JPH10163627A - Via hole formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit board having high reliability, when forming a blind hole in a multilayer wiring board by a laser processing method, without leaving an insulating resin residue or the like between layers, thereby improving efficiency. A method for forming via holes is provided. SOLUTION: At least a first conductor layer of a multilayer wiring board in which a first conductor layer, an insulating resin layer and a second conductor layer are sequentially laminated is etched, and then a blind hole is formed by laser processing. Forming a conductive layer in a blind hole, and then performing soft etching after laser processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming via holes in a multilayer wiring board, and more particularly, to a method for forming a via hole in a multilayer wiring board in which a conductor layer, an insulating resin layer and a conductor layer are sequentially laminated. The present invention relates to a method for forming a via hole provided for electrically connecting a conductor layer and a conductor layer therebelow via an insulating resin layer.

[0002]

2. Description of the Related Art A printed wiring board is made of an insulating material obtained by impregnating and hardening a thermosetting resin such as an epoxy resin or a polyimide resin into a reinforcing fiber such as a glass fiber or an aromatic polyamide fiber. There is a rigid wiring board formed with the above conductor layer. Also, a flexible wiring board (FPC) using a polyimide resin or the like having flexibility as an insulating layer material.
There is. Furthermore, a multilayer wiring board is obtained by laminating the above printed wiring board so that the conductor layer and the insulation layer are alternately positioned, or by laminating the insulation layer and the conductor layer alternately under pressure and heat to cure. There is a build-up wiring board.

In these multilayer wiring boards, in order to form a via hole for electrically connecting an outer layer copper foil and an inner layer copper foil, a through hole is formed in a copper clad laminate with a mechanical drill, and a through hole is formed on the back surface. A method of forming a circuit after electroless copper plating or electrolytic copper plating has been generally used. This method is called a subtractive method, and other methods include the formation of a circuit board such as an additive method or a circuit transfer (a method in which a circuit is formed in advance on a metal plate and a prepreg is pressed to transfer the circuit). Although there is a method, the formation of a through hole is also required in these formation methods.

As a method of forming via holes in a multilayer wiring board, there is known a laser processing method in which a laser device such as a carbon dioxide laser or an excimer laser is used to irradiate an insulating layer with a laser beam to make holes. In this method, a fine hole is previously formed in a predetermined portion of an outer layer copper foil by a mechanical drill, chemical etching, or the like, and a laser beam is irradiated using the outer layer as a mask, thereby forming the outer layer copper foil and the inner layer copper foil. Remove the resin in between to expose the inner layer copper foil,
In this method, a blind hole is formed, and finally a via hole is formed by plating or the like.

However, in the conventional via hole forming method by laser processing, the epoxy resin or the polyimide resin between the layers remains as a smear on the roughened portion of the inner layer copper foil. There has been a problem that the via hole is disconnected due to a decrease in adhesion and the reliability of the circuit wiring board is reduced.

As a method for solving this problem, for example, Japanese Unexamined Patent Publication (Kokai) No. 5-55724 discloses that a processing laser pulse having a relatively long oscillation time and a cleaning laser pulse having a relatively short oscillation time are used. A method has been proposed in which after forming a blind hole in an insulating layer with a laser pulse for cleaning, the hole is irradiated with a laser pulse for cleaning to form a blind hole with no residue. However, this method requires two types of laser devices and cannot remove stains such as an oxide film of a copper foil exposed by laser processing.

Japanese Patent Application Laid-Open No. Hei 5-305468 discloses a composite of an aromatic polyamide fiber and a thermosetting resin using a carbon dioxide laser having a rectangular pulse waveform in order to prevent generation of burrs and carbides in laser processing. A method of heating a desired portion of an insulating layer made of a material or a green sheet has been proposed. However, this method is not a blind hole, but a method for forming a through hole (through hole), and an insulating material to be used is specified, so that it cannot be applied to FPC.

Further, Japanese Patent Application Laid-Open No. 3-210984 discloses that when a polyimide substrate is pierced by a carbon dioxide laser,
There has been proposed a method of forming a via hole that defocuses a laser beam and reflects the laser beam, so that there is no undercut and there is no need to remove polyimide residues. However, this method is effective for forming a through hole, but when applied to the formation of a blind hole, a disadvantage is that the laser beam is irregularly reflected on the exposed conductor layer at the bottom of the blind hole, and the inner surface of the via hole is side-etched. There is. In addition, since the surface of the conductor layer at the bottom of the exposed blind hole is roughened, it is impossible to remove polyimide that has entered the roughened surface only by laser irradiation. Therefore, as described in the publication, it is extremely difficult to remove the polyimide that has penetrated the roughened surface even if a post-treatment for chemically dissolving and removing the remaining polyimide is performed.

[0009]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a circuit board having high reliability.
It is an object of the present invention to provide a method for forming a via hole efficiently without leaving an insulating resin residue between layers when forming a blind hole in a multilayer wiring board by a laser processing method.

