JP2001053450A - Method for forming blind via hole - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a via hole whose shape is satisfactory without having effect on an adjacent matellic layer at the formation of a blind via hole in the insulating layer of a multilayer wiring board. SOLUTION: A process for forming a blind via hole is provided with a first process for opening a taper-shaped hole in an insulating layer 12 by focusing layer beams 14 on a work, and a second process for forming a vertical hole by just focusing the laser beams 14 on the work and for removing a taper part 16 by reducing the laser power. The laser beams 14 are circularly scanned in the both processes. Thus, it is possible to form a satisfactory via hole without having any effect on an adjacent matellic layer 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a blind via hole, and more particularly, to a method for forming a blind via hole in an insulating layer of a multi-layer substrate generally used as a printed circuit board and having two or more layers. The present invention relates to a method for forming a blind via hole.

[0002]

2. Description of the Related Art In recent years, technical development for downsizing ICs in the field of electronic equipment and communication has been rapidly advanced. Along with this, a high-quality, high-precision drilling method for a small multilayer substrate utilizing interlayer bonding has been required for high-density mounting.

FIG. 5 shows a two-layer substrate which is an example of a multilayer substrate. In the two-layer substrate, a polyimide layer 10 as an electrical insulating layer is formed on the surface, and a copper layer 11 as a conductive layer is formed on the lower layer, respectively, and further, an adhesive layer 12 for bonding these two layers is provided therebetween. It has the structure of. In the two-layer substrate, as shown, a blind via hole 17 for connecting a wiring to the copper layer 11 is provided with the polyimide layer 10 and the adhesive layer 12.
Is formed to reach the surface of the copper layer 11.

[0004]

Conventionally, blind via holes are formed by selectively exposing photosensitive polyimide to light and then etching to form a pattern, or by wet etching using a solvent. Etc. were used. However, according to these methods, it was difficult to accurately process the blind via hole vertically (columnar) and to form the lower copper layer without affecting the processing.

In view of the above, according to the present invention, a blind via hole can be formed in an insulating layer of a multi-layer substrate having two or more layers with higher dimensional accuracy and without affecting a metal layer therebelow. And a method of forming a blind via hole.

[0006]

In order to achieve the above object, a method of forming a blind via hole according to the present invention comprises irradiating a beam onto a wiring substrate having at least a metal layer and an insulating layer adjacent to each other, thereby forming an insulating layer. Forming a first via hole by selectively removing the insulating layer with a beam shifted in focus from the insulating layer forming the blind via hole. It is characterized by having a process.

According to the method of forming a blind via hole of the present invention, the first hole is formed by a beam whose focal position is shifted from the insulating layer, so that the effect of the beam on the metal layer adjacent to the insulating layer is reduced. The damage that occurs on the surface is reduced.

Here, it is preferable that the beam whose focal position is shifted is scanned in a substantially circular shape. In this case, damage caused particularly to the metal layer is reduced.

In a preferred embodiment of the present invention, the method further comprises a second step of removing the edge of the first hole with a beam focused on an insulating layer, following the first step. In this case, the removal of the edge turns the first hole into a good blind via hole having a vertical shape.

Further, it is a preferred embodiment of the present invention that the irradiation energy of the beam in the second step is set lower than the irradiation energy of the beam in the first step. This is because damage caused to the metal layer can be further reduced.

It is possible to scan the focused beam with a substantially circular shape, and in this case, it is possible to further reduce damage to the metal layer.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the drawings based on embodiments of the present invention. FIG.
1A and 1B are cross-sectional views of a multi-layer substrate (two-layer substrate) in which a via hole is formed by a method of forming a blind via hole according to an embodiment of the present invention, at each process step.

The formation of a blind via hole is generally to expose a copper layer by penetrating an insulating layer of polyimide or the like and forming a via hole up to a copper layer which is a lower metal layer. As an important condition, it is required that the copper layer is not affected by processing. In addition, the insulating layer must be surely removed. In the present embodiment, for this purpose, the processing steps are divided into two and high-quality, high-precision processing is performed.

First, as shown in FIG. 1A, a process for selectively removing the polyimide layer 10 which is an insulating layer on the surface is performed in a first step. At this time, the laser beam 14 is shifted to the beam focus position 13 so as not to affect the processing on the copper layer 11.
To defocus (focus the laser beam at a position above the work). As shown in FIG. 2, the laser beam 14 thus defocused is circumferentially scanned in accordance with the outer peripheral dimension of the processing hole diameter, thereby performing circumferential processing.

In the first step, processing by defocusing is performed so as not to affect the processing on the copper layer 11 as described above. However, since the processing by the defocus is weak processing, as shown in FIG. 2, a mortar-shaped hole including the tapered portion 16 is formed as the hole shape after the processing.
For this reason, in the second step, a process of removing the tapered portion 16 is performed to form a high-quality and high-precision hole.

Before performing the processing in the second step, the laser beam is just focused at the beam focal position 15 (the laser beam is focused so that the beam has the minimum diameter on the work surface).
Also, by adjusting the set current to the LD,
Automatically vary the laser beam energy to reduce the output. In order to remove the tapered portion 16 in the state where the above setting has been performed, circumferential processing for circumferentially scanning the laser beam as shown in FIG. 2 is performed. Thereby, a vertical cylindrical hole shape as shown in FIG. 5 is obtained, and a high-quality, high-precision machined hole is formed. In particular, the effect on the copper layer 11 by reducing the laser output is minimized.

