A thermoelectric die bonding method

Abstract

The application provides a thermoelectric crystal grain welding method, which is based on existing alloy solder welding technology, constructs a metalized graphene flexible layer at a welding interface, and realizes stable metallurgical connection of the graphene and an electrode layer through a hot-press bonding method. Through design of welding interface materials and structures of the thermoelectric device, the welding interface thermal stress matching is optimized under the condition that the heat and electricity transmission performance and force connection stability are not affected, and the nickel metalized graphene structure can effectively play a role of a copper atom barrier layer, which is beneficial to improving the device stability and long-term stable service ability.

Description

Technical Field

[0001] This invention relates to the field of thermoelectric device manufacturing technology, and in particular to a thermoelectric grain welding method. Background Technology

[0002] In the manufacturing process of thermoelectric devices, after the thermoelectric material is metallized to form electrodes, it needs to be connected to the metal electrodes of the packaging substrate. Currently, the main methods used are soldering or brazing, where alloy solder is filled at the connection interface and solidified to achieve integration. The temperature is generally around 250–400℃. The working principle is that the metal elements composing the solder form a eutectic structure at low temperatures. Soldering methods are widely used in electronic manufacturing and have advantages in terms of cost and process maturity. In addition, technologies such as arc spraying, thermocompression bonding, and spark plasma sintering (SPS) have been applied to the packaging manufacturing of thermoelectric devices, offering greater connection strength and lower interface resistance and thermal resistance, while being more suitable for high-temperature operation. However, with existing welding technologies, thermal stress during the service life of thermoelectric devices can cause new cracks and defects to form at the weld interface.

[0003] Therefore, finding a suitable welding method to solve the problems caused by existing welding technologies has become one of the focal points of widespread attention for many forward-thinking researchers in the field. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a thermoelectric grain welding method. The present invention achieves a stable metallurgical connection between graphene and metal electrodes by encapsulating a single-layer or multi-layer metallized graphene structure at the connection interface, while simultaneously leveraging the role of the graphene structure in regulating interfacial thermal stress and enhancing the welding interface's ability to absorb thermal stress.

[0005] This invention provides a thermoelectric grain welding method, comprising the following steps:

[0006] 1) A nano-metal needle-cone structure is prepared on the surface of the copper structure layer of a copper-clad substrate to obtain a copper-clad substrate with nano-metal needle-cones on the surface.

[0007] A copper metal layer was deposited on graphene to obtain a graphene-copper composite material;

[0008] 2) Transfer the graphene-copper composite material to the surface of a copper-clad substrate, so that the copper metal layer faces the copper-clad substrate, then deposit nickel metal on the graphene surface, and then obtain a semi-finished product after hot pressing.

[0009] 3) The semiconductor die with a metal barrier layer deposited on its surface and the semi-finished product obtained in the above steps are soldered together to obtain a single-sided integrated package of the thermoelectric die and the copper-clad substrate.

[0010] Preferably, the nano-metal needle cone includes a nano-copper needle cone;

[0011] The diameter of the base of the nano-metal needle is 20–50 nm;

[0012] The length of the nano-metal needle is 10–30 nm.

[0013] Preferably, the copper clad layer on the surface of the copper-clad substrate is a patterned copper structure layer;

[0014] The copper-clad substrate includes a copper-clad ceramic substrate.

[0015] Preferably, the graphene is a graphene film.

[0016] The graphene includes single-layer graphene or multi-layer graphene.

[0017] Preferably, the specific preparation steps of the graphene-copper composite material include: preparing a graphene film on a substrate, transferring it to a transfer medium, dissolving and removing the substrate, and then depositing a copper metal layer on the graphene surface;

[0018] The thickness of the copper metal layer is 5–10 nm;

[0019] The thickness of the nickel metal layer is 5–10 nm.

[0020] Preferably, the substrate comprises copper foil;

[0021] The transfer medium includes PMMA;

[0022] The process before hot pressing also includes an annealing step.

[0023] Preferably, the pressure of the hot pressing is 1-5 MPa;

[0024] The hot pressing temperature is 250–350°C;

[0025] The hot pressing time is greater than or equal to 30 minutes.

