JPH0946042A - Circuit forming method for printed wiring board - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To solve the problem of film thickness to be etched, which is the biggest obstacle in forming a high density circuit by the subtractive method.
A low-cost and high-precision circuit can be formed on a double-sided plate having a via hole or the like or a multilayer plate. A circuit forming method for a printed wiring board,
The first conductive layer 1 is provided on one side and the second conductive layer is provided on the other side with the insulating layer 3 interposed therebetween.
In the laminated substrate A having the conductive layer 2, a via hole hole 4 having a bottom is formed which penetrates the second conductive layer 2 and the insulating layer 3 on one surface but does not penetrate the first conductive layer 1 on the other surface. Then, after plating only the inner surface of the hole 4 and the surface of the second conductive layer 2, the second conductive layer 2 and the plated film 5 on the upper surface, and the first conductive layer 1 are each etched to form both surfaces. A printed wiring board B having circuits 6 and 7 is formed. Alternatively, a second insulating layer and a third conductive layer are further laminated, a second bottomed hole portion similar to the above is formed, plating is performed only from the third conductive layer side, and then etching is performed to obtain a new layer. Form a circuit.

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 a circuit on a printed wiring board, and more particularly to a method for forming a high density printed circuit by a subtractive method.

[0002]

[Prior art]

Circuit forming methods on a printed wiring board are roughly classified into a subtractive method and an additive method. The subtractive method is a method of forming a circuit by etching a copper foil as a conductive layer which is previously attached to the insulating layer surface, and the additive method is a method of directly plating the circuit on the insulating layer. The subtractive method is the most general-purpose because it has a relatively simple technology and is inexpensive.

When a printed wiring board having circuits on the front and back surfaces is formed by the subtractive method, as shown in FIGS. 7 to 10, conductive layers are formed on both the front and back surfaces of the insulating layer 3. First, a through hole 4 is formed by a drill or the like on a laminated substrate A having (copper foils) 1 and 2, and plated films 5 and 5 are simultaneously formed on the hole 4 and the conductive layers 1 and 2 on the front and back surfaces.
It has been customary in the past to form the printed wiring board B by forming the circuits 6 and 7 by etching the conductive layers 1 and 2 on both sides after forming the.

Recently, instead of a drill, a laser or the like is used, and a through hole or a via hole (V
Although a technique of forming a circuit after forming an ia hole (also referred to as a via hole) and then forming a circuit by the same method is widely used, it was usual to plate both the front and back surfaces of the laminated substrate at this time as well. .

Further, a laser technique is used in a method of forming a circuit on a printed wiring board, which is mainly for drilling a through hole or a via hole as described above. Examples of lasers include carbon dioxide lasers, YAG lasers, excimer lasers, etc.
An excimer laser, a YAG laser, or an impact laser which is an improved carbon dioxide laser is used for processing a circuit board in a printed wiring board.

Regarding the application of the excimer laser to the circuit formation of a printed wiring board, for example, Japanese Laid-Open Patent Publication No. 5-1
It is disclosed in Japanese Patent No. 36650, Japanese Patent Application Laid-Open No. 5-152744, Japanese Patent Application Laid-Open No. 5-152748, and the like. Similarly, for applying the impact laser, see, for example, J. M. "A Larg" by Morrison and others
e Format Modified TEA CO ₂
Laser Based Process for
Cost Effective Via Genera
“Tion” (1994 International C
onferecne on Multichip Mo
dules, April 13-15, 1994, p. 36
9).

Regarding the YAG laser and its application to a printed circuit board, see, for example, M.G. "New by Owen"
Laser Technology for Dri
Ling Through-and Blind-
vias in Copper Clad Rein
Forced Circuit Boards ”(Pr
oc. IPC Technical Conference
ce, April 30-May 4, 1995, p. 19-1
-1 to 19-1-10).

[0009]

By the way, the demand for higher density of the printed wiring board is further increasing, and it is very important to make the surface pattern fine. For example, conventionally, the line width and the space width are each 125.
Circuits that were μm are 100 μm and 50
It is becoming finer to μm.

