Micro-hole structures are widely used in devices such as aerospace turbine blades, automotive engine injector nozzles, and probe cards. With the improvement of the device performance requirements, the requirements of diameter and taper for micro-holes are also further raised. Conventional micro-hole processing methods include electrical discharge machining (EDM) and electrochemical machining (ECM). The shape of micro-hole cannot be precisely controlled by EDM, and the micro-hole machining precision is unsatisfactorily controlled by ECM. The general laser drilling methods include single-pulse drilling, multi-pulse drilling, and circular drilling. In all three drilling methods, the focusing position of beam is only controlled, but the beam incidence attitude is not controlled, and there were taper problems for the micro-hole. As an upgrade, the helical drilling can control the diameter and taper of micro-hole by precisely controlling the beam incident position and focusing orientation during the processing procedure. The research on helical drilling and related processing equipment is mainly aimed at the circular hole processing, and the irregular micro-hole processing still needs to be further studied. To obtain the square holes with adjustable tapers and controllable hole diameters on probe card materials, relevant studies and experiments are conducted in this study.
A new type of laser helical drilling system is presented. The system is composed of four-axis galvanometer groups controlled by linkage and Z axis moving device controlled independently. The processing plane is divided into two directions (X and Y directions) by double galvanometer groups, and the beam focusing position and incident orientation in each direction are controlled by two galvanometers. The physical model of micro-hole laser helical drilling is established. First, a coordinate system is applied to the micro-hole, and the shape of the micro-hole is determined by the edge profile. Second, the micro-hole is processed by a layer-by-layer filling method, while the laser focusing position is determined during processing. Third, the beam is controlled to shift in the opposite direction so that the focused beam is not blocked by the upper layer material during the process, and the minimum deflection motion of the galvanometer is required by optimizing the filling path. According to the above principles, the deflection angles of four galvanometers (X1, Y1 and X2, Y2) are determined. Finally, by changing the data of edge profile endpoint, the diameter and taper of micro-hole can be conveniently controlled.
In this study, a 15 W ultraviolet picosecond laser, two sets of identical galvanometers, a telecentric lens with a focal length of 32 mm, and a three-dimensional translation stage are used to build the laser helical drilling hardware system, and the polygon laser helical drilling control software is developed. The relevant experiments are completed on a 250 μm-thick Si3N4 sample. The processing parameters are as follows: the power of the laser is 12 W, the repetition frequency is 50 kHz, the scanning speed of the galvanometer is 0.4 m/s, and the Z-axis movement speed is 2 mm/s. In the experiment, the taper of micro-hole is adjusted by changing the offset distance of the beam, and 55 μm×55 μm square micro-holes with positive taper, zero taper, and negative taper are achieved (Fig. 6). The cross sections of the hole wall are observed (Fig. 7). The beam offset distance for the square micro?hole with the zero taper is determined by the taper adjustment, and the 30-80 μm square micro-holes with zero taper are realized by adjusting the data of the edge profile endpoints (Fig. 8). Finally, by adjusting the number of profile endpoints to change the shapes of micro-holes, the triangular, pentagonal, hexagonal and other shapes of micro-holes are realized (Fig. 9).
In this study, a new type of laser helical drilling system is presented. The physical model of micro-hole laser helical drilling is established, in which the shape of the micro-hole is determined by edge contours and the laser focusing position is determined by the layer-by-layer filling method. The beam is controlled to shift in the opposite direction so that the focused beam is not blocked by the upper layer material during the process, and the minimum deflection motion of the galvanometer is required by optimizing the filling path. According to the above principles, and the deflection angles of four galvanometers (X1, Y1 and X2, Y2) are determined. Finally, by changing the edge profile endpoint data, the size and taper of micro-hole can be conveniently controlled. A 15 W ultraviolet picosecond laser, two sets of identical galvanometers, a telecentric lens with a focal length of 32 mm, and a three-dimensional translation stage are used to build the laser helical drilling hardware system, and the polygon laser helical drilling control software is developed. By adjusting the processing parameters for relevant experiments, the micro-holes with different tapers under the same diameter and the micro-holes with the zero taper and different diameters are realized, and the micro-holes with different shapes are completed.
