Manufacturing method for wiring board

The method includes: preparing a first substrate including first wirings; preparing a mold having a stamping surface that includes convex portions formed depending on wiring patterns of a second substrate to be laminated on the first substrate and projections formed depending on via patterns; pressing, while heating, the mold against the second insulating sheet so that end portions of the projections are exposed at the other main surface side of the second insulating sheet; laminating, while heating, the second insulating sheet on a first insulating sheet so that the exposed end portions contact the first wirings; releasing, the mold from the second insulating sheet; and filling a conductive material in groove portions and holes formed in the second insulating sheet.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to a manufacturing method for a wiring board.

For those designated countries which permit the incorporation by reference, the contents described and/or illustrated in the documents relevant to Patent Application No. 2010-161743 filed with Japan Patent Office on Jul. 16, 2010 and Patent application No. 2010-161776 filed with Japan Patent Office on Jul. 16, 2010 will be incorporated herein by reference as a part of the description and/or drawings of the present application.

2. Description of the Related Art

In order to achieve highly-dense wiring in association with downsizing electronic devices and enhancing the functionality thereof, an imprint method is known in which a mold is used to transfer concave shapes to an insulating sheet and the concave shapes are filled with a conductive material to form fine patterns (such as wiring patterns and via patterns).

In this imprint method, after the mold is released from the insulating sheet, if some resin remains in opening areas which have been formed by the mold and are to be connection portions for via patterns, then connection failures in via patterns or other troubles may possibly occur. In this respect, there is known an approach for removing such resin residues in opening areas using plasma etching or laser ablation (Patent Document 1: U.S. Pat. No. 7,351,660).

PRIOR ART DOCUMENT(S)

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

However, if, in order to remove resin residues, plasma or laser light is irradiated to a substrate formed thereon with wiring patterns, then problems occur including that the wiring patterns may be damaged or partially lost.

Problems to be solved by the present invention include providing a manufacturing method for a wiring board in which resin is unlikely to remain on the bottom of an opening area formed in an insulating sheet, when a mold is released from the insulating sheet in an imprint method.

Means for Solving the Problems

(1) A first invention in this application solves the above one or more problems by a manufacturing method for a wiring board. The method includes preparing a first substrate. The first substrate comprises a first insulating sheet and a first wiring formed on one main surface of the first insulating sheet. The method includes preparing a mold having a stamping surface. The stamping surface includes a convex portion and a projection. The convex portion is formed depending on a wiring pattern constituting at least a part of patterns of a second substrate to be laminated on the first substrate. The projection is formed depending on a via pattern constituting at least a part of the patterns. The method includes locating the stamping surface of the mold to face one main surface side of a second insulating sheet and heating the second insulating sheet to a first set temperature to press the mold against the one main surface of the second insulating sheet so that at least an end portion of the projection of the stamping surface is exposed at the other main surface side of the second insulating sheet. The method includes heating at least the second insulating sheet to a second set temperature to laminate the second insulating sheet on the first insulating sheet so that the end portion of the projection exposed at the other main surface of the second insulating sheet contacts the first wiring of the first insulating sheet. The method includes cooling at least the second insulating sheet to release the mold from the second insulating sheet and filling a conductive material in a groove portion and a hole. The groove portion and the hole are formed in the second insulating sheet respectively by the convex portion of the mold and the projection of the mold.

(2) In the above first invention, the pressing the mold against the one main surface of the second insulating sheet may be such that a length h1of the projection formed depending on the via pattern is a thickness h2of the second insulating sheet or more, and the laminating the second insulating sheet on the first insulating sheet may be such that the length h1of the projection formed depending on the via pattern and the thickness h2of the second insulating sheet are substantially the same.

(3) In the above first invention, the pressing the mold against the one main surface of the second insulating sheet may include locating a cushion sheet on the other main surface side of the second insulating sheet, and the laminating the second insulating sheet on the first insulating sheet may include removing the cushion sheet.

(4) A second invention in this application solves the above one or more problems by a manufacturing method for a wiring board. The method includes preparing a first substrate. The first substrate comprises a first insulating sheet and a first wiring formed on one main surface of the first insulating sheet. The first wiring may be embedded in the first insulating sheet. The method includes forming a wiring portion on one main surface of a flat plate-like supporting member. The wiring portion includes a convex portion and a projection. The convex portion functions as a wiring pattern constituting at least a part of patterns of a second substrate to be laminated on the first substrate. The projection functions as a via pattern constituting at least a part of the patterns. The method includes locating the wiring portion formed on the supporting member to face one main surface side of a second insulating sheet and heating the second insulating sheet to a first set temperature to press the wiring portion against the one main surface of the second insulating sheet so that at least an end portion of the projection of the wiring portion is exposed at the other main surface side of the second insulating sheet. The method includes heating the second insulating sheet to a second set temperature to laminate the second insulating sheet on the first insulating sheet so that the end portion of the projection exposed at the other main surface of the second insulating sheet contacts the first wiring exposed at the one main surface of the first insulating sheet. The second insulating sheet may be heated to the second set temperature in a state where the wiring portion is inserted in the second insulating sheet due to the pressing the wiring portion against the one main surface of the second insulating sheet. The second set temperature may be lower than the first temperature. The method includes removing the supporting member from the second insulating sheet.

(5) In the above second invention, the pressing the wiring portion formed on the supporting member against the one main surface of the second insulating sheet may be such that a length h3of the projection functioning as the via pattern is a thickness h4of the second insulating sheet or more, and the laminating the second insulating sheet on the first insulating sheet may be such that the length h3of the projection functioning as the via pattern and the thickness h4of the second insulating sheet are substantially the same.

(6) In the above second invention, the pressing the wiring portion formed on the supporting member against the one main surface of the second insulating sheet may include locating a cushion sheet on the other main surface side of the second insulating sheet, and the laminating the second insulating sheet on the first insulating sheet may include removing the cushion sheet.

Advantageous Effect of the Invention

According to the present invention, a manufacturing method for a wiring board can be provided in which resin residue is unlikely to remain on the bottom of an opening area of an insulating sheet to be formed therein a via pattern, when the via pattern is formed by using an imprint method. Therefore, plasma irradiation, laser irradiation and chemical etching are not necessary for removing resin residue. As a result, the wiring pattern can be prevented from damages such as generating defects and being lost due to plasma irradiation, laser irradiation and chemical etching etc, and a wiring board having high reliability can thus be provided.

DESCRIPTION OF THE PREFERRED EMBODIMENT

<First Embodiment of First Invention>

Hereinafter, the manufacturing method for a wiring board according to the first embodiment of the first invention will be described. The first invention is for the purpose of providing a manufacturing method for a wiring board in which resin residues are unlikely to remain in holes, corresponding to via patterns, of an insulating sheet when a mold for imprinting is released from the insulating sheet. That is, an object of the first invention is to provide a manufacturing method for a wiring board in which processes, such as plasma irradiation, laser irradiation and chemical etching, are not necessary to be performed for removing resin residues remaining in holes of the insulating sheet.

The configuration of a wiring board100obtained by the manufacturing method according to the first embodiment of the present invention will first be described with reference toFIG. 1, and the manufacturing method according to the first embodiment of the present invention will then be described with reference toFIG. 2toFIG. 7.

