CN1659750A - Laser processing system and laser processing method - Google Patents

Abstract

A laser processing system is provided with: a pulse laser oscillator (2) capable of changing the characteristics of a laser beam (6) by changing the discharge power applied between electrodes (24) by switching a discharge command pulse having a predetermined frequency, and an optical system (3) for guiding the laser beam (6) output from the laser oscillator (2) to a workpiece.

Description

Laser processing system and laser processing method

field of invention

The present invention relates to a laser processing system and a laser processing method for performing through holes, blind holes, etc., or groove processing, shape cutting, etc. on a workpiece, and particularly relates to the improvement of processing quality and productivity.

Background technique

The printed circuit board is formed by laminating multiple insulating substrates with conductive layers.

Furthermore, the conductive layers provided on the respective insulating substrates are electrically connected between any conductive layers in the vertical direction through via holes called through holes or blind holes.

14 is a cross-sectional view illustrating such an existing multilayer printed circuit board. In the figure, 1 is a printed circuit board, 11a and 11b are insulating substrates, 12a to 12c are conductor layers, 13 is a metal plating layer, and 14a 14b is the conduction between the conductive layer 12a of the conductive insulating substrate 11a and the conductive layer 12c laminated by the insulating substrate 11b. hole.

The via hole 14a is generally called a blind via hole (Blind Via Hole), and the via hole 14b is generally called a through hole (Through Hole).

Printed circuit boards with via holes 14a, 14b as shown in Figure 14, along with the high performance of electronic equipment, require multilayer and miniaturization (higher density) of printed circuit boards, in order to meet this requirement, propose The method of processing the via holes 14a, 14b shown in FIG. 14 using a laser beam has also been advanced.

Fig. 15 is a schematic diagram for explaining a laser processing system for forming through holes and blind holes in a printed circuit board with a laser beam.

In the figure, 1 is a printed circuit board as an object to be processed, 2 is a laser oscillator, 3 is an optical system, 4 is a processing table, 5 is a control device for the overall control system, and the various parts are connected by cables. 6 and 7 are laser beams, 9 is an example of a laser irradiation pattern, Pi on the laser irradiation pattern 9 is the peak power of the laser beam, Wi is the pulse width (beam irradiation time), and Ti is the rest time of the beam irradiation.

The actual processing operation will be described below.

The laser beam 6 output from the laser oscillator 2 is formed into a beam by the optical system 3 , and is transmitted and irradiated to the printed circuit board 1 which is the object to be processed.

At this time, the laser beam is irradiated with a plurality of laser pulses to each hole in a pulsed laser irradiation pattern like 9 shown in FIG. 15 . The irradiated laser beam melts the printed circuit board 1 with heat and removes it, resulting in the formation of holes in the printed circuit board.

FIG. 16 shows an example of a cross-sectional view of a printed circuit board thus processed.

In Figure 16, 15a is the machining upper aperture, 15b is the machining middle aperture, 15c is the machining lower aperture, 16 is the machining depth, 17 is the machining resin residue, 18 is the copper foil damage on the inner surface, and the rest of the same parts as in Figure 14 are marked same symbols, and their descriptions are omitted.

When processing with a laser beam, in order to ensure the processing quality, it is usually necessary to pay attention to the processing apertures 15a-15c, processing depth 16, processing defects 7, 18, etc. in Figure 16, and control the beam diameter, beam energy (peak power × pulse width) and The rest time of beam irradiation, especially the beam energy, is an important control parameter because it affects the damage and deformation of the material and material composition, and plasma generation.

Assume that the energy of the i-th laser beam is Ei, the peak power at the exit of the laser oscillator is Pi, the transmission rate of the peak power at the exit of the laser oscillator controlled by the optical system is αi (hereinafter referred to as the beam transmission rate), and the beam pulse width is Wi, the number of shots irradiated on one hole is S, then the beam energy Et irradiated on each hole is usually expressed by Equation 1:

$\mathrm{Et}=\underset{i=1}{\overset{\mathrm{no}}{\mathrm{\Σ}}}\mathrm{Ei}=\underset{i=1}{\overset{\mathrm{no}}{\mathrm{\Σ}}}[(\mathrm{\α\; i}\×\mathrm{Pi})\×\mathrm{wi}]$ …Formula 1

By controlling the beam transmission rate αi, peak power Pi, Wi, the beam energy Et can be controlled.

Here, the beam transmission rate αi is determined by the loss that occurs when the optical system 3 forms a beam pattern in the conventional laser processing system and the loss due to absorption of optical components and the like.

As a method of changing αi, there is, for example, a method of adding an object composed of a mask 31 and a collimator lens 32 to the optical system 3 as shown in FIG. 17 .

In FIG. 17, the light propagating with the beam diameter Di is condensed by the collimator lens 32, and the beam pattern is shaped by the mask 31 (creating the beam pattern required for the processing point).

The difference between the input beam mode volume and the output beam mode volume at this point is the loss that occurs when the beam mode is shaped.

The loss is determined by the diameter D of the mask 31 , the focal length f of the collimator lens 32 , and the distance L between the mask diameter D and the collimator lens 32 from the mask 31 .

For example, when the mask diameter D is large and the focal length f is approximately equal to the distance L, there is almost no loss, the output beam mode volume is approximately equal to the input beam mode volume, and the beam transmission rate αi increases.

Conversely, when the mask diameter D is small, the focal length f is long, and the distance L is short, most of it is loss. Compared with the input mode volume, the output beam mode volume becomes very small, and the beam transmission rate αi becomes small.

In the existing processing system, among the three parameters of D, f, and L, the mask diameter D is the beam diameter required by the processing point, that is, it is determined by the processing aperture, the focal length f is fixed, and the distance L can be moved mechanically , so it is necessary to move distance L in order to change αi.

However, since the change of the distance L is performed by the servo motor, several hundreds of ms or more are required for the change.

In addition, the peak power Pi is fixed or assumed to be variable by about ±20% of the rated value, and it takes several hundreds of ms or more to change it.

