JPH10284843A - Multilayered circuit board and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a multilayer circuit board having extremely highly reliable via holes with high productivity by connecting conductor circuit layers to each other after the bottom sections of small holes for forming the via holes are etched and the carbon concentrations on the bottoms of the holes are made lower than a specific value. SOLUTION: After a conductor circuit layer 2 is provided on a substrate 1, another conductor circuit layer 4 is formed on the layer 2 through an insulating layer 3. Then holes are formed into the outermost conductor circuit layer 4 by partially etching off the layer 4 at prescribed positions and the insulating layer 3 exposed in the holes is removed with a laser beam. Therefore, small holes for electrical connection can be formed with high dimensional accuracy without giving any damage to the peripheral sections of the holes. After the holes are bored, the depths of the holes are increased to >=3 μm by etching the holes with an aqueous solution of ferric chloride, cupric chloride, etc., so that the carbon concentrations on the bottoms of the holes may become <=6×10<-8> g/mm<2> . Then the conductor circuit layers 4 and 2 are electrically connected to each other by forming via holes 5 by plating the holes with solder or copper.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer circuit board having excellent via hole reliability and excellent productivity, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, for the purpose of achieving high-density mounting of semiconductor elements, a multilayer circuit board in which a plurality of wiring circuits are stacked via an insulating layer has attracted attention. In particular, a multilayer circuit board obtained by a method (build-up method) in which a wiring circuit is formed on at least one principal surface of a substrate with an insulating layer interposed therebetween and a wiring circuit is further formed with the insulating layer interposed therebetween is repeatedly used. It is attracting attention because it is easy to cope with density mounting and is advantageous in terms of cost.

In general, a multilayer circuit board employs a structure such as a wire bonding, a via hole, a through hole or the like in order to electrically connect wiring circuits arranged spatially in multiple layers. In recent years, via holes have been increasingly used from the viewpoints of increasing the density of substrates and improving productivity, etc., but achieve stable and highly productive via holes with high electrical reliability. It is not easy.

In particular, with respect to a multilayer circuit board obtained by the above build-up method, in order to obtain a highly reliable interlayer connection, a small hole for a via hole connected to a conductor circuit layer is provided, and after a desmear process, copper is removed. Although it is necessary to rely on a method of electrical connection by plating, this method tends to make the copper plating on the bottom edge of the via hole thinner, which lowers the reliability of interlayer connection and at the same time reduces productivity by desmearing. Had to be forced.

[0005] The present invention has been made in view of the above circumstances, and by etching the bottom of a small hole for a via hole to lower the carbon concentration, and then connecting between the conductor circuit layers, extremely reliable. Based on the finding that it is possible to form a multilayer circuit board having via holes excellent in productivity with high productivity.

That is, an object of the present invention is to provide a multilayer circuit board having via holes with extremely high reliability with high productivity.

[0007]

According to the present invention, a plurality of conductive circuit layers are mounted on at least one principal surface of a substrate via an insulating layer, and the outermost conductive circuit layer is shifted to a non-outermost conductive circuit layer. A multi-layer circuit board provided with small holes for electrical connection to the substrate, wherein the carbon concentration at the bottom surface of the small holes is 6 × 10
^-8 g / mm ² or less, and preferably, the bottom surface of the small hole is at least 3 μm lower than the surface of the non-outermost conductive circuit layer forming the bottom surface. The multilayer circuit board is recessed.

Further, the present invention provides a method for mounting a plurality of conductive circuit layers on at least one principal surface of a substrate via an insulating layer, wherein the outermost conductive circuit layer and the non-outermost conductive circuit layer among the conductive circuit layers are provided. What is claimed is: 1. A method for manufacturing a multi-layer circuit board, wherein a small hole for electrically connecting a circuit layer is provided, wherein after forming the small hole, the bottom surface of the small hole is etched and then electrically connected. Preferably, the method is a method of manufacturing a multilayer circuit board, characterized in that the bottom surface of the small hole is etched to control the carbon concentration at the bottom surface of the small hole.

Further, the present invention relates to a method for manufacturing a multilayer circuit board, wherein the small holes are formed by laser irradiation, and the bottom surface of the small holes is etched by 3 μm or more. It is.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 shows a cross-sectional view of an example of the multilayer circuit board of the present invention. Conductive circuit layer 2 on substrate 1
Further, an insulating layer 3 is mounted on the conductive circuit layer 2, a conductive circuit layer 4 is further mounted on the insulating layer 3, and the outermost conductive circuit layer 4 is It is electrically connected by the hole 5. Although not shown, an electronic element may be mounted on the outermost conductive circuit layer 4 as necessary, or may be connected to other components by wire bonding or the like.

