JP4163319B2 - Desmear method and desmear apparatus for laser drilling apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a desmear method for removing a residual component remaining in a via hole by being incorporated in or combined with a laser drilling apparatus for forming a via hole in a printed wiring board, particularly a multilayer printed wiring board using a laser beam, and It relates to a desmear device.
[0002]
[Prior art]
In response to the demand for higher density of printed wiring boards accompanying downsizing of electronic equipment and higher density mounting, multilayer printed wiring boards in which a plurality of printed wiring boards are laminated have recently appeared. In such a multilayer printed wiring board, it is necessary to electrically connect conductive layers (copper substrates) between printed wiring boards stacked one above the other. Such a connection is realized by forming a hole called a via hole reaching the lower conductive layer in the resin layer (polyimide, epoxy resin, etc.) of the printed wiring board and plating the inside of the hole. Is done.
[0003]
In the past, mechanical micro drills have been used as a method for forming via holes. However, along with the reduction of the diameter of the via hole accompanying the increase in the density of the printed wiring board, a laser drilling apparatus using a laser beam instead of a fine drill has recently been adopted.
[0004]
For example, a laser drilling apparatus that forms a via hole using a carbon dioxide gas laser or a YAG laser is well known, and has an advantage of being inexpensive and capable of high-speed processing. However, the via hole formed by such a laser drilling apparatus is thin on the bottom surface of the hole formed in the resin layer, that is, on a part or the entire surface of the conductive layer to be exposed (in the case of polyimide or epoxy resin). (Thickness of 1 μm or less) There is a problem that a residual component (called smear) remains.
[0005]
This residual component cannot be completely removed even if the same laser light is irradiated thereafter. This is because even if laser light is further irradiated to evaporate the residue component, the surrounding resin is eluted at this time (since the conductive layer is often copper and heat diffusion is fast), a new residue component It seems that it will form.
[0006]
In contrast, recently, a laser oscillator for removing residual components (hereinafter referred to as desmear) has been prepared separately from the laser oscillator for drilling, and the via hole after drilling is irradiated with laser light for desmear. The present inventors have proposed a desmear apparatus that performs desmearing. This will be described with reference to FIG.
[0007]
In FIG. 5, the desmear apparatus includes a laser oscillator 51 that generates laser light having a predetermined wavelength ω, a component of wavelength ω and a component of second harmonic 2ω from the laser light generated by the laser oscillator 51. Wavelength separation for separating the SHG (Second Harmonic Generator) element 52 that is generated and emitted as the same laser light, and the laser light emitted from the SHG element 52 into laser light having a wavelength ω and laser light having a second harmonic 2ω Instrument 53. In this apparatus, only the laser beam of the second harmonic 2ω is used for desmear. Therefore, the second harmonic 2ω laser light from the wavelength separator 53 is guided to the output optical system (not shown) via the reflection mirror 54.
[0008]
As the laser oscillator 51, for example, a YAG or YLF pulse laser oscillator is used. The wavelength separator 53 is, for example, a mirror that transmits laser light having a wavelength ω and reflects laser light having a second harmonic 2ω. Further, the emission optical system usually includes a scanning means for oscillating the laser beam to a desired position, for example, a galvano scanner.
[0009]
[Problems to be solved by the invention]
In any case, since the desmear apparatus proposed above uses only the laser beam of the second harmonic 2ω, there is a problem that the energy loss is large. That is, assuming that the energy of the laser light emitted from the laser oscillator 51 is 100, the energy of the laser light having the wavelength ω emitted from the wavelength separator 53 is about 50 in consideration of the energy loss in the SHG element 52. The energy of the laser beam of the second harmonic 2ω is about 30. This means that only about 30% of the laser output in the laser oscillator 51 can be used for desmear.
[0010]
Therefore, an object of the present invention is to provide an energy efficient desmear method that can effectively use the laser output of a laser oscillator.
[0011]
The other subject of this invention is providing the desmear apparatus suitable for said desmear method.
