Process for substrate incorporating component

In a process for producing the component-embedded substrate, a first electronic component is connected and fixed onto a first electrode pattern with a conductive bonding material, the first electrode pattern being provided on a first supporting layer. A second supporting layer including a second electrode pattern is press-bonded onto the electronic component-fixed surface of the first supporting layer with a first prepreg therebetween to perform transfer. Then, the first supporting layer and the second supporting layer are separated from the first prepreg. After separation, the first prepreg is cured. A second electronic component is connected and fixed onto the back surface of the second electrode pattern with a conductive bonding material. A third supporting layer including a third electrode pattern is press-bonded onto the second electronic component-fixed surface with a second prepreg therebetween to perform transfer. Then, the third supporting layer is separated from the second prepreg, and the second prepreg is cured. In this manner, the prepregs and electrode patterns are sequentially laminated, thereby reducing the connection resistance between laminated electrode patterns or between an electrode pattern and an electronic component.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for producing a substrate including therein an electronic component, such as a semiconductor element and a chip component.

2. Description of the Related Art

Demands for miniaturization and higher performance of electronic devices require a further reduction in the profile of components having a smaller mounting area. To meet such requirements, a component-embedded substrate is known in which multiple resin layers including a semiconductor element and a chip component therein are laminated.

Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2002-76637) discloses a process for producing the component-embedded substrate by press-bonding and transferring a supporting layer including a component-connected electrode pattern onto one surface of a prepreg, and then laminating the resulting prepreg with another prepreg in which a component is embedded by press bonding in a single step.

FIG. 8is an example shown in FIG. 15 in Patent Document 1. In step (a), a prepreg1501including via holes1502and a supporting layer1504including an electrode pattern on which electronic components1510and1511are connected are prepared. In step (b), the prepreg1501and the supporting layer1504are laminated by press bonding. In step (c), the supporting layer1504is separated to form a wiring layer1515. In step (d), the wiring layer1515, another wiring layer1514in which an electronic component1505is embedded, wiring layers1512and1513including an electrode pattern1506and an interlayer via1507, respectively, are laminated by press bonding in a single step to form a multilayer component-embedded substrate1516as shown in (e).

However, in such a single-step lamination process, at the interlayer between the laminated prepregs, an electrode pattern transferred on the surfaces of the prepregs is only in contact with another electrode pattern or an electronic component to provide an electrical connection. Thus, the connection resistance is disadvantageously increased, which results in insufficient connection reliability. Furthermore, since two electrode layers are disposed between the laminated prepregs, the bonding strength between the prepregs is low, thus possibly causing delamination.

To overcome these problems, in FIG. 16 in Patent Document 1, discloses a process in which a prepreg defining an adhesive layer including a through hole is provided between the cured resin layers to ensure the connection reliability between the electrode patterns or between the electrode pattern and the electronic component. However, this process disadvantageously requires an interlayer prepreg including no component. Thus, the thickness of the component-embedded substrate is increased.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of the present invention provide a process for producing a component-embedded substrate having low connection resistance between laminated electrode patterns or between an electrode pattern and an electronic component, the electrode pattern and the electronic component being laminated, and having improved connection reliability.

According to another preferred embodiments of the present invention, when electronic components are connected onto front and back surfaces of an inner layer electrode, a process is provided for producing a component-embedded substrate having improved connection reliability between the inner layer electrode and the electronic components.

According to a first preferred embodiment of the present invention, a process is provided for producing a component-embedded substrate, including the steps of connecting and fixing a first electronic component to a first electrode pattern on a first supporting layer with a conductive bonding material, press-bonding a second supporting layer including a second electrode pattern onto the electronic component-fixed surface of the first supporting layer with a first prepreg therebetween to perform transfer, separating the first supporting layer and the second supporting layer from the first prepreg, curing the first prepreg before or after the separating step, connecting and fixing a second electronic component onto the back surface of the second electrode pattern with a conductive bonding material, press-bonding a third supporting layer including a third electrode pattern onto a second electronic component-fixed surface with a second prepreg therebetween to perform transfer, separating the third supporting layer from the second prepreg, and curing the second prepreg before or after the separating step, wherein the prepregs and the electrode patterns are sequentially laminated.

