Ni surface chemistry and quality of the Al/Ni bond in electronic devices

Four chemically different nickel surfaces, as revealed by ESCA, have been ultrasonically bonded to Al/Mg wires. Under normal conditions there was found to be very little difference in the pull strength of the various surfaces; there were small variations when the samples were tested in stress conditions such as high temperature storage (200 ° C), or a water vapour pressure environment (121 °C, 1.04 atm). However, the bonds have been found to be reliable for the four surfaces and when tested in the encapsulating resin environment of an actual electronic device. The thickness of nickel chemical species overlaying the nickel substrate was estimated to range from 5 to 13 A for the four nickel surfaces simulating possible plant conditions. This relatively low thickness is considered to be responsible for the above positive results. These results are compared with those previously obtained for the Al/Cu joints.