JP4680871B2 - Beam profile measuring apparatus and laser processing apparatus - Google Patents

Description

  The present invention is equipped with a laser beam profile measuring device that can monitor the presence or absence of a high peak in the profile of a top hat laser beam, and is equipped with the laser beam profile measuring device to drill a workpiece such as a printed circuit board. The present invention relates to a laser processing apparatus that performs the above.

  FIG. 4 is a conceptual diagram showing a configuration example of a conventional laser processing apparatus. First, a case where there is no top hat optical system 2 between the laser oscillator 1 and the total reflection mirror 8 will be described. In FIG. 4, a pulsed laser beam emitted from the laser oscillator 1 (hereinafter simply referred to as “laser beam” or “laser pulse”) has its beam diameter and divergence angle adjusted appropriately by a plurality of movable lenses 3. After that, the mask 4 is shaped into a laser beam having a shape used for processing. The laser beam shaped by the mask 4 is two-dimensionally scanned by two galvano scan mirrors 5 and focused and irradiated on an arbitrary position of a work (workpiece such as a printed board) 7 by an fθ lens 6 to be processed. The object 7 is drilled in a predetermined shape.

  In order to reduce the size of the apparatus, the optical path from the laser oscillator 1 to the mask 4 is formed by being bent by total reflection mirrors 8 and 9 as transmission mirrors, and from the mask 4 to the two galvano scan mirrors 5. The optical path is formed by being bent by total reflection mirrors 10 and 11 which are transmission mirrors. The plurality of movable lenses 3 are disposed between the total reflection mirrors 8 and 9.

  FIG. 5 is a schematic diagram for explaining various aspects of the intensity distribution (profile) of the laser beam formed on the mask 4. FIG. 5A shows a general Gaussian distribution shape formed when the top hat optical system 2 is not provided. The drilling process includes a through hole process and a blind hole process. In general, the intensity distribution of the laser beam emitted from the laser oscillator 1 has a Gaussian distribution and is formed on the mask 4. Similarly, the intensity distribution has a Gaussian distribution (FIG. 5A). When drilling is performed with a laser beam having such a Gaussian intensity distribution, a so-called tapered drilling process in which the diameter of the processed hole gradually decreases from the irradiated surface side toward the non-irradiated surface side. There are many cases.

  By the way, as a blind hole processing method, a workpiece is formed by superposing a resin layer and a copper layer, and conventionally, an infrared laser beam having an extremely high reflectance to copper is irradiated to the resin layer. However, in recent years, printed circuit boards, which are workpieces, have been demanded for fine hole processing with a smaller hole diameter in response to a demand for higher density. Therefore, the laser beam to be used is changed from the infrared laser beam to the short wavelength ultraviolet laser beam.

  When this ultraviolet laser beam is used, the reflectance of the ultraviolet laser beam to copper is smaller than that of the infrared laser beam. Therefore, in blind hole processing with an ultraviolet laser beam, the intensity distribution of the irradiated laser beam is a Gaussian distribution. In the case of the shape, the surface of the copper layer located at the central portion where the intensity distribution of the laser beam is strong may be damaged, in addition to the taper hole being drilled in the resin layer. Therefore, in a conventional laser processing apparatus that performs blind hole processing using an ultraviolet laser beam, in order to eliminate the influence of the intensity distribution, the intensity distribution of the laser beam to be irradiated is made flat by reducing the diameter of the shaping hole of the mask 4. By approaching, a method of avoiding damage to the copper layer and obtaining a blind hole that does not taper the resin layer is adopted.

  Here, one of the problems in the laser processing apparatus is to reduce the time required for drilling in order to improve productivity. As a method of reducing the time required for drilling, a method of reducing the number of laser pulses applied to the printed board in order to process one hole can be considered. In this method, it is necessary to increase the energy per laser pulse, but a normal laser pulse has an intensity distribution having a Gaussian distribution shape as shown in FIG. In other words, if a printed circuit board is directly irradiated with a laser beam having such a Gaussian intensity distribution, the energy is large even if the number of irradiations is small, so that damage to the copper layer cannot be avoided, and conversely, damage is caused. It becomes easy. Therefore, this method is not effective.

