Method of manufacturing multilayered circuit board Number:7,415,761 from the United States Patent and Trademark Office (PTO) owispatent An opening is formed in resin 20 by a laser beam so that a via hole is formed. At this time, copper foil 22, the thickness of which is reduced (to 3 .mu.m) by performing etching to lower the thermal conductivity is used as a conformal mask. Therefore, an opening 20a can be formed in the resin 20 if the number of irradiation of pulse-shape laser beam is reduced. Therefore, occurrence of undercut of the resin 20 which forms an interlayer insulating resin layer can be prevented. Thus, the reliability of the connection of the via holes can be improved.<H manufacturing, multilayered, Method, of, manuf, 7415761.html, Patent, pto, 7415761

Title: Method of manufacturing multilayered circuit board

Abstract: An opening is formed in resin 20 by a laser beam so that a via hole is formed. At this time, copper foil 22, the thickness of which is reduced (to 3 .mu.m) by performing etching to lower the thermal conductivity is used as a conformal mask. Therefore, an opening 20a can be formed in the resin 20 if the number of irradiation of pulse-shape laser beam is reduced. Therefore, occurrence of undercut of the resin 20 which forms an interlayer insulating resin layer can be prevented. Thus, the reliability of the connection of the via holes can be improved.

Patent Number: 7,415,761 Issued on 08/26/2008 to Hirose, et al.

Inventors: Hirose; Naohiro (Ibi-gun, JP), Noda; Kouta (Ibi-gun, JP), Segawa; Hiroshi (Ibi-gun, JP), En; Honjin (Ibi-gun, JP), Tsukada; Kiyotaka (Ogakishi, JP), Ishida; Naoto (Ogakishi, JP), Asano; Kouji (Ogakishi, JP), Shouda; Atsushi (Ogakishi, JP)
Assignee: IBIDEN Co., Ltd. (Ogaki-shi, JP)

Appl. No.: 10/356,464

Filed: February 3, 2003

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
09797916	Mar., 2001	6591495
PCT/JP99/04142	Jul., 1999

Foreign Application Priority Data


Sep 03, 1998 [JP]			10-249382
Sep 16, 1998 [JP]			10-281940
Sep 16, 1998 [JP]			10-281942
Oct 09, 1998 [JP]			10-303247
Feb 22, 1999 [JP]			11-043514
Feb 22, 1999 [JP]			11-043515
Mar 08, 1999 [JP]			11-060240
Apr 23, 1999 [JP]			11-116246

Current U.S. Class: 29/852 ; 216/35; 29/830; 29/832; 29/846; 427/97.2; 430/314; 430/318

Current International Class: H01K 3/10 (20060101)

Field of Search: 29/852,830,832,846 430/314,318 427/97.2 216/35

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Primary Examiner: Tugbang; A. Dexter
Assistant Examiner: Phan; Thiem
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt, P.C.

Parent Case Text

This is a Divisional of U.S. application Ser. No. 09/797,916 Mar. 5, 2001, now U.S. Pat, No. 6,591,495 B2, which is a continuation of International Application No. PCT/J99/04142 filed Jul. 30, 1999 which designated the U.S.

Claims

What is claimed is:

1. A method of manufacturing a multilayered printed circuit board comprising a substrate on which a lower conductive circuit is formed, an insulating resin layer and an upper conductive circuit formed on the lower conductive circuit and having a structure that the lower conductive circuit and the upper conductive circuit are connected to each other through a via hole, the method of manufacturing a multilayered printed circuit board comprising: forming the lower conductive circuit on the substrate; forming the insulating resin layer on the lower conductive circuit; coarsening an entire surface of the insulating resin layer; forming a metal layer on the coarsened surface; etching the metal layer so as to form a first opening in the metal layer through which a portion of the coarsened surface of the insulating resin layer is exposed; irradiating the coarsened surface exposed through the first opening with a laser beam to remove the insulating resin layer to form a second opening for the via hole through which a portion of the lower conductive circuit is exposed; and forming the upper conductive circuit electrically connected to the lower conductive circuit through the via hole, wherein the coarsened entire surface has a maximum roughness of 0.01 .mu.m to 5 .mu.m.

2. The method of manufacturing a multilayered printed circuit board according to claim 1, wherein the insulating resin layer contains particles which are dissolved by acid or an oxidizer, and the particles are dissolved by the acid or the oxidizer so that the coarsened surface is formed on the surface of the insulating resin layer.

3. The method of manufacturing a multilayered printed circuit board according to claim 1, wherein the laser beam is a carbon dioxide gas laser beam.

4. The method of manufacturing a multilayered printed circuit board according to claim 1, wherein said coarsened surface is connected to said metal layer.

5. The method of manufacturing a multilayered printed circuit board according to claim 1, wherein said coarsened surface is formed so as to prevent reflection of the laser beam.

