TW202000764A - Solder paste - Google Patents

Abstract

The present invention relates to a solder paste which contains solder particles and a flux. A part of the surface of the solder particles has a flat portion.

Description

Solder paste

The invention relates to a solder paste.

Since the past, the use of solder particles has been investigated as conductive particles formulated in anisotropic conductive materials such as anisotropic conductive films and anisotropic conductive pastes. For example, Patent Document 1 describes a conductive paste containing a thermosetting component and a plurality of solder particles subjected to a specific surface treatment. [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2016-76494

[Problems to be solved by the invention] The object of the present invention is to provide a novel solder paste.

[Means to solve the problem] One aspect of the present invention relates to a solder paste including solder particles and flux, the solder particles having a flat portion on a part of the surface.

In one embodiment, the average particle size of the solder particles may also be 1 μm to 30 μm, and the coefficient of variation (C.V.) value may also be 20% or less.

In one embodiment, the ratio (A/B) of the diameter A of the flat portion to the diameter B of the solder particles may also satisfy the following formula. 0.01＜A/B＜1.0

In one embodiment, when two pairs of parallel lines are used to form a quadrilateral circumscribed from the projection image of the solder particles, when the distance between the opposing sides is set to X and Y (where Y<X), X And Y can also satisfy the following formula. 0.8＜Y/X＜1.0

In one embodiment, the solder particles may also include at least one selected from the group consisting of tin, tin alloy, indium, and indium alloy.

In one embodiment, the solder particles may also be selected from In-Sn alloy, In-Sn-Ag alloy, In-Bi alloy, Sn-Au alloy, Sn-Bi alloy, Sn-Bi-Ag alloy, Sn-Ag -At least one tin alloy in the group consisting of Cu alloy and Sn-Cu alloy.

[Effect of invention] According to the present invention, a novel solder paste can be provided. By using the solder particles having a flat portion on a part of the surface, a solder paste having excellent wettability and spreadability can be obtained.

Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the following embodiments. In addition, unless otherwise specified, the materials exemplified below may be used alone or in combination of two or more. The content of each component in the composition refers to the total amount of the plurality of substances present in the composition, unless there is a plurality of substances corresponding to each component in the composition, unless otherwise specified. The numerical range indicated using "-" indicates a range including the numerical values described before and after "-" as the minimum value and the maximum value, respectively. In the numerical range described in stages in this specification, the upper limit or lower limit of the numerical range in a certain stage may be replaced with the upper limit or lower limit of the numerical range in other stages. In the numerical range described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the values shown in the examples.

<Solder paste> The solder paste of this embodiment contains solder particles and flux. The paste may further contain thermosetting components and other components.

(Solder pellets) The solder particles have a flat portion on a part of the surface. The details of the solder particles and the manufacturing method thereof will be described later.

Based on the total mass of the solder paste, the content of the solder particles may be 1% by mass or more, 2% by mass or more, 10% by mass or more, 20% by mass or more, or 30% by mass or more. In addition, based on the total mass of the solder paste, the content may be 99% by mass or less, 90% by mass or less, or 85% by mass or less. When the content of the solder particles is within the above range, it is easier to arrange the solder particles on the electrodes, and it is easier to arrange a large number of solder particles between the electrodes, which tends to improve the conduction reliability.

(Flux) Examples of the flux include compounds generally used in solder bonding and the like, and examples thereof include zinc chloride, a mixture of zinc chloride and an inorganic halide, a mixture of zinc chloride and an inorganic acid, molten salt, phosphoric acid, and derivatization of phosphoric acid Substances, organic halides, hydrazine, organic acids, rosin, etc. These fluxes may be used alone or in combination of two or more.

In addition, examples of the molten salt include ammonium chloride. Examples of organic acids include lactic acid, citric acid, stearic acid, glutamic acid, glutaric acid, and the like. Examples of the rosin include activated rosin and non-activated rosin. In addition, as the rosin, more specifically, rosins containing rosin acid as a main component can be cited. The flux is preferably rosin, more preferably rosin acid. By using these fluxes, the conduction reliability between the electrodes is further improved.

The melting point of the flux may be 50°C or higher, 70°C or 80°C. The melting point may be 200°C or lower, 160°C or lower, 150°C or lower, or 140°C or lower. When the melting point of the flux is within the above range, there is a tendency that the flux effect is easily exerted, and the solder particles are effectively arranged on the electrode. For example, as a flux having a melting point within the above range, succinic acid (melting point 186°C), glutaric acid (melting point 96°C), adipic acid (melting point 152°C), pimelic acid (melting point 104°C) may be mentioned. ), suberic acid (melting point 142°C) and other dicarboxylic acids, benzoic acid (melting point 122°C), malic acid (melting point 130°C), etc.

In addition, as the flux, an organic acid having a hydroxyl group and a carboxyl group can be used. In terms of efficiently removing the surface oxide film of the solder particles and providing good bonding reliability, aliphatic dihydroxycarboxylic acid is preferred. For example, tartaric acid, 2,2-bis(hydroxymethyl)propionic acid, 2,2-bis(hydroxymethyl)butanoic acid, 2,2-bis(hydroxymethyl)valeric acid, etc. may be mentioned.

The flux is not only contained in the solder paste, but also adheres to the surface of the solder particles.

Based on the total mass of solder paste, the flux content can also be 0.5% by mass or more. In addition, based on the total mass of the solder paste, the content may be 30% by mass or less, or 25% by mass or less. If the content of the flux is within the above range, it is difficult to form an oxide film on the surfaces of the solder and the electrode, and it is easy to effectively remove the oxide film formed on the surface of the solder and the electrode.

(Thermosetting component) The thermosetting component may include a thermosetting compound and a thermosetting agent. Examples of thermosetting compounds include oxetane compounds, epoxy compounds, episulfide compounds, (meth)acrylic compounds, phenol compounds, amino compounds, unsaturated polyester compounds, and polyurethanes. Compounds, silicone compounds, polyimide compounds, etc.

Based on the total mass of the solder paste, the content of the thermosetting compound may be 10% by mass or more, 40% by mass or more, or 50% by mass or more. In addition, based on the total mass of the solder paste, the content may be 99% by mass or less, 98% by mass or less, 90% by mass or less, or 80% by mass or less.

Examples of the thermal hardener include imidazole hardener, amine hardener, phenol hardener, polythiol hardener, acid anhydride, thermal cation initiator, thermal radical generator, and the like. These thermosetting agents may be used alone or in combination of two or more.

From the viewpoint of making the solder paste easily harden quickly at low temperatures, imidazole hardeners, polythiol hardeners, amine hardeners, and the like can be used as the thermal hardener. From the viewpoint of storage stability, a latent thermosetting agent can be used. As the latent hardener, a latent imidazole hardener, a latent polythiol hardener, a latent amine hardener, etc. can be used.

The reaction initiation temperature of the thermosetting agent may be 50°C or higher, 70°C or higher, or 80°C or higher. In addition, the temperature may be 250°C or lower, 200°C or lower, 150°C or lower, or 140°C or lower. If the reaction starting temperature of the thermosetting agent is within the above range, it is easy to effectively arrange the solder particles on the electrode. In this specification, the reaction starting temperature of the thermosetting agent refers to the temperature at which the peak of heat generation in DSC starts to rise.

The content of the thermosetting agent may be 0.01 part by mass or more, or 1 part by mass or more with respect to 100 parts by mass of the thermosetting compound. In addition, the content may be 200 parts by mass or less, or 100 parts by mass or 75 parts by mass or less. If the content of the thermosetting agent is within the above range, there is a tendency that the solder paste is easily cured, and the remaining thermosetting agent that does not participate in curing after curing hardly remains, and the heat resistance of the cured product becomes high.

(Other ingredients) The solder paste may further contain an organic solvent, a thixotropy control agent, a coupling agent, a reactive diluent, etc. as needed.

＜Solder grains＞ The solder particles of this embodiment have a flat portion on a part of the surface. In this case, the surface other than the plane portion is preferably spherical. That is, the solder particles may have a flat portion and a spherical curved portion. When using such solder particles to obtain an anisotropic conductive material, excellent conduction reliability and insulation reliability can be achieved. The reason will be described below.

First, by connecting the flat portion of the solder particles to the electrode, a wide contact area can be ensured between the flat portion and the electrode. For example, in the case of connecting an electrode formed of a material that is easy to wet and expand with solder and an electrode formed with a material that is difficult to wet and expand with solder, it is preferable to adjust the plane portion of the solder particles to the electrode side of the latter Ground between the two electrodes.

In addition, when the contact area between the solder particles and the electrode is wide, the solder easily wets and expands. For example, as a method for wetting and spreading the solder particles arranged on the electrode (substrate) onto the electrode, there is a method of applying flux in advance on the solder particles themselves or on the electrode, by reflow (heating) The solder particles melt. At this time, regarding the thickness of the oxide film of the solder particles, the weak flux, etc., if the contact area of the solder particles and the electrode is narrow, it is difficult for the solder to wet and spread. On the other hand, if there is a flat portion on a part of the surface of the solder particles, the contact area between the electrode and the solder particles becomes wider, and there is a tendency for the wetting to spread easily. This is presumably because when the oxide film is removed, if the electrode comes into contact with the surface of the solder particles, the thinned oxide film will crack, and the melted solder or flux will flow, making it easy to remove the oxide film. In this way, if the contact area between the solder particles and the electrode is wide, the contact point between the electrode and the surface of the solder particles increases, so that the time for wetting expansion is advanced and wetting expansion is easy. In addition, since the solder particles are easy to wet and expand, the amount of solder flux can be reduced, and the occurrence of ion migration caused by flux residues can be suppressed.

Furthermore, the stability of the solder particles having a flat portion is good. Therefore, when the solder particles are arranged on the electrode so that the flat portion is in contact with the electrode, the position of the solder particles is less likely to shift due to its stable shape. That is, it is easy to suppress the decrease in the reliability of conduction between the opposing electrodes and the decrease in the insulation reliability between adjacent electrodes due to the solder particles rolling out between the electrodes before reflow.

FIG. 1 is a diagram schematically showing an example of solder particles 1 of the present embodiment. As shown in FIG. 1, the solder grain 1 has a shape in which a flat portion 11 of a diameter A is formed on a part of the surface of a ball having a diameter B. From the viewpoint of achieving excellent conduction reliability and insulation reliability, the ratio (A/B) of the diameter A of the planar portion to the diameter B of the solder grain 1 may exceed, for example, 0.01 and less than 1.0 (0.01<A/B <1.0), or 0.1 to 0.9, 0.1 to 0.5, 0.1 to 0.3, or 0.1 to 0.2. The diameter B of the solder particles and the diameter A of the planar portion can be observed with a scanning electron microscope or the like, for example. Specifically, an arbitrary particle is observed with a scanning electron microscope, and an image is taken. The diameter B of the solder particles and the diameter A of the planar portion were measured from the obtained image, and the A/B of the particles was obtained. This operation was performed on 300 solder particles and the average value was calculated as A/B of the solder particles.

Regarding the solder particles 1, the average particle diameter may be 1 μm to 30 μm, and the C.V. value is 20% or less. Such solder particles have both a small average particle size and a narrow particle size distribution, and can be preferably used as conductive particles suitable for anisotropic conductive materials with high conduction reliability and insulation reliability.

The average particle diameter of the solder particles is not particularly limited as long as it is within the above range, and is preferably 30 μm or less, more preferably 25 μm or less, and still more preferably 20 μm or less. In addition, the average particle diameter of the solder particles is preferably 1 μm or more, more preferably 2 μm or more, and still more preferably 4 μm or more.

The average particle diameter of the solder particles can be measured using various methods consistent with the size. For example, methods such as dynamic light scattering method, laser diffraction method, centrifugal sedimentation method, electrical detection zone method, resonance mass measurement method, and the like can be used. Furthermore, a method of measuring the particle size from an image obtained by an optical microscope, an electron microscope, or the like can be used. As a specific device, a flow-type particle image analysis device, a microtrac, a Coulter counter, etc. may be mentioned.

