KR102830817B1 - Laser processing method for printed circuit board and laser processing machine for printed circuit board - Google Patents

Abstract

[assignment]
To provide a method for laser processing a printed circuit board and a laser processing machine for a printed circuit board, which have excellent processing efficiency and quality, by effectively using a laser generator.
[Solution]
In a laser processing method of a printed circuit board, laser processing is performed using a laser generator (1) that oscillates a laser by applying an RF pulse.
By resuming the application of the RF pulse while the laser is being output after the application of the RF pulse has ended, the laser oscillation is continued, and the continuously oscillating laser (2) is cut off for a desired period of time to perform laser processing of the printed circuit board.

Description

Laser processing method for printed circuit board and laser processing machine for printed circuit board {LASER PROCESSING METHOD FOR PRINTED CIRCUIT BOARD AND LASER PROCESSING MACHINE FOR PRINTED CIRCUIT BOARD}

[0001]

The present invention relates to a method for laser processing of a printed circuit board, and a laser processing machine for a printed circuit board, which is suitable for forming a blind hole (a blind hole; hereinafter, simply referred to as a hole or BH) in an insulating layer made of an ABF material or a PET-attached ABF material built up on a copper layer in a manufacturing process of a package substrate.

[0002]

A conventional build-up type printed circuit board laminates a copper layer and an insulating layer (hereinafter simply referred to as an "insulating layer") formed of a resin containing glass fibers or fillers on top of a copper layer, with the insulating layer interposed between them, and uses a laser to process holes of 40 to 120 ㎛ for interlayer connection by plating the copper layer on the surface and the copper layer on the lower layer.

[0003]

First, the configuration of a conventional laser processing machine is explained.

Figure 9 is a configuration diagram of a conventional two-head type laser processing machine.

A carbon dioxide laser generator (1) (hereinafter referred to as a laser generator (1)) outputs a pulsed linearly polarized laser (2). A beam diameter adjustment device (3) arranged between the laser generator (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 generator (1). That is, the energy of the laser (2) does not change before and after the beam diameter adjustment device (3). Therefore, the laser (2) output from the beam diameter adjustment device (3) can be regarded as the laser (2) output from the laser generator (1), and therefore, hereinafter, the laser generator (1) and the beam diameter adjustment device (3) are combined and referred to as a laser output device (1A). In addition, the beam diameter adjustment device (3) is not used in some cases.

A beam splitter (4) is arranged between the beam diameter adjustment device (3) and the polarization conversion device (5A). The beam splitter (4) splits the laser (2) into two orthogonal lasers (2A) and (2B). The laser (2A) is supplied to a first processing head (A) not shown, and the laser (2B) is supplied to a second processing head (B) not shown. Here, since the first processing head (A) and the second processing head (B) have the same configuration, hereinafter, those having the same configuration (symbols 5 to 12) are distinguished by adding suffixes A and B, and only the case of the first processing head (A) is described.

The polarization conversion device (5A) converts a linearly polarized laser (2A) into a circularly polarized laser (6A). In addition, the polarization conversion device (5A) has a reflection blocking mechanism (details are omitted) that blocks the laser (6A) reflected from the processing section during processing, and has a function of preventing damage to the laser generator (1) caused by the laser (6A) reflected from the processing section. The plate (7A) arranged between the polarization conversion device (5A) and the galvano mirror (10Aa) is formed of a material (e.g., copper) that does not transmit the laser (6A), and has a plurality of apertures (windows, in this case, circular through holes) (8A) that are selectably formed at predetermined positions. The plate (7A) is driven by a driving device (not shown) and positions the axis of the selected aperture (8A) coaxially with the axis of the laser (6A). The galvano device (9A) is composed of a pair of galvano mirrors (10Aa, 10Ab), and is a rotating material around a rotation axis as indicated by an arrow in the drawing, and a reflective surface can be positioned at an arbitrary angle. An fθ lens (condenser lens) (11A) is held in a processing head (A), which is not shown. An optical axis positioning device is configured by the galvano mirrors (10Aa, 10Ab) and the fθ lens (11A), which positions the optical axis of the laser (6A) to a desired position on the printed circuit board (12A), and the scan area (i.e., processing area) (12A) determined by the rotation angle of the galvano mirrors (10Aa, 10Ab) and the diameter of the fθ lens (11A) has a size of about 50 mm × 50 mm. A printed circuit board (13) composed of a work-in copper layer and an insulating layer is fixed to an X-Y table (14). In addition, the first processing head (A) and the second processing head (B) sometimes process a printed circuit board (13) having the same pattern, and sometimes process printed circuit boards (13) having different patterns. The control device (20) controls the laser generator (1), the beam diameter adjustment device (3), the driving device of the plates (7A, 7B), the galvano mirrors (10Aa, 10Ab, 10Ba, 10Bb), and the XY table (14A) (and sometimes includes an X-Y table (14B)) according to the input control program.

