Study On UV Laser Microprocessing Technology And Mechanism For Electronic Materials

UV laser, with the advantages of short wavelength, high absorptivity as well as small heat-affected zone and focusing spot size, has played an important role in the field of electronic semiconductor manufacturing and communications engineering, biotechnology and medical, precision mechanics, aerospace and national defense. Particularly, during the last decade, diode-pumped solid state (DPSS) lasers have been applied widely in semiconductor and electronics micro-fabrication industry due to the advantages of high efficiency, high frequency, low operating cost, good beam quality and flexibility as well as miniature size. It has great significance to enhance the technical level and core competitiveness in the field of micro-fabrication by developing UV laser micro-machining equipment with independent intellectual property and by studying UV laser microprocessing techniques, mechanisms and modeling.Fistly, a multi-functional UV laser microprocessing equipment, which had both short focus and scanning galvanometer processing methods, had been developed for the application in electronics and semiconductor industry in this dissertation. The stability of the equipment was tested according to the standard deviation of etched width and depth of silicon wafers. The results showed that both short focus and scanning galvanometer microprocessing methods had a higher machining stability, which was qualified for the requirements of industrial application.Secondly, an innovative method of drilling blind holes—percussion-concentric scanning drilling was proposed to solve the rugged bottom surface produced by the traditional concentric or spiral scanning drilling methods. The key point of the percussion-concentric scanning drilling method was that the laser percussion and concentric scanning drilling were taken respectively to remove the blind hole center and surrounding material. Based on the theoretical calculation of both single pulse etching rate and pulses canning etching rate, the relationships between laser etching parameters (such as laser fluence, frequency, scanning speed) and concentric circle spacing were achieved for this method drilling blind holes in PI and Cu materials and first-order blind holes (diameter of 200μm) with smooth bottom, small taper, and good structure in multi-layer FPC were obtained by calculating the optimal parameters. Measurement results showed that bottom surface roughness Ra and maximum height difference were 1.06μm and 7.16μm respectively, which could meet the needs of electronics industry.Thirdly, CCL and FPC cutting and etching experiments were carried out by using 355nm Nd:YVO4 laser and 1064nm Nd:YAG laser respectively to compare the impact of lasers with different wavelengths on microprocessing precision and quality. The resuts showed that no matter in the microprocessing accuary or quality, UV laser is better than IR laser. Therefore, the effects of UV laser fluence and scanning speed on etching width and depth of Cu and PI as well as cutting quality of FPC goldfingers were investigated and analyzed systematically.Next, a finite element simulation of nanosecond pulsed UV laser etching copper was carried out. The laser pulse duration was divided into several sub-pulse duration in simulation calculation process to calculate the removal of material at each sub-pulse duration. In this way, the simulation results were closer to the actual etching process, and made the simulation results more precision. Comparied with the experimental results of UV laser etching copper, the simulated maximum errors of both etching width and depth were 4.5μm and 2μm respectively under the conditions of different laser fluence and 2μm and 3.5μm respectively in the case of different scanning speed as well as 1μm and 2μm respectively at different scanning number when the scanning speeds were 100mm/s and 200mm/s respectively. The experimental results showed that the simulation results of the mathematical model has good accuracy, which could predict the results of UV pulse laser processing copper and guidance how to carry out the UV pulse laser microprocessing copper. When simulation on UV pulse laser scanning etching FPC, the maximum errors are 0.1μm in etching width of copper,0.6μm in etching width of PI and 1μm in etching depth of copper, which is more accurate than the simulation etching depth of PI due to very complex interaction mechanism between PI materials and UV laser and incomplete parameters in thermophysical properties of PI.Finally, a method combining UV laser cutting and post chemical etching was studied to fabricate a multi-layer microchip substrate of ultrathin ceramic plates (125μm). The effects of the key factors and optimized parameters on laser microprocessing accuracy and quality were investigated by means of a 4X4 orthogonal design. The key microprocessing parameters were determined and optimized to achieve a narrow kerf width and minimal Ra on the kerf sidewall under the conditions of keeping high production efficiency. Subsequent chemical etching on the laser processed areas was performed to remove debris on the kerf surface and recast layer on the kerf sidewall in order to reach the requirements of both size precision and post gilding treatment. The results showed that the combining UV laser cutting and post chemical corrosion method could get not only a higher laser processing size precision, but also a clean surface on both kerf top and sidewall surface with a roughness Ra of 0.16μm, which fully met the requirements of subsequent metal deposition process.