Packaging structure and packaging method of nuclear battery

Abstract

The present invention provides a packaging structure and packaging method for a nuclear battery, comprising: a first transducer and a second transducer, comprising a first surface and a second surface respectively, wherein the first surface is provided with a first and a second upper electrode, and the second surface is provided with a first and a second back electrode, and the first and the second upper electrodes include a grid electrode and a surrounding electrode surrounding the grid electrode; a radiation source film, arranged between the grid electrodes; a metal bonding layer, comprising an annular metal layer bonded between the surrounding electrodes and a lead-out metal part connected to one side of the annular metal part. The present invention can greatly increase the number of stacks within a certain volume and improve the volume power density. The grid structure of the present invention can provide a good non-blocking area for transducer incidence. The present invention uses a transient liquid phase bonding process to perform a completely sealed package of a carbon-14 radiation-voltaic nuclear battery, which can effectively achieve complete sealing of the radiation source and fixed position of the transducer device, and can achieve good electrode contact.

Description

Technical Field

[0001] The invention belongs to the field of nuclear battery design and manufacture, and in particular relates to a packaging method for a nuclear battery packaging structure. Background Art

[0002] The radiovoltaic effect radioisotope battery (hereinafter referred to as radiovoltaic nuclear battery) is a device that generates electricity by combining radioisotopes with semiconductor devices. In the industrialization process of radiovoltaic nuclear batteries, it is very important to realize the integrated packaging of radiovoltaic nuclear batteries.

[0003] The radioisotope battery with radiovoltaic effect is an integrated microsystem component, which includes a power generation device and energy storage components. The power generation device includes an electromagnetic energy collection chip, a vibration generator and a photovoltaic cell, and the energy storage components include a supercapacitor, a thin-film lithium battery and a microcapacitor.

[0004] Because the power density of a single cell of a radiovoltaic battery is relatively low, generally less than 150nW / cm 2 , so the semiconductor transducer devices must be superimposed in series and parallel.

[0005] Since nuclear batteries do not need to be laid out like solar cells, it is necessary to stack the radiation source and semiconductor transducer devices in a 3D integrated package to obtain a smaller volume and greater than 5μW / cm 3 The power density of the radiation-induced nuclear battery stack is currently mainly based on PCB board integration, support shell integration and compression integration.

[0006] (1) Integrated packaging solution based on PCB boards. Isotope battery modules using PCB board integrated packaging can be stacked in parallel and in series. However, the volume of the stacked PCB boards is too large to form a sufficiently high volume power density, and cannot be integrated into the MEMS system.

[0007] (2) Stacking packaging technology based on diamond and Ni-63. Currently, one method of self-supporting 3D stacking packaging is to use nickel-63 and diamond materials. The method is to electroplate the nickel-63 radiation source onto an ordinary nickel sheet. Since the nickel-63 radiation source is a metal radiation source, it will become copper after decay, so it does not affect the conductivity. Therefore, the planar diamond Schottky diodes are stacked vertically, all the Schottky surfaces are connected together, the ohmic contact surfaces are connected together, and they are directly compacted by compression springs or screws. However, the biggest problem with this method is that it is very easy to fall apart, causing the transducer to fall off and lose the parallel output capability. Moreover, the direct compaction method cannot be used on silicon carbide and carbon-14 batteries. The carbon-14 radiation source is made of an insulating polymer film, so it cannot be conductive by direct contact, and the edge contact is not firm, and the risk of detachment is greater.

[0008] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present application and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because they are described in the background technology section of the present application. Summary of the invention

[0009] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a packaging method for a nuclear battery packaging structure, so as to solve the problems of insufficient structural stability and power density in the prior art.

[0010] To achieve the above-mentioned purpose and other related purposes, the present invention provides a packaging structure of a nuclear battery, the packaging structure includes at least one packaging unit, the packaging unit includes: a first transducer and a second transducer, each including a first surface and a second surface opposite to each other, the first surface of the first transducer is provided with a first upper electrode, and the second surface is provided with a first back electrode, the first surface of the second transducer is provided with a second upper electrode, and the second surface is provided with a second back electrode, the first upper electrode and the second upper electrode include a grid electrode and a surrounding electrode surrounding the grid electrode and connected to the grid electrode; a radiation source film, the radiation source film is arranged between the grid electrode of the first upper electrode and the grid electrode of the second upper electrode; a metal bonding layer, including an annular metal layer bonded between the surrounding electrodes of the first upper electrode and the second upper electrode, and a lead-out metal part connected to one side of the annular metal part and extending outside the surrounding metal part.

[0011] Optionally, the radiation source film includes a β radiation source film, the β radiation source film includes a solidified film containing carbon-14, the thickness of the radiation source film is 20 microns to 50 microns, and the size of the radiation source film is smaller than the inner diameter of the surrounding electrode.

[0012] Optionally, the first transducer and the second transducer further include a back metal layer, which covers surfaces of the first back electrode and the second back electrode and extends from the other side opposite to the lead-out metal portion to outside the first back electrode and the second back electrode.

[0013] Optionally, the back metal layer includes a main metal layer, a bonding layer is plated on the surface of the main metal layer, the thickness of the main metal layer is 40 micrometers to 60 micrometers, and the thickness of the bonding layer is greater than 200 nanometers.