6. The method of manufacturing a multilayered printed circuit board according to claim 1, further comprising: reducing a thickness of the metal layer by etching.

7. The method of manufacturing a multilayered printed circuit board according to claim 1, wherein the coarsened surface of the insulating resin layer is formed on a top surface of the insulating resin layer.

8. The method of manufacturing a multilayered printed circuit board according to claim 1, wherein said metal layer is plated on the coarsened surface of the insulating resin layer.

9. The method of manufacturing a multilayered printed circuit board according to claim 1, wherein the surface of the insulating resin layer is coarsened by laminating a metal foil on the insulating resin layer, the metal foil having a coarsened surface, on which the insulating resin layer is laminated so that a form of the coarsened surface of the metal foil is transferred to the surface of the insulating resin layer.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multilayered printed circuit board and a manufacturing method therefor, and more particularly to a method of manufacturing a multilayered printed circuit board with which an opening is formed by using laser beam and by forming a plated film in the opening to form a via hole, an opening in a solder-resist layer and an opening for forming a through hole. The present invention relates to the structure of a substrate which is a core.

2. Background Art

A method of manufacturing a multilayered printed circuit board has been suggested in Japanese Patent Laid-Open No. 9-130038 which uses a so-called conformal mask such that a conductive layer is formed on the surface of an insulating resin layer. Moreover, an opening is formed in a portion of the conductive layer by etching, followed by irradiating the opening with a laser beam to form an opening in the insulating resin layer.

The foregoing technique, which uses a thick copper film having a thickness of 12 mm to 18 mm as the conformal mask, encounters a large thermal conductivity, causing heat to easily be dispersed. Hence it follows that a high output laser beam or a pulse-shape laser beam must be applied a multiple of times. Therefore, when the opening is formed in the insulating resin layer, undercut occurs with which the opening is widened in the lateral. If a via hole is formed by applying an electrolytic copper plated film and an electroless copper plated film to the opening, separation of the electrolytic copper plated film and the electroless copper plated film easily occurs. As a result, reliability in the connection has been unsatisfactory.

To a worse extent, the foregoing technique cannot form a conductive circuit having fine pitch. In the manufacturing process, the electroless copper plated film (0.1 .mu.m to 5 .mu.m) and the copper foil (12 .mu.m to 18 .mu.m) under the resist must be removed after the electrolytic copper plated film has been performed. Therefore, the width of the conductive circuit cannot be reduced.

Since the thick copper foil is employed as the conformal mask, a via hole having a small diameter cannot be formed. In the manufacturing process, the electroless copper plated film (2 .mu.m) and the copper foil (12 .mu.m to 18 .mu.m) under the resist must be removed, the diameter of the via hole cannot easily be reduced.

To solve the foregoing problems, an object of the present invention is to suggest a multilayered printed circuit board which is capable of preventing occurrence of undercut if a conformal mask is employed.

A method disclosed in Japanese Patent Publication No. 4-3676 and using a "conformal mask" has the steps of previously forming a metal layer on an insulating resin layer; etching and removing the metal layer in the portion in which a via hole will be formed; and irradiating the opening with a laser beam so that only the insulating resin layer exposed through the opening is removed. The foregoing technique, which is capable of forming a plurality of via holes in the insulating resin layer, exhibits satisfactory productivity.

However, studies performed by the inventor of the present invention have resulted in resin which is left in the opening for forming the via hole, causing the residual resin to expand and unsatisfactorily move the via hole in the upward direction. Thus, there arises a problem in that the upper and lower layers are electrically insulated from each other.

Another problem has been detected as a result of the studies performed by the inventor of the present invention in that the resin in the periphery of the opening is raised excessively and, thus, the via hole is disconnected.

A still further object of the present invention is to obtain a multilayered printed circuit board having furthermore improved reliability in the connection in the via hole portion.

On the other hand, a multilayer forming technique which employs so-called RCC (RESIN COATED COPPER: Copper film having resin) as the built-up multilayered printed circuit board has been suggested. The foregoing technique has the steps of laminating RCC on a circuit substrate; etching the copper foil to form a through hole in a portion in which the via hole will be formed; irradiating the resin layer in the through hole portion with a laser beam to remove the resin layer opening as to form an opening; and filling the opening with plating so that the via hole is formed.

Another technique has been developed as disclosed in Japanese Patent Laid-Open No. 9-36551 with which one-side circuit substrates each having a through hole filled with a conductive substance are laminated through adhesive layers so that a multilayered structure is formed.

The foregoing multilayered printed circuit board is subjected to a process for coarsening the surface of the lower conductive circuit to maintain the adhesiveness between the surface of the lower conductive circuit and the interlayer insulating resin layer.