A schematic diagram of a carbon dioxide laser oscillator in FIG. 18 will be described below. Among the figure, 21 is the casing, 22 is the mixed gas that has added the laser medium, namely CO ₂ , 23 is the partial reflection mirror, 27 is the total reflection mirror, 28 is the aperture of the prescribed laser oscillation mode, 29 is the optical axis of the laser beam, 6 is the output laser beam.

In the carbon dioxide laser oscillator constructed as shown in FIG. 18, by applying a voltage from an AC power source 23, an excitation discharge 25 is formed between electrodes 24, and CO ₂ gas is excited to an upper energy level. The particle density excited by the discharge at this time is called the discharge power density. Inside the resonator composed of the partial reflection mirror 26 and the total reflection mirror 27 , the excited CO ₂ amplifies the laser light by induced emission, and outputs the laser beam 6 around the laser beam axis 29 .

Here, in the case of a gas laser such as a carbon dioxide laser, when the resonator loss is constant, the peak power of the laser beam is generally approximately proportional to the discharge power density. The discharge power density is roughly proportional to the power applied to the electrodes 24 by the AC power source 23 . Therefore, in order to change the discharge power density, the conventional laser oscillator controls the voltage applied between the electrodes. When the voltage is too high, the load on the power supply will increase, which will lead to power failure or damage to the electrodes. Also, if the voltage is too low, the discharge will not occur, resulting in a state where the laser beam cannot be output. Therefore, the range of changing the voltage is generally limited to ±20% relative to the rated value, and correspondingly, the peak power of the laser beam can only be changed by ±20%. In addition, since the response speed of the voltage change is slow, it takes several hundreds of ms or more to stabilize the discharge, so when the peak power is changed every pulse (in the range below the maximum oscillation frequency of the pulse laser oscillator, instantaneously) Under this condition, it is impossible to obtain a stable beam energy.

In addition, the laser pulse time width Wi (hereinafter referred to as pulse width) of the output laser light is approximately equal to the time width obtained by subtracting the laser oscillation delay from the discharge time width of the excited discharge (hereinafter referred to as discharge width). The reason is that when the excitation discharge starts, the discharge energy (discharge power density × time) is lower than the laser oscillation threshold, and no laser is output, so the laser oscillation start time is later than the excitation discharge start time. (Of course, this delay varies depending on the resonator configuration and gas composition.) In addition, by controlling the discharge width, specifically, the time width for supplying input power, the laser pulse width can be freely changed. The range below the maximum oscillation frequency of the laser oscillator) is a control parameter for switching. However, the input power has a limit depending on the load, and the pulse width has an upper limit.

As mentioned above, in the existing laser processing system, since it is difficult to change the peak power, the beam energy is controlled by the beam transmission rate αi and the beam pulse width Wi based on the optical system, especially when the condition is switched instantaneously, the beam Pulse width Wi is the only control parameter.

The laser irradiation pattern will be described below.

Laser irradiation patterns can be broadly classified into two types, that is, after the beam irradiation position is positioned at the opening position as shown in Fig. 19, only the number S necessary to form the hole is continuously irradiated with laser pulses, that is, the pulse group. Processing; and as shown in Figure 20, when the number of holes n and the necessary number S of holes are formed, the beam irradiation position is positioned at the opening position, and the processing of repeating n×s times of irradiating 1 laser pulse is cycle processing.

In the pulse group addition formula, the laser oscillation time required from the kth to the (k+1)th hair in each hole is Tok (equivalent to the rest time of beam irradiation in the pulse group processing), and the pulse width of the sth hair is Ws, when the positioning time from (j-1) to the jth hole is Tgj, the processing time Tb required for n holes is shown in Equation 2:

$\mathrm{Tb}=\mathrm{no}\&times;(\underset{K=1}{\overset{\mathrm{the\; s}-1}{\mathrm{\&Sigma;}}}\mathrm{Tok}+w)+\underset{j=1}{\overset{\mathrm{no}}{\mathrm{\&Sigma;}}}\mathrm{<figure-callout\; id="2"\; label="Tg\; ...Formula"\; filenames="A0381269700211.png"\; state="\{\{state\}\}">Tg</figure-callout>}$ ...Formula 2

Usually because Ws<<∑Tok, there is

…式3

...formula 3

Suppose the average value of Tok is recorded as To, and the average value of Tgj is recorded as Tg, then the average value Tba of Tb is

Tban×{(s-1)×To+Tg}…Formula 4

Therefore, the processing time is determined by the laser oscillation time To, the number of shots s and the positioning time Ts.

On the other hand, in cycle processing, if the i-th pulse width of each hole is Wi, and the positioning time from (j-1) to the j-th hole is Tgij, then the processing time Tc required for n holes As shown in formula 5:

$\mathrm{Tc}=\mathrm{no}\&times;\underset{i=1}{\overset{\mathrm{the\; s}}{\mathrm{\&Sigma;}}}\mathrm{wi}+\underset{i=1}{\overset{\mathrm{the\; s}}{\mathrm{\&Sigma;}}}\underset{j=1}{\overset{\mathrm{no}}{\mathrm{\&Sigma;}}}\mathrm{Tgij}$ ...Formula 5

Usually because Wj<<Tgij, so there is

...formula 6

Let the average value of Tgij be Tg, then the average value Tca of Tc is

Tcan×s×Tg ...Formula 7

Therefore, the processing time in cycle processing is determined by the number of shots s and the positioning time Tg.

Here, the difference between cyclic processing and pulse group addition will be described. In cyclic processing, the rest time Tqc of beam irradiation for each hole can be made longer, and the thermal influence on the periphery of the processing hole is reduced, which can improve the processing quality.

On the contrary, in the case of pulse group machining, each hole is machined with laser oscillation time To, and beam irradiation rest time Tqb is shorter than Tqc (Tqc>>Tqb), which tends to cause thermal influence on the periphery of the machined hole. As for the processing time, if Tg>To is usually considered in formula 4 and formula 7, then

Tca-Tba＝n×(s-1)×(Tg-To)＞0…Formula 8

Therefore, compared with cycle processing, pulse group processing has shorter processing time and higher productivity.

