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Y. Dai and C. S. Tan
Hence, it is inferred that the cracks in the nano-particles paste may occur dependent
on the paste thickness. The bond strength might increase as the thickness increases
but cracks increase as well when the thickness is higher. Therefore, the nano-particles
paste needs a very precise thickness control to ensure a high bond strength. Another
possible reason for the higher bond strength could be the pressure applied during the
doctor blading technique. Since the nano-particles paste has lesser solvents remain
before sintering, it requires additional pressure to be applied on the die and wafer for
spreading it to maintain the uniformity.
9.4.3 Summary
The die to wafer bonding was conducted to verify the paste mechanical property and
reliability. During bonding, no external pressure was applied. The bonding conditions
are 10 min ramping and 10 min bonding in N 2 atmosphere. Shear test is then used
to test their bond strength.
The results show that the mixed paste has the highest bond strength on average.
After testing, the fracture mechanisms are analysed by observing the die and wafer
interfaces. The mixed paste and micro-particles paste have adhesives on both die
and wafer surfaces while the nano-particles paste only has adhesives on the die
surface. Since the majority of the mixed paste is comprised of the micro-particles, it
is reasonable that the failure mechanism of micro-particles and mixed paste are the
same.
The mixed paste and micro-particles paste failure is a result of the separation
of the copper particle layrs whereas the nano-particles paste is a result of the bad
adhesion between the adhesive and interface. As for the nano-particles paste that
has the highest shear bond strength, the microscope image shows that there is a very
uniform region without crack. It is speculated that the reliability of the nano-particles
paste is related to the paste thickness and the bond strength might follow a Gaussian
distribution. When the paste thickness reaches an optimum point, the bond strength
is expected to be the highest.
Some of the challenges such as paste viscosity, thickness uniformity and contact
areas are not yet fully addressed during the die to wafer bonding experiment. Therefore, although the shear test results reveal that the mixed paste has high shear bond
strength, the long term reliability still require careful and thorough study.
Y. Dai and C. S. Tan
Hence, it is inferred that the cracks in the nano-particles paste may occur dependent
on the paste thickness. The bond strength might increase as the thickness increases
but cracks increase as well when the thickness is higher. Therefore, the nano-particles
paste needs a very precise thickness control to ensure a high bond strength. Another
possible reason for the higher bond strength could be the pressure applied during the
doctor blading technique. Since the nano-particles paste has lesser solvents remain
before sintering, it requires additional pressure to be applied on the die and wafer for
spreading it to maintain the uniformity.
9.4.3 Summary
The die to wafer bonding was conducted to verify the paste mechanical property and
reliability. During bonding, no external pressure was applied. The bonding conditions
are 10 min ramping and 10 min bonding in N 2 atmosphere. Shear test is then used
to test their bond strength.
The results show that the mixed paste has the highest bond strength on average.
After testing, the fracture mechanisms are analysed by observing the die and wafer
interfaces. The mixed paste and micro-particles paste have adhesives on both die
and wafer surfaces while the nano-particles paste only has adhesives on the die
surface. Since the majority of the mixed paste is comprised of the micro-particles, it
is reasonable that the failure mechanism of micro-particles and mixed paste are the
same.
The mixed paste and micro-particles paste failure is a result of the separation
of the copper particle layrs whereas the nano-particles paste is a result of the bad
adhesion between the adhesive and interface. As for the nano-particles paste that
has the highest shear bond strength, the microscope image shows that there is a very
uniform region without crack. It is speculated that the reliability of the nano-particles
paste is related to the paste thickness and the bond strength might follow a Gaussian
distribution. When the paste thickness reaches an optimum point, the bond strength
is expected to be the highest.
Some of the challenges such as paste viscosity, thickness uniformity and contact
areas are not yet fully addressed during the die to wafer bonding experiment. Therefore, although the shear test results reveal that the mixed paste has high shear bond
strength, the long term reliability still require careful and thorough study.