A rare earth enhanced electromigration resistance SnAgCu solder and its preparation method and application

Abstract

The application discloses a kind of rare earth enhanced electromigration resistance SnAgCu solder and its preparation method and application, belong to electronic packaging solder field.The application solves the problem of insufficient anti-electromigration capacity of existing SnAgCu alloy solder etc.The application adds rare earth element Ce, La in Sn3.5Ag0.75Cu alloy solder, and controls its content in alloy, utilizes the higher affinity of rare earth element Ce, La element and Sn element, after welding, in alloy solder organization, it tends to form Ce-La-Sn regular polygon second phase by Ce, La, Sn, which is jointly composed, the second phase particle effectively refines the organizational structure of alloy solder, and effectively resists the movement of dislocation line when alloy solder produces plastic deformation, so that Sn3.5Ag0.75Cu alloy solder strength and anti-electromigration performance are improved.

Description

Technical Field

[0001] This invention relates to a rare earth-enhanced electromigration resistance SnAgCu solder, its preparation method and application, belonging to the field of electronic packaging solder. Background Technology

[0002] SnAgCu alloy solders are widely used in the consumer electronics industry due to their relatively low melting temperature and relatively good wetting properties. However, with the increasing packaging density of commercial electronic products, higher requirements are placed on the strength and electromigration resistance of the packaged solder joints. Electromigration in the packaging industry mainly refers to the interaction between electrons in the current flowing through the solder joint and metal atoms, causing the metal atoms to move directionally along the direction of electron movement. This leads to phenomena such as cracks in the solder joint or aggregation of intermetallic compounds at the interface, ultimately resulting in solder joint failure. Existing SnAgCu alloy solders have shortcomings in both mechanical properties and electromigration resistance, requiring further optimization. Therefore, it is essential to provide a rare-earth-enhanced SnAgCu solder with improved electromigration resistance and its preparation method. Summary of the Invention

[0003] This invention addresses the problem of insufficient electromigration resistance in existing SnAgCu alloy solders by providing a rare-earth-enhanced SnAgCu solder, its preparation method, and its application.

[0004] The technical solution of this invention:

[0005] One of the objectives of this invention is to provide a rare earth-enhanced electromigration resistance SnAgCu solder, specifically, this solder is based on SnAgCu alloy solder with the addition of rare earth elements Ce and La.

[0006] Further specifying, the SnAgCu alloy solder is Sn3.5Ag0.75Cu alloy solder.

[0007] Further specifying, the mass ratio of added Ce to La is 1:1.

[0008] Further specifying, the amount of Ce added is 0.6% by weight.

[0009] Further specifying, the amount of La added is 0.6% by weight.

[0010] Further specified, the solder is composed of the following elements by weight percentage: 3.5% Ag, 0.75% Cu, 0.6% Ce, 0.6% La, with the balance being Sn, and is named Sn3.5Ag0.75Cu0.6Ce0.6La alloy solder.

[0011] Further specifying, the Sn3.5Ag0.75Cu0.6Ce0.6La alloy solder has a melting point of 220.9℃, a melting range of 3.3℃, ​​a tensile strength of 37.85MPa, and a Young's modulus of 44.94GPa.

[0012] A second objective of this invention is to provide a method for preparing the above-mentioned solder, the method comprising the following steps:

[0013] (1) The Sn, Ag, Cu, Ce and La metal particles were polished to remove the surface oxide layer, then ultrasonically cleaned in anhydrous ethanol and dried. The treated Sn, Ag, Cu, Ce and La metal particles were placed in a quartz crucible according to the ratio for later use.

[0014] (2) Place KCl particles and LiCl particles in a graphite crucible, heat until completely melted and stir evenly to obtain a molten mixed salt. Then pour the molten mixed salt into a quartz crucible containing metal particles so that the molten salt completely covers the surface of the metal particles.

[0015] (3) Place the quartz crucible covered with molten mixed salt into a high-temperature melting furnace for melting and stirring during the melting process. After melting, pour the liquid metal into a graphite mold, let it cool naturally to room temperature, demold, remove the surface salt block, and obtain rare earth-enhanced electromigration resistance SnAgCu solder.

[0016] Further specifying, the purity of Sn, Ag, Cu, Ce and La metal particles in (1) is all higher than 99.99%.

[0017] Further specified, (2) the heating temperature is 650℃ and the time is 10 to 15 minutes.

[0018] Further specified, (2) the mass ratio of KCl particles to LiCl particles in the mixed salt is 1:1.3; the total mass of the mixed salt is 20-30% of the total mass of the metal particles.

[0019] Further specified, (3) the melting temperature is 500℃, the time is 2h, and the stirring is done once every 20min.

[0020] The third objective of this invention is to provide an application of the above-mentioned solder, specifically as a solder for electronic product packaging.

[0021] Beneficial effects:

[0022] This invention improves the strength and electromigration resistance of Sn3.5Ag0.75Cu alloy solder by adding rare earth elements Ce and La and controlling their content in the alloy. Utilizing the high affinity between Ce and La and Sn, after welding, a regular polygonal second phase composed of Ce, La, and Sn tends to form in the alloy solder microstructure. This second phase effectively refines the microstructure of the alloy solder and effectively resists the movement of dislocation lines during plastic deformation, thereby increasing the strength of the alloy solder. Furthermore, due to the large addition of Ce and La, the numerous large-sized second-phase particles in the microstructure play a crucial role in resisting electron wind during electromigration. Compared to solder joints without added Ce and La, the degree of intermetallic compound growth and aggregation is reduced, and no failure phenomena such as cracks occur, effectively improving the electromigration resistance. Test results show that the Sn3.5Ag0.75Cu0.6Ce0.6La alloy solder prepared in this invention has a melting point of 220.9℃, a melting range of 3.3℃, ​​a tensile strength of 37.85MPa, and a Young's modulus of 44.94GPa. Furthermore, the solder joints of Sn3.5Ag0.75Cu0.6Ce0.6La after welding have a weld strength of 25A / mm. 2 No cracks appeared after 240 hours of continuous current intensity, indicating that IMC growth was relatively slow. Attached Figure Description

[0023] Figure 1 SEM images of the alloy solders prepared in Examples 1 and Comparative Examples 1-3, wherein (a) is Sn3.5Ag0.75Cu alloy solder, (b) Sn3.5Ag0.75Cu0.6Ce alloy solder, (c) Sn3.5Ag0.75Cu0.6La alloy solder, and (d) Sn3.5Ag0.75Cu0.6Ce0.6La alloy solder;

[0024] Figure 2 DSC curves of the alloy solders prepared in Example 1 and Comparative Example 1;

[0025] Figure 3 This is a schematic diagram of a tensile specimen used for mechanical property testing.

[0026] Figure 4 A comparison diagram of the mechanical properties of the alloy solders prepared in Example 1 and Comparative Example 1;

[0027] Figure 5 This is a schematic diagram of an electromigration test for alloy solder, where (a) is the welded assembly and (b) is the circuit diagram for the electromigration test.

[0028] Figure 6SEM images of the solder joints of the alloy solder prepared for Comparative Example 1 after electromigration testing (a and b are different locations of the solder joints, respectively);

[0029] Figure 7 SEM images of the solder joints of the alloy solder prepared in Example 1 after electromigration testing. Detailed Implementation

[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0031] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0032] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0033] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, all materials, reagents, methods, and instruments used are conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art. Furthermore, all solid and liquid reagents used are of analytical grade.

