JPH1187886A - Production of printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate open circuit or short circuit incident to formation of a through hole by hot pressing metal foils having two layer structure of a copper layer and a different metal layer to the opposite sides of a resin board, making a through hole in the integrated resin board and then removing the different metal by etching. SOLUTION: A metal foil 4 having two layer structure of a copper layer 2 and an aluminum layer 3 for forming a wiring layer is hot pressed to the surface of a board 1 with the copper side directing toward the insulating board 1 and a through hole 5 is made in the integrated board 1. Subsequently, the aluminum layer 3 is dissolved by an aqueous solution of sodium hydroxide and removed to expose the copper layer 2 and an electroless plating layer 6 is formed on the wiring layer and the inner wall face of the through hole 5 followed by formation of an electrolytic copper plating layer 7. Since burrs and residual carbon are removed simultaneously with foreign metals, open circuit clue to defective plating around the through hole or inter-wiring short circuit due to carbon does not take place in a printed wiring board thus obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a printed wiring board manufactured mainly by a stacking method or a laminating method.

[0002]

2. Description of the Related Art In recent years, with the development of electronic devices, printed wiring boards have been provided with higher density wiring and multilayer wiring. The conventional method for manufacturing a printed wiring board was as follows. First, a copper-clad laminate is manufactured by laminating a copper foil on an insulating substrate (core substrate) in which an insulating resin is impregnated into a glass cloth. After drilling using a drill or laser on the copper-clad laminate, the burrs generated during laser processing and laser processing
The attached carbon residue is removed using a chemical solution. Next, electroless plating is performed on the inner wall surface of the through hole and the entire surface of the copper foil, and if necessary, further electrolytic plating is performed to obtain a required thickness as a wiring layer. Perform formation. If necessary, the lamination of the insulating layer and the wiring layer is repeated to perform multi-layering.

[0003]

A drill or a laser is used for drilling a through hole in a copper-clad laminate, but burrs are likely to be generated at an edge portion around the through hole after the processing, and this is a problem in a later plating step. This causes disconnection between the copper foil surface and the plated conductor in the through hole. Furthermore, when a laser is used, carbon residue is likely to adhere around the through-hole, and plating is deposited on the carbon residue in a later plating process, which is one of the causes of a short circuit between fine wirings. I was Further, when the diameter of the through hole becomes 50 μm or less, it becomes difficult for the chemical solution in the desmearing process to enter the retaining hole, so that the resin remaining inside the through hole becomes difficult to be removed, and the subsequent plating is performed. Disconnection failure occurred in the process.

As a method of solving such a problem, a copper foil in a region where a through-hole is to be formed on a copper-clad substrate is removed by etching before forming a through-hole, thereby preventing burrs and burrs on the copper foil. The method is disclosed in JP-A-1-228196. However, when the diameter of the through hole becomes 50 μm or less or the pitch becomes small, it becomes difficult to form the through hole in accordance with the etching hole formed on the copper foil.

It is an object of the present invention to provide a method for manufacturing a printed wiring board which solves the problems such as disconnection and short circuit involved in forming these through holes.

[0006]

Means for Solving the Problems In order to solve the above problems, a method for manufacturing a printed wiring board according to the present invention is characterized by including the following steps.

The present invention will be described by taking a method of manufacturing a core substrate as an example. First, a metal foil having a two-layer structure of a copper layer to be a wiring circuit and a dissimilar metal layer to be removed by etching on both surfaces of a resin substrate (core substrate) is hot-pressed with the copper surface facing the resin surface. And unite. After a through hole is formed at a predetermined position using a drill or a laser, burrs generated on the dissimilar metal layer and carbon residue attached thereto are removed by etching the dissimilar metal layer at the same time.

Here, as the dissimilar metal layer, a metal foil made of, for example, aluminum, tin or nickel is often used. Such a metal foil having a two-layer structure of a dissimilar metal layer and a copper layer is obtained by pressing a copper foil on one side of an aluminum foil, plating copper on one side of an aluminum foil, or tinning a copper foil. Or nickel plating. Of course, after the usual copper foil is applied, the surface of the copper foil may be plated with tin or nickel. Especially when forming a dissimilar metal layer by plating,
The wiring circuit serving as the base is not limited to the copper foil, and may be formed by electroless plating or a combination of electroless plating and electrolytic plating. The dissimilar metal material is not limited to aluminum, tin or nickel. Any metal other than aluminum, tin, and nickel can be used as long as it is a metal that can be selectively etched away from copper.

