Composite wiring board and semiconductor device

Abstract

A composite wiring board according to the present disclosure includes a base substrate, a bonding material that is variable melting point type, and a relay substrate that is electrically connected to the base substrate by means of the bonding material. The base substrate has a first core base material, a first organic base material that is formed from an organic resin and is bonded to the first core base material, and a plurality of first wiring lines that are positioned inside the first organic base material. The relay substrate has a second organic base material that is formed from an organic resin, and a plurality of second wiring lines that are positioned inside the second organic base material. The second wiring lines each have a diffusion suppressing layer on side surfaces.

Description

Composite wiring board and semiconductor device

[0001] The present disclosure relates to a composite wiring board and a semiconductor device.

[0002] 2. Description of the Related Art Conventionally, a technique is known in which a plurality of semiconductor elements are mounted on a single base substrate via an intermediate substrate called an interposer.

[0003] Patent Document 1 discloses a composite wiring board in which an FC-BGA substrate, in which an organic resin substrate with metal wiring formed therein is bonded to a core substrate made of glass cloth, and an organic resin interposer with metal wiring formed therein are bonded together via a bonding material such as solder.

[0004] JP 2023-083003 A

[0005] The composite wiring board according to the present disclosure includes a base substrate, a melting point changeable bonding material, and an interposer substrate electrically connected to the base substrate via the bonding material. The base substrate includes a first core substrate, a first organic base material made of organic resin bonded to the first core substrate, and a plurality of first wirings located inside the first organic base material. The interposer substrate includes a second organic base material made of organic resin and a plurality of second wirings located inside the second organic base material. The second wirings have a diffusion suppression layer on their side surfaces.

[0006] FIG. 1 is a schematic cross-sectional view showing the configuration of a semiconductor device according to an embodiment. FIG. 2 is a schematic cross-sectional view showing the configuration of a base substrate according to an embodiment. FIG. 3 is a schematic enlarged view of region III shown in FIG. 2. FIG. 4 is a schematic cross-sectional view showing the configuration of an intermediate substrate and its periphery according to an embodiment. FIG. 5 is a schematic enlarged view of region V shown in FIG. 4. FIG. 6 is a schematic view for explaining a method for manufacturing a second organic substrate according to an embodiment. FIG. 7 is a schematic view for explaining a method for manufacturing a second organic substrate according to an embodiment. FIG. 8 is a schematic view for explaining a method for manufacturing a second organic substrate according to an embodiment. FIG. 9 is a schematic view for explaining a method for manufacturing a second organic substrate according to an embodiment. FIG. 10 is a schematic view for explaining a method for manufacturing a second organic substrate according to an embodiment. FIG. 11 is a schematic view for explaining a method for manufacturing a second organic substrate according to an embodiment. FIG. 12 is a schematic view for explaining a method for manufacturing a second organic substrate according to an embodiment.

[0007] Hereinafter, embodiments for carrying out a composite wiring board and a semiconductor device according to the present disclosure (hereinafter referred to as "embodiments") will be described in detail with reference to the drawings. Note that the present disclosure is not limited to these embodiments. Furthermore, the embodiments can be appropriately combined within the scope of not causing any contradiction in the processing content. Furthermore, the same components in the following embodiments will be given the same reference numerals, and redundant explanations will be omitted.

[0008] Furthermore, in the following embodiments, expressions such as "constant," "orthogonal," "perpendicular," or "parallel" may be used, but these expressions do not necessarily mean "constant," "orthogonal," "perpendicular," or "parallel" in the strict sense. In other words, the above expressions allow for deviations due to, for example, manufacturing precision or installation precision.

[0009] In addition, in the drawings referred to below, for ease of understanding, an orthogonal coordinate system may be shown in which the X-axis direction, Y-axis direction, and Z-axis direction, which are perpendicular to each other, are defined, and the positive Z-axis direction is the vertically upward direction.

[0010] If there is a difference in the thermal expansion coefficient between the base substrate and the relay substrate, when the base substrate and the relay substrate are bonded using a bonding material during the manufacturing process, the difference in thermal expansion between the base substrate and the relay substrate may cause distortion in the bonding material. The distortion of the bonding material may reduce the reliability of the connection between the base substrate and the relay substrate. Furthermore, during the subsequent cooling process, the difference in thermal contraction between the base substrate and the relay substrate may cause cracks in the bonding material. This may also reduce the reliability of the connection between the base substrate and the relay substrate.

[0011] The difference in the thermal expansion coefficient between the base substrate and the relay substrate may be caused by, for example, the difference between the proportion of metal wiring in the organic resin substrate of the base substrate and the proportion of metal wiring in the relay substrate. Generally, the organic resin substrate of the base substrate has a solid pattern such as ground wiring or power wiring arranged thereon, whereas the relay substrate rarely has a solid pattern arranged thereon. Therefore, due to the difference in the proportion of metal wiring, the thermal expansion coefficient of the relay substrate becomes higher than that of the base substrate.

