JP2002224873A - Laser beam machining method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser beam machining method and a device therefor by which a precise small hole such as a fine via hole is rapidly formed with high quality in a work such as a multilayered distributing board in which different materials are laminated. SOLUTION: When a precise hole of small diameter is machined at a prescribed place by the laser beam machining method, the prescribed place of the work is simultaneously irradiated with at least two or more laser beams 7, 12 and 17 different in wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-layered circuit board or the like to be processed, which is formed by laminating different materials.
The present invention relates to a laser processing method and a processing apparatus for processing a precision small hole such as a via hole for dimensionally wiring.

[0002]

2. Description of the Related Art With the recent increase in the performance of electronic equipment, there has been a demand for a higher density of wiring on a wiring board used therein, and in order to satisfy this demand, a multilayer and smaller wiring board has been required. ing. In order to realize such multi-layering and miniaturization, it is necessary to form a fine hole called a via hole and having a hole diameter of about 150 μm for interlayer conductive connection. But,
In the current drilling, it is difficult to drill holes of φ0.2 mm or less.
It is difficult to control the depth with this precision, and it is impossible to form a fine via hole by drilling.

[0003] As an alternative to the drilling, a method of forming a BVH is disclosed in IBM Journal of Research and Development (IBM J. Res. Develo).
p. ) Vol. 26, No. 3, pp. 306-317 (1982)
Year) and Japanese Patent Publication No. 4-3676,
Attention has been paid to a method of applying a laser beam such as a CO ₂ gas laser, and some methods have been put to practical use. The processing method using these laser beams is based on CO ₂ for resin or glass fiber, which is an absolutely green base material constituting a wiring board, and Cu, which is a conductor layer.
This is based on the difference in the absorptivity of the light energy of the gas laser.

FIG. 5 is a view for explaining a conventional laser processing method. FIG. 6 (a) shows a wiring board during laser processing.
(B) shows the wiring board after laser processing. In the figure, reference numeral 101 denotes a wiring board, and 102 denotes Cu which is provided on the surface of
A foil 103 is a laser beam emitted from a CO ₂ gas laser processing apparatus.

In addition, Cu which cannot be processed by a CO ₂ laser
In order to process such a metal, the third or fourth harmonic of an infrared laser such as a Nd: YAG laser is used.

[0006] As shown in FIG.
Foil removing section 10 having a hole diameter required for Cu foil 102 on the surface of
2a is formed in advance by a third or fourth harmonic of an infrared laser such as a Nd: YAG laser or by etching or the like, and is irradiated with a CO ₂ laser beam 103 through the removing portion 102a. Resin or glass in the wiring board 101 is selectively decomposed and removed to form fine processing holes 104 in the wiring board 101. Here, Cu is CO ₂
Since it has a characteristic of almost reflecting a gas laser, only the portion where the Cu foil 102 is removed is processed, and the portion where the Cu foil 102 is present is not processed.
A processing hole 104 as shown in FIG.

Further, as shown in FIG. 7, if the inner layer Cu foil 102b is previously laminated inside the processed portion, the decomposition and removal of the insulating base material is stopped at the inner layer Cu foil 102b. When stopped, the hole 104 can be formed.

[0008] However, as shown in FIG. 7, when stopping at the Cu foil and processing the perforated hole with a CO ₂ gas laser,
Even if the laser beam is sufficiently irradiated, the resin as the insulating base material having a thickness of 1 μm or less remains on the inner layer Cu foil. For this reason, after laser processing, it is necessary to completely remove the residual resin by etching the residual resin with permanganic acid or the like.

[0009]

SUMMARY OF THE INVENTION As described above, CO ₂
In the laser processing, a metal such as Cu cannot be processed. Therefore, a laminated substrate is manufactured using a Cu substrate having a hole in advance, and a non-metal such as epoxy or polyimide is opened later. For this reason, the number of processes increases, which causes a delay in tact time and an increase in manufacturing cost. Further, when the hole diameter is 50 μm or less, there is a disadvantage that the laser beam cannot be narrowed down and processing cannot be performed.

