Adhesion energy measurements for silver films on alumina using micro-cold spray

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Goyal, Aditya

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Conducting patterned silver traces are deposited onto substrates for use as electrical interconnects on many devices. Unlike existing processes that require a high temperature post-deposition step, the micro cold spray (MCS) process can be conducted at room temperature. A key issue for this application is the adhesion of the silver to the substrate. There are a variety of qualitative methods for evaluating adhesion of films that include the tape test where adhesives of different strengths are applied to the surface and then peeled off to determine the relative adhesion of the film to the substrate. This thesis is focused on the development of a sandwich specimen geometry to enable a quantitative measurement of the adhesion energy of films deposited onto substrates using the micro cold spray process. Silver films were deposited onto alumina films using the MCS process. Sandwich specimens were then produced where a second alumina substrate was bonded to the top of the silver film using different adhesives. Of the adhesives that were tested, it was found that fast acting epoxy provided the best combination of properties for this purpose. The samples were then tested using a previously developed flexural test that was used to supply the driving force to first drive the crack through the lower substrate and then for delamination of the film. The experiments revealed that the force required to initiate fracture was sufficiently high that the crack propagated dynamically until it fully delaminated the film which did not enable a direct measurement of the adhesion energy. Analysis showed that an upper bound of the adhesion energy could be determined. However, the obtained interfacial energy from these experiments was found out to be around 10 J/m². The results and suggestions for improving the tests are discussed.


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