A microstructural study of dislocation substructures formed in metal foil substrates during ultrasonic wire bonding |
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Authors: | Nikhil Murdeshwar James E Krzanowski |
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Affiliation: | (1) Present address: Mechanical Engineering Department, University of New Hampshire, USA;(2) IBM, 13760 Endicott, NY;(3) the Mechanical Engineering Department, University of New Hampshire, 03824 Durham, NH |
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Abstract: | A study has been conducted on the deformation mechanisms in metal substrates subject to aluminum ultrasonic wire bonding (UWB).
Aluminum wires were bonded to copper, nickel, stainless steel, and aluminum bronze foil substrates and then removed in aqueous
sodium hydroxide to permit thin sections of bonded areas to be examined in the transmission electron microscope (TEM). The
results showed a variety of dislocation substructures formed during bonding, including dislocation cells, subgrains, and planar
arrays. Aluminum and copper showed evidence of thermal effects on microstructural evolution during bonding, such as dislocation
annihilation at cell walls in copper and complete recrystallization in aluminum. In the nickel and stainless steel substrates,
which have higher recrystallization temperatures, thermal effects on microstructure were not observed. In addition, it was
found that low stacking-fault energy (SFE) materials, such as aluminum bronze, were less likely to undergo cell formation,
and only planar dislocation arrays formed. In general, it is clear that the process of UWB induces cyclic stresses in the
substrates, which exceed the yield strength of the metals examined. In addition, there is some heat generated during the bonding
process, which can influence the resultant deformation microstructure. |
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