[0014] Optionally, the first transducer and the second transducer include a silicon carbide PIN junction epitaxial wafer, and the thickness of the silicon carbide PIN junction epitaxial wafer is 100 microns to 200 microns.

[0015] Optionally, the total electrode area of ​​the first upper electrode and the second upper electrode accounts for less than 20% of the upper surface area of ​​the first transducer and the second transducer respectively.

[0016] Optionally, the grid line width of the grid electrode is 30 microns to 60 microns, the spacing between two adjacent grid lines is 1.2 mm to 2 mm, the frame width of the surrounding electrode is 0.4 mm to 1 mm, and the distance between the outer edge of the surrounding electrode and the edge of the upper surface of the first transducer and the second transducer is 1 mm to 2 mm.

[0017] Optionally, the thickness of the first upper electrode and the second upper electrode is greater than 200 nanometers, and their outermost layer is a nickel layer. The first back electrode and the second back electrode fully cover the second surface of the first transducer and the second transducer, with a thickness of 80 nanometers to 200 nanometers, and their outermost layer is a nickel layer or a gold layer.

[0018] Optionally, the metal bonding layer includes a main metal layer, and the bonding layer is plated on both surfaces of the main metal layer, the bonding layer has a melting point lower than the main metal layer and the first upper electrode and the second upper electrode, and the bonding layer diffuses into the main metal layer and the first upper electrode and the second upper electrode to form a homogenized alloy to achieve bonding.

[0019] Optionally, the thickness of the main metal layer is 35 microns to 50 microns, the thickness of the bonding layer is 1 micron to 10 microns, the frame width of the annular metal layer is greater than or equal to the frame width surrounding the electrode, the main metal layer includes a nickel layer, and the bonding layer includes a tin layer.

[0020] Optionally, at least two packaging units are included, wherein the back electrodes of two adjacent packaging units are bonded via a back metal layer to form a three-dimensional stacked packaging structure.

[0021] Optionally, the three-dimensional stacked packaging structure further includes a plastic packaging layer, and the plastic packaging layer is arranged between the lead-out metal parts of two adjacent packaging units.

[0022] The present invention also provides a packaging method for a packaging structure of a nuclear battery, the packaging structure includes a packaging unit, and the preparation of the packaging unit includes the steps of: providing a first transducer and a second transducer, respectively including a first surface and a second surface opposite to each other, the first surface of the first transducer is provided with a first upper electrode, and the second surface is provided with a first back electrode, the first surface of the second transducer is provided with a second upper electrode, and the second surface is provided with a second back electrode, the first upper electrode and the second upper electrode include a grid electrode and a surrounding electrode surrounding the grid electrode and connected to the grid electrode; providing a metal bonding layer, the metal bonding layer includes an annular metal layer corresponding to the surrounding electrode and a metal layer connected to one side of the annular metal part and extending outside the surrounding metal part The lead-out metal part, the metal bonding layer includes a main metal layer, the two surfaces of the main metal layer are plated with bonding layers, the melting point of the bonding layer is lower than the main metal layer and the first upper electrode and the second upper electrode, the first upper electrode of the first transducer is aligned with the annular metal part and placed on one side of the metal bonding layer; a radiation source film is provided, and the radiation source film is fixed on the grid electrode of the first transducer; the second upper electrode of the second transducer is aligned with the annular metal part and placed on the other side of the metal bonding layer; the bonding layer is formed into an instantaneous liquid film by rapid annealing and kept warm, so that the bonding layer diffuses to the main metal layer and the first upper electrode and the second upper electrode to form a homogenized alloy respectively, so as to bond the metal bonding layer with the first upper electrode and the second upper electrode.

[0023] Optionally, when bonding the metal bonding layer to the first upper electrode and the second upper electrode, it also includes applying pressure between the metal bonding layer and the first upper electrode and the second upper electrode to enhance the contact between the bonding layer and the first upper electrode and the second upper electrode.

[0024] Optionally, forming a transient liquid film on the bonding layer by rapid annealing and keeping the temperature includes: keeping the packaging structure warm for 3 minutes to 60 minutes in a nitrogen atmosphere at a temperature of 200° C. to 350° C.

[0025] Optionally, at least two packaging units are prepared, wherein the back electrodes of two adjacent packaging units are bonded via a back metal layer to form a three-dimensional stacked packaging structure.

[0026] Optionally, the packaging method further comprises the step of: forming a plastic packaging layer on a side surface of the three-dimensionally stacked packaging structure, wherein the plastic packaging layer is disposed between the lead-out metal portions of two adjacent packaging units.

[0027] As described above, the packaging structure and packaging method of the nuclear battery of the present invention have the following beneficial effects:

[0028] In order to solve the problem of difficult volume control, the present invention does not add any supporting structure, abandons all PCB board solutions, uses as little material as possible for internal connections, and makes the entire structure self-supporting. In addition, the thickness of each component of the present invention is relatively thin, basically ranging from ten to a hundred microns, which can greatly increase the number of stacking within a certain volume and improve the volume power density.

[0029] The present invention makes the surface electrode into a grid structure, and uses the grid structure to divide the entire silicon carbide area into blocks, ensuring that there are some electrodes near each block. At the same time, the duty cycle of the total electrode area is about 20%, which does not occupy too much transducer area and tries to provide a good non-blocking area for transducer incidence.

