Mounting structure

Abstract

A mounting structure according to the present disclosure includes: a wiring board having a first surface and a second surface located on the opposite side from the first surface; an electronic component located on the first surface; and a stiffener located on the first surface so as to surround the electronic component. The wiring board includes a substrate with an insulating layer and a conductor layer. Provided that a first portion is defined to be the electronic component and the portion of the wiring board spanning from the first surface to the second surface where the electronic component is located, a second portion is defined to be the stiffener and the portion of the wiring board spanning from the first surface to the second surface where the stiffener is located, a first lower portion is defined to be the side containing the second surface as bounded by a first imaginary line bisecting the thickness of the first portion, and a second lower portion is defined to be the side containing the second surface as bounded by a second imaginary line bisecting the thickness of the second portion, a first member having a first coefficient of thermal expansion smaller than the coefficient of thermal expansion of the substrate is located in the first lower portion, and / or a second member having a second coefficient of thermal expansion larger than the coefficient of thermal expansion of the substrate is located in the second lower portion.

Description

Implementation Structure

[0001] The present invention relates to a mounting structure.

[0002] Known LSI packages in which LSI electronic components are mounted on a wiring substrate include FC-BGA (Flip Chip Ball Grid Array) etc. Wiring substrates used in such LSI packages are provided with stiffeners for the purposes of reinforcement and warpage correction, as described in Patent Document 1, for example.

[0003] International Publication No. 2020 / 162417

[0004] A mounting structure according to the present disclosure includes a wiring board having a first surface and a second surface opposite to the first surface, an electronic component located on the first surface, and a stiffener located on the first surface so as to surround the electronic component. The wiring board includes a base having an insulating layer and a conductor layer. When the electronic component and a portion of the wiring board extending from the first surface on which the electronic component is located to the second surface are defined as a first portion, the stiffener and a portion of the wiring board extending from the first surface on which the stiffener is located to the second surface are defined as a second portion, and a portion of the wiring board between the first and second portions is defined as a third portion, the side including the second surface, separated by a first imaginary line that halves the thickness of the first portion, is defined as a first lower portion, and the side opposite the first lower portion is defined as a first upper portion, the side including the second surface, separated by a second imaginary line that halves the thickness of the second portion, is defined as a second lower portion, and the side opposite the second lower portion is defined as a second upper portion, and the side including the second surface, separated by a third imaginary line that halves the thickness of the third portion, is defined as a third lower portion, and the side opposite the third lower portion is defined as the third upper portion, at least one of a first member having a first thermal expansion coefficient smaller than the thermal expansion coefficient of the base is located in the first lower portion, and a second member having a second thermal expansion coefficient greater than the thermal expansion coefficient of the base is located in the second lower portion.

[0005] 5A to 5C are enlarged explanatory views illustrating modified examples of region X shown in FIG. 2.

[0024] FIG. 5A is a plan view of a mounting structure according to an embodiment of the present disclosure.

[0025] FIG. 5C is an explanatory view illustrating a cross section taken along line A-A shown in FIG. 1.

[0026] FIG. 5A is an explanatory view illustrating a first virtual line, a second virtual line, and a third virtual line.

[0027] FIG. 5C is an explanatory view illustrating modified examples of region X shown in FIG. 2.

[0006] Stiffeners are generally made of a metal such as copper, which has a relatively large coefficient of thermal expansion. Therefore, a relatively large difference in the coefficient of thermal expansion occurs between the substrate, the electronic component, and the stiffener. Thermal changes, such as those occurring during mounting of the electronic component, can cause warping due to this difference, and stress tends to concentrate in the area between the electronic component and the stiffener (the edge of the stiffener). As a result, cracks tend to occur in the plane conductors (particularly the plane conductors around the solder used for mounting) on ​​the surface facing this area (the opposite surface). Therefore, there is a demand for a mounting structure that reduces the occurrence of warping and, thereby, cracks.

[0007] The mounting structure according to the present disclosure has the configuration described in the section on means for solving the above problems, thereby reducing the occurrence of warping and cracks.

[0008] A mounting structure according to an embodiment of the present disclosure will be described with reference to Figures 1 to 5C. Figure 1 is a plan view of a mounting structure 10 according to an embodiment of the present disclosure. The mounting structure 10 according to the embodiment includes a wiring substrate 1, an electronic component 2, and a stiffener 3.