The multi-layer circuit board of the present invention may be a multi-layer circuit board having via holes for electrically connecting from the outermost conductive circuit layer to a non-outermost conductive circuit layer. Of course, a conductive circuit layer may be further laminated on the layer 4 with an insulating layer interposed therebetween. Further, the conductor circuit layer may be laminated on at least a part of at least one main surface of the substrate 1, and at least one other circuit board may be laminated on the outermost conductor circuit layer. .

In the multilayer circuit board of the present invention, the surface of the conductor circuit layer forming the bottom of the small hole used in the via hole 5 has a carbon concentration of 6 × 10 ⁻⁸ g / mm ² or less, preferably It is not more than 4 × 10 ⁻⁸ g / mm ² . Although the reason for this is not clear, according to experimental studies by the present inventors, when the carbon concentration is higher than 6 × 10 ⁻⁸ g / mm ² , the small holes are plated with solder or copper. When forming a via hole, solder wettability and copper plating property at the bottom surface of the small hole are poor, and it is not preferable because a via hole having high electrical reliability cannot be formed. Especially when the carbon concentration is 4 × 1
When it is 0 ^-8 g / mm ² or less, via holes having high electrical reliability can be stably obtained, which is preferable.

Further, in the present invention, the bottom surface of the small hole is more than the surface of the conductor circuit layer which is not the outermost layer and forms the bottom surface.
It is preferable that it is recessed toward the substrate side by at least 5 μm, particularly at least 5 μm. For this reason, when conducting electrical connection by soldering or copper plating in the small hole, the boundary between the conductor circuit layer constituting the bottom of the small hole and the insulating layer immediately above it is on the same plane as the bottom. It is presumed that by avoiding this, the contact area between the solder or copper plating and the conductor circuit increases and unnecessary stress concentration on the corners of the solder or copper plating can be avoided. Although there is no particular reason for the upper limit, the thickness of the conductor circuit layer is generally 9 to 30.
0 μm, which is limited by this.

In the present invention, the method of measuring the carbon concentration at the bottom of a small hole is as follows: a copper foil having the same history as the bottom surface of the small hole is scanned by a SEM-EDX method on a surface thereof, and a chemical analysis method is performed in advance. The method is based on a method of measuring the carbon concentration by comparing with a calibration curve prepared using a test piece having a known carbon concentration.

The small hole for electric connection of the present invention can be formed by using a general method for processing a via hole or a through hole. These methods include, for example, an excimer laser, a CO ₂ laser, and a YAG laser. A method of using various laser beams such as a laser, a method of dissolving the small holes for electrical connection after patterning by exposing the insulating layer with a photosensitive resin, or a method of chemically dissolving the insulating layer by chemical drilling, There is a method of mechanically removing the insulating layer by sandblasting. However, according to the study of the present inventors, a predetermined position of the outermost conductive circuit layer 4 is removed by etching, a hole is formed up to the insulating layer 3 immediately below, and the bottom of the hole is irradiated with a laser beam to form the insulating layer 3. The method of forming a small hole for electrical connection by removing is preferred because the dimensional accuracy is high, the peripheral portion is not damaged, and the productivity is good.

The carbon concentration on the bottom surface of the electrical connection hole is not more than 6 × 10 ⁻⁸ g / mm ² , preferably 4 × 10 ⁻⁸ g / mm ^2.
g / mm ² or less, such as a method of desmearing the surface of the conductive circuit layer on the bottom surface of the small hole with potassium permanganate, concentrated sulfuric acid, or the like after the opening, ferric chloride, cupric chloride, or the like. An etching method using an aqueous solution of persulfates, sulfuric acid + hydrogen peroxide, alkali etchant, or the like can be employed. Among them, the most preferable method is the method of etching from the viewpoint of productivity and from the viewpoint that the bottom of the small hole can be recessed as described above.
The etching depth is 3 μm or more, preferably 5 μm.
The above is preferred. If it is less than 3 μm, the carbon concentration on the bottom surface of the hole may not be 6 × 10 ⁻⁸ g / mm ² or less, and the solder wettability may be poor. According to the study of the present inventors, when the etching depth is set to 5 μm or more, the carbon concentration is 4 × 10 ⁻⁸ g / mm ^2.
The following can be achieved, and a multilayer circuit board having a highly reliable via hole can be obtained.

