JP2002217550A - Laser processing method, laser processing device and manufacturing method of multilayer printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser boring method and a laser borer which can process a via hole for an insulation resin layer and a metal layer, forming a multilayer substrate successively with high efficiency and high yield in the same process. SOLUTION: Identical wavelength output from one unit of pulse laser oscillator 1 is used for a laser beam L emitted for irradiating metal layers 11a, 11b and insulation resin layers 12a, 12b. The metal layers 11a, 11b are processed, without the use of a uniform optical system 4 and a mask 5. The insulation resin layers 12a, 12b are processed by using the uniform optical system 4 and the mask 5. Different wavelengths output from two units of pulse laser oscillators 15, 16 are used for laser beams L1, L2, emitted for irradiating the metallic layers 11a, 11b and the insulation resin layers 12a, 12b. The metallic layers 11a, 11b and the insulation resin layers 12a, 12b are processed, by using the same uniform optical system 20 and mask 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser drilling method and apparatus for forming a via hole in a laminated substrate in which a metal layer and an insulating resin layer are superposed, and a method for manufacturing a multilayer wiring board using the same.

[0002]

2. Description of the Related Art A printed circuit board on which electronic components used for a cellular phone, a personal computer, and the like are mounted. Particularly, in the production of a laminated board, an insulating resin between wiring layers is used to make electrical connection between laminated wiring patterns. It is necessary to form holes (via holes) in the layer. In the case of a high-density laminated substrate, the number of via holes per substrate is in the range of thousands to tens of thousands.
Therefore, high-speed drilling is indispensable in the production line of the laminated substrate.

[0003] Conventionally, a method of forming a via hole by drilling or by photolithography has been used. However, in the current drilling, it is difficult to form a hole of φ0.2 mm or less. In a wiring board, the thickness of the insulating layer is 100 μm or less, and it is difficult to control the depth with this precision. Therefore, it is impossible to form a fine via hole by drilling. Further, the method using photolithography complicates the process and is not suitable for improving the productivity. Along with these circumstances, with the demand for a multilayer substrate on which electronic components are mounted at a higher density, laser processing capable of forming a via hole with a smaller diameter has been used.

In a conventional technique using laser processing, a method called a conformal method has been used. In this method, holes are formed in the outermost metal layer by etching, the surface of the insulating resin layer is exposed, and then the exposed surface is irradiated with laser light to process the insulating resin layer. 10μ by CO ₂ gas laser oscillator for processing of insulating resin layer
m laser light is used.

As a method of processing the metal layer and the insulating resin layer in the same step, a method using an ultraviolet laser beam such as a third harmonic of a YAG laser may be used.

Usually, the metal layer has a higher laser intensity (fluence) required for processing than the insulating resin layer. For example, when a copper foil is used as the metal layer, the fluence is 3 J / c.
m ² or more is required. Further, it is necessary that the third metal layer serving as the bottom surface of the formed via hole is not damaged by laser irradiation. Further, after the formation of the via hole, it is necessary that the insulating resin is completely removed at a desired diameter at the bottom of the via hole in order to perform interlayer connection by plating, for example.

[0007] Therefore, in order to continuously process the metal layer and the insulating resin layer in the same step, a means for changing the fluence during the processing of the metal layer and the processing of the insulating resin layer is required. When processing the resin, it is necessary to flatten the intensity distribution of the laser beam and to process with a fluence that does not damage the metal layer serving as the bottom of the via hole.

As such a laser processing apparatus, a method of inserting an attenuator for limiting a laser power on an optical path of a laser beam and changing a fluence during a processing step is sometimes used.

Japanese Unexamined Patent Publication No. 2000-190088 discloses that a laser beam generated from a laser oscillator for generating two or more wavelengths is selected by a harmonic generator or a beam switching device to perform drilling or the like. A technique is disclosed in which the main processing is performed with a fundamental wave and the sub processing such as smear removal is performed with a harmonic.

[0010]

However, in the above-mentioned conformal method, separate processing steps are required for the metal layer and the insulating resin layer forming the laminated substrate, and equipment is required. Processing in separate steps is not preferred in terms of productivity.

In addition, when fluence control is performed on laser light using an attenuator, when processing an insulating resin layer of a laminated substrate, laser energy is greatly lost. Further, generally, when an optical system for flattening the laser intensity distribution is installed, energy loss increases, and thus there is a problem in that the processing speed when processing the metal layer also decreases.

