Solder material, solder paste, foam solder, and solder joint

Abstract

The purpose of the present invention is to provide a solder material capable of suppressing non-wetting by improving solder wetting performance on a core material during primary mounting.　This solder material comprises a conductive core material and a solder layer present around the core material, and satisfies the following formula (1).　Formula (1): Ts ≥ −0.25Dc + 105 (where Dc is the diameter of the core material (μm), and Ts is the thickness of the solder layer present on both sides of the core material (μm)).

Description

Solder materials, solder pastes, foam solders, and solder joints

[0007] ,

[0001] The present invention relates to solder materials, solder pastes containing such solder materials, foam solders, and solder joints.

[0002] In recent years, with the development of small information devices, the electronic components mounted thereon are rapidly miniaturizing. To meet the requirements of miniaturization, such as narrowing of connection terminals and reduction of mounting areas, ball grid arrays (hereinafter referred to as "BGAs") with electrodes installed on the back surface are applied.

[0003] Examples of electronic components to which BGAs are applied include semiconductor packages. In a semiconductor package, a semiconductor chip having electrodes is encapsulated with resin. Solder bumps are formed on the electrodes of the semiconductor chip. These solder bumps are formed by joining solder balls to the electrodes of the semiconductor chip. A semiconductor package to which a BGA is applied is placed on a printed circuit board so that each solder bump contacts a conductive land on the printed circuit board, and the solder bump melted by heating and the land are joined to mount the semiconductor package on the printed circuit board.

[0004] Solder bumps that do not cause defects such as the solder balls being crushed by their own weight or deformed during solder melting have been proposed. To prevent such defects, specifically, it has been proposed to use balls molded with metal or resin as nuclei and use core materials coated with solder on these nuclei as solder bumps.

[0005] In Patent Document 1, a Cu core ball using a Cu ball as a nucleus and plated with a metal containing Sn is disclosed.

[0006] Patent No. 6572998

[0007] When joining Cu core balls to electrodes, it is assumed that the core portion will remain covered with a solder layer. However, areas where the solder layer is absent from the surface of the core portion may occur. If a solder layer is absent from the surface of the core portion when attempting to join substrates to substrates, a CPU to a substrate, or a component to a substrate, a problem called "non-wetting" occurs. Non-wetting is a bonding defect that occurs when the surface of the core material is exposed at the joint when secondary mounting is performed with insufficient solder on the surface of the core portion after primary mounting. For example, if a barrier layer is provided on the core material, an intermetallic compound may be formed by the reaction between the barrier layer (such as a Ni layer) and the solder layer. This intermetallic compound repels the solder, causing non-wetting. When joining laminated substrates using Cu core balls, solder paste may be applied to the electrodes on the substrate side where the Cu core balls are not joined. However, even in such cases, if insufficient solder adheres to the surface of the Cu core balls during primary mounting, and secondary mounting is performed with insufficient solder, non-wetting will occur. Such non-wetting can occur, as described above, for example, when an intermetallic compound formed on the surface of the barrier layer repels the solder paste, degrading the solder's wetting performance towards the core material. In view of these circumstances, the present invention aims to provide a solder material that can suppress non-wetting by improving the solder's wetting performance towards the core material during primary mounting.

[0008] The inventors of the present invention conducted intensive research to solve the above problems and found that the above problems can be solved by satisfying the conditions of formula (1) described later, and thus completed the present invention. Specific embodiments of the present invention are as follows.

[0009] [1] A solder material comprising a conductive core material and a solder layer present around the core material, wherein the solder material satisfies the following formula (1): Ts ≥ -0.25Dc + 105 (1) (Dc: diameter of the core material (μm), Ts: thickness of the solder layer present on both sides of the core material (μm)). [2] The solder material according to [1], wherein Dc is 75 to 425 μm. [3] The solder material according to [1] or [2], wherein Ts is 20 to 425 μm. [4] The solder material according to any one of [1] to [3], wherein the solder layer comprises at least one selected from the group consisting of Sn, Ag, Cu, In, Ni, Bi, Sb, Zn, Ti, Ce, P, Ge, Ga, As, Fe, Co, Pd, Pb, and alloys thereof. [5] A solder material according to any one of [1] to [4], wherein the core material comprises at least one selected from the group consisting of Cu, Ni, Au, Al, Mo, Mg, Zn, Co, and alloys thereof. [6] A solder material according to any one of [1] to [5], wherein the core material is a spherical core ball. [7] A solder material according to any one of [1] to [5], wherein the core material is a columnar core column. [8] A solder material according to any one of [1] to [7], further comprising a barrier layer comprising at least one selected from the group consisting of Ni and Co between the core material and the solder layer. [9] A solder paste comprising the solder material according to any one of [1] to [8].