[0004]

And, when processing a hole, the X-Y table (14A, 14B) is moved to place the designated processing area (12A, 12B) against the fθ lens (11A, 11B), and then first, all copper layers within the processing area (12A, 12B) are processed with one beam irradiation (i.e., irradiation with one pulse) to form a hole, and then the insulating layer is processed with one or more pulse irradiations to complete the hole in the processing area (12A, 12B).

[0005]

Figure 10 is a drawing showing the setting time of the galvano mirror and the laser irradiation time. The horizontal axis in the drawing represents time, and (a) is for the processing head (A), and (b) is for the processing head (B).

Among the galvano mirrors (10Aa and 10Ab) of the head (A), the time for which the positioning time at which processing location is longer is called the galvano time (GA) of the head (A), and among the galvano mirrors (10Ba and 10Bb) of the head (B), the time for which the positioning time at which processing location is longer is called the galvano time (GB) of the head (B). L1 is the time for one laser irradiation.

If the processing contents of the printed circuit board (13A) and the printed circuit board (13B) processed by the processing head (A) and the processing head (B) are the same and the galvano times (GA and GB) are the same, the laser (2) can be supplied to the two processing heads simultaneously. However, if the processing contents of the processing head (A) and the processing head (B) are different and the galvano times (GA and GB) are different, in order to supply the laser (2) to the processing head (A) and the processing head (B) simultaneously, the longer galvano time must be matched. That is, if GA1<GB1, GA2>GB2, a waiting time of (GB1-GA1) occurs in the processing head (A) and a waiting time of (GA2-GB2) occurs in the processing head (B). As a result, the processing efficiency as a whole decreases.

[0006]

Recently, as substrates become thinner, cases of forming holes in insulating layers without copper layers on the surface as substrates for packaging are increasing. In such cases, the diameter of the hole to be formed is 60㎛ or less, and the power required for forming is about 20W.

Next, we will explain an actual processing example.

Fig. 11 is a drawing explaining an example of a conventional laser irradiation, where the vertical axis represents output and the horizontal axis represents time. In addition, the upper part represents the on/off of an RF pulse (hereinafter simply referred to as RF) that excites the laser medium of the laser generator (1).

For example, when processing a 60 μm hole in an insulating layer, the laser is irradiated and processed by an output curve (A1) in which the output is 20 W at an RF application time of 20 μs, and then the laser is irradiated again under the same conditions at the next pulse cycle. That is, the processing time in this case is 180 μs, which is the pulse cycle of the first pulse irradiated after the galvano mirror positioning, 100 μs, plus 80 μs (including 60 μs for the time until the laser is extinguished after the RF is stopped) during the second pulse cycle of 100 μs following the first pulse. Here, the reason why the laser can be irradiated consecutively twice is because, unlike the case of processing a copper layer with a high processing threshold or processing an insulating layer whose thickness after processing the copper layer exceeds 60 μm, the processing threshold is low and the amount of heat accumulated in the processing portion is small in the insulating layer with a thickness of about 30 μm.

Also, as shown in this drawing, the output curve (A1) has a first peak output (the duration of the output is short) immediately after RF application. This first peak output is about half of the second peak output at the rated RF application time (20 μs in this case). In addition, after the RF application is stopped, the energy accumulated in the laser medium in the laser generator is output as a laser. In the case of the drawing, the duration of the laser based on the laser medium in the laser generator is about 60 μs.

[0007]

However, the above processing causes the following inconveniences.

(1) Due to the influence of the first peak output, the diameter of the entrance of the machined hole may increase by 2 to 3 μm.

(2) The diameter of the processed hole fluctuates as the laser output fluctuates.

Here, the output variation of the laser is explained with reference to the drawing.

Fig. 12 is a diagram showing the output variation of the second peak output, where (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, when the spacing of the holes to be machined is almost the same, the second peak output hardly varies. However, the spacing of the holes to be machined is not the same because it is determined by the spacing of the components to be mounted on the printed circuit board or the position of the holes connected to the lower copper layer. As a result, the output accumulated in the laser medium varies as the laser excitation interval (i.e., duty) varies. As shown in this drawing (a), when the frequency is 1 to 5 kHz, the output varies by about ±3%, and as shown in this drawing (b), when the frequency is 1 to 10 kHz, the output varies by about ±5%. Therefore, the diameter of the machined hole varies.

(3) Even in the RF stop period following the RF application time of 20 μs, the temperature of the processing portion increases because the energy accumulated in the laser medium is irradiated to the processing portion for a period of about 60 μs after the RF is stopped. Even if the temperature rise value of the processing portion is lower than the processing threshold of the insulating layer, if this period continues for 10 μs or more, the insulating layer of the hole bottom and the hole wall is likely to carbonize, thereby deteriorating the processing quality of the hole.

As described above, it is desirable to uniformize the diameter of the hole being processed and prevent deterioration of the quality of the insulating layer.

