Wiring board, multilayer wiring board, and method for manufacturing the same

A method for manufacturing a wiring board comprising an insulating member, comprising: a penetrating hole formation process of forming a penetrating hole in the insulating member; a placement process of inserting a conductive connecting particle into the penetrating hole; a connecting particle pressing process of disposing the conductive layers on both surfaces of the insulating member, pressing the conductive layers toward the connecting particle in the penetrating hole, and deforming the connecting particle in the pressing direction to obtain the connecting member; and a patterning process of patterning the conductive layers, wherein, in the connecting particle pressing process, the pressing is performed such that the cross-sectional area in the direction along the insulating member surface of at least a portion of the connecting member is greater than the contact area of the connecting member with the conductive layers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wiring board in which conductive layers are formed on both surfaces of an insulating member, a multilayer wiring board in which an outer-layer wiring substrate is stacked onto at least one side of a wiring board, and a method for manufacturing these boards.

Priority is claimed from Japanese Patent Application No. 2005-110653, filed Apr. 7, 2005, the content of which is incorporated herein by reference.

2. Description of the Related Art

FIG. 27shows an example of a conventional multilayer wiring board. In the multilayer wiring board shown in this figure, outer-layer wiring substrates110are formed on both sides of the wiring board100A.

In the wiring board100A, conductive layers102are formed on both sides of the insulating member101having a penetrating hole (through-hole)103. Openings are formed in the conductive layers102at positions corresponding to the penetrating hole103. The conductive layers102are connected together by a conductive layer105formed on the surfaces of the conductive layers102and on the inner surface of the penetrating hole103.

The outer-layer wiring substrates110comprise an insulating layer107in contact on one side with the conductive layer105, and a conductive layer106formed on the other side of the insulating layer107.

As shown inFIG. 28andFIG. 29, in order to manufacture this multilayer wiring board, after using laser machining, drilling or the like to form the penetrating hole103in the insulating member101, a plating method is used to form the conductive layer105on the surfaces of the conductive layers102and on the inner surface of the penetrating hole103, followed by formation of the insulating layers107and conductive layers106.

FIG. 30shows another example of a conventional multilayer wiring board. The multilayer wiring board shown inFIG. 30has outer-layer wiring substrates110formed on both surfaces of a wiring board100B.

The wiring board100B has conductive layers102aand102bformed on the both surface of the insulating member101which has an opening104(via). An opening is formed in the conductive layer102aat a position corresponding to the opening104. A conductive layer108is formed on the surface of the conductive layer102aand on the inner surface of the opening104. The conductive layer108formed on the conductive layer102bwithin the opening104and thus the conductive layers102aand102bare connected.

As shown inFIG. 31andFIG. 32, to manufacture this multilayer wiring board, after using laser machining or the like to form the opening104in the insulating member101, a plating method is used to form the conductive layer108on the surface of the conductive layer102aand on the inner surface of the opening104, and then the insulating layer107and conductive layer106are formed.

However, because the penetrating hole103and opening104remain opened in this multilayer wiring board, there is the possibility that a recess may be generated in the conductive layer106in the portion corresponding to this penetrating hole103and opening104. If a recess is generated in the conductive layer106, it becomes difficult to mount an electronic component or the like in this portion, and the component mounting density is reduced, which is a disadvantage from the standpoint of reducing size and thickness.

In the wiring board100B, the conductive layer108formed by a plating method is also formed on the surface of the conductive layer102ain addition to the inner surface of the opening104. Consequently, in the wiring board100B, the conductive layer is thick, and formation of fine wiring patterns is difficult.

FIG. 33shows an example of a wiring board which may be used in a multilayer wiring board. In this wiring board100C, the conductive layer109is formed on the surface of the conductive layer102aand in the opening104, and the conductive layers102aand102bare connected by the conductive layer109. The conductive layer109is formed so as to fill the opening104, and accordingly the surface is flat.

When forming the conductive layer109by a plating method, the layer may be formed by continuing the supply of metallic material until the opening104is completely filled.

Because the surface of the conductive layer109is flat in a multilayer wiring board which uses this wiring board100C, there is the advantage that recesses are not generated in the conductive layer of the outer-layer wiring substrate formed on the top.

