Composition for forming solder bump, film for forming solder bump, and method for forming solder bump

Abstract

Provided is a composition for forming a solder bump, the composition containing polyvinyl alcohol, a flux, and solder particles, wherein the hydrogen dissociation energy of the flux is 170-230 kJ / mol. Also provided is a film for forming a solder bump, the film being obtained by forming the composition for forming a solder bump into a film shape. Also provided is a method for forming a solder bump, the method comprising: an arrangement step for arranging, on an electrode-side surface of a substrate having an electrode, said film for forming a solder bump; a bump formation step for heating said film for forming a solder bump to a temperature equal to or higher than the melting point of solder particles and then cooling said film; and a cleaning step for cleaning the surface with a cleaning liquid.

Description

Solder bump formation composition, solder bump formation film, and solder bump formation method

[0001] The present invention relates to a composition for forming solder bumps, a film for forming solder bumps, and a method for forming solder bumps.

[0002] One known method for mounting electronic components onto a circuit board is to form solder bumps on the board's electrodes and then join them by reflow soldering. Methods for forming solder bumps include mounting solder balls and printing solder paste.

[0003] The solder ball application method can reduce variations in solder bump height, but it is costly and the process is complex. On the other hand, the solder paste printing method is prone to void formation within the bumps, which can lead to variations in bump height.

[0004] Recently, a new solder bump formation method utilizing self-assembly has been proposed. For example, Patent Document 1 describes a method for forming solder bumps by creating a film (solder bump formation film) using a composition containing a thermoplastic resin and solder particles, and then melting the solder in the film to cause the solder components to segregate on the electrode surface.

[0005] Japanese Patent Publication No. 2006-100775

[0006] If the height of the solder bump is too low, it is not possible to ensure a secure connection between electronic devices. Therefore, when forming solder bumps using a solder bump-forming film, it is required that the solder bumps be of sufficient height.

[0007] One aspect of the present invention relates to a solder bump forming composition capable of forming solder bumps having sufficient height. Another aspect of the present invention relates to a solder bump forming film obtained using the solder bump forming composition. Yet another aspect of the present invention relates to a solder bump forming method using the solder bump forming film.

[0008] One aspect of the present invention includes, for example, the following: [1] A solder bump forming composition comprising polyvinyl alcohol, flux, and solder particles, wherein the hydrogen dissociation energy of the flux is 170 to 230 kJ / mol. [2] The solder bump forming composition according to [1], wherein the content of the polyvinyl alcohol is 5 to 70% by mass based on the total amount of the solder bump forming composition. [3] The solder bump forming composition according to [1] or [2], wherein the flux comprises at least one selected from the group consisting of adipic acid, linoleic acid, nonanoic acid, and salts thereof. [4] The solder bump forming composition according to any one of [1] to [3], wherein the content of the flux is 1 to 20 parts by mass per 100 parts by mass of the polyvinyl alcohol. [5] The solder bump forming composition according to any one of [1] to [4], wherein the average particle diameter of the solder particles is 1 to 50 μm. [6] A solder bump forming composition according to any one of [1] to [5], wherein the content of the solder particles is 10 to 300 parts by mass per 100 parts by mass of the polyvinyl alcohol. [7] A solder bump forming composition according to any one of [1] to [6], further containing a plasticizer. [8] A solder bump forming composition according to [7], wherein the plasticizer is glycerin. [9] A solder bump forming film formed from a solder bump forming composition according to any one of [1] to [8].

[10] A solder bump forming method comprising: an arrangement step of placing the solder bump forming film according to [9] on the electrode-side surface of a substrate having electrodes; a bump forming step of heating the solder bump forming film to a temperature above the melting point of the solder particles and then cooling it; and a cleaning step of cleaning the surface with a cleaning solution.

[11] The solder bump forming method according to

[10] , further comprising a jig placement step of placing a flat jig on the solder bump forming film between the arrangement step and the bump forming step, wherein the heating of the solder bump forming film in the bump forming step is performed while pressing the jig in the thickness direction of the solder bump forming film.

[12] The solder bump forming method according to

[10] or

[11] , wherein the heating of the solder bump forming film in the bump forming step is performed in an inert gas atmosphere.

[0009] According to one aspect of the present invention, a solder bump forming composition is provided that can form solder bumps having sufficient height. According to another aspect of the present invention, a solder bump forming film obtained using the solder bump forming composition is provided. According to yet another aspect of the present invention, a solder bump forming method using the solder bump forming film is provided.

[0010] Figures 1(a) and 1(b) are cross-sectional views illustrating a method for forming solder bumps. Figures 2(a) and 2(b) are cross-sectional views illustrating a method for forming solder bumps.

[0011] Embodiments of the present invention will be described below. The present invention is not limited to the embodiments described below. Unless otherwise specified, the materials exemplified below may be used individually or in combination of two or more. The content of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified, if there are multiple substances corresponding to each component in the composition. Numerical ranges indicated using "~" indicate a range that includes the numbers written before and after "~" as the minimum and maximum values, respectively. In numerical ranges described stepwise in this specification, the upper or lower limit of a numerical range in one step may be replaced with the upper or lower limit of a numerical range in another step. In numerical ranges described in this specification, the upper or lower limit of a numerical range may be replaced with the values ​​shown in the examples.

