JP2003136268A - Method for drilling printed board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the shape of a hole drilled in a resin film layer, a surface- roughened external conductor copper layer, and an insulating resin layer in this order from above, which are different from each other in materials. SOLUTION: By making a laser beam pulse to-hat shaped and controlling a pulse width, these can be controlled diameters of the lower part of the hole of the resin film layer, of the hole of the external conductor layer, and of the upper part of the hole of the insulating resin layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of drilling a printed circuit board by laser processing.

[0002]

2. Description of the Related Art A printed wiring board (hereinafter referred to as a printed board) used for high-density mounting of semiconductor ICs in a mobile phone or the like generally has a multi-layer structure of an insulating resin layer containing glass fiber and a conductor layer of copper. The mounting wiring density has rapidly increased year by year, and as a technique for drilling holes in printed circuit boards, the diameter of blind holes (holes with a bottom) in the build-up layer is particularly demanding, and it is set to 100 μmφ or less.

A laser processing method using a carbon dioxide gas laser has been adopted as a method for making a hole having such a minute diameter. The wavelength of the carbon dioxide gas laser (9.3 to 10.6 μm)
Since the copper used for the outer conductor layer has a high reflectance, it must be partially removed by another method (drill, chemical etching, etc.) in advance and a window for directly irradiating the insulating resin layer with the laser must be opened. did not become.

As means for making holes in the outer conductor copper layer with a carbon dioxide laser, Japanese Patent Laid-Open Nos. 9-107168 and 2000-15338 are available.
By roughening the surface of the copper layer as disclosed in Japanese Patent Publication No. 4, a method of making a hole to increase the absorptivity of the copper layer surface is proposed, but the copper layer, glass fiber or resin There was a problem that debris was scattered around the hole and adhered. In addition, in this case, the hole diameter of the copper layer is smaller than the hole diameter of the insulating resin layer below, which causes a problem that a part of the copper layer is overhanged.

In order to prevent the adhesion of debris and remove the overhang of the outer conductor copper layer, a photosensitive resist film is formed on the surface of the roughened copper layer as disclosed in JP 2001-244604 A. A method has been proposed in which the copper layer surface is formed and laser drilling is performed to protect the surface of the copper layer from adhesion of debris, and chemical etching is performed with the resist film still attached to remove the overhanging portion of the copper layer.

[0006]

It is known that when a plurality of layers made of different materials are processed by a laser, the irradiation condition of the laser has a great influence on the shape of the hole. It has been difficult to control the shape of the holes formed in the resin film layer added on the layer, the surface-roughened outer conductor copper layer, and the insulating resin layer.

Further, when a carbon dioxide laser pulse having a Gaussian distribution type energy distribution in the beam used in conventional laser processing is used, the diameter of the lower hole of the resin film layer is 170% or more of the upper diameter of the hole of the insulating resin layer. Also, if you perform chemical etching with the resin film layer attached to remove the overhang portion of the outer conductor copper layer, the removed portion of the outer conductor copper layer will also become large, so apply the subsequent copper plating. When forming a wiring pattern on the outer conductor copper layer, there was a problem that the wiring pattern had to be enlarged.
Further, when the outer conductor layer is removed and the exposed surface of the insulating resin layer is plated with copper, there is a problem that it is easily peeled off.

Further, since a thick insulating resin layer remains at the corner portion of the hole bottom on the inner layer conductor, if the laser pulse width is widened for a long time to remove it, the insulating resin layer is over-etched. There was a problem that the holes of the insulating resin layer spread in a barrel shape. Furthermore, when the normal Gaussian distribution is used as the energy distribution of the laser beam, the center of the hole of the inner conductor layer may be damaged even in an extreme case.

On the other hand, when the resin film layer added to the surface of the outer conductor copper layer is made of a photosensitive resist agent, unevenness in the film quality will occur unless it is exposed before laser processing, which affects processing characteristics. There was a problem of doing.

Further, since no consideration has been given to the scattering of debris (particularly copper scattered matter having a large specific gravity), there is a problem that the surface of the fθ lens for condensing the laser light is soiled.

An object of the present invention is to solve the above problems of the prior art.