From the viewpoint of achieving more excellent conduction reliability and insulation reliability, the CV value of the solder particles is preferably 20% or less, more preferably 10% or less, further preferably 7% or less, and most preferably 5% or less . In addition, the lower limit of the C.V. value of the solder particles is not particularly limited. For example, the C.V. value of the solder particles may be 1% or more, or 2% or more.

The C.V. value of the solder particles can be calculated by multiplying the value obtained by dividing the standard deviation of the particle diameter measured by the method by the average particle diameter by 100.

In the case of using two pairs of parallel lines to make a quadrilateral circumscribed from the projection image of the solder particles, when the distance between the opposing sides is set to X and Y (where Y <X), the ratio of Y to X ( Y/X) can exceed 0.8 and less than 1.0 (0.8<Y/X<1.0), and can also be 0.81 to 0.99 or 0.81 to 0.95. Such solder particles can be called particles closer to true spheres. When the solder particles are accommodated in the concave portion 62 of the base 60 again, if the solder particles are close to a spherical shape, there is a tendency to be easily accommodated. In addition, when the solder particles are close to a true sphere, when electrically connecting between a plurality of electrodes facing each other through the solder particles, uneven contact between the solder particles and the electrodes is unlikely to occur, and there is a tendency for stable connection to be obtained. In addition, when producing a conductive film or paste in which solder particles are dispersed in a resin material, high dispersibility can be obtained, and there is a tendency that dispersion stability at the time of manufacturing can be obtained. Furthermore, when a film or paste in which solder particles are dispersed in a resin material is used for connection between electrodes, even if the solder particles rotate in the resin, if the solder particles are in the shape of a sphere, they are observed with a projection image The projected areas of the solder particles are close to each other. Therefore, there is a tendency that it is easy to obtain a stable electrical connection with less deviation when connecting the electrodes. From the viewpoint, the roundness of the solder particles (the radius ratio r/R of the two concentric circles of the solder particles (radius r of the minimum circumscribed circle and radius R of the maximum inscribed circle)) can be 0.85 or more , Can also be 0.90 or more.

FIG. 2 is a diagram showing the distances X and Y (where Y<X) between the opposing sides when a quadrilateral that is circumscribed from the projection image of the solder particles is formed by using two pairs of parallel lines. For example, a scanning electron microscope is used to observe arbitrary particles to obtain a projection image. Draw two pairs of parallel lines on the obtained projection image, one pair of parallel lines is arranged at the position where the distance of the parallel lines becomes the smallest, and the other pair of parallel lines is arranged at the position where the distance of the parallel lines becomes the maximum, and the Y of the particle is obtained /X. This operation was performed on 300 solder particles and the average value was calculated as Y/X of the solder particles.

The solder particles may include tin or tin alloy. As the tin alloy, for example, In-Sn alloy, In-Sn-Ag alloy, Sn-Au alloy, Sn-Bi alloy, Sn-Bi-Ag alloy, Sn-Ag-Cu alloy, Sn-Cu alloy, or the like can be used. Specific examples of these tin alloys include the following examples. ·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℃) ·Sn-Bi (Sn 43% by mass, Bi 57% by mass, melting point 138°C) ·Sn-Bi-Ag (Sn 42 mass%, Bi 57 mass%, Ag 1 mass%, melting point 139℃) ·Sn-Ag-Cu (Sn 96.5 mass%, Ag 3 mass%, Cu 0.5 mass%, melting point 217℃) ·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) The solder particles may include indium or indium alloy. As the indium alloy, for example, In-Bi alloy, In-Ag alloy, or the like can be used. As specific examples of these indium alloys, the following examples may be mentioned. ·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℃)

The tin alloy or indium alloy can be selected according to the purpose of the solder particles (temperature at the time of use) and the like. For example, when the solder particles are used for welding at a low temperature, the In-Sn alloy or the Sn-Bi alloy may be used. In this case, the welding may be performed at 150° C. or lower. When a material having a high melting point such as Sn-Ag-Cu alloy or Sn-Cu alloy is used, high reliability can be maintained even after being left at a high temperature.

The solder particles may also contain one or more kinds selected from Ag, Cu, Ni, Bi, Zn, Pd, Pb, Au, P, and B. Among these elements, Ag or Cu may be included from the following viewpoint. That is, when the solder particles contain Ag or Cu, the melting point of the solder particles can be reduced to about 220° C., and the bonding strength with the electrode is further improved, so it is easy to obtain better conduction reliability.

The Cu content of the solder particles is, for example, 0.05% by mass to 10% by mass, or 0.1% by mass to 5% by mass or 0.2% by mass to 3% by mass. If the Cu content is 0.05% by mass or more, it is easy to achieve better solder connection reliability. In addition, if the Cu content is 10% by mass or less, it is easy to form solder particles having a low melting point and excellent wettability, and as a result, the connection reliability of the joint portion by the solder particles tends to be good.

The Ag content of the solder particles is, for example, 0.05% by mass to 10% by mass, or 0.1% by mass to 5% by mass or 0.2% by mass to 3% by mass. If the Ag content is 0.05% by mass or more, it is easy to achieve better solder connection reliability. In addition, if the Ag content is 10% by mass or less, it is easy to form solder particles having a low melting point and excellent wettability. As a result, the connection reliability of the joint portion due to the solder particles tends to be good.

The use of the solder particles is not particularly limited, and for example, it can be preferably used as conductive particles for anisotropic conductive materials. In addition, it can also be preferably used for the purpose of electrically connecting electrodes to each other, such as a ball grid array connection method (BGA (ball grid array) connection) widely used in the mounting of semiconductor integrated circuits, or a microelectromechanical system (microelectro mechanical systems, MEMS) and other parts such as sealing or sealing tube, brazing, spacers for height or gap control. That is, the solder pellets can be used in general applications where solder was previously used.

<Manufacturing method of solder pellets> The manufacturing method of the solder pellet of this embodiment is not particularly limited, and an example of the manufacturing method will be described below. For example, the solder particles of this embodiment can be manufactured by a method of manufacturing solder particles, which includes: a preparation step of preparing a substrate having a plurality of recesses and solder particles; and a storage step of storing at least a portion of the solder particles in the substrate And the fusing step, fusing the solder particles contained in the recess to form solder particles inside the recess. According to this manufacturing method, it is possible to manufacture solder particles having a flat portion on a part of the surface.