[0012]
[Means for Solving the Problems]
The present invention provides a desmear method for removing residual components remaining in a via hole formed by irradiating a resin layer formed on a metal film in a workpiece with a laser beam for drilling. The component of the wavelength ω and the component of the second harmonic 2ω are generated from the laser beam from the laser oscillator that generates the laser beam having the generated wavelength ω, and the generated component of the wavelength ω and the second harmonic are generated. The desmear is performed by irradiating the via hole with a laser beam including a component of the wave 2ω.
[0013]
In the above desmear method, the generated component of the wavelength ω and the component of the second harmonic 2ω are separated in the optical path, and the second harmonic 2ω is separated from the separated component of the second harmonic 2ω. And the third harmonic 3ω component, and the separated wavelength ω component, the generated second harmonic component 2ω component, and the third harmonic component 3ω component in the optical path. Desmearing may be performed by combining and irradiating the via hole.
[0014]
According to the present invention, in a desmear apparatus for removing residual components remaining in a via hole formed by irradiating a laser beam for drilling to a resin layer formed on a metal film in a workpiece, A laser oscillator that generates laser light having a predetermined wavelength ω, and a component of the wavelength ω and a component of the second harmonic 2ω are generated from the laser light generated by the laser oscillator, and the same laser light is generated. There is provided a desmearing device for a laser drilling apparatus, comprising: an optical system that emits light; and an irradiation system that irradiates the via hole with laser light emitted from the optical system.
[0015]
According to the present invention, in the desmear apparatus for removing residual components remaining in the via hole formed by irradiating the laser beam for drilling processing to the resin layer formed on the metal film in the workpiece. A laser oscillator that generates a laser beam having a predetermined wavelength ω, a component of the wavelength ω and a component of the second harmonic 2ω are generated from the laser beam generated by the laser oscillator, and the same laser beam A second optical system that separates the laser light emitted from the first optical system into the laser light having the wavelength ω and the laser light having the second harmonic 2ω; A third optical system that generates a component of the second harmonic 2ω and a component of the third harmonic 3ω from the separated laser light of the second harmonic 2ω, and emits the same as the laser light; 2 separated by the optical system A fourth optical system that synthesizes laser light of wavelength ω and laser light from the third optical system, and an irradiation system that irradiates the via hole with synthetic laser light emitted from the fourth optical system; A desmear apparatus for a laser drilling apparatus is provided.
[0016]
In any of the above desmear apparatuses, for example, an Nd: YAG or Nd: YLF or Nd: YAP or Nd: YVO ₄ pulse laser oscillator can be used as the laser oscillator.
[0017]
In any of the above methods and apparatuses, the laser beam from the laser oscillator preferably has a pulse width of 1 to 50 (nsec ) .
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Prior to the description of the preferred embodiment of the present invention, a laser drilling apparatus in which a desmear apparatus according to the present invention is incorporated or combined will be described with reference to FIG. In FIG. 4, pulsed laser light generated by a laser oscillator 40 using a CO ₂ (carbon dioxide) laser is guided to a mask 43 by a reflection mirror 41 while changing an angle of 90 °. In the mask 43, the beam diameter of the laser beam is narrowed by passing through a hole that defines the via hole diameter, and guided to an XY scanner (also called a galvano scanner) 44. The XY scanner 44 is for oscillating a laser beam. The oscillated laser beam acts as a focusing lens, and a work (on a XY stage 46 through a processing lens 45 called an fθ lens) (Printed wiring board) 47 is irradiated. The XY stage 46 has a drive mechanism in the X-axis direction and a drive mechanism in the Y-axis direction, and can adjust the position by moving the work 47 on the XY plane.
[0019]
In the case of a laser beam by a CO ₂ laser, a hole with a diameter of about 100 (μm) is formed by irradiating a pulsed laser beam several times (usually 2-3 times) per via hole. Usually, the scanning range by the XY scanner 44 is an area of several centimeters, but the size of the work 47 is usually about 50 (cm) × 60 (cm). Therefore, an area determined by the scanning range of the XY scanner 44 is set in the work 47 in a matrix as a processing area. Then, the laser drilling apparatus performs a plurality of drilling processes in the processing area, and when the drilling process of a certain processing area is completed, the laser drilling apparatus moves to the next processing area and performs the drilling process of the same pattern. The movement to the next processing area is usually performed by the XY stage 46.