  On the other hand, in the method of reducing the number of laser pulses irradiated to the printed circuit board, as described above, the mask diameter is reduced in order to eliminate the influence of the intensity distribution, and the intensity distribution of the laser beam used for processing is made flat. Although processing is possible, as a result of reducing the mask diameter, the energy of the laser pulse used for processing becomes very small, and the effect of increasing the emission energy of the laser oscillator becomes small.

  For this reason, in recent years, a technique has been used in which the intensity distribution of a laser pulse emitted from a laser oscillator is shaped into an intensity distribution having a shape suitable for drilling and irradiated onto a printed circuit board. In general, an ordinary Gaussian distribution shape gradually decreasing symmetrically with respect to a peak point as shown in FIG. 5A possessed by a laser pulse emitted from a laser oscillator has a flat intensity distribution shown in FIG. 5B. A technique of shaping a top hat shape and irradiating a printed circuit board is often used.

  The intensity distribution of the top hat shape is created using an optical element such as an aspheric lens. In FIG. 4, a top hat optical system 2 disposed between the laser oscillator 1 and the total reflection mirror 8 is an optical element composed of an optical element such as an aspheric lens that creates such a top hat-shaped intensity distribution. It is a system. In this case, in FIG. 4, the top hat optical system 2 is constructed so that the intensity distribution of the top hat shape is formed on the mask 4, and the profile on the mask 4 is transferred to the work 7. Optical design is made.

  According to the processing method using the laser pulse having the intensity distribution of the top hat shape, it becomes easy to make a hole which is hard to be tapered, and at the same time, even a laser pulse having a low reflectivity with respect to copper such as an ultraviolet laser beam. When drilling with the same energy, the copper layer is less likely to be damaged. As a result, the laser energy actually used for processing can be further increased. Further, since the laser beam at the mask position has a flat top hat shape with an intensity distribution, a mask having a large diameter can be used when shaping and extracting the beam used for processing with the mask.

  However, in the laser processing apparatus shown in FIG. 4 using a laser beam having a top hat-shaped intensity distribution, what kind of processing hole is formed is determined by the intensity distribution of the laser beam formed on the mask 4. However, there is a problem that the intensity distribution varies greatly depending on the degree of adjustment of the top hat optical system 2 constituted by an aspheric lens or the like. Specifically, when the arrangement position of the aspherical lens in the top hat optical system 2 with respect to the laser optical axis is shifted from the optimum position for constructing the top hat shape, the intensity distribution formed on the mask 4 is shown in FIG. Since a locally high peak 28 as shown in c) occurs, the problem as shown in FIG. 6 occurs.

  FIG. 6 is a schematic diagram for explaining a processing state when processing is performed with a top hat laser beam having a locally high peak 28 shown in FIG. That is, when a van pattern of a top hat laser beam having a locally high peak 28 shown in FIG. 5C is obtained at the position of the mask 4 and irradiated to the printed circuit board, as shown in FIG. 30 is formed on the resin layer 31, and the surface of the copper layer 32, which is the bottom surface of the hole, is generally flat, but the copper layer 32 is melted in a partial region corresponding to the portion where the laser pulse has a high peak 28. Thus, there is a problem that the groove (copper layer damaged portion) 33 is formed.

  By the way, the conventional laser processing apparatus has a function of monitoring the energy used for processing one hole in order to find a processing defect at an early stage. This monitoring function captures the laser pulse waveform in the transmission optical path into the control device and integrates it to monitor the amount of energy used for drilling one hole and determine whether the specified amount has been reached. An alarm is issued when the amount is not reached. However, since the energy amount of the entire laser pulse is monitored by this method, even if the intensity distribution of the laser beam has a locally high peak, the total energy amount is within the desired amount. An alarm will never occur.

  In other words, when the laser beam is constructed in a top hat shape in the top hat optical system in question here, the occurrence of a local high peak should be distributed to the periphery of the peak. Since the energy component is considered to be a result of local distribution due to insufficient position adjustment of the element in the top hat optical system, the amount of energy of the entire laser beam does not change. Therefore, it is considered impossible to detect such a local change in the intensity distribution (profile) of the laser beam by the function of monitoring the amount of energy provided in the conventional laser processing apparatus.