According to a second preferred embodiment of the present invention, a process is provided for producing a component-embedded substrate including the steps of connecting and fixing a first electronic component on the surface of an electrode pattern on a supporting layer with a conductive bonding material, press-bonding a first prepreg onto the first electronic component-fixed surface of the supporting layer, separating the supporting layer from the first prepreg, curing the first prepreg before or after the separating step, connecting and fixing a second electronic component onto the back surface of the electrode pattern with a conductive bonding material, press-bonding a second prepreg onto the second electronic component-fixed surface, and curing the second prepreg.

According to a third preferred embodiment of the present invention, a process is provided for producing a component-embedded substrate including the steps of connecting and fixing a first electronic component onto the surface of a first electrode pattern on a first supporting layer with a conductive bonding material, press-bonding a second supporting layer including a second electrode pattern onto the electronic component-fixed surface of the first supporting layer with a first prepreg therebetween to perform transfer, separating the first supporting layer and the second supporting layer from the first prepreg, curing the first prepreg before or after the separating step, connecting and fixing a second electronic component onto the back surface of the first electrode pattern with a conductive bonding material, press-bonding a third supporting layer including a third electrode pattern onto a second electronic component-fixed surface with a second prepreg therebetween to perform transfer, separating the third supporting layer from the second prepreg, and curing the second prepreg before or after the separating step, wherein the prepregs and the electrode patterns are sequentially laminated.

According to the first preferred embodiment of the present invention, a plurality of layers are not laminated in a single step, but instead, are sequentially laminated. The first electronic component is connected and fixed onto the first electrode pattern with the conductive bonding material. The first electrode pattern is integrally press-bonded to the second electrode pattern with the first prepreg therebetween. In this preferred embodiment, a process for transferring the electrode patterns by forming the electrode patterns on the supporting layers, press-bonding the resulting electrode patterns to the prepregs, and then performing separation is preferably used. Next, the second electronic component is connected and fixed onto the back surface of the second electrode pattern with the conductive bonding material. The third electrode pattern is press-bonded and transferred onto the resulting second electrode pattern with the second prepreg therebetween.

In this manner, by sequentially laminating the prepregs and the electrode patterns, a component-embedded substrate having a multilayer structure is produced.

The electrode pattern is connected to the electronic component with the conductive bonding material (solder, a conductive adhesive, a bump, or the like), thus reducing connection resistance between the electrode pattern and the electronic component and achieving high connection reliability.

According to the first preferred embodiment, the electrode pattern is transferred to the prepreg. After curing this prepreg, the next prepreg is press-bonded simultaneously with the transfer of the electrode pattern to the surface. Consequently, the resulting inner layer electrode between the prepregs (resin layers) is a single layer and is different from the conventional structure having two inner layer electrodes. Therefore, it is unnecessary to contact and electrically connect the inner layer electrodes to each other. Furthermore, the occurrence of delamination between the inner layer electrodes is prevented.

The electrode pattern is transferred to the prepreg, and after curing this prepreg, the next prepreg is laminated. Thus, the first prepreg is not compressed during every lamination, and no problems, such as the poor electrical connection of the electrical component embedded in the first prepreg or the deformation of the electrode pattern, occur.

Curing of the prepreg may be performed before or after separation of the supporting layer.

According to the second preferred embodiment of the present invention, when the electronic components are connected onto the front and back surfaces of the inner layer electrode, the process is provided in which the electronic component is connected and fixed onto the surface of the electrode pattern with the conductive bonding material, this is transferred to the first prepreg, the first prepreg is cured, the second electronic component is connected and fixed onto the back surface of the electrode pattern with the conductive bonding material, and the second prepreg is press-bonded thereon.

Conventionally, when electronic components are connected onto the front and back surfaces of an inner layer electrode, the electrodes of the electronic components must be brought into contact with and electrically connected to the inner layer electrode, which results in low conduction reliability and high connection resistance between the component electrodes and the inner layer electrode. In contrast, according to the second preferred embodiment, not only is lamination sequentially performed one layer at a time, but the second electronic component is also connected and fixed onto the back surface of the first electrode pattern with the conducive bonding material, the first electrode pattern connecting and fixing the first electronic component on the front surface with the conducive bonding material, thus resulting in high conduction reliability and low connection resistance between the inner layer electrode and the electronic component.

