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

Abstract

The application relates to a method for improving the electromigration reliability of lead-free interconnection welding spots based on superfast laser processing hexagons, and relates to the technical field of material processing and welding. A hexagonal array groove microstructure is prepared on the end face of a to-be-interconnected welding body by adopting a superfast laser processing process, the hexagonal array groove microstructure is composed of multiple independent hexagonal linear groove units, the six edges of the hexagonal linear groove unit correspond to linear grooves, and each edge of each hexagonal linear groove unit is provided with another hexagonal linear groove unit outside; then lead-free interconnection welding is adopted to improve the electromigration reliability. The multi-scale hexagonal array micro-nano structure 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 the existing linear welding spots.

Description

Technical Field

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

[0002] As electronic devices evolve towards higher power and greater integration, packaging density continues to increase, placing higher demands on the electromigration failure performance of interconnect structures between electronic components. The reduction in solder joint size leads to electromigration problems, making the research on the electromigration reliability of micro-solder joints a crucial research direction in microelectronic packaging technology. This research focuses on the stability and reliability of solder joints under various operating conditions. Electromigration (EM) refers to the structural changes and diffusion of metal materials caused by electron migration when current passes through a solder joint. It can lead to solder joint failures and performance degradation, severely impacting the reliability of electronic products. Currently, the electromigration failure performance of soldered joints can be effectively improved by preparing composite solders and optimizing welding processes. 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 improving the electromigration reliability of lead-free interconnect solder joints based on ultrafast laser processing. By processing a special hexagonal array-shaped 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, this invention provides a copper surface with a special hexagonal array microstructure, prepared using an ultrafast laser processing technology. The preparation method is as follows:

[0005] A method for improving the electromigration reliability of lead-free interconnect solder joints based on ultrafast laser processing of hexagons is characterized by the following steps: A microstructure with a hexagonal array trench is fabricated on the end face of the body to be interconnected using an ultrafast laser processing technique. The hexagonal array trench microstructure is composed of multiple independent hexagonal linear trench units, where each hexagonal linear trench unit has six sides corresponding to linear trenches. Each side of each hexagonal linear trench unit is surrounded by another hexagonal linear trench unit, and adjacent hexagonal linear trench units do not share sides and have gaps between them. Micro- and nano-particles are densely distributed within and around the trenches. The trench 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. The side length of each hexagon is 0.01 mm-1 mm. Lead-free interconnect soldering is then employed to improve electromigration reliability.

[0006] Furthermore, the interconnect welding body is a copper rod. A layer of mesh-like trench multi-scale micro-nano structure is obtained on the end face of the copper rod through ultrafast laser processing. The interconnect structure is formed by filling the space between the two copper rods with SAC305 lead-free solder paste and then sintering at high temperature.

[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, to process a hexagonal array 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] Optionally, the solder used is SAC305 lead-free solder paste.

[0011] Electromigration tests were performed on the prepared linear solder joints, and samples were removed at specific times for observation of their microstructure. During electromigration, macroscopic migration of micro-atoms in the solder joint occurred under the continuous action of a large number of electrons. When the current density passing through the solder joint reached 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.

[0012] The advantage of this invention is that it can obtain special surface structures through ultrafast laser processing. The multi-scale hexagonal array micro-nano structure effectively increases the surface area of ​​the connection surface, which is conducive 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

[0013] 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.

[0014] Figure 1 This is a schematic diagram of the laser processing path;

[0015] Figure 2 The microstructure of the copper rod after ultrafast laser processing is shown in the diagrams: (a) top view and (b) cross-sectional view.

[0016] Figure 3 Microscopic structures of cross-sections of ordinary linear solder joints and linear solder joints with laser-processed end faces; (a) Cross-section of linear solder joint without laser processing; (b) Cross-section of linear solder joint after laser processing.

[0017] Figure 4 This is a schematic diagram of the complete processing flow. Detailed Implementation

[0018] 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.

[0019] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the following embodiments.

[0020] Example 1: The following describes the implementation method of the patent in detail.

[0021] 1. Preparation of copper rod: Use wire cutting to make a regular square prism polycrystalline copper rod with dimensions of 10mm × 0.6mm × 0.6mm;

[0022] 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.

[0023] 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 10 scans, 25W laser power, and 400kHz laser frequency. Figure 1The graphic shown is processed;

[0024] 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.

[0025] 5. Fill the space between the soldering surfaces with SAC305 lead-free solder paste, place the device under a preheated hot air gun and heat it at 150°C and then 400°C for 60 seconds each time to perform soldering.