[0009] 2, the wiring board 1 includes a core layer 11, a build-up layer 12, and a solder resist 6. Fig. 2 is an explanatory diagram for illustrating a cross section taken along line AA shown in Fig. 1.

[0010] The core layer 11 is located approximately at the center in the thickness direction of the wiring board 1. Although not shown, the core layer 11 includes a core insulating layer and a core conductor layer. The core insulating layer is not particularly limited as long as it is made of an insulating material. Examples of insulating materials include resins such as epoxy resin, bismaleimide-triazine resin, polyimide resin, and polyphenylene ether resin. These resins may be used alone or in combination of two or more. The thickness of the core insulating layer is not particularly limited and may be, for example, 0.2 mm or more and 1.4 mm or less.

[0011] The core insulating layer may contain a reinforcing material. Examples of reinforcing materials include insulating fabric materials such as glass fiber, glass nonwoven fabric, aramid nonwoven fabric, aramid fiber, and polyester fiber. Only one type of reinforcing material may be used, or two or more types may be used in combination. Furthermore, the core insulating layer may have dispersed therein an inorganic insulating filler such as silica, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide. Only one type of inorganic insulating filler may be used, or two or more types may be used in combination.

[0012] The core conductor layer is located on the surface of the core insulating layer. The core conductor layer is not particularly limited as long as it is made of a conductive material. Examples of conductive materials include metals such as copper. The thickness of the core conductor layer is not particularly limited, and is, for example, 10 μm or more and 30 μm or less.

[0013] A through-hole conductor is located in the core insulating layer to electrically connect the upper and lower surfaces of the core insulating layer. The through-hole conductor is located in a through-hole that penetrates the upper and lower surfaces of the core insulating layer. The through-hole conductor is formed of a metal such as copper. The through-hole conductor may be formed only on the inner wall surface, or may fill the through-hole. The through-hole conductor is connected to the core conductor layer on the surface of the core insulating layer.

[0014] The buildup layers 12 are located on both sides of the core layer 11. Although not shown, the buildup layers 12 have a structure in which at least one buildup insulating layer and at least one buildup conductor layer are laminated together. Although the buildup layers 12 are located on both sides of the core layer 11 in FIG. 2, it is sufficient that the buildup layers 12 are located on at least one side of the core layer 11.

[0015] The build-up insulating layer is not particularly limited as long as it is made of an insulating material. Examples of insulating materials include resins such as epoxy resin, bismaleimide-triazine resin, polyimide resin, and polyphenylene ether resin. These resins may be used alone or in combination of two or more.

[0016] The build-up insulating layers may be made of the same resin or different resins. The build-up insulating layers and the core insulating layers may be made of the same resin or different resins. The thickness of the build-up insulating layers is not particularly limited and may be, for example, 10 μm or more and 50 μm or less. The build-up insulating layers may have the same thickness or different thicknesses.

[0017] The build-up insulating layer may contain a reinforcing material. Examples of reinforcing materials include insulating fabric materials such as glass fiber, glass nonwoven fabric, aramid nonwoven fabric, aramid fiber, and polyester fiber. Only one type of reinforcing material may be used, or two or more types may be used in combination. Furthermore, the build-up insulating layer may have dispersed therein an inorganic insulating filler such as silica, barium sulfate, talc, clay, glass, calcium carbonate, and titanium oxide. Only one type of inorganic insulating filler may be used, or two or more types may be used in combination.

[0018] The build-up conductor layer is located on the surface of the build-up insulating layer. The build-up conductor layer is not particularly limited as long as it is made of a conductive material. Examples of conductive materials include metals such as copper. The thickness of the build-up conductor layer is not particularly limited, and is, for example, 10 μm or more and 30 μm or less.

[0019] Via-hole conductors are located in the build-up insulating layer to electrically connect the upper and lower surfaces of the build-up insulating layer. The via-hole conductors are located in via holes that penetrate the upper and lower surfaces of the build-up insulating layer. The via-hole conductors are made of a metal such as copper. The via-hole conductors are connected to build-up conductor layers that are located on both sides of the build-up insulating layer. The via-hole conductors may fill the via holes or may be located only on the inner surfaces of the via holes.

[0020] As shown in Fig. 2, solder resist 6 is located on both surfaces of wiring board 1. Although solder resist 6 is located on both surfaces of wiring board 1 in Fig. 2, it may be located on only one surface, or may not be located at all. When solder resist 6 is located as shown in Fig. 2, the surfaces of solder resist 6 correspond to "first surface 1a" and "second surface 1b" of wiring board 1. When solder resist 6 is not located, the surfaces of buildup layer 12 correspond to "first surface 1a" and "second surface 1b."