The coarsening method is exemplified by a method (hereinafter called a "Cu--Ni--P plating method") of covering and coarsening the surface of the conductive circuit with a needle shape or porous plating layer made of a Cu--Ni--P alloy; a coarsening method (hereinafter called a "blackening and reducing method") with which the surface of the conductive circuit is blackened (oxidized) and reduced; a coarsening method (hereinafter called a "soft etching method") which uses mixed solution of peroxide and sulfuric acid to soft-etch the surface of the conductive circuit; and a coarsening method (hereinafter called a "scratching method") with which the surface of the conductive circuit is scratched with a sandpaper or the like.

However, if the conductive circuit is coarsened by the Cu--Ni--P plating method of the blackening and reducing method, followed by forming an interlayer insulating resin layer, and followed by applying a laser beam to form an opening for forming the via hole in the interlayer insulating resin layer, the coarsened surface of the conductive circuit is undesirably removed and flattened owing to the irradiation with the laser beam. Thus, there arises a problem in that the adhesiveness with the via hole formed above the coarsened surface becomes defective.

The reason for this lies in that the coarsened surface formed by the above-mentioned process is colored and, thus, the colored surface undesirably absorbs the laser beam.

When the coarsened surface has been provided for the conductive circuit by the soft etching method or the scratching method, the coarsened surface does not absorb the laser beam. Since the coarsened surface has not sufficiently been coarsened, there arises a problem in that satisfactory adhesiveness cannot be realized between the conductive circuit and the interlayer insulating resin layer.

To solve the above-mentioned problems experienced with the conventional technique, a still further object of the present invention is to provide a multilayered printed circuit board and a manufacturing method each of which is able to realize satisfactory adhesiveness with the interlayer insulating resin layer which is formed on the conductive circuit, with which flattening of the coarsened surface of the surface of the conductive circuit can be prevented when a laser beam is applied to form the via hole in the interlayer insulating resin layer and which has a via hole (conductive circuit) having satisfactory adhesiveness.

With the conventional technique, the via hole is formed by drilling a through hole in the interlayer insulating resin layer and by disposing a metal film in the through hole. Hitherto, the through hole has been formed by employing photosensitive resin to constitute the interlayer insulating resin layer and by exposing a position corresponding to the through hole through a mask on which a black circle has been drawn to sensitize the interlayer insulating resin layer so as to dissolve the non-sensitized portion corresponding to the position of the black circle.

The foregoing photolithography method, however, encounters a limitation of the smallest diameter of the through hole, the limitation being a diameter of about 80 .mu.m. Therefore, the foregoing method cannot meet a requirement for raising the density of the multilayered printed circuit board. Therefore, the inventor of the present invention has come up with an idea that the through hole is formed by using a laser beam and performed experiments. As a result, a through hole having a diameter not larger than 80 .mu.m can be formed.

However, a fact has been detected that the reliability of the via hole is unsatisfactory when the via hole has been formed by using the through hole having a diameter not larger than 80 .mu.m. The cause of the foregoing fact has been studied, thus resulting in a problem of insufficient adhesiveness between the through hole and the electroless copper plated film. That is, the via hole is formed by depositing the electroless copper plated film. Satisfactory adhesiveness cannot be realized between the through hole formed by using a laser beam and having a small diameter and the electroless copper plated film. As a result, separation of the electroless copper plated film from the through hole causes disconnection to occur.

On the other hand, the conventional photolithography technique has been performed such that the through hole is formed by performing exposure and development. Therefore, only photosensitive materials are permitted to be used. Hence it follows that the performance required for the multilayered printed circuit board cannot sometimes be satisfied.

The conventional multilayered printed circuit board suffers from unsatisfactory reliability of solder bumps. The cause has been studied, thus resulting in the insufficient adhesiveness between the through hole and the metal film. That is, the solder bump is formed by enclosing solder in a portion on a nickel plated film deposited on the surface of the conductive circuit below the opening. The adhesiveness between the conductive circuit and the nickel plated film has been unsatisfactory, causing the nickel plated film to be separated. It leads to a fact that disconnection of the solder bump occurs.

To solve the above-mentioned problems, a still further object of the present invention is to provide a multilayered printed circuit board and a manufacturing method therefor each of which is capable of forming a via hole exhibiting satisfactory reliability and having a small diameter.

To solve the above-mentioned problems, a still further object of the present invention is to provide a multilayered printed circuit board and a manufacturing method therefor each of which permits selection of high-performance material for the solder resist.

A still further object of the present invention is to provide a multilayered printed circuit board and a manufacturing method therefor each of which is capable of forming a reliable solder bump.

On the other hand, the through hole provided for a core substrate must precisely be formed. Thus, a through hole having a diameter smaller than 100 .mu.m cannot easily be formed by drilling. Therefore, the through hole is formed in a copper-plated laminated board by using a laser beam.