[0012] The present disclosure provides a technique that can improve the connection reliability between a base substrate and an interconnect substrate.

[0013] First, the configuration of a semiconductor device 100 according to the embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic cross-sectional view showing the configuration of a semiconductor device 100 according to the embodiment.

[0014] As shown in FIG. 1, the semiconductor device 100 includes a motherboard 1, a composite wiring board 2, and a plurality of semiconductor elements 3.

[0015] The composite wiring board 2 includes a base substrate 4 and an interconnect substrate 5 .

[0016] The base substrate 4 is mounted on the motherboard 1. Details of the base substrate 4 will be described later.

[0017] The relay substrate 5 is a so-called interposer. The relay substrate 5 relays the electrical connection between the base substrate 4 and the semiconductor element 3. The relay substrate 5 is bonded to the semiconductor element 3 via a bonding material 6, and is also bonded to the base substrate 4 via a bonding material 7.

[0018] The Young's modulus of the relay substrate 5 may be smaller than that of the base substrate 4. In this case, the relay substrate 5 may have flexibility that allows it to deform according to the shape of the surface of the base substrate 4. The bonding materials 6 and 7 are, for example, solder. The relay substrate 5 and the bonding material 7 will be described in detail later.

[0019] The semiconductor element 3 is mounted on the relay substrate 5. The semiconductor element 3 is, for example, a chip or chiplet in which circuits or elements are formed on a substrate made of a material other than a semiconductor, such as a semiconductor chip or a glass substrate. The chiplet is a functional block that constitutes part of the integrated circuit of the semiconductor device 100.

[0020] 1 shows two semiconductor elements 3, the semiconductor device 100 may include three or more semiconductor elements 3. The semiconductor device 100 may also include only one semiconductor element 3. For example, when the semiconductor element 3 is a chiplet, an integrated circuit having one function may be configured by a plurality of semiconductor elements 3.

[0021] Next, the configuration of the base substrate 4 according to the embodiment will be described with reference to Fig. 2 and Fig. 3. Fig. 2 is a schematic cross-sectional view showing the configuration of the base substrate 4 according to the embodiment. Fig. 3 is a schematic enlarged view of region III shown in Fig. 2.

[0022] The base substrate 4 has a first core substrate 10 and a first organic substrate 20. The base substrate 4 is a laminate of the first core substrate 10 and the first organic substrate 20. The base substrate 4 also has a first conductor section 30 and a second conductor section 40.

[0023] <First Core Substrate> The first core substrate 10 is a ceramic substrate. The first core substrate 10 may be formed using a ceramic composite material containing a glass component, known as glass ceramic. The glass ceramic may be any of the following: a composite of a glass phase and ceramic particles; a composite of a glass phase and a crystalline phase formed by the crystallization of a portion of the glass phase; a composite in which ceramic particles exist in the glass phase; and a composite in which a glass phase exists at the grain boundaries between ceramic particles. The first core substrate 10 formed using ceramic in this manner has higher rigidity than a core material made of glass.

[0024] For example, the first core substrate 10 may be made of low temperature co-fired ceramics (LTCC). When LTCC is used as the first core substrate 10, a low-melting-point metal such as copper or silver, which has a relatively low electrical resistance, can be used as the wiring. In this embodiment, the low-melting-point metal is a metal with a melting point lower than that of typical metals used for wiring in ceramic substrates, such as tungsten or molybdenum.

[0025] The first core substrate 10 may contain a ceramic filler as ceramic particles. Examples of the ceramic filler that can be used include alumina (aluminum oxide), calcium titanate, and magnesium titanate. In particular, a first core substrate 10 containing alumina has high rigidity.

[0026] The first core substrate 10 has a first surface 101 and a second surface 102 located on the opposite side to the first surface 101. The first core substrate 10 may be a plate-like body having the first surface 101 and the second surface 102 as main surfaces.

[0027] In the embodiment, the first core substrate 10 has a plurality of ceramic layers 11. The plurality of ceramic layers 11 are stacked along the thickness direction of the first core substrate 10. A base substrate 4 having such a first core substrate 10 has a high degree of design freedom. Furthermore, by forming the first core substrate 10 using a plurality of ceramic layers 11, the first core substrate 10 can be manufactured while checking whether the first conductor portion 30 is properly formed for each layer, thereby improving the yield of the first core substrate 10.

[0028] 1 and 2, the first core substrate 10 has four ceramic layers 11, but the number of ceramic layers 11 is not limited to four. The number of ceramic layers 11 may be two, three, or five or more.

