Solder paste, method for forming solder bumps, and method for manufacturing member with solder bumps

Abstract

The present invention provides a method for forming solder bumps in which a solder paste containing solder particles and a volatile dispersion medium is used, wherein the method comprises a step for applying the solder paste to a member having a plurality of electrodes on the surface thereof, a step for forming a solder-particle-containing layer by heating the member and the solder paste at a temperature lower than the melting point of the solder constituting the solder particles, a step for forming solder bumps by heating the member and the solder-particle-containing layer in a reductive atmosphere at a temperature not lower than the melting point of the solder constituting the solder particles, and a step for cleaning off residues of the solder-particle-containing layer remaining between adjacent solder bumps. The average particle diameter of the solder particles is 10 μm or less, and the dispersion medium content of the solder paste is 30 mass% or more.

Description

[Technical field]

[0001] The present invention relates to a solder paste, a method for forming solder bumps, and a method for manufacturing a member having solder bumps. [Background technology]

[0002] As a method for mounting an electronic component on an electronic member, a method (solder precoat method) is known in which an electrode surface is coated with solder in advance, and then the electronic component is mounted on the electronic member and bonded.

[0003] A known example of a solder precoating method is to apply solder paste to an area on an electronic component where electrodes are arranged (e.g., the entire surface of the electronic component) and then heat it to form solder bumps on each electrode (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-4347 A Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, as electronic devices become smaller and lighter, the pitch between electrodes on members (e.g., electronic members such as electronic circuit boards) on which electronic components are mounted has become narrower, and for example, the gap between electrodes has become smaller than 25 μm.

[0006] As a result of the inventors' investigations, it became clear that when solder bumps are formed on components with narrow gaps between electrodes such as those described above using the method described in Patent Document 1, a phenomenon known as "bridging" occurs in which adjacent electrodes are connected to each other by molten solder in the gap between the electrodes, resulting in a short circuit, or a phenomenon known as "solder non-wetting" occurs in which the electrode surface is not sufficiently covered with solder, resulting in defective solder bump shapes.

[0007] Therefore, one aspect of the present invention aims to provide a method for forming solder bumps while suppressing the occurrence of bridging and solder non-wetting even when the gap between electrodes is narrow (for example, less than 25 μm), a solder paste used in the method, and a method for manufacturing a member with solder bumps using the method. [Means for solving the problem]

[0008] As a result of extensive research into achieving the above-mentioned object, the inventors have discovered that by using a solder paste that combines very fine solder particles with a volatile dispersion medium and contains a larger amount of the dispersion medium than conventional solder pastes, and by forming a solder bump by heating to volatilize the dispersion medium to form a layer containing the solder particles (solder particle-containing layer), and then heating to melt the solder in a reducing atmosphere, it is possible to suppress the occurrence of bridging and solder non-wetting, which has led to the completion of the present invention.

[0009] One aspect of the present invention relates to a method for forming a bump as described in [1] below.

[0010] [1] A method for forming a solder bump using a solder paste containing solder particles and a volatile dispersion medium, comprising the steps of: applying the solder paste to an area of ​​a member having a plurality of electrodes on its surface, where the electrodes are arranged; and heating the member and the solder paste to a temperature T lower than the melting point of the solder constituting the solder particles. 1 a step of volatilizing the dispersion medium in the solder paste and forming a solder particle-containing layer on the member by heating the member and the solder particle-containing layer in a reducing atmosphere at a temperature T 2and removing by cleaning any residue of the solder particle-containing layer remaining between adjacent solder bumps, wherein the solder particles have an average particle size of 10 μm or less, and the content of the dispersion medium in the solder paste is 30 mass % or more.

[0011] According to the above-mentioned method for forming solder bumps on side surfaces, even when the gap between the electrodes is narrow (eg, less than 25 μm), it is possible to form solder bumps while suppressing the occurrence of bridges and solder non-wetting.

[0012] The method for forming the solder bumps on the side surfaces may be any of the methods described below in [2] to [8].

[0013] [2] The method for forming a solder bump according to [1], wherein the melting point of the solder constituting the solder particles is 180° C. or lower.

[0014] [3] The method for forming a solder bump according to [1] or [2], wherein the reducing atmosphere is an atmosphere containing at least one selected from the group consisting of hydrogen gas, hydrogen radicals, and formic acid gas.

[0015] [4] The method for forming a solder bump according to any one of [1] to [3], wherein the average particle size of the solder particles is not more than one-third of the distance between adjacent electrodes in the plurality of electrodes.

[0016] [5] Said temperature T 1 The method for forming a solder bump according to any one of [1] to [4], wherein the temperature is 50° C. or higher.

[0017] [6] The method for forming a solder bump according to any one of [1] to [5], wherein the thickness of the solder particle-containing layer is not more than two-thirds of the distance between adjacent electrodes in the plurality of electrodes.

[0018] [7] The method for forming a solder bump according to any one of [1] to [6], wherein the member is a semiconductor substrate having a plurality of electrodes on its surface.

[0019] Another aspect of the present invention relates to a method for producing a member having solder bumps, as described in [8] below.

[0020] [8] A method for producing a member having solder bumps, comprising a step of forming solder bumps by the method according to any one of [1] to [7].

[0021] Another aspect of the present invention relates to a solder paste as described in [9] below.

[0022] [9] A solder paste containing solder particles and a volatile dispersion medium, the solder particles having an average particle size of 10 μm or less, and a content of the dispersion medium of 30 mass % or more.

[0023] According to the solder paste of the above aspect, a solder bump is formed by a method in which heating is performed to volatilize the dispersion medium to form a layer containing solder particles (solder particle-containing layer), and then heating is performed to melt the solder in a reducing atmosphere. This makes it possible to form a solder bump while suppressing the occurrence of bridging and solder non-wetting, even when the gap between the electrodes is narrow (for example, less than 25 μm).

[0024] The solder paste on the side surface may be any of the solder pastes described in

[10] to

[12] below.

[0025]

[10] The solder paste according to [9], wherein the melting point of the solder constituting the solder particles is 180°C or lower.

[0026]

[11] The solder paste according to [9] or

[10] , which is used for forming solder bumps on electrodes of a component having a plurality of electrodes on its surface by a solder precoat method.