[0030] The present invention uses a bonding material with a lower melting point than the metal bonding layer and the electrode as an intermediate layer between the metal bonding layer and the surface electrode. When heated to the connection temperature, the intermediate layer melts and forms an instantaneous liquid film on the bonding surface. During the heat preservation process, as the low melting point component diffuses to the metal bonding layer and the electrode, the thickness of the liquid film decreases until it disappears. After a certain period of heat preservation, the composition is homogenized. The generation of the liquid phase sandwiches the intermediate layer material between the connected surfaces, applies a certain pressure, or relies on the deadweight of the workpiece to make contact with each other. The unique feature of the present invention is that the liquid phase bonding interface solidifies by diffusion rather than cooling below the melting point, so that a lower process temperature can be achieved, and a higher temperature stability can be achieved after bonding, and it is not easy to debond. Moreover, the essence of the process is metal alloying, and the entire contact position is made of metal materials with very low resistance, which does not affect the conduction of low and weak currents. In addition, the alloying of the bonding makes the tensile strength of the adhesion particularly strong, which can effectively avoid the scattering of the structure due to impact or thermal expansion of high and low temperatures. The present invention utilizes instant liquid phase bonding technology to completely seal and package the carbon-14 radiation-voltaic nuclear battery, which can effectively achieve complete sealing of the radiation source and fixed position of the transducer device, and can achieve good electrode contact. At the same time, the radiation source can be completely sealed through a unique electrode structure, which can ensure the fixed position of the radiation source and the packaging stability during long-term operation, avoiding the risk of radiation source diffusion and environmental contamination. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The included drawings are used to provide a further understanding of the embodiments of the present application, which constitute a part of the specification, are used to illustrate the implementation of the present application, and together with the text description, explain the principles of the present application. Obviously, the drawings described below are only some embodiments of the present application.

[0032] Figure 1 Shown is a schematic structural diagram of the packaging structure of a nuclear battery according to an embodiment of the present invention.

[0033] Figure 2Shown is a schematic diagram of the upper electrode structure of the packaging structure of a nuclear battery according to an embodiment of the present invention.

[0034] Figure 3 Shown is a schematic diagram of the metal bonding layer structure of the packaging structure of the nuclear battery according to an embodiment of the present invention.

[0035] Figure 4 Shown is a schematic diagram of the stacking structure of the packaging structure of a nuclear battery according to an embodiment of the present invention.

[0036] Figure 5 Shown is a schematic diagram of the outer shell structure of the packaging structure of a nuclear battery according to an embodiment of the present invention.

[0037] Figure 6 to Figure 11 Shown is a schematic structural diagram of each step of the nuclear battery packaging method according to an embodiment of the present invention.

[0038] Component number description

[0039] 1 Packaging unit

[0040] 11. First transducer

[0041] 12. First upper electrode

[0042] 121 grid electrode

[0043] 122 Surround electrode

[0044] 13. First back electrode

[0045] 21 Second transducer

[0046] 22. Second upper electrode

[0047] 221 grid electrode

[0048] 222 Surround Electrode

[0049] 23. Second back electrode

[0050] 31. Radioactive source film

[0051] 41 Metal bonding layer

[0052] 411 Ring metal part

[0053] 412 Lead out metal part

[0054] 51 Back metal layer

[0055] 61 Plastic layer

[0056] 71 Battery housing

[0057] 72 Battery cover

[0058] 73 Battery pin DETAILED DESCRIPTION

[0059] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0060] It should be emphasized that the term “include / comprises” when used herein refers to the presence of features, integers, steps or components, but does not exclude the presence or addition of one or more other features, integers, steps or components.

[0061] Features described and / or illustrated with respect to one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments.

[0062] For example, when describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional view showing the device structure will not be partially enlarged according to the general scale, and the schematic view is only an example, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional space dimensions of length, width and depth should be included.

[0063] For ease of description, spatially relative terms such as "under", "below", "below", "below", "above", "on", etc. may be used herein to describe the relationship of one element or feature shown in the drawings to other elements or features. It will be understood that these spatially relative terms are intended to encompass other orientations of the device in use or operation in addition to the orientation depicted in the drawings. In addition, when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present.

[0064] In the context of the present application, a structure in which a first feature is described as being "above" a second feature may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0065] It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and therefore the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0066] The parallel integrated packaging of radiation-type nuclear batteries needs to meet the following structures in physical principles: the positive poles of all devices need to be connected and conducted; the negative poles of all devices need to be connected and conducted; but during the conduction of the positive and negative poles of each device, the positive and negative poles of each device need to be independent of each other to avoid crossover, and be separately connected to the power management system, which is connected to the bus. Based on this, the present invention provides a packaging structure of a nuclear battery (such as a carbon-14 radiation-type nuclear battery), the packaging structure mainly includes a silicon carbide transducer device, a radioactive source film, an electrode sheet, wiring and insulation.

[0067] Based on the basic principles, the current radiation-nuclear battery packaging needs to increase the volume power density as much as possible while ensuring the packaging stability. After research and analysis, there are several difficulties in the packaging of carbon-14 radiation-nuclear batteries:

[0068] 1) Extremely difficult volume control. The output power of a nuclear battery is relatively low, generally tens of nanowatts. In order to control the volume per unit volume (1cm 3 )To achieve higher power density, we need to stack more transducers and radiation sources, which has strict requirements on the thickness of any component. Too thick or too large will affect the volume power density.

