Control board and manufacturing method thereof

Abstract

To suppress breakage due to crack propagation in the solder joints of a wiring board of a control board of a quantum computer that operates in a low-temperature environment.SOLUTION: A control board 1 connects a chip-type electronic component 10 having a plurality of electrodes 12, 13 formed thereon to a wiring board 2 having a wiring pattern and soldering pads 4, 5 formed on its surface, by solders 32, 33. and after soldering, the electrodes 12, 13 are covered with solder joints 32, 33 at the corners 12c, 13c on the wiring board and the entire lower surface of the electrodes 12, 13, and the corners 4a, 4b, 5a, 5b of the pads 4, 5 close to the electronic component and the entire upper surface of the electrodes 12, 13 are covered with the solder joints 32, 33.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a control board suitable for use in a quantum computer realized using a dilution refrigerator or the like, and relates to a quantum chip that operates at extremely low temperatures near absolute zero and a structure of an electrode portion for joining a quantum control chip to a wiring board, and a manufacturing method thereof by soldering. [Background technology]

[0002] Recent progress in quantum computer technology has been remarkable, and expectations for the realization of practical quantum computers are also rising in conjunction with this. Quantum computers use superconducting logic-based devices and typically operate in a state cooled to an extremely low temperature in order to function in a superconducting state. Patent Document 1 discloses a quantum computing device in which a quantum device die and a control circuit die for controlling the operation of the quantum device die are arranged on a substrate. The quantum device and the substrate are connected by solder bumps or the like. Patent Document 2 discloses an electronic component in which an end face electrode is provided on an end face of a substantially rectangular body 1 at 2 / 3 or less of the end face height, and the pad part of the printed circuit board is formed at a position less than twice the end face height h from the position of the end face electrode, thereby appropriately controlling the wetting and thickness of the solder and forming the solder fillet in an ideal shape. However, Reference 2 assumes operation at room temperature and does not assume use in an extremely low temperature environment. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2019-537239 [Patent Document 2] JP 2009-4490 A Summary of the Invention [Problem to be solved by the invention]

[0004] Quantum computers operate at extremely low temperatures near absolute zero. In wiring boards on which quantum chips, quantum control chips, and various electronic components are mounted, LSIs and various electronic components are mounted on the wiring boards using bonding materials. These components may be subject to brittle fracture at extremely low temperatures, and it is important to improve this. In quantum computers, solder is often used to bond the electrodes of the wiring board to the electronic components. When solder is used, the materials to be bonded and the solder each shrink at extremely low temperatures, and there is a risk of cracks occurring between the materials due to the difference in linear expansion coefficients of the respective components, resulting in failure. In addition, when electronic components and wiring boards are bonded using solder mainly composed of tin (Sn), there is a risk of allotropic transformation due to exposure to low temperatures, which may impair the reliability of the bond. Patent Document 1 mentions the reliability of the bond of electronic components at extremely low temperatures, but does not mention the bond structure between the electrodes and the solder material.

[0005] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to suppress low-temperature brittle fracture of components and interfacial cracking of solder joints in control boards equipped with quantum chips, quantum control chips, and other electronic components that operate at extremely low temperatures, and to improve the joint reliability of surface-mounted electronic components. Another object of the present invention is to provide an improved manufacturing method using soldering for improving the solder joint condition at extremely low temperatures of surface-mount electronic components that are connected to a circuit board by soldering. [Means for solving the problem]

[0006] Representative features of the invention disclosed in this application are as follows. According to one feature of the present invention, a control board that operates in a low-temperature environment of 77K or less absolute temperature includes a surface-mounted electronic component having an electrode formed on its bottom surface, a wiring board having a wiring pattern formed on its surface and a pad for connecting the electrode of the electronic component, and a solder joint mainly composed of tin (chemical symbol Sn) that is disposed on the pad and solders the pad to the electrode. The solder joint is formed so as to cover the entire outer corner of the electrode close to the wiring board and the surface adjacent to the outer corner, and to cover the entire corner of the pad close to the electronic component and the surface adjacent to the corner. The electronic component is, for example, a chip resistor or a chip capacitor. After soldering, the solder is formed so that the electrode is covered up to the upper outer corner farthest from the wiring board.