  Therefore, for example, in Patent Document 1, a part of a laser beam irradiated to a workpiece is separated, the intensity distribution of the laser beam is measured by a light receiving sensor such as a CCD element, and the quality of the image is judged to determine the quality of the laser oscillator. A method for controlling the oscillation condition has been proposed, but not only the amount of energy of the laser pulse but also the profile of the laser beam is monitored by using the technique described in Patent Document 1, which is used for processing. Since the profile of the laser beam can be ascertained reliably, it is considered possible to detect the processing defect due to the change in the beam profile earlier and more reliably.

JP 2003-46173 A

  However, the technique described in Patent Document 1 requires a complicated measurement system for determining the quality of an image, and also requires that the quality determination of the image follow a laser pulse generated at a high repetition rate. Realization is difficult with a laser processing apparatus.

  As described above, the current laser processing apparatus uses an ultraviolet laser. However, an ultraviolet laser generally has less energy per pulse than an infrared laser that has been used before. The number of pulses required for drilling one hole is overwhelmingly large. Specifically, processing with an infrared laser requires only a few pulses, but processing with an ultraviolet laser requires at least several tens of pulses, and in some cases, a pulse number close to 100 pulses.

  Therefore, at present, in laser processing apparatuses using an ultraviolet laser, in order to obtain high productivity, further increase in output of the laser oscillator is advanced, and at the same time, increase in repetition rate is also promoted. In other words, if the image quality determination is performed by applying the technique described in Patent Document 1, a system capable of following a laser pulse generated at several hundred kHz is required.

  For example, assuming that machining is performed using a laser pulse generated at 100 kHz, it is assumed that several tens of pulses are required for one machining hole. In this case, even if the waveform of one pulse is observed every 10 pulses, it is necessary to take the intensity distribution of the laser pulse into the measurement system every 100 μs and judge whether it is good or bad. Therefore, a measurement system having a high processing capacity is required, which is expensive.

  That is, in a laser processing apparatus using a laser beam having a top hat beam profile, in order to avoid the occurrence of the copper layer damaged portion 33 shown in FIG. It is necessary to equip a mechanism that can monitor the occurrence of high peaks. In that case, it is desirable that the monitoring result that a high peak is generated can be reflected in the position adjustment of the aspherical lens. The problem is how to build such a simple and inexpensive monitor mechanism.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a laser beam profile measuring apparatus capable of monitoring the presence or absence of a high peak in a top hat-shaped beam profile with a simple and inexpensive configuration.

  An object of the present invention is to obtain a laser processing apparatus provided with the laser beam profile measuring apparatus of the above invention.

  In order to achieve the above-described object, a laser beam profile measuring apparatus according to the present invention is arranged on an optical path of a laser beam having a top hat shape and has a high peak region generated on the top hat shape. An aperture provided with an arc-shaped opening at a position where the laser beam is transmitted, and first measuring means for measuring the intensity of the laser beam that has passed through the aperture and determining whether there is an intensity exceeding a certain value; It is characterized by having.

  According to the present invention, since the aperture always transmits only the laser beam component of the high peak region generated on the top hat shape, the high peak region is generated on the top hat shape in the first measuring means. In normal times, a laser beam with a substantially constant intensity is input, and when there is an abnormality in which a high peak area is generated, a laser beam with a higher intensity than the constant intensity is input. Changes in the beam profile can be reliably detected with a simple and inexpensive configuration without requiring a complicated system to analyze.

  According to the present invention, it is possible to monitor whether or not a high peak is generated in the top hat beam profile with a simple and inexpensive configuration.

  Exemplary embodiments of a laser beam profile measuring apparatus and a laser processing apparatus according to the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a block diagram showing the configuration of a laser processing apparatus equipped with a laser beam profile measuring apparatus according to an embodiment of the present invention. In FIG. 1, components that are the same as or equivalent to those shown in the conventional example (FIG. 4) are assigned the same reference numerals. Here, the description will be focused on the parts related to this embodiment.