[0010]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that when forming a blind hole in a multilayer wiring board by a laser processing method, the insulating resin residue remaining at the bottom of the blind hole is removed from the conductive layer. It has been found that the above problem can be solved by etching and removing the portion, and the present invention has been completed.

That is, according to the present invention, at least a first conductor layer of a multilayer wiring board in which a first conductor layer, an insulating resin layer, and a second conductor layer are sequentially laminated is etched, In a method of forming a via hole in which a blind hole is formed by laser processing, and then a conductive layer is formed in the blind hole, the method is a method of forming a via hole, which comprises performing laser processing and then soft etching.

Hereinafter, the present invention will be described in detail. The multilayer wiring board to which the present invention is applied is one in which an insulating resin layer such as an epoxy resin and a polyimide, and a conductor layer such as a copper foil are sequentially laminated on a circuit wiring board, and at least the first conductor This is a multilayer wiring board in which a layer, an insulating resin layer and a second conductor layer are sequentially laminated. Such a multilayer wiring board may be one in which a plurality of circuit wiring boards formed in advance are bonded together. However, it is preferable that a laminate in which an insulating layer and a conductor layer are alternately laminated is hardened by heating and pressing. It is a wiring board.

Examples of the insulating resin used in the present invention include an epoxy resin, a polyimide resin, a triazine resin, a polybutadiene resin, a fluororesin, a diarylphthalate resin and the like. These resins may be reinforced with glass fibers or aromatic polyamide fibers, if necessary. Of these, rigid multilayer wiring boards include:
A glass epoxy resin obtained by impregnating and curing an epoxy resin in a glass fiber bundle is preferable. For the FPC, a polyimide resin or a modified polyimide resin is preferable. These insulating resin layers may be formed by applying a resin solution or a precursor resin solution thereof on a circuit-processed wiring board, or by laminating a film made of a resin or a precursor resin thereof. May be formed.

The conductive layer used in the present invention may be a conductive metal foil or metal paste, preferably a copper foil. Further, a conductor layer can be formed on the insulating resin layer by plating.

In the present invention, the method of laminating the insulating resin material and the conductor layer on the circuit-processed wiring board is not particularly limited, but copper foil is used for the conductor layer and polyimide is used for the insulating resin. A method of laminating by a hot press molding method such as a hot press is preferable.

In forming a via hole in a multilayer wiring board, the outermost conductor layer is first etched using an etching resist or the like as a mask to form a desired pattern. In general, there is a known method in which a photosensitive resist ink is applied to a multilayer wiring board, exposed and developed through a mask, and the exposed conductor layer of the multilayer wiring board is etched with an etching solution such as ferric chloride. Used. Further, a screen printing ink may be used instead of the photosensitive resist ink.

Next, blind holes are formed in the insulating resin layer below the multilayer wiring board having the fine holes formed in the conductor layer by laser processing. For laser processing, a known laser device can be used, and a carbon dioxide laser device or an excimer laser device is particularly preferable. In normal laser processing, a mask is required to protect a portion not to be processed from a laser beam.In the present invention, however, the conductor layer itself having the fine holes serves as a mask, and a blind hole is formed in a predetermined portion of the insulating resin layer. Can be formed.

When a blind hole is formed in an insulating resin layer by laser processing, an insulating resin residue or the like remains on the surface of the conductor layer at the bottom of the hole. In the present invention, this residue is removed by soft etching. . That is, by the soft etching of the present invention, the exposed surface layer of the conductor layer is removed by etching, and the remaining insulating resin residue can be completely removed, and an extremely reliable via hole can be formed in the multilayer wiring board. . This soft etching uses a commercially available soft etching solution,
This can be performed by cleaning the multilayer wiring board that has been laser-processed. The soft etching is also called flash etching or light etching, and is generally performed as cleaning for lightly dissolving and removing about 1 to 5 μm of the copper foil surface.

In the present invention, it is preferable that the soft etching is performed under irradiation of ultrasonic waves. Irradiation of ultrasonic waves makes it easier for the soft etching liquid to penetrate into the fine blind holes, shortens the soft etching time, and improves reliability.

For soft etching under ultrasonic irradiation, a bat containing a soft etching liquid and a laser-processed multilayer wiring board is placed in a commercially available ultrasonic cleaning tank, and an oscillation frequency of 10 to 10 is applied at room temperature or slightly heated. It may be carried out at 50 KHz for 4 to 6 minutes, depending on the output.

Finally, the multilayer wiring board subjected to soft etching under irradiation of ultrasonic waves is subjected to copper plating of a thickness of about 10 μm on the entire surface of the base material by, for example, electroless copper plating or electrolytic plating. A via hole is formed at a connection between the upper copper foil and the lower circuit board.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for forming via holes in a circuit wiring board according to the present invention will be described in detail below with reference to embodiments. Example 1 First, as shown in FIG. 1, a copper foil 1 (18 μm in thickness) and a polyimide adhesive sheet 2 (SPB-050A manufactured by Nippon Steel Chemical Co., Ltd.) were used as an insulating resin on a circuit board 3 after circuit processing. Were laminated using a hot press. The specific conditions for lamination are as follows: the copper foil 1 and the polyimide adhesive sheet 2 are put together on the circuit board 3 which has been subjected to circuit processing and put into a hot press.
The mixture was heated at a rate of ° C / min, kept at 180 ° C for 1 hour, and then cooled to room temperature in a water-cooled manner for 20 minutes. The obtained laminate is
The thickness of the polyimide resin layer is 50 μm and the total thickness is 86 μm
m.