[0007] According to another feature of the present invention, the wiring board is manufactured such that, when mounting chip resistors and chip capacitors, the inner corners of the pads of the wiring board are offset so as to be positioned outward from the lower inner corners of the corresponding electrodes of the electronic component as viewed from the center of the electronic component, and the outer corners of the pads of the wiring board are offset so as to be positioned outward from the lower inner corners of the corresponding electrodes of the electronic component as viewed from the center of the electronic component. A first amount of outward offset of the inner corners of the pads is made smaller than a second amount of outward offset of the outer corners of the pads.

[0008] According to yet another feature of the present invention, the electronic component is a surface mount type component having a plurality of flat electrodes formed on its bottom surface, a plurality of flat pads corresponding to the electrodes are formed on the wiring board, and soldering is performed by heating and melting the entirety with solder sandwiched between each of the electrodes and the pads, so that the entirety of the surfaces adjacent to the lower corners of all the electrodes of the electronic components and the entirety of the surfaces adjacent to the upper corners of all the pads are covered with solder, and the electronic components are operated in a low-temperature environment of an absolute temperature of 77 K or less. The soldering is performed by, for example, BGA bonding or QFN bonding. Effect of the Invention

[0009] According to the present invention, in a control board for a quantum computer having an electrode structure covered with solder, the entire surfaces adjacent to the lower corners of all the electrodes of the electronic components and the entire surfaces adjacent to the upper corners of all the pads are covered with solder, so that interfacial cracks, which are a cause of low temperatures around the solder joints, can be effectively suppressed. Further configurations and effects of the invention will become apparent from the entire specification below. [Brief description of the drawings]

[0010] [Figure 1] 1 is a top view of a control board 1 according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view of the AA portion of FIG. [Diagram 3] 3 is a cross-sectional view showing a state immediately before the electronic component 10 in FIG. 2 is attached to the control board 1. FIG. [Figure 4] 13 is a partial cross-sectional view showing a soldered joint 37 according to a modified example of the present embodiment. FIG. [Diagram 5] 1 is a partial vertical cross-sectional view of a wiring board 2 according to a second embodiment of the present invention (corresponding to the portion BB in FIG. 1). [Figure 6] 1A and 1B are diagrams for explaining the state of a soldered component soldered to a wiring board 2 after it has been left in an extremely low temperature environment, where (A) shows the result obtained by a conventional soldering method and (B) shows the result obtained by a soldering method according to a second embodiment. [Figure 7] 7 is a cross-sectional photograph of the portion described in FIG. 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following drawings, the same parts are given the same reference numerals, and repeated explanations will be omitted. In addition, in this specification, the inside, outside, and up and down directions will be described as directions shown in the drawings.

[0012] FIG. 1 is a top view of a control board 1 according to an embodiment of the present invention. This control board 1 is mounted on a plate in a dilution refrigerator, which is one of the components of a quantum computer, and is mainly intended to operate at extremely low temperatures, for example, absolute temperatures of about 4K to 77K. When a dilution refrigerator is used, the temperatures of the cooling stage are often divided into 50K and 4K. In addition, in a cooling method using liquid nitrogen, since the boiling point of liquid nitrogen is 78K, the main operating range of the control board of the present invention is a temperature range of 77K or less. However, the temperature range of 77K or less is merely an example, and does not exclude the implementation of the present invention at a temperature range higher than that range.

[0013] The control board 1 is a wiring board 2 on which a quantum bit control circuit (RFGEN BVG) and the like are mounted, and is mounted, for example, on a 4K plate of a dilution refrigerator (not shown). Therefore, the environment in which the control board 1 operates is an extremely low temperature of about 4K to several tens of K. The control board 1 is configured by mounting a control LSI 9 using a silicon chip, electronic components 20 such as chip resistors and electronic components 10 such as chip capacitors, connector components 7, package components 8, and the like on the wiring board 2. The control board 1 shown in FIG. 1 is, for example, a small daughter board of about 5×6 cm, and quantum chips bonded using silver paste and the quantum bit control circuit and the like are mounted on a mother board (not shown). However, the control board 2 of the present invention is applicable regardless of size.