In the above existing laser processing system, the beam diameter is controlled by the mask diameter, the beam energy is controlled by the discharge power density and discharge width, and the above-mentioned optical system, and the selection of pulse group processing and cycle processing or pulse group processing is used. The laser oscillation frequency controls the off-time of beam irradiation to ensure processing quality and productivity.

In addition, JP-A-4-41091 discloses laser processing for processing two kinds of materials. The laser output with peak power as shown in FIG. Inner surface copper foil 16.

Copper foil is usually difficult to process, so it is necessary to increase the energy of the irradiated beam. On the other hand, since copper foil has a high light reflectance, when a laser beam with a high peak power is irradiated for a long time, plasma is generated, and this plasma causes absorption of laser energy. In addition, copper foil has a high thermal conductivity and is easy to heat and cold. Therefore, it is generally considered that the method of irradiating large beam energy for a short time, that is, irradiating a laser beam with high peak power and short pulse width (S1 in FIG. 21 ), is suitable for penetrating the copper foil.

In addition, processing insulating resin is easier than the above-mentioned copper foil, so even small energy can be processed, but usually because the thickness of insulating resin used in printed circuit boards is thicker than copper foil, it is necessary to increase the total energy used for processing all resins.

However, if a large beam energy is irradiated for a short time (increasing the peak power) like the above-mentioned copper foil, the insulating resin with low thermal conductivity cannot conduct thermal energy in the depth direction, and the energy will be spread in the lateral direction, which cannot be obtained. The processing depth required by the purpose results in resin residue 17 and internal expansion 19 as shown in Figure 24 . Therefore, it is generally considered that it is appropriate to irradiate several shots (S2-S6 in FIG. 21) of low-peak-power laser beams in order to penetrate the insulating resin.

It is well known that by selecting various conditions for irradiating laser pulses as described above, it is possible to perform penetration processing of the surface layer copper foil 12a and penetration processing of the inner surface copper foil 12b up to the insulating resin 11 without deteriorating the processing quality.

However, if the existing laser processing system is used in actual processing, it will be limited as described below.

First, in the existing laser processing system, there is no method for changing the peak power greatly as mentioned above, especially it cannot be changed instantaneously (in the range below the maximum oscillation frequency of the laser oscillator).

Second, among existing pulsed laser oscillators, due to power supply capacity, etc., the oscillator that outputs a laser beam with a high peak power cannot output a laser beam with a long pulse width; on the contrary, the oscillator that outputs a laser beam with a long pulse width cannot Outputs a laser beam with high peak power.

Therefore, since the existing laser processing system performs processing with laser irradiation patterns as shown in Figs. 22 and 23, it is difficult to ensure both processing quality and productivity, and one of them must be sacrificed.

FIG. 22 shows laser irradiation patterns and processing states when a conventional laser oscillator outputting a laser beam with high peak power and short pulse width (1 to 15 μs) is used as the laser oscillator 2 of FIG. 15 .

As shown in S11 in FIG. 22 , a laser beam with a high peak power and a short pulse width is irradiated as the first shot to penetrate the surface copper foil 12 a.

In order to process the insulating resin 11a, the peak power is lowered, and four laser beams S12 to S15 are irradiated. In addition, a laser beam with slightly increased derating power was fired as the sixth shot for the purpose of removing residual resin.

A certain degree of processing quality can be obtained by processing based on FIG. 22 . However, in order to significantly reduce the peak power after the second shot as described above, the above-mentioned optical system cannot change instantaneously, so pulse group processing cannot be realized. Therefore, it is necessary to perform cyclic processing with low productivity and to increase the number of shots, which greatly reduces productivity. For example, when the number of holes n=10000, the average positioning time Tg=0.001 second (1kHz) considering the time required for condition conversion, and the number of rounds s=6 rounds, the processing time is 60 seconds, assuming that the pulse is performed with the same number of rounds The productivity is 1/2 compared to the processing time of 30 seconds in group processing (assuming To=0.0005 seconds (2kHz)).

FIG. 23 shows that the laser oscillator 2 of FIG. 15 uses an oscillator that outputs a laser beam with a low peak power (less than 1/4 of the oscillator in FIG. 22 ) and a long pulse width (such as 16 to 150 μs) with an existing oscillator. The laser irradiation pattern and processing status at the time.

As shown in S21 in Fig. 23, by lengthening the pulse width of the irradiated laser beam for the first shot, the energy of the beam is increased in order to penetrate the surface copper foil 12a, but compared with the first shot of Fig. 22, due to the peak power It is 1/4 or less. For the above-mentioned reasons, when the beam energy is not injected above the energy of the first shot shown in FIG. 22 , penetration is difficult. However, when the pulse width is longer than necessary to increase the beam energy, absorption due to plasma occurs, and the energy cannot reach the copper foil. Therefore, in order to penetrate the surface copper foil 12a, it is necessary to irradiate multiple high-energy laser beams (in this example, it is assumed that the surface copper foil 12a can be penetrated by 2 shots). The third shot irradiates a laser pulse S23 with a low peak power and a long pulse width to penetrate the insulating resin to the inner surface copper foil 12b. In the fourth shot, resin residues are removed by using a laser pulse S24 with a shorter pulse width than the peak rate of the third shot.

As mentioned above, although the processed surface copper foil 12a and the insulating resin 11a can be penetrated, the processing quality is deteriorated compared with the example of FIG. 22 due to too much energy for the copper foil. In addition, as in the description in FIG. 22, since the peak power cannot be changed instantaneously, burst processing cannot be performed, and only cyclic processing is possible.

As mentioned above, when processing printed circuit boards made of laminated materials of completely different materials, it is difficult to balance both processing quality and productivity with existing laser processing systems.

In addition, since there are various types of printed circuit boards, each processing content is different from resin processing to copper foil and resin mixed processing. Therefore, it is difficult to perform all processing with one laser processing system, and equipment investment is required. Big expense.

