Printed circuit board laser processing method and printed circuit board laser processing machine

Abstract

To provide a laser processing method of a printed circuit board which effectively uses a laser oscillation machine and is excellent in the processing performance and the quality, and a laser processing machine of the printed circuit board.SOLUTION: Provided is a laser processing method for performing laser processing on a printed circuit board by using a laser oscillator 1 that oscillates a laser by applying an RF pulse, including continuing laser oscillation by restarting an RF pulse application while a laser after completing the RF pulse application is output, cutting off the continuously oscillated laser 2 for a desired time, and performing laser processing on the printed circuit board.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laser processing method and machine for printed circuit boards that are suitable for forming blind holes (hereinafter simply referred to as holes or BHs) in an insulating layer made of ABF material or PET-attached ABF material built up on a copper layer during the manufacturing process of a package board. [Background technology]

[0002] In conventional build-up printed circuit boards, an insulating layer (hereinafter simply referred to as "insulating layer") made of a resin containing glass fiber or filler and a copper layer are stacked on top of each other with the insulating layer sandwiched between them, and 40 to 120 μm holes are drilled using a laser for interlayer connection, connecting the surface copper layer with the underlying copper layer by plating.

[0003] First, the configuration of a conventional laser processing machine will be described. FIG. 9 is a diagram showing the configuration of a conventional two-head laser processing machine. A carbon dioxide laser oscillator 1 (hereinafter referred to as the laser oscillator 1) outputs a pulsed linearly polarized laser beam 2. A beam diameter adjustment device 3, located between the laser oscillator 1 and a beam splitter 4, is a device for adjusting the energy density of the laser beam 2, and adjusts the energy density of the laser beam 2 by changing the outer diameter of the laser beam 2 output from the laser oscillator 1. In other words, the energy of the laser beam 2 does not change before or after the beam diameter adjustment device 3. Therefore, the laser beam 2 emitted from the beam diameter adjustment device 3 can be regarded as the laser beam 2 output from the laser oscillator 1, and therefore, hereinafter, the laser oscillator 1 and the beam diameter adjustment device 3 will be collectively referred to as a laser output device 1A. Note that the beam diameter adjustment device 3 may not be used in some cases. A beam splitter 4 is disposed between the beam diameter adjustment device 3 and the polarization conversion device 5A. The beam splitter 4 splits the laser 2 into two perpendicular beams, laser 2A and laser 2B. Laser 2A is supplied to a first processing head A (not shown), and laser 2B is supplied to a second processing head B (not shown). Here, the first processing head A and the second processing head B have the same configuration, so hereinafter, those with the same configuration (reference numerals 5 to 12) are distinguished by adding suffixes A and B, and only the case of the first processing head A will be described. The polarization conversion device 5A converts the linearly polarized laser beam 2A into a circularly polarized laser beam 6A. The polarization conversion device 5A is equipped with a reflected light blocking mechanism (details omitted) that blocks the laser beam 6A reflected from the processing area during processing, thereby preventing damage to the laser oscillator 1 caused by the laser beam 6A reflected from the processing area. A plate 7A, located between the polarization conversion device 5A and the galvanometer mirror 10Aa, is made of a material (e.g., copper) that does not transmit the laser beam 6A. It has multiple selectable apertures (windows, in this case, circular through-holes) 8A formed at predetermined positions. The plate 7A is driven by a drive device (not shown) to position the axis of the selected aperture 8A coaxially with the axis of the laser beam 6A. The galvanometer device 9A is composed of a pair of galvanometer mirrors 10Aa and 10Ab, and is rotatable around the axis indicated by the arrow in the figure, allowing the reflecting surface to be positioned at any angle. The fθ lens (condensing lens) 11A is held by a machining head A (not shown). The galvanometer mirrors 10Aa and 10Ab and the fθ lens 11A constitute an optical axis positioning device that positions the optical axis of the laser 6A at a desired position on a printed circuit board 12A. The scan area (i.e., machining area) 12A, determined by the rotation angle of the galvanometer mirrors 10Aa and 10Ab and the diameter of the fθ lens 11A, is approximately 50 mm x 50 mm. The workpiece, a printed circuit board 13 made of a copper layer and an insulating layer, is fixed to an XY table 14. The first machining head A and the second machining head B may machine printed circuit boards 13 with the same pattern or may machine printed circuit boards 13 with different patterns. The control device 20 controls the laser oscillator 1, the beam diameter adjusting device 3, the driving devices for the plates 7A and 7B, the galvanometer mirrors 10Aa, 10Ab, 10Ba, and 10Bb, and the XY table 14A (and possibly also the XY table 14B) according to the input control program.

[0004] When drilling holes, the XY tables 14A and 14B are moved to position the designated machining areas 12A and 12B opposite the fθ lenses 11A and 11B, respectively, and then holes are drilled into all of the copper layers in the machining areas 12A and 12B by a single beam irradiation (i.e., one pulse irradiation), and then the insulating layer is processed by one or more pulse irradiations to complete the holes in the machining areas 12A and 12B.