In addition, after curing the first prepreg, the second prepreg is press-bonded in a similar manner to the first preferred embodiment. Thus, the deviation and the breakage of the electrode pattern transferred to the first prepreg and a poor connection between the electronic component and the electrode pattern are prevented. Furthermore, the delamination between the prepregs does not occur.

According to the third preferred embodiment, in the step of press-bonding the first prepreg and the second prepreg in the process according to the second preferred embodiment, a substep of disposing the supporting layer having the electrode pattern on the surface opposite the press-bonded surface of the prepreg and then press-bonding this supporting layer to the prepreg simultaneously with the above-described press-bonding step is included, and after the press-bonding substep, the second supporting layer is separated from the prepreg to transfer the electrode pattern to the prepreg.

In the process according to the second preferred embodiment, when the electrode pattern is provided on the surface opposite the press-bonded surface of the prepreg, a process of separately forming a thick-film electrode pattern or a thin-film electrode pattern after curing the prepreg is provided. This disadvantageously increases the number of steps.

Accordingly, in the process according to the third preferred embodiment, by simultaneously transferring the electrode patterns to both of the front and back surfaces, it is unnecessary to form a new electrode pattern after press-bonding the prepreg. Therefore, the number of steps is reduced.

According to a fourth preferred embodiment, the process preferably further includes the steps of forming a through hole in the resin layer in the thickness direction after curing the prepreg, and forming a conducting path inside the hole, the conducting path electrically connecting the electrode patterns provided on the front surface and the back surface of the resin layer.

Conventionally (in Patent Document 1), a through hole is formed in a prepreg and is then filled with a conducting material. After performing lamination, the prepreg is thermally cured. However, during the thermal curing, the contraction of the prepreg due to curing may cause a deviation of the position of the electrode pattern being in contact with the through hole, thus possibly reducing connection reliability.

In contrast, in accordance with the fourth preferred embodiment, after curing the prepreg, a hole (a through hole or a via hole) is provided, and a conducting path is formed inside the hole. Therefore, it is possible to securely connect the hole with the electrode patterns without any positional deviation of the electrode patterns on the front and back surfaces of the resin layer.

As a process for forming the conducting path, the inner surface of the hole may be plated. Alternatively, the conducting path may be formed by filling the inside of the hole with a conducting paste and then curing the paste.

According to a fifth preferred embodiment, the process preferably further includes the steps of forming the hole connecting the electrode pattern provided on the front surface or the back surface of the resin layer with the external electrode of the electronic component after curing the prepreg, and forming the conducting path inside the hole, the conducting path electrically connecting the electrode pattern with the external electrode of the electronic component.

In accordance with the fourth preferred embodiment, the electrode patterns on the front and back surfaces of the resin layer are connected to each other. On the other hand, in accordance with the fifth preferred embodiment, one of the electrode patterns is directly connected to the external electrode of the electronic component. The wiring resistance of the through holes and via holes is higher than that of usual copper wiring. Therefore, the hole desirably has the minimal length. In this case, since the length of the hole is reduced by the thickness of the component, the resistance of the conducting path is advantageously reduced.

In accordance with a sixth preferred embodiment, the step of curing the prepreg preferably includes a substep of performing temporary curing before separating the supporting layer from the prepreg, and performing complete curing after separating the supporting layer from the prepreg.

When the supporting layer is separated without curing the prepreg, problems, such as difficulty in the separation of the supporting layer or breakage of the prepreg, may occur because of the adhesion between the prepreg and the supporting layer. In contrast, performing temporary curing before separating the supporting layer from the prepreg facilitates separation of the supporting layer from the prepreg while deformation of the prepreg is prevented.

When the next prepreg is laminated in the temporarily cured state, the prepreg being in the temporarily cured state may be deformed by compression. Therefore, complete curing should be performed before the lamination of the next prepreg.

When an epoxy resin is used in the prepreg, as the temporary curing conditions, for example, heat treatment should be performed at about 120° C. for about 10 to 15 minutes. As the complete curing conditions, heat treatment should be performed at about 170° C. to about 200° C. for about 1 hour.

In accordance with a seventh preferred embodiment, after curing the second prepreg, a step of press-bonding a fourth supporting layer having a fourth electrode pattern onto the surface of the first prepreg with a third prepreg therebetween to perform transfer, the surface being opposite to the surface bonded to the second prepreg, a step of separating the fourth supporting layer from the third prepreg, and curing the prepreg before or after the separating step, are preferably provided.