An optimum laser beam is a carbon dioxide laser because of a low cost from the viewpoint of industrial production. However, the carbon dioxide laser is undesirably reflected by the surface of the copper foil. Therefore, it is a technical common sense that the through hole cannot be formed directly in the copper-plated laminated board by the laser machining. Thus, a technique has been disclosed in Japanese Patent Laid-Open No. S61-99596 with which the surface of the copper foil of the copper-plated laminated board is subjected to a blackening process (an oxidizing process), followed by applying a laser beam.

The foregoing technique, however, requires the blackening process to be performed first, causing a problem to arise in that a long manufacturing process is required.

As a result of energetic studies performed by the inventors of the present invention, an unexpected fact has been found that reduction in the thickness of the copper foil enables an opening to be formed in the copper foil in spite of the reflection by the surface.

To solve the above-mentioned problems, a still further object of the present invention is to realize a technique which is capable of directly forming an opening in a copper-plated laminated board and provide a substrate having the through hole formed by the foregoing method and a multilayered printed circuit board.

Since a high density and multilayered structure has been required in recent years, a built-up multilayered printed circuit board has attracted attention. The multilayered circuit board is a multilayered circuit board having a core substrate on which conductive circuits and interlayer insulating resin layers are alternately formed. The conductive circuits in the layers are connected to one another through a via hole.

As the core substrate of the foregoing built-up multilayered printed circuit board, a glass epoxy resin substrate of FR-4 grade has been employed.

However, the glass epoxy resin substrate of the FR-4 grade encounters a problem in that the insulation resistance between the through holes is reduced in a HAST test and a steam test. Another problem arises in that the resistance of the through hole chain was excessively changed as a result of the heat cycle test. That is, the reliability realized after use for a long time has been unsatisfactory.

To solve the above-mentioned problem, a core substrate which employs BT (Bis maleimide-Triazine) resin has been suggested. The foregoing substrate is, however, a costly substrate.

Inventors of the present invention have considered probability of preventing reduction in the insulation resistance between the through holes and change in the resistance of the conductive circuit for connecting the through holes to each other by using low-cost resin such as epoxy resin in place of the costly resin, such as the BT resin. As a result, an unexpected fact was found that the foregoing problem is caused from the Tg point of the resin.

According to the present invention, a low-cost multilayered printed circuit board is suggested which is free from reduction in the insulation resistance between through holes as a result of the HAST test and the steam test and change in the resistance of the conductive circuit for connecting the through holes to each other as a result of a heat cycle test.

The method of manufacturing the printed circuit board is broadly divided into a subtractive method (a Subtractive Process) and an additive method (an Additive Process). The subtractive method is also called an etching method which is characterized by chemically corroding the surface copper foil of a copper-plated laminated board. A method of manufacturing a printed circuit board (a double-side board) by the subtractive process will now briefly be described.

Initially, a copper-plated laminated board is prepared which incorporates an insulating substrate having two sides each of which is coated with copper foil having tens of .mu.m. Then, an opening for forming a through hole is formed at a predetermined position of the copper-plated laminated board by drilling or the like. If a drilling step is performed, smears occurs in the opening for forming the through hole, desmear solution is used to process the copper-plated laminated board to dissolve and remove the smears. After the desmear process has been completed, electroless copper plating of the overall ground layer constituted by copper foil and the inner surface of an opening for forming the through hole is performed so that a thin plated layer is formed. After the foregoing plating process has been completed, a mask is formed on the thin plated layer. Then, thick plated layers are formed in the portions exposed through openings of the mask by electrolytic copper plating. After the foregoing plating process has been completed, the mask is separated. Then, etching is performed in a state in which an etching resist has been formed on the thick plated layer by solder plating or the like. The etching process is so performed as to remove the thin plated layer and the ground layer so as to divide the conductive pattern. Finally, the etching resist is separated so that a required printed-circuit board is manufactured.

The foregoing method, however, is impossible to accurately form a fine pattern having a satisfactory shape. The characteristics of the etching causes a so-called divergent conductive pattern having a bottom which is longer than the top to easily be formed. Therefore, a pattern cannot easily be formed in a portion (for example, a bonding pad portion) which must have a fine and precise structure.

In view of the foregoing, a still further object of the present invention is to provide a method of manufacturing a printed circuit board with which a fine conductive pattern having a satisfactory shape can be formed.

SUMMARY OF THE INVENTION

A method of manufacturing a multilayered printed circuit board according to an aspect of the present invention comprising the steps (1) to (5):

(1) pressing resin to form an interlayer insulating resin layer having a metal film formed thereon against a substrate for forming a conductor circuit;

(2) reducing the thickness of a whole surface of the metal film by etching;

(3) forming an opening in the metal film so as to expose the interlayer insulating resin layer;

(4) applying a laser beam from opening of the metal film side to remove the resin forming the interlayer insulating resin layer exposed through the opening so as to provide an opening for a via hole; and

(5) depositing a plating conductor in the opening to form the via hole.