[0029] <First Organic Base Material> The first organic base material 20 is a base material containing an organic component. The organic component may be an organic resin. The organic resin may be, for example, an epoxy resin, an acrylic resin, a polycarbonate resin, a polyimide resin, an olefin resin, or a polyphenylene resin.

[0030] The organic resin may be, for example, polytetrafluoroethylene (PTFE) or other fluororesins or polyphenylene ether resins. The first organic base material 20 may contain components other than the organic resin. In the present disclosure, the organic resin may be, for example, a material that accounts for 30% by mass or more of the materials that constitute the first organic base material 20.

[0031] The first organic base material 20 has a third surface 103 and a fourth surface 104 located on the opposite side to the third surface 103. The first organic base material 20 may be a plate-like body having the third surface 103 and the fourth surface 104 as main surfaces.

[0032] The base substrate 4 according to the embodiment has two first organic base materials 20. One of the two first organic base materials 20 is bonded to the first surface 101 of the first core base material 10, and the other is bonded to the second surface 102 of the first core base material 10.

[0033] The first organic base material 20 located on the first surface 101 of the first core substrate 10 has its third surface 103 bonded to the first surface 101 of the first core substrate 10, and multiple semiconductor elements 3 are placed on the fourth surface 104 of the first organic base material 20 via an intermediate substrate 5 (see Figure 1).

[0034] The first organic base material 20 located on the second surface 102 of the first core substrate 10 has its third surface 103 bonded to the first surface 101 of the first core substrate 10, and its fourth surface 104 bonded to the motherboard 1 via a bonding portion 8 (see Figure 1).

[0035] The first organic base material 20 has a plurality of organic resin layers 21. The plurality of organic resin layers 21 are stacked along the thickness direction of the first organic base material 20. A base substrate 4 having such a first organic base material 20 has a high degree of freedom in design. In the example shown in FIG. 2 , the first organic base material 20 has four organic resin layers 21, but the number of organic resin layers 21 is not limited to four. The number of organic resin layers 21 may be two, three, or five or more.

[0036] 1 and 2 show an example in which base substrate 4 has first organic base material 20 on each of both main surfaces (first surface 101 and second surface 102) of first core substrate 10. However, the present invention is not limited to this, and base substrate 4 may have first organic base material 20 on at least first surface 101 of first core substrate 10.

[0037] The first organic base material 20 containing an organic component is easier to form a fine wiring pattern on than an inorganic substrate, whereas the first core base material 10 made of ceramic has higher rigidity and lower density than the first organic base material 20.

[0038] The base substrate 4 according to the embodiment can increase rigidity while achieving finer wiring and narrower pitches by combining the first core substrate 10 and the first organic substrate 20. Since warping of the substrate becomes more pronounced as the substrate becomes larger, the configuration of the base substrate 4 in which the first core substrate 10 compensates for the low rigidity of the first organic substrate 20 is particularly useful for increasing the size of the substrate.

[0039] The first core substrate 10 and the first organic substrate 20 are bonded together, for example, by hydrogen bonding. Specifically, the first core substrate 10 and the first organic substrate 20 are bonded together by bonding between hydroxyl groups of the first core substrate 10 and the first organic substrate 20. In this case, a ceramic material such as alumina having surface hydroxyl groups may be used for the first core substrate 10, and an epoxy resin, which is a resin material containing hydroxyl groups, may be used for the first organic substrate 20. By directly bonding the first core substrate 10 and the first organic substrate 20 in this way without using solder, underfill, or the like, the thickness of the base substrate 4 can be reduced and the manufacturing process can be simplified.

[0040] Furthermore, the first core substrate 10 may contain a glass component, and the first organic substrate 20 may contain a coupling agent that chemically bonds with the glass component. For example, a silane coupling agent may be used as the coupling agent. Alternatively, a titanium-based coupling agent or an aluminum-based coupling agent may be used as the coupling agent. With this configuration, the first core substrate 10 and the first organic substrate 20 are chemically bonded together, thereby more firmly bonding the first core substrate 10 and the first organic substrate 20, which are made of different materials.

[0041] <First conductor portion> The first conductor portion 30 is a through-hole conductor located in the first core substrate 10. Specifically, the first conductor portion 30 has a through hole 31 that penetrates the first core substrate 10, and a conductor 32. The conductor 32 is mainly composed of metal and is located inside the through hole 31.

[0042] The first conductor portion 30 also has lands 33 on the first surface 101 and the second surface 102 of the first core substrate 10 .

[0043] <Second Conductor Portion> The second conductor portion 40 has a plurality of vias 41, a plurality of lands 42, and a plurality of first wirings 43. The vias 41 penetrate one or a plurality of organic resin layers 21. The lands 42 are located between adjacent organic resin layers 21 and electrically connect the plurality of vias 41 to one another. The first wirings 43 are located inside the first organic base material 20. The first wirings 43 located on the first organic base material 20 bonded to the first surface 101 of the first core substrate 10 and the first wirings 43 located on the first organic base material 20 bonded to the second surface 102 are electrically connected via conductors 32 that penetrate the first core substrate 10. This enables the first wirings 43 to be arranged at a high density. Details of the first wirings 43 will be described later.

