Fabrication process of through-Si-via (TSV) interconnects and their electrical characterization method were investigated for 3-D stacked packaging. A prototype, three-layer module with a flip-chip bonding process with anisotropic conductive film (ACF) was fabricated with the process. To measure a single interconnect resistance, a Kelvin structure was designed and applied on the chip and substrate. A theoretical model to calculate the connection resistance of the 3-D TSV interconnects was also derived and used to verify the experimentally measured resistance by applying the Kelvin structure designed. Optimum conditions for the formation of through-holes with the deep reactive ion-etching process were a coil power of 200 W, cycle time of 6.5/5 s, and SF6:C4F8 gas flow rate of 260:100 sccm. Pulse-reverse current provided the finest grain growth during the Cu electroplating and thus prevented the trapping of voids. The experimentally measured resistance was successfully verified by the theoretical model, and the model shows that the resistance value was mainly contributed by the ACF interconnect, not by TSVs.
Microwave performance of the anisotropic conductive film
(ACF) and nonconductive film (NCF) interconnects was investigated by
measuring the scattering parameters (S-parameters) of the flip chip
modules employing the films. To compare the accurate intrinsic microwave
performance of the ACF and NCF interconnects without lossy effect
of chip and substrate, a de-embedding technique was employed.
The effects of two chip materials, Si and quartz (SiO2), and of the metal
pattern gap between the signal line and ground plane in the coplanar
waveguide (CPW) on the microwave performance of the flip chip module
were also investigated. The transmission properties of the quartz were
markedly improved over those of the Si chip, which was not suitable for
the measurement of the S-parameters of the flip chip interconnect. Extracted
impedance parameters showed that the microwave performance
of the flip chip interconnect with NCF was slightly better than that of the
interconnect with ACF, mainly due to the inductive effect of the conductive
particle surface and capacitance of the epoxy matrix in the ACF
interconnect.
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