Further, in the technique disclosed in Japanese Patent Application Laid-Open No. 2000-190088, there is disclosed a technique for removing a smear remaining on a bottom copper foil of a hole when the hole is formed and the hole is formed. It's just that.

The present invention has been made based on these circumstances, and via holes can be continuously formed in a metal layer and an insulating resin layer forming a laminated substrate in the same process with high efficiency and high yield. It is an object of the present invention to provide a laser drilling method, a laser drilling apparatus, and a method for manufacturing a multilayer wiring board using the same.

[0014]

According to the first aspect of the present invention, a metal layer is formed by laminating a metal layer on a surface of an insulating resin layer, and the metal layer is irradiated with a laser beam. In the laser processing method for performing a drilling process that communicates with a layer and the insulating resin layer, the laser light to the metal layer and the insulating resin layer can switch the same wavelength output from one pulse laser oscillator. Performed using two optical paths,
The processing on the metal layer is performed in one path without using the uniformizing optical system and the mask, and the processing on the insulating resin layer is performed in the other optical path using the uniforming optical system and the mask. This is a laser processing method.

According to the second aspect of the present invention,
The laser light output from the pulse laser oscillator is Y
A laser processing method characterized by being a third harmonic of an AG laser.

According to the third aspect of the present invention,
In a laser processing method of irradiating a laser beam to the metal layer of the laminated substrate formed by laminating a metal layer on the surface of the insulating resin layer and performing a drilling process communicating with the metal layer and the insulating resin layer, The laser processing method is characterized in that the laser light applied to the metal layer and the insulating resin layer is performed using different wavelengths output from two pulse laser oscillators.

Further, according to the means of the present invention,
The laser processing method is characterized in that the laser light output from the two pulse laser oscillators is ultraviolet light.

According to the fifth aspect of the present invention,
The laser processing method is characterized in that the processing on the metal layer and the processing on the insulating resin layer are performed in the same step.

Further, according to the means of the invention of claim 6,
A laser oscillator, and a laser processing apparatus in which two optical paths for irradiating a workpiece are formed by switching a movable mirror provided in front of an optical axis on an output side of the laser oscillator; Is a laser processing apparatus in which a uniforming optical system and a mask are arranged, and an f-θ lens arranged in front of the optical axis is shared with the other optical path.

According to the means of the invention of claim 7,
In a laser processing apparatus in which two laser oscillators and two optical paths for irradiating a workpiece with a dichroic mirror provided on the optical axis of a common optical path on the output side of the two laser oscillators are formed, In front of the dichroic mirror on the optical axis, a uniforming optical system, a mask and f
A laser processing apparatus, wherein a -θ lens is disposed.

According to the means of the invention of claim 8,
A method for manufacturing a multilayer wiring board, wherein the above-described laser processing method is used for forming a through hole penetrating an insulating layer and a conductive layer formed on a surface thereof.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view showing a laser drilling apparatus which is an example of a laser processing apparatus according to the present invention.

The laser drilling device includes a reflection mirror 2 for reflecting the emitted laser light L, and a laser light L reflected by the reflection mirror 2 in front of an optical axis of a pulse laser oscillator 1 for generating an ultraviolet laser. Scan mirror 3 for selectively changing the optical path of the first scan mirror 3
In one of the selectively changed optical paths, a uniforming optical system 4 for flattening the intensity distribution of the laser light L, and a part of the transmission of the laser light L, and a desired hole shape at the processing point. A pair of second scan mirrors 6a and 6b for operating the laser beam L at the processing point;
An f-θ lens 8 for condensing the laser light L emitted from the second scan mirrors 6a and 6b at a processing point is provided.

A third scan mirror 7 is provided on the other optical path of the first scan mirror 3 selectively changed via a reflection mirror 9. This third scan mirror 7 cooperates with one second scan mirror 6b,
The emitted laser light L enters the f-θ lens 8.

First to third scan mirrors 3 and 6
Reference numerals a, 6b, and 7 are mounted on mirror driving devices (not shown), respectively. The mirror driving devices are controlled by a controller described later, and each of the scan mirrors 3, 6a, and 6 is controlled.
b and 7 are configured to be able to change the angle with respect to the optical axis.

An XYZ table 9 is provided in front of the f-θ lens 8 for moving the working range of the scan mirror 6b and changing the working distance of the work 14 such as a laminated substrate. ing. In addition,
The operation of the XYZ table 9 is based on the XYZ table 9
Are controlled by a controller connected to the drive unit (not shown).

