Laser drilling equipment for improving UV laser drilling processing technology

Abstract

The invention relates to laser drilling equipment for improving a UV laser drilling processing technology, the laser drilling equipment for improving the UV laser drilling processing technology comprises a laser device and a lens, and laser generated by the laser device acts on a workpiece to be processed after being processed by the lens. An acousto-optic modulator is also arranged on a laser light path between the laser and the lens; the acousto-optic modulator can be controlled to turn off the laser when the laser energy is abnormal. According to the laser drilling equipment for improving the UV laser drilling processing technology, the laser light path can be selectively turned off through the acousto-optic modulator additionally arranged in the light path, and therefore when laser energy is abnormal, for example, when the first laser energy is too strong, laser can be actively turned off, and therefore the processing defect caused by the too strong laser energy is avoided.

Description

Technical Field

[0001] The invention relates to the technical field, and in particular to a laser drilling device for improving a UV laser drilling process. Background Art

[0002] The drilling process in the PCB printed circuit board processing is completed by UV laser drilling equipment. However, due to the obvious high peak value of the initial laser energy after laser pumping, obvious over-etching and over-burning will appear at the beginning of cutting and drilling, forming obvious holes. The dots at the starting point have a very serious impact on the effect of drilling. For example Figure 1 Similar problems occur not only in the PCB drilling process, but also in other UV laser cutting scenarios.

[0003] At the same time, due to the linear polarization light generated by the laser, when the absorption of S (vertical) polarized light and P (parallel) polarized light is asymmetric, irregular shaped small holes may appear, affecting the roundness of the hole type, such as Figure 2 shown.

[0004] In order to solve the problem of poor hole edge caused by excessive first-shot energy, the laser frequency can be reduced, the first-shot energy value can be reduced, or the roundness problem can be improved by reducing the scanning speed of the galvanometer, using the center area of ​​the field mirror (not using edge area processing), and other processes. However, reducing the laser frequency parameter can only reduce the first-shot energy value, but there are still dots on the edge of the hole, and the first-shot problem has not been completely solved; and the roundness problem cannot be effectively improved. At the same time, reducing the scanning speed of the galvanometer sacrifices the processing efficiency. Reducing the laser frequency and the first-shot energy value, this process is difficult to accurately control the frequency reduction amplitude and the timing of the frequency reduction. In addition to the difficulty in accurately controlling the first-shot energy amplitude to achieve edge cutting with the same effect, it will also bring about the problem of uneven cutting edges caused by the unsmooth connection between the frequency reduction drilling stage and the subsequent drilling stage. The second is to set the first drilling point in the material area to be removed by designing the cutting and drilling path in a targeted manner. This approach requires the addition of additional cutting paths, which will lead to a reduction in production rhythm, is not conducive to optimizing the planning and design of the cutting path, and is difficult to achieve during the drilling process. Summary of the invention

[0005] In view of the problem of overburning and over-etching at the starting point of a path due to excessive first energy in the process of laser processing using UV laser in the prior art, the present invention provides a laser drilling device for improving the UV laser drilling processing technology.

[0006] The technical solution of the present invention provides a laser drilling device for improving the UV laser drilling processing technology, comprising a laser and a lens. The laser generated by the laser acts on a workpiece to be processed after being processed by the lens. The device is characterized in that an acousto-optic modulator is also arranged in the laser optical path between the laser and the lens; the acousto-optic modulator can be controlled to shut off the laser when the laser energy is abnormal.

[0007] Preferably, it further comprises a plane scanner, and the plane scanner is used to control the circumferential deflection of the laser on the incident optical axis of the plane scanner.

[0008] Preferably, the planar scanner comprises an X deflector and a Y deflector which are sequentially arranged along the optical path and whose deflection directions are at right angles to each other in a plane perpendicular to the incident optical axis, and a half-wave plate arranged between the X deflector and the Y deflector.

[0009] Preferably, the deflection direction of the X deflector is consistent with the polarization direction of the incident light of the plane scanner; The fast axis or the slow axis of the half-wave plate is between the deflection direction of the X deflector and the deflection direction of the Y deflector, and is at 45 degrees to both of them.

[0010] Preferably, it further comprises an aperture arranged after the Y deflector, the aperture being used to pass the first-order diffracted light; Or, it also includes an aperture arranged after the Y deflector, and the aperture is used to pass the first-order diffraction light; and a beam expander for adjusting the diameter of the laser beam is arranged after the aperture.

[0011] Preferably, it further comprises a polarization converter, wherein the polarization converter is placed before the acousto-optic modulator on the optical path.

[0012] Preferably, it further comprises a polarization converter, wherein the polarization converter is placed between the AOM and the planar scanner on the optical path.

