A method for efficiently improving electromigration reliability of lead-free interconnection solder joints based on ultrafast laser processing

Abstract

The application relates to a method for efficiently improving electromigration reliability of lead-free interconnection welding spots based on ultrafast laser processing, and relates to the technical field of material processing and welding. A special grid-shaped groove microstructure is prepared on the end face of a to-be-interconnected welding body by adopting an ultrafast laser processing process, and micro-nano particles are densely arranged in and around the grid-shaped groove; then lead-free interconnection welding is adopted to improve the electromigration reliability. The groove spacing is 20-200 um, the width is 30-50 um, and the depth is about 10-50 um. The special surface structure obtained through the ultrafast laser processing effectively improves the surface area of the connecting face, is beneficial to the uniform distribution of series brazing filler metals and the mechanical combination after solidification, and is used for solving the problem of poor electromigration failure performance of existing linear welding spots.

Description

Technical Field

[0001] This invention relates to the field of materials processing and welding technology, specifically to a method for efficiently improving the electromigration reliability of lead-free interconnect solder joints based on ultrafast laser processing. Background Technology

[0002] As electronic devices evolve towards higher density and miniaturization, the interconnect structures between electronic components face increasingly stringent requirements regarding their electromigration failure performance. Electromigration refers to the phenomenon of material failure caused by the migration of metal atoms under high current density, severely impacting the reliability of electronic products. Currently, improving welding materials and optimizing welding processes can effectively enhance the electromigration failure performance of welded joints. However, existing technologies still have many limitations in practical applications, necessitating a more effective solution. Summary of the Invention

[0003] This invention provides a method for efficiently improving the electromigration reliability of lead-free interconnect solder joints based on ultrafast laser processing. By processing a special grid-like multi-scale micro-nano surface structure using ultrafast laser processing, the surface area of ​​the connection surface is increased, which is beneficial to the uniform distribution of a series of solders and their mechanical bonding after curing. This solves the problems of long processing time and poor reliability of existing lead-free interconnect solder joints.

[0004] To achieve the above objectives, the present invention provides a copper surface with a special mesh-like microstructure, which is prepared by an ultrafast laser processing technology.

[0005] A method for efficiently improving the electromigration reliability of lead-free interconnect solder joints based on ultrafast laser processing is characterized by the following steps: A microstructure with grid-like grooves is prepared on the end face of the body to be interconnected using ultrafast laser processing. Micro- and nano-particles are densely distributed within and around the grid-like grooves. The groove spacing is 20-200 μm, the width is 30-50 μm, and the depth is approximately 10-50 μm. The covering micro- and nano-particles form a high-porosity overall structural feature. Lead-free interconnect soldering is then employed to improve electromigration reliability.

[0006] Furthermore, the interconnecting weldment is made of copper rods.

[0007] Optionally, the selected copper rod is made of polycrystalline copper in the shape of a regular square prism, with a cross-sectional side length of 0.6 mm and a length of 1 cm. After the surface of the selected copper rod is polished smooth and flat, it is pickled with acetone solution and hydrochloric acid alcohol solution to remove the organic matter and oxides attached to the surface of the copper rod to be welded.

[0008] Set the ultrafast laser processing parameters: 5-20 scans, 10-50W laser power, 400kHz laser frequency, and process a mesh structure.

[0009] Two treated copper rods are placed on the PCB board, ensuring the welding plane is perpendicular to the PCB board, the two welding planes are aligned and parallel, and the distance between the two welding planes is maintained at a preset distance. The two treated copper rods are fixed with high-temperature silicone. After the silicone solidifies, solder balls are filled into the solidified treated copper rods, and then a hot air gun is used to weld the copper rods to obtain the desired linear solder joints.

[0010] Preferably, the solder used is SAC305 lead-free solder paste. Electromigration tests are performed on the prepared linear solder joints, and samples are removed at specific times for microstructural observation. During electromigration, under the continuous action of a large number of electrons, macroscopic migration of micro-atoms in the solder joint occurs. When the current density passing through the solder joint reaches the threshold value (10⁻⁶) for electromigration to occur... 4 A / cm 2 When the solder joint forms a void at the cathode, the void accumulates and microcracks initiate, eventually leading to solder joint cracking and device open-circuit failure. Therefore, a sharp increase in solder joint resistance is used as the failure criterion, and the failure time is recorded.

[0011] The advantage of this invention is that it can obtain a special surface structure through ultrafast laser processing. The multi-scale mesh-like micro-nano structure effectively increases the surface area of ​​the connection surface, which is beneficial to the uniform distribution of the series of solders and their mechanical bonding after curing, thereby solving the problem of poor electromigration failure performance of existing linear solder joints. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this patent. For those skilled in the art, other drawings can be obtained from the following drawings without creative effort.

[0013] Figure 1 A schematic diagram of a mesh-like processing path for ultrafast laser processing;

[0014] Figure 2 The images show the microstructure of the copper rod after ultrafast laser processing: (a) top view, (b) top view, and (c) cross-sectional view.

[0015] Figure 3 The microstructure diagrams of the linear weld joint cross-section are shown below: (a) Cross-section of the linear weld joint without laser processing; (b) Cross-section of the linear weld joint after laser processing.