  As shown in FIG. 1, the laser processing apparatus according to this embodiment reduces the reflectivity in place of the total reflection mirrors 9 and 10 arranged before and after the mask 4 in the configuration shown in the conventional example (FIG. 4). Partially reflecting mirrors 9a and 10a that partially transmit light are provided. A plurality of lenses 12, an aperture 13 having a slit (see FIG. 3), and a photoelectric element 14 such as a photodiode are arranged in this order on the optical path of the transmitted light of the partial reflecting mirror 9a, and receives the output of the photoelectric element 14. A control device 15 is provided. The plurality of lenses 12 are arranged as necessary. In addition, a photoelectric device 16 such as a photodiode is disposed on the optical path of the transmitted light of the partial reflecting mirror 10a, and a control device 17 that receives the output of the photoelectric device 16 is provided.

  Each of the partial reflection mirrors 9a and 10a constitutes a spectroscopic means. Moreover, the whole photoelectric element 14 and the control apparatus 15 and the whole photoelectric element 16 and the control apparatus 17 respectively constitute a measuring apparatus.

  First, the path from the partial reflection mirror 9a to the lens 12 to the aperture 13 to the photoelectric element 14 to the control device 15 will be described. FIG. 2 is a diagram showing a form example of the aperture 13 determined based on the experimental result shown in FIG. FIG. 3 shows a change in the position where a high peak is generated by taking out a van pattern of a laser beam in a state where a locally high peak 28 is generated as shown in FIG. It is a figure which shows the experimental result which investigated the aspect.

  As described above, when the arrangement position of the aspheric lens in the top hat optical system 2 with respect to the laser optical axis is shifted from the optimum position for constructing the top hat shape, that is, the central axis of the aspheric lens is the original laser beam. When deviating from the axis, a locally high peak 28 as shown in FIG. 5C is generated in the intensity distribution formed on the mask 4. Then, when such a van pattern of a top hat laser beam having a locally high peak is taken out by the mask 4 and irradiated onto the work 7, a copper layer damaged portion 33 as shown in FIG. 6 is generated.

  Therefore, processing was actually performed with a laser beam having a local high peak in the profile of the top hat shape by the method shown in FIG. 3, and the relationship between the high peak position and the formation position of the damaged portion of the copper layer was investigated. In FIG. 3, reference numeral 20 denotes a beam outer shape cut out by the mask 4. Reference numeral 21 denotes a part deeply processed by the peak portion generated on the beam profile when the arrangement position of the aspherical lens is shifted in a certain direction from the optimum position, and a certain width at a position at a certain distance from the beam center. It is formed by drawing an arc shape. Although not shown, when the arrangement position of the aspherical lens is shifted from the optimum position in one direction, the fixed distance from the beam center is the same, and is similarly at different positions on the circumference of the fixed distance. It has been found that it is formed in a circular arc shape having a width. Since the deeply processed portion 21 corresponds to the copper layer damaged portion 33 shown in FIG. 6, the deeply processed portion 21 is hereinafter referred to as a copper layer damaged portion 21.

  From the results of such experiments, the peak position generated in the top-hat shaped beam profile varies depending on the direction in which the central axis of the aspherical lens deviates from the original laser optical axis (beam center). It has been found that even if they deviate, they occur on a concentric circle at a certain distance from the beam center. This indicates that the deviation direction of the laser beam passing through the top hat optical system 2 from the original laser optical axis is substantially determined by the direction in which the central axis of the aspherical lens is displaced from the laser optical axis. The distance of the laser beam passing through the top hat optical system 2 in the direction deviated from the original laser optical axis is a constant distance substantially determined by the top hat optical system 2.

  That is, in this embodiment, an arcuate opening determined from a machining state (see FIG. 3) when machining is performed with a laser beam in which a high peak is actually generated and the beam profile is broken from the top hat shape. An aperture 13 having a slit portion 22 (see FIG. 2) was formed. In consideration of the fact that the diameter processed as a whole is a transfer of the hole diameter of the mask 4, the top hat-shaped profile formed on the aperture 13 is formed on the mask 4 by irradiation. The aperture 13 was disposed at a position where the optical distance from the laser oscillator 1 was the same as that of the mask 4 so that the same was obtained.

  In the aperture 13, as shown in FIG. 2, arc-shaped slit portions 22 having a certain width are arranged on a concentric circle at a certain distance from the original laser optical axis. Since the width and the formation position of the slit portion 22 are determined in consideration of the fact that the diameter processed as a whole is a transfer of the hole diameter of the mask 4, the width and the formation position of the slit portion 22 It is the same. As shown in FIG. 2, the slit portion 22 is provided in each of the four quadrants of the orthogonal coordinates so that it can cope with any orientation of the center axis of the aspheric lens deviating from the original laser optical axis. .

