Rapid preparation method of Ni / Cu-IMC / Ni composite joint for high-temperature packaging

Abstract

The invention discloses a method for quickly preparing a composite joint for high-temperature packaging, which mainly comprises the following steps of: preparing a soldering lug in advance by taking foamy copper as a bracket and tin as a filling material; and a nickel material or a surface nickel-plated material is adopted as an upper substrate and a lower substrate, and the upper substrate and the lower substrate are welded together with the prepared soldering lug under a certain welding process to prepare the bonding process of the composite joint. A connecting joint generated by the method is different from other intermetallic compound joints, a final micro welding spot is mainly composed of a copper-nickel-tin ternary metal compound and foamy copper left after reaction, compared with a traditional copper-tin compound joint, the finally generated joint has more excellent comprehensive performance, the preparation cost is low, the steps are simple and convenient, and the method is suitable for industrial production. And the requirements of a third-generation semiconductor package can be better met.

Description

Technical Field

[0001] The invention relates to the field of semiconductor packaging interconnection, and in particular to a method for quickly preparing a Ni / Cu-IMC / Ni composite joint for high-temperature packaging. Background Art

[0002] In recent years, the rapid development of third-generation semiconductor technology has led to its wide application in many fields such as integrated circuits, new energy vehicles, wind power photovoltaic energy storage and new displays. Thanks to its excellent performance, third-generation semiconductors are promoting progress and innovation in these fields. As a new welding technology adapted to it, instantaneous liquid phase connection technology achieves efficient connection between metals by utilizing the rapid wetting and diffusion of liquid metal. The welding temperature required for instantaneous liquid phase connection technology is low and the thermal stability of the post-welding structure is relatively good. It can perfectly meet the requirements of "low temperature connection and high temperature service" required for electronic device packaging, and is the inevitable direction for the development of semiconductor welding methods in the future.

[0003] In the current research field of instantaneous liquid phase connection technology, low melting point metals such as Sn and In are mainly used as intermediate layers, and high melting point metals such as Cu, Ni, and Ag are often used as substrate base materials in electronic packaging to achieve bonding. The copper-tin system is the most widely used in instantaneous liquid phase connection due to its low cost and reliable performance. In general, Cu-Sn compounds produce two common intermetallic compounds, Cu6Sn5 and Cu3Sn, after bonding. Cu3Sn has better comprehensive properties than Cu6Sn5, so the microstructure and performance of the produced welded joints have received more scientific research attention and application. However, in actual applications, the welding time required to produce all-Cu3Sn joints is relatively long, and Cu3Sn itself is relatively brittle and has poor electrical and thermal conductivity. In addition, the copper-tin system compounds shrink in volume during high-temperature service and produce holes. These shortcomings greatly limit the application scope of copper-tin joints in real life. In the copper-nickel-tin ternary system, (Cu,Ni)6Sn5 is a compound that is easily produced in the copper-nickel-tin system, and its shear strength, hardness and other properties are better than those of Cu6Sn5 and Cu3Sn. In recent years, more and more researchers have begun to pay attention to the application of copper-nickel-tin ternary compounds in instantaneous liquid phase connection. However, the diffusion rate of nickel (Ni) atoms in copper-nickel-tin joints is slow, resulting in a long time for the formation of complete compound joints in traditional ternary system joints. This feature constitutes a significant limitation in practical applications. Therefore, exploring methods to accelerate the formation of nickel-copper-tin composite joints not only has important scientific research value, but also has practical significance, and has a far-reaching impact on promoting the development of the semiconductor industry.