[0012]

In order to solve the difficulty of controlling the shapes of holes processed in a resin film layer, a surface-roughened outer conductor copper layer, and an insulating resin layer, an outer conductor layer is formed. A printed circuit board consisting of an insulating resin layer and an inner conductor layer, the outer conductor layer is subjected to a roughening treatment to increase the laser light absorption rate, and the outer conductor layer has a resin film layer with good laser processability ( (Hereinafter, simply referred to as a resin film layer), in the method of blind hole processing with a carbon dioxide gas laser, the laser light pulse is made into a top hat shape, and the diameter of the lower hole of the resin film layer and the outer conductor layer are controlled by controlling the pulse width. It has been found that it is preferable to use a laser drilling method characterized by controlling the hole diameter and the hole upper diameter of the insulating resin layer.

According to the present invention, a carbon dioxide laser pulse has a top-hat type in which the energy distribution in the beam is uniform (for example, Japanese Patent Application No.
2001-138204 specification), and as described later, when the relationship between the pulse width and the hole shape was examined in detail,
This is due to the finding that the hole shape can be controlled.

Further, a plurality of laser light pulses having a narrow pulse width are irradiated following the laser light pulse for controlling the diameter of the lower hole of the resin film layer, the diameter of the outer conductor layer, and the diameter of the upper hole of the insulating resin layer. As a result, a thick insulating resin layer can be formed in the corner portion of the hole bottom on the inner layer conductor.

Here, the resin film layer has a thickness of 10 to 60.
This can be solved by using a μm acrylic film, polyethylene film, vinyl chloride film, or an adhesive film having a multilayer structure of these films. As a result, it is possible to solve the problem that when the resin film layer is used as a photosensitive resist agent, the quality of the film becomes uneven unless it is exposed to light before laser processing, which affects processing characteristics. The exposure step can be omitted.

In order to solve the problem that the diameter of the lower hole of the resin film layer becomes 170% or more of the diameter of the upper hole of the insulating resin layer, the carbon dioxide gas laser pulse has a top hat with a uniform energy distribution in the beam. It was found that the diameter of the hole in the resin film layer, the diameter of the hole in the outer conductor layer, and the diameter of the upper hole in the insulating resin layer should be controlled by controlling the pulse width. This is as described below
By examining the relationship between the pulse width and the hole shape in detail, it was found that the lower hole diameter of the resin film layer can be suppressed to 140 to 160% of the upper hole diameter of the insulating resin layer.

Further, a printed board consisting of an outer conductor layer, an insulating resin layer, and an inner conductor layer is subjected to a roughening treatment on the surface of the outer conductor layer in order to increase the absorption rate of laser light, and the surface of the outer conductor layer is laser-treated. A resin film layer with good workability is added, and in blind hole processing with a carbon dioxide laser, the resin film layer is a resin film layer with good laser workability that is a material with a high absorption rate, and the absorption rate is about half that low. It was found that the laser drilling method, which is characterized by a multi-layer structure of the material, can suppress the scattering of debris and prevent the fθ lens from being contaminated. This is because the temperature rise of the layer having a low absorptance is suppressed and the viscosity is high, and the scattering is suppressed because the momentum of the melt evaporation of the lower outer conductor copper layer is absorbed.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows a method of forming blind holes in a printed circuit board according to the present invention in the order of steps.
A) is a substrate state after buildup, 1 is an outer conductor layer made of copper, 2 is an insulating resin layer, 3 is an inner conductor layer made of copper. B) is a state after the surface of the outer conductor layer is roughened, C) is a state after the resin film layer 4 is coated on the surface of the outer conductor layer, and D) is a state after laser drilling. Drt is the hole upper diameter of the resin film layer 4, Drb is the hole lower diameter of the resin film layer 4, Dc is the hole diameter of the outer conductor layer 1,
Indicates. E) shows a state in which the overhang portion of the outer conductor layer 1 and a part on the hole are removed by chemical etching, F) a state in which the resin fume layer 4 is peeled off, and G) a part remains at the bottom of the hole by the desmear treatment. With the insulating resin layer 2 removed,
H) shows a state where irregularities on the surfaces of the outer conductor layer 1 and the inner conductor layer 3 are removed by soft etching, I) a state after copper plating, and J) a state after a wiring pattern is formed on the outer conductor layer. Among them, the present invention relates to the steps C) and D).