[0008]

The purpose of the present invention is to provide a method for laser processing a printed circuit board and a laser processing machine for a printed circuit board having excellent processing efficiency and quality by effectively utilizing a laser generator.

[0009]

To solve the above problem, the first means of the present invention is,

In a laser processing method of a printed circuit board, laser processing is performed using a carbon dioxide laser generator that oscillates a laser by applying RF pulses.

The invention is characterized in that the laser is continuously oscillated by resuming the application of the RF pulse while the laser is being output after the application of the RF pulse is terminated, and the laser that is continuously oscillated is cut off for a desired period of time to perform laser processing of a printed circuit board.

[0010]

The second means of the present invention is a method for laser processing a printed circuit board as described in claim 1.

It is characterized by generating a sawtooth-shaped pulse and processing the generated sawtooth-shaped pulse by controlling the application time of the RF pulse and the off time of the RF pulse.

[0011]

The third means of the present invention is a method for laser processing a printed circuit board as described in claim 2,

It is characterized by controlling at least one of the sum of the application time of the RF pulse and the off time of the RF pulse, or the ratio of the application time of the RF pulse and the off time of the RF pulse.

[0012]

The fourth means of the present invention is a laser processing device for a printed circuit board that performs laser processing using a carbon dioxide gas laser generator that oscillates a laser by applying the RF pulse.

It is characterized by having a control device that controls to continue laser oscillation by resuming the application of the RF pulse while the laser is being output after the application of the RF pulse is terminated, and to supply the continuously oscillated laser to a processing section by cutting it for a desired period of time.

[0013]

The fifth means of the present invention is a laser processing device for a printed circuit board as described in claim 4,

The present invention is characterized by comprising a control device configured to distribute a laser from a single laser generator to each of the plurality of processing heads, and supplying a laser to the processing head without considering the positioning status of another processing head when the positioning of one processing head is completed.

[0014]

It is possible to make the hole diameter of the hole being processed uniform, and at the same time improve the quality of the hole wall surface, and also improve the processing efficiency. In addition, since a stable laser is continuously oscillated, when supplying lasers to multiple heads, the necessary laser can be supplied to any head independently of the other heads, and thus the processing efficiency as a laser processing machine can be improved.

[0015]
FIG. 1 is a drawing illustrating elements of a sawtooth wave related to the present invention.
Figure 2 is an example of an output waveform.
Figure 3 is a drawing explaining the generation sequence of a sawtooth wave related to the present invention.
Figure 4 is a drawing explaining an example of processing by a rectangular wave pulse of a saw tooth n.
Figure 5 is a diagram explaining the energy spatial distribution of the output.
Figure 6 is a configuration diagram of a two-head laser processing machine related to the present invention.
Figure 7 is a drawing showing the setting time of the galvano mirror and the laser irradiation time.
Figure 8 is an explanatory diagram of a rectangular wave pulse when processing an insulating layer containing filler.
Figure 9 is a configuration diagram of a conventional two-head type laser processing machine.
Figure 10 is a drawing showing the setting time of the galvano mirror and the laser irradiation time.
Figure 11 is a drawing explaining an example of a conventional laser irradiation.
Figure 12 is a diagram showing the output fluctuation of the second peak output.

[0016]

FIG. 1 is a drawing explaining components of a sawtooth wave related to the present invention. In addition, an output curve (C) (basic wave pulse waveform) in this drawing is an output curve of rated duty 60% (RF application time/pulse period. Hereinafter, “rated duty” is simply expressed as “Dty”), pulse frequency 10 kHz, and maximum output 250 W, and the vertical axis represents the output of the oscillating laser, and the horizontal axis represents time. In addition, the upper part represents the on/off of RF for exciting the laser medium of the laser oscillator (1).

First, the output curve (C) will be described. When RF is turned on at time T0, the laser is output explosively at time T1, reaches the first peak output Wj at time Tj, then decays until time Td, then switches to increasing again, and reaches the second peak output (250 W) at time T2, 60 μs after the RF application time from time T0. Here, the output indicated by the solid line during the RF application period is the sum of the output transferred from the N ₂ gas, which is a laser medium, to the CO ₂ gas by RF (the output indicated by the dotted line around 60 μs in this figure) and the output in which the CO ₂ gas is directly excited by the RF (i.e., the output sandwiched between the output indicated by the dotted line and the output indicated by the solid line). Therefore, when the RF application is stopped, the output in which the CO ₂ gas is directly excited by the RF becomes 0, and after time T2, the energy accumulated in the N ₂ gas, which is a laser medium in the laser generator, is output as a laser. Additionally, the energy accumulated in the laser medium is output 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 Dty 60% (pulse width 60 μs) and pulse frequency 10 kHz, the output of the oscillated laser gradually increases and reaches a maximum at a pulse width of 60 μs, as shown in the output curve (C). And, when the RF application is stopped, the output is attenuated. And, when the laser is oscillated within the Dty range of the laser oscillator, even if the RF application time changes, the output rises along the same output curve (the output curve (C) shown). That is, when oscillation is performed with Dty 40% (pulse width 40 μs) and 10 kHz, the output rises along the output curve (C), reaches a maximum at a pulse width of 40 μs, and attenuates as in the case above. Also, when oscillating at 10 kHz with Dty 20% (pulse width 20 μs), it rises along the output curve (C), reaches a maximum at a pulse width of 20 μs, and attenuates as in the above case.

[0018]

2. Requirement 2

In the case of a _CO2 laser, when RF application is initiated at time T0, laser oscillation is initiated by the excited output accumulated in the laser medium at time T1, and the output rapidly increases to become the first peak output Wj at time Tj, then decays once (time Td), and after that, the output increases again to become the second peak output when RF application is stopped.

In this case, the time Td is 0.4 to 0.5 μs from the time T0, and it was found that the output response (output change per unit time) (Ws) at the time Td is almost constant even if Dty and pulse width change.

[0019]

3. Requirement 3

When the RF input is stopped, the output switches from 250 W to the residual output accumulated in the laser medium. The switching time is 0.4 to 0.5 μs, and the output first drops and then slightly increases and then decays. Hereinafter, the output response when the output switches is called the output response (Wc), and the output response when it slightly increases is called the output response (Wd).

And, it was found that the output response (Wc) has a value that hardly changes even when Dty and pulse width change. In addition, although the output response (Wc) and the output response (Ws) have different output directions, the sizes of the output components are almost the same.

[0020]

4. Requirement 4

Fig. 2 is an example of an output waveform, which is an output waveform when the energy accumulated in the laser medium resumes RF application at the end point of the pulse cycle. As shown in the figure, when there is a residual output (Δz indicated by an oblique line in the figure, and the output at the start of RF application is ΔW. Here, ΔW>0) accumulated in the laser medium at the start of RF application, when the excitation of the next (second) pulse cycle is initiated, the excited output is superimposed on the residual output, and the output increases in the output response (Ws) after 0.4 to 0.5 μs, but at this time, the first peak output (Wj) does not occur. Although the connection between the first pulse cycle and the second pulse cycle has been described here, when repeating up to the nth pulse cycle, the level of the output at which the output response (Ws) occurs gradually increases, whereas the second peak output gradually decreases, but becomes stable in about 1 second.

Here, in the case of the above Fig. 11, since the residual energy accumulated in the laser medium is 0 before the start of the second pulse cycle, the output curve of the second pulse cycle becomes the same output curve as that of the first pulse cycle.

[0021]

Here, the integral value of the output continuously oscillated at Dty 60% on the output curve (C) (i.e., the total output output with a pulse period of 0 to 100 μs) divided by the pulse period of 100 μs is called the average output (Wav).

In addition, when Dty is made constant, the average output (Wav) shown in Fig. 1 hardly changes in the range of the pulse cycle of 20 to 200 KHz. On the other hand, when the pulse frequency is made constant, the average output (Wav) increases in proportion to Dty. In addition, the tangential output response (Wr) in the average output of the RF on period of the output curve (C) and the tangential output response (Wf) in the average output of the RF off period of the output curve (C) become values unique to the average output.

Also, although sawtooth waves of 100 kHz and 200 kHz are described in Fig. 1, details are explained using Fig. 3.

[0022]

Figure 3 is a drawing explaining the generation sequence of a sawtooth wave related to the present invention.

When Dty = Trf1/tm (wherein tm is a pulse period and is composed of an RF application period (Trf1) and an RF application stop period (Trf0)) is set in the output curve (C), the average output (Wav) is determined. Even if the pulse period (tm) is shortened, if the ratio of the RF application time (trf1) and the RF application stop time (trf0) is the same, Dty is the same and the average output (Wav) hardly changes. Therefore, the sawtooth wave related to the present invention is generated based on the basic wave pulse waveform (the output curve (C)) and the requirements 1 to 4.

[0023]

The sequence of generation of sawtooth waves is as follows:

Step 1) Set Dty, pulse period (tm), average output (Wav), upper limit output (Wp), and lower limit output (Wv) with the vertical axis as the output axis. Here, the upper limit output (Wp) is the output level [J/s] that can obtain the target hole diameter by the investigated pulse, and is set to a value according to the threshold value of the material. The lower limit output (Wv) is the output level at the rising time of the output response (Ws) when RF is on in a sawtooth pulse with stable continuous oscillation.

Step 2) Using the horizontal axis as the time axis, the point on the lower limit output (Wv) at time t0 is designated as Q1, and the point on the lower limit output (Wv) at time t2, which is the pulse period, is designated as Q6. Then, plot the output response (Ws) with point Q1 as the starting point, and the end point of the output response (Ws) is designated as point Q2.