When the third or fourth harmonic of an infrared laser such as an Nd: YAG laser is used, the conversion efficiency is about 30% since the fundamental laser beam is wavelength-converted at least twice. Below and low. In addition, since a conductive layer of Cu or the like can be easily processed by UV light, it is difficult to stop the hole processing at an intermediate conductive layer.

The present invention has been made on the basis of these circumstances, and is capable of quickly and accurately forming small holes such as fine via holes on a workpiece such as a multilayer wiring board on which different materials are laminated. It is an object of the present invention to provide a laser processing method and a laser processing method which can be formed on a substrate.

[0012]

According to the first aspect of the present invention, a workpiece formed by laminating different materials is irradiated with laser light from a solid-state laser oscillator to form a precise small hole at a predetermined location. In the laser processing method for processing a plurality of laser beams, the wavelength of the plurality of laser beams simultaneously applied to the object to be processed is a combination of two or more wavelengths of 400 nm to 600 nm and 400 nm or less.

According to the second aspect of the present invention,
A laser processing method, wherein two or more harmonics generated from a fundamental wave of the laser oscillator are simultaneously irradiated on the workpiece.

According to the third aspect of the present invention,
The laser processing method is characterized in that the laser beam of the laser oscillator has a variable number of repetitions of oscillation for each material of a workpiece to be irradiated.

According to a fourth aspect of the present invention,
A laser oscillator that outputs a fundamental wave as a laser beam using a solid-state laser medium, and a harmonic generation unit that is disposed in front of an optical axis on the output side of the laser oscillator and generates a harmonic with respect to the fundamental wave; An optical system for simultaneously irradiating a harmonic generated by the harmonic generating means and the fundamental wave to the same portion of the workpiece.

According to the fifth aspect of the present invention,
A plurality of laser oscillators that output laser beams of mutually different wavelengths using a solid-state laser medium, and are provided on the optical axis on the output side of the laser oscillator, and the laser beams of mutually different wavelengths are applied to the workpiece. An optical system for simultaneously irradiating the same location with an optical system.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a solid-state laser processing method and apparatus according to the present invention will be described.

First, the phenomena underlying the present invention and the concept thereof will be described.

When a laser beam is applied to a workpiece to perform laser processing, when the workpiece is a metal such as Cu, the reflectance is high when the oscillation wavelength of the laser oscillator is longer than 600 nm. Not suitable for On the contrary,
When the oscillation wavelength of the laser oscillator is 600 nm or less, it can be used for processing because the transparency of laser light is improved.

When the object to be processed is a non-metallic material, it has a high transmittance in the visible region (400 nm to 700 nm).
Since they have large absorption characteristics at wavelengths of nm or less, processing at those short wavelengths is indispensable.

That is, in order to form a hole such as a via hole with a laser beam on a laminated substrate in which a metal such as Cu and a non-metal such as an epoxy resin are alternately laminated, a wavelength for metal processing is required. Laser light of 400 nm to 600 nm,
It suffices to prepare a laser beam having a wavelength of 400 nm or less for non-metal processing.

As described above, when the workpiece is metal,
This indicates that the second harmonic of about 500 nm can be effectively used for processing. That is, when the second harmonic is used for the processing, the output of the substantial laser beam acting on the processing is improved, and the processing efficiency can be improved to 30% or more. As a result, power consumption and processing time can be reduced.

Therefore, in the case of laser processing, Nd: YA
It is advisable to use the second harmonic generated in the process together with the third or fourth harmonic of an infrared laser such as a G laser for the processing.

In the case where the object to be processed has a laminated structure and the conductive layer and the non-conductive layer are alternately laminated, when the hole processing is stopped at the intermediate conductive layer, the material of each layer to be processed is required. The processing can be controlled by changing the number of laser oscillation repetitions.

Specifically, in the case of Cu or the like which is a conductive layer, the number of repetitions is reduced, and processing is performed using a laser beam having a short pulse width and a high peak output. On the other hand, when the target is a nonmetal that is a nonconductive layer, the pulse repetition rate is increased. This is because a conductive layer such as Cu has better thermal conductivity than a nonmetal such as an epoxy resin or a polyimide resin, so that brilliant processing cannot be performed unless a laser beam having a shorter pulse width is irradiated. Conversely, it is difficult to process with a long pulse width.
On the other hand, for the non-metal layer, the wavelength is more important than the pulse width, and as described above, the visible region (400 nm to 700 nm) is used.
m) has high transmittance, has a large absorption characteristic at a wavelength of 400 nm or less, and processing at a short wavelength is indispensable.