[0020]
The desmear apparatus according to the present invention is incorporated in or combined with the laser drilling apparatus as described above, but is not particularly restricted by the type of the laser oscillator.
[0021]
A first embodiment of the present invention will be described with reference to FIG. This desmear apparatus is for removing residual component remaining in the via hole of the workpiece 47 which is formed by laser drilling apparatus described in FIG. 4, a laser beam having a wavelength ω defined nitrous et beforehand An SHG element 11 for generating a wavelength ω component and a second harmonic 2ω component from the laser light generated by the laser oscillator 10 and emitting the same as the laser light; A uniform optical system 12 that converts the laser light emitted from the element 11 into a beam having a uniform energy density distribution, and an irradiation system (not shown) that irradiates the via hole in the workpiece with the beam from the uniform optical system 12. And.
[0022]
The SHG element 11 is the same as that in FIG. On the other hand, the uniform optical system 12 is also well known. Referring to FIG. 2A, here, the concave lens 12-1 and the convex lens 12-2 acting as a beam expander, and the energy density distribution of the laser beam are irradiated. And a lens 12-3 that is uniform over the entire area. The lens 12-3 includes a lens 12-3a for cutting a vertical portion having a circular cross section and a lens 12-3b for cutting a horizontal portion. FIG. 2B is a view of the lens 12-3 of FIG. According to such a uniform optical system 12, the cross-sectional shape of the emitted laser beam is enlarged to a square, and the beam profile in the cross-section has a peak value almost in the entire region as shown in FIG. It has energy density distribution. When a large number of holes having a diameter of about 100 (μm) are formed adjacent to each other by performing full surface scanning or partial scanning on the workpiece using such a laser beam, a plurality of holes are formed. These holes can be desmeared together. The laser beam from the uniform optical system 12 is guided to an irradiation system including an XY scanner.
[0023]
In particular, in the present embodiment, about 80% (%) of the laser output of the laser oscillator 10 can be used by performing desmearing with laser light including not only the second harmonic 2ω component but also the fundamental wavelength ω component. it can. As a result, the energy efficiency is about (8/3) times that when desmear is performed using only the second harmonic 2ω component as described in FIG. Is also improved by about (8/3) times.
[0024]
A second embodiment of the present invention will be described with reference to FIG. The same parts as those in FIG. In FIG. 3, the desmear apparatus includes a laser oscillator 10 that generates laser light having a predetermined wavelength ω, a component of wavelength ω and a second harmonic component 2ω from the laser light generated by the laser oscillator 10. SHG element (first optical system) 11 that emits as the same laser light, and the laser light emitted from the SHG element 11 is separated into laser light of wavelength ω and laser light of second harmonic 2ω And a second harmonic component 2ω and a third harmonic component 3ω are generated from the separated second harmonic 2ω laser light, and the same laser. A THG (Third Harmonic Generator) element (third optical system) 23 that emits as light, a combination of the laser light of wavelength ω separated by the wavelength separator 22 and the laser light from the THG element 23. A study system (fourth optical system) 24, a uniform optical system 12 for converting the synthesized laser light emitted from the synthetic optical system 24 into a beam having a uniform energy density distribution, and a beam from the uniform optical system 12 as a workpiece And an irradiation system (not shown) for irradiating the via hole.
[0025]
A reflection mirror 25 is disposed between the wavelength separator 22 and the THG element 23, and a reflection mirror 26 is disposed between the wavelength separator 22 and the combining optical system 24.
[0026]
The SHG element 11 and the THG element 23 are functionally the same except that the generated wavelengths are different. The wavelength separator 22 is also the same as the wavelength separator 53 as described with reference to FIG. Further, the combining optical system 24 can use an optical element that transmits a laser beam having a wavelength ω and reflects a laser beam having a wavelength 2ω or 3ω using a multilayer film, such as a dichroic mirror. Apart from this, a photosynthesis method as proposed in Japanese Patent Application No. 10-317848 may be used.