[10] A foamed solder comprising the solder material according to any one of [1] to [8].

[11] A solder joint comprising the solder material according to any one of [1] to [8].

[0010] The solder material of the present invention can suppress non-wetting by improving the solder wetting performance on the core material during primary mounting.

[0011] This is a cross-sectional view showing the schematic structure of the core ball of this embodiment. This is a graph showing the relationship between the diameter Dc (μm) of the core material and the thickness Ts (μm) of the solder layers on both sides of the core material in the solder materials of the examples and comparative examples. This is a cross-sectional view showing the schematic structure of the Cu core column of this embodiment. This is a configuration diagram showing an example of a solder bump formed with core balls. This is an appearance photograph of the sample taken from above the solder bump to evaluate the solder wetting performance of the core material. This is a photograph of the cross-section of a sample with the surface of the core material exposed during primary mounting. This is a photograph of the cross-section after secondary mounting on a printed circuit board (PCB) using a sample with the surface of the core material exposed during primary mounting.

[0012] The following describes the solder material of the present invention, as well as solder paste, foam solder, and solder joints containing the solder material. In this specification, "solder wetting performance on the core material" means that when the solder layer of the solder material containing the core material is melted during primary mounting, the molten solder does not concentrate on the underside of the core material, but spreads to the sides, top, etc. of the core material. The higher the solder wetting performance on the core material, the easier it is for the surface of the core material to be covered with solder during primary mounting. In this specification, "non-wetting" means a bonding defect in which the surface of the core material is exposed at the joint when secondary mounting is performed with insufficient solder adhering to the surface of the core material after primary mounting. In this specification, when a numerical range is expressed using "X to Y", the range includes both ends of the range.

[0013] 1. Solder Material The solder material of the present invention comprises a conductive core material and a solder layer surrounding the core material, and satisfies the following formula (1): Ts ≥ -0.25Dc + 105 (1) (Dc: diameter of the core material (μm), Ts: thickness of the solder layer on both sides of the core material (μm)). The solder material of the present invention can suppress non-wetting.

[0014] Furthermore, when an electric current flows through a material, a phenomenon called electromigration (EM) occurs, in which atoms receive the kinetic energy of the electron flow and are pushed towards the positive electrode (anode). When EM occurs, the mechanical and electrical reliability of the conductive part decreases due to the generation of vacancies and segregation of components. In parallel, due to the miniaturization of semiconductor package structures in recent years, or the need to handle larger currents, the current density flowing through solder joints is increasing, and the risk of EM generation from a structural and application perspective is rising. The solder material of this embodiment can, in some cases, suppress not only non-wetting but also the occurrence of electromigration.

[0015] Figure 1 is a cross-sectional view showing the schematic structure of the core ball of this embodiment. The core ball 1A of this embodiment is composed of a spherical core 2A and a solder layer 3A covering the core 2A. From the viewpoint of controlling the standoff height, the core 2A preferably has a sphericity of 0.95 or higher. More preferably, the sphericity is 0.990 or higher. In this specification, sphericity represents the deviation from a perfect sphere. Sphericity can be determined by various methods, such as the least squares center method (LSC method), the smallest area center method (MZC method), the largest inscribed center method (MIC method), and the smallest circumscribed center method (MCC method). More specifically, sphericity is the arithmetic mean calculated when the diameter of each of the 500 cores 2A is divided by the major axis, and the closer the value is to the upper limit of 1.00, the closer it is to a perfect sphere. The length of the major axis and the length of the diameter can be measured using the Mitutoyo UltraQuickVision, ULTRA QV350-PRO measuring device. A solder layer 3A is formed on the surface of the core ball 1A by solder plating. A barrier layer 4 may be provided between the core ball 1A and the solder layer 3A. The barrier layer 4 prevents the Cu constituting the core ball 2A from diffusing into the solder layer 3A.