However, in such a multilayer wiring board, the conductive layer109must be formed so as to fill the opening104, and thus an increase in the thickness for the conductive layer109is unavoidable. As a result, formation of a fine pattern in the conductive layer109is difficult. Further, the conductive layer109is thick and the overall thickness is increased, which are disadvantageous for the reduction in the size and the thickness of the electrical/electronic apparatus.

Techniques relating to a variety of the above multilayer wiring boards are described in Kiyoshi Takagi, Birudoappu Tasou Purinto Haisenban Gijutsu, Nikkan Kogyo Shimbunsha.

SUMMARY OF THIS INVENTION

The present invention was conceived based on the above circumstances, and has as an aspect the provision of a wiring board, a multilayer wiring board using this wiring board, and a manufacturing method for these boards, which enables finer wiring patterns formed in conductive layers, while also raising the mounting density of components on the surfaces of conductive layers, by this means enabling greater thinness and compactness.

A method for manufacturing a wiring board according to a first exemplary, but nonlimiting, aspect of the invention is a method for manufacturing a wiring board having an insulating member having a penetrating hole; and conductive layers formed on both surfaces of the insulating member, and a conductive connecting member connecting the two conductive layers together is provided inside the penetrating hole; the method of manufacture includes a penetrating hole formation process of forming the penetrating hole in the insulating member, a placement process of inserting a conductive connecting particle into the penetrating hole, a connecting particle pressing process of placing the conductive layers on both surfaces of the insulating member, pressing the conductive layers toward the connecting particle in the penetrating hole, and deforming the connecting particle in the pressing direction to obtain the connecting member, and a patterning process of patterning the conductive layers; and, in the connecting particle pressing process, the pressing is performed such that the cross-sectional area in the direction along the insulating member surface of at least a portion of the connecting member is greater than the contact area of the connecting member with the conductive layers.

A method for manufacturing a wiring board according to a second exemplary, but nonlimiting, aspect of the invention is the above method of manufacture, in which, in the placement process, the dimension of the connecting particle in the insulating member thickness direction is larger than the thickness of the insulating member.

A method for manufacturing a wiring board according to a third exemplary, but nonlimiting, aspect of the invention is the above method of manufacture, in which, after the pressing process, the contact area of the connecting member with the conductive layers is greater than the contact area of the connecting particle with the conductive layers prior to the pressing process.

A method for manufacturing a wiring board according to a fourth exemplary, but nonlimiting, aspect of the invention is the above method of manufacture, in which, in the penetrating hole formation process, the penetrating hole is formed such that the inner diameter at one end is greater than the size of the connecting particle, and the inner diameter at the other end is smaller than the size of the connecting particle.

A method for manufacturing a multilayer wiring board according to a fifth exemplary, but nonlimiting, aspect of the invention is a method for manufacturing a multilayer wiring board in which one or more outer-layer wiring substrates is stacked onto a wiring board having an insulating member having a penetrating hole; and conductive layers formed on both surfaces of the insulating member, and a conductive connecting member connecting the conductive layers together is provided in the penetrating hole; the method of manufacture includes an outer-layer wiring substrate pressing process of placing an outer-layer wiring substrate on at least one surface of a wiring board obtained by one of the above manufacturing methods, and, by pressing the outer-layer wiring substrate toward the wiring board, connecting the outer-layer wiring substrate to the wiring board; and the pressing pressure in the outer-layer wiring substrate pressing process is made lower than the pressing pressure in the connecting particle pressing process.

A method for manufacturing a multilayer wiring board according to a sixth exemplary, but nonlimiting, aspect of the invention is the above method of manufacture, in which outer-layer wiring substrates are stacked onto both surfaces of the wiring board, and the number of outer-layer wiring substrates provided on one surface of the wiring board is equal to the number of outer-layer wiring substrates provided on the other surface.

A method for manufacturing a multilayer wiring board according to a seventh exemplary, but nonlimiting, aspect of the invention is the above method of manufacture, in which outer-layer wiring substrates are provided with an outer-layer side conductive layer of silver foil on one surface of the insulating layer having an opening, and the opening is filled with conductive paste so as to effect connection to the outer layer-side conductive layer.

A wiring board according to an eighth exemplary, but nonlimiting, aspect of the invention has conductive layers formed on both sides of an insulating member having a penetrating hole, with a conductive connecting member provided in the penetrating hole to connect the conductive layers together, and with at least a portion of the connecting member having cross-sectional area in the direction along the insulating member surface greater than the area of contact with the conductive layers.