[0027]
In such a desmear apparatus, assuming that the laser output of the laser oscillator 10 is 100, the energy of the laser light of wavelength ω emitted from the wavelength separator 22 is about 50, and the energy of the laser light of wavelength 2ω is about 30. It is. Further, of the laser light emitted from the THG element 23, the energy of the wavelength 2ω component is about 15 (30 × 0.5), and the energy of the wavelength 3ω component is about 9 (30 × 0.3). is there. As a result, in the present embodiment, by performing desmearing with a laser beam including not only the fundamental wavelength ω component and the second harmonic 2ω component but also the third harmonic 3ω component, approximately 74 of the laser output of the laser oscillator 10 is obtained. (%) Can be used. As a result, the energy efficiency is about (7.4 / 3) times that when performing desmearing with only the second harmonic 2ω component as described in FIG. The tact time is also improved by about (7.4 / 3) times. In particular, it has been confirmed that by performing desmearing with a laser beam including a third harmonic 3ω component, the desmear effect is also improved as compared with the case of performing desmearing with only the second harmonic 2ω component.
[0028]
As the laser oscillator 10, any one of Nd: YAG, Nd: YLF, Nd: YAP, and Nd: YVO ₄ solid-state pulse laser oscillators may be used. Further, a second harmonic having a wavelength of 532 (nm) and a third harmonic having a wavelength of 266 (nm) can be obtained from pulsed laser light from these laser oscillators. Furthermore, as a laser oscillator, a solid-state laser with a Q switch can be mentioned. The energy density on the irradiated surface may be about 0.05 to ² (J / cm ² ). Furthermore, in this desmear apparatus, as a result of using a laser beam having a pulse width of 30 (nsec), it has been confirmed that the desmear effect is superior to that of a laser beam having a width of 200 (nsec). A preferred range for the pulse width is about 50-1 (nsec).
[0029]
For reference, FIGS. 6 to 7 show a processing result when the present invention is applied to a via hole processed by a CO ² laser and a processing result by a conventional method.
[0030]
6A is an enlarged view of a via hole processed with a CO ² laser, and FIG. 6B is an enlarged view of the upper edge of the via hole in FIG. 6A. FIG. 6C shows the bottom of the via hole in FIG.
[0031]
FIG. 7A shows an enlarged view of the via hole when the desumi process is performed only with the laser beam of the second harmonic 2ω, the via hole processed with the CO ² laser shown in FIG. FIG. 7B is an enlarged view of the upper edge of the via hole in FIG. 7A, and FIG. 7C is an enlarged view of the bottom of the via hole in FIG.
[0032]
FIG. 8A shows an enlarged view of the via hole when the desmear processing is performed on the via hole processed by the CO ² laser shown in FIG. 6 with the laser light having the fundamental wavelength ω and the second harmonic 2ω. 8 (b) shows the upper edge of the via hole in FIG. 8 (a) further enlarged, and FIG. 8 (c) shows the bottom of the via hole in FIG. 8 (a) further enlarged. ing. The via hole in FIG. 6 is formed by irradiating three shots of a CO ² laser having an energy density of 6.7 (J / cm ² ). FIG. mJ) Desmear is performed by irradiating one shot of a corresponding laser beam.
[0033]
The desmear apparatus described above can be applied to all laser drilling apparatuses that require removal of residual components, and further, as shown in Japanese Patent Application No. 9-125422 proposed by the present inventor. The present invention can also be applied to a laser processing apparatus using a multi-axis galvano scanner.
[0034]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a desmear apparatus with high energy efficiency and greatly improved tact time, and the time required for drilling processing including desmear processing is greatly reduced. can do. Further, the desmear apparatus according to the present invention can be easily assembled to an existing laser drilling apparatus, and in this case, space saving is possible.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a first embodiment of a desmear apparatus according to the present invention.
2 is a diagram showing a configuration (FIGS. (A) and (b)) of the uniform optical system in FIG. 1 and an energy density distribution (FIG. (C)) in a cross section of a laser beam obtained thereby.
FIG. 3 is a diagram showing a configuration of a second embodiment of a desmear apparatus according to the present invention.
FIG. 4 is a diagram showing a configuration of an example of a laser drilling apparatus combined with the present invention.
