18 Fault Isolation and Failure Analysis of 3D Packaging
583
stacked dice can be defined by TDR, which suggests the promising application of
TDR in 3D packages with die stacking configuration.
18.3.1.3 Lock-in Thermography (LIT)
The key to the precisely locating shorts and resistive opens failures in 3D microelectronic packages is to obtain z dimensional information of defects in addition to
the x and y location data. Lock-In Thermography (LIT) is a very promising technique developed to locate the dissipated heat by resistive failures using the real-time
graphical lock-in methodology, which is designed to detect small signal buried in
random noise of higher magnitude [11]. The z dimensional locations of defects could
be detected by LIT as the heat propagation is time depended. The time delay of the
underlying thermal diffusion process determines the phase shift between the excitation signal and thermal response, which is related to the frequency of the stimulation
signal (lock-in frequency) as well as thermal properties and thicknesses of different
layers in the stack. The z position of hot spots within the package can be identified
by their Lock-in frequency vs phase shift curves which can be compared to reference
units with defects at each relevant z-position. As illustrated in Fig. 18.9 [11, 12], it
is demonstrated that LIT could differentiate hot spots in the stacked dice of a 3D
package. As pointed out in Table 18.1, LIT provides direct imaging of leakage failures with a reasonable TPT, but is not capable to isolate hard open failures and dead
short failures with resistance less than one ohm. It is also not accurate for failures
having multiple defect locations. With known application limitations and further
Fig. 18.9 Measurement
results of Lock-in frequency
vs phase shift curves from
reference units with short
failures at die 1, die 2, and
die 3 of a 3D packages with
stacked die configuration
showing in dots compared to
a calibrated simulation
model (lines) (Adapted from
Ref. [11, 12])
583
stacked dice can be defined by TDR, which suggests the promising application of
TDR in 3D packages with die stacking configuration.
18.3.1.3 Lock-in Thermography (LIT)
The key to the precisely locating shorts and resistive opens failures in 3D microelectronic packages is to obtain z dimensional information of defects in addition to
the x and y location data. Lock-In Thermography (LIT) is a very promising technique developed to locate the dissipated heat by resistive failures using the real-time
graphical lock-in methodology, which is designed to detect small signal buried in
random noise of higher magnitude [11]. The z dimensional locations of defects could
be detected by LIT as the heat propagation is time depended. The time delay of the
underlying thermal diffusion process determines the phase shift between the excitation signal and thermal response, which is related to the frequency of the stimulation
signal (lock-in frequency) as well as thermal properties and thicknesses of different
layers in the stack. The z position of hot spots within the package can be identified
by their Lock-in frequency vs phase shift curves which can be compared to reference
units with defects at each relevant z-position. As illustrated in Fig. 18.9 [11, 12], it
is demonstrated that LIT could differentiate hot spots in the stacked dice of a 3D
package. As pointed out in Table 18.1, LIT provides direct imaging of leakage failures with a reasonable TPT, but is not capable to isolate hard open failures and dead
short failures with resistance less than one ohm. It is also not accurate for failures
having multiple defect locations. With known application limitations and further
Fig. 18.9 Measurement
results of Lock-in frequency
vs phase shift curves from
reference units with short
failures at die 1, die 2, and
die 3 of a 3D packages with
stacked die configuration
showing in dots compared to
a calibrated simulation
model (lines) (Adapted from
Ref. [11, 12])