[0026] 6. Place the welded structure in the electromigration tester, connect the circuit, and then apply a 1.0 × 10⁻⁶ ohmmeter. 4 Electromigration failure performance was tested using a current density of A / cm², with a 15% increase in solder joint resistance as the failure criterion. The failure time was recorded. The results are shown in Table 1 and... Figure 3 .

[0027] Comparative Example 1: The following details the implementation method of the patent.

[0028] 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.

[0029] Electromigration failure performance tests were performed on the connection structure, and the results are shown in Table 1.

[0030] Comparative Example 2: The following details the implementation methods of the patent.

[0031] Except for the ultrafast laser processing parameters in step 3, the rest is basically the same as in Example 1.

[0032] The parameters of the ultrafast laser processing equipment in this comparative example are: the side length of the scanned hexagon is 100um, the number of scans is 10, the laser power is 25w, and the laser frequency is 400kHz.

[0033] Electromigration failure performance tests were performed on the connection structure, and the results are shown in Table 1.

[0034] Comparative Example 3: The following details the implementation methods of the patent.

[0035] Except for the ultrafast laser processing parameters in step 3, the rest is basically the same as in Example 1.

[0036] The parameters of the ultrafast laser processing equipment in this comparative example are: the side length of the scanned hexagon is 60um, the number of scans is 20, the laser power is 25w, and the laser frequency is 400kHz.

[0037] 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.

[0038] Table 1. Electromigration performance test results of each connection structure.

[0039] Connection structure Failure time / hour Example 1 217.4 Comparative Example 1 165.1 Comparative Example 2 198 Comparative Example 3 211.5

[0040] 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 improving electromigration reliability of lead-free interconnect solder joints based on ultrafast laser processing hexagon, characterized in that, The six-hexagon array groove microstructure is prepared on the end face of the welding body to be interconnected by using an ultrafast laser processing technology, the six-hexagon array groove microstructure is composed of a plurality of independent six-hexagon linear groove units, the six-hexagon linear groove unit refers to six linear grooves corresponding to six sides of a hexagon, each side of each six-hexagon linear groove unit is provided with another six-hexagon linear groove unit, and the adjacent two six-hexagon linear groove units have a gap between them; the grooves are densely filled with micro-nano particles, and then lead-free interconnection welding is used to improve the electromigration reliability.

2. A method for improving electromigration reliability of lead-free interconnect joints based on ultrafast laser processing hexagon according to claim 1, characterized in that, The groove width is 30-50um, the depth is 10-50um, and the length of each hexagon is 0.01mm-1mm.

3. A method for improving electromigration reliability of lead-free interconnect joints based on ultrafast laser processing hexagon according to claim 1, characterized in that, The interconnection welding body is a copper rod, a six-hexagon array groove multi-scale micro-nano structure is obtained on the end face of the copper rod by using an ultrafast laser processing technology, and the interconnection structure is obtained by filling SAC305 lead-free solder paste between the two copper rods and then high-temperature sintering.

4. A method for improving electromigration reliability of lead-free interconnect joints based on ultrafast laser processing hexagon according to claim 3, characterized in that, The selected copper rod is a regular quadrangular prism polycrystalline copper material with a cross-sectional side length of 0.6mm and a length of 1cm; after polishing the surface of the selected copper rod smooth and flat, the copper rod is acid washed with acetone solution and hydrochloric acid alcohol solution to remove organic matter and oxides attached to the surface of the copper rod to be welded.

5. A method for improving electromigration reliability of leadless interconnect solder joints based on ultrafast laser processing hexagon according to claim 1, characterized in that, The ultrafast laser processing parameters are set to process the six-hexagon array groove microstructure, and then the surface structure is observed by an optical microscope to confirm that the six-hexagon array groove microstructure is formed.

6. A method for improving electromigration reliability of leadless interconnect solder joints based on ultrafast laser processing hexagon according to claim 4, characterized in that, The two treated copper rods are fixed by using heat-conducting silicone, so that the processed end faces are opposite and a certain distance is maintained, then the treated copper rods are filled with filler metal after solidification, and then the copper rods are welded to obtain linear welds.

7. A method for improving electromigration reliability of leadless interconnect solder joints based on ultrafast laser processing hexagon according to claim 4, characterized in that, According to the preset spatial position, the two treated copper rods are fixed, specifically including: placing the two treated copper rods on a PCB board, the welding plane is perpendicular to the PCB board, the two welding planes are aligned and placed in parallel, the distance between the two welding planes is kept at a preset distance, and high-temperature silicone is used to fix the two treated copper rods.

8. A method of improving electromigration reliability of leadless interconnect solder joints based on ultrafast laser processing hexagon according to claim 6, characterized in that, The filler metal is SAC305 lead-free solder paste.

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