As the pulse laser oscillator 1, for example, the third harmonic (wavelength: 355 nm) of a YAG laser is used. Further, as the uniformizing optical system 4, for example, an array lens group, a kaleidoscope, an optical fiber, or the like is used.
The mask 5 is made of, for example, a copper plate, and has, for example, a circular hole 5a according to the shape to be processed.

Next, a description will be given of processing on a laminated substrate which is a workpiece to be processed by these configurations. FIG. 2 shows the workpiece 1
4 is a cross-sectional view of the laminated substrate, in which metal layers 11a and 11b and insulating resin layers 12a and 12b are alternately laminated. Further, via holes 13 are sequentially formed in the laminated substrate by the hole forming method of the present invention.

The laser beam L emitted from the pulse laser oscillator 1 is first changed in optical path by the first scan mirror 3 in order to process the metal layer 11 a of the laminated substrate 14, and the uniform optical system 4 and the mask 5 Without passing through, the third scan mirror 7 and one of the second scan mirrors 6b are introduced into the f-θ lens 8 by the second scan mirror 6b, and are mounted on the XYZ table 9 (workpiece 14). Then, a predetermined pulse is applied to the surface of the metal layer 11a of the laminated substrate, and a hole is formed in the metal layer 11a.

Subsequently, after the drilling of the metal layer 11a is completed, the drilling of the insulating resin layer 12a is performed. At that time, the laser light L emitted from the pulse laser oscillator 1 is introduced into the homogenizing optical system 4 and the mask 5 by the first scan mirror 3, and is transmitted to the f-θ lens 8 by the second scan mirrors 6a and 6b. The insulating resin layer 12a is introduced at a position equal to the irradiation position of the metal layer 11a on the laminated substrate 14a.

At the time of these processings, the laser beam L passing through the circular hole 5a of the mask 5 by the f-θ lens 8
Is the metal layer 11 of the laminated substrate at a magnification of 1/10 to 1/20.
An image is formed at a processing point on the surface a.

The laser beam L whose optical path has been changed by the first scan lens 3 for processing the metal layer 11a.
Is equal to or more than 3 J / cm ² at the processing point, and the laser light L that has passed through the uniformizing optical system 4 and the mask 5 for processing the insulating resin layer 12a is reflected or absorbed by the uniformizing optical system 4. The intensity is set to be less than 3 J / cm ² at the processing point due to the energy loss caused by the mask 5 and the loss caused by the mask 5.

Thus, the processing of the metal layer 11a can suppress energy loss and can be processed efficiently, and the insulating resin layer 12a is formed on the bottom of the via hole 13 in the metal layer 1a.
1b can be processed without damaging the surface.

When processing the metal layer 11a,
In order to work with a desired diameter, the Z of the XYZ table 9
Defocusing is performed by moving an axis (not shown), or processing is performed while the beam is circularly scanned by the first scan mirror-3 and the second scan mirror 6b.

The controller 10 controls the number of laser oscillation pulses, the change of the optical path by the scanner, the scanning of the laser beam L at the processing point, the movement of the processing area, and the X for the defocus.
-Control the movement of the YZ table 9.

As described above, in the present embodiment, the energy efficiency can be increased when the metal layer is processed, and the insulating resin layer 12
When processing a, since the metal layer 11b on the bottom surface is not damaged, the metal layer 11a and the insulating resin layer 12a can be formed in the same step with high processing efficiency and high yield.

Next, a second embodiment according to the present invention will be described. FIG. 3 is a schematic view showing a laser drilling apparatus according to a second embodiment of the present invention.

This laser drilling device uses an ultraviolet laser beam L
₁ and two laser oscillators, a second pulse laser oscillator 16 having a higher output than the first pulse laser oscillator 15 and different wavelengths.

Light on the output side of the first pulse laser oscillator 15
A reflection mirror 17 is provided in front of the road, and
Is provided with a dichroic mirror 18. this
The dichroic mirror 18 is used for transmitted light and reflected light.
1st pulsed laser oscillator 1
5 to laser light L₁Is output, the laser light L
₁And the laser beam from the second pulse laser oscillator 16
The light L₂Is output, the laser light L₂Wavelength of
Is reflected and output. Therefore, this dichroic
The operation of the dichroic mirror 18
The lasers output from the following two laser oscillators 15 and 16
The light L₁, L₂Have the same optical axis.

