Soldering flux coating spheres and methods of making the same

Abstract

The present invention provides a flux-coated solder ball and a method for producing the same. The flux-coated solder ball 100 of the present invention has a core 110 and a shell 120 covering the core 110. The core 110 is made of a solder ball or a copper core ball. The shell 120 is made of a flux layer containing at least one selected from an activator and a resin component. The oxide film thickness in the flux-coated solder ball 100 is 3 nm or less. According to the present invention, a flux-coated solder ball having improved wettability on a wafer is provided. A method for producing the flux-coated solder ball as a simple method is provided, which is difficult to cause agglomeration of the balls.

Description

Technical Field

[0001] This invention relates to a flux-coated ball and a method for preparing the same. This application claims priority based on Japanese Patent Application No. 2022-019052, filed on February 9, 2022, the contents of which are incorporated herein by reference. Background Technology

[0002] Methods for forming solder bumps include plating, solder paste printing, and ball mounting, and each method is considered to have its own advantages and disadvantages.

[0003] Among these methods, the ball-mount method involves directly mounting small spherical solder balls onto the electrodes and forming bumps through reflow soldering. Compared to other methods, it has advantages such as improving bump size and reducing bump height deviation. On the other hand, the ball-mount method requires mounting solder balls across the entire wafer surface, and due to the large number of solder balls, improving yield becomes a problem.

[0004] In forming solder bumps using the ball-mounting method, firstly, flux is applied to the electrodes on the wafer through a metal mask. Then, solder balls are mounted by aligning them with the flux-coated electrodes on the wafer. Next, the wafer with the solder balls mounted is reflow soldered, melting the solder balls to form solder bumps.

[0005] With the development of small information devices, the electronic components they carry are rapidly becoming miniaturized. This miniaturization necessitates smaller connection terminals and a smaller mounting area. Consequently, it becomes difficult to stably print flux onto narrow-pitch patterns when forming solder bumps.

[0006] In response, flux-coated balls have been proposed, in which flux is pre-coated onto the surface of the solder ball. For example, a flux-coated ball is disclosed that is made by coating the surface of a small spherical solder ball with liquid flux and then drying it (see Patent Document 1).

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Publication No. 2017-119291 Summary of the Invention

[0010] The problem to be solved by the present invention

[0011] However, in conventional flux-coated balls, there is a problem of agglomeration during the preparation process, where liquid flux is applied to the ball and then dried. Furthermore, from the viewpoint of wafer wettability, existing flux-coated balls require further improvement.

[0012] The present invention was made in view of the above circumstances, and its object is to provide a flux-coated ball that improves the wettability of a wafer; and to provide a simple method for preparing flux-coated balls that are difficult to generate agglomerates.

[0013] Problem-solving methods

[0014] To solve the above problems, the present invention employs the following methods.

[0015] [1] A flux-coated ball, characterized in that it comprises a core and a shell covering the core, the core being composed of a solder ball or a copper core ball, the shell being composed of a flux layer containing at least one selected from an activator and a resin component, and the oxide film thickness of the flux-coated ball being less than 3 nm.

[0016] [2] According to the flux-coated ball of [1], wherein the sphericity of the flux-coated ball is 0.990 or higher.

[0017] [3] The flux-coated ball according to [1] or [2], wherein the thickness of the flux layer is more than 0.5 μm and less than 2.5 μm.

[0018] [4] A flux-coated ball according to any one of [1]-[3], wherein the surface roughness (Ra) of the flux layer is less than 2.0 μm.

[0019] [5] A flux-coated ball according to any one of [1]-[4], wherein the activator contains at least an organic acid.

[0020] [6] The flux-coated ball according to [5], wherein the organic acid is at least one selected from glutaric acid, diethylene glycol, malonic acid, citric acid, pimelic acid, adipic acid and 2,2-di(hydroxymethyl)propionic acid.

[0021] [7] The flux-coated ball according to any one of [1]-[6], wherein the diameter of the ball as a whole is more than 30 μm and less than 300 μm.

[0022] [8] A method for preparing a flux-coated ball, characterized in that it is a method for preparing a flux-coated ball having a core and a shell, wherein the core is composed of a solder ball or a copper core ball, and the shell is composed of a flux layer containing at least one selected from an activator and a resin component, and covers the core, wherein the method for preparing the flux-coated ball has a dry processing step, wherein the dry processing step involves heating the solder ball or copper core ball and the flux material while oscillating and stirring, wherein the flux material contains at least one selected from an activator and a resin component.

[0023] [9] According to the preparation method of flux-coated balls described in [8], in the dry processing step, the ratio (mass ratio) of the solder ball or copper core ball to the flux material is set to 1 to 10, and the solder ball or copper core ball and the flux material are stirred by vibration while being heated.

[0024] The effects of the invention

[0025] According to the present invention, a flux-coated ball with improved wettability to wafers can be provided; a method for preparing flux-coated balls that is easy to generate and is difficult to aggregate can be provided. Attached Figure Description

[0026] Figure 1 This is a cross-sectional view showing one embodiment of a flux-coated ball.

[0027] Figure 2 These are photographs showing the appearance of the flux-coated ball of Example 1 and the flux-coated ball of Comparative Example 1.

[0028] Figure 3 These are photographs showing only the appearance of the flux-coated balls and solder balls in Examples 2 to 5.