[0026] Preferably, the semiconductor grains with metal barrier layers deposited on their surfaces include semiconductor grains with metal barrier layers deposited on both sides;

[0027] The semiconductor grains include bismuth antimonide grains;

[0028] The semiconductor die is soldered to the copper-clad substrate from the side with the deposited metal barrier layer.

[0029] Preferably, the semiconductor grain includes one or more sets of PN-type cuboid grain thermocouple pairs;

[0030] The thickness of the nickel layer is 1–3 μm.

[0031] Preferably, the solder comprises a eutectic alloy solder;

[0032] The welding method includes vacuum reflow soldering;

[0033] The welding method also includes the step of welding the other side of the semiconductor die to the copper-clad substrate.

[0034] This invention provides a method for welding thermoelectric grains, comprising the following steps: First, a nano-metal needle-like structure is prepared on the surface of a copper structural layer of a copper-clad laminate to obtain a copper-clad laminate with nano-metal needles on its surface; a copper metal layer is deposited on graphene to obtain a graphene-copper composite material; then, the graphene-copper composite material is transferred to the surface of the copper-clad laminate, with the copper metal layer facing the copper-clad laminate; then, nickel metal is deposited on the graphene surface, followed by hot pressing to obtain a semi-finished product; finally, a semiconductor grain with a metal barrier layer deposited on its surface and the semi-finished product obtained in the above steps are welded together with solder to obtain a single-sided integrated package of the thermoelectric grain and the copper-clad laminate. Compared with the prior art, this invention addresses the defect of existing welding techniques, which can lead to the formation of new cracks at the welding interface due to thermal stress during the service of thermoelectric devices. This invention suggests that by designing the interface materials and structure, the thermal stress matching at the welding interface can be optimized to a certain extent.

[0035] Based on this, the present invention provides a specific thermoelectric grain welding method. Building upon existing alloy solder welding technology, a metallized graphene flexible layer is constructed at the welding interface, and a stable metallurgical connection is achieved between the graphene and the electrode layer via hot-press bonding. By designing the welding interface material and structure of the thermoelectric device, the present invention optimizes the thermal stress matching of the welding interface without affecting the heat and electrical transfer performance and the stability of the force connection. Simultaneously, the nickel-metallized graphene structure effectively utilizes the copper atom barrier layer, which is beneficial for improving the stability and long-term stable service capability of the device. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a welding method provided in an embodiment of the present invention. Detailed Implementation

[0037] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention and not for limiting the claims of the present invention.

[0038] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0039] There are no particular restrictions on the purity of any of the raw materials used in this invention. It is preferred to use analytical grade or the purity commonly used in the field of thermoelectric device manufacturing.

[0040] This invention provides a thermoelectric grain welding method, comprising the following steps:

[0041] 1) A nano-metal needle-cone structure is prepared on the surface of the copper structure layer of a copper-clad substrate to obtain a copper-clad substrate with nano-metal needle-cones on the surface.

[0042] A copper metal layer was deposited on graphene to obtain a graphene-copper composite material;

[0043] 2) Transfer the graphene-copper composite material to the surface of a copper-clad substrate, so that the copper metal layer faces the copper-clad substrate, then deposit nickel metal on the graphene surface, and then obtain a semi-finished product after hot pressing.

[0044] 3) The semiconductor die with a metal barrier layer deposited on its surface and the semi-finished product obtained in the above steps are soldered together to obtain a single-sided integrated package of the thermoelectric die and the copper-clad substrate.

[0045] The present invention first prepares a nano-metal needle-cone structure on the surface of the copper structure layer of a copper-clad substrate, thereby obtaining a copper-clad substrate with nano-metal needle-cones on the surface.

[0046] A copper metal layer is deposited on graphene to obtain a graphene-copper composite material.

[0047] In this invention, the nano-metal needle cone preferably includes a nano-copper needle cone.

[0048] In this invention, the diameter of the cone base of the nano-metal needle is preferably 20-50 nm, more preferably 25-45 nm, and even more preferably 30-40 nm.

[0049] In this invention, the length of the nano-metal needle is preferably 10-30 nm, more preferably 14-26 nm, and even more preferably 18-22 nm.

