Bump-equipped circuit member, method for manufacturing bump-equipped circuit member, connection structure, and method for manufacturing connection structure

Abstract

A bump-equipped circuit member 1 comprises a substrate 2, an electrode 3 provided to one surface of the substrate 2, and a bump 4 provided to the electrode 3. The bump 4 includes electroconductive particles 11, and a base layer 5 that contains tin or a tin alloy and electrically connects the electroconductive particles 11 and the electrode 3 in a state of covering at least some of the electroconductive particles 11. The base layer 5 includes an alloy layer 5A with a metal constituting the electrode 3, and an eutectic solder layer 5B.

Description

Circuit member with bumps, manufacturing method of circuit member with bumps, connection structure, and manufacturing method of connection structure

[0001] The present disclosure relates to a circuit member with bumps, a method for manufacturing a circuit member with bumps, a connection structure, and a method for manufacturing a connection structure.

[0002] In recent years, with the trend toward higher definition electronic devices, the pitch and area of ​​bumps in circuit components used in electronic devices have become increasingly narrower. As a result, the conductive particles used in the circuit components may leak between electrodes, causing short circuits, which has been cited as a technical issue that must be resolved.

[0003] To address these technical challenges, methods have been proposed that use composite particles in which a plurality of insulating particles are attached to the surface of conductive particles. For example, in the methods described in Patent Documents 1 and 2, spherical resin particles are attached to the surface of conductive particles. In Patent Document 3, first insulating particles and second insulating particles having a lower glass transition temperature than the first insulating particles are attached to the surface of conductive particles.

[0004] Japanese Patent No. 4773685 Japanese Patent No. 3869785 Japanese Patent Laid-Open No. 2014-17213

[0005] In the current situation where the size of electrodes of circuit members that are electrically connected to each other is becoming increasingly smaller, there is a demand for technology that can further improve both the reliability of conduction and the reliability of insulation.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a bumped circuit member, a method for manufacturing a bumped circuit member, a connection structure, and a method for manufacturing a connection structure that can further improve both conductivity reliability and insulation reliability.

[0007] A bumped circuit member according to one aspect of the present disclosure comprises a substrate, an electrode provided on one surface of the substrate, and a bump provided on the electrode, wherein the bump has conductive particles and a base layer containing tin or a tin alloy, and electrically connecting the conductive particles to the electrode while covering at least a portion of the conductive particles, and the base layer is configured to include an alloy layer with a metal constituting the electrode and a eutectic solder layer.

[0008] In this bumped circuit member, bumps containing tin or a tin alloy are provided on the electrodes, and the bumps are electrically connected to the electrodes via a base layer composed of an alloy layer with the metal constituting the electrodes and a eutectic solder layer. In this bumped circuit member, the presence of the eutectic solder layer in the base layer ensures that the conductive particles are firmly crushed between the electrodes when the bumped circuit member is connected to another circuit member, allowing for sufficient solder wetting and spreading. This improves electrical conductivity reliability. Furthermore, in this bumped circuit member, the conductive particles are bonded to the electrodes by the base layer, preventing the conductive particles from flowing into the space between the electrodes when the bumped circuit member is connected to another circuit member. This also improves insulation reliability.

[0009] The conductive particles may have a portion that directly contacts the electrode without the base layer in between. In this case, the conductive particles are firmly supported by the base layer, which can more reliably improve the reliability of conduction and insulation.

[0010] The effective amount of the eutectic solder layer in the base layer may be 5% to 95%. By making the effective amount of the eutectic solder layer in the base layer 5% or more, the conductive particles can be sufficiently deformed together with the base layer when connecting a circuit component with bumps to another circuit component. This reduces the connection resistance and stabilizes the resistance value. By making the effective amount of the eutectic solder layer in the base layer 95% or less, the bonding strength of the conductive particles to the electrodes can be sufficiently ensured. This improves the stability of the connection.

[0011] The conductive particles have a base particle and a metal layer covering the base particle, and the melting point of the metal constituting the metal layer may be higher than the melting point of tin or a tin alloy. In this case, melting of the metal layer when joining the conductive particles to an electrode can be suppressed. Therefore, the conductive particles and the electrode can be firmly joined by the molten solder layer at a predetermined position on the surface of the electrode, while the state in which the metal layer covers the base particle is sufficiently maintained, and excellent connection reliability can be obtained when the bumped circuit member is connected to another circuit member.

[0012] A method for manufacturing a circuit member with bumps according to one aspect of the present disclosure comprises a preparation step of preparing a circuit member having an electrode on one side of a substrate and conductive particles at least partially covered with a solder layer containing tin or a tin alloy, and a formation step of forming bumps made of the conductive particles on the electrode, wherein in the formation step, the conductive particles are joined to the electrode at a temperature below the melting point of the tin or tin alloy, and a base layer is formed that includes an alloy layer with the metal that constitutes the electrode and a eutectic solder layer, thereby electrically connecting the conductive particles to the electrode.

