A solder ball, a preparation method thereof and an application

Abstract

The present invention discloses a solder ball, a preparation method and an application thereof, relating to the field of semiconductor devices. The preparation method of the solder ball comprises the following steps: S1. providing a flat plate, wherein a plurality of limiting grooves for accommodating solder sheets are arranged on the surface of the flat plate; a hemispherical limiting pit is arranged on the bottom surface of the limiting groove; S2. placing the solder sheet in the limiting groove; S3. heating the flat plate and the solder sheet until the solder melts, and the molten solder falls into the limiting pit, and after cooling, solder balls are obtained after the solder solidifies again. The present invention provides a preparation method of a solder ball. By using a more easily processed sheet-shaped solder as a production raw material, it is not necessary to first process the solder into a filament shape, thereby reducing the requirements for the processability of the solder. After the solder in the method of the present invention is heated and melted, it will fall into the hemispherical limiting pit of the flat plate. By controlling the diameter of the limiting pit, good roundness of the solder ball is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor devices, and more particularly, to a solder ball, a preparation method thereof, and an application thereof. Background Art

[0002] Solder balls are widely used in the semiconductor industry and can be used in applications such as ball grid array (BGA) ball planting, solder bump preparation, and laser welding. With the increasing popularity of advanced packaging forms such as BGA and chip scale package (CSP), and with the increasing chip integration level and the rising number of I / Os, the usage of solder balls will continue to climb.

[0003] The mainstream preparation technology of solder balls is the wire cutting and remelting method. The processing process is to first make the solder into filaments of a certain specification, then use a cutting machine to cut them into uniform segments, immerse the segments in hot oil with a temperature higher than the melting point of the solder, and the solder melts in the hot oil and solidifies into solder balls under the action of liquid surface tension and gravity. After the hot oil cools, the solder balls sink to the bottom, the oil is poured out, the solder balls are taken out, and then the solder balls are cleaned and dried. However, since the smoke point of the oil is generally between 200 and 300 °C, and the ignition point and boiling point are generally between 300 and 400 °C, its thermal stability is poor at high temperatures. In practical applications, problems such as combustion, smoking, and deterioration will occur before reaching the boiling point of the hot oil. Therefore, it is greatly limited in the preparation of high melting point solder balls. At the same time, the premise of the wire cutting and remelting method is that the alloy can be made into filaments. However, solders such as gold-tin alloy are difficult to make into continuous, uniformly performing, and winding wires due to their high brittleness and low elongation. Therefore, it is difficult to use the wire cutting and remelting method to mass-produce high melting point solder balls.

[0004] The existing preparation of high melting point solder balls generally uses the uniform droplet spraying method. For example, in the article "Preparation of Precision Solder Balls by Uniform Droplet Spraying" published by the Composite Materials Center of the General Research Institute for Nonferrous Metals in "The Chinese Journal of Nonferrous Metals", it is recorded that the uniform droplet forming method is used to melt and superheat Sn3.0Ag-0.5Cu to 270 °C to obtain precision solder balls. However, from the particle size distribution diagram of the solder balls prepared by this method, only solder balls with a particle size of 265-295 μm can be obtained, which is difficult to meet the requirements of larger size solder balls. Moreover, the solder balls with a particle size of 265-295 μm only account for 70% of the total, indicating that the particle size distribution of the solder balls prepared by this method is too wide to meet the requirements of precision ball planting such as ball placement and laser ball planting.

[0005] In order to solve the defects and deficiencies in the prior art that it is impossible to simultaneously meet the preparation of solder balls with high melting points and large sizes, the prior art also discloses a device and method for preparing solder balls by droplet ejection. The solder is heated to a molten state, and a suitable nozzle aperture is selected according to the diameter of the solder ball, so that the molten solder is ejected through the small hole of the nozzle and falls into the coolant to solidify into solder balls. This device can be used for the preparation of low melting point solder balls below 400 °C and solder balls with a diameter greater than 1 mm. However, this method for preparing solder balls still has defects and deficiencies such as a complex device, high requirements for the processing shape of the nozzle, and a cumbersome cleaning operation for the solder balls in the subsequent process. Summary of the Invention

[0006] In order to overcome the above-mentioned defects and deficiencies in the prior art, the present invention provides a method for preparing solder balls, which uses solder sheets to prepare solder balls with higher melting points and larger sizes. The prepared solder balls have good roundness and good universality for solder raw materials that are not suitable for being processed into wires.

