T. Yoshioka et al., Effect of oxygen content in copper on the tensile strength of diffusion bonding joints between copper and several metals, J JPN METAL, 63(8), 1999, pp. 1036-1042
Diffusion bonding is a useful method to join different metals, though it is
indicated that the tensile strength of the joint decreases due to the form
ation of oxide at the bonding interface.
In this study, diffusion bonding process was employed to make the joint of
copper (tough pitch copper described as TPC, and oxygen free high conductiv
ity copper expressed as OFHC) and several metals (molybdenum, nickel and pl
atinum). The effect of oxygen content in the copper and kind of coupling me
tal on the tensile strength of the joint was investigated using XRD and SEM
.
When TPC was joined to molybdenum or nickel, molybdenum oxide or nickel oxi
de formed at the bonding interface and the tensile strength of the joint de
creased extremely. While when platinum was used as the coupling metal, the
oxide did not form there.
In the case of OFHC, the oxide did not form at the bonding interface betwee
n OFHC and any metal.
These results could be explained thermodynamically. If TPC was joined to a
metal, whose standard free energy of formation of oxide was lower than that
of Cu2O, Cu2O dispersed in TPC was reduced and a metal oxide formed at the
bonding interface. If TPC was joined to a metal, which had a higher standa
rd free energy of formation of oxide than that of Cu2O, Cu2O remained stabl
e and the oxide did not form at the interface.
In OFHC, oxygen is dissolved in copper, therefore the activity of oxygen mu
st be considered for the calculation of free energy change. The calculated
free energy change indicated that the oxide did not form at the bonding int
erface between OFHC and any metal.