[0034] Example 1

[0035] (1) Polish the surface of Sn, Ag, Cu, Ce and La metal particles (>99.99%) to remove the surface oxide layer, place them in anhydrous ethanol for ultrasonic cleaning for 5 min and then dry them. Place the treated Sn, Ag, Cu, Ce and La metal particles in a quartz crucible according to the following ratio: Ag content is 3.5%, Cu content is 0.75%, Ce content is 0.6%, La content is 0.6% and Sn content is the balance.

[0036] (2) Place KCl particles and LiCl particles in a graphite crucible with a mass ratio of 1:1.3 (the total mass of the mixed salt is 20-30% of the total mass of the metal particles), heat at 650℃ for 15 minutes until completely melted and stirred evenly to obtain a molten mixed salt. Then quickly pour the molten mixed salt into a quartz crucible containing metal particles so that the molten salt completely covers the surface of the metal particles.

[0037] (3) Place the quartz crucible covered with molten mixed salt into a high-temperature melting furnace and melt it at 500°C for 2 hours. During the melting process, use a quartz rod to mechanically stir the liquid alloy covered with molten salt every 20 minutes. Preheat the quartz rod before stirring to prevent liquid splashing. After melting, pour the liquid metal into a graphite mold, let it cool naturally to room temperature, demold it, remove the surface salt block, and obtain rare earth-enhanced electromigration resistance SnAgCu solder, named Sn3.5Ag0.75Cu0.6Ce0.6La.

[0038] Comparative Example 1

[0039] The difference between this comparative example and Example 1 is that (1) the content of Ag element is 3.5%, the content of Cu element is 0.75%, the content of Ce element is 0%, the content of La element is 0%, and the balance of Sn element is 0%. The remaining process steps and parameter settings are the same as in Example 1, and the resulting alloy solder is named Sn3.5Ag0.75Cu.

[0040] Comparative Example 2

[0041] The difference between this comparative example and Example 1 is that (1) the content of Ag element is 3.5%, the content of Cu element is 0.75%, the content of Ce element is 0.6%, the content of La element is 0%, and the balance of Sn element is 0%. The remaining process steps and parameter settings are the same as those in Example 1. The resulting alloy solder is named Sn3.5Ag0.75Cu0.6Ce.

[0042] Comparative Example 3

[0043] The difference between this comparative example and Example 1 is that (1) the content of Ag element is 3.5%, the content of Cu element is 0.75%, the content of Ce element is 0%, the content of La element is 0.6%, and the balance of Sn element; the remaining process steps and parameter settings are the same as in Example 1, and the resulting alloy solder is named Sn3.5Ag0.75Cu0.6La.

[0044] Example of effect

[0045] (1) The microstructure of the alloy solders prepared in Example 1 and Comparative Examples 1-3 was characterized. SEM images are shown below. Figure 1 As shown, by Figure 1 It can be seen that the solder alloy without rare earth elements has a coarse Ag3Sn phase structure. Adding only Ce or La forms a star-shaped Ce-Sn or La-Sn second phase. Adding Ce and La at the same time forms a polygonal Sn-Ce-La second phase, and the Ag3Sn phase structure is refined.

[0046] (2) The melting characteristics of the alloy solders prepared in Example 1 and Comparative Example 1 were tested. Specifically, the prepared alloy solders were cut into small pieces of 0.5mm × 0.5mm × 0.5mm. The solder pieces were placed in an argon atmosphere and heated at 5℃ / min. The DSC curves of the alloy solders were tested using a TG / DSC simultaneous thermal analyzer (STA449F3) manufactured by Netzsch GmbH, Germany. The test results are as follows: Figure 2 As shown. By Figure 2 It can be seen that the melting point of the alloy solder prepared in Example 1 is 220.9℃ and the melting range is 3.3℃; while the melting point of the alloy solder prepared in Comparative Example 1 is 218.2℃ and the melting range is 6.9℃.