[0044] The first conductor portion 30 and the second conductor portion 40 may be, for example, a metal conductor whose main component is copper or silver. For example, both the first conductor portion 30 and the second conductor portion 40 may be a metal conductor whose main component is copper. Alternatively, both the first conductor portion 30 and the second conductor portion 40 may be a metal conductor whose main component is silver. Alternatively, one of the first conductor portion 30 and the second conductor portion 40 may be a metal conductor whose main component is copper, and the other may be a metal conductor whose main component is silver.

[0045] By making all of the first conductor portion 30 and the second conductor portion 40 metal conductors whose main component is copper or silver, it is possible to obtain higher electrical characteristics compared to, for example, when one of the first conductor portion 30 and the second conductor portion 40 is made of a metal conductor other than copper or silver.

[0046] Of the first conductor 30 and the second conductor 40, only the first conductor 30 may contain a glass component. In this case, the first conductor 30 is firmly bonded to the first core substrate 10, which also contains a glass component, via the glass component. This allows the rigidity of the first core substrate 10 to be increased.

[0047] Furthermore, in the firing process when manufacturing the base substrate 4, the shrinkage rates of the first core substrate 10 and the first conductor portion 30 can be made to be somewhat uniform, making it less likely that the first conductor portion 30 will become misaligned.

[0048] The first conductor 30 may be formed, for example, by printing a conductive paste containing copper and glass components on a green sheet that is the raw material of the ceramic layer 11, and firing the green sheet simultaneously with the green sheet. Specifically, the conductive paste may contain, for example, copper powder, borosilicate glass powder, and silica particles.

[0049] On the other hand, the second conductor 40 may be formed by copper plating, which allows the first conductor 30 and the second conductor 40 to be configured such that only the first conductor 30 contains a glass component.

[0050] The second conductor 40 may be electrically and thermally connected to the semiconductor element 3 via the relay substrate 5. By thermally connecting the second conductor 40, which is mainly composed of copper or silver, which has a relatively high thermal conductivity, to the semiconductor element 3, which serves as a heat source, the heat generated from the semiconductor element 3 can be efficiently dissipated via the second conductor 40 and the first conductor 30.

[0051] Next, the configuration of the relay substrate 5 according to the embodiment will be described with reference to Fig. 4 and Fig. 5. Fig. 4 is a schematic cross-sectional view showing the configuration of the relay substrate 5 according to the embodiment and its surroundings. Fig. 5 is a schematic enlarged view of region V shown in Fig. 4.

[0052] The relay substrate 5 has a second core substrate 50 and a second organic substrate 60. The relay substrate 5 is a laminate of the second core substrate 50 and the second organic substrate 60. The relay substrate 5 also has a third conductor 70 and a fourth conductor 80.

[0053] <Second Core Substrate> The second core substrate 50 is a ceramic substrate. The second core substrate 50 may be formed using a ceramic composite material containing a glass component, known as glass ceramic. The glass ceramic may be any of the following: a composite of a glass phase and ceramic particles; a composite of a glass phase and a crystalline phase formed by the crystallization of a portion of the glass phase; a composite in which ceramic particles exist in the glass phase; and a composite in which a glass phase exists at the grain boundaries between ceramic particles. The second core substrate 50 formed using ceramic in this manner has higher rigidity than a core material made of glass.

[0054] For example, the second core substrate 50 may be made of low temperature co-fired ceramics (LTCC). When LTCC is used as the second core substrate 50, a low-melting-point metal such as copper or silver, which has a relatively low electrical resistance, can be used as wiring.

[0055] The second core substrate 50 may contain a ceramic filler as ceramic particles. Examples of the ceramic filler that can be used include alumina (aluminum oxide), calcium titanate, and magnesium titanate. In particular, the second core substrate 50 containing alumina has high rigidity.

[0056] The second core substrate 50 has a fifth surface 501 and a sixth surface 502 located opposite the fifth surface 501. The second core substrate 50 may be a plate-like body having the fifth surface 501 and the sixth surface 502 as main surfaces.

[0057] It should be noted that the relay substrate 5 according to this embodiment only needs to have at least the second organic base material 60 , and does not necessarily need to have the second core base material 50 .

[0058] <Second Organic Base Material> The second organic base material 60 is a base material containing an organic component. The organic component may be an organic resin. The organic resin may be, for example, an epoxy resin, an acrylic resin, a polycarbonate resin, a polyimide resin, an olefin resin, or a polyphenylene resin.

