JP3259797B2 - Multilayer printed wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer printed wiring board, and more particularly to a multilayer printed wiring board having high-precision and high-density wiring.

[0002]

2. Description of the Related Art In recent years, electronic devices requiring high-speed operation, such as communication devices, have been widely used. The need for high-speed operation includes not only the need for high-speed signal propagation, but also various requirements such as accurate switching of high-frequency signals. In order to cope with such electronic devices, there is a demand for a printed wiring board suitable for high-speed operation. In order to perform high-speed operation, it is necessary to reduce the length of wiring and the time required for transmitting an electric signal. In order to reduce the length of the wiring, it is required to perform so-called high-density wiring in which the width of the wiring is reduced and the gap between the wirings is reduced.

In order to enable high-density wiring,
Wiring needs to be formed with high accuracy so that a gap between the wirings is maintained. Further, since the width and thickness of the wiring affect the characteristic impedance of the printed wiring board and affect the electrical characteristics, high-precision wiring is also required from this point. A typical example of the demand for a printed wiring board that takes into account the high density, high-precision wiring, and electrical characteristics described above is a typical example in which one or more semiconductor chips are directly mounted on the printed wiring board, and resin-sealed. Etc. to make a module, a single chip module (SC
M) or a multi-chip module (MCM).

[0004] Printed wiring boards include single-sided printed wiring boards having wiring formed only on one side, double-sided printed wiring boards having wiring formed on both sides, and so-called multilayer printed wiring boards having wiring formed on inner layers. There are various things. The number of wiring layers is determined based on the wiring density required for the printed wiring board in consideration of the width of the wiring. The insulating substrate used for the printed wiring board is made of glass cloth impregnated with an epoxy resin, a polyimide resin or the like, or a ceramic material or the like. A copper-clad laminate to which a copper foil is adhered is used.

[0005] Then, a hole is drilled in the copper-clad laminate by a method such as drilling, a conductor is formed on the inner wall of the hole by plating or the like to form a via hole, etching is performed, a wiring pattern is formed, and a wiring pattern is formed. It is manufactured by a method of providing an overcoat layer such as a solder resist for protecting the substrate. In forming the wiring pattern, either a subtractive method of forming a wiring pattern by etching after plating the entire surface as described above or an additive method of selectively plating a portion where the wiring pattern is formed as described above. Good. Also,
Instead of plating, a conductor serving as a wiring pattern may be adhered by vapor deposition or the like, but plating is generally used.

On the other hand, in order to meet the above demand for high-density wiring, a surface wiring printed wiring board (SLC) has been proposed (hereinafter, referred to as SLC) and used (electronic material, April 1991). No. 103-108). SL
In manufacturing C, a construction method generally called a build-up method is used. In this method, a printed wiring board is formed by repeating a process of forming a wiring pattern on a rigid substrate, forming an insulating layer thereon, forming a wiring pattern thereon, and further forming an insulating layer. It is to do. It is also called a surface wiring structure.

In this specification, an insulating substrate made of a hard material is referred to as a “rigid substrate”, and a rigid substrate having wiring formed on at least one surface is referred to as a “rigid wiring board”.
, And the wiring layer formed by the build-up method is referred to as “surface wiring layer”. In addition, in order to make connection between conductor layers, a hole provided through a printed wiring board and having metal deposited on the wall surface is called a "through hole", to connect between conductor layers without inserting components A hole in which a metal is deposited on a wall surface is called a "via hole". The “via holes” include those that do not penetrate the printed wiring board, generally include blind via holes, valid via holes, or those generally referred to as interstitial via holes.

Specifically, in the SLC, a photosensitive epoxy resin is used for an insulating layer, and a photo via hole is used for interlayer connection of a surface wiring layer instead of a through hole by a drill. It goes without saying that the above-described subtractive method and additive method can be applied to the formation of the wiring pattern of each layer. The rigid substrate essentially has a role as a support structure, and actual wiring is performed inside a surface wiring layer. In the above-mentioned document (Electronic Materials, April 1991, pp. 103-108), a double-sided copper-clad laminate is used, and a power supply layer is moved to a surface opposite to a first signal layer to form a surface wiring layer. Then, a structure has been proposed in which a hole is formed by drilling and a through hole is formed by copper plating.

