JPH1093242A - Printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printed wiring board which has a structure such that through-wiring path may be constituted of conductor bumps, and which is free of an interfacial peel-off which can be caused easily, in an interface between an end face of each conductor bump and a part of a conductor pattern to be electrically connected to the end face of the conductor bump by a difference between coefficients of linear expansion of the constituent materials of the bump and the pattern, and which can have high reliability in both the mechanical and electrical connections. SOLUTION: In a printed wiring board provided with insulating material layers 2, conductor bumps 3 which pass through the insulating material layers 2 and form wiring path, conductor patterns 6a which, being located airtightly on the surface of the insulator material layer 2, have sections 22 to be electrically connected to end faces 4 of the conductor bumps 3. The sections 22 are as large as or less than the size of the end faces 4 and are located within the projected images, which are obtained by projecting the end faces 4 in the direction of the conductor bumps 3 passing through the insulator layers 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board capable of ensuring the reliability of mechanical and electrical connections.

[0002]

2. Description of the Related Art As is well known, recently, there has been an increasing demand for smaller, lighter, faster, multifunctional, and more reliable electronic devices. For these reasons, high integration and high speed of semiconductor integrated circuit elements incorporated in electronic devices are being promoted.

When a semiconductor integrated circuit device is incorporated in an electronic device, the semiconductor integrated circuit device is usually packaged, these packages are mounted on a printed wiring board, and the printed wiring substrate is incorporated in the electronic device. The method is adopted. In this case, if the influence of the electric signal propagation delay due to the wiring between the packages via the printed wiring board cannot be neglected as compared with the electric signal propagation delay inside the semiconductor integrated circuit element, the performance of the electronic device is thereby limited. It could be bundled. That is, even if the integration degree and speed of the semiconductor integrated circuit element are increased, if the electric signal propagation delay of the wiring path passing through the printed wiring board is large, the performance of the electronic device is determined by the propagation delay. .
Therefore, a wiring board technology that achieves high-density mounting and high-speed signal transmission is indispensable.

[0004] For these reasons, recently, there has been proposed a printed wiring board having a structure that can be easily multilayered unlike conventional printed wiring boards. This newly proposed printed wiring board,
A multi-layer structure can be realized without a drilling step or a complicated plating step. For example, a four-layer structure is configured as shown in FIG.

That is, the printed wiring board 1 includes an insulating material layer 2, a conductive bump 3 that penetrates the insulating material layer 2 to form a wiring path, and a conductive material that is disposed in close contact with the surface of the insulating material layer 2. A conductor pattern 6 having a portion 5 electrically connected to the end face 4 of the body bump 3 is used as a basic element 7, and a plurality of the basic elements 7 are stacked.

Here, a method of manufacturing the printed wiring board 1 will be briefly described with reference to FIG. First, FIG.
As shown in (a), for example, an electrolytic copper foil 1 having a thickness of 20 μm
Prepare 1 Next, on the upper surface of the electrolytic copper foil 11 in the drawing,
For example, with a thickness of 200 μm and 0.3 mm
Positioning is performed by applying a stainless metal mask having a plurality of holes having a diameter. Next, using a hole provided in the metal mask, for example, a silver-based conductive paste is printed on the upper surface of the electrolytic copper foil 11 in the drawing. After this conductive paste was dried, the conductive paste was printed again at the same position using the same metal mask and dried, and this operation was repeated as many times as necessary, so that the height of the upper surface of the electrolytic copper foil 11 in the figure was 200 μm. Conductor bumps 12 are formed to a degree. Of course, the conductor bumps 12 can be formed in a single printing process.

Next, a synthetic resin sheet 13 having a thickness of, for example, 150 μm, for example, in which glass cloth is impregnated with an epoxy resin, is placed on the side from which the conductive bumps 12 protrude. A patch plate made of a silicone rubber plate with a thickness of about 3 mm is placed on top. Next, the laminate is set on a press device equipped with a heating, pressurizing and cooling mechanism. And then cooled.