[0007] The above object of the present invention is achieved by the following technical solutions:

[0008] A method for preparing solder balls, comprising the following steps:

[0009] S1. Provide a flat plate, and a plurality of limiting grooves for accommodating solder sheets are arranged on the surface of the flat plate; a hemispherical limiting pit for accommodating molten solder is arranged on the bottom surface of the limiting groove;

[0010] S2. Place the solder sheet in the limiting groove;

[0011] S3. Heat the flat plate and the solder sheet until the solder melts, and the melted solder falls into the limiting pit, cools, and after the solder solidifies again, solder balls are obtained;

[0012] Among them, the material of the solder sheet is a metal with a melting temperature greater than 270 °C,

[0013] The length of the solder sheet is a, the width is b, and the thickness is c,

[0014] The diameter of the limiting pit is d, d ≥ 0.5 mm;

[0015] Satisfy a > d, and b > d,

[0016] And The value of is 2.7 - 3.6.

[0017] The present invention provides a method for preparing solder balls. After the solder in the method of the present invention is heated and melted, it will fall into the hemispherical limiting pit of the flat plate. By controlling the diameter d of the limiting pit, it is ensured that the solder balls have larger sizes and good roundness.

[0018] Compared with the preparation method of wire cutting and remelting, the present invention does not need to use high-temperature oil as the spheroidizing medium, reducing the limitation on the melting temperature of the solder, so it is applicable to the preparation of solder balls with a melting temperature greater than 270 °C. Moreover, since there is no need to use high-temperature oil as the spheroidizing medium, the cleaning process after spheroidization is eliminated. The present invention selects sheet solder which is easier to process as the production raw material, without first processing the solder into filaments, reducing the requirements for the processability of the solder.

[0019] Compared with the uniform droplet formation method, the preparation method of solder balls of the present invention is particularly applicable to the preparation of larger solder balls with a diameter of more than 0.5 mm. By controlling the precision of the limiting groove and the limiting pit, larger solder balls with a narrow particle size distribution can be obtained.

[0020] Compared with the droplet jetting method, the preparation method of solder balls of the present invention requires a simple structure of the limiting groove and the limiting pit, without a complex preparation device, nor a nozzle with high shape requirements, and the equipment cost is lower.

[0021] In the specific implementation manner, The values of are 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6.

[0022] In practical applications, the size of the limiting groove can be slightly larger than the size of the solder sheet, so that the solder sheet can be placed flat in the limiting groove.

[0023] In the specific implementation manner, the ratio of the length of the limiting groove to the length of the solder sheet is 1.005 to 1.05, and the ratio of the length of the limiting groove to the length of the solder sheet can be 1.005, 1.01, 1.015, 1.02, 1.025, 1.03, 1.035, 1.04, 1.045 or 1.05.

[0024] In the specific implementation manner, the ratio of the width of the limiting groove to the width of the solder sheet is 1.005 to 1.05, and the ratio of the width of the limiting groove to the width of the solder sheet can be 1.005, 1.01, 1.015, 1.02, 1.025, 1.03, 1.035, 1.04, 1.045 or 1.05.

[0025] In the specific embodiment, the ratio of the depth of the limiting groove to the thickness of the solder sheet is 1.01 to 1.30. The ratio of the depth of the limiting groove to the thickness of the solder sheet can be 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20, 1.21, 1.22, 1.23, 1.24, 1.25, 1.26, 1.27, 1.28, 1.29, 1.30.

[0026] In practical applications, the center of the limiting groove is correspondingly arranged with the center of the limiting pit.

[0027] Preferably, The value of is 2.8 to 3.5.

[0028] More preferably, The values of are 3.11, 3.12, 3.13, 3.14, 3.15, 3.16, 3.17, 3.18, 3.19, 3.2.

[0029] The value of within the range of 2.8 to 3.5 is more conducive to improving the roundness rate of the solder balls.

[0030] Preferably, the diameter d of the limiting pit is greater than or equal to 1 mm.

[0031] More preferably, 1 mm ≤ d ≤ 5 mm.

[0032] Preferably, 1.4 mm < d < 1.6 mm.

[0033] The method for preparing the solder balls of the present invention is particularly suitable for the preparation of solder balls with a larger diameter, and the prepared solder balls have good roundness.

[0034] Preferably, the solder sheet satisfies that the length a is equal to the width b.

[0035] The cross-sectional shape of the solder sheet is square. During actual operation, it is easier to place it in the limiting groove of the flat plate, and it is also easier to make the center of the solder sheet correspond to the center of the limiting pit, which is beneficial for the molten solder to fall into the limiting pit.

[0036] Preferably, the material of the solder sheet is a metal with a melting temperature of 270 to 1000 °C.

[0037] Preferably, the solder sheet is a silver-copper alloy, a gold-tin alloy or a gold-germanium alloy.

[0038] Alloys such as gold-tin alloy or gold-germanium alloy are brittle and have a low elongation rate, making it difficult to process them into continuous, uniform-performance and wound welding wires. However, these types of alloys are easier to process into sheets. Silver-copper alloy has a high melting temperature and is not suitable for preparation by the wire cutting and remelting method. Therefore, the method for preparing solder balls of the present invention is particularly applicable to alloys such as silver-copper alloy, gold-tin alloy or gold-germanium alloy.

[0039] In silver-copper alloy, the mass fraction of silver can be 50% - 95%, and the melting temperature is generally 600 - 1000°C.

[0040] In gold-tin alloy, the mass fraction of gold can be 70% - 80%, and the melting temperature is generally above 310°C.

[0041] In gold-germanium alloy, the mass fraction of gold can be 85% - 91%, and the melting temperature is generally above 400°C.

[0042] For alloys that can be processed into both wire and sheet, compared with the wire cutting and remelting method, the solder balls prepared by the method of the present invention have a higher roundness rate, indicating that the method of the present invention has better universality and is applicable to preparing solder balls from solders that can be processed into both wire and sheet.

[0043] In the present invention, the wetting angle between the flat plate and the molten solder is greater than 90°.

[0044] The flat plate is not wetted by the liquid molten solder, and the liquid molten solder can form solder balls with good roundness under the action of surface tension.

[0045] Preferably, the material of the flat plate is ferroalloy, titanium alloy, aluminum alloy or graphite.

[0046] The flat plates prepared from materials such as ferroalloy, titanium alloy, aluminum alloy or graphite are not easily wetted by the solder and can withstand high heating temperatures, so they are applicable to the method for preparing solder balls of the present invention.

[0047] Preferably, in step S3, the heating atmosphere is a vacuum or an inert gas atmosphere.

[0048] The heating atmosphere being a vacuum or an inert gas atmosphere ensures that the solder is not oxidized and avoids the pollution of the solder balls by hot oil in the prior art, greatly simplifying the cleaning process after the preparation of the solder balls.

[0049] The inert gas atmosphere can be nitrogen or argon.

[0050] More preferably, the heating atmosphere is a vacuum.

[0051] The air pressure in the vacuum environment does not exceed 10 Pa.

[0052] The present invention also protects a solder ball prepared by the preparation method of the solder ball described in any one of the above.

[0053] Preferably, the roundness rate of the solder ball is greater than or equal to 95%.

[0054] The solder ball prepared by the preparation method of the solder ball of the present invention has good roundness, and the roundness rate is greater than or equal to 95%.

[0055] For the solder ball prepared by the preparation method of the solder ball of the present invention, when the diameter of the solder ball is 1 mm to 1.5 mm, the roundness rate is greater than or equal to 96%. Further, the roundness rate can reach 96 - 99.9%.

[0056] The roundness rate is the ratio of the minor axis to the major axis of the largest cross-section of the solder ball multiplied by 100%. When the roundness rate is close to 100%, it is close to a theoretical circle.

[0057] The present invention also protects the application of the above solder ball in the semiconductor industry.