[0009] The SLC is used to overcome the limitation of high density and the like in the method of manufacturing a multilayer printed wiring board in which a copper-clad laminate is punched, a via hole and a wiring are formed and laminated as described above. It is proposed in. In addition, the thickness of the insulating layer is reduced to avoid crosstalk noise accompanying the increase in density, and cost reduction is also considered. Specifically, it has been proposed to solve the following problems. (A) Increased cost for using thin copper foil. (B) Increase in cost for thinning the insulating layer. (C) Limit of drill diameter for processing small diameter through hole. (D) Limit of reliability of through holes with high aspect ratio due to multilayering.

A conventional method for manufacturing a printed wiring board using the build-up method will be described with reference to FIG. First, as shown in FIG. 5A, a wiring pattern 52 is formed on an insulating substrate 51 made of a rigid material such as a glass epoxy substrate. In this case, a method of forming a wiring pattern by etching using a double-sided copper-clad glass epoxy substrate may be simple. Subsequently, as shown in FIG. 5B, a photosensitive epoxy resin is applied to form an insulating layer 53, and the photosensitive epoxy resin in a portion 54 where a via hole is to be formed is exposed, developed and removed. The material of the insulating layer is not limited to the photosensitive epoxy resin, but a photosensitive material is used to facilitate processing of the via hole.

Further, the dielectric constant of the material of the insulating layer is an important parameter that affects the electrical characteristics such as the signal propagation speed of the wiring layer and the characteristic impedance of the printed wiring board. It is necessary to select a material that satisfies. Further, in forming the insulating layer, a method of applying a resin is preferable in view of the fact that the insulating layer can be formed with a uniform thickness, and a material that can be applied is generally used.

As a coating method, a curtain coating method or a spin coating method is applied. Then, FIG.
, A copper foil is formed on the insulating layer 53 by electroless plating and electrolytic plating, a via hole 55 is provided, and the formed copper foil is etched to form a wiring pattern 56.
To form At this time, the electroless plating is performed to impart conductivity to the insulating layer so that the electrolytic plating can be performed, and is formed with a thickness of about 0.3 μm.
The electrolytic plating is for obtaining a wiring pattern having a desired thickness, and is formed with a thickness of about 20 μm. This thickness is the thickness of the wiring pattern, and is determined by the magnitude of the current flowing through the printed wiring board, required electrical characteristics such as characteristic impedance, and the like.

In the case where a wiring pattern is formed by a subtractive method, it is advantageous in terms of manufacturing that a thinner wiring pattern can perform fine etching since it is thinner. Also in the case of the additive method, the thinner the wiring pattern, the smaller the variation in plating, which is advantageous.

Next, as shown in FIG.
7 is formed on the entire surface, and the via holes are exposed and developed. The method of formation may be the same as the method used in the step of FIG. Further, a through hole 5 for a through hole is formed using a drill.
8 is formed. Then, plating is performed in the same process as in FIG. 5C to form via holes 59 and through holes 60 (FIG. 5E). In this case, it is preferable that the diameter of the through hole 60 is as small as possible so as not to hinder the formation of the wiring pattern at high density. However, in the case of a through hole having a small hole diameter, that is, in the case of a high aspect ratio, it is difficult to uniformly coat the inside of the through hole. When the printed wiring board is mass-produced, the thickness of the printed wiring board at the time of forming the through hole is, for example, 1.2 mm in order to secure the reliability in consideration of plating variations.
And the diameter of the drill for forming through holes is 0.3
In the case of about mm, it is considered that it is desirable to provide a plating thickness of about 30 μm.

Subsequently, the wiring pattern 6 is etched by etching.
Form one. At this time, the copper foil on the surface opposite to the surface on which the surface wiring layer is formed is simultaneously etched to form the power supply layer pattern 62. Then, a solder resist 63 for protecting the wiring pattern 61 and the power supply layer pattern 62 is provided to complete the printed wiring board (FIG. 5F).

[0016]

However, the above method has the following problems.

First, it cannot be said that (D) the problem of the limitation on the reliability of through holes having a high aspect ratio due to multilayering has been completely solved. This is because drilling is performed to a thickness that is the sum of the thickness of the rigid wiring board and the thickness of the surface wiring layer to form a through hole, so that the aspect ratio increases and the reliability of the through hole decreases. .

The second problem is that the dimensional accuracy and density of the wiring pattern on the outermost side of the printed wiring board are reduced. That is, since the aspect ratio becomes high, in order to increase the reliability of the through hole, it is necessary to form a thick plating. However, the outermost wiring pattern 61
After forming the surface wiring layers other than the above, the wiring pattern 61 and the through hole 60 are formed simultaneously by drilling and drilling by copper plating. The thickness is adjusted to the thickness, and the wiring becomes thicker.

