Micro-texture and physical properties of the cold-sprayed copper deposit

Abstract

The cold spray (CS) method is a new deposition technique. In this technique, small solid particles impact and deposit on a substrate without melting. The deposition rate of the CS method is much higher than that of the other deposition processes. Expected applications of this technology are not only coating film production but also direct copper wiring technique for electronic products. This method also can be applied to patterning of thin films without photomasks. For example, an arbitrary geometry thin-film pattern can be formed on a substrate by scanning a spray nozzle. However, mechanical properties of the CS deposit and its micro-texture are found to be quite different from those of bulk copper. The previous researches showed that the CS deposit has high strength and indicates brittle-like fracture. The cold-sprayed copper deposit has a micro-texture which is stacked heavily deformed particles. The difference of the micro-texture between the cold-sprayed copper deposit and bulk copper is the main reason of the different mechanical properties. Thus, there is a possibility that the electrical properties of the cold-sprayed copper deposit are also different from bulk copper. In this study, both micro-texture and the electrical properties of the cold-sprayed copper deposit were measured by using SEM and EBSD technique and a four-point probe method. From the EBSD evaluation results, it was found that the average grain size in the deposited particles was much smaller than that of feed stock powder and bulk copper. The electrical resistivity of cold-sprayed copper deposit was much higher than that of bulk copper. The fine grain texture of the cold-sprayed copper deposit is one of the reasons for this high electrical resistivity.