Composite columnar soft solder material and preparation method and application thereof

Abstract

The present invention discloses a composite columnar soft solder material and a preparation method and application thereof. The composite columnar soft solder material comprises a single crystal solder column and a thin layer of solder covering the two opposite end surfaces of the single crystal solder column; the contact surface between the single crystal solder column and the thin layer of solder is a specific orientation surface, and the melting point of the thin layer of solder is lower than the melting point of the single crystal solder column. The soft solder material provided by the present invention has a low welding temperature. When applied to the welding of electronic devices, a single crystal solder joint with high yield strength and good anti-electromigration performance can be obtained; by selecting the orientation of the solder joint, the single crystal solder joint has good anti-electromigration and anti-plastic deformation performance at the same time, thereby significantly improving the overall life and reliability of the electronic equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of welding and electronic packaging, and in particular to a composite columnar soft solder material and a preparation method and application thereof, and is particularly used in the welding field of microelectronic devices or optoelectronic devices in harsh service environments. Background Art

[0002] Soft soldering technology is widely used in electronic packaging. The solder joints in electronic components not only play the role of power supply, but also provide mechanical support. Thermal fatigue and electromigration are the main causes of solder joint failure. How to improve the reliability of solder joints has always been an important issue faced by the electronics industry. Especially in the fields of aerospace, military equipment, etc., the requirements for solder joint reliability are higher.

[0003] As the size of solder joints decreases, tin solder joints often form single crystals, and the plastic deformation and electromigration of single crystal solder joints show strong anisotropy. For example, when the current direction and the grain orientation are at a certain angle, the electromigration rate is extremely high, while at another angle, the electromigration is suppressed; the yield strength of single crystal solder joints is also related to the orientation. When the orientation factor is high, the yield strength of the solder joint is low, and vice versa.

[0004] For example, in a BGA array consisting of a large number of solder joints, some oriented single-crystal solder joints are damaged first, and their lifespan is lower than that of polycrystalline solder joints, which seriously reduces the lifespan of the device.

[0005] If single crystal solder joints with controllable orientation can be obtained, the solder joint orientation can be selected to have good resistance to electromigration and plastic deformation, thereby significantly improving the overall life and reliability of electronic equipment. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention aims to provide a composite columnar soft solder material and a preparation method and application thereof.

[0007] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes:

[0008] In a first aspect, the present invention provides a composite columnar soft solder material, comprising a single crystal solder column and a solder thin layer covering two opposite end surfaces of the single crystal solder column;

[0009] The contact surface between the single crystal solder column and the solder thin layer is a specific orientation surface, and the melting point of the solder thin layer is lower than the melting point of the single crystal solder column.

[0010] In a second aspect, the present invention further provides a method for preparing a composite columnar solder material with controllable orientation, comprising:

[0011] Providing a single crystal block and obtaining an orientation of the single crystal block, wherein the single crystal block is composed of a first solder material;

[0012] 1) cutting the single crystal block along a specific orientation plane of the single crystal block to obtain a solder sheet;

[0013] 2) coating the second solder material having a lower melting point than the first solder material on both sides of the solder sheet to form a composite material assembly;

[0014] 3) Extruding the composite material assembly along the thickness direction to obtain a composite material precursor;

[0015] 4) Shearing the composite material precursor along the thickness direction of the composite material precursor to separate and obtain composite columnar soft solder material from the composite material precursor.

[0016] In a third aspect, the present invention further provides a method for welding an electronic device, comprising:

[0017] Providing the composite columnar soft solder material;

[0018] The composite columnar soft solder material is used to weld the area to be welded of the electronic device.

[0019] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention at least include:

[0020] The soft solder material provided by the present invention has a low welding temperature. When applied to the welding of electronic devices, a single crystal solder joint with high yield strength and good anti-electromigration performance can be obtained. The strength of the single crystal solder joint can reach 160MPa, and the electromigration rate is reduced by more than 90%. By selecting the orientation of the solder joint, it has good anti-electromigration and anti-plastic deformation performance, thereby significantly improving the overall life and reliability of the electronic equipment.

[0021] The above description is only an overview of the technical solution of the present invention. In order to enable those skilled in the art to more clearly understand the technical means of the present application and implement them according to the contents of the specification, the following is a description of the preferred embodiments of the present invention in conjunction with detailed drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of a preparation process of a composite columnar soft solder material provided by a typical implementation case of the present invention;

[0023] Figure 2 The present invention provides an electron microscope morphology photograph of a composite columnar soft solder material according to a typical embodiment of the present invention. DETAILED DESCRIPTION

[0024] In view of the deficiencies in the prior art, the inventor of this case has proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution, its implementation process and principle will be further explained as follows.

