Tungsten Carbide Micro Drills and Micro Drilling Ⅶ

In part 6 we know that the micro drilling speeds and feeds are varied according to materials, but not in high speed in order to avoid the tungsten carbide micro drill staying in the hole bottom. Here we talk about the applicability of micro drilling in integrated circuit industry as a complementary process to lithography and electroplating.

The applicability of micro drilling as a complementary process with features produced by lithography and electroplating has been investigated. A cross section of a copper micro gear made by lithography is shown. The average roughness of the hub wall is 0.4 micrometers. A micro drilled hole in the same material gave a roughness of 0.15 micrometers over a much longer bore length. Micro drilling can also be used to augment lithography for mesoscopic (millimeter and larger) sized components. Often parallelism of deep holes is of concern. To determine typical values for parallelism of micro drilled holes, glass fibers were inserted into a number of holes drilled with a very slow starting sequence. This is necessary to ensure the tungsten carbide micro drill does not walk on the surface of the part and that the hole axis aligns with the un-deflected axis of rotation of the drill. Holes with a length-to-diameter ratio of 8 were drilled at 4000 rpm. The three-dimensional misalignment of the inserted fibers was measured to be 0.08 degrees (1.5 milliradians), which included skewing of the fiber in the hole due to oversize of the hole which was estimated to be 0.5 micrometers.

(To be continued. This article is divided into several parts and this is part 7, for part 6 please refer to http://news.chinatungsten.com/en/tungsten-information/80077-ti-10281; for part 8 please refer to  http://news.chinatungsten.com/en/tungsten-information/80116-ti-10290)

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