18 Fault Isolation and Failure Analysis of 3D Packaging
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Fig. 18.6 Conventional TDR spectra from a failed unit, a golden unit, a bare SIP substrate, and
a SIP package without FPGA die, showing the open failure is close to the FLI solder joint in the
FPGA package of a SIP package (Adapted from Ref. [1])
units are used to determine locations of the MLI and the FLI. The overlapping of the
blue spectrum from a SIP package without FPGA die with the red waveform taken
from the failed unit suggesting that the failure is close to the FLI joint in the FPGA
package. Based on the limited 500 μm resolution of TDR, the failure could be a
crack in the trace routing very close to the FLI joint, the FLI solder joint open, or
FPGA die defects close to the FLI joint.
18.3.1.2 Electro Optic Terahertz Pulse Reflectometry (EOTPR)
EOTPR is the next generation of TDR, developed to further improve its resolution.
Unlike TDR, EOTPR uses an ultrafast laser pulse to produce a 40 GHz to 4 THz
electrical pulse with a sharp peak, which is injected into the package under test [1].
Due to the much faster rise time of 5.7 ps and the THz range system bandwidth,
the resolution of EOTPR could be about 10 μm, much higher than that of TDR [6].
Since EOTPR uses a pulse with a sharp peak as the input signal, open interconnects in
packages show as peaks and shorting in interconnects as valleys in EOTPR spectra.
As illustrated in Fig. 18.7, the same set of data shown in Fig. 18.6 was collected by
EOTPR. By comparing with the blue spectrum defining the FLI location in FPGA
package, the failure is isolated to be inside the FPGA substrate right before the FLI
interconnect. The exact failure location can also be estimated by converting the time
domain EOTPR raw data into the distance domain data through the phase velocity,
ν p , of the electromagnetic wave, which can be expressed as [9]:
v p =
c
√ ε e f f
(18.2)
where, ν p , is the phase velocity, c is velocity of light in free space, and ε eff is the
effective dielectric constant of the package, which is different for different packages
and can be estimated using known package structure locations in EOTPR waveform.
581
Fig. 18.6 Conventional TDR spectra from a failed unit, a golden unit, a bare SIP substrate, and
a SIP package without FPGA die, showing the open failure is close to the FLI solder joint in the
FPGA package of a SIP package (Adapted from Ref. [1])
units are used to determine locations of the MLI and the FLI. The overlapping of the
blue spectrum from a SIP package without FPGA die with the red waveform taken
from the failed unit suggesting that the failure is close to the FLI joint in the FPGA
package. Based on the limited 500 μm resolution of TDR, the failure could be a
crack in the trace routing very close to the FLI joint, the FLI solder joint open, or
FPGA die defects close to the FLI joint.
18.3.1.2 Electro Optic Terahertz Pulse Reflectometry (EOTPR)
EOTPR is the next generation of TDR, developed to further improve its resolution.
Unlike TDR, EOTPR uses an ultrafast laser pulse to produce a 40 GHz to 4 THz
electrical pulse with a sharp peak, which is injected into the package under test [1].
Due to the much faster rise time of 5.7 ps and the THz range system bandwidth,
the resolution of EOTPR could be about 10 μm, much higher than that of TDR [6].
Since EOTPR uses a pulse with a sharp peak as the input signal, open interconnects in
packages show as peaks and shorting in interconnects as valleys in EOTPR spectra.
As illustrated in Fig. 18.7, the same set of data shown in Fig. 18.6 was collected by
EOTPR. By comparing with the blue spectrum defining the FLI location in FPGA
package, the failure is isolated to be inside the FPGA substrate right before the FLI
interconnect. The exact failure location can also be estimated by converting the time
domain EOTPR raw data into the distance domain data through the phase velocity,
ν p , of the electromagnetic wave, which can be expressed as [9]:
v p =
c
√ ε e f f
(18.2)
where, ν p , is the phase velocity, c is velocity of light in free space, and ε eff is the
effective dielectric constant of the package, which is different for different packages
and can be estimated using known package structure locations in EOTPR waveform.