[0005] FIG. 10 is a diagram showing the setting time of the galvanometer mirror and the laser irradiation time, where the horizontal axis represents time, and (a) is for processing head A, and (b) is for processing head B. The time that takes longer to position the galvanometer mirrors 10Aa and 10Ab of head A at a certain processing location is called the galvanometer time GA of head A, and the time that takes longer to position the galvanometer mirrors 10Ba and 10Bb of head B at a certain processing location is called the galvanometer time GB of head B. L1 is the time for one laser irradiation. If the processing contents of the printed circuit boards 13A and 13B processed by processing head A and processing head B are the same and the galvano times GA and GB are the same, laser 2 can be supplied to the two processing heads simultaneously. However, if the processing contents of processing head A and processing head B are different and the galvano times GA and GB are different, in order to supply laser 2 to processing head A and processing head B simultaneously, it is necessary to match the galvano time to the longer one. In other words, GA1<GB1、GA2> If the waiting time is GB2, a waiting time of (GB1-GA1) occurs for machining head A, and a waiting time of (GA2-GB2) occurs for machining head B. This reduces the overall machining efficiency. Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, as circuit boards have become thinner, there has been an increase in the need to drill holes in insulating layers that have no copper layer on the surface of package boards. In such cases, the diameter of the holes to be drilled is 60 μm or less, and the power required for drilling is around 20 W. Next, an actual processing example will be described. 11 is a diagram illustrating an example of conventional laser irradiation, where the vertical axis represents output power and the horizontal axis represents time. The upper part shows the on / off state of an RF pulse (hereinafter simply referred to as RF) that excites the laser medium of the laser oscillator 1. For example, to drill a 60 μm hole in an insulating layer, a laser is irradiated using output curve A1, which has an output of 20 W for a 20 μs RF application time, and then the same laser is irradiated again in the next pulse period. In other words, the processing time in this case is 180 μs, which is the sum of the 100 μs pulse period of the first pulse irradiated after the galvanometer mirror is positioned and the 80 μs laser duration of the second 100 μs pulse period following the first pulse (including the 60 μs time it takes for the laser to disappear after the RF is stopped). The reason the laser can be irradiated twice consecutively is because the insulating layer has a low processing threshold and is approximately 30 μm thick, which reduces the amount of heat accumulated in the processed area, unlike when machining copper layers, which have a high processing threshold, or insulating layers whose thickness exceeds 60 μm after copper layer processing. As shown in the figure, the output curve A1 has a first peak output (the output duration is short) immediately after RF application. This first peak output is about half the second peak output during the rated RF application time (20 μs in this case). After the RF application is stopped, the energy stored in the laser medium in the laser oscillator is output as laser light. In the illustrated example, the duration of laser light based on the laser medium in the laser oscillator is about 60 μs.

[0007] However, the above processing causes the following problems. (1) Due to the influence of the first peak output, the diameter of the entrance of the drilled hole may become 2 to 3 μm larger. (2) The diameter of the machined hole varies due to fluctuations in the laser output. Here, the above-mentioned fluctuation in laser output will be explained with reference to the drawings. Figure 12 shows the output fluctuation of the second peak output. (a) shows the case where the pulse frequency is 1 to 5 kHz, and (b) shows the case where the pulse frequency is 1 to 10 kHz. For example, if the spacing between the holes to be drilled is approximately the same, the second peak output hardly fluctuates. However, the spacing between the holes to be drilled is not uniform because it is determined by the spacing between the components mounted on the printed circuit board and the position of the holes connected to the underlying copper layer. As a result, the output power accumulated in the laser medium changes due to changes in the laser excitation interval (i.e., duty). As shown in Figure 12(a), the output power fluctuates by approximately ±3% when the frequency is 1 to 5 kHz, and as shown in Figure 12(b), the output power fluctuates by approximately ±5% when the frequency is 1 to 10 kHz. This causes variations in the diameter of the drilled holes. (3) Even during the RF stop period following the 20 μs RF application time, the energy stored in the laser medium is irradiated onto the processing area for approximately 60 μs after the RF is stopped, causing the temperature of the processing area to rise. Even if the temperature rise in the processing area is lower than the processing threshold of the insulating layer, if this period continues for 10 μs or more, the insulating layer at the bottom and wall of the hole becomes more likely to be carbonized, resulting in a decrease in the processing quality of the hole. As explained above, it is desirable to make the diameter of the holes to be machined uniform and to prevent deterioration in the quality of the insulating layer.