From these, the repetition is increased in a non-metal layer such as an epoxy resin or a polyimide resin, and the non-metal layer is processed by processing with a laser beam having a short pulse width and a low peak output. Processing does not proceed any further even if the laser beam is irradiated to any conductive layer, and the processing can be stopped cleanly on the surface of the conductive layer only by processing the non-metal layer.

When the hole processing is stopped at the intermediate conductive layer, the light generated from the laser irradiation position (processing point) is detected by the photodetector. At the processing point, energy is injected into the workpiece by laser light irradiation, so that light having a wavelength specific to the constituent atoms and molecules is generated. By detecting this light, the material being processed can be specified. This is performed in real time, and the laser irradiation is stopped when the processing of an arbitrary layer is started, whereby the processing of the layer can be stopped. Next, as a first embodiment of the present invention, referring to FIGS. 1 and 2, a second harmonic (SHG) and a third harmonic (THG) are output by a solid-state laser device using an Nd: YAG laser.
HG) is generated to process the workpiece.

FIG. 1 is a configuration diagram of a solid-state laser device, and FIG. 2 is a schematic perspective view of a laser processing device equipped with the fixed laser device.

First, the solid-state laser device 27 will be described. The solid-state laser device 27 includes an Nd: YAG laser oscillator 6, a second harmonic generator 10, a third harmonic generator 15, and a beam shaping optical system 28. Have been.

In the Nd: YAG laser oscillator 6, an optical resonator is constituted by a pair of opposed resonator mirrors 1a and 1b, in which an Nd: YAG rod 3 and an AO using an acousto-optic effect are used. -Q switch 4, Polarizer 5
Is built-in. Nd: YAG rod 3 is LD
Excited at 2. The LD 2 is connected to the LD power supply 20 and oscillates a laser beam by an electric input from the controller 30. The AO-Q switch 4 has a Q switch driver 2
The Q switch driver 21 receives an ON / OFF repetitive signal from the controller 30.

Note that LD2 and Nd: YAG rod 3, A
The OQ switch 4 is cooled by the cooler 19.

With these configurations, the Nd: YAG rod 3 excited by the LD 2 oscillates a laser beam having a wavelength of 1064 nm at the resonator mirrors 1a and 1b. At this time, AO
RF ON / OFF of the -Q switch 4 is repeated at a frequency of several kHz to several tens kHz from the Q switch driver 21. HF (Hig) from the Q switch driver 21
Laser oscillation is performed when the (h Frequency) input is OFF. The laser light oscillated by the volatilizer 5 installed in the resonator mirrors 1a and 1b is restricted to linearly polarized light.

The laser light (fundamental wave 7) oscillated by the Nd: YAG laser oscillator 6 is guided to the second harmonic generation unit 10, and the condensing lens 8a provided in the second harmonic generation unit 10
Is incident on the nonlinear crystal LBO _{(LiB 3 O} 4) 9 through a fundamental wave 7 which is incident is about half this LBO9 inside is converted into SHG12 (second harmonic). And LB
After the transmission through 09, the light is collimated again by the condenser lens 8b. Accordingly, the polarization direction of the fundamental wave 7 and the SHG 12 emitted from the SHG (second harmonic) generator 10 are orthogonal to each other.

The LBO 9 is controlled by the temperature controller 11 to 150
The temperature is controlled at around ℃. This is because the refractive index is not only a function of the wavelength but also a function of the temperature, so that the size of the birefringence is adjusted by changing the temperature of the crystal.

The fundamental wave 7 and the SHG 12 output from the second harmonic generator 10 are input to a third harmonic generator 15. In the third harmonic generation unit 15, the light enters the nonlinear crystal LB014 via the condenser lens 13a. LB014 is controlled by the temperature controller 16 at a temperature of about 30 ° C.
About half of the incident fundamental wave 7 and SHG 12 are converted into THG (third harmonic) 17 inside the LBO 14. After passing through the LBO 14, the light is collimated again by the condenser lens 13b.

