JP3869736B2 - Laser processing method and multilayer wiring board - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser processing method and a multilayer wiring board, and more particularly to a laser processing method in which a laser beam is incident on a multilayer wiring board to form a hole, and a multilayer wiring board manufactured by the laser processing method.
[0002]
[Prior art]
With reference to FIG. 3, a conventional method for drilling a multilayer wiring board will be described.
As shown in FIG. 3A, the multilayer wiring board to be drilled has a stacked structure in which a support substrate 100, an inner layer wiring 101, an insulating layer 102, and an upper layer wiring 103 are stacked in this order. The support substrate 100 and the insulating layer 102 are made of, for example, an epoxy resin, and the inner layer wiring 101 and the upper layer wiring 103 are made of, for example, copper.
[0003]
A pulse laser beam in the ultraviolet wavelength region is incident on the upper layer wiring 103 to form a hole penetrating the upper layer wiring 103. This pulse laser beam is generally a Gaussian beam (a beam whose power density distribution in the beam cross section can be approximated by a Gaussian curve). For this reason, the energy density per pulse is high at the center in the beam cross section and low at the periphery. Thereby, the etching rate at the center of the beam spot becomes faster than the etching rate at the periphery.
[0004]
When the pulse laser beam is incident until the formed hole penetrates the upper wiring 103 even in the peripheral portion of the beam spot, excessive etching occurs in the central portion. Since the epoxy resin is easier to etch than copper, the formed hole easily penetrates the insulating layer 102. When the insulating layer 102 is penetrated and the surface of the inner layer wiring 101 is exposed, a part of the inner layer wiring 101 is melted or etched.
[0005]
When the upper wiring 15 is completely etched also in the periphery of the beam spot, the fluence per pulse of the pulse laser beam is lowered and a hole is formed in the insulating layer 102 as shown in FIG. . At this time, the fluence per pulse is set to a size that does not etch copper. For this reason, even if the inner layer wiring 101 is exposed on the bottom surface of the formed hole, the inner layer wiring 101 is hardly damaged.
[0006]
[Problems to be solved by the invention]
As described above, after reducing the fluence per pulse of the pulse laser beam, the inner layer wiring 101 is not damaged even after the hole penetrating the insulating layer 102 is formed. However, as shown in FIG. 3A, when the upper layer wiring 103 is etched, if the hole penetrates the insulating layer 102, the inner layer wiring 101 is damaged.
[0007]
An object of the present invention is to provide a laser processing method in which an inner layer wiring is not easily damaged.
Another object of the present invention is to provide a multilayer wiring board manufactured by the laser processing method.
[0008]
[Means for Solving the Problems]
According to one aspect of the present invention, an inner layer wiring formed on a surface of a base substrate, in which a lower layer made of a conductive first material and an upper layer made of a second material are laminated in this order, Formed on the surface of the base substrate so as to cover the inner layer wiring, formed on the surface of the insulating layer made of an insulating material that is more easily etched by the laser beam than the first and second materials, and the surface of the insulating layer; A step of preparing a multilayer wiring board having an upper layer wiring made of a conductive third material; and a hole that allows a laser beam to enter the upper layer wiring, penetrates the upper layer wiring and the insulating layer, and reaches the inner layer wiring And the reflectivity of the laser beam on the surface of the second material is higher than the reflectivity of the laser beam on the surfaces of the first and third materials. 1st, 2nd And laser processing method is provided in which the third material is selected.
[0009]
Since the reflectance of the laser beam on the surface of the second material is higher than the reflectance of the laser beam on the surface of the first material, damage to the inner layer wiring after the inner layer wiring is exposed can be reduced.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1A shows a schematic view of an apparatus used in a laser processing method according to an embodiment of the present invention. The laser light source 1 emits a pulse laser beam for processing. The laser light source 1 includes, for example, an Nd: YAG laser oscillator and a wavelength conversion element, and emits the third harmonic (wavelength 355 nm) of the Nd: YAG laser. A laser beam emitted from the laser light source 1 enters the mask 2. The laser beam that has passed through the through hole provided in the mask 2 enters the folding mirror 3.
[0011]
The laser beam reflected by the folding mirror 3 enters the galvano scanner 4. The galvano scanner 4 includes a pair of swingable reflecting mirrors, and scans the laser beam in a two-dimensional direction. The laser beam scanned by the galvano scanner 4 is focused by the fθ lens 5 and enters the workpiece 8 held on the XY stage 6. The fθ lens 5 images the through hole of the mask 2 on the surface of the workpiece 8.
[0012]
Next, a laser processing method according to an embodiment of the present invention will be described with reference to FIG.
FIG. 2A shows a cross-sectional view of a printed wiring board to be processed. Inner layer wiring 13 is formed on a part of the surface of the support substrate 10. The inner layer wiring 13 has a stacked structure in which a lower layer 11 made of copper and having a thickness of 5 to 18 μm and an upper layer 12 made of Ni and having a thickness of about 1 μm are stacked in this order. In the ultraviolet wavelength region, the reflectance on the surface of the upper layer 12 is larger than the reflectance on the surface of the lower layer 11. An insulating layer 14 is formed on the support substrate 10 so as to cover the inner layer wiring 13. An upper wiring 15 made of copper is formed on the surface of the insulating layer 13. The support substrate 10 and the insulating layer 14 are made of, for example, an epoxy resin.
[0013]
As shown in FIG. 2B, a pulse laser beam having a wavelength of 355 nm is incident on the upper wiring 15. The fluence per pulse of the pulse laser beam on the surface of the upper wiring 15 is 10 J / cm ² or more, which is large enough to etch copper. The pulse width is 100 ns, the pulse repetition frequency is 10 kHz, and the beam spot diameter on the surface of the upper wiring 15 is 50 μm.
[0014]
Since the pulse laser beam is generally a Gaussian beam, the etching rate at the center of the beam spot is faster than the etching rate at the periphery. For this reason, when the upper layer wiring 15 in the peripheral part of the beam spot is etched to the bottom surface, the hole formed in the central part penetrates the insulating film 14 to expose the inner layer wiring 13. Since the reflectance at the surface of the upper layer 12 is higher than the reflectance at the surface of the lower layer 11, the inner layer wiring 13 is less damaged than when the lower layer 11 is exposed.
[0015]
As shown in FIG. 2C, irradiation with the pulse laser beam is continued without changing the irradiation conditions. Also in the periphery of the beam spot, the insulating layer 14 penetrates and the inner layer wiring 13 is exposed. At this time, the exposed inner layer wiring 13 is exposed to the laser beam. However, since the reflectance at the surface of the upper layer 12 is high, the lower layer 11 is less damaged.
[0016]
The upper layer 12 is exposed at the bottom of the hole. By etching the exposed upper layer 12, the lower layer 11 is exposed. The upper layer 12 is etched during the desmear treatment with the permanganic acid solution after drilling. Since the upper layer 12 has conductivity and is sufficiently thin, the upper layer 12 may be left on the bottom surface of the hole.
[0017]
In the above embodiment, drilling was performed using the third harmonic of the Nd: YAG laser. However, the fourth harmonic may be used, or another solid laser such as the third harmonic of the YLF laser or 4 Double harmonics may be used. More generally, a laser beam in the ultraviolet wavelength region may be used. In particular, it is preferable to use a laser beam having a wavelength of 350 nm to 400 nm.
[0018]
Moreover, in the said Example, although the lower layer 11 of the inner layer wiring 13 was formed with copper and the upper layer 12 was formed with Ni, you may form with another material. At this time, it is necessary to use a combination of materials in which the reflectance on the surface of the upper layer 12 is higher than the reflectance on the surface of the lower layer 11 in the ultraviolet wavelength region. Note that a material having a reflectance of 60% or more is preferably selected as the material of the upper layer 12.
[0019]
For example, you may form the lower layer 11 with the alloy which has copper as a main component. Candidates for the material of the upper layer 12 include, in addition to Ni, Al, an alloy containing Ni as a main component, or an alloy containing Al as a main component. The reflectivity of ultraviolet light on the copper surface is about 40%.
[0020]
In the above embodiment, the insulating layer 14 can be drilled under the same conditions as when the upper wiring 15 is drilled. For this reason, productivity can be improved.
Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.
[0021]
【The invention's effect】
As described above, according to the present invention, the upper layer portion of the inner layer wiring embedded in the multilayer wiring board is formed of a material that easily reflects the laser beam for processing, thereby reducing damage to the inner layer wiring. be able to.
[Brief description of the drawings]
FIG. 1 is a schematic view of a laser processing apparatus used in an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a printed wiring board for explaining a laser processing method according to an embodiment of the present invention.
FIG. 3 is a cross-sectional view of a printed wiring board for explaining a conventional laser processing method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Laser light source 2 Mask 3 Folding mirror 4 Galvano scanner 5 f (theta) lens 6 XY stage 8 Process target 10 Support substrate 11 Lower layer 12 Upper layer 13 Inner layer wiring 14 Insulating layer 15 Upper layer wiring