FIG. 3 shows a configuration of a UV processing machine for performing the processing method of the above embodiment. The UV processing machine includes a control unit 31 that controls output of a laser beam and sequence control of the entire apparatus, and a processing optical system unit 32 that irradiates a processing surface with a laser. Referring to FIG. 4, the processing optical system unit 32 includes a laser diode (hereinafter, referred to as LD) pumped solid-state laser 41 and a third harmonic conversion unit (hereinafter, referred to as a THG unit) that guides laser light from the solid-state laser 41. ) 42, attenuator 43, beam expander 4
4, a galvanomirror 45, an fθ lens 46, a large number of reflecting mirrors 17, and a processing table 47 on which a multilayer substrate is mounted.

The LD-pumped solid-state laser 41 is, for example, a solid-state laser device that oscillates a fundamental wave having an oscillation wavelength of 1064 nm. This fundamental wave is converted into a third harmonic (oscillation wavelength 355n), which is UV light (ultraviolet light), by the THG unit 42.
m), and irradiates the work set on the processing surface 47 to process the work.

The attenuator 43 has a function of changing the laser power by attenuating the laser power. The beam expander 44 has a function of changing the focal position of the laser light. By using the beam expander 44, the defocus and the just focus can be arbitrarily set for the work on the processing surface 47 when performing the blind via hole processing.

The galvanomirror 45 moves the X
It has a function to move the laser irradiation position in the axial and Y-axis directions. The processing command is transmitted to the driver of the galvanomirror 45, and the galvanomirror 45 controls the laser irradiation position.

The fθ lens 46 operates so that the laser beam can be irradiated onto the work on the processing table 47 without changing the focal position, even when the laser irradiation position is moved by the galvanomirror 45.

When a blind via hole is formed by the method of the present invention using the above-mentioned UV processing machine, the expander 44 is automatically changed by electric control before performing the processing in the second step. As a result, the beam focal position 15 is just-focused (the laser beam is focused so as to have a minimum diameter on the work surface) on the processing work. Also,
By adjusting the set current for the LD, the laser beam energy is automatically varied, thereby reducing the laser power.

The processing control method is as follows.
D current, a processing program, a focus position parameter, and the like are set, and a command is given from the control unit 31 to the processing optical system unit 32 to perform processing.

In the above embodiment, the laser beam energy is reduced by adjusting the LD current in the second step.
Instead, the laser oscillation repetition frequency can be varied. This is to control the laser power by changing the set frequency. According to this method, a small laser power required only for removing the tapered portion 16 can be obtained.

Although the present invention has been described based on the preferred embodiment, the method of forming a blind via hole according to the present invention is not limited to the configuration of the above-described embodiment. Various modifications and changes from the configuration described above are also included in the scope of the present invention.

[0026]

As described above, according to the method for forming a blind via hole of the present invention, a via hole is formed in an insulating layer by defocusing a laser beam, so that an adjacent metal layer is not damaged. There is an effect that a good blind via hole can be formed.

[Brief description of the drawings]

FIGS. 1A and 1B are cross-sectional views of a wiring substrate sequentially showing steps in a method of forming a blind via hole according to the present invention.

FIG. 2 is a plan view showing beam scanning in each step of FIG. 1;

FIG. 3 is a block diagram illustrating a configuration of a UV processing machine that performs the method of FIG. 1;

FIG. 4 is a schematic block diagram illustrating a configuration of a processing optical system unit in FIG. 3;

FIG. 5 is a cross-sectional view of a two-layer substrate showing a conventional method of forming a blind via hole.

[Explanation of symbols]

 11: Copper layer (metal layer) 12: Polyimide layer (insulating layer) 13: Beam focus position (defocus) 14: Laser beam 15: Beam focus position (just focus) 16: Tapered portion 17: Blind via hole. 31: Control unit 32: Processing optical system unit 41: LD pumped solid laser 42: THG unit 43: Attenuator 44: Beam expander 45: Galvanometer mirror 46: fθ lens 47: Processing table 48: Reflecting mirror

Claims (5)

[Claims] 1. A method for forming a blind via hole, comprising: irradiating a beam onto a wiring board having at least a metal layer and an insulating layer adjacent to each other to form a blind via hole in the insulating layer. A method for forming a blind via hole, comprising a first step of forming a first hole by selectively removing the insulating layer with a beam whose focal position is shifted from the layer. 2. The method for forming a blind via hole according to claim 1, wherein the beam whose focal position is shifted is scanned in a substantially circular shape. 3. The method according to claim 1, further comprising a second step following the first step, wherein an edge of the first hole is removed by a beam focused on the insulating layer. A method of forming a blind via hole. 4. The method according to claim 3, wherein the irradiation energy of the beam in the second step is lower than the irradiation energy of the beam in the first step. 5. The method of forming a blind via hole according to claim 2, wherein the focused beam is scanned in a substantially circular shape.