[0013] In this method for manufacturing a circuit member with bumps, conductive particles are bonded to electrodes at a temperature below the melting point of tin or a tin alloy, forming a base layer including an alloy layer with the metal constituting the electrode and a eutectic solder layer. In the circuit member with bumps obtained by this manufacturing method for a circuit member with bumps, the presence of a eutectic solder layer in the base layer ensures that the conductive particles are firmly crushed between the electrodes when the circuit member with bumps is connected to another circuit member, allowing for sufficient solder spreading. This improves electrical conductivity reliability. Furthermore, because the conductive particles are bonded to the electrodes by the base layer, the conductive particles are prevented from flowing into the space between the electrodes when the resulting circuit member with bumps is connected to another circuit member. This also improves insulation reliability.

[0014] A connection structure according to one aspect of the present disclosure is a connection structure in which a first circuit member constituted by the above-mentioned bumped circuit member and a second circuit member having electrodes corresponding to the electrodes of the first circuit member are electrically connected via bumps, the bumps having conductive particles and a base layer containing tin or a tin alloy and electrically connecting the conductive particles to the electrodes of the first circuit member while covering at least a portion of the conductive particles, and the base layer is constituted by including an alloy layer with a metal constituting the electrode and a eutectic solder layer.

[0015] In this connection structure, the presence of a eutectic solder layer in the base layer of the first circuit member ensures that the conductive particles are firmly crushed between the electrodes, allowing for sufficient solder wetting and spreading. This improves electrical conductivity reliability. Furthermore, in this connection structure, the conductive particles are bonded to the electrodes by the base layer, preventing the conductive particles from flowing into the space between the electrodes when connecting a circuit member with bumps to another circuit member. This also improves insulation reliability.

[0016] A method for manufacturing a connection structure according to one aspect of the present disclosure includes a preparation step of preparing the above-mentioned bumped circuit member as a first circuit member and preparing a second circuit member having electrodes corresponding to the electrodes of the first circuit member, and a connection step of electrically connecting the conductive particles to the electrodes of the second circuit member by facing the electrodes of the second circuit member to the bumps of the first circuit member and heating the conductive particles to a temperature higher than the melting point of tin or a tin alloy.

[0017] In this method for manufacturing a connection structure, the presence of a eutectic solder layer on the base layer of the first circuit member allows the conductive particles to be firmly crushed between the electrodes, and the solder spreads sufficiently. This improves the reliability of electrical continuity. Furthermore, in this method for manufacturing a connection structure, the base layer bonds the conductive particles to the electrodes, preventing the conductive particles from flowing into the space between the electrodes. This also improves the reliability of insulation.

[0018] According to the present disclosure, it is possible to further improve both the electrical conductivity reliability and the insulation reliability.

[0019] 1 is a schematic cross-sectional view showing a bumped circuit member according to an embodiment of the present disclosure; (a) is a schematic cross-sectional view showing an example of conductive particles used in the bumped circuit member shown in FIG. 1 , and (b) is a schematic cross-sectional view showing another example of conductive particles; (a) is a schematic cross-sectional view showing a preparation step of a method for manufacturing a bumped circuit member according to an embodiment of the present disclosure; (b) is a schematic cross-sectional view showing a step subsequent to (a); and (c) is a schematic cross-sectional view showing a step subsequent to (a); (a) is a schematic cross-sectional view showing a formation step of a method for manufacturing a bumped circuit member according to an embodiment of the present disclosure; and (b) is a schematic cross-sectional view showing a step subsequent to (a); and (b) is a schematic cross-sectional view showing a connection structure according to an embodiment of the present disclosure; (a) is a schematic cross-sectional view showing an insulation step of a method for manufacturing a connection structure according to an embodiment of the present disclosure; and (b) is a schematic cross-sectional view showing a step subsequent to (a). 1A is a schematic cross-sectional view showing a preparation step of a manufacturing method of a connection structure according to an embodiment of the present disclosure, and FIG. 1B is a schematic cross-sectional view showing a connection step subsequent to the preparation step. 2A is a diagram showing the results of a conduction reliability test of a bumped circuit member according to the present disclosure. 3A is a diagram showing the results of an insulation reliability test of a bumped circuit member according to the present disclosure.

[0020] Hereinafter, preferred embodiments of a circuit member with bumps, a method for manufacturing a circuit member with bumps, a connection structure, and a method for manufacturing a connection structure according to one aspect of the present disclosure will be described in detail with reference to the drawings.

[0021] Unless otherwise specified, the materials exemplified in the following description may be used alone or in combination of two or more. When multiple substances corresponding to each component are present in the composition, the content of each component in the composition means the total amount of the multiple substances present in the composition unless otherwise specified. Numerical ranges indicated using "to" indicate ranges that include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in this specification, the upper or lower limit of a numerical range in one stage may be replaced with the upper or lower limit of a numerical range in another stage.

