10 Fundamentals of Bonding Technology and Process Materials …
315
Fig. 10.61 SEM images of a
single solder joint processed
via (a) reflow bonding and
(b) TCB. The view field of
both images are 150 μm.
Cu 6 Sn 5 IMCs are depicted
with red arrows in both
images
Fig. 10.62 Schematic representation of diffusion of Cu and Ni atoms through the IMC scallops into
the SAC 305 solder matrix. Diffusion of Cu and Ni atoms from the (a) chip-side and (b) substrate
side. Note that a thicker red arrow represents higher amounts of Cu and Ni atoms diffusing through
the Sn matrix, and a shorter blue arrow represents faster diffusion of Cu and Ni atoms
Fig. 10.63 Positive
feedback loop showing
acceleration of the growth of
voids, in which void growth
increases local current
density that increases the
temperature of flip-chip
package due to Joule heating.
The temperature increase in
the package further
accelerates the void growth
than ~5 μm, and that is dominated by reflow joints when the grain size in the solder
joint is higher than ~5 μm. In short, grain size in the solder joint is smaller when the
flip-chip package was TCB-processed. It is, however, important that this difference
is negligible when juxtaposing the cooling rates of two bonding processes: ~2.5 °C/s
(reflow) versus ~60 °C/s (TCB).
315
Fig. 10.61 SEM images of a
single solder joint processed
via (a) reflow bonding and
(b) TCB. The view field of
both images are 150 μm.
Cu 6 Sn 5 IMCs are depicted
with red arrows in both
images
Fig. 10.62 Schematic representation of diffusion of Cu and Ni atoms through the IMC scallops into
the SAC 305 solder matrix. Diffusion of Cu and Ni atoms from the (a) chip-side and (b) substrate
side. Note that a thicker red arrow represents higher amounts of Cu and Ni atoms diffusing through
the Sn matrix, and a shorter blue arrow represents faster diffusion of Cu and Ni atoms
Fig. 10.63 Positive
feedback loop showing
acceleration of the growth of
voids, in which void growth
increases local current
density that increases the
temperature of flip-chip
package due to Joule heating.
The temperature increase in
the package further
accelerates the void growth
than ~5 μm, and that is dominated by reflow joints when the grain size in the solder
joint is higher than ~5 μm. In short, grain size in the solder joint is smaller when the
flip-chip package was TCB-processed. It is, however, important that this difference
is negligible when juxtaposing the cooling rates of two bonding processes: ~2.5 °C/s
(reflow) versus ~60 °C/s (TCB).