[0069] 2) How to combine the radiation source with the device. Carbon-14 radiation source is different from metal radiation sources such as nickel-63. Carbon-14 radiation source is non-conductive and highly insulator. It is impossible to directly connect the electrode to the radiation source in the same way as Russian diamond. Moreover, beta rays are particularly easy to be scattered. It is best for the radiation source to be in direct contact with silicon carbide. Adding any material in the middle will greatly affect the incidence of the rays. This means that where there is a radiation source, there cannot be other things, and where there are other things, there cannot be a radiation source, otherwise it will affect the efficiency of the device and increase the cost. However, if the coverage area of ​​the electrode is insufficient, it is very easy for the electrical energy generated by the radiation source to not be collected by the electrode, resulting in unnecessary losses. Therefore, increasing the collection of electrical signals by the electrode and increasing the contact area of ​​the radiation source to generate more electrical signals are contradictory in themselves.

[0070] 3) Stability of the connection between electrodes and structures. In order to ensure volume power density, 100 or more silicon carbide and radiation source combinations need to be stacked in a small volume. The connection stability of each piece needs to be guaranteed, and it must not fall off in high temperature, low temperature, vibration and other environments. The power of a single nuclear battery is very low, and a sufficient number of them need to be connected in parallel to achieve high output. If they fall off due to vibration and other reasons, the overall output will be reduced, and the fallen parts are very likely to short-circuit other structures.

[0071] Based on the above, if Figure 1 to Figure 5As shown, this embodiment provides a packaging structure of a nuclear battery, the packaging structure includes at least one packaging unit 1, the packaging unit 1 includes: a first transducer 11 and a second transducer 21, respectively including a first surface and a second surface opposite to each other, the first surface of the first transducer 11 is provided with a first upper electrode 12, and the second surface is provided with a first back electrode 13, the first surface of the second transducer 21 is provided with a second upper electrode 22, and the second surface is provided with a second back electrode 23, the first upper electrode 12 and the second upper electrode 22 include grid electrodes 121, 221 and surrounding electrodes 122, 222 surrounding the grid electrodes 121, 221 and connected to the grid electrodes 121, 221; a radiation source film 31, the radiation source film 31 is provided between the grid electrode 121 of the first upper electrode 12 and the grid electrode 221 of the second upper electrode 22; a metal bonding layer 41, including an annular metal layer bonded between the surrounding electrodes of the first upper electrode 12 and the second upper electrode 22, and a lead-out metal portion 412 connected to one side of the annular metal portion 411 and extending outside the surrounding metal portion.

[0072] In one embodiment, Figure 1 As shown, the radiation source film 31 includes a β radiation source film 31, which includes a solidified film containing carbon-14, and the thickness of the radiation source film 31 is 20 microns to 50 microns. The size of the radiation source film 31 is smaller than the inner diameter of the surrounding electrode. The radioactive isotope carbon-14 has pure β radioactivity, and the average energy of the β particles is 49.47keV and 156.475keV. The energy is moderate and does not contain accompanying γ rays, which is suitable for use as a radiation source for a β radiation voltaic effect nuclear battery. In a specific example, the area of ​​the radiation source film 31 can be 7 mm×7 mm to 7.5 mm×7.5 mm.

[0073] In one embodiment, Figure 4 As shown, the first transducer 11 and the second transducer 21 further include a back metal layer 51, which covers the surface of the first back electrode 13 and the second back electrode 23, and extends from the other side opposite to the lead-out metal portion 412 to the outside of the first back electrode 13 and the second back electrode 23. The back metal layer 51 and the lead-out metal portion 412 are respectively led out from different two sides, which can greatly reduce the difficulty of subsequent pinning, thereby effectively reducing the cost of nuclear battery design and manufacturing.

[0074] In one embodiment, the back metal layer 51 includes a main metal layer, a bonding layer is plated on the surface of the main metal layer, the thickness of the main metal layer is 40 microns to 60 microns, and the thickness of the bonding layer is greater than 200 nanometers. For example, the main metal layer can be copper foil or nickel foil, and the bonding layer can be, for example, thermosetting silver paste.

[0075] In one embodiment, the first transducer 11 and the second transducer 21 include a silicon carbide PIN junction epitaxial wafer, and the thickness of the silicon carbide PIN junction epitaxial wafer is 100 microns to 200 microns. The first transducer 11 and the second transducer 21 are used to convert the decay energy of the radiation source film 31 into electrical energy.

[0076] In one embodiment, Figure 2 As shown, the total electrode area of ​​the first upper electrode 12 and the second upper electrode 22 occupies less than 20% of the upper surface area of ​​the first transducer 11 and the second transducer 21 respectively, which does not occupy too much transducer area and provides a good non-blocking area for transducer incidence as much as possible.