[0022] Fig. 1 is a schematic cross-sectional view showing a bumped circuit member according to an embodiment of the present disclosure. As shown in the figure, the bumped circuit member 1 includes a substrate 2, an electrode 3 provided on one surface 2a of the substrate 2, and a bump 4 provided on the electrode 3. The bumped circuit member 1 is formed by bonding a metal layer 13 and a solder layer 14 (see Fig. 2(a) or 2(b)) of conductive particles 11 that constitute the bump 4 to the electrode 3. While Fig. 1 shows one electrode 3 and one bump 4, in an actual bumped circuit member 1, a plurality of electrodes 3 and bumps 4 are arranged in a lattice pattern at a predetermined pitch on the one surface 2a of the substrate 2.

[0023] The electrodes 3 are formed in a predetermined pattern on one surface 2a of the substrate 2 by using a technique such as electroless plating, electrolytic plating, or sputtering. Examples of materials constituting the electrodes 3 include copper, copper / nickel, copper / nickel / gold, copper / nickel / palladium, copper / nickel / palladium / gold, copper / nickel / gold, copper / palladium, copper / palladium / gold, copper / tin, copper / silver, and indium tin oxide.

[0024] The bump 4 is formed using conductive particles 11. As shown in FIG. 2( a), the conductive particles 11 include a base particle 12, a metal layer 13 covering the base particle 12, and a solder layer 14 covering at least a portion of the metal layer 13. In the example shown in FIG. 2( a), the conductive particles 11 are spherical, but are not limited to being perfectly spherical and may also be ellipsoids or any solid of revolution of a plane curve. In this case, the aspect ratio of the conductive particles 11 (the ratio of the length in the major axis direction to the length in the minor axis direction) may be 0.5 or more, or may be 0.8 or more.

[0025] The particle size of the conductive particles 11 may be, for example, 2.3 μm to 25 μm, 3 μm to 20 μm, or 3.5 μm to 10 μm. If the particle size of the conductive particles 11 is 2.3 μm or more, the conductive particles 11 tend to be able to sufficiently absorb impact even when an impact is applied to the conductive particles 11. If the particle size of the conductive particles 11 is 25 μm or less, the variation in particle size of the conductive particles 11 can be sufficiently reduced, making it easier to achieve both electrical conductivity reliability and insulation reliability. The particle size of the conductive particles 11 can be measured by observation using a scanning electron microscope (hereinafter referred to as SEM). The average particle size of the conductive particles 11 can be calculated by measuring the particle sizes of, for example, 300 random particles using SEM and averaging the measured values.

[0026] The substrate particle 12 is spherical and made of a non-conductive material. The particle size of the substrate particle 12 may be, for example, 1.5 μm to 10 μm, or 2 μm to 10 μm. If the particle size of the substrate particle 12 is 1.5 μm or more, the substrate particle 12 tends to be able to sufficiently absorb the impact even if the conductive particle 11 is subjected to an impact. If the particle size of the substrate particle 12 is 10 μm or less, the variation in particle size of the substrate particle 12 can be sufficiently reduced. The particle size of the substrate particle 12 can be measured by observation using an SEM, as with the conductive particle 11. The average particle size of the substrate particle 12 can be calculated by measuring the particle sizes of 300 arbitrary substrate particles by observation using an SEM and averaging the measured values.

[0027] The constituent material of the base particle 12 is not particularly limited, but resin or silica can be used. Specific examples include acrylic resins such as polymethyl methacrylate and polymethyl acrylate; polyolefin resins such as polyethylene, polypropylene, polyisobutylene, and polybutadiene; glass; and silica. When resin particles are used as the base particle 12, cross-linked acrylic particles, cross-linked polystyrene particles, etc. can be used.

[0028] Assuming that reflow connection using solder is performed, the glass transition point (Tg) of the base particle 12 is preferably higher than the melting point of the solder. Taking the commonly used Sn-3 mass % Ag-0.5 mass % Cu as an example, its melting point is 217 to 219°C. For this reason, a material with a Tg of, for example, 220°C or higher may be used as the base particle 12. By using such a material, deformation of the base particle 12 is sufficiently suppressed as long as the temperature during joining of the solder layer 14 is lower than the Tg of the base particle 12. Therefore, the base particle 12 exhibits excellent dimensional stability, achieving good connection reliability and insulation reliability.

[0029] The metal layer 13 is, for example, a layer containing nickel or a nickel alloy. The nickel content of the metal layer 13 may be, for example, 85% to 98% by mass, 87% to 96% by mass, or 90% to 95% by mass. If the nickel content is 85 to 98% by mass, the metal layer 13 is likely to remain stably even after the solder layer 14 described below is bonded to the electrode 3, and high connection reliability can be maintained. The metal layer 13 does not necessarily have to cover the entire surface of the base particle 12. It is sufficient that the metal layer 13 covers 80% or more, more preferably 90% or more, of the surface of the base particle 12.