[0008] An object of the present invention is to provide a laser processing method and machine for printed circuit boards that are excellent in processing efficiency and quality by effectively utilizing a laser oscillator. [Means for solving the problem]

[0009] In order to solve the above problems, the laser processing method for a printed circuit board according to claim 1 comprises: By restarting the application of RF pulses during the laser output period after the application of RF pulses has ended, laser oscillation continues. RF pulses of a predetermined frequency are applied continuously for a period determined by the rating of the carbon dioxide laser oscillator from the start of each cycle, so that the output value of the pulses in each cycle is equal to an average output Wav (wherein the average output Wav is the value obtained by dividing the integral value of the output in any pulse cycle when the carbon dioxide laser oscillator is continuously oscillated at the rating by the pulse cycle), By controlling the application time of the RF pulse and the off time of the RF pulse, a sawtooth pulse in which the output of one cycle of the pulse changes in a sawtooth pattern is generated and processed.

[0010] In order to solve the above problems, the present invention provides the Laser processing equipment for printed circuit boards By restarting the application of RF pulses during the laser output period after the application of RF pulses has ended, laser oscillation continues. RF pulses of a predetermined frequency are applied continuously for a period determined by the rating of the carbon dioxide laser oscillator from the start of each cycle, so that the output value of the pulses in each cycle becomes the average output Wav; The feature of this method is that the output of one cycle of pulse is processed into a sawtooth pulse by controlling the application time of the RF pulse and the off time of the RF pulse.

[0011] To solve the above problems, The laser processing device for printed circuit boards according to claim 3 is The system is characterized by being provided with a plurality of machining heads, configured to distribute laser light from one laser oscillator to each of the plurality of machining heads, and having a control device that, when the positioning of any one of the machining heads is completed, supplies laser light to that machining head without taking into account the positioning status of the other machining heads. [Effects of the Invention]

[0014] This not only makes it possible to make the diameter of the holes uniform and improve the quality of the hole wall surface, but also improves processing efficiency. Furthermore, since the laser is continuously oscillated in a stable manner, when laser is supplied to multiple heads, the required laser can be supplied to each head independently of the other heads, thereby improving processing efficiency as a laser processing machine. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a diagram illustrating elements of a sawtooth wave according to the present invention. [Figure 2] 10 is an example of an output waveform. [Figure 3] 10A to 10C are diagrams illustrating a procedure for generating a sawtooth wave according to the present invention. [Figure 4] 10A and 10B are diagrams illustrating an example of machining using a rectangular wave pulse of sawtooth n. [Figure 5] FIG. 10 is a diagram illustrating the energy spatial distribution of the output. [Figure 6] 1 is a configuration diagram of a two-head laser processing machine according to the present invention. [Figure 7] FIG. 10 is a diagram showing the setting time of the galvanometer mirror and the laser irradiation time. [Figure 8] FIG. 10 is an explanatory diagram of a rectangular wave pulse when processing an insulating layer containing a filler. [Figure 9] FIG. 1 is a diagram showing the configuration of a conventional two-head laser processing machine. [Figure 10] FIG. 10 is a diagram showing the setting time of the galvanometer mirror and the laser irradiation time. [Figure 11] FIG. 10 is a diagram illustrating an example of conventional laser irradiation. [Figure 12] FIG. 10 is a diagram showing output fluctuations of a second peak output. DETAILED DESCRIPTION OF THE INVENTION

[0016] FIG. 1 is a diagram illustrating the components of a sawtooth wave according to the present invention. Note that output curve C (fundamental pulse waveform) in the figure is an output curve with a rated duty of 60% (RF application time / pulse period. Hereinafter, "rated duty" will be simply referred to as "Dty"), a pulse period of 10 kHz, and a maximum output of 250 W, with the vertical axis representing the output power of the oscillated laser and the horizontal axis representing time. The upper part also shows the on / off state of the RF that excites the laser medium of laser oscillator 1. First, let us consider output curve C. When RF power is turned on at time T0, the laser bursts at time T1, reaches a first peak output Wj at time Tj, then decays until time Td, and then begins to increase again, reaching a second peak output of 250 W at time T2, 60 μs after RF application time from time T0. The output shown by the solid line during the RF application period is the sum of the output transferred to CO2 gas via the N2 gas laser medium by RF (the output shown by the dotted line around 60 μs in the figure) and the output directly excited by RF from CO2 gas (i.e., the output between the dotted and solid lines). Therefore, when RF application is stopped, the output directly excited by RF from CO2 gas becomes zero, and from time T2 onward, the energy stored in the N2 gas laser medium in the laser oscillator is output as laser light. The energy stored in the laser medium is output for approximately 60 μs after time T2.

[0017] The inventors have confirmed the following requirements through experiments and simulations. 1. Requirement 1 For example, when RF is applied with a Dty of 60% (pulse width of 60 μs) and a pulse period of 10 kHz, the output of the oscillated laser gradually increases and reaches a maximum at a pulse width of 60 μs, as shown in output curve C. Then, when the RF application is stopped, the output decays. When the laser is oscillated within the Dty range of the laser oscillator, the output rises along the same output curve (output curve C shown in the figure) even if the RF application time changes. That is, when oscillating at 10 kHz with a Dty of 40% (pulse width of 40 μs), the output rises along output curve C, reaches a maximum at a pulse width of 40 μs, and decays in the same way as in the above case. Similarly, when oscillating at 10 kHz with a Dty of 20% (pulse width of 20 μs), the output also rises along output curve C, reaches a maximum at a pulse width of 20 μs, and decays in the same way as in the above case.