  As described above, the aperture 13 is configured to always transmit the laser beam component at the peak position generated in the top hat-shaped beam profile when the central axis of the aspherical lens is shifted from the original laser optical axis. As an example of the numerical value of the slit portion 22, if the beam radius extracted by the mask 4 is 1, the slit portion 22 has a slit with a width of 0.2 surrounded by an arc having a radius of 0.8 and an arc having a radius of 0.6. is doing.

  Since the actual beam diameter at the position of the mask 4 is small, a plurality of lenses 12 may be arranged in front of the aperture 13 to enlarge the beam diameter as shown in FIG. In this case, the position of the slit portion 22 changes depending on the magnification by the lens 12, but it goes without saying that the relative position does not change.

  According to this configuration, the laser beam that passes through the aperture 13 and is received by the photoelectric element 14 is only that that has passed through the slit portion 22. That is, the laser beam received by the photoelectric element 14 is only the laser beam component at the peak position generated in the top hat beam profile due to the deviation from the central axis of the aspherical lens.

  The output voltage of the photoelectric element 14 is a substantially constant value in a normal time when a high peak is not generated in the top hat-shaped beam profile. However, if a high peak occurs and the beam profile is broken from the normal time, The voltage value is higher than a certain value. In this case, damage has occurred on the surface of the copper layer, which is the bottom surface of the processed hole.

  Therefore, the control device 15 monitors the output voltage value of the photoelectric element 14 and generates an alarm signal when the value exceeds a certain value that causes damage to the surface of the copper layer. Measures to stop are taken.

  Since the control device 15 here only needs to monitor the change in the output voltage value of the photoelectric element 14, it does not require a complicated system for capturing the entire beam profile and analyzing the change, and is simple and inexpensive. The change in the beam profile can be reliably detected by the configuration.

  The above is the case where the laser beam component from the slit portion 22 of each quadrant provided in the aperture 13 is received by one photoelectric element 14, but the photoelectric element 14 is disposed in association with the slit portion 22 of each quadrant. For example, it is possible to determine in which direction the central axis of the aspheric lens is deviated from the original laser optical axis, and based on this, the operation of adjusting the aspheric lens to an appropriate position can be performed, so that the adjustment operation can be facilitated. become.

  Next, the partial reflection mirror 10 a takes out a part of the laser beam that passes through the mask 4 and irradiates the workpiece 7 and applies the part to the photoelectric element 16. The control device 17 integrates the voltage value corresponding to the waveform of the vane pattern of the machining laser beam output from the photoelectric element 16 and monitors the amount of energy used for one drilling process. As a result, it is possible to detect at an early stage the occurrence of non-hole drilling due to a shortage of energy input to one hole drilling.

  Thus, according to this embodiment, in a laser processing apparatus that performs blind hole processing on a printed circuit board or the like using a top hat-shaped beam profile, among the top hat laser beam irradiated to the printed circuit board or the like, Since the top hat-shaped beam profile is collapsed due to the displacement of the aspherical lens, it is possible to monitor the presence or absence of high peaks by extracting only the areas that are prominently affected. It is possible to detect a processing defect in which damage is generated on the surface of the copper layer that is the bottom surface of the hole.

  And when a processing defect occurs due to damage to the copper layer surface, it is possible to detect the direction of misalignment of the aspheric lens, and based on this, the work to adjust the aspheric lens to an appropriate position can be performed quickly. Measures can be taken to avoid the occurrence of similar defects.

  In addition, since the energy amount of the entire top hat laser beam irradiated onto the printed circuit board or the like can be monitored, occurrence of unholed processing due to insufficient energy amount can be detected at an early stage.

  As described above, the laser beam profile measuring apparatus according to the present invention is useful for monitoring the presence or absence of a high peak in a top hat-shaped beam profile with a simple and inexpensive configuration. It is suitable for mounting on a laser processing apparatus using a beam profile.