[0077] In one embodiment, Figure 2 As shown, the grid line width of the grid electrodes 121 and 221 is 30 microns to 60 microns, the spacing between two adjacent grid lines is 1.2 mm to 2 mm, the frame width of the surrounding electrodes 122 and 222 is 0.4 mm to 1 mm, and the distance between the outer side of the surrounding electrodes 122 and 222 and the upper surface edge of the first transducer 11 and the second transducer 21 is 1 mm to 2 mm. In a specific example, the size of the first transducer 11 and the second transducer 21 is 10 mm × 10 mm, and the thickness is reduced to 100 microns to 200 microns. The structure of the grid electrodes 121 and 221 of the first upper electrode 12 and the second upper electrode 22 can be, for example, 25 grids, 5 grids distributed horizontally and 5 grids distributed vertically, wherein the internal grid electrode width is 50 microns, and the spacing between two adjacent grid electrodes is 1.44 mm. The width of the surrounding electrode is 0.5 mm, and the outermost frame is 8.8 mm long. Of course, the electrode width, spacing, number of grids, etc. of the grid electrodes 121 and 221 can be set according to the actual required parameters. For example, the number of grids can be 36 grids, with 6 grids distributed horizontally and 6 grids distributed vertically; 49 grids, with 7 grids distributed horizontally and 7 grids distributed vertically; 64 grids, with 8 grids distributed horizontally and 8 grids distributed vertically, etc., and are not limited to the examples listed above.

[0078] In one embodiment, the thickness of the first upper electrode 12 and the second upper electrode 22 is greater than 200 nanometers, and their outermost layer is a nickel layer. The first back electrode 13 and the second back electrode 23 fully cover the second surface of the first transducer 11 and the second transducer 21, with a thickness of 80 nanometers to 200 nanometers, and their outermost layer is a nickel layer or a gold layer.

[0079] In one embodiment, Figure 3 As shown, the metal bonding layer 41 includes a main metal layer, and the bonding layer is plated on both surfaces of the main metal layer. The melting point of the bonding layer is lower than that of the main metal layer and the first upper electrode 12 and the second upper electrode 22, and the bonding layer diffuses into the main metal layer and the first upper electrode 12 and the second upper electrode 22 to form a homogenized alloy to achieve bonding.

[0080] In one embodiment, Figure 3 As shown, the thickness of the main metal layer is 35 microns to 50 microns, the overall width of the main metal layer can be 10 mm to 15 mm, and the length can be 10 mm to 30 mm. An opening is provided in the main metal layer to form an annular metal layer around the opening. The width of the opening is preferably consistent with the overall width of the grid electrodes 121, 221, and the width of the opening is greater than the width of the radiation source film 31. The width of the opening can be 7.5 mm×7.5 mm to 7.8 mm×7.8 mm. The thickness of the bonding layer is 1 micron to 10 microns, the frame width of the annular metal layer is greater than or equal to the frame width of the surrounding electrode, the main metal layer includes a nickel layer, and the bonding layer includes a tin layer.

[0081] In one embodiment, Figure 4 As shown, the package structure includes at least two package units 1, wherein the back electrodes of two adjacent package units 1 are bonded through a back metal layer 51 to form a three-dimensional stacked package structure. The present invention seals and leads the first end electrode of the package structure from one side through the metal bonding layer 41, and bonds the adjacent package units 1 through the back metal layer 51 and leads the second end electrode of the package structure from the other side, so that more package units 1 can be vertically stacked according to actual needs. There is no specific limit on the number of stackings, and 2 to 100 or even more package units 1 can be stacked, which greatly improves the volume power density of the package structure.

[0082] In one embodiment, Figure 4 As shown, the three-dimensional stacked packaging structure also includes a plastic layer 61, which is arranged between the lead-out metal parts 412 of two adjacent packaging units 1. The thickness of the plastic layer 61 can be, for example, 235 microns to 350 microns. On the one hand, the plastic layer 61 can further strengthen the mechanical strength of the packaging structure, greatly improve the sealing of the packaging structure, and avoid the risk of leakage. On the other hand, the plastic layer 61 is arranged between adjacent metal bonding layers 41 and between adjacent back metal layers 51, which can ensure the insulation between the metal bonding layers 41 and the insulation between the back metal layers 51.

[0083] In one embodiment, Figure 5 As shown, the packaging structure may further include a battery shell 71, a battery top cover 72 and a battery pin 73, wherein the metal bonding layer 41 and the back metal layer 51 may be electrically led out to the corresponding battery pin 73 respectively, and a sealed cavity is formed by a sealed connection between the battery shell 71 and the battery cover top, and the packaging structure is further sealed into the sealed cavity.

[0084] This embodiment also provides a packaging method for a packaging structure of a nuclear battery, wherein the packaging structure includes a packaging unit 1, and the preparation of the packaging unit 1 includes the following steps:

[0085] like Figure 6-7 As shown, firstly, step 1) is performed to provide a first transducer 11 and a second transducer 21, which respectively include a first surface and a second surface opposite to each other, the first surface of the first transducer 11 is provided with a first upper electrode 12, and the second surface is provided with a first back electrode 13, the first surface of the second transducer 21 is provided with a second upper electrode 22, and the second surface is provided with a second back electrode 23, the first upper electrode 12 and the second upper electrode 22 include grid electrodes 121, 221 and surrounding electrodes 122, 222 surrounding the grid electrodes 121, 221 and connected to the grid electrodes 121, 221.