[0012] <Solder bump formation composition> A solder bump formation composition according to one embodiment of the present invention contains polyvinyl alcohol, flux, and solder particles, wherein the hydrogen dissociation energy of the flux is 170 to 230 kJ / mol.

[0013] According to one embodiment of the solder bump-forming composition, solder bumps having sufficient height can be formed. Specifically, in the method described in the examples below, the average height of the solder bumps can be set to 14 μm or more (preferably 15 μm or more, 16 μm or more, 17 μm or more, 18 μm or more, 19 μm or more, etc.). The inventors speculate that the factors that produce such effects are as follows. However, the factors are not limited to those described below. That is, if the hydrogen dissociation energy is large to a certain extent, the flux is less likely to ionize, the repulsive force between flux molecules increases, and the uniform dispersion of the flux and the uniform dispersion of solder particles adsorbed on the surface of the flux are promoted. On the other hand, if the hydrogen dissociation energy is too large, the hydrophobicity of the flux also becomes too large, making it difficult to disperse in polyvinyl alcohol, water, etc. By promoting the dispersion of solder particles in the composition, the formed solder bumps can have sufficient height.

[0014] (Polyvinyl alcohol) One embodiment of the solder bump forming composition contains polyvinyl alcohol.

[0015] The average degree of polymerization of polyvinyl alcohol may be 100 or more, 150 or more, 200 or more, or 250 or more, from the viewpoint of easily forming solder bumps of sufficient height, and may be 1000 or less, 900 or less, 800 or less, or 700 or less, from the same viewpoint. The average degree of polymerization of polyvinyl alcohol refers to the value measured in accordance with JIS K 6726 (Test method for polyvinyl alcohol).

[0016] The weight-average molecular weight of polyvinyl alcohol may be 3000 or more, 5000 or more, or 8000 or more, from the viewpoint of easily forming solder bumps of sufficient height, and may be 30000 or less, 20000 or less, or 15000 or less, from the same viewpoint.

[0017] The weight-average molecular weight is calculated from a calibration curve using standard polystyrene by gel permeation chromatography (GPC). The calibration curve is approximated by a cubic equation using a set of five standard polystyrene samples (PStQuick MP-H, PStQuick B [Tosoh Corporation, product name]). The GPC conditions are as follows, for example. The injection volume is adjusted according to the peak height and peak resolution. Instrument: High-speed GPC instrument "HLC-8320GPC" (Tosoh Corporation, product name) Detector: Ultraviolet absorption detector "UV-8320" (Tosoh Corporation, product name) Columns: Guard column; TSKgel guardcolumn Super(HZ)-M+, Column; TSKgel SuperMultipore HZ-M (2), Reference column; TSKgel SuperH-RC (2) (all Tosoh Corporation, product names) Column size: 4.6 × 20 mm (guard column), 4.6 × 150 mm (column), 6.0 × 150 mm (reference column) Eluent: Tetrahydrofuran Sample concentration: 10 mg / 1 mL Injection volume: 20 μL or 2 μL Flow rate: 0.35 mL / min Measurement temperature: 40°C

[0018] The melting point of polyvinyl alcohol may be 150°C or higher, 170°C or higher, or 180°C or higher, and may be 250°C or lower, 220°C or lower, or 200°C or lower. The melting point of polyvinyl alcohol may be lower than or equal to the melting point of solder particles. In this specification, the melting point means the temperature at which the first endothermic peak occurs when a DSC (Differential Scanning Calorimeter) measurement is performed in a He gas flow at a heating rate of 10°C / min using a DSC.

[0019] The polyvinyl alcohol content may be 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, or 55% by mass or more, based on the total amount of the solder bump forming composition, from the viewpoint of ease of removing resin components with water in the cleaning process, and 70% by mass or less, 65% by mass or less, or 60% by mass or less, from the viewpoint of film handling (film toughness). From these viewpoints, the polyvinyl alcohol content may be 5 to 70% by mass, 5 to 60% by mass, 20 to 70% by mass, 20 to 60% by mass, 40 to 70% by mass, or 40 to 60% by mass, based on the total amount of the solder bump forming composition.

[0020] (Flux) The solder bump forming composition according to one embodiment contains flux. Examples of flux include organic acids, salts of organic acids, inorganic acids, and salts of inorganic acids. Examples of salts of organic acids include sodium salts and potassium salts. The flux may be an organic acid from the viewpoint of easily forming solder bumps with sufficient height.

[0021] When the flux is an organic acid, examples of organic acids include carboxylic acids, sulfonic acids, phosphoric acids, phosphonic acids, phosphinic acids, and thiosulfonic acids. The organic acid may be a carboxylic acid from the viewpoint of easily forming solder bumps of sufficient height. When the flux is a salt of an organic acid, the salt of the organic acid may be a salt of a carboxylic acid, sulfonic acid, phosphoric acid, phosphonic acid, phosphinic acid, or thiosulfonic acid, and may be a salt of a carboxylic acid from the same viewpoint as the organic acid.