[0004] The present invention uses tin-immersion treated foamed copper as the middle layer, firstly prepares it into a composite welding piece that can be used for connection under a certain welding process, then nickel-treats the surfaces of the upper and lower substrates to be connected and builds a sandwich structure with the composite welding piece, and then completes the preparation of the composite joint through a certain welding process and means. In the prepared joint, a layer of (Cu, Ni)6Sn5 will be generated on the welding surface of the upper and lower substrates, and the interior of the joint is Cu3Sn, (Cu, Ni)3Sn produced by the reaction, and the foamed copper remaining from the reaction. Compared with the traditional Cu3Sn joint, the composite structure joint has better shear strength, hardness, electrical and thermal conductivity and other comprehensive mechanical properties, and the addition of nickel element refines the grain size of the joint, improving the brittleness of the joint to a certain extent, and the foamed copper remaining from the reaction can not only improve the electrical conductivity of the joint to a certain extent, but also form an interlocking structure with the Cu3Sn generated by the reaction, further enhancing the strength of the joint. Summary of the invention

[0005] The main purpose of the present invention is to solve the problems of many defects, poor electrical and thermal conductivity and insufficient mechanical properties in the copper-tin system joints in the current instantaneous liquid phase connection applications, and to provide a rapid preparation method for a composite joint based on foamed copper, nickel metal and tin alloy. Through a specific welding process and means, a composite joint is prepared, and the electrical and thermal conductivity and comprehensive mechanical properties of the micro-solder points in the joint are improved. This preparation method is relatively simple, low-cost, and the welding time is short. The prepared welded joint has excellent comprehensive mechanical properties and good thermal stability, and has a wide range of application prospects, especially in the semiconductor industry. It has important practical value.

[0006] The preparation scheme of the present invention is to use foam copper, nickel metal and tin alloy as basic materials. The presence of foam copper reduces the diffusion distance of copper atoms, so that Cu3Sn and (Cu, Ni)3Sn can be generated faster at the foam copper and form a composite micro solder joint with the remaining foam copper. The presence of the remaining foam copper can also improve the conductivity of the joint. The nickel in the upper and lower substrates can provide nickel atoms for the joint and form a dense layer of (Cu, Ni)6Sn5 on the surface of the substrate. In addition, the addition of nickel can also refine the grain size of the joint, thereby improving the brittleness of the joint.

[0007] The composite joint prepared by the present invention has relatively excellent comprehensive mechanical properties and its preparation cost is low. The thermal stability and resistance to high-temperature creep and electromigration of the generated composite joint are also excellent. It can meet the vast majority of packaging service requirements on the market and has broad application prospects and use value in the semiconductor packaging market. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1It is a schematic diagram of the welding process of sandwich structure composite joints.

[0009] Figure 2 OM diagram of foam copper composite solder sheet.

[0010] Figure 3 It is the element distribution diagram of the composite joint after welding.

[0011] Figure 4 It is the SEM microstructure diagram of the weld point of the composite joint after welding.

[0012] Figure 5 This is the EDS spectrum analysis diagram of the composite joint near the substrate after welding.

[0013] Figure 6 This is the EDS spectrum analysis diagram of the composite joint near the foam copper after welding.

Claims

1. A rapid preparation method for a Ni / Cu-IMC / Ni composite joint for high temperature packaging, which is characterized by comprising the following main steps: (a) Selection and cleaning of welding materials: tin alloy and copper foam required for welding are selected, the copper foam is cut into appropriate sizes and then immersed in acetone solution with tin respectively, the oil stains on the surface of the tin alloy and copper foam are removed by ultrasonic cleaning, and then the tin alloy and copper foam are ultrasonically cleaned with alcohol solution and air-dried; then the copper foam is successively immersed in hydrochloric acid and nitric acid alcohol solutions with a mass concentration of 1%, and then ultrasonically cleaned to remove surface oxides and chlorides; finally, it is immersed in alcohol solution, ultrasonically cleaned and air-dried for use; (b) Melting treatment of tin: placing the tin alloy treated in step (a) into a crucible, heating it with a heating device until it is completely melted, and removing the oxide layer on its surface with tweezers; (c) Tin immersion treatment of the copper foam: coating the copper foam obtained in (a) with flux and immersing it in the melted tin alloy in step (b) until the molten tin alloy is evenly absorbed and the surface is made flat to prepare a copper foam pre-solder sheet; (d) Preparation of foam copper composite welding sheet: The foam copper composite structure pre-welding sheet prepared in step (c) is welded under a hot press with certain process parameters to prepare a composite welding sheet that can be used for semiconductor chip packaging. (e) Selection and treatment of upper and lower connection substrates: Select a material with a nickel material on the surface to be welded as the upper and lower welding substrates, or perform nickel plating on the surface of the upper and lower substrates to be connected to ensure that the surface to be welded is made of nickel or nickel-containing metal, and then clean it with alcohol and air-dry it for use; (f) Preparation of welding joints: The surface of the composite welding sheet prepared in step (d) is coated with flux again to form a sandwich structure with the upper and lower substrates to be connected, and then the composite joint connection is completed by hot pressing welding with a certain welding process.