[0086] In one embodiment, the transducer wafer is first thinned to 100 microns to 200 microns. Then, an upper electrode is formed on the surface of each transducer on the transducer wafer, such as Figure 6 As shown, the wafer is then sliced ​​into single pieces of transducer devices using a laser slicer, and the slice size is 10 mm×10 mm. In a specific example, the structure of the grid electrodes 121 and 221 of the upper electrode can be, for example, 25 grids, 5 grids distributed horizontally and 5 grids distributed vertically, wherein the width of the internal grid electrode is 50 microns, and the spacing between two adjacent grid electrodes is 1.44 mm. The width of the surrounding electrodes 122 and 222 is 0.5 mm, and the outermost frame is 8.8 mm long.

[0087] The grid electrodes 121 , 221 and the surrounding electrodes 122 , 222 are fully connected and conductive on the surface, and other areas outside the grid electrodes 121 , 221 and the surrounding electrodes 122 , 222 are not covered with electrodes.

[0088] The outermost metal layer of the grid electrodes 121, 221 and the surrounding electrodes 122, 222 is nickel (Ni) with a thickness greater than 200 nanometers. The back electrode is a full-cover electrode, and the outermost layer of the material is nickel (Ni) or gold (Au) with a thickness of 80 nanometers to 200 nanometers.

[0089] like Figure 8 As shown, step 2) is then performed to provide a metal bonding layer 41, the metal bonding layer 41 includes an annular metal layer corresponding to the surrounding electrode and a lead-out metal portion 412 connected to one side of the annular metal portion 411 and extending outside the surrounding metal portion, the metal bonding layer 41 includes a main metal layer, and the two surfaces of the main metal layer are plated with a bonding layer, the melting point of the bonding layer is lower than the main metal layer and the first upper electrode 12 and the second upper electrode 22, the first upper electrode 12 of the first transducer 11 is aligned with the annular metal portion 411 and placed on one side of the metal bonding layer 41.

[0090] In one embodiment, a nickel foil with a thickness of 35 microns to 50 microns can be prepared, and a layer of tin metal with a thickness of 1 micron to 10 microns can be electroplated or electron beam evaporated on the surface of the nickel foil. The nickel foil has a width of 10 mm to 15 mm and a length of 10 mm to 30 mm. An opening is dug in the middle of one side, and the opening width is 7.5 mm×7.5 mm-7.8 mm×7.8 mm.

[0091] During the packaging process, the first transducer 11 may be placed in a fixed frame first, and then a metal bonding layer 41 may be placed thereon.

[0092] like Fig. 9 As shown, step 3) is then performed to provide a radiation source film 31 and fix the radiation source film 31 on the grid electrode 121 of the first transducer 11 .

[0093] In one embodiment, the radiation source film 31 includes a β radiation source film 31, the β radiation source film 31 includes a solidified film containing carbon-14, the thickness of the radiation source film 31 is 20 microns to 50 microns, and the size of the radiation source film 31 is smaller than the inner diameter of the surrounding electrode. In a specific example, the area of ​​the radiation source film 31 can be 7 mm×7 mm to 7.5 mm×7.5 mm.

[0094] like Fig.10 As shown, the next step is to perform step 4), aligning the second upper electrode 22 of the second transducer 21 with the annular metal portion 411 and placing them on the other surface of the metal bonding layer 41 .

[0095] In one embodiment, the grid electrodes 121 , 221 and the surrounding electrodes 122 , 222 of the first transducer 11 and the second transducer 21 are arranged opposite to each other, and both the grid electrodes 121 , 221 and the surrounding electrodes 122 , 222 are positive electrodes.

[0096] like Fig.10 As shown, step 5) is then performed to form an instantaneous liquid film on the bonding layer through rapid annealing and keep it warm, so that the bonding layer diffuses into the main metal layer and the first upper electrode 12 and the second upper electrode 22 to form a homogenized alloy, so as to bond the metal bonding layer 41 with the first upper electrode 12 and the second upper electrode 22.

[0097] In one embodiment, the structure is placed in an RTP rapid annealing furnace or other heating furnace. In a nitrogen atmosphere, the temperature is raised to 200°C to 350°C, kept warm for 3min to 60min, and then cooled to room temperature. The present invention uses a bonding material with a lower melting point than the metal bonding layer 41 and the electrode as an intermediate interlayer between the metal bonding layer 41 and the surface electrode. When heated to the connection temperature, the intermediate interlayer melts and forms an instantaneous liquid film on the bonding surface. During the insulation process, as the low-melting point component diffuses to the metal bonding layer 41 and the electrode, the thickness of the liquid film decreases until it disappears. After a certain period of insulation, the composition is homogenized. The generation of the liquid phase sandwiches the intermediate interlayer material between the connected surfaces, applies a certain pressure, or relies on the weight of the workpiece to make contact with each other. The unique feature of the present invention is that the liquid phase bonding interface solidifies by diffusion rather than cooling below the melting point, so that a lower process temperature can be achieved, and at the same time, a higher temperature stability can be achieved after bonding, and it is not easy to debond. Moreover, the essence of this process is metal alloying. The entire contact position is made of metal materials with very low resistance, which does not affect the conduction of low and weak currents. In addition, the alloying of the bonding makes the adhesion tensile strength particularly strong, which can effectively prevent the structure from falling apart due to impact or thermal expansion at high and low temperatures. The present invention utilizes an instantaneous liquid phase bonding process to completely seal and package the carbon-14 radiation-voltaic nuclear battery, which can effectively achieve complete sealing of the radiation source and fixed position of the transducer device, and can achieve good electrode contact. At the same time, the radiation source can be completely sealed through a unique electrode structure, which can ensure the fixed position of the radiation source and the stability of the packaging during long-term operation, avoiding the risk of radiation source diffusion and environmental contamination.