[0030] The thickness of the metal layer 13 may be, for example, 0.05 μm to 5 μm, 0.1 μm to 3 μm, or 0.2 μm to 2 μm. If the thickness of the metal layer 13 is 0.05 μm or more, the metal layer 13 is likely to remain stable even after the solder layer 14 is bonded to the electrode 3, and high connection reliability can be maintained. The metal layer 13 may contain at least one of phosphorus and boron, and may particularly contain phosphorus. In this case, when the solder layer 14 is bonded to the electrode 3, nickel contained in the metal layer 13 can be prevented from diffusing into the tin or tin alloy contained in the solder layer 14. This prevents a decrease in the thickness of the metal layer 13.

[0031] The metal layer 13 can be formed by, for example, electroless nickel plating. In this case, for example, the surface of the base particle 12 may be subjected to a palladium catalytic treatment, followed by electroless nickel plating. More preferably, by using a phosphorus-containing compound such as sodium hypophosphite as a reducing agent, phosphorus can be co-deposited, thereby forming a metal layer 13 containing an alloy containing nickel and phosphorus (nickel-phosphorus alloy). By using a boron-containing compound such as dimethylamine borane, sodium borohydride, or potassium borohydride as a reducing agent, boron can be co-deposited, thereby forming a metal layer 13 containing an alloy containing nickel and boron (nickel-boron alloy).

[0032] The melting point of the metal constituting the metal layer 13 may be higher than the melting point of tin or a tin alloy (the melting point of the solder layer 14). In this case, melting of the metal layer 13 can be suppressed when the conductive particles 11 are joined to the electrode 3. Therefore, the solder layer 14 can firmly join the conductive particles 11 and the electrode 3, while the state in which the metal layer 13 covers the base particle 12 is sufficiently maintained, resulting in excellent connection reliability.

[0033] The solder layer 14 is a layer containing tin or a tin alloy. Examples of tin alloys that make up the solder layer 14 include In—Sn, In—Sn—Ag, Sn—Bi, Sn—Bi—Ag, Sn—Ag—Cu, and Sn—Cu. Specific examples are listed below.・In-Sn (In 52 mass%, Bi 48 mass%, melting point 118°C) ・In-Sn-Ag (In 20 mass%, Sn 77.2 mass%, Ag 2.8 mass%, melting point 175°C) ・Sn-Bi (Sn 43 mass%, Bi 57 mass%, melting point 138°C) ・Sn-Bi-Ag (Sn 42 mass%, Bi 57 mass%, Ag 1 mass%, melting point 139°C) ・Sn-Ag-Cu (Sn 96.5 mass%, Ag 3 mass%, Cu 0.5 mass%, melting point 217°C) ・Sn-Cu (Sn 99.3 mass%, Cu 0.7 mass%, melting point 227°C)

[0034] The tin alloy is selected depending on the connection temperature. When an In-Sn alloy or an Sn-Bi alloy is selected, connection at low temperatures of 150°C or less becomes possible. When a material with a high melting point, such as Sn-Ag-Cu or Sn-Cu, is used, high reliability tends to be achieved even when the circuit member 1 with bumps is left at high temperatures. In addition to tin or a tin alloy, the solder layer 14 may contain trace amounts of metals such as Ni, Mn, Sb, Al, and Zn as needed.

[0035] The solder layer 14 may cover, for example, 20% to 60% or 30% to 50% of the surface of the metal layer 13. The thickness (thickest part) of the solder layer 14 may be, for example, 0.03 μm to 3 μm, 0.05 μm to 2 μm, or 0.1 μm to 1 μm. If the thickness of the solder layer 14 is 0.03 μm or more, high reliability can be achieved when the solder layer 14 is bonded to the electrode 3. From the viewpoint of preventing the conductive particles 11 and the transfer mold 21 (see FIG. 3( a) , etc.) from being connected by the solder layer 14 formed by sputtering, it is preferable that the upper limit of the thickness of the solder layer 14 be approximately 3 μm, as described above.

[0036] The solder layer 14 may contain Ag, Cu, Ni, Bi, Zn, Pd, Pb, Au, P, B, or an alloy of two or more selected from these. The solder layer 14 may contain Ag or Cu. By including Ag or Cu in the solder layer 14, the melting point of the solder layer 14 can be lowered to about 220°C. In addition, the bonding strength with the electrode 3 is improved, and good connection reliability can be obtained.

[0037] The Cu content of the solder layer 14 may be, for example, 0.05% by mass to 10% by mass, 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, good connection reliability is more likely to be obtained. If the Cu content is 10% by mass or less, the melting point of the solder layer 14 is lowered and the solder wettability is improved. As a result, good connection reliability is more likely to be obtained.