The fundamental wave 7, SHG 12, and THG 17 emitted from the third harmonic generation unit 10 are transmitted through the first dichroic mirror 28a forming the beam shaping optical system 28, and only the fundamental wave 7 is transmitted. The SHG 12 is reflected by the THG 17, and the SHG 12 and the THG 17 are guided to a predetermined optical path by the second dichroic mirror 12b.

Next, the above-mentioned modification will be described with reference to FIG. The same functional portions as those in FIG. 1 are denoted by the same reference numerals, and their description will be omitted.

In this case, the wavelength is 4 as the fundamental wave 7a.
Laser light between 00 nm and 600 nm (for example, Nd-
YAG) is used.

This solid-state laser device 27a is composed of Nd: YA
It comprises a G laser oscillator 6, a second harmonic generator 10, and a beam shaping optical system 28.

With these configurations, the metal layer is processed with the fundamental wave 7a, and the non-metal layer is processed with a wavelength of 4.
The processing is performed by the SHG 12a having a thickness of 00 nm or less.

As further modified examples, although not shown, there are a first laser oscillator having a wavelength of 400 nm to 600 nm and a second laser oscillator having a wavelength of 400 nm or less.
The metal layer and the non-metal layer can be processed using a single laser oscillator, respectively. Nd: Y as a solid-state laser medium used for these laser oscillators
AG, Nd: YLF, Nd: YVO ₄ , Yb: YAG and the like can be used.

Hereinafter, with reference to FIG. 2, a description will be given of a laser processing apparatus equipped with the solid-state laser device shown in the above-described embodiment and each modified example. Although the solid laser device is designated by the reference numeral 27, the solid laser device shown in each modification is also included therein.

The SHG 12 and the THG 17 emitted from the beam shaping optical system 28 of the solid-state laser device 27 are shaped into an arbitrary shape and profile by the beam shaping optical system 28 and are incident on the scanner 22. The scanner 22 has two scanner mirrors 23 and 24,
3a and 24a are connected to each other. The mirror driving devices 23a and 24a change the angles of the scanner mirrors 23 and 24 so that the irradiation position of the laser beam can be changed two-dimensionally. The SHG 12 and the THG 17 reflected by the scanner mirror 23 are condensed by the fθ lens 24 so as to be focused near the surface of the substrate 25 to be processed.

Normally, the scanner mirror 23 and the fθ lens 2
The range that can be moved by 4 is about 100 on the substrate 25 to be processed.
It is about mm × 100 mm. Therefore, when processing a larger area, the XY stage 26 on which the substrate 25 is mounted may be operated to move the substrate 25. As a result, portions of the substrate 25 to be irradiated with the laser beams SHG12 and THG17 are perforated at a depth corresponding to the number of pulses of the laser beam.

Next, a working example using the laser device of the present invention will be described. (Example) Fundamental wave output 10 W (repetition rate 10 kHz),
Using a SHG output of 4 W and a THG output of 1 W, drilling was performed on a multilayer wiring board (not shown). The multilayer wiring board used for the drilling process has a seven-layer structure, and has a Cu layer 12
μm, epoxy layer 50 μm, Cu layer 18 μm, glass epoxy layer 500 μm, Cu layer 18 μm, epoxy layer 50
μm and a Cu layer of 12 μm.

At the time of processing this multilayer wiring board, the Cu layer 12 μm has approximately 5 pulses and the epoxy layer 50 μm.
μm is 15 pulses, and each hole having a diameter of about 30 μm was formed.

When the SHG light was irradiated together, the effect was particularly observed in the processing on the Cu layer, and the processing was possible with about half the number of pulses.

The results of this example will be further described in terms of the spectral reflectance characteristics of Cu shown in Table 1.

[Table 1] The spectral reflectance characteristic of Cu is as high as 98% for a fundamental wave (1064 nm). Therefore, it turns out that it is not suitable for processing into Cu.

