A method for high-reliability interconnection of carbon nanotube fibers with metals by brazing

Abstract

The present application relates to the field of reliable interconnection between carbon nanotube fibers and metals, and particularly to a method for realizing high-reliability interconnection between carbon nanotube fibers and metals through brazing. Traditional tin-based brazing filler metal is selected, and a metal substrate to be welded is heated to a predetermined temperature in air by using a plane hot table. After the brazing filler metal alloy is melted and wet-spreads on the surface of the substrate, the part to be welded of the pre-processed carbon nanotube fiber is placed on the surface of the molten liquid brazing filler metal alloy. After the brazing filler metal alloy on the surface of the carbon nanotube fiber is solidified, it is rapidly solidified, thereby realizing brazing interconnection between the carbon nanotube fiber and the metal. In the welding process, the molten brazing filler metal is sprayed with deionized water to realize rapid cooling and solidification, thereby solving the problem that the carbon nanotube fiber and the metal cannot be welded due to large density difference, and solving the problem that the welding is not firm by introducing a high-binding-energy intermediate buffer layer at the part to be welded of the carbon nanotube fiber. The prepared carbon nanotube fiber-metal interconnection part has high service reliability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of reliable interconnection between carbon nanotube fibers and metals, in particular to a method for realizing high-reliability interconnection between carbon nanotube fibers and metals through brazing. BACKGROUND

[0002] Lightweight, high-strength, high-conductivity carbon nanotube fibers are one of the most competitive candidates for the next generation of new wire materials. Carbon nanotube fibers have the characteristics of corrosion resistance, high flexibility, high tensile strength, weak skin effect at high frequency, light weight, etc., and excellent weight reduction effect as a new type of wire material, thus having great application prospects in aerospace, national defense, civil and many other fields. However, due to the chemical inertness of carbon nanotubes, they do not react with metals at medium and low temperatures, and have poor wettability with traditional solder. Therefore, the interconnection between carbon nanotube fibers and metal electrodes in functional elements faces the problems of "not being able to be welded" and "not being able to be welded firmly", which seriously restricts the application of carbon nanotube fibers as circuit wires. Therefore, realizing reliable electrical interconnection between carbon nanotube fibers and metal electrodes is the key to promoting their practical application. At present, representative works to realize the interconnection between carbon nanotube fibers and metals include: (1) half-moon local electrodeposition interconnection (Document 1: Zhao C., Luo Z., Ao S., et al. Carbon, 2017, 125, 269-279); (2) ultrasonic welding interconnection (Document 2: Peng L., Jiang K., Liu M., et al. Appl. Phys. Lett. 2003, 82, 1763-1765); (3) mechanical pressure interconnection (Document 3: Schauerman C.M., Alvarenga J., Staub J., et al. Adv. Eng. Mater. 2015, 17, 76-83.); (4) conductive adhesive interconnection (Document 4: Kim E.J., Luan V.H., Tien H.N., et al. J. Mater. Chem. 2012, 22, 8649-8653); (5) traditional brazing interconnection (Document 5: Burda M., Lekawa-Raus A., Gruszczyk A., et al. ACS Nano 2015, 9(8), 8099-8107). In order to be compatible with integrated circuit, microelectronic device and other production processes, it is necessary to develop a high-reliability interconnection process with lower welding temperature. Among the above interconnection methods, traditional brazing has low cost, simple process and strong operability at relatively low temperature, thus having great application potential in the interconnection of carbon nanotube fibers.