This aspect of the present invention employs a metal film thinned by etching and thus having a lowered thermal conductivity as a conformal mask. Therefore, an opening can be formed by a small output laser. Hence it follows that generation of undercut of resin for forming an interlayer insulating resin layer can be prevented.

A method of manufacturing a multilayered printed circuit board according to another aspect of the present invention comprising the steps (1) to (8):

(1) pressing resin to form a interlayer insulating resin layer having a metal film formed thereon against a substrate for forming a conductor circuit;

(2) reducing the thickness of the metal film by etching;

(3) forming an opening in the metal film so as to expose the interlayer insulating resin layer;

(4) applying a laser beam from the formed opening of the metal film side to remove the resin for forming the interlayer insulating resin layer exposed through the opening to provide an opening for forming a via hole;

(5) forming an electroless plated film on the substrate forming the conductor circuit;

(6) forming a plating resist on the substrate forming the conductor circuit;

(7) electrolytic-plating a portion in which the plating resist is not formed; and

(8) removing the plating resist to remove the metal film and the electroless plated film below the plating resist by performing etching so as to form the via hole and the conductor circuit.

This aspect of the present invention employs a metal film thinned by etching and thus having a lowered thermal conductivity as a conformal mask. Therefore, an opening can be formed by a small output laser. Hence it follows that generation of undercut of resin for forming an interlayer insulating resin layer can be prevented.

After an opening for forming a via hole has been formed, an electroless copper plated film is formed on the metal film. Then, an electrolytic copper plated film is formed on the electroless copper plated film. When the conductive circuit and the via hole are formed, the electroless copper plated film lower than the resist layer is removed by etching. Since the metal film and the electroless copper plated film, which are thin films, can easily be removed, the electrolytic copper plated film constituting the conductive circuit and the via hole is not corroded during the etching process. As a result, a circuit having a fine pitch and a via hole having a precise diameter can be formed.

According to anothter aspect of the present invention, the metal film is copper foil.

According to another aspect of the present invention, the thickness of the metal film is made to be 5 .mu.m to 0.5 .mu.m in the step for reducing the thickness of the metal film by performing etching.

According to this aspect of the present invention, the thickness of the metal film is made to be 5 .mu.m to 0.5 .mu.m. The reason for this lies in that undercut occurs if the thickness of the metal film is larger than 5 .mu.m. If the thickness is not larger than 0.5 .mu.m, the function of the conformal mask cannot be obtained.

According to another aspect of the present invention, an interlayer insulating resin layer incorporating a metal film having a thickness of 5 .mu.m to 0.5 .mu.m is pressed against a substrate having a conductive circuit formed thereon.

In the present invention, the resin film having a metal film formed previously is pressed. Therefore, satisfactory flexibility can be realized which permits the resin film to easily be pressed against the substrate having the conductive circuit formed thereon.

According to the present invention, a method of manufacturing a multilayered printed circuit board is provided, incorporating a substrate on which a lower conductive circuit is formed, an insulating resin layer and an upper conductive circuit formed on the lower conductive circuit and having a structure that the lower conductive circuit and the upper conductive circuit are connected to each other through a via hole, the method of manufacturing a multilayered printed circuit board comprising the steps of: forming the lower conductive circuit on the substrate; forming the insulating resin layer on the lower conductive circuit; forming a coarsened surface on the surface of the insulating resin layer; forming, on the coarsened surface, a metal layer having an opening through which a portion of the coarsened surface is exposed; irradiating the coarsened surface exposed through the opening with a laser beam to remove the insulating resin layer to form an opening for the via hole; and forming the upper conductive circuit and the via hole.

According to the present invention, a method of manufacturing a multilayered printed circuit board is provided, incorporating a substrate on which a lower conductive circuit is formed, an insulating resin layer and an upper conductive circuit formed on the lower conductive circuit and having a structure that the lower conductive circuit and the upper conductive circuit are connected to each other through a via hole, the method of manufacturing a multilayered printed circuit board comprising the steps of: forming the lower conductive circuit on the substrate; laminating, heating and compressing metal foil having a coarsened surface formed either surface thereof and the insulating resin layer formed on the coarsened surface such that the insulating resin layer makes contact with the lower conductive circuit so that the metal foil is integrated; etching a portion of the metal foil to form an opening to expose the coarsened surface of the insulating resin layer; irradiating the coarsened surface exposed through the opening with a laser beam to remove the insulating resin layer so as to form an opening for forming the via hole; and forming the upper conductive circuit and the via hole.

As a result of energetic studies performed by the inventors of the present invention, a fact has been found that the cause of residues produced in the operation for forming the opening for forming the via hole is the structure that the surface which is irradiated with the laser beam is a mirror surface which reflects the laser beam to inhibit complete removal of the insulating resin layer.

The present invention uses the detected fact such that the surface irradiated with the laser beam is formed into the coarsened surface to prevent reflection of the laser beam.