[0016] (Core material) The core material is electrically conductive and functions as a conductive pathway material. Here, the core material may contain or consist of a conductive metal as an electrical pathway. Such metals are not particularly limited, but elements of metals selected from the group consisting of Cu, Ni, Ag, Pb, Al, Sn, Fe, Zn, In, Sb, Co, Au, Pt, Cr, La, Mo, Nb, Pd, Ti, Zr, Mg, Rh, Ir, W, and Ru, alloys of two or more of these, metal oxides of these, or mixed oxides of these metals can be used. As a metal capable of exhibiting drop resistance reliability, elements of metals selected from the group consisting of Cu, Ni, Pb, Al, Sn, Fe, Zn, In, Sb, Co, Au, Pt, Cr, La, Mo, Nb, Pd, Ti, Zr, Mg, Rh, Ir, W, and Ru, alloys of two or more of these, metal oxides thereof, or mixed oxides thereof may be used. In particular, the core material may be composed of elemental Cu, or an alloy composition with Cu as the main component. When the core material is composed of a Cu alloy, the Cu content can be 50% by mass or more. The core material may also be a spherical core ball or a columnar core column. From the viewpoint of conductivity, the core material is preferably a spherical Cu core ball. In addition, as one of the practical core materials other than Cu cores, a core ball made of Sn-based solder may be selected. Specifically, a Pb-free solder composition centered around Sn-3.0Ag-0.5Cu (each value is in mass%) is used as the core ball composition for Sn-based solder, which offers excellent strength and processability.

[0017] The core material is not particularly limited, but can have a single composition, a shell structure, a fibrous structure, or a porous structure. The core material only needs to have a structure that contributes to conductivity; the remaining non-conductive portion can be made of a low-conductivity material. For example, metal-plated plastic is included in the core material.

[0018] Dc (diameter of the core material (μm)) is not particularly limited, but is preferably 75 to 425 μm, more preferably 100 to 400 μm, and most preferably 200 to 380 μm. The above Dc does not have any particular value, but can be 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, 210 μm, 220 μm, 230 μm, 240 μm, 250 μm, 260 μm, 270 μm, 280 μm, 290 μm, 300 μm, 310 μm, 320 μm, 330 μm, 340 μm, 350 μm, 360 μm, 370 μm, 380 μm, 390 μm, 400 μm, 410 μm, or 420 μm, and may be within the range of any two of these values.

[0019] (Solder layer) The composition of the solder layer is not particularly limited and may include or consist of Sn-Ag-Cu alloys, Sn-Ag-Cu-Bi alloys, Sn-Cu-Bi alloys, Sn-Ag alloys, Sn-Cu alloys, Sn-In alloys, Sn-Pb alloys, Sn-Bi alloys, Sn-Bi-Ag alloys, Sn-Cu-Bi-Ni alloys, or combinations of two or more of these.

[0020] The solder layer may contain Cu. The Cu content is preferably 0.1 to 3.0 mass%, more preferably 0.3 to 1.5 mass%, and most preferably 0.5 to 1 mass%. When the Cu content is within the above numerical range, strength and microstructure can be improved, and the occurrence of electrode erosion and the growth of IMC (intermetallic compounds) at the bonding interface can be suppressed.

[0021] The solder layer may contain Bi. The Bi content may be 0.1 to 60% by mass, preferably 0.5 to 5.0% by mass, more preferably over 1.0% by mass and 5.0% by mass or less, and most preferably 1.5 to 3.0% by mass. When the Bi content is within the above numerical range, the melting point of the solder layer can be lowered.