[0029] Explanation of symbols

[0030] 100 Flux-coated Balls, 110 Core, 120 Shell Detailed Implementation

[0031] Hereinafter, the flux-coated ball of this embodiment will be described in detail with reference to the accompanying drawings. In addition, in the following drawings, the dimensions, proportions, etc., of each component are appropriately varied for ease of reading.

[0032] In embodiments of this disclosure, the size ratios of the constituent elements in the reference drawings are not limited to those shown in the drawings.

[0033] The specific structure of the embodiments of the present invention is not limited to the embodiments disclosed herein. As long as it does not depart from the spirit of the present disclosure, changes and substitutions can be made.

[0034] (Fluoride-coated balls)

[0035] One aspect of the present invention is a flux-coated ball comprising a core and a shell covering the core.

[0036] In this flux-coated ball, the core is composed of solder balls or copper core balls. The shell is composed of a flux layer containing at least one selected from activators and resin components.

[0037] In this flux-coated ball, the oxide film thickness is less than 3 nm.

[0038] <First Implementation>

[0039] Figure 1 This is a cross-sectional view showing one embodiment of a flux-coated ball.

[0040] exist Figure 1 In the process, the flux-coated ball 100 has a spherical core 110 and a shell 120 that covers the entire core 110.

[0041] • Regarding the oxide film thickness of flux-coated ball 100

[0042] In this invention, the so-called oxide film thickness of the flux-coated ball refers to the thickness of the oxide film existing on the surface of the core, which is a SiO2 conversion value.

[0043] The thickness of the oxide film present on the core surface (the thickness of the oxide film on the core surface) was measured as follows.

[0044] The flux-coated balls used as test samples were ultrasonically cleaned in acetone for 20 minutes. Then, the surface of the ultrasonically cleaned test samples was measured by Auger electron spectroscopy.

[0045] For example, an Auger electron spectroscopy analyzer (such as the PHI700 manufactured by ULVAC-PHI Corporation) was used as the analytical apparatus. The analytical conditions were set as follows: accelerating voltage 10 kV, current 10 nA, and analytical diameter 20 μm.

[0046] In the flux-coated ball 100, the oxide film thickness on the surface of the core 110 is 3 nm or less, preferably 2.5 nm or less, and more preferably 2.0 nm or less.

[0047] If the oxide film thickness on the surface of the core 110 is below the upper limit of the above range, the wetting spread relative to the wafer is good and the wettability is improved.

[0048] The smaller the oxide film thickness on the surface of the core 110, the thinner the oxide film, which is therefore preferred. The lower limit of the oxide film thickness on the surface of the core 110 is, for example, 0.5 nm.

[0049] Regarding the diameter of flux-coated ball 100

[0050] In this invention, the diameter of the so-called flux-coated ball refers to the overall diameter of the flux-coated ball, i.e., the diameter, which is equivalent to... Figure 1 The "R" in 100 ".

[0051] The diameter (R) of the flux-coated ball 100 100For example, it can be 30μm or more and 300μm or less, or 35μm or more and 200μm or less, or 40μm or more and 150μm or less, or 45μm or more and 100μm or less.

[0052] By adjusting the diameter (R) of the flux-coated ball 100 100 Within the above range, it is easy to meet the requirements for narrower pattern spacing.

[0053] • Regarding the sphericity of flux-coated balls 100

[0054] The sphericity of the flux-coated balls 100 is, for example, 0.990 or higher.

[0055] By making the sphericity of the flux coating balls 100 greater than 0.990, it is easy to adjust the height of the solder bumps to a more uniform height.

[0056] There is no particular upper limit to the sphericity of the flux-coated balls 100; for example, it can be 0.999, or it can be 1.000 in the measurement.

[0057] The sphericity of the flux-coated ball is determined as follows.

[0058] For 500 flux-coated balls used as test samples, calculate the arithmetic mean of their diameter divided by their major diameter. The closer this arithmetic mean is to 1.000 (the upper limit), the closer the shape of the flux-coated ball is to a sphere.

[0059] The major and minor lengths of a sample can be measured, for example, using the ULTRA QV350-PRO measuring device manufactured by Mitutoyo Corporation.

[0060] • Relationship regarding the mass ratio in flux-coated balls 100

[0061] The proportion of the core 110 in the flux-coated ball 100 is, for example, 95% by mass or more, 96% by mass or more and 99.8% by mass or less, 97% by mass or more and 99.7% by mass or less, or 98% by mass or more and 99.6% by mass or less.

[0062] The proportion of the shell portion 120 in the flux-coated ball 100 is, for example, 5% by mass or less, or 0.2% by mass or more and 4% by mass or less, or 0.3% by mass or more and 3% by mass or less, or 0.4% by mass or more and 2% by mass or less.

[0063] When the proportions of the core portion 110 and the shell portion 120 in the flux-coated ball 100 are within the range described above, a certain amount of flux is ensured to further improve the wettability of the wafer.

[0064] The proportions of the core 110 and the shell 120 in the flux-coated ball 100 can be determined by washing the flux-coated ball 100 with acetone and then drying it, based on the mass before washing and the mass after drying.

[0065] • Regarding the surface roughness of flux-coated ball 100

[0066] In this invention, the surface roughness of the flux-coated ball refers to the surface roughness (Ra) of the flux layer.