Step 3) Connect point Q3 on the upper limit output (Wp) at point Q2 and time t1 to the output response (Wr). Also, time t1 is the end point of Trf1 (the start point of Trf0).

Step 4) Plot the output response (Wc) with point Q3 as the starting point, and set the end point of the output response (Wc) as point Q4.

Step 5) Plot the small output response (Wd) on the extension line connecting points Q1 and Q4, and set the endpoint as Q5.

Step 6) Connect points Q5 and Q6 with an output line segment (Wf). That is, point Q5 is the intersection of the extension connecting points Q1 and Q4 and the output response (Wf) that ends at point Q6.

By the above sequence, a sawtooth wave added to the lower output (Wv) is completed.

Hereinafter, a sawtooth-shaped pulse formed by superimposing a polygon in the above order on the lower limit output (Wv) is called a “sawtooth pulse.”

As described in paragraph 0024, the output of the laser generator becomes stable after 1 second, and the fluctuation range of the average output (Wav) and the upper limit output (Wp) is approximately ±1% as long as the laser generator is in operation.

In addition, as shown in this drawing, if points Q1 and Q4 are connected by a dotted line, the output enclosed in the square Q1Q2Q3Q4 corresponds to the output in which _CO2 gas is directly excited by RF as described in paragraph 0016.

Here, Fig. 1 shows one 100 KHz sawtooth pulse and one 200 KHz sawtooth pulse each written in the above order.

[0024]

Here, when Dty is constant and the pulse period (tm) is changed, the output response (Ws, Wc) does not change. On the other hand, the output response (Wr, Wd, Wf) changes with the pulse period (tm), but the average output (Wav) hardly changes. In addition, when the pulse period (tm) is constant and Dty is changed, the output response (Ws, Wc) hardly changes, but the output response (Wr, Wd, Wf) changes. In this case, when Dty decreases, the increase rate (rise) of the output response (Wr, Wd) becomes steeper, and the decrease rate (decrease) of the output response (Wf) becomes gradual. On the other hand, when Dty increases, the increase rate (rise) of the output response (Wr, Wd) becomes gradual, and the decrease rate (decrease) of the output response (Wf) becomes steeper. And the average output varies with Dty, each of which 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 processing, the waveform generation process described above is performed continuously to form n sawtooth pulses (n is an integer greater than or equal to 1). Hereinafter, a pulse composed of n sawtooth pulses supplied during processing is collectively referred to as a "rectangular wave pulse of sawtooth n."

[0025]

Figure 4 is a drawing explaining an example of processing by a rectangular wave pulse of sawtooth n, where the vertical axis represents output and the horizontal axis represents time.

Here, if the hole to be processed is the same hole as described in the above Fig. 11, in the case of the prior art, since processing was performed with 2 pulses at a pulse frequency of 10 kHz, the laser irradiation time was 20 μs twice, and the processing time was 180 μs, which is the pulse period of the first pulse of 100 μs, the RF application time of the second pulse of 20 μs, and the non-excitation time of 60 μs added. On the other hand, in the case of the present invention, if processing is performed by irradiating twice a rectangular wave pulse of sawtooth 2 with a pulse frequency of 100 kHz, which can obtain pulse energy equivalent to the prior art, the pulse period is not affected, so the interval between the two rectangular pulses can be arbitrarily set, and if the interval between the two rectangular wave pulses of sawtooth 2 is 60 μs, the processing time is 100 μs. Therefore, according to the present invention, the processing time can be shortened by 80 μs compared to the prior art.

[0026]

Next, the present invention and prior art will be described with reference to the shape of the machined hole.

FIG. 5 is a drawing explaining the energy spatial distribution of the output, where (a) is the case of the present invention and (b) is the case of the prior art, where the vertical axis represents a standardized energy level and processing depth, and the horizontal axis represents the diameter direction of the hole. In this drawing, Ds represents the beam spot diameter of the processing section, DR represents the target hole diameter, DR1 and DR' represent hole diameters smaller than DR, and DB and DB' represent the hole bottom diameters, respectively. In addition, 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 value of the insulating layer.

In addition, ep represents the energy distribution at the time of output (Wp), ev represents the energy distribution at the time of output (Wv), ev represents the energy distribution at the time of average output (Wav), 1e represents the energy distribution of the first pulse, and 2e represents the energy distribution of the second pulse, respectively. The output (Wp), the output (Wv), and the average output (Wav) are as shown in Fig. 3.

The machining process of the present invention is explained below in accordance with the diameter direction of the machined hole. In addition, the energy distribution when the machining diameter increases during the RF application period (trf1) is called the diameter increase energy distribution, and the energy distribution when the machining diameter decreases during the RF application stop period (trf0) is called the diameter decrease energy distribution. At the same time as the RF application, machining is started with an output response (Ws) of approximately 0.4 μs of output increase superimposed on the output (Wv), and then machining is performed with the machining diameter increase energy distribution of the output response (Ws), and after the elapse of time (trf1), the target hole diameter is formed. At the same time as the RF application is stopped, additional machining is performed by the output response (Wc) of the machining diameter decrease energy distribution, the machining diameter fine increase output response (Wd), and the machining diameter decrease energy distribution output response (Wf).