[0014] In the structure for joining electronic components to the wiring board 2, the surface mount components are fixed to the pads of the wiring board 2, which are the connection points, by printing solder paste on the wiring board 2 and heating and melting it. For components such as the connector component 7, which are mounted by inserting the terminals of the connector into the through holes (not shown in the figure), solder paste is printed in the through holes of the wiring board 2, and then the terminals are inserted and joined by heating and melting. In addition, after inserting multiple terminals of the connector component 9 into multiple through holes of the wiring board 2, they can be joined to the board electrodes by flow soldering or spot soldering. The composition of these solder materials is generally Sn-3.0Ag-0.5Cu, but Bi, Sb, Ni, etc. may be contained to improve reliability. In this specification, the solder before heating and melting is referred to as the "solder material", and the solder after cooling with a specified shape is simply referred to as the "solder" or "solder joint", but since it is the same material, it may also be simply referred to as "solder" regardless of whether it is before or after heating.

[0015] Many electronic components are connected to the wiring board 2 via solder as surface-mounted components or insert components, and after soldering, an intermetallic compound is formed at the interface between the pads and solder on the control board 1 and between the electrodes and solder. At extremely low temperatures, due to differences in the linear expansion coefficients of the various components such as the solder and electrodes, deformation occurs when subjected to temperature load, and cracks may grow at the interface between the intermetallic compound and the electrodes, which may result in a shortened lifespan of the control board 1. Also, unlike at room temperature, at extremely low temperatures, there is an increased risk of fracture due to cleavage caused by cracks growing within the solder, compromising the reliability of the control board 1.

[0016] FIG. 2 is a partial cross-sectional view of the control board 1, that is, a cross-sectional view of the AA portion of FIG. 1, showing a cross-section after the electronic component 10 is soldered to the wiring board 2. The electronic component 10 is a capacitor housed in a main body 11 made of ceramic or the like, and is commercially available as a chip-side capacitor. The electronic component 10 is a rectangular parallelepiped when viewed from above as shown in FIG. 1, and the main body 11 is an exterior, cover, package, etc. made of an electrically non-conductive material that houses an electronic element (not shown), and its vertical cross-sectional shape is, for example, rectangular. Two electrodes 12 and 13 for wiring are provided on the short sides of the main body 11 in the vertical cross-sectional view. The electrode 12 is made of metal and is formed so as to extend to a part of the surface (upper surface), the side surface on the short side, and a part of the bottom surface (lower surface) of the main body 11 of the rectangular parallelepiped. The electrode 13 is made of metal and has a symmetrical shape with the electrode 12, and is formed so as to extend to a part of the surface, the side surface on the short side, and a part of the bottom surface of the main body 11 of the rectangular parallelepiped.

[0017] An electronic component 20 made of a chip-type resistor has a similar shape to electronic component 10, but the soldering method of this embodiment and the pattern arrangement of the control board for soldering are not affected by the type of electronic component housed inside main body 11, so the soldering method of Figures 2 to 4 can be similarly applied to electronic component 20.

[0018] The wiring board 2 is, for example, a printed circuit board, and one that can be used even in an extremely low temperature environment is used. A plurality of wiring patterns are printed on at least the surface of the wiring board 2, and a plurality of pads 4, 5 are formed by exposing parts of the wiring patterns. The pads 4, 5 are provided in a number corresponding to the number of electrodes 12, 13 of the electronic component 10, and are the portions to which the solder material adheres after melting. By soldering to the pads 4, 5, the electronic component 10 is fixed, and an electrical conduction state between the electrodes 12, 13 and the pads 4, 5 is established.

[0019] The solder joints 32 and 33 shown in FIG. 2 are in a state after the solder material is heated and melted, and cooled and solidified. The solder joint 32 is formed by cooling the solder material before heating and melting, and has a generally ball-like shape as a whole, and is formed so that almost the entire electrode 12 and almost the entire metal pad 4 are included inside the ball-like outer surface of the solder. Also, the solder joint 33 is formed so that almost the entire electrode 13 and almost the entire metal pad 5 are covered with solder. In this way, the solder joints 32 and 33 are shaped so that the lower surfaces of the electrodes 12 and 13 of the electronic component 10 are convex downward, the side surfaces are convex laterally, and the upper surfaces are convex upward. The solder joint 33 is formed in a symmetrical shape to the solder joint 32. To form such solder joints 32, 33, it is important to adjust the amount of solder material before performing reflow soldering, to specify the relationship between the sizes and relative positions of electrode 12 and pad 4, and to specify the relationship between the sizes and relative positions of electrode 13 and pad 5.