[0067] The surface roughness (Ra) of the flux-coated ball 100, i.e. the surface roughness of the flux layer 120, is, for example, 2.0 μm or less, preferably 1.8 μm or less, and more preferably 1.6 μm or less.

[0068] If the surface roughness (Ra) of the flux layer 120 is below the upper limit of the above range, the sphericity of the flux-coated balls 100 is improved.

[0069] Since a lower surface roughness (Ra) of the flux layer 120 results in a smoother surface, this is preferred. The lower limit of the surface roughness (Ra) of the flux layer 120 is, for example, 0.5 μm.

[0070] The surface roughness of the flux-coated ball is calculated as follows.

[0071] The surface roughness of the flux-coated spheres used as test samples, i.e., the surface of the flux layer, is measured within a specified range using a laser microscope. For example, using a confocal microscope manufactured by Lasertec Corporation, the objective lens magnification is adjusted to 50x, the measurement interval on the z-axis is set to 0.1 μm, and the surface roughness (Ra) of any three flux-coated spheres is measured. Then, their arithmetic mean is calculated.

[0072] Core

[0073] In the flux-coated ball 100, the core 110 is composed of solder balls or copper core balls.

[0074] The diameter of core 110 (R) 110 For example, it can be 30μm or larger and 295μm or smaller, or it can be 30μm or larger and 250μm or smaller, or it can be 40μm or larger and 200μm or smaller.

[0075] In addition, the diameter (R) of the core 110 110 ) refers to the diameter of the core 110, which is equivalent to the diameter of the solder ball or copper core ball.

[0076] Materials used for the solder balls constituting the core 110 include, for example, Sn and solder alloys with Sn as the main component. The Sn content in a solder alloy with Sn as the main component is, for example, 5% by mass or more, 10% by mass or more, or 40% by mass or more, relative to the total amount of the solder alloy.

[0077] Examples of solder alloys include Sn-Ag alloys, Sn-Cu alloys, Sn-Ag-Cu alloys, Sn-In alloys, Sn-Pb alloys, Sn-Bi alloys, and Sn-Bi-Ag-Cu alloys.

[0078] Any alloying element can be added to the solder alloy. Examples of such alloying elements include Ag, Cu, In, Ni, Co, Sb, Ge, P, Fe, and Ga.

[0079] As a copper core ball constituting the core 110, an example is a copper core ball on which a plating treatment has been performed. The composition of the plating is not particularly limited, and the plating treatment can be performed multiple times with the same or different plating compositions. For example, an example is a Ni plating treatment performed on the surface of the copper ball as a diffusion-preventing barrier layer, followed by a Sn-Ag-Cu alloy plating treatment on the surface of this Ni plating layer.

[0080] Shell section

[0081] In the flux-coated ball 100, the shell portion 120 is composed of a flux layer containing at least one selected from activators and resin components.

[0082] The thickness of flux layer 120 (T) 120 For example, it can be 0.10μm or higher and 2.0μm or lower, or 0.15μm or higher and 1.5μm or lower, or 0.20μm or higher and 1.0μm or lower, or 0.25μm or higher and 0.80μm or lower.

[0083] When the thickness of flux layer 120 (T) 120 When the flux content is above the lower limit of the above range, a certain amount of flux can be ensured, further improving the wettability of the wafer. On the other hand, if the flux content is below the upper limit of the above range, it is less likely to cause the agglomeration of flux-coated balls 100.

[0084] The flux layer constituting the shell 120 contains at least one selected from activators and resin components, and may also contain other components as needed.

[0085] As an active agent, it can be appropriately selected according to the required properties, such as organic acids and amines.

[0086] Examples of organic acids include aliphatic carboxylic acids, aromatic carboxylic acids, and other organic carboxylic acids; as well as aliphatic sulfonic acids, aromatic sulfonic acids, and other organic sulfonic acids.

[0087] Examples of amines include azoles, guanidines, alkylamine compounds, and amino alcohols.

[0088] As a resin component, it can be appropriately selected according to the required properties. Examples include rosin, terpene resin, modified terpene resin, terpene phenol resin, modified terpene phenol resin, styrene resin, modified styrene resin, xylene resin, modified xylene resin, acrylic resin, polyethylene resin, acrylic-polyethylene copolymer resin, epoxy resin, etc.

[0089] Of the above, from the perspective of suppressing oxidation of the core and imparting wettability, the flux layer constituting the shell 120 preferably contains at least an activator.

[0090] The surfactant here, from the viewpoint of coating the core 110, preferably contains at least one selected from organic acids and amines, and more preferably contains at least an organic acid.

[0091] The flux layer constituting the shell 120 is preferably a layer containing at least an organic acid. Examples include a layer consisting only of organic acids, a layer containing organic acids and resin components, a layer containing organic acids and amines, and a layer containing organic acids, resin components, and amines.

[0092] The organic acid here is preferably an organic carboxylic acid, more preferably an aliphatic carboxylic acid, and particularly preferably at least one selected from glutaric acid, diethylene glycol, malonic acid, citric acid, pimelic acid, adipic acid and 2,2-di(hydroxymethyl)propionic acid.

[0093] The flux layer may contain one or more components.

[0094] The content of activator in the flux layer is, for example, 10% by mass or more and 100% by mass or less, relative to the entire flux layer.

[0095] The resin content in the flux layer is, for example, 0% by mass or more and 90% by mass or less, relative to the entire flux layer.