[0027]

[12] The solder paste according to

[11] , wherein the average particle size of the solder particles is less than or equal to one-third of the distance between adjacent electrodes in the plurality of electrodes. Effect of the Invention

[0028] According to one aspect of the present invention, even when the gap between electrodes is narrow (eg, less than 25 μm), it is possible to form a solder bump while suppressing the occurrence of bridging and solder non-wetting. [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 is a schematic plan view showing an example of a member to which a method of forming a solder bump according to an embodiment is applied. [Diagram 2] FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 3 is a schematic cross-sectional view for explaining a method for forming a solder bump according to an embodiment. [Figure 4] FIG. 4 is a schematic cross-sectional view illustrating a method for manufacturing a connection structure according to one embodiment. [Diagram 5] FIG. 5 is a photograph showing the appearance of the semiconductor chips used in the examples and comparative examples. [Figure 6] FIG. 6 is a photograph showing the appearance of the semiconductor chip of Example 1 after the reflow process. [Figure 7] FIG. 7 is a photograph showing the appearance of the semiconductor chip of Example 1 after the cleaning process. [Figure 8] FIG. 8 shows cross-sectional photographs of the semiconductor chips used in the examples and comparative examples, and a cross-sectional photograph of the semiconductor chip of Example 1 after the cleaning process. [Figure 9] FIG. 9 is a photograph showing an example of a location where bridging occurs observed in the evaluation of bridging suppression. [Figure 10] FIG. 10 is a photograph showing an example of a solder bump observed in the solder non-wetting suppression evaluation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] In the present specification, the numerical range indicated by "~" indicates a range including the numerical values ​​described before and after "~" as the minimum and maximum values, respectively. In the numerical ranges described in stages in the present specification, the upper limit or lower limit of a certain numerical range may be replaced with the upper limit or lower limit of the numerical range of another stage. In the numerical ranges described in the present specification, the upper limit or lower limit of the numerical range may be replaced with a value shown in the examples. In addition, the upper limit and lower limit values ​​described individually can be arbitrarily combined. In the present specification, "(meth)acrylic" means at least one of acrylic and the corresponding methacrylic. In addition, "A or B" may include either A or B, or may include both. In addition, the materials exemplified below may be used alone or in combination of two or more types, unless otherwise specified. When a plurality of substances corresponding to each component are present in the composition, the content of each component in the composition means the total amount of the plurality of substances present in the composition, unless otherwise specified. In addition, the melting point and boiling point mean values ​​at 1 atmosphere.

[0031] Hereinafter, an embodiment of the present invention will be described in detail. However, the present invention is not limited to the following embodiment.

[0032] <Solder paste> The solder paste of one embodiment is a solder paste used, for example, by a solder precoat method, to form solder bumps on the electrodes of a component (e.g., an electronic component such as a circuit component) having multiple electrodes on its surface, and contains solder particles and a volatile dispersion medium.

[0033] In this embodiment, the average particle size of the solder particles is 10 μm or less, and the content of the dispersion medium (content based on the total mass of the solder paste) is 30 mass % or more. According to the solder paste of this embodiment having such a configuration, as described below, by drying on a member to remove the dispersion medium, and then heating in a reducing atmosphere at a temperature equal to or higher than the melting temperature of the solder particles, it is possible to form a solder bump while suppressing the occurrence of bridges and solder non-wetting, even when the gap between electrodes is narrow (for example, less than 25 μm).

[0034] The present inventors speculate that the reason why the above effects are obtained is as follows.

[0035] First, in solder particles, tin exists in bulk and is exposed on the particle surface, but since the tin exposed on the particle surface is easily oxidized, it is known that tin oxide is formed on at least a part of the surface of the solder particle (above the bulk tin). When solder particles coated with such tin oxide are heated above the melting point of the solder, the inside of the solder particle melts, but since the tin oxide on the outermost surface is difficult to melt, it is assumed that the growth of the solder particles due to the melting bonding between the solder particles is difficult to occur. Therefore, when the average particle size of the solder particles is reduced to 10 μm or less, the ratio of tin oxide increases due to the increase in the specific surface area, making it even more difficult for the solder particles to grow, and it is assumed that the formation of bridges due to the melting of the solder particles remaining between the solder bumps is easily suppressed. In addition, even if the tin on the surface of the solder particles is oxidized, the solder particles on the electrode are likely to react with the metal on the electrode surface due to the effect of the reducing substance (reducing gas, etc.) in the reducing atmosphere, and the tin can easily spread on the electrode surface by wetting. For example, when the electrode is an Au electrode, an AuSn alloy layer is formed on the outermost layer of the Au electrode, which allows tin to easily spread over the surface of the Au electrode. The surface of the spread tin is not oxidized by the effect of the reducing substance (reducing gas, etc.) in the reducing atmosphere, so the effect of melting the oxide film on the surface of the solder particles present on or near the electrode is obtained, and the solder particles near the electrode are selectively melted. As a result, it is possible to selectively melt the solder particles on or near the electrode, and it is believed that the occurrence of bridges can be suppressed and a solder bump can be formed.

[0036] Furthermore, if the thickness of the solder particle-containing layer becomes uneven and thicker areas occur in some places, bridges are more likely to occur in those areas and the wetting and spreading of the solder on the electrode surface is also likely to be hindered. However, if the dispersion medium content is 30 mass % or more, the thickness of the solder particle-containing layer deposited on and between the electrodes is more likely to be uniform, and as a result, it is presumed that the occurrence of bridges and solder non-wetting is suppressed.

[0037] (solder particles) The solder particles include tin. The solder particles may include simple tin or may include 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 alloys. The solder particles may be used alone or in combination of two or more kinds.

[0038] Specific examples of tin alloys are shown below. In-Sn (In: 52% by mass, Sn: 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: 42% by mass, Bi: 58% 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℃) Sn-Cu (Sn: 99.3% by mass, Cu: 0.7% by mass, melting point: 227°C)

[0039] The tin content in the solder particles may be, for example, 40 mass % or more, 60 mass % or more, or 80 mass % or more, and 99.5 mass % or less, 80 mass % or less, or 60 mass % or less.

[0040] The tin in the solder particles is present, for example, in bulk (with a purity of 99.9% or more). Since tin is a metal that is easily oxidized, the solder particles usually contain tin oxide on at least a portion of their surface (for example, on top of the bulk tin).

[0041] The melting point of the solder (melting point of the solder constituting the solder particles) may be 250°C or less or 220°C or less, and from the viewpoint of being able to form a solder bump at a low temperature and reducing the load on the member on which the solder bump is formed, may be 180°C or less, 160°C or less, or 140°C or less. The melting point of the solder may be, for example, 90°C or more so that the solder does not melt when the dispersion medium is volatilized. The melting point of the solder may also be referred to as the melting point of the solder particles before oxidation.

[0042] In order to further suppress the occurrence of bridges, the average particle size of the solder particles may be 9.0 μm or less, 8.0 μm or less, 5.0 μm or less, 3.0 μm or less, or 2.0 μm or less. The smaller the average particle size of the solder particles, the more likely it is that the occurrence of bridges is suppressed.

[0043] The average particle size of the solder particles may be, for example, 0.1 μm or more, or may be 0.3 μm or more, 0.5 μm or more, 1.0 μm or more, or 2.0 μm or more, from the viewpoint of enabling the solder particles to melt uniformly when heated to or above the melting point of the solder.

[0044] The average particle size of the solder particles may be set according to the distance between adjacent electrodes on the member to which the solder paste is applied. Specifically, when the average particle size of the solder particles is equal to or less than one-third of the distance between adjacent electrodes, the occurrence of bridges tends to be further suppressed. To obtain this tendency more significantly, the average particle size of the solder particles may be equal to or less than one-quarter or one-fifth of the distance between adjacent electrodes.