[0050] In this invention, the copper cladding layer on the surface of the copper-clad substrate is preferably a patterned copper structure layer.

[0051] In this invention, the copper-clad substrate preferably includes a copper-clad ceramic substrate.

[0052] In this invention, the graphene is preferably a graphene film layer.

[0053] In this invention, the graphene preferably comprises single-layer graphene or multi-layer graphene.

[0054] In this invention, the specific preparation steps of the graphene-copper composite material preferably include: preparing a graphene film on a substrate, transferring it to a transfer medium, dissolving and removing the substrate, and then depositing a copper metal layer on the graphene surface.

[0055] In this invention, the thickness of the copper metal layer is preferably 5-10 nm, more preferably 6-9 nm, and even more preferably 7-8 nm.

[0056] The present invention further transfers the graphene-copper composite material to the surface of a copper-clad substrate, so that the copper metal layer faces the copper-clad substrate, then deposits nickel metal on the graphene surface, and then obtains a semi-finished product after hot pressing.

[0057] In this invention, the thickness of the nickel metal layer is preferably 5-10 nm, more preferably 6-9 nm, and even more preferably 7-8 nm.

[0058] In this invention, the substrate preferably comprises copper foil.

[0059] In this invention, the transfer medium preferably comprises PMMA.

[0060] In this invention, the hot pressing process preferably includes an annealing step.

[0061] In this invention, the pressure of the hot pressing is preferably 1 to 5 MPa, more preferably 1.5 to 4.5 MPa, more preferably 2 to 4 MPa, and even more preferably 2.5 to 3.5 MPa.

[0062] In this invention, the temperature of the hot pressing is preferably 250-350°C, more preferably 270-330°C, and even more preferably 290-310°C.

[0063] In this invention, the hot pressing time is preferably greater than or equal to 30 min, more preferably greater than or equal to 32 min, and even more preferably greater than or equal to 35 min.

[0064] Finally, the present invention integrates the semiconductor die with a metal barrier layer deposited on its surface and the semi-finished product obtained in the above steps by soldering them together to obtain a single-sided integrated package of the thermoelectric die and the copper-clad substrate.

[0065] In this invention, the semiconductor grains with metal barrier layers deposited on their surfaces preferably include semiconductor grains with metal barrier layers deposited on both sides.

[0066] In this invention, the semiconductor grains preferably include bismuth antimonide grains.

[0067] In this invention, the semiconductor die is preferably soldered to the copper-clad substrate from the side with the metal barrier layer deposited on it.

[0068] In this invention, the semiconductor grain preferably includes one or more sets of PN-type cuboid grain thermocouple pairs.

[0069] In this invention, the thickness of the nickel layer is preferably 1 to 3 μm, more preferably 1.4 to 2.6 μm, and even more preferably 1.8 to 2.2 μm.

[0070] In this invention, the solder preferably comprises a eutectic alloy solder.

[0071] In this invention, the welding method preferably includes vacuum reflow soldering.

[0072] In this invention, the welding method preferably includes the step of welding the other side of the semiconductor die to the copper-clad substrate.

[0073] To complete and refine the overall fabrication process, better ensure welding results, reduce the stress impact on thermoelectric devices, and improve device stability and long-term stable service capability, the following preferred welding method for the aforementioned thermoelectric grains is proposed:

[0074] A thermoelectric grain welding method includes the following steps:

[0075] Step 1: After slicing the bismuth antimonide material, a nickel metal barrier layer is deposited on both sides to form a welding connection surface A. Then, cuboid grains of a certain size are cut out according to the design requirements.

[0076] Step 2: Fabricate nano-copper needle-cone structures on the copper structure layer of a copper-clad ceramic substrate;

[0077] Step 3: Prepare a graphene film on a copper foil, transfer it to a PMMA film, dissolve and remove the copper foil, and then deposit a copper metal layer on the graphene surface;

[0078] Step 4: The graphene prepared in Step 3 is transferred to the surface of the nano-copper needle-cone structure, so that the deposited copper metal layer is connected to the nano-copper needle-cone structure. Then, PMMA is dissolved and removed, and after drying, nickel metal is deposited on the graphene surface. A certain temperature and pressure are applied to the formed structure to achieve metallurgical connection.

[0079] Step 5: Apply eutectic alloy solder to the nickel metal layer described in step 4 by dispensing to form welding connection surface B;

[0080] Step 6: After aligning the two connecting surfaces, complete the welding by reflow soldering.

[0081] Specifically, the graphene can be a single layer or multiple layers.

[0082] Specifically, the nano-copper needle-cone structure has a base diameter of 20–50 nanometers and a length of 10–30 nanometers.

[0083] Specifically, the applied pressure is 1-5 MPa, the temperature is 250-350°C, and the time is more than 30 minutes.

[0084] Specifically, the thickness of the deposited copper and nickel metal layer is 5 to 10 nanometers.

[0085] The above steps of this invention provide a thermoelectric grain welding method. Based on existing alloy solder welding technology, this invention constructs a metallized graphene flexible layer at the welding interface and achieves a stable metallurgical connection between the graphene and the electrode layer through a thermocompression bonding method. By designing the welding interface material and structure of thermoelectric devices, this invention optimizes the thermal stress matching of the welding interface without affecting the heat and electrical transport performance and the stability of the force connection. Simultaneously, the nickel-metallized graphene structure effectively utilizes the copper atom barrier layer, which is beneficial to improving the stability and long-term stable service capability of the device.

[0086] This invention achieves a stable metallurgical connection between graphene and metal electrodes by encapsulating a single-layer or multi-layer metallized graphene structure at the connection interface, while leveraging the role of the graphene structure in regulating interfacial thermal stress and enhancing the welding interface's ability to absorb thermal stress.

[0087] To further illustrate the present invention, the following describes in detail a thermoelectric grain welding method provided by the present invention with reference to embodiments. However, it should be understood that these embodiments are implemented under the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. They are only for further illustrating the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention. The scope of protection of the present invention is not limited to the following embodiments.

[0088] Example 1

[0089] like Figure 1 As shown in the diagram. 1 is a nickel barrier layer, 2 is a hot spot, 3 is a nano-copper metal needle-cone structure layer, 4 is the copper surface layer of the copper-clad ceramic substrate, 5 is the copper-clad ceramic substrate, 6 is the hot plate, 7 is the nickel barrier layer, 8 is the graphene layer in the graphene-copper composite material, 9 is the copper metal layer in the graphene-copper composite material, 10 is the eutectic alloy solder layer, and 11 is the new electrode layer 11.

[0090] The packaging method of the thermoelectric cooling chip of the present invention includes:

[0091] (1) The bonding surface of the thermoelectric element 2 is cleaned using the standard RCA process, and then a 1-micron thick layer of metallic nickel 1 (Ni) is deposited on the substrate by magnetron sputtering. After completion, the substrate is granulated and cleaned to form the welding surface A.

[0092] (2) The copper surface 4 of the copper-clad ceramic substrate 5 is degreased and derusted, and then placed in an electroplating solution (copper sulfate pentahydrate 1.5 mol / L, copper nitrate 0.2 mol / L, ethylenediamine 2 mol / L, boric acid 0.3 mol / L, additives SPS 15 ppm, PEG 1000 ppm, JGB 40 ppm, solution temperature 30℃, pH 5.0). The substrate is used as the cathode, and the copper plate or insoluble electrode plate is used as the anode. A circuit is formed between the substrate, the copper plate, and the electroplating power supply through a wire. A direct current (2 A / dm²) is applied to the substrate through the electroplating power supply. 2 The electroplating time is 60 seconds, forming a nano-copper metal needle-cone structure layer 3.

[0093] (3) Graphene 8 was grown on the copper metal surface of a copper-clad ceramic substrate using CVD. The vacuum degree was less than 10⁻⁴ Torr. The chamber was heated at 1000℃ for 1 hour in H₂ (10 sccm) environment, and a mixed gas of CH₄ (60 sccm) and H₂ (10 sccm) was introduced for 20 minutes. Then, it was cooled to room temperature in H₂ (10 sccm) environment. PMMA was then suspended and coated on the graphene surface. After curing, the copper foil was dissolved and dried. Then, a copper metal layer 9 with a thickness of 5 nm was deposited on the graphene surface using magnetron sputtering.

