JP2011012887A - Cryogenic cooling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem in cryogenic cooling using a refrigerator wherein it is required to sufficiently secure thermal conductivity between a chip and a cooling head to effectively cool the chip and increase in tightening torque of a screw to improve contact causes damage and deformation, and thus, improve thermal contact between a chip and a cooling head without damaging the chip for mounting.SOLUTION: In a cryogenic cooling device, when the chip is mounted to the cooling head of a refrigerator, a substrate for processing and a power transmission component with a square frame shape etc. are provided and while a chip carrier substrate mounted with the chip, a printed wiring substrate, the power transmission component and the substrate for processing are superposed on each other, the substrate for processing is fixed to the refrigerator by screws etc. By tightening the screws etc., the substrate for processing presses the power transmission component, the power transmission component presses the printed wiring substrate, and the printed wiring substrate presses the chip carrier substrate. Thus, thermal contact performance is improved between the chip carrier substrate and the cooling head.

Description

  The present invention relates to a cryogenic cooling device that mounts a superconducting element or the like on a cooling head of a refrigerator with good thermal conductivity.

  With the recent increase in accuracy of electronic measuring instruments, the Josephson voltage standard (JVS) has been developed as a standard voltage generator capable of generating and measuring more accurate voltages. This is realized by integrating superconducting Josephson elements on a chip and requires a cryogenic cooling technique of 4 to 10K. Conventionally, the cooling method using liquid helium has been the mainstream. Although it is possible to easily cool the chip simply by immersing the chip in liquid helium, liquid helium is expensive due to the depleted resources and will be difficult to obtain in the future. In order to further use and spread JVS, it is necessary to reduce cooling costs, and development of a cooling technique using a cryogenic refrigerator is desired.

  In order to cool the JVS chip using the refrigerator, the chip needs to be brought into thermal contact with the cooling head of the refrigerator. This is because cooling is performed by removing heat from the chip to the cooling head based on heat conduction between the two. There are Patent Documents 1 to 4 regarding technologies for cooling a JVS chip using a refrigerator.

  FIG. 4 shows a conventional example in which the chip 1 is mounted on the refrigerator. In FIG. 4, a chip 1 mounted on a chip carrier substrate is connected to a printed wiring board 3 or the like, and these are fixed to a cooling head 2 of a refrigerator with screws 7 or the like and are in thermal contact. Here, if the thermal contact is insufficient, the chip temperature immediately rises due to the heat generated by the chip itself. The characteristics of the Josephson element are extremely sensitive to changes in temperature. When the temperature rises due to heat generated by the operation of the chip, the characteristics deteriorate. In the worst case, even the superconducting state cannot be maintained.

JP 2007-40561 A Japanese Patent Laid-Open No. 7-1331078 Japanese Patent Application Laid-Open No. 11-97753 Japanese Patent Application Laid-Open No. 2003-101088

  5 and 6 are diagrams showing in detail a conventional example relating to mounting of a chip on a refrigerator. FIG. 5 is an exploded view of a conventional example, and FIG. 6 is an explanatory view of the conventional example viewed from the top and side. In the conventional example, the chip 1 is mounted on the chip carrier substrate 3, and both are thermally and mechanically connected by soldering or the like as necessary. A chip carrier substrate 3 on which the chip 1 is mounted is placed on the cooling head 2 and an indium sheet (or grease, metal paste, etc.) is sandwiched between them in order to improve the contact between them. . The chip 1 is electrically connected to the printed wiring board 4 on the chip carrier substrate 3 by bonding wires 6. For the purpose of fixing the chip carrier substrate 3 on the cooling head 2 and the purpose of pressing the chip carrier substrate 3 against the cooling head 2 to make thermal contact, the corner of the printed wiring board 4 on the chip carrier substrate 3 is formed. The screw 7 is fixed to the screw hole 8 of the cooling head. The reason why the chip carrier substrate is not directly fixed with screws is that the substrate material having excellent thermal conductivity used as the chip carrier substrate is usually poor in workability and lacks strength.