[0018] 2. Requirement 2 In the case of a CO2 laser, when RF application begins at time T0, the laser starts oscillating at time T1 due to the excitation power accumulated in the laser medium, and the output power increases rapidly to reach the first peak output Wj at time Tj, after which it decays once (at time Td), and then increases again to reach the second peak output when RF application is stopped. In this case, it was found that time Td was 0.4 to 0.5 μs from time T0, and the output response (output change per unit time) Ws at time Td was almost constant even if Dty and pulse width changed.

[0019] 3. Requirement 3 When the RF application is stopped, the output power switches from 250 W to the residual power stored in the laser medium. The switching time is 0.4 to 0.5 μs, and the output power drops once, then rises slightly, and then decays. Hereafter, the output response when the output power switches is referred to as the output response Wc, and the output response when the output power rises slightly is referred to as the output response Wd. It was also found that the output response Wc remains almost unchanged even when Dty and pulse width are changed. Although the output response Wc and the output response Ws have different output directions, the magnitude of the output component is almost the same.

[0020] 4. Requirement 4 Figure 2 shows an example of an output waveform when the energy stored in the laser medium is reactivated by restarting RF application at the end of a pulse period. As shown in the figure, if there is residual power (Δz indicated by the diagonal lines in the figure, and the power at the start of RF application is ΔW, where ΔW>0) stored in the laser medium at the start of RF application, when excitation for the next (second) pulse period begins, the excited power is superimposed on the residual power, and the power increases with the output response Ws after 0.4 to 0.5 μs, but the first peak power Wj does not occur. Note that while the connection between the first and second pulse periods has been described here, when the process is repeated up to the nth pulse period, the power level generated by the output response Ws gradually increases, while the second peak power gradually decreases, but stabilizes within about 1 second. In the case of Figure 11 above, the residual energy stored in the laser medium becomes 0 before the second pulse period starts, so the output curve for the second pulse period is the same as the output curve for the first pulse period.

[0021] Here, the value obtained by dividing the integral value of the output of continuous oscillation with Dty 60% on output curve C (i.e., the total output output during the pulse period of 0 to 100 μs) by the pulse period of 100 μs is called the average output Wav. When Dty is kept constant, the average output Wav shown in Figure 1 remains almost constant over the pulse period range of 20 to 200 kHz. On the other hand, when the pulse frequency is kept constant, the average output Wav increases in proportion to Dty. Furthermore, the tangential output response Wr of the average output during the RF-on period of output curve C and the tangential output response Wf of the average output during the RF-off period of output curve C are values ​​specific to the average output. Note that FIG. 1 shows sawtooth waves of 100 kHz and 200 kHz, but details will be explained using FIG. 3.

[0022] FIG. 3 is a diagram illustrating a procedure for generating a sawtooth wave according to the present invention. In output curve C, setting Dty=Trf1 / tm (where tm is the pulse period, consisting of the RF application period Trf1 and the RF application stop period Trf0) determines the average output Wav. Even if the pulse period tm is shortened, as long as the ratio between the RF application period trf1 and the RF application stop period trf0 remains the same, Dty remains the same and the average output Wav also remains almost unchanged. Therefore, the sawtooth wave according to the present invention is generated based on the fundamental pulse waveform (output curve C above) and requirements 1 to 4 above.

[0023] The procedure for generating a sawtooth wave is as follows. Step 1) With the vertical axis as the output axis, set Dty, pulse period tm, average output Wav, upper limit output Wp, and lower limit output Wv. Here, the upper limit output Wp is the output level [J / s] at which the desired hole diameter is obtained with the irradiated pulse, and is set to a value according to the material's threshold. Also, the lower limit output Wv is the output level at the rise time of the output response Ws when the RF is on, for a sawtooth pulse with stable continuous oscillation. Step 2) With the horizontal axis as the time axis, the point on the lower limit output Wv at time t0 is designated Q1, and the point on the lower limit output Wv at time t2, which is the pulse period, is designated Q6. Then, the output response Ws is plotted starting from point Q1, and the end point of the output response Ws is designated point Q2. Step 3) Connect point Q2 to point Q3 on the upper limit output Wp at time t1 with the output response Wr. Note that time t1 is the end point of Trf1 (the start point of Trf0). Step 4) Plot the output response Wc starting from point Q3, and set the end point of the output response Wc as point Q4. Step 5) Plot a small output response Wd on the extension line connecting points Q1 and Q4, and set the end point as point Q5. Step 6) Connect points Q5 and Q6 with the output line segment Wf. That is, point Q5 is the intersection of the extension line connecting points Q1 and Q4 and the output response Wf, which ends at point Q6. By following the above steps, the sawtooth wave added to the lower limit output Wv is completed. Hereinafter, the sawtooth pulse obtained by superimposing the polygon formed by the above procedure on the lower limit output Wv will be referred to as a "sawtooth pulse." As explained in paragraph 0024, the output of the laser oscillator stabilizes after 1 second, and as long as the laser oscillator is in operation, the fluctuation range of the average output Wav and upper limit output Wp is approximately ±1%. Also, as shown in the figure, if points Q1 and Q4 are connected by a dotted line, the output surrounded by the rectangle Q1Q2Q3Q4 corresponds to the output when CO2 gas is directly excited by RF as described in paragraph 0016. FIG. 1 shows one 100 KHz sawtooth pulse and one 200 KHz sawtooth pulse created by the above procedure.