[0058] The above solder ball can be applied in BGA ball planting, solder bump preparation, and laser welding.

[0059] Compared with the prior art, the beneficial effects of the present invention are:

[0060] The present invention provides a preparation method of a solder ball. By not using a high-temperature oil spheroidizing medium, the limitation on the melting temperature of the solder is reduced, and the cleaning process after spheroidization is eliminated; by selecting a more easily processable sheet solder as the production raw material, there is no need to first process the solder into a filament shape, reducing the requirement for the processability of the solder. After the solder is heated and melted in the present invention, it will fall into the hemispherical limiting pits on the flat plate. By controlling the diameter d of the limiting pits, good roundness of the solder ball is ensured. The method of the present invention is applicable to the preparation of solder balls with a relatively high melting point and a relatively large size. The prepared solder balls have a high roundness rate and a narrow particle size distribution, and can meet the precise ball planting requirements such as ball placement and laser ball planting. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 It is a schematic structural diagram of a flat plate.

[0062] Figure 2 It is a side view of the solder sheet and the flat plate.

[0063] Figure 3 It is a top view of the solder ball sheet and the flat plate.

[0064] Figure 4 It is a schematic structural diagram of the solder ball and the flat plate.

[0065] In the figure, 1 - flat plate, 11 - limiting groove, 12 - limiting pit, 2 - solder sheet, 3 - solder ball. Detailed implementation manners

[0066] The present invention will be further described below in conjunction with specific implementation manners, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw material reagents used in the embodiments of the present invention are conventionally purchased raw material reagents.

[0067] Example 1

[0068] As Figures 1 to 4 shown, a method for preparing solder balls includes the following steps:

[0069] S1. Provide a flat plate 1, and a plurality of limiting grooves 11 for accommodating solder sheets 2 are arranged on the surface of the flat plate 1; a hemispherical limiting pit 12 for accommodating molten solder is arranged on the bottom surface of the limiting groove 11;

[0070] S2. Place the solder sheet 2 in the limiting groove 11;

[0071] S3. Heat the flat plate 1 and the solder sheet 2 until the solder melts, and the molten solder falls into the limiting pit 12, and after cooling, solder balls 3 are obtained after the solder solidifies again;

[0072] Among them, the length of the limiting groove 11 is A = 4.3 mm, the width is B = 4.3 mm, and the depth is C = 0.12 mm,

[0073] the length of the solder sheet 2 is a = 4.2 mm, the width is b = 4.2 mm, and the thickness is c = 0.1 mm,

[0074] the diameter of the limiting pit 12 is d = 1.5 mm,

[0075] satisfy a > d and b > d,

[0076] and the value of is 3.136.

[0077] Among them, the solder sheet 2 is a gold-tin alloy Au80Sn20, that is, the mass fraction of gold is 80% and the mass fraction of tin is 20%.

[0078] The material of the flat plate 1 is graphite.

[0079] In step S3, the heating atmosphere is a vacuum atmosphere.

[0080] The air pressure in the vacuum environment does not exceed 10 Pa.

[0081] The heating temperature is 310 °C.

[0082] Example 2

[0083] A method for preparing solder balls includes the following steps:

[0084] S1. Provide a flat plate 1, on the surface of which there are provided a number of limiting grooves 11 for accommodating solder sheets 2; on the bottom surface of the limiting grooves 11, there are provided hemispherical limiting pits 12 for accommodating molten solder;

[0085] S2. Place the solder sheet 2 in the limiting groove 11;

[0086] S3. Heat the flat plate 1 and the solder sheet 2 until the solder melts, and the molten solder falls into the limiting pit 12, and after cooling, solder balls 3 are obtained after the solder solidifies again;

[0087] Among them, the length of the limiting groove 11 is A = 4.3 mm, the width is B = 4.3 mm, and the depth is C = 0.12 mm,

[0088] the length of the solder sheet 2 is a = 1.65 mm, the width is b = 1.65 mm, and the thickness is c = 0.1 mm,

[0089] the diameter of the limiting pit 12 is d = 0.8 mm,

[0090] satisfy a > d and b > d,

[0091] and The value of is 3.19.