Claims (5)

An inner layer wiring formed on the surface of the base substrate, in which a lower layer made of a conductive first material and an upper layer made of a second material are laminated in this order, the base layer so as to cover the inner layer wiring An insulating layer made of an insulating material formed on the surface of the substrate and more easily etched by the laser beam than the first and second materials, and a conductive third material formed on the surface of the insulating layer Preparing a multilayer wiring board having an upper layer wiring,
Reflecting the laser beam on the surface of the second material, including the step of causing a laser beam to enter the upper layer wiring and forming a hole that penetrates the upper layer wiring and the insulating layer and reaches the inner layer wiring. The laser processing method in which the first, second, and third materials are selected such that the rate is higher than the reflectance of the laser beam on the surfaces of the first and third materials. 2. The laser according to claim 1, wherein the first material and the third material are copper or an alloy containing copper as a main component, and the second material is Ni, Al, or an alloy containing these as a main component. Processing method. The laser beam is a pulse laser beam, and in the step of forming the hole, a plurality of shots are incident on the multilayer wiring board without changing the energy density per pulse on the surface of the multilayer wiring board. The laser processing method according to claim 1, wherein the hole is formed. A support substrate;
A lower layer made of a conductive first material and an upper layer made of a second material, which are formed on the surface of the support substrate, are laminated in this order, and in the ultraviolet wavelength region. An inner layer wiring having a light reflectance on the surface of the second material higher than a light reflectance on the surface of the first material;
An insulating layer formed on the support substrate so as to cover the inner layer wiring and formed of an insulating material that is more easily etched by a laser beam than the first and second materials;
An upper wiring formed on the surface of the insulating layer and made of a conductive third material;
A multilayer wiring board having a hole penetrating the upper layer wiring and the insulating film and exposing a part of the inner layer wiring. The multilayer according to claim 4, wherein the first material and the third material are copper or an alloy containing copper as a main component, and the second material is Ni, Al, or an alloy containing these as a main component. Wiring board.

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