Next, as shown in FIG. 2, an opening for connection between the copper foil 1 of the laminated wiring board and the wiring board 3 subjected to circuit processing is formed.
Etching was performed with an aqueous ferric chloride solution to form micropores in a desired pattern. Further, as shown in FIG. 3, using the copper foil 1 as a processing mask, a carbon dioxide gas laser beam 5 was applied to substantially the entire surface, and a blind hole 6 connecting the copper foil 1 and the circuit board 3 subjected to the circuit processing was formed. The carbon dioxide laser device used has a laser pulse width of 5 μs and an output energy of 20 μs.
w, laser energy per pulse is 48.8 mJ
Was 95 J / cm ² . Furthermore, 20 liters of air is used as assist gas.
Separately irradiate 14 pulses per hole continuously,
The entire surface of the wiring board was scanned and processed. The hole diameter of the blind hole 6 was 80 μm.

A soft etching solution is placed in a stainless steel vat, and the laminated wiring board is immersed therein and irradiated with ultrasonic waves, so that the penetration of the soft etching solution is improved. The resin remaining on the bottom was removed. For soft etching liquid,
Using a microetching solution (Meltems G-6) manufactured by MacDammit Japan Co., Ltd., the temperature of the solution was adjusted to 25 ° C., and the entire wiring board was immersed. The ultrasonic treatment of the soft etching solution was performed by using an ultrasonic cleaning tank UT-30B manufactured by Shinmeidai Kogyo Co., Ltd., and a stainless steel bat containing the soft etching solution was placed in the ultrasonic cleaning tank.
The operation was performed for 5 minutes at KHz and an output of 600 w.

After performing soft etching under ultrasonic irradiation and observing the multilayer wiring board sufficiently washed with an electron microscope, the resin on the hole wall surface was not affected, and the resin on the hole bottom surface was completely removed. Was confirmed. Finally, copper plating is performed by a general electroless copper plating method to a thickness of 10 μm.
A via hole 7 as shown in FIG.
Was formed.

Example 2 In the same procedure as in Example 1, fine holes for connection were formed in predetermined portions of the copper foil of the wiring board by hard etching, and then blind holes were formed in the resin layer using a carbon dioxide laser device. Further, using Preposit Etch 748 manufactured by Shipley Far East Co., Ltd., the entire wiring board was immersed by adjusting the liquid temperature to 25 ° C., and soft etching was performed in the same manner as in Example 1 under ultrasonic irradiation. Observation of the soft-etched multilayer wiring board with an electron microscope confirmed that the resin on the hole wall surface was not affected, and that the resin on the hole bottom surface was completely removed. Finally, copper plating was applied to the entire surface of the substrate around 10 μm by a general electroless copper plating method to form via holes.

Example 3 Via holes were formed in a multilayer wiring board in the same manner as in Example 1 except that no ultrasonic wave was applied during soft etching. As a result, it took 7 minutes to completely remove the resin from the bottom of the hole. Observation of the soft-etched multilayer wiring board with an electron microscope confirmed that the resin on the hole wall surface was not affected, and that the resin on the hole bottom surface was completely removed. Finally, copper plating was applied to the entire surface of the substrate around 10 μm by a general electroless copper plating method to form via holes.

[0028]

According to the present invention, after forming a blind hole by laser processing, by soft etching under ultrasonic irradiation, the resin remaining on the bottom of the hole can be completely removed without damaging the insulating resin layer. To improve plating adhesion on the bottom surface of the inner copper foil.
A highly reliable via hole can be formed. In particular, a highly reliable connection can be made even with a fine via hole.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a side laminate of a multilayer wiring board substrate before processing according to the present invention.

FIG. 2 is a side sectional view of a multilayer wiring board base material in which fine holes are formed in the uppermost copper foil by etching.

FIG. 3 is a side sectional view of a multilayer wiring board base material in which blind holes are formed in an insulating resin by laser processing.

FIG. 4 is a side sectional view of a multilayer wiring board having via holes formed according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Copper foil 2 Polyimide adhesive sheet 3 Circuit-processed wiring board 4 Fine hole formed by etching 6 Blind hole 7 Via hole

Claims (3)

[Claims] At least a first conductor layer of a multilayer wiring board in which a first conductor layer, an insulating resin layer, and a second conductor layer are sequentially laminated is etched, and then is blinded by laser processing. A method for forming a via hole in which a hole is formed and then a conductive layer is formed in the blind hole, the method comprising laser etching and then soft etching. 2. The method according to claim 1, wherein the soft etching is performed under ultrasonic irradiation. 3. The via hole forming method according to claim 1, wherein the laser processing is performed by a carbon dioxide gas laser or an excimer laser.