[0024] Here, if Dty is kept constant and the pulse period tm is changed, the output responses Ws and Wc do not change. On the other hand, the output responses Wr, Wd, and Wf change according to the pulse period tm, but the average output Wav changes very little. Also, if the pulse period tm is kept constant and Dty is changed, the output responses Ws and Wc change very little, but the output responses Wr, Wd, and Wf change. In this case, as Dty decreases, the increase rate (rise) of the output responses Wr and Wd becomes steeper, and the decrease rate (fall) of the output response Wf becomes gradual. On the other hand, as Dty increases, the increase rate (rise) of the output responses Wr and Wd becomes gradual, and the decrease rate (fall) of the output response Wf becomes steeper. And although the average output changes according to Dty, each is determined as a unique value. Therefore, by setting the pulse period tm, RF application time trf1, and RF application stop time trf0 within the Dty range, the waveform and output of the sawtooth pulse can be controlled. In actual machining, the waveform generation process described above is carried out continuously, and n sawtooth pulses (n is an integer greater than or equal to 1) are formed. Hereinafter, a pulse consisting of n sawtooth pulses supplied during machining will be collectively referred to as an "n-sawtooth rectangular wave pulse."

[0025] FIG. 4 is a diagram for explaining an example of processing using a rectangular wave pulse with sawtooth n, where the vertical axis represents output and the horizontal axis represents time. Here, assuming the hole to be machined is the same as that described in Figure 11 above, in the conventional technology, machining was performed using two pulses with a pulse frequency of 10 kHz, resulting in a laser irradiation time of 20 μs twice, and a machining time of 180 μs, which is the sum of the pulse period of the first pulse (100 μs), the RF application time of the second pulse (20 μs), and the non-excitation time of 60 μs. In contrast, in the present invention, when machining is performed using two rectangular pulses with a pulse frequency of 100 kHz, which provides the same pulse energy as the conventional technology, the pulse period is not affected, so the interval between the two rectangular pulses can be set arbitrarily. If the interval between the two rectangular pulses with the two sawtooth teeth 2 is 60 μs, the machining time is 100 μs. Therefore, according to the present invention, the machining time can be shortened by 80 μs compared to the conventional technology.

[0026] Next, the present invention and the prior art will be described with reference to the shape of the drilled hole. Figure 5 illustrates the spatial distribution of output energy, with (a) for the present application and (b) for the prior art. The vertical axis represents the normalized energy level and processing depth, and the horizontal axis represents the diameter of the hole. In the figure, Ds represents the beam spot diameter at the processing area, DR represents the target hole diameter, DR1 and DR' represent hole diameters smaller than DR, and DB and DB' represent the hole bottom diameters. Furthermore, Lv0 represents the position of energy level 0, Lv1 represents the surface position of the insulating layer, Lv2 represents the bottom position of the insulating layer, and k represents the processing threshold of the insulating layer. Also, ep denotes the energy distribution at output Wp, ev denotes the energy distribution at output Wv, eav denotes the energy distribution at average output Wav, 1e denotes the energy distribution of the first pulse, and 2e denotes the energy distribution of the second pulse. Note that the outputs Wp, Wv, and average output Wav are as shown in Figure 3. The machining process of the present invention will be described below in relation to the diameter of the machined hole. The energy distribution during the RF application period trf1 when the machining diameter increases is referred to as the diameter-increasing energy distribution, and the energy distribution during the RF application stop period trf0 when the machining diameter decreases is referred to as the diameter-decreasing energy distribution. Upon RF application, machining begins with an output response Ws superimposed on the output Wv, with an output rise time of approximately 0.4 μs. Then, machining is performed using the machining diameter-increasing energy distribution of the output response Ws, and after the elapse of time trf1, the desired hole entrance diameter is formed. Upon RF application stop, further machining is performed using the machining diameter-decreasing energy distribution output response Wc, the machining diameter slight increase output response Wd, and the machining diameter-decreasing energy distribution output response Wf. In the above processing process, processing is performed alternately with spot diameters DR and DB, and DR' and DB'. The power rise at the start of processing is steeper than with conventional pulses, and the irradiation time is short. In addition, the energy distribution diameter after RF application is stopped is smaller and moves away from the hole entrance and hole sidewalls, reducing heat conduction to the hole entrance and hole sidewalls during insulating layer processing. As a result, the thermal impact of the insulating layer on the hole wall surface is reduced, improving hole quality. Furthermore, because processing is performed with continuous sawtooth pulses, laser irradiation after RF application is stopped, which is not involved in processing, is not performed as in conventional technology. Therefore, the quality of the hole entrance and hole sidewalls is not degraded. Furthermore, since there is no influence from the first peak output, the hole entrance diameter does not widen.