  In order to perform effective cooling, it is necessary to ensure sufficient thermal conductivity between the chip 1 and the cooling head 2, and for that purpose, thermal contact between the chip 1 and the cooling head 2 is important. It is necessary to increase the thermal conductivity as much as possible. Specifically, it is important to employ a material having high thermal conductivity for the chip carrier substrate and to increase the thermal conductivity at the interface between the chip and the chip carrier substrate and between the chip carrier substrate and the cooling head. In order to improve the contact, it is necessary to increase the tightening torque of the screw fixing the printed wiring board 4 to increase the force for pressing the chip carrier board 3 against the cooling head 2. However, if the screw is tightened strongly, the printed wiring board 4 will be bent this time. Then, the bonding wire 6 for electrically connecting the chip 1 and the printed wiring board 4 may be disconnected, or the printed wiring board 4 and further the chip itself may be stressed and broken, resulting in a problem in reliability. was there. Conversely, if the screw 7 is loosened, it will not be possible to make thermal contact. If the screw hole 8 is positioned near the center instead of the four corners of the chip carrier substrate, the above problem can be reduced, and since the force can be applied closer to the chip, the thermal contact is also improved. In general, the central portion of the substrate 4 has a problem that it is not practical to screw the wiring density because of high wiring density.

  An object of the present invention is to solve these problems of a cryogenic cooling device and to provide a structure in which a chip is mounted on a cooling head with improved thermal contact.

  In order to achieve the above object, the present invention has the following features.

  The present invention is a cryogenic cooling device that fixes a chip to a cooling head of a refrigerator, and stacks a chip carrier substrate on which the chip is mounted, a first substrate, a force transmission component, and a second substrate in order. The second substrate is fixed to the refrigerator so that the second substrate presses the first substrate and the chip carrier substrate against the cooling head via the force transmission component. . The first substrate of the present invention is specifically a wiring substrate. Further, the force transmission component has a frame shape surrounding the chip. In the cryogenic cooling device of the present invention, the first substrate includes a plurality of cavities in which chips are arranged, and the second substrate is connected to the first substrate via the plurality of force transmission components. In addition, the second substrate is fixed to a refrigerator so as to press the chip carrier substrate against the cooling head.

  In the present invention, a first substrate such as a printed wiring board is not pressed by screws at the four corners as in the prior art, but is pressed from a pressurizing substrate that is a second substrate via a force transmission component. . Specifically, a portion closer to the center of the printed wiring board (a portion near the chip periphery) is pressed. For this reason, the printed wiring board is less likely to warp. Further, since the printed wiring board itself is not warped, there is no fear that the bonding wire is disconnected, and the printed wiring board or chip is not damaged, so that the reliability is improved. Since it is not damaged in this way, it is possible to tighten the screw with a torque nearly ten times stronger than the conventional one, and the thermal contact between the chip carrier substrate and the cooling head can be improved as compared with the conventional one. In the present invention, if the tightening torque of the screw is excessively increased, the strongest stress is applied to the pressurizing substrate, which is the second substrate, and this is first damaged. At this time, since there is no fear of damage to the printed wiring board and the chip including the force transmission component, it is safe and has a fail-safe function.

  In the present invention, the force transmission component can be arranged at an arbitrary position without any restriction, and can be arranged near the chip. Therefore, the vicinity of the chip carrier substrate and the printed circuit board in the vicinity of the chip can be pushed through the force transmission component, so that the thermal conductivity in the vicinity of the chip between the chip, the chip carrier substrate and the cooling head is improved. The cooling effect is very high.

  In the present invention, the positions of the screws and screw holes for mounting may be the same as conventional positions, and may be arbitrary places where the wiring density is sparse, such as the four corners of the printed wiring board. The degree of freedom is improved.