[0009] Through holes are formed in the substrate on which the metal foil of the two-layer structure is stretched by using a drill or a laser. Here, laser is CO ₂ laser, excimer laser or YA
You can select from G lasers. Burrs or carbon residues are generated around the edges of the through holes formed on the surface of the dissimilar metal layer on the outermost layer. Thereafter, the dissimilar metal layer is removed by etching to remove burrs or carbon residues around the edges of the through holes simultaneously with the dissimilar metal layer. In this way, a copper-clad substrate free of burrs or carbon residue around the edges of the retaining holes and the bottom of the retaining holes is obtained.

Thereafter, electroless plating is applied to the entire surface of the substrate including the inner wall surface of the through hole. Further, after a resist layer is formed on the electroless plating surface, the wiring pattern is formed by exposing and developing the wiring pattern via a photomask. After the electroless plating surface of the wiring pattern is electroplated to have a predetermined conductor thickness, the resist layer is peeled off. And chemically remove the vicinity of the surface of the electroless plating layer and the electrolytic plating layer,
The formation of the wiring circuit is completed. As described above, the generated burrs and attached carbon residues are removed at the same time as the dissimilar metal layer, so the resulting printed wiring board has disconnections due to plating defects around the through holes and shorts between wires due to carbon. Such a trouble does not occur.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. (Example 1) As shown in FIG. 1 (a), a copper layer 2 having a thickness of 5 μm to be a wiring layer and an aluminum layer having a thickness of 40 μm were formed on the surface of an insulating substrate 1 made of a BT (bismaleimide-triazine) resin-glass composite material. Metal foil 4 having a two-layer structure of layer 3
Were integrated by hot pressing with the copper side facing the insulating substrate 1.

As shown in FIG. 1B, a YAG laser was irradiated (not shown) from the aluminum layer 3 to form a through hole 5 having a diameter of 50 μm at a predetermined position.

Next, as shown in FIG. 1C, the aluminum layer 3 was dissolved and removed with an aqueous solution of sodium hydroxide to expose the copper layer 2 serving as a wiring layer.

[0014] Then, as shown in FIG.
First, an electroless copper plating layer 6 having a thickness of 0.5 μm is applied to the inner wall surface of the through hole 5, and then an electroless copper plating layer 7 having a thickness of 12 μm.
μm.

Then, as shown in FIG. 2A, after a resist layer 8 is stuck on an electrolytic copper plating layer 7 to be a wiring layer by using a hot laminator, the resist layer 8 is exposed and developed through a photomask 9 to form a pattern. Perform formation.

In the state shown in FIG. 2B, the exposed copper layer is treated with an etching agent mainly composed of ferric chloride to remove all the copper layers other than the wiring circuit protected by the resist layer 8.

The remaining resist layer 8 is peeled off, and FIG.
The formation of the wiring circuit as shown in (c) is completed.

(Embodiment 2) As shown in FIG.
5 μm thick to become a wiring layer on the surface of insulating substrate 10 made of T (bismaleimide-triazine) resin-glass composite material
The metal foil 13 having a two-layer structure of the copper layer 11 and the aluminum layer 12 having a thickness of 40 μm was integrated by hot pressing with the copper side facing the insulating substrate 10.

As shown in FIG. 3B, a through hole 1 having a diameter of 250 μm is formed at a predetermined position using a drill (not shown).
4 was formed.

Next, as shown in FIG. 3C, the aluminum layer 12 is dissolved and removed with an aqueous sodium hydroxide solution.
The copper layer 11 serving as a wiring layer was exposed.

Then, as shown in FIG.
First, the electroless copper plating layer 1
5 was applied in a thickness of 0.5 μm, and then an electrolytic copper plating layer 16 was applied in a thickness of 12 μm.

Then, as shown in FIG. 4A, after a resist layer 17 is stuck on an electrolytic copper plating layer 16 to be a wiring layer by using a hot laminator, the resist layer 17 is exposed and developed through a photomask 18 to form a pattern. Perform formation.

In the state shown in FIG. 4B, the exposed copper layer is treated with an etching agent mainly composed of ferric chloride to remove all copper layers other than the wiring circuit protected by the resist layer 17.

The remaining resist layer 17 is peeled off, and FIG.
The formation of the wiring circuit as shown in (c) is completed.

Comparative Example 1 As shown in FIG.
18 μm thick copper foil 2 on both surfaces of an insulating substrate 19 made of T (bismaleimide-triazine) resin-glass composite material
0 is hot-pressed and integrated.

Then, as shown in FIG. 5B, a predetermined position is irradiated with a YAG laser (not shown), and a diameter of 50 mm is applied.
A through hole 21 of μm is formed.

Next, as shown in FIG.
And an electroless copper plating layer 22 on the inner wall surface of the through hole 21.
Was applied in a thickness of 0.5 μm, and then an electrolytic copper plating layer 23 was applied in a thickness of 12 μm.

Then, as shown in FIG. 6A, a resist layer 24 is stuck on the electrolytic copper plating layer 23 using a hot laminator, and then exposed and developed through a photomask 24 to form a pattern.