When three or more prepregs are laminated, a process of laminating a second prepreg defining a second layer on a first prepreg defining a first layer and then laminating a third prepreg defining a third layer on the second layer prepreg is preferable. However, the first resin layer (prepreg) is warped toward the second layer prepreg by the contraction of the second layer prepreg during curing. Thus, when the third layer prepreg is laminated thereon, the resulting laminate is further warped by the contraction of the third layer prepreg during curing.

Accordingly, in the seventh preferred embodiment, when the second layer prepreg is laminated on the first layer prepreg, the third layer prepreg is not laminated on the second layer prepreg, but rather, on the first layer prepreg. As a result, the influence of the warpage caused by the contraction of the second layer prepreg during curing is compensated by the contraction of the third layer prepreg during curing, thereby resulting in a laminate reduced warpage.

Other features, elements, steps, advantages and characteristics of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1shows a component-embedded substrate A produced by a process according to a first preferred embodiment of the present invention.

InFIG. 1, reference numerals1and2represent resin layers defining the substrate. Patterned outer layer electrodes3and4are provided on the front and back surfaces of the resin layers1and2, respectively. A patterned inner layer electrode5is provided between the resin layers1and2. An electronic component6is connected and fixed onto the inner surface of the outer layer electrode4, which is provided on the lower side, with a conductive bonding material7. An electronic component8is connected and fixed onto the upper surface of the inner layer electrode5with a conductive bonding material9. As the conductive bonding materials7and9, solder, conducting adhesives, bumps, or other suitable conductive bonding materials are preferably used. The outer layer electrode4, which is provided on the lower side, is appropriately connected to the inner layer electrode5through a via hole10filled with a conducting material. The outer layer electrode3, which is provided on the upper side, is connected to the inner layer electrode5through a via hole11.

The via holes10and11each have a diameter of, for example, about 100 μm to about 500 μm and a length of about 100 μm to about 1,000 μm, and are preferably formed by a laser or by drilling. As a conducting material with which the via holes10and11are filled, for example, a binder that is composed of glass, a resin, or other suitable binder and that contains Cu, Ag, Ni, Au, Sn, Zn, Pd, or Pt or a mixture thereof serving as a conductive material is preferably used, the content of the conductive material being about 20% to about 90%.

The outer layer electrodes3and4and the inner layer electrode5are each made of, for example, a metal thin film having a thickness of about 10 μm to about 40 μm. As the electrodes3,4, and5, for example, a copper foil is preferably used. The copper foil may be gold plated, tin plated, or preflux treated.

As the resin layers1and2, for example, an epoxy resin including an inorganic filler is preferably used. The content of the inorganic filler is, for example, about 60% to about 95%. The inorganic filler is preferably composed of an insulating material, such as SiC, Al2O3, or AlN, and preferably has a size of, for example, about 0.1 μm to about 10 μm. In this manner, by incorporating the inorganic filler, the linear expansion coefficient of the prepreg described below is reduced, and thus, the linear expansion coefficient of the prepreg is close to the linear expansion coefficient of a wiring material defining the electrode pattern and to the linear expansion coefficient of the conductive bonding material. Furthermore, stress applied to a junction during heating is reduced. Therefore, the reliability of the junction is improved.

A process for producing the component-embedded substrate A having the structure described above will be described below according toFIG. 2. This production process corresponds to the first preferred embodiment.

In step (a), an electrode that is made of a copper foil and that is bonded onto a supporting layer12is etched to form a circuit pattern4. The circuit pattern4may be directly formed on the supporting layer12by plating, evaporation, or other suitable method. The supporting layer12may be formed of, for example, a thin metal plate composed of stainless steel (SUS) or other suitable material and having a thickness of, for example, about 1.0 mm.

The conducting adhesive7is applied to a predetermined location of the electrode pattern4. The electronic component6is mounted on the conductive bonding material7and is placed in, for example, an oven set at about 120° C. to cure the conductive bonding material7. With respect to a method of applying the conducting adhesive7, printing using a mesh screen or a metal mask, dispensing, or other suitable method is used. In this case, the conducting adhesive used as the conductive bonding material7is thermosetting, and thus, is cured in an oven. When a UV curable adhesive is used, curing is performed by UV irradiation. When a cyanoacrylate adhesive is used, curing is performed with a minute amount of water present on the surface of an adherend. When an anaerobic adhesive is used, curing is performed by blocking air (oxygen).