Contents of the invention

An object of the present invention is to solve the above-mentioned problems, and to provide a laser processing system capable of improving the processing quality of printed circuit boards of various materials without impairing productivity, and a laser processing method using the same.

In order to achieve this object, the laser processing system of the first invention is equipped with: a pulse laser oscillator capable of changing the characteristics of the laser beam by changing the discharge power input between the electrodes by switching the discharge command pulse composed of a predetermined frequency, and the The laser beam output from the laser oscillator is guided to the optical system of the workpiece.

In addition, the optical system has: a filter member that makes the peak power of the laser beam variable by transmitting the laser beam output from the laser oscillator, and a switch that switches an appropriate path that can pass through the filter member with different beam transmittances. means.

Furthermore, it is provided with: a laser oscillator that oscillates and outputs a laser beam by causing an excitation discharge between electrodes, and a filter member that makes the peak power of the laser beam variable by causing the laser beam to be output from the laser oscillator. , and switching means that can pass through the appropriate path of the filter member with different beam transmittance, and guide the laser beam to the optical system to be processed.

The on-off of the switch means is used to switch the path that can pass through the filter member, and at the same time control the pulse width of the pulse-oscillated laser beam.

Also, the laser processing method of the present invention uses a laser beam output from a pulsed laser oscillator whose characteristics of the laser beam can be changed by switching the discharge command pulse formed at a predetermined frequency to change the discharge power input between the electrodes, wherein, In the range below the maximum oscillation frequency of the laser oscillator, according to the material of the workpiece, the processing thickness, etc., the three conditions of the peak power and pulse width of the multiple laser pulses irradiated instantaneously for each pulse, and the off-time of beam irradiation .

Also, for the removal of the conductor layer, the output is close to the maximum peak power of the laser oscillator and the first pulse with a short width of 1 to 15 μs is used for processing; for the removal of the insulating layer, about 1/3 of the first pulse is used 2-1/10 peak power output and 16-200μs wide-width second pulse for processing.

In addition, by switching the discharge command pulse, the peak power is varied during the laser output period of one pulse, and the laser beam output by this pulse is used for processing.

In addition, using the first region having approximately the maximum peak power of the laser oscillator and a short time period of 1 to 15 μs, and the second region having a peak power of about 1/2 to 1/10 of the above-mentioned first region and a long period of 16 to 200 μs Laser output of 1 pulse of the area is processed.

Description of drawings

Fig. 1 is a schematic diagram for explaining a laser processing system according to the first embodiment.

Fig. 2 is a state diagram showing the means for controlling the laser irradiation pattern in the laser processing system according to the first embodiment.

Fig. 3 is a schematic diagram showing a laser irradiation pattern used in the laser processing method using the laser processing system of the first embodiment.

FIG. 4 is a schematic diagram for explaining a state of laser processing using the laser irradiation pattern of FIG. 3 .

Fig. 5 is a schematic diagram for explaining a laser processing system according to a second embodiment.

FIG. 6 shows a state diagram of a change in beam transmission rate caused by an object.

FIG. 7 is a structural diagram showing the structure of an object.

FIG. 8 is a state diagram showing changes in beam transmission rate and pulse width due to an object.

Fig. 9 is a schematic diagram for explaining a laser processing system according to a second embodiment.

Fig. 10 is a schematic diagram for explaining a laser processing system according to a third embodiment.

Fig. 11 is a schematic diagram for explaining a laser processing system according to a fourth embodiment.

Fig. 12 is a schematic diagram for explaining the means for controlling the laser irradiation pattern in the laser processing system according to the fourth embodiment.

Fig. 13 is a schematic diagram showing an irradiation pattern of a laser beam when the laser processing system according to Embodiment 4 is used for pulse group processing.

Fig. 14 is a schematic diagram for explaining hole-drilling of a general printed circuit board.

Fig. 15 is a schematic diagram for explaining a conventional laser processing system for drilling a printed circuit board.

Fig. 16 is a cross-sectional view of a printed circuit board for explaining the processing quality of laser drilling.

FIG. 17 is a structural diagram showing the configuration of an object consisting of a mask and a collimator lens.

Fig. 18 is a configuration diagram for explaining a CO ₂ laser oscillator.

Fig. 19 is a diagram illustrating a laser irradiation pattern for burst processing as a conventional laser processing method for drilling a printed circuit board.

Fig. 20 is a diagram illustrating laser irradiation patterns for circular processing as a conventional laser processing method for drilling holes in printed circuit boards.

Fig. 21 is a schematic diagram of a conventional laser irradiation pattern and a cross-sectional view of a printed circuit board.

Fig. 22 is a schematic diagram of a conventional laser irradiation pattern and a cross-sectional view of a printed circuit board.

Fig. 23 is a schematic diagram of a conventional laser irradiation pattern and a cross-sectional view of a printed circuit board.

Fig. 24 is a cross-sectional view showing a conventional printed circuit board of processing quality.

Detailed ways

Embodiment 1

1 and 2 relate to Embodiment 1. FIG. 1 is a schematic diagram for explaining the laser processing system of the present invention, and FIG. 2 is a schematic diagram for explaining means for controlling the laser irradiation pattern of the present invention.

In Fig. 1, 6a, 8a represent the laser beam and the laser radiation pattern output by the laser oscillator 2A, 7a, 9a represent the laser beam and the laser radiation pattern formed by the optical system 3, and the rest of the same parts as in Fig. 15 are labeled with the same symbols and omitted. illustrate.

In Fig. 2, 41a, 41b are discharge command pulse groups, 42a, 42b are discharge power pulse groups, 43a. 43b is discharge energy, 44a, 44b are output laser beam energy.

Also, fh and fl represent AC power frequency, Iu and Id represent effective discharge power density, Nu and Nd represent average discharge power density, Ds and Dl represent discharge width, Pu and Pd represent peak power, Ws and Wl represent pulse width, and Ls , Ll represent laser oscillation delay.

As described in the prior art, in gas laser oscillators such as _CO2 laser oscillators, in order to change the peak power and pulse width of the laser beam output by the oscillator, when the loss of the resonator is constant, the discharge power density is controlled. and discharge width. Since the discharge power density is directly proportional to the input power, the discharge power density is changed by changing the voltage applied between the electrodes in the prior art.

