer or
parametric analyzer.
• Functional failures -> Schmoo plotting
(characterization as a function of
temperature, power supply voltage or
freq.) or scan testing
BEFORE ALL ELSE
• UPON FAILURE & FA FLOW
DOCUMENTATION
• ==>ELECTRICALLY CHARACTERISE
DEVICE<====> BENCH TESTS!
BENCH TESTING
• process of characterizing the failure
mode of the sample using various
bench equipment for exciting the device
and measuring its responses
NDT
WHAT TO LOOK FOR?
Electrical Testing
= detecting shorts,
= opens,
= parametric shifts / changes in resistance,
= abnormal electrical behavior on the die,
between the die and the interconnects,
between the interconnects and the circuit
card, within the circuit card, and among the
various connections between circuit cards.
DO IT RIGHT!
Correct electrical testing
- provides the failure mode (catastrophic,
functional, parametric, programming or
timing),
- identify the failure site .
ASSUMPTIONS
• During FA- test has to be performed on the
assumption that the device is not the same as a
standard or “normal” device.
– The device may have been electrically overstressed.
– The device may have been damaged by ESD
(electrostatic discharge).
– The device may be altered internally due to chemical
reactions.
– The device may have been misassembled.
– The device may include a manufacturing defect.
TOOLS FOR ELECTRICAL
CHARACTERIZATION
Multimeters,
Freq. counters,
OSC,
Manual curve tracer,
Computer controlled curve tracer
Semiconductor parametric analyzer
TDR,
ATE
etc…
MULTIMETERS
Basic tests - electrical connection, short,
open
--general localization of fault area
==>IFF => PRIOR KNOWLEDGE
FREQ. CNTR. & OSC.
A STEP HIGHER / DEEPER
-TIMING RELATIONS
-FREQ. RESPONSES
-BEHAVIOURS @ DIFFERENT f’s
V-I CHARACTERISTICS
• Curve tracing - current-voltage characteristics of an
electrical path using a curve tracer - identify electrical
failures that exhibit abnormal V-I relationships
between pins - 2pt probe
• objective of curve tracing = open or shorted pins &
pins with abnormal I/V characteristics (excessive
leakage, abnormal breakdown voltages, etc.).
• FA focused on circuits with anomalous pins.
• Dynamic curve tracing, unit powered, while
curve tracing, if static curve tracing does not
reveal any anomalies
• Curve tracing can also be done on an
electrical path inside the die circuitry itself,
where the nodes defining the electrical path
are not connected to any external pins.
==>Microprobing - achieve electrical contact
with the selected nodes, with the probe
needles also attached to the curve tracer.
CURVE TRACER
• Curve tracing = easiest, safest, fastest and
most reliable way to gather electrical
characteristics information of DUT
• Curve tracer - visual nature easy to spot
certain categories of errors (opens, shorts,
leakages, etc...) including problems that
might not be obvious from a series of single
point measurements- CT =continuous
CURVE TRACER
• Continuous "sweep" - possible to plot the
reaction of DUT for entire range of conditions.
• Curve tracer - store trace information, operate
at low voltage and current levels - allows
detection of certain electrical failure
mechanisms that would be hidden by the
higher voltage and/or current levels generally
associated with verification testing.
CURVE TRACER
CURVE TRACER
- graphical representation of electrical
characteristics on screen.
- common configuration- apply voltage to DUT
pin (series resistor~1) and measure the
resulting voltage and current.
- sweeping applied voltage & displaying current
versus voltage plot
CURVE TRACER
• Y axis = current & X axis = voltage.
• Values on axis increase with distance from
the origin
• Two extreme conditions:
– a vertical line crossing origin = short
(no voltage measured on the pin),
– a flat horizontal line crossing origin = open
(no current through the pin).
fundamentally…
• Standard behaviours - V & I
– Resistors
– Diodes
– Transistors
– Zener diodes
– combinations
– etc.
I
V
I
V
I
V
I
V
TDR
• Old principle BUT new application
• Good for BGA / high pin count packages uses
electron speed / reflection - pinpoint exact point /
layer of defect
• TDR instrument
= very wide BW equivalent sampling oscilloscope (1820 Ghz) with an internal step generator.
= connected to DUT via cables, probes and fixtures
TDR
Due to wide BW of the oscilloscope, and to ensure that
this BW and fast rise time can be delivered to the
DUT,
- must use high-quality cables, probes, and fixtures,
==>these cables, probes and fixtures can significantly
degrade the rise time of the instrument, reduce the
resolution, and decrease the impedance
measurement accuracy.
==>In a TDR probe, both a signal and a ground contact
are normally required during the measurement.
v
t
t
T=2t
d = T/v
TDR
• impedance profile analysis
-observe open fault occurred, but also to determine the
exact location of the fault in time.
-If velocity of propagation in the given segment is
known, then the physical location of the fault can be
determined easily.
-velocity of propagation - determined using a reference
device with known physical length.
open fault = occurred shortly after the package-to-die
bondwire connection
Computer controlled CT
- Overcomes the limitations of the
manual curve tracer for high pin count
devices and has become standard tool
for I/O electrical characterization
- Controls the application of the stimulus
to each pin and records the measured
data for display or comparison to
previously stored data
SPA
• For characterization diodes, transistors,
performing circuit level parametric
testing which includes DC functional
testing of analog circuits such as
voltage references, regulators, and opamps
• Can measure very low levels of current
and voltages
ATE
• Used in production
• For characterization -> high pin count
devices & timing complexity
• Provides a software toolkit for debug
tools available are wave, vector or
pattern, and schmoo tools