1. Technical Field
The present invention relates to a wiring board having high-density micro wiring, and a method for manufacturing the wiring board.
2. Background
Conventionally, a wiring board including a plurality of insulating layers has wiring conductors between the insulating layers or on the surface of the outermost insulating layer. A plurality of via holes are formed in each insulating layer. Inside each via hole, a via conductor integrally formed with the wiring conductor is deposited. The via conductor enables a conduction between the wiring conductors formed on each insulating layer. A wiring conductor in the highest layer is buried in the insulating layer in such a manner as to have the top surface exposed to the surface of the insulating layer. Further, a part of each wiring conductor in the highest layer forms a semiconductor element connection pad. To the semiconductor element connection pad, an electrode of a semiconductor element such as a semiconductor integrated circuit element is connected via a solder. A part of each wiring conductor formed in the lowest layer forms a circuit board connection pad. To the circuit board connection pad, an electrode of the circuit board on which the wiring board is mounted is connected. Then, an electrical signal is transmitted between the semiconductor element and the circuit board via the wiring conductor, so that the semiconductor element is operated. Such a wiring board is described in Japanese Unexamined Patent Publication No. S63-232483, for example.
A wiring board of the present disclosure includes an insulating layer and a wiring conductor, wherein the wiring conductor is buried in the insulating layer in such a manner as to have a top surface exposed to a surface of the insulating layer, and wherein the wiring conductor includes, at a portion buried in the insulating layer, a wiring level difference part or a wiring inclined part having a width larger than a width of the top surface.
A method for manufacturing a wiring board of the present disclosure includes the following processes. On an underlying metal layer, there is formed a resist layer for plating which has an opening pattern including an opening level difference part or an opening inclined part having a width being smaller toward the underlying metal layer. In the opening pattern, there is filled with a plated metal layer for a wiring conductor having a wiring level difference part or a wiring inclined part corresponding to the opening level difference part or the opening inclined part, and the resist layer for plating is removed. An insulating layer burying entirely the plated metal layer is formed on the underlying metal layer and on the plated metal layer, and the underlying metal layer is removed by etching. Finally, there is formed a wiring conductor having a top surface exposed from the insulating layer and including, at a portion buried in the insulating layer, the wiring level difference part or the wiring inclined part having a width larger than a width of the top surface.
Along the progress of miniaturization of a wiring conductor, a contact area between a wiring conductor and an insulating layer becomes smaller. As a result, the adhesion strength of the wiring conductor becomes smaller, and the wiring conductor becomes easily peeled off from the insulating layer. Therefore, the electrical signal cannot be satisfactorily transmitted via the wiring conductor, and thus a semiconductor element does not stably operate in some cases.
In the wiring board of the present disclosure, a wiring conductor buried in an insulating layer in such a manner as to have a top surface exposed to a surface of the insulating layer includes, at a portion buried in the insulating layer, a wiring level difference part or a wiring inclined part having a width larger than a width of the top surface. As described above, because the wiring level difference part or the wiring inclined part having a width larger than a width of the top surface is buried in the insulating layer, peeling off of the wiring conductor from the insulating layer can be suppressed. Hereinafter, a wiring board according to one embodiment of the present disclosure will be described with reference to
As shown in
The wiring conductor 2 is formed of a satisfactory conductive material such as a non-electrolytic plating or an electrolytic plating. A part of the wiring conductor 2 in the highest layer forms a semiconductor element connection pad 5. To the semiconductor element connection pad 5, there is connected an electrode of a semiconductor element such as a semiconductor integrated circuit element. A part of each wiring conductor 2 formed in the lowest layer forms a circuit board connection pad 6. To the circuit board connection pad 6, there is connected an electrode of the circuit board on which the wiring board A is mounted. Then, an electrical signal is transmitted between the semiconductor element and the circuit board via the wiring conductor 2, so that the semiconductor element is operated. As shown in
As described above, according to the wiring board of the present disclosure, the wiring inclined part 2a having a width larger than a width of the top surface is buried in the insulating layer 1. Therefore, even when miniaturization of the wiring conductor 2 is progressed, the adhesion strength of the wiring conductor 2 does not easily become small, and peeling off of the wiring conductor 2 from the insulating layer 1 can be prevented. As a result, because the electrical signal can be transmitted satisfactorily via the wiring conductor 2, a wiring board enables a stable operation of the semiconductor element.
Next, a method for manufacturing a wiring board according to an embodiment of the present disclosure will be described with reference to
As shown in
The product-forming region X is a region of a quadrangular shape, and the wiring board A is formed on the product-forming region X. In the one embodiment, for simplicity, only the product-forming region X corresponding to one wiring board A is shown. Actually, the product-forming region has an area corresponding to dozens to several thousand wiring boards A. The margin region Y is in a quadrangular frame shape surrounding the product-forming region X. The prepreg 7 has approximately a quadrangular shape, and may have a thickness of about 0.1 mm to 0.2 mm, and may have longitudinal and lateral lengths of 400 mm to 900 mm each. The prepreg 7 has a plate shape in a semi-cured state by having a glass fiber impregnated with a thermosetting resin such as an epoxy resin.