[0038] The Ag content of the solder layer 14 may be, for example, 0.05% by mass to 10% by mass, 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, good solder connection reliability is more likely to be obtained. If the Ag content is 10% by mass or less, the melting point of the solder layer 14 is lowered and the solder wettability is improved. As a result, good connection reliability is more likely to be obtained. When the solder layer 14 contains Ag, Ag in the solder layer 14 ３ Sn is formed. Ag ３ The dispersion of Sn in the solder layer 14 improves the strength of the solder layer 14 against impacts.

[0039] The solder layer 14 can be formed by, for example, sputtering. To form the solder layer 14 by sputtering, for example, a barrel-type sputtering device can be used. For example, when a cylindrical, oblique, polygonal, or other barrel sputtering device is used, aggregation of particles tends to be suppressed. The solder layer 14 can also be formed by vapor deposition or ion plating, without being limited to sputtering.

[0040] Vapor deposition is a method of depositing a vapor deposition material on the surface of an object by heating and evaporating the vapor deposition material under vacuum. A vacuum vapor deposition apparatus includes, for example, a vacuum chamber. The vacuum chamber is equipped with a container for storing the vapor deposition material, a heating mechanism for heating the vapor deposition material in the container, and a stage for placing the object to be vapor deposited.

[0041] When multiple deposition materials are used, multiple containers and heating mechanisms may be provided. In this case, for example, two types of metals are placed in separate containers and heated and evaporated simultaneously, thereby depositing an alloy or mixture of the two types of metals on the deposition target. Since the deposition rate at different heating temperatures varies depending on the type of deposition material, it is preferable that the heating mechanism be able to individually control the temperature of each container. This allows the ratio of the alloy or mixture deposited on the non-deposition target to be freely adjusted.

[0042] The heating mechanism can be various heating methods, such as electric heating wire (resistance) heating, induction heating, radiation heating, and electron beam heating. A mechanism for heating the object to be vapor-deposited may be provided. Heating the object to be vapor-deposited can improve adhesion between the vapor deposition material and the object to be vapor-deposited and shape the deposition layer of the vapor deposition material (e.g., flattening). A mechanism for rotating and swinging the object to be vapor-deposited may also be provided. The rotation of the object to be vapor-deposited may be by rotation or a combination of rotation and revolution. In this case, the deposition thickness of the vapor deposition material on the object to be vapor-deposited is made uniform. The positional relationship between the vapor deposition material container and the object to be vapor-deposited is not particularly limited, but arranging them opposite each other enables more uniform film formation. The position of the vapor deposition material container and the distance from the object to be vapor-deposited are appropriately adjusted depending on the vapor deposition material, the size of the object to be vapor-deposited, and the like.

[0043] In this embodiment, a mixed film layer of tin and bismuth was used as the solder layer 14. Tin and bismuth evaporation materials were respectively placed in two containers (molybdenum boats) inside the vacuum chamber. The two evaporation materials were installed concentrically at a radius of 250 mm from the revolution axis of the substrate located at the center of the vacuum chamber, and each was equipped with a resistance heating mechanism. The object to be evaporated was fixed to a holder and rotated at a height of 1100 mm from the evaporation material. Rotation and revolution here refers to the substrate rotating around its rotation axis while simultaneously revolving around its revolution axis.

[0044] A shielding mask was installed about 100 mm below the substrate. The shielding mask was processed into a pre-designed shape so that a film could be formed on the substrate with a uniform film thickness. In addition, a film thickness monitor placed at the center of the revolution plane monitored the film formation rate, and a mechanism was provided to control the current value of the resistance heating so that the film formation rate was constant. The pressure inside the vacuum chamber during film formation was 5.0 x 10 －４ The pressure was set to 1 Pa, and the temperature of the object to be vapor-deposited was set to 50° C. Then, the conditions were adjusted so that the film formation ratio of tin and bismuth was 42:58, and a specified amount of a mixed film of tin and bismuth was formed on the surface of the object to be vapor-deposited.

[0045] Ion plating is a method of heating and evaporating the deposition material, similar to vapor deposition. In ion plating, the vapor of the deposition material is positively charged while a negative charge is applied to the target object, which then attracts the positively charged vapor of the deposition material, forming a film with good adhesion to the target object.

[0046] As shown in FIG. 2( b), the conductive particle 11 may have a configuration in which the metal layer 13 is covered with a surface layer 15. The surface layer 15 is, for example, a layer containing palladium or a palladium alloy. The surface layer 15 is formed, for example, through a plating process. The surface layer 15 may be an electroless plated palladium layer. Electroless palladium plating may be either a substitution type (a type that does not contain a reducing agent) or a reduction type (a type that contains a reducing agent). Examples of electroless palladium plating include reduction type APP (product name, manufactured by Ishihara Pharmaceutical Co., Ltd.) and substitution type MCA (product name, manufactured by World Metal Co., Ltd.). When comparing substitution type and reduction type, reduction type tends to have fewer voids. Compared to substitution type, which precipitates while dissolving the inner metal, reduction type makes it easier to ensure a covering area.

[0047] The surface layer 15 may have a multilayer structure. In this case, the surface layer 15 may be composed of a first palladium plating film provided on the outside of the metal layer 13 and a second palladium plating film provided on the outside of the first palladium plating film. The first palladium plating film is, for example, a displacement or electroless palladium plating film with a purity of 99% by mass or more. The second palladium plating film is, for example, an electroless palladium plating film with a purity of 90% by mass or more but less than 99% by mass.

[0048] When a substitutional or reduction-type electroless palladium plating coating having a purity of 99% by mass or more is formed alone as surface layer 15, the inclusion of Pd in ​​Sn-Cu-Ni-based compounds or Sn-Ni-based compounds provides an effect of suppressing the growth of these compounds, but a reduction-type electroless palladium plating coating having a purity of 90% by mass or more but less than 99% by mass is more effective in suppressing the growth of these compounds.

[0049] On the other hand, if a reduced-type electroless palladium plating coating having a purity of 90% by mass or more but less than 99% by mass is formed alone as the surface layer 15, the phosphorus content of the electroless palladium plating coating can be increased, but it is difficult to deposit a coating with a uniform thickness over the entire substrate particle 12 on which the metal layer 13 is formed. In this case, particles on which a phosphorus-containing coating (electroless palladium-phosphorus coating) is not formed or particles on which the phosphorus-containing coating is extremely thin tend to be produced. This phenomenon tends to occur more easily as the particle size of the conductive particles 11 becomes smaller. As a result, if a reduced-type electroless palladium plating coating having a purity of 90% by mass or more but less than 99% by mass is formed alone, the palladium-phosphorus alloy plating coating may no longer function as a protective layer for the metal layer 13.

[0050] A displacement or reduction-type electroless palladium plating coating with a purity of 99% by mass or more is more likely to deposit on the metal layer 13 than a reduction-type electroless palladium plating coating with a purity of 90% by mass or more but less than 99% by mass, and deposition occurs with a sufficiently uniform thickness over the entire substrate particle 12 on whose surface the metal layer 13 is formed, and deposition occurs independently of the particle size of the substrate particle 12. After a displacement or reduction-type electroless palladium plating coating with a purity of 99% by mass or more but less than 99% by mass is formed, deposition of a reduction-type electroless palladium plating coating with a purity of 90% by mass or more but less than 99% by mass is more likely to occur on the surface, and therefore deposition occurs independently of the particle size of the substrate particle 12.

[0051] For these reasons, as described above, surface layer 15 preferably has a first palladium plating coating provided on the outside of metal layer 13 and a second palladium plating coating (an electroless palladium plating coating having a purity of 90% by mass or more but less than 99% by mass) provided on the outside of the first palladium plating coating.

[0052] The surface layer 15 may disappear due to the diffusion of palladium into the solder layer 14 after the solder layer 14 is bonded to the electrode 3. In this case, the diffusion of palladium into the solder layer 14 forms a Sn—Cu—Ni—Pd-based compound or a Sn—Ni—Pd-based compound between the metal layer 13 and the solder layer 14. The Pd content in these compounds may be 0.01% by mass to 3% by mass, 0.02% by mass to 1% by mass, or 0.05% by mass to 0.5% by mass. When the Pd content of the above compounds is 0.01% by mass or more, the effect of suppressing the growth of Sn—Cu—Ni-based compounds or Sn—Ni-based compounds in a high-temperature environment of approximately 100°C is easily achieved. When the Pd content of the above compounds is 3% by mass or less, the surface layer 15 diffuses into the solder layer 14, improving drop impact resistance reliability.

[0053] The surface layer 15 also functions as a layer ensuring the wetting and spreading of the solder layer 14. The thickness of the surface layer 15 may be, for example, 0.01 μm to 0.5 μm, 0.03 μm to 0.4 μm, or 0.05 μm to 0.3 μm. If the thickness of the surface layer 15 is 0.01 μm or more, the Pd content of the Sn—Cu—Ni—Pd-based compound or Sn—Ni—Pd-based compound can be easily set to 0.01 mass % or more after the solder layer 14 is bonded to the electrode 3. As a result, the effect of suppressing the growth of Sn—Cu—Ni-based compounds or Sn—Ni-based compounds in a high-temperature environment of approximately 100°C can be easily achieved. If the thickness of the surface layer 15 is 0.5 μm or less, the surface layer 15 diffuses into the solder layer 14, improving drop impact resistance reliability.

[0054] The bump 4 is bonded to the electrode 3 by heating and pressurizing the conductive particles 11 against the electrode 3. In the bonded state with the electrode 3, the bump 4 has a base layer 5, as shown in Fig. 1. The base layer 5 is formed by the above-mentioned solder layer 14 being deformed and altered during bonding with the electrode 3. In other words, the base layer 5 contains tin or a tin alloy, and electrically connects the conductive particles 11 to the electrode 3 while covering at least a portion of the conductive particles 11.

[0055] When joining the solder layer 14 and the electrode 3, the conductive particles 11 are joined to the electrode 3 at a temperature below the melting point of the tin or tin alloy contained in the solder layer 14. By setting the joining temperature below the melting point of the tin or tin alloy contained in the solder layer 14, an alloy layer 5A with the metal constituting the electrode 3 and a eutectic solder layer 5B that originally constitutes the solder layer 14 coexist in the base layer 5. The alloy layer 5A is located in a portion of the base layer 5 closer to the electrode 3, and the eutectic solder layer 5B is located in a portion of the base layer 5 closer to the conductive particles 11. In this embodiment, the effective amount of the eutectic solder layer 5B in the base layer 5 is 5% to 95%.

[0056] 1 , in the bump 4, the conductive particles 11 have a portion P that is in direct contact with the electrode 3 without the base layer 5 therebetween. In this portion P, the metal layer 13 or the surface layer 15 of the conductive particles 11 is in contact with the surface of the electrode 3. The conductive particles 11 may be bonded to the electrode 3 via the base layer 5. In this case, the thickness of the base layer 5 between the conductive particles 11 and the electrode 3 can be adjusted by the temperature and pressure when bonding the conductive particles 11 of the electrode 3.

[0057] Next, a method for manufacturing the above-mentioned circuit member 1 with bumps will be described.

[0058] The manufacturing method of the bumped circuit member 1 includes a preparation step of preparing a circuit member 25 (see Figure 4(a)) having an electrode 3 on one surface 2a of a substrate 2 and conductive particles 11 at least partially covered with a solder layer 14 containing tin or a tin alloy, and a formation step of forming a bump made of the conductive particles 11 on the electrode 3.

[0059] Here, a transfer mold 21 is used in carrying out the preparation process and the formation process, as shown in FIG. 3( a). The transfer mold 21 is formed in a sheet shape from an inorganic material such as silicon, various ceramics, glass, metals such as stainless steel, or an organic material such as various resins. The transfer mold 21 may be formed from a flexible resin material. One surface 21 a of the transfer mold 21 is provided with a recess 22 in which conductive particles 11 are held. The recess 22 is formed using a known method such as photolithography. The recess 22 has a shape in which the opening area expands from the bottom toward the opening.

[0060] 3(b), the transfer mold 21 is placed facing a sputtering electrode 23. The sputtering electrode 23 is composed of a layer containing tin or a tin alloy. By sputtering using the sputtering electrode 23, a solder layer 14 is formed so as to cover a portion of the metal layer 13 of the conductive particles 11. Note that by sputtering, a layer containing tin or a tin alloy is also formed on one surface 21a of the transfer mold 21.

[0061] After the solder layer 14 is formed, as shown in Figure 4(a), a circuit member 25 having an electrode 3 is prepared on one surface 2a of the substrate 2, and a transfer mold 21 is placed on the circuit member 25 so that the electrode 3 faces the conductive particles 11. It is preferable to use a transfer mold 21 in a state where the conductive particles 11 are still contained in the recesses 22 after the solder layer 14 is formed by sputtering. This improves the efficiency of the manufacturing process and makes it easy to position the thickest portion of the solder layer 14 facing the surface of the electrode 3.

[0062] Next, as shown in Figure 4(b), a solder layer 14 is brought into contact with the surface of the electrode 3. The conductive particles 11 are then heated and pressurized at a temperature below the melting point of tin or a tin alloy to form a base layer 5 including an alloy layer 5A with the metal constituting the electrode 3 and a eutectic solder layer 5B. The conductive particles 11 and the electrode 3 are electrically connected by the base layer 5, and bumps 4 are formed on the electrode 3, thereby obtaining the circuit member 1 with bumps shown in Figure 1. The reason that the conductive particles 11 and the electrode 3 are joined even at a temperature below the melting point of tin or a tin alloy is presumably due to slight interdiffusion of metal elements between the tin or tin alloy and the metal constituting the electrode 3.

[0063] The lower limit of the heating temperature is set appropriately depending on the constituent material of the solder layer 14, but from the viewpoint of forming a good bond between the solder layer 14 and the electrode 3, when the melting point of tin or a tin alloy is Tc, the lower limit of the heating temperature may be (Tc-40)°C or higher, or may be (Tc-20)°C or higher. The lower limit of the heating temperature may be (Tc-15)°C or higher, or may be (Tc-15)°C or higher.