[0025] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0026] Moreover, relational terms such as “first” and “second”, “1)” and “2)”, etc. are merely used to distinguish one component or method step from another with the same name, but do not necessarily require or imply any such actual relationship or order between these components or method steps.

[0027] The present invention is aimed at microelectronic devices or optoelectronic devices with large solder joint current density and high load, such as components used in electronic equipment of aerospace and military equipment. In view of their high reliability requirements for solder joints, a high and low temperature composite columnar sandwich soft solder material is provided to replace conventional solder balls for reflow soldering, which can significantly improve the performance of solder joints in resisting electromigration and fatigue damage.

[0028] See also Figure 1 and Figure 2 An embodiment of the present invention provides a composite columnar soft solder material, comprising a single crystal solder column and a thin solder layer covering two opposite end surfaces of the single crystal solder column.

[0029] The contact surface between the single crystal solder column and the solder thin layer is a specific orientation surface, and the melting point of the solder thin layer is lower than the melting point of the single crystal solder column.

[0030] Among them, the orientation of the single crystal solder column can be adjusted according to the following preparation method, and the adjustment allows the interface between the single crystal solder column and the thin layer (i.e., the above-mentioned contact surface) to be selected as a pre-set specific orientation surface, which makes the overall orientation of the solder controllable; during the welding process, the main function of the columnar single crystal solder column is to serve as the main body of the solder joint to achieve high yield strength and low electromigration rate of the solder joint, and the main function of the solder thin layer on the two end faces is to carry out welding metallurgical reaction.

[0031] As some typical application examples, the composite columnar soft solder material is a high-low temperature composite columnar soft solder material, comprising a tin-based high-melting point solder single crystal solder column in the middle part and a tin-based low-melting point solder thin layer at the upper and lower ends. Its manufacturing process can preferably include directional solidification, orientation detection, cutting, pressurized composite, low-speed extrusion and precision punching and shearing to obtain the above-mentioned columnar high-low temperature composite sandwich solder containing a single crystal solder column with a specific orientation.

[0032] In some embodiments, the single crystal solder pillar may be a tin-based solder.

[0033] In some embodiments, the single crystal solder pillar may further include silver and / or copper.

[0034] In some embodiments, the liquidus temperature of the single crystal solder pillar may be greater than 220°C.

[0035] In some embodiments, the thin layer of solder may be a tin-based solder.

[0036] In some embodiments, the solder thin layer may further include bismuth element and / or indium element.

[0037] In some embodiments, the liquidus temperature of the solder thin layer may be below 140°C.

[0038] In some embodiments, the specific orientation plane may include any one of the (100) crystal plane or an equivalent crystal plane, the (110) crystal plane or an equivalent crystal plane, and the (210) crystal plane or an equivalent crystal plane of β-Sn.

[0039] In some embodiments, the thickness of the solder thin layer may be less than 0.5 mm. The height refers to the distance between the two contact surfaces (i.e., the upper and lower contact surfaces) of the single crystal solder column.

[0040] Continue to see Figure 1 The embodiment of the present invention further provides a method for preparing a composite columnar solder material with controllable orientation, comprising the following steps:

[0041] A single crystal block is provided and an orientation of the single crystal block is obtained, the single crystal block being composed of a first solder material.

[0042] 1) Cutting the single crystal block along a specific orientation plane of the single crystal block to obtain a solder sheet.

[0043] 2) A second solder material having a lower melting point than the first solder material is coated on both sides of the solder sheet to form a composite material assembly.

[0044] 3) Extruding the composite material assembly along the thickness direction to obtain a composite material precursor.

[0045] 4) Shearing the composite material precursor along the thickness direction of the composite material precursor to separate and obtain composite columnar soft solder material from the composite material precursor.

[0046] In some embodiments, step 1) may specifically include:

[0047] Depending on the orientation of the single crystal block, a cutting direction is obtained.

[0048] The single crystal block is cut along the cutting direction to obtain a solder sheet precursor.

[0049] The cut surface of the solder sheet precursor is polished to obtain the solder sheet.

[0050] In some embodiments, the solder sheet has a thickness of 0.5-2 mm.

