JP2002299794A - Method of forming via hole and laminated wiring board having via hole - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming via holes, which can be worked efficiently by enhancing the laser machining property of a conductor layer after its treatment, and to provide a laminated wiring board having the via hole. SOLUTION: A treatment solution is used, in which concentration of NaOH is increased more than its recommended value to be set at a concentration in a range of 25 to 40 g/l, and chemical treatment is applied to a copper foil. Consequently, the surface of the copper foil, after its treatment displays a needle crystal whose irregularities due to a large crystal are intense, and it has many places whose crystal interval is larger than 9.4 μm for the laser wavelength. As a result, the absorption factor of light is high at 20 to 40%. Consequently, after its treatment, the copper foil and an interlayer insulating layer under it are worked by a laser machining operation with satisfactory working efficiency, and the satisfactory via hole is formed. In this manner, the laser machining property of the conductor layer after its treatment is enhanced, and the conductor layer can be worked with satisfactory efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the formation of via holes in the production of a multilayer wiring board. More specifically,
Method of forming via hole in a conductor layer and an insulating layer thereunder at once by laser irradiation without previously forming a window in the uppermost conductor layer, and laminated wiring board having via hole formed in this way It is about.

[0002]

2. Description of the Related Art Conventionally, an upper insulating layer and a conductor layer (in this case, a copper foil) are laminated using, for example, RCF or the like, and are processed to form a via hole having an interlayer conduction structure. I have. Here, a so-called copper direct method of processing a copper foil and an insulating layer by irradiating a laser to the copper foil without providing a window in advance may be used.

[0003]

However, conventionally,
The workability of the copper foil by laser was not always good. For this reason, processing defects occur or a large load is applied to the production line.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems associated with the above-described conventional via hole formation. That is, an object of the present invention is to provide a method of forming a via hole and a laminated wiring board having a via hole, which are capable of improving the laser workability of a conductor layer and enabling efficient processing.

[0005]

SUMMARY OF THE INVENTION In order to solve this problem, a method of forming a via hole according to the present invention has been described.
When a via hole is formed by irradiating a laser to the conductor layer on the insulating layer and piercing the conductor layer and the insulating layer therebelow, the NaOH concentration of the conductor layer must be 25 to 4 in advance.
The chemical treatment is performed using a treatment liquid within the range of 0 g / l. Alternatively, NaOH of the processing solution during chemical processing
The concentration is increased within the range of 10 to 25 g / l from the recommended condition. Alternatively, the chemical treatment is performed under the condition that the light absorptivity of the surface of the conductor layer after the treatment is in the range of 20 to 40%. By doing this,
Laser processing is performed efficiently, and good via holes are formed.

In the laminated wiring board having a via hole formed by laser processing according to the present invention, the surface of the upper conductive layer at the time when the via hole is formed has a light within a range of 20 to 40% (light used for laser processing). This is a treated surface having an absorptance of the same light. Alternatively, the surface of the upper conductor layer at the time when the via hole is formed is made of a needle-like crystal having an interval of a laser wavelength or more between crystals. In these laminated wiring boards, the upper conductor layer at the time when the via hole is formed has a surface cleaning with good laser workability. For this reason, laser processing is performed efficiently, and via holes are formed favorably.

[0007]

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

The object of this embodiment is a laminated wiring board as shown on the left side of FIG. The copper foil 1 and the interlayer insulating layer 2 are processed by a copper direct method using a laser beam as shown on the right side of FIG.
Is partially exposed. The copper foil 1 and the interlayer insulating layer 2 in FIG. 1 are generally formed by laminating a copper foil provided with a resin on a patterned inner copper layer 3. is there. The surface of the copper foil 1 is previously subjected to a chemical treatment. After the state shown on the right side of FIG. 1 is reached, via holes are formed through the plating step as an interlayer conduction structure between the copper foil 1 and the inner copper layer 3.

The chemical treatment previously applied to the surface of the copper foil 1 is provided as a treating agent,
This is performed using a material containing H as a main component. However, the NaOH concentration in the processing solution was adjusted to the recommended value (15 g /
l) As a result, the surface of the copper foil 1 is
As shown in the scanning electron micrograph of (1), needle-like crystals with severe irregularities are exhibited. In the photograph, bright portions are convex portions (mostly CuO crystals), and dark portions are concave portions. The whole looks black to the naked eye. FIG.
This is the surface of the copper foil 1 chemically treated with a treatment liquid having an OH concentration of 31.3 g / l. In this case, there are very many places where the distance between the crystals is larger than the laser wavelength of 9.4 μm (CO ₂ laser).

On the other hand, N which is not much different from the recommended value
Copper foil 1 chemically treated with a treatment solution having an aOH concentration of 18.0 g / l
As shown in FIG. 3, although the surface is also acicular, the crystal size is much smaller than that of FIG. No portion where the crystal spacing is larger than the laser wavelength of 9.4 μm is not seen at all. Regarding the unevenness in the height direction, it is considered that FIG. 3 is much smaller than that of FIG.