[0096] The flux layer constituting the shell 120 may also contain components other than activators and resin components (any components).

[0097] Examples of such components include antioxidants and colorants.

[0098] According to the first embodiment described above, a flux-coated ball 100 with improved wettability to a wafer can be provided.

[0099] The flux-coated ball 100 of the first embodiment includes a core 110 and a shell 120 covering the core 110. The core 110 is composed of solder balls or copper core balls and electrically bonds electrodes on a wafer to electrodes in a semiconductor package. The shell 120 is composed of a flux layer containing at least one selected from surfactants and resin components, which removes the oxide film on the surface of the core 110 and the metal oxide film on the surface of the electrodes during reflow soldering, thereby improving the wettability of the core 110 and the electrodes.

[0100] The flux-coated ball 100 of the first embodiment has an oxide film thickness (i.e., the thickness of the oxide film present on the surface of the core) of 3 nm or less. This oxide film thickness of 3 nm or less is substantially the same as the oxide film thickness of the individual solder balls or copper core balls constituting the core. Thus, by controlling the oxide film thickness to be relatively thin, the wettability to the wafer can be improved through the flux-coated ball 100.

[0101] <Other Implementation Methods>

[0102] In the first embodiment described above, the shell portion 120 covering the core portion 110 was described as a structure consisting of a single-layer flux layer, but it is not limited to this structure. An embodiment could also be implemented where the shell portion covering the core portion 110 is composed of multiple flux layers. According to this embodiment, each of the multiple flux layers can have different effects.

[0103] In the flux-coated ball 100 of the first embodiment described above, it is explained that the shell portion 120 covers the entire core portion 110, but this description is not limited to this. It is also possible for the shell portion to cover a portion of the core portion 110. For example, it is also possible for an embodiment to have a shell portion that covers a portion of the core portion 110 in such a way that the shell portion is in contact with at least the electrode on the wafer when the flux-coated ball is directly mounted on the electrode.

[0104] One aspect of the present invention is a flux-coated ball useful in forming solder bumps by a ball-mounting method. According to this flux-coated ball, flux can be stably supplied over a narrow-pitch pattern during solder bump formation.

[0105] (Preparation method of flux-coated balls)

[0106] One aspect of the present invention is a method for preparing a flux-coated ball, which is a method for preparing a flux-coated ball having a core and a shell, wherein the core is composed of a solder ball or a copper core ball, and the shell is composed of a flux layer containing at least one selected from an activator and a resin, and covers the core.

[0107] The preparation method of the flux-coated ball includes a dry processing step, in which the solder ball or copper core ball and flux material are heated and stirred by vibration. The flux material contains at least one selected from activators and resin components.

[0108] The flux-coated ball 100 of the above embodiment can be prepared using the flux-coated ball preparation method described in one of the above embodiments.

[0109] The diameter of the solder ball or copper core ball used in the core 110 is, for example, 30 μm or more and 295 μm or less, 30 μm or more and 250 μm or less, or 40 μm or more and 200 μm or less.

[0110] As examples of solder balls or copper core balls used in the core 110, those illustrated in the above description of the "Core" can be cited.

[0111] Flux materials can be in powder form, for example. As a powdered flux material, it is preferable to use a powdered flux material in which 50% of the particle size when the total volume of the powder group is set to 100% and the cumulative curve is obtained has a particle size of 100 μm or more and 1000 μm or less.

[0112] Examples of flux materials include those exemplified in the description of the above-mentioned organic acid, amine, and resin components.

[0113] <Dry Processing Procedure>

[0114] In the dry processing step, solder balls or copper core balls and flux material containing at least one selected from activators and resin components are agitated and stirred while being heated.

[0115] The mixing ratio of solder balls or copper core balls to flux material can be adjusted appropriately according to the required thickness of the flux layer and the diameter of the solder balls or copper core balls.

[0116] For example, when the ball diameter is 30 μm or more and 100 μm or less, the ratio (mass ratio) of the solder ball or copper core ball to the flux material is preferably ball / flux material = 1 to 10, more preferably 1.5 to 7.5, and even more preferably 2 to 6.

[0117] If the mass ratio is above the lower limit of the above-mentioned preferred range, the flux material can easily coat the entire ball; on the other hand, if it is below the upper limit of the above-mentioned preferred range, the flux layer can be prevented from becoming too thick.

[0118] The heating temperature in the dry processing step is preferably set according to the melting point of the flux material. If the heating temperature is too high, the balls may stick to the inner wall of the container where the agitation is performed; on the other hand, if the heating temperature is too low, the flux material may not adequately coat the surface of the balls.

[0119] The preferred heating temperature is a flux material with a melting point of -35°C or higher and a melting point of -5°C or lower, and more preferably a flux material with a melting point of -25°C or higher and a melting point of -10°C or lower.

[0120] The oscillation and stirring operation in the dry processing step is preferably performed simultaneously with heating at the aforementioned temperature conditions. Alternatively, it is preferable to preheat before performing the oscillation and stirring operation. Preheating can, for example, be performed at the same temperature conditions as the heating described above.

[0121] In the dry processing step, the flux material and solder balls or copper core balls are placed into any container such as a centrifuge tube. Then, the container is heated to a temperature suitable for the flux material used, while simultaneously being agitated with a specified number of strokes.