FIG. 1 shows the pulse width of the carbon dioxide laser pulse, the hole upper diameter Drt (◯) of the resin film layer 4, the hole lower diameter Drb (Δ) of the resin film layer 4, and the hole diameter Dc of the outer conductor layer 1.
The relationship between (□), the hole top diameter Dit (●) of the insulating resin layer and the hole bottom diameter Dib (■) of the insulating resin layer is shown. Here, the wavelength of the carbon dioxide laser is 9.36 μm, and the peak output of the rectangular pulse is 1
The beam shape is a top hat shape as described in Japanese Patent Application No. 2001-138204 and the beam diameter is 120 μmφ. In this experiment, a copper plate with resin (or what is commonly called a laminate of prepreg and copper foil) was used. Insulating resin layer 2 is about 70μ
The outer conductor layer 1 has a thickness of about 8 μm and its surface is roughened to a roughness of 1.0 to 2.0 μm by MultiBond treatment (MacDermid) to increase the light absorption rate. Here, as the surface roughening treatment, in addition to this, existing blackening treatment, etch bond treatment (Mech Co.), α
-Prep processing (αMetal) or Bond film processing (Ato
(tech company) is also completely equivalent. Resin film layer 4
Is a light-sensitive dry film of about 30 μm attached and exposed. Since the hole diameters Drt, Drb, and Dc are almost saturated even when the pulse width of the carbon dioxide laser pulse is increased in this way, if the pulse width is set to 14 μs or more, the hole diameter of each layer is determined by the laser beam diameter, and control is performed. It will be easy to understand. Further, when compared at the pulse width of 14 μs, it can be seen that the hole diameters Drt and Drb of the resin film layer 4 can be made larger than the hole upper diameter Dit of the insulating resin layer. still,
It is presumed that the hole diameters Drt and Drb of the resin film layer 4 are larger than the laser beam diameter due to diffuse reflection from the outer conductor layer 1 that has been thermally diffused or roughened.

Here, when the energy distribution of the laser beam is performed by a normal Gaussian distribution type, the hole diameter of the resin film layer 4 becomes 180 μmφ or more in the hole lower diameter Drb, and the insulating resin layer upper diameter Dit
It is 170% or more of the above, but in the case of the top hat type, it can be seen by comparing at the pulse width of 14 μs in FIG.
It can be reduced to about 40 to 160%.

Further, in the case of the Gaussian distribution, such a saturation phenomenon does not appear because the energy is concentrated in the central portion of the beam, and the hole diameter gradually increases as the pulse width increases, so it is difficult to select an appropriate pulse width. become. In an extreme case, it may even damage the central portion of the hole of the inner conductor layer 3 whose surface is roughened to improve the adhesion with the insulating resin layer 2.

As the resin film layer 4, an acrylic film, a polyethylene film, a vinyl chloride film or an adhesive film having a multi-layer structure of these films can control the hole system in the same manner. In this case, unlike the case where a photosensitive dry film is used, there is an advantage that the exposure process is unnecessary. However, when an adhesive film such as an acrylic film or a vinyl chloride film is used, it cannot withstand the chemical etching in the subsequent step, and therefore a polyethylene film may be attached below. Further, the polyethylene film is inferior in laser processability due to its low absorptivity, but the processability can be improved by adopting the above-mentioned multi-layer structure.

Although the optimum drilling pulse width has been found as described above, as is well known in drilling with a carbon dioxide laser, the corner portion of the hole bottom remains thick as shown by the arrow in FIG. Then, when a pulse with a short pulse width (3 to 6 μs) is irradiated at the next pulse interval of 500 μs (repetition frequency 2 kHz), the corner portion is removed as shown by the dotted line in FIG. 3, and the hole can be shaped. In some cases, a pulse having a shorter pulse width may be emitted at the next pulse interval.

Further, as the resin film layer 4, a resin film layer having good laser processability has a multi-layer structure of a material having a high absorptivity and a material having an absorptivity as low as about one half thereof. It was found that the laser drilling method can suppress the scattering of debris and prevent the fθ lens from being soiled. This is a state in which the temperature rise of the layer having a low absorptance is suppressed and the viscosity is high, and the lower outer conductor copper layer 1
Because the momentum of the melt evaporation of is absorbed, the scattering is suppressed.

[0025]

EXAMPLE A concrete processing result by the laser drilling method of the present invention will be described.