The laser oscillator involved in this embodiment focuses on the fact that the input power is divided into instantaneous power and time-averaged average power, and the peak power of the laser beam is dominated by the time-averaged average power. ), the average discharge power density is controlled by controlling the number of discharge power pulses per unit time, so that the peak power of the laser beam is changed. In other words, the three conditions of peak power, pulse width, and beam irradiation rest time of the plurality of laser pulses to be irradiated are instantaneously changed for each pulse according to the material, material composition, and processing thickness of the processed portion of the printed circuit board.

Here, in the prior art, since the number of discharge power pulses is constant, the effective discharge power density and the average discharge power density are in a proportional relationship, and the effective discharge power density is changed by voltage variation to control the average discharge power density.

The operation will be described below using FIG. 2 .

First, when a discharge command pulse is supplied at a time interval of 1/fp, a discharge power pulse is input between the electrodes from an AC power supply in synchronization with this (step fp). The height of the discharge power pulse is the instantaneous effective discharge power density I, which is the average discharge power density N after time averaging.

If the voltage applied between the electrodes is constant, the effective discharge power density is constant, and the more discharge power pulses m input per unit time, the higher the average discharge power density and the higher the peak power of the laser beam.

For example, when the discharge instruction pulse is provided at a short time interval (1/fh), in synchronization with it, the AC power supply puts in the discharge power pulse at a high frequency fh (the number of discharge power pulses input per unit time increases), and the average discharge power density Nu increases , output a laser beam with high peak power Pn.

On the contrary, when the discharge command pulse is provided at a long time interval (1/fl), in synchronization with it, the AC power supply puts in the discharge power pulse at a low frequency fl (the number of discharge power pulses input per unit time decreases), and the average discharge power density Nd decreases, Outputs a laser beam with low peak power Pd.

As described above, the pulse width of the laser beam is changed by changing the timing of applying power to the electrodes.

The power input time width D is expressed by the following formula:

D＝(1/fp)×m …Formula 9

Therefore, any pulse width can be obtained by controlling the discharge command pulse interval 1/fp and the discharge power pulse number m.

As mentioned above, in this embodiment, the peak power of the laser beam is obtained by modulating the frequency of the AC power supply, and an arbitrary laser pulse is obtained by changing the power input time and controlling the pulse width of the laser beam.

Specifically, arbitrary laser pulses are obtained by controlling the time interval and the number of discharge command pulses for supplying discharge command pulses.

Also, according to the present invention, a shorter pulse width is used when the peak power is high, and a lower peak power is used when the pulse width is long, thereby having the effect of expanding the selection range of pulse waveforms within a certain power supply load range.

Use the above control to change the peak power and pulse width of each laser pulse arbitrarily to obtain an arbitrary laser irradiation pattern 8a, and perform beam shaping on the obtained laser irradiation pattern through an optical system, and send it to the object to be processed as a laser irradiation pattern 9a, that is, to print The circuit board 1 is processed.

The pulse group processing method using the above-mentioned laser processing system will be described below.

As an example, the case of processing the same printed circuit board as in FIG. 21 , that is, a printed circuit board composed of a first-layer surface copper foil 12a, a second-layer insulating resin 11a, and a third-layer inner surface copper foil 12b, will be described.

FIG. 3 is a schematic diagram showing an irradiation pattern of a laser beam, and FIG. 4 is a schematic diagram for explaining a processing state at this time.

In FIG. 3 , S31 to S33 are the first to third laser beams of each hole, and each area represents the energy of the beam. P is the peak power, W is the pulse width, To is the laser oscillation time, and Tg is the positioning time.

In Fig. 4, 12a is the surface copper foil, 11a is the insulating resin, 12b is the inner surface copper foil, 20a is the predetermined processing position, 14a is the blind hole after processing, S31-S33 are respectively the first to third laser pulse waveforms, a1 ˜a3 are the parts to be processed processed by the 1st to 3rd irradiating laser beams.

In this embodiment, the laser irradiation pattern shown in FIG. 3 is used, and the peak power, pulse width, and beam irradiation rest time of the laser beam are instantaneously switched for each pulse according to the material, material composition, and processing thickness of the printed circuit board. Simultaneously, the shortening of the processing time was measured by the burst processing method.

Next, the laser processing method of this embodiment will be described with reference to FIGS. 3 and 4 on the premise of the relationship between the material and the laser beam described in the prior art.

First, the first laser beam S31 is irradiated as a laser pulse for processing the first layer of copper foil 12a. In order to stably penetrate the first layer of copper foil that can meet the copper foil removal conditions, a high peak power (about 1 to 3 kW) is irradiated. ) and short pulse width (1 ~ 15μs) laser pulse.

Next, the second laser beam S32 is irradiated as a laser pulse for processing the second layer of insulating resin 11a. In order to satisfy the insulating resin removal conditions and improve productivity, low peak power (about 0.05-0.5kW) and long pulse width ( 80-200μs) laser pulse.

This laser pulse is different from that shown in Figure 21. It uses a laser pulse with a low peak power of less than 1/6 of the first laser pulse and a laser pulse with a long pulse width more than 5 times that. Therefore, in Figure 21, it is necessary to irradiate multiple laser shots to penetrate the insulating resin. Beam, but adopt the present invention to only need to irradiate 1 round and get final product. That is, by extremely reducing the peak power to suppress the spread of energy in the radial direction, and by lengthening the pulse width to inject energy in the depth direction, it is possible to use one shot to penetrate the insulating resin and keep the machining hole diameter unchanged. As a result, since the number of shots can be reduced while ensuring the processing quality, unnecessary rest time of beam irradiation can be saved, thereby improving productivity.