As shown inFIG. 1, the wiring board100according to the first embodiment of the present invention is a multilayer board that comprises a first substrate1and a second substrate2laminated on one main surface side (upper side in the figure) of the first substrate1. While the present embodiment is described for an example of the wiring board100which is configured of two substrates, the present invention is applicable to a wiring board100which is configured of three or more substrates. Note that the present embodiment is described with reference to an x-y plane shown in the figure as a plane along the wiring board100(substrates1and2and insulating sheets10and20) and a z-axis direction as the laminating direction, and the upper side along the z-axis in the figure represents the one main surface side.

The first substrate1located on the lower side in the figure comprises: a first insulating sheet10; first upper side wirings11to17formed on one main surface (the upper side in the figure: here and hereinafter) of the first insulating sheet10; first lower side wirings21and22formed on the other main surface (the lower side in the figure: here and hereinafter) of the first insulating sheet10; and first vias18and19respectively connecting the first upper side wirings12and16and the first lower side wirings21and22.

The second substrate2comprises: a second insulating sheet20laminated on the one main surface (the upper side in the figure) of the first insulating sheet10; second upper side wirings31to37formed on one main surface (main surface on the upper side in the figure) of the second insulating sheet20; and second vias38and39respectively connecting the second upper side wirings32and36and the first upper side wirings12and16, wherein the second upper side wirings32and36are included in the second upper side wirings31to37.

The second upper side wirings31to37and the second vias38and39are convexly formed toward the interior of the second insulating sheet20from the one main surface (the upper side main surface) of the second insulating sheet20. That is, the one main surface of the second insulating sheet20formed with the second upper side wirings31to37and connection portions for the second vias38and39is flat, so that another substrate not shown can be laminated flatly thereon, i.e. without any space, or other electric components not shown can be mounted thereon.

As a material for the first insulating sheet10and the second insulating sheet20, thermosetting resin such as epoxy resin or thermoplastic resin such as thermoplastic polyimide and liquid-crystal polymer may be used, for example. As a material for the first upper side wirings11to17, the first lower side wirings21and22, the first vias18and19, the second upper side wirings31to37and the second vias38and39, copper (Cu), silver (Ag), gold (Au) or other materials having conductivity may be used.

Although not particularly limited, in the first upper side wirings11to17and the first lower side wirings21and22constituting a part of wiring patterns of the first substrate1and the second upper side wirings31to37constituting a part of wiring patterns of the second substrate2, line-and-space areas may be arranged such that the wiring width is approximately 5 μm to 15 μm and the wiring space is approximately 5 μm to 15 μm. In addition, the diameter (thickness) of the first vias18and19and the second vias38and39is 2 μm or more and 35 μm or less, preferably 2 μm or more and 15 μm or less, and more preferably 2 μm or more and less than 10 μm. The length of the first vias18and19and the second vias38and39in the present embodiment is 1 μm or more and 50 μm or less, and preferably 10 μm or more and 40 μm or less. The aspect ratio is 0.5 to 25 and preferably 1 to 25, and may be about 1 to 4 in the present example.

(Manufacturing Method for Wiring Board)

One example of a manufacturing method for the wiring board100according to the first embodiment of the present invention will then be described with reference toFIG. 2toFIG. 7.

At first, the first substrate1shown inFIG. 2is prepared. As the first substrate1, a substrate may be used which comprises at least the first insulating sheet10and the first upper side wirings11to17formed on one main surface (surface on which the second substrate2is to be laminated) of the first insulating sheet10, but in the present example, a double-side substrate is used as the first substrate1, in which the first upper side wirings11to17are formed on the one main surface of the first insulating sheet10so as to be embedded therein and the first lower side wirings21and22are formed on the other main surface.

While the product ion method for the first substrate1shown inFIG. 2is not particularly limited, a mold is used for example, which comprises a stamping surface including convex portions and projections formed respectively depending on the first upper side wirings11to17and the first vias18and19, to transfer patterns to the one main surface (upper surface in the figure) of the first insulating sheet10thereby forming groove portions (concave portions) and holes respectively depending on the first upper side wirings11to17and the first vias18and19, a plating process or other appropriate process is performed to fill these concave portions and holes with a conductive material, and the first substrate1can thereby be produced as a single-side substrate, in which the first upper side wirings11to17and the first vias18and19are formed on the one main surface side of the first insulating sheet10. Further, a resist is applied to the other main surface (lower surface in the figure) of the first insulating sheet10, photolithography is used to pattern the resist depending on the first lower side wirings21and22, plating is then performed, and the first substrate1can thereby produced as a double-side substrate, in which the first lower side wirings21and22are further formed on the other main surface side of the first insulating sheet10. Of course, both surfaces may be formed thereon with resists having certain patterns, and thereafter a plating process may be concurrently performed for the both surfaces.

Alternatively, holes depending on the first vias18and19are formed by irradiating laser beam or other beam to the one main surface (upper surface in the figure) side of the first insulating sheet10, thereafter, photolithography is used to pattern a resist depending on patterns of the first upper side wirings11to17and the first vias18and19, concave portions depending on the first upper side wirings11to17and the holes depending on the first vias18and19are subjected to nonelectrolytic plating and/or electrolytic plating, and the first substrate1can thereby be produced as a single-side substrate, in which the first upper side wirings11to17and the first vias18and19are formed on the one main surface side of the first insulating sheet10. Note that the plating may be substituted by screen printing which uses conductive paste to fill a conductive material in concave portions depending on the first upper side wirings11to17and in holes depending on the first vias18and19. Further, the first substrate formed thereon with the first lower side wirings21and22can be produced by printing conductive paste to the other main surface (lower surface in the figure) side of the first insulating sheet10using a printing plate depending on patterns of the first lower side wirings21and22. As the production method for the first substrate1, any production method for double-side substrate known in the art at the time of filing this application may appropriately be utilized. If no wiring pattern is necessary for the other main surface side of the first substrate1, then any production method for single-side substrate known in the art at the time of filing this application may appropriately be utilized.

Before or after or in parallel with the preparation of the first substrate1, a mold4shown inFIG. 3is prepared. As shown inFIG. 3, the mold4according to the present embodiment has a stamping surface4athat includes: convex portions41to47formed depending on the second upper side wirings31to37constituting a part of patterns of the second substrate2to be laminated on the first substrate1; and projections48and49formed depending on the second vias38and39constituting another part of the patterns.

The stamping surface4afunctions as a working-purpose plate (original plate) for transferring a concave-convex shape (including the projections48and49and the convex portions41to47), which is used for constituting desired patterns, to the second insulating sheet20. Reference character4ainFIG. 3specifies the entire surface to be pressed against the second insulating sheet, on the other main surface side (lower side in the figure) of the mold4formed thereon with the concave-convex shape including the convex portions41to47and projections48and49for constituting the desired patterns.