In order to achieve high density of the circuit in the subtractive method, improvement of the resist and the etching solution has been conventionally advanced, but the most important factor in achieving high density is the conductive layer ( Copper foil) and the thickness of the plating film. That is, in the case of a single-sided plate, the copper foil as the conductive layer may simply be thinned, but in the case of a double-sided plate, the plating film is formed on the conductive layer (copper foil) for plating through holes and via holes as described above. Is added, and the film thickness inevitably increases. If the film thickness to be etched at the time of etching for forming a circuit is large, the accuracy of the circuit pattern is deteriorated, which is a great obstacle to high density and is a problem.

The problem to be solved by the present invention is to provide a double-sided plate or a multi-layered plate having through holes and via holes,
The present invention is to solve the problem that the film thickness to be etched is large, which is the biggest obstacle in increasing the density of the circuit by the subtractive method, and the present invention thereby forms a highly accurate circuit at low cost. Is intended.

[0012]

The main part of the method for forming a circuit in a printed wiring board according to the present invention is that a first conductive layer 1 is provided on one side and a second conductive layer 2 is provided on the other side with an insulating layer 3 in between. In the laminated substrate A (see FIG. 1) having a bottomed via hole hole 4 that penetrates the second conductive layer 2 and the insulating layer 3 on one surface but does not penetrate the first conductive layer 1 on the other surface. (See FIG. 3), and after plating 5 only on the inner surface of the hole 4 and on the surface of the second conductive layer 2 (see FIG. 4), the second conductive layer 2 and the plated film 5 on the upper surface, and By etching each of the conductive layers 1, circuits 6 and 7 are formed on both surfaces (see FIG. 5) to form the printed wiring board B.

The printed wiring board B formed as described above is
Although the product itself is a product, in addition to that, a second insulating layer 8 and a third conductive layer 9 are newly stacked to form the third conductive layer 9
And a bottomed second via hole hole 10 that penetrates the second insulating layer 8 but does not penetrate the second conductive layer 2, and then forms the inner surface of the hole 10 and the third conductive layer. Alternatively, a new circuit 12 may be formed by plating only the 9th surface and then etching the third conductive layer 3 and the plating film 11 on the upper surface (see FIG. 6). Needless to say, this may be further multilayered in the same manner.

In the above structure, the insulating layer 3 preferably contains a reinforcing material made of an inorganic fiber or an organic fiber, but may not contain it. First, second and third conductive layers 1, 2, 9
Is preferably a thin copper foil, but each surface may be plated with copper or a copper alloy. Various methods such as mechanical, chemical, or optical are used to form the bottomed via hole portions 4 and 10, and it is particularly preferable to use a laser in terms of accuracy.

[0015]

According to the present invention, the first conductive layer 1 and the second conductive layer 1 of the laminated substrate A having the first conductive layer 1 on one surface and the second conductive layer 2 on the other surface with the insulating layer 3 interposed therebetween are provided. The conductive layer 2 is
A metal, particularly a copper foil is preferable, but a copper alloy plated film may be used.

As the resin contained in the insulating layer 3, either a thermosetting resin or a thermoplastic resin can be used. Among thermosetting resins, epoxy resin, polyimide resin,
Bismaleimide triazine resin, polycyanurate resin, polysilane resin, polybenzimidazole resin, etc. can be used.

The insulating layer 3 may or may not contain a reinforcing material made of an organic fiber or an inorganic fiber. As the inorganic fiber when including a reinforcing material, for example, glass fiber,
Examples of organic fibers include aramid fiber, Teflon fiber,
Polyether ether ketone fiber, polybenzimidazole fiber, or the like may be used. Of these, aramid fiber and Teflon fiber are desirable because they have excellent laser processability and electrical characteristics. Among the aramid fibers, copolyparaphenylene 3,4′oxydiphenyl terephthalamide fiber is particularly suitable because of low ionic impurities and low moisture absorption.

When the insulating layer 3 does not contain a reinforcing material, the insulating layer 3 may be in the form of a film or sheet, and examples of the material include polyester, polyimide, polyetheretherketone, polyamide, and especially aramid. In particular, polyparaphenylene terephthalamide is preferable. The thickness of the insulating layer 3 is several μm to several 1
00 μm is optimal, but typical thickness is 20-100
μm.