As the resin constituting the insulating layer, various engineering plastics such as epoxy resin, phenol resin and polyimide resin can be used alone or in combination of two or more. It is preferable because of its excellent bonding strength. Particularly, among the epoxy resins, bisphenol A type epoxy resin and bisphenol F type epoxy resin, which have high fluidity and are excellent in mixing with various ceramic powders, are more preferable resins. These resins may be filled with glass fiber or ceramic powder.

The material of the conductor circuits 2 and 4 is copper, aluminum, nickel, iron, tin, silver, titanium, an alloy containing two or more of these metals, and a clad foil using each metal. Can be used.
At this time, the foil may be manufactured by an electrolytic method or a rolling method, and the foil may be plated with a metal such as Ni plating, Ni + Au plating, or solder plating. from the viewpoint of adhesion to the 3, the surface of the conductor circuit 2 and 4 a further preferred if it is previously roughened by etching or plating.

In the present invention, the material and thickness of the substrate 1 are not particularly limited, and general resin substrates and metal substrates can be widely used.

Hereinafter, the present invention will be described in more detail with reference to Examples.

[0021]

Example 1 After forming a predetermined circuit on both sides of a double-sided glass epoxy substrate (R1766, manufactured by Matsushita Electric Works, Ltd .; 250 mm × 500 mm × 1.6 mm, each having a copper foil thickness of 35 μm), Prepreg (Matsushita Electric Works, Ltd .; R16
61), a copper foil having a thickness of 35 μm was press-laminated on both sides to form a predetermined circuit on the outer copper foil, thereby producing a four-layer board. I drilled a small hole reaching the insulating layer immediately below a drill in a desired position of the outermost layer of the conductor circuit layer of the circuit board, by applying a CO ₂ laser at the bottom of the small hole, the inner layer from the outermost conductor circuit layer A small hole reaching the conductor circuit layer was provided.
The surface of the conductor circuit layer corresponding to the bottom surface of the small hole has a depth of 5 μm.
After etching to a depth of m, solder was filled into the voids of the small holes, and the inner layer circuit and the outer layer circuit were electrically connected to produce a multilayer circuit board. The reliability of the via holes and the productivity of the multilayer circuit board were examined by the following methods. The results are shown in Table 1.

<Evaluation Method of Solder Wettability> When a pre-flux was applied to a multilayer circuit board and immersed in a solder bath at 260 ° C., the solder coating area ratio of the copper foil surface having a size corresponding to the bottom surface of the small hole was measured. Was evaluated.

<Method of Evaluating Reliability of Via Hole> J
In accordance with the thermal shock (high temperature immersion) test method specified in IS C 5012, the evaluation was made based on the rate of change of the conductor resistance to the initial value after 100 cycles of thermal shock was applied to the substrate.

<Productivity Evaluation Method> Business card size (90 m
The evaluation was based on the time required to manufacture 10,000 substrates (m × 50 mm).

[0025]

[Table 1]

Example 2 250 mm × 500 mm ×
After a predetermined circuit is formed on both sides of a double-sided glass epoxy substrate (R1766, manufactured by Matsushita Electric Works, Ltd .; R1766, manufactured by Matsushita Electric Works, Ltd.) having a thickness of 35 μm and a thickness of 1.6 mm, a prepreg (R1661, manufactured by Matsushita Electric Works, Ltd.) is interposed. Then, a copper foil having a thickness of 35 μm was press-laminated on both sides to form a four-layer board. Next, a portion to be a via hole of the outermost copper foil was removed by etching to form a small hole, and then a small hole reaching the inner conductive circuit layer from the bottom of the small hole was formed using a CO ₂ laser using a CO ₂ laser. The copper foil surface forming the bottom surface of the small hole has a depth of 5 μm.
After etching to a depth of 20 m, the inner layer circuit and the outermost layer circuit were electrically connected by copper plating with a thickness of 20 μm. A predetermined circuit was formed on the outermost copper foil of this, and a multilayer circuit board was formed. Table 1 shows the reliability and productivity of the via holes of this multilayer circuit board.