[0047] (3) Tensile mechanical properties were tested on the alloy solders prepared in Example 1 and Comparative Example 1. Specifically, an electrical discharge machining (EDM) machine was used to cut the alloy solders prepared in Example 1 and Comparative Example 1 into the following shapes: Figure 3 The tensile specimens shown (unit: mm) were subjected to room temperature tensile tests using an electronic universal testing machine with a range of 20 kN. The shear rate was set to 0.5 mm / min. The maximum tensile strength and Young's modulus of the alloy solder are as follows: Figure 4 As shown. By Figure 4 It can be seen that the tensile strength of the alloy solder prepared in Comparative Example 1 is 23.3 MPa and the Young's modulus is 20.89 GPa, while the tensile strength of the alloy solder prepared in Example 1 is 37.85 MPa (31.01% higher than that of Comparative Example 1) and the Young's modulus is 44.94 GPa (115.13% higher than that of Comparative Example 1).

[0048] (4) The electromigration resistance of the alloy solders prepared in Example 1 and Comparative Example 1 was tested. Specifically, one end of a Cu wire with a diameter of 1 mm and a length of 10 mm was smoothed with 2000# sandpaper, ultrasonically cleaned with 5% acetic acid aqueous solution for 5 min, and then ultrasonically cleaned with anhydrous ethanol for 5 min before use. Then, a layer of commercially available ALPHAOM338PT flux was applied to the smoothed end of the Cu wire and assembled with the solder as shown in the figure. Figure 5 The welded assembly shown in (a) is placed in a V-groove and fixed for reflow welding at a peak temperature of 260°C for 5 minutes. Figure 5 As shown in (b), the obtained linear solder joint is connected to the circuit so that the current density at the solder joint cross-section reaches 25 A / mm². 2 The experiment lasted 240 hours.

[0049] The cross-section of the solder joint was observed using SEM to analyze the electromigration process. The SEM image of the solder joint cross-section is shown below. Figure 6 and Figure 7 As shown. By Figure 7It can be seen that the maximum size of Cu6Sn5 IMC at the weld interface in Example 1 is 10.9 μm, with no large-sized Ag3Sn IMC and no cracks. Figure 6 It can be seen that the maximum size of Cu6Sn5IMC at the weld interface of Comparative Example 1 is 18.15μm, and the maximum size of Ag3Sn IMC is 11.05μm, and cracks are generated at the interface.

[0050] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A rare-earth-enhanced electromigration resistance SnAgCu solder, characterized in that, This solder is based on SnAgCu alloy solder with the addition of rare earth elements Ce and La; The solder is composed of the following elements by weight percentage: 3.5% Ag, 0.75% Cu, 0.6% Ce, 0.6% La, with the balance being Sn.

2. A method for preparing the solder according to claim 1, characterized in that, include: (1) Polish Sn, Ag, Cu, Ce and La metal particles respectively to remove the surface oxide layer, then place them in anhydrous ethanol for ultrasonic cleaning and drying, and place the treated Sn, Ag, Cu, Ce and La metal particles in a quartz crucible according to the ratio for later use. (2) Place KCl particles and LiCl particles in a graphite crucible, heat until completely melted and stir evenly to obtain a molten mixed salt. Then pour the molten mixed salt into a quartz crucible containing metal particles so that the molten salt completely covers the surface of the metal particles. (3) Place the quartz crucible covered with molten mixed salt into a high-temperature melting furnace for melting and stirring during the melting process. After melting, pour the liquid metal into a graphite mold, let it cool naturally to room temperature, demold, remove the surface salt block, and obtain rare earth-enhanced electromigration resistance SnAgCu solder.

3. The preparation method according to claim 2, characterized in that, (2) The mass ratio of KCl particles to LiCl particles in the mixed salt is 1:1.3; the total mass of the mixed salt is 20-30% of the total mass of the metal particles.

4. The preparation method according to claim 2, characterized in that, (3) The melting temperature is 500℃ and the time is 2h, with stirring once every 20min.

5. An application of the solder according to claim 1, characterized in that, Solder used for packaging electronic products.

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