A multilayer wiring board according to a ninth exemplary, but nonlimiting, aspect of the invention has an outer-layer wiring substrate stacked onto at least one surface of the above wiring board; the outer-layer wiring substrate is provided with an outer layer-side conductive layer of silver foil on one surface of an insulating layer having an opening, and the opening is filled with a conductive paste so as to be connected to the outer layer-side conductive layer.

In a method for manufacturing a wiring board in an exemplary, nonlimiting aspect, of the present invention, a connecting particle is deformed into a connecting member by pressing a conductive layer. At this time, pressing is performed such that the cross-sectional area of at least a portion of the connecting member is greater than the area of contact of the connecting member with a conductive layer.

By this, sufficient pressing pressure may be applied to the conductive layer, so that the surface may be made flat, and consequently the component mounting density on the conductive layer surface may be increased. Further, since the conductive layer may be formed thinner compared with cases in which a plating method is used to form a conductive layer in the opening, fine wiring patterns may be formed.

Consequently, the degree of flexibility in design may be increased, and an electrical/electronic apparatus employing this wiring board may be made thinner, more compact, and lighter in weight.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a first nonlimiting exemplary embodiment of a method for manufacturing a multilayer wiring board of the present invention is explained.

First, a method for manufacturing a wiring board10is explained.

As shown inFIG. 1, an insulating member1, in a plate shape and formed from an insulating material, is provided. The insulating member1may use, for example, at least one of a polyimide resin, an epoxy resin, an LCP (liquid crystal polymer) resin, a glass epoxy, an aramid fiber, and Teflon®. However, one of skill in the art would recognize that other suitable insulating materials may be used.

By means of laser machining, drilling or the like, a penetrating hole (through-hole)3is formed in the insulating member1. A CO2laser, YAG laser, or the like may be used in laser machining.

The penetrating hole3may be formed with the inner diameter at one end (the inner diameter at one surface1aof the insulating member1) larger than the size of the connecting particle4, and with the inner diameter at the other end (the inner diameter at the other surface1b) smaller than the size of the connecting particle4so that the connecting particle4may be prevented from dropping out of the penetrating hole3. In the example shown, the penetrating hole3is formed with a tapered shape, in which the inner diameter gradually becomes smaller from one end to the other end.

The process of forming a penetrating hole3in the insulating member1is referred to as the penetrating hole formation process.

Next, the connecting particle4may be placed into the penetrating hole3, as shown inFIG. 2.

As the connecting particle4, a particle of a conductive metal, such as copper, aluminum, chromium, titanium, or another metal is used. In particular, a copper or a copper alloy may be used so that the conductivity with the inner layer-side conductive layer2is increased. For example, the connecting particle4be formed from high-purity copper; for example, copper of a purity of 99% or higher may be used.

There are no particular limitations on the shape of the connecting particle4, and shapes such as, for example, a substantially spherical shape, a substantially ellipsoidal shape, a substantially columnar shape, a substantially polyhedral columnar shape, a substantially conic shape, and a substantially pyramidal shape, may be used. In particular, however, a shape may be used such that in the pressing process described below, the contact area with the inner layer-side conductive layer2is greater than that before pressing.

Of these shapes, a shape such that a point contact is established with the inner layer-side conductive layer2, such as, for example, a substantially spherical shape, may be used. By adopting this shape, the amount of deformation in the pressing process when the connecting particle4becomes the connecting member5is large, and thus the electrical resistance between the inner layer-side conductive layers2and the connecting member5may be reduced and the bonding strength may be increased.

Also the dimension of the connecting particle4in the direction of thickness of the insulating member1may be greater than the thickness of the insulating member1. In the example shown, the diameter of the connecting particle4is greater than the thickness of the insulating member1, so that a portion of the connecting particle4protrudes from the surfaces of the insulating member1.

As the connecting particle, a particle the dimension in the insulating member thickness direction of which is smaller than the thickness of the insulating member may also be used.

Hereinafter, the process of placing the connecting particle4into the penetrating hole3is referred to as the placement process.