  In addition to the above-described effects, the present invention has a structure in which the chip carrier substrate is further held by the surface of the printed wiring board, which is the first substrate, as compared with the technique of the conventional patent document 4 and the like. Therefore, there is an effect that the chip can be pressed toward the cooling head with a stronger force without applying mechanical stress. By being able to hold down with a strong force, the cooling effect in the superconducting circuit application in which the low-temperature superconductor having the operating temperature of 4 to 10 K is used is excellent, and the change in the operating characteristics can be suppressed.

  In addition, maintenance of the apparatus is important in superconducting circuits such as chip replacement and wiring board replacement. In particular, when the means for fixing the substrate for pressurization to the refrigerator is a detachable means such as a screw, the workability of the apparatus of the present invention is greatly improved from the viewpoint of maintenance. Furthermore, the present invention can be realized only by introducing a pressurizing substrate and a force transmission component with respect to the conventional method, and is very economical with a small number of additional components.

The exploded assembly figure explaining the 1st Embodiment of this invention. The figure explaining the 1st Embodiment of this invention. The figure explaining the 2nd Embodiment of this invention. The figure which shows the structure which mounts the chip | tip of a prior art example in a refrigerator, and cools. The exploded assembly figure explaining the mounting structure of a prior art example. The figure explaining the mounting structure of a prior art example.

  When the chip is mounted on the cooling head, the cryogenic cooling device of the present invention does not directly clamp the printed wiring board and fix it to the cooling head as in the prior art. By tightening and fixing the substrate to the refrigerator, the chip and the chip carrier substrate are pressed against the cooling head to improve the thermal contact. Hereinafter, embodiments will be described.

(First embodiment)
A first embodiment will be described with reference to FIG. 1 and FIG. FIG. 1 is an exploded view illustrating the first embodiment. FIG. 2 is an explanatory view of the mounting structure of the first embodiment viewed from the top and side surfaces. A chip 1 is fixedly mounted on a chip carrier substrate 3, a printed wiring board 4 is provided on the chip carrier substrate 3, and a pressurizing substrate 11 is provided thereon via a force transmission component 12. . Screw holes are formed in the corners of the substrate 11 for pressurization, and are located at the same positions as the screw holes 14 in the corners of the printed wiring board 4. In a state where the chip carrier substrate 3, the printed wiring board 4, the force transmission component 12, and the pressurizing substrate 11 are overlapped, the pressurizing substrate 11 is fixed to the refrigerator with screws 13. By tightening the corner screws 13, the pressurizing substrate 11 presses the force transmission component 12, the force transmission component presses the printed circuit board 4, and the printed circuit board 4 presses the chip carrier substrate 3. When the chip carrier substrate 3 is pressed, the thermal contact between the chip carrier substrate 3 and the cooling head 2 is improved.

  The chip 1 is a Josephson voltage standard chip or the like. The chip 1 is mounted on the chip carrier substrate 3. Since the chip carrier substrate 3 is preferably made of a material having a thermal expansion coefficient close to that of the chip 1 and excellent in thermal conductivity, a Si substrate or a sapphire substrate is used. Further, a metal substrate may be used as the chip carrier substrate 3. The shape and size of the chip carrier substrate 3 can be changed as appropriate, and can be made as large as the printed wiring board 4. The chip 1 and the chip carrier substrate 3 are fixed by soldering or the like. Fixing by soldering has the effect of improving the thermal conductivity by improving the thermal contact. Soldering may be omitted. Further, it can be fixed by grease other than soldering.

  The printed wiring board 4 has a void in which the chip 1 is disposed, and has wiring for input / output terminals for electrical connection with the electrodes of the chip 1 disposed in the void. The electrodes of the chip 1 and the terminals of the printed wiring board 4 are electrically connected by bonding wires 6. The printed wiring board 4 is fixed on the chip carrier board 3. It may be fixed with an adhesive. Although an example in which the printed wiring board 4 and the chip carrier board 3 are separated is shown, an integrally formed board may be used. In that case, screw holes may be provided in both the integrated printed wiring board 4 and the chip carrier board 3.