However, the reflectance of Cu decreases when the wavelength is 600 nm or less, and the THG (355) after 400 nm is used.
nm) or about 40% for FHG (266 nm), which is about 6%.
0% is absorbed. In the middle SHG (532 nm), the reflectance is about 60%, and it can be seen from Table 1 that about 30 to 40% of absorption is performed. From this,
It can be confirmed that SHG is effective for processing into Cu.

FIG. 4 is a graph showing characteristics when the number of repetitions of the fundamental wave in the above embodiment is changed. Increasing the number of repetitions increases the average output, but increases the pulse width. Thereby, the peak output emitted from the solid-state laser device also decreases. When processing a metal having good thermal conductivity such as Cu, it is essential to input energy in a short time for processing.

In the above embodiment, the repetition rate is set to 20 kHz.
, The processing speed of Cu was remarkably reduced. Therefore, when processing the first Cu layer, the number of repetitions is 10 k.
Hz and 20k when processing the second epoxy layer
Processing was performed at a repetition rate of Hz. Actually, since it is not known where the layer changes, the irradiation was carried out at 10 kHz in advance by several pulses more than the number of pulses through which Cu penetrated (for example, 5 pulses), and thereafter, processing was performed at 20 kHz. This allows
Even if the epoxy layer was over and the next Cu layer appeared, the Cu was not processed even if irradiation was performed for 10 pulses or more.
In this connection, in addition to Cu, Au, Ag, P
Similar results were confirmed for t, Al, Ni, Ti, Mo, and alloys containing them.

Thus, since the variation in the number of pulses for each processing until the hole is penetrated by the hole processing is larger, the processing can be reliably stopped at an arbitrary Cu layer.

Next, as a second embodiment of the present invention,
A description will be given of a laser processing apparatus with a monitor provided with a monitor whose configuration is shown in FIG.

The basic configuration of the laser processing device with monitor
1, a solid-state laser device 27, a scanner 22, and an XY stage 26 similar to those of the first embodiment shown in FIGS.
And the substrate 2 to be processed mounted on the XY stage 26
In this configuration, a monitor 29 for observing the machining point 9 is provided.
Therefore, to avoid duplication, FIG.
1 and 2 are denoted by the same reference numerals as in FIG. 1 and FIG.

The monitor 29 is constituted by a photodetector, and optically detects a processing point of the substrate 25a being processed.
On the light receiving surface side of the light receiving portion of the photodetector, a filter that transmits light having a wavelength of only around 578 nm and does not transmit light having a wavelength of 532 nm, 355 nm, or the like is provided.

Thus, since Cu has a strong light emission spectrum at 578 nm, it can be detected when laser light is irradiated. The detection signal of 578 nm is input to the controller 30a, and when the detection signal reaches an arbitrary size or more, C
It is determined that the laser light has been irradiated to u, and an OFF signal is sent to the Q switch driver 21a (the trigger signal is stopped). Thus, the processing can be stopped at the Cu layer of the substrate 25a to be processed.

That is, by measuring the number of times that the signal from the photodetector increases, the processing can be stopped at an arbitrary layer of Cu. Further, the number of repetitions can be switched before and after the processing of the Cu layer, and processing can be performed under conditions of the optimum number of repetitions for processing each material. The transmission or absorption area of the filter provided on the light receiving surface side of the light receiving section of the photodetector is
Depends on the material to be detected.

As described above, in the processing of a multilayer wiring board, SHG light having a wavelength of 400 nm to 600 nm is also effective for processing Cu, and when used together with THG or FHG, efficient and fast processing becomes possible. .

Further, by changing the repetition number for each material to be processed and changing the pulse width and peak output of the laser beam to be irradiated, the processing can be easily stopped at an arbitrary layer. Furthermore, by detecting the light generated by the laser beam irradiation, the material currently being processed can be clarified, and processing can be stopped at an arbitrary layer, and the optimum number of repetitions for each material can be selected. Reliability and efficiency can be improved.