By the above-mentioned heating, pressing and cooling steps,
As shown in FIG. 5B, a laminate 14 in which each conductive bump 12 penetrates the synthetic resin sheet 13 is obtained. Next, an electrolytic copper foil 15 having a thickness of, for example, 20 μm is placed on the upper surface of the laminated body 14, that is, on the side from which the tip of the conductive bump 12 protrudes, and a rigid backing plate is placed thereon. Next, this laminate is set on a press device having a heating, pressurizing and cooling mechanism, and while the whole is heated to, for example, 170 ° C., the electrolytic copper foil 15 is pressed against the laminate 14 via a backing plate. After a certain time, cool slowly.

By this step, as shown in FIG. 5C, both sides are covered with copper foil, and the conductive bumps 1 are formed between the copper foils on both sides.
2 to obtain the printed wiring board elements 16 electrically connected to each other. Next, as shown in FIG. 5 (d), the copper foil on both sides is processed into a required shape by etching, and the conductor pattern 1 is formed.
7 is formed. Therefore, when corresponding to FIG. 3, the synthetic resin sheet 13 corresponds to the insulating material layer 2, the conductor bumps 12 correspond to the conductor bumps 3, and the conductor patterns 17 correspond to the conductor patterns 6.

FIG. 3 shows a printed wiring board 1 having a four-layer structure.
However, when the printed wiring board 1 is formed, the laminate 14 shown in FIG. 5B is provided on both sides of the element shown in FIG. 1
Each of the laminates 14 is pressed so as to come in contact with 7 and is heated to a predetermined temperature. In this state, each of the laminates 14 is pressed and gradually cooled after a certain period of time. The copper foil present on both sides of the laminate thus obtained is processed into a required shape by etching to form the conductor pattern 6. With such a structure in which the through wiring path is formed by the conductive bumps 3, a multilayer printed wiring board can be easily manufactured by the above-described method.

However, the following problems still remain in the printed wiring board configured as described above.
That is, when mounting a semiconductor package on a printed wiring board capable of such high-density mounting, the surface mounting form,
Specifically, BGA (Ball Grid Ar) using solder bumps
ray) configuration. In this BGA configuration, solder bumps are provided on the respective electrodes provided on the semiconductor package side, and these solder bumps are brought into contact with the respective electrode patterns provided on the printed wiring board. A method of melting and mechanically and electrically connecting the bumps is adopted.

During such a reflow process, the printed wiring board is heated to a high temperature. At this time, there is no particular problem if the linear expansion coefficients of the constituent materials of the insulating material layer 2, the conductive bumps 3, and the conductive patterns 6 match, but these constituent materials usually have different linear expansion coefficients. Therefore, thermal stress is generated at the interface between the constituent materials due to the difference in the coefficient of linear expansion.

In the conventional printed wiring board 1, the portion 5 of the conductor pattern 6 electrically connected to the end face 4 of the conductor bump 3 is formed to be larger than the end face 4. There is a possibility that a large thermal stress may be generated at the interface 21 of the substrate. That is, when the insulating material layer 2 is formed of, for example, a glass epoxy resin, the linear expansion coefficient of this material in the thickness direction at 200 ° C. (the thickness direction of the printed wiring board) is 15 × 10 ^−5.
(1 / ° C). On the other hand, when the conductor bump 3 is formed of a silver paste, the linear expansion coefficient of this material in the thickness direction at 200 ° C. is 3 × 10 ⁻⁵ (1 / ° C.). Therefore, in the combination of the glass epoxy resin and the silver paste, a large thermal stress is generated at the interface 21 at the time of the reflow treatment, such that the portion 5 is peeled off from the end face 4 due to a difference in the coefficient of linear expansion. As a result, the reliability of mechanical and electrical connections may be reduced. This is not limited to the combination of the glass epoxy resin and the silver paste, but the same problem may occur in common with the combination of the insulator and the conductor.

[0014]

As described above, in a conventional printed wiring board adopting a structure in which a through wiring path is formed by a conductive bump, a difference in the coefficient of linear expansion of a constituent material causes a problem. In particular, at the time of the solder reflow treatment, interface separation occurs at the interface between the end face of the conductor bump and the portion connected to the end face of the conductor pattern, and there is a concern that the reliability of mechanical and electrical connection may be reduced. .