[0051] In some embodiments, step 2) may specifically include:

[0052] The second solder material is bonded to both sides of the solder sheet and subjected to pressure diffusion treatment to obtain the composite material assembly.

[0053] In some embodiments, the pressure of the pressurized diffusion treatment is lower than 10 MPa, the temperature is lower than 120° C., and the time is 0.1-2 h.

[0054] In some embodiments, the second solder material has a thickness of 0.05-0.5 mm.

[0055] In some embodiments, in step 3), the extrusion temperature may be above 30°C, and the strain rate may be above 1×10 -4 s -1 Below, the plastic deformation amount may be below 50%.

[0056] In some embodiments, the composite material precursor is sheared into a plurality of cylinders.

[0057] In some embodiments, the radial width of the column is 0.1-1 mm.

[0058] Among them, the radial width refers to the maximum radial dimension of the columnar soft solder material (with its thickness direction as the axial direction). For example, if its cross-section is circular, the radial width is its diameter. If it is elliptical, its radial width is its maximum diameter. If it is rectangular, the radial width refers to its diagonal length, and so on.

[0059] Based on the above technical solution, as some typical application examples, the preparation method of the above soft solder material can be implemented by the following steps:

[0060] First, a tin-based high melting point solder (i.e., the first solder material) is melted in a vacuum furnace, a single crystal block is prepared by the Bridgman method, its orientation is detected, the cutting direction is determined, and the solder sheet is cut into a solder sheet by electric spark wire cutting, the surface of the solder sheet is the (100), (110), (210) crystal plane or equivalent crystal plane of β-Sn, and the solder sheet is polished to a thickness of 0.5-2 mm; a low melting point solder thin layer (i.e., the second solder material) with a thickness of 0.05-0.5 mm is attached to the upper and lower surfaces of the single crystal solder sheet, and pressure diffusion is applied to achieve interface bonding, and then low strain rate extrusion with a certain deformation amount is performed to reduce the thickness of the composite solder sheet, and recrystallization is avoided during the extrusion process by controlling the strain rate and the total deformation amount. Finally, a precision punching and shearing device is used for precision punching and shearing to obtain a high-low temperature composite sandwich solder (i.e., the composite columnar solder material) containing a single crystal solder column with a specific orientation.

[0061] The embodiment of the present invention further provides a welding method for an electronic device, comprising the following steps:

[0062] A composite columnar solder material according to any one of the above embodiments is provided.

[0063] The composite columnar soft solder material is used to weld the area to be welded of the electronic device.

[0064] In some embodiments, when performing face-to-face soldering, the solder thin layers on both sides of the composite columnar solder material have the same melting point.

[0065] In some embodiments, when flip-chip bonding is performed, the difference in melting point between the two sides of the solder film is more than 10°C.

[0066] In some embodiments, the flip chip bonding specifically comprises the following steps:

[0067] The composite columnar soft solder material is soldered to a surface to be soldered of a first electronic device at a first temperature.

[0068] The first electronic device is turned over with the surface to be welded facing downward, and the composite columnar soft solder material is used to weld the first electronic device and the second electronic device at a second temperature.

[0069] Wherein, the first temperature is lower than the second temperature.

[0070] In some embodiments, the first electronic device has a higher heat resistance than the second electronic device.

[0071] Based on the above technical solution, as some specific application examples, the above welding method can be implemented by the following steps:

[0072] When soldering electronic components, if the forward soldering is adopted, the upper and lower surfaces of the first solder material are attached with the same second solder material, and the composite columnar solder material is directly fixed between the pads of the upper and lower electronic components, and the soldering is performed once; if the flip-chip soldering is adopted, the melting point difference of the second solder material attached to the upper and lower surfaces of the first solder material must be more than 10°C. First, the composite columnar solder material is soldered and fixed on the more heat-resistant device at a lower temperature, and then turned over, and then flipped at a higher temperature. Among them, the flip-chip soldering technology refers to a technology in which the IC chip faces down and is directly interconnected with the package shell or wiring substrate. It is also called flip-chip soldering technology.

[0073] The technical solution of the present invention is further described in detail below through several embodiments and in conjunction with the accompanying drawings. However, the selected embodiments are only used to illustrate the present invention, and do not limit the scope of the present invention.

[0074] Unless otherwise specified, the raw materials, chemical reagents, and analytical testing methods and equipment used in the embodiments of the present invention are all conventionally obtained.