In step (b), another supporting layer13including the electrode pattern5provided on a surface thereof is press-bonded onto the component-mounted side of the supporting layer12with the prepreg2therebetween. At the same time, the prepreg2is temporarily cured. By the press-bonding, the electronic component6is embedded in the prepreg2, and the electrode patterns4and5are bonded to the front and back surfaces of the prepreg2. As the temporary curing conditions, for example, heat treatment is preferably performed at about 120° C. for about 10 to about 15 minutes. The electrode pattern5is formed on the supporting layer13by the same process as that for of electrode pattern4. The material and shape of the supporting layer13are preferably identical to those of the supporting layer12. In this manner, an electronic component is not mounted on the surface of the electrode pattern5but temporarily fixed.

In step (c), after thermocompression-bonding and curing of the prepreg2, the supporting layers12and13are separated from the temporarily cured prepreg2, thereby transferring the electrode patterns4and5onto the front and back surfaces of the prepreg2. After the separation, the prepreg2is completely cured. As the complete curing conditions, for example, heat treatment is preferably performed at about 170° C. to about 200° C. for about 1 hour.

In step (d), the through hole or via hole10is formed in the cured resin layer2and is then filled with a conducting material to electrically connect the front-side electrode pattern5to the back-side electrode pattern4. The via hole10is formed by a laser or by drilling. In this manner, since the via hole10is formed in the cured resin layer2, deviations of the connection locations of the via hole10and the electrode patterns4and5caused by curing contraction does not occur, thus resulting in a highly precise connection structure. When the prepreg2is cured after separating the supporting layers12and13from the prepreg2, it is also possible to form the via hole10by irradiating the uncured prepreg with a laser.

In step (e), the electronic component8is connected and fixed onto the electrode pattern5with the conductive bonding material9, the electrode pattern5being provided on the front side. Also in this case, a conducting adhesive is used as the conductive bonding material9. The conducting adhesive9is preferably cured in an oven set at, for example, about 120° C.

In step (f), another supporting layer14including the electrode pattern3provided on a surface thereof is press-bonded onto the surface of the resin layer2with the prepreg1therebetween, the surface fixing the electronic component8. At the same time, the prepreg1is temporarily cured. By press-bonding, the electronic component8is embedded in the prepreg1, and electrode patterns5and3are bonded onto the front and back surfaces of the prepreg1. The temporary curing conditions are the same as those described above. The electrode pattern3is preferably formed on the supporting layer14by the same process as that for the electrode pattern4. The material and shape of the supporting layer14are preferably identical to those of the supporting layer12. In this case, an electronic component is not mounted on the outer layer electrode3but may be appropriately connected and fixed using the conductive bonding material.

In step (g), after thermocompression-bonding and curing the prepreg1, the supporting layer14is separated from the temporarily cured prepreg1, thereby transferring the electrode pattern3onto the surface of the prepreg1. After separation, the prepreg is completely cured. The complete curing conditions are the same as those described above.

In step (h), the through hole or via hole11is formed in the cured resin layer1and is then filled with a conducting material to electrically connect the electrode pattern3with the electrode pattern5.

Steps (a) to (h) are included in the process for producing the component-embedded substrate A having two resin layers1and2. By sequentially laminating other resin layers on the outer surface of the resin layer1or2, it is also possible to form a component-embedded substrate having a multilayer structure.

As shown inFIG. 2, after connecting the electronic components6and8with the electrode patterns4and5using the conductive bonding materials7and9, the prepregs2and1are press-bonded, thus preventing detachment of the electronic components6and8from the electrode patterns4and5during the press-bonding of the prepregs2and1, and reducing the connection resistance. Since the electrode pattern5interposed between the resin layers1and2is a single layer, the two resin layers1and2are securely bonded with the electrode pattern5provided therebetween. Therefore, delamination of the resin layers1and2from the electrode pattern5is eliminated.

FIG. 3shows a process for producing a component-embedded substrate B according to a second preferred embodiment of the present invention.