[0094] (4) Using the copper metal layer deposited in step (3) as the bonding surface, align and bond it with the structural layer 3 formed in step (2). Dissolve and remove PMMA and dry it. Then, deposit a nickel metal layer 7 with a thickness of 10 nanometers on the graphene surface using magnetron sputtering and anneal it at 500°C. Afterward, apply a pressure of 5 MPa and a temperature of 300°C for 30 minutes using a hot plate 6. The nanoneedle-cone structure is then bonded to the copper metal layer of the graphene to form a new electrode layer 11.

[0095] (5) Apply Au to the surface of the nickel metal barrier layer using a dispensing machine. 80 Sn 20 Eutectic alloy solder 10 forms the welding surface B.

[0096] (6) After aligning the two connecting surfaces, the welding is completed by reflow soldering.

[0097] The above provides a detailed description of a thermoelectric grain welding method provided by the present invention. Specific examples have been used to illustrate the principles and implementation methods of the invention. The descriptions of these embodiments are merely for the purpose of helping to understand the method and core ideas of the present invention, including the best mode, and also to enable any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements that are not different from the textual description of the claims, or if they include equivalent structural elements that are not substantially different from the textual description of the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A method for thermoelectric grain welding, characterized in that, Includes the following steps: 1) A nano-metal needle-cone structure is prepared on the surface of the copper structure layer of a copper-clad substrate to obtain a copper-clad substrate with nano-metal needle-cones on the surface. The diameter of the base of the nano-metal needle is 20~50nm; The length of the nano-metal needle-like cone is 10~30nm; A copper metal layer was deposited on graphene to obtain a graphene-copper composite material; The graphene is a graphene film layer; 2) Transfer the graphene-copper composite material to the surface of the copper-clad substrate, so that the copper metal layer faces the nano-metal needles on the surface of the copper-clad substrate. Then, deposit nickel metal on the graphene surface and then hot press to obtain a semi-finished product. The pressure of the hot pressing is 1~5MPa; The hot pressing temperature is 250~350℃; 3) The semiconductor die with a metal barrier layer deposited on its surface and the semi-finished product obtained in the above steps are soldered together to obtain a single-sided integrated package of thermoelectric die and copper-clad substrate.

2. The welding method according to claim 1, characterized in that, The nano-metal needles include nano-copper needles.

3. The welding method according to claim 1, characterized in that, The copper clad layer on the surface of the copper-clad substrate is a patterned copper structure layer; The copper-clad substrate includes a copper-clad ceramic substrate.

4. The welding method according to claim 1, characterized in that, The graphene includes single-layer graphene or multi-layer graphene.

5. The welding method according to claim 1, characterized in that, The specific preparation steps of the graphene-copper composite material include: preparing a graphene film on a substrate, transferring it to a transfer medium, dissolving and removing the substrate, and then depositing a copper metal layer on the graphene surface. The thickness of the copper metal layer is 5~10nm; The thickness of the nickel metal is 5~10 nm.

6. The welding method according to claim 5, characterized in that, The substrate includes copper foil; The transfer medium includes PMMA; The process before hot pressing also includes an annealing step.

7. The welding method according to claim 1, characterized in that, The hot pressing time is greater than or equal to 30 minutes.

8. The welding method according to claim 1, characterized in that, The semiconductor grains with metal barrier layers deposited on their surfaces include semiconductor grains with metal barrier layers deposited on both sides. The semiconductor grains include bismuth antimonide grains; The semiconductor die is soldered to the copper-clad substrate from the side with the deposited metal barrier layer.

9. The welding method according to claim 1, characterized in that, Semiconductor grains include one or more sets of PN-type cuboid grain thermocouple pairs; The metal barrier layer is a nickel layer; The thickness of the nickel layer is 1~3μm.

10. The welding method according to claim 1, characterized in that, The solder includes eutectic alloy solder; The welding method includes vacuum reflow soldering; The welding method also includes the step of welding the other side of the semiconductor die to the copper-clad substrate.

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