[0045] The maximum diameter of the solder particles may be 1.0 μm or more or 2.0 μm or more, and may be 10 μm or less, 9.0 μm or less, 8.0 μm or less, 5.0 μm or less, 3.0 μm or less, or 2.0 μm or less. The smaller the variation in the particle size of the solder particles, the easier it is to uniformly melt the solder particles on the electrodes of the component, and the better the bump shape is. In addition, the smaller the variation in the particle size of the solder particles, the easier it is to prevent the solder particles remaining between the solder bumps from melting and causing a bridge, and also to prevent the occurrence of a bridge caused by large-sized solder particles. From these viewpoints, the proportion of the solder particles having the above maximum diameter may be 80 mass % or more, 90 mass % or more, or 95 mass % or more.

[0046] The maximum diameter and average particle diameter of the solder particles can be calculated from an SEM image, for example, by the following procedure. A powder of solder particles is placed on a carbon tape for SEM with a spatula to prepare an SEM sample. This SEM sample is observed at 5000 times magnification with an SEM device to obtain an SEM image. From the obtained SEM image, a rectangle circumscribing the solder particle is drawn using image processing software, and the long side of the rectangle is taken as the maximum diameter of the particle. This measurement is performed on 50 or more solder particles using multiple SEM images, and the average value of the maximum diameters of these solder particles is calculated, which is taken as the average particle diameter (average maximum diameter). The maximum diameter and average particle diameter of the solder particles in the solder paste can be determined by the above method after washing with an organic solvent such as acetone, filtering, and drying at room temperature (e.g., 25°C).

[0047] The shape of the solder particles may be, for example, spherical, blocky, needle-like, flat (flake-like), or substantially spherical. The solder particles may be an aggregate of solder particles having these shapes. Among these, when the solder particles are spherical, the solder particles are more likely to be uniformly dispersed on and between the electrodes of the member (particularly on the electrodes of the member). As a result, the solder particle-containing layer obtained by drying the solder paste is uniformly formed on and between the electrodes of the member, and when the solder particle-containing layer is heated to a temperature equal to or higher than the melting point of the solder, the solder particles located on the upper part of the electrodes are more likely to melt preferentially compared to the solder particles located between the electrodes due to the effect of the reducing substance in the reducing atmosphere. This has the effect of further suppressing the occurrence of bridges and making it easier to form solder bumps with a better shape. Here, the spherical solder particles refer to particles having an aspect ratio ("long side of particle / short side of particle") of 1.3 or less, as determined from the SEM image.

[0048] The content of the solder particles in the solder paste is 70% by mass or less based on the total mass of the solder paste. The content of the solder particles may be 65% by mass or less, 60% by mass or less, or 50% by mass or less from the viewpoint that the solder particle-containing layer is easily uniformly formed on and between the electrodes of the member, thereby making the bump shape on the upper part of the electrodes uniform and making the bump height and shape uniform, and that the solder particles are easily uniformly dispersed between the electrodes, making it difficult for the solder particles between the electrodes to melt, thereby further suppressing the occurrence of bridges between the electrodes. The content of the solder particles in the solder paste 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, or 50% by mass or more based on the total mass of the solder paste, from the viewpoint of suppressing the precipitation of the solder particles in the paste and improving the uniformity of the solder paste when applied.

[0049] (dispersion medium) The dispersion medium is not particularly limited as long as it is a volatile medium (e.g., liquid) capable of dispersing solder particles. The dispersion medium may be, for example, an organic compound having a vapor pressure of 0.1 to 500 Pa at 20°C. Compounds having flux properties are not included in the dispersion medium, and compounds having thermosetting properties are also not included in the dispersion medium.

[0050] Examples of the dispersion medium include monohydric and polyhydric alcohols such as pentanol, hexanol, heptanol, octanol, decanol, ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, terpineol, and isobornylcyclohexanol (MTPH); ethylene glycol butyl ether, ethylene glycol phenyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol butyl ether, diethylene glycol isobutyl ether, diethylene glycol hexyl ether, triethylene glycol methyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol butyl ether, diethylene glycol isopropyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol butyl ether, propylene glycol propyl ether, and dipropylene glycol methyl ether. ethers such as ether, dipropylene glycol ethyl ether, dipropylene glycol propyl ether, dipropylene glycol butyl ether, dipropylene glycol dimethyl ether, tripropylene glycol methyl ether, and tripropylene glycol dimethyl ether; esters such as ethylene glycol ethyl ether acetate, ethylene glycol butyl ether acetate, diethylene glycol ethyl ether acetate, diethylene glycol butyl ether acetate, dipropylene glycol methyl ether acetate (DPMA), ethyl lactate, butyl lactate, γ-butyrolactone, and propylene carbonate; acid amides such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide; aliphatic hydrocarbons such as cyclohexane, octane, nonane, decane, and undecane; aromatic hydrocarbons such as benzene, toluene, and xylene; mercaptans having an alkyl group having 1 to 18 carbon atoms; and mercaptans having a cycloalkyl group having 5 to 7 carbon atoms.Examples of mercaptans having an alkyl group having 1 to 18 carbon atoms include ethyl mercaptan, n-propyl mercaptan, i-propyl mercaptan, n-butyl mercaptan, i-butyl mercaptan, t-butyl mercaptan, pentyl mercaptan, hexyl mercaptan, and dodecyl mercaptan. Examples of mercaptans having a cycloalkyl group having 5 to 7 carbon atoms include cyclopentyl mercaptan, cyclohexyl mercaptan, and cycloheptyl mercaptan. These may be used alone or in combination of two or more.

[0051] The vapor pressure of the dispersion medium at 20° C. may be 0.1 to 500 Pa, or may be 0.2 to 100 Pa, 0.3 to 50 Pa, or 0.5 to 10 Pa. When the vapor pressure at 20° C. is 0.1 Pa or more, it is easy to achieve both coatability and volatility. In particular, when solder particles with a low melting point are used, the temperature T 1 Therefore, by using a dispersion medium with a vapor pressure of 0.1 Pa or more, the amount of residual dispersion medium can be reduced. On the other hand, if the vapor pressure at 20°C is 500 Pa or less, the dispersion medium is less likely to volatilize during coating, and the increase in the concentration of solder particles due to the volatilization of the dispersion medium during continuous use is suppressed. Therefore, it becomes easier to control the coating thickness during continuous coating.

[0052] Examples of dispersion media (organic compounds) having a vapor pressure of 0.3 to 50 Pa at 20°C include 1-heptanol (vapor pressure 28 Pa), 1-octanol (vapor pressure 8.7 Pa), 1-decanol (vapor pressure 1 Pa), ethylene glycol (vapor pressure 7 Pa), diethylene glycol (vapor pressure 2.7 Pa), propylene glycol (vapor pressure 10.6 Pa), 1,3-butylene glycol (vapor pressure 8 Pa), terpineol (vapor pressure 3.1 Pa), ethylene glycol monophenyl ether (vapor pressure 0.9 Pa), diethylene glycol methyl ether (ethyl carbitol) (vapor pressure 13 Pa), and diethylene glycol monobutyl ether (vapor pressure 3 Pa). When at least one of these dispersion media is used, the volatilization of the dispersion media during coating is easily suppressed, making it easier to control the coating thickness during continuous coating, while the temperature T 1 This allows the dispersion medium to be easily volatilized.