[0022] The solder layer may or may not contain Ag. In this specification, "not containing" a certain component means that the component is not intentionally added, and may also include the component being included as an impurity. The Ag content is preferably 0 to 5% by mass, more preferably 0.1 to 4.5% by mass, and most preferably more than 1.5% by mass and 4.5% by mass or less. When the Ag content is within the above numerical range, resistance to temperature cycle testing (TCT), hardness, strength, microstructure, and EM resistance can be improved.

[0023] The solder layer may or may not contain Ni. The Ni content is preferably 0 to 0.1% by mass, and more preferably 0.02 to 0.08% by mass. When the Ni content is within the above numerical range, strength and microstructure fineness can be improved, and the occurrence of electrode erosion and the growth of IMC (intermetallic compounds) at the bonding interface can be suppressed.

[0024] The solder layer may further contain Sb, Zn, Ti, Ce, P, Ge, Ga, As, Fe, Co, Pd, Pb, In, or combinations of two or more of these. Adding Sb can improve resistance to temperature cycling tests (TCT), hardness, strength, microstructure fineness, and electromagnetic interference (EM) resistance. Adding Zn, Ti, Ce, and / or In can improve strength and microstructure fineness, and suppress electrode erosion and the growth of IMC (intermetallic compounds) at the joint interface. Adding P, Ge, Ga, and / or As can modify the surface and suppress oxidation. Adding Fe and / or Co can modify the microstructure and compound state. Specifically, Fe and / or Co refine the solidification structure of the alloy by forming compounds with Sn in the solder, and also refine the interfacial compounds by solid-solubilizing them. These refinements are useful in improving reliability and electrical properties. Adding Pd stabilizes the interaction between the plating (the barrier layer of the core material) and the solder layer, making it easier to form the solder layer. Adding Pb further reduces non-wetting.

[0025] The solder layer may contain 0 to 10 mass% of Sb. The solder layer may also contain Zn, Ti, Ce, P, Ge, Ga, As, Fe, Co, Pd, In, or Pb in a content of 0 to 0.1 mass% each. The content of each of these elements can be applied in combination of two or more types. By keeping the content of each of these elements (Sb, Zn, Ti, Ce, P, Ge, Ga, As, Fe, Co, Pd, Pb, In) within the above numerical range, it is possible to achieve miniaturization of IMC, improvement of TCT resistance, reduction of melting point, improvement of ductility, improvement of wettability, improvement of conductivity, etc.

[0026] The solder layer may contain Sn. The lower limit of the Sn content is not particularly limited, but is preferably 30% by mass or more, more preferably 35% by mass or more, even more preferably 40% by mass or more, and most preferably 42% by mass or more. The upper limit of the Sn content is not particularly limited, but is preferably 97.65% by mass or less, more preferably 97% by mass or less, even more preferably 80% by mass or less, even more preferably 75% by mass or less, particularly preferably 70% by mass or less, and most preferably 65% ​​by mass or less. The above numerical ranges for the lower and upper limits of the Sn content can be arbitrarily combined. The remainder of the solder layer may also be Sn.

[0027] The solder layer may contain or consist of the above-mentioned elements (at least one selected from the group consisting of Cu, Bi, Ag, Ni, Sb, Zn, Ti, Ce, P, Ge, Ga, As, Fe, Co, Pd, In, and Pb), unavoidable impurities, and the remainder being Sn. Even if unavoidable impurities are present, this does not affect the aforementioned effects.

[0028] In this specification, the solder layers present on both sides of the core material refer to the solder layers present on a straight line drawn through the center or centroid of the core material and through both sides (both surfaces) of the solder material (including the core material and the solder layers). Ts (thickness of the solder layers present on both sides of the core material (μm)) is not particularly limited, but is preferably 20 to 425 μm, more preferably 150 to 400 μm, and most preferably 96 to 300 μm. The above Ts does not particularly have any specific values, but 30 μm, 32 μm, 40 μm, 42 μm, 46 μm, 50 μm, 56 μm, 60 μm, 70 μm, 80 μm, 86 μm, 90 μm, 96 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 146 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 196 μm, 200 μm, 210 μm, 220 μm, 23 It can be 0 μm, 240 μm, 246 μm, 250 μm, 260 μm, 270 μm, 280 μm, 290 μm, 296 μm, 300 μm, 310 μm, 320 μm, 330 μm, 340 μm, 350 μm, 360 μm, 370 μm, 376 μm, 380 μm, 390 μm, 400 μm, 410 μm, or 420 μm, and may be within the range of any two of these values.

[0029] The thickness of the solder layer present on one side of the core material is not particularly limited, but is preferably 10 to 200 μm, more preferably 25 to 190 μm, and most preferably 48 to 150 μm. The thickness of the solder layer present on one side is not particularly limited, but can be 10 μm, 15 μm, 16 μm, 20 μm, 21 μm, 23 μm, 25 μm, 28 μm, 30 μm, 33 μm, 43 μm, 48 μm, 50 μm, 73 μm, 98 μm, 100 μm, 123 μm, 148 μm, 150 μm, 188 μm, 190 μm, or 200 μm, and may be within the range of any two of these values. The thickness of the solder layer present on one side of the core material can also be calculated by Ts × 1 / 2.

[0030] (Equation (1)) Figure 2 is a graph showing the relationship between the diameter of the core material (Dc (μm)) and the thickness of the solder layers on both sides of the core material (Ts (μm)) in the solder materials of the examples and comparative examples described later. In Figure 2, linear (1) is a straight line Ts = -0.25Dc + 105, which corresponds to the above-mentioned equation (1). In Figure 2, non-wetting is suppressed in the range that satisfies equation (1), while non-wetting is not sufficiently suppressed in the range that does not satisfy equation (1).

[0031] The solder material of this embodiment may satisfy the formula: Ts ≤ Dc. The solder material of this embodiment may satisfy either or both of the formulas: Ts ≤ 1.3Dc - 25 and Ts ≥ 1.3Dc - 155. The solder material of this embodiment does not have to include the range where Dc is 240 to 260 μm and Ts is 40 to 110 μm. Also, the solder material of this embodiment does not have to include the range where Dc is 290 to 310 μm and Ts is 190 to 210 μm.

[0032] (Barrier layer) The solder material is not particularly limited, but it may further include a barrier layer between the core material and the solder layer, which includes at least one selected from the group consisting of Ni and Co. The presence of a barrier layer in the solder material allows for control of the reaction amount between the outer solder (solder present on the outer periphery of the core material) and the core material. The barrier layer may be formed on the surface of the core material.

[0033] The thickness of the barrier layer on one side of the core material is not particularly limited, but is preferably 1 to 20 μm, more preferably 1.5 to 18 μm, and most preferably 2 to 16 μm. If the thickness of the barrier layer (on one side) is less than 1 μm, it becomes difficult to control the amount of reaction between the outer solder and the core material. The thickness of the barrier layers on both sides of the core material is not particularly limited, but is preferably 2 to 40 μm, more preferably 3 to 36 μm, and most preferably 4 to 32 μm. If the thickness of the barrier layers (on both sides) is less than 2 μm, it becomes difficult to control the amount of reaction between the outer solder and the core material.

[0034] The diameter of the solder material can be calculated by summing the diameter of the core material, the thickness of the solder layers on both sides of the core material, and the thickness of any barrier layer on both sides of the core material. The diameter of the solder material is not particularly limited, but is preferably 150 to 900 μm, more preferably 200 to 800 μm, and most preferably 300 to 600 μm.

[0035] The ratio of the thickness of the solder layers on both sides of the core material to the diameter (Dc (μm)) of the core material (thickness of the solder layers on both sides of the core material / diameter of the core material) is not particularly limited, but is preferably 0.05 to 1.0, more preferably 0.10 to 0.98, and most preferably 0.25 to 0.98. When the ratio of the thickness of the solder layers on both sides of the core material to the diameter of the core material is within the above numerical range, it becomes easier to control the standoff height.

[0036] The volume of the core material can be calculated, for example, by assuming that the core material is spherical. The volume of the solder layer can be calculated, for example, by assuming that the solder layer covers the surface of the core material with a uniform thickness and that the solder material (including the core material and solder layer) is spherical. The ratio of the volume of the solder layer to the volume of the core material (volume of the solder layer / volume of the core material) is not particularly limited, but is preferably 0.2 to 9, more preferably 0.4 to 8.0, and most preferably 0.5 to 7.0. When the ratio of the volume of the solder layer to the volume of the core material is within the numerical range, it is easier to ensure bonding strength and exhibit sufficient conductivity.

[0037] Figure 3 is a cross-sectional view showing a schematic structure of the Cu nucleus column of this embodiment. In the example of Figure 1 described above, a case in which spherical nucleus balls 1A were used as the solder material was explained, but it is not limited to this. For example, a cylindrical nucleus column (Cu nucleus column) 1B can also be used as the solder material. Note that the configuration and materials of the Cu nucleus column 1B are the same as those of the Cu nucleus balls 1A described above, so only the differences will be explained below. The Cu nucleus column 1B of this embodiment comprises a column (Cu column) 2B which is an example of a nucleus having a predetermined size to secure a gap between the semiconductor package and the printed circuit board, and a solder layer 3B which is an example of a coating layer that covers the Cu column 2B. Note that in this example, the Cu column 2B is configured in a cylindrical shape, but it is not limited to this, and may be a rectangular prism, for example. The Cu column 2B preferably has a wire diameter (diameter) D2 of 20 to 1000 μm and a length L2 of 20 to 10000 μm. The thickness of the solder layer 3B is not particularly limited, but for example, 100 μm (on one side) or less is sufficient. Generally, 20 to 50 μm is acceptable. The Cu nucleus column 1B preferably has a wire diameter (diameter) D1 of 22 to 2000 μm and a length L1 of 22 to 20000 μm. In this embodiment, a barrier layer may be provided between the Cu column 2B and the solder layer 3B. The configuration (type, thickness, etc.) of the barrier layer can be the one described in the above section (barrier layer).

[0038] Figure 4 is a diagram showing an example of a solder bump formed with a core ball. In the solder bump 5A, the electrode 60A of the substrate 6A and the electrode 70A of the semiconductor package 7A are joined together with solder alloy 30A. In the solder bump 5A using the core ball 1A shown in Figure 1, even if the weight of the semiconductor package 7A, which is joined to the substrate 6A with solder alloy 30A, is added to the solder bump 5A, the core 2A, which does not melt at the melting point of the solder alloy 30A, can support the semiconductor package 7A. Therefore, the collapse of the solder bump 5A due to the weight of the semiconductor package 7A is suppressed.

[0039] Next, an example of a solder material manufacturing method will be described. A copper (Cu) metal material is placed on a heat-resistant plate such as ceramic (hereinafter referred to as the "heat-resistant plate") and heated together in a furnace. The heat-resistant plate is provided with numerous circular grooves with hemispherical bottoms. The diameter and depth of the grooves are appropriately set according to the particle size of the Cu balls. In addition, chip-shaped Cu material obtained by cutting Cu fine wires is placed one by one into the grooves of the heat-resistant plate. The heat-resistant plate with the Cu material placed in the grooves is heated to 1100 to 1300°C in a furnace filled with ammonia decomposition gas and heat-treated for 30 to 60 minutes. At this time, when the furnace temperature exceeds the melting point of Cu, the Cu material melts and becomes spherical. After that, the furnace is cooled, and the Cu balls (core material) are rapidly cooled and formed in the grooves of the heat-resistant plate. Another method involves dropping molten Cu from an orifice at the bottom of a crucible, rapidly cooling the droplet to room temperature (e.g., 25°C) to form Cu balls (atomization method), or heating a Cu cut metal to over 1000°C with thermal plasma to form the balls. As the raw material for the Cu balls, nugget material, wire material, plate material, etc., can be used. The purity of the Cu material should be between 4N5 and 6N or less, from the viewpoint of not lowering the purity of the Cu balls too much. As a method for forming a barrier layer on the Cu balls, known methods such as electroplating can be used. As a method for forming a solder layer on the Cu balls, known methods such as hot-dip plating, electroless plating, and electroplating can be used.

[0040] 2. Solder Paste, Formed Solder, and Solder Joints Examples of applications of the solder material of this embodiment will be described. The solder material can be used in a solder paste in which solder powder, core balls 1A, and flux are mixed together. Here, when the core balls 1A are used in a solder paste, the "core balls" may be referred to as "core powder." "Core powder" is an aggregate of many core balls 1A, each possessing the characteristics described above. It is distinguished from a single core ball in its form of use, for example, by being incorporated as powder in a solder paste. Similarly, when used to form solder bumps, it is usually treated as an aggregate, and therefore, "core powder" used in such a form is distinguished from a single core ball. When "core balls" are used in a form referred to as "core powder," the diameter of the core balls is generally 1 to 300 μm. Furthermore, the solder material of this embodiment can be used in formed solder in which the core balls 1A are dispersed in the solder. For solder paste and solder foam, for example, a solder alloy with a composition of Sn-3.0Ag-0.5Cu (each value is in mass%) is used. However, the present invention is not limited to this solder alloy. Furthermore, the solder material of this embodiment can be used for solder joints of electronic components. In addition, the solder material of this embodiment may be applied in the form of columns, pillars, or pellets with columnar Cu as the core. The solder material described in "1. Solder Material" above can be used as the solder material in the solder paste, solder foam, and solder joint.

[0041] The present invention will be described in detail below with reference to examples, but the present invention is not limited to what is described in the examples.

[0042] 1. Preparation of Evaluation Samples [Example 1] A substrate (semiconductor package) (Cu-OSP treated electrode pads, opening size of electrode pads: diameter 0.24 mm, pitch between electrodes: 0.5 mm) was prepared, and a flux (WF-6317, manufactured by Senju Metal Industry Co., Ltd.) was applied onto the Cu electrodes of the substrate. Further, a core ball (Example 1) having a solder layer of Sn-3.0Ag-0.5Cu composition (the numbers are mass%, and the balance is Sn) shown in Tables 1A and 1B described below was mounted onto the Cu electrodes after the flux application, and the solder of the core ball was joined to the Cu electrodes by a reflow process to form solder bump electrodes (evaluation samples). The above reflow process was set to a triangular profile with a peak of 245°C.

[0043] [Examples 2 to 28 and Comparative Examples 1 to 12] Except that each configuration of the core ball having the above solder layer was changed as described in Tables 1A and 1B and Tables 2A and 2B described below, each solder bump electrode (evaluation sample) of Examples 2 to 28 and Comparative Examples 1 to 12 was prepared in the same manner as in Example 1.

[0044] 2. Evaluation For each of the evaluation samples of Examples 1 to 28 and Comparative Examples 1 to 12 prepared as described above, the following evaluations were performed. The results of each evaluation are shown in Tables 1A and 1B and Tables 2A and 2B.

[0045] (Wetting Performance of Solder with Respect to Nuclear Material) Five each of the evaluation samples (solder bump electrodes) were prepared, and for each of the five evaluation samples, the appearance was observed with an optical microscope. Regarding the appearance of each evaluation sample, if the solder bump electrodes after the first mounting were sufficiently covered with the solder layer in all the evaluation samples, it was evaluated as "〇" (excellent), while if the nuclear material was exposed on the surface in even one of the five evaluation samples, it was evaluated as "×" (poor).

[0046] Figure 5 is an external photograph of the evaluation of the wetting performance of solder on a nuclear material taken from above the solder bump of an evaluation sample. In Figure 5, (A) is an example where the evaluation of the wetting performance of solder on the nuclear material is "×" (poor), and (B) is an example where the evaluation of the wetting performance of solder on the nuclear material is "〇" (excellent). Figure 6 is a photograph of the cross-section of a sample where the evaluation of the wetting performance of solder on the nuclear material is "×" (poor). As can be seen from Figures 5 and 6, in the example where the evaluation of the wetting performance of solder on the nuclear material is poor, there are many parts where the nuclear ball is not covered with solder.

[0047] Figure 7 is a photograph of the cross-section after the secondary mounting on a printed circuit board (PCB) using a sample (solder bump electrode) with poor evaluation of the wetting performance of solder on the nuclear material. (B) in Figure 7 is an enlarged photograph of the periphery of the sample in (A) of Figure 7. In (A) and (B) of Figure 7, X is the semiconductor package side (substrate side with Cu electrodes), and Y is the printed circuit board side. There is a non-wetting part not covered with solder at the part of the arrow Z in (B) of Figure 7.

[0048] As described above, by determining whether the surface of the nuclear material is sufficiently covered by the solder layer (whether the wetting performance of the solder on the nuclear material is excellent) in the state of the evaluation sample (solder bump electrode) (the state after the primary mounting), it is possible to accurately predict whether non-wetting will occur after the secondary mounting.

[0049]

[0050]

[0051] Examples 1 to 28 relate to solder bump electrodes using a conductive nuclear material and a solder layer existing around the nuclear material, and using a solder material that satisfies the above formula (1) (Ts ≧ -0.25Dc + 105). Comparative Examples 1 to 12 relate to solder bump electrodes using a nuclear material and a solder layer, but using a solder material that does not satisfy the above formula (1) (Ts < -0.25Dc + 105).

[0052] Figure 2 is a graph showing the relationship between the diameter of the core material (Dc (μm)) and the thickness of the solder layers on both sides of the core material (Ts (μm)) in the solder materials of Examples 1 to 28 and Comparative Examples 1 to 12. In Figure 2, the notation "Excellent" corresponds to Examples 1 to 28, in which the evaluation of the solder wetting performance on the core material was excellent, and the notation "Poor" corresponds to Comparative Examples 1 to 12, in which the evaluation of the solder wetting performance on the core material was poor. In Figure 2, the notation "Linear (1)" indicates a straight line Ts = -0.25Dc + 105.

[0053] From the results in Tables 1A and 1B, Tables 2A and 2B, and Figure 2, the solder bump electrodes of Examples 1 to 28 showed excellent solder wetting performance on the core material. On the other hand, the solder bump electrodes of Comparative Examples 1 to 12 showed poor solder wetting performance on the core material.

[0054] From the above, it has been found that the solder material of the present invention, which includes a conductive core material and a solder layer surrounding the core material and satisfies the above formula (1) (Ts ≥ -0.25Dc + 105), can suppress the occurrence of non-wetting by improving the solder wetting performance to the core material during primary mounting.

[0055] 1A...Nuclear ball 1B...Nuclear column 2A...Nucleus 2B...Column 3A, 3B...Solder layer 30A...Solder alloy 4...Barrier layer 5A...Solder bump 6A...Substrate 60A...Electrode 7A...Semiconductor package 70A...Electrode

Claims

1. A solder material comprising a conductive core material and a solder layer surrounding the core material, wherein the solder material satisfies the following formula (1): Ts ≥ -0.25Dc + 105 (1) (Dc: diameter of the core material (μm), Ts: thickness of the solder layers on both sides of the core material (μm)).

2. The solder material according to claim 1, wherein the Dc is 75 to 425 μm.

3. The solder material according to claim 1 or 2, wherein the Ts is 20 to 425 μm.

4. The solder material according to any one of claims 1 to 3, wherein the solder layer comprises at least one selected from the group consisting of Sn, Ag, Cu, In, Ni, Bi, Sb, Zn, Ti, Ce, P, Ge, Ga, As, Fe, Co, Pd, Pb, and alloys thereof.

5. The solder material according to any one of claims 1 to 4, wherein the core material comprises at least one selected from the group consisting of Cu, Ni, Au, Al, Mo, Mg, Zn, Co, and alloys thereof.

6. The solder material according to any one of claims 1 to 5, wherein the core material is a spherical core ball.

7. The solder material according to any one of claims 1 to 5, wherein the nucleus material is a columnar nucleus column.

8. The solder material according to any one of claims 1 to 7, further comprising a barrier layer between the core material and the solder layer, the barrier layer comprising at least one selected from the group consisting of Ni and Co.

9. A solder paste comprising the solder material according to any one of claims 1 to 8.

10. A foamed solder comprising the solder material according to any one of claims 1 to 8.

11. A solder joint comprising the solder material described in any one of claims 1 to 8.

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