In the above processing step, processing is performed alternately with spot diameters DR and DB and DR' and DB'. The output increase at the start of processing is more rapid than with a conventional pulse, and the irradiation time is shorter. In addition, the energy distribution diameter after the RF application is stopped becomes smaller and moves away from the hole entrance and the hole side wall, so that the heat conduction to the hole entrance and the hole side wall surface during the insulating layer processing is reduced. As a result, the heat influence of the insulating layer on the hole wall surface is reduced, and the hole quality is improved. In addition, since processing is performed with continuous sawtooth pulses, laser irradiation after the RF application is stopped, which does not participate in the processing as in the conventional technology, is not performed. Therefore, the quality of the hole entrance and the hole side wall surface is not deteriorated. In addition, since it is not affected by the first peak output, the hole entrance diameter does not widen.

[0027]

FIG. 6 is a configuration diagram of a two-head type laser processing machine related to the present invention. Objects identical to those in FIG. 8 or objects having the same function are given the same reference numerals and detailed descriptions are omitted.

The laser generator (1) outputs a continuous linearly polarized sawtooth laser (2) having a frequency of 50 kHz or more by setting the application time and the pause time of high-frequency RF that drives laser oscillation. The beam diameter adjustment device (3) arranged between the laser generator (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 generator (1). That is, the energy of the laser (2) does not change before and after the beam diameter adjustment device (3). Therefore, the laser (2) output from the beam diameter adjustment device (3) can be regarded as the laser (2) output from the laser generator (1), and therefore, hereinafter, the laser generator (1) and the beam diameter adjustment device (3) are referred to in combination as a laser output device (1A). The beam diameter adjustment device (3) is not always used.

An AOM (50A) driven by a driver (61A) is placed between the beam splitter (4) and the polarization converter (5A). The AOM (50A) branches the laser (2A) into a first-order laser (2A1K) and a zero-order laser (2A0), and adjusts the output of the laser (2A1K) used for processing by changing the branching ratio (opening degree). The laser (2A0) not used for processing is discarded by a damper that does not diffuse to the surroundings.

[0028]

This laser processing machine is configured so that the second head (B) can be positioned in the X direction with respect to the fixed first head (A) by a second head (B) moving device, not shown, and so that the position of the second head (B) can be expanded by a maximum of S with respect to the first head (A). The mirrors (31) and (34) are fixed at predetermined positions, and the mirrors (32, 33) are supported by a mirror moving device, not shown, and are free to be positioned in the X direction. The mirrors (31 to 34) are arranged so that the axis of the aperture (8B) coincides with the center of the galvano mirror (10Ba) regardless of the position of the mirrors (32, 33) in the X direction. The control device (20) controls the laser generator (1), the beam diameter adjustment device (3), the AOM driver (61A, 61B), the driving device of the plates (7A, 7B), the galvano mirrors (10Aa, 10Ab, 10Ba, 10Bb) and the X-Y table (14A) (including the X-Y table (14B) as the case may be), the moving device of the second head (B) not shown, and the mirror moving device.

[0029]

Below, the processing sequence is explained. Also, although the processing content is different for each head, since the operation is substantially the same, the case of the first head (A) is explained.

When the start of processing is instructed, the control device (20) drives the moving device of the second head (B) to move the second head (B) to a designated position. Next, the X-Y table is controlled to position the first head (A) at the processing position, and at the same time, the galvano mirrors (10Aa, 10Ab) are positioned at the first processing position and standby. In addition, the moving device of the second head (B), not shown, is operated to move the second head (B) with respect to the first head (A) by a distance s. Thereafter, the mirror moving device, not shown, is operated to move the position of the mirror (32) by a distance s/2 in the moving direction of the head (2). As a result, since the distance between the aperture (8) and the galvano mirror (10Ba) always becomes constant, the image size of the aperture (8) can always be maintained constant regardless of the position of the second head (B).

[0030]

And, first, the laser generator (1) is operated, and after a predetermined waiting time has elapsed, the processing program is started to initiate processing. Here, the reason for the waiting time is that the output of the laser generator (1) is unstable until it reaches a state of thermal equilibrium, and the time is approximately 1 to 2 seconds.