Hereinafter, a method of manufacturing solder particles will be described with reference to FIGS. 3( a) to 6.

First, the solder particles and the base 60 for storing the solder particles are prepared. FIG. 3(a) is a plan view schematically showing an example of the base 60, and FIG. 3(b) is a cross-sectional view taken along the line IIIb-IIIb shown in FIG. 3(a). The base 60 shown in FIG. 3( a) has a plurality of recesses 62. The plurality of recesses 62 may be regularly arranged in a predetermined pattern.

The concave portion 62 of the base 60 is preferably formed in a tapered shape whose opening area expands from the bottom 62 a side of the concave portion 62 toward the surface 60 a side of the base 60. That is, as shown in FIGS. 3(a) and 3(b), the width of the bottom 62a of the recess 62 (the width a in FIGS. 3(a) and 3(b)) is preferably more than the surface 60a of the recess 62 The width of the opening (width b in FIGS. 3(a) and 3(b)) is narrow. Moreover, the size of the recess 62 (width a, width b, volume, taper angle, depth, etc.) may be set according to the size of the target solder particles.

In addition, the shape of the recess 62 may be other than the shapes shown in FIGS. 3( a) and 3 (b ). For example, the shape of the opening of the surface 60a of the recess 62 may be an ellipse, a triangle, a quadrangle, a polygon, etc. in addition to the circle shown in FIGS. 3(a) and 3(b).

In addition, the shape of the recess 62 in the cross section perpendicular to the surface 60a may be, for example, the shape shown in FIGS. 4(a) to 4(d). FIGS. 4( a) to 4 (d) are cross-sectional views schematically showing examples of the cross-sectional shape of the recessed portion included in the base. In any of the cross-sectional shapes shown in FIGS. 4(a) to 4(d), the bottom surface is flat. With this, a flat portion is formed in a part of the surface of the solder particles. In addition, in any of the cross-sectional shapes shown in FIGS. 4( a) to 4 (d ), the width (width b) of the opening of the surface 60 a of the recess 62 becomes the maximum width in the cross-sectional shape. With this, the solder particles formed in the recess 62 are easily taken out, and the workability is improved.

As the material constituting the base 60, for example, inorganic materials such as silicon, various ceramics, glass, stainless steel, and other metals, and organic materials such as various resins can be used. Among these, the base 60 preferably includes a material having heat resistance that does not deteriorate at the melting temperature of the solder particles. In addition, the concave portion 62 of the base 60 can be formed by a known method such as photolithography, imprinting, mechanical processing, electron beam processing, and radiation processing.

The solder particles prepared in the preparation step may be those containing particles having a particle size smaller than the width (width b) of the opening of the surface 60a of the recess 62, and preferably containing more particles having a particle size than the width b Smaller particles. For example, the solder particles preferably have a particle size distribution D10 particle size smaller than the width b, more preferably a particle size distribution D30 particle size smaller than the width b, and more preferably a particle size distribution D50 particle size wider than the width b In terms of being smaller.

The particle size distribution of the solder particles can be measured using various methods consistent with the size. For example, methods such as dynamic light scattering method, laser diffraction method, centrifugal sedimentation method, electrical detection zone method, resonance mass measurement method, and the like can be used. Furthermore, a method of measuring the particle size from an image obtained by an optical microscope, an electron microscope, or the like can be used. As specific devices, there may be mentioned a flow-type particle image analysis device, a Macchik, a Coulter counter, and the like.

The C.V. value of the solder particles prepared in the preparation step is not particularly limited, but the C.V. value is preferably high from the viewpoint of improving the fillability of the recess 62 by the combination of particles of large and small sizes. For example, the C.V. value of the solder particles may exceed 20%, preferably 25% or more, and more preferably 30% or more.

The C.V. value of the solder particles can be calculated by multiplying the value obtained by dividing the standard deviation of the particle diameter measured by the method by the average particle diameter (D50 particle diameter) by 100.

The solder particles may include tin or tin alloy. As the tin alloy, for example, In-Sn alloy, In-Sn-Ag alloy, Sn-Au alloy, Sn-Bi alloy, Sn-Bi-Ag alloy, Sn-Ag-Cu alloy, Sn-Cu alloy, or the like can be used. Specific examples of these tin alloys include the following examples. ·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℃) ·Sn-Bi (Sn 43% by mass, Bi 57% by mass, melting point 138°C) ·Sn-Bi-Ag (Sn 42 mass%, Bi 57 mass%, Ag 1 mass%, melting point 139℃) ·Sn-Ag-Cu (Sn 96.5 mass%, Ag 3 mass%, Cu 0.5 mass%, melting point 217℃) ·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) The solder particles may include indium or indium alloy. As the indium alloy, for example, In-Bi alloy, In-Ag alloy, or the like can be used. As specific examples of these indium alloys, the following examples may be mentioned. ·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℃)

The tin alloy or indium alloy can be selected according to the purpose of the solder particles (temperature at the time of use) and the like. For example, when it is desired to obtain solder particles for welding at a low temperature, an In-Sn alloy or a Sn-Bi alloy may be used, and in this case, solder particles that can be welded at 150° C. or less can be obtained. When a material having a high melting point such as Sn-Ag-Cu alloy or Sn-Cu alloy is used, solder particles capable of maintaining high reliability even after being left at a high temperature can be obtained.

The solder fine particles may contain one or more types selected from Ag, Cu, Ni, Bi, Zn, Pd, Pb, Au, P, and B. Among these elements, Ag or Cu may be included from the following viewpoint. That is, when the solder fine particles contain Ag or Cu, it is possible to obtain the effect of obtaining solder particles excellent in the bonding strength with the electrode, which can lower the melting point of the obtained solder particles to about 220°C, thereby obtaining good conduction reliability.

The Cu content of the solder fine particles is, for example, 0.05% by mass to 10% by mass, or 0.1% by mass to 5% by mass or 0.2% by mass to 3% by mass. If the Cu content is 0.05% by mass or more, it is easy to obtain solder particles that can achieve good solder connection reliability. In addition, if the Cu content is 10% by mass or less, solder particles having a low melting point and excellent wettability are easily obtained, and as a result, the connection reliability of the joint portion due to the solder particles tends to be good.

The Ag content of the solder fine particles is, for example, 0.05% by mass to 10% by mass, or 0.1% by mass to 5% by mass or 0.2% by mass to 3% by mass. If the Ag content is 0.05% by mass or more, it is easy to obtain solder particles that can achieve good solder connection reliability. In addition, if the Ag content is 10% by mass or less, it is easy to obtain solder particles having a low melting point and excellent wettability. As a result, the connection reliability of the joint portion due to the solder particles tends to be good.

In the storage step, the solder particles prepared in the preparation step are stored in each of the recesses 62 of the base 60. Regarding the storage step, it may be a step of storing all the solder particles prepared in the preparation step in the concave portion 62, or may be a part of the solder particles prepared in the preparation step (for example, the width b of the opening of the concave portion 62 in the solder particles) If it is smaller, it is stored in the recess 62.

FIG. 5 is a cross-sectional view schematically showing a state in which the solder particles 111 are accommodated in the recess 62 of the base 60. As shown in FIG. 5, a plurality of solder particles 111 are stored in each of the plurality of recesses 62.

The amount of the solder particles 111 stored in the recess 62 is preferably 20% or more, more preferably 30% or more, further preferably 50% or more, and most preferably 60% or more with respect to the volume of the recess 62, for example. This can suppress variations in the storage volume and easily obtain solder particles with a smaller particle size distribution.

The method of storing the solder particles in the recess 62 is not particularly limited. The storage method may be either dry or wet. For example, the solder particles prepared in the preparation step are arranged on the base 60, and the surface 60a of the base 60 is rubbed with a squeegee, whereby excess solder particles can be removed, and sufficient solder particles are accommodated in the recess 62. When the width b of the opening of the recess 62 is larger than the depth of the recess 62, solder particles may fly out of the opening of the recess 62. If a coating blade is used, the solder particles flying out of the opening of the recess 62 are removed. As a method of removing excess solder particles, a method of blowing compressed air, rubbing the surface 60a of the base 60 with a non-woven fabric or a fiber bundle, and the like can also be mentioned. These methods are weaker in physical force than coated squeegees, and therefore are preferable in terms of handling solder particles that are easily deformed. In addition, in these methods, solder particles flying out of the opening of the recess 62 may remain in the recess.

The fusing step is a step of fusing the solder particles 111 accommodated in the recess 62 to form the solder particles 1 inside the recess 62. FIG. 6 is a cross-sectional view schematically showing a state where the solder particles 1 are formed in the recess 62 of the base 60. The solder fine particles 111 accommodated in the recess 62 are integrated by melting and formed into a spherical shape by surface tension. At this time, in the contact portion of the recess 62 with the bottom 62a, molten solder follows the bottom 62a to form the flat portion 11. As a result, the formed solder particles 1 have a shape having a flat portion 11 on a part of the surface.

FIG. 1 is a view of the solder grain 1 viewed from the side opposite to the opening of the recess 62 in FIG. 6.

As a method of melting the solder fine particles 111 accommodated in the recess 62, a method of heating the solder fine particles 111 to the melting point of the solder or more can be mentioned. The solder fine particles 111 are affected by the oxide film: they do not melt even when heated at a temperature above the melting point, do not cause wetting and expansion, and cannot be integrated. Therefore, the solder fine particles 111 are exposed to a reducing environment to remove the surface oxide coating of the solder fine particles 111, and then heated to a temperature above the melting point of the solder fine particles 111, whereby the solder fine particles 111 can be melted, wetted, expanded, and integrated. In addition, the melting of the solder particles 111 is preferably performed in a reducing environment. By heating the solder particles 111 to the melting point of the solder particles 111 or more and setting it as a reducing environment, the oxide film on the surface of the solder particles 111 is reduced, and the solder particles 111 are easily and effectively melted, wet-spreaded, and integrated.

The method for setting the reduction environment is not particularly limited as long as it can obtain the above-mentioned effects, and for example, there are methods using hydrogen gas, hydrogen radicals, formic acid gas, and the like. For example, by using a hydrogen reduction furnace, a hydrogen radical reduction furnace, a formic acid reduction furnace, or these conveyor furnaces or continuous furnaces, the solder particles 111 can be melted in a reducing environment. These devices may include a heating device, a chamber filled with an inert gas (nitrogen, argon, etc.) in the furnace, a mechanism that sets the chamber to a vacuum, etc., thereby controlling the reducing gas becomes easier. In addition, if a vacuum is formed in the chamber, after melting and integration of the solder particles 111, voids can be removed by reduced pressure, and solder particles 1 having more excellent connection stability can be obtained.

The setting files of reduction, melting conditions, temperature, and furnace environment adjustment of the solder particles 111 can be appropriately set in consideration of the melting point, particle size, recess size, material of the substrate 60, etc. of the solder particles 111. For example, after inserting the substrate 60 filled with solder particles 111 into the furnace and evacuating the furnace, a reducing gas is introduced to fill the furnace with the reducing gas to remove the oxide film on the surface of the solder particles 111, and then the reducing gas is removed by vacuuming. After heating to the melting point of the solder particles 111 or more, the solder particles are melted and integrated, and the solder particles are formed in the recess 62. After filling with nitrogen, the temperature in the furnace is returned to room temperature to obtain the solder particles 1. In addition, for example, after inserting the substrate 60 filled with the solder particles 111 into the furnace and evacuating the furnace, a reducing gas is introduced to fill the furnace with the reducing gas, and the solder particles 111 are heated by the furnace heating heater to remove the solder particles 111 After the oxide film on the surface is removed by vacuum, the reducing gas is removed, and then heated to the melting point of the solder particles 111 or more, so that the solder particles are melted and integrated, and the solder particles are formed in the recess 62. After filling with nitrogen, the temperature in the furnace is restored To room temperature, the solder particles 1 can be obtained. By heating the solder particles in a reducing environment, it has the following advantages: the reducing power is increased, and the surface oxide film of the solder particles is easily removed.