While the production method for the mold4is not particularly limited, the mold4comprising the stamping surface4acan be obtained for example through: preparing a resin plate body applied to a main surface of a supporting plate body for producing a mold; irradiating laser or electron beam to a main surface of the resin plate body to form holes depending on via patterns; laminating a resist layer on the resin plate body; exposing or heating predetermined regions of the resist layer depending on wiring patterns and thereafter selectively removing the predetermined regions using etching liquid to form groove portions depending on the wiring patterns; and filling a mold material in the holes and the groove portions formed in the resin plate body while covering the main surface of the resin plate body with the mold material.

Further, while the filling method using the mold material is not particularly limited, the mold material can be filled in the holes and in the groove portions for example through: employing sputtering or other appropriate approach to form conductive layers, which will be seed layers in a plating process or the like to be subsequently performed, in regions to be filled with the mold material, such as in the holes and groove portions of the resin plate body; and thereafter performing plating using the mold material such as copper (Cu) or nickel (Ni). Of course, the holes and the groove portions may also be filled with the mold material by print ing conductive nano-paste including copper (Cu), silver (Ag) and/or other appropriate conductive material. Examples of the mold material to be used include, but not limited to, conductive materials such as copper (Cu), silver (Ag) and other metals as well as insulating materials (nonconductive materials) such as glass. As the supporting plate body, a copper foil or other appropriate material capable of being removed by etching may be used. The thickness of a copper foil to function as the supporting plate body may be approximately 80 to 120 μm. In addition, as the resin plate body, a light-curable or heat-curable resist film may for example be used, which is a material soluble in alkaline or acidic solution. The thickness of the resin plate body may be 15 to 40 μm.

Subsequently, the supporting plate body is removed by using etching liquid such as ferric chloride solution to expose the surface of the resin plate body. Finally, the resin plate body is also removed through swelling by using aqueous solution of sodium hydroxide or other appropriate liquid. The stamping surface4acan thereby be obtained which comprises the convex portions41to47and the projections48and49as will be described later with reference toFIG. 3. In view of the handling ability, the produced stamping surface4ais applied to a main surface of a plate-like supporting member40, and the mold4according to the present embodiment is thus obtained.

Note that the manufacturing method for the mold4is not particularly limited, and processes known in the art at the time of filing this application, such as a process using photolithography, a plating process, a polishing process and a laser irradiation process, may be combined to produce the mold4which comprises the stamping surface4aformed thereon with the convex portions41to47and the projections48and49.

Thereafter, as shown inFIG. 3, the mold4is located so that the stamping surface4afaces a stage6of an imprint apparatus, on which a target object to be transferred thereto is to be placed. As shown in the figure, if the second insulating sheet20is set on the platen of the stage6, then the stamping surface4aof the mold4faces the one main surface side (upper side in the figure) of the second insulating sheet20. Although not particularly limited, as the second insulating sheet20, uncured (semi-cured) thermosetting resin such as epoxy resin or thermoplastic resin such as liquid-crystal polymer or thermoplastic polyimide may be used, for example.

As shown inFIG. 3, in a state at ambient temperature (T0) before mold clamping (before transfer process), the depth of the stamping surface4a, i.e. the length h1(T0) of the projections48and49formed on the stamping surface4a, may be set as being the thickness h2(T0) of the second insulating sheet20or more. The second insulating sheet20tends to expand in the subsequent heating process to increase in its thickness h2, and therefore, the thickness h2(T0) of the second insulating sheet20at ambient temperature is preferred to be set as being equal to or thinner than the length h1(T0) of the projections48and49.

Subsequently, the second insulating sheet20is heated until it becomes a first set temperature T1. The first set temperature T1is a temperature which is suitable for transferring the stamping surface4aand which is defined depending on the heat deformation temperature or glass transition temperature (Tg) of the second insulating sheet20. The first set temperature T1when the pattern shape of the stamping surface4ais transferred may be freely determined depending on the characteristics and the thickness of the second insulating sheet20. As one example, the first set temperature T1may be approximately 260° C. to 300° C. Note that heating the second insulating sheet20may be performed by directly heating the second insulating sheet20or by heating the mold4to indirectly heat the second insulating sheet which contacts the mold4.

After the second insulating sheet20is heated to the first set temperature T1(or after the mold4is heated to a temperature capable of heating the second insulating sheet20to the first set temperature T1at the time of transferring), the stamping surface4aof the mold4is pressed against the second insulating sheet20, as shown inFIG. 4.

The projections48and49and the convex portions41to47of the stamping surface4aare pressed into the second insulating sheet20having been heated to the first set temperature T1to be softened. In the present embodiment, as shown inFIG. 4, the mold4may be pressed against the one main surface (upper side in the figure) of the second insulating sheet20so that at least end portions48aand49aof the projections48and49of the stamping surface4aare exposed at the other main surface side (lower side in the figure) of the second insulating sheet20. The end portions48aand49aof the projections48and49in the present embodiment include at least end surfaces (surfaces to contact first the second insulating sheet20) of the projections48and49, but not limited thereto, and portions with a certain distance toward the supporting member40from these end surfaces may also be included therein.

As shown inFIG. 4, the second insulating sheet20, which the stamping surface4ahas been pressed into, is formed therein with concave portions51to57depending on the shapes of the convex portions41to47and holes (via holes)58and59depending on the shapes of the projections48and49.

In this step for pressing the mold4against the second insulating sheet20(referred also to as a transfer step, hereinafter), as shown inFIG. 4, the length of the projections48and49and the material and the thickness of the second insulating sheet20may be set such that the length h1(T1) of the projections48and49formed depending on the via patterns is the thickness h2(T1) of the second insulating sheet20or more at the first set temperature T1(260° C. to 300° C., for example) (h1(T1)≧h2(T1)).

In this transfer step, the second insulating sheet20is heated to the first set temperature T1to expand with a larger thickness h2than that at ambient temperature (T0), but the end portions48aand49aof the projections48and49are ensured to be exposed at the other main surface side of the second insulating sheet20because the length of the projections48and49and the material and the thickness of the second insulating sheet20are preliminarily set such that the length h1(T1) of the projections48and49is the thickness h2(T1) of the second insulating sheet20or more at the first set temperature T1(h1(T1)≧h2(T1)).

Subsequently, as shown inFIG. 5, the other main surface (lower surface in the figure) of the second insulating sheet20is caused to face the one main surface (upper surface in the figure) of the first substrate1in a state where the projections48and49and the convex portions41to47of the mold4still remain inserted in the second insulating sheet20. Thereafter, the end portions48aand49aof the projections48and49exposed at the other main surface (lower surface in the figure) of the second insulating sheet20are aligned to respectively contact the first upper side wirings12and16of the first insulating sheet10using image recognition, pin-alignment or other appropriate means, and the second insulating sheet20is laminated on the first insulating sheet10, as shown inFIG. 6.

In this laminating step, the second insulating sheet20laminated on the one main surface side (upper side in the figure) of the first insulating sheet10is hot-pressed along the laminating direction (z-axis direction) while being heated to a second set temperature T2.

The second set temperature T2in the laminating step may be, such as, but not limited to, a temperature where the first insulating sheet10and the second insulating sheet20are softened to exhibit adhesiveness. At the second set temperature T2, the first insulating sheet10and the second insulating sheet20are fused or adhere to each other. The second set temperature T2may be set as being less than the first set temperature T1, and may be 220° C. to 260° C., for example.

