18 Fault Isolation and Failure Analysis of 3D Packaging
607
18.4.2.4 Electron Backscatter Diffraction (EBSD)
EBSD also known as backscatter Kikuchi diffraction (BKD) is a microstructuralcrystallographic technique used to define the crystallographic orientation of materials. EBSD data is typically acquired from a cross sectioned unit sitting in SEM.
It has been demonstrated that EBSD is critical for the root-cause understanding
of electro migration (EM) induced open interconnects [60–62]. Electro migration
(EM) in interconnects of 3D packages becomes a major reliability concern due to
the much smaller interconnect dimension in advanced packages. EM can cause solder
joint open failures due to Sn self-diffusion through a void nucleation and propagation
mechanism. On the other hand, electron wind can also accelerate the dissolution of
under bump metallization (UBM) on the cathode side and cause failures due to depletion of UBM. It has been reported that metallization dissolution is closely related to
Sn grain orientations [60]. It is found that at given temperature and current density,
the time to dissolve 2 μm Ni UBM can vary from 100 h (when Sn c-axis is in parallel
to electron flow direction) to 1800 h (when c-axis is perpendicular to electron flow)
[61]. EBSD is used to analyze the Sn grain orientation distributions to explore the
relation between metal grain orientation and EM induced open failures. As illustrated
in Fig. 18.32, solder interconnects with c-axis of Sn crystals in-line with the electron
flow direction have much faster Ni dissolution compared with those having c-axis
perpendicular to the electron flow direction, and could lead to open failures during
the EM reliability tests [62].
TSV extrusion, which is shown to be related to the mechanical properties of TSV,
has been a major concern for yield and reliability of 3D packages with stacked die and
TSV configuration [63]. EBSD is employed to perform the Cu grain size distribution
analysis in two type of TSVs with different reliability performance. It has been found
that TSVs with smaller and more uniform Cu grains have a higher yield strength are
more favorable for inhibiting extrusion [63].
18.5 Failure Analysis Strategies for 3D Packages
Good failure analysis strategies are critical for the efficient applications of multiple
FI-FA techniques to achieve the ultimate goal of failure analysis: root cause finding
and solution path suggestions.
18.5.1 Understanding the Package Assembly Process,
Reliability Stress, and Failure Rate Distribution
Understanding the package assembly process, reliability stress, and failure density
distribution is the first key step for flawless failure analysis service. 3D packages
607
18.4.2.4 Electron Backscatter Diffraction (EBSD)
EBSD also known as backscatter Kikuchi diffraction (BKD) is a microstructuralcrystallographic technique used to define the crystallographic orientation of materials. EBSD data is typically acquired from a cross sectioned unit sitting in SEM.
It has been demonstrated that EBSD is critical for the root-cause understanding
of electro migration (EM) induced open interconnects [60–62]. Electro migration
(EM) in interconnects of 3D packages becomes a major reliability concern due to
the much smaller interconnect dimension in advanced packages. EM can cause solder
joint open failures due to Sn self-diffusion through a void nucleation and propagation
mechanism. On the other hand, electron wind can also accelerate the dissolution of
under bump metallization (UBM) on the cathode side and cause failures due to depletion of UBM. It has been reported that metallization dissolution is closely related to
Sn grain orientations [60]. It is found that at given temperature and current density,
the time to dissolve 2 μm Ni UBM can vary from 100 h (when Sn c-axis is in parallel
to electron flow direction) to 1800 h (when c-axis is perpendicular to electron flow)
[61]. EBSD is used to analyze the Sn grain orientation distributions to explore the
relation between metal grain orientation and EM induced open failures. As illustrated
in Fig. 18.32, solder interconnects with c-axis of Sn crystals in-line with the electron
flow direction have much faster Ni dissolution compared with those having c-axis
perpendicular to the electron flow direction, and could lead to open failures during
the EM reliability tests [62].
TSV extrusion, which is shown to be related to the mechanical properties of TSV,
has been a major concern for yield and reliability of 3D packages with stacked die and
TSV configuration [63]. EBSD is employed to perform the Cu grain size distribution
analysis in two type of TSVs with different reliability performance. It has been found
that TSVs with smaller and more uniform Cu grains have a higher yield strength are
more favorable for inhibiting extrusion [63].
18.5 Failure Analysis Strategies for 3D Packages
Good failure analysis strategies are critical for the efficient applications of multiple
FI-FA techniques to achieve the ultimate goal of failure analysis: root cause finding
and solution path suggestions.
18.5.1 Understanding the Package Assembly Process,
Reliability Stress, and Failure Rate Distribution
Understanding the package assembly process, reliability stress, and failure density
distribution is the first key step for flawless failure analysis service. 3D packages