FIG. 5 is a diagram showing a configuration of a desmear apparatus proposed by the present inventors.
6A is an enlarged view of a via hole processed with a CO ² laser, and FIG. 6B is an enlarged view of the upper edge of the via hole in FIG. c) is a photomicrograph showing the bottom of the via hole in FIG.
7A is an enlarged view of a via hole when the via hole shown in FIG. 6 is desmeared with only the laser beam of the second harmonic 2ω, and FIG. The upper edge part of the via hole of (a) is further enlarged and shown, and FIG. (C) is a photomicrograph showing the enlarged bottom part of the via hole of FIG.
FIG. 8A is an enlarged view of the via hole shown in FIG. 6 when the desmear process is performed with the laser light having the fundamental wavelength ω and the second harmonic 2ω according to the present invention. (B) is an enlarged view of the upper edge of the via hole in FIG. (A), and FIG. (C) is a photomicrograph showing the enlarged bottom of the via hole in FIG. (A).
[Explanation of symbols]
10, 40, 51 Laser oscillator 11 SHG element 23 THG element 12 Uniform optical system 22, 53 Wavelength separator 24 Synthesis optical system 25, 26 Reflection mirror 44 XY scanner 45 Processing lens 46 XY stage 47 Workpiece

Claims (7)

In a desmear method for removing residual components remaining in via holes formed by irradiating a resin layer formed on a metal film in a workpiece with laser light for drilling,
Generating a component of the wavelength ω and a component of the second harmonic 2ω from a laser beam from a laser oscillator that generates a laser beam having a predetermined wavelength ω;
A desmearing method for a laser drilling apparatus, wherein desmearing is performed by irradiating the via hole with a laser beam including the generated component of the wavelength ω and the component of the second harmonic 2ω. 2. The desmear method according to claim 1, wherein the generated component of the wavelength ω and the component of the second harmonic 2ω are separated in an optical path,
A component of the second harmonic 2ω and a component of the third harmonic 3ω are generated from the separated components of the second harmonic 2ω,
Desmearing is performed by combining the separated wavelength ω component, the generated second harmonic 2ω component, and the third harmonic 3ω component in an optical path and irradiating the via hole. A desmear method for a laser drilling apparatus characterized by the above. 3. The desmear method for a laser drilling apparatus according to claim 1, wherein the laser light from the laser oscillator has a pulse width of 1 to 50 (nsec ) . In a desmear apparatus for removing residual components remaining in a via hole formed by irradiating a resin layer formed on a metal film in a workpiece with a laser beam for drilling,
A laser oscillator that generates laser light having a predetermined wavelength ω;
An optical system that generates the component of the wavelength ω and the component of the second harmonic 2ω from the laser beam generated by the laser oscillator and emits the same as the laser beam;
A desmearing device for a laser drilling apparatus, comprising: an irradiation system for irradiating the via hole with laser light emitted from the optical system. In a desmear apparatus for removing residual components remaining in a via hole formed by irradiating a resin layer formed on a metal film in a workpiece with a laser beam for drilling,
A laser oscillator that generates laser light having a predetermined wavelength ω;
A first optical system that generates the component of the wavelength ω and the component of the second harmonic 2ω from the laser light generated by the laser oscillator and emits the same as the laser light;
A second optical system for separating laser light emitted from the first optical system into laser light having the wavelength ω and laser light having the second harmonic 2ω;
A third optical system that generates a component of the second harmonic 2ω and a component of the third harmonic 3ω from the separated laser light of the second harmonic 2ω, and emits the same as the laser light;
A fourth optical system for synthesizing the laser light of the wavelength ω separated by the second optical system and the laser light from the third optical system;
A desmearing device for a laser drilling device, comprising: an irradiation system for irradiating the via hole with a synthetic laser beam emitted from the fourth optical system. In desmear apparatus according to claim 4 or 5, wherein, as said laser oscillator, desmear apparatus for laser drilling apparatus, which comprises using a YAG or YLF, or YAP or YVO ₄ pulsed laser oscillator. 6. The desmearing device according to claim 4 or 5, wherein the laser beam from the laser oscillator has a pulse width of 1 to 50 (nsec ) .

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