Inner layer-side conductive layers2, each made of metal foil, are disposed on the two surfaces of the insulating member1. Copper, aluminum, chromium, titanium, or other metallic materials may be used for the inner layer-side conductive layers2. Of these, a copper or a copper alloy may be effective.

The inner layer-side conductive layers2are pressed toward the connecting particle4in the penetrating hole3. That is, the inner layer-side conductive layers2are pressed in the direction to bring them closer to each other (in the thickness direction of the insulating member1).

At this time, a pressing pressure of 30 kgf/cm2or higher is appropriate. Here 1 kgf is equivalent to 9.80665 N. It is appropriate that the temperature during pressing be 200° C. or higher.

As shown inFIG. 3, the connecting particle4is deformed in the pressing direction, and becomes a connecting member5having a thickness substantially equal to the thickness of the insulating member1, and in addition may be bonded with the inner layer-side conductive layers2.

The connecting member5is directly bonded to the inner layer-side conductive layers2. That is, the connecting member5and the inner layer-side conductive layers2are firmly bonded by metallic bonding or the like, substantially without requiring an additional member. Hence, the reliability of the connection between the connecting member5and the inner layer-side conductive layers2may be enhanced.

The connecting member5extends into the entire penetrating hole3, and substantially assumes a shape which fills the penetrating hole3.

It is believed that a firm bond is formed between the inner layer-side conductive layers2and the connecting member5because the oxide film that is present therebetween is broken, and in this portion the inner layer-side conductive layer2and the connecting member5may bond directly, without an intervening oxide film.

In this manufacturing method, pressing may be performed such that the cross-sectional area of at least a portion of the connecting member5, in the direction along the surface of the insulating member1(the horizontal direction), is greater than the contact area between the connecting member5and the inner layer-side conductive layer2.

In the nonlimiting exemplary embodiment shown inFIG. 3, the cross-sectional area along the horizontal direction of the connecting member5, at the center in the thickness direction of the insulating member1, is greater than the area of contact with the inner layer-side conductive layer2.

By performing pressing such that the cross-sectional area of the connecting member5is greater than the area of contact with the inner layer-side conductive layer2, sufficient pressing pressure may be applied to the inner layer-side conductive layer2, so that the surface of the inner layer-side conductive layer2may be made flat. Hence, the component mounting density on the surface of the inner layer-side conductive layer2may be increased. Also, fine wiring patterns may be formed in the inner layer-side conductive layer2.

Hereinafter, the process of deforming the connecting particle4into the connecting member5is referred to as the connecting particle pressing process.

The area of contact after pressing between the connecting member5and the inner layer-side conductive layer2is greater than the area of contact before pressing between the connecting particle4and the inner layer-side conductive layer2. By thus performing pressing such that the contact area increases, the amount of deformation when the connecting particle4becomes the connecting member5may be increased sufficiently, and the electrical resistivity between the inner layer-side conductive layers2and the connecting member5may be reduced, while increasing the bonding strength.

As shown inFIG. 4, the inner layer-side conductive layer2is patterned by etching or other techniques.

In patterning, for example, the subtractive method may be employed. More specifically, a resist layer is formed, and after forming the resist into a pattern according to the wiring pattern by photolithography techniques, the inner layer-side conductive layer2is etched.

Hereinafter, the process of patterning the inner layer-side conductive layer2is referred to as the patterning process.

After the above series of processes, a wiring board10is obtained in which inner layer-side conductive layers2, formed on both surfaces of the insulating member1, are connected together by the connecting member5.

In the wiring board10, the inner layer-side conductive layers2are connected by the connecting member5obtained by pressing and deforming the connecting particle4; hence the electrical resistance between the inner layer-side conductive layers2and the connecting member5is reduced, and the conductivity between the inner layer-side conductive layers2may be increased.

Next, a method for manufacturing an outer-layer wiring substrate13is explained according to a nonlimiting exemplary embodiment.

As is shown inFIG. 5, a metal-clad stacked substrate12(e.g., copper-clad stacked substrate), in which an outer layer-side conductive layer6is formed on one surface (the upper surface) of an insulating layer7, is provided. Copper, aluminum, chromium, titanium, or other metallic materials is used in the outer layer-side conductive layer6. In particular, a copper foil or other metal foils are appropriate. The same material as is used in the insulating member1may be used in the insulating layer7.

Next, a pattern of wiring is formed in the outer layer-side conductive layer6by etching or other techniques, as shown inFIG. 6.