[0003] However, the reliable interconnection of carbon nanotube fibers and metals by brazing currently still faces great challenges: (1) poor wettability of carbon nanotube fibers and brazing filler metal, resulting in low service reliability due to "poor welding"; (2) the density of carbon nanotube fibers is between 1.1-2.0 g / cm3, which is much lower than the density of tin-based solder (6.5-8.8 g / cm3), so the carbon nanotube fibers are easily floated on the surface of the molten liquid solder, resulting in "welding failure" due to separation of the two; (3) although the addition of high content of transition metal elements to the traditional solder formulation can significantly improve the wettability of carbon nanotube fibers and solder alloy (Document five: Burda M., Lekawa-Raus A., Gruszczyk A., et al. ACS Nano 2015, 9(8), 8099-8107), but the welding temperature is high (350℃), which causes a large amount of brittle intermetallic compounds in the welding spot, resulting in a significant decrease in the service reliability of the welding spot; (4) there is a large difference between the thermal expansion coefficient of carbon nanotube fibers and the thermal expansion coefficient of solder alloy, and residual stress is easily generated at the interface of the welding workpiece in the service environment with large temperature changes, thereby causing crack initiation at the interface; (5) the bonding strength of the carbon nanotube fiber and the solder heterogeneous interface is low, resulting in a low service life of the solder.

[0004] In summary, the main problem currently faced is: how to develop a carbon nanotube fiber-metal brazing interconnection method with simple process, low cost and high service reliability without changing the classic component formula of the solder alloy, which is compatible with the traditional brazing micro-interconnection technology process, and solves the problems of "welding failure" and "poor welding" in the brazing interconnection process of carbon nanotube fibers and metal matrix. SUMMARY

[0005] The purpose of the present application is to provide a carbon nanotube fiber-metal high-reliability interconnection method by brazing, which has the advantages of simple process, low cost and high service reliability, solves the problems of "welding failure" and "poor welding" between carbon nanotube fibers and metals, and realizes the reliable interconnection of carbon nanotube fibers and metals.

[0006] The technical solution of the present application is:

[0007] A carbon nanotube fiber-metal high-reliability interconnection method by brazing, which selects a traditional tin-based brazing solder, heats the metal matrix to be welded to a predetermined temperature in air using a flat heat table, spreads the molten solder on the surface of the matrix after the solder ball is molten, places the pre-processed carbon nanotube fiber to be welded on the surface of the molten liquid solder alloy, and solidifies the solder alloy on the surface of the carbon nanotube fiber to realize the brazing interconnection of the carbon nanotube fiber and the metal;

[0008] The pretreatment process of the to-be-welded part of the carbon nanotube fiber is as follows: a nickel plating layer or a copper plating layer is deposited on the to-be-welded part of the carbon nanotube fiber by using an electroplating method, a solder alloy layer is coated on the to-be-welded part of the carbon nanotube fiber by using a mechanical pressure bonding method, and the carbon nanotube fiber to-be-welded sample with mechanical interconnection strength is obtained after being rolled and pressed.

[0009] The solder alloy used in the method for realizing high-reliability interconnection between the carbon nanotube fiber and the metal by brazing is a commercialized classic solder component, including a tin-lead solder, a tin-copper solder, a tin-silver solder or a tin-bismuth solder.

[0010] The contact time of the carbon nanotube fiber with the molten liquid solder alloy is short, and is usually between 3-10s.

[0011] The thickness of the nickel plating layer or the copper plating layer is 0.1-0.7 microns, and the length is 1-2 cm.

[0012] In order to prevent the carbon nanotube fiber from being separated from the liquid solder alloy, the temperature of the molten liquid solder alloy is rapidly reduced to below the melting point by spraying deionized water, so that rapid solidification is realized.

[0013] The spraying time of the deionized water is 2-5s.

[0014] The method for realizing high-reliability interconnection between the carbon nanotube fiber and the metal by brazing improves the bonding strength, wettability and difference in thermal expansion coefficient of the interface between the carbon nanotube fiber and the solder by pretreating the to-be-welded part of the carbon nanotube fiber to modify the surface of the to-be-welded part of the carbon nanotube fiber and prepare an interconnection welding point.

[0015] The interconnection welding point prepared by modifying the to-be-welded part of the carbon nanotube fiber has excellent cold-hot impact resistance in the thermal shock cycle test under extreme environment, and the resistance change rate is less than 30% after 450 cycles of thermal shock test when the temperature is rapidly reduced from 150℃ to -196℃ in 2-5s.