A reflecting mirror 19 is provided in front of the dichroic mirror 18 on the optical axis, and further in front thereof, a uniforming optical system 20 for making the intensity distribution of the laser beams L ₁ and L ₂ uniform, and Mask 21 for shaping the beam shape
And a scan mirror 2 for scanning a laser at a processing point
2a, a 22b, the laser beam _{L 2} of the laser beam _{L 1} and the second laser oscillator 16 from the first pulse laser oscillator 15
An f-θ lens 23 having corrected chromatic aberration is disposed.

The scan mirrors 22a and 22b are mounted on a mirror driving device (not shown), and the mirror driving device is controlled by a controller described later so that the scan mirrors 22a and 22b can change the angle with respect to the optical axis. It is configured as follows.

In front of the f-θ lens 23, a laminated substrate, which is the object to be processed 14, is placed and a scan mirror 22 is mounted.
X-Y table 24 for moving the scanning range of the laser beam _L 1, _{L 2} are provided by b. The oscillations of the first pulse laser oscillator 15 and the second pulse laser oscillator 16, the scan mirrors 22a and 22b, and the X-
The operation of the Y table 24 is controlled by the controller 25, respectively.

The first pulsed laser oscillator 15 has, for example, a third harmonic of a YAG laser (wavelength 35
5 nm) is used. Further, the second pulse laser oscillator 16 is, for example, a YAG laser fundamental wave (wavelength 1064 nm) that can obtain a higher output than the first pulse laser oscillator.
Or a YAG laser second harmonic (wavelength 532 nm). When a YAG laser third harmonic is used for the first pulse laser oscillator 15, it is desirable to use a fundamental wave or a second harmonic accompanying the generation of the third harmonic as the second laser light L.

With these configurations, the work piece 14
Similarly to the above, in the case of performing the drilling process on the laminated substrate shown in FIG. 2, first, the second pulse laser oscillator 16 is oscillated to process the metal layer 11a of the laminated substrate. In this case, the first pulse laser oscillator 15 may be oscillated simultaneously with the second pulse laser oscillator 16. The laser beam _{L 1} or _{L 2} which is oscillated uniformizing optical system 20, passes through the mask 21, is positioned by the scanning mirror 22b,
An image is formed at a predetermined location on the surface of the metal layer 11a via the f-θ lens 23, and a predetermined process is performed on the metal layer 11a of the laminated substrate.

Next, processing of the metal layer 11a is completed, when performing processing of the insulating resin layer 12a, the laser beam L ₂ from the second pulse laser oscillator 16 is stopped, from the first pulse laser oscillator only the laser light _{L 1} is the insulating resin layer 12
a.

Laser from first pulse laser oscillator 15
Light L₁Is 3J / cm at the processing point²So that it has the following strength
F-θ lens 23 is the first pulse laser
Laser light L from oscillator 15₁And second pulse laser
Laser light L from oscillator 16 ₂To correct chromatic aberration,
The metal layer 11a and the insulating resin layer 12a are added in the same shape.
Work.

As described above, in this embodiment, since the metal layer is processed by the laser oscillator having a high output, the processing speed can be increased, and when the insulating resin layer is processed, the metal layer on the bottom surface is processed. Processing without damage can be performed, and processing of the metal layer and the insulating resin layer in the same step can be performed efficiently and with high yield.

FIG. 4 is a schematic view showing a laser drilling apparatus showing a modification of the above-described second embodiment. In FIG. 4, the same reference numerals are given to the same functional portions as in FIG. 3, and the individual description thereof is omitted.

In this case, the first pulse laser oscillator 15
And the optical path of the second pulse laser oscillator 16 are separated. The optical path of the second pulse laser oscillator 16 is the same as the optical path shown in FIG.
The optical path 5 is provided with an independent optical path.
0, the mask 21 and the scan mirror 22a do not pass. Therefore, the position of the reflection mirror 17 is different from that in FIG. The scan mirror 2 is located in front of the reflection mirror 17.
A movable reflection mirror 29 interlocked with 2b is provided.

[0051] With these configurations, the laser beam L ₁ output from the first pulse laser oscillator 15 proceeds the optical path independent until the scan mirror 22b, is positioned by the scanning mirror 22b later, on the surface of the metal layer 11a Is processed through the f-θ lens 23 at a predetermined position.

Next, a description will be given of a method of manufacturing a multilayer wiring board using the formation of via holes in the multilayer wiring board by the laser processing method of the present invention.

