阅读说明：本技术 多层布线板的制造方法 (Method for manufacturing multilayer wiring board ) 是由 沟口美智 吉川和广 清水俊行 于 2019-03-22 设计创作，主要内容包括：本发明提供一种即使在使电路极薄化的情况下,电路密合性也优异且能够极其有效地防止激光加工导致的该电路的贯通的多层布线板的制造方法。该多层布线板的制造方法包含：准备层叠体的工序,该层叠体具备金属箔、在金属箔上设置的绝缘层、在绝缘层的与金属箔相反的那侧的面设置的第1布线层；从金属箔的表面对层叠体实施激光加工而形成导通孔的工序；以及对层叠体的形成有导通孔的那侧实施镀敷和图案化而形成多层布线板的工序,对于第1布线层的至少与金属箔相对的面,波长10.6μm的激光的反射率为80％以上,且峰的顶点密度Spd为7000个/mm～2以上且15000个/mm～2以下,金属箔的厚度T-2相对于第1布线层的厚度T-1的比即T-2/T-1为0.23以上。(The invention provides a method for manufacturing a multilayer wiring board, which has excellent circuit adhesion even when a circuit is extremely thinned and can extremely effectively prevent the circuit from penetrating due to laser processing. The method for manufacturing the multilayer wiring board comprises the following steps: a step of preparing a laminate comprising a metal foil, an insulating layer provided on the metal foil, and an insulating layerThe 1 st wiring layer provided on the side opposite to the metal foil; a step of forming a via hole by laser processing the laminate from the surface of the metal foil; and a step of forming a multilayer wiring board by plating and patterning the side of the laminate on which the via holes are formed, wherein the reflectance of a laser beam having a wavelength of 10.6 μm is 80% or more and the peak density Spd of the peaks is 7000 pieces/mm on at least the surface of the 1 st wiring layer facing the metal foil 2 Above and 15000 pieces/mm 2 The thickness T of the metal foil is as follows 2 Thickness T relative to the 1 st wiring layer 1 Ratio of (1) or T 2 /T 1 Is 0.23 or more.)

1. A method of manufacturing a multilayer wiring board, wherein,

the method for manufacturing the multilayer wiring board comprises the following steps:

(a) a step of preparing a laminate including a metal foil, an insulating layer provided on the metal foil, and a 1 st wiring layer provided on a surface of the insulating layer on a side opposite to the metal foil;

(b) a step of forming a via hole penetrating the metal foil and the insulating layer to reach the 1 st wiring layer by performing laser processing on the laminate from the surface of the metal foil; and

(c) a step of forming a multilayer wiring board including the 1 st wiring layer and the 2 nd wiring layer derived from the metal foil by plating and patterning the side of the laminate body on which the via hole is formed,

a reflectance of a laser beam having a wavelength of 10.6 [ mu ] m, measured by a Fourier transform infrared spectrophotometer (FT-IR), of 80% or more with respect to at least a surface of the 1 st wiring layer facing the metal foil, and a peak density Spd of 7000 peaks/mm measured in accordance with ISO25178²Above and 15000 pieces/mm²In the following, the following description is given,

thickness T of the metal foil₂A thickness T relative to the 1 st wiring layer₁Ratio of (1) or T₂/T₁Is 0.23 or more.

2. The method for manufacturing a multilayer wiring board according to claim 1,

thickness T of the 1 st wiring layer₁Is 2 to 15 μm in diameter.

3. The method of manufacturing a multilayer wiring board according to claim 1 or 2, wherein,

thickness T of the metal foil₂Is 0.5 to 6 μm in diameter.

4. The method of manufacturing a multilayer wiring board according to any one of claims 1 to 3,

the T is₂/T₁Is 1.0 or less.

5. The manufacturing method of a multilayer wiring board according to any one of claims 1 to 4,

the output density of the laser in the laser processing is 8MW/cm²Above and 14MW/cm²The following.

6. The manufacturing method of a multilayer wiring board according to any one of claims 1 to 5,

the diameter of the via hole is 30 [ mu ] m or more and 80 [ mu ] m or less.

7. The method of manufacturing a multilayer wiring board according to any one of claims 1 to 6,

the metal foil is provided in the form of a carrier-attached metal foil including a carrier, a release layer, and the metal foil in this order, and the carrier is released from the laminate before the metal foil is subjected to laser processing.

Technical Field

The present invention relates to a method of manufacturing a multilayer wiring board.

Background

In recent years, multilayer printed wiring boards have been widely used to increase the mounting density of printed wiring boards and to reduce the size of printed wiring boards. Such a multilayer printed wiring board is used in many portable electronic devices for the purpose of weight reduction and size reduction. Further reduction in the thickness of the interlayer insulating layer, and further reduction in thickness and weight as a wiring board are required for the multilayer printed wiring board.

As a technique for satisfying such a demand, a method for manufacturing a multilayer printed wiring board using a coreless lamination method is adopted. The coreless lamination method is: a method of forming a multilayer structure by alternately stacking (laminating) insulating layers and wiring layers without using a so-called core substrate. In the coreless build-up method, in order to easily peel the support from the multilayer printed wiring board, it is proposed to use a metal foil with a carrier. For example, patent document 1 (japanese patent No. 4460013) discloses a method for manufacturing a wiring board, the method including: an insulating layer and a metal layer having a thickness of 18 μm were sequentially laminated on the metal foil side of the metal foil with a carrier, the metal layer was processed to form an inner layer circuit (1 st conductor pattern), the insulating layer and the metal foil were further sequentially laminated on the inner layer circuit, the carrier was peeled off to form a substrate having the metal foils on both surface sides of the inner layer circuit, and then the inner layer circuit and the metal foils on both surfaces of the substrate were electrically connected via vias. Patent document 1 also discloses the following: the method includes forming via holes, which penetrate a metal foil and an insulating layer and reach an inner layer circuit, from both surfaces of a substrate by laser processing, patterning the metal foil on both surfaces of the substrate with a dry film, filling the via holes with plating by electroplating, and forming outer layer circuits (conductor patterns) on both surfaces of the substrate.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 4460013

Patent document 2: japanese patent No. 3142270

Disclosure of Invention

Problems to be solved by the invention

In recent years, with further thinning of multilayer printed wiring boards, the thickness of metal foils used for circuits in multilayer wiring boards has also been reduced. In this regard, it is also desirable to use an extremely thin metal foil in the production of the wiring substrate as described in patent document 1. However, when a circuit (for example, an inner layer circuit) is formed using a conventional extremely thin copper foil (for example, 6 μm to 12 μm in thickness), the following problems occur: in the step of forming via holes for interlayer connection, laser processing not only penetrates the metal foil and the insulating layer on both surfaces (outer layers) to form holes, but also penetrates the circuit to form holes. For example, patent document 2 (japanese patent No. 3142270) discloses the following for a substrate with an inner layer circuit: in the case where the thickness of the inner layer circuit is less than 4.5 times the thickness of the outer layer copper foil (in other words, the thickness T of the outer layer copper foil)₂Relative to each otherThickness T in inner layer circuit₁Ratio of (1) or T₂/T₁If the ratio is less than 1/4.5(═ 0.22), there is a risk of damage to the inner layer circuit and the like occurring when the hole is opened by laser irradiation.

The inventors have now found the following: by using a wiring layer having a predetermined surface for which the reflectance of a laser beam having a wavelength of 10.6 μm and the peak density Spd of the peak satisfy predetermined conditions, and manufacturing a multilayer wiring board, the multilayer wiring board has excellent circuit adhesion even when the circuit is extremely thin, and can extremely effectively prevent penetration of the circuit by laser processing.

Accordingly, an object of the present invention is to provide a method for manufacturing a multilayer wiring board, which has excellent circuit adhesion even when a circuit is extremely thin and can extremely effectively prevent penetration of the circuit by laser processing.

In accordance with one aspect of the present invention, there is provided a method for manufacturing a multilayer wiring board, comprising: (a) a step of preparing a laminate including a metal foil, an insulating layer provided on the metal foil, and a 1 st wiring layer provided on a surface of the insulating layer on a side opposite to the metal foil; (b) a step of forming a via hole penetrating the metal foil and the insulating layer to reach the 1 st wiring layer by performing laser processing on the laminate from the surface of the metal foil; and (c) a step of forming a multilayer wiring board including the 1 st wiring layer and the 2 nd wiring layer derived from the metal foil by plating and patterning the side of the laminate on which the via hole is formed, wherein a reflectance of a laser beam having a wavelength of 10.6 μm, which is measured by a fourier transform infrared spectrophotometer (FT-IR), is 80% or more with respect to at least a surface of the 1 st wiring layer facing the metal foil, and a peak density Spd of 7000 pieces/mm is measured in accordance with ISO25178²Above and 15000 pieces/mm²Hereinafter, the thickness T of the metal foil₂A thickness T relative to the 1 st wiring layer₁Ratio of (1) or T₂/T₁Is 0.23 or more.

Drawings

Fig. 1 is a process flow chart showing the steps (step (i) to step (iii)) in one example of the production method of the present invention.

Fig. 2 is a process flow chart showing the steps (i) to (iv)) of producing the laminate for evaluation of laser processability and forming the via hole in examples 1 to 6.

Detailed Description

Definition of

In the following, definitions of parameters used for determining the present invention are shown.

In the present specification, "reflectance of laser light having a wavelength of 10.6 μm" means a ratio of the amount of light reflected by a sample to the amount of light reflected by a reference plate (e.g., Au deposition mirror) when the laser light having a wavelength of 10.6 μm is irradiated onto the surface of the sample (metal foil) as measured by a fourier transform infrared spectrometer (FT-IR). The reflectance of the laser beam having a wavelength of 10.6 μm can be measured under the conditions described in the examples of the present specification using a commercially available fourier transform infrared spectrometer. Further, the wavelength of a carbon dioxide laser typically used for laser processing is 10.6 μm, and thus the laser wavelength of a fourier transform infrared photometer is made 10.6 μm.

In the present specification, the "peak top density Spd" is a parameter indicating the number of peak tops per unit area measured in accordance with ISO 25178. A larger value indicates a larger number of contact points with other objects. The peak density Spd can be calculated by measuring the surface profile of a predetermined measurement area (for example, a region of 107 μm × 143 μm) on the surface of the metal foil or the wiring layer with a commercially available laser microscope.

Method for manufacturing multilayer wiring board

The present invention relates to a method of manufacturing a multilayer wiring board. The method of the present invention comprises the following steps: (1) preparation of a laminate, (2) formation of a via hole, and (3) formation of a 2 nd wiring layer.

Hereinafter, each of the steps (1) to (3) will be described with reference to fig. 1.

(1) Preparation of laminate

A laminate 16 is prepared, and the laminate 16 includes a metal foil 10, an insulating layer 12 provided on the metal foil 10, and a 1 st wiring layer 14 provided on a surface of the insulating layer 12 opposite to the metal foil 10. Typically, the laminate 16 corresponds to an intermediate product before peeling the support in the method for manufacturing a multilayer wiring board such as the coreless lamination method. For example, as shown in fig. 1 (i), the laminate 16 may be formed by further laminating an insulating layer 12' on the surface on the 1 st wiring layer 14 side (i.e., the side opposite to the metal foil 10). In this case, the 1 st wiring layer 14 becomes an inner layer circuit buried between the insulating layer 12 and the insulating layer 12'. Alternatively, the laminate 16 may be in a form in which a metal foil or a wiring layer (not shown) is further laminated or formed on the surface on the 1 st wiring layer 14 side with the insulating layer 12' interposed therebetween (for example, a form in which metal foils are provided on both surfaces). The 1 st wiring layer 14 may be provided in the insulating layer 12. In any case, the laminate 16 is not particularly limited as long as it includes at least the metal foil 10, the insulating layer 12, and the 1 st wiring layer 14.

The metal foil 10 may have a known structure used for metal foils for printed wiring boards. For example, the metal foil 10 may be a metal foil formed by a wet film formation method such as electroless plating and electrolytic plating, a dry film formation method such as sputtering and chemical vapor deposition, or a combination thereof. Examples of the metal foil 10 include an aluminum foil, a copper foil, a stainless steel (SUS) foil, and a nickel foil, and a copper foil is preferable. The copper foil may be either one of a rolled copper foil and an electrolytic copper foil.

The metal foil 10 may also be provided in the form of a metal foil with a carrier. Typically, the metal foil with a carrier includes a carrier (not shown), a release layer (not shown), and the metal foil 10 in this order. The carrier is a foil or layer for supporting the metal foil 10 to improve its handling. Preferred examples of the carrier include aluminum foil, copper foil, stainless steel (SUS) foil, resin film with a surface coated with a metal such as copper, resin plate, glass plate, and a combination thereof. The thickness of the support is typically 5 μm or more and 250 μm or less, and preferably 9 μm or more and 200 μm or less. The material of the release layer is not particularly limited as long as the release layer can release the carrier. For example, the release layer may be formed of a known material used for a release layer of a metal foil as a tape carrier. The release layer may be either an organic release layer or an inorganic release layer, or may be a composite release layer of an organic release layer and an inorganic release layer. The thickness of the release layer is typically 1nm or more and 1 μm or less, preferably 5nm or more and 500nm or less, and more preferably 6nm or more and 100nm or less. When the metal foil 10 is provided in the form of a metal foil with a carrier, it is preferable that the carrier is peeled from the laminate 16 before laser processing is performed on the metal foil 10 described later. In this way, laser processing can be performed from the metal foil 10 in the via hole forming step described later.

One surface of the laminate 16 may be bonded to a support (not shown) such as a prepreg to impart rigidity thereto. The prepreg is a generic name of a composite material obtained by impregnating a synthetic resin into a base material such as a synthetic resin plate, a glass woven fabric, a glass nonwoven fabric, or paper. In this case, it is preferable that the metal foil with the carrier is attached to both surfaces of the support body in a vertically symmetrical manner, the laminate 16 is formed on both surfaces of the obtained temporary laminate with the support body in a vertically symmetrical manner, and then the support body is removed together with the carrier. For example, a metal foil with a carrier including the metal foil 10 is bonded to a support, and the insulating layer 12 and the 1 st wiring layer 14 are sequentially stacked or formed on the metal foil 10 to form a stacked body 16. Alternatively, a metal foil with a carrier, which is provided with a metal foil different from the metal foil 10, is bonded to the support, and the 1 st wiring layer 14, the insulating layer 12, and the metal foil 10 are sequentially stacked or formed on the metal foil to form a stacked body 16. As described above, the laminate 16 prepared in the present invention may be prepared by laminating or forming one of the metal foil 10 and the 1 st wiring layer 14.

The insulating layer 12 may have a known structure used for insulating layers in the coreless lamination method, and is not particularly limited. For example, the insulating layer 12 can be preferably formed by: an insulating resin material such as a prepreg or a resin sheet is laminated on the metal foil 10, and then hot press molding is performed. Preferred examples of the insulating resin impregnated into the prepreg to be used include epoxy resin, cyanate resin, bismaleimide triazine resin (BT resin), polyphenylene ether resin, phenol resin, and the like. Preferred examples of the insulating resin constituting the resin sheet include epoxy resin, polyimide resin, and polyester resin. In addition, the insulating layer 12 may contain filler particles made of various inorganic particles such as silica and alumina, from the viewpoint of improving the insulating property. The thickness of the insulating layer 12 is not particularly limited, but is preferably 1 μm or more and 100 μm or less, more preferably 5 μm or more and 40 μm or less, and further preferably 10 μm or more and 30 μm or less. The 1 st insulating layer 12 may be composed of a plurality of layers. In the case where the laminate 16 includes the insulating layer 12 ', as shown in fig. 1 (i), the insulating layer 12 ' may have a standard structure as long as the insulating layer 12 is used, and the above-described preferable embodiment of the insulating layer 12 is also directly applied to the insulating layer 12 '.

The 1 st wiring layer 14 can be preferably formed by, for example, laminating a 1 st wiring layer metal foil on the insulating layer 12 or the insulating layer 12' and patterning the 1 st wiring layer metal foil. Alternatively, the 1 st wiring layer 14 may be formed by patterning a metal foil different from the metal foil 10 by metal plating or the like. The metal foil for the 1 st wiring layer may be a metal foil formed by a wet film formation method such as electroless plating and electrolytic plating, a dry film formation method such as sputtering and chemical vapor deposition, or a combination thereof. Examples of the metal foil for the 1 st wiring layer include an aluminum foil, a copper foil, a stainless steel (SUS) foil, and the like, and a copper foil is preferable. The copper foil may be either one of a rolled copper foil and an electrolytic copper foil. The thickness of the metal foil for the first wiring layer 1 is preferably 0.1 μm or more and 12 μm or less, more preferably 1 μm or more and 9 μm or less, and further preferably 5 μm or more and 7 μm or less. Within such a range, it is extremely suitable for forming a fine circuit. The patterning for forming the first wiring layer 14 is not particularly limited as long as it is performed by a known method such as a subtractive method, an MSAP (modified semi-additive) method, and an SAP (semi-additive) method. In the case where the insulating layer 12 or the insulating layer 12' is laminated on the 1 st wiring layer 14, an interlayer process may be performed on the 1 st wiring layer 14 in advance. The inner layer treatment preferably includes roughening treatment such as CZ treatment, which can be preferably performed by: the surface of the 1 st wiring layer 14 is roughened finely by using an organic acid-based microetching agent (for example, product number CZ-8101, manufactured by MEC corporation). In this way, the fine irregularities are formed on the surface of the 1 st wiring layer 14, and adhesion to the insulating layer to be stacked later can be improved.

The surface of the 1 st wiring layer 14 facing at least the metal foil 10 has a reflectance of 80% or more of a laser beam having a wavelength of 10.6 μm measured by a Fourier transform infrared spectrophotometer (FT-IR), and a peak density Spd of 7000 peaks/mm measured in accordance with ISO25178²Above and 15000 pieces/mm²The following. By using a wiring layer satisfying such a condition as a circuit (for example, an inner layer circuit) and manufacturing a multilayer wiring board, it is possible to obtain excellent circuit adhesion and extremely effectively prevent penetration of the circuit by laser processing.

That is, by increasing the reflectance of the laser light having a wavelength of 10.6 μm measured by a fourier transform infrared spectrophotometer on the surface of the 1 st wiring layer 14 facing the metal foil 10 to 80% or more, the laser light used for forming the via hole can be effectively prevented from being absorbed. As a result, even when the 1 st wiring layer 14 is extremely thinned (i.e., when the thickness T of the metal foil 10 is made to be very thin)₂Thickness T relative to the 1 st wiring layer 14₁Ratio of (1) or T₂/T₁Increased to 0.23 or more), penetration of the 1 st wiring layer 14 by laser processing can be prevented extremely effectively. It can be said that the more the surface of the 1 st wiring layer 14 is made smooth, the greater the reflectance of the laser light of the wavelength of 10.6 μm. However, when the surface of the 1 st wiring layer 14 is simply smoothed in order to increase the laser reflectance, the adhesion between the 1 st wiring layer 14 and the insulating layer 12 is reduced, and circuit peeling is likely to occur. Thus, it is not easy to achieve both of circuit adhesion and prevention of circuit penetration by laser processing. In this regard, in the present invention, a laser beam contributing to a wavelength of 10.6 μm is secured on the surface of the 1 st wiring layer 14 facing the metal foil 10Improved smoothness of reflectance and a peak density Spd of 7000 peaks/mm²Above and 15000 pieces/mm²As a result, the 1 st wiring layer 14 can be secured to enter the insulating layer 12 with a large number of contacts. As a result, it is possible to prevent penetration of the inner layer circuit by laser processing extremely effectively while ensuring high circuit adhesion.

From the above viewpoint, the reflectance of the laser beam having a wavelength of 10.6 μm measured by a fourier transform infrared spectrophotometer (FT-IR) on the surface of the 1 st wiring layer 14 facing the metal foil 10 is 80% or more, preferably 85% or more, more preferably 90% or more, and still more preferably 95% or more. The upper limit value is not particularly limited, and may be 100%, but is typically 98% or less. In addition, the peak density Spd of the surface of the 1 st wiring layer 14 facing the metal foil 10 measured according to ISO25178 was 7000/mm²Above and 15000 pieces/mm²Preferably 10000 pieces/mm or less²Above and 15000 pieces/mm²Hereinafter, 13000 pieces/mm are more preferable²Above and 15000 pieces/mm²The following. Within the above preferred range, it is possible to more effectively prevent the penetration of the 1 st wiring layer 14 during laser processing while still further ensuring high circuit adhesion.

The reflectance of the laser beam having a wavelength of 10.6 μm and the peak density Spd in the above range on the surface of the 1 st wiring layer 14 facing the metal foil 10 may be provided in advance on the surface of the 1 st wiring layer metal foil on which the 1 st wiring layer 14 is to be formed, or may be given to the surface of the 1 st wiring layer 14 after the inner layer process (for example, a roughening process such as a CZ process). Therefore, the surface of the 1 st wiring layer 14 facing the metal foil 10 is preferably a rough surface. The metal foil for the 1 st wiring layer having a surface satisfying the above conditions can be realized by roughening the surface of the metal foil under known or desired conditions. Further, a commercially available metal foil having a surface satisfying the above-described conditions can be selectively obtained.

Similarly to the surface of the 1 st wiring layer 14 facing the metal foil 10, the surface of the 1 st wiring layer 14 facing the metal foil 10 may have a reflectance of the laser light having a wavelength of 10.6 μm and a peak density Spd within the above-described ranges. In this way, high adhesion can be secured between the layers (for example, the insulating layer 12') laminated on the side of the first wiring layer 14 opposite to the metal foil 10, and penetration of the first wiring layer 14 can be effectively prevented even when laser processing is performed from the surface of the laminated body 16 opposite to the metal foil 10.

Thickness T of the metal foil 10₂Thickness T relative to the 1 st wiring layer 14₁Ratio of (1) or T₂/T₁Is 0.23 or more, preferably 0.25 or more, and more preferably 0.30 or more. As described above, according to the present invention, the 1 st wiring layer 14 has a surface that is difficult to absorb laser light, and therefore, even if the 1 st wiring layer 14 is extremely thinned so as to satisfy the above range, damage of the 1 st wiring layer 14 due to laser processing can be suppressed. T is₂/T₁Preferably 1.0 or less, more preferably 0.50 or less, and further preferably 0.33 or less. In the case where the surface treatment is performed on the 1 st wiring layer 14 and/or the metal foil 10 before the laser processing is performed (that is, the thickness of the 1 st wiring layer 14 and/or the metal foil 10 is changed), T is set as described above₁And T₂The thickness of the 1 st wiring layer 14 after the surface treatment and the thickness of the metal foil 10 are referred to, respectively. For example, in the case where the above-described inner layer process is performed on the 1 st wiring layer 14, T is₁The thickness of the 1 st wiring layer 14 after the inner layer processing.

Thickness T of the 1 st wiring layer 14₁Preferably 2 to 15 μm, more preferably 3 to 12 μm, still more preferably 5 to 10 μm, and particularly preferably 5 to 8 μm. Within such a range, it is extremely advantageous for the reduction in thickness required for the multilayer printed wiring board. On the other hand, the thickness T of the metal foil 10₂Preferably 0.5 to 6 μm, more preferably 0.7 to 4.0 μm, still more preferably 1.2 to 3.0 μm, and particularly preferably 1.5 to 2.0 μm. Within this range, the via hole 18 can be easily formed by directly performing laser processing on the metal foil 10 in a via hole forming step described later. In addition, the first and second substrates are,when the metal foil 10 is used for forming a wiring layer, if the metal foil 10 is within the above thickness range, the fine circuit formability is also excellent.

(2) Formation of via holes

As shown in fig. 1 (ii), the multilayer body 16 is laser-processed from the surface of the metal foil 10, whereby a via hole 18 penetrating the metal foil 10 and the insulating layer 12 to reach the 1 st wiring layer 14 is formed. For laser processing, various lasers such as a carbon dioxide laser, an excimer laser, a UV laser, and a YAG laser can be used, and a carbon dioxide laser is particularly preferably used. With the method of the present invention, since the 1 st wiring layer 14 has a surface that is less likely to absorb laser light, penetration of the 1 st wiring layer 14 by laser processing can be prevented extremely effectively in the via hole forming step. In particular, even when the output density of laser light is increased for efficient laser processing, it can be said that the penetration of the 1 st wiring layer 14 is less likely to occur by the present invention. From this viewpoint, the output density of the laser in laser processing is preferably 8MW/cm²Above and 14MW/cm²Hereinafter, more preferably 8MW/cm²Above and 12MW/cm²Hereinafter, more preferably 9MW/cm²Above and 12MW/cm²The following. Therefore, in the via hole 18 of the present invention, it is preferable that the via hole 18 is formed by irradiating 1 laser beam for 1 via hole using the laser beam having the output density within the above range.

The diameter of the via hole 18 is preferably 30 μm or more and 80 μm or less, more preferably 30 μm or more and 60 μm or less, and further preferably 30 μm or more and 40 μm or less. Within such a range, it is extremely advantageous for the multilayer printed wiring board to have a higher density. In order to form the via hole 18 having a small diameter as described above, it is desirable to reduce the beam diameter (spot diameter) of the laser beam. In this case, since the energy of the laser light is likely to be concentrated on the laser light irradiated portion of the 1 st wiring layer 14, it can be said that the penetration of the 1 st wiring layer 14 is likely to occur originally. In this regard, with the method of the present invention, since the 1 st wiring layer 14 has a surface that hardly absorbs laser light, penetration of the 1 st wiring layer 14 can be effectively prevented even when the energy of laser light is concentrated.

In the step of forming the via hole, it is preferable to further include a desmear step using at least one of a chromate solution and a permanganate solution as a treatment for removing resin residue (smear (japanese: スミア)) at the bottom of the via hole generated when the via hole is formed by laser processing. The desmear step is a treatment in which treatments such as a swelling treatment, a chromic acid treatment, a permanganic acid treatment, and a reduction treatment are sequentially performed, and a known wet process can be employed. An example of the chromate is potassium chromate. Examples of the permanganate include sodium permanganate and potassium permanganate. In particular, permanganate is preferably used from the viewpoint of reduction of environmental load substances in the desmear treatment liquid, electrolytic regenerability, and the like.

(3) Formation of the 2 nd Wiring layer

As shown in fig. 1 (iii), plating and patterning are performed on the side of the laminated body 16 where the via hole 18 is formed, thereby forming a multilayer wiring board 24, the multilayer wiring board 24 including the 1 st wiring layer 14 and the 2 nd wiring layer 22 derived from the metal foil 10. Thus, the via hole 18 is filled with the metallization, and the 1 st wiring layer 14 and the 2 nd wiring layer 22 are electrically connected via the via hole 18. The 2 nd wiring layer 22 typically contains a metal derived from the metal foil 10, but the 2 nd wiring layer 22 may also be formed as a new wiring layer (containing no metal derived from the metal foil 10) that inherits only the surface profile of the metal foil 10. The method for forming the 2 nd wiring layer 22 is not particularly limited, and a known method such as a subtractive method, an MSAP method, or an SAP method can be used. Here, fig. 1 (iii) shows circuit formation by the MSAP method. As an example of circuit formation by the MSAP method, first, a photoresist layer (not shown) is formed in a predetermined pattern on the surface of the metal foil 10. The photoresist layer is preferably a photosensitive film, and in this case, a predetermined wiring pattern may be provided to the photoresist layer by exposure and development. Next, a plating layer 20 is formed on the exposed surface (i.e., the portion not masked by the photoresist layer) of the metal foil 10 and the via hole 18. At this time, since the via hole 18 is filled with the metallization, the 1 st wiring layer 14 and the metal foil 10 are electrically connected via the via hole 18. The plating is not particularly limited as long as it is carried out by a known method. After the photoresist layer is stripped, the metal foil 10 and the plating layer 20 are subjected to etching processing, whereby a multilayer wiring board 24 in which the 2 nd wiring layer 22 is formed can be obtained.

A build-up wiring layer may be further formed on the multilayer wiring board 24. That is, by further alternately arranging insulating layers and wiring layers including wiring patterns on the multilayer wiring board 24, a multilayer wiring board formed up to the n-th wiring layer (n is an integer of 3 or more) can be obtained. This process may be repeated until a desired number of build-up wiring layers are formed. Further, if necessary, bumps for mounting such as solder resist layers and posts may be formed on the outer layer surface.

Examples

The present invention will be described in more detail with reference to the following examples.

Examples 1 to 6

6 kinds of copper foils used as metal foils for forming inner layer circuits of multilayer wiring boards were prepared and subjected to various evaluations. The specific steps are as follows.

(1) Preparation of copper foil

6 kinds of electrolytic copper foils having the respective parameters shown in Table 1 on at least one side and having a thickness of 9 μm were prepared. Some of these copper foils are commercially available, and the remaining copper foils are separately produced according to a known method. The methods for measuring and calculating the parameters of the prepared copper foil are as follows.

(reflectance of laser light having a wavelength of 10.6 μm in FT-IR)

IR spectrum data was obtained by measuring the surface of the copper foil using an infrared spectrophotometer (Nicolet Nexus 640 FT-IR Spectrometer, manufactured by Thermo Fisher SCIENTIFIC) under the following conditions. The obtained IR spectrum data was analyzed to calculate the reflectance of the laser beam having a wavelength of 10.6 μm.

< measurement Condition >

-measurement: positive reflection method

-background: au evaporation mirror

-resolution: 4cm^－1

-number of scans: 64scan

-a detector: DTGS (Deuterium Tri-Glycine Sulfate) detector

(Peak Density Spd)

The peak density Spd of the peak on the copper foil surface was measured according to ISO25178 under the conditions of a cut-off wavelength of 0.8 μm and a magnification of 2000 times (measurement area 107 μm × 143 μm) using a laser microscope (VK-X100, manufactured by yankee corporation) using an S filter.

(2) Evaluation of copper foil

The prepared copper foil was evaluated for various properties as follows.

< laser processability >

As shown in fig. 2, a laminate for evaluation of laser processability was produced as follows using the copper foil prepared in (1) above as a metal foil for forming an inner layer circuit, and laser processability was evaluated. First, a copper foil having a thickness of 2 μm was prepared as the metal foil 110, and a prepreg (GHPL-830 NSF, manufactured by Mitsubishi gas chemical Co., Ltd.) having a thickness of 0.02mm was laminated on the metal foil 110 as the insulating layer 112. Next, the copper foil prepared in (1) above was laminated as a metal foil 113 for a first wiring layer so that the surface having the parameters shown in table 1 was in contact with the insulating layer 112, and hot press molding was performed for 90 minutes under conditions of a pressure of 4.0MPa and a temperature of 220 ℃. After the surface of the metal foil 113 for the 1 st wiring layer was etched by 1 μm using a microetching solution, a dry film was attached, and exposure and development were performed in a predetermined pattern to form a resist coating. The surface of the metal foil 113 for the 1 st wiring layer was treated with a copper chloride etching solution, and after dissolving and removing copper from the resist coating, the resist coating was peeled off to form the 1 st wiring layer 114, and a 2 nd laminate 116 was obtained (fig. 2 (ii)). The surface of the 1 st wiring layer 114 is subjected to roughening treatment (CZ treatment). The thickness of the 1 st wiring layer 114 after the roughening treatment was 7 μm. Then, a prepreg (GHPL-830 NSF, manufactured by Mitsubishi gas chemical Co., Ltd.) having a thickness of 0.02mm was sequentially laminated on the 2 nd laminate 116 having the 1 st wiring layer 114 formed thereonAnd a copper foil having a thickness of 2 μm as the insulating layer 112 'and the metal foil 110', respectively, were subjected to hot press forming under a pressure of 4.0MPa and a temperature of 220 ℃ for 90 minutes. Thus, a laminate 117 for evaluation of laser processability was obtained (fig. 2 (iii)). In addition, the thickness T of the metal foil 110 in the laminate 117 for evaluation of laser processability₂(2 μm) thickness T relative to the 1 st wiring layer 114₁Ratio of (7 μm), namely T₂/T₁2/7, i.e., equal to about 0.29. The laminate 117 for evaluation of laser processability thus obtained was irradiated with a carbon dioxide laser beam at 9.5MW/cm²The output density of (2) is laser-processed from the metal foil 110 side to form a via hole 118 having a diameter of 65 μm penetrating the metal foil 110 and the insulating layer 112 and reaching the 1 st wiring layer 114 ((iv) of fig. 2). The via hole 118 was observed from the metal foil 110 side with a metal microscope, and the presence or absence of penetration of the 1 st wiring layer 114 was determined. For each example, the formation and the penetration determination of the via hole 118 were performed for 88 holes per example, and the penetration ratio of the 1 st wiring layer 114 after laser processing was calculated from the number of via holes 118 formed and the number of penetrations of the 1 st wiring layer 114.