[0122] The number of strokes and the mixing time can be adjusted appropriately. The number of strokes is preferably 500-4000 strokes per minute, more preferably 1500-2500 strokes per minute. The mixing time is preferably 10-120 minutes, more preferably 30-90 minutes.

[0123] According to the above description of the method for preparing flux-coated balls, since a dry method is used, even after heating and oscillating, it is difficult for the balls to agglomerate, and flux-coated balls with good dispersion can be prepared.

[0124] Furthermore, the method for preparing this flux-coated ball only requires the operation of oscillating and stirring the solid materials, and does not require operations such as solvent removal in wet processes, making it a simple method.

[0125] In this method for preparing flux-coated balls, because a dry method is used, it is easy to control the oxide film thickness (the thickness of the oxide film present on the core surface) to be thinner, and flux-coated balls with improved wettability to wafers can be prepared stably.

[0126] Furthermore, in the preparation method of this flux-coated ball, since the operation of oscillation and stirring is adopted, it is easy to control the flux layer constituting the shell to a uniform thickness, which makes it easy to improve the sphericity and achieve improved performance as a ball.

[0127] The method for preparing a flux-coated ball according to the above-described embodiment has been described as a preparation method having a dry processing step, but it is not limited to this embodiment. Embodiments may also include any steps other than the dry processing step. As an example of an arbitrary step, a step of further forming a second flux layer on the first flux layer constituting the shell portion 120 can be cited. According to this embodiment, a flux-coated ball whose shell portion covering the core portion 110 is composed of multiple flux layers can be prepared.

[0128]

Example

[0129] The present invention will be described below through embodiments, but the present invention is not limited to the following embodiments.

[0130] In this embodiment, the respective materials of the core and shell used in the preparation of flux-coated balls are shown.

[0131] As the core material, a spherical metal ball as shown below is used.

[0132] Solder ball (C-1): A solder ball composed of an alloy of 99.3% by mass Sn and 0.7% by mass Cu, with a diameter (R) 110 63μm.

[0133] Solder balls (C-2): Solder balls composed of an alloy of 96.5% by mass Sn, 3.0% by mass Ag, and 0.5% by mass Cu, with a diameter (R) 110 100μm.

[0134] Solder balls (C-3): Solder balls composed of an alloy of Sn43 by mass and Bi57 by mass, with a diameter (R) 110 The value is 100μm.

[0135] Copper core ball (C-4): A copper core ball with Sn-3Ag-0.5Cu plating treatment on its surface, with a diameter (R) 110 220μm.

[0136] Solder balls (C-5): Solder balls composed of an alloy of 96.5% by mass Sn, 3.0% by mass Ag, and 0.5% by mass Cu, with a diameter (R) 110 300μm.

[0137] Solder ball (C-6): A solder ball composed of an alloy of 99.3% by mass Sn and 0.7% by mass Cu, with a diameter (R) 110 44μm.

[0138] The following flux material was used as the material for the shell.

[0139] Flux material (S-1): glutaric acid (melting point 95℃), 50% particle size 314μm

[0140] Flux material (S-2): Diethylene glycol (melting point 144℃), 50% particle size 335μm

[0141] Flux material (S-3): malonic acid (melting point 135℃), 50% particle size 362μm

[0142] Flux material (S-4): Citric acid (melting point 153℃), 50% particle size 288μm

[0143] Flux material (S-5): Pyridic acid (melting point 106℃), 50% particle size 254μm

[0144] Flux material (S-6): Adipic acid (melting point 152℃), 50% particle size 325μm

[0145] <Preparation of flux-coated balls (1)>

[0146] (Example 1)

[0147] 1.2g of powdered flux material (S-1) with a particle size of 314μm (50% of the total volume used to calculate the cumulative curve) and 6g of solder balls (C-1) were added to a cylindrical centrifuge tube (4cm in diameter and 12cm in length) and sealed.

[0148] Next, the centrifuge tube containing flux material (S-1) and solder balls (C-1) was preheated at 75°C for 5 minutes. The preheating temperature was set to the melting point of flux material (S-1) -20°C.

[0149] Next, the preheated centrifuge tube is heated to 75°C, while simultaneously agitating and stirring along its long axis for 60 minutes. The heating temperature is set to the same temperature as the preheating temperature: the melting point of the flux material (S-1) - 20°C. The agitation and stirring is performed at 2000 strokes per minute.

[0150] Next, after oscillation and stirring, the mixture is cooled to room temperature (23°C), thereby obtaining a flux-coated ball having a core composed of solder balls (C-1) and a shell composed of a layer of glutaric acid (flux layer) covering the entire core.

[0151] (Comparative Example 1)

[0152] Dissolve the flux material (S-1) in acetone to prepare a glutaric acid solution with a concentration of 100 g / L.

[0153] Next, 6g of solder ball (C-1) was immersed in the solution and stirred at room temperature (23°C) for 1 hour.

[0154] Next, the stirred solder ball (C-1) is removed from the solution and dried to evaporate and remove acetone, thereby obtaining a flux-coated ball having a core composed of solder ball (C-1) and a shell composed of a layer of glutaric acid (flux layer) covering the entire core.