[0013] Preferably, the polarization converter comprises at least a quarter wave plate, and the quarter wave plate is used to convert the linearly polarized light emitted from the planar scanner into circularly polarized light.

[0014] Preferably, the polarization converter further comprises a radial wave plate arranged on the optical path after the quarter wave plate.

[0015] Preferably, the polarization converter comprises a rotating wave plate arranged after the planar scanner, wherein the rotating wave plate is a half wave plate, and a rotation period of the rotating wave plate is twice a modulation period of the planar scanner.

[0016] The laser drilling device for improving the UV laser drilling process of the present invention can selectively shut off the laser light path by adding an acousto-optic modulator in the light path. Therefore, the laser can be actively shut off when the laser energy is abnormal, such as when the initial laser energy is too strong, thereby avoiding processing defects caused by excessive laser energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of defects in the prior art; Figure 2 A schematic diagram of defects in the prior art; Figure 3 A schematic diagram of a beam expander 55 of a laser drilling device for improving the UV laser drilling process of the present application; Figure 4 A schematic diagram of the overall optical path of a laser drilling device for improving the UV laser drilling process of the present application; Figure 5 It is a schematic diagram of an embodiment of a polarization converter 4 of a laser drilling device for improving a UV laser drilling process according to the present application.

[0018] In the figure: 1: Laser; 2: Lens; 21: Galvanometer; 22: Field mirror; 3: Acousto-optic modulator; 4: Polarization converter; 41: Quarter wave plate; 42: Radial wave plate; 5: Planar scanner; 51: X deflector; 52: Y deflector; 53: Half wave plate; 54: Aperture; 55: Beam expander; 6: Beam splitter; 7: Photodetector. DETAILED DESCRIPTION

[0019] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. In this specification, the size ratios in the drawings do not represent the actual size ratios, but are only used to reflect the relative position relationship and connection relationship between the components. Components with the same name or the same number represent similar or identical structures and are only for illustrative purposes.

[0020] Figure 3 This is a schematic diagram of the principle of the laser drilling equipment for improving the UV laser drilling process of this application. It has a laser optical path in the usual sense, which is used to modulate the laser emitted by the laser 1 and irradiate it to the surface of the workpiece to be processed through the lens 2 to achieve the processing of the workpiece to be processed. Unless otherwise specified, the optical path refers to the laser propagation path between the laser 1 and the lens 2. In order to solve the problem of over-etching and producing dots at the starting point of drilling processing caused by the excessive intensity of the initial laser, Figure 3In the laser drilling equipment for improving the UV laser drilling process shown, an acousto-optic modulator 3 is added to the optical path between the laser 1 and the lens 2 to realize short-time shutdown control of the laser. In this way, during the processing, the laser can be specifically turned off at the first laser firing by the acousto-optic modulator 3 to prevent the first laser firing from acting on the workpiece to be processed. The lens 2 is used to perform terminal adjustment on the emitted laser, and usually includes a galvanometer and a field lens. The laser beam is projected to the processing area of ​​the workpiece to be processed through the high-speed deflection of the galvanometer and the focusing effect of the field lens, and the diameter and taper of the processing hole can be adjusted accordingly.

[0021] The diffraction efficiency η of the AOM 3 is controlled by applying a radio frequency signal. When the light beam is required to pass through, the diffraction efficiency η is 0%, and the energy of the 0th order light is I0; when the light beam is not required to pass through (the first energy is not needed), the diffraction efficiency η is 100%, and the energy of the 0th order light is 0, and the energy of the 1st order light is I0 (absorbed by the light absorption device). There may be side effects, that is, the AOM 3 fails to switch in time, allowing part of the light pulse to leak out. How to avoid: In order to achieve timely switching of the light pulse by the AOM 3, the rise time of the AOM 3 needs to be faster than the laser. The repetition rate of this laser is 100kHz, and the corresponding rise time is about 4us. The rise time of the AOM 3 is on the order of several hundred ns, which can achieve switching.

[0022] Specific to this application Figure 3 In the embodiment of the present invention, a plane scanner 5 is also included in the optical path. The plane scanner 5 is used to control the laser to deflect in the 360-degree circumferential direction of the optical axis of the incident plane scanner 5, so that the emitted light spot is distributed in a plane perpendicular to the incident light axis. In the drilling operation, the plane scanner 5 is controlled to work so that the emitted light spot is distributed in a plane perpendicular to the incident light axis in a circular shape with the projection of the incident light axis as the center.

[0023] The plane scanner 5 is processing the optical pulses all the time, and the acousto-optic modulator 3 only suppresses one or several optical pulses, and does not affect the plane scanner 5. The good connection between the starting point and the end point can be realized by software, and the scanning of the galvanometer 22 can be controlled.