Next, irradiate the third laser beam S33 as a laser pulse for processing the insulating grease 11a that has not been completely removed by the second laser beam S32. If a large energy is irradiated, the inner layer copper foil will be damaged, so the irradiation energy E3 is as low as Well, in order to suppress resin residue, the peak power should be higher than that of the second shot, so laser pulses with a slightly higher peak power (about 0.1 to 1kW) and shorter pulse width (about 1 to 30μs) than the second shot are irradiated.

As described above, in the present embodiment, in the case of the above-mentioned printed circuit board, it is possible to reduce the number of laser beams while ensuring good processing quality by irradiating with three laser beams.

As described above, in this embodiment, the peak power and pulse width of the laser beam are optimized for each pulse in accordance with the material and material composition of the printed circuit board, and are instantaneously changed in the range below the oscillation frequency of the pulsed laser oscillator. The peak power is processed by pulse groups, such as the laser irradiation pattern in FIG. 3 , so as to obtain the effect of improving both processing quality and productivity.

For example, the number of holes n=10000, the average positioning time To=0.0005 seconds (2kHz) considering the time necessary for condition switching, and the number of rounds s=3 rounds, the processing time is 15 seconds. Compared with the cycle processing of the irradiation pattern, it is shortened to 45 seconds. This is especially effective when it is desired to perform high-density hole processing on printed circuit boards processed by laminating layers of different materials.

In addition, the processing of blind holes has been described above, but when it is used for through hole processing, the peak power, pulse width, and irradiation rest time of the laser beam are configured in a pulse oscillator according to the material and material of the printed circuit board. The range below the oscillation frequency is optimized for each pulse, which has the effect of improving processing quality and productivity.

In addition, although the pulse group processing has been described above, it is of course also applicable to the cycle processing. Compared with the pulse group processing, the production efficiency is somewhat lower, but it has the effect of obtaining a good processing quality more stably. .

It can also be used in machining methods that use both pulse group machining and cycle machining. That is, not only focusing on the off-time of beam irradiation, but also optimizing the peak power and pulse width of the laser pulse according to the material and material composition of the printed circuit board, and using pulse group processing separately as a means to greatly change the off-time of irradiation And cycle processing, so that not only can obtain good processing quality stably, but also can improve the effect of productivity.

Moreover, by using the laser processing system of the printed circuit board of this invention, processing of various printed circuit boards can be performed with one laser processing system.

Implementation form 2

In the first embodiment described above, the case where the peak power and pulse width of the laser beam are changed by changing the average discharge power and the discharge width has been described, but the beam transmission rate of the optical system may also be changed. Therefore, this embodiment focuses on the beam transmission rate of the optical system.

Fig. 5, Fig. 6, Fig. 7, and Fig. 8 are all related to Embodiment 2. Fig. 5 is a schematic diagram illustrating the laser processing system of the present invention. Fig. 6 is a schematic diagram illustrating the means for controlling laser irradiation patterns. Fig. 7 shows Fig. 8 is a schematic diagram of an example of an object used as a means for controlling a laser irradiation pattern, and Fig. 8 is an operation diagram of the object.

In Fig. 6, 45a, 45b are laser beam energy shaped by the optical system.

Among Fig. 7, Fig. 8, 33 is the control unit that can change the laser beam transmission rate at any time, i.e. the object, 34 is the optical high-speed switch element that is used to suitably change the path of the laser beam 6b that is incident on the object 33, and 35 is an optical high-speed switch element that can change The half mirrors have different beam transmittance (beam transmittance) of the laser peak power of the incident laser light, and 36 is a damper for absorbing the laser light reflected by the half mirror 35 . Also, for convenience of description, the laser beams whose paths are changed by the switching elements 34a and 34b are used as 37a, 37b, and 38c.

Hereinafter, changes in the peak power and pulse width of the laser beam output from the optical system of this embodiment to the processing point will be described.

First, the operation of changing the laser peak power and pulse width when changing the beam transmission rate will be described with reference to FIG. 6 .

When the beam transmission rate of the optical system is, for example, 100% (usually less than 50%, but it is assumed to be 100% for simplification of explanation), the laser beam output from the laser oscillator is transmitted with the same peak power and pulse width as it is. to the processing point.

Here, when it passes through an object with a predetermined beam transmission rate, of the laser beam output from the laser oscillator, A% is transmitted through the object, B% is absorbed by the object, and C% is reflected by the object (A+B+ C = 100%). As a result, A% of the laser beam is output through the object, and the output peak power changes. For example, during the output of the laser beam 44a output by the laser oscillator shown in FIG. 6, when the beam transmission rate is reduced, the peak power changes from Pu to Pm (<Pu) and the pulse width of the laser beam 45a is still Ws.

Moreover, when the beam transmission rate of the laser beam 44b output by the laser oscillator is instantaneously set to 0%, the pulse width is changed from W ₁ to Wm (<W ₁ ) while keeping the peak power constant at Pd. Laser beam 45b.

As described above, in this embodiment, arbitrary peak power and pulse width can be obtained by controlling the beam transmission rate of the optical system. However, in order to convert the laser beam output by the laser oscillator to obtain any laser pulse, the maximum peak power and the longest pulse width are determined by the laser beam output by the laser oscillator, and the optical system cannot be used to convert the laser beam to a value greater than its peak power or Pulse Width.

Specifically, as an example of means for changing the beam transmission rate and pulse width of the above-mentioned optical system, an object 33 shown in FIG. 8 that can change the laser beam transmission rate at any time will be described.

The object 33 is composed of optical high-speed switching elements 34 a to 34 d , half mirrors 35 a to 35 b having different transmittances, and a damper 36 . In addition, the peak power and pulse width of the laser beam input to the object 33 will be described assuming that they are constant, and it will be assumed that the light is deflected when the high-speed switching element is turned on.

First, when the switching element 34a is turned ON, the laser beam 6b is transmitted to the switching element 34c as the laser beam 37a as it is. If the switching element 34c is turned off (OFF) at this time, the laser beam 36a is transmitted to the next switching element 34d as it is. When the switching element 34d is instantaneously switched from OFF to ON during beam transmission, the laser beam during the OFF period is 7b, but the laser beam is deflected during the ON period and is irradiated to the damper 36 . When the OFF time is short, a laser pulse 7b1 with a high peak power and a short pulse width is obtained as a result.

