Method for efficiently improving electromigration reliability of lead-free interconnection welding spots based on ultrafast laser processing

Abstract

The invention discloses 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 microstructure with a special latticed groove is prepared on the end face of a welding body to be interconnected by adopting an ultrafast laser processing technology, and micro-nano particles are densely distributed in the latticed groove and around the latticed groove; and then lead-free interconnection welding is adopted, so that the electromigration reliability is improved. The distance between the grooves is 20-200 microns, the width is 30-50 microns, and the depth is about 10-50 microns, a special surface structure is obtained through ultrafast laser processing, the surface area of a connecting surface is effectively increased through the multi-scale latticed micro-nano structure, uniform distribution of a series of brazing filler metal and mechanical combination of the series of brazing filler metal after solidification are facilitated, and the problem that existing linear welding spots are poor in electromigration failure performance is solved.

Description

Technical Field

[0001] The invention relates to the technical field of material processing and welding, and in particular to a method for efficiently improving the reliability of electromigration of lead-free interconnect solder joints based on ultrafast laser processing. Background Art

[0002] As electronic devices develop towards high density and miniaturization, the interconnection structure between electronic components has put forward higher requirements for its electromigration failure performance. Electromigration refers to the phenomenon that the migration of metal atoms under high current density leads to material failure, which seriously affects the reliability of electronic products. At present, the electromigration failure performance of welded joints can be effectively improved by improving welding materials and optimizing welding processes. However, the existing technology still has many limitations in practical applications, and a more effective solution is urgently needed. Summary of the invention

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

[0004] In order to achieve the above-mentioned object, the present invention provides a copper surface with a special grid-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, characterized in that an ultrafast laser processing process is used to prepare a grid-line groove microstructure on the end face of the interconnected solder body, and micro-nano particles are densely distributed in and around the grid-line grooves; the groove spacing is 20-200um, the width is 30-50um, and the depth is about 10-50um. The covered micro-nano particles form an overall structural feature with high porosity, and then lead-free interconnect soldering is used to improve the electromigration reliability.

[0006] Furthermore, the interconnecting welding body is a copper rod.

[0007] Optionally, the selected copper rod is made of regular quadrangular prism-shaped polycrystalline copper with a cross-sectional side length of 0.6 mm and a length of 1 cm; the surface of the selected copper rod is polished to be smooth and flat, and then pickled 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.

[0008] Set the ultrafast laser processing parameters: scan times 5-20 times, laser power 10-50w, laser frequency 400kHz, and process the grid structure.

[0009] Place the two treated copper rods on the PCB board, ensure that the welding plane is perpendicular to the PCB board, align the two welding planes and place them in parallel, keep the distance between the two welding planes at a preset distance, and use high-temperature silicone to fix the two treated copper rods. Then wait for the silicone to solidify, fill the solidified treated copper rods with solder balls, and then use a hot air gun to solder the copper rods to obtain the required linear solder joints; Preferably, the solder is SAC305 lead-free solder paste. The prepared linear solder joint is subjected to electromigration test, and samples are taken out at a specific time to observe the microstructure of the sample. During the electromigration process, under the continuous action of a large number of electrons, the microscopic atoms in the solder joint undergo macroscopic migration. When the current density passing through the solder joint reaches the threshold value (10 4 A / cm 2 ), the solder joint forms a cavity at the cathode, and then the cavity gathers and initiates microcracks, and finally the microcracks expand and cause the solder joint to crack, and the device fails to open the circuit. Therefore, the sudden increase of solder joint resistance is used as the failure criterion, and the failure time is recorded.

[0011] The advantage of the present invention is that a special surface structure can be obtained through ultrafast laser processing. The multi-scale grid-like micro-nano structure effectively increases the surface area of ​​the connection surface, which is beneficial to the uniform distribution of a series of solders and their mechanical bonding after solidification, so as to solve the problem of poor electromigration failure performance of existing linear solder joints. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of this patent. For ordinary technicians in this field, other drawings can be obtained based on the following drawings without creative work.

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

[0014] Figure 2 Microstructure diagram of the copper rod after ultrafast laser processing; (a) top view, (b) top view, (c) cross-sectional view.

[0015] Figure 3 Microstructure diagram of the linear solder joint cross section; (a) Cross section of the linear solder joint without laser processing (b) Cross section of the linear solder joint after laser processing.