[0059] The organic resin may be, for example, polytetrafluoroethylene (PTFE) or other fluororesins or polyphenylene ether resins. The second organic base material 60 may contain components other than the organic resin. In the present disclosure, the organic resin may be, for example, a material that accounts for 30% by mass or more of the materials that constitute the second organic base material 60.

[0060] The second organic base material 60 has a seventh surface 603 and an eighth surface 604 located opposite to the seventh surface 603. The second organic base material 60 may be a plate-like body having the seventh surface 603 and the eighth surface 604 as main surfaces.

[0061] The seventh surface 603 of the second organic base material 60 is bonded to the fifth surface 501 of the second core base material 50 via a bonding material 9, and multiple semiconductor elements 3 are placed on the eighth surface 604 of the second organic base material 60 via a bonding material 6 (see Figure 1).

[0062] The second organic base material 60 has a plurality of organic resin layers 61. The plurality of organic resin layers 61 are stacked along the thickness direction of the second organic base material 60. The relay substrate 5 having such a second organic base material 60 has a high degree of freedom in design. In the example shown in FIG. 4 , the second organic base material 60 has three organic resin layers 61, but the number of organic resin layers 61 is not limited to three. The number of organic resin layers 61 may be one or two, or may be four or more.

[0063] <Third conductor portion> The third conductor portion 70 is a through-hole conductor located in the second core substrate 50. Specifically, the third conductor portion 70 has a through hole 71 that penetrates the second core substrate 50, and a conductor 72. The conductor 72 is mainly composed of metal and is located inside the through hole 71.

[0064] The third conductor 70 also has lands 73 on the fifth surface 501 and the sixth surface 502 of the second core substrate 50 .

[0065] <Fourth Conductor> The fourth conductor 80 has a plurality of vias 81, a plurality of lands 82, and a plurality of second wirings 83. The vias 81 penetrate one or a plurality of organic resin layers 61. The lands 82 are located between adjacent organic resin layers 61, and electrically connect the plurality of vias 81 to each other. The lands 82 are formed integrally with the vias 81 located in the same organic resin layer 61. The second wirings 83 are located inside the second organic base material 60. Details of the second wirings 83 will be described later.

[0066] The third conductor portion 70 and the fourth conductor portion 80 may be, for example, a metal conductor whose main component is copper or silver. For example, the third conductor portion 70 and the fourth conductor portion 80 may both be metal conductors whose main component is copper. Alternatively, the third conductor portion 70 and the fourth conductor portion 80 may both be metal conductors whose main component is silver. Alternatively, one of the third conductor portion 70 and the fourth conductor portion 80 may be a metal conductor whose main component is copper, and the other may be a metal conductor whose main component is silver.

[0067] By making all of the third conductor portion 70 and the fourth conductor portion 80 metal conductors whose main component is copper or silver, it is possible to obtain higher electrical characteristics compared to, for example, when one of the third conductor portion 70 and the fourth conductor portion 80 is made of a metal conductor other than copper or silver.

[0068] Of the third conductor 70 and the fourth conductor 80, only the first conductor 30 may contain a glass component. In this case, the third conductor 70 is firmly bonded to the second core substrate 50, which also contains a glass component, via the glass component. This allows the rigidity of the second core substrate 50 to be increased.

[0069] Furthermore, in the firing process when manufacturing the relay substrate 5, the shrinkage rates of the second core substrate 50 and the third conductor portion 70 can be made to be somewhat uniform, making it less likely that the third conductor portion 70 will become misaligned.

[0070] The third conductor 70 may be formed, for example, by printing a conductive paste containing copper and glass components onto a green sheet that is the raw material for the second core substrate 50, and firing the green sheet simultaneously with the green sheet. Specifically, the conductive paste may contain, for example, copper powder, borosilicate glass powder, and silica particles.

[0071] On the other hand, the fourth conductor 80 may be formed by copper plating, which allows the third conductor 70 and the fourth conductor 80 to have a configuration in which only the third conductor 70 contains a glass component.

[0072] The fourth conductor 80 may be electrically and thermally connected to the semiconductor element 3 via the bonding material 6. By thermally connecting the fourth conductor 80, which is mainly composed of copper or silver, which has a relatively high thermal conductivity, to the semiconductor element 3, which serves as a heat source, the heat generated from the semiconductor element 3 can be efficiently dissipated via the fourth conductor 80 and the third conductor 70.