The end portions48aand49aof the projections48and49longer than the thickness of the second insulating sheet20are exposed at the other main surface side (lower side in the figure) of the second insulating sheet20before the second insulating sheet20is laminated on the first insulating sheet, so that the ends of the projections48and49and the first upper side wirings12and16can be ensured to contact each other, respectively, without any resin interposed in the contact portions between the ends of the projections48and49and the first upper side wirings12and16, as shown inFIG. 6.

In addition, during this laminating step, the height h1of the projections48and49formed depending on the second vias38and39and the thickness h2of the second insulating sheet20can be made to be substantially the same. More specifically, the difference between the length h1of the projections48and49and the thickness h2of the second insulating sheet20may be about less than 10% of the length of the projections48and49, preferably less than 5%, more preferably less than 3%, and most preferably less than 1%.

Thus, in the laminating step, the length h1of the projections48and49and the thickness h2of the second insulating sheet20are made to be substantially the same thereby to avoid the resin from flowing into the contact portions between the ends of the projections48and49and the first upper side wirings12and16even if a part of the second insulating sheet20is fluidized due to heating during the laminating. As a result, resin residues can be prevented from remaining between the ends of the projections48and49and the first upper side wirings12and16. That is, the shapes of the projections48and49can be transferred to the second insulating sheet20without any change, and the second vias38and39can thus be formed to have the same shapes as the projections48and49. Moreover, in the laminating step, the length h1of the projections48and49and the thickness h2of the second insulating sheet20are made to be substantially the same thereby to prevent the ends of the projections48and49from strongly pressing against the first upper side wirings12and16to destroy them even if the second insulating sheet20is pressed against the first insulating sheet10during the laminating.

In fact, the present embodiment is such that the transfer step shown inFIG. 4is performed at the first set temperature T1and under the condition where the length h1(T1) of the projections48and49of the stamping surface4ais the thickness h2(T1) of the second insulating sheet20or more while the laminating step shown inFIG. 6is performed at the second set temperature T2lower than the first set temperature T1and under the condition where the length h1(T2) of the projections48and49of the stamping surface4aand the thickness h2(T2) of the second insulating sheet20are substantially the same. Here, the condition, where the thickness of the second insulating sheet20is thinner than the length h1of the projections48and49at the relatively high first set temperature T1while the thickness of the second insulating sheet20is substantially the same as the length h1of the projections48and49at the relatively low second set temperature T2, may appear to be contrary to the common general technical knowledge that the second insulating sheet20expands to become thicker as the temperature increases. As shown inFIG. 4, however, even if being applied with a relatively large pressing force during mold clamping in the transfer step, the softened second insulating sheet20is allowed to laterally expand toward the outer edge (right and left end portions of the second insulating sheet20in the figure). As shown in the figure, the end portions of the second insulating sheet20are rounded to absorb the expanded volume of the second insulating sheet. Accordingly, the condition can be established in the present embodiment, where: T1>T2; (the length h1(T1) of the projections48and49)≧(the thickness h2(T1) of the second insulating sheet20); and the length h1(T2) of the projections48and49and the thickness h2(T2) of the second insulating sheet20are substantially the same, as described in the above.

After the laminating, the second insulating sheet20, if being thermosetting resin, is completely cured by being heated for example at 180° C. during one hour using oven or other appropriate means. The second insulating sheet20, if being thermoplastic resin, is cured by being cooled.

Subsequently, as shown inFIG. 7, the mold4is released from the second insulating sheet20. This releasing process may be performed after the second insulating sheet20is cooled to lower than the glass transition temperature Tg or the heat deformation temperature or cooled to ambient temperature. The second insulating sheet20is contracted in the direction of being separated from the stamping surface4aas the temperature decreases, so that cooling the second insulating sheet20assists the releasing, which is an action of causing the stamping surface4ato be separated from the stamping surface4a.

FIG. 8is an enlarged view of region A surrounded by broken line inFIG. 7. As shown inFIG. 8, no resin remains on the bottom of a hole59having been formed by the projection49, and the first upper side wiring16is exposed without being covered by resin. In this state, a conductive material can be filled in the hole59to form the second via39which is interlayer-connected with the first upper side wiring16without any resin interposed therebetween. That is, the second via39can be formed to have the same shape as that of the projection49of the mold4. As a result, the wiring board100can be formed to have high connection reliability. In addition, resin residue removing processes are not necessary, such as plasma irradiation, laser irradiation and chemical etching, for removing resin remaining in holes for forming via patterns, which would be required in the conventional method.

If a wiring board is obtained by a manufacturing method including plasma irradiation or laser irradiation, then the patterns and/or the insulating sheets thereof will involve lost parts and/or defect traces, while if a wiring board is obtained by a manufacturing method including chemical etching process, then the patterns and/or the insulating sheets thereof will involve chemical erosion traces. In contrast, according to the manufacturing method of the present embodiment, the wiring board100can be provided which can avoid such lost parts, defects or chemical erosions caused due to resin residue removing processes.

In order to confirm advantageous effects resulted from the manufacturing method according to the present embodiment, a manufacturing method according to Comparative Example 1 has been carried out in which the step for pressing the mold4against the one main surface of the second insulating sheet20is different from the present embodiment only in the point that the length h1of the projections48and49is less than the thickness h2of the second insulating sheet20, and an observation has also been performed for the condition of the bottom of a hole159after the mold4was released.FIG. 9schematically illustrates the condition of a portion in this comparative example, which corresponds to region A. As shown inFIG. 9, resin S remains on the bottom of the hole159after the releasing. If, in this condition, a conductive material is filled in the hole159to form the second via39, then the connection reliability will be deteriorated because the resin S remains between the second via39and the first upper side wiring16thereby to reduce the contact area therebetween.

Similarly, a manufacturing method according to Comparative Example 2 has been carried out in which the step for laminating the second insulating sheet20on the first insulating sheet10is different from the present embodiment only in the point that the length h1of the projections48and49is less than the thickness h2of the second insulating sheet20, and an observation has also been performed for the condition of the bottom of a hole159after the mold4was released. Like the above Comparative Example 1, resin S remains on the bottom of the hole159after the releasing. This condition is similar to the condition schematically illustrated inFIG. 9, which corresponds to the previously-described region A inFIG. 7. If, in this condition, a conductive material is filled in the hole159to form the second via39, then the connection reliability will be deteriorated because the resin S remains between the second via39and the first upper side wiring16thereby to reduce the contact area therebetween.

Finally, a conductive material such as copper (Cu), silver (Ag) or other appropriate material is filled in the concave portions51to57, which correspond to the convex portions41to47of the mold4, and the holes58and59, which correspond to the projections48and49of the mold4, formed in the second insulating sheet20, and the wiring board100shown inFIG. 1can thus be obtained. Filling method with a conductive material is not particularly limited, and plating process or screen printing may be employed to fill the conductive material in the concave portions51to57and the holes58and59. The plating process may include, such as, but not limited to, applying a resist to the one main surface of the second insulating sheet20, using photolithography to perform patterning, and plating to fill a metal in the concave portions51to57and the holes58and59. As the filling method with a conductive material into the concave portions and the holes formed on the one main surface of the second insulating sheet20, any known method in the art at the time of filing this application may freely be used. Thereafter, excess portions of the conductive material may be removed by polishing, etching or other appropriate means.