[0022] When the flux is a carboxylic acid, examples of carboxylic acids include saturated carboxylic acids such as adipic acid, stearic acid, and nonanoic acid; and unsaturated carboxylic acids such as linoleic acid. From the viewpoint of easily forming solder bumps of sufficient height, the flux may contain at least one selected from the group consisting of carboxylic acids and their salts, and may contain at least one selected from the group consisting of adipic acid, linoleic acid, nonanoic acid, and their salts.

[0023] If the flux is a carboxylic acid, the number of carboxyl groups in the carboxylic acid may be 3 or less, or 2 or less, from the viewpoint of easily forming solder bumps of sufficient height. If the flux is a salt of a carboxylic acid, the number of carboxylic acid bases in the salt of the carboxylic acid may be 3 or less, or 2 or less, from the same viewpoint.

[0024] The hydrogen dissociation energy of the flux is 170–230 kJ / mol. The hydrogen dissociation energy is the amount of protons (H) released from the flux. ＋ This refers to the energy change ΔE before and after the separation of the flux molecules. When ΔE is sufficiently large, the flux is less likely to ionize, the repulsive force between flux molecules increases, and uniform dispersion of the flux and the solder particles adsorbed on the surface are promoted. On the other hand, if ΔE becomes too large, the hydrophobicity of the flux also becomes too high, making dispersion in polyvinyl alcohol, water, etc. difficult.

[0025] The hydrogen dissociation energy is calculated by the following procedure. First, the relative permittivity ε of the Classius-Mossotti relationship, expressed by equation (1) below, ｒ This is calculated as the dielectric constant. In equation (1), α is the polarizability and V is the volume.

[0026] The polarizability α is calculated using quantum chemical calculations with Gaussian 16. Structural optimization calculations are performed at the B3LYP / 6-31G(d) level for the molecule (flux) being calculated to determine the polarizability α.

[0027] The volume V is calculated using molecular dynamics simulations. Charges are assigned to the molecules (fluxes) being calculated. Using the quantum chemistry simulation software Gaussian 16, structural optimization calculations are performed at the B3LYP / 6-31G(d) level, followed by energy calculations at the HF / 6-31G(d) level. Then, based on the obtained electrostatic potential, RESP charges are assigned to each molecule using the free software AmberTools 22.

[0028] Next, we assign the force field to the molecule (flux) to be calculated. We use AmberTools 22 to assign the force field parameters for atoms, bonds, angles, and dihedral angles in the molecule (flux). In this calculation, we use the General Amber Force Field for the force field of the molecule (flux).

[0029] Next, molecules (fluxes) are randomly placed in the simulation cell so that the total number of particles is 10,000. After sufficient relaxation using molecular dynamics calculations with an NPT ensemble, a 1ns calculation is performed for sampling. The volume V is calculated by averaging the volume profiles of the sampled 1ns.

[0030] Next, quantum chemical calculations are performed using Gaussian 16, which calculates the dielectric constant from the calculated polarizability α and volume V using equation (1). For each molecule being calculated, structural optimization calculations are performed at the B3LYP / 6-31G(d) level to calculate the energy for the "molecule before hydrogen ion detachment," the "molecule after hydrogen ion detachment," and the "detached hydrogen ion." The energy change ΔE (= E) before and after hydrogen ion detachment is calculated. １ (Energy of the molecule before hydrogen ions are released) - [E] ２ (Energy of the molecule after hydrogen ions are removed) + E ３ The energy of the hydrogen ions that are released is calculated as the hydrogen dissociation energy.

[0031] The hydrogen dissociation energy of the flux may be 175 kJ / mol or more, 180 kJ / mol or more, 185 kJ / mol or more, or 190 kJ / mol or more, from the viewpoint of easily forming solder bumps of sufficient height, and from the same viewpoint, it may be 220 kJ / mol or less, 210 kJ / mol or less, 200 kJ / mol or less, or 195 kJ / mol or less.

[0032] The hydrogen dissociation energy of a flux tends to be lower if the flux has a small molecular weight and a highly symmetrical structure.

[0033] The molecular weight of the flux may be 500 or less, 400 or less, 300 or less, 200 or less, or 150 or less, from the viewpoint of being easily soluble in polyvinyl alcohol and easily forming solder bumps of sufficient height. The molecular weight of the flux may be 100 or more, 120 or more, or 140 or more, from the viewpoint of easily forming solder bumps of sufficient height.

[0034] The melting point of the flux may be 10°C or higher, 30°C or higher, 50°C or higher, 80°C or higher, 100°C or higher, 120°C or higher, or 150°C or higher, from the viewpoint of efficiently positioning solder particles on the electrode and easily forming solder bumps of sufficient height, and from the same viewpoint, it may be 200°C or lower, 180°C or lower, or 160°C or lower.

[0035] The flux content may be 0.1% by mass or more, 0.5% by mass or more, 0.8% by mass or more, or 1% by mass or more, based on the total amount of the solder bump forming composition, from the viewpoint of easily forming solder bumps with sufficient height and from the viewpoint of easily removing polyvinyl alcohol, etc., by washing after the solder bumps have been formed, or 10% by mass or less, 5% by mass or less, 3% by mass or less, or 1.5% by mass or less, from the viewpoint of easily forming solder bumps with sufficient height.