It is an object of the present invention to provide a printed wiring board which can effectively solve the above-mentioned disadvantages and thereby maximize the features of the structure in which the through wiring path is formed by the conductive bumps. .

[0016]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides an insulating material layer, a conductor bump penetrating the insulating material layer to form a wiring path, and a surface of the insulating material layer. And a conductive pattern having a portion electrically connected to an end face of the conductive bump, the conductive pattern being electrically connected to the conductive bump of the conductive pattern. The portion is not larger than the size of the end face, and is located in a projected image obtained by projecting the end face in a direction in which the conductive bump penetrates.

It is to be noted that some or all of the portions of the conductor pattern that are electrically connected to the conductor bumps may be partially or entirely embedded in the end surface portions of the conductor bumps. Good.

In the printed wiring board according to the present invention, the portion of the conductor pattern electrically connected to the end face of the conductor bump has a size equal to or smaller than the size of the end face of the conductor bump, and It is located in the projected image obtained by projecting in the penetrating direction of the conductor bump. Therefore, even if the linear expansion coefficient in the thickness direction of the constituent material of the insulating material layer and the constituent material of the conductor bump are different, the portion electrically connected to the end face of the conductor bump and the end face of the conductor pattern A large thermal stress can be prevented from being generated at the interface with the substrate. As a result, reliability after the solder reflow process can be ensured.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a four-layer printed wiring board 1a according to an embodiment of the present invention. In this figure, the same functional parts as those in FIG. 3 are indicated by the same reference numerals. This printed wiring board 1a is formed by the method described with reference to FIG.

The printed wiring board 1a according to this embodiment is different from the conventional printed wiring board in that a portion 22 which is closely attached to the surface of the insulating material layer 2 and is electrically connected to the end face 4 of the conductor bump 3 is provided. In the structure of the conductive pattern 6a. Specifically, it is at the size and position of the portion 22. That is,
The portion 22 has a size equal to or smaller than the size of the end face 4 and is located in a projected image obtained by projecting the end face 4 in a direction in which the conductive bump 3 penetrates. In this example, the portion 22 is provided so as to have the same size as the size of the end face 4 and not protrude from the projected image of the end face 4.

The shape of the portion 22 electrically connected to the end face 4 of the conductor bump 3 is not limited, but a circle is usually employed. The formation of the conductor pattern 6a is performed by partially printing the etching resist ink on the conductive metal foil and masking the portion to be the conductor pattern, as described partially with reference to FIG. Is used as an etching solution, followed by removing the resist mask. At this time, the portion 22 which is in contact with and electrically connected to the end face 4 of the conductor bump 3 is smaller than the size of the end face 4 and the end face 4 is projected in the penetrating direction of the conductor bump 3. By setting the size and position of the mask so as to make contact with each other in the obtained projected image, the conductive pattern 6a satisfying the above-described conditions can be formed.

With such a structure, the portion 22 of the conductor pattern 6a that is electrically connected to the end face 4 of the conductor bump 3 is located only within a range facing the end face 4 of the conductor bump 3. Will be. Therefore, the insulating material layer 2
Even if the constituent material of the conductive bump 3 and the constituent material of the conductor bump 3 have different linear expansion coefficients in the thickness direction, a large thermal stress is generated at the interface 21 between the end face 4 and the portion 22 of the conductor bump 3 due to this difference. Nothing happens. That is, even in a high-temperature atmosphere, a large thermal stress does not act on the portion 22 to peel the portion 22 from the end face 4. Therefore, mechanical and electrical reliability after the solder reflow process can be ensured.

FIG. 2A shows a schematic structure of a printed wiring board 1b having a four-layer structure according to another embodiment of the present invention. In this figure, the same functional parts as those in FIG. 1 are indicated by the same reference numerals. This printed wiring board 1b is also formed by the method described with reference to FIG.

The printed wiring board 1b according to this embodiment is different from the printed wiring board 1a shown in FIG. 1 in that the printed wiring board 1b is closely attached to the surface of the insulating material layer 2 and is electrically connected to the end face 4 of the conductor bump 3. In the structure of the conductor pattern 6b having the portion 23 which is formed. Specifically, it is at the size and position of the portion 23.