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

[0017] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

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

[0019] Example 1: The following specifically describes the implementation method 1. Preparation of copper rod: Use wire cutting to make a regular quadrangular prism-shaped polycrystalline copper rod with a size of 10 mm × 0.6 mm × 0.6 mm; 2. Soak the copper rod in the prepared acetone solution and hydrochloric acid alcohol solution for a few minutes to remove organic matter and oxides on the surface of the copper substrate. After cleaning, use sandpaper to polish to ensure that the oxide layer is completely removed and the connection surface is flat. Polish after grinding and dry for later use; 3. Fix the pre-treated copper rod with a fixture, and then place it horizontally with the end face facing upward on the processing platform. Adjust the platform height so that the end face is in the focal plane of the laser. Adjust the parameters of the ultrafast laser processing equipment so that the scanning line spacing is 100um, the number of scans is 10 times, the laser power is 25w, and the laser frequency is 400kHz. Figure 1 The graphics shown are processed; 4. Next, place the two copper rods treated as above on the PCB board, with the welding plane perpendicular to the PCB board, and use the laser processed surface as the welding plane. Align the two welding planes and place them in parallel. The distance between the two welding planes is kept at 30um, and use high-temperature silicone to fix the two copper rods treated as above; 5. Fill the soldering plane with SAC305 lead-free solder paste, place the device under a preheated hot air gun and heat it at 150℃ and then 400℃ for 60s respectively for soldering; 6. Place the soldered structure in the electromigration tester and connect the circuit to 1.0×10 4 A / cm 2 The electromigration failure performance test was carried out with a current density of 15%, and the failure criterion was that the solder joint resistance increased by 15% of the original value, and the failure time was recorded. The results are shown in Table 1 and Figure 3 .

[0026] Comparative Example 1: The following specifically describes the implementation method of the patent

[0027] The process is basically the same as that of Example 1 except that the ultrafast laser processing is not performed and the solder is directly filled between the pretreated copper rods.

[0028] The electromigration failure performance test of the connection structure is carried out, and the results are shown in Table 1.

[0029] Comparative Example 2: The following specifically describes the implementation method 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 of this comparative example are: the scanning line spacing is 200um, the number of scans is 10 times, the laser power is 25w, and the laser frequency is 400kHz;

[0032] The electromigration failure performance test of the connection structure is carried out, and the results are shown in Table 1.

[0033] Comparative Example 3: The following specifically describes the implementation method 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 of this comparative example are: the scanning line spacing is 100um, the number of scans is 20 times, the laser power is 25w, and the laser frequency is 400kHz;

[0036] The electromigration failure performance test was carried out on the connection structure. Table 1 records the total time from the start of power-on to the fracture failure of the linear solder joint.

[0037] Table 1 Electromigration performance test results of various connection structures

[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, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 the electromigration reliability of lead-free interconnect solder joints based on ultrafast laser processing, characterized in that: An ultrafast laser processing process is used to prepare a special grid-line groove microstructure on the end surface of the interconnected welding body, and micro-nano particles are densely distributed in and around the grid-line grooves; then lead-free interconnect welding is used to improve electromigration reliability.

2. The method according to claim 1, characterized in that The groove spacing is 20-200um, the groove width is 30-50um, and the depth is 10-50um.

3. The method according to claim 1, characterized in that The interconnecting solder body is a copper rod.

4. The method according to claim 3, characterized in that The selected copper rod is made of regular quadrangular prism-shaped polycrystalline copper, with a cross-sectional side length of 0.6 mm and a length of 1 cm. The surface of the selected copper rod is polished to be smooth and flat, and then pickled 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. The method according to claim 1, characterized in that The ultrafast laser processing parameters were set to process the grid-like structure, and then the surface structure was observed through an optical microscope to confirm the microscopic structure of the grid-like structure.

6. The method according to claim 1, characterized in that The two processed copper rods are fixed with thermally conductive silicone so that their processed end faces face each other and maintain a certain distance, and then they are waited for solidification, and solder is filled into the solidified processed copper rods, and then the copper rods are welded to obtain linear solder joints.

7. The method according to claim 1, characterized in that According to a preset spatial position, the method for fixing the two processed copper rods includes: placing the two processed copper rods on the 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 maintained at a preset distance, and high-temperature silicone is used to fix the two processed copper rods.

8. The method according to claim 1, characterized in that The solder adopts SAC305 lead-free solder paste.

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