[0027] FIG. 6 is a diagram showing the configuration of a two-head laser processing machine according to the present invention, and the same components as those in FIG. 8 or components having the same functions are designated by the same reference numerals and detailed explanations thereof will be omitted. The laser oscillator 1 outputs a continuous linearly polarized sawtooth laser beam 2 with a frequency of 50 kHz or higher by setting the application time and pause time of the high-frequency RF that drives the laser oscillation. The beam diameter adjustment device 3, located between the laser oscillator 1 and the beam splitter 4, is a device for adjusting the energy density of the laser 2, and adjusts the energy density of the laser 2 by changing the outer diameter of the laser 2 output from the laser oscillator 1. In other words, the energy of the laser 2 does not change before or after the beam diameter adjustment device 3. Therefore, the laser 2 output from the beam diameter adjustment device 3 can be considered to be the laser 2 output from the laser oscillator 1, and therefore, hereinafter, the laser oscillator 1 and the beam diameter adjustment device 3 will be collectively referred to as the laser output device 1A. Note that the beam diameter adjustment device 3 may not be used in some cases. Between the beam splitter 4 and the polarization conversion device 5A is disposed an AOM 50A driven by a driver 61A. The AOM 50A splits the laser 2A into a laser 2A1K of 1st order light and a laser 2A0 of 0th order light, and by changing the split ratio (aperture), adjusts the output of the laser 2A1K used for processing. The laser 2A0 not used for processing is disposed of in a dumper (not shown) so as not to diffuse into the surrounding area.

[0028] This laser processing machine is configured so that second head B can be positioned in the X direction relative to fixed first head A by a second head B moving device (not shown), and the position of second head B can be expanded by a maximum distance S relative to first head A. Mirrors 31 and 34 are fixed in predetermined positions, and mirrors 32 and 33 are supported by a mirror moving device (not shown) and can be freely positioned in the X direction. Mirrors 31 to 34 are arranged so that the axis of aperture 8B coincides with the center of galvanometer mirror 10Ba regardless of the position of mirrors 32 and 33 in the X direction. Controller 20 controls laser oscillator 1, beam diameter adjusting device 3, AOM drivers 61A and 61B, drive devices for plates 7A and 7B, galvanometer mirrors 10Aa, 10Ab, 10Ba, and 10Bb, XY table 14A (including XY table 14B in some cases), a second head B moving device, and a mirror moving device (not shown).

[0029] The processing procedure will be explained below. Although the processing content differs for each head, the operation is essentially the same, so the case of the first head A will be explained. When a command to start machining is issued, the control device 20 drives the movement device of the second head B to move the second head B to a specified position. Next, the XY table is controlled to position the first head A at the machining position, and the galvanometer mirrors 10Aa and 10Ab are positioned at the initial machining positions and wait. The movement device of the second head B (not shown) is then operated to move the second head B by a distance s relative to the first head A. Then, the mirror movement device (not shown) is operated to move the position of the mirror 32 by a distance s / 2 in the movement direction of the head 2. As a result, the distance between the aperture 8 and the galvanometer mirror 10Ba is always constant, so the size of the image of the aperture 8 can be kept constant regardless of the position of the second head B.

[0030] First, the laser oscillator 1 is operated, and after a predetermined waiting time has elapsed, the processing program is started to commence processing. The reason for providing a waiting time here is that the output of the laser oscillator 1 becomes unstable until it reaches a thermal equilibrium state, and the waiting time is approximately 1 to 2 seconds. After the waiting time has elapsed, the control device 20, in accordance with a pre-entered machining program, causes the laser oscillator 1 to emit a sawtooth-shaped laser beam 2 (hereinafter simply referred to as laser 2). The beam diameter of the laser beam 2 is adjusted by the beam diameter adjustment device 3, and the beam is split into laser beams 2A by the beam splitter 4, which then enter the AOM 50. The AOM 50 discards the laser beam 2A in a dumper until it receives an operation command from the control device 20. When the control device 20 receives a positioning completion signal from the galvanometer mirror 10Aa or 10Ab, whichever was positioned later, the control device 20 operates the AOM 50A via the driver 61A, causing the laser beam 2A to output a rectangular wave pulse 2A1K consisting of n sawtooth pulses attenuated to a pre-specified output. The rectangular wave pulse 2A1K is positioned by the galvanometer mirrors 10Aa and 10Ab, and is incident on the specified position on the printed circuit board 13A, drilling a hole in the printed circuit board 13A. As in the conventional case, the above drilling operation is repeated until the specified machining is completed. In the above processing, the laser oscillator 1 turns on and off the RF at a predetermined cycle and pulse cycle, thereby causing the laser 2 to be output continuously from the start to the end of processing.