As described above, in the above-described embodiment, Nd: YAG is used as the laser medium of the solid-state laser device, but Nd: YAG, Nd: YLF, Nd: YAG
d: YVO ₄ and Yb: YAG can be used.
The laser medium does not need to be particularly limited, and does not depend on its material, shape, or size. That is, the same effect can be obtained as long as laser oscillation can be performed. Also,
Although an LD is used to excite the laser medium, the excitation method can be arbitrarily selected by other means as long as the laser oscillates.

Although an AO-Q switch utilizing an acousto-optic effect such as a Bragg cell is used for the Q switch,
Similar effects can be obtained by using an EO-Q switch utilizing an electro-optical effect such as the Kerr effect or the Pockels effect, or a mechanical Q switch system such as a shutter or a rotating prism.

Although the LBO crystal is used for SHG and THG, SHG, THG, FHG
The same effect can be obtained with a non-linear crystal that is effective for equal wavelength change.

In the above embodiment, SHG and THG are generated from one solid-state laser, but the same effect can be obtained by combining and irradiating laser beams generated by a plurality of solid-state lasers.

In the above-described embodiment, an example has been described in which a via hole is formed in a multilayer wiring board as a processing target. However, the processing target is not limited to this, and any processing may be performed if different materials are laminated. The laser processing method and apparatus of the present invention can be applied to them.

[0065]

According to the present invention, a rapid and accurate via hole can be formed in a multilayer wiring board formed of different materials.

Also, besides the multilayer wiring board, optimum processing conditions can be similarly set for processing objects including different materials, so that improvement in processing efficiency can be expected.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a solid-state laser device according to the present invention.

FIG. 2 is a schematic perspective view of a laser processing apparatus according to the present invention.

FIG. 3 is a configuration diagram of a modified example of the solid-state laser device of the present invention.

FIG. 4 is a graph showing output characteristics when the number of repetitions of a fundamental wave is changed.

FIG. 5 is a configuration diagram of a modified example of the laser processing apparatus of the present invention.

FIG. 6A is an explanatory view of a conventional wiring board during laser processing. (B) Explanatory drawing of the wiring board after the laser processing.

FIG. 7 is an explanatory view of another wiring board during the conventional laser processing.

[Explanation of symbols]

6 Nd: YAG laser oscillator, 7 fundamental wave, 9 LB
O, 10: second harmonic generator, 12: SHG, 14: L
BO, 15: third harmonic generator, 17: THG, 27,
27a: solid laser device, 28: beam shaping optical system, 3
0 ... controller

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) H05K 3/46 H05K 3/46 X B23K 101: 42 B23K 101: 42 F term (Reference) 2K002 AA04 AB12 BA03 CA02 HA20 4E068 AF00 CA04 CD02 CE03 DA11 DB14 5E346 AA43 CC09 CC10 CC32 GG15 HH32 5F072 AB02 AK01 JJ02 JJ07 JJ09 KK06 KK12 MM04 PP07 QQ02 SS06 YY06

Claims (5)

[Claims] 1. A laser processing method for irradiating a laser beam from a solid-state laser oscillator to a workpiece formed by laminating different materials to form a precise small hole at a predetermined position, simultaneously irradiating the workpiece. The wavelengths of the plurality of laser beams are
Wavelength 400 nm to 600 nm and wavelength 2
A laser processing method characterized by combining wavelengths or more. 2. The laser processing method according to claim 1, wherein two or more harmonics generated from a fundamental wave of the laser oscillator are simultaneously applied to the workpiece. 3. The laser processing method according to claim 1, wherein the laser beam emitted from the laser oscillator has a variable number of repetitions of oscillation for each material of a workpiece to be irradiated. 4. A laser oscillator for outputting a fundamental wave as a laser beam using a solid-state laser medium, and a harmonic disposed on the optical axis on the output side of the laser oscillator to generate a harmonic with respect to the fundamental wave. A laser processing apparatus comprising: a harmonic generation unit; and an optical system that simultaneously irradiates a harmonic generated by the harmonic generation unit and the fundamental wave to the same portion of a workpiece. 5. A plurality of laser oscillators for outputting laser beams of mutually different wavelengths using a solid-state laser medium, and the laser beams of different wavelengths provided on the optical axis on the output side of the laser oscillator. And an optical system for simultaneously irradiating the same portion of the workpiece with the laser beam.