[0011] Further, these two showed a clear difference in the light absorptivity. That is, the absorption rate of FIG. 2 was about 33%, which was much higher than the absorption rate of about 10% of FIG. As shown in FIG. 4, the measurement of the light absorptance was performed by dividing the intensity of the reflected light (CO ₂ laser light) by the intensity of the incident light to calculate the reflectivity.
Performed by subtracting from%.

Further, when the via diameter after laser processing was measured for each sample chemically treated with treatment solutions having various NaOH concentrations, the results shown in the graph of FIG. 5 were obtained. It can be seen from the graph that good results were obtained at a NaOH concentration of 25 g / l or more, but poor results were obtained at lower NaOH concentrations. It is considered that this is because when the NaOH concentration is less than 25 g / l, the light reflectance of the treated surface is high and the processing efficiency is poor. Although it is out of the range of FIG.
Again, the results were poor when g / l was exceeded.

[0013]

[Table 1]

Further, the light absorption rate (see FIG. 4) of each sample chemically treated with treatment solutions having various NaOH concentrations was measured, and the results shown in Table 1 were obtained. This and FIG.
In comparison with the graph of FIG.
It can be seen that laser workability is good when it is within the range of 0 to 40%. It is considered that the reason is that when the light absorptivity is low, most of the irradiated laser light is reflected and is not effectively used for processing. In addition,
Each numerical value of the light absorptance shown in Table 1 is an average value of the measured values for each NaOH concentration.

As described above in detail, in the present embodiment, the NaOH concentration is increased from its recommended value to 25 to 40 g.
The copper foil 1 is subjected to a chemical treatment using a treatment solution having a concentration within the range of / l. For this reason, the surface of the copper foil 1 after the treatment exhibits acicular crystals with large irregularities due to large crystals, and the crystal spacing is 9.4 μm, which is the laser wavelength.
It has many places larger than m. Therefore, the light absorptance is as high as 20 to 40%. Therefore, after chemical treatment,
When the copper foil 1 and the interlayer insulating layer 2 thereunder are processed by laser processing, the processing efficiency is good, and a good via hole is formed. In this manner, a via hole forming method and a laminated wiring board having via holes, which are capable of improving the laser workability of the conductor layer after the chemical treatment and enabling efficient processing, have been realized.

By using this method, for example, the following is also possible. That is, consider a four-layer wiring board having conductor layers 11, 12, 13, and 14 as shown in FIG. It is assumed that the outer surfaces of the conductor layers 11 to 14 are respectively subjected to the chemical treatment described in the present embodiment. Then, by irradiating a laser beam to a position indicated by an arrow in FIG.
The broken line portions 1 and 22 can be processed at once. Thereby, via holes connecting the three layers of the conductor layers 11 to 13 can be formed.

The present embodiment is merely an example, and does not limit the present invention. Therefore, naturally, the present invention can be variously modified and modified without departing from the gist thereof.

[0018]

As is apparent from the above description, according to the present invention, a method of forming a via hole which improves the laser workability of a conductor layer after chemical treatment and enables efficient processing, and a laminated wiring having a via hole are provided. A board is provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a structure of a laminated wiring board before and after processing.

FIG. 2 is a scanning electron micrograph showing a shape of a copper foil surface after a chemical treatment.

FIG. 3 is a scanning electron micrograph showing a shape of a copper foil surface after a chemical treatment in a comparative example.

FIG. 4 is a conceptual diagram illustrating a method for measuring the light absorption rate of a chemically treated surface.

FIG. 5 is a graph showing the relationship between the NaOH concentration during chemical processing and the via diameter after laser processing.

FIG. 6 is a cross-sectional view showing a state in which a three-layer via hole is formed in a four-layer wiring board.

[Description of Signs] 1 Copper foil 2 Interlayer insulating layer

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 4E068 AF01 CF01 CF03 DA11 DB14

Claims (5)

[Claims] In a method of forming a via hole for performing a chemical treatment on a conductor layer on an insulating layer and further irradiating a laser to irradiate a laser on the conductor layer and the insulating layer thereunder, the chemical treatment is performed when the NaOH concentration is reduced. A method for forming a via hole, wherein the method is performed using a processing solution within a range of 25 to 40 g / l. 2. A method for forming a via hole in which a conductor layer on an insulating layer is subjected to a chemical treatment and a laser is irradiated to form a hole in the conductor layer and the insulating layer therebelow. NaOH concentration of 10
A method for forming a via hole, wherein the amount of the via hole is increased within a range of 25 g / l. 3. A method of forming a via hole for performing a chemical treatment on a conductor layer on an insulating layer and irradiating a laser to irradiate a laser on the conductor layer and the insulating layer thereunder, wherein the chemical treatment is performed after the treatment. The light absorptance of the surface of the conductor layer is 2
A method for forming a via hole, wherein the method is performed under conditions that fall within a range of 0 to 40%. 4. In a laminated wiring board having via holes formed by laser processing, the surface of the upper conductor layer at the time when the via holes are formed is a treated surface having a light absorptance in the range of 20 to 40%. A laminated wiring board having via holes. 5. In a multilayer wiring board having via holes formed by laser processing, the surface of the upper conductor layer at the time when the via holes are formed is formed of needle-like crystals having a spacing of a laser wavelength or more between crystals. A laminated wiring board having via holes.