[0031] 7A and 7B are diagrams illustrating the setting time of the galvanometer mirror and the laser irradiation time in the present invention, where (a) shows the case of processing head A and (b) shows the case of processing head B. The horizontal axis in the diagram represents time. As shown in the figure, sawtooth pulse lasers 2A and 2B are constantly output during machining. For the first head A, once galvano time GA1 or GA2 is completed, AOM 50 irradiates the machining area with a square-wave pulse 2A1K consisting of the required n sawtooth pulses to drill a hole. In this case, first head A continues its work without considering the galvano times GB1 and GB2 of second head B. Similarly, second head B continues its work without considering the galvano times GA1 and GA2 of first head A. As a result, there is no waiting time for each head, and machining efficiency can be improved by 20 to 30% compared to conventional methods. Note that, according to a clock in a device not shown, once the positioning of the galvano mirror is completed, AOM 50 controls its output to coincide with the start time of RF application of the first sawtooth pulse to prevent any missing or missing sawtooth n square-wave pulses supplied to the machining area.

[0032] The sawtooth configuration according to the present invention will now be described in more detail. 8 is an explanatory diagram of a square wave pulse when processing an insulating layer containing a filler (reinforcing material), where the horizontal axis is time, and t0 to tn9 are times relative to t0. Also, TH is a square wave pulse with one sawtooth n. Here, the top row shows the operation of the AOM, with A being 100% open and mA being m% open. The middle row shows the RF on / off, with tm being the pulse period, trf1 being the RF on time, and trf0 being the RF off time. The bottom row shows the output, with Wpf in the diagram being the upper limit output power that can process the filler in the insulating layer, and Wpr being the upper limit output power that can process the resin in the insulating layer. In the case of Figure 1(a), the laser diameter is increased during the RM-on period to mainly process the filler, and the laser diameter is reduced during the RM-off period, which allows the gas and processing debris generated by processing to be quickly removed from the processing area, improving the processing quality of the hole wall surface and hole bottom.In addition, in the case of Figure 1(b), as in the case of Figure 1(a), the gas and processing debris generated by processing can be quickly removed from the processing area, improving the processing quality of the hole wall surface and hole bottom. Figure 1(c) is a modified version of the portion enclosed by the dotted line in Figure 1(a), and is an example of waveform control in which the AOM is turned on for a period of time ta, starting midway through the rise in output of the RM during the on-period in Figure 1(a) (time td1 in the figure). In this way, machining is performed with a high average output Wavh during the rising output portion, resulting in uniformity in the hole entrance and sidewall, improving hole quality. Also, FIG. 1(d) is used when it is desired to create a slope in the depth direction of the hole, for example.

[0033] Next, a processing example will be described. The results of applying the sawtooth n square wave pulse shown in Figure 8(a)(b)(c) and the conventional pulse in Figure 4(b) to an insulating layer containing filler for packaging (ABF material from Ajinomoto Co., Ltd., approximately 30 μm thick) with a processing spot of the same diameter of 60 μm are as follows: Note that this figure shows the shape of the sawtooth pulse, but does not show the sawtooth n square wave pulse used in processing. In the case of Figure 8(a), with two sawtooth 3 square wave pulses at a frequency of 100 kHz, Dty 60% (trf1 = 6 μs, trf0 = 4 μs), Wpf = 20 W, the AOM opening was 100% during period trf1 and 0% during period trf0, the hole entrance diameter was approximately 62 μm and the hole (bottom diameter / entrance diameter) ratio was approximately 80%. Note that when the AOM opening was 0%, the output of the shaded area in Figure 8(a) was 0. In the case of Figure 1(b), when two sawtooth 3 rectangular wave pulses with a frequency of 100 kHz, Dty 60% (trf1 = 6 μs, trf0 = 4 μs), Wpf = 20 W, the AOM opening of the first sawtooth was 100%, the AOM opening of the second sawtooth was 0%, and the AOM opening of the third sawtooth was 100%, the hole entrance diameter was approximately 60 μm and the hole (bottom diameter / entrance diameter) ratio was approximately 80%. In the case of Figure 1(c), when a square wave pulse with two sawtooth teeth 3 at a frequency of 100 kHz, Dty 60%, td1 = 6 μs with an AOM opening of 0%, and ta = 4 μs with an AOM opening of 100%, the hole entrance diameter was approximately 60 μm and the hole (bottom diameter / entrance diameter) ratio was approximately 81%. In the cases of (a), (b), and (c) in the same figure, there was almost no carbonization of the resin on the surface of the copper layer at the bottom of the hole. Incidentally, when machining with the conventional technology shown in Figure 11 using a pulse width of 20 μs, a pulse frequency of 10 kHz, and four pulses, the hole entrance diameter was approximately 63 μm, and the hole (bottom diameter / entrance diameter) ratio was approximately 78%. Carbonized resin adhesion was also observed on the copper surface at the bottom of the hole. Furthermore, when machining was performed with increased output using pulses in which the first peak power Wj was higher than the second peak power WP, the diffracted light from the first peak power Wj caused the hole entrance diameter to become approximately 65 μm, and ring-shaped damage occurred around the hole entrance.