[0053] The content of the dispersion medium is 30% by mass or more based on the total mass of the solder paste, and from the viewpoint of further suppressing the occurrence of bridges and solder non-wetting, it may be 35% by mass or more or 38% by mass or more. From the viewpoint of suppressing the settling of solder particles and improving uniformity after application, the content of the dispersion medium may be 80% by mass or less, 70% by mass or less, or 60% by mass or less based on the total mass of the solder paste. From these viewpoints, the content of the dispersion medium may be 30 to 80% by mass, 35 to 70% by mass, or 38 to 60% by mass based on the total mass of the solder paste.

[0054] (Other Ingredients) The solder paste may further contain components other than the above components (other components), such as flux, a compound having thermosetting properties (such as a thermosetting resin), and the like.

[0055] [Flux] As the flux, those generally used for solder joints etc. can be used. Specific examples include zinc chloride, a mixture of zinc chloride and an inorganic halide, a mixture of zinc chloride and an inorganic acid, a molten salt, phosphoric acid, a derivative of phosphoric acid, an organic halide, hydrazine, rosin, an organic acid, an amino acid, an amine, and an amine hydrohalide salt. These may be used alone or in combination of two or more.

[0056] Examples of the molten salt include ammonium chloride. Examples of the organic acid include lactic acid, citric acid, stearic acid, glutamic acid, glutaric acid, succinic acid, adipic acid, pimelic acid, suberic acid, benzoic acid, malic acid, and the like. Examples of the rosin include activated rosin and non-activated rosin. Rosin is a rosin containing abietic acid as the main component. Examples of the amino acid include glycine, alanine, glutamic acid, and the like. As the amine, a general amine can be used, for example, a primary amine, a secondary amine, a tertiary amine, and the like. The hydrohalide salt of an amine may be a combination of an amine and a halogen element.

[0057] By using an organic acid or rosin having two or more carboxyl groups as the flux, the effect of further increasing the reliability of conduction between electrodes is achieved. In particular, by using an organic acid having two or more carboxyl groups as the flux, the tin oxide on the surface of the solder particles is removed to expose the bulk tin, thereby improving the wettability with the electrodes, and the effect of preventing the occurrence of solder non-wetting and forming a solder bump with a good shape is remarkably obtained. For example, when rosins containing abietic acid as the main component, which are known as the base resin of flux, are used, the function of preventing re-oxidation or adjusting viscosity is high, but the effect of removing tin oxide on the surface of the solder particles and promoting the wetting and spreading of the solder on the electrode surface is low. On the other hand, organic acids having two or more carboxyl groups have a higher effect of removing tin oxide on the surface of the solder particles to expose the bulk tin and improving the wettability with the electrodes than rosins containing abietic acid as the main component. Furthermore, organic acids having two or more carboxy groups can be effective in smaller amounts (for example, 5 parts by mass or less per 100 parts by mass of solder particles) compared to the above-mentioned rosins, making it easier to apply the acid to the electrodes and between the electrodes in a uniform thickness, which makes it possible to make the shape of the solder bumps more uniform and further suppress the occurrence of bridges.

[0058] The flux may be a low molecular weight compound having a molecular weight of 200 or less, from the viewpoint of being easily dissolved in a dispersion medium and being easily applied as a solder paste. The molecular weight of the flux may be 180 or less or 150 or less, from the viewpoint of obtaining the above-mentioned effect more significantly. The molecular weight of the flux may be 100 or more, 150 or more, 180 or more, or 200 or more. In this embodiment, the solder paste may contain a polymer compound such as a resin (e.g., a compound having a weight average molecular weight of 300 or more) as a flux, but from the viewpoint of removing tin oxide on the surface of the solder particles to expose the bulk tin and further improving wettability with the electrode, the content of the polymer compound may be 10 parts by mass or less, or may be 0 parts by mass, relative to 100 parts by mass of the solder particles.

[0059] The melting point of the flux may be 50° C. or more, 70° C. or more, or 80° C. or more, and may be 200° C. or less, 160° C. or less, 150° C. or less, or 140° C. or less. When the melting point of the flux is within the above range, the flux effect is more effectively exerted, and the solder particles can be more efficiently arranged on the electrodes. From the viewpoint of obtaining such an effect more significantly, the melting point of the flux may be 80 to 190° C. or 80 to 140° C.

[0060] Examples of fluxes having a melting point in the range of 80 to 190°C include dicarboxylic acids such as succinic acid (melting point: 186°C), glutaric acid (melting point: 96°C), adipic acid (melting point: 152°C), pimelic acid (melting point: 104°C), and suberic acid (melting point: 142°C), as well as benzoic acid (melting point: 122°C) and malic acid (melting point: 130°C).

[0061] The content of the flux may be 10 parts by mass or less, 8 parts by mass or less, 6 parts by mass or less, or 5 parts by mass or less, relative to 100 parts by mass of the solder particles, from the viewpoint of improving the cleanability in the step of removing the residue of the solder particle-containing layer remaining between adjacent solder bumps by cleaning after the step of forming solder bumps on the electrodes. The content of the flux may be 0.1 parts by mass or more, 0.2 parts by mass or more, or 0.3 parts by mass or more, relative to 100 parts by mass of the solder particles, from the viewpoint of more effectively exerting the flux effect. From these viewpoints, the content of the flux may be 0.1 to 10 parts by mass, 0.2 to 8 parts by mass, 0.3 to 6 parts by mass, or 0.3 to 5 parts by mass, relative to 100 parts by mass of the solder particles.

[0062] [Thermosetting compounds] Examples of the thermosetting compound include oxetane compounds, epoxy compounds, episulfide compounds, (meth)acrylic compounds, phenol compounds, amino compounds, unsaturated polyester compounds, polyurethane compounds, silicone compounds, polyimide compounds, etc. The content of the thermosetting compound may be, for example, 0 to 10 parts by mass based on the total mass of the solder paste.

[0063] The solder paste may further contain additives such as a thixotropic agent, an antioxidant, an anti-fungal agent, and a matting agent as other components.

[0064] <Method of forming solder bumps> A method for forming a solder bump according to one embodiment includes a step of applying the solder paste according to the above embodiment to an area where electrodes of a member having a plurality of electrodes on a surface are arranged (application step), and a step of heating the member and the solder paste at a temperature T 1 The solder paste is heated at a temperature T 2 , and the dispersion medium in the solder paste is evaporated to form a solder particle-containing layer on the component (drying step). The component and the solder particle-containing layer are then heated in a reducing atmosphere at a temperature T 3 , which is equal to or higher than the melting point of the solder. 2 The method includes a step of heating the solder particle-containing layer at 400 K to melt the solder particles in the solder particle-containing layer and form solder bumps on the electrodes of the component (reflow step), and a step of removing residues of the solder particle-containing layer remaining between adjacent solder bumps by cleaning (cleaning step). According to this method, a component having solder bumps on the electrodes can be obtained.