In the state shown in FIG. 6B, the exposed copper layer is treated with an etching agent mainly composed of ferric chloride to remove all the copper layers other than the wiring circuit protected by the resist layer 24.

The remaining resist layer is peeled off, and FIG.
The formation of the wiring circuit shown in FIG.

Comparative Example 2 As shown in FIG.
12 μm thick copper foil 27 on both sides of an insulating substrate 26 made of T (bismaleimide-triazine) resin-glass composite material
Are hot-pressed and integrated.

Then, as shown in FIG. 7B, a through hole 28 having a diameter of 250 μm is formed at a predetermined position using a drill (not shown).

Next, as shown in FIG.
And an electroless copper plating layer 29 on the inner wall surface of the through hole 28.
Was applied in a thickness of 0.5 μm, and then an electrolytic copper plating layer 30 was applied in a thickness of 12 μm.

Then, as shown in FIG. 8A, after a resist layer 31 is stuck on the electrolytic copper plating layer 30 by using a hot laminator, it is exposed and developed through a photomask 32 to form a pattern.

In the state shown in FIG. 8B, the exposed copper layer is treated with an etching agent mainly composed of ferric chloride to remove all the copper layers other than the wiring circuit protected by the resist layer 31.

The remaining resist layer is peeled off, and FIG.
The formation of the wiring circuit shown in FIG.

Using the methods of the first and second embodiments and the first and second comparative examples, 100 printed circuit boards 33 for a hole test having the cross-sectional structure shown in FIG. 9 were manufactured. The presence / absence was inspected using the continuity tester 34, and the disconnection rates were compared for each manufacturing method.

As shown in FIG. 10, Embodiment 1 of the present invention
In both of the samples using No. 2, the disconnection occurrence rate was 0%. On the other hand, in the samples using Comparative Examples 1 and 2, the disconnection occurrence rates were 12% and 20%, respectively.

[0039]

As described above, according to the method for manufacturing a printed wiring board of the present invention, when a through-hole is formed by using a laser or a drill, the formation of a burr or adhesion of carbon causes the through-hole. It is possible to effectively suppress the occurrence of troubles such as disconnection and short circuit around.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a method for manufacturing a printed wiring board according to Example 1 of the present invention.

FIG. 2 is an explanatory diagram illustrating a method for manufacturing a printed wiring board according to Embodiment 1 of the present invention.

FIG. 3 is an explanatory view illustrating a method for manufacturing a printed wiring board according to Embodiment 2 of the present invention.

FIG. 4 is an explanatory view illustrating a method for manufacturing a printed wiring board according to Embodiment 2 of the present invention.

FIG. 5 is an explanatory view illustrating a method for manufacturing a printed wiring board according to Comparative Example 1 of the present invention.

FIG. 6 is an explanatory view illustrating a method for manufacturing a printed wiring board according to Comparative Example 1 of the present invention.

FIG. 7 is an explanatory view illustrating a method for manufacturing a printed wiring board according to Comparative Example 2 of the present invention.

FIG. 8 is an explanatory view illustrating a method for manufacturing a printed wiring board according to Comparative Example 2 of the present invention.

FIG. 9 is a diagram showing a cross-sectional structure of a printed wiring board for a through-hole continuity test.

FIG. 10 is a diagram showing a summary of a disconnection rate for each method by a through-hole continuity test.

[Explanation of symbols]

 1: Insulating substrate 2: Copper foil layer 3: Aluminum foil layer 4: Two-layer metal foil 5: Through hole 6: Electroless plating layer 7: Electrolytic plating layer 8: Resist layer 9: Photomask

Continued on the front page (51) Int.Cl. ⁶ Identification code FI H05K 3/46 H05K 3/46 X

Claims (7)

[Claims] 1. A resin layer comprising a copper layer and a dissimilar metal layer on both sides of a resin substrate.
After forming a through hole in the integrated substrate by hot pressing the metal foil having a layer structure with the copper surface facing the resin surface to form a through hole, the method includes a step of removing the dissimilar metal layer by etching. Manufacturing method of a printed wiring board. 2. The method for manufacturing a printed wiring board according to claim 1, wherein said dissimilar metal layer is formed of a metal which is more easily removed by chemical etching than copper. 3. The method for manufacturing a printed wiring board according to claim 1, wherein said dissimilar metal layer is formed of aluminum. 4. The method according to claim 1, wherein said dissimilar metal layer is formed of tin. 5. The method according to claim 1, wherein said dissimilar metal layer is formed of nickel. 6. The method according to claim 1, wherein the through hole is formed by a drill. 7. The method for manufacturing a printed wiring board according to claim 1, wherein said through holes are formed by a laser.