That is, the portion 23 is smaller than the size of the end face 4 and is located within a range facing the end face 4. Then, of the portions 23, those located in the printed wiring board 1b are, as shown in FIG.
Are provided so as to be partially or wholly embedded in the end face portion.

With such a structure, a portion 23 of the conductor pattern 6b electrically connected to the end face 4 of the conductor bump 3 is smaller than the end face 4 of the conductor bump 3,
In addition, the end face 4 is located in a projected image obtained by projecting the end face 4 in the penetrating direction of the conductive bump 3. For this reason, even if the linear expansion coefficients in the thickness direction of the constituent material of the insulating material layer 2 and the constituent material of the conductor bump 3 are different, the difference between the end face 4 of the conductor bump 3 and the portion 23 is caused by this difference. The generation of a large thermal stress at the interface 21 can be suppressed. Therefore, mechanical and electrical reliability after the solder reflow process can be ensured.

The conductor bump 3 is made of, for example, silver,
Conductive powders such as gold, copper, solder powders, alloy powders or composite (mixed) metal powders thereof, and binder components such as polycarbonate resin, polysulfone resin, polyester resin, phenoxy resin, phenol resin, and polyimide resin. A conductive composition prepared by mixing
Alternatively, it can be made of a conductive metal or the like. When the conductive bump 3 is formed of a conductive composition, a bump having a high aspect ratio can be formed by, for example, a printing method using a relatively thick metal mask, and the bump has a general height. About 100 μm to 400 μm is desirable. The material for forming the insulating material layer 2 includes epoxy resin, bismaleimide triazine resin, polyimide resin, phenol resin, polyester resin, melamine resin, butadiene rubber, butyl rubber, natural rubber,
Examples include sheets of raw rubber such as neoprene rubber and silicone rubber. These synthetic resins may be used alone or may contain an insulating inorganic or organic filler, and are further combined with a reinforcing material such as glass cloth or mat, organic synthetic fiber cloth or mat, or paper. It may be a sheet. In addition, as a material for forming the conductor patterns 6a and 6b, an electrolytic copper foil is often used. Although FIGS. 1 and 2 illustrate a four-layer printed wiring board, the present invention is also effective for a double-sided board or a multilayer board other than the four-layer board.

[0028]

As described above, according to the present invention,
Even if the materials constituting the insulating material layer, the conductive bumps, and the conductive pattern have different linear expansion coefficients, due to this difference, the end face of the conductive bump and the end face of the conductive pattern are electrically connected. Thermal stress easily generated at the interface with the part to be electrically connected can be reduced, so that the reliability of mechanical and electrical connection can be ensured.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a printed wiring board according to an embodiment of the present invention.

2A is a schematic cross-sectional view of a printed wiring board according to another embodiment of the present invention, and FIG. 2B is an enlarged perspective view showing a portion B in FIG.

FIG. 3 is a schematic sectional view of a conventional printed wiring board.

FIG. 4 is a view taken along the line AA in FIG. 3 and viewed in the direction of the arrow.

FIG. 5 is a view for explaining an example of a method of manufacturing the printed wiring board shown in FIG.

[Explanation of symbols]

 1a, 1b ... printed wiring board 2 ... insulating material layer 3 ... conductor bump 4 ... end face 5a, 6b ... conductor pattern 21 ... interface 22, 23 ... part electrically connected to the end face

Claims (2)

[Claims] 1. An insulating material layer, a conductive bump penetrating the insulating material layer to form a wiring path, and electrically connected to an end face of the conductive bump disposed closely on a surface of the insulating material layer. A conductive pattern having a portion to be electrically connected to the conductive bumps of the conductive pattern, the portion having a size equal to or less than the size of the end face, and A printed wiring board, wherein the printed wiring board is located in a projected image obtained by projecting an end face in a direction in which the conductor bump penetrates. 2. Some or all of the portions of the conductor pattern that are electrically connected to the conductor bumps are partially or entirely embedded in the end surface portions of the conductor bumps. The printed wiring board according to claim 1, wherein: