Method of manufacturing multilayer wiring substrate, and multilayer wiring substrate

A method of manufacturing a multilayer wiring substrate, which can preserve the dimensional stability of a conductor pattern at a fine pitch, solve the restriction on a process from the viewpoint of material selection, and further reduce a manufacturing cost, and a multilayer wiring substrate. A second wiring substrate formed on a supporting sheet made of metal and an adhesive layer are partially stacked on a predetermined region of a first wiring substrate by using the supporting sheet. After the lamination of the second wiring substrate, the supporting sheet is finally etched and removed. The second wiling substrate is stacked only on the portion required to be multilayered on the first wiring substrate to thereby reduce the amount of the construction material of the second wiring substrate.

This application claims priority to Japanese Patent Application Number JP2002-099883 filed Apr. 2, 2002 which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing a multilayer wiring substrate in which two or more wiring substrates are stacked on each other, and a multilayer wiring substrate.

2. Description of Related Art

In association with the miniaturization and the usage of multiple functions in electronic apparatuses, the request for higher density of wiring substrates (printed circuit boards) and miniaturization of mounted parts are becoming increasingly restrictive. In the wiring substrate, the higher density in a direction parallel to a substrate surface has been conventionally tried by reducing a wiring rule. However, in recent years, the higher density in a direction vertical to the surface of the wiring substrate has been advanced by employing a buildup process, stacking the wiring substrates, and forming via holes (interlayer connections) to electrically connect any layers to each other.

As this type of a conventional technique, for example, Japanese Laid Open Patent Application (JP-A-Heisei, 10-107445) discloses a method of manufacturing a multilayer wiring substrate, which forms a conductor pattern (a wiring pattern) on a wiring substrate by using a transferring method. The conventional method of manufacturing a multilayer wiring substrate will be described below with reference toFIGS. 15A to 15E.

At first, as shown inFIG. 15A, a wiring substrate in which a first conductor pattern2is formed on a surface of an insulator1is produced or prepared. Then, as shown inFIG. 15B, an insulating layer3is formed by coating insulation slurry on the surface of the insulator1. Next, as shown inFIG. 15C, via holes4linked to the first conductor pattern2are formed in the insulating layer3by using laser machining and the like, and a conductive paste5is filled in the formed via holes4. In succession, as shown inFIG. 15D, a second conductor pattern6previously formed on a transfer sheet7is transferred onto the insulating layer3. The first and second conductor patterns2,6are connected through the conductive paste5.

The transfer sheet7is mainly made of synthetic resin material such as polyethylene terephthalate (PET) and the like. The conductor pattern6is formed by patterning a conductor layer put or deposited on this transfer sheet7to a predetermined shape by using a wet etching method. The transfer of the conductor pattern6to the insulating layer3from the transfer sheet7is carried out by using the differences in adhesion between the conductor pattern6and the insulating layer3and between the conductor pattern6and the transfer sheet7.

When three or more conductive layers are formed, the processes similar to the above-mentioned case are repeated. In short, as shown inFIG. 15E, an insulating layer8is further formed on the insulating layer3. Via holes are formed in this insulating layer8, and a conductive paste10is filled in the formed via holes. After that, a third conductor pattern11is formed by the transferring method.

As mentioned above, in the case of the multilayer wiring substrate manufactured by the transferring method, the via holes for the connection between the layers are formed in any portions of the insulating layer. Consequently, the multilayer can be easily attained.

However, in the case of the above-mentioned conventional method of manufacturing the multilayer wiring substrate, the transfer sheet7is mainly made of the resin film. Thus, this method has a problem that the expansion/contraction and the warp of the transfer sheet7occurring at a time of handling cause an error to be easily induced in the pattern shapes (the dimensions) of the transferred conductor patterns6,11. Thus, in this conventional method of manufacturing the multilayer wiring substrate, it will be very difficult to cope with the hyperfine structure (fine pitch structure) of the conductor patterns expected to continue to evolve in the future. Hence, it is impossible to obtain the multilayer wiring substrate of a high quality which corresponds to the fine pitch structure.

By the way, the transfer sheet is thought to be made of metal material such as stainless steel and the like. In this case, as compared with the case in which the transfer sheet is made of the resin film, a rigidity of the transfer sheet is increased to thereby improve the dimensional stability of the conductor pattern. However, in this case, if the rigid property of the transfer destination is strong, it is difficult to remove the transfer sheet. Thus, this method has a problem that the operation for transferring the conductor pattern is not able to be properly done.

Also, in the case of the conventional method of manufacturing the multilayer wiring substrate, the process for producing the multilayer is the steps of alternately stacking the insulating layer and the conductive layer by one layer at a time. For example, if any step defect occurs in the upper layer, all of the steps until that time become vain, and the entire wiring substrate is treated as a defect. Thus, the conventional method of manufacturing the multilayer wiring substrate has a problem that its productivity is poor and its yield is low.

Moreover, the conventional method of manufacturing the multilayer wiring substrate is designed so as to form the insulating layers3,8on the entire surface of a bedding layer when producing the multilayer. Thus formed insulating layers3,8need to be baked and cured. Thus, the conventional method must impose a certain limit on the selection for the construction materials of the insulating layers3,8, in order to protect the miss match of a baking temperature. Consequently, this method has a problem that the degree of the freedom of the board design becomes low.

On the other hand, when the board design is carried out for producing the multilayer only in a partial region on the bedding substrate and improving the wiring density, the conventional manufacturing process needs to uniformly form the insulating layers even in the other regions on the bedding substrate. Thus, the conventional method also has a problem that the burden of a material cost when an expensive material is used for the insulating layer is increased.

As mentioned above, the conventional method of manufacturing the multilayer wiring substrate has the problems that it is difficult to cope with the finer pitch structure of the conductor pattern and that the restriction on the material selection is always accompanied and that the producing cost or the material cost is expensive.

SUMMARY OF THE INVENTION

The present invention is accomplished in view of the above mentioned problems. Accordingly, there has been a need to provide a method of manufacturing a multilayer wiring substrate, which can preserve the dimensional stability in a conductor pattern of a fine pitch and remove the restriction on a process from the viewpoint of material selection and further reduce a manufacturing cost, and a multilayer wiring substrate.

In order to solve the above-mentioned problems, a method of manufacturing a multilayer wiring substrate according to the present invention is a method of manufacturing a multilayer wiring substrate, in which a first wiring substrate having a first conductor pattern and a second wiring substrate having a second conductor pattern are stacked on each other, including the steps of: forming the second wiring substrate on a supporting sheet made of metal; forming an adhesive layer on the formed second wiring substrate; forming an interlayer connection linked to the second conductor pattern, for the adhesive layer; stacking the second wiring substrate through the adhesive layer on a predetermined region of the first wiring substrate, and electrically connecting the interlayer connection and the first conductor pattern; and removing the supporting sheet from the second wiring substrate.

In the present invention, the first wiring substrate and the second wiring substrate are formed independently of each other. The second wiring substrate is formed on the supporting sheet made of metal. The adhesive layer is formed on the second wiring substrate, and that interlayer connection and the second conductor pattern are electrically connected. After that, the second wiring substrate is stacked through the adhesive layer on the predetermined region of the first wiring substrate. At this time, the supporting sheet functions as the support to maintain the flatness of the second wiring substrate, and the supporting sheet is removed after both of the substrates are stacked. Consequently, even if the first and second wiring substrates are made of materials different from each other, they can be stacked on each other. Thus, the restriction on the process from the viewpoint of material selection is solved.

The method of manufacturing the multilayer wiring substrate, according to the present invention, is preferable when the second wiring substrate is made of the material relatively weak in rigid property and in self-support property. The supporting sheet made of the metal can maintain the flatness of the second wiring substrate and the adhesive layer. Thus, the dimensional stability of the second conductor pattern and the interlayer connection can be preserved to properly stack on the first wiring substrate.

Also, the present invention is designed so as to stack the second wiring substrate on the predetermined region of the first wiring substrate. Thus, the second wiring substrate can be formed smaller in area than the first wiring substrate. Hence, the material cost can be reduced.

On the other hand, another method of manufacturing a multilayer wiring substrate according to the present invention includes the steps of: forming an adhesive layer on a supporting sheet made of metal; forming a conductive interlayer connection for linking between the layers for the adhesive layer; stacking the second wiring substrate on the adhesive layer and electrically connecting the interlayer connection and the second conductor pattern; removing the supporting sheet from the adhesive layer; and stacking the second wiring substrate through the adhesive layer on a predetermined region of the first wiring substrate, and electrically connecting the interlayer connection and the first conductor pattern.

Also in the present invention, the first wiring substrate and the second wiring substrate are formed independently of each other. The second wiring substrate is formed on the supporting sheet through the adhesive layer. Then, the second wiring substrate is stacked on the predetermined region of the first wiring substrate after the removal of the supporting sheet.

The present invention is preferably applied to a case when the second wiring substrate is made of the material that is relatively strong in rigid property and self-support property.

On the other hand, the multilayer wiring substrate according to the present invention is characterized in that it is a multilayer wiring substrate, in which a first wiring substrate and a second wiring substrate electrically connected to the first wiring substrate are stacked on each other, wherein the second wiring substrate is partially stacked on a predetermined region of the first wiring substrate.

According to the present invention, the second wiring substrate can be formed smaller in area than the first wiring substrate. Thus, as compared with the case in which the second wiring substrate is formed on the entire surface of the first wiring substrate, the usage amount of the construction material of the second wiring substrate can be reduced to thereby reduce the material cost. Moreover, the multilayer wiring substrate can be entirely lightened.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a configuration of a multilayer wiring substrate according to the first embodiment of the present invention. A multilayer wiring substrate20in this embodiment is provided with a first wiring substrate21, a second wiring substrate22, and an adhesive material layer23placed between those first and second wiring substrates21,22.

The first wiring substrate21in this embodiment is made of, for example, double-side copper-clad stack, and it includes: an insulator base material24serving as an insulating layer; and conductor patterns25A,25B (corresponds to a first conductor pattern of the present invention) formed by patterning copper foils on the double sides to predetermined shapes. By the way, Ni/Au (Nickel/Gold) plating layers may be formed on surface layers of the conductor patterns25A,25B.

The construction material of the insulator base material24is suitably selected depending on an application target, a use application and the like. For example, it is made of organic material, such as glass epoxy resin (element in which epoxy resin is impregnated in fiber glass), element in which polyimide resin is impregnated in fiber glass, BT resin (Brand Name) in which mixture of bismale-imide-triazine resin and epoxy resin is impregnated in fiber glass, element in which phenol resin is impregnated in paper, and the like. However, besides them, it can be made of ceramic-based material, such as alumina or glass inclusion ceramics, aluminum nitride, and the like.

The conductor patterns25A,25B are partially electrically connected to each other via through-bores26. The through-bore26is composed of a through-bore27formed in the insulator base material24and a copper plating28formed on the inner wall plane thereof. By the way, a filler29made of conductive material or non-conductive material is filled in the through-bore26.

The regions in which the conductor patterns25A,25B on the top and bottom surfaces of the insulator base material24are not formed are covered with layers of insulating materials37A,37B, and the step on the insulator base material24caused by the formations of the conductor patterns25A,25B is removed. Consequently, the lamination plane of the first wiring substrate21is flattened to thereby preserve the proper lamination condition with the second wiring substrate22.

Moreover, outer surfaces of the first wiring substrate21formed by the conductor patterns25A,25B and the insulating materials37A,37B are coated by solder resists38A,38B. However, the region on which the second wiring substrate22is stacked is exposed through an opening39toward the outside.

FIGS. 2A to 2Eshow an example of the process for producing the first wiring substrate21. At first, the through-bores27,27are formed in predetermined portions of the previously prepared double-side copper-clad stack by using a micro drill and the like. Moreover, the copper plating28is formed on the inner wall plane of the through-bore27(FIGS. 2A,2B). Next, the filler29is filled in the through-bore27, and copper foils25,25are patterned to predetermined shapes to thereby form the conductor patterns25A,25B (FIGS. 2C,2D). Then, the portions on the insulator base material24on which the conductor patterns25A,25B are not formed are coated with the insulating materials37A,37B. After that, the solder resists38A,38B are formed on the double sides (FIG. 2E). The first wiring substrate21in this embodiment is formed as mentioned above.

With reference toFIG. 1, the second wiring substrate22itself is constituted as the multilayer substrate, and it has a conductor pattern (corresponds to a second conductor pattern of the present invention)35. As shown, the second wiring substrate22is formed smaller in area than the first wiring substrate21. It is partially stacked on a predetermined portion on the first wiring substrate21through the adhesive material layer23. In this embodiment, the above-mentioned predetermined portion designates the region required to be multilayered (higher wiring density) on the first wiring substrate21.

An insulator base material34serving as an insulating layer is made of photosensitive resin material having high resolution, for example, poly-benzo-oxadole (PBO), benzo-cyclobutene, photosensitive polyimide, and the like.

The conductor pattern35is formed by a damascening method widely used in a micro wiring forming process for a semiconductor device, and it is composed of: conductor lands35A,35B exposed on the top and bottom surfaces of the insulator base material34; and an inner wiring layer35C through which they are connected. By the way, the conductor pattern35may be formed, for example, by using a semi-additive method besides the damascening method.

The conductor land35A on the top side of the insulator base material34is formed at a pitch narrower than that of the conductor land35B on the bottom side (the side of the first wiring substrate21). Although this is not shown, a semiconductor chip can be installed on the second wiring substrate22in the well known manner such as a flip chip mount or a wire bonding connection or the like. In this case, an arrangement pitch between the conductor lands35A is defined correspondingly to a bump pitch of the semiconductor chip. In short, the second wiring substrate22is designed so as to be able to function as an interposer substrate when the semiconductor chip is mounted on the first wiring substrate21.

Now, the second wiring substrate22is stacked through the adhesive material layer23on the first wiring substrate21. The adhesive material layer23is composed of an interlayer insulating layer31and a plurality of conductive interlayer connections32. The interlayer connection32penetrates a predetermined portion of the interlayer insulating layer31and electrically connects the conductor pattern25A of the first wiring substrate21and the conductor pattern35of the second wiring substrate22.

Here, the interlayer insulating layer31constituting the adhesive material layer23is made of, for example, photosensitive adhesive. The interlayer connection32is formed at that predetermined portion by filling conductive material in the holes made by using a photolithography technique. In this embodiment, the interlayer connection32is composed of an electroplating layer of copper (Cu). However, besides this, it can be composed of other metals such as nickel (Ni), tin (Sn), and the like.

The multilayer wiring substrate20in this embodiment is configured as mentioned above. According to the multilayer wiring substrate20in this embodiment, the first wiring substrate21and the second wiring substrate22are configured so as to be stacked on each other through the adhesive material layer23. Thus, although the respective insulator base materials24,34are made of different materials, they can be easily stacked to thereby attain the multilayer.

For example, the insulator base material of the first wiring substrate is made of glass epoxy resin, and the insulator base material of the second wiring substrate is made of benzo-cyclobutene. The benzo-cyclobutene is a low dielectric material and suitable for the base material for a high frequency circuit. The thus-configured first and second wiring substrates are stacked to thereby give the performance of the second wiring substrate to the necessary region on the first wiring substrate. Hence, it is possible to obtain the multilayer wiring substrate that can attain a systematic function.

Also, the multilayer wiring substrate20in this embodiment is designed such that the second wiring substrate22is partially stacked on the predetermined region of the first wiring substrate21, as shown inFIG. 1. Thus, the multilayer can be formed only in the originally required region. Consequently, the area of the second wiring substrate22can be decreased to thereby reduce the material cost. Moreover, the multilayer wiring substrate can be entirely carried out weight-saving.

The method of manufacturing the multilayer wiring substrate20in this embodiment will be described below with reference toFIGS. 3A to 7. Here,FIGS. 3A to 3Hare sectional views explaining the method of manufacturing the second wiring substrate22at each step,FIGS. 4A to 61are sectional views explaining the method of manufacturing the multilayer wiring substrate20at each step, andFIG. 7is a process flowchart explaining the method of manufacturing the multilayer wiring substrate20.

At first, a supporting sheet40having the configuration diagrammatically shown inFIG. 4Ais prepared. The supporting sheet40provides the three-layer structure composed of: a metal base member41which is made of copper and has a thickness of, for example, about 100 μm; a conductive adhesive resin layer42; and a melting metal layer43which is made of chrome (Cr) and has a thickness of, for example, 5 μm or less. The metal base member41and the melting metal layer43can be separated (stripped) from each other through the conductive adhesive resin layer42.

The metal base member41occupies the main portion of the total thickness of the supporting sheet40, and it is mainly configured so as to have the mechanical property, such as a strength and the like, which is required at the time of the handling, and the material property such as a heat-resistive temperature and the like. The conductive adhesive resin layer42is made of the material which enables the preservation of the electric continuity between the metal base member41and the melting metal layer43and also enables both of them to be separated and removed. For example, the benzo-triazole formed in the shape of layer is applied. The melting metal layer43is made of metal foil and metal plating layer and also made of a metal material different from the interlayer connection32so that it can be selectively etched from the interlayer connection32of the adhesive material layer23.

By the way, the configuration example in which the metal base member41and the melting metal layer43are separated and removed from each other is not limited to the above-mentioned example. Other configuration examples can be employed. However, their detailed explanations will be described later.

Next, the second wiring substrate22is formed on the side surface of the melting metal layer43of the supporting sheet40in step S11ofFIG. 4B. Here,FIGS. 3A to 3Hshow the process for manufacturing the second wiring substrate22. The second wiring substrate22is formed, for example, by the dual damascening method that uses the poly-benzo-oxadole (PBO) of positive photosensitive material, and the like as the insulating layer.

As shown inFIG. 3A, the photosensitive material made of the poly-benzo-oxadole is coated on the side surface of the melting metal layer43of the supporting sheet40by using a spin coating method and the like. Then, a predetermined baking process is carried out to thereby form an insulating layer34A. Next, exposing light is irradiated through a mask (not shown) to a predetermined region of the formed insulating layer34A. Then, a developing process is carried out to thereby form an opening36A as shown inFIG. 3B. The opening36A constitutes the via holes for the connection between the layers and a part of the wiring layer. The exposure depths are differed by a two-stage exposure.

Next, as shown inFIG. 3C, an electroplating layer33A made of, for example, copper is formed on the insulating layer34A containing the inside of the opening36A. At this time, a sputter barrier layer such as Ti/Cu and the like may be formed between the inner wall plane of the opening36A and the electroplating layer33A. The electroplating layer33A is removed from the surface of the insulating layer34A, for example, by using a CMP (Chemical Mechanical Polishing) method and the like as shown inFIG. 3D.

Next, the same kind of the photosensitive material (the poly-benzo-oxadole) is again coated on the insulating layer34A by the spin coating method, and the predetermined baking process is carried out to thereby form an insulating layer34B as shown inFIG. 3E. The exposing light is irradiated to a predetermined region of the formed insulating layer34B, and an opening36B linked to the inner wiring layer35C is formed as shown inFIG. 3F. Then, an electroplating layer33B similarly made of copper is formed on the insulating layer34B containing the inside of the opening36B as shown inFIG. 3G. The electroplating layer33B is removed from the surface of the insulating layer34B by the CMP method and the like to thereby form the inner wiring layer35C containing the conductor lands35A,35B as shown inFIG. 3H.

As mentioned above, the second wiring substrate22is formed on the supporting sheet40. The second wiring substrate22in this embodiment has the wiring pattern with the super fine structure and the high precision, since the photosensitive resin material with the high resolution is used as the insulating layer, and the dual damascening method used in the wiring forming process of the semiconductor device is used for it to thereby form the conductor pattern.

Also, the thickness of the insulator base material34is several 10 μm. The rigid property or the self-support property is weak to an extent that it is difficult for only the insulator base material34to maintain a predetermined flatness. For this reason, the insulator base material34needs to be supported by the supporting sheet40during the process and handled through the supporting sheet40. However, the supporting sheet40is made of metal. Thus, the flatness of the insulating layers34A,34B can be properly maintained. Moreover, it has the heat resistance property at which the dimensional change is never induced even at a baking temperature (for example, 300° C.) of the insulating layers34A,34B. Also, the conductor pattern35can be formed by using the electroplating method. Hence, the super fine conductor pattern can be formed at the extremely high precision.

Now, returning back toFIGS. 4A to 4C, the photosensitive adhesive constituting the interlayer insulating layer31of the adhesive material layer23is coated on the second wiring substrate22formed on the supporting sheet40in step S12. The exposing and developing processes are performed thereon to thereby form a through-bore31A linked to the conductor land35B of the second wiring substrate22in step S13ofFIG. 4C. Then, as shown inFIG. 5D, the supporting sheet40is used as a seeding layer (electric power supplying layer), and the electroplating process is carried out. The electroplating layer made of, for example, copper is filled in the through-bore31A to thereby form the interlayer connection32in step S14. By the way, the photosensitive adhesive is not limited to the liquid type, and a sheet type may be used.

As mentioned above, the adhesive material layer23composed of the interlayer insulating layer31and the interlayer connection32is formed on the second wiring substrate22.

In this embodiment, as mentioned above, the interlayer connection32is formed by the electroplating method. Moreover, at this step, the power distribution inspection of the second wiring substrate22can be carried out at the same time. In short, the interlayer connection32is electrically connected through the second wiring substrate22to the supporting sheet40. Thus, as for the through-bore31A on which the electroplating layer is not deposited as shown inFIG. 4C, it can be judged that the conductor pattern35of the second wiring substrate22at that portion is cut away. Consequently, the wiring inspection of the conductor pattern35can be carried out without using an expensive inspecting apparatus and the like.

Also, this embodiment is designed such that the interlayer connection32is formed by the electroplating method. At this time, the previously formed interlayer insulating layer31can be used as resist for plating. Consequently, the conductor layer can be homogeneously formed on the insides of the respective through-bores31A made at micro pore size. Also, the interlayer connection32can be formed at the fine pitch.

Typically, since an electroplating bath is acid, the interlayer insulating layer31made of the resin is never deteriorated in the plating bath. Thus, as described later, after the formation of the interlayer connection32, the interlayer insulating layer31can be used as the adhesive layer between the first and second wiring substrates21,22.

By the way, this is not limited to the configuration that the interlayer connection32is entirely made of copper. For example, only the surface layer may be composed of the electroplating layer of tin (Sn). In this case, if the surface layer of the conductor pattern25A of the first wiring substrate21is a gold plating layer, the connection of lamination boundary can be attained by Sn—Au junction. Thus, it is possible to attain the lower temperature and the smaller load in the stacking step.

Next, a dicing step of cutting the second wiring substrate22together with the adhesive material layer23and the supporting sheet40to the piece of the size corresponding to the lamination on the first wiring substrate21is carried out in step S15ofFIG. 5E.

After that, as shown inFIG. 5F, the supporting sheet40is reversed such that the respective interlayer connections32of the adhesive material layer23are opposite to the conductor pattern25A on the first wiring substrate21. Then, the second wiring substrate22is stacked on the predetermined portion (an opening39A of the solder resist38A) of the first wiring substrate21through the adhesive material layer23so that the interlayer connections32and the conductor pattern25A are electrically connected in Step S16ofFIG. 6G. Thus, the conductor patterns25A,35of the first and second wiring substrates21,22are electrically connected.

Here, in this embodiment, the supporting sheet40for supporting the second wiring substrate22is made of the metal. Thus, the stacking process on the first wiring substrate21can be carried out in the condition that the second wiring substrate22is maintained at the predetermined flatness. Consequently, it is possible to properly connect to the conductor pattern25A on the first wiring substrate21while preserving the dimensional stability of the interlayer connection32of the adhesive material layer23and the conductor pattern35of the second wiring substrate22.

By the way, the thermosetting condition of the adhesive material layer23is determined depending on the construction material of the insulator base material24in the first wiring substrate21. Thus, the construction material of the adhesive material layer23is selected depending on the construction material in the insulator base material24. For example, if the first wiring substrate21is made of FR-4 (Brand Name) substrate, the above-mentioned stacking step is carried out under the heating and compressed condition of, for example, 160° C.×10 s.

Next, as shown inFIGS. 6H,6I, a step of removing the supporting sheet40from the second wiring substrate22is carried out in steps S17, S18. The removal of the supporting sheet40is constituted by a step of separating and removing the metal base member41from the melting metal layer43in step S17ofFIG. 61and a step of melting and removing the melting metal layer43in step S18ofFIG. 6I.

With reference toFIGS. 6G,6H, the step of separating and removing the metal base member41from the melting metal layer43is carried out by stripping the metal base member41from the melting metal layer43through the conductive adhesive resin layer42in step S17. By the way, in order to separate the conductive adhesive resin layer42together with the metal base member41from the melting metal layer43, mold releasing agent may be coated on a predetermined portion on the side surface of the melting metal layer43.

The removal of the metal base member41can be easily done, for example, by inserting the notch for stripping into the boundary between the melting metal layer43and the metal base member41at the edge of the supporting sheet40. Also, during the process for stripping the metal base member41, the melting metal layer43is supported by the second wiring substrate22. Thus, the separation and the removal between the metal base member41and the melting metal layer43can be properly performed.

On the other hand, the step of melting and removing the melting metal layer43uses the etching solution, which melts the melting metal layer43and does not melt the conductor pattern35(the conductor land35A), and selectively removes only the melting metal layer43in step S18.

In this embodiment, the conductor pattern35is made of copper, and the melting metal layer43is made of chrome. Thus, for example, the usage of the etching solution of a hydrochloric acid group enables only the melting metal layer43to be melt and removed while the conductor pattern is left.

The multilayer wiring substrate20in this embodiment is manufactured as mentioned above. According to this embodiment, the first wiring substrate21and the second wiring substrate22are formed independently of each other. Finally, both of them are integrated through the adhesive material layer23into the single unit. Thus, the trouble that one step defect causes the entire multilayer wiring substrate to be defective is never induced. Hence, it is possible to attain the cost-cutting due to the usage of only confirming articles and the reduction in a tact time due to the parallel processing.

In addition, it is possible to solve the restriction on the material selection between the first wiring substrate21and the second wiring substrate22. For example, if the conventional build-up process is used to try the formations of the first wiring substrate made of the glass epoxy resin and the second wiring substrate made of the PBO as described in this embodiment, the baking temperature of the PBO is high such as 300° C. Thus, it has the inconvenience that the first wiring substrate as the bedding can not endure the temperature. As a result, all of the insulating layers must be made of the PBO. In this embodiment, the PBO can be used only for the necessary layer. Hence, the further reduction in the manufacturing cost can be attained. At the same time, the substrate material suitable for the circuit property can be selected to thereby contribute to the higher function of the set.

In particular, this embodiment is designed so as to cut the second wiring substrate22to the pieces of the predetermined size and partially stack them on the necessary region on the first wiring substrate21. Thus, the substrate material cost can be further reduced. Moreover, increasing the installation number of the second wiring substrates22can largely reduce the board manufacturing cost.

Also, this embodiment is designed such that the second wiring substrate22and the adhesive material layer23are supported by the supporting sheet40made of the metal, and with the supporting sheet40as the transfer sheet member, the second wiring substrate22and the adhesive material layer23are transferred onto the first wiring substrate21. Thus, the dimensional stabilities of the adhesive material layer23and the second wiring substrate22relatively weak in rigid property or self-support property can be preserved to properly stack them on the first wiring substrate21.

Moreover, the supporting sheet40is configured so as to include the metal base member41and the melting metal layer43separately stacked on this metal base member41, and the removing operation for the supporting sheet40is constituted by the step of separating and removing the metal base member41from the melting metal layer43and the step of melting and removing the melting metal layer43. Thus, the supporting sheet40can be removed properly and easily to thereby improve the productivity.

FIG. 8shows the configuration of a multilayer wiring substrate according to a second embodiment of the present invention. A multilayer wiring substrate50in this embodiment is provided with a first wiring substrate51, a second wiring substrate52and an adhesive material layer53placed between those first and second wiring substrates51,52.

The first wiring substrate51in this embodiment has the configuration similar to that of the first wiring substrate21explained in the first embodiment. It is made of the double-side copper-clad stack, and it includes: an insulator54serving as an insulating layer; and conductor patterns55A,55B (corresponds to a first conductor pattern of the present invention) formed by patterning the copper foils on the double sides to the predetermined shapes. By the way, the Ni/Au plating layers may be formed on the surface layers of the conductor patterns55A,55B.

The construction material of the insulator54is suitably selected depending on the application target, the use application and the like. For example, it is made of the organic material, such as the glass epoxy resin (the element in which the epoxy resin is impregnated in the fiber glass), the element in which the polyimide resin is impregnated in the fiber glass, the BT resin (Brand Name) in which the mixture of the bismale-imide-triazine resin and the epoxy resin is impregnated in the fiber glass, the element in which the phenol resin is impregnated in the paper, and the like. However, besides them, it can be made of the ceramic-based material, such as the alumina glass inclusion ceramics, the aluminum nitride and the like.

The conductor patterns55A,55B are partially electrically connected to each other via through-bores56. The through-bore56is constituted by a through-bore57formed in the insulator54and a copper plating58formed on the inner wall plane thereof. By the way, a filing band59made of conductive material or non-conductive material is filled in the through-bore56.

The regions in which the conductor patterns55A,55B on the top and bottom surfaces of the insulator54are not formed are covered with layers of insulating materials57A,57B, and the step on the insulator54caused by the formations of the conductor patterns55A,55B is removed. Consequently, the lamination plane of the first wiring substrate51is flattened to thereby preserve the proper lamination condition between it and the second wiring substrate52.

On the other hand, the second wiring substrate52itself is configured as the multilayer substrate, and it has a conductor pattern (corresponds to a second conductor pattern of the present invention)65. The conductor pattern65is composed of: conductor lands65A,65B exposed on the top and bottom surfaces of the insulator base material64; and an inner wiring layer65C through which they are connected. By the way, the Ni/Au plating layers may be formed on the surface layers of the conductor lands65A,65B.

As shown, the second wiring substrate52is formed smaller in area than the first wiring substrate51. It is partially stacked on a predetermined portion on the first wiring substrate51through the adhesive material layer53. Also in this embodiment, the above-mentioned predetermined portion designates the region required to be multilayered (higher wiring density) on the first wiring substrate51.

The insulator base material64serving as the insulating layer is made of the material relatively strong in rigid property or self-support property, for example, the organic material, such as the glass epoxy resin (the element in which the epoxy resin is impregnated in the fiber glass), the element in which the polyimide resin is impregnated in the fiber glass, the BT resin (Brand Name) in which the mixture of the bismale-imide-triazine resin and the epoxy resin is impregnated in the fiber glass, the element in which the phenol resin is impregnated in the paper, and the like.

FIGS. 9A to 9Gshow an example of the process for manufacturing the second wiring substrate52. The second wiring substrate52is formed, for example, by the conventional known build-up process and the like.

At first, a through-bore66B is formed in a predetermined portion of the insulating layer64B. Then, conductive material is filled therein to thereby form a via penetrating body69B inFIGS. 9A,9B. Moreover, a conductor layer66such as copper foil and the like is formed on a top surface of the insulating layer64B, and this is patterned inFIGS. 9C,9D. Next, the insulating layer64A is formed on the insulating layer64B, and a through-bore66A linked to the conductor layer66is formed. Then, the conductive material is filled therein to form a via penetrating body69A inFIGS. 9E,9F and9G. The inner wiring layer65C is composed of the via penetrating bodies69A,69B and the conductor layer66. The second wiring substrate52is formed as mentioned above.

Next, the adhesive material layer53is configured similarly to the adhesive material layer23explained in the first embodiment. It is composed of an interlayer insulating layer61made of photosensitive adhesive and a plurality of interlayer connections62formed at predetermined portions so as to penetrate this interlayer insulating layer.

Through the interlayer connection62, the conductor pattern55A of the first wiring substrate51and the conductor pattern65of the second wiring substrate52are linked correspondingly to each other. In this embodiment, the interlayer connection62is made of an electroplating layer of copper (Cu). However, besides this, it can be composed of other metals such as nickel (Ni), tin (Sn) and the like.

The multilayer wiring substrate50in this embodiment is configured as mentioned above. According to the multilayer wiring substrate50in this embodiment, the first wiring substrate51and the second wiring substrate52are configured so as to be stacked on each other through the adhesive material layer53. Thus, although the respective insulators54,64are made of the different materials, they can be easily stacked to thereby attain the multilayer.

Also, in the case of the multilayer wiring substrate50in this embodiment, as shown inFIG. 8, the second wiring substrate52is partially stacked on the predetermined region of the first wiring substrate51. Thus, the multilayer can be formed only on the originally necessary region in the first wiring substrate51. Consequently, the smaller area of the second wiring substrate52can be attained to thereby reduce the material cost. Moreover, the multilayer wiring substrate can be entirely lightened.

The method of manufacturing the multilayer wiring substrate50in this embodiment will be described below with reference toFIGS. 10A to 13. Here,FIGS. 10AtoFIG. 12Jare sectional views explaining the method of manufacturing the multilayer wiring substrate50at each step, andFIG. 13is a process flowchart explaining the method of manufacturing the multilayer wiring substrate50.

At first, a supporting sheet80having the configuration diagrammatically shown inFIG. 10Ais prepared. The supporting sheet80has the configuration similar to that of the supporting sheet40explained in the first embodiment and provides the three-layer structure composed of: a metal base member81which is made of copper and has a thickness of, for example, about 100 μm; a conductive adhesive resin layer82; and a melting metal layer83which is made of chrome (Cr) and has a thickness of, for example, 5 μm or less. The metal base member81and the melting metal layer83can be separated (stripped) from each other through the conductive adhesive resin layer82.

By the way, the configuration example in which the metal base member81and the melting metal layer83are separated and removed from each other is not limited to the above-mentioned example. Other configuration examples can be employed. However, their detailed explanations will be described later.

Next, a photosensitive adhesive85is coated on the side surface of the melting metal layer83of the supporting sheet80in step S21ofFIG. 10B. The photosensitive adhesive85constitutes the interlayer insulating layer61of the adhesive material layer53through which the first wiring substrate51and the second wiring substrate52are adhered. By the way, the photosensitive adhesive85is not limited to the liquid type, and the sheet type may be used.

After the photosensitive adhesive85is cured, the respective exposing and developing processes are carried out to thereby form a through-bore86, as shown inFIG. 10Cin step S22. Then, conductive material is filled in the formed through-bore86to thereby form the interlayer connection62in step S23ofFIG. 10D. The adhesive material layer53is formed as mentioned above.

The interlayer connection62in this embodiment is composed of the electroplating layer formed by the electroplating method that uses the supporting sheet80as a seeding layer (an electric power supplying layer). In this case, the photosensitive adhesive85functions as resist for plating. Consequently, the copper plating is deposited only on the region on which the photosensitive adhesive85of the supporting sheet80immersed in the plating bath is not coated. Thus, the conductive layer can be homogeneously formed on the insides of the respective through-bores46made at the micro pore size. Also, the interlayer connection62can be formed at the fine pitch.

By the way, also, this embodiment is not limited to the configuration that the interlayer connection62is entirely made of copper. For example, only the surface layer portion may be constituted by the electroplating layer of tin (Sn). Consequently, if the surface layer of the conductor pattern55A (65) of the first (second) wiring substrate51(52) is a gold plating layer, the connection of lamination boundary can be done by Sn—Au junction. Thus, it is possible to attain the lower temperature and the smaller load of the stacking step.

In succession, as shown inFIG. 11E, the previously formed second wiring substrate52is stacked on the adhesive material layer53on which the interlayer connections62are formed, and the interlayer connections62and the conductor pattern65are electrically connected in step S24.

At a next dicing step, the second wiring substrate52together with the adhesive material layer53and the supporting sheet80is cut to the piece of the size corresponding to the lamination on the first wiring substrate51in step S25ofFIG. 11F.

After that, as shown inFIGS. 11G,12H, the step of removing the supporting sheet80from the adhesive material layer53is carried out in steps S26,27. The removal of the supporting sheet80is constituted by a step of separating and removing the metal base member81from the melting metal layer83in step S26ofFIG. 11Gand a step of melting and removing the melting metal layer83in step S27ofFIG. 12H.

With reference toFIGS. 11F,11G, the step of separating and removing the metal base member81from the melting metal layer83is carried out by stripping the metal base member81from the melting metal layer83through the conductive adhesive resin layer82in step S26. By the way, in order to separate the conductive adhesive resin layer82together with the metal base member81from the melting metal layer83, the mold releasing agent may be coated on a predetermined portion on the side surface of the melting metal layer83.

The strip and the removal of the metal base member81can be easily done, for example, by inserting the notch for the stripping into the boundary between the melting metal layer83and the metal base member81at the edge of the supporting sheet80. Also, during the process for stripping the metal base member81, the melting metal layer83is supported by the adhesive material layer53. Thus, the separation and the removal between the metal base member81and the melting metal layer83can be properly performed.

On the other hand, the step of melting and removing the melting metal layer83uses the etching solution, which melts the melting metal layer83and does not melt the interlayer connection62, and selectively removes only the melting metal layer83in step S27ofFIG. 12H. Consequently, the supporting sheet80is properly removed from the adhesive material layer53.

In this embodiment, the interlayer connection62is made of copper, and the melting metal layer83is made of chrome. Thus, for example, the usage of the etching solution of the hydrochloric acid group enables only the melting metal layer83to be melt and removed while the interlayer connection62is left.

The second wiring substrate52is stacked on the predetermined portion of the first wiring substrate51through the adhesive material layer53from which the supporting sheet80is removed in step S28ofFIGS. 12I,12J. The adhesive action between the first wiring substrate51and the second wiring substrate52is obtained by thermally curing the adhesive material layer53under predetermined heating and compressing operations.

Here, the insulator base material64constituting the second wiring substrate52is made of the material relatively strong in rigid property or self-support property. Thus, the dimensional variation in the interlayer connection62of the adhesive material layer53and the conductor land65B can be suppressed at the time of the lamination on the first wiring substrate51.

The multilayer wiring substrate50in this embodiment is manufactured as mentioned above. According to this embodiment, the first wiring substrate51and the second wiring substrate52are formed independently of each other. Finally, both of them are integrated through the adhesive material layer53into the single unit. Thus, the trouble that one step defect causes the entire multilayer wiring substrate to be defective is never induced. Hence, it is possible to attain the cost-cutting due to the usage of only the confirming articles and the reduction in the tact time due to the parallel processing.

In addition, it is possible to solve the restriction on the material selection between the first wiring substrate51and the second wiring substrate52. Hence, the further reduction in the manufacturing cost can be attained. At the same time, the substrate material suitable for the circuit property can be selected to thereby contribute to the higher function of the set.

In particular, this embodiment is designed so as to cut the second wiring substrate52to the pieces of the predetermined size and partially stack them on the necessary region on the first wiring substrate51. Thus, the substrate material cost can be further reduced. Moreover, increasing the installation number of the second wiring substrates52can largely reduce the board manufacturing cost.

On the other hand, this embodiment is designed such that the second wiring substrate52and the adhesive material layer53are supported by the supporting sheet80made of the metal immediately before the lamination on the first wiring substrate51. The supporting sheet80is higher in strength than the conventional transfer sheet7(refer toFIGS. 15Ato15E) made of the resin film. Thus, at the time of the handling of the supporting sheet80required when the adhesive material layer53is formed and the second wiring substrate52is tentatively installed, it is possible to preserve the high dimensional stability of the formed adhesive material layer53and attain the high precise positioning to the second wiring substrate52.