Next, when the switching element 34a is OFF and the switching element 34b is ON, the laser beam 6b passes through the switching element 34a, is deflected by the switching element 34b, and is transmitted to the half mirror 35a. When the transmittance of the half mirror 35a is, for example, 50%, the laser beam 37b has half the peak power of 6b and the same pulse width. The laser beam 37b is transmitted to the switching element 34c, is deflected when the 34c is turned on (ON), and is transmitted to the switching element 34d. The same operation as described above is performed in the switching element 34d, and as a result, the laser pulse 7b2 is obtained.

Next, when the switching elements 34a, 34b are OFF, the laser beam 6b is transmitted to the half mirror 35b through the switching elements 34a, 34b. Assuming that the transmittance of the half mirror 35b is, for example, 25%, the laser beam 37c becomes a laser beam whose peak power is 1/4 of that of 6b and whose pulse width is the same. Then, the laser beam 37c is transmitted to the switching element 34d. The operation opposite to the operation described above is performed in the switching element 34d. That is, the laser beam is deflected during the ON period of the switching element 34 d, and the laser beam passes through during the OFF period and is irradiated to the damper 36 . When the ON time is long, a laser beam 7b3 with low peak power and long pulse width is obtained as a result.

In addition, the method of controlling three types of peak powers is shown in the above description, but the same method can also be used to control two or more types of peak powers to obtain laser pulses with arbitrary peak powers and pulse widths.

In this embodiment, the laser beam output from the laser oscillator is converted into laser pulses with arbitrary peak power and pulse width by inserting the above-mentioned object into the optical system and switching ON/OFF of light at high speed.

If the above-mentioned optical system is installed in the laser processing system shown in FIG. 5, the same effect as that shown in Embodiment 1 is obtained, that is, the peak value of the laser beam is adjusted for each pulse according to the material and material composition of the printed circuit board. The power, pulse width and off-time of beam irradiation are optimized to achieve the effect of improving processing quality and productivity.

In addition, it is also possible to configure a processing system in which the above-mentioned optical system is combined with the laser oscillator described in Embodiment 1 (FIG. 9). As a result, the peak power and pulse width of the laser beam can be varied finer and more widely.

Therefore, if the above-mentioned laser processing system is used, the selection range is further expanded according to the material and material composition of the printed circuit board, and the peak power, pulse width, and beam energy of the laser beam are optimized for each pulse. The effect of improving processing quality and productivity can also be obtained by using a suitable material composition.

Implementation form 3

In the above-mentioned forms 1 and 2, the laser processing system composed of a single laser oscillator was described, but in this embodiment, a laser system composed of at least two laser oscillators having different peak powers and pulse widths of laser beams is provided. processing system.

FIG. 10 shows a schematic configuration diagram of the laser processing system of the present invention. In the figure, 2C and 2D are laser oscillators with different laser oscillation outputs, 3C and 3D are optical systems, 6c, 8c, 6d, and 8d are laser beams and laser irradiation patterns output by laser oscillators 2C and 2D respectively, 7d, 7d is the laser beam shaped by the optical system 3C, 3D.

Next, the operation of Fig. 10 will be described.

The laser oscillator 2C, for example, outputs the best high peak power and short pulse width laser pulse 6c through copper foil, and the laser oscillator 2D outputs the best low peak power and long pulse width laser pulse 7d through, for example, insulating resin. The laser pulses 8c and 8d are respectively transmitted to and irradiated on the printed circuit board 1 by the optical systems 3C and 3D. At this time, the copper foil on the printed circuit board 1 is irradiated with the laser beam 7c under control, and the insulating resin is irradiated with the laser beam 7d. That is, by control, in the case of the printed circuit board of FIG. 21 , the laser beam 7c is irradiated for the first time, the laser beam 7d is irradiated for the second time, and the peak power of the laser beam output by the laser oscillator 2C is reduced for the third time. By irradiation, the effect of improving the processing quality can be obtained as in the first embodiment.

Embodiment 4

Fig. 11 and Fig. 12 relate to Embodiment 4. Fig. 11 is a schematic diagram for explaining the laser processing system of the present invention, and Fig. 12 is a schematic diagram for explaining means for controlling the laser pulse waveform of the present invention.

In Fig. 11, 46a-e are discharge instruction pulse groups, 47a-e are discharge power pulse groups, 48a-e are input discharge energy, 49a-e are output laser beam energy.

The basic consideration of this embodiment is that the laser beam 6e output from the laser oscillator 2E in FIG. 11 is determined by the average discharge power density and discharge width when the resonator loss is constant as described in Embodiment 1. It can also be applied in the middle of laser oscillation. That is, in the general operation, by performing laser pulse waveform control as shown in FIG. 12, an arbitrary laser irradiation pattern 8e is obtained.

The operation of Fig. 12 will be described below.

Fig. 12 is applicable to the basic thinking method of Embodiment 1 above, that is, the resonator loss is taken as a constant, the peak power is controlled by the average discharge power density, and the pulse width is controlled by the discharge width. Also, as in the first embodiment, as a specific control method, a method of modulating the frequency of the AC power source for changing the average discharge power density and changing the time of power input for changing the discharge width is adopted.

First, when the discharge command pulse 46a is provided at a high frequency, the number of discharge power pulses input per unit time increases, and a high average discharge power density 48a can be obtained. With respect to this discharge energy 48a (N1×T1), laser oscillation is delayed by L1, and beam energy 49a (P1×W1) of high peak power is output.

Then, when the discharge command pulse 46b with a slightly lower frequency is continuously provided without presetting the time difference (light beam irradiation rest time), the discharge power pulse 47b is put in to obtain the discharge energy 48b (N2×T2). There is no delay in the laser oscillation this time. The front 49a sequentially outputs beam energy 49b (P2*W2).