[0020] FIG. 3 is a cross-sectional view showing the state immediately before the electronic component 10 of FIG. 2 is attached to the control board 1. The electronic component 10 has a longitudinal size of L, and the front and bottom surfaces of the main body 11 of the electronic component are covered with metal electrodes 12 and 13 except for a portion of the longitudinal center with a length L1. This shape is widely adopted for commercially available chip resistors and chip capacitors. In this embodiment, the arrangement and size of the pads 4 and 5 are devised to enable the soldering method according to the present invention. When viewed from the electrode 12 side, the position of the corner 4b of the pad 4 is set so as to be shifted outward in the longitudinal direction by a distance S2 from the outer end of the pad 4, and the position of the corner 4a of the pad 4 is set so as to be shifted outward in the longitudinal direction by a distance S1 from the corner 12a of the electrode 12. The definition of the outside and the inside here is that the side closer to the longitudinal center position of the rectangular parallelepiped electronic component 10 is called the inside, and the side farther away is called the outside, as shown by the arrow in FIG. 3.

[0021] On the electrode 13 side, the position of the corner 5b of the pad 5 is set so as to be shifted outward in the longitudinal direction by a distance S2 from the end 13c of the electrode 13, and the position of the corner 5a of the pad 5 is set so as to be shifted outward in the longitudinal direction by a distance S1 from the corner 13a of the electrode 13. Here, the relationship of S2>S1 is satisfied. In this manner, the wiring pattern is formed so that the distance between the pads 4 and 5 is wider, L2, than the distance L1 between the electrodes 12 and 13, so that the inner ends 12a and 13a of the electrodes 12 and 13 are shifted closer to the longitudinal center than the inner ends 4a and 5a of the pads 4 and 5.

[0022] Solder materials 34, 35 are formed on the pads 4, 5 in advance by printing or coating. Before soldering, the amount of solder material may be adjusted by adding solder balls (not shown) in addition to the solder materials 34, 35. After this, the wiring board 2 and the entire mounted object are heated to heat and melt the solder materials 34, 35 and the solder balls (not shown), and then cooled and solidified to form the solder joints 32, 33. The solder joints 32, 33 are formed into a substantially spherical shape that is convex outward due to surface tension. In this way, the soldered state shown in FIG. 2 is achieved. In the soldered state shown in FIG. 2, the upper and inner corner 4a of the pad 4 and the upper and inner corner 5a of the pad 5 are completely buried in the solder joints 32, 33. In addition, since the outer end 12c of the electrode 12 facing the pad 4 is shifted inward (toward the center of the main body 11) from the end of the corner 4b of the pad 4 facing it, the outer side surface 4b facing the pad 4 is also covered with the solder 32. Similarly, the upper inner corner 5a of the pad 5 and the upper outer corner 5b of the pad 5 are completely buried in the solder joint 33. In addition, since the outer end 13c of the electrode 13 facing the pad 5 is shifted inward (toward the center of the main body 11) from the end of the corner 5b facing it, the outer side surface 5b facing the pad 5 is also covered with the solder 33. As a result of the above, both of the outer corners 12c, 13c of the electrode 12 are buried in the solder joints 32, 33.

[0023] Furthermore, by adjusting the amount of solder to be melted, the outer corners 12e, 13e of the upper surfaces of the electrodes 12, 13 can also be formed to be completely covered in the solder 32, 33. It is not necessary that the corners 12a, 12g, 13a, 13g shown in FIG.

[0024] As described above, in this embodiment, the corners 12c, 13c and the corners 4a, 4b, 5a, 5b, which are likely to be the starting point of interface cracks caused by low temperatures, are completely buried in the solder joints 32, 33, so that the occurrence of interface cracks can be effectively suppressed. In the example of Figs. 2 and 3, only one of the electronic components 10 shown in Fig. 1 is described, but the same method is used for soldering a large number of electronic components 10 mounted on the control board 1, the chip capacitor 20, and other electronic components (not shown) having a similar terminal structure. For example, the chip resistor and the chip capacitor have two electrodes on the main body 11, but the main body 11 can also be applied to a rectangular parallelepiped body having one or more electrodes on the opposing short / long sides of the same length, a body having electrodes only on the short or long sides of the component, or a body having one or more electrodes on any or all of the sides.

[0025] The state of the solder joint 37 according to the modified example of this embodiment will be described with reference to FIG. 4. When the solder material is heated and melted to form the solder joint 32, an intermetallic compound 38a is formed at the interface between the pad 4 and the solder joint 32. Similarly, an intermetallic compound 38b is also formed at the interface between the electrode 12 side and the solder joint 33 shown in FIG. 2. These may grow due to heating and melting during manufacturing. The solder joint 37 formed from the side of the electronic component 10 to the outer periphery of the pad 4 in FIG. 4 is not convex to the outside of the solder joint 32 shown in FIG. 2, but has a gentle shape. Even in this case, the stress applied to the solder joint on the outside of the component is smaller than that of the solder joint on the component's lower electrode, so it is considered that cracks starting from this side are less likely to occur. EXAMPLES

[0026] Next, a second embodiment of the present invention will be described with reference to Figs. 5 to 7. Fig. 5 is a partial vertical cross-sectional view of the wiring board 2 showing the second embodiment of the present invention, which corresponds to, for example, the portion BB in Fig. 1. As shown in Fig. 5, the electronic component 40 is an area array type electronic component, and is composed of a main body 40A and electrodes 41 to 45. Solder balls are formed on the electrodes 41 to 45. A plurality of pads 51 to 55 are arranged at positions facing the plurality of electrodes 41 to 45 formed on the bottom surface of the main body 40A of the electronic component 40. The electrodes 41 to 45 are connected to the plurality of pads 51 to 55 by substantially spherical solder joints 61 to 65. The solder joints 61 to 63 are formed by placing solder balls between the electronic component 40 and the wiring board 2, and then heating the entirety (the wiring board 2, the solder balls, the electronic component 40, etc.) to heat and melt the solder joints 61 to 65. The cooled solder balls 66 to 68 are the solder joints 61 to 65, and are made of the same material. As can be seen from FIG. 4, the solder joints 61 to 65 have an outwardly protruding barrel shape in vertical cross section.

[0027] As described above, in the second embodiment, the shape of the solder joints 61-65 after soldering is controlled to a desired shape for the electrodes of the electronic component 40 to be surface-mounted. By heating and melting the entirety of the solder joints 61-63, etc., sandwiched between the electrodes 41-45, etc., and the pads 51-53, etc., of the electronic component 40, the lower corners and the entire side surfaces (surfaces adjacent to the lower corners) of all the electrodes of the electronic component 40 are located inside the solder joints 61-65 after melting and are covered with solder. According to the second embodiment, it is possible to configure the entire upper corners and side surfaces (surfaces adjacent to the upper corners) of the pads 51-58, etc., for mounting the electronic components mounted on the wiring board 2, to be covered with the solder joints 61-65, etc. after cooling. The solder material prepared on the upper surfaces of the pads 51-55 before heating may be a solder layer formed on the pads 51-55 by printing or coating, and the method of preparing the solder material is arbitrary.

[0028] 6 is a diagram showing a soldered state of the wiring board, and in (A), the pad 151 on the circuit board 2 side is formed relatively smaller than the electrode 141 of the electronic component 140. Also, the solder joint 161 is joined to the lower surface of the electrode 141, but the lower corners 141a, 141b of the electrode 141 and the side surfaces extending upward from them are exposed and not covered by the solder joint 161. On the pad 51 side, not only the upper surface but also the side surfaces are covered by the solder joint 161, and the corners 51a, 51b of the upper surface of the pad 51 are located inside the solder joint 161. On the other hand, (B) shows the joining method shown in the second embodiment, in which the entire lower surface and side surfaces of the electrode 41 provided on the electronic component 40 and the entire upper surface and side surfaces of the pad 51 are exposed before soldering, but when heated, the solder material melts and spreads to cover the electrode 41 and the side surfaces of the pad 51, and then hardens, so that the electrode 41 and the pad 51 are covered with the solder material. As a result, corners 41a, 41b of electrode 41 and corners of portions not visible in the figure (there are four corners on the underside) are covered with solder joints 61.

[0029] 6(A) and (B) were left in a low-temperature environment of 77K for 300 hours, it was found that because the control board in (A) does not have solder joints 161 formed on the side of electrode 141 and is joined on a single plane, a crack may propagate inward from the joint near corner 141b on the electrode 141 side as indicated by arrow 170, causing the board to break. On the other hand, no cracks were generated in the control board according to the second embodiment, and the joint state between electrode 14 and solder joints 61 was good.

[0030] Fig. 7 is a photograph showing the state shown in Fig. 6 confirmed by an experiment. Fig. 7(A) shows the configuration shown in Fig. 6(A), where the electrode 141 and the solder joint 161 are in surface contact with each other on only one surface. When this control board was left at an extremely low temperature, each component contracted, and cracks occurred at the interface between the components as shown by arrows 81 and 82 due to the difference in linear expansion coefficient. On the other hand, in the bonding method according to the second embodiment shown in Fig. 7(B), the side of the electrode 41 is covered with the solder joint 61, and the solder joint 61 is also bonded to the lower surface of the electrode 41 and the side surface adjacent to the lower surface. Therefore, even if each component contracts, cracks do not progress at the interface so as to cause separation, and it was confirmed that the bonding reliability in a low-temperature environment is improved.

[0031] As described above, the present invention is directed to a structure in which a general surface mount component is joined with solder, and in the joint between the electrode on the board and the solder, or the joint between the electrode of the electronic component and the solder, the side and corner of the electrode are covered with solder and the electrode is not exposed. This protects the crack origin that causes interface cracking due to low temperature, and extends the life of the joint between the solder and the electrode. In addition, since there is no need to change the material or composition of the solder from the conventional solder, a commercially available product containing general copper and silver can be used. The present invention is particularly suitable for use in outer space, control circuits used in quantum computers that operate in a cryogenic environment of 77K or less using helium gas, or electronic devices that operate in a cryogenic environment.

[0032] In this specification, the invention has been described based on two embodiments, but the present invention is not limited to the above embodiments and can be modified in various ways without departing from the gist of the invention. For example, the above-mentioned control board has a structure in which the solder joints that join the wiring board and the electronic components are mainly composed of Sn, and the soldering surfaces of the pads of the wiring board and the electrodes of the electronic components, their corners, and the side surfaces that contact the corners are covered with solder after melting and cooling, and the electrodes are not exposed. With such a structure, the dimensions, ratios, shapes, etc. of each are not limited to the configurations described in the embodiments. Furthermore, the type, shape, and size of the electronic components used, and the configuration of whether the wiring board, etc. is single-layered or multi-layered, etc. may be formed arbitrarily. [Explanation of symbols]

[0033] 1 Control Board 2. Wiring board 4, 5 pads 4a, 4b, 5a, 5b corner 7 Connector parts 8 Package Parts 9. Control LSI 10 Electronic Components (Chip Capacitors) 11 (Electronic component) main body 12, 13 electrodes 12a, 12c, 12e, 12g, 13a, 13c, 13e, 13g corner 12b, 13b bottom 12d, 13d side 12f, 13f top surface 20 Electronic Components (Chip Resistors) 32, 33, 37 Solder joints 34, 35 Solder material 38a, 38b Intermetallic compounds 40 Electronic Components 40A (Electronic component) main body 41~45 electrode 41a, 41b (electrode) corners 51~55 Pad 51a, 51b (pad) corners 61~65 Solder joints 81, 82 (Solder) peeling 140 Electronic Components 141 Electrode 151 Pad 161 Solder joint

Claims

1. A control board that operates in a low-temperature environment at an absolute temperature of 77 K or less, A surface mount electronic component having an electrode formed on a bottom surface thereof; a wiring board having a wiring pattern formed on its surface and pads for connecting electrodes of the electronic component; a solder joint portion mainly composed of Sn, the solder joint portion being disposed on the pad and soldering the pad and the electrode; A control board characterized in that the solder joint covers the entire outer corner of the electrode on the side closer to the wiring board and the surface adjacent to the outer corner, and covers the entire corner of the pad on the side closer to the electronic component and the surface adjacent to the corner.