Moreover, the supporting sheet80is configured so as to include the metal base member81and the melting metal layer83separately stacked on this metal base member81, and the removing operation for the supporting sheet80is constituted by the step of separating and removing the metal base member81from the melting metal layer83and the step of melting and removing the melting metal layer83. Thus, the supporting sheet80can be removed properly and easily. Hence, the conductor pattern can be formed at the high precision, and the productivity can be improved.

As mentioned above, the respective embodiments of the present invention is explained. Of course, the present invention is not limited to them. Various variations can be carried out, in accordance with the technical idea of the present invention.

For example, the above-mentioned embodiments are designed such that as the supporting sheets40,80, as shown inFIGS. 4A,10A, the conductive adhesive resin layers42,82are placed between the metal base members41,81and the melting metal layers43,83, and the metal base members41,81and the melting metal layers43,83can be separated from each other. However, the configuration of the supporting sheets40,80is not limited thereto. If the metal base member and the melting metal layer can be configured so as to be separated from each other, any configuration can be employed.

For example, a supporting sheet101whose sectional structure is shown inFIG. 14Ais configured such that a middle layer103made of chrome-plated material is placed between a metal base member102made of copper and a melting metal layer104made of nickel-plated material, and the usage of plating stress difference causes the melting metal layer (Ni)104and the middle layer (Cr)103to be stripped on the boundary. At the step of melting and removing the melting metal layer (Ni)104after the removal of the metal base member102and the middle layer103, if the conductor portion (the interlayer connection32and the conductor land65A) integrated with it is made of copper, for example, the etching solution of a sulfasion hydrogen peroxide group may be used.

Also, inFIG. 14A, if the middle layer103is made of chrome-plated material and if the melting metal layer104is made of nickel-cobalt-plated material, respectively, the respective layers103,104can be easily separated on the boundary between them. In this case, at the step of melting and removing the melting metal layer (Ni/Co)104, the conductor portion (the interlayer connection32and the conductor land65A) integrated with it is made of copper, for example, soft etching agent in which sulfasion hydrogen peroxide is used as a base can be applied.

Also, the above-mentioned respective embodiments are explained by using the example in which the removal of the supporting sheets40,80is constituted by the step of separating and removing the metal base members41,81and the step of melting and removing the melting metal layers43,83. Instead of that example, the entire supporting sheets may be melted and removed. In this case, the case in which the supporting sheets are made of the same metal is naturally allowable, and the case in which they are constituted by the lamination bodies made of different metals is allowable. In particular, in the latter case, the different etching solutions may be used to selectively etch the respective metal layers.

For example,FIG. 14Bshows the configuration of a supporting sheet111composed of first and second metal layers112,114different from each other. Here, if the first metal layer112is made of copper and the second metal layer114is made of nickel, the usage of alkali etchant enables only the first metal layer (Cu)112to be etched. Similarly, if the first metal layer112is made of copper and the second metal layer114is made of aluminum, the usage of sulfuric acid hot water as etching solution enables only the first metal layer (Cu)112to be etched. In addition, as the combination example of the first and second metal layers112,114, there are the combination of nickel and gold and the combination of copper and chrome.

Also, those combination examples of the different metals can be applied as the combination example between the configuration metals of the melting metal layers43,83and the configuration metals of the conductor patterns (the interlayer connection32and the conductor land65A).

Moreover, the supporting sheet may be composed of the two layers of the metal base member and the melting metal layer, and those respective layers may be separated depending on the difference in the thermal expansion coefficient between the respective layers. Or, as shown in a supporting sheet121inFIG. 14C, a thermally expanding layer123is placed between a metal base member122and a melting metal layer124. Then, a heating process to a predetermined temperature may be carried out to expand the thermally expanding layer123and thereby separate the metal base member122and the melting metal layer124.

On the other hand, in the above-mentioned respective embodiments, the metal base members41,81of the supporting sheets40,80are made of copper. However, they are not limited thereto. That is, if the material can satisfy the mechanical strength, the thermal expansion coefficient and the like which are required depending on the forming process condition and the lamination condition of the supported wiring substrate and the like, any material can be applied.

Also, the interlayer connections32,62of the adhesive layers23,53are constituted by the electroplating layer. Instead of it, the interlayer connection may be formed by filling conductive particles, for example, such as solder and the like, in the through-bores31A,86.

Moreover, the above-mentioned respective embodiments have been explained by exemplifying the lamination of the first and second two wiring substrates. Of course, the present invention is not limited thereto. The present invention can be applied to even the case in which first to n-th of n wiring substrates are stacked to obtain the multilayer.

As mentioned above, according to the method of manufacturing the multilayer wiring substrate in the present invention, even if the first and second wiring substrates are made of the different materials, they can be stacked on each other through the adhesive layer. Thus, it is possible to solve the restriction on the process resulting from the material selection.

Also, the second wiring substrate is stacked on the predetermined portion of the first wiring substrate. Thus, the second wiring substrate can be formed smaller in area than the first wiring substrate. Hence, the material cost can be reduced.

Moreover, the supporting sheet for supporting the second wiring substrate is made of the metal. Thus, the dimensional stability of the interlayer connection and the second conductor pattern formed at the fine pitch can be preserved to properly stack on the first wiring substrate.

On the other hand, according to the multilayer-wiring substrate of the present invention, the second wiring substrate can be formed smaller in area than the first wiring substrate. Thus, as compared with the case in which the second wiring substrate is formed on the entire surface of the first wiring substrate, the usage amount of the construction material of the second wiring substrate can be reduced to thereby reduce the material cost. Moreover, the multilayer wiring substrate can be entirely weight saving.