< circuit sealing >

3 sheets of a prepreg (GHPL-830 NSF, manufactured by mitsubishi gas chemical) having a thickness of 0.1mm were stacked, and the copper foil prepared in (1) was stacked such that the surface having the parameters shown in table 1 was in contact with the stacked prepreg, and hot press molding was performed at a pressure of 4.0MPa and a temperature of 220 ℃ for 90 minutes, thereby producing a copper-clad laminate sample. Dry films were attached to both sides of the copper-clad laminate sample to form a resist coating. Then, on the resist coatings on both sides, a circuit for a peel strength measurement test having a width of 0.8mm was exposed and developed to form an etching pattern. Thereafter, the circuit was etched with a copper etching solution, and the resist was peeled off to obtain a circuit. The thus-formed circuit (thickness 9 μm, circuit width 0.8mm) was peeled in a direction of 90 ° with respect to the prepreg surface and peel strength (kgf/cm) was measured in accordance with JIS C6481-1996.

Examples 7 to 10

Various properties were evaluated in the same manner as in examples 1 to 6, except that an electrolytic copper foil having parameters shown in table 1 on at least one side and a thickness of 7 μm was used instead of the electrolytic copper foil having a thickness of 9 μm. In addition, the thickness of the 1 st wiring layer 114 after the roughening treatment (CZ treatment) in the laminate 117 for evaluation of laser processability was 5 μm, T₂/T₁2/5, i.e., 0.40.

Results

The evaluation results obtained in examples 1 to 10 are shown in table 1.

TABLE 1

TABLE 1

The following shows comparative examples.

Example 11

1) Using a copper foil having a thickness of 3 μm instead of a copper foil having a thickness of 2 μm as the metal foils 110 and 110', respectively, 2) adjusting the etching amount so that the thickness of the 1 st wiring layer 114 after the roughening treatment (CZ treatment) becomes 5 μm (that is, T is set to be T)₂/T₁3/5 (0.60)) and 3) adjusting the output density of the carbon dioxide laser from 9.5MW/cm²Changed to 9.75MW/cm²Except for this, evaluation of laser processability was performed in the same manner as in example 5.

Example 12

1) As the metal foils 110 and 110', a copper foil having a thickness of 3 μm was used instead of a copper foil having a thickness of 2 μm, respectively, 2) the output density of the carbon dioxide laser was adjusted from 9.5MW/cm²Changed to 9.75MW/cm²Except for this, evaluation of laser processability was performed in the same manner as in example 10. In addition, the thickness of the 1 st wiring layer 114 after the roughening treatment (CZ treatment) in the laminate 117 for evaluation of laser processability was 5 μm, T₂/T₁3/5, i.e., 0.60.

Example 13

1) As metalsFoils 110, 110' using copper foils of 3 μm thickness instead of 2 μm thickness, respectively, 2) adjusting the output density of carbon dioxide laser from 9.5MW/cm²Changed to 9.75MW/cm²Except for this, evaluation of laser processability was performed in the same manner as in example 8. In addition, the thickness of the 1 st wiring layer 114 after the roughening treatment (CZ treatment) in the laminate 117 for evaluation of laser processability was 5 μm, T₂/T₁3/5, i.e., 0.60.

Example 14

1) As the metal foils 110, 110', a copper foil having a thickness of 5 μm was used instead of a copper foil having a thickness of 3 μm, 2) the output density of the carbon dioxide laser was adjusted from 9.75MW/cm²Changed to 10.25MW/cm²Except for this, evaluation of laser processability was performed in the same manner as in example 11. In addition, the thickness of the 1 st wiring layer 114 after the roughening treatment (CZ treatment) in the laminate 117 for evaluation of laser processability was 5 μm, T₂/T₁5/5, i.e., 1.0.

Example 15

1) As the metal foils 110, 110', a copper foil having a thickness of 5 μm was used instead of a copper foil having a thickness of 3 μm, 2) the output density of the carbon dioxide laser was adjusted from 9.75MW/cm²Changed to 10.25MW/cm²Except for this, evaluation of laser processability was performed in the same manner as in example 12. In addition, the thickness of the 1 st wiring layer 114 after the roughening treatment (CZ treatment) in the laminate 117 for evaluation of laser processability was 5 μm, T₂/T₁5/5, i.e., 1.0.

Example 16

1) As the metal foils 110, 110', a copper foil having a thickness of 5 μm was used instead of a copper foil having a thickness of 3 μm, 2) the output density of the carbon dioxide laser was adjusted from 9.75MW/cm²Changed to 10.25MW/cm²Except for this, evaluation of laser processability was performed in the same manner as in example 13. In addition, the thickness of the 1 st wiring layer 114 after the roughening treatment (CZ treatment) in the laminate 117 for evaluation of laser processability was 5 μm, T₂/T₁5/5, i.e., 1.0.

Results

The evaluation results obtained in examples 11 to 16 are shown in table 2.

TABLE 2

TABLE 2

The following shows comparative examples.