[0034] Furthermore, the optimum values ​​of output responses Ws, Wc, Wr, Wd, and Wf differ depending on the material of the workpiece. Therefore, by optimizing the values ​​of output responses Ws, Wc, Wr, Wd, and Wf according to the material of the workpiece, it is possible to improve the machining quality and machining speed.

[0035] In actual machining, the output levels Wp and Wv and the output responses Ws, Wc, Wr, Wd, and Wf are known in advance for each workpiece. The maximum output of the laser oscillator when the rated duty and pulse period are determined is also known in advance. Furthermore, the aperture diameter appropriate for the hole diameter to be machined is also known. Therefore, when machining a new material, for example, the levels Wp and Wv are first provisionally determined based on previous data, and the hole diameter measured in a test is compared with the target hole diameter to determine the power level Wp. Next, machining is performed using sawtooth pulses n, and the value of n is determined based on the depth of the hole. Since increasing n can cause quality degradation due to heat in the insulation layer, if n is large, n is divided and multiple sawtooth pulses m are used, with a period between each square wave pulse allowed for cooling of the machined area.

[0036] In the two-head laser processing machine shown in Figure 6, if the output of laser oscillator 1 is 250 W, the average output is 125 W, so it is split by beam splitter 4 and 62.5 W is supplied to each head. Therefore, as explained in paragraph 0033, if Wpf = 20 W, either head A or B can be used for processing. However, for example, when processing resin with a carrier PET film, Wpf = 70 W is required. Therefore, if Wpf = 70 W is required, the output of laser oscillator 1 in Figure 6 must be set to, for example, 500 W.

[0037] Furthermore, the above description has been given using as an example a laser oscillator having output characteristics of a fundamental wave pulse waveform (output curve C, output curve A1) in which the first peak output output immediately after RF application is smaller than the second peak output when RF application is stopped, but the present application can also be applied to a laser oscillator having output characteristics of a fundamental wave pulse waveform in which the first peak output output immediately after RF application is larger than the second peak output when RF application is stopped. [Explanation of symbols]

[0038] 1. Laser oscillator 2. Laser

Claims

1. By restarting the application of RF pulses during the laser output period after the application of RF pulses has been terminated, the laser oscillation continues. RF pulses of a predetermined frequency are applied continuously for a period determined by the rating of the carbon dioxide laser oscillator from the start of each cycle, so that the output value of the pulses in each cycle is equal to an average output Wav (wherein the average output Wav is the value obtained by dividing the integral value of the output in any pulse cycle when the carbon dioxide laser oscillator is continuously oscillated at the rating by the pulse cycle), A laser processing method for printed circuit boards, characterized in that a sawtooth pulse in which the output of a pulse in one cycle changes in a sawtooth pattern is generated by controlling the application time of an RF pulse and the off time of the RF pulse.

2. 2. The laser processing method for printed circuit boards according to claim 1, further comprising a control device that is configured to provide a plurality of processing heads, distribute a laser beam from a single laser oscillator to each of the plurality of processing heads, and, when positioning of any of the processing heads is completed, supply a laser beam to that processing head without taking into account the positioning status of the other processing heads.

3. By utilizing the fact that laser oscillation continues by restarting the application of RF pulses during the period when the laser is being output after the application of RF pulses has been terminated, RF pulses of a predetermined frequency are applied continuously for a period determined by the rating of the carbon dioxide laser oscillator from the start of each cycle, so that the output value of the pulses in each cycle is equal to an average output Wav (wherein the average output Wav is the value obtained by dividing the integral value of the output in any pulse cycle when the carbon dioxide laser oscillator is continuously oscillated at the rating by the pulse cycle), A laser processing device for printed circuit boards characterized in that the output of one pulse cycle is processed into a sawtooth pulse by controlling the application time of the RF pulse and the off time of the RF pulse.

4. 4. The laser processing device for printed circuit boards according to claim 3, further comprising a control device that is configured to have a plurality of processing heads, distribute a laser from one laser oscillator to each of the plurality of processing heads, and, when positioning of any of the processing heads is completed, supply a laser to that processing head without taking into account the positioning status of the other processing heads.

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