[0036] The flux content may be 0.1 parts by mass or more, 1 part by mass or more, 1.5 parts by mass or more, or 2 parts by mass or more per 100 parts by mass of polyvinyl alcohol, from the viewpoint of easily forming solder bumps of sufficient height and easily removing polyvinyl alcohol etc. by washing after the solder bumps have been formed, or 20 parts by mass or less, 15 parts by mass or less, 10 parts by mass or less, 5 parts by mass or less, or 3 parts by mass or less from the viewpoint of easily forming solder bumps of sufficient height. From these viewpoints, the flux content may be 0.1 to 20 parts by mass, 0.1 to 10 parts by mass, 0.1 to 3 parts by mass, 1 to 20 parts by mass, 1 to 10 parts by mass, or 1 to 3 parts by mass per 100 parts by mass of polyvinyl alcohol.

[0037] (Solder Particles) One embodiment of the solder bump forming composition contains solder particles. Solder bumps can be formed on the electrode by placing the solder bump forming composition (or the solder bump forming film described later) on the electrode-side surface of the substrate, heating the solder bump forming composition (or the solder bump forming film) above the melting point of the solder particles, and then cooling it. The inventors speculate that this is because solder has high wettability with respect to the electrode metal, but low wettability with respect to areas of the substrate surface other than the electrode (e.g., solder resist). On the electrode surface with high wettability, the contact angle of the droplets (solder droplets) produced by the melting of solder with respect to the electrode surface is small, the center of gravity of the solder droplets is low with respect to the contact surface and thus stable, and the attractive interaction between the solder droplets and the electrode holds the solder droplets on the electrode. On the other hand, for areas other than the electrode with low wettability, the contact angle of the solder droplet is large, and the center of gravity of the solder droplet becomes high relative to the contact surface, making it unstable. As a result, the solder droplet is less likely to adhere to areas other than the electrode. For these reasons, it is presumed that solder accumulates on the electrode. Furthermore, the reason why solder accumulates on the electrode can also be explained by Laplace's equation, which describes the pressure difference inside the solder droplet. In the process where droplets of different sizes come into contact to form one large droplet, it is known that the smaller droplet is drawn into the larger droplet. This phenomenon is thought to be due to the fact that the internal pressure of the smaller droplet is higher than that of the larger droplet, and this pressure difference causes the smaller droplet to be drawn into the larger droplet. Therefore, when a solder droplet exists across both the electrode and the surrounding area, the contact angle of the solder droplet with respect to the electrode is small, resulting in a large radius of curvature of the solder droplet, while the contact angle of the solder droplet with respect to the surrounding area is large, resulting in a small radius of curvature of the solder droplet. Furthermore, solder droplets with a small radius of curvature are under higher pressure than those with a large radius of curvature. Therefore, it is thought that solder droplets in areas other than the electrode move towards the electrode due to the pressure difference. It is presumed that this movement is repeated, causing the solder to accumulate on the electrode.

[0038] The solder particles may contain, for example, tin. The solder particles may contain pure tin or a tin alloy. Examples of the tin alloy include In-Sn, In-Sn-Ag, Sn-Bi, Sn-Bi-Ag, Sn-Ag-Cu, and Sn-Cu.

[0039] Specific examples of the tin alloy include the following: - In-Sn (In 52% by mass, Bi 48% by mass, melting point 118°C) - In-Sn-Ag (In 20% by mass, Sn 77.2% by mass, Ag 2.8% by mass, melting point 175°C) - Sn-Bi (Sn 43% by mass, Bi 57% by mass, melting point 138°C) - Sn-Bi-Ag (Sn 42% by mass, Bi 57% by mass, Ag 1% by mass, melting point 139°C) - Sn-Ag-Cu (Sn 96.5% by mass, Ag 3% by mass, Cu 0.5% by mass, melting point 217°C) - Sn-Cu (Sn 99.3% by mass, Cu 0.7% by mass, melting point 227°C) - Sn-Au (Sn 21.0% by mass, Au 79.0% by mass, melting point 278°C)

[0040] The content of tin in the solder particles may be, for example, 40% by mass or more, 60% by mass or more, or 80% by mass or more, and may be 99.5% by mass or less, 80% by mass or less, or 60% by mass or less.

[0041] The solder particles may contain indium. The solder particles may contain pure indium or an indium alloy. Examples of the indium alloy include In-Bi, In-Ag, etc.

[0042] Specific examples of the indium alloy include the following: - In-Bi (In 66.3% by mass, Bi 33.7% by mass, melting point 72°C) - In-Bi (In 33.0% by mass, Bi 67.0% by mass, melting point 109°C) - In-Ag (In 97.0% by mass, Ag 3.0% by mass, melting point 145°C)

[0043] The content of indium in the solder particles may be, for example, 30% by mass or more, 50% by mass or more, or 60% by mass or more, and may be 99.5% by mass or less, 80% by mass or less, or 40% by mass or less.

[0044] The melting point of the solder (the melting point of the solder constituting the solder particles) may be, for example, 100°C or higher, 130°C or higher, 150°C or higher, 170°C or higher, 180°C or higher, 190°C or higher, or 200°C or higher. From the viewpoint of enabling the formation of solder bumps at low temperatures and reducing the load on the member on which the solder bumps are formed, it may be 300°C or lower, 280°C or lower, 260°C or lower, or 250°C or lower.