[0075] Example 1

[0076] This embodiment illustrates a method for preparing a composite columnar solder material, which is specifically as follows:

[0077] Sn-3.5Ag-0.7Cu (wt%) solder was melted in an argon protection furnace at a melting temperature of 500°C. The solder single crystal block was prepared by the Bridgman method, and its orientation was detected by EBSD.

[0078] The above-mentioned single crystal block is cut into a 2.0 mm thick solder sheet by electric spark wire cutting along a certain cutting direction. The surface of the sheet is the (100) crystal plane of β-Sn. The sheet is mechanically polished to a thickness of 1.0 mm. Pay attention to controlling the deformation of the solder during the grinding process.

[0079] A 0.1 mm thick Sn-52In (wt%) solder thin layer was attached to the upper and lower surfaces of the single crystal solder sheet, and the interface bonding was achieved by diffusion for 2 hours under a pressure of 1 MPa and a temperature of 30° C., thereby forming a composite material assembly.

[0080] The obtained composite material assembly was extruded to a thickness of 0.6 mm at 60 °C with an extrusion rate of 5 × 10 -5 ·s -1 , and obtain a composite material precursor.

[0081] Finally, the composite material precursor is precisely punched and sheared by a precision punching and shearing device to obtain a high-low temperature composite sandwich soft solder material containing a single crystal solder column. The (100) crystal plane of the single crystal solder column is parallel to the surface, and its morphology is as follows: Figure 2 shown.

[0082] Example 2

[0083] This embodiment illustrates the application of the composite columnar soft solder material prepared in Example 1 in flip-chip soldering of electronic components, as shown below:

[0084] (1) Preparing a Cu pad on the surface of a silicon wafer;

[0085] (2) applying a paste flux on the pad, adhering a single crystal solder column with the (100) crystal plane parallel to the surface to the flux layer and fixing it, heating it for a short time to melt the low-temperature solder layer, and connecting the single crystal solder column to the pad after the solder layer solidifies to obtain a preform;

[0086] (3) The preform is flipped over and placed upside down on a substrate with a solder pad coated with flux, the solder layer on the substrate is heated to melt again, and the preform is connected to the solder pad of the substrate to obtain a single crystal solder joint with a shear strength of 60 MPa. The growth rate of the interface compound is reduced by 90% under the same current.

[0087] Example 3

[0088] This embodiment illustrates the application of the composite columnar soft solder material prepared in Example 1 in the front-mounted soldering of electronic components, as shown below:

[0089] (1) Preparing Cu pads on the surface of silicon wafer and substrate;

[0090] (2) Apply paste flux on the pad, clamp a single crystal solder column with the (110) crystal plane parallel to the surface between the pad of the silicon wafer and the substrate, heat it for a short time to melt the low-temperature solder layer, and after the solder layer solidifies, connect the single crystal solder column to the pad to obtain a single crystal solder joint;

[0091] (3) The shear strength of the single crystal solder joint reaches 65 MPa, and the growth rate of the interface compound is reduced by 85% under the same current.

[0092] Example 4

[0093] This embodiment illustrates a method for preparing a composite columnar solder material, which is specifically as follows:

[0094] Sn-0.7Cu (wt%) solder was melted in an argon protection furnace at a melting temperature of 500°C. The solder single crystal block was prepared by the Bridgman method, and its orientation was detected by EBSD.

[0095] The above-mentioned single crystal block is cut into 1.8 mm thick solder sheets by electric spark wire cutting along a certain cutting direction. The surface of the sheet is the (110) crystal plane of β-Sn. The sheet is mechanically polished to a thickness of 1.2 mm. Pay attention to controlling the deformation of the solder during the grinding process.

[0096] A 0.15 mm thick Sn-58Bi (wt%) solder thin layer was attached to the upper and lower surfaces of the single crystal solder sheet, pressurized at 0.5 MPa and at a temperature of 20° C., and diffused for 1 hour to achieve interface bonding and form a composite material assembly.

[0097] The obtained composite material precursor was extruded to a thickness of 0.8 mm at 60 °C with an extrusion rate of 1 × 10 -4 ·s -1 A composite material precursor is obtained.

[0098] Finally, a precision punching and shearing device is used for precision punching and shearing to obtain a high-low temperature composite sandwich soft solder containing a single crystal solder column, wherein the (110) crystal plane of the single crystal solder column is parallel to the surface.

[0099] Example 5

[0100] This embodiment illustrates a method for preparing a composite columnar solder material, which is specifically as follows:

[0101] Sn-4.0Ag (wt%) solder was melted in an argon protection furnace at a melting temperature of 500°C. The solder single crystal block was prepared by the Bridgman method, and its orientation was detected by EBSD.