Similarly, when the discharge command pulses 46c, 46d, 46e are continuously provided without preset time difference, the discharge energy 47c (N3×T3), 47d (N4×T4), 47e (N5×T5) is correspondingly obtained, which is the same as the previous 49b continuously outputs beam energy 49c (P3×W3), 49d (P4×W4), 49e (P5×W5). As a result, five kinds of laser pulse waveforms with arbitrary peak power were obtained.

In addition, as in the second embodiment, the obtained laser irradiation pattern 8e is beam-formed by the optical system 3E, and the laser beam waveform may be appropriately changed by the optical system to form the laser irradiation pattern 9e. That is, by controlling the switching operation of the object during laser oscillation to control the waveform of the laser beam described in Embodiment 2, a laser pulse waveform in which a plurality of peak powers as described above is mixed is obtained.

As described above, the same method of thinking as in Embodiments 1 and 2 is used during laser oscillation to obtain a laser pulse waveform in which a plurality of peak powers are mixed. However, as compared with Embodiments 1 and 2, if higher-speed and more stable control is not performed, the deviation per pulse may increase.

Next, a processing method using the above-mentioned laser processing system as a means will be described.

The processing method of the present embodiment is a case where the conditions of the laser pulse waveform are set in more detail in the processing method of the first embodiment.

FIG. 13 is a schematic diagram showing an irradiation pattern of a laser beam when the laser processing system of the present invention is used for pulse group processing.

In Fig. 13, it is assumed that the vth peak power among the u kinds of peak powers present in the first round is Piv, and when the time width maintained by Piv is Wiv, then the beam energy Ei of the laser beam irradiating the ith round is given by the following formula Certainly:

$\mathrm{Ei}=\underset{i=1}{\overset{\mathrm{no}}{\mathrm{\&Sigma;}}}(\mathrm{Piv}\&times;\mathrm{wiv})$ ...Formula 10

Here, in the present invention, Piv and Wiv are both control parameters that can be switched instantaneously (less than 1/2 of the laser pulse width), and can be switched by the above-mentioned method according to the processing content.

In FIG. 13 , S41 and S42 are the irradiation laser beams of P11×W11 and P12×W12 in the first shot, respectively, and S43 is the irradiation laser beam of P21×W21 in the second shot.

The operation will be described below.

The irradiation light beams S41 to S43 are used corresponding to the respective irradiation light beams of S31 to S33 described in the first embodiment. That is, S41 is a laser beam with a high peak power and a short time width, S42 is a low peak power and a long time width, and S42 is a laser beam with a peak power slightly higher than S42 and a short pulse width. Using the respective laser beams, substantially the same processing results as those of the processing method described in Embodiment 1 were obtained. That is, S41 is used to penetrate the surface copper foil 12a, S42 is used to penetrate the insulating resin 11a, and S43 is used to remove resin residues without damaging the inner surface copper foil 12b.

Also, since S41 and S42 are the same laser pulse, the number of shots required for each hole is reduced from 3 to 2. Therefore, there is an effect of reducing the rest time of beam irradiation, and the processing time required for opening n holes can be shortened more than in the first embodiment. For example, in the example shown in Embodiment 1, the processing time is 10 seconds. Compared with the pulse group processing of Embodiment 1, the processing time can be shortened by 5 seconds, and the productivity can be increased by 1.5 times.

As mentioned above, by using a laser processing system that controls the laser pulse waveform, the processing quality is improved, and the number of shots is reduced (reduced beam irradiation pause time), so productivity is also improved.

In addition, there is an effect of obtaining both processing quality and productivity that cannot be achieved in conventional laser processing systems.

Industrial availability

As described above, the laser processing apparatus of the present invention is suitable for drilling processing of workpieces such as printed boards.

Claims (8)

1. a laser-processing system is characterized in that possessing

Change the interelectrode discharge power of input by switching the discharge command pulse that constitutes with assigned frequency, can make the pulsed laser oscillator of the characteristic changing of laser beam, and

Optical system with the described laser beam direction machined object of this laser oscillator output.

2. laser-processing system as claimed in claim 1, it is characterized in that, optical system has: by making the laser beam transmission of laser oscillator output, the peak power that makes described laser beam is variable optical filtering member and the switch means of switching suitable path that can be by the different optical filtering member of light beam transmissivity.

3. laser-processing system is characterized in that possessing:

Between electrode, cause the excitation discharge, the laser oscillator of vibration outgoing laser beam, and

Have by making the described laser beam of described laser oscillator output, make the variable optical filtering member of peak power of described laser beam, with the switch means of switching the suitable path that can pass through the different optical filtering member of light beam transmissivity,

Optical system with the laser beam direction machined object.

4. as claim 2 or 3 described laser-processing systems, it is characterized in that, utilize the break-make of switch means, switching can be by the path of optical filtering member, the pulse duration of the laser beam of control impuls vibration simultaneously.

5. laser processing is used by switching the discharge command pulse that constitutes with assigned frequency to change and drop into interelectrode discharge power, and the laser beam of the variable pulsed laser oscillator output of the characteristic of laser beam is processed, it is characterized in that,

Scope below the maximum oscillation frequency of laser oscillator is according to the material of machined object, processing thickness etc., to a plurality of peak-power of laser pulse and pulse duration and these three conditions of light beam irradiates off time of the instantaneous switching irradiation of each pulse.

6. laser processing as claimed in claim 5 is characterized in that,

For removing of conductor layer, with the output of the maximum peak power that approaches laser oscillator and be that the 1st pulse of the short width of 1～15 μ s is processed;

For removing of insulating barrier, with the output of about 1/2～1/10 peak power of above-mentioned the 1st pulse and be that the 2nd pulse of the big width of 16～200 μ s is processed.

7. laser processing as claimed in claim 5 is characterized in that, and is variable in the laser period of output chien shih peak power of 1 pulse by the switch discharges command pulse, processes with the laser beam of this pulse output.

8. laser processing as claimed in claim 7, it is characterized in that, process with the laser output of 1 pulse in long the 2nd zone of about 1/2～1/10 peak power in the 1st zone of the short time with the roughly largest peaks power of laser oscillator and 1～15 μ s, above-mentioned the 1st zone and 16～200 μ s.

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