[0045] The average particle diameter of the solder particles may be 50 μm or less, 30 μm or less, 20 μm or less, 10 μm or less, or 5.5 μm or less, from the viewpoint of suppressing bridging of the formed solder bumps, and may be 0.5 μm or more, 1 μm or more, or 3 μm or more, from the viewpoint of easily forming solder bumps with sufficient height. From these viewpoints, the average particle diameter of the solder particles may be 0.5 to 50 μm, 0.5 to 20 μm, 0.5 to 10 μm, 1 to 50 μm, 1 to 20 μm, or 1 to 10 μm.

[0046] The average particle size of the solder particles may be set according to the distance between adjacent electrodes on the substrate to which the solder bump-forming composition (or solder bump-forming film) is applied. Specifically, when the average particle size of the solder particles is less than or equal to the distance between adjacent electrodes, the occurrence of bridges tends to be suppressed. From the viewpoint of further suppressing the occurrence of bridges, the average particle size of the solder particles may be less than or equal to half or one-third of the distance between adjacent electrodes.

[0047] The average particle size of solder particles can be calculated from an SEM image using, for example, the following procedure: Observe the solder particle powder at 5000x magnification using an SEM device to obtain an SEM image. From the obtained SEM image, draw a rectangle circumscribing the solder particle using image processing software, and define the longest side of the rectangle as the maximum diameter of the particle. Perform this measurement on 50 or more solder particles using multiple SEM images, calculate the average of the maximum diameters of these solder particles, and define this as the average particle size (average maximum diameter). The maximum and average particle sizes of solder particles in a solder bump forming composition can be determined by washing with an organic solvent such as acetone, filtering, drying at room temperature (e.g., 25°C), and then using the method described above.

[0048] The solder particle content may be 5% by mass or more, 10% by mass or more, or 15% by mass or more, based on the total amount of the solder bump forming composition, from the viewpoint of containing a sufficient amount of solder particles and easily forming solder bumps with sufficient height, and may be 30% by mass or less, 25% by mass or less, or 20% by mass or less, from the viewpoint of easily suppressing the occurrence of bridges.

[0049] The solder particle content may be 10 parts by mass or more, 15 parts by mass or more, 20 parts by mass or more, or 25 parts by mass or more per 100 parts by mass of polyvinyl alcohol, from the viewpoint of containing a sufficient amount of solder particles and easily forming solder bumps of sufficient height, and from the viewpoint of easily suppressing the occurrence of bridges, it may be 300 parts by mass or less, 200 parts by mass or less, 150 parts by mass or less, 100 parts by mass or less, 50 parts by mass or less, 40 parts by mass or less, 35 parts by mass or less, or 30 parts by mass or less. From these viewpoints, the solder particle content may be 10 to 300 parts by mass, 10 to 150 parts by mass, or 10 to 50 parts by mass per 100 parts by mass of polyvinyl alcohol.

[0050] (Plasticizer) The solder bump forming composition according to one embodiment may further contain a plasticizer. The inclusion of a plasticizer in the solder bump forming composition makes it easier to suppress the increase in viscosity of the solder bump forming composition when forming solder bumps.

[0051] Examples of plasticizers include polyhydric alcohols such as glycerin, sorbitol, ethylene glycol, and propion glycol. From the viewpoint of good compatibility with polyvinyl alcohol and excellent dispersibility in the composition, glycerin may be used as the plasticizer.

[0052] The molecular weight of the plasticizer may be 300 or less, 200 or less, or 100 or less, from the viewpoint of easily reducing the viscosity of the solder bump forming composition. The molecular weight of the plasticizer may be 50 or more, 70 or more, or 90 or more, from the viewpoint of making it easier to suppress the increase in viscosity of the solder bump forming composition when forming solder bumps by making the plasticizer less volatile.

[0053] The melting point of the plasticizer may be 150°C or higher, 200°C or higher, or 250°C or higher, from the viewpoint of suppressing the increase in viscosity of the solder bump forming composition when forming solder bumps by making the plasticizer less volatile, and may be 400°C or lower, 350°C or lower, or 300°C or lower, from the viewpoint of melting in the bump forming process and ensuring the fluidity of the solder particles.

[0054] The plasticizer content may be 10% by mass or more, 15% by mass or more, or 20% by mass or more, from the viewpoint of easily reducing the viscosity of the solder bump forming composition, and may be 35% by mass or less, 30% by mass or less, or 25% by mass or less, from the viewpoint of easily removing the resin component with water in the cleaning process.

[0055] The plasticizer content may be 30 parts by mass or more, 35 parts by mass or more, or 40 parts by mass or more per 100 parts by mass of polyvinyl alcohol, from the viewpoint of easily reducing the viscosity of the solder bump forming composition, and may be 55 parts by mass or less, 50 parts by mass or less, or 45 parts by mass or less, from the viewpoint of easily removing the resin component with water in the washing process.

[0056] (Water-soluble polymer) The solder bump forming composition according to one embodiment may further contain a water-soluble polymer other than polyvinyl alcohol. A water-soluble polymer means a polymer that dissolves in 0.1 g or more per 100 g of water. Examples of water-soluble polymers include water and organic solvents. Examples of organic solvents include polyvinylpyrrolidone, polyethylene glycol, polypropylene glycol, polyacrylic acid, polyacrylamide, starch, and modified cellulose.

