Pulse laser drilling method

Abstract

The invention designs a pulse laser drilling method. The problem that in an existing pulse laser drilling technology, the light spot overlapping rate is too high, and consequently a serious heat affected zone is caused is solved. And the generated plasma cannot avoid the influence on the next laser pulse, the shielding of the plasma causes the attenuation of pulse energy to seriously influence the absorption of the target material at the bottom of the hole on the light beam, and the chip removal is difficult. Therefore, compared with an existing pulse laser drilling mode, the machining quality can be improved.

Description

Technical Field

[0001] The invention belongs to the field of pulse laser processing, and in particular provides a pulse laser drilling method. Background Art

[0002] With the rapid development of modern industry, the industry fields and scale of laser drilling technology applications at home and abroad are constantly expanding, and its industrial processing advantages are constantly highlighted in various fields. For drilling holes on hard and brittle targets, traditional mechanical processing methods can no longer meet the requirements of dense through-hole processing and production efficiency. For example, in the processing of small holes and micro-holes on multi-layer ceramic substrates, semiconductor SOS substrates, multi-layer printed circuit boards, composite targets, and other high-hardness, high-melting-point, and fragile targets, it is necessary to meet requirements that are difficult to achieve with ordinary processing technology. [1,2] Although there are many ways to use pulse laser drilling, there are certain problems in the actual processing process. The first is the problem of heat-affected zone (HAZ). The size of the spot overlap rate is closely related to the formation of the heat-affected zone. [3,4] In the process of pulse laser drilling, the removal of target material mainly depends on the material gasification removal. However, the higher the spot overlap rate, the more serious the heat accumulation, which leads to serious heat affected zone problems, such as inducing material recondensation and reducing processing accuracy. [5-7] In addition, if the spot overlap rate is too high during the processing, the generated photo-induced plasma will not be able to avoid the next laser pulse, and the shielding of the plasma will cause the pulse energy to attenuate. [8-10] , which seriously affects the absorption of the beam by the target at the bottom of the hole, and also makes it difficult to remove chips, making it more difficult to remove the target during deep hole processing. Therefore, in order to effectively avoid the problem of plasma shielding, it is urgent to rely on new technical solutions to solve it. References [1] Wang Xiaodong, Zhao Xuemin, Wang Shenglie, et al. Research on laser dynamic high-speed drilling system [J]. Laser Technology, 2003, (06): 563-566. [2] Yan Xuguang, Gao Wenbin, Yang Shuiqi, et al. Laser precision micro-hole processing technology and its application in the electronics industry [J]. Journal of Hangzhou Institute of Electronic Industry, 1994, (03): 4-10. [3] Fan Xinhu, Huang Yu, Rong Youmin. Subnanosecond laser cutting of Ni-Zn-ferrite composite sheets[J]. Applied Laser, 2023, 43(03): 48-58. [4] Wang Yifei, Yu Zhou, Li Kangmei, et al. Research on nanosecond laser ablation of titanium alloy microgrooves[J]. Journal of Donghua University (Natural Science Edition), 2023, 49(01): 84-94. [5]Freitag C,Kononenko T V,Weber R,et al.Influence ofpulse repetitionrate and pulse energy on the heat accumulation between subsequent laserpulses during laser processing ofCFRPwith ps pulses[J].Applied Physics A,2018,124:1-9. [6]Li Y,He G,Liu H,et al.Investigation of Heat Accumulation inFemtosecond Laser Drilling of Carbon Fiber-Reinforced Polymer[J].Micromachines,2023,14(5):913. [7]Weber R,GrafT,Berger P,et al.Heat accumulation during pulsed lasermaterials processing[J].Optics express,2014,22(9):11312-11324. [8]Weber R,GrafT,Berger P,et al.Heat accumulation during pulsed lasermaterials processing[J].Optics express,2014,22(9):11312-11324. [9]Bulgakova N M,Panchenko A N,Zhukov V P,et al.Impacts of ambientand ablation plasmas on short-and ultrashort-pulse laser processing ofsurfaces[J].Micromachines,2014,5(4):1344-1372.

[10] Yilbas BS, Yilbas Z, Akcakoyun N. Investigation into absorption of the incident laser beam during Nd:YAG laser processing of metals[J]. Optics&Laser Technology, 1996, 28(7):503-511. Summary of the invention

[0003] The purpose of the present invention is to provide a pulse laser drilling method to alleviate the problem of severe heat affected zone caused by excessive spot overlap in the prior art, and the problem that the generated plasma cannot avoid the next laser pulse, the shielding of the plasma causes the pulse energy to attenuate, seriously affecting the absorption of the light beam by the target material at the bottom of the hole and the difficulty in chip removal.

[0004] Based on the above purpose, the present invention provides a pulse laser drilling method, which includes the following steps: step S1: determine the radius R of the circular hole; step S2: focus the laser beam on the surface to be processed of the target material; step S3: the adjacent spots of the pulse laser beam operate at a certain deflection angle θ along the set circular hole path, and N1 spots are punched in one circle of rotary cutting, and then N2 circles of rotary cutting are continued to be completed, and a layer of drilling is completed at this time; step S4: according to the thickness of the target material, the defocus amount is appropriately changed after completing step S3; step S5: repeat the above steps until the through hole processing is completed.