[0016] The design idea of the present application is as follows:

[0017] The present application proposes to use lightweight, high-strength and high-conductivity carbon nanotube fibers as new type of wires, first, the surface of the carbon nanotube fiber to be welded is modified to improve the bonding strength, wettability and the difference of thermal expansion coefficient between the carbon nanotube fiber and the solder; meanwhile, a rapid solidification welding process is developed, through the method of rapid solidification, the controllable preparation of the welding interconnection between the carbon nanotube fiber and the metal matrix is realized, under the premise of not changing the traditional classic solder components, the reliable interconnection between the carbon nanotube fiber and the metal is realized.

[0018] The solder alloy used in the present application is a commercialized classic solder component, without adding transition metal components into the traditional solder alloy, the brazing temperature is not more than 300 DEG C, which guarantees the service reliability of the solder alloy itself, and also realizes the good infiltration between the solder alloy and the carbon nanotube fiber, improves the bonding strength of the carbon nanotube fiber / solder heterogeneous interface, thereby improving the interconnection reliability between the carbon nanotube fiber and the metal matrix. In addition, the present application adopts the electroplating method to deposit a nickel plating layer or a copper plating layer on the welding part of the carbon nanotube fiber, the nickel plating layer or the copper plating layer serves to improve the bonding strength, wettability and the difference of thermal expansion coefficient between the carbon nanotube fiber and the solder.

[0019] The advantages and beneficial effects of the present application are:

[0020] (1) The present application uses a tin-based alloy with traditional classic component ratio as solder, and develops a spraying deionized water rapid cooling welding process, which sprays deionized water on the molten solder to realize rapid cooling and solidification, solving the problem that the carbon nanotube fiber and the metal cannot be welded due to the large difference in density.

[0021] (2) The present application introduces a buffer layer on the surface of the welding part of the carbon nanotube fiber, which significantly improves the wettability of the solder and the carbon nanotube fiber and reduces the difference of thermal expansion coefficient, improves the bonding strength of the interface between the carbon nanotube fiber and the solder alloy, and solves the problem that the carbon nanotube fiber and the metal cannot be firmly welded by introducing a high bonding energy nickel plating layer or a copper plating layer as an intermediate buffer layer on the welding part of the carbon nanotube fiber.

[0022] (3) The present application uses a simple and effective method to get rid of the constraint that transition metal elements must be added to the tin-based solder alloy to obtain a "carbon-based special" solder, and can use traditional classic tin-based solder, which has high compatibility with traditional brazing microelectronic packaging technology and is convenient to apply and popularize.

[0023] (4) The carbon nanotube fiber-metal interconnection prepared by the present application has high service reliability, which lays a foundation for promoting the electrical application of carbon nanotube fibers as lightweight, high-strength and high-conductivity transmission lines. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 (a) Scanning electron microscope image of the surface of the carbon nanotube fiber to be welded with a nickel coating. (b) Backscattered electron morphology of the radial cross section of the nickel-coated carbon nanotube fiber.

[0025] Figure 2 (a) Scanning electron microscope image of the interface between carbon nanotube fiber / nickel plating / solder alloy. (b) Linear scan of nickel from the fiber to the solder interior, with the horizontal axis representing position (μm) and the vertical axis representing intensity (counts).

[0026] Figure 3 Scanning electron microscope image of the carbon nanotube fiber / nickel plating / solder interface after 450 thermal shock tests.

[0027] Figure 4 (a) Scanning electron microscope image of nickel-coated carbon nanotube composite fiber fabric. (b) Contact angle of Sn-37Pb solder ball liquefied by heating at 250°C on the surface of nickel-coated carbon nanotube fiber fabric.

[0028] Figure 5 Scanning electron microscope image of copper plating on the surface of carbon nanotube fibers.

[0029] Figure 6 Scanning electron microscope image of the carbon nanotube fiber / copper plating / solder interface after 450 thermal shock tests.

[0030] Figure 7 Scanning electron microscope image of the carbon nanotube fiber / solder interface without buffer layer modification after 450 thermal shock tests.

[0031] Figure 8 (a) Scanning electron microscope image of carbon nanotube fiber fabric without buffer layer modification. (b) Contact angle of Sn-37Pb solder balls liquefied by heating at 250°C on the surface of carbon nanotube fiber fabric. Detailed Implementation

[0032] In the specific implementation process, this invention proposes a method for achieving highly reliable interconnection between carbon nanotube fibers and metals through brazing. It utilizes electrodeposition technology to introduce a metal buffer layer on the surface of the carbon nanotube fiber to be welded, uses tin-gold alloy as solder, and uses traditional brazing method to achieve interconnection between carbon nanotube fibers and metals.

[0033] First, an electroplating process is used to deposit a metal layer of a certain thickness on the areas of the carbon nanotube fibers to be soldered. The purpose of this is that the presence of a metal buffer layer can improve the bonding strength of the carbon nanotube fiber / solder interface and reduce the residual stress generated by the carbon nanotube fiber and solder alloy in service environments with large temperature variations. Then, tin-based solder is used, and a rapid cooling process is employed to achieve the brazing interconnection between the carbon nanotube fibers and the metal.

[0034] The preparation steps of this method are as follows:

[0035] (1) Pretreatment of carbon nanotube fibers:

[0036] Carbon nanotube fibers are wound around a stainless steel square frame, and the two ends of the fibers are adhered and fixed to the surface of the stainless steel frame with conductive carbon adhesive. A metal plating layer (nickel plating layer) is deposited on the part of the carbon nanotube fiber to be welded using a two-electrode method.

[0037] (2) Brazing process:

[0038] Solder balls are placed on the polished metal substrate surface. A planar hot plate is used to heat both the metal substrate and the solder balls. With the aid of a resin-based flux, the molten solder alloy wets and spreads on the metal substrate surface, thus pre-forming a solder buffer layer on the copper substrate surface. Modified carbon nanotube fibers coated with the solder alloy are then placed on the surface of the molten solder alloy. When the molten liquid solder alloy fully wets and immerses the carbon nanotube fibers, deionized water is sprayed to rapidly solidify the solder alloy, thereby forming a carbon nanotube fiber-metal interconnect conductor.

[0039] The present invention will now be further described in detail with reference to embodiments and accompanying drawings.

[0040] Example 1

[0041] In this embodiment, the carbon nanotube fibers are surface modified using step (1) described above. The length of the nickel plating layer is controlled by adjusting the depth of the carbon nanotube fiber immersion in the electrolyte, and the thickness of the nickel plating layer is controlled by adjusting the plating time. The nickel plating solution consists of 50 g / L nickel sulfate, 10 g / L nickel chloride, 80 g / L sodium citrate, and the remainder is water; the deposition time is 30 s, the temperature is 65 °C, and the current density is 1–1.5 A / dm³. 2 .like Figure 1 As shown in Figure a, the scanning electron microscope image of the surface of the carbon nanotube fiber to be welded, which is coated with a nickel layer, shows that the nickel coating is uniformly coated on the surface of the carbon nanotube fiber, with a thickness of 0.5–0.7 μm. Figure 1 b) The length is 1 to 2 cm.

[0042] The Sn-37Pb eutectic solder ball is placed on the surface of the polished copper substrate by using the above step (2), heated to 250°C to melt the solder ball, and spread on the surface of the copper substrate, and the solder / copper interface is firmly combined by forming intermetallic compounds. The solder alloy is used to coat the nickel-plated carbon nanotube fiber to be welded again, and then placed on the surface of the molten solder on the copper substrate. When the solder fully wets the carbon nanotube fiber, deionized water is sprayed for 3s to rapidly reduce the temperature of the molten liquid solder alloy below the melting point, realizing rapid solidification of the solder and welding and interconnection of the carbon nanotube fiber and the copper substrate. As shown in Figure 2 a, the microstructure of the carbon nanotube fiber / nickel / solder interface shows that the nickel plating layer is well combined with the carbon nanotube fiber and the solder. As shown in Figure 2 b, the linear scanning energy spectrum of the nickel element at the carbon nanotube fiber / nickel / solder interface position also proves that the nickel plating layer exists at the solder joint interface.

[0043] The carbon nanotube fiber-copper welding interconnection is subjected to 450 thermal shock cycle tests (the sample is rapidly reduced from 150°C to -196°C in 5-10s), and the resistance change rate is 29.8%. As shown in Figure 3 , the scanning electron microscope photograph of the carbon nanotube fiber / nickel plating layer / solder interface shows that only one fine crack appears at the carbon nanotube fiber / solder interface modified by the nickel plating layer, indicating that the carbon nanotube fiber-copper welding interconnection modified by the nickel plating layer has relatively high service reliability in extreme environments and has great application potential. In addition, as shown in Figure 4 a, the carbon nanotube fiber fabric modified by the nickel plating layer is made, and a Sn-37Pb solder ball with a diameter of 760μm is placed on the surface of the carbon nanotube fiber fabric modified by the nickel plating layer, and the fabric and the Sn-37Pb solder ball are heated at 250°C by using a flat heating table. Then the contact angle of the wet-spread solder on the fabric surface is measured by using a contact angle measuring instrument, and the contact angle is about 0° Figure 4 b). The results show that the liquid solder alloy and the carbon nanotube fiber have good wettability after modification by the nickel plating layer.

[0044] Example 2:

[0045] In this embodiment, step (1) is the same as step (1) of the example. The formula of the copper plating solution is: 180g / L copper sulfate, 0.56mol / L sulfuric acid, 0.001mol / L hydrochloric acid, and the balance is water; the deposition time is 30s, and the current density is 1-1.5A / dm 2 . As shown in Figure 5 , the scanning electron microscope photograph of the copper plating layer on the surface of the carbon nanotube fiber shows that the copper plating layer is uniformly coated on the surface of the carbon nanotube fiber, and the thickness of the plating layer is 0.5-0.7μm and the length is 1-2cm.

[0046] Step (2) is the same as step (2) of the example. The carbon nanotube fiber-copper solder joint interconnect modified by the copper plating layer was subjected to 450 thermal shock tests (the sample was rapidly reduced from 150 °C to -196 °C within 5-10 s), and the resistance change rate was measured to be 33.2%. As shown in FIG. 1 (a), the scanning electron microscope image of the carbon nanotube fiber / solder alloy interface shows that the introduction of the copper buffer layer can maintain excellent thermal shock resistance of the carbon nanotube fiber / solder alloy interface, thereby significantly improving the service reliability of the carbon nanotube fiber-copper solder joint interconnect in extreme environments. Figure 6

[0047] Comparative Example 1: Solder joint interconnection of carbon nanotube fiber without buffer layer and metal copper

[0048] In this comparative example, step (1) of Example 1 is not performed, and the soldering process is the same as step (2) of the example, i.e., the carbon nanotube fiber is used to replace the nickel-coated carbon nanotube fiber in Example (1), and the other processes are exactly the same. The results show that the carbon nanotube fiber without buffer layer modification can also achieve solder joint interconnection of carbon nanotube fiber and copper matrix by the process of step (2) of the example.

[0049] The carbon nanotube fiber-copper solder joint interconnect modified by the above metal buffer layer was subjected to 450 thermal shock tests (the sample was rapidly reduced from 150 °C to -196 °C within 5-10 s), and the resistance change rate was measured to be 235.3%. As shown in FIG. 2 (a), the scanning electron microscope image of the carbon nanotube fiber / solder alloy interface shows that large-sized holes appear at the carbon nanotube fiber / solder alloy interface without a buffer layer, which seriously weakens the thermal shock resistance of the carbon nanotube fiber-copper interconnect, thereby reducing its service reliability in extreme thermal environments. As shown in FIG. 2 (b), the contact angle of the solder alloy on the carbon nanotube fiber fabric surface after wetting and spreading is about 107°. Figure 7 Figure 8 As shown in FIG. 3 (a), the carbon nanotube fiber fabric without a metal buffer layer was made into a fabric, a Sn-37Pb solder ball with a diameter of 760 μm was placed on the surface of the carbon nanotube fiber fabric, and the fabric and the Sn-37Pb solder ball were heated at 250 °C using a flat hot stage. The contact angle of the solder alloy on the carbon nanotube fiber fabric surface after wetting and spreading is about 107°. Figure 8