In step (a), an electrode pattern21is formed on a supporting layer20, and an electronic component22is connected and fixed onto the surface of the electrode pattern21with a conductive bonding material23. The supporting layer20, the electrode pattern21, and the conductive bonding material23are the same as those in the first preferred embodiment shown inFIGS. 1 and 2. Thus, the descriptions thereof are omitted.

In step (b), another supporting layer25is press-bonded onto the component-mounted surface of the supporting layer20with a prepreg24therebetween. At the same time, the prepreg24is temporarily cured. By press-bonding, the electronic component22is embedded in the prepreg24, and the electrode pattern21is bonded to the lower surface of the prepreg24. The temporary curing conditions are preferably the same as those in the first preferred embodiment.

In step (c), after thermocompression-bonding and curing the prepreg24, the supporting layers20and25are separated from the temporarily cured prepreg24, thereby transferring the electrode pattern21to the lower surface of the prepreg24. Then, the prepreg24is completely cured. The complete curing conditions are preferably the same as those in the first preferred embodiment.

In step (d), the cured resin layer24is flipped over, and an electronic component26is connected and fixed onto the back surface of the electrode pattern21with a conductive bonding material27.

In step (e), another supporting layer29is press-bonded onto the surface fixing the electronic component26with a prepreg28therebetween. At the same time, the prepreg28is temporarily cured. By press-bonding, the electronic component26is embedded in the prepreg28, and the prepreg28is bonded to the electrode pattern21. The temporary curing conditions are the same as those described above.

In step (f), after thermocompression-bonding and curing the prepreg28, the supporting layer29is separated from the temporarily cured prepreg28. After the separation, the prepreg28is completely cured. The complete curing conditions are the same as those in the first preferred embodiment.

As described above, the component-embedded substrate B having a two-layer structure is obtained. Next, electrode patterns are formed on the front and back surfaces of the resin layers24and28, and the inner layer electrode21is preferably connected to the exterior by providing a through hole or a via hole.

As described above, when the electronic components22and26are connected onto the front and back surfaces of one inner layer electrode21, the electronic components22and26are connected and fixed onto the inner layer electrode21with the conductive bonding materials23and27, respectively. Thus, the conduction reliability between the inner layer electrode21and the electronic components22and26is improved, and the connection resistance is reduced.

FIG. 4shows a process for producing a component-embedded substrate C according to a third preferred embodiment of the present invention.

In step (a), an electrode pattern31is formed on a supporting layer30, and an electronic component32is connected and fixed onto the surface of the electrode pattern31with a conductive bonding material33. Since the supporting layer30, the electrode pattern31, and the conductive bonding material33are identical to those in the first preferred embodiment shown inFIGS. 1 and 2, the descriptions thereof are omitted.

In step (b), another supporting layer35including an electrode pattern36provided on the surface thereof is press-bonded onto the component-mounted surface of the supporting layer30with a prepreg34therebetween. At the same time, the prepreg34is temporarily cured. The temporary curing conditions are preferably the same as those in the first preferred embodiment.

In step (c), after thermocompression-bonding and curing the prepreg34, the supporting layers30and35are separated from the temporarily cured prepreg34. After separation, the prepreg34is completely cured. The complete curing conditions are the same as those in the first preferred embodiment.

In step (d), a through hole37or a via hole38is formed in the cured resin layer34and is then filled with a conducting material to electrically connect the front-side electrode pattern31with the back-side electrode pattern36and to electrically connect the electrode pattern36with the external electrode of the electronic component32. The via hole37or38is formed by the same process as that in the first preferred embodiment. In this manner, since the electrode pattern36is electrically connected to the external electrode of the electronic component32through the via hole38, the length of the via hole38is reduced by the thickness of the electronic component32, and thus, the resistance of a conducting path is reduced.

In step (e), the cured resin layer34is flipped over, and an electronic component39is connected and fixed onto the back surface of the electrode pattern31with a conductive bonding material40.

In step (f), another supporting layer42including an electrode pattern43provided on the surface thereof is press-bonded onto the surface fixing the electronic component39with a prepreg41therebetween. At the same time, the prepreg41is temporarily cured. The temporary curing conditions are the same as those in the first preferred embodiment.