[0102] The above-mentioned single crystal block is cut into a 2.4 mm thick solder sheet by electric spark wire cutting along a certain cutting direction. The surface of the sheet is the (210) crystal plane of β-Sn. It is mechanically polished to a solder sheet thickness of 1.4 mm. Pay attention to controlling the solder deformation during the grinding process.

[0103] A 0.1 mm thick Sn-52In (wt%) solder thin layer is attached to the upper surface of the single crystal solder sheet, and a 0.1 mm thick Sn58Bi (wt%) solder thin layer is attached to the lower surface; pressure of 1 MPa, temperature of 25°C, diffusion for 1.5 hours, to form a composite material assembly.

[0104] The obtained composite material precursor was extruded to a thickness of 0.8 mm at 60 °C with an extrusion rate of 6 × 10 -5 ·s -1 A composite material precursor is obtained.

[0105] Finally, a precision punching and shearing device is used for precision punching and shearing to obtain a high-low temperature composite sandwich soft solder containing a single crystal solder column, wherein the (210) crystal plane of the single crystal solder column is parallel to the surface.

[0106] Based on the above embodiments, it can be clearly seen that the composite columnar soft solder material provided by the present invention has a controllable solder column orientation, and can simultaneously have good resistance to electromigration and plastic deformation through the selection of solder joint orientation, thereby significantly improving the overall life and reliability of electronic equipment.

[0107] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for welding electronic components, characterized in that: The welding is performed by flip-chip welding, and the flip-chip welding includes: Soldering the composite columnar solder material to a surface to be soldered of a first electronic device at a first temperature; Turning over the first electronic device with the surface to be welded facing downward, and welding the first electronic device and the second electronic device with the composite columnar solder material at a second temperature; Wherein, the first temperature is lower than the second temperature, and the heat resistance of the first electronic device is higher than that of the second electronic device; The composite columnar soft solder material comprises a single crystal solder column and a solder thin layer covering two opposite end surfaces of the single crystal solder column; the contact surface between the single crystal solder column and the solder thin layer is a specific orientation surface, and the melting point of the solder thin layer is lower than the melting point of the single crystal solder column, and the difference in melting points of the solder thin layers on the two sides is more than 10°C; the single crystal solder column is a tin-based solder, the single crystal solder column further comprises silver element and / or copper element, and the liquidus temperature of the single crystal solder column is higher than 220°C; the solder thin layer is a tin-based solder, the solder thin layer further comprises bismuth element and / or indium element, and the liquidus temperature of the solder thin layer is below 140°C; The method for preparing the composite columnar solder material comprises: Providing a single crystal block and obtaining an orientation of the single crystal block, wherein the single crystal block is composed of a first solder material; 1) cutting the single crystal block along a specific orientation plane of the single crystal block to obtain a solder sheet; 2) laminating a second solder material to both sides of the solder sheet and performing a pressure diffusion treatment to obtain a composite material assembly, wherein the pressure of the pressure diffusion treatment is below 10 MPa, the temperature is below 120° C., and the time is 0.1-2 h; the thickness of the second solder material is 0.05-0.5 mm; 3) Extruding the composite material assembly along the thickness direction to obtain a composite material precursor; 4) Shearing the composite material precursor along the thickness direction to separate and obtain composite columnar soft solder material from the composite material precursor.

2. The welding method according to claim 1, characterized in that: The specific orientation plane includes any one of the (100) crystal plane or its equivalent crystal plane, the (110) crystal plane or its equivalent crystal plane, and the (210) crystal plane or its equivalent crystal plane of β-Sn; and the thickness of the solder thin layer is less than 0.5 mm.

3. The welding method according to claim 1, characterized in that: Step 1) specifically includes: Obtaining a cutting direction according to the orientation of the single crystal block; Cutting the single crystal block along the cutting direction to obtain a solder sheet precursor; The cut surface of the solder sheet precursor is polished to obtain the solder sheet, and the thickness of the solder sheet is 0.5-2 mm.

4. The welding method according to claim 1, characterized in that: In step 3), the extrusion temperature is above 30°C and the strain rate is 1×10 -4 s -1 Below, the plastic deformation is less than 50%.

5. The welding method according to claim 1, characterized in that: In step 4), the composite material precursor is cut into a plurality of columns with a radial width of 0.1-1 mm.

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