  The force transmission component 12 is placed on the printed circuit board 4 near the chip. Furthermore, the substrate 11 for pressurization is placed on the force transmission component 12 so as to cover the entire printed wiring board 4. For the pressurizing substrate 11, a metal plate such as copper or a substrate material such as dielectric or resin is used. Screw holes are made in the four corners of the substrate 11 for pressurization, and are opened in the same arrangement as the screw holes 14 made in the four corners of the printed wiring board 4. The position of the screw is not limited to the four corners, and can be provided at a position where it can be firmly tightened.

  The screw 13 is passed from above the pressurizing substrate 11, the screw hole 14 of the printed wiring board 4 is also passed, and is screwed into the screw hole 14 of the cooling head 2 to fix the pressurizing substrate 11. Although the example which provided the screw hole in the cooling head itself is shown in figure, you may screw to the member of the refrigerator which hold | maintains a cooling head. By tightening the screw 13, the pressurizing substrate 11 is pushed by the screw 13 and pushes the force transmission component 12, thereby pressing the printed wiring board 4, and heat is generated between the chip carrier substrate 3 and the cooling head 2. Contact can be taken. Only the pressurizing substrate 11 is directly pressed by the screw 13. About the screw hole 14 of the printed wiring board 4, only a screw is penetrated, and the printed wiring board 4 is not directly pressed by the screw 13.

  The shape and structure of the force transmission component 12 are not particularly limited as long as the force transmission component 12 has a function of transmitting the pressing force from the pressurizing substrate 11 to the printed wiring board 4. In FIG. 1, a shape of a square frame having a space at the center is illustrated as the force transmission component 12. Thus, the frame shape surrounding the chip as the force transmission component 12 is preferable. Basically, the force transmission component 12 only needs to have a constant height so that the printed wiring board 4 can be uniformly pressed around the vicinity of the chip. Also, if the pressurization board is damaged by the fail-safe function, to prevent damage to the chip, a U-shaped chip cover is formed so as to cover the chip, and the leg is a predetermined part of the printed wiring board. You may make it press. The force transmission component 12 is formed of a material such as a dielectric or resin.

  Further, it is desirable to sandwich a metal sheet such as an indium sheet or grease between the chip carrier substrate 3 and the cooling head 2 in order to improve thermal contact. These can also be omitted.

  In FIG. 1, one chip is shown in the cooling head in order to explain the present invention. However, a plurality of chips may be similarly mounted on the cooling head.

  In the conventional method shown in FIG. 5, the chip or the chip carrier was damaged only by applying a torque of 2 cNm or less when the screw was tightened. On the other hand, when the mounting structure of the first embodiment as shown in FIG. 1 is used, even when a torque close to 20 cNm is applied, it is not damaged. As described above, according to the present invention, it is possible to hold down with a force nearly ten times larger than that of the prior art.

(Second Embodiment)
In the second embodiment, a multi-chip mounting structure for mounting a large number of chips is shown. In this structure, a plurality of chips are mounted using a common printed circuit board or a common substrate for pressurization. FIG. 3 is an exploded view illustrating the second embodiment. A plurality of chips 1 are fixedly mounted on a chip carrier substrate 3, a common printed wiring board 4 is provided on the chip carrier substrate 3, and a plurality of force transmission components 12 are provided thereon. In addition, a single pressurizing substrate 11 is provided via the force transmission component 12. A screw hole is formed in the substrate 11 for pressurization, and is located at the same position as the screw hole 14 in the printed wiring board 4. The pressurizing substrate 11 and the printed wiring board 4 are fixed to the cooling head 2 with the screws 13 in a state where they are stacked. By tightening the screw 13, the pressing substrate 11 pushes the plurality of force transmission components 12, the force transmission component 12 pushes the printed wiring board 4, and the printed wiring board 4 pushes the chip carrier substrate 3. When the chip carrier substrate 3 is pressed against the cooling head, thermal contact between the chip carrier substrate 3 and the cooling head 2 is improved.