[0155] <Evaluation (1)>

[0156] For the flux-coated balls of Example 1 and Comparative Example 1 obtained above, the appearance and diameter (R) of the flux-coated balls were evaluated respectively. 100 ) and its standard deviation, sphericity of flux-coated balls and its standard deviation, thickness of flux layer (T) 120 The following factors were considered: the proportion of the shell in the flux-coated balls, the thickness of the oxide film on the flux-coated balls, the surface roughness (Ra) of the flux layer, the difficulty of peeling off the flux layer, the wettability of the flux-coated balls, and the dispersion state of the freshly prepared balls.

[0157] The details of each evaluation are as follows.

[0158] [Appearance]

[0159] Figure 2 These are photographs showing the appearance of the flux-coated ball of Example 1 and the flux-coated ball of Comparative Example 1.

[0160] from Figure 2 It can be confirmed that in either Example 1 or Comparative Example 1, the solder ball (C-1) at the core is entirely covered by a layer of glutaric acid (flux layer).

[0161] It was confirmed that the surface of the flux-coated ball of Example 1 had higher smoothness compared to the surface of the flux-coated ball of Comparative Example 1.

[0162] [Diameter of flux-coated ball (R)] 100 ) and sphericity

[0163] The diameter (R) of the flux-coated ball was determined using a CNC image measurement system. 100 ) and sphericity. Specifically, the ULTRA QUICK VISION and ULTRA QV350-PRO measuring devices manufactured by Mitutoyo Co., Ltd. were used.

[0164] Using this measuring device, the length of the major axis and the length of the diameter of each flux-coated ball are measured. The arithmetic mean of the diameter divided by the major axis of each of the 500 flux-coated balls is calculated to determine the sphericity. The closer the value is to the upper limit of 1.000, the closer it is to a sphere.

[0165] In addition, the arithmetic mean of the diameters of the 500 flux-coated balls was calculated, and the diameter (R) was determined. 100 ).

[0166] The diameter (R) of the flux-coated ball as calculated above 100 The sphericity and standard deviation of the flux-coated balls, as well as the sphericity and standard deviation of the flux-coated balls, are shown in Table 1.

[0167] [Thickness of flux layer (T)] 120 )]

[0168] The thickness of the flux layer (T) 120 The diameter (R) of the flux-coated ball is obtained from the above. 100 Subtract the diameter (R) of the solder ball (C-1) 110 The thickness of the layer on one side is calculated by dividing the thickness by 2 after reaching 63 μm. The results are shown in Table 1.

[0169] [Percentage of shell in flux-coated balls]

[0170] The proportion of the shell portion in the flux-coated balls was determined by washing the flux-coated balls with acetone and then drying them, based on the mass before washing and the mass after drying. The results are shown in Table 1.

[0171] The washing process with acetone involves immersing the flux-coated balls in acetone at room temperature (23°C) for 30 minutes. The drying process is then carried out at room temperature.

[0172] Shell content = Mass of flux-coated balls before washing - Mass after drying

[0173] Shell content percentage (mass%) = Shell content / Mass of flux-coated balls before cleaning treatment × 100

[0174] [Oxide film thickness of flux-coated balls]

[0175] The oxide film thickness of the flux-coated ball is determined by measuring the thickness of the oxide film present on the core surface (the oxide film thickness on the core surface).

[0176] The flux-coated balls used as test samples were ultrasonically cleaned in acetone for 20 minutes. Then, using an Auger electron spectroscopy analyzer (ULVAC-PHI 700, manufactured by ULVAC-PHI Corporation), the surface thickness of the ultrasonically cleaned test samples was measured under the following analytical conditions to determine the oxide film thickness. This oxide film thickness is a SiO2 equivalent. The results are shown in Table 1.

[0177] Analysis conditions: Accelerating voltage set to 10kV, current set to 10nA, and analysis diameter set to 20μm.

[0178] [Surface roughness (Ra) of the flux layer]

[0179] The surface roughness of the flux-coated ball, i.e. the surface roughness (Ra) of the flux layer, is determined by measuring as follows.

[0180] The surface of the flux-coated spheres used as test samples, i.e., the surface of the flux layer, was measured using a confocal microscope (model name: OPTELICS C130, manufactured by Lasertec Corporation). The objective lens magnification was adjusted to 50x, and the measurement interval on the z-axis was set to 0.1 μm. The surface roughness (Ra) of any three flux-coated spheres was measured, and their arithmetic mean was used as the true arithmetic mean roughness to calculate the surface roughness (Ra) of the flux layer. The results are shown in Table 1.

[0181] [Difficulty in peeling off the flux layer]

[0182] For each example of flux-coated ball, the ease of peeling off the flux layer was evaluated using the following test method. The results are shown in Table 1.

[0183] Experimental method (1): 5g of flux-coated balls were added to a cylindrical centrifuge tube (4cm in diameter and 12cm in length) and sealed. Then, the centrifuge tube containing the flux-coated balls was subjected to a shaking and stirring operation along the long axis of the centrifuge tube at room temperature (23℃) for 60 minutes. The surface condition of the flux-coated balls after the shaking and stirring operation was observed under a microscope.

[0184] Experimental Method (2): 100 flux-coated balls and 100 solder balls (solder balls composed of an alloy of 96.5% by mass Sn, 3.0% by mass Ag, and 0.5% by mass Cu, with a diameter of 0.6 mm) were placed in a cylindrical centrifuge tube (4 cm in diameter and 12 cm in length) and sealed. The centrifuge tube containing these balls was then subjected to a stirring and oscillation operation along its long axis for 60 minutes at room temperature (23°C). The surface condition of the flux-coated balls after the stirring and oscillation operation was observed using a microscope.