[0016] Figure 4 This is a schematic diagram of the complete processing flow. Detailed Implementation

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. The described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0018] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the following embodiments.

[0019] Example 1: The implementation method is described in detail below.

[0020] 1. Preparation of copper rod: Use wire cutting to make a regular square prism-shaped polycrystalline copper rod with dimensions of 10mm × 0.6mm × 0.6mm;

[0021] 2. Immerse the copper rod in the prepared acetone solution and hydrochloric acid-alcohol solution for a few minutes to remove organic matter and oxides from the surface of the copper substrate. After cleaning, use sandpaper to polish to ensure complete removal of the oxide layer and a smooth connection surface. After polishing, dry and set aside.

[0022] 3. Secure the pre-treated copper rod with a clamp, then place it horizontally upwards on the processing platform. Adjust the platform height so that the end face is at the laser focal plane. Adjust the ultrafast laser processing equipment parameters to achieve a line spacing of 100µm, 10 scans, a laser power of 25W, and a laser frequency of 400kHz. Figure 1 The graphic shown is processed;

[0023] 4. Next, place the two copper rods that have been treated above on the PCB board, with the welding plane perpendicular to the PCB board. Use the laser-processed surface as the welding plane, align the two welding planes and place them parallel to each other. Keep the distance between the two welding planes at 30um. Use high-temperature silicone to fix the two copper rods.

[0024] 5. Fill the space between the solder surfaces with SAC305 lead-free solder paste, place the device under a preheated hot air gun, and perform soldering by heating at 150°C and then 400°C for 60 seconds each.

[0025] 6. Place the welded structure in the electromigration tester, connect the circuit, and then apply a 1.0 × 10⁻⁶ ohmmeter. 4 A / cm 2 Electromigration failure performance was tested using the current density, with a 15% increase in solder joint resistance as the failure criterion, and the failure time was recorded. The results are shown in Table 1 and... Figure 3 .

[0026] Comparative Example 1: The following details the implementation method of the patent.

[0027] Except for not performing ultrafast laser processing and directly filling the spaces between the pretreated copper rods with brazing filler metal, the rest is basically the same as in Example 1.

[0028] Electromigration failure performance tests were performed on the connection structure, and the results are shown in Table 1.

[0029] Comparative Example 2: The following details the implementation methods of the patent.

[0030] Except for the ultrafast laser processing parameters in step 3, the rest is basically the same as in Example 1.

[0031] The parameters of the ultrafast laser processing equipment in this comparative example are: the line spacing of the scan is 200um, the number of scans is 10, the laser power is 25w, and the laser frequency is 400kHz.

[0032] Electromigration failure performance tests were performed on the connection structure, and the results are shown in Table 1.

[0033] Comparative Example 3: The following details the implementation methods of the patent.

[0034] Except for the ultrafast laser processing parameters in step 3, the rest is basically the same as in Example 1.

[0035] The parameters of the ultrafast laser processing equipment in this comparative example are: the line spacing of the scan is 100um, the number of scans is 20, the laser power is 25w, and the laser frequency is 400kHz.

[0036] Electromigration failure performance tests were conducted on the connection structure. Table 1 records the total time from the start of energization to fracture failure of the linear solder joint.

[0037] Table 1. Electromigration performance test results of each connection structure.

[0038] Connection structure Failure time / hour Example 1 225.3 Comparative Example 1 165.1 Comparative Example 2 201.1 Comparative Example 3 211.5

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for efficiently improving electromigration reliability of lead-free interconnect solder joints based on ultrafast laser processing, characterized in that, The end surface of the welding body to be interconnected is prepared with a special grid line-shaped groove microstructure by using an ultrafast laser processing technology, and the grid line-shaped groove is densely filled with micro-nano particles inside and around the grid line-shaped groove; then lead-free interconnection welding is used to improve electromigration reliability; The groove spacing is 20-200 um, the groove width is 30-50 um, and the depth is 10-50 um; The interconnection welding body is a copper rod; The method for fixing the two treated copper rods at the preset spatial position comprises the following steps: placing the two treated copper rods on a PCB board, with the welding planes being perpendicular to the PCB board, the two welding planes being placed in alignment and parallel, the distance between the two welding planes being kept at a preset distance, and using high-temperature silicone to fix the two treated copper rods.

2. The method of claim 1, wherein, The selected copper rod is a regular quadrangular prism polycrystalline copper material with a cross-sectional side length of 0.6 mm and a length of 1 cm; after the surface of the selected copper rod is polished smooth and flat, the copper rod is acid-washed with an acetone solution and a hydrochloric acid alcohol solution to remove organic matter and oxides attached to the surface of the copper rod to be welded.

3. The method of claim 1, wherein, The ultrafast laser processing parameters are set to process the grid structure, and then the surface structure is observed by using an optical microscope to confirm the microstructure of the grid structure.

4. The method of claim 1, wherein, The two treated copper rods are fixed by using heat-conducting silicone, so that the processed end surfaces are opposite to each other and kept at a certain distance, then the treated copper rods are allowed to solidify after waiting, the treated copper rods after solidification are filled with filler metal, and then the copper rods are welded to obtain linear welding points.

5. The method of claim 4, wherein, The filler metal is SAC305 lead-free solder paste.

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