It is a block diagram which shows the structure of the laser processing apparatus equipped with the profile measurement apparatus of the laser beam by one Embodiment of this invention. It is a figure which shows the form example of the aperture shown in FIG. 1 defined based on the experimental result shown in FIG. FIG. 5C shows a result of an experiment in which a van pattern of a laser beam in a state where a locally high peak is generated is taken out with a mask and irradiated to acrylic, and a change mode of a high peak generation position is examined. FIG. It is a conceptual diagram which shows the structural example of the conventional laser processing apparatus. 5A and 5B are schematic diagrams for explaining various aspects of the intensity distribution (profile) of a laser beam formed on the mask shown in FIG. 4, and FIG. 5A shows a Gaussian distribution shape formed when there is no top hat optical system. (B) shows a top hat shape formed when a top hat optical system is provided, and (c) shows a state in which a region having a locally high peak is generated on the top hat shape. It is a schematic diagram explaining the processing state at the time of processing with the top hat shape laser beam which has a locally high peak shown in Drawing 5 (c).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser oscillator 2 Top hat optical system 3 Movable lens 4 Mask 5 Galvano mirror 6 f (theta) lens 7 Work 8, 11 Total reflection mirror 9a, 10a Partial reflection mirror 12 Lens 13 Aperture 14, 16 Photoelectric element 15, 17 Control apparatus

Claims (8)

An aperture having an intensity distribution disposed on the optical path of a laser beam having a top hat shape, and an arcuate opening provided at a position where the laser beam in a high peak region generated on the top hat shape is transmitted;
A beam profile measuring apparatus comprising: a first measuring unit that measures the intensity of a laser beam that has passed through the aperture and determines whether or not there is an intensity exceeding a certain value. A spectroscopic means for splitting the laser beam having an intensity distribution in a top-hat shape in two directions and guiding one of the laser beams to the aperture;
Measure the intensity of the other laser beam split by the spectroscopic means and shaped into a predetermined shape with a mask whose optical distance from the laser light source is located at the same position as the aperture. The beam profile measuring device according to claim 1, further comprising: a second measuring unit that determines an energy amount of the laser beam that passes through the mask.   The beam profile measuring apparatus according to claim 1, wherein the optical system that forms a laser beam having a top hat shape in intensity distribution includes an aspheric lens.   The arc-shaped opening provided in the aperture is provided at a position where the laser beam in the high peak region generated on the top hat shape is transmitted when the center axis of the aspherical lens is deviated from the laser beam optical axis. 4. The beam profile measuring device according to claim 3, wherein the beam profile measuring device is provided. A laser oscillator that emits a laser beam, a top hat optical system that shapes the intensity distribution of the laser beam emitted from the laser oscillator into a top hat shape, and a workpiece that is irradiated with the laser beam that has passed through the top hat optical system A laser comprising a mask for shaping into a shape suitable for the above, a galvano mirror for two-dimensionally scanning the laser beam that has passed through the mask, and an fθ lens for condensing and irradiating the laser beam from the galvano mirror on the workpiece In processing equipment,
A first spectroscopic unit that splits the laser beam that has passed through the top hat optical system in two directions and guides one of the laser beams to the mask;
An optical distance from the laser oscillator is disposed at the same position as the mask on the optical path of the other laser beam dispersed by the first spectroscopic means, and a laser beam in a high peak region generated on the top hat shape. An aperture provided with an arc-shaped opening at a position where it passes through;
1. A laser processing apparatus comprising: a first measuring unit that measures the intensity of a laser beam that has passed through the aperture and determines whether or not an intensity exceeding a certain value exists. A second spectroscopic unit that splits the laser beam that has passed through the mask in two directions and guides one of the laser beams to the galvanometer mirror;
And a second measuring means for measuring the intensity of the other laser beam split by the second spectroscopic means and judging whether the energy amount of the laser beam transmitted through the mask is excessive or insufficient. The laser processing apparatus according to claim 5.   The laser processing apparatus according to claim 5, wherein the top hat optical system includes an aspheric lens.   The arc-shaped opening provided in the aperture is provided at a position where the laser beam in the high peak region generated on the top hat shape is transmitted when the center axis of the aspherical lens is deviated from the laser beam optical axis. The laser processing apparatus according to claim 7, wherein the laser processing apparatus is provided.

Images