Then, when a wiring pattern is formed by the subtractive method, it is difficult to perform fine etching, and the dimensional accuracy of the wiring pattern is reduced. Further, it is difficult to form a high-density wiring. Even when a wiring pattern is formed by the additive method, the variation in plating becomes large, and it becomes difficult to form a wiring pattern having a uniform dimension, and the accuracy particularly in the thickness direction is reduced.
It becomes difficult to form high-density wiring. If a thick plating is to be formed only in the through hole 60, a portion other than the through hole 60 is masked and the wiring pattern 61 is formed.
It is necessary to take measures such as preventing plating from being applied on the upper surface and re-applying wiring pattern plating after removing the mask, which increases the number of steps and increases the cost.

Third, since the through-holes 60 penetrate the surface wiring layer, a large area can be used for wiring as the surface wiring layer, which hinders high-density wiring.
SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and it is an object of the present invention to provide a through-hole with high reliability, high precision, high-density wiring, and easy connection to the outside. It is to provide a multilayer printed wiring board.

[0021]

In order to solve the above-mentioned problems, a printed wiring board according to the present invention comprises a liquid resin made of glass cloth.
An insulating layer formed by curing impregnated with the scan, and a rigid substrate having a multilayer structure in which wiring layers are formed on both surfaces and the inner layer, is a liquid resin consisting of front and back the same material was coated hardened on both sides of the rigid substrate Through the insulating layer obtained by the above, a surface wiring layer provided by plating and a wiring layer provided on the rigid substrate and a surface wiring layer are connected through the insulating layer, and penetrate the rigid substrate. and via holes formed so as not to, a multilayer printed wiring board having a via hole, a connecting between the mutual wiring layer provided on the rigid substrate, mutual interconnection layer provided on the rigid substrate Are characterized in that they do not penetrate the surface wiring layers on both sides. Further, an insulating layer is formed above the via hole connecting the wiring layers provided on the rigid substrate to each other.

Further, a terminal is provided around the multilayer printed wiring board, and a lead for external connection is electrically connected to the terminal.

[0023]

According to the present invention, since the via holes connecting the wiring layers provided on the rigid substrate do not penetrate the surface wiring layer, the aspect ratio can be reduced.

Further, the plating thickness in the through hole does not affect the thickness of the wiring of the surface wiring layer, and the wiring of the surface wiring layer does not become thick.

Further, the via holes connecting the wiring layers provided on the rigid substrate do not consume the wirable area of the surface wiring layer.

[0026]

Hereinafter, the present invention will be described in more detail with reference to basic examples and examples.

[Basic Example] A basic example will be described with reference to FIG. First, as shown in FIG.
A double-sided copper-clad laminate 3 having a copper foil 2 having a thickness of about 12 μm adhered to both sides of a substrate 1 having a thickness of 1.0 mm impregnated with a T resin (bismaleimide-triazine resin) was prepared. Drilling was performed using a 0.30 mm drill, plating was performed in the hole to a thickness of 25 μm, plating layer 4 was provided, and via hole 5 was formed. Then, as shown in FIG. 1B, both surfaces were etched to form a wiring pattern 6 and a rigid wiring board 7 was formed. In FIGS. 1B to 1E, the copper foil 2 and the plating layer 4 are shown integrally, and the boundaries are not shown. The rigid wiring board only needs to have wirings formed on both sides, and it is a matter of course that a multilayer wiring board having wirings formed on inner layers may be used.

Then, a step of forming a surface wiring layer was performed to form a surface wiring layer on both surfaces of the rigid wiring board 7. As described above, in order to mount an element such as a semiconductor chip on both sides of the printed wiring board, a pattern is required on both sides of the printed wiring board. Then, in order to perform higher-density wiring, a surface wiring layer may be formed on both surfaces of the rigid wiring board 7. Therefore, in this basic example , surface wiring layers are formed on both surfaces of the rigid wiring board 7.

The step of forming the surface wiring layer will be described.

First, from the state of FIG. 1B, a wiring pattern 6 formed on a rigid substrate by etching,
A blackening treatment was performed to improve the adhesion to the insulating layer 8 formed thereon. For the blackening treatment, for example, an aqueous solution of sodium chlorite, an aqueous solution of potassium persulfate or the like is used. In this basic example , the blackening process was performed under the following conditions.