In the present invention, the resist against the laser beam is metal layer or metal foil. Moreover, the opening is formed in the metal layer or the metal foil. The opening is irradiated with a laser beam capable of realizing a diameter of a spot light which is larger than the diameter of the opening so that the opening for forming the via hole is formed in the insulating resin layer.

In the present invention, the surface of the insulating resin layer exposed through the opening in the metal layer or the like is formed into the coarsened surface. Therefore, reflection of the laser beam can be prevented and the insulating resin layer can completely be removed. Since upward expansion of the periphery of the insulating resin layer can be prevented, also disconnection of the via hole can be prevented.

Although the reason why the expansion can be prevented cannot clearly be detected, an estimation can be made that the coarsened surface has a high absorption with respect to a laser beam and the resin is easily formed into plasma.

The inventors of the present invention have energetically studied in order to realize the foregoing object. As a result, etching solution containing a cupric complex and organic acid is used to etch the conductive circuit. Thus, flattening can be prevented when the surface of the conductive circuit is irradiated with a laser beam. Moreover, a coarsened surface exhibiting satisfactory adhesiveness with the interlayer insulating resin layer formed on the conductive circuit and the via hole can be formed. The foregoing detected fact is used to establish the present invention having the following essential portion.

A multilayered printed circuit board according to another aspect of the present invention comprising: a substrate on which a conductive circuit is formed; an interlayer insulating resin layer formed on the conductive circuit; an opening for forming a via hole formed in the interlayer insulating resin layer; and another conductive circuit including a via hole and formed on the interlayer insulating resin layer, wherein

the surface of the conductive circuit is subjected to a coarsening process using etching solution containing cupric complex and organic acid, and

stripe pits and projections are formed on the inner wall of the opening for forming the via hole.

According to another aspect of the present invention, a method of manufacturing a multilayered printed circuit board including (1) a step of forming a conductive circuit; (2) a step of forming an interlayer insulating resin layer on the conductive circuit; (3) a step of applying a laser beam to form an opening for forming a via hole in the interlayer insulating resin layer; and (4) a step of forming another conductive circuit including a via hole on the interlayer insulating resin layer, wherein

the surface of the conductive circuit is subjected to a coarsening process by using etching solution containing cupric complex and organic acid.

It is preferable that the method of manufacturing the multilayered printed circuit board has the step of spraying etching solution containing the cupric complex and the organic acid to the surface of the conductive circuit or the conductive circuit is immersed in the etching solution under a bubbling condition so that the surface of the conductive circuit is subjected to the coarsening process.

According to another aspect of the present invention, a multilayered printed circuit board incorporating interlayer insulating resin layers and conductive layers laminated alternately and structured such that the conductive layers are connected to one another through via holes each of which is formed by forming a metal film in a through hole formed in each of the interlayer insulating resin layers, said multilayered printed circuit board according to the present invention comprising:

stripe pits and projections formed on the side wall of the through hole.

This aspect of the present invention has the structure that stripe pits and projections are provided for the side wall of the through hole. Thus, the area of connection with the metal film can be enlarged, causing the adhesiveness to be improved. Thus, a reliable via hole can be formed.

Since the stripe pits and projections are formed in the direction of the opening, separation of the via hole can be prevented if force is exerted in the vertical direction of the via hole. Therefore, if the resin is left in the through hole for forming the via hole and the residue is expanded owing to heat to upwards move the via hole, separation can be prevented and reliability can be maintained in the connection.

The bump is provided for the via hole. If an element, such as an IC chip, having a different coefficiency of thermal expansion is mounted, force is exerted in the vertical direction of the via hole owing to the heat cycle. Also in the foregoing case, the stripe pits and projections in the direction of the opening prevent separation of the via hole.

It is preferable that the stripe pits and projections have the structure that the intervals between projections (or pits) are 1 .mu.m to 20 .mu.m. If the interval is too long or too short, the adhesiveness effect with the metal film deteriorates. The foregoing interval is substantially the same as 1/2 of the wavelength of the laser beam.

It is preferable that the metal film for forming the via hole is formed such that the electroless copper plated film and the electrolytic copper plated film are formed in this order from a position adjacent to the side wall of the through hole. The electroless copper plated film is harder than the electrolytic copper plated film. Moreover, the stripe pits and projections are formed into a pseudo coarsened surface. Therefore, if separating force is exerted, breakage of the metal film does not cause the via hole to be separated from the through hole.

It is most preferable that a coarsened surface having an average surface roughness Ra of about 0.05 .mu.m to about 5 .mu.m is formed (FIG. 31(A) which is an enlarged view) on the surface of the stripe pits and projections. The reason for this lies in that the adhesiveness can furthermore be improved.

When the coarsened surface of the sidewall of the through hole is complicated, transmission of a high-frequency signal causes delay in transmission to occur and noise to be produced owing to the skin effect. The stripe pits and projections according to the present invention are formed at the intervals of 1 .mu.m to 20 .mu.m. Therefore, the skin effect does not raise a critical problem. Moreover, the adhesiveness can be improved.