2. 2. The control board according to claim 1, A control board, characterized in that after the pads are soldered, the electronic component is covered with solder up to the upper outer corners of the electrodes that are farther from the wiring board.

3. 3. The control board according to claim 2, The control board, wherein the electronic component is a chip resistor or a chip capacitor having two electrodes.

4. 4. The control board according to claim 2, an inner corner of the pad of the wiring board is offset from a lower inner corner of the corresponding electrode of the electronic component so as to be positioned outward when viewed from a center of the electronic component; A control board characterized in that an outer corner of the pad of the wiring board is positioned so as to be offset outward from the center of the electronic component relative to the lower inner corner of the corresponding electrode of the electronic component.

5. 5. The control board according to claim 4, wherein a first amount of outward offset of said inner corner of said pad is smaller than a second amount of outward offset of said outer corner of said pad.

6. 2. The control board according to claim 1, A plurality of the electronic components are mounted on the wiring board, A plurality of the flat electrodes are formed on a bottom surface of the electronic component, A plurality of flat pads corresponding to the electrodes are formed on the wiring board, The solder material is sandwiched between the electrode and the pad, and the entirety is heated and melted, A control board characterized in that the entire lower corners of the electrodes of all of the electronic components and the surfaces adjacent to the lower corners, and the entire upper corners of the pads and the surfaces adjacent to the upper corners are covered with solder.

7. 2. The control board according to claim 1, The soldering is by BGA bonding or QFN bonding, A control board characterized in that, of the electronic components mounted on the control board, the outer corners of the electrodes closest to the wiring board and the entire surfaces adjacent to the outer corners are covered with solder, and the corners of the pads closest to the electronic components and the entire surfaces adjacent to the corners are covered with solder.

8. A control board that operates in a low-temperature environment at an absolute temperature of 77 K or less, a plurality of surface mount electronic components each having a plurality of electrodes formed on a bottom surface thereof are connected by a solder material to a wiring board each having a wiring pattern and pads formed on a surface thereof for connecting the electrodes of the electronic components; the electrodes are disposed in a plurality of portions on an inner portion of a bottom surface of the electronic component that is not in contact with an edge portion, A control board characterized in that, after soldering, the entire corner of the electrode closest to the wiring board and the lower surface adjacent to the corner are covered with solder, and the entire corner of the pad closest to the electronic component and the upper surface adjacent to the corner are covered with solder.

9. 9. The control board according to claim 8, A control board, characterized in that the area of ​​the lower surfaces of the multiple electrodes is larger than the area of ​​the upper surfaces of the opposing pads.

10. 10. The control board according to claim 9, The control board, wherein the electronic component is a chip resistor or a chip capacitor.

11. A method for manufacturing a control board, comprising the steps of: connecting an electronic component having a plurality of electrodes formed at corners of a bottom surface to a wiring board having a wiring pattern and pads formed on a surface thereof for connecting the electrodes of the electronic component, using a solder material; The pads on the control board are disposed so as to be positioned on the outer side of the electrodes to be joined to the pads, and the pads are disposed .... A solder material mainly composed of Sn is placed on the pad, and an electrode of the electronic component is placed on the solder material and heated to melt the solder material, thereby soldering the electrode to the pad; A method for manufacturing a control board, characterized in that after the soldering, the amount of solder material is adjusted so that the entire corner of the electrode closest to the wiring board and the lower surface adjacent to the corner are covered with the solder material, and the entire corner of the pad closest to the electronic component and the upper surface adjacent to the corner are covered with the solder material.

12. The method according to claim 11, Each of the electrodes has a short side surface of the electronic component, a lower surface extending from the short side surface to a part of a bottom surface, and a top surface extending from the short side surface to a part of a surface, The method for manufacturing a control board, wherein the soldering is performed such that the upper corners of the electrodes, which are farthest from the wiring board, are covered with solder.

13. The method according to claim 12, the electronic component is a chip-type resistor having two of the electrodes, A method for manufacturing a control board, characterized in that the wiring board is manufactured so that an inner corner of the pad of the wiring board is offset so that it is positioned outward from the center of the electronic component relative to a lower inner corner of the corresponding electrode of the electronic component, and an outer corner of the pad of the wiring board is offset so that it is positioned outward from the center of the electronic component relative to a lower inner corner of the corresponding electrode of the electronic component.

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