The first conductive layer 1 is formed on the laminated substrate A having the first conductive layer 1, the second conductive layer 2 and the insulating layer 3 between them.
And a bottomed via-hole 5 which penetrates the insulating layer 3 but does not penetrate the second conductive layer 2. Here, as a method of forming the holes 5, various means such as mechanical, chemical, or optical are used. In particular, an opening using a laser is optimal because it is simple and highly accurate.

As the laser, carbon dioxide laser, Y
Either an AG laser or an excimer laser can be used, but since the inner surfaces of the holes 4 and 10 are smoothed and processed without roughening, an impact laser, which is a kind of carbon dioxide laser, a YAG laser, an excimer laser, etc. Is desirable.

In this laser processing, the laser beam may be focused on a certain area and irradiated from above the second conductive layer 2. Masking such as a mask image method, a contact mask method, and a conformal mask method can be used to limit the irradiated portion.

With respect to the laminated substrate A in which the bottomed via hole hole 4 is formed as described above, from one side of the second conductive layer 2 where the hole part 4 is opened, the inner surface of the hole part 4 and the second conductive layer 2 are formed. 2 The conductive layer 2 is plated. The first conductive layer 1, which is the other surface, is not plated. The plating material used here is preferably copper as a main component. In order to plate only the side surface of the second conductive layer 2 on one surface and not plate the surface of the first conductive layer 1 on the other surface, it is sufficient to mask the surface of the first conductive layer 1 on the other surface. Not limited to this, two laminated substrates A having conductive layers on both sides are stuck back to back on the first conductive layer 1 side, and the exposed second conductive layer 2 sides are plated and then peeled off. You may

Further, since the purpose of the plating here is to conduct electricity to the hole portion 4 as a via hole, the thickness of the plating film 5 may be thinner than that of the usual through-hole plating.
The thickness may be several μm to several tens of μm. Typical thickness is 8 to 15 μm. The plating may be electroless plating, electrolytic plating, or a combination thereof.

After the above plating treatment, the second conductive layer 2 on one surface and the plating film 5 on the upper surface thereof, and the first conductive layer 1 on the other surface.
Are etched by the usual subtractive method. As a result, the circuits 6 and 7 are formed on both the front and back surfaces of the laminated substrate A, and the printed wiring board B having a double-sided circuit is completed.

According to the present invention, the printed wiring board B is obtained by the above, and is a product itself. However, a so-called multi-layered structure is formed by further coating or laminating resin, prepreg or the like on the printed wiring board B. It can also be applied to build-up boards. Also in that case, the formation of the second via hole hole 10 having a height and the plating treatment are performed only on the third conductive layer 9 side on the laminated second insulating layer 8. After that, the third conductive layer 9 side is etched, and a new circuit 1 is formed on that side.
2 will be formed (see FIG. 6).

As described above, in the method for forming a circuit in the printed wiring board according to the present invention, even a double-sided board having the conductive layers 1 and 2 on both sides is plated only on one side and not on the other side. Moreover, since the purpose of the plating is to establish conduction with the holes 4 and 10 as via holes, the thickness of the plated films 5 and 11 may be extremely thin.

Therefore, in the circuit forming method by the subtractive method of the present invention, during the etching for forming the circuit,
On the side of the second conductive layer 2 or the third conductive layer 3 on one side, the film thickness to be etched is the copper foil and the extremely thin plating films 5 and 11 on the side, and on the side of the first conductive layer 1 on the other side. All that is required is to etch the copper foil. Therefore, in the present invention, the film thickness to be etched, which is the biggest obstacle to attaining high density by the subtractive method, is thin, and a highly accurate circuit pattern can be drawn.

[0028]

Example 1 First, a laminated substrate A (thickness: about 0. 0) in which the resin component of the insulating layer 3 is an epoxy resin and aramid fiber (copolyparaphenylene.3,4'oxydiphenylene terephthalamide) is added as a reinforcing material. 1mm) on both sides
Copper foil (thickness about 18 μm) is used as the conductive layer 1 and the second conductive layer 2.
m) is attached (see FIG. 1).

Then, the copper foil of the second conductive layer 2 on one side is etched to form an opening having an inner diameter of about 0.1 mm (see FIG. 2), and then a KrF excimer laser is irradiated from above. As a result, a bottomed via-hole portion 4 that penetrates the insulating layer 3 but does not penetrate the first conductive layer 1 on the opposite surface is formed (see FIG. 3).