Next, an adhesive layer8is formed on the other surface (the lower surface) of the insulating layer7, as shown inFIG. 7. As the adhesive used in the adhesive layer8, epoxy resin, polyimide resin, acrylic resin, or the like may be used.

Next, as shown inFIG. 8, an opening (via)9is formed in the insulating layer7and adhesive layer8from the lower-surface side of the metal-clad stacked substrate12. The opening9is formed so as to reach the outer layer-side conductive layer6.

The opening9may be formed by laser machining, drilling, or other techniques. Also, a mold or die may be used in molding or stamping to fabricate an insulating layer7having the opening9.

Next, as shown inFIG. 9, the opening9may be filled with a conductive paste to form a connecting portion11which is connected to the outer layer-side conductive layer6.

As the conductive paste, a mixture of a conducting material and a binder resin may be used.

As the conducting material, at least one of silver, nickel, carbon, and copper may be used. The conducting material may be in particle form. As the binder, at lest one of an acrylic resin, vinyl acetate resin, epoxy resin, and polyester resin may be used. The amount of the binder used may be from 0.2 to 10 parts by weight to 100 parts by weight of the conducting material, and 0.5 to 5 parts by weight may be used.

The opening9may be filled with the conductive paste using a printing method or a dot injection method.

By this, an outer-layer wiring substrate13is obtained in which an outer layer-side conductive layer6is formed on one surface of the insulating layer7, and a connecting portion11is provided in the opening9.

Next, a method of manufacturing a multilayer wiring board using the wiring board10and outer-layer wiring substrates13is explained according to a nonlimiting exemplary embodiment.

As shown inFIG. 10andFIG. 11, outer-layer wiring substrates13may be stacked onto both surfaces of the wiring board10, the outer-layer wiring substrates13may be pressed toward the wiring board10, and the outer-layer wiring substrates13may be bonded to the wiring board10by the adhesive layer8. The connecting portion11of the outer-layer wiring substrates13may be connected to the inner-layer side conductive layer2of the wiring board10.

This process of pressing the outer-layer wiring substrates13toward the wiring board10is referred to as the outer-layer wiring substrate pressing process.

The pressing pressure in the outer-layer wiring substrate pressing process may be lower than the pressing pressure in the above-described connecting particle pressing process. The pressing pressure may be less than 30 kgf/cm2.

By lowering the pressing pressure below the pressing pressure in the connecting particle pressing process, softening of the adhesive layer8may be prevented, and misalignment of the positions of the outer-layer wiring substrates13, as well as the squeeze-out of adhesive, may be prevented. Further, deformation of the insulating member1may be prevented.

The temperature in the outer-layer wiring substrate pressing process is lower than the temperature in the connecting particle pressing process; for example, a temperature of under 200° C. is may be used and a temperature of under 180° C. may also be used. By setting the temperature in this range, softening of the adhesive layer8may be prevented, and misalignment of the positions of the outer-layer wiring substrates13, as well as the squeeze-out of adhesive, can be prevented.

By this, a multilayer wiring board15is obtained in which a wiring board10and outer-layer wiring substrates13are stacked.

As shown inFIG. 12andFIG. 13, a additional outer-layer wiring substrates13may be stacked onto the multilayer wiring board15.

That is, by stacking outer-layer wiring substrates13onto both surfaces of the multilayer wiring board15, and performing pressing in the thickness direction, the outer-layer wiring substrates13may be connected to the multilayer wiring board15by means of adhesive layers8. The pressing pressure, the temperature and other conditions during pressing may be made the same as the conditions used when stacking outer-layer wiring substrates13onto the wiring board10.

By this, a multilayer wiring board16is obtained in which two outer-layer wiring substrates13are stacked onto each of the surfaces of a wiring board10.

In the multilayer wiring board16, since a plurality of outer-layer wiring substrates13are formed on both surfaces of a wiring board10, the wiring density may be increased.

In the multilayer wiring boards15and16shown inFIG. 11andFIG. 13, since the number of outer-layer wiring substrates13provided on one surface of the wiring board100and the number of outer-layer wiring substrates13provided on the other surface are equal, the forces applied to both surfaces of the wiring board10during heating and the like are equal, and thus warping does not readily occur.

