Analysis method of tool topography change and identification of wear indicators for heavy copper wire wedge bonding

Abstract

One of the main cost factors in the wire bonding process are consumables such as bonding tools. The technological transition to copper as wire material causes significant wear on the millimeter size effective contact area of the bonding tool. This wear leads to a reduction of the number of reliable interconnections which can be produced using a single tool by a factor of 30 replacing the wire material from aluminum to copper. To reduce setup time in the production and minimize costs, an increase in bonding tool lifetime is desired. Consequently a better understanding of the wear and recognition of wear pattern is required. This paper presents a method to analyze tool topography change of a heavy wire bonding tool by using a confocal laser scanning microscope. Furthermore, this paper discusses the identification of the main wear indicators by help of the change in topography. Wear test has been carried out by choosing typical parameters of the production line. This topography change is compared to the topography change caused by increasing the ultrasonic voltage. To evaluate whether the quality requirement of the bond connections made by a single tool cannot be fulfilled, shear tests of the source bond were made in predefined intervals. All worn tools show dominant areas of wear especially for plastic deformation and accordingly abrasion. These wear mechanisms can be referred to the change of main parts of the groove geometry like the rounding of the front and back radius. The most loss in height was identified in the lower part of the tool flanks or rather at the transition from groove flank to the front or back radius. Furthermore the observation of the center of the groove flank shows just a little change. All in all, the identification of the wear indicators will be discussed with the objective of increasing the tool lifetime by optimizing the tool geometry without losses in bond quality and reliability.