  The printed wiring board 4 has a plurality of voids for disposing the chip 1, and has input / output terminal wirings for electrical connection with the electrodes of the chip 1. The electrodes of the chip 1 and the input / output terminals of the printed wiring board 4 are electrically connected by bonding wires. The printed wiring board 4 is fixed on the plurality of chip carrier boards 3.

  The force transmission component 12 is placed at a predetermined position on the printed wiring board 4. Further, a single pressurizing substrate 11 is placed on the plurality of force transmission components 12 in a shape that covers the entire printed wiring board 4. The screw 13 is passed from above the pressurizing substrate 11, the screw hole 14 of the printed wiring board 4 is also passed, and screwed into the screw hole 14 of the cooling head 2 to fix the pressurizing substrate 11. Although the example which provided the screw hole in the cooling head itself is shown in figure, you may screw to the member of the refrigerator which supports a cooling head. By tightening the screw 13, the pressurizing substrate 11 is pushed by the screw 13 and pushes the plurality of force transmission components 12, thereby also pushing the printed wiring board 4, and between the chip carrier substrate 3 and the cooling head 2. Can make thermal contact. Only the pressurizing substrate 11 is directly pressed by the screw 13.

  In the second embodiment, the shape and structure of the force transmission component 12 are not particularly limited as long as the force transmission component 12 has a function of transmitting the pressing force from the pressing substrate 11 to the printed wiring board 4. In FIG. 2, a cylindrical shape is illustrated as the force transmission component 12, but the shape is not limited as long as the height is the same so that the printed wiring board 4 can be uniformly pressed. A frame shape may be used as in the first embodiment. The force transmission component 12 may be disposed so as to uniformly transmit the force to the vicinity of the chip or to an arbitrary position between the space and the space.

  According to the second embodiment, in addition to the function and effect obtained in the first embodiment, the structure in which a plurality of chips are mounted on a single printed wiring board is also strong. Contact can be obtained.

  In carrying out the present invention, the first and second embodiments can be appropriately combined. In the embodiment of the present invention, the printed wiring board 4 has been exemplified and described as the first board, but it is not necessarily limited to the wired board or the printed board. Further, a printed wiring board may be used as the second board which is a pressurizing board. Further, in the embodiment of the present invention, with respect to tightening with screws, the positions of the screws are exemplified at the four corners. For example, a wire may be used for fixing.

  In the present invention, the JVS chip of the standard voltage generator is cited as an example of the chip. However, the present invention is not limited to the JVS chip element, and is mounted for cryogenic cooling. Can be used for mounting a semiconductor element chip that requires. Moreover, the examples shown in the above-described embodiment and the like are described for easy understanding of the invention, and are not limited to this embodiment.

  The present invention is particularly useful in the Josephson voltage standard that implements chips that integrate superconducting Josephson devices. In addition, it is useful in the superconducting electronics field and the cryogenic cooling technology field in the semiconductor field.

DESCRIPTION OF SYMBOLS 1, Chip 2, Cooling head 3, Chip carrier board 4, Printed wiring board 5, Input / output terminal 6, Bonding wire 7, Screw 8, Screw hole 11, Pressurizing board 12, Force transmission component 13, Screw 14, Screw hole

Claims (3)

  A cryogenic cooling device for fixing a chip to a cooling head of a refrigerator, wherein a chip carrier substrate on which a chip is mounted, a first substrate, a force transmission component, and a second substrate are sequentially stacked, and the second A cryogenic cooling device, wherein the second substrate is fixed to a refrigerator so that the substrate presses the first substrate and the chip carrier substrate against the cooling head via the force transmission component. .   The cryogenic cooling device according to claim 1, wherein the force transmission component has a frame shape surrounding the chip.   The first substrate includes a plurality of cavities for disposing chips, and the second substrate presses the first substrate and the chip carrier substrate against the cooling head via the plurality of force transmission components. The cryogenic cooling device according to claim 1, wherein the second substrate is fixed to a refrigerator.

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