In a method for manufacturing the above multilayer wiring boards15and16, since the connecting member5of the wiring board10fills the penetrating hole3, there is no void left in the penetrating hole3and no recess is generated on the surface of the outer layer-side conductive layers6. Consequently, it is possible to prevent problems during mounting of other components (integrated circuits and the like) on the multilayer wiring board15or16.

Hence, the component mounting density may be raised, the degree of flexibility in design may be enhanced, and an electric/electronic apparatus may be made smaller, thinner, and more lightweight.

In the multilayer wiring boards15and16, the inner layer-side conductive layers2may be formed thinner than in cases in which conductive layers are formed within openings by a plating method (shown inFIG. 30andFIG. 33).

Therefore, a finer pattern may be formed in the inner layer-side conductive layers2. Also, since the wiring board10may be formed thinner, the multilayer wiring boards15and16may be made thinner.

Hence an electrical/electronic apparatus may be made even smaller, thinner, and lighter in weight.

Further, because the inner layer-side conductive layers2may be made thinner, the flexibility in the wiring board10may be enhanced, for still greater freedom of design.

According to the above method of manufacture, since the outer layer-side conductive layers6and inner layer-side conductive layers2are connected by means of a connecting portion11formed from the conductive paste11in the outer-layer wiring substrates13, the connecting portion11adheres closely to the inner layer-side conductive layers2without a void and the conductivity therebetween may be increased. Hence, the reliability of connection between the outer layer-side conductive layers6and the inner layer-side conductive layers2may be improved.

According to the above method of manufacture, a method is adopted in which, after bonding the outer-layer wiring substrates13to the wiring board10by stacking and pressing, additional outer-layer wiring substrates13are stacked and pressed; but manufacture is not limited to this method, and a method may be employed in which a plurality of outer-layer wiring substrates13are stacked onto the wiring board10and are all pressed at once. The pressing pressure, the temperature, and other conditions during pressing may be made the same as the conditions when stacking outer-layer wiring substrates13to the wiring board10.

When this method is adopted, a plurality of outer-layer wiring substrates13may be bonded at once to the wiring board10, the number of processes may be reduced, which is advantageous from the standpoint of manufacturing costs.

In the present invention, a configuration is also possible in which one or a plurality of outer-layer wiring substrates are stacked onto only one surface of a wiring board. Further, in the multilayer wiring board16, although two outer-layer wiring substrates13are stacked onto each surface of the wiring board10, the number of stacked outer-layer wiring substrates per surface of the wiring board may be three or greater.

Next, a second nonlimiting exemplary embodiment of a method for manufacturing a multilayer wiring board of the present invention is explained.

The manufacturing method of this embodiment differs from the manufacturing method of the first embodiment in that, after first stacking onto the wiring board10an outer-layer wiring substrate13on which a wiring pattern has not yet been formed, the wiring pattern is formed in the outer layer-side conductive layer6. The following is a detailed explanation.

As shown inFIG. 14andFIG. 15, outer-layer wiring substrates13in the outer layer-side conductive layers6of which a wiring pattern has not been formed are stacked onto both surfaces of a wiring board10, and by performing pressing in the thickness direction, the outer-layer wiring substrates13and wiring board10are bonded together.

Next, as shown inFIG. 16, a pattern of wiring is formed in the outer layer-side conductive layers6of the outer-layer wiring substrates13, to obtain the multilayer wiring board15.

As shown inFIG. 17andFIG. 18, additional layers may be added to the multilayer wiring board15.

That is, the outer-layer wiring substrates13in the outer layer-side conductive layers6of which wiring patterns have not been formed are stacked onto the multilayer wiring board15, and by performing pressing in the thickness direction, the outer-layer wiring substrates13are bonded to the multilayer wiring board; then, a wiring pattern is formed in the outer layer-side conductive layers6, to obtain the multilayer wiring board16.

According to the manufacturing method of the above second embodiment, since a wiring pattern is formed in the outer layer-side conductive layers6after stacking outer-layer wiring substrates13onto a wiring board10, adverse effects of the pressing process on wiring may be prevented. Hence, the wiring of the outer layer-side conductive layers6may be made even finer.

Next, a third nonlimiting exemplary embodiment of a method for manufacturing a multilayer wiring board of the present invention is explained.