Furthermore, for example, after inserting the substrate 60 filled with solder particles 111 into the furnace and evacuating the furnace, a reducing gas is introduced to fill the furnace with the reducing gas, and the substrate 60 is heated to above the melting point of the solder particles 111 by the furnace heating heater. , The surface oxide film of the solder particles 111 is removed by reduction, and the solder particles are melted and integrated at the same time to form solder particles in the recess 62, and the reducing gas is removed by vacuuming, thereby reducing the voids in the solder particles and filling After nitrogen gas, the temperature in the furnace is returned to room temperature, thereby obtaining solder particles 1. In this case, the adjustment of the rise and fall of the temperature in the furnace can be performed once, which has the advantage that it can be processed in a short time.

After the solder particles are formed in the concave portion 62, a step of setting the furnace inside again as a reducing environment to remove the surface oxide film that has not been completely removed can reduce solder particles remaining without fusion or oxidation remaining without fusion Residues such as part of the coating.

In the case of using a conveyor furnace of atmospheric pressure, the base 60 filled with the solder fine particles 111 in the concave portion can be placed on a conveyor for conveyance, and the solder particles 1 can be obtained by continuously passing through a plurality of areas. For example, the substrate 60 filled with the solder particles 111 in the concave portion is placed on a conveyor set at a constant speed, and then passed through an area filled with an inert gas such as nitrogen or argon whose temperature is lower than the melting point of the solder particles 111, and then passes through the low temperature In the area where the reducing gas such as formic acid gas at the melting point of the solder particles 111 exists, the surface oxide film of the solder particles 111 is removed, and then the area is filled with an inert gas such as nitrogen or argon whose temperature is higher than the melting point of the solder particles 111 to make the solder The fine particles 111 are melted and integrated, and then pass through a cooling area filled with an inert gas such as nitrogen or argon, whereby the solder particles 1 can be obtained. For example, a substrate 60 filled with solder particles 111 in a recessed portion is placed on a conveyor set at a constant speed, filled with an inert gas such as nitrogen or argon whose temperature is above the melting point of the solder particles 111, and then passed through Solder particles 111 are melted and integrated in the area where reducing gas such as formic acid gas above the melting point of the solder particles 111 is removed, and then melted and integrated. Then, the cooling area filled with inert gas such as nitrogen or argon can be used to obtain solder Grain 1. Since the conveying furnace can be processed under atmospheric pressure, the film-like material can also be processed continuously on a roll-to-roll basis. For example, a continuous roll product made in a substrate 60 in which recesses are filled with solder particles 111 is provided with a coiler at the entrance side of the conveyor furnace, and a coiler at the outlet side of the conveyor furnace, and the substrate is transported at a constant speed 60, passing through each area in the conveyor furnace, whereby the solder particles 111 filled in the recesses can be fused.

The formed solder particles 1 can be taken out from the concave portion 62 to be recovered and used for preparation of solder paste. 7 is an SEM image showing an example of the solder particles obtained in the above manner. In addition, the solder particles 1 can be transported, stored, or the like while being accommodated in the recess 62 of the base 60.

According to the manufacturing method of this embodiment, regardless of the material and shape of the solder particles, solder particles of uniform size can be formed. For example, indium-based solder can be deposited by plating, but it is difficult to precipitate in particles, and it is soft and difficult to handle. However, in the production method of the present embodiment, by using indium-based solder fine particles as a raw material, indium-based solder particles having a uniform particle diameter can be easily produced. In addition, the formed solder grains 1 can be handled while being accommodated in the recess 62 of the base body 60, and therefore can be transported and stored without deforming the solder grains. Furthermore, since the formed solder particles 1 are only in a state of being accommodated in the recess 62 of the base 60, they are easy to take out, and they can be recovered and surface-treated without deforming the solder particles.

In addition, the solder fine particles 111 may have a large deviation in particle size distribution, and the shape may be distorted. If it can be accommodated in the recess 62, it can be used as a raw material for the manufacturing method of this embodiment.

In addition, regarding the manufacturing method of the present embodiment, the base 60 can freely design the shape of the recess 62 using a lithography method, an imprint method, an electron beam processing method, a radiation processing method, a machining method, or the like. Since the size of the solder particles 1 depends on the amount of the solder particles 111 stored in the recess 62, in the manufacturing method of this embodiment, the size of the solder particles 1 can be freely designed by the design of the recess 62.

The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. [Example]

Hereinafter, the present invention will be further described in detail through examples, but the present invention is not limited to these examples.

<Production of solder pellets> [Example 1] (Step a1: Classification of solder particles) 100 g of Sn-Bi solder particles (manufactured by 5N Plus, melting point 139°C, Type 8) were immersed in distilled water for ultrasonic dispersion, and then allowed to stand and recover the solder particles suspended in the supernatant. This operation was repeated, and 10 g of solder particles were recovered. The average particle diameter of the obtained solder particles was 1.0 μm, and the C.V. value was 42%. (Step b1: placement on the substrate) Prepare a substrate (polyimide film, which has multiple recesses with an opening diameter of 1.2 μm, a bottom diameter of 1.0 μm ϕ, and a depth of 1.0 μm (the bottom diameter is 1.0 μm ϕ, which is located at the center of the opening diameter of 1.2 μm ϕ when the opening is viewed from the upper surface). 100 μm thick). The multiple recesses are regularly arranged at intervals of 1.0 μm. The solder fine particles (average particle diameter 1.0 μm, C.V. value 42%) obtained in step a were arranged in the concave portion of the substrate. Furthermore, by rubbing the surface of the base body on which the recesses are formed with the micro-adhesion roller, excess solder particles are removed, thereby obtaining a substrate in which solder particles are arranged only in the recesses. (Step c1: Formation of solder particles) In step b1, the substrate in which the solder particles are arranged in the concave portion is placed in a hydrogen reduction furnace, and after evacuation, hydrogen gas is introduced into the furnace to fill the furnace with hydrogen. After the furnace was kept at 280°C for 20 minutes, vacuum was drawn again, nitrogen was introduced and the atmospheric pressure was restored, and the temperature in the furnace was reduced to room temperature to form solder particles.

Furthermore, by tapping the substrate passing through step c1 from the back side of the recessed portion, the solder particles are recovered from the recessed portion. Observe the obtained solder particles by the following method. Place the obtained solder particles on the conductive tape fixed on the surface of the scanning electron microscope (SEM) observation stand, and tap the SEM observation stand on a 5 mm thick stainless steel plate to spread the solder particles uniformly on the conductive tape . Then, compressed nitrogen is blown onto the surface of the conductive tape to fix the solder particles on the conductive tape in a single layer. The observation result is shown in Fig. 7. 7 is an SEM image of solder particles obtained in Example 1. FIG. As shown in the figure, the obtained solder particles have a shape in which a flat portion is formed on a part of the surface of the ball. Furthermore, the solder particles obtained in other embodiments also have the same shape.

<Evaluation of solder particles> After attaching the conductive tape so as to face the concave portion of the substrate passing through the step c1 and peeling off, a sample for observation in which the plane portion of the solder particles and the surface of the conductive tape are arranged in parallel is obtained. After the surface of the observation sample on which the solder particles were arranged was subjected to Pt sputtering, SEM observation was performed. Observing 300 solder particles, the average diameter B (average particle diameter) of the solder particles, the average diameter A, C.V. value, roundness, A/B, and Y/X of the plane portion were calculated. The results are shown in Table 1. Roundness: the ratio r/R of the radius of the two concentric circles of the solder particles (the radius r of the smallest circumscribed circle and the radius R of the largest inscribed circle). A/B: The ratio of the diameter A of the flat surface to the diameter B of the solder particles. Y/X: When using two pairs of parallel lines to make a quadrilateral circumscribed from the projected image of the solder particles, Y is relative to Y when the distance between the opposing sides is X and Y (where Y<X) X ratio.

[Example 2 to Example 12] Except for changing the size of the concave portion as described in Table 1, solder pellets were produced in the same manner as in Example 1, and the solder pellets were evaluated.

<Production of solder paste> [Production Example 1] 16.0 parts by mass of YL980 (manufactured by Mitsubishi Chemical Co., Ltd., bisphenol A type epoxy resin), 0.8 parts by mass of 2P4MHZ-PW (manufactured by Shikoku Chemicals Co., Ltd., trade name of imidazole compounds), and 3.2 parts by mass of adipic acid of the flux activator were mixed, and the mixture was passed through three rolls three times to prepare an adhesive component.

Next, with respect to 20 parts by mass of the adhesive component, 80 parts by mass of Sn-Bi solder particles having a flat portion formed on a part of the surface of the ball prepared in Example 1 were added, and the obtained mixture was stirred and kneaded with a planetary mixer , Defoaming treatment is performed at 500 Pa or less for 10 minutes to obtain solder paste.

[Production Example 2 to Production Example 12] Except for using Sn-Bi solder particles having flat portions formed on part of the surface of the balls obtained in Examples 2 to 12, the solder paste was produced by the same method as in Production Example 1.

[Production Example 13] 16.7 parts by mass of YL980 (manufactured by Mitsubishi Chemical Corporation, bisphenol A type epoxy resin), 0.8 parts by mass of 2P4MHZ-PW (manufactured by Shikoku Chemicals Co., Ltd., trade name of imidazole compounds), and 2.5 parts by mass of adipic acid of the flux activator were mixed, and the mixture was passed through three rollers three times to prepare an adhesive component.

Next, with respect to 20 parts by mass of the adhesive component, 80 parts by mass of Sn-Bi solder particles having a flat portion formed on a part of the surface of the ball produced in Example 5 were added, and the obtained mixture was stirred and kneaded with a planetary mixer , Defoaming treatment is performed at 500 Pa or less for 10 minutes to obtain solder paste.

[Comparative Production Example 1] Instead of using Sn-Bi solder particles with a flat surface formed on a part of the surface of the ball, use SnBi solder particles without such a flat portion ("ST-3" manufactured by Mitsui Metals Co., Ltd.), and use and manufacture The solder paste was produced in the same manner as in Example 1. Furthermore, the average particle diameter of the SnBi solder particles was 4 μm, and the C.V. value was 31%.

[Comparative Production Example 2] Instead of using Sn-Bi solder grains with a planar portion formed on a part of the surface of the ball, use SnBi solder grains ("Type-4" manufactured by Mitsui Metals Co., Ltd.) that do not have such a planar portion, and use and manufacture otherwise The solder paste was produced in the same manner as in Example 1. Furthermore, the average particle diameter of the SnBi solder particles was 26 μm, and the C.V. value was 25%.

[Comparative Production Example 3] 15.4 parts by mass of YL980 (manufactured by Mitsubishi Chemical Corporation, bisphenol A type epoxy resin), 0.8 parts by mass of 2P4MHZ-PW (manufactured by Shikoku Chemicals Co., Ltd., product name of imidazole compound), and 3.9 parts by mass of adipic acid of the flux activator were mixed, and the mixture was passed through three rollers three times to prepare an adhesive component.

Next, with respect to 20 parts by mass of the adhesive component, 80 parts by mass of SnBi solder particles ("ST-3" manufactured by Mitsui Metals Co., Ltd.) without plane parts were added as described above, and the planetary mixer was used to obtain The mixture was stirred and kneaded, and defoamed at 500 Pa or less for 10 minutes to obtain solder paste.

[Comparative Production Example 4] 16.7 parts by mass of YL980 (manufactured by Mitsubishi Chemical Corporation, bisphenol A type epoxy resin), 0.8 parts by mass of 2P4MHZ-PW (manufactured by Shikoku Chemicals Co., Ltd., trade name of imidazole compounds), and 2.5 parts by mass of adipic acid of the flux activator were mixed, and the mixture was passed through three rollers three times to prepare an adhesive component.

Next, with respect to 20 parts by mass of the adhesive component, 80 parts by mass of SnBi solder particles ("ST-3" manufactured by Mitsui Metals Co., Ltd.) without plane parts were added as described above, and the planetary mixer was used to obtain The mixture was stirred and kneaded, and defoamed at 500 Pa or less for 10 minutes to obtain solder paste.

The characteristics of the solder pastes of the production examples and the comparative production examples were measured by the following methods. The results are summarized and shown in Table 2.