[0092] Among them, the solder sheet 2 is a gold-tin alloy Au80Sn20, that is, the mass fraction of gold is 80% and the mass fraction of tin is 20%.

[0093] The material of the flat plate 1 is graphite.

[0094] In step S3, the heating atmosphere is a vacuum atmosphere.

[0095] The air pressure in the vacuum environment does not exceed 10 Pa.

[0096] The heating temperature is 310 °C.

[0097] The difference between Example 2 and Example 1 is that the length of the solder sheet and the diameter of the limiting pit are different.

[0098] Example 3

[0099] A method for preparing solder balls, comprising the following steps:

[0100] S1. Provide a flat plate 1, on the surface of which there are provided a number of limiting grooves 11 for accommodating solder sheets 2; on the bottom surface of the limiting grooves 11, there are provided hemispherical limiting pits 12 for accommodating molten solder;

[0101] S2. Place the solder sheet 2 in the limiting groove 11;

[0102] S3. Heat the flat plate 1 and the solder sheet 2 until the solder melts. The molten solder falls into the limiting pit 12, cools, and after the solder solidifies again, solder balls 3 are obtained;

[0103] Among them, the length of the limiting groove 11 is A = 4.3 mm, the width is B = 4.3 mm, and the depth is C = 0.12 mm.

[0104] The length of the solder sheet 2 is a = 4.2 mm, the width is b = 4.2 mm, and the thickness is c = 0.1 mm.

[0105] The diameter of the limiting pit 12 is d = 1.5 mm.

[0106] It satisfies a > d and b > d.

[0107] And The value of is 3.136.

[0108] Among them, the solder sheet 2 is a silver-copper alloy Ag72Cu28, that is, the mass fraction of silver is 72% and the mass fraction of copper is 28%.

[0109] The material of the flat plate 1 is graphite.

[0110] In step S3, the heating atmosphere is a vacuum atmosphere.

[0111] The air pressure in the vacuum environment does not exceed 10 Pa.

[0112] The heating temperature is 810 °C.

[0113] The difference between Example 3 and Example 1 lies in the type of solder sheet and the heating temperature.

[0114] Example 4

[0115] A method for preparing solder balls, comprising the following steps:

[0116] S1. Provide a flat plate 1, and a plurality of limiting grooves 11 for accommodating the solder sheet 2 are arranged on the surface of the flat plate 1; a hemispherical limiting pit 12 for accommodating molten solder is arranged on the bottom surface of the limiting groove 11;

[0117] S2. Place the solder sheet 2 in the limiting groove 11;

[0118] S3. Heat the flat plate 1 and the solder sheet 2 until the solder melts. The molten solder falls into the limiting pit 12, cools, and after the solder solidifies again, solder balls 3 are obtained;

[0119] Among them, the length of the limiting groove 11 is A = 4.3 mm, the width is B = 4.3 mm, and the depth is C = 0.12 mm.

[0120] The length of the solder sheet 2 is a = 4.2 mm, the width is b = 4.2 mm, and the thickness is c = 0.1 mm.

[0121] The diameter of the limiting pit 12 is d = 1.5 mm.

[0122] It satisfies a > d and b > d.

[0123] And The value of is 3.136.

[0124] Among them, the solder sheet 2 is a gold-germanium alloy Au88Ge12, that is, the mass fraction of gold is 88% and the mass fraction of germanium is 12%.

[0125] The material of the flat plate 1 is graphite.

[0126] In step S3, the heating atmosphere is a vacuum atmosphere.

[0127] The air pressure in the vacuum environment does not exceed 10 Pa.

[0128] The heating temperature is 400 °C.

[0129] The difference between Example 4 and Example 1 lies in the type of solder sheet and the heating temperature.

[0130] Comparative Example 1

[0131] A method for preparing solder balls includes the following steps:

[0132] S1. Put a square Au80Sn20 with a side length of 4.2 mm and a thickness of 0.1 mm into hot oil, and the heating temperature of the hot oil is 310 °C.

[0133] S2. After the solder in the hot oil in step S1 is cooled and solidified, take out the solder and wash to remove the hot oil on the surface, and solder balls with a diameter of 1.5 mm are obtained.