As heretofore described, according to the manufacturing method for the wiring board100in the present embodiment of this invention, the end portions48aand49aof the projections48and49are exposed at the lower surface side of the second insulating sheet20when the second insulating sheet20is laminated on the first insulating sheet10, thereby ensuring the second vias38and39and the first upper side wirings12and16to respectively be connected with each other, and the wiring board100can thus be produced which has high connection reliability.

<Second Embodiment of First Invention>

A second embodiment of the first invention will hereinafter be described with reference toFIG. 10toFIG. 12. The present embodiment is characterized in that a cushion sheet (cushion member)60is located on the other main surface side of the second insulating sheet20in the transfer step in the first embodiment of the first invention. In order to avoid redundant descriptions, different aspects from the first embodiment will hereinafter be focused, and descriptions for common entities will be represented by those for the first embodiment of the first invention.

FIG. 10is a process cross-sectional view which illustrates a set condition before the transfer step and which corresponds toFIG. 3in the first embodiment. As shown inFIG. 10, in the present embodiment, the cushion member60which has elasticity is located on the other main surface side (lower surface side in the figure) of the second insulating sheet20. As the cushion member60, a film or a porous member may be used, such as made of thermoplastic resin, polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) or fluorine resin.

Under a similar condition to the first embodiment, i.e. under the first set temperature T1, the stamping surface4aof the mold4is pressed against the second insulating sheet20. In this transfer step, the length h1(T1) of the projections48and49is set as being larger than the thickness h2(T1) of the second insulating sheet20.

As shown inFIG. 11, in the transfer step, the end portions48aand49aof the projections48and49are exposed at the other main surface side (lower surface side in the figure) of the second insulating sheet20, and these exposed end portions48aand49apress against the cushion member60. The cushion member60is pressed by the end portions48aand49ato be depressed and deforms along the shapes of the end portions48aand49a. An enlarged view of region B ofFIG. 11in this state is shown inFIG. 12. As shown inFIG. 12, the end portion49ais exposed at the other main surface of the second insulating sheet20and further sinks into the cushion member60.

Thus, the cushion member60having elasticity is located on the other main surface side (lower surface side in the figure) of the second insulating sheet20thereby allowing the end portions48aand49ato penetrate the second insulating sheet20even with small force.

Particularly, if, in the transfer step of the present embodiment, the length h1(T1) of the projections48and49is set as being the thickness h2(T1) of the second insulating sheet20or more under the first set temperature T1while, in the laminating step, the length h1(T2) of the projections48and49and the thickness h2(T2) of the second insulating sheet20are set as being substantially the same under the second set temperature T2, then high accuracy is required for the control of the material, the thickness and the temperature of the second insulating sheet20and the length of the projections48and49. Given such a situation, even in the case where some variation occurs in the relationship between the length h1of the projections48and49and the thickness h2of the second insulating sheet20, if the cushion member60is located, then the pressing force to the second insulating sheet20in the transfer step can be controlled to thereby expose the end portions48aand49aof the projections48and49at the other main surface side of the second insulating sheet20.

As described in the above, according to the manufacturing method for the wiring board100in the second embodiment of the first invention, similar actions and advantageous effects to those in the first embodiment can be obtained, and in addition to this, the projections48and49can be exposed at the other main surface side of the second insulating sheet20with relatively small force because the cushion member60is located on the other main surface side of the second insulating sheet20in the transfer step. Moreover, even if a variation occurs in the relationship between the length h1of the projections48and49and the thickness h2of the second insulating sheet20, such a variation will be absorbed and the projections48and49can thus be ensured to expose at the other main surface side of the second insulating sheet20.

<First Embodiment of Second Invention>

Hereinafter, a manufacturing method for wiring board100according to the first embodiment of the second invention will be described.

An object of the second invention is to provide a manufacturing method for the wiring board100in which resin residues are unlikely to remain on the contact areas of via patterns. Further, the second invention is for the purpose of providing a manufacturing method for the wiring board100in which the filling process can be omitted, which would be necessary for an imprint method.

In order to achieve highly-dense wiring in association with downsizing electronic devices and enhancing the functionality thereof, an imprint method is known in which a mold is used to transfer concave shapes to an insulating sheet and the concave shapes are filled with a conductive material to form fine patterns (such as wiring patterns and via patterns).

In this imprint method, after the mold is released from the insulating sheet, if some resin remains in opening areas which have been formed by the mold and are to be connection portions for via patterns, then connection failures in via patterns or other troubles may possibly occur. In this respect, there is known an approach for removing such resin residues in opening areas using plasma etching or laser ablation (Patent Document 1: U.S. Pat. No. 7,351,660).

However, if, in order to remove resin residues, plasma or laser light is irradiated to a substrate formed thereon with wiring patterns, then problems occur including that the wiring patterns may be damaged or partially lost.

Problems to be solved by the present invention include avoiding resin from remaining between via patterns and wiring patterns contacting therewith, during the formation of via patterns.

The configuration of the wiring board100obtained by the manufacturing method according to the first embodiment of the present invention will first be described with reference toFIG. 13, and the manufacturing method according to the first embodiment of the present invention will then be described with reference toFIG. 14toFIG. 19.

As shown inFIG. 13, the wiring board100according to the first embodiment of the second invention is a multilayer board that comprises a first substrate1and a second substrate2laminated on one main surface side (upper side in the figure) of the first substrate1. While the present embodiment is described for an example of the wiring board100which is configured of two substrates, the pre sent invention is applicable to a wiring board100which is configured of three or more substrates. Note that the present embodiment is described with reference to an x-y plane shown in the figure as a plane along the wiring board100(substrates1and2and insulating sheets10and20) and a z-axis direction as the laminating direction, and the upper side along the z-axis in the figure represents the one main surface side.

The first substrate1located on the lower side in the figure comprises: a first insulating sheet10; first upper side wirings11to17formed on one main surface (the upper side in the figure: here and hereinafter) of the first insulating sheet10; first lower side wirings21and22formed on the other main surface (the lower side in the figure: here and hereinafter) of the first insulating sheet10; and first vias18and19respectively connecting the first upper side wirings12and16and the first lower side wirings21and22.

The second substrate2comprises: a second insulating sheet20laminated on the one main surface (the upper side in the figure) of the first insulating sheet10; second upper side wirings71P to77P formed on one main surface (main surface on the upper side in the figure) of the second insulating sheet20; and second vias78P and79P respectively connecting the second upper side wirings72P and76P and the first upper side wirings12and16, wherein the second upper side wirings72P and76P are included in the second upper side wirings71P to77P.

The second upper side wirings71P to77P and the second vias78P and79P are convexly formed toward the interior of the second insulating sheet20from the one main surface (the upper side main surface) of the second insulating sheet20. That is, the one main surface of the second insulating sheet20formed with the second upper side wirings71P to77P and connection portions for the second vias78P and79P is flat, so that another substrate not shown can be laminated flatly thereon, i.e. without any space, or other electric components not shown can be mounted thereon.

As a material for the first insulating sheet10and the second insulating sheet20, thermosetting resin such as epoxy resin or thermoplastic resin such as thermoplastic polyimide and liquid-crystal polymer may be used, for example. As a material for the first upper side wirings11to17, the first lower side wirings21and22, the first vias18and19, the second upper side wirings71P to77P and the second vias78P and79P, copper (Cu), silver (Ag), gold (Au) or other materials having conductivity may be used.

Although not particularly limited, in the first upper side wirings11to17and the first lower side wirings21and22constituting a part of wiring patterns of the first substrate1and the second upper side wirings71P to77P constituting a part of wiring patterns of the second substrate2, line-and-space areas may be arranged such that the wiring width is approximately 5 μm to 15 μm and the wiring space is approximately 5 μm to 15 μm. In addition, the diameter (thickness) of the first vias18and19and the second vias78P and79P is 2 μm or more and 35 μm or less, preferably 2 μm or more and 15 μm or less, and more preferably 2 μm or more and less than 10 μm. The length of the first vias18and19and the second vias78P and79P in the present embodiment is 1 μm or more and 50 μm or less, and preferably 10 μm or more and 40 μm or less. The aspect ratio is 0.5 to 25 and preferably 1 to 25, and may be about 1 to 4 in the present example.

(Manufacturing Method for Wiring Board)

One example of a manufacturing method for the wiring board100according to the first embodiment of the second invention will then be described with reference toFIG. 14toFIG. 19.

At first, the first substrate1shown inFIG. 14is prepared. As the first substrate1, a substrate may be used which comprises at least the first insulating sheet10and the first upper side wirings11to17formed on one main surface (surface on which the second substrate2is to be laminated) of the first insulating sheet10, but in the present example, a double-side substrate is used as the first substrate1, in which the first upper side wirings11to17are formed on the one main surface of the first insulating sheet10so as to be embedded therein and the first lower side wirings21and22are formed on the other main surface.

While the product ion method for the first substrate1shown inFIG. 14is not particularly limited, a mold is used for example, which comprises a stamping surface including convex portions and projections formed respectively depending on the first upper side wirings11to17and the first vias18and19, to transfer patterns to the one main surface (upper surface in the figure) of the first insulating sheet10thereby forming concave portions and holes respectively depending on the first upper side wirings11to17and the first vias18and19, a plating process or other appropriate process is performed to fill these concave portions and holes with a conductive material, and the first substrate1can thereby be produced as a single-side substrate, in which the first upper side wirings11to17and the first vias18and19are formed on the one main surface side of the first insulating sheet10. Further, a resist is applied to the other main surface (lower surface in the figure) of the first insulating sheet10, photolithography is used to pattern the resist depending on the first lower side wirings21and22, plating is then performed, and the first substrate1can thereby produced as a double-side substrate, in which the first lower side wirings21and22are further formed on the other main surface side of the first insulating sheet10. Of course, both surfaces may be formed thereon with resists having certain patterns, and thereafter a plating process may be concurrently performed for the both surfaces.

Alternatively, holes depending on the first vias18and19are formed by irradiating laser beam or other beam to the one main surface (upper surface in the figure) side of the first insulating sheet10, thereafter, photolithography is used to pattern a resist depending on patterns of the first upper side wirings11to17and the first vias18and19, concave portions depending on the first upper side wirings11to17and the holes depending on the first vias18and19are subjected to nonelectrolytic plating and/or electrolytic plating, and the first substrate1can thereby be produced as a single-side substrate, in which the first upper side wirings11to17and the first vias18and19are formed on the one main surface side of the first insulating sheet10. Note that the plating may be substituted by screen printing which uses conductive paste to fill a conductive material in concave portions depending on the first upper side wirings11to17and in holes depending on the first vias18and19. Further, the first substrate formed thereon with the first lower side wirings21and22can be produced by printing conductive paste to the other main surface (lower surface in the figure) side of the first insulating sheet10using a printing plate depending on patterns of the first lower side wirings21and22. As the production method for the first substrate1, any production method for double-side substrate known in the art at the time of filing this application may appropriately be utilized. If no wiring pattern is necessary for the other main surface side of the first substrate1, then any production method for single-side substrate known in the art at the time of filing this application may appropriately be utilized.

Before or after or in parallel with the preparation of the first substrate1, a wiring body7shown inFIG. 15is prepared. As shown inFIG. 15, the wiring body7in the present embodiment has a wiring surface7athat includes: convex portions71to77functioning as the second upper side wirings71P to77P to be a part of patterns of the second substrate2which will be laminated on the first substrate1in the wiring board100as a product; and projections78and79functioning as the second vias78P and79P to be another part of the patterns.

The convex portions71to77and the projections78and79of the wiring surface7aconstitute respectively the second upper side wirings71P to77P themselves and the second vias78P and79P themselves in the wiring board100as a product, and function as a working-purpose plate (original plate) for forming a concave-convex shape (the projections78and79and the convex portions71to77), which depends on shapes of these second vias78P and79P and the second upper side wirings71P to77P, on the second insulating sheet20. Reference character7ainFIG. 15specifies the entire surface to be pressed against the second insulating sheet, on the other main surface side (lower side in the figure) of the wiring body7formed thereon with the concave-convex shape including the convex portions71to77and projections78and79for constituting desired patterns.

While the production method for the wiring body7is not particularly limited, the wiring body7can be obtained for example through: preparing a mold provided with concaves and convexes depending on wiring portions including the convex portions71to77and the projections78and79; filling regions among these concaves and convexes with a conductive material such as copper (Cu), gold (Au), silver (Ag) or nickel (Ni) by plating or printing; thereafter performing solidification; and applying them to the supporting member70.

Note that the mold for producing the convex portions71to77of the wiring portions may be obtained, such as, but not limited to, by the following approach. For example, a mold provided with concave portions depending on the convex portions71to77and holes depending on the projections78and79can be obtained through: preparing a resin plate body applied to a main surface of a supporting plate body for producing a mold; irradiating laser or electron beam or performing etching process to a main surface of the resin plate body to form holes depending on the second vias78P and79P; laminating a resist layer on the resin plate body; and exposing or heating predetermined regions of the resist layer depending on wiring patterns and thereafter selectively removing the predetermined regions using etching liquid to form groove portions depending on the wiring patterns.

The production method for the wiring body7is not limited to the above, and the convex portions71to77and the projections78and79can be formed on the main surface of the supporting member70using a method for forming wiring patterns known in the art at the time of filing this application. For example, screen printing may be employed using ink including a conductive material to form the convex portions71to77and the projections78and79on the other main surface (lower surface in the figure) of the supporting member70, or plating process may be performed for concave portions of a mask removed therefrom predetermined regions using photolithography thereby to form the convex portions71to77and the projections78and79.

As shown inFIG. 15, the wiring body7is located so that the wiring surface7afaces a stage6, on which a target object to be transferred thereto is to be placed. As shown in the figure, if the second insulating sheet20is set on the platen of the stage6, then the wiring surface7aof the wiring body7faces the one main surface side (upper side in the figure) of the second insulating sheet20. Although not particularly limited, as the second insulating sheet20, uncured (semi-cured) thermosetting resin such as epoxy resin or thermoplastic resin such as liquid-crystal polymer or thermoplastic polyimide may be used, for example.

As shown inFIG. 15, in a state at ambient temperature (T0) before mold clamping, the depth of the wiring surface7a, in particular the length h3(T0) of the projections78and79formed on the wiring surface7adepending on the second vias78P and79P, may be set as being the thickness h4(T0) of the second insulating sheet20or more. The second insulating sheet20tends to expand in the subsequent heating process to increase in its thickness h4, and therefore, the thickness h4(T0) of the second insulating sheet20at ambient temperature is preferred to be set as being equal to or thinner than the depth of the wiring surface7a.

Using the above-described wiring body7shown inFIG. 15, the second substrate2is obtained. Specifically, the second insulating sheet20is heated at first until it becomes a first set temperature T1. The first set temperature T1is a temperature which is suitable for transferring the wiring surface7aand which is defined depending on the heat deformation temperature or glass transition temperature (Tg) of the second insulating sheet20. The first set temperature T1when the pattern shape of the wiring surface7ais transferred may be freely determined depending on the characteristics and the thickness of the second insulating sheet20. As one example, the first set temperature T1may be approximately 260° C. to 300° C. Note that heating the second insulating sheet20may be performed by directly heating the second insulating sheet20or by heating the wiring body7to indirectly heat the second insulating sheet which contacts the wiring body7.

As shown inFIG. 16, after the second insulating sheet20is heated to the first set temperature T1(or after the wiring body7is heated to a temperature capable of heating the second insulating sheet20to the first set temperature T1at the time of transferring), the wiring surface7aof the wiring body7is pressed against the second insulating sheet20.

The projections78and79and the convex portions71to77of the wiring surface7aare pressed into the second insulating sheet20having been heated to be softened. In the present embodiment, the wiring body7may be pressed against the one main surface (upper side in the figure) of the second insulating sheet20so that at least end portions78aand79aof the projections78and79of the wiring surface7aare exposed at the other main surface side (lower side in the figure) of the second insulating sheet20. The end portions78aand79aof the projections78and79in the present embodiment include at least end surfaces (surfaces to contact first the second insulating sheet20) of the projections78and79, but not limited thereto, and portions with a certain distance toward the supporting member70from these end surfaces may also be included therein.

As shown inFIG. 16, the convex portions71to77depending on the second upper side wirings71P to77P and the projections78and79depending on the second vias78P and79P are formed on the one main surface of the second insulating sheet20in a state of being embedded therein.

In this step for pressing the wiring body7against the second insulating sheet20(referred also to as an embedding step, hereinafter), as shown inFIG. 6, the length of the projections78and79and the material and the thickness of the second insulating sheet20may be set such that the length h3(T1) of the projections78and79formed depending on the second vias78P and79P is the thickness h4(T1) of the second insulating sheet20or more at the first set temperature T1(260° C. to 300° C., for example) (h3(T1)≧h4(T1)).

In this embedding step, the second insulating sheet20is heated to the first set temperature T1to expand with a larger thickness h4than that at ambient temperature (T0), but the end portions78aand79aof the projections78and79are ensured to be exposed at the other main surface side of the second insulating sheet20because the length of the projections78and79and the material and the thickness of the second insulating sheet20are preliminarily set such that the length h3(T1) of the projections78and79is the thickness h4(T1) of the second insulating sheet20or more at the first set temperature T1(h3(T1)≧h4(T1)).

Subsequently, as shown inFIG. 17, the other main surface (lower surface in the figure) of the second insulating sheet20is caused to face the one main surface (upper surface in the figure) of the first substrate1in a state where the projections78and79and the convex portions71to77of the wiring body7still remain inserted in the second insulating sheet20. Thereafter, the end portions78aand79aof the projections78and79exposed at the other main surface (lower surface in the figure) of the second insulating sheet20are aligned to respectively contact the first upper side wirings12and16of the first insulating sheet10using image recognition, pin-alignment or other appropriate means, and the second insulating sheet20is laminated on the first insulating sheet10, as shown inFIG. 18.

In this laminating step, the second insulating sheet20laminated on the one main surface side (upper side in the figure) of the first insulating sheet10is hot-pressed along the laminating direction (z-axis direction) while being heated to a second set temperature T2.

The second set temperature T2in the laminating step may be, such as, but not limited to, a temperature where the first insulating sheet10and the second insulating sheet20are softened to exhibit adhesiveness. At the second set temperature T2, the first insulating sheet10and the second insulating sheet20are fused or adhere to each other. The second set temperature T2may be set as being less than the first set temperature T1, and may be 220° C. to 260° C., for example.

The end portions78aand79aof the projections78and79longer than the thickness of the second insulating sheet20are exposed at the other main surface side (lower side in the figure) of the second insulating sheet20before the second insulating sheet20is laminated on the first insulating sheet, so that the ends of the projections78and79and the first upper side wirings12and16can be ensured to contact each other, respectively, without any resin interposed in the contact portions between the ends of the projections78and79and the first upper side wirings12and16, as shown inFIG. 18.

In addition, during this laminating step, the height h3of the projections78and79and the thickness h4of the second insulating sheet20can be made to be substantially the same. More specifically, the difference between the length h3of the projections78and79and the thickness h4of the second insulating sheet20may be about less than 10% of the length of the projections78and79, preferably less than 5%, more preferably less than 3%, and most preferably less than 1%.

Thus, in the laminating step, the length h3of the projections78and79and the thickness h4of the second insulating sheet20are made to be substantially the same thereby to avoid the resin from flowing into the contact portions between the ends of the projections78and79and the first upper side wirings12and16even if a part of the second insulating sheet20is fluidized due to heating during the laminating. As a result, resin residues can be prevented from remaining between the ends of the projections78and79and the first upper side wirings12and16. Moreover, in the laminating step, the length h3of the projections78and79and the thickness h4of the second insulating sheet20are made to be substantially the same thereby to prevent the ends of the projections78and79from strongly pressing against the first upper side wirings12and16to destroy them even if the second insulating sheet20is pressed against the first insulating sheet10during the laminating.

In fact, the present embodiment is such that the embedding step shown inFIG. 16is performed at the first set temperature T1and under the condition where the length h3(T1) of the projections78and79of the wiring surface7ais the thickness h4(T1) of the second insulating sheet20or more while the laminating step shown inFIG. 18is performed at the second set temperature T2lower than the first set temperature T1and under the condition where the length h3(T2) of the projections78and79of the wiring surface7aand the thickness h4(T2) of the second insulating sheet20are substantially the same. Here, the condition, where the thickness of the second insulating sheet20is thinner than the length h3of the projections78and79at the relatively high first set temperature T1while the thickness of the second insulating sheet20is substantially the same as the length h3of the projections78and79at the relatively low second set temperature T2, may appear to be contrary to the common general technical knowledge that the second insulating sheet20expands to become thicker as the temperature increases. As shown inFIG. 16, however, even if being applied with a relatively large pressing force during mold clamping in the embedding step, the softened second insulating sheet20is allowed to laterally expand toward the outer edge (right and left end portions of the second insulating sheet20in the figure). As shown in the figure, the end portions of the second insulating sheet20are rounded to absorb the expanded volume of the second insulating sheet. Accordingly, the condition can be established in the present embodiment, where: T1>T2; (the length h3(T1) of the projections78and79)≧(the thickness h4(T1) of the second insulating sheet20); and the length h3(T2) of the projections78and79and the thickness h4(T2) of the second insulating sheet20are substantially the same, as described in the above.