Example 3 250 mm × 500 mm ×
A predetermined circuit is formed on both surfaces of a double-sided glass epoxy substrate (R1766, manufactured by Matsushita Electric Works, Ltd .; R1766, manufactured by Matsushita Electric Works, Ltd.) having a thickness of 1.6 mm and a copper foil thickness of 35 μm. Then, a copper foil having a thickness of 35 μm was press-laminated on both sides to form a four-layer board. After forming a predetermined circuit on the outer layer copper foil, a small hole is formed at a desired position of the circuit by etching, and a small hole reaching the inner conductor circuit layer from the bottom of the small hole using a CO ₂ laser. And After etching the surface of the copper foil forming the bottom surface of the small hole to a depth of 3 μm, the gap portion of the small hole is filled with solder, and the inner layer circuit and the outer layer circuit are electrically connected to form a multilayer circuit board. did. Table 1 shows the reliability and productivity of the via holes of this multilayer circuit board.

Example 4 250 mm × 500 mm ×
A predetermined circuit is formed on both surfaces of a double-sided glass epoxy substrate (R1766, manufactured by Matsushita Electric Works, Ltd .; R1766, manufactured by Matsushita Electric Works, Ltd.) having a thickness of 1.6 mm and a copper foil thickness of 35 μm. Then, a copper foil having a thickness of 35 μm was press-laminated on both sides to form a four-layer board. Next, after a predetermined circuit is formed on the outermost copper foil, a desired position of the outermost copper foil is etched to form a small hole, and the bottom of the small hole is irradiated with a CO ₂ laser to form a conductor circuit in the inner layer. The pores reached the layer. After cleaning the surface of the copper foil forming the bottom surface of the small hole with a potassium permanganate solution at 80 ° C. for 10 minutes, the void portion of the small hole is filled with solder to electrically connect the inner layer circuit and the outermost layer circuit. By connecting, a multilayer circuit board was produced. Table 1 shows the reliability and productivity of via holes in this multilayer circuit board.
It was shown to.

Comparative Example 250 mm × 500 mm × 1.
After forming a predetermined circuit on both sides of a double-sided glass epoxy substrate (R1766, manufactured by Matsushita Electric Works, Ltd .; 6 mm in thickness, 35 μm in copper foil), a prepreg (Matsushita Electric Works, Ltd.)
(R1661), a copper foil having a thickness of 35 μm was press-laminated on both sides to form a four-layer board. Next, after a predetermined circuit is formed on the outermost copper foil, a small hole reaching the insulating layer is drilled at a desired position of the circuit with a drill, and the bottom of the small hole is irradiated with a CO ₂ laser to form an inner layer. The holes were small holes reaching the conductor circuit layer. Attempts were made to electrically connect the inner layer circuit and the outermost layer circuit by filling the voids of the small holes with solder, but the connection was not possible due to insufficient solder wettability.

[0030]

The multilayer circuit board of the present invention has a highly reliable via hole, so that it can be used in various applications without worry. According to the manufacturing method of the present invention,
Since the multilayer circuit board can be provided with high productivity, it is industrially very useful.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a multilayer circuit board of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 board 2 conductive circuit layer 3 insulating layer 4 (outermost) conductive circuit layer 5 via hole

Claims (6)

[Claims] 1. A method for mounting a plurality of conductive circuit layers on at least one principal surface of a substrate via an insulating layer and electrically connecting the outermost conductive circuit layers to the non-outermost conductive circuit layers. A multilayer circuit board provided with small holes, wherein the carbon concentration at the bottom surface of the small holes is 6 × 10 ⁻⁸ g / mm ² or less. 2. The multilayer circuit board according to claim 1, wherein the bottom surface of the small hole is recessed toward the substrate by at least 3 μm lower than the surface of the conductor circuit layer which is not the outermost layer forming the bottom surface. 3. A plurality of conductive circuit layers are mounted on at least one principal surface of a substrate via an insulating layer, and an outermost conductive circuit layer and a non-outermost conductive circuit layer among the conductive circuit layers are separated from each other. What is claimed is: 1. A method for manufacturing a multilayer circuit board comprising a small hole for electrical connection, comprising: after forming the small hole, etching the bottom surface of the small hole; and then electrically connecting. A method for manufacturing a multilayer circuit board. 4. The method according to claim 3, wherein the carbon concentration at the bottom surface of the small hole is controlled by etching the bottom surface of the small hole.
A method for manufacturing the multilayer circuit board according to the above. 5. The method for manufacturing a multilayer circuit board according to claim 3, wherein the small holes are formed by laser irradiation. 6. The method according to claim 3, wherein the bottom surface of the small hole is etched by 3 μm or more.