[0098] In one embodiment, bonding the metal bonding layer 41 to the first upper electrode 12 and the second upper electrode 22 also includes applying pressure between the metal bonding layer 41 and the first upper electrode 12 and the second upper electrode 22 to enhance the contact between the bonding layer and the first upper electrode 12 and the second upper electrode 22 .

[0099] In one embodiment, at least two packaging units 1 can also be prepared, wherein the back electrodes of two adjacent packaging units 1 are bonded by the back metal layer 51 to form a three-dimensional stacked packaging structure, and more packaging units 1 can be repeatedly prepared until the required power is reached.

[0100] like Fig.11 As shown, step 6) is finally performed. The packaging method further includes the steps of: forming a plastic packaging layer 61 on the side of the three-dimensional stacked packaging structure, and the plastic packaging layer 61 is arranged between the lead-out metal parts 412 of two adjacent packaging units 1.

[0101] As described above, the packaging structure and packaging method of the nuclear battery of the present invention have the following beneficial effects:

[0102] In order to solve the problem of difficult volume control, the present invention does not add any supporting structure, abandons all PCB board solutions, uses as little material as possible for internal connections, and makes the entire structure self-supporting. In addition, the thickness of each component of the present invention is relatively thin, basically ranging from ten to a hundred microns, which can greatly increase the number of stacking within a certain volume and improve the volume power density.

[0103] The present invention makes the surface electrode into a grid structure, and uses the grid structure to divide the entire silicon carbide area into blocks, ensuring that there are some electrodes near each block. At the same time, the duty cycle of the total electrode area is about 20%, which does not occupy too much transducer area and tries to provide a good non-blocking area for transducer incidence.

[0104] The present invention uses a bonding material with a lower melting point than the metal bonding layer 41 and the electrode as an intermediate layer between the metal bonding layer 41 and the surface electrode. When heated to the connection temperature, the intermediate layer melts and forms an instantaneous liquid film on the bonding surface. During the heat preservation process, as the low melting point component diffuses to the metal bonding layer 41 and the electrode, the thickness of the liquid film decreases until it disappears. After a certain period of heat preservation, the composition is homogenized. The generation of the liquid phase sandwiches the intermediate layer material between the connected surfaces, applies a certain pressure, or relies on the deadweight of the workpiece to make contact with each other. The unique feature of the present invention is that the liquid phase bonding interface solidifies by diffusion rather than cooling below the melting point, so that a lower process temperature can be achieved, and a higher temperature stability can be achieved after bonding, and it is not easy to debond. Moreover, the essence of the process is metal alloying, and the entire contact position is made of metal materials with very low resistance, which does not affect the conduction of low and weak currents. In addition, the alloying of the bonding makes the adhesion particularly strong in tensile strength, which can effectively avoid the scattering of the structure due to impact or thermal expansion of high and low temperatures. The present invention utilizes instant liquid phase bonding technology to completely seal and package the carbon-14 radiation-voltaic nuclear battery, which can effectively achieve complete sealing of the radiation source and fixed position of the transducer device, and can achieve good electrode contact. At the same time, the radiation source can be completely sealed through a unique electrode structure, which can ensure the fixed position of the radiation source and the packaging stability during long-term operation, avoiding the risk of radiation source diffusion and environmental contamination.

[0105] Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

[0106] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A packaging structure of a nuclear battery, characterized in that: The packaging structure includes at least one packaging unit, and the packaging unit includes: The first transducer and the second transducer respectively include a first surface and a second surface opposite to each other, the first surface of the first transducer is provided with a first upper electrode, the second surface is provided with a first back electrode, the first surface of the second transducer is provided with a second upper electrode, the second surface is provided with a second back electrode, the first upper electrode and the second upper electrode include a grid electrode and a surrounding electrode surrounding the grid electrode and connected to the grid electrode; A radiation source film, wherein the radiation source film is disposed between the grid electrode of the first upper electrode and the grid electrode of the second upper electrode; The metal bonding layer includes an annular metal layer bonded between the first upper electrode and the surrounding electrodes of the second upper electrode and a lead-out metal portion connected to one side of the annular metal portion and extending outside the surrounding metal portion.

2. The packaging structure of a nuclear battery according to claim 1, characterized in that: The radiation source film comprises a β radiation source film, the β radiation source film comprises a solidified film containing carbon-14, the thickness of the radiation source film is 20 microns to 50 microns, and the size of the radiation source film is smaller than the inner diameter of the surrounding electrode.

3. The packaging structure of a nuclear battery according to claim 1, characterized in that: The first transducer and the second transducer further include a back metal layer, which covers the surface of the first back electrode and the second back electrode and extends from the other side opposite to the lead-out metal portion to outside the first back electrode and the second back electrode.

4. The packaging structure of a nuclear battery according to claim 3, characterized in that: The back metal layer comprises a main metal layer, a bonding layer is plated on the surface of the main metal layer, the thickness of the main metal layer is 40 micrometers to 60 micrometers, and the thickness of the bonding layer is greater than 200 nanometers.

