Multi-response optimisation of thermosonic copper wire-bonding process with correlated responses

Multi-response optimisation has become an increasingly important issue in complex industrial processes, particularly in situations where more than one correlated responses must be assessed simultaneously. This study discusses the optimisation of a multi-response thermosonic copper wire-bonding process, used in the semiconductor assembly industry. Since nine process parameters were adopted as control factors for this experiment, the design of the experiment was based on the Taguchi method as per L 12 orthogonal array. Three responses, assumed to be correlated, were considered for each experimental trial. In order to take into account correlations among responses, a specific method for analysis was used, drawing on multi-criterion methodology based on Taguchi's quality loss function, principal component analysis and grey relational analysis. Finally, experimental confirmation was carried out to identify effectiveness of the method. It has been shown that the generic approach in the analysis for correlated responses provides better results than traditional method of analysis, in terms of optimal parameter design that meets the specifications of all three responses, for the observed process optimisation.