Then, when the waiting time has elapsed, the control device (20) outputs a sawtooth-shaped laser (2) (hereinafter, simply referred to as laser (2)) from the laser generator (1) according to a pre-input processing program. The laser (2) has its diameter changed by the beam diameter adjustment device (3), is split into lasers (2A) by the beam splitter (4), and is incident on the AOM (50). The AOM (50) discards the laser (2A) with a damper until it receives an operation command from the control device (20). When the control device (20) receives a positioning completion signal of the galvano mirror (10Aa, 10Ab) whose positioning has been determined later, it operates the AOM (50A) through the driver (61A) to output the laser (2A) as a rectangular wave pulse (2A1K) composed of n sawtooth pulses that have been attenuated to a pre-designated output. A rectangular wave pulse (2A1K) is positioned by a galvanometer mirror (10Aa, 10Ab) and is incident on a designated position of a printed circuit board (13A) to create a hole in the printed circuit board (13A). Hereinafter, as in the conventional case, the hole-punching operation is repeated until the designated processing is completed. In addition, in the processing, the laser generator (1) continuously outputs the laser (2) from the start to the end of the processing by turning RF on and off at a predetermined cycle and pulse cycle.

[0031]

Figure 7 is a drawing explaining the setting time of the galvano mirror and the irradiation time of the laser in the present invention, (a) shows the case of the processing head (A), and (b) shows the case of the processing head (B). Also, the horizontal axis in the drawing represents time.

As shown in this drawing, the laser (2A, 2B) composed of sawtooth pulses is always output during processing, and in the case of the first head (A), when the galvano time (GA1 or GA2) is completed, a rectangular wave pulse (2A1K) composed of n required sawtooth pulses is irradiated to the processing part by the AOM (50) to create a hole. In this case, the first head (A) continues the work without considering the galvano time (GB1, GB2) of the second head (B). Similarly, the second head (B) continues the work without considering the galvano time (GA1, GA2) of the first head (A). As a result, no waiting time occurs in each head, and the processing efficiency can be improved by 20 to 30% compared to the conventional one. In addition, when the positioning of the galvano mirror is completed according to the clock of the device that omits the city, the AOM (50) is controlled so that the output matches the RF application start time of the first sawtooth pulse so that no loss or omission occurs in the rectangular wave pulse of the sawtooth n supplied to the processing section.

[0032]

Next, the configuration of the gear according to the present invention will be described in more detail.

Figure 8 is an explanatory diagram of a rectangular wave pulse when processing an insulating layer containing filler (reinforcing material). The horizontal axis represents time, and t is the time based on t0.

Here, the upper part represents the operation of the AOM, A is the opening degree of the AOM 100%, and mA is the opening degree of the AOM m%. In addition, the middle part represents the on/off of the RF, tm is the pulse cycle, trf1 is the on time of the RF, and trf0 is the off time of the RF. In addition, the lower part represents the output, and in the drawing, Wpf is the upper limit output that can process the filler of the insulating layer, and Wpr is the upper limit output that can process the resin of the insulating layer.

In the case of this drawing (a), the RF on period mainly processes the filler by increasing the laser diameter, and the RF off period reduces the laser diameter, so that gas and processing debris generated by processing can be quickly removed from the processing area, thereby improving the processing quality of the hole wall surface and the hole bottom. In addition, in the case of this drawing (b), similarly to the case of this drawing (a), gas and processing debris generated by processing can be quickly removed from the processing area, thereby improving the processing quality of the hole wall surface and the hole bottom.

In addition, this drawing (c) is a modified example of the part surrounded by the dotted line in this drawing (a), and is an example of waveform control that turns on the AOM only from the time ta during the output rise (time td1 in the drawing) of the RM on period in this drawing (a). In this way, as a result of processing with the high average output (Wavh) of the output rise section, the hole entrance and the hole side wall become uniform, and the hole quality is improved. tg is the AOM off time. This drawing (d) is used, for example, when it is desired to create a slope in the depth direction of the hole.

[0033]

Next, we will explain a processing example.

The results of processing the packaging fillers at a processing spot of 60 ㎛ with the same diameter on the insulating layer (ABF material of Ajinomoto Co., Ltd., thickness of approximately 30 ㎛) by applying the rectangular wave pulse of sawtooth n shown in Figs. 8(a)(b)(c) and the conventional pulse of Fig. 4(b) are as follows. In addition, this drawing shows the shape of the sawtooth pulse and does not show the rectangular wave pulse of sawtooth n used for processing.

· In the case of this drawing (a), 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 period trf1 is when the AOM opening is 100%, and the period trf0 is when the AOM opening is 0%, the hole inlet diameter is approximately 62 μm, and the hole (bottom diameter/inlet diameter) ratio is approximately 80%. In addition, when the AOM opening is 0%, the output of the part indicated by the diagonal line in Fig. 8 (a) is 0.

· For this drawing (b), when two 3-tooth rectangular wave pulses with a frequency of 100 kHz, Dty 60% (trf1 = 6 μs, trf0 = 4 μs), Wpf = 20 W, the first tooth has 100% AOM opening, the second tooth has 0% AOM opening, and the third tooth has 100% AOM opening, the hole entrance diameter was approximately 60 μm, and the hole (bottom diameter/entrance diameter) ratio was approximately 80%.

