High-aspect ratio mechanical microdrilling process for a microhole array of nitride ceramics

In semiconductor industry, wafer testing requires a microhole array constructed by high-density holes below phi 100m for stabilizing the microprobe used in conduction testing. This study conducted mechanical microdrilling experiments of a nitride ceramic sheet to investigate the effects of drilling parameters on quality characteristics of the microhole drilled. Fabrications of a high-aspect ratio microhole must be implemented by segmented machining. A center pilot hole was first made and then drilled the microhole by a two-segment process. Drilling factors analyzed in this study included depth of the center pilot hole, depth ratio of the hole segments, and machining parameters of cutting speed (spindle rotation rate), tool feed rate, and step in peck drilling in the microdrilling. Because both diameter and position of the microhole affect the functionality of hole array directly, this is a multi-objective problem. This study proposes a new decision method for deriving the optimal parameter level set in the multi-object problem based on the level effects obtained from Taguchi's analyses. In addition, this study used a scanning electron microscopy (SEM) to observe the influences of drilling stroke on flank wear of the microdrill. This study implemented two series experiments of phi 69m and phi 55m with aspect ratios of 15.36 and 11.64, respectively. Experimental results indicate that applying the optimal parameter level set derived in phi 55m experiment could obtain excellent performances after the drilling stroke of 384mm, 600 holes drilled. The microdrills have fulfilled a high use efficiency.