Then, from the side of the second conductive layer 2 where the hole 4 on one surface is opened, the inner surface of the hole 4 is subjected to normal copper sulfate plating for conducting as a via hole (see FIG. 4).
This copper plating was performed by electroless plating. As a result, the copper plating film 5 (having a thickness of about 20
μm) was formed. At this time, the first conductive layer 1 which is the other surface
The surface is masked with a dry film to prevent the plating from adhering.

Thereafter, the copper plating film 5 on the copper foil of the second conductive layer 2 on one side and the copper foil of the first conductive layer 1 on the other side are each coated with a resist by an electrodeposition method (thickness: approx. 8μ
m), etching for forming a circuit was performed using ferric chloride to form patterns of circuits 6 and 7 having a minimum line / space of 50 μm / 50 μm (see FIG. 5). In this way, 10 test substrates (size 250 mm x 250 m
m) was obtained.

When the short-circuited portions of each of the test substrates obtained above were measured, the average number of short-circuited portions on one side of the second conductive layer 2 was 10.5, and the short-circuited portions on the other side of the first conductive layer 1 were measured. The number of shorts on the side was 0.2 on average.

Thus, in the double-sided substrate having the conductive layers 1 and 2 on both sides, plating is applied only to one side (here, the second conductive layer 2 side), and the circuit is formed by etching it for circuit formation. But line / space 50μm / 50μ
It was proved that it is suitable for forming a fine pattern of m.

The above is the data about the printed circuit board B in which the circuit is formed on the double-sided circuit board having the first conductive layer 1 and the second conductive layer 2. The copper foil is coated or laminated with resin or prepreg. The same test was performed on a printed wiring board (see FIG. 6) of a multi-layered build-up board having the third conductive layer 3 attached thereto, and a short circuit occurred in the circuit formed on the surface of the third conductive layer 3 side. The number of points was 10.6 on average.

[0035]

Comparative Example 1 In the same manner as in Example 1, a copper foil (thickness: about 18 μm) was attached as a first conductive layer and a second conductive layer on each surface of the laminated substrate A (thickness: about 0.1 mm). After forming a bottomed hole in it, this time, the same copper plating (thickness about 20 μm) as above is applied to both front and back surfaces (first conductive layer surface and second conductive layer surface), and then both surfaces are processed by the same method. 50 μm
Patterning was performed with a line / space of / 50 μm.

When the short-circuited portions of the test board thus obtained were measured, the average number of short-circuited portions was 10.7 on the one side of the second conductive layer and the average of the short-circuited points on the other side of the first conductive layer. There were 11.5 places. As a result, it has been proved that it is difficult to form a fine pattern when plating is performed on both sides of a laminated substrate as in the conventional case.

[0037]

As is apparent from the above, the circuit forming method for a printed wiring board according to the present invention is capable of forming a high-density printed circuit even though the technique is a subtractive method which is relatively simple and inexpensive. it can.

That is, in the conventional subtractive method, when a circuit is formed on a double-sided board having a conductive layer such as a copper foil on both sides, the circuit is formed on both the front and back sides for conductive plating in via holes. The film thickness to be etched was the sum of the copper foil as the conductive layer and the plated film. Therefore, if the film thickness to be etched is thicker, the accuracy of the circuit pattern to be formed becomes worse, and it has not been possible to meet the recent demand for a fine pattern / high density circuit.

On the other hand, the present invention is a subtractive method of forming a circuit by etching, but even in a double-sided board having conductive layers on both sides, plating is applied only to the conductive layer surface on one side and the other surface is plated. In addition, the plating film is made extremely thin for conducting to the hole portion as the via hole. Therefore, the film thickness to be etched by the circuit-forming etching only needs to be a conductive layer copper foil and a very thin plated film on one side, and a conductive layer copper foil on the other side.

Therefore, according to the present invention, it is possible to reduce the film thickness to be etched, which is the biggest obstacle for achieving the high density by the subtractive method, and it is possible to form a double-sided plate or a multi-layered plate having through holes or via holes. In addition, it is possible to form a high-density circuit pattern by the low-cost subtractive method, and it is possible to achieve high precision of the pattern, so it is possible to sufficiently meet the recent demands for fine patterns and high-density circuits. Will be able to.