[0065] In the conventional method for forming solder bumps, when a solder paste containing a large amount of dispersion medium, such as 30 mass % or more, is used, the solder is likely to be non-wetted and the shape of the solder bumps is likely to be non-uniform. 2 Before heating, the temperature T is lower than the melting point of the solder. 1 Since the dispersion medium is removed by heating at 300 K, solder non-wetting is unlikely to occur and the shape of the solder bump is unlikely to become uneven. This is presumably because the dispersion medium in the solder paste is removed in advance, which makes it easier for a reaction to occur on the electrode surface due to a reducing substance (reducing gas, etc.) in a reducing atmosphere, and also because the solder particles on the electrode come into close proximity to each other, increasing the concentration of the reducing substance between the solder particles on the electrode, facilitating the melting of the solder particles.

[0066] In addition, in the above method, the temperature T 1Heating at a temperature T below the melting point of the solder promotes the oxidation of the solder particle surface, which is effective in suppressing the occurrence of bridges. As mentioned above, the oxidation of the solder particle surface inhibits the growth of the solder particles due to the fusion bonding between the solder particles between the electrodes. 1 It is presumed that heating at this temperature thickens the oxide film on the surface of the solder particles, or that the oxide film is formed uniformly on the surface of the solder particles, making it even easier to inhibit the growth of the solder particles, and as a result, improving the effect of suppressing the occurrence of bridges.

[0067] The method of forming solder bumps according to the above embodiment will be described below with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and duplicated explanations will be omitted.

[0068] Fig. 1 is a plan view showing an example of a member (a member having a plurality of electrodes on its surface) to which the method for forming solder bumps of the embodiment is applied, and Fig. 2 is a schematic cross-sectional view taken along line II-II in Fig. 1. Fig. 3 is a schematic cross-sectional view for explaining the method for forming solder bumps of the embodiment. Specifically, Fig. 3(a) is a schematic cross-sectional view for explaining the coating step, Fig. 3(b) is a schematic cross-sectional view for explaining the drying step, Fig. 3(c) is a schematic cross-sectional view for explaining the reflow step, and Fig. 3(d) is a schematic cross-sectional view for explaining the cleaning step.

[0069] (Materials) 1 is, for example, an electronic component such as a circuit component, and includes an insulating substrate 2 and an electrode 3 provided on the surface of the insulating substrate 2. The insulating substrate 2 includes, for example, a substrate 4 and an insulating resin coating 5 that covers an area of ​​the surface of the substrate 4 where the electrode 3 is not provided.

[0070] Specific examples of the member 1 include a semiconductor substrate (e.g., a semiconductor wafer such as a silicon wafer) having an electrode formed on its surface, a glass substrate having an electrode formed on its surface, a ceramic substrate having an electrode formed on its surface, a printed wiring board, a semiconductor package substrate, and the like. Among these, a semiconductor substrate (e.g., a silicon substrate) has good adhesion with an electrode, so that when a semiconductor substrate having an electrode formed on its surface is used, good adhesion between the substrate and the electrode tends to be maintained even after the formation of solder bumps. In addition, since the base material of the semiconductor substrate is smooth, the height of the electrode can be easily controlled when forming an electrode on the surface of the semiconductor substrate, and the electrode height can be made lower. Therefore, the electrode height of the electrodes formed on the surface of the semiconductor substrate tends to be low, and the occurrence of solder bridges between the electrodes is easily suppressed.

[0071] Examples of the electrode 3 include electrodes containing titanium, nickel, chromium, copper, aluminum, palladium, platinum, gold, and the like. From the viewpoint of adhesion to the substrate 4, the electrode 3 may be an electrode formed by laminating a titanium layer, a nickel layer, and a copper layer in this order. When the substrate 4 is a silicon wafer, the surface of the silicon wafer is oxidized to form silicon oxide, and a titanium layer is formed on the silicon oxide, thereby improving adhesion. Furthermore, by providing a nickel layer on the titanium layer and providing a copper layer on the nickel layer, it is possible to suppress the diffusion of copper into the silicon wafer, compared to the case where a copper layer is directly provided on the titanium layer. From the viewpoint of making tin more easily wettable and spreadable, the surface of the electrode may contain at least one selected from the group consisting of gold, palladium, and copper. In particular, by forming a palladium layer and / or a gold layer on the surface of the electrode, the wettability of the solder to the electrode is improved.

[0072] The shape of the electrode 3 in a plan view may be various shapes such as a square, a rectangle, a circle, etc., depending on the size of the member 1. The shape of the electrode 3 in a plan view may be a square in that the insulating base material 2 can be made smaller.

[0073] As shown in FIG. 1, for example, the electrodes 3 are arranged in a dot pattern in the peripheral portion (peripheral portion) of the insulating substrate 2 in a plan view, and the distance between adjacent electrodes 3, 3 is very narrow. Specifically, the distance p between adjacent electrodes 3, 3 is, for example, less than 25 μm. From the viewpoint of making it even more difficult for bridges to occur, the distance p between adjacent electrodes 3, 3 may be 3 μm or more, 5 μm or more, or 10 μm or more. The distance p between adjacent electrodes 3, 3 is the length of the portion indicated by p in FIG. 2, and is the value at the point where the distance between adjacent electrodes is the smallest.

[0074] The height d1 of the electrode 3 exposed from the insulating base material 2 may be 30 μm or less, 20 μm or less, or 10 μm or less, from the viewpoint of further reducing the likelihood of bridging. Here, the height d1 of the electrode 3 is the length of the portion shown by d1 in FIG. 2, and is calculated by the following formula (I). Height of electrode 3 = [shortest distance d2 from the surface of electrode 3 to substrate 4] - [shortest distance d3 from the surface of insulating substrate 2 (surface of resin coating 5) to substrate 4] (I)

[0075] The height d1 of the electrode 3 may be a negative value. In other words, the shortest distance d2 from the surface of the electrode 3 to the substrate 4 may be smaller than the shortest distance d3 from the surface of the insulating substrate 2 (the surface of the resin coating 5) to the substrate 4. The height d1 of the electrode 3 may be, for example, 1 μm or more.

[0076] The resin coating 5 may be a film made of a cured product of a curable resin composition containing a thermosetting compound such as an oxetane compound, an epoxy compound, an episulfide compound, a (meth)acrylic compound, a phenol compound, an amino compound, an unsaturated polyester compound, a polyurethane compound, a silicone compound, a polyimide compound, etc. When an epoxy compound or a polyimide compound is used as the thermosetting compound, the curability and viscosity of the curable resin composition become even better, and the resin coating 5 has excellent characteristics and insulation reliability when left at high temperatures.

[0077] (coating process) 3(a), in the application step, the solder paste of the above embodiment containing solder particles 6 is applied to the area of ​​the component 1 where the electrodes 3 are arranged, to form a solder paste layer 7 on the component 1. In this way, a component 8 with solder paste is obtained.