5. The packaging structure of a nuclear battery according to claim 1, characterized in that: The first transducer and the second transducer include a silicon carbide PIN junction epitaxial wafer, and the thickness of the silicon carbide PIN junction epitaxial wafer is 100 microns to 200 microns.

6. The packaging structure of a nuclear battery according to claim 1, characterized in that: The total electrode area of ​​the first upper electrode and the second upper electrode accounts for less than 20% of the upper surface area of ​​the first transducer and the second transducer respectively.

7. The packaging structure of a nuclear battery according to claim 1, characterized in that: The grid line width of the grid electrode is 30 microns to 60 microns, the spacing between two adjacent grid lines is 1.2 mm to 2 mm, the frame width of the surrounding electrode is 0.4 mm to 1 mm, and the distance between the outer edge of the surrounding electrode and the edge of the upper surface of the first transducer and the second transducer is 1 mm to 2 mm.

8. The packaging structure of a nuclear battery according to claim 1, characterized in that: The thickness of the first upper electrode and the second upper electrode is greater than 200 nanometers, and their outermost layer is a nickel layer. The first back electrode and the second back electrode fully cover the second surface of the first transducer and the second transducer, and the thickness is 80 nanometers to 200 nanometers, and their outermost layer is a nickel layer or a gold layer.

9. The packaging structure of a nuclear battery according to claim 1, characterized in that: The metal bonding layer includes a main metal layer, and the bonding layer is plated on both surfaces of the main metal layer. The melting point of the bonding layer is lower than that of the main metal layer and the first and second upper electrodes, and the bonding layer diffuses into the main metal layer and the first and second upper electrodes to form a homogenized alloy to achieve bonding.

10. The packaging structure of a nuclear battery according to claim 9, characterized in that: The thickness of the main metal layer is 35 microns to 50 microns, the thickness of the bonding layer is 1 micron to 10 microns, the frame width of the annular metal layer is greater than or equal to the frame width of the surrounding electrode, the main metal layer includes a nickel layer, and the bonding layer includes a tin layer.

11. The packaging structure of a nuclear battery according to claim 1, characterized in that: It comprises at least two packaging units, wherein the back electrodes of two adjacent packaging units are bonded via a back metal layer to form a three-dimensional stacked packaging structure.

12. The packaging structure of a nuclear battery according to claim 11, characterized in that: The three-dimensional stacked packaging structure further includes a plastic packaging layer, and the plastic packaging layer is arranged between the lead-out metal parts of two adjacent packaging units.

13. A packaging method for a nuclear battery packaging structure according to any one of claims 1 to 12, characterized in that: The packaging structure includes a packaging unit, and the preparation of the packaging unit includes the steps of: Providing a first transducer and a second transducer, comprising a first surface and a second surface opposite to each other, wherein the first surface of the first transducer is provided with a first upper electrode, and the second surface is provided with a first back electrode, and the first surface of the second transducer is provided with a second upper electrode, and the second surface is provided with a second back electrode, and the first upper electrode and the second upper electrode comprise a grid electrode and a surrounding electrode surrounding the grid electrode and connected to the grid electrode; Providing a metal bonding layer, the metal bonding layer comprising an annular metal layer corresponding to the surrounding electrode and a lead-out metal portion connected to one side of the annular metal portion and extending outside the surrounding metal portion, the metal bonding layer comprising a main metal layer, both surfaces of the main metal layer are plated with bonding layers, the melting point of the bonding layer is lower than that of the main metal layer and the first and second upper electrodes, aligning the first upper electrode of the first transducer with the annular metal portion and placing them on one side of the metal bonding layer; Providing a radiation source film, and fixing the radiation source film on the grid electrode of the first transducer; aligning a second upper electrode of the second transducer with the annular metal portion and placing the second upper electrode on the other surface of the metal bonding layer; The bonding layer is formed into a transient liquid film by rapid annealing and kept warm, so that the bonding layer diffuses into the main metal layer and the first upper electrode and the second upper electrode to form a homogenized alloy, so as to bond the metal bonding layer with the first upper electrode and the second upper electrode.

14. The packaging method of the nuclear battery packaging structure according to claim 13, characterized in that: When bonding the metal bonding layer to the first upper electrode and the second upper electrode, it also includes applying pressure between the metal bonding layer and the first upper electrode and the second upper electrode to enhance the contact between the bonding layer and the first upper electrode and the second upper electrode.

15. The packaging method of the nuclear battery packaging structure according to claim 14, characterized in that: The bonding layer is formed into an instant liquid film by rapid annealing and is kept warm, comprising: keeping the packaging structure warm for 3 minutes to 60 minutes in a nitrogen atmosphere at a temperature of 200° C. to 350° C.

16. The packaging method of the nuclear battery packaging structure according to claim 13, characterized in that: At least two of the packaging units are prepared, wherein the back electrodes of two adjacent packaging units are bonded via a back metal layer to form a three-dimensional stacked packaging structure.

17. The packaging structure of a nuclear battery according to claim 16, characterized in that: The step further includes: forming a plastic encapsulation layer on the side of the three-dimensional stacked encapsulation structure, wherein the plastic encapsulation layer is arranged between the lead-out metal parts of two adjacent encapsulation units.

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