9 Copper Micro and Nano Particles Mixture for 3D Interconnection …
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Fig. 9.24 Fracture interface
of nano-particles paste, the
die surface has no paste left
between the die and paste other than at the intermediate copper particles region. This
is due to the existence of the macro cracks in the copper paste, thus leads to brittle
fracture.
It is noted that one of the nano-particles paste samples has a high bond strength
which is about 1.2 MPa. This sample surface is then observed as shown in Fig. 9.25.
There is a very uniform part remaining on the wafer that is circled in Fig. 9.25. The
uniform part is further analysed and observed under the wide-field microscope and
the images are shown in Fig. 9.26.
Figure 9.26 presents the surface morphology of the uniform region that is circled
in Fig. 9.25. It is seen that this region is dense and compact without any cracks.
Fig. 9.25 Surface
observation of the
nano-particles paste sample
with highest shear strength
Fig. 9.26 Wide-filed microscope image of the nano-particles paste sample with highest shear
strength