[0134] Comparative Example 2

[0135] A method for preparing solder balls includes the following steps:

[0136] S1. Cut a Au80Sn20 wire with a diameter of 1 mm into a cylinder with a length of 2.25 mm and put it into hot oil, and the heating temperature of the hot oil is 310 °C.

[0137] S2. After the solder in the hot oil in step S1 is cooled and solidified, take out the solder and wash to remove the hot oil on the surface, and solder balls with a diameter of 1.5 mm are obtained.

[0138] Result detection

[0139] Measure the roundness and circularity rate of the solder balls prepared in the examples and comparative examples.

[0140] The roundness rate is measured by a microscope, and the calculation method is the ratio of the minor axis to the major axis of the maximum cross-section of the solder ball multiplied by 100%.

[0141] The test results of each example and comparative example are shown in Table 1.

[0142] Table 1 Test results of each example and comparative example

[0143]

[0144] It can be seen from Table 1 that the solder balls with a diameter of 0.8 - 1.5 mm and a relatively high melting point can be prepared in the examples of the present invention. The roundness rate of the solder balls can reach 95.2 - 97.2%, showing good roundness. From the maximum and minimum diameters, it can be seen that the particle size distribution of the solder balls prepared in the examples of the present invention is narrow, which can meet the requirements of precision ball placement such as ball placement and laser ball placement.

[0145] It can be seen from Example 1 and Comparative Example 1 that, compared with directly adding sheet solder into hot oil to melt it into a spherical shape, the solder balls prepared by the method of the present invention have better roundness. This is because in Comparative Example 1, due to the too high heating temperature of the oil, the thermal stability of the oil is poor at high temperatures, which will reduce the roundness of the solder balls during the preparation process.

[0146] It can be seen from Example 1 and Comparative Example 2 that since the processing difficulty of gold-tin alloy sheet is lower than that of wire, the production difficulty is reduced while ensuring a relatively high roundness rate.

[0147] It can be seen from Example 3 and Example 4 that the method of the present invention has better universality and is suitable for the preparation of solder balls with high melting temperatures.

[0148] It can be seen from Example 1 and Example 2 that the preparation method of the present invention is more suitable for preparing larger-sized solder balls, and the larger-sized solder balls also have good roundness.

[0149] Obviously, the above-mentioned examples of the present invention are only examples for clearly explaining the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing solder balls, characterized in that, It includes the following steps: S1. Provide a flat plate, on the surface of which there are several limiting grooves for accommodating solder pieces; on the bottom surface of the limiting grooves, there are hemispherical limiting pits for accommodating molten solder; S2. Place the solder pieces in the limiting grooves; S3. Heat the flat plate and the solder pieces until the solder melts, and the molten solder falls into the limiting pits, and after cooling, solder balls are obtained after the solder solidifies again; Wherein, the solder piece is a gold-tin alloy or a gold-germanium alloy; In the gold-tin alloy, the mass fraction of gold is 70% - 80%; In the gold-germanium alloy, the mass fraction of gold is 85% - 91%; The length of the solder piece is a, the width is b, and the thickness is c, The diameter of the limiting pit is d, d≥0.5mm; Satisfy a > d, and b > d, and has a value of 2.7 to 3.

6.

2. The method for preparing a solder ball according to claim 1, wherein, The value is 2.8 to 3.

5.

3. The method for preparing solder balls according to claim 1, wherein, 1mm ≤ d ≤ 5mm.

4. The method for preparing solder balls according to claim 1, wherein The solder piece satisfies that the length a is equal to the width b.

5. The method for preparing solder balls according to claim 1, characterized in that, The material of the flat plate is ferroalloy, titanium alloy, aluminum alloy or graphite.

6. The method for preparing solder balls according to claim 1, wherein, In step S3, the heating atmosphere is a vacuum or an inert gas atmosphere.

7. A solder ball prepared by the method for preparing a solder ball according to any one of claims 1 - 6.

8. The solder ball according to claim 7, wherein, The roundness rate of the solder ball is greater than or equal to 95%.

9. The application of the solder ball according to claim 7 or 8 in the semiconductor industry.

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