· For this drawing (c), when two sawtooth 3 rectangular wave pulses with a frequency of 100 kHz, Dty 60%, td1 = 6 μs when AOM opening is 0%, and ta = 4 μs when AOM opening is 100%, the hole entrance diameter was approximately 60 μm, and the hole (bottom diameter/entrance diameter) ratio was approximately 81%.

And, in the case of these drawings (a), (b), and (c), there was almost no carbonization of the resin on the surface of the copper layer at the bottom of the hole.

For reference, when processing was performed with a pulse width of 20 μs, a pulse frequency of 10 kHz, and a pulse number of 4 by the prior art technique shown in Fig. 11, the hole entrance diameter was approximately 63 μm, and the hole (bottom diameter/entrance diameter) ratio was approximately 78%. In addition, the attachment of carbonized resin to the copper surface of the hole bottom could be observed. In addition, when processing was performed by increasing the output in a pulse in which the first peak output (Wj) was higher than the second peak output (WP), the hole entrance diameter became approximately 65 μm due to the diffracted light of the first peak output (Wj), and there were cases in which the area around the hole entrance was damaged in a ring shape.

[0034]

In addition, the values of the optimal output responses Ws, Wc, Wr, Wd, and Wf are different depending on the material of the workpiece. Therefore, by setting the values of the output responses Ws, Wc, Wr, Wd, and Wf to the optimal values depending on the material of the workpiece, the processing quality and processing speed can be improved.

[0035]

In addition, in actual processing, the values of output levels Wp and Wv and the values of output responses Ws, Wc, Wr, Wd and Wf for each work are known in advance. In addition, the maximum output of the laser generator when the rated duty and pulse cycle are determined is also known in advance. In addition, the diameter of the aperture suitable for the diameter of the hole to be processed is also known.

Therefore, in the case of processing the first material, for example, first, the values of levels Wp and Wv are temporarily determined by referring to the conventional data, and the output level Wp is increased or decreased by comparing the hole diameter processed by the test with the target hole diameter. Next, processing is performed with a sawtooth pulse n, and the value of n is determined according to the depth of the processed hole. At this time, since quality deterioration due to heat of the insulating layer occurs when n increases, when the number of n increases, n is divided to employ a plurality of sawtooth m rectangular wave pulses, and a period for cooling the processed part is provided between each rectangular wave pulse.

[0036]

Also, in the two-head type laser processing machine illustrated in Fig. 6, when the output of the laser generator (1) is 250 W, the average output is 125 W, so it is split by the beam splitter (4) and 62.5 W is supplied to each head. Therefore, as described in paragraph 0033, when Wpf = 20 W, either head (A, B) can be processed. However, for example, when processing a carrier PET film-attached resin, Wpf needs to be 70 W. Therefore, when it is necessary to set Wpf = 70 W, the output of the laser generator (1) of Fig. 6 needs to be, for example, 500 W.

[0037]

In addition, although the above description has been made using as an example a laser generator having output characteristics of a fundamental 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, the present invention can also be applied to a laser generator having output characteristics of a fundamental 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.

[0038]
1: Laser generator
2: Laser

Claims (5)

A method for laser processing a printed circuit board, wherein laser processing is performed using a single carbon dioxide gas laser generator that oscillates a laser by applying an RF pulse.
A method for laser processing of a printed circuit board, characterized in that the laser oscillation is continued by resuming the application of the RF pulse to the carbon dioxide gas laser generator while the laser is being output by the carbon dioxide gas laser generator after the application of the RF pulse to the carbon dioxide gas laser generator is terminated, and the laser oscillation is continuously cut off for a desired period of time to perform laser processing of the printed circuit board. In the first paragraph,
A laser processing method for a printed circuit board, characterized in that a sawtooth pulse is generated by controlling the application time of the RF pulse and the off time of the RF pulse, and processing is performed using the generated sawtooth pulse. In the second paragraph,
A method for laser processing a printed circuit board, characterized in that at least one of the sum of the application time of the RF pulse and the off time of the RF pulse or the ratio of the application time of the RF pulse and the off time of the RF pulse is controlled. In a laser processing device for a printed circuit board that performs laser processing using a single carbon dioxide gas laser generator that oscillates a laser by applying an RF pulse,
A laser processing device for a printed circuit board, characterized by including a control device that controls to continue laser oscillation by resuming the application of the RF pulse to the carbon dioxide gas laser generator while the laser is being output by the carbon dioxide gas laser generator after the application of the RF pulse to the carbon dioxide gas laser generator has been terminated, and to supply the continuously oscillated laser to a processing section by cutting it for a desired period of time. In paragraph 4,
A laser processing device for a printed circuit board, characterized in that it comprises a plurality of processing heads, and is configured to distribute a laser from the carbon dioxide laser generator to each of the plurality of processing heads, and has a control device that supplies a laser to the processing head without considering the positioning state of another processing head when the positioning of one processing head is completed.