[0057] (Solvent) The solder bump forming composition according to one embodiment may further contain a solvent other than polyvinyl alcohol. Examples of solvents include water and organic solvents. Examples of organic solvents include methanol and ethanol. The solvent content may be the remainder obtained by subtracting the content of the other components from the total amount of the solder bump forming composition.

[0058] A solder bump forming composition according to one embodiment may further contain other additives such as antioxidants, colorants, and flame retardants.

[0059] <Solder bump forming film> A solder bump forming film (reflow film) can be obtained by forming the above-described solder bump forming composition into a film. Another embodiment of the present invention is a solder bump forming film obtained by forming the solder bump forming composition into a film. Note that the content of each component can be read as "based on the total amount of the solder bump forming composition" instead of "based on the total amount of the solder bump forming film".

[0060] The solder bump forming film comprises a resin layer containing polyvinyl alcohol and flux, and solder particles dispersed in the resin layer. In addition to polyvinyl alcohol and flux, the resin layer may also contain plasticizers, water-soluble polymers, solvents, etc.

[0061] A solder bump-forming film can be manufactured by the following method. Specifically, first, the components constituting the solder bump-forming composition are dissolved or dispersed by stirring, mixing, kneading, etc., to prepare the solder bump-forming composition. Then, the solder bump-forming composition is applied to the substrate using a knife coater, roll coater, applicator, comma coater, die coater, etc., and the solvent is evaporated by heating to form a solder bump-forming film on the substrate.

[0062] As a base material, for example, a base material (e.g., a film) made of stretched polypropylene (OPP), polyethylene terephthalate (PET), polyethylene naphthalate, polyethylene isophthalate, polybutylene terephthalate, polyolefin, polyacetate, polycarbonate, polyphenylene sulfide, polyamide, polyimide, cellulose, ethylene-vinyl acetate copolymer, polyvinyl chloride, polyvinylidene chloride, synthetic rubber, liquid crystal polymer, etc. can be used.

[0063] The heating conditions for volatilizing the solvent from the solder bump-forming composition applied to the substrate may be, for example, 40°C to 120°C for 0.1 minutes to 10 minutes.

[0064] The thickness of the solder bump forming film may be, for example, 10 μm or more, 50 μm or more, or 100 μm or more, and may be 500 μm or less, 400 μm or less, or 300 μm or less.

[0065] <Solder Bump Forming Method> Solder bumps can be formed using the solder bump forming film described above. Another embodiment of the present invention is a solder bump forming method comprising: a placement step of placing the solder bump forming film described above on the electrode-side surface of a substrate having electrodes; a bump forming step of heating the solder bump forming film to a temperature above the melting point of solder particles and then cooling it; and a cleaning step of cleaning the electrode-side surface of the substrate with a cleaning solvent. The solder bump forming method will be described below with reference to the drawings.

[0066] (Placement Process) Figure 1(a) is a diagram illustrating the placement process of the solder bump formation method. As shown in Figure 1(a), the placement process involves placing the solder bump formation film 10 on the surface of the electrode surface of the substrate 20 having electrodes 21. The solder bump formation film 10 comprises a resin layer 11 containing polyvinyl alcohol and flux, and solder particles 12 dispersed in the resin layer 11.

[0067] The substrate 20 may be degreased beforehand to better suppress variations in the height of solder bumps. Ultrasonic cleaning may be performed during the degreasing process. In addition, the substrate 20 may be dried beforehand to prevent water adsorbed on the substrate 20 from foaming during heating.

[0068] The substrate 20 only needs to have one or more electrodes, and may be, for example, a printed circuit board on which electronic components such as semiconductor chips, interposers, and motherboards are mounted. An Under Bump Metallization (UBM) layer may be formed on the electrode 21 to improve solder wettability. The electrode 21 may contain Cu, Ni, Au, Pt, etc.

[0069] (Jig placement step) The solder bump formation method may further include a jig placement step between the placement step and the bump formation step, in which a flat jig is placed on the solder bump formation film. By heating the solder bump formation film while placing the jig on the solder bump formation film, the height of the formed solder bumps will be at most the distance between the electrode and the jig, making it easier to suppress variations in the solder bumps.

[0070] Figure 1(b) is a diagram illustrating the jig placement step of the solder bump formation method. As shown in Figure 1(b), the jig placement step involves placing the jig 30 on the solder bump formation film 10.

[0071] The jig 30 is not particularly limited as long as it has a smooth surface and possesses rigidity and heat resistance so as not to deform during the bump formation process; for example, it may be a glass plate. The jig 30 may be fixed with a clamp or other jig. From the viewpoint of suppressing variations in the height of the solder bumps, the jig 30 may be positioned substantially parallel to the electrode 21 side surface of the substrate 20.

[0072] (Bump Formation Process) Figure 2(a) is a diagram illustrating the bump formation process of the solder bump formation method. In the bump formation process, the solder bump formation film is heated to a temperature above the melting point of the solder particles, and then cooled. As a result, solder bumps 40 are formed on the electrode 21, as shown in Figure 2(a).

[0073] The bump formation process may include a step of heating the resin layer to a temperature above the melting point of the resin layer (for example, above the melting point of polyvinyl alcohol) (first heating step), a step of heating it to a temperature above the melting point of the solder particles (second heating step), and a step of cooling it to a temperature below the melting point of the solder particles (cooling step).