[0024] Figure 3A specific implementation of the planar scanner 5 is given, which includes an X deflector 51 and a Y deflector 52, which are arranged in sequence along the optical path and whose deflection directions are at right angles to each other in a plane perpendicular to the incident optical axis, and a half-wave plate 53 placed between the X deflector 51 and the Y deflector 52. The incident laser is first deflected by an angle in the X direction by the X deflector 51, and then deflected by an angle in the Y direction by the Y deflector 52. In a specific case, those skilled in the art should know that for the linearly polarized laser emitted by the laser 1, in order to reduce energy loss and achieve the desired deflection effect, the rotation directions of the X deflector 51, the Y deflector 52 and the half-wave plate 53 may need to be determined at a specific angle. For example, the X deflector 51 and the Y deflector 52 can both be acousto-optic deflectors, which deflect the laser in a specific direction and require the laser polarization direction to be along this direction to minimize energy loss. Therefore, the deflection direction of the X deflector 51 needs to be consistent with the amplitude vibration direction of the incident light. In order to achieve in-plane adjustment scanning, the deflection direction of the Y deflector 52 should be perpendicular to the deflection direction of the X deflector 51, and the polarization direction of the incident light entering the Y deflector 52 is required to rotate 90 degrees to keep it consistent with the deflection direction of the Y deflector 52. This usually requires that the direction of the main crystal section of the half-wave plate 53 is between the deflection direction of the X deflector 51 and the deflection direction of the Y deflector 52, and is 45 degrees to both.

[0025] The plane scanner 5 can also be provided with an aperture 54 after the Y deflector 52. The aperture 54 obtains the first-order diffraction light and filters out the zero-order diffraction light and other high-order diffraction light. Optionally, a beam expander 55 is provided after the aperture 54. The first-order diffraction light passing through the aperture 54 can adjust the beam diameter through the beam expander 55. This special aperture is designed to absorb the 0th-order light and pass the 1st-order light. Figure 4 As shown, the aperture size of the aperture is calculated based on the scanning angle of the deflector in the plane scanner 5 being 2.2 mrad and the separation angle being 10.5 mrad@170 MHz (minimum: 8.03 mrad@130 MHz; maximum: 13 mrad@210 MHz): ①Scan length=FL*tan(scan angle)=1.43mm ②Separation length=FL*tan(Separation angle)=8.45mm Scan length is the scanning range of the plane scanner 51 and 52, FL is the focal length of the plane scanner PCX lens, and scan angle is the scanning angle of the plane scanner 51 and 52; Separation length is the separation distance between the 0th order and 1st order diffraction light generated by the plane scanner 51 and 52, FL is the focal length of the plane scanner PCX lens, and Separation angle is the separation angle between the 0th order and 1st order diffraction light generated by the plane scanner 51 and 52.

[0026] The function of the aperture inclination design is to increase the light irradiation area, reduce the whitening speed and reduce the energy density of light at the same time.

[0027] The laser drilling equipment for improving the UV laser drilling process is preferably provided with a polarization converter 4 in the optical path. The polarization converter 4 is preferably placed before the acousto-optic modulator 3. The polarization converter 4 is placed after the optical path of the plane scanner 5. The polarization converter 4 includes at least a quarter wave plate 41 for converting the linearly polarized light emitted from the plane scanner 5 into circularly polarized light, the purpose of which is to avoid the influence of the linearly polarized light on the roundness of the punched hole and the appearance quality of the edge of the hole. The linearly polarized light directly acts on the workpiece to be processed in the direction perpendicular to the polarization direction and in the direction parallel to the polarization direction. The removal effect of the material is different, which will lead to Figure 2 Since the linearly polarized light is converted into circularly polarized light by the quarter wave plate 41, the de-circularity phenomenon can be avoided to a certain extent.

[0028] The polarization converter 4 can further be provided with a radial wave plate 42 on the optical path after the quarter wave plate 41, and the second wave plate 42 is used to convert the circularly polarized light into radially polarized light, so as to provide a processing quality with better roundness than the circularly polarized light. The polarization converter 4 can be only a rotating wave plate coordinated and controlled with the plane scanner 5, the rotating wave plate is a half wave plate, and its rotation period is twice the modulation period of the plane scanner 5, and the fast axis of the rotating wave plate is the same as the initial phase of the polarization direction of the outgoing light of the plane scanner 5, so under the rotation of the rotating wave plate, the polarization direction of the outgoing light can synchronously follow the deflection direction of the plane scanner 5, and achieve an effect similar to that of obtaining radially polarized light, that is, because the polarization direction is always parallel to the radial direction of the hole to be processed during the polarization process, the uniformity of the laser material removal effect at the edge of the hole is guaranteed, and the edge quality of the drilling process and the roundness of the hole are improved.