[0050] Comparative Example 2: Without the process of spraying deionized water for rapid solidification

[0051] Step (1) of this comparative example is exactly the same as step (1) of the example. Step (2) is exactly the same as step (2) of the example, except that the process of spraying deionized water for rapid solidification is missing. It is found that when the rapid solidification process is missing in the soldering process, the carbon nanotube fiber floats on the surface of the liquid solder due to its low density, and finally the solder joint interconnection of carbon nanotube fiber and copper matrix cannot be achieved. ​​​

[0052] The above examples and comparative examples show that the present application develops a spray deionized water rapid cooling welding process, solves the problem of "welding failure" of carbon nanotube fibers and metal matrix, and solves the problem of "welding failure" by introducing a metal buffer layer technology (nickel and copper) at the welding position. Although the present application has been described in detail with general description and specific embodiments above, some modifications or improvements can be made on the basis of the present application, which is obvious to those skilled in the art. Therefore, these modifications or improvements made on the basis of not deviating from the spirit of the present application, all belong to the scope of protection required by the present application.

Claims

1. A method for achieving highly reliable interconnection between carbon nanotube fibers and metals via brazing, characterized in that, Traditional tin-based brazing solder is used. The metal substrate to be soldered is heated to a predetermined temperature in air using a planar hot plate. After the solder ball melts, it wets and spreads on the substrate surface. The pre-treated carbon nanotube fiber to be soldered is placed on the surface of the molten liquid solder alloy. When the solder alloy on the surface of the carbon nanotube fiber melts, it is rapidly solidified, thereby achieving brazing interconnection between the carbon nanotube fiber and the metal. To prevent the carbon nanotube fiber from separating from the liquid solder alloy, deionized water is rapidly sprayed to quickly reduce the temperature of the molten liquid solder alloy below its melting point, thereby achieving rapid solidification. The pretreatment process for the carbon nanotube fiber to be welded is as follows: a nickel or copper plating layer is deposited on the carbon nanotube fiber to be welded using an electroplating method. The nickel or copper plating layer improves the bonding strength, wettability, and thermal expansion coefficient difference between the carbon nanotube fiber and the solder interface. A solder alloy layer is then coated on the carbon nanotube fiber to be welded using a mechanical pressing method. After rolling, the sample to be welded is formed by mechanical pressure to achieve a carbon nanotube fiber sample with mechanical interconnection strength.

2. The method for achieving highly reliable interconnection between carbon nanotube fibers and metals by brazing according to claim 1, characterized in that, The solder alloys used are commercially available classic solder compositions, including tin-lead solder, tin-copper solder, tin-silver solder, or tin-bismuth solder.

3. The method for achieving highly reliable interconnection between carbon nanotube fibers and metals by brazing according to claim 1, characterized in that, The contact time between carbon nanotube fibers and molten liquid solder alloy is relatively short, typically between 3 and 10 seconds.

4. The method for achieving highly reliable interconnection between carbon nanotube fibers and metals by brazing according to claim 1, characterized in that, The thickness of the nickel or copper plating is 0.1~0.7 μm and the length is 1~2 cm.

5. The method for achieving highly reliable interconnection between carbon nanotube fibers and metals by brazing according to claim 1, characterized in that, The spraying time for deionized water is 2-5 seconds.

6. The method for achieving highly reliable interconnection between carbon nanotube fibers and metals by brazing according to claim 1, characterized in that, By pretreating the areas of carbon nanotube fibers to be welded, surface modification is performed on these areas to prepare interconnecting solder joints, thereby improving the bonding strength, wettability, and thermal expansion coefficient difference between the carbon nanotube fibers and the solder interface.

7. The method for achieving highly reliable interconnection between carbon nanotube fibers and metals by brazing according to claim 6, characterized in that, The interconnected solder joints prepared by modifying the welding parts of carbon nanotube fibers exhibit excellent resistance to thermal shock after thermal shock cycle testing in extreme environments. When the temperature drops rapidly from 150 °C to -196 °C in 2 to 5 seconds, the resistance change rate is less than 30% after 450 cycles of thermal shock testing.

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