In step (g), after thermocompression-bonding and curing the prepreg41, the supporting layer42is separated from the temporarily cured prepreg41. After the separation, the prepreg41is completely cured. The complete curing conditions are the same as those in the first preferred embodiment.

In step (h), a through hole44or a via hole45is formed in the cured resin layer41and is then filled with a conducting material to electrically connect the front-side electrode pattern43with the back-side electrode pattern31and to electrically connect the electrode pattern43with the external electrode of the electronic component39.

In this component-embedded substrate C, in the same manner as for the component-embedded substrate B, the electronic components32and39are connected and fixed onto the front and back surfaces of one inner layer electrode31with conductive bonding materials33and40. Therefore, the conduction reliability between the inner layer electrode31and the electronic components32and39is improved, and the connection resistance is reduced. Furthermore, the outer layer electrodes36and43are simultaneously formed by transfer with the press-bonding of the prepregs34and41. Thus, the steps of forming the outer layer electrodes36and43are omitted.

FIG. 5shows a process for producing a component-embedded substrate D according to a fourth preferred embodiment of the present invention. This production process provides an exemplary component-embedded substrate including a shield electrode therein.

In step (a), a shield electrode55and an electrode pattern52that includes an electronic component53connected and fixed onto a surface thereof with a conductive bonding material54are transferred onto the front and back surfaces of a resin layer51to prepare a sheet50. A process for producing this sheet50includes the same steps as, for example, steps (a) to (d) shown inFIG. 2, except that the front-side electrode is the shield electrode55covering substantially the entire front surface. The electrode pattern52is connected to the shield electrode55through the via hole56.

Another supporting layer58including an electrode pattern59provided on a surface thereof is press-bonded onto the shield electrode55of the sheet50with a prepreg57therebetween. An electronic component60is connected and fixed onto the electrode pattern59with a conductive bonding material61. The prepreg57is temporarily cured simultaneously with the press-bonding.

In step (b), the supporting layer58is separated. In this state, the prepreg57is securely bonded and fixed onto the back surface of the shield electrode55. The electronic component60is embedded in the prepreg57. At the same time, the electrode pattern59is transferred onto the prepreg57. Then, the prepreg57is completely cured.

In step (c), a via hole62is formed in the cured resin layer57and is then filled with a conducting material to connect the shield electrode55with the electrode pattern59.

As described above, since the shield electrode55which functions as the inner layer electrode is included, noise generated from the electronic component mounted another layer in the component-embedded substrate D and the noise of electromagnetic waves from the exterior are shielded, and satisfactory electrical characteristics are obtained. To achieve a satisfactory shielding effect, the electrode area of the shield electrode55must be at least about 60% and preferably at least about 90% of the single-layer area (the total of the electrode area and the non-electrode area).

FIG. 6shows the structure of a component-embedded substrate E according to a fifth preferred embodiment of the present invention.

In this preferred embodiment, similar to the component-embedded substrate D, an example in which a shield electrode is included is provided, except that a shield electrode70is provided as the outer layer electrode.

In this component-embedded substrate E, two resin layers72and73are provided with an inner layer electrode71provided therebetween, and electronic components74and75are connected and fixed onto the front and back surfaces of the inner layer electrode71with conductive bonding materials76and77. The electronic component74is a chip component mounted on the inner layer electrode71with solder or a conducing adhesive76. The electronic component75is a bare chip mounted on the inner layer electrode71with a bump77. The electrode pattern71is connected to a electrode pattern78through a via hole79a. The shield electrode70is connected to the inner layer electrode71through a via hole79b.

The component-embedded substrate E is produced by the same process as that shown inFIG. 4, except that the shield electrode70is provided in place of the electrode pattern43.

FIG. 7shows a process for producing a component-embedded substrate F according to a sixth preferred embodiment of the present invention. This process provides an exemplary component-embedded substrate having three-layer structure.

Steps (a) to (f) are substantially identical to steps (b) to (h) in the third preferred embodiment (seeFIG. 4). Thus, the same reference numerals are assigned, and descriptions thereof are omitted.

In step (g), a component-embedded substrate having a two-layer structure is flipped vertically. In step (h), an electronic component80is connected and fixed onto the back surface of the upper-side electrode pattern36with a conductive bonding material81.