[Brief description of drawings]

FIG. 1 is a partially enlarged vertical side view of a laminated substrate used in an example of the present invention.

FIG. 2 is a partially enlarged vertical cross-sectional side view showing a state in which an opening is formed in a part of a conductive layer on one surface of the laminated substrate shown in FIG.

FIG. 3 is a partially enlarged vertical sectional side view showing a state in which a via hole is formed in the laminated substrate shown in FIG.

FIG. 4 is a partially enlarged vertical side view showing a state in which only one surface of the laminated substrate shown in FIG. 3 is plated.

5 is a partially enlarged vertical side view showing a printed wiring board in which a circuit is formed on the laminated substrate shown in FIG. 4 by etching.

FIG. 6 is a partially enlarged vertical sectional side view showing a printed wiring board when the present invention is applied to a multilayer board by a build-up method.

FIG. 7 is a partially enlarged vertical side view of a laminated substrate used in an example of a conventional subtractive method.

FIG. 8 is a partially enlarged vertical side view showing a state in which a through hole is formed in the laminated substrate shown in FIG.

9 is a partially enlarged vertical cross-sectional side view showing a state in which both surfaces of the laminated substrate shown in FIG. 8 are plated.

10 is a partially enlarged vertical side view showing a printed wiring board in which a circuit is formed by etching on the laminated substrate shown in FIG.

[Explanation of symbols]

 A-Layered substrate 6-Circuit B-Printed wiring board 7-Circuit 1-First conductive layer 8-Second insulating layer 2-Second conductive layer 9-Third conductive layer 3-Insulating layer 10-Hole part 4-Hole Part 11-circuit 5-plating film

Claims (12)

[Claims] 1. A laminated substrate having a first conductive layer and a second conductive layer with an insulating layer interposed between the second conductive layer on one side and the insulating layer, but the first conductive layer on the other side. After forming a bottomed via-hole hole, and then plating only the inner surface of the hole and the surface of the second conductive layer, the second conductive layer and the plated film on the upper surface, and the first conductive layer A method for forming a circuit in a printed wiring board, characterized in that each of them is etched to form a circuit on each side. 2. A laminated substrate having a first conductive layer and a second conductive layer with an insulating layer interposed between the second conductive layer on one side and the insulating layer but the first conductive layer on the other side. A bottomed via-hole hole is formed, and then plating is performed only on the inner surface of the hole and the surface of the second conductive layer, and then the second conductive layer and the plated film on the upper surface, and the first conductive layer. Are respectively etched to form circuits on both sides, and a second insulating layer and a third conductive layer are further laminated on the second conductive layer side, and the third conductive layer and the second insulating layer are penetrated. After forming a bottomed second via hole hole that does not penetrate the previous second conductive layer 2 and then plating only the inner surface of the second hole and the surface of the third conductive layer, A method of forming a circuit in a printed wiring board, characterized in that the third conductive layer and the plating film on the upper surface are etched to form a new circuit. . 3. The method for forming a circuit in a printed wiring board according to claim 1, wherein at least one of the conductive layer and the plated film is made of copper. 4. The method for forming a circuit in a printed wiring board according to claim 1, wherein the holes are formed by laser processing. 5. The method for forming a circuit in a printed wiring board according to claim 4, wherein the laser is an excimer laser. 6. The method for forming a circuit in a printed wiring board according to claim 4, wherein the laser is an impact laser. 7. The laser is a YAG laser.
A method for forming a circuit in a printed wiring board according to. 8. The method for forming a circuit in a printed wiring board according to claim 1, wherein the insulating layer contains a reinforcing material. 9. The method for forming a circuit in a printed wiring board according to claim 8, wherein the insulating layer contains a reinforcing material made of an inorganic or organic fiber. 10. The method for forming a circuit in a printed wiring board according to claim 9, wherein the insulating layer contains aramid fiber. 11. The method for forming a circuit in a printed wiring board according to claim 9, wherein the insulating layer contains Teflon fiber. 12. The method for forming a circuit in a printed wiring board according to claim 1, wherein the insulating layer does not contain a reinforcing material.