The manufacturing method of this embodiment differs from the manufacturing method of the first embodiment in that, after first stacking onto the wiring board10an outer-layer wiring substrate13ain which an opening9and connecting portion11have not yet been formed, the opening9and connecting portion11are formed. The following is a detailed explanation.

As shown inFIG. 19, outer-layer wiring substrates13ain which an opening9and connecting portion11are formed are stacked onto both surfaces of the wiring board10, and by performing pressing in the thickness direction, the outer-layer wiring substrates13aare bonded to the wiring board10by means of the adhesive layers8.

As shown inFIG. 20andFIG. 21, openings9are formed in the outer layer-side conductive layers6, insulating layers7and adhesive layers8, and by filling the openings9with a conductive paste, the connecting portions11are formed.

As shown inFIG. 22, by forming a pattern of wiring in the outer layer-side conductive layers6, a multilayer wiring board15is obtained.

As shown inFIG. 23, by bonding outer-layer wiring substrates13ato the multilayer wiring board15, and then forming openings9and connecting portions11in the outer-layer wiring substrates13a, the number of stacked outer-layer wiring substrates13may be increased.

According to the method of manufacturing of the above third embodiment, after stacking outer-layer wiring substrates13ato a wiring board10, the openings9and connecting portions11are formed, so that the connecting portions may be reliably brought into contact with the conducting layers2and6, and the conductivity therebetween may be improved. Hence, the reliability of electrical connections may be improved.

According to the manufacturing methods of the first through third embodiments, as shown inFIG. 1throughFIG. 4, when manufacturing the wiring board10, the connecting particle4is placed into the penetrating hole3, and by performing pressing in the thickness direction, the particle is deformed into the connecting member5. However, the wiring board10may also be manufactured by the method described below.

As shown inFIG. 24, printing or other means are used to provide a protrusion for connection18on one surface (the lower surface) of an inner layer-side conductive layer2.

The protrusion for connection18may be formed from copper or a copper alloy, and the thickness of the protrusion for connection18may be a little larger than the thickness of the insulating member1.

The inner layer-side conductive layer2is stacked onto the insulating member1such that the protrusion for connection18is placed into the penetrating hole19, and the two are pressed together in the thickness direction. The temperature, the pressure and other conditions during pressing may be the same as in the above connecting particle pressing process.

The protrusion for connection18is deformed in the thickness direction by pressing to become a connecting member5, and the wiring board10shown inFIG. 3is obtained.

As shown inFIG. 25, an outer-layer wiring substrate13may be provided with an exhaust hole21, the inner diameter of which is smaller than the opening9, in the outer layer-side conductive layer6at a position equivalent to the opening9.

By this configuration, when the opening9is filled with conductive paste from the side of the adhesive layer8to form the connecting portion11, air in the opening9may be discharged from the exhaust hole21.

Hence, since the lingering of bubbles in the opening9may be prevented, and the conductive paste may be made to fill the opening9without voids, defects in formation of the connecting portion11may be prevented. Consequently, the reliability of the electrical connection may be improved.

When the wiring formed in outer layer-side conductive layers need not be fine, the following configuration may also be adopted in a multilayer wiring board of the present invention.

In the multilayer wiring board22shown inFIG. 26, outer-layer wiring substrates23are formed on both surfaces of a wiring board10.

In the outer-layer wiring substrates23, an outer layer-side conductive layer26is formed on one surface of the insulating layer25having an opening24, and the outer layer-side conductive layer26is formed so as to fill the opening24.

When using a plating method to form an outer layer-side conductive layer26, the supply of metallic material may be continued until the opening24is completely filled to form the conductive layer.

In some cases an oxide layer, with a higher oxygen concentration than in other portions, may be formed at the boundary between the conductive layer and the connecting member. This oxide layer has a portion with high oxygen concentration (high-oxygen region), and a portion with low oxygen concentration (low-oxygen region).

It is believed that the low-oxygen region may, for example, be formed by the destruction of the oxide film at the surface due to deformation of the connecting particle in the process to form the connecting member. In the low-oxygen region, the conductive layer and the connecting member are bonded by metallic bonds and the like, the electrical resistance tends to be low, and the bonding strength tends to be high.

A wiring board of the present invention may be employed as a printed wiring board or other circuit board or semiconductor board on which are mounted display devices or sensor devices.