[0074] The heating temperature in the first heating step may be, for example, 100°C or higher, 120°C or higher, or 150°C or higher, and may be 220°C or lower, 200°C or lower, or 180°C or lower. The heating time in the first heating step (the time spent heating at or above the heating temperature) may be, for example, 30 seconds or higher, 50 seconds or higher, or 70°C or higher, and may be 150 seconds or lower, 130 seconds or lower, or 110°C or lower.

[0075] The heating temperature in the second heating step may be, for example, 200°C or higher, 220°C or higher, or 240°C or higher, and may be 320°C or lower, 300°C or lower, or 280°C or lower. The heating time in the first heating step (the time spent heating at or above the heating temperature) may be, for example, 10 seconds or more, 20 seconds or more, or 30°C or higher, and may be 100 seconds or less, 90 seconds or less, or 80°C or lower.

[0076] If the solder bump formation method includes a jig placement step, the heating of the solder bump formation film (heating in the first heating step and the second heating step) may be performed while applying pressure to the jig in the thickness direction of the solder bump formation film. The pressure applied to the jig may be, for example, 0.1 MPa or more, 0.5 MPa or less, 0.3 MPa or less, or 0.2 MPa.

[0077] In the bump formation process, the heating of the solder bump formation film (heating in the first and second heating steps) may be carried out under an inert gas atmosphere. The inert gas atmosphere may be, for example, a nitrogen atmosphere.

[0078] The cooling step may involve cooling to, for example, 200°C or below, 150°C or below, or 100°C or below. The cooling time of the cooling step (the time required to cool to a specific temperature or below) may be, for example, 200 seconds or more, 250°C or above, or 300°C or above, and may be 500 seconds or less, 400 seconds or less, or 350 seconds or less.

[0079] (Cleaning Process) Figure 2(b) is a diagram illustrating the cleaning process of the solder bump formation method. In the cleaning process, the electrode 21 side surface of the substrate 20 is cleaned with a cleaning solution. As a result, as shown in Figure 2(b), the resin layer 11 is removed from the electrode 21 side surface of the substrate 20, and a substrate 100 with solder bumps is obtained.

[0080] The cleaning solution can be any liquid capable of dissolving and removing the resin layer, and may be an inorganic solvent such as water, or an organic solvent such as methanol or ethanol. The cleaning solution may also be a mixture of water and an organic solvent. From the viewpoint of efficiently removing the resin layer, cleaning with the cleaning solution may be performed while heating the cleaning solution or while irradiating with ultrasound.

[0081] <Method for Manufacturing a Substrate with Solder Bumps> A substrate with solder bumps formed on the electrodes can be obtained using the solder bump forming film described above. That is, another embodiment of the present invention is a method for manufacturing a substrate with solder bumps, comprising: a placement step of placing the solder bump forming film described above on the electrode-side surface of a substrate having electrodes; a bump formation step of heating the solder bump forming film to a temperature above the melting point of solder particles and then cooling it; and a cleaning step of cleaning the electrode-side surface of the substrate with a cleaning solvent. Each step in the method for manufacturing a substrate with solder bumps can be referenced from the description of the solder bump formation method described above.

[0082] A substrate with solder bumps may be, for example, a semiconductor chip or an interposer. A substrate with solder bumps can be used in the manufacture of a semiconductor device; for example, a semiconductor device can be manufactured by connecting a substrate with solder bumps to a semiconductor chip or an interposer via the solder bumps.

[0083] Although preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments.

[0084] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0085] (Examples 1-3, Comparative Examples 1-3) Polyvinyl alcohol (PVA, weight-average molecular weight 13000, melting point 180°C), glycerin, flux shown in Table 1, and solder particles (composition: SAC305 (Sn: 96.5%, Ag: 3.0%, Cu: 0.5%), average particle size 5.5 μm) were mixed to prepare a varnish containing 58.1% by mass of PVA, 23.3% by mass of glycerin, 1.2% by mass of flux, and 17.4% by mass of solder particles.

[0086] The prepared varnish was applied to a polyethylene terephthalate film that had been treated with a release agent on its surface to form a coating. The coating was then heated and dried at 120°C for 1 hour to obtain a reflow film with a thickness of 100 μm on the polyethylene terephthalate film.

[0087] [Calculation of Hydrogen Dissociation Energy] The hydrogen dissociation energy was calculated using the following procedure. First, the relative permittivity ε of the Classius-Mossotti relationship expressed by the following equation (1) ｒ This was calculated as the dielectric constant. In equation (1), α is the polarizability and V is the volume.

[0088] The polarizability α was calculated using quantum chemical calculations with Gaussian 16. Structural optimization calculations were performed at the B3LYP / 6-31G(d) level for the target molecule (flux) to determine the polarizability α.

[0089] The volume V was calculated using molecular dynamics simulations. Charges were assigned to the molecules (fluxes) being calculated. Using the quantum chemistry simulation software Gaussian 16, structural optimization calculations were performed at the B3LYP / 6-31G(d) level, followed by energy calculations at the HF / 6-31G(d) level. Then, based on the obtained electrostatic potential, RESP charges were assigned to each molecule using the free software AmberTools 22.