[0078] The solder paste is applied so that a solder paste layer 7 is formed at least on the electrode 3 and between the electrodes 3, 3. The solder paste may be applied onto the component 1 so as to cover all of the electrodes of the component 1, for example, the entire surface of the component 1 (the entire surface on which the electrodes 3 are formed). Examples of methods for applying the solder paste include methods of applying the solder paste using screen printing, transfer printing, offset printing, jet printing, a dispenser, a jet dispenser, a needle dispenser, a comma coater, a slit coater, a die coater, a gravure coater, a slit coat, letterpress printing, intaglio printing, gravure printing, stencil printing, soft lithography, a bar coat, an applicator, a particle deposition method, a spray coater, a spin coater, a dip coater, or the like.

[0079] The thickness D1 of the solder paste layer 7 can be appropriately changed depending on the thickness of the solder particle-containing layer 9 obtained after drying, and may be, for example, 1 μm or more, 2 μm or more, 3 μm or more, 5 μm or more, 10 μm or more, 15 μm or more, or 20 μm or more, and may be 120 μm or less, 100 μm or less, 80 μm or less, or 50 μm or less. The thickness D1 of the solder paste layer 7 is the length of the portion indicated by D1 in FIG. 3(a), and is the shortest distance from the surface of the insulating substrate 2 (the surface of the resin coating 5) to the surface of the solder paste layer 7.

[0080] (drying process) In the drying step, as shown in FIG. 3B, the solder paste-attached member 8 is heated to a temperature T 1 By heating at 400° C., the dispersion medium in the solder paste (solder paste layer 7) is volatilized, and a solder particle-containing layer 9 is formed on the member 1. In this way, a member 10 with a solder particle-containing layer is obtained.

[0081] Drying temperature T 1 is a temperature below the melting point of the solder, for example, 30 to 120° C. 1 From the viewpoint of oxidizing the surfaces of the solder particles, the temperature may be close to the melting point of the solder, and may be, for example, 50° C. or higher, 70° C. or higher, or 90° C. or higher.

[0082] The drying time may be adjusted appropriately depending on the type and amount of the dispersion medium used. Specifically, for example, it may be 1 minute or more and 120 minutes or less.

[0083] The atmosphere during drying may be an air atmosphere or a nitrogen atmosphere. By using an air atmosphere during drying, the surfaces of the solder particles are more likely to be oxidized. As a result, when forming the solder bumps (during the reflow process described below), the solder particles dispersed between the electrodes 3, 3 melt and bond with each other, which inhibits the growth of the solder particles, and tends to further suppress the occurrence of bridges between the electrodes. This effect is enhanced by the drying temperature T 1 This is even more likely to be achieved when the temperature is close to the melting point of the solder.

[0084] The solder particle-containing layer 9 formed in the drying step contains at least the solder particles 6, and may further contain other components (such as flux) that can be contained in a solder paste. A portion of the dispersion medium may remain in the solder particle-containing layer 9 without being volatilized, and the content of the dispersion medium in the solder particle-containing layer 9 may be 5 mass % or less, 1 mass % or less, or 0.1 mass % or less based on the total mass of the solder particle-containing layer.

[0085] The thickness D2 of the solder particle-containing layer 9 may be two-thirds or less of the distance p between the adjacent electrodes 3, 3 from the viewpoint of further suppressing the occurrence of bridges. Specifically, the thickness D2 of the solder particle-containing layer 9 may be, for example, 50 μm or less, 40 μm or less, 30 μm or less, or 25 μm or less. From the viewpoint of further suppressing the occurrence of solder non-wetting, the thickness D2 of the solder particle-containing layer 9 may be, for example, 3 μm or more, 5 μm or more, 10 μm or more, or 15 μm or more. The thickness D2 of the solder particle-containing layer 9 is the length of the portion indicated by D2 in FIG. 3(b), and is the shortest distance from the surface of the insulating substrate 2 (the surface of the resin coating 5) to the surface of the solder particle-containing layer 9.

[0086] (Reflow process) In the reflow process, as shown in FIG. 3C, the member 10 with the solder particle-containing layer (the member 1 and the solder particle-containing layer 9) is heated in a reducing atmosphere at a temperature T 2 By heating at 400 K, the solder particles 6 in the solder particle-containing layer 9 are melted to form solder bumps 11 on the electrodes 3 of the component 1. At this stage, residues of the solder particle-containing layer 9 are present between the solder bumps 11, 11 (between the electrodes 3, 3). The residues of the solder particle-containing layer 9 include, for example, the solder particles 6 and organic components 12 derived from other components (flux, etc.) that may be contained in the solder paste. The solder particles 6 include, for example, coarse particles 13 that have grown as a result of solder particles melting and bonding to each other.

[0087] The reducing atmosphere is an atmosphere containing a reducing substance such as a reducing gas. From the viewpoint of efficiently reducing the oxide film on the surface of the solder particles 6, the reducing atmosphere may be an atmosphere containing at least one selected from the group consisting of hydrogen gas, hydrogen radicals, and formic acid gas (for example, a hydrogen gas atmosphere, a hydrogen radical atmosphere, a formic acid gas atmosphere, or a mixed atmosphere thereof). By removing the oxide film on the surface of the solder particles 6 by reduction, the melting, wetting, spreading, and coalescence of the solder particles 6 are more likely to proceed.

[0088] Heat treatment in a reducing atmosphere (temperature T above the melting point of solder)2 The heating at room temperature) can be carried out using, for example, a hydrogen reduction furnace, a hydrogen radical reduction furnace, a formic acid reduction furnace, or a conveyor furnace or continuous furnace thereof.

[0089] Heat treatment temperature T 2 is a temperature equal to or higher than the melting point of the solder, and may be, for example, a temperature higher than the melting point of the solder by 5° C. or more, 10° C. or more, 20° C. or more, 30° C. or more, or 40° C. or more. 2 When the heat treatment temperature T is 10°C or more higher than the melting point of the solder, the occurrence of solder non-wetting tends to be further suppressed. 2 The difference between the heat treatment temperature T and the melting point of the solder may be 40° C. or less, 30° C. or less, or 20° C. or less. 2 When the difference between the melting point of the solder and the heat treatment temperature T is 40° C. or less, the occurrence of bridges tends to be further suppressed. 2 The temperature may be higher than the melting point of the solder by 10 to 40° C. The heat treatment time may be, for example, 1 minute or more and 120 minutes or less.

[0090] The height of the solder bumps can be adjusted by the composition and application amount of the solder paste, and can be set to, for example, 3 to 30 μm.

[0091] (Cleaning process) 3(d), in the cleaning step, the uncleaned solder bumped member 14 obtained in the reflow step is cleaned to remove residues of the solder particle-containing layer 9 remaining between adjacent solder bumps 11, 11. In this way, a solder bumped member 15 is obtained.

[0092] The cleaning may be, for example, cleaning with water or solvent cleaning. Examples of cleaning liquids used for cleaning include water, alcohol-based solvents, terpene-based solvents, petroleum-based solvents, hydrocarbon-based solvents, and alkaline-based solvents. These may be used alone or in combination of two or more. The cleaning liquid may contain a cleaning agent (such as a surfactant).