(1) Evaluation of subsequent strength A silver plated copper plate (10 mm×15 mm, thickness: 0.20 mm) was coated with 0.5 mg of solder paste, and a rectangular flat plate-shaped tinned copper wafer (2 mm×2 mm, thickness 0.25) was deposited thereon. mm), apply a heat history of 150°C for 10 minutes using a hot plate to obtain a test piece. For this test piece, a bonding tester (manufactured by DAGE Corporation, 2400) was used, and the shear strength at 25° C. was measured under the conditions of a shear rate of 500 μm/sec and a gap of 100 μm.

(2) Temperature cycle test A thin rectangular FR4 substrate with a rectangular flat plate shape of 100 mm×50 mm×0.5 mm with two adjacent copper foil pads (0.2 mm×0.4 mm) and a distance between the copper foil pads of 100 μm is prepared. Next, a metal mask (thickness 100 μm, opening size 0.2 mm×0.3 mm) was used to print the solder paste onto the copper foil pad, and a small chip resistor (0.2 mm×0.4 mm) with a distance of 100 μm between electrodes was mounted. A test substrate for evaluation of TCT resistance was obtained by applying the same thermal history as in (1) above to this component mounting substrate. After confirming the initial resistance of the test substrate using a simple test machine, it was put into a thermal shock test machine (1 cycle: held at -55°C for 30 minutes and heated for 5 minutes to 125°C, held at 125°C for 30 minutes and spent Cool down to -55°C for 5 minutes) to measure the connection resistance. The evaluation of TCT resistance is based on the number of cycles showing a resistance change rate within ±10% relative to the initial resistance.

(3) Insulation resistance test After measuring the insulation resistance value of the component mounting board produced by the same method as (2) above, a migration test (temperature 60°C, humidity 90%, 50 V applied) was performed. The evaluation of the migration resistance is based on the test time in which the leakage between the electrodes occurs and the insulation resistance value shows 10 ⁹ Ω or less.

All of Production Examples 1 to 13 showed good adhesion strength, and both the temperature cycle test and the insulation resistance test showed good results.

In Comparative Production Example 1 and Comparative Production Example 2, it was confirmed that the subsequent strength was significantly reduced and the temperature cycle resistance was reduced.

In Comparative Production Example 3, although the improvement in connectivity due to the increase in the flux component was found, it was confirmed that the insulation property due to migration decreased.

In Comparative Production Example 4, although the improvement in insulation reliability due to the reduction in the flux component was found, it was confirmed that the connection strength decreased and the temperature cycle resistance decreased due to the decrease in solder wettability.

Although the solder particles having an average particle diameter of 4 μm were used in Production Example 5 and Comparative Production Example 1, differences were found in connection strength and connection reliability affected by the wettability of the solder particles. The wettability of Production Example 5 and Comparative Production Example 1 were evaluated.

Use a metal mask for printing (opening: 5 mm×5 mm, thickness: 0.1 mm) to print a specified amount of solder paste on the rolled copper foil (10 mm×15 mm, thickness: 0.04 mm) and apply it using a hot plate A heat history of 150°C for 3 minutes was used to evaluate the wettability and spreadability. The evaluation results of wettability and expansion are shown in FIGS. 8(a) and 8(b).

FIG. 8( a) is a diagram showing the wetting spreadability of Production Example 5. FIG. It can be confirmed that the shape after printing is maintained as a square, and it quickly wets and spreads to the copper foil.

FIG. 8( b) is a diagram showing the wet spreadability of Comparative Production Example 1. FIG. It was confirmed that the wettability and spreadability to the copper foil was poor, and the wettability and spread were performed sparsely.

[Table 1]

[Table 2]

1‧‧‧ solder particles 11‧‧‧ Plane Department 60‧‧‧Matrix 60a‧‧‧Surface 62‧‧‧recess 62a‧‧‧Bottom 111‧‧‧ solder particles A‧‧‧Diameter a‧‧‧Width B‧‧‧Diameter b‧‧‧Width

FIG. 1 is a diagram schematically showing an example of solder particles. FIG. 2 is a diagram showing the distances X and Y (where Y≦X) between the opposing sides when a quadrilateral that is circumscribed from the projection image of the solder particles is formed by using two pairs of parallel lines. FIG. 3( a) is a plan view schematically showing an example of the base, and FIG. 3( b) is a cross-sectional view taken along the line IIIb-IIIb shown in FIG. 3( a ). 4( a) to 4 (d) are cross-sectional views schematically showing examples of the cross-sectional shape of the concave portion of the base. 5 is a cross-sectional view schematically showing a state in which solder fine particles are accommodated in a concave portion of a base. FIG. 6 is a cross-sectional view schematically showing a state where solder particles are formed in the concave portion of the base. 7 is an SEM image showing an example of solder particles. 8(a) and 8(b) are diagrams showing the evaluation results of wettability and spreadability.

1‧‧‧ solder particles

11‧‧‧ Plane Department

A‧‧‧Diameter

B‧‧‧Diameter

Claims (6)

A solder paste, containing solder particles and flux, The solder particles have a flat portion on a part of the surface. The solder paste as described in item 1 of the patent application, wherein the average particle diameter of the solder particles is 1 μm to 30 μm, and the coefficient of variation value is 20% or less. The solder paste according to item 1 or item 2 of the patent application range, wherein the ratio (A/B) of the diameter A of the planar portion to the diameter B of the solder particles satisfies the following formula, 0.01<A/B<1.0. For the solder paste as described in any one of the first to third patent applications, when two quadrilaterals are used to form a quadrilateral circumscribed from the projected image of the solder particles, the opposing sides When the distance is set to X and Y (where Y <X), X and Y satisfy the following formula, 0.8<Y/X<1.0. The solder paste according to any one of claims 1 to 4, wherein the solder particles include at least one selected from the group consisting of tin, tin alloy, indium, and indium alloy. The solder paste as described in item 5 of the patent application range, wherein the solder particles comprise a material selected from the group consisting of In-Sn alloy, In-Sn-Ag alloy, In-Bi alloy, Sn-Au alloy, Sn-Bi alloy, Sn- At least one tin alloy in the group consisting of Bi-Ag alloy, Sn-Ag-Cu alloy, and Sn-Cu alloy.

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