[0090] Next, the force field of the molecule (flux) to be calculated was assigned. The force field parameters of atoms, bonds, angles, and dihedral angles in the molecule (flux) were assigned using AmberTools 22. In this calculation, the General Amber Force Field was used for the force field of the molecule (flux).

[0091] Next, the molecules (fluxes) were randomly placed in the simulation cell so that the total number of particles was 10,000. After sufficient relaxation by molecular dynamics calculation in the NPT ensemble, a 1-ns calculation was performed for sampling. The volume profile of the sampled 1 ns was averaged to calculate the volume V.

[0092] Next, quantum chemical calculations were performed using Gaussian 16 to calculate the dielectric constant from the calculated polarizability α and volume V according to Equation (1). Structure optimization calculations were performed at the B3LYP / 6-31G(d) level for each of the "molecule before hydrogen ion desorption", "molecule after hydrogen ion desorption", and "hydrogen ion to be desorbed" of the molecule to be calculated, and the energies were calculated. The energy change ΔE (= E １ (energy of the molecule before hydrogen ion desorption) - [E ２ (energy of the molecule after hydrogen ion desorption) + E ３ (energy of the hydrogen ion to be desorbed)]) was calculated as the hydrogen dissociation energy. The calculation results are shown in Table 1.

[0093] [Evaluation] <Formation of solder bumps> A reflow film was placed on the substrate side surface of a test substrate (Waltz, FBW80A-0000JY) having copper electrodes (height 10 μm). A glass plate was placed on the reflow film and fixed in place with a pressure of 0.1 MPa. Next, the reflow film was placed in a reflow oven (Unitem, benchtop reflow oven, RSS-210-S) and heated under a nitrogen atmosphere. The reflow film was heated by raising the temperature of the reflow oven at 3°C / second with the set temperature at 200°C, so that the time it took for the reflow film to reach a temperature of 150-180°C was within 90 seconds. Next, the set temperature of the reflow oven was maintained at 200°C and the reflow film was heated to 180°C over 90 seconds to melt the resin layer of the reflow film. Next, the reflow oven was set to a temperature of 340°C and the temperature was increased at 3°C / second while heating the reflow film so that the time it took for the reflow film temperature to reach 200°C or higher was within 60 seconds, the time it took for it to reach 230°C or higher was within 40 seconds, and the maximum temperature of the reflow film was 260°C or lower, thereby melting the solder particles in the reflow film. Then, the reflow film was cooled to below 40°C over 300 seconds, allowing the melted solder particles in the reflow film to accumulate on the electrodes of the substrate. After cooling, the electrode-side surface of the substrate was cleaned with water for 5 minutes using an ultrasonic cleaner (Honda Electronics Co., Ltd., W-113 MK-II) to remove the resin layer of the reflow film. This resulted in a substrate with solder bumps formed on the electrodes.

[0094] <Evaluation of Bump Height> Nine solder bumps on the electrode were observed using a laser microscope (Keyence VK-X250), and the height of each solder bump was measured. The average value of the solder bump heights was then measured. The measurement results are shown in Table 1.

[0095]

[0096] 10... Solder bump formation film, 11... Resin layer, 12... Solder particles, 20... Substrate, 21... Electrode, 30... Jig, 40... Solder bump, 100... Substrate with solder bump.

Claims

1. A composition for forming solder bumps, comprising polyvinyl alcohol, flux, and solder particles, wherein the hydrogen dissociation energy of the flux is 170 to 230 kJ / mol.

2. The solder bump forming composition according to claim 1, wherein the polyvinyl alcohol content is 5 to 70% by mass based on the total amount of the solder bump forming composition.

3. The solder bump forming composition according to claim 1, wherein the flux comprises at least one selected from the group consisting of adipic acid, linoleic acid, nonanoic acid, and salts thereof.

4. The solder bump forming composition according to claim 1, wherein the flux content is 1 to 20 parts by mass per 100 parts by mass of polyvinyl alcohol.

5. The solder bump forming composition according to claim 1, wherein the average particle size of the solder particles is 1 to 50 μm.

6. The solder bump forming composition according to claim 1, wherein the content of the solder particles is 10 to 300 parts by mass per 100 parts by mass of the polyvinyl alcohol.

7. The solder bump forming composition according to claim 1, further comprising a plasticizer.

8. The solder bump forming composition according to claim 7, wherein the plasticizer is glycerin.

9. A solder bump forming film, comprising a solder bump forming composition according to any one of claims 1 to 8, formed into a film.

10. A solder bump forming method comprising: a placement step of placing a solder bump forming film according to claim 9 on the electrode-side surface of a substrate having electrodes; a bump forming step of heating the solder bump forming film to a temperature above the melting point of the solder particles and then cooling it; and a cleaning step of cleaning the surface with a cleaning solution.

11. The solder bump forming method according to claim 10, further comprising a jig placement step of placing a flat jig on the solder bump forming film between the arrangement step and the bump forming step, wherein the heating of the solder bump forming film in the bump forming step is performed while applying pressure to the jig in the thickness direction of the solder bump forming film.

12. The solder bump forming method according to claim 10, wherein the heating of the solder bump forming film in the bump forming step is performed under an inert gas atmosphere.

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