It is most preferable that the surface of the conductive circuit to which the through hole reaches is made of an electrolytic copper plated film. The electrolytic copper plated film has small crystal particles as compared with those of the electroless copper plated film. Moreover, the electrolytic copper plated film exhibits excellent glossiness to easily reflect a laser beam. Therefore, the electrolytic copper plated film is an optimum film in a case where incident light of the laser beam and reflected light are caused to interfere with each other as described later.

It is preferable that the surface of the conductive circuit to which the through hole reaches has a metal coarsened layer.

When the metal coarsened layer is formed on the surface of the conductive circuit, the laser beam is reflected by the surface of the metal coarsened layer to enable the laser beam to be reflected by the surface of the metal coarsened layer to cause the incident light of the laser beam and the reflected wave to interfere with each other. Thus, the stripe pits and projections formed in the direction of the opening can be provided for the surface of the wall of the through hole of the interlayer insulating resin layer.

Since the coarsened layer enables the reflection of the laser beam to be prevented to a level not higher than a predetermined level, residual resin on the surface of the conductive circuit can be prevented. Since the coarsened layer enables the adhesiveness with the interlayer insulating resin layer to be maintained, separation of the interlayer insulating resin layer owing to deterioration in the thermal shock of the laser beam can be prevented.

When the coarsened layer is not provided, the reflection is raised excessively, causing residue of the resin to easily occur. If an oxidizing (a blackening) process is performed to form the coarsened layer, the laser beam is undesirably absorbed. Thus, the laser beam cannot be reflected.

It is preferable that Rj of the coarsened layer is 0.05 .mu.m to 20 .mu.m. If Rj is 0.05 .mu.m or smaller, the reverse side is blackened. Thus, the laser beam is undesirably absorbed. If Rj is larger than 20 .mu.m, the laser beam scatters. In either of the two cases, incident light a reflected wave cannot cause to interfere with each other.

It is preferable that the coarsened layer is a coarsened layer obtained by non-acidic chemical coarsening process, such as physical coarsening including a polishing process, an oxidizing (a blackening) and reducing process, a process using sulfuric acid and hydrogen peroxide solution or a coarsening process using etching solution composed of cupric complex and organic acid under coexistence of oxygen. As an alternative to this, it is preferable that the coarsened layer is a coarsened layer obtainable from a plating process using an alloy, such as Cu--Ni--P or Cu--Co--P. The reason for this lies in that the foregoing coarsened layer is able to reflect the laser beam.

Plating of Cu--Ni--P maybe performed by using electroless plating bath, the pH of which is 9 and which is water solution of, for example, copper sulfate (0.1.times.10.sup.-2 to 25.times.10.sup.-2 mol/l), nickel sulfate (0.1.times.10.sup.-3 to 40.times.10.sup.-3 mol/l), citric acid (1.times.10.sup.-2 to 20.times.10.sup.-2 mol/l), sodium hypophosphite (1.times.10.sup.-1 to 10.times.10.sup.-1 mol/l), boric acid (1.times.10.sup.-1 to 10.0.times.10.sup.-1 mol/l) or a surface active agent (Surfinol 465 manufactured by Nissin Chemical Industry) (0.1 g/l to 10 g/l).

It is preferable that the cupric complex according to the present invention is a cupric complex of azole. The cupric complex of azole is employed as an oxidizer for oxidizing metal copper. The azole may be diazole, triazole or tetra azole. Among the foregoing materials, it is preferable that any one of the following material is employed: imidazole, 2-methyl imidazole, 2-ethyl imidazole, 2-ethyl-4-methyl imidazole, 2-phenyl imidazole or 2-undecyl imidazole. It is preferable that the quantity of cupric complex of azole which must be added is 1 wt % to 15 wt %. The reason for this lies in that noble metal, such as Pd, exhibiting satisfactory solubility, stability and constituting crystal core can be dissolved

To dissolve copper oxide, organic acid is mixed with the cupric complex of azole.

Specifically, it is preferable that the organic acid is at least one type of material selected from a group consisting of formic acid, acetic acid, propionic acid, butyric acid, valerianic acid, capronic acid, acrylic acid, crotonic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, maleic acid, benzoic acid, glycollic acid, lactic acid, malic acid and sulfamic acid. It is preferable that the content of the organic acid is 0.1 wt % to 30 wt % to maintain the solubility of oxidized copper and dissolution stability.

The produced cuprous complex is dissolved owing to an action of the acid so as to be combined with oxygen so that cupric complex is produced which is again contributed to the oxidation of copper.

To assist the dissolution of copper and oxidation of azole, halogen ions, for example, fluorine ions, chlorine ions or bromine ions, may be added to the etching solution. In the present invention, hydrochloric acid or sodium chloride may be added to supply halogen ions. It is preferable that the quantity of halogen ions is 0.01 wt % to 20 wt % to improve the adhesiveness between the formed coarsened surface and the interlayer insulating resin layer.