[0073] Generally, a solid pattern such as a ground wiring or a power wiring is arranged on the first organic base material 20 of the base substrate 4, whereas a solid pattern is rarely arranged on the relay substrate 5. Therefore, due to the difference in the proportion of metal wiring, the thermal expansion coefficient of the relay substrate 5 is often higher than that of the base substrate 4. As another example, if the first core substrate 10 of the base substrate 4 and the second core substrate 50 of the relay substrate 5 are made of different materials, a difference in the thermal expansion coefficient of the base substrate 4 and that of the relay substrate 5 will occur. Furthermore, if the inorganic material content of the first organic base material 20 of the base substrate 4 and that of the second organic base material 60 of the relay substrate 5 are different, a difference in the thermal expansion coefficient of the base substrate 4 and that of the relay substrate 5 will occur. If there is a difference in the thermal expansion coefficient of the base substrate 4 and that of the relay substrate 5, when the base substrate 4 and the relay substrate 5 are bonded using a bonding material during the manufacturing process, the difference in thermal expansion between the base substrate 4 and the relay substrate 5 may cause distortion in the bonding material. The distortion of the bonding material may reduce the reliability of the connection between the base substrate 4 and the relay substrate 5 .

[0074] Therefore, in the composite wiring board 2 according to this embodiment, a variable melting point bonding material 7 is used as the bonding material for bonding the base substrate 4 and the relay substrate 5 together.

[0075] The variable-melting-point bonding material 7 has different melting points in its initial paste state and in its state after being heated to form an intermetallic compound. Specifically, the variable-melting-point bonding material 7 melts at a first melting point (e.g., about 140°C) and then remelts to a second melting point (e.g., about 245°C) higher than the first melting point. The first melting point of the variable-melting-point bonding material 7 is lower than the melting point of a typical bonding material (e.g., lead-free solder or lead-containing solder). Therefore, when the variable-melting-point bonding material 7 is used, the difference in thermal expansion between the base substrate 4 and the relay substrate 5 during the bonding process can be reduced compared to when a typical bonding material is used. This makes it less likely for distortion to occur in the bonding material 7 during the above process. Furthermore, the difference in thermal contraction between the base substrate 4 and the relay substrate 5 during the subsequent cooling process is also reduced, making the bonding material 7 less likely to crack. As such, the composite wiring board 2 of this embodiment provides high connection reliability between the base substrate 4 and the relay substrate 5.

[0076] Furthermore, the second melting point of the variable-melting-point bonding material 7 is higher than the first melting point. Specifically, the second melting point is higher than the melting point of the bonding material 6 used to bond the relay substrate 5 and the semiconductor element 3. Therefore, even if the composite wiring board 2 is heated again in the process of melting the bonding material 6 to bond the relay substrate 5 and the semiconductor element 3, the bonding material 7 (variable-melting-point bonding material) that bonds the base substrate 4 and the relay substrate 5 will not re-melt. Therefore, with the composite wiring board 2 of this embodiment, a decrease in the connection reliability between the base substrate 4 and the relay substrate 5 due to re-melting of the bonding material 7 is unlikely to occur.

[0077] As described above, the first conductor portion 30 and the second conductor portion 40 of the base substrate 4 and the third conductor portion 70 and the fourth conductor portion 80 of the relay substrate 5 may be primarily composed of copper. Specifically, the first wiring 43 (see FIG. 3 ) of the base substrate 4 and the second wiring 83 of the relay substrate 5 may be primarily composed of copper. In this case, the bonding material 7 may contain Sn and at least one selected from Ag, Bi, In, Cu, and Sb.

[0078] The thermal expansion coefficient of the melting point variable bonding material 7, which contains Sn and at least one selected from Ag, Bi, In, Cu, and Sb, is close to that of copper. That is, in the composite wiring board 2 according to this embodiment, the thermal expansion coefficient of the first wiring 43 and the second wiring 83 is close to that of the bonding material 7. Therefore, in the composite wiring board 2 according to this embodiment, cracks are less likely to occur at the bonding interface due to the difference in thermal expansion between the first wiring 43 and the second wiring 83 and the bonding material 7. Therefore, the composite wiring board 2 according to this embodiment can further improve the connection reliability between the base substrate 4 and the relay substrate 5.

[0079] As described above, the relay board 5 according to this embodiment may include a second core substrate 50. The thermal expansion coefficient of the relay board 5 having the second core substrate 50 is smaller than that of the relay board 5 without the second core substrate 50. Therefore, a difference in thermal expansion coefficient is likely to occur between the relay board 5 having the second core substrate 50 and the base substrate 4. The composite wiring board 2 according to this embodiment uses a melting-point-changing bonding material 7 for bonding the base substrate 4 and the relay board 5. Therefore, even if there is a difference in thermal expansion coefficient between the base substrate 4 and the relay board 5, the difference in thermal expansion between the base substrate 4 and the relay board 5 can be kept small during the process of bonding the base substrate 4 and the relay board 5. For these reasons, the composite wiring board 2 according to this embodiment is effective as a configuration for a composite wiring board 2 having a cored relay board 5.

[0080] Next, the configurations of the first wiring 43 of the base substrate 4 and the second wiring 83 of the relay substrate 5 according to the embodiment will be described with reference to FIGS. 3 and 5. FIG.

[0081] As shown in Fig. 5, the second wiring 83 located inside the second organic base material 60 of the relay substrate 5 has a diffusion suppression layer 90 on its side and bottom surfaces. In contrast, as shown in Fig. 3, the first wiring 43 located inside the first organic base material 20 of the base substrate 4 may have a diffusion suppression layer 90 only on its bottom surface. In other words, the side surfaces of the first wiring 43 are in direct contact with the first organic base material 20, and no diffusion suppression layer 90 is present on the side surfaces of the first wiring 43, but the diffusion suppression layer 90 is present on the side surfaces of the second wiring 83. The top surface of the second wiring 83 is located at the boundary between two adjacent organic resin layers 61 of the second organic base material 60.

[0082] The multiple second wirings 83 located inside the second organic base material 60 are formed finer than the multiple first wirings 43 (see FIG. 3 ) located inside the first organic base material 20 of the base substrate 4. The distance between adjacent wirings in the in-plane direction of the base material (hereinafter referred to as the "inter-wiring distance") is also shorter between the second wirings 83 than between the first wirings 43. The shorter the inter-wiring distance, the more difficult it is to ensure insulation between the wirings. That is, it is more difficult to ensure insulation between the second wirings 83 than between the first wirings 43. In contrast, the composite wiring board 2 according to this embodiment has a diffusion suppression layer 90 on the side of the second wirings 83, which have a shorter inter-wiring distance. The diffusion suppression layer 90 suppresses diffusion of metal components contained in the second wirings 83 into the second organic base material 60. That is, in the composite wiring board 2 according to this embodiment, the diffusion suppression layer 90 can reduce the possibility that the metal components contained in the second wirings 83 will diffuse into the second organic base material 60, causing electrical conduction between adjacent second wirings 83 via the metal components diffused into the second organic base material 60. In other words, the insulation reliability is high.

[0083] As shown in FIG. 5, the side and bottom surfaces of the via 81 and the side surfaces of the land 82 may have a diffusion suppression layer 90 in the same manner as the second wiring 83 .

[0084] The diffusion suppression layer 90 may contain any of Cr, Ti, Ni, and a compound of a combination of two or more of these elements. This configuration effectively reduces the diffusion of the metal contained in the second wiring 83 into the second organic base material 60.

[0085] <Method for manufacturing second organic base material> Next, a method for manufacturing the second organic base material 60 according to the embodiment, specifically, an example of a method for forming the above-described second wiring 83 on the second organic base material 60, will be described with reference to Figures 6 to 12. Figures 6 to 12 are schematic diagrams for explaining the method for manufacturing the second organic base material 60 according to the embodiment. The second organic base material 60 has, for example, three insulating layers (organic resin layers 61) stacked on top of each other.

[0086] First, as shown in Fig. 6, a release layer 220 is formed on one surface of a support 210. Since light may be irradiated onto the release layer 220 through the support 210, it is preferable that the support 210 be light-transmitting. For example, a glass plate can be used as the support 210. The material of the release layer 220 may be a resin that absorbs ultraviolet light (UV light) and becomes peelable.

[0087] Next, as shown in FIG. 7, an insulating resin layer 230 is formed on the release layer 220, and then a through-hole 240 is formed by laser processing or the like, penetrating the insulating resin layer 230 in the thickness direction.

[0088] Next, as shown in FIG. 8, a diffusion suppression layer 90 is formed on the surface of the insulating resin layer 230 in which the through holes 240 are formed, followed by electrolytic copper plating, and as shown in FIG. 9, the surface is polished to remove excess copper plating 260.

[0089] Next, as shown in FIG. 10, a mask layer 270 is formed on the surface using titanium or the like, and then the portions other than the mask layer 270 are dry etched.

[0090] 11, a diffusion suppression layer 90 is again formed on the etched surface, followed by electrolytic copper plating, and then the surface is polished to remove excess copper plating 260, as shown in Fig. 12. As a result, second wiring 83 is formed in which diffusion suppression layers 90 are located on the side and bottom surfaces.

[0091] The above-described steps shown in FIGS. 6 to 12 are repeated (three times in this example) to produce the second organic base material 60.

[0092] The present technology may also be configured as follows. (1) A composite wiring board (for example, a composite wiring board 2) includes a base substrate (for example, a base substrate 4), a melting-point-changing bonding material (for example, a bonding material 7), and an interposer substrate (for example, an interposer substrate 5) electrically connected to the base substrate via the bonding material. The base substrate includes a first core substrate (for example, a first core substrate 10), a first organic base material (for example, a first organic base material 20) made of an organic resin bonded to the first core substrate, and a plurality of first wirings (for example, first wirings 43) located inside the first organic base material. The interposer includes a second organic base material (for example, a second organic base material 60) made of an organic resin and a plurality of second wirings (for example, second wirings 83) located inside the second organic base material. The second wirings have a diffusion suppression layer on a side surface. (2) In the composite wiring board described in (1) above, the first wiring and the second wiring may be primarily composed of copper, and the bonding material may contain Sn and at least one selected from Ag, Bi, In, Cu, and Sb. (3) In the composite wiring board described in (1) or (2) above, the diffusion suppression layer may contain Cr, Ti, Ni, or a compound combining two or more of these. (4) In the composite wiring board described in any one of (1) to (3) above, the side of the first wiring may be in direct contact with the first organic base material. (5) In the composite wiring board described in any one of (1) to (4) above, the relay substrate may have a second core base material (e.g., second core base material 50), and the second organic base material may be bonded to the second core base material. (6) In the composite wiring board described in any one of (1) to (5) above, the first core base material may be made of ceramic. (7) In the composite wiring board described in (6) above, the first core substrate may have a plurality of ceramic layers (for example, ceramic layer 11). (8) The composite wiring board described in (6) or (7) above may have two first organic base materials, and the first core substrate may have a first surface (for example, first surface 101) and a second surface (for example, second surface 102) located opposite the first surface, and a first organic base material may be bonded to each of the first surface and the second surface.(9) The composite wiring board described in (8) above may have a conductor (e.g., conductor 32) penetrating the first surface and the second surface of the first core substrate, and the first wiring located on the first organic base material bonded to the first surface and the first wiring located on the first organic base material bonded to the second surface may be electrically connected via the conductor. (10) In the composite wiring board described in any one of (6) to (9) above, the first core substrate may contain a glass component, and the first organic base material may contain a coupling agent that chemically bonds with the glass component. (11) The semiconductor device may have a motherboard (e.g., motherboard 1), the composite wiring board described in any one of (1) to (10) above mounted on the motherboard, and a semiconductor element mounted on an interconnect substrate.

[0093] The disclosed embodiments should be considered in all respects as illustrative and not restrictive. Indeed, the above-described embodiments may be embodied in various forms. Furthermore, the above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims.

[0094] REFERENCE SIGNS LIST 1 Motherboard 2 Composite wiring board 3 Semiconductor element 4 Base substrate 5 Intermediate substrate 10 First core substrate 20 First organic substrate 30 First conductor portion 40 Second conductor portion 43 First wiring 50 Second core substrate 60 Second organic substrate 70 Third conductor portion 80 Fourth conductor portion 83 Second wiring 100 Semiconductor device

Claims

1. A composite wiring board comprising: a base substrate; a melting point changing bonding material; and an intermediate substrate electrically connected to the base substrate via the bonding material, wherein the base substrate comprises: a first core substrate; a first organic substrate made of organic resin bonded to the first core substrate; and a plurality of first wirings located inside the first organic substrate; the intermediate substrate comprises: a second organic substrate made of organic resin; and a plurality of second wirings located inside the second organic substrate, wherein the second wirings have a diffusion suppression layer on a side surface.

2. The composite wiring board according to claim 1, wherein the first wiring and the second wiring are mainly composed of copper, and the bonding material contains at least one selected from the group consisting of Ag, Bi, In, Cu and Sb, and Sn.

3. The composite wiring board according to claim 1 or 2, wherein the diffusion suppression layer contains any one of Cr, Ti, Ni and a compound combining two or more of these elements.

4. The composite wiring board according to any one of claims 1 to 3, wherein a side surface of the first wiring is in direct contact with the first organic base material.

5. The composite wiring board according to any one of claims 1 to 4, wherein the intermediate substrate has a second core substrate, and the second organic substrate is bonded to the second core substrate.

6. The composite wiring board according to any one of claims 1 to 5, wherein the first core substrate is made of ceramic.

7. The composite wiring board according to claim 6, wherein the first core substrate has a plurality of ceramic layers.

8. A composite wiring board as described in claim 6 or 7, comprising two first organic base materials, the first core base material having a first surface and a second surface located opposite the first surface, and the first organic base material being bonded to each of the first surface and the second surface.

9. A composite wiring board as described in claim 8, having a conductor penetrating the first surface and the second surface of the first core substrate, wherein the first wiring located on the first organic substrate bonded to the first surface and the first wiring located on the first organic substrate bonded to the second surface are electrically connected via the conductor.

10. A composite wiring board according to any one of claims 6 to 9, wherein the first core substrate contains a glass component, and the first organic substrate contains a coupling agent that chemically bonds with the glass component.

11. A semiconductor device comprising: a motherboard; a composite wiring board according to any one of claims 1 to 10 mounted on said motherboard; and a semiconductor element mounted on said relay substrate.

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