Experimental determination of the variation of feed force values during drilling of printed circuit boards

Instrument production techniques


Аuthors

Zwe M. M.

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

e-mail: zwemaungmaung@gmail.com

Abstract

The article defines the experimental dependence of the drilling force on the number of drilled holes when drilling mounting and adapter holes in printed circuit boards. Expressions for the calculation of the temperature in the cutting zone and statistical characteristics of the envelope family of the maximum values of the drill vertex temperature are given. Dispersion of the instantaneous temperature distribution of the drill tip is revealed. The number of mounting and adapter holes in one Board can be up to several thousand pieces. The defects appeared in the surface of the holes for drilling printed circuit boards. Occurrence of these defects is connected first of all with heating of a drill during drilling. At the same time, the drilling accuracy significantly affects the quality of the printed circuit Board, which, in turn, depends on the quality of the layer combination and on the material parameters. It should be noted that defects formed at the stage of drilling, not only can lead to failures, but also increase the cost of products by increasing the cost of subsequent stages, as require the introduction of additional operations in the manufacture of printed circuit boards. The reliability of the drilling process depends on: the material of the dielectric base and foil; tools, mainly drills; machine tools; drilling modes; human factor. Problems of providing process of drilling of mounting holes in printed circuit boards are caused by considerable differences in hardness of components of base materials. The main tool for obtaining mounting holes in printed circuit boards are carbide drills. They are made of tungsten carbide with cobalt carbide additives (VK6, VK8 according to GOST 3882). Drilling modes have the greatest impact on the reliability of the drilling process, since, on the one hand, they can vary in a sufficiently large range of values, and on the other hand, they provide the technologist with sufficient freedom in choosing these values. During drilling, the heating occurs during the hole drilling due to the friction force on the back surface of the drill. The cooling of the drill bit provides pupils with the transition of the tool from hole to hole. Educated family of functions allows to statistically assess the variation of the technological characteristics of drills within a single batch and, consequently, to predict the durability of the drills and, consequently, the probability of failure of the process of drilling holes. At each moment of time, the dispersion of the maximum temperature values in the heating-cooling cycle will be subject, based on the conditions of operation, to the normal distribution law. The experiment showed the degree of dispersion of the feed force values when drilling holes in printed circuit boards. Experimentally, the determination of the change of drilling force from the number of tested holes makes it possible to calculate the variation of the force directed normal to the rear surface. This force significantly affects the temperature in the cutting zone during drilling of printed circuit boards.

Keywords:

feed force, tensor table, the number of drilled holes in PCBs, the temperature of the drill point, the force is directed normal to the rear surface

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