[0093] <Method of Manufacturing Connection Structure> Next, a method for manufacturing a connection structure (eg, a semiconductor device) using the solder bumped member 15 obtained by the method for forming solder bumps of the above embodiment will be described.

[0094] 4 is a schematic cross-sectional view for explaining a method for manufacturing a connection structure using a member with solder bumps 15. In the method for manufacturing the connection structure, first, as shown in (a) of FIG. 4, a member with solder bumps 15 as a first member and a second member 21 are prepared and arranged so that their electrodes (first electrode 3 and second electrode 23) face each other. Next, as shown in (b) of FIG. 4, the member with solder bumps 15 and the second member 21 are heated while being pressed in the opposing direction, thereby electrically connecting the electrodes (first electrode 3 and second electrode 23) through the solder bumps 11. In this way, a connection structure 30 is obtained.

[0095] The second member 21 is, for example, an interposer substrate, and includes an insulating base material 22 and an electrode (second electrode) 23 provided on the surface of the insulating base material 22. The insulating base material 22 includes, for example, a base material 24 and an insulating resin coating 25 that covers an area of ​​the surface of the base material 24 where the electrode 23 is not provided. As the second member 21, the member 1 exemplified for use in manufacturing the member 15 with solder bumps can be used. The second member 21 may be the same as or different from the member 1 used for manufacturing the member 15 with solder bumps. Solder bumps may be formed on the electrodes 23 of the second member 21. EXAMPLES

[0096] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0097] <Preparing materials> [Solder particles] The following solder particles A1 to A5 were prepared as solder particles having a Bi content of 58 mass % and a Sn content of 42 mass % (Bi58-Sn42 solder particles, melting point: 138° C.). Solder particles A1 (average particle size: 1.8 μm or less (d90 = 1.8 μm), manufactured by 5N Plus, Type 10) Solder particles A2 (average particle size: 2.9 μm or less (d90 = 2.9 μm), manufactured by 5N Plus, Type 9) Solder particles A3 (average particle size: 5.0 μm or less (d90 = 5.0 μm), manufactured by 5N Plus, Type 8) Solder particles A4 (average particle size: 8.0 μm or less (d90 = 8.0 μm), manufactured by 5N Plus, Type 7) Solder particles A5 (average particle size: 12.0 μm or less (d90 = 12.0 μm), manufactured by 5N Plus, Type 6)

[0098] The solder particles B1 and B2 shown below were prepared as solder particles having a Sn content of 96.5 mass %, an Ag content of 3.0 mass %, and a Cu content of 0.5 mass % (Sn96.5-Ag3.0-Cu0.5 solder particles, melting point: 218° C.). Solder particles B1 (average particle size: 1.8 μm or less (d90 = 1.8 μm), manufactured by 5N Plus, Type 10) Solder particles B2 (average particle size: 8.0 μm or less (d90 = 8.0 μm), manufactured by 5N Plus, Type 7)

[0099] The average particle size of the solder particles A1 to A5 and the solder particles B1 to B2 was measured by the following method. First, the powder of the solder particles was placed on a carbon tape for SEM with a spatula to prepare a sample for SEM. Next, the sample for SEM was observed at 5000 times magnification with an SEM device to obtain an SEM image. From the obtained SEM image, a rectangle circumscribing the solder particle was drawn using image processing software, and the long side of the rectangle was taken as the maximum diameter of the particle. Using multiple SEM images, this measurement was performed on 100 solder particles, and the average value of the maximum diameters of 50 solder particles was calculated, which was taken as the average particle size.

[0100] [others] As a volatile dispersion medium, diethylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., boiling point: 244° C., vapor pressure: 2.7 Pa) was prepared.

[0101] <Examples 1 to 48 and Comparative Examples 1 to 5> (Preparation of solder paste) The solder particles and diethylene glycol shown in Tables 1 to 4 were mixed in the amounts (unit: parts by mass) shown in Tables 1 to 4 to obtain the solder pastes of Examples 1 to 48 and Comparative Examples 1 to 5.

[0102] (Preparation of semiconductor chips) A semiconductor chip (manufactured by Waltz Corporation, WALTS-TEG IP80-0101JY, product name) was prepared on a silicon substrate on which a plurality of electrodes were formed, each of which was formed by laminating a nickel layer and a gold layer in this order. The plurality of electrodes were arranged in two rows of 39 terminals x 40 terminals (total of 79 terminals) on the periphery of the silicon substrate having a square shape in plan view, with one electrode being one terminal. More specifically, the electrode group of 39 terminals x 40 terminals was formed along the four sides of the silicon substrate having a square shape in plan view, with two locations per side (total of 8 locations). As shown in (a) and (b) of FIG. 5, the pitch between the electrodes was 80 μm, the electrode size was 58 μm x 58 μm, and the space between the electrodes (the distance between adjacent electrodes) was 22 μm. The height d1 of the electrode exposed from the silicon substrate (the distance from the surface of the silicon substrate to the surface of the electrode) was 3 μm.

[0103] (Solder bump formation) [Coating process] The solder paste prepared above was applied by a tabletop roll coater onto the surface of the semiconductor chip prepared above on which the electrodes were formed.

[0104] [Drying process] Next, the semiconductor chip coated with the solder paste was placed on a hot plate set at a temperature (drying temperature) shown in Tables 1 to 4 to volatilize the diethylene glycol. This formed a solder particle-containing layer, and a semiconductor chip with a solder particle-containing layer was obtained. The drying time (placement time) was 60 minutes at 30°C, 30 minutes at 50°C, and 1 minute at 90°C.

[0105] [Measurement of thickness of solder particle-containing layer] The thickness D2 of the solder particle-containing layer formed by the drying process was measured using a laser displacement meter (Keyence Corporation, product name LK-G5000). Specifically, measurements were taken at a total of five points between the electrodes, and the average value was taken as the thickness D2 of the solder particle-containing layer.

[0106] [Reflow process] The semiconductor chip (semiconductor chip with solder particle-containing layer) after the drying process was placed in a formic acid reduction furnace (Shinko Seiki Co., Ltd., vacuum soldering device), and after evacuation, formic acid gas was introduced into the furnace to fill the furnace with formic acid gas. Next, the furnace was heated to 180°C or 240°C, and after being held for 1 minute, evacuation was performed again. Thereafter, nitrogen was introduced to return the pressure to atmospheric pressure, and the temperature in the furnace was lowered to room temperature to terminate the heat treatment. The temperature in the furnace (heat treatment temperature) was 180°C in Examples 1 to 32 and Comparative Examples 1 to 5 using solder particles A1 to A5, and 240°C in Examples 33 to 48 using solder particles B1 to B2. The temperature rise time (time until the temperature in the furnace reaches the heat treatment temperature) was 20 minutes in Examples 1 to 32 and Comparative Examples 1 to 5, and 30 minutes in Examples 33 to 48. By the above operations, the solder particles were melted to form solder bumps on the electrodes.