[0185] [Wettability of Flux-Coated Balls]

[0186] For each example of flux-coated ball, the wettability of the flux-coated ball was evaluated by the following FC ball wetting propagation test. The results are shown in Table 1.

[0187] The FC ball wetting propagation test in this evaluation involved placing a sintered copper plate on a hot plate at 150°C for 1 hour, then mounting flux-coated balls on the copper plate and reflow soldering under a nitrogen atmosphere. The reflow soldering conditions were set to a peak temperature of 250°C and a heating rate of 1°C / sec. After reflow soldering, the diameter of the balls in the wetting propagation state (ball propagation diameter) was measured. This measurement was performed on 10 flux-coated balls, and the average value was calculated.

[0188] The larger the diameter of the sphere in the wetted and expanded state (sphere expanded diameter), the better the wettability.

[0189] [Dispersion state of the freshly prepared spheres]

[0190] Regarding the dispersion state of the freshly prepared balls, in Example 1, the dispersion state of the flux-coated balls after oscillation and stirring was evaluated. In Comparative Example 1, the dispersion state of the flux-coated balls after acetone was evaporated was evaluated. The results are shown in Table 1.

[0191] [Table 1]

[0192]

[0193] The results shown in Table 1 confirm that the flux-coated ball of Example 1, which is applicable to the present invention, has a larger ball expansion diameter than the flux-coated ball of Comparative Example 1, and its wettability on the copper plate is further improved.

[0194] Furthermore, in the preparation of the flux-coated balls of Example 1, the balls did not agglomerate immediately after preparation. On the other hand, in the preparation of the flux-coated balls of Comparative Example 1, some of the balls agglomerated after preparation.

[0195] Furthermore, the flux-coated balls of Example 1 were prepared by heating and agitating powdered flux material (S-1) and solder balls (C-1) in a sealed container. This confirms that the flux-coated balls of Example 1 can be prepared using a dry process, which is simpler than a wet process.

[0196] <Preparation of Flux-Coated Balls (2)>

[0197] (Examples 2-4)

[0198] Except for changing the flux material (S-1) to flux material (S-2), flux material (S-3), and flux material (S-4), the same method as the preparation method of the flux-coated ball in Example 1 was used to obtain the flux-coated balls of Examples 2 to 4.

[0199] In all embodiments, the preheating temperature and the heating temperature during vibration and stirring were set to the melting point of the flux material -20°C. That is, it was set to 124°C in Embodiment 2, 115°C in Embodiment 3, and 133°C in Embodiment 4.

[0200] The oscillation and stirring operation was performed in the same manner as in Example 1 in all embodiments.

[0201] (Example 5)

[0202] Except for changing the solder ball (C-1) to the solder ball (C-6) and the flux material (S-1) to the flux material (S-5), the flux-coated ball of Example 5 was obtained by operating in the same manner as the preparation method of the flux-coated ball of Example 1.

[0203] The preheating temperature and the heating temperature during vibration and stirring were set to the melting point of pimelic acid, which is used as a flux material, at -20°C, i.e., 86°C in Example 5. The vibration and stirring operation was performed in the same manner as in Example 1.

[0204] (Example 6)

[0205] 1.2g of powdered flux material (S-1) with a particle size of 314μm (50% of the total volume used to calculate the cumulative curve) and 6g of solder balls (C-2) were added to a cylindrical centrifuge tube (4cm in diameter and 12cm in length) and sealed.

[0206] Next, the centrifuge tube containing flux material (S-1) and solder balls (C-2) was preheated at 132°C for 5 minutes. The preheating temperature was set to the melting point of flux material (S-1) - 20°C.

[0207] Next, the preheated centrifuge tube was subjected to a stirring and agitation operation along its long axis at 132°C for 60 minutes. The heating temperature was set to the same temperature as the preheating temperature: the melting point of the flux material (S-1) - 20°C. The stirring and agitation operation was performed at 2000 sppm.

[0208] Next, after oscillation and stirring, the mixture is cooled to room temperature (23°C), thereby obtaining a flux-coated ball having a core composed of solder balls (C-2) and a shell composed of a layer of glutaric acid (flux layer) covering the entire core.

[0209] (Example 7)

[0210] Except for changing the flux material (S-1) to flux material (S-6), the same procedure as the preparation method of the flux-coated ball in Example 6 was followed to obtain the flux-coated ball of Example 7.

[0211] The preheating temperature and the heating temperature during vibration and stirring were set to the melting point of adipic acid, which is used as a flux material, at -20°C, i.e., 165°C in Example 7. The vibration and stirring operation was performed in the same manner as in Example 6.

[0212] (Examples 8-10)

[0213] Except for changing solder ball (C-1) to solder ball (C-3), solder ball (C-4), and solder ball (C-5), the same method as the preparation method of flux-coated ball in Example 1 was used to obtain flux-coated balls of Examples 8 to 10.

[0214] In all embodiments, the preheating temperature and the heating temperature during vibration and stirring were set to the melting point of glutaric acid, which is the flux material, at -20°C, i.e., 75°C in Examples 8 to 10. The vibration and stirring operation was performed in the same manner as in Example 1 in all embodiments.