2. A rapid preparation method for a Ni / Cu-IMC / Ni composite joint for high temperature packaging according to claim 1, characterized in that: The specific steps of step (a) are: (1) The tin alloy can be selected from a range including but not limited to pure tin, one or more of SAC (Sn-Ag-Cu), SnBi, SnIn, and Sn-Cu-Ni solders. The process parameters can be reset according to the type of solder selected to achieve rapid preparation of composite joints; (2) The material of the foam copper may include but is not limited to one or more of pure copper, nickel silver, and brass; (3) The pore size of the foam copper can be selected between 100 and 500 ppi, the thickness can be between 0.1 and 10 mm, and the porosity can be selected between 40 and 98%.

3. The rapid preparation method of a Ni / Cu-IMC / Ni composite joint for high temperature packaging according to claim 1, characterized in that: The specific steps of step (b) are: (1) The tin alloy melting methods include but are not limited to vacuum melting furnace, small high-frequency melting furnace constant temperature heating platform, vacuum furnace, etc.; (2) The melting temperature of tin alloy can be selected between 240 and 400°C.

4. The rapid preparation method of a Ni / Cu-IMC / Ni composite joint for high temperature packaging according to claim 1, characterized in that: The specific steps of step (d) are: (1) The methods used to prepare the foam copper composite solder sheet include but are not limited to hot pressing welding machine, reflow soldering furnace, vacuum hot pressing furnace, tube furnace, wave soldering, etc.; (2) The temperature set for preparing the composite welding sheet can be between 240 and 500°C; (3) The welding pressure set for preparing the composite welding sheet can be between 5 and 100 MPa; (3) The welding time set for preparing the composite welding sheet can be between 1 and 300 minutes.

5. A rapid preparation method for a Ni / Cu-IMC / Ni composite joint for high temperature packaging according to claim 1, characterized in that: The specific steps of step (e) are: (1) The selected upper and lower substrates include but are not limited to pure metal nickel plates, copper-nickel alloy plates, nickel-plated chips, nickel-plated PCBs, nickel-plated DBCs or other nickel-plated metal plates; (2) The size of the selected nickel substrate can be between 0.1-20 mm, and the thickness of the nickel plating layer can be between 1-100 um. (3) The selected coating method includes but is not limited to vapor deposition, ultrasonic assisted electrodeposition, chemical plating, cold spraying, evaporation or sputtering.

6. The rapid preparation method of a Ni / Cu-IMC / Ni composite joint for high temperature packaging according to claim 1, characterized in that: The specific steps of step (f) (1) The welding methods that can be selected when bonding the composite solder sheet to the upper and lower substrates include hot pressing welding machine, reflow oven, vacuum hot pressing furnace, tube furnace, wave soldering, etc.; (3) The temperature selected when the composite solder sheet is bonded to the upper and lower substrates is between 240 and 500°C; (3) The welding pressure selected for bonding the composite welding sheet to the chip is between 0.1 and 100 MPa.

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