[0107] For reference, FIG. 6 shows an external view of the semiconductor chip (uncleaned semiconductor chip with solder bumps) of Example 1 after the reflow process. FIG. 6(a) is a micrograph taken using a microscope (digital microscope VHX-5000, manufactured by Keyence Corporation), and FIG. 6(b) and FIG. 6(c) are enlarged photographs of the space between the electrodes in FIG. 6(a). As shown in FIG. 6(a), it was confirmed that the solder bumps were uniformly formed on the electrodes in the example. Also, as shown in FIG. 6(b) and FIG. 6(c), it was confirmed that the solder particles remained as fine particles and existed independently between the electrodes in the example, and no bridges were formed. The above external view was taken using a microscope (digital microscope VHX-5000, manufactured by Keyence Corporation).

[0108] [Cleaning process] The semiconductor chip after the reflow process (uncleaned semiconductor chip with solder bumps) was immersed in an acetone solution (special grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and ultrasonically cleaned for 10 minutes. This removed the residue of the solder particle-containing layer remaining between the solder bumps, and a semiconductor chip with solder bumps was obtained.

[0109] Fig. 7 shows a photograph of the appearance of the semiconductor chip of Example 1 (semiconductor chip with solder bumps) after the cleaning process. Fig. 7(a) is a micrograph taken using a microscope (digital microscope VHX-5000, manufactured by Keyence Corporation), and Fig. 7(b) is a magnified photograph of the space between the electrodes in Fig. 7(a). As shown in Figs. 7(a) and (b), in the example, it was confirmed that bumps were formed on the electrodes and that residues such as solder particles between the electrodes were removed.

[0110] [Cross-section observation] Using a microscope (digital microscope VHX-5000 manufactured by Keyence Corporation), the cross section of the electrode portion of the semiconductor chip (semiconductor chip with solder bumps) after the cleaning process was observed, and the height of the solder bumps was measured. In all examples, the height of the solder bumps was about 10 μm.

[0111] For reference, a micrograph of the cross section of the electrode portion of the semiconductor chip before the solder paste was applied, obtained by observing the cross section in the same manner as described above, is shown in FIG. 8(a), and a cross-sectional photograph of the semiconductor chip of Example 1 (semiconductor chip with solder bumps) obtained by the above cross-sectional observation is shown in FIG. 8(b).

[0112] (evaluation) [Bridge suppression (insulation) evaluation] Eight electrode groups (39 terminals x 40 terminals) on a semiconductor chip were observed using a microscope (digital microscope VHX-5000, manufactured by Keyence Corporation) to confirm the number of locations where bridges had occurred. For reference, a photograph (example) of a location where bridges had occurred is shown in Figure 9.

[0113] The bridging inhibition was evaluated according to the following criteria. If the evaluation was C or higher, it was determined that the occurrence of bridging was inhibited. The results are shown in Tables 1 to 4. A: Number of bridges: 0 B: Locations where bridges occur: 1 to 5 C: Bridge locations: 6 to 9 D: Bridge locations: 10 to 19 E: Bridge locations: 20 to 49 F: Bridge occurrence locations: 50 or more

[0114] [Evaluation of solder non-wetting suppression (bump formation)] Eight electrode groups (39 terminals x 40 terminals) on the semiconductor chip were observed using a microscope (Keyence Digital Microscope VHX-5000) to confirm the number of electrodes where solder non-wetting had occurred. As shown in Figure 10(a), electrodes whose entire surface (100% of the surface area) was covered with solder were judged to be good products, and as shown in Figure 10(b), electrodes whose surface was partially not covered with solder (electrodes where the gold electrode was partially exposed) were judged to be electrodes where solder non-wetting had occurred.

[0115] The suppression of solder non-wetting was evaluated according to the following criteria. If the evaluation was C or higher, it was determined that the occurrence of solder non-wetting was suppressed. The results are shown in Tables 1 to 4. A: Number of electrodes with solder non-wetting: 0 B: Number of electrodes with solder non-wetting: 1 to 5 C: Number of electrodes with solder non-wetting: 6 to 9 D: Number of electrodes with solder non-wetting: 10 to 19 E: Number of electrodes with solder non-wetting: 20 to 49 F: Number of electrodes with solder non-wetting: 50 or more

[0116] [Table 1]

[0117] [Table 2]

[0118] [Table 3]

[0119] [Table 4] [Explanation of symbols]

[0120] 1...member, 2...insulating substrate, 3...electrode (first electrode), 4...substrate, 5...resin coating, 6...solder particle, 7...solder paste layer, 9...solder particle-containing layer, 11...solder bump, 15...member with solder bump (first member), 21...second member, 23...second electrode, 30...connection structure.

Claims

1. A method for forming a solder bump using a solder paste containing solder particles and a volatile dispersion medium, comprising the steps of: applying the solder paste to a region of a component having a plurality of electrodes on a surface thereof, the electrodes being disposed; The component and the solder paste are heated to a temperature T lower than the melting point of the solder constituting the solder particles. １ heating the solder paste at a temperature of 1000° C. to volatilize the dispersion medium in the solder paste and form a solder particle-containing layer on the member; The member and the solder particle-containing layer are heated in a reducing atmosphere at a temperature T equal to or higher than the melting point of the solder constituting the solder particles. ２ to melt the solder particles in the solder particle-containing layer and form solder bumps on the electrodes of the component; and removing residue of the solder particle-containing layer remaining between adjacent solder bumps by cleaning. The average particle size of the solder particles is 10 μm or less, The method for forming a solder bump, wherein the content of the dispersion medium in the solder paste is 30 mass % or more.

2. 2. The method for forming a solder bump according to claim 1, wherein the melting point of the solder constituting the solder particles is 180° C. or lower.

3. 3. The method for forming a solder bump according to claim 1, wherein the reducing atmosphere is an atmosphere containing at least one selected from the group consisting of hydrogen gas, hydrogen radicals, and formic acid gas.

4. 4. The method for forming a solder bump according to claim 1, wherein an average particle size of the solder particles is equal to or less than one third of a distance between adjacent electrodes in the plurality of electrodes.

5. The temperature T １ The method for forming a solder bump according to any one of claims 1 to 4, wherein the temperature is 50°C or higher.

6. 6. The method for forming a solder bump according to claim 1, wherein the thickness of the solder particle-containing layer is equal to or less than two-thirds of the distance between adjacent electrodes in the plurality of electrodes.

7. 7. The method for forming a solder bump according to claim 1, wherein the member is a semiconductor substrate having a plurality of electrodes on a surface thereof.

8. A method for manufacturing a member having solder bumps, comprising the step of forming solder bumps by the method according to any one of claims 1 to 7.

9. The solder paste contains solder particles and a volatile dispersion medium, The average particle size of the solder particles is 10 μm or less, The solder paste has a dispersion medium content of 30 mass % or more.

10. 10. The solder paste according to claim 9, wherein the melting point of the solder constituting the solder particles is 180° C. or lower.

11. The solder paste according to claim 9 or 10, which is used for forming solder bumps on electrodes of a component having a plurality of electrodes on its surface by a solder precoat method.

12. The solder paste according to claim 11 , wherein the average particle size of the solder particles is equal to or less than one-third of the distance between adjacent electrodes in the plurality of electrodes.

Images