[0029] like Figure 3As shown, a beam splitter 6 is also provided in the optical path between the laser 1 and the plane scanner 5, which is used to split the laser light generated by the laser 1 into two beams, wherein the beam with strong energy is used as the laser light for drilling and other processing, and acts on the surface of the workpiece to be processed through the plane scanner 5, the polarization converter 4, the acousto-optic modulator 3 and the lens 2. The other beam of laser light with weaker energy enters the corresponding photodetector 7. The control system detects the signal collected by the photodetector 7 to monitor the laser intensity of the laser 1.

[0030] The laser wavelength is 355nm, the typical power value is 20W, the repetition frequency is 0-500kHz, and the pulse width is <25ns@100kHz. The linearly polarized light pulse emitted from the laser is divided into two light paths through a beam splitter (99% reflection, 1% transmission): one path passes through the attenuation plate and enters the photodetector for laser monitoring; the other path passes through the first-order diffraction light generated by two acousto-optic deflectors, which will have a small angle deflection in the X and Y directions. The zero-order and first-order diffraction lights are imaged on the special aperture through the converging lens. Due to the aperture effect of the special aperture, the first-order diffraction light passes through, while the zero-order diffraction light is absorbed. The diameter of the first-order diffraction light passing through is adjusted by the beam expander, and the linear polarization light is converted into circular polarization light through a quarter-wave plate. After that, the light beam is projected into the processing area through the high-speed deflection of the galvanometer and the focusing effect of the field lens. The switch function of the acousto-optic modulator realizes the shutdown of the first laser, thereby solving the problem of excessive energy in the first drilling.

[0031] The above content only describes the preferred implementation mode of the present invention, and does not limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solution of the present invention by ordinary technicians in this field should fall within the protection scope determined by the claims of the present invention.

Claims

1. A laser drilling device for improving UV laser drilling processing technology, comprising a laser (1) and a lens (2), wherein the laser generated by the laser (1) is processed by the lens (2) and acts on a workpiece to be processed, wherein: An acousto-optic modulator (3) is also provided on the laser light path between the laser (1) and the lens (2); the acousto-optic modulator (3) can controllably shut off the laser when the laser energy is abnormal.

2. The laser drilling device for improving the UV laser drilling process as claimed in claim 1, characterized in that: It also comprises a plane scanner (5), wherein the plane scanner (5) is used to control the circumferential deflection of the laser light on the incident optical axis of the plane scanner (5).

3. The laser drilling device for improving the UV laser drilling process as claimed in claim 2, characterized in that: The planar scanner (5) comprises an X deflector (51) and a Y deflector (52) which are sequentially arranged along an optical path and whose deflection directions are at right angles to each other in a plane perpendicular to an incident optical axis, and a half-wave plate (53) arranged between the X deflector (51) and the Y deflector (52).

4. The laser drilling device for improving the UV laser drilling process as claimed in claim 3, characterized in that: The deflection direction of the X deflector (51) is consistent with the polarization direction of the incident light of the plane scanner (5); The fast axis or the slow axis of the half-wave plate (53) is between the deflection direction of the X deflector (51) and the deflection direction of the Y deflector (52), and is at 45 degrees to both.

5. The laser drilling device for improving the UV laser drilling process as claimed in claim 3, characterized in that: It also includes an aperture (54) disposed after the Y deflector (52), the aperture (54) being used to pass the first-order diffracted light; Alternatively, it further includes an aperture (54) disposed after the Y deflector (52), wherein the aperture (54) is used to pass the first-order diffracted light; and a beam expander (55) for adjusting the diameter of the laser beam is disposed after the aperture (54).

6. The laser drilling device for improving the UV laser drilling process as claimed in claim 1, characterized in that: It also includes a polarization converter (4), which is placed before the acousto-optic modulator (3) on the optical path.

7. The laser drilling device for improving the UV laser drilling process as described in any one of claims 2 to 5, characterized in that: It also includes a polarization converter (4), which is placed between the acousto-optic modulator (3) and the planar scanner (5) on the optical path.

8. The laser drilling device for improving the UV laser drilling process as claimed in claim 7, characterized in that: The polarization converter (4) comprises at least a quarter wave plate (41), and the quarter wave plate (41) is used to convert linearly polarized light emitted from the planar scanner (5) into circularly polarized light.

9. The laser drilling device for improving the UV laser drilling process as claimed in claim 8, characterized in that: The polarization converter (4) further comprises a radial wave plate (42) arranged on the optical path after the quarter wave plate (41).

10. The laser drilling device for improving UV laser drilling processing technology according to claim 7, characterized in that: The polarization converter (4) comprises a rotating wave plate arranged after the planar scanner (5); the rotating wave plate is a half wave plate, and its rotation period is twice the modulation period of the planar scanner (5).

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