The cupric complex of azole and the organic acid (and halogen ions if necessary) are dissolved in water to adjust the etching solution.

The oxidizing and reducing process may be performed by using an oxidizing bath of 1 g/l to 100 g/l NaOH, 1 g/l to 100 g/l NaClO.sub.2 and 1 g/l to 50 g/l Na.sub.3PO.sub.4 and a reducing bath of 1 g/l to 100 g/l NaOH to 1 g/l to 50 g/l NaBH.sub.4.

The metal coarsened layer may be coated with at least one type of metal materials selected from a group consisting of Ti, Al, Cr, Zn, Fe, In, Tl, Co, Ni, Sn, Pb, Bi and noble metal to maintain glossiness and improve adhesiveness with the solder resist. It is preferable that the thickness of the selected metal material is 0.01 .mu.m to 10 .mu.m.

In the present invention, it is preferable that the diameter of the through hole for forming the via hole is 80 .mu.m or smaller. The foregoing precise via hole has a small area of contact between the metal film for forming the via hole and the side wall of the through hole for forming the via hole. Therefore, separation considerably easily occurs. Therefore, the formation of the conventional coarsened surface cannot satisfactorily prevent the separation. If the coarsened surface is made to be excessively complicated, the foregoing skin effect problem of delay in transmission and production of noise arises. The present invention is able to overcome the foregoing problems.

According to another aspect of the present invention, the interlayer insulating resin layer is made of thermosetting resin or a composite material of the thermosetting resin and thermoplastic resin.

This aspect of the present invention has a structure that the interlayer insulating resin layer is made of thermosetting resin or a composite material of thermosetting resin and thermoplastic resin. Therefore, stripe pits and projections can easily be formed owing to interference of the laser beam. Note that only the thermosetting resin, which encounters dissolution of resin, cannot form clear stripe pits and projections.

According to another aspect of the present invention, the interlayer, insulating resin layer contains acrylic monomer.

It is preferable that this aspect of the present invention is structured such that the interlayer insulating resin layer contains acrylic monomer. The reason for this lies in that residues of the resin can be reduced.

The acrylic monomer crosslinks monomer or oligomer of the thermosetting resin (including the thermosetting resin, a portion of which has been sensitized).

The acrylic monomer can be decomposed relatively easily. Therefore, the acrylic monomer is contained in the molecular chain, the acrylic monomer is decomposed owing to a laser beam, causing the thermosetting resin to have low molecular weight. Moreover, the resin having the low molecular weight is decomposed by the laser beam. Therefore, formation into plasma can easily be formed, causing residue of resin to substantially be eliminated.

The acrylic monomer may be any one of a variety of commercial products. For example, DPE-6A KAYAMAER PM-2 or PM-21 manufactured by Nihon Kayaku, R-604 manufactured by Kyoei or Aronix M-315, M-325 or M-215 manufactured by Toa may be employed.

DPE-6A is expressed by chemical formula 1 shown in FIG. 59, R-604 is expressed by chemical formula 2, Aronix M-315 is expressed by chemical formula 3, M215 is expressed by chemical formula 4 shown in FIG. 60 and KAYAMAER PM-2 and PM-21 is expressed by chemical formula 5.

A method of manufacturing a multilayered printed circuit board in another aspect of the present invention comprising at least the steps (a) to (d):

(a) forming a conductive circuit;

(b) coating the conductive circuit with resin;

(c) irradiating the resin with a carbon-dioxide gas laser beam to form a through hole which reaches the conductive circuit such that the carbon-dioxide gas laser beam is vertically applied to the conductive circuit below the resin to cause interference of reflected wave from the conductive circuit and incident wave to occur so that stripe pits and projections are formed on the side wall of the through hole; and

(d) coating the through hole with metal to form a via hole.

In this aspect of the present invention, an aspect has a structure that the conductive circuit below the resin is vertically irradiated with a carbon-dioxide-gas laser beam to cause interference between reflected-wave from the conductive circuit and incident wave to occur. Therefore, the stripe pits and projections can be formed on the side wall of the through hole. Therefore, the adhesiveness with metal can be improved so that a reliable via hole can be formed.

According to another aspect of the present invention, the resin is thermosetting resin or a composite material of the thermosetting resin and thermoplastic resin.

This aspect of the present invention has a structure that the interlayer insulating resin layer is made of the thermosetting resin or a composite of the thermosetting resin and thermoplastic resin. Therefore, the stripe pits and projections can easily be formed by the laser beam.

According to another aspect of the present invention, the step of forming the via hole includes a step of forming a resist after an electroless copper plated film has been formed in the through hole and supplying electric power through the electroless plated film to form an electrolytic plated film in a portion in which the resist is no