[0215] (Example 11)

[0216] Except for changing solder ball (C-1) to solder ball (C-2) and changing the amount of powdered flux material (S-1) with a particle size of 314 μm, which is 50% of the total volume when the cumulative curve is obtained, to 3 g, the flux-coated ball of Example 11 was obtained by the same method as the preparation method of flux-coated ball of Example 1.

[0217] The preheating temperature and the heating temperature during vibration and stirring were set to the melting point of glutaric acid, which is used as a flux material, at -20°C, i.e., 75°C in Example 11. The vibration and stirring were performed in the same manner as in Example 1.

[0218] (Example 12)

[0219] Except for changing solder balls (C-1) to solder balls (C-2) and changing the amount of powdered flux material (S-1) with a particle size of 314 μm, which is 50% of the total volume when the cumulative curve is obtained, to 10 g, the flux-coated balls of Example 12 were obtained by the same method as the preparation method of flux-coated balls of Example 1.

[0220] The preheating temperature and the heating temperature during vibration and stirring were set to the melting point of glutaric acid, which is used as a flux material, at -20°C, i.e., 75°C in Example 12. The vibration and stirring were performed in the same manner as in Example 1.

[0221] <Evaluation (2)>

[0222] For the flux-coated balls obtained in Examples 2 to 12 above, the appearance and diameter (R) of the flux-coated balls were evaluated respectively. 100 ) and its standard deviation, sphericity of flux-coated balls and its standard deviation, thickness of flux layer (T) 120 The following factors were considered: the proportion of the shell in the flux-coated balls, the thickness of the oxide film on the flux-coated balls, the surface roughness (Ra) of the flux layer, the difficulty of peeling off the flux layer, the wettability of the flux-coated balls, and the dispersion state of the freshly prepared balls.

[0223] The details of each evaluation are the same as those described in Evaluation (1) above. These results are presented in Figure 3 See Tables 2-4.

[0224] [Appearance]

[0225] Figure 3 These are photographs showing only the appearance of the flux-coated balls and solder balls in Examples 2 to 5.

[0226] from Figure 3 It can be confirmed that in the dry processing step of oscillation and stirring, by appropriately setting the heating temperature conditions, various flux materials can be used to coat the metal balls that serve as the core.

[0227] [Table 2]

[0228]

[0229] [Table 3]

[0230]

[0231] [Table 4]

[0232]

[0233] The results shown in Tables 2-4 confirm that the flux-coated balls of Examples 2-12 of the present invention have relatively large ball width diameters, which further improves the wettability of the copper plate.

[0234] Furthermore, in the preparation of the flux-coated balls in Examples 2 to 12, the balls did not agglomerate immediately after preparation in any case.

[0235] Furthermore, the flux-coated balls of Examples 2-12 were prepared by heating and agitating the powdered flux material and solder balls in a sealed container. This confirms that the flux-coated balls of Examples 2-12 can all be prepared by a dry process, which is simpler than wet processing.

Claims

1. A flux-coated ball comprising a core and a shell covering the core, The core is composed of solder balls or copper core balls. The shell portion is composed of a flux layer containing at least one selected from activators and resin components. The thickness of the flux layer, calculated by subtracting the diameter of the core from the diameter of the flux-coated ball and then dividing by 2, is 0.10 μm or more and 2.0 μm or less. The diameter of the core is 30 μm or more and 295 μm or less. The thickness of the oxide film present on the surface of the core, as measured by the following method, is less than 3 nm. Measurement method: The flux-coated ball used as the test sample was ultrasonically washed in acetone. Then, the surface of the ultrasonically washed test sample was measured using an Auger electron spectroscopy analyzer under the analytical conditions of 10kV acceleration voltage, 10nA current, and 20μm analysis diameter. The thickness of the oxide film was calculated using the SiO2 conversion value.

2. The flux-coated ball according to claim 1, wherein, The sphericity of the flux-coated balls is 0.990 or higher.

3. The flux-coated ball according to claim 1 or 2, wherein, The thickness of the flux layer is greater than 0.15 μm and less than 1.5 μm.

4. The flux-coated ball according to claim 1 or 2, wherein, The surface roughness (Ra) of the flux layer is below 2.0 μm.

5. The flux-coated ball according to claim 1 or 2, wherein, The activator contains at least an organic acid.

6. The flux-coated ball according to claim 5, wherein, The organic acid is selected from at least one of glutaric acid, diethylene glycol, malonic acid, citric acid, pimelic acid, adipic acid, and 2,2-di(hydroxymethyl)propionic acid.

7. The flux-coated ball according to claim 1 or 2, wherein, The diameter of the flux-coated ball is greater than 30 μm and less than 300 μm.

8. A method for preparing a flux-coated ball, comprising a core and a shell, wherein the core is composed of a solder ball or a copper core ball, and the shell is composed of a flux layer containing at least one selected from an activator and a resin component, and covers the core. The method for preparing the flux-coated balls includes a dry processing step, in which solder balls or copper core balls and powdered flux material are heated and stirred simultaneously. The powdered flux material contains at least one component selected from activators and resins. The heating temperature conditions in the dry processing step are above -35°C and below -5°C for the flux material.

9. The method for preparing flux-coated balls according to claim 8, wherein, In the dry processing step, the ratio (mass ratio) of the solder ball or copper core ball to the flux material is set to 1 to 10, and the solder ball or copper core ball and the flux material are oscillated and stirred while being heated.

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