Composition of treatment liquid: NaOH 21 g /
1 Na ₃ PO ₄ .12H ₂ O 17 g / l NaClO ₂ 43 g / l Temperature of processing solution: 90 ° C. Processing time: 270 seconds

Next, description will be made with reference to FIG. After the above blackening treatment, the insulating layer 8 was formed. As the material of the insulating layer, a material having high insulation properties and a low dielectric constant is preferable, and a photosensitive resin such as an epoxy resin or a polyimide resin is preferable because fine processing can be easily performed. For example, Provimer 52 (manufactured by Ciba-Geigy Japan; trade name) can be applied. As a forming method, application was performed by a curtain coat method, and temporary drying was performed to blow off the solvent.

Here, if an insulating layer is not formed also on the upper portion 9 of the via hole, it is impossible to form a surface wiring layer on that portion, which becomes an obstacle to high-density wiring. In order to form the insulating layer in the hole, there is a method in which screen printing is performed using a solder resist ink having high viscosity, and printing is performed a plurality of times as necessary. By using this method, a film of ink can be formed in a hole in a tent shape, which is described in, for example, JP-A-64-22096. When the pore size is small, it can be achieved by using a curtain coating method to make the viscosity of the material appropriate. The viscosity needs to be set more accurately as the hole diameter is larger. However, when the drill diameter is about 0.3 mm, the viscosity may be about 300 to 800 poise by the curtain coating method. In addition, before forming the insulating layer, it is a matter of course that a step of filling the via holes formed in the rigid wiring board with a paste or the like by using a method such as screen printing may be performed.

After the insulating layer 8 was formed as described above, a mask having a desired via hole pattern formed thereon was overlaid, exposed and developed, and the insulating layer in the via hole forming portion was removed. The removing means is not limited to exposure and development. For example, processing may be performed using a laser such as a carbon dioxide laser or a method of forming a resist and performing dry etching. Then, baking was performed to completely cure the insulating layer. Thereafter, the surface was polished to eliminate surface irregularities. The reason for performing this step is that if the insulating layer is curtain-coated,
Irregularities occur in the insulating layer in the existing and non-existing portions of the wiring of the underlying layer, but by repeating the build-up process, the irregularities are accumulated, and plating and etching are difficult to perform in the wiring pattern forming process. This is because of such obstacles.

Then, the surface of the insulating layer was roughened by immersion treatment in a 55 g / l potassium permanganate solution for 5 minutes. This step is a process for improving the adhesion between the insulating layer and the plating layer. Subsequently, electroless plating was performed to form a copper foil having a thickness of 20 μm on the entire surface of the insulating layer. At this time, it is needless to say that plating is performed also in the concave portion which will be a via hole and is formed by exposure and development. Then, similarly to the wiring forming step of the printed wiring board, a resist was coated, exposed, developed, and etched to form a wiring pattern 10 on the copper foil.

In order to form a surface wiring layer on both surfaces of the rigid wiring board, the above steps were performed on both surfaces.
In the developing step and the plating step, the treatment on both sides can be performed simultaneously. It is preferable to use the same material for the insulating layers on both surfaces from the viewpoint of the manufacturing process.

Through these steps, four wiring layers were formed together with the wiring on both surfaces of the rigid wiring board. Further, by repeating the steps after the above-described blackening step, a desired number of surface wiring layers can be obtained. An electrode 11 used for external connection was formed around one side of the printed wiring board. Even if the electrodes are formed at the same time as forming the outermost wiring layer 10 as in the basic example , the electrodes are formed at the time of the step of FIG. Alternatively, the surface wiring layer may be formed inside the electrode. After a nickel plating layer having a thickness of about 3 to 5 μm is formed on the electrode 11 to enhance surface protection and connection reliability, a noble metal plating layer such as gold having a thickness of about 0.3 to 0.5 μm is formed. Is preferably formed.

Thereafter, as shown in FIG. 1D, solder resists 12 were formed on both surfaces. The same material as the insulating layer may be used. For example, Provimer 52 (trade name, manufactured by Nippon Ciba Geigy Co., Ltd.) of the above example can be applied, and it can be formed by the same method as the insulating layer. Through such steps, the printed wiring board was completed. Note that a lead may be connected to the electrode 11 for connection to the outside. For example, the lead 13 and the connection terminal 11 of the wiring board were connected using solder. The means for connection is not particularly limited as long as the two are electrically connected, and wire bonding, thermocompression bonding, laser bonding, connection using a conductive paste, or the like can be applied.

The lead 13 can be made of the same material as a lead frame used in a conventional integrated circuit.
The same applies to the shape, as long as the printed wiring board can be arranged at the center. Of lead frame,
After forming the base plating such as nickel plating on the inner lead corresponding to the connection part with the printed wiring board,
It is preferable to perform plating of silver, palladium or the like. In addition, it is preferable that the other parts are subjected to solder plating or the like to increase resistance to oxidation or the like. FIG. 1 (e) shows a semiconductor chip 16 mounted on a printed wiring board prepared in the above-described process, connected to a wiring pattern on the printed wiring using gold wires 14, and a sealing resin such as an epoxy resin. This is a semiconductor device produced by performing resin sealing using No. 15.

Embodiment 1 Referring to FIG. 2,
Two double-sided copper-clad laminates each having 18 μm-thick copper foil adhered to both sides of a 0.3 mm-thick base material impregnated with BT resin (bismaleimide-triazine resin) in a glass cloth 2
Prepare 1, 22 and for each, 0.30m in diameter
Holes were drilled using a drill having a thickness of 25 μm, and via holes 23 and 24 were formed in the holes by plating with a thickness of 25 μm. Then, only one side was exposed, developed, and etched to form wiring patterns 25 and 26, thereby producing two double-sided wiring boards. Then, the prepreg 29 was sandwiched between the two double-sided wiring boards to perform lamination. At this point, the melted prepreg 29 is contained in the via holes 23 and 24.
Flowed in and filled. Then, a hole is drilled using a 0.35 mm drill, and plating is applied in the hole to a thickness of 25 μm.
To form a via hole 30. Further, both sides are exposed, developed and etched to form wiring patterns 27 and 28.
Was formed.

Thus, the rigid wiring board 31 having the four wiring layers shown in FIG. 2 was prepared. And then Figure 3
As shown in (1), a surface wiring layer 32 and an electrode 33 were formed on one side of a rigid wiring board 31 using the same method as in the basic example . Then, a solder resist 34 was formed on both surfaces.
In this way, a printed wiring board can be obtained.

Example 2 A lead 35 was joined to an electrode 33 by thermocompression bonding using the printed wiring board manufactured in Example 1 . Thus, a printed wiring board as shown in FIG. 4 was obtained.

[0043]

According to the present invention, since the aspect ratio can be reduced, the reliability of the through hole is improved. In addition, the wiring of the surface wiring layer does not become thick, and the via holes connecting the wiring layers provided on the rigid substrate do not consume the wirable area of the surface wiring layer. High-density wiring becomes possible. Further, terminals are provided around the multilayer printed wiring board,
Since a lead for external connection is electrically connected to the terminal, connection to the outside can be easily performed. A multilayer printed wiring board having the above-described excellent effects can be obtained.

[0044]

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a printed wiring board according to a basic example of the present invention and a semiconductor device using the same in a manufacturing process order.

FIG. 2 is an explanatory diagram of a rigid board portion of the printed wiring board according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of the printed wiring board according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram of a printed wiring board according to a second embodiment of the present invention.

FIG. 5 is an explanatory view showing an example of a method for manufacturing a printed wiring board using a conventional build-up method.

Claims (3)

(57) [Claims] 1. A rigid substrate having a multilayer structure in which an insulating layer obtained by impregnating a liquid resin into a glass cloth and hardening is used, and a wiring layer is formed on both surfaces and an inner layer, and both surfaces of the rigid substrate are made of the same material on both sides. Through an insulating layer obtained by applying and curing a liquid resin, a surface wiring layer provided by plating, and a wiring layer provided on a rigid substrate and a surface wiring layer, penetrating the insulating layer. connect Te, and the via holes formed so as not to penetrate the rigid substrate, met multilayer printed wiring board having a via hole, a connecting between the mutual wiring layer provided on the rigid substrate
And a via hole for connecting the wiring layers provided on the rigid board does not penetrate the surface wiring layers on both sides. 2. The multilayer printed wiring board according to claim 1, wherein an insulating layer is formed above the via holes connecting the wiring layers provided on the rigid substrate. 3. The multilayer printed circuit according to claim 1, wherein a terminal is provided around the multilayer printed wiring board, and a lead for external connection is electrically connected to the terminal. Wiring board.