[0021] The solder resist 6 is made of a resin, such as an acrylic-modified epoxy resin. The solder resist 6 has openings for electrically connecting the conductor layer (build-up conductor layer) to the electrodes of the electronic component 2 via solder 7. Examples of the electronic component 2 include a semiconductor integrated circuit element and an optoelectronic element.

[0022] As shown in FIG. 1 , in the mounting structure 10, a stiffener 3 is located on the first surface 1 a of the wiring board 1 so as to surround the electronic component 2. The stiffener 3 is used to improve the rigidity of the wiring board 1 and correct warpage of the wiring board 1. Examples of materials for the stiffener 3 include a metal-based composite material, an aluminum alloy material, and a ceramic material. Examples of metal-based composite materials include a composite material (AlSiC) in which fine silicon carbide (SiC) particles are dispersed in an aluminum alloy. The stiffener 3 is located on the upper surface of the wiring board 1 via, for example, solder or an adhesive. Among these, if the stiffener 3 is located via solder, warpage and stress can be reduced, while improving the heat dissipation of heat generated when the electronic component 2 is mounted and when the mounting structure 10 is operated.

[0023] The mounting structure 10 according to one embodiment includes a first member 51 and a second member 52. The first member 51 has a first thermal expansion coefficient that is smaller than the thermal expansion coefficient of the base. The second member 52 has a second thermal expansion coefficient that is larger than the thermal expansion coefficient of the base. The base refers to the portion of the wiring board 1 that is formed of the insulating layer, the conductor layer, and the solder resist 6. Specifically, the base refers to the portion that is formed of the core layer 11 that includes the core insulating layer and the core conductor layer, the buildup layer 12 that includes the buildup insulating layer and the buildup conductor layer, and the solder resist 6.

[0024] The first member 51 has a relatively small first thermal expansion coefficient. That is, the first member 51 is formed of a material with a small thermal expansion coefficient. The first member 51 is formed of, for example, silicon, ceramics, 42 alloy (nickel-iron alloy), an organic core (glass fiber reinforced resin, etc.), glass, etc. Specifically, the material forming the first member 51 is selected in consideration of the thermal expansion coefficients of the wiring board 1, electronic component 2, and stiffener 3 to be used.

[0025] The thickness of the first member 51 is not limited. For example, in order to further reduce the occurrence of warping, the first member 51 may be relatively thick, for example, 30 μm or more. The upper limit may be, for example, about 500 μm, taking into account the thickness of the wiring substrate 1, etc. The elastic modulus of the first member 51 is also not limited. For example, in order to further reduce the occurrence of warping, the first member 51 may have a relatively high elastic modulus, for example, 70 GPa or more. The upper limit is not limited and may be, for example, about 150 GPa.

[0026] The second member 52 has a relatively large second thermal expansion coefficient. That is, the second member 52 is made of a material with a large thermal expansion coefficient. The second member 52 is made of, for example, duralumin, nickel steel (such as 20Ni), or aluminum. Specifically, the material for the second member 52 is selected in consideration of the thermal expansion coefficients of the wiring board 1, electronic component 2, and stiffener 3 to be used.

[0027] The thickness of the second member 52 is not limited. For example, in order to further reduce the occurrence of warping, the second member 52 may be relatively thick, for example, 30 μm or more. The upper limit may be, for example, about 500 μm, taking into account the thickness of the wiring substrate 1, etc. The elastic modulus of the second member 52 is also not limited. For example, in order to further reduce the occurrence of warping, the second member 52 may have a relatively high elastic modulus, for example, 70 GPa or more. The upper limit is not limited and may be, for example, about 150 GPa.

[0028] In the mounting structure 10, the first member 51 is located at a first lower portion 41L of the first portion 41. As shown in FIG. 2 , the first portion 41 is a region including the electronic component 2 and a portion of the wiring board 1 extending from the first surface 1a on which the electronic component 2 is located to the second surface 1b. That is, the first portion 41 corresponds to the region from the surface of the electronic component 2 to the second surface 1b of the wiring board 1 in the thickness direction of the mounting structure 10. Furthermore, as shown in FIG. 3 , the first portion 41 includes a first upper portion 41U and a first lower portion 41L. FIG. 3 is an explanatory diagram for explaining the first virtual line L1, the second virtual line L2, and the third virtual line L3.

[0029] 3, a first imaginary line L1 is a line that bisects the thickness (length) of the first portion 41. With this first imaginary line L1 as a boundary, the side that includes the second surface 1b of the wiring substrate 1 is a first lower portion 41L, and the side opposite the first lower portion 41L is a first upper portion 41U.

[0030] In the mounting structure 10, the second member 52 is located in a second lower portion 42L of the second portion 42. As shown in FIG. 2 , the second portion 42 is a region that includes the stiffener 3 and a portion of the wiring board 1 that extends from the first surface 1a to the second surface 1b where the stiffener 3 is located. That is, the second portion 42 corresponds to the region from the surface of the stiffener 3 to the second surface 1b of the wiring board 1 in the thickness direction of the mounting structure 10. Furthermore, as shown in FIG. 3 , the second portion 42 includes a second upper portion 42U and a second lower portion 42L.

[0031] 3, a line that bisects the thickness (length) of the second portion 42 is defined as a second imaginary line L2. The side of the second imaginary line L2 that includes the second surface 1b of the wiring substrate 1 is a second lower portion 42L, and the side opposite the second lower portion 42L is a second upper portion 42U.

[0032] 2, the third portion 43 is a region including a part of the wiring board 1 between the first portion 41 and the second portion 42. That is, the third portion 43 corresponds to the region from the first surface 1a to the second surface 1b of the wiring board 1 in the thickness direction of the mounting structure 10. Furthermore, the third portion 43 includes a third upper portion 43U and a third lower portion 43L as shown in FIG.

[0033] 3, a third imaginary line L3 is a line that bisects the thickness (length) of the third portion 43. With this third imaginary line L3 as a boundary, the side that includes the second surface 1b of the wiring substrate 1 is a third lower portion 43L, and the side opposite the third lower portion 43L is a third upper portion 43U.

[0034] The first member 51 is located at the first lower portion 41L, and the second member 52 is located at the second lower portion 42L, thereby reducing the occurrence of warpage, and as a result, reducing the occurrence of cracks in the mounting structure 10.

[0035] The position of the first member 51 is not limited as long as it is located in the first lower portion 41L, and the position of the second member 52 is not limited as long as it is located in the second lower portion 42L. For example, as shown in FIG. 4 , when the first lower portion 41L is viewed in cross section, the first member 51 may be located closer to the second surface 1b than a fourth virtual line L4 that bisects the thickness from the first virtual line L1 to the second surface 1b. Furthermore, when the second lower portion 42L is viewed in cross section, the second member 52 may be located closer to the second surface 1b than a fifth virtual line L5 that bisects the thickness from the second virtual line L2 to the second surface 1b. FIG. 4 is an explanatory diagram illustrating the fourth virtual line L4 and the fifth virtual line L5.

[0036] If the first member 51 is located closer to the second surface 1b than the fourth imaginary line L4, it is possible to further reduce warpage of the mounting structure 10. If the second member 52 is located closer to the second surface 1b than the fifth imaginary line L5, it is possible to further reduce warpage of the mounting structure 10.

[0037] Even if the first member 51 is located closer to the second surface 1b than the fourth imaginary line L4, when the wiring board 1 is viewed in cross section, the first member 51 may be located in the center of the wiring board 1. In other words, the first member 51 may be located closer to the center of the wiring board 1 rather than closer to the second surface 1b. When the first member 51 is located in the center of the wiring board 1, warping of the wiring board 1 itself is further reduced.

[0038] Even if the second member 52 is located closer to the second surface 1b than the fifth imaginary line L5, when the wiring board 1 is viewed in cross section, the second member 52 may be located in the center of the wiring board 1. In other words, the second member 52 may be located closer to the center of the wiring board 1 rather than closer to the second surface 1b. When the second member 52 is located in the center of the wiring board 1, warping of the wiring board 1 itself is further reduced.

[0039] As described above, warpage is more likely to occur when the difference in thermal expansion coefficients between the wiring board 1, the electronic component 2, and the stiffener 3 increases. Therefore, warpage is less likely to occur when the difference in thermal expansion coefficients between the upper and lower sides of the first portion 41, the second portion 42, and the third portion 43 is small. Therefore, the difference in thermal expansion coefficient between the first upper portion 41U and the first lower portion 41L may be 7 ppm / °C or less, the difference in thermal expansion coefficient between the second upper portion 42U and the second lower portion 42L may be 7 ppm / °C or less, and the difference in thermal expansion coefficient between the third upper portion 43U and the third lower portion 43L may be 7 ppm / °C or less. In particular, warpage is more likely to occur when the difference in thermal expansion coefficient between the first upper portion 41U and the first lower portion 41L, the difference in thermal expansion coefficient between the second upper portion 42U and the second lower portion 42L, and the difference in thermal expansion coefficient between the third upper portion 43U and the third lower portion 43L are all 7 ppm / °C or less.

[0040] The electronic component 2 and stiffener 3 are not located in the third portion 43. However, in the buildup layers 12 located on the upper and lower surfaces of the core layer 11, differences in the thermal expansion coefficients may occur depending on the number of buildup insulating layers and buildup conductor layers and the ratio of the buildup conductor layers. Therefore, the difference in the thermal expansion coefficients between the third upper portion 43U and the third lower portion 43L may also be 7 ppm / °C or less.

[0041] To keep the difference in thermal expansion coefficients at 7 ppm / °C or less, it is necessary to take into consideration the material of the first member 51 and the material of the second member 52, the thickness of the first member 51 and the thickness of the second member 52, the elastic modulus of the first member 51 and the elastic modulus of the second member 52, or the position of the first member 51 and the position of the second member 52, etc.

[0042] 2 , both the first member 51 and the second member 52 are located in the mounting structure 10. However, both the first member 51 and the second member 52 do not necessarily have to be located; it is sufficient that at least one of the first member 51 and the second member 52 is located. For example, if the difference in thermal expansion coefficient between the first upper portion 41U and the first lower portion 41L is relatively small, the first member 51 does not have to be located. If the difference in thermal expansion coefficient between the second upper portion 42U and the second lower portion 42L is relatively small, the second member 52 does not have to be located.

[0043] The contact area between the first member 51 and the third portion 43 is a portion where the thermal expansion coefficient is likely to change due to the difference in the thermal expansion coefficients between the first member 51 and the third portion 43. The contact area between the second member 52 and the third portion 43 is also a portion where the thermal expansion coefficient is likely to change. Therefore, at least one of the first member 51 and the second member 52 may have a structure as shown in Figures 5A to 5C. Figures 5A to 5C are enlarged explanatory views for explaining modified examples of region X shown in Figure 2.

[0044] 5A , at least one of the first member 51 and the second member 52 may be coated with a resin (coating resin 5a) having a lower elastic modulus than the insulating layer included in the wiring substrate 1. With this configuration, even if the thermal expansion coefficient changes significantly at the contact portion between the first member 51 and the third portion 43, the coating resin 5a absorbs the rate of change. As a result, cracks are less likely to occur at the contact portion between the first member 51 and the third portion 43.

[0045] 5B , at least one of the first member 51 and the second member 52 may have at least one through-hole 5b penetrating from the top surface to the bottom surface, and a conductor may be located in the through-hole 5b. With this configuration, even if the thermal expansion coefficient changes significantly at the contact points between the first member 51 and the second member 52 and the third portion 43, the conductor located in the through-hole 5b absorbs the rate of change. As a result, cracks are less likely to occur at the contact points between the first member 51 and the second member 52 and the third portion 43.

[0046] 5C , in at least one of the first member 51 and the second member 52, the thickness of the end 5 c may be gradually reduced, and the end 5 c may be located in the third portion 43. With this configuration, the thermal expansion coefficient at the contact portion between the first member 51 and the second member 52 and the third portion 43 changes gradually, and it is possible to reduce the occurrence of cracks at the contact portion.

[0047] The method for arranging the first member 51 and the second member 52 in the mounting structure 10 is not limited. For example, they may be arranged in the following manner. First, the core layer 11 and the buildup layers 12 are laminated on both sides of the core layer 11 to obtain a laminate. The core layer 11 and the buildup layers 12 are as described above, and a detailed description thereof will be omitted.

[0048] Next, a cavity is formed in the obtained laminate in a portion where the first member 51 and the second member 52 will be disposed. Taking the first imaginary line L1 and the second imaginary line L2 into consideration, the cavity is formed so that the first member 51 is positioned in the first lower portion 41L and the second member 52 is positioned in the second lower portion 42L.

[0049] Next, the first member 51 and the second member 52 are inserted into the formed cavity. In a plan view, for example, the first member 51 is arranged so as to overlap the electronic component 2 to be mounted, and the second member 52 is arranged so as to overlap the stiffener 3 to be adhered. After the first member 51 and the second member 52 are inserted into the cavity, they are sealed with resin, and solder resist 6 is formed on both sides of the laminate. By this procedure, the wiring board 1 in which the first member 51 and the second member 52 are located is obtained.

[0050] Next, the electronic component 2 is mounted in the mounting area of ​​the wiring board 1, and the stiffener 3 is adhered to the wiring board 1 so as to surround the electronic component 2. By this procedure, the mounting structure 10 is obtained.

[0051] Next, a stress simulation was performed on the mounting structure 10 according to one embodiment. First, E-705G(X) (manufactured by Resonac Co., Ltd., thickness 1440 μm) was used as the core insulating layer, and copper (thickness 21 μm) was laminated as the core conductor layer on both sides of the core insulating layer to obtain a core layer 11. ABF GL-102F (manufactured by Ajinomoto Fine-Techno Co., Ltd., thickness 30 μm) as the buildup insulating layer and copper (thickness 15 μm) as the buildup conductor layer were alternately laminated on both sides of the obtained core layer 11 to form a buildup layer 12. The buildup layer 12 had a structure in which six layers of buildup insulating layers and six layers of buildup conductor layers were alternately laminated. Next, a solder resist 6 was formed on the surface of the buildup layer 12 to obtain a wiring board 1. SR7400GRA (manufactured by Resonac Co., Ltd., thickness 15 μm) was used as the solder resist 6.

[0052] When forming the buildup layer 12, a second member 52 made of duralumin was inserted into the portion overlapping with the placement location of the stiffener 3. The second member 52 made of duralumin had a thickness of 135 μm, and was inserted into a cavity formed in the buildup layer 12 located on the lower surface of the core layer 11. The second member 52 made of duralumin was positioned so that its surface was located approximately 40 μm from the second surface 1 b of the wiring board 1.

[0053] An electronic component 2 was mounted via solder 7 in the mounting area of ​​the obtained wiring board 1. Next, a stiffener 3 made of copper was adhered to the first surface 1 a of the wiring board 1 so as to surround the electronic component 2. Through this procedure, a mounting structure 10 (sample 1) according to one embodiment was obtained.

[0054] As a result of stress simulation for Sample 1, the increased stress was 303.8 MPa. For a mounting structure (Comparative Sample 1) obtained using the same procedure as Sample 1 except that the second member 52 made of duralumin was not used, the increased stress was 319.0 MPa. The stress generated in Sample 1 was approximately 95.2% of the stress generated in Comparative Sample 1.

[0055] In Sample 1, the second upper portion 42U of the second portion 42 had a thermal expansion coefficient of approximately 19.5 ppm / ° C., and the second lower portion 42L of the second portion 42 had a thermal expansion coefficient of approximately 13.32 ppm / ° C. The difference in thermal expansion coefficient between the second upper portion 42U and the second lower portion 42L was 6.18 ppm / ° C., which was less than 7 ppm / ° C.

[0056] Next, when forming the buildup layer 12, a first member 51 made of silicon was inserted into the portion overlapping with the mounting area of ​​the electronic component 2. The first member 51 made of silicon had a thickness of 45 μm, and was inserted into a cavity formed in the buildup layer 12 located on the lower surface of the core layer 11. The first member 51 made of silicon was positioned so that its surface was located approximately 40 μm from the second surface 1 b of the wiring substrate 1.

[0057] Using the same procedure as for sample 1, electronic component 2 was mounted, and stiffener 3 made of copper was adhered to first surface 1a of wiring board 1. Using this procedure, mounting structure 10 (sample 2) was obtained.

[0058] As a result of stress simulation for Sample 2, the increased stress was 243.8 MPa. The increased stress for Sample 2 was about 76.4% of the increased stress for Comparative Sample 1.

[0059] In Sample 2, the first upper portion 41U of the first portion 41 had a thermal expansion coefficient of approximately 3.71 ppm / ° C., and the first lower portion 41L of the first portion 41 had a thermal expansion coefficient of approximately 10.06 ppm / ° C. The difference in thermal expansion coefficient between the first upper portion 41U and the first lower portion 41L was 6.35 ppm / ° C., which was less than 7 ppm / ° C.

[0060] Next, a mounting structure 10 (sample 3) was obtained using the same procedure as sample 2, except that a first member 51 made of ceramic was used instead of the first member 51 made of silicon. As a result of performing a stress simulation on sample 3, the increased stress was 267.7 MPa. The increased stress in sample 3 was approximately 83.9% of the increased stress in comparative sample 1.

[0061] In Sample 3, the first upper portion 41U of the first portion 41 had a thermal expansion coefficient of approximately 3.71 ppm / °C, and the first lower portion 41L of the first portion 41 had a thermal expansion coefficient of approximately 10.15 ppm / °C. The difference in thermal expansion coefficient between the first upper portion 41U and the first lower portion 41L was 6.44 ppm / °C, which was less than 7 ppm / °C.

[0062] Next, a mounting structure 10 (sample 4) was obtained using the same procedure as sample 2, except that a first member 51 made of 42 alloy was used instead of the first member 51 made of silicon. As a result of performing a stress simulation on sample 4, the increased stress was 253.2 MPa. The increased stress in sample 4 was approximately 79.4% of the increased stress in comparative sample 1.

[0063] In Sample 4, the first upper portion 41U of the first portion 41 had a thermal expansion coefficient of approximately 3.71 ppm / °C, and the first lower portion 41L of the first portion 41 had a thermal expansion coefficient of approximately 10.20 ppm / °C. The difference in thermal expansion coefficient between the first upper portion 41U and the first lower portion 41L was 6.49 ppm / °C, which was less than 7 ppm / °C.

[0064] Next, when forming the buildup layer 12, a first member 51 made of silicon was inserted in a portion overlapping the mounting area of ​​the electronic component 2, and a second member 52 made of duralumin was inserted in a portion overlapping the placement location of the stiffener 3. The first member 51 made of silicon had a thickness of 45 μm, and was inserted into a cavity formed in the buildup layer 12 located on the lower surface of the core layer 11. The first member 51 made of silicon was positioned so that its surface was located approximately 40 μm from the second surface 1 b of the wiring board 1. The second member 52 made of duralumin had a thickness of 135 μm, and was inserted into a cavity formed in the buildup layer 12 located on the lower surface of the core layer 11. The second member 52 made of duralumin was positioned so that its surface was located approximately 40 μm from the second surface 1 b of the wiring board 1.

[0065] Using the same procedure as for Sample 1, an electronic component 2 was mounted, and a stiffener 3 made of copper was bonded to the first surface 1a of the wiring board 1. Using this procedure, a mounting structure 10 (Sample 5) was obtained. A stress simulation was performed on Sample 5, and the result was that the increased stress was 221.4 MPa. The increased stress in Sample 5 was approximately 69.4% of the increased stress in Comparative Sample 1.

[0066] The embodiments of the present disclosure have been described above. However, the invention according to the present disclosure is not limited to the above-described embodiments, and various modifications and improvements are possible within the scope of the present disclosure as shown in (1) to (9) below.

[0067] (1) A mounting structure according to the present disclosure includes a wiring board having a first surface and a second surface opposite the first surface, an electronic component located on the first surface, and a stiffener located on the first surface so as to surround the electronic component. The wiring board includes a base having an insulating layer and a conductor layer. When the electronic component and a portion of the wiring board extending from the first surface on which the electronic component is located to the second surface are defined as a first portion, the stiffener and a portion of the wiring board extending from the first surface on which the stiffener is located to the second surface are defined as a second portion, and a portion of the wiring board between the first and second portions is defined as a third portion, the side including the second surface, separated by a first imaginary line that halves the thickness of the first portion, is defined as a first lower portion, and the side opposite the first lower portion is defined as a first upper portion, the side including the second surface, separated by a second imaginary line that halves the thickness of the second portion, is defined as a second lower portion, and the side opposite the second lower portion is defined as a second upper portion, and the side including the second surface, separated by a third imaginary line that halves the thickness of the third portion, is defined as a third lower portion, and the side opposite the third lower portion is defined as the third upper portion, at least one of a first member having a first thermal expansion coefficient smaller than the thermal expansion coefficient of the base is located in the first lower portion, and a second member having a second thermal expansion coefficient greater than the thermal expansion coefficient of the base is located in the second lower portion. (2) In the mounting structure described in (1) above, the difference in thermal expansion coefficient between the first upper and first lower portions, the difference in thermal expansion coefficient between the second upper and second lower portions, and the difference in thermal expansion coefficient between the third upper and third lower portions are all 7 ppm / °C or less. (3) In the mounting structure described in (1) or (2) above, when the first lower portion is viewed in cross section, the first member is located closer to the second surface than a fourth imaginary line that bisects the thickness from the first imaginary line to the second surface, and when the second lower portion is viewed in cross section, the second member is located closer to the second surface than a fifth imaginary line that bisects the thickness from the second imaginary line to the second surface. (4) In the mounting structure described in (3) above, when the wiring board is viewed in cross section, at least one of the first member and the second member is located in the center of the wiring board. (5) In the mounting structure described in any of (1) to (4) above, at least one of the first member and the second member has a thickness of 30 μm or more. (6) In the mounting structure described in any one of (1) to (5) above, at least one of the first member and the second member has an elastic modulus of 70 GPa or more.(7) In the mounting structure described in any one of (1) to (6) above, at least one of the first member and the second member is coated with a resin having a lower elastic modulus than an insulating layer included in the wiring board. (8) In the mounting structure described in any one of (1) to (7) above, at least one of the first member and the second member has at least one through-hole that penetrates from the top surface to the bottom surface, and a conductor is located in the through-hole. (9) In the mounting structure described in any one of (1) to (8) above, at least one of the first member and the second member has an end portion whose thickness gradually decreases, and the end portion is located in a third portion.

[0068] REFERENCE SIGNS LIST 1 wiring board 11 core layer 12 build-up layer 1a first surface 1b second surface 2 electronic component 3 stiffener 41 first portion 41U first upper portion 41L first lower portion 42 second portion 42U second upper portion 42L second lower portion 43 third portion 43U third upper portion 43L third lower portion 51 first member 52 second member 5a coating resin 5b through hole 5c end portion 6 solder resist 7 solder 10 mounting structure L1 first virtual line L2 second virtual line L3 third virtual line L4 fourth virtual line L5 fifth virtual line

Claims

1. A mounting structure comprising: a wiring board having a first surface and a second surface located on the side opposite to the first surface; an electronic component located on the first surface; and a stiffener located on the first surface so as to surround the electronic component, wherein the wiring board includes a substrate having an insulating layer and a conductor layer, taking the electronic component and a part of the wiring board extending from the first surface on which the electronic component is located to the second surface as a first part, taking the stiffener and a part of the wiring board extending from the first surface on which the stiffener is located to the second surface as a second part, taking a part of the wiring board between the first part and the second part as a third part, with a first virtual line that bisects the thickness of the first part as a boundary, the side including the second surface being a first lower part and the side opposite to the first lower part being a first upper part, with a second virtual line that bisects the thickness of the second part as a boundary, the side including the second surface being a second lower part and the side opposite to the second lower part being a second upper part, and with a third virtual line that bisects the thickness of the third part as a boundary, the side including the second surface being a third lower part and the side opposite to the third lower part being a third upper part, wherein at least one of a first member having a first coefficient of thermal expansion smaller than that of the substrate and a second member having a second coefficient of thermal expansion larger than that of the substrate is located in the first lower part.

2. The mounting structure according to claim 1, wherein the differences in the coefficients of thermal expansion between the first upper part and the first lower part, between the second upper part and the second lower part, and between the third upper part and the third lower part are all 7 ppm / °C or less.

3. The mounting structure according to claim 1 or 2, wherein when the first lower part is viewed in cross section, the first member is located closer to the second surface side than a fourth virtual line that bisects the thickness from the first virtual line to the second surface, and when the second lower part is viewed in cross section, the second member is located closer to the second surface side than a fifth virtual line that bisects the thickness from the second virtual line to the second surface.

4. The mounting structure according to claim 3, wherein when the wiring board is viewed in cross section, at least one of the first member and the second member is located in the central part of the wiring board.

5. The mounting structure according to any one of claims 1 to 4, wherein at least one of the first member and the second member has a thickness of 30 μm or more.

6. The mounting structure according to any one of claims 1 to 5, wherein at least one of the first member and the second member has an elastic modulus of 70 GPa or more.

7. The mounting structure according to any one of claims 1 to 6, wherein at least one of the first member and the second member is coated with a resin having an elastic modulus lower than that of the insulating layer included in the wiring substrate.

8. The mounting structure according to any one of claims 1 to 7, wherein at least one of the first member and the second member has at least one through hole penetrating from the upper surface to the lower surface, and a conductor is located in the through hole.

9. The mounting structure according to any one of claims 1 to 8, wherein in at least one of the first member and the second member, the thickness of the end portion gradually decreases, and the end portion is located in the third portion.

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