Magnetic Current Imaging

Technology
Quality,Fault
Worldwide
Analytical Services,
Burlington VT
Advanced
Isolation
Techniques
for Microelectronics Packaging
Dave Vallett
PeakSource Analytical, LLC
Fairfax, Vermont, USA
Purpose
Highlight the importance of rapid problem solving
during technology development, manufacturing,
and end-user service
 Summarize the challenges of non-destructive
localization of electrically active faults in dense
assemblies
 Review techniques and recent advancements

IBM Research
5/5/15
D. Vallett, PeakSource Analytical, LLC
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Outline
Introduction
 Microelectronic package fault isolation challenges
 Limitations of acoustic and X-ray imaging
 Methods

 EOTPR – electro-optical teraHertz pulsed reflectometry
 Lock-in thermography
 Magnetic current imaging

Summary and Conclusions
5/5/15
D. Vallett, PeakSource Analytical, LLC
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Fault Isolation - the Most Critical Step
Development
failures, yield
loss, field returns
Failure Analysis
Verification &
characterization
Fault isolation
Deprocessing
Inspection
Physical & chemical
analysis
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Density Challenges in NDE
Package-on-Package



Sub-surface imaging limited by
opacity, absorption, thickness,
heterogeneous materials,
numerous interfaces
Physical imaging alone (e.g. Xray, acoustic) leaves electrically
active defects indistinguishable
from inert anomalies
“Needle in haystack” challenge
IBM Research
5/5/15
D. Vallett, PeakSource Analytical, LLC
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Acoustic, X-ray Image only Physical
Structure




Active defects, anomalies,
structures, interfaces imaged
simultaneously (2D or 3D)
No definitive causality
with electrical failure mode
Subsequent analysis
(e.g. cross-section, SEM)
time-consuming, expensive,
not definitive, destructive
Precise, accurate,
non-destructive fault isolation
required
5/5/15
D. Vallett, PeakSource Analytical, LLC
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Isolating Electrically Active Faults
TeraHertz TDR
Lock-in Thermography
Sensor
Magnetic Current
Imaging
5/5/15
D. Vallett, PeakSource Analytical, LLC
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Time Domain Reflectometry – TDR / EOTPR
 Package conductors have
transmission line characteristics
 Defects alter characteristic
impedance
– Opens: cracks notches, resistive films, etc.
– Shorts: extra conductor material, foreign
material, etc.
 Impedance changes cause reflections
– Reflection time correlates to distance
(P. Perdu, EUFANET / IPFA 2012)
5/5/15
5/5/15
 Electro-optical TeraHertz pulsed
reflectometry (EOTPR) significantly
improves resolution
D. Vallett,
D. Vallett,
PeakSource
PeakSource
Analytical,
Analytical,
LLCLLC
8
EOTPR – Cracked Substrate Trace
 Resolution / accuracy < 10 um
(P. Perdu, EUFANET / IPFA 2012)
5/5/15
D. Vallett, PeakSource Analytical, LLC
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EOTPR – Flip-Chip Open Circuit
83 um
(P. Perdu, EUFANET / IPFA 2012)
5/5/15
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Lock-in Thermography (LIT)
 Images surface thermal
gradient from sub-surface heat
source
 Pulsed source with lock-in
amplification
 Signal depth derived
from phase delay
 Absolute depth using thermal
diffusion constants
 Relative depth using reference
heat source(s)
 Resolution: single microns
 Sensitivity: micro-watts
5/5/15
D. Vallett, PeakSource Analytical, LLC
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Thermal Phase-delay Estimates Defect Depth
(H. Deslandes, DCG Systems)
5/5/15
D. Vallett, PeakSource Analytical, LLC
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LIT – BGA Pin Short, Fused Bond Wires
(H. Deslandes, DCG Systems)
5/5/15
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LIT Depth Estimation in Stacked Die
 13-ohm pin-pin short
 Fwd-biased diodes as depth references
 Depth correlates with phase-shift
(H. Deslandes, DCG Systems)
5/5/15
D. Vallett, PeakSource Analytical, LLC
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Magnetic Current Imaging (MCI)

Magnetic permeability
relative to free space
Sensor
5/5/15
Magnetic field from buried currents
propagates freely to the surface
Al
1.000022
Si
0.999996
Cu
0.999990
W
1.000068
Pb
0.999982

Scanned magnetic sensor maps
field distribution

Magnetic field data converted
to current density image

High current density or abnormal
current paths indicate defect location

Resolution: single microns

Sensitivity: nano-amps / femto-watts
D. Vallett, PeakSource Analytical, LLC
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MCI – Leadframe Pin-Pin Shorts
(J. Gaudestad, Neocera)
5/5/15
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MCI – PLCC / Flex Cable Shorts
5/5/15
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MCI - Plane-to-Plane MLC Short
short
(J. Gaudestad, Neocera)
5/5/15
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Power Short in Fully Assembled PCB
Short
(J. Gaudestad, Neocera)
5/5/15
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MCI – Subtle Leakage Analysis in PCB
Fail
5/5/15
Good
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MCI - Open Circuits

5/5/15
Magnetic field from standing wave current
vanishes at open circuit location
D. Vallett, PeakSource Analytical, LLC
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Broken Copper Trace in Substrate
(J. Gaudestad, Neocera)
5/5/15
D. Vallett, PeakSource Analytical, LLC
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Open Failure in the Die Region
(J. Gaudestad, Neocera)
5/5/15
D. Vallett, PeakSource Analytical, LLC
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Summary
5/5/15
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Conclusions
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