The adhesive film 8 is interposed between the prepreg 7 and the separable metal foil 9, and causes the cured prepreg 7 and the separable metal foil 9 to be deposited together. The adhesive film 8 may have a thickness of about 24 μm to 50 μm, and may have longitudinal and lateral lengths of 400 mm to 900 mm each. The adhesive film 8 is formed of a heat-resistant film such as an epoxy resin or a polyimide resin.
The separable metal foil 9 includes a first metal foil 9a and a second metal foil 9b. The first metal foil 9a and the second metal foil 9b are separably held by a small adhesive force, via an adhesion layer (not shown). The first metal foil 9a has a size larger than the product-forming region X and smaller than the second metal foil 9b. The first metal foil 9a may have a thickness of about 15 μm to 20 μm. The second metal foil 9b has longitudinal and lateral sizes smaller by about 5 mm than longitudinal and lateral sizes of the prepreg 7. The first metal foil 9a may have a thickness of about 5 μm to 9 μm.
The separable metal foil 9 includes copper, for example. The adhesion layer may be formed of a heat-resistant pressure-sensitive adhesive such as a silicon resin system or an acrylic resin system, or of a metal layer of a nickel system, that can bear heat load applied during the forming of the wiring board A. Such an adhesion layer may have a small pressure-sensitive adhesive force of about 1 N/m to 9 N/m, in separating the first metal foil 9a and the second metal foil 9b without leaving a peel-off remain, at the time of separating a build-up portion 12 described later from the supporting substrate 10.
Next, as shown in
As shown in
For example, the opening inclined part Pa is formed by flattening the surface of the conductor layer 11. The conductor layer 11 may have a surface roughness (Ra) equal to or smaller than 60 nm. Based on the flattening of the surface of the conductor layer 11, incident light at the time of exposure which reaches the surface of the conductor layer 11 is not blocked by a convex part of the surface of the conductor layer 11. As a result, by making the light at the time of exposure incident to the wiring pattern region, the photosensitive resin near the conductor layer 11 is cured so that the opening inclined part Pa is formed.
As shown in
As shown in
As described above, each insulating layer 1 is formed of a thermosetting resin such as an epoxy resin or a bismaleimide triazine resin. The insulating layer 1 is formed as follows, for example. First, a film is formed by dispersing an inorganic insulating filler on an uncured substance such as an epoxy resin or bismaleimide triazine resin composition. The insulating layer 1 is formed by thermally compressing the formed film to the surface of the conductor layers 11 on both main surfaces of the supporting substrate 10 and to the surface of the lower insulating layer 1 in a state covered in vacuum. In the insulating layer 1, a plurality of via holes 3 in which a via conductor 4 is filled to enable a conduction between the insulating layers 1 are formed, by laser processing, for example.
As shown in
Next, as shown in
Next, as shown in
As described above, according to the method for manufacturing the wiring board in the present disclosure, there is formed the wiring conductor 2 having the top surface exposed from the insulating layer 1 and including, at a portion buried in the insulating layer 1, the wiring inclined part 2a of a width larger than a width of the top surface. In this way, the wiring inclined part 2a of a width larger than a width of the top surface is buried in the insulating layer 1. Therefore, even when miniaturization of the wiring conductor 2 is progressed, the adhesion strength of the wiring conductor 2 does not easily become small, and peeling off of the wiring conductor 2 from the insulating layer 1 can be prevented. As a result, because the electrical signal can be transmitted satisfactorily via the wiring conductor 2, a wiring board enables a stable operation of the semiconductor element.
The wiring board and the method for manufacturing a wiring board in the present disclosure are not limited to the above embodiments, and various modifications are possible without departing from the scope of the present disclosure.
For example, in the wiring board of the one embodiment, the wiring conductor 2 has the wiring inclined part 2a having a width larger than the width of the top surface. However, as shown in
For example, according to the method for manufacturing of the one embodiment, the insulating layer 1 is covered after the resist R for plating is removed, as shown in
By such an etching process, the surface of the conductor layer 11 and the surface of the plated metal layer 2P are gradually solved. On the other hand, in the wiring inclined part 2a formed in the plated metal layer 2P, the etching liquid remains and the solving speed becomes faster than in other parts. Therefore, as compared with the case of not performing the etching process, the region that the wiring inclined part 2a occupies in the plated metal layer 2P is enlarged. By enlarging in this way the wiring inclined part 2a buried in the insulating layer 1, the adhesion strength of the wiring conductor 2 can be more improved.
Number | Date | Country | Kind |
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2015-126539 | Jun 2015 | JP | national |
2015-147375 | Jul 2015 | JP | national |