A multilayer printed wiring board, which is a printed wiring board in which a conductor pattern is formed not only on the front and back surfaces of the insulating layer but also on the inner surface, has been developed by a computer or the like in accordance with the miniaturization and high-density mounting of electronic devices. 4-layer plate (conductor pattern formed by laminating four copper foil layers), 6-layer plate, 8
Laminated plates or more (for example, 44-layered plates) have been put into practical use, and each copper foil layer is formed with a conductor pattern corresponding to an electric circuit. The continuity between the copper foil layers is obtained by using plated through holes (through via holes or interstitial via holes).

The plated through-holes are provided at predetermined positions on each of the conductive layers formed on the insulating resin.
The through hole is processed by the laser processing method of the present invention, and thereafter, the through hole is plated to form a plated through hole. After that, they are accurately aligned and bonded to produce a multilayer wiring board.

The method of manufacturing a multilayer wiring board is usually
Regarding the three-layer board to the eight-layer board, the lamination process is performed by mass lamination (Massl) performed by a copper-clad laminate manufacturer.
a lamination method is the mainstream, and when lamination of 10 or more layers is performed, all the processes are performed by a printed wiring board maker.
The method is adopted.

In either method, after each inner layer pattern is formed, bonding is performed in a state where the positional relationship between the respective layers is accurately matched to manufacture a multilayer wiring board.

[0057]

According to the present invention, the metal layer of the laminated substrate can be processed at a high speed by using a laser beam, and the metal layer surface on the bottom surface of the via hole is not damaged when the insulating resin layer is processed. High quality processing can be performed.

Further, it is possible to efficiently process the metal layer and the insulating resin layer in the same step with a high yield.

[Brief description of the drawings]

FIG. 1 is a schematic view of a laser drilling apparatus according to the present invention.

FIG. 2 is a cross-sectional view of a laminated substrate.

FIG. 3 is a schematic view of another laser drilling device of the present invention.

FIG. 4 is a schematic view of a modified example of another laser drilling device of the present invention.

[Explanation of symbols]

1 ... pulse laser oscillator, 3 ... first scan mirror,
4, 20: uniform optical system, 5: mask, 6a, 6b: second scan mirror, 7: third scan mirror, 8: f-θ
Lens, 11a, 11b: metal layer, 12a, 12b: insulating resin layer, 13: via hole, 14: laminated substrate, 15:
1st pulse laser oscillator, 16 ... second pulse laser oscillator, 17 ..., 18 ... switching mirror, 21 ... mask, 23
… F-θ lens

Claims (8)

[Claims] 1. A laser beam is applied to the metal layer of a laminated substrate formed by laminating a metal layer on the surface of an insulating resin layer to perform a drilling process communicating with the metal layer and the insulating resin layer. In the laser processing method, the laser light to the metal layer and the insulating resin layer is performed using two optical paths that can switch the same wavelength output from one pulse laser oscillator, and the processing into the metal layer is performed. A laser processing method, wherein the laser processing method is performed in one path without using the uniformizing optical system and the mask, and the processing on the insulating resin layer is performed in the other optical path using the uniformizing optical system and the mask. 2. The laser processing method according to claim 1, wherein the laser light output from the pulse laser oscillator is a third harmonic of a YAG laser. 3. A laser beam is applied to the metal layer of a laminated substrate formed by laminating a metal layer on the surface of an insulating resin layer to perform a drilling process communicating with the metal layer and the insulating resin layer. In the laser processing method, a laser beam applied to the metal layer and the insulating resin layer is performed using different wavelengths output from two pulse laser oscillators. 4. The laser processing method according to claim 3, wherein the laser light output from the two pulse laser oscillators is ultraviolet light. 5. The laser processing method according to claim 1, wherein the processing on the metal layer and the processing on the insulating resin layer are performed in the same step. 6. A laser processing apparatus in which two optical paths for irradiating a workpiece are formed by switching between a laser oscillator and a movable mirror provided in front of an optical axis on the output side of the laser oscillator. Laser processing, wherein a homogenizing optical system and a mask are arranged in one of the optical paths, and an f-θ lens arranged in front of the optical axis is shared with the other optical path. apparatus. 7. Two optical paths for irradiating a workpiece are formed by two laser oscillators and a dichroic mirror provided on the optical axis of a common optical path on the output side of the two laser oscillators. A laser processing apparatus, wherein a homogenizing optical system, a mask, and an f-θ lens are disposed in front of the dichroic mirror on an optical axis. 8. The use of the laser processing method according to claim 1 for forming a through hole penetrating an insulating layer and a conductive layer formed on the surface of the insulating layer. A method for manufacturing a multilayer wiring board, which is characterized in that: