Wiring boards, electronic devices, and electronic modules

Abstract

This wiring board comprises: an insulated substrate having a first surface, a second surface on the reverse side from the first surface, and a through-hole extending from the first surface to the second surface; a through-conductor located inside the through-hole and on the opening of the through-hole on the first surface side; and a wiring conductor that is located on the first surface and that is connected to the through-conductor. The through-conductor and the wiring conductor contain copper as a main constituent, and the mean size of the Cu crystal grains in the through-conductor is larger than the mean size of the Cu crystal grains in the wiring conductor.

Description

【Technical Field】 【0001】 The present disclosure relates to a wiring board, an electronic device, and an electronic module. 【Background Art】 【0002】 There is a phenomenon called electromigration in which the conductor of a wiring board is damaged due to the movement of conductor atoms accompanying energization. International Publication No. 2008 / 084867 discloses a semiconductor device with improved electromigration resistance by forming the wiring of a wiring board from a seed layer, a noble metal liner layer, and a copper wiring film. 【Summary of the Invention】 【Means for Solving the Problems】 【0003】 The wiring board in the present disclosure has a first surface, a second surface opposite to the first surface, and a through hole extending from the first surface to the second surface. Ceramic An insulating substrate, a through conductor located in the through hole and on the opening of the through hole on the first surface side, and a wiring conductor located on the first surface and connected to the through conductor, the through conductor and the wiring conductor contain copper as a main component, and the average size of Cu crystal grains in the through conductor is larger than the average size of Cu crystal grains in the wiring conductor. The wiring conductor includes a first main body portion mainly composed of Cu, and a first intermediate layer located between the first main body portion and the first surface, the first intermediate layer containing Ti oxide. . 【0004】 The electronic device according to the present disclosure the above wiring board, electronic components mounted on the wiring board, and. 【0005】 The electronic module according to the present disclosure the above electronic device, a module substrate on which the electronic device is mounted, and. 【Brief Description of the Drawings】 【0006】 [Figure 1] It is a perspective view showing a wiring board according to an embodiment of the present disclosure. [Figure 2] This is a cross-sectional view showing the main part of the wiring board in Figure 1. [Figure 3] This diagram illustrates a method for measuring the size of Cu crystal grains. [Figure 4A] This is a cross-sectional view showing the main part of the wiring board. [Figure 4B] This is a plan view showing the main parts of the wiring board. [Figure 5] This is an explanatory diagram showing an example of a method for manufacturing a wiring board according to the embodiment. [Figure 6] This figure shows an electronic device and an electronic module according to an embodiment of the present disclosure. [Modes for carrying out the invention] 【0007】 Embodiments of this disclosure will be described in detail below with reference to the drawings. Figure 1 is a perspective view showing a wiring board according to an embodiment of this disclosure. Figure 2 is a cross-sectional view showing the main part of the wiring board of Figure 1. Figure 2 shows a cross-section of the portion of the wiring board 1 where the through conductor 25 is located. 【0008】 The wiring board 1 of this embodiment comprises an insulating substrate 10 having a first surface 11, a second surface 12 opposite to the first surface 11, and a through hole 13 extending from the first surface 11 to the second surface 12; a wiring conductor 21 located on the first surface 11; a through conductor 25 located on the through hole 13 and the opening 13a of the through hole 13; and a wiring conductor 23 located on the second surface 12. The through conductor 25 is also located on the opening 13b on the second surface 12 side (opposite to the through hole 13). The through conductor 25 is connected to the wiring conductors 21 and 23. 【0009】 The insulating substrate 10 may be made of a ceramic mainly composed of aluminum nitride, silicon nitride, silicon carbide, alumina, zirconia, etc. 【0010】 The through-hole 13 has an opening 13a on the first surface 11 side and an opening 13b on the second surface 12 side, as shown by the dashed line in Figure 2. The through-hole 13 and the openings 13a and 13b are not open spaces because the through-conductor 25 is located within them. The inner diameters of the openings 13a and 13b are larger than the inner diameter of the intermediate portion 13i of the through-hole 13. The intermediate portion 13i refers to the planar portion within the through-hole 13 parallel to the first surface 11, between the openings 13a and 13b. The inner diameter of the through-hole 13 may gradually increase from the intermediate portion 13i to the opening 13a on the first surface 11 side. Similarly, the inner diameter of the through-hole 13 may gradually increase from the intermediate portion 13i to the opening 13b on the second surface 12 side. This configuration makes it easy to control the Cu crystal grain t1 of the through-conductor 25 that fills the through-hole 13 during the manufacturing stage of the wiring board 1. 【0011】 Furthermore, the through-hole 13 does not need to have a circular cross-sectional shape (a cross-sectional shape parallel to the first surface 11). If it is not circular, the "inner diameter" mentioned above should be read as "maximum width". 【0012】 The wiring conductor 21 includes a main body portion 211 mainly composed of Cu (copper) and an intermediate layer 212 located between the main body portion 211 and the first surface 11. The through conductor 25 includes a main body portion 251 mainly composed of Cu and an intermediate layer 252 located between the main body portion 251 and the inner circumferential surface of the through hole 13. The wiring conductor 23 includes a main body portion 231 mainly composed of Cu and an intermediate layer 232 located between the main body portion 231 and the second surface 12. The intermediate layers 212, 232, and 252 contain Cu, Ti (titanium), and O (oxygen). Note that the main component means a component that is present in 80% by mass or more. 【0013】 The leading portions 211 and 231 of the wiring conductors 21 and 23, and the leading portion 251 of the through conductor 25, are polycrystalline metal composed of multiple Cu crystal grains t1. Figures 2, 3, 4A, and 4B schematically depict the Cu crystal grains t1. Actual Cu crystal grains t1 have various shapes, such as granular and columnar, and vary in size. 【0014】 The intermediate layers 212 and 232 of the wiring conductors 21 and 23, and the intermediate layer 252 of the through-conductor 25 are polycrystalline metals in which a plurality of Cu crystal grains and a plurality of titanium oxide crystal grains are aggregated. 【0015】 <Size of Cu crystal grains> Next, the sizes of the Cu crystal grains t1 of the wiring conductors 21 and 23, the Cu crystal grains t1 of the through-conductor 25, and the Cu crystal grains of the intermediate layers 212, 232, and 252 will be described. Hereinafter, when simply referring to the Cu crystal grains t1 of the wiring conductors 21 and 23 and the Cu crystal grains t1 of the through-conductor 25, it shall mean the Cu crystal grains t1 of the main conductor portions 211, 231, and 251. Also, the size of the Cu crystal grains shall be the size represented in units of length. 【0016】 The wiring conductors 21 and the through-conductor 25 are distinguished by the different average sizes of the Cu crystal grains t1, and the average size of the Cu crystal grains t1 of the through-conductor 25 is larger than the average size of the Cu crystal grains t1 of the wiring conductor 21. The difference in the average size of the Cu crystal grains t1 is a difference at a level exceeding the error. The difference at a level exceeding the error may mean a difference of 1.5 times or more, or 2 times or more of the standard deviation σ of the size of the Cu crystal grains t1 measured at an arbitrary portion. 【0017】 Electromigration is likely to occur around the opening 13a of the through-hole 13 where the direction of the current changes and the current concentrates when charges flow from the wiring conductor 21 to the through-conductor 25. However, since the average size of the Cu crystal grains t1 of the through-conductor 25 is larger than the average size of the Cu crystal grains t1 of the wiring conductor 21, it becomes difficult for the Cu crystal grains t1 to move in the through-conductor 25, and the electromigration resistance around the opening 13a of the through-hole ɼ can be improved. 【0018】 Furthermore, the difference between the average size of the Cu crystal grains t1 of the through-conductor 25 and the average size of the Cu crystal grains t1 of the wiring conductor 21 is 3 μm or less. With this configuration, the difference in the size of the Cu crystal grains t1 at the boundary between the wiring conductor 21 and the through-conductor 25 becomes small, and the electromigration resistance can also be improved at this boundary. 【0019】 Although the above has been described for the first side 11, the same may apply to the second side 12. That is, the average size of the Cu crystal grains t1 of the through-conductor 25 may be larger than the average size of the Cu crystal grains t1 of the wiring conductor 23 on the second side 12. The difference in the average size is a difference at a level exceeding the error and may be 3 μm or less. With this configuration, even on the second side 12, the resistance to electromigration, which is likely to occur around the opening 13b when charge flows from the wiring conductor 23 to the through-conductor 25, can be improved. 【0020】 Since the Cu crystal grains t1 have various shapes such as granular and columnar, the average size of each Cu crystal grain t1 is obtained by the following steps 1 to 3. FIG. 3 is a diagram for explaining a method of measuring the size of Cu crystal grains. In FIG. 3, the Cu crystal grains t1 are simplified, and the number of Cu crystal grains t1 in the target region Rt is different from the actual number. 1. In the SEM (Scanning Electron Microscope) image or SIM (Scanning Ion Microscope) image of the cross-section including the through-conductor 25 and the wiring conductor 21, extract the boundary (grain boundary) lines of each Cu crystal grain t1. 2. Arbitrarily select a region having a size that includes 20 to 100 Cu crystal grains t1 from the above image as the target region Rt. The target region Rt is selected from a plurality of locations in the main part of the conductor to be measured (if it is the through-conductor 25, it is the main conductor part 251; if it is the wiring conductors 21 and 23, it is the main conductor parts 211 and 231). 3. Count the number of Cu crystal grains t1 in each target region Rt, and calculate the average cross-sectional area of one Cu crystal grain t1 by dividing the area of each target region Rt by the above number. Further, assuming that the cross-sectional shape of each Cu crystal grain t1 is a circle, calculate the diameter of the circle from the above area, and obtain the diameter as the average size of the Cu crystal grain t1. 【0021】 <Example> When the average size of the Cu crystal grains t1 was measured for the through-conductor 25 and the wiring conductor 21 of the wiring substrate 1 of one embodiment of the present disclosure, the result of measurement result 1 was obtained. [Table 1] These results indicate that the average size of the Cu crystal grains t1 in the through conductor 25 is larger than the average size of the Cu crystal grains t1 in the wiring conductor 21, and the difference between the two is 3 μm or less. 【0022】 <Boundary between wiring conductor and through conductor> Figures 4A and 4B illustrate the boundary between the wiring conductor and the through conductor. Figure 4A is a cross-sectional view of the main part of the wiring board, and Figure 4B is a plan view of the same main part. The cross-section in Figure 4A is a cross-section that passes through the through hole 13 and is perpendicular to the first surface 11. 【0023】 By setting multiple target regions Rt around the opening 13a of the through hole 13, measuring the average size of the Cu crystal grains t1 for each target region Rt, and extracting boundary lines (shown as dashed lines in Figure 4A) where the average size changes in steps, these boundary lines can be identified as the boundary E1 between the through conductor 25 and the wiring conductor 21. 【0024】 The boundary E1 may be located outside the through-hole 13 (i.e., outside the opening 13a of the through-hole 13) in the cross-section of Figure 4A. The entire boundary E1 may be located outside the through-hole 13. Electromigration is likely to occur around the opening 13a of the through-hole 13 where the direction of the current changes and the current concentrates when charge flows from the wiring conductor 21 to the through-conductor 25. However, with the above configuration of boundary E1, the Cu crystal grains t1 of the through-conductor 25 occupy both the inside and outside of the opening 13a, thus reducing the difference in the size of the Cu crystal grains t1 inside and outside the opening 13a. Therefore, the resistance to electromigration around the opening 13a of the through-hole 13 can be improved. 【0025】 The boundary E1 exhibits a similar tendency regardless of the orientation of the cross-section (the orientation of the rotational direction around the central axis of the through-hole 13). Therefore, when the wiring board 1 is viewed from a direction perpendicular to the first surface 11, as shown in Figure 4B, the boundary E1 has a portion that overlaps with the opening 13a of the through-hole 13 of the insulating substrate 10. In the area having the above overlap, the difference in the size of the Cu crystal grains t1 between the inside and outside of the opening 13a becomes smaller. Therefore, this configuration can improve the resistance to electromigration around the opening 13a of the through-hole 13. The boundary E1 may overlap with the opening 13a over the entire circumferential area of ​​the opening 13a of the through-hole 13. This configuration can improve the resistance to electromigration over the entire circumferential area of ​​the opening 13a of the through-hole 13. 【0026】 Furthermore, in the cross-section of Figure 4A, boundary E1 includes a first boundary line E1a on the left and a second boundary line E1b on the right, and the distance between the first boundary line E1a and the second boundary line E1b may become narrower as it moves away from the through-hole 13 (opening 13a). Also, the width of the through-conductor 25 may become narrower as it moves away from the through-hole 13 (opening 13a). With this configuration, the difference in the size of Cu crystal grains t1 can be reduced at locations where the direction of current changes and current concentrates when charge flows from the wiring conductor 21 to the through-conductor 25. Therefore, the resistance to electromigration at such locations can be improved. Furthermore, in the above cross-section, the angle between each part of boundary E1 and the line segment indicating the opening 13a may become smaller as it approaches the edge of the opening 13a. With this configuration, the difference in the size of Cu crystal grains t1 can be reduced at locations where the direction of charge changes and charge flow concentrates. Therefore, the resistance to electromigration at such locations can be improved. 【0027】 The above description concerns the first surface 11 side, but the same may apply to the second surface 12 side. That is, the boundary E1 between the wiring conductor 23 and the through conductor 25 may be the same as the relationship between the boundary E1 and the opening 13a on the first surface 11 side in relation to the opening 13b on the second surface 12 side. With this configuration, when charge flows from the wiring conductor 23 to the through conductor 25, the difference in the size of the Cu crystal grains t1 can be reduced at the point where the direction of the charge changes and the charge flow concentrates. Therefore, the resistance to electromigration at that point can be improved. 【0028】 <Middle class> As mentioned earlier, the intermediate layers 212, 232, and 252 contain at least Cu, Ti, and O, and are polycrystalline metals composed of multiple Cu crystal grains and multiple titanium oxide crystal grains. Comparing the intermediate layer 252 of the through conductor 25 with the main body portion 251 of the through conductor 25, the average size of the Cu crystal grains is larger in the main body portion 251. Comparing the intermediate layers 212 and 232 of the wiring conductors 21 and 23 with the main body portions 211 and 231 of the wiring conductors 21 and 23, the average size of the Cu crystal grains is larger in the main body portions 211 and 231. 【0029】 The intermediate layers 212 and 232 of the wiring conductors 21 and 23, and the intermediate layer 252 of the through conductor 25, may have approximately the same composition and average size of the Cu crystal grains. 【0030】 The presence of intermediate layers 212, 232, and 252 mitigates thermal stress concentration even when thermal stress occurs between the insulating substrate 10 and the wiring conductors 21 and 23, and between the insulating substrate 10 and the through-conductor 25, thereby improving the TCT (temperature cycle test) resistance of the wiring substrate 1. 【0031】 <Manufacturing method> Figure 5 illustrates an example of a method for manufacturing a wiring board according to an embodiment. 【0032】 The manufacturing method of this embodiment includes, in chronological order, a substrate molding step J1 of the insulating substrate 10, a Ti film coating step J2, a firing step J3, a Cu plating and sintering step J4, an electrolytic plating step J5, and a resist stripping step J6. 【0033】 In the substrate forming process J1, the ceramic green sheet, which is a ceramic material before sintering, is formed into a substrate shape by punching or die processing, etc., to form a substrate 70 before firing. The substrate 70 is provided with through holes 73 and side grooves 74 that extend from the first surface 71 to the second surface 72 opposite the first surface 71. The through holes 73 are formed such that the diameter at the intermediate depth (height between the first surface 71 and the second surface 72) is smaller than the diameter of the opening on the first surface 71 and the diameter of the opening on the second surface 72. Subsequently, the substrate 70 is fired, and the substrate 70 becomes an insulating substrate 10 made of ceramic, and the through holes 73 and side grooves 74 of the substrate 70 before firing become through holes 13 and side grooves 14, maintaining the same shape. Alternatively, the through holes 13 and side grooves 14 may be formed after firing the ceramic green sheet by methods such as laser or blasting. 【0034】 In the Ti film coating process J2, organic Ti liquid 81 is applied to the fired insulating substrate 10. The organic Ti liquid 81 is also applied to the inner wall surfaces of the through holes 73 and the side grooves 74. The organic Ti liquid 81 may be applied to the first surface 71, the second surface 72, the inner wall surface of the through holes 73, and the inner wall surface of the side grooves 74 with the same thickness. 【0035】 In the firing process J3, the organic Ti liquid 81 applied to the insulating substrate 10 is fired, causing the applied organic Ti liquid 81 to become a Ti oxide film 83. 【0036】 In the Cu plating and sintering process J4, first, electroless Cu plating is applied to the Ti oxide film 83 on the surface of the insulating substrate 10, and then a sintering process is performed to diffuse elements at the interface between the Ti oxide film 83 and the Cu plating film. Through the sintering process, Cu is diffused into the Ti oxide film 83, and a seed layer 85 is formed. The seed layer 85 corresponds to the intermediate layers 212, 232, and 252 in the wiring board 1 after the manufacturing process. 【0037】 In the electroplating process J5, a resist pattern 91 is formed excluding the areas of the wiring conductors 21 and 23 and the through-conductor 25, and electroplated Cu is applied to the seed layer 85 that is not covered by the resist pattern 91. Electroplating forms Cu deposited conductors 88 on the seed layer 85, filling the through-holes 13 and side grooves 14 with the Cu deposited conductors 88. The Cu deposited conductors 88 correspond to the leading body portions 211 and 231 of the wiring conductors 21 and 23, and the leading body portion 251 of the through-conductor 25. For electroplating, a plating solution containing copper sulfate for through-holes and via filling (e.g., VF-II manufactured by JCU Corporation) can be used. The substrate is placed in a conductive rack, degreased and acid-treated, and then immersed in the plating solution at 0.5~3.0 A / dm 2 By applying a current of a certain magnitude, a Cu deposited conductor 88 is formed. 【0038】 In the resist stripping step J6, the resist pattern 91 is removed and the seed layer 85 not covered by the Cu deposited conductor 88 is etched, thereby manufacturing the wiring substrate 1. With the above manufacturing method, a wiring substrate 1 can be manufactured in which the average size of the Cu crystal grains t1 differs between the wiring conductors 21, 23 and the through conductor 25, as described above. The wiring substrate 1 in Figure 5 has the configuration of Figure 1 with the addition of wiring conductors 21a, 21b and castellations 25a, 25b. 【0039】 <Electronic devices and electronic modules> Figure 6 is a cross-sectional view showing an electronic device and an electronic module according to an embodiment of the present disclosure. 【0040】 The electronic device 60 according to this embodiment is constructed by mounting electronic components 50 on a wiring board 1. The terminals of the electronic components 50 are connected to the wiring conductors 21, and these terminals may be electrically connected to the wiring conductors 23 on the second surface 12 side via the wiring conductors 21 and the through conductors 25. A Ni film may be provided on the surfaces of the wiring conductors 21 and 23. 【0041】 Various electronic components can be applied as electronic components 50, such as optical elements like LD (Laser Diode), PD (Photo Diode), and LED (Light Emitting Diode); image sensors like CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor); piezoelectric oscillators like quartz crystal oscillators; surface acoustic wave elements; semiconductor elements like semiconductor integrated circuit elements (IC); capacitance elements; inductor elements; or resistors. 【0042】 The electronic module 100 according to this embodiment is constructed by mounting an electronic device 60 on a module substrate 110. In addition to the electronic device 60, other electronic devices, electronic elements, and electrical elements may be mounted on the module substrate 110. Electrode pads 111 are provided on the module substrate 110, and the wiring conductors 23 of the electronic device 60 may be joined to the electrode pads 111 via a bonding material 113 such as solder. 【0043】 According to the electronic device 60 and electronic module 100 of this embodiment, the reliability of the electronic device 60 and electronic module 100 can be improved by providing a wiring board 1 with improved resistance to electromigration around the opening 13a. 【0044】 Embodiments of the present disclosure have been described above. However, the wiring boards, electronic devices, and electronic modules of the present disclosure are not limited to the above embodiments. For example, in the above embodiments, the wiring conductors are exposed on the outer surface of the wiring board, and the through-conductors are located between two wiring conductors exposed on the outer surface of the wiring board. However, the wiring conductors may be wiring layers located inside the substrate of a multilayer wiring board, and the through-conductors may be interlayer vias of the multilayer wiring board. Furthermore, the through-conductors may be conductors that constitute through-holes or conductors that constitute castellations. [Industrial applicability] 【0045】 This disclosure can be used in wiring boards, electronic devices, and electronic modules. [Explanation of symbols] 【0046】 1 Wiring board 10 Insulating substrate 11 Page 1 12 Side 2 13 Through hole 13a, 13b opening 13i middle section 21, 23 Wiring conductors 25 Through-conductor 211, 231, 251 Main body 212, 232, 252 Middle layer t1 Cu grain E1 boundary E1a 1st boundary E1b 2nd border 50 Electronic Components 60 Electronic equipment 100 Electronic Modules 110 Module Board

Claims

[Claim 1] A ceramic insulating substrate having a first surface, a second surface opposite to the first surface, and a through hole extending from the first surface to the second surface, A through conductor located inside the through hole and on the opening of the through hole on the first surface side, A wiring conductor located on the first surface and connected to the through conductor, Equipped with, The through conductor and the wiring conductor mainly contain copper, The average size of the Cu crystal grains in the through conductor is larger than the average size of the Cu crystal grains in the wiring conductor. The wiring conductor includes a first leading portion mainly composed of Cu and a first intermediate layer located between the first leading portion and the first surface. The first intermediate layer contains Ti oxide, Wiring board. [Claim 2] The through conductor includes a second leading body portion mainly composed of Cu, and a second intermediate layer located between the second leading body portion and the inner circumferential surface of the through hole. The wiring substrate according to claim 1, wherein the second intermediate layer contains Ti oxide. [Claim 3] The through hole has a first opening that opens to the first surface, a second opening that opens to the second surface, and an intermediate portion which is a flat portion within the through hole parallel to the first surface between the first opening and the second opening, The inner diameter of the first opening or the second opening is larger than the inner diameter of the intermediate portion. A wiring board according to any one of claims 1 to 2. [Claim 4] The difference between the average size of the Cu crystal grains in the through-conductor and the average size of the Cu crystal grains in the wiring conductor is 3 μm or less. A wiring board according to any one of claims 1 to 3. [Claim 5] The boundary between the through conductor and the wiring conductor is located outside the through hole. A wiring board according to any one of claims 1 to 4. [Claim 6] When viewed from a direction perpendicular to the first surface, the boundary between the through conductor and the wiring conductor includes the portion that overlaps with the through conductor. A wiring board according to any one of claims 1 to 5. [Claim 7] In a cross-section perpendicular to the first surface passing through the through-hole, the distance between the first boundary line indicating the left boundary between the through-conductor and the wiring conductor and the second boundary line indicating the right boundary between the through-conductor and the wiring conductor narrows as it moves away from the through-hole. A wiring board according to any one of claims 1 to 6. [Claim 8] In a cross-section perpendicular to the first surface passing through the through-hole, the angle between each part of the boundary line indicating the boundary between the through-conductor and the wiring conductor and the line segment on the cross-section indicating the opening of the through-hole is smaller as it approaches the edge of the opening. A wiring board according to any one of claims 1 to 7. [Claim 9] A ceramic insulating substrate having a first surface, a second surface opposite to the first surface, and a through hole extending from the first surface to the second surface, A through conductor located inside the through hole and on the opening of the through hole on the first surface side, A wiring conductor located on the first surface and connected to the through conductor, Equipped with, The through conductor and the wiring conductor mainly contain copper, The average size of the Cu crystal grains in the aforementioned wiring conductor is greater than the average size of the Cu crystal grains in the aforementioned through conductor. The through conductor includes a second leading body portion mainly composed of Cu, and a second intermediate layer located between the second leading body portion and the inner circumferential surface of the through hole. The second intermediate layer contains Ti oxide, Wiring board. [Claim 10] A wiring board according to any one of claims 1 to 9, The electronic components mounted on the aforementioned wiring board, An electronic device equipped with the following features. [Claim 11] The electronic device according to claim 10, A module substrate on which the aforementioned electronic device is mounted, An electronic module equipped with the following features.

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