After the laminating, the second insulating sheet20, if being thermosetting resin, is completely cured by being heated for example at 180° C. during one hour using oven or other appropriate means. The second insulating sheet20, if being thermoplastic resin, is cured by being cooled. Thereafter, the supporting member70of the wiring body7is removed from the second insulating sheet20.

FIG. 19is an enlarged view of region C surrounded by broken line inFIG. 18. As shown inFIG. 19, it is possible to avoid resin from remaining at connection portion between the projection79and the first upper side wiring16after the laminating. Thus, the second via79P can be formed which is capable of being interlayer-connected to other element (the first upper side wiring16) without any resin interposed therebetween, thereby enhancing the connection reliability. In addition, resin residue removing processes are not necessary, such as plasma irradiation, laser irradiation and chemical etching, for removing resin remaining in holes for forming via patterns, which would be required in the conventional method.

If a wiring board is obtained by a manufacturing method including plasma irradiation or laser irradiation, then the patterns and/or the insulating sheets thereof will involve lost parts and/or defect traces, while if a wiring board is obtained by a manufacturing method including chemical etching process, then the patterns and/or the insulating sheets thereof will involve chemical erosion traces. In contrast, according to the manufacturing method of the present embodiment, the wiring board100can be provided which can avoid such lost parts, defects or chemical erosions caused due to resin residue removing processes.

In order to confirm advantageous effects resulted from the manufacturing method according to the present embodiment, a manufacturing method according to Comparative Example 3 has been carried out in which the step for pressing the wiring body7against the one main surface of the second insulating sheet20is different from the present embodiment only in the point that the length h3of the projections78and79is less than the thickness h4of the second insulating sheet20, and an observation has also been performed for the condition of the connection portion between the projection79of the wiring body7and the first upper side wiring16.FIG. 20schematically illustrates the condition of this comparative example, which corresponds to region C inFIG. 18. As shown inFIG. 20, resin S remains at the connection portion between the projection79of the wiring body7and the first upper side wiring16. Due to this resin S, the contact area for the connection portion between the projection79and the first upper side wiring16is reduced, and the connection reliability is thus deteriorated.

Similarly, a manufacturing method according to Comparative Example 4 has been carried out in which the step for laminating the second insulating sheet20on the first insulating sheet10is different from the present embodiment only in the point that the length h3of the projections78and79is less than the thickness h4of the second insulating sheet20, and an observation has also been performed for the condition of the connection portion between the projection79and the first upper side wiring16after the laminating. Like the above Comparative Example 3, resin S remains at the connection portion between the projection79and the first upper side wiring16. This condition is similar to the condition schematically illustrated inFIG. 20, which corresponds to the previously-described region C inFIG. 18. Due to this resin S, the contact area for the connection portion between the projection79and the first upper side wiring16is reduced, and the connection reliability is thus deteriorated.

As heretofore described, according to the manufacturing method for the wiring board100in the present embodiment of this invention, the end portions78aand79aof the projections78and79are exposed at the lower surface side of the second insulating sheet20when the second insulating sheet20is laminated on the first insulating sheet10, thereby ensuring the second vias78P and79P and the first upper side wirings12and16to respectively be connected with each other, and the wiring board100can thus be produced which has high connection reliability.

In addition, production cost can be reduced because a step for filling a conductive material in grooves and holes formed depending on patterns is not necessary, which would be required in the conventional method.

<Second Embodiment of Second Invention>

A second embodiment of the second invention will hereinafter be described with reference toFIG. 21toFIG. 23. The present embodiment is characterized in that a cushion sheet60is located on the other main surface side of the second insulating sheet20in the embedding step in the first embodiment of the second invention. In order to avoid redundant descriptions, different aspects from the first embodiment will hereinafter be focused, and descriptions for common entities will be represented by those for the first embodiment of the second invention.

FIG. 21corresponds toFIG. 15in the first embodiment, which illustrates a set condition before the embedding step. As shown inFIG. 21, in the present embodiment, the cushion member60which has elasticity is located on the other main surface side (lower surface side in the figure) of the second insulating sheet20. As the cushion member60, a film or a porous member may be used, such as made of thermoplastic resin, polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) or fluorine resin.

Under a similar condition to the first embodiment, i.e. under the first set temperature T1, the wiring surface7aof the wiring body7is pressed against the second insulating sheet20. In this embedding step, the length h3(T1) of the projections78and79is set as being larger than the thickness h4(T1) of the second insulating sheet20.

As shown inFIG. 22, in the embedding step, the end portions78aand79aof the projections78and79are exposed at the other main surface side (lower surface side in the figure) of the second insulating sheet20, and these exposed end portions78aand79apress against the cushion member60. The cushion member60is pressed by the end portions78aand79ato be depressed and deforms along the shapes of the end portions78aand79a. An enlarged view of region D ofFIG. 22in this state is shown inFIG. 23. As shown inFIG. 23, the end portion79ais exposed at the other main surface of the second insulating sheet20and further sinks into the cushion member60.

Thus, the cushion member60having elasticity is located on the other main surface side (lower surface side in the figure) of the second insulating sheet20thereby allowing the end portions78aand79ato penetrate the second insulating sheet20even with small force.

Particularly, if, in the embedding step of the present embodiment, the length h3(T1) of the projections78and79is set as being the thickness h4(T1) of the second insulating sheet20or more under the first set temperature T1while, in the laminating step, the length h3(T2) of the projections78and79and the thickness h4(T2) of the second insulating sheet20are set as being substantially the same under the second set temperature T2, then high accuracy is required for the control of the material, the thickness and the temperature of the second insulating sheet20and the length of the projections78and79. Given such a situation, even in the case where some variation occurs in the relationship between the length h3of the projections78and79and the thickness h4of the second insulating sheet20, if the cushion member60is located, then the pressing force to the second insulating sheet20in the embedding step can be controlled to thereby expose the end portions78aand79aof the projections78and79at the other main surface side of the second insulating sheet20.

As described in the above, according to the manufacturing method for the wiring board100in the second embodiment of the second invention, similar actions and advantageous effects to those in the first embodiment can be obtained, and in addition to this, the projections78and79can be exposed at the other main surface side of the second insulating sheet20with relatively small force because the cushion member60is located on the other main surface side of the second insulating sheet20in the embedding step. Moreover, even if a variation occurs in the relationship between the length h3of the projections78and79and the thickness h4of the second insulating sheet20, such a variation will be absorbed and the projections78and79can thus be ensured to expose at the other main surface side of the second insulating sheet20.

It should be appreciated that the embodiments heretofore explained are described to facilitate understanding of the present invention and are not described to limit the present invention. Therefore, it is intended that the elements disclosed in the above embodiments include all design changes and equivalents to fall within the technical scope of the present invention.

DESCRIPTION OF REFERENCE NUMERALS