FIG. 4 is a cross-sectional photograph of a hole machined according to the present invention by a scanning electron microscope, and corresponds to D) of FIG. 1 is an outer conductor layer made of copper, 2 is an insulating resin layer, 3 is an inner conductor layer made of copper, and 4 is a resin film layer. Here, the wavelength of the carbon dioxide laser is 9.36 μm, the peak output of the rectangular pulse is 1000 W, the beam shape is top hat, and the beam diameter is about 120 μmφ. The insulating resin layer 2 of the printed circuit board is about 70 μm, and the outer conductor layer 1 is about 8 μm thick.
Roughness 1.0 ~ by MultiBond treatment (MacDermid) on the surface with μm
It is roughened to 2.0 μm. The resin film layer 4 is formed by attaching a photosensitive dry film of about 30 μm and subjecting it to an exposure treatment. In this embodiment, the first pulse width is set to 25 μs, and
It is formed by irradiating a pulse with a pulse width of 3 μs after a pulse cycle (500 μs). In this way, it was possible to form a hole having a square shape up to the bottom of the hole, the hole diameter of the insulating resin layer was about 100 μmφ, and the lower hole diameter of the resin layer was about 150 μmφ, which was increased by only 150%.

[0027]

According to the present invention, the hole shape can be controlled by the pulse width of the top hat type carbon dioxide gas laser pulse.

Further, the exposure step could be eliminated by using a resin film layer having good laser processability with an adhesive as the resin layer added to the surface of the copper layer.

By setting the diameter of the lower hole of the resin film layer on the outer conductor layer to be 160% or less of the upper diameter of the hole of the insulating resin layer, the wiring pattern could be made thin.

Further, by forming the resin film layer having good laser processability into a multi-layer structure of a material having a high absorptivity and a material having an absorptivity as low as about one half thereof, scattering of debris is suppressed and fθ I was able to prevent the lens from getting dirty.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a pulse width and a hole diameter according to the present invention.

FIG. 2 is a diagram sequentially showing an outline of all steps of a hole drilling process according to the present invention.

FIG. 3 is a view of a corner portion of a hole bottom according to the processing method of the present invention.

FIG. 4 is a cross-sectional photograph of a hole processed by the processing method of the present invention by a scanning electron microscope.

[Explanation of symbols]

1 ... Outer conductor layer 2 ... Insulating resin layer 3 ... Inner conductor layer 4 ... Resin film layer

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) // B23K 101: 42 B23K 101: 42

Claims (5)

[Claims] 1. A printed circuit board comprising an outer conductor layer, an insulating resin layer, and an inner conductor layer is subjected to a roughening treatment on the surface of the outer conductor layer in order to increase the absorption rate of laser light, and a laser is applied to the surface of the outer conductor layer. By adding a resin film layer with good workability,
In the method of blind hole processing with a carbon dioxide gas laser, by making the laser light pulse into a top hat shape and controlling the pulse width, the hole lower diameter of the resin film layer on the outer conductor layer, the hole diameter of the outer conductor layer, and the insulating resin layer Laser drilling method characterized by controlling the diameter of the upper part of the hole. 2. A laser light pulse for controlling the diameter of the lower hole of the resin film layer, the diameter of the hole of the outer conductor layer, and the upper diameter of the hole of the insulating resin layer is irradiated with a plurality of laser light pulses having a narrow pulse width. The laser drilling method according to claim 1, wherein the shape of the hole bottom portion on the inner conductor layer is shaped by doing so. 3. The resin film layer is an acrylic film, a polyethylene film, a vinyl chloride film having a thickness of 10 to 60 μm, or an adhesive film having a multi-layer structure of these films. Laser drilling method. 4. The diameter of the lower hole of the resin film layer is 160% or less of the upper diameter of the upper hole of the insulating resin layer.
The laser drilling method described. 5. A printed circuit board comprising an outer conductor layer, an insulating resin layer and an inner conductor layer is subjected to a roughening treatment on the surface of the outer conductor layer in order to increase the absorption rate of laser light, and a laser is applied to the surface of the outer conductor layer. By adding a resin film layer with good workability,
In blind hole processing with carbon dioxide laser,
A laser drilling method, characterized in that a resin film layer having good laser processability has a multi-layer structure of a material having a high absorptivity and a material having an absorptivity as low as about one half thereof.