In step (i), another supporting layer83including an electrode pattern84provided on a surface thereof is press-bonded onto the surface fixing the electronic component80with a prepreg82therebetween. At the same time, the prepreg82is temporarily cured. That is, the prepreg82is press-bonded onto the surface of the first layer prepreg34, the surface being opposite the surface bonded to the second layer prepreg41.

In step (j), after thermocompression-bonding and curing the prepreg82, the supporting layer83is separated from the temporarily cured prepreg82.

In step (k), after the temporarily cured prepreg82is completely cured, a through hole or via hole85is formed in the resin layer82and is then filled with a conducting material to electrically connect the front- and back-side electrode patterns36and84. Alternatively, the electrode pattern84may be directly connected to the electronic component80through the via hole85.

In this preferred embodiment, the third layer prepreg82is laminated on the surface of the first layer prepreg34, the surface being opposite the surface bonded to the second prepreg41. The reason for this is described below.

After curing the first layer prepreg34, when the second layer prepreg41is laminated and cured, the substrate having the two-layer structure is warped toward the second layer prepreg41because of the curing contraction of the second layer prepreg41.

Accordingly, the third layer prepreg82is laminated on the surface of the first layer prepreg34, the surface being opposite the surface bonded to the second layer prepreg41. Thereby, the substrate that has the two-layer structure and that has been warped toward the second layer prepreg41can be warped in the opposite direction because of the curing contraction of the third layer prepreg82. As a result, a substrate having a three-layer structure and having a low warpage is produced.

In the above-described preferred embodiments, the electronic components are preferably connected and fixed onto the electrode patterns with the conducting adhesives. Alternatively, solder may be used, and lead-free solder is preferably used in view of environmental concerns. For example, Sn including one to four elements selected from Ag, Bi, Cu, Zn, and In is preferably used.

With respect to the conducting adhesive, a binder that is composed of epoxy or urethane and that includes Ag, Cu, Ni, Au, Sn, Zn, or Pt serving as a conductive material or a mixture of these may be used.

In the above-described preferred embodiments, the prepreg is temporarily cured before separating the supporting layer, and the prepreg is completely cured after separating the supporting layer. Alternatively, the prepreg may be completely cured before separating the supporting layer.

As is clear from the descriptions above, according to the first preferred embodiment of the present invention, a plurality of layers are not laminated in a single step. By sequentially laminating the prepregs and the electrode patterns, it is possible to produce a component-embedded substrate having a multilayer structure.

Therefore, the electrode pattern can be connected to the electronic component with the conductive bonding material. The connection resistance between the electrode pattern and the electronic component is reduced. The connection reliability is greatly improved.

Furthermore, the inner layer electrode between the prepregs (resin layers) is a single layer and is different from a structure having two inner layer electrodes. Therefore, it is unnecessary to contact and electrically connect the inner layer electrodes to each other. Furthermore, it is possible to prevent the occurrence of delamination between the inner layer electrodes.

The electrode pattern is transferred to the prepreg, and after curing this prepreg, the next prepreg is laminated. Thus, the first prepreg is not compressed during every lamination, and there are no problems, such as the poor electrical connection of the electrical component embedded in the first prepreg or the deformation of the electrode pattern.

According to the second preferred embodiment, in the case in which the electronic components are connected onto the front and back surfaces of the inner layer electrode, the first electronic component is connected and fixed onto the surface of the first electrode pattern with the conductive bonding material, and the first electrode pattern is transferred to the prepreg. Then, the second electronic component is connected and fixed onto the back surface of the first electrode pattern with the conductive bonding material, and another prepreg is press-bonded onto the back surface of the first electrode pattern.

Therefore, high conduction reliability between the first electrode pattern defining the inner layer electrode and the electronic components is achieved and the connection resistance is reduced. As a result, a component-embedded substrate having reliable electrical characteristics is produced.

According to the third preferred embodiment, in the case in which the electronic components are connected onto the front and back surfaces of the inner layer electrode, the supporting layer having the electrode pattern is disposed on the surface opposite the press-bonded surface of the prepreg, and then the electrode pattern is transferred simultaneously with press-bonding. Therefore, in addition to an effects obtained in the second preferred embodiment, it is unnecessary to form a new electrode pattern after press-bonding the prepreg. Thus, the number of steps is reduced.