[0005] The relationship between the circular hole radius R, the spot radius r, and the deflection angle θ of the adjacent pulse spot in step S1 satisfies:

[0006] In step S3, N2 is the number of rotations required to complete the drilling of one layer, which can be set by the number of cyclic processing times of the pulse laser.

[0007] In step S3, the number of spots per circle N1, the number of circles N2 of a cycle of peeling, and the peeling deflection angle θ of adjacent spots satisfy: in That is, N2 is the largest integer of 360° / θ.

[0008] Note that θ cannot be divided by 360°. Because θ is divided by 360°, after the light spot scans a circle, the position of the light spot in the second circle is the same as the first circle, so some places in the circular hole surface cannot be scanned, so it cannot be divided by 360°.

[0009] As described in step S3, the adjacent light spots of the pulsed laser beam are deflected at a certain angle θ, and the relationship is achieved by changing the pulsed laser scanning speed v: Where f is the pulse frequency.

[0010] The reason for adjusting the laser beam waist position in step S4 is that the laser beam generated by the laser has a certain divergence angle. As the drilling depth increases, the position of the laser beam waist center no longer acts on the material surface but is above the processed surface of the target material. The laser energy density on the surface of the laser acting on the material decreases, and the processing efficiency decreases. Therefore, it is necessary to adjust the position during the next processing cycle.

[0011] By controlling the beam angle, adjacent beams can have little or no overlap. In addition, after the light spot rotates one circle, the target material of this layer cannot be completely removed due to little or no overlap between the light spots. When the light beam rotates for the next circle, if the beam irradiation position is the same as the position of a certain beam in the previous circle, the target material cannot be completely removed. Therefore, when drilling deep holes, a certain layer of target material must be completely removed, which requires that the position of the next circle of light spots cannot be the same as the position of the previous circle of light spots before a certain layer of target material is completely removed. When the removal of target material in a certain cycle is completed, the starting removal position of the light spot in the next cycle is the same as the starting removal position of the light spot in the previous cycle, and a new cycle of processing begins, and finally the target material is removed layer by layer.

[0012] Compared with the prior art, the beneficial effects of the present invention are mainly: The present invention reduces the overlap rate of two adjacent pulse laser spots or even eliminates the overlap, effectively avoiding the problem of too many pulses accumulated at the same processing point, plasma shielding caused by incomplete dissipation of the plasma generated by the target material, and enables the generated etched material to be discharged smoothly to avoid absorbing the energy of the next laser pulse, and to a certain extent increases the energy coupling between the laser and the processed target material, so that the laser energy absorbed by the target material increases and the processing depth is improved. Moreover, the heat of the steam and plasma generated by the gasification of the target material will not accumulate to cause the temperature in the cavity to rise and produce the heat-affected zone problem of material recondensation and reduced processing accuracy, thereby improving the utilization rate of laser energy and the drilling quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of the processing principle in the pulse laser drilling method provided by the present invention.

[0014] Figure 2 This is a schematic diagram of the processing flow in the pulse laser drilling method provided by the present invention.

Claims

1. A pulse laser drilling method characterized by , the steps are as follows: Step S1: determine the radius R of the circular hole; Step S2: focus the laser beam on the surface to be processed of the target material; Step S3: the adjacent light spots of the pulsed laser beam operate at a certain deflection angle θ along the set circular hole path, and N1 light spots are formed after one circle of rotary cutting, and then N2 circles of rotary cutting are continued to complete, and a layer of drilling is completed at this time; Step S4: according to the thickness of the target material, the defocus amount is appropriately changed after completing step S3; Step S5: repeat the above steps until the through hole processing is completed.

2. A pulse laser drilling method according to claim 1, characterized in that: The relationship between the circular hole radius R, the spot radius r, and the deflection angle θ of the adjacent pulse spot in step S1 satisfies:

3. A pulse laser drilling method according to claim 1, characterized in that: In step S3, the number of spots per circle N1, the number of circles N2 of a cycle of peeling, and the peeling deflection angle θ of adjacent spots satisfy: in That is, N2 is the largest integer of 360° / θ.

4. A pulse laser drilling method according to claim 1, characterized in that: Note that θ cannot be divided by 360°. Because θ is divided by 360°, after the light spot scans a circle, the position of the light spot in the second circle is the same as the first circle, so some places in the circular hole surface cannot be scanned, so it cannot be divided by 360°.

5. A pulse laser drilling method according to claim 1, characterized in that: As described in step S3, the adjacent light spots of the pulsed laser beam are deflected at a certain angle θ, and the relationship is achieved by changing the pulsed laser scanning speed v: Where f is the pulse frequency.

6. A pulse laser drilling method according to claim 1, characterized in that: The reason for adjusting the laser beam waist position in step S4 is that the laser beam generated by the laser has a certain divergence angle. As the drilling depth increases, the position of the laser beam waist center no longer acts on the material surface but is above the processed surface of the target material. The laser energy density on the surface of the laser acting on the material decreases, and the processing efficiency decreases. Therefore, it is necessary to adjust the position during the next processing cycle.

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