[0064] For example, if the tin alloy is a Sn—Bi alloy (melting point 138°C), by heating the conductive particles 11 to a temperature of 125°C or higher but lower than 138°C, the bump 4 can be formed on the electrode 3 while maintaining the eutectic state of the Sn—Bi alloy. A Sn—Bi alloy generally contains 42% by mass of Sn and 58% by mass of Bi. By heating within the above temperature range, the mass ratio Sn / Bi of Sn to Bi in the Sn—Bi alloy contained in the eutectic solder layer 5B can be set to 0.2 or higher. From the viewpoint of suppressing deformation of the bump 4, the mass ratio Sn / Bi may be 0.3 or higher, or may be 0.5 or higher.

[0065] The heating time is not particularly limited and can be adjusted appropriately depending on the pressure conditions or heating atmosphere. As an example, the heating time can be 0.1 to 20 minutes. A heating time of 0.1 minute or more allows the conductive particles 11 and the electrodes 3 to be bonded more effectively. Furthermore, a heating time of 20 minutes or less makes it easier to maintain the eutectic solder layer 5B. From this perspective, the heating time may be 1 to 15 minutes, or 3 to 10 minutes.

[0066] The pressure is not particularly limited, but may be, for example, about 0.5 MPa to 100 MPa. By heating the conductive particles 11 and the electrode 3 while they are in contact under pressure, the heating temperature can be set lower, and a portion P (see FIG. 1) can be formed in the bump 4 where the conductive particles 11 are in direct contact with the electrode 3 without the base layer 5 interposed therebetween. From this perspective, the pressure may be 0.7 MPa to 70 MPa, or 1.0 MPa to 50 MPa.

[0067] The conductive particles 11 may be heated and pressurized in a reducing atmosphere. By heating the conductive particles 11 at a temperature below the melting point of tin or a tin alloy and creating a reducing atmosphere, the oxide films on the surfaces of the solder layer 14 and the electrode 3 are reduced, making it easier to bond the conductive particles 11 to the electrode 3 better. Examples of reducing gases include hydrogen gas, hydrogen radicals, and formic acid gas.

[0068] Next, a connection structure using the circuit member 1 with bumps will be described.

[0069] Fig. 5 is a schematic cross-sectional view showing a connection structure according to an embodiment of the present disclosure. As shown in Fig. 5, a connection structure 31 is formed by electrically connecting a first circuit member 32A, which is formed by the above-described circuit member 1 with bumps, to a second circuit member 32B, which has electrodes 34 corresponding to the electrodes 3 of the first circuit member 32A, via bumps 4. In the example shown in Fig. 5, the second circuit member 32B has a substrate 33 and electrodes 34 provided on one surface 33a of the substrate 33. An insulating resin layer 35 is provided between the first circuit member 32A and the second circuit member 32B to cover the electrodes 3, 34, and the bumps 4. Because electrical connection between the electrodes 3, 34 is ensured by the bumps 4, it is not necessary to use an anisotropic conductive adhesive for the insulating resin layer 35; instead, an insulating resin material that does not contain conductive particles can be appropriately used.

[0070] The connection structure 31 can be applied to electronic devices such as liquid crystal displays, personal computers, mobile phones, smartphones, and tablets. One of the first circuit member 32A and the second circuit member 32B is, for example, a chip component such as an IC chip (semiconductor chip), a resistor chip, a capacitor chip, or a driver IC; or a rigid package substrate. These circuit members generally have a large number of circuit electrodes. One of the first circuit member 32A and the second circuit member 32B is a wiring substrate such as a flexible tape substrate having metal wiring, a flexible printed wiring board, or a glass substrate on which indium tin oxide (ITO) or zinc oxide (IZO) is vapor-deposited.

[0071] Next, a method for manufacturing the above-mentioned connection structure 31 will be described.

[0072] The manufacturing method of the connection structure 31 includes a preparation step of preparing a bumped circuit member 1 as a first circuit member 32A and preparing a second circuit member 32B having an electrode 34 corresponding to the electrode 3 of the first circuit member 32A, and a connection step of facing the electrode 34 of the second circuit member 32B to the bump 4 of the first circuit member 32A and electrically connecting the conductive particles 11 to the electrode 34 of the second circuit member 32B by heating the conductive particles 11 to a temperature higher than the melting point of tin or a tin alloy.

[0073] First, as shown in Fig. 6(a), a first circuit member 32A and an insulating resin film F made of an insulating resin material are prepared. Next, as shown in Fig. 6(b), the insulating resin film F is laminated onto one surface 2a of the substrate 2 of the first circuit member 32A. This covers the electrodes 3 and bumps 4 of the first circuit member 32A with the insulating resin film F. After laminating the insulating resin film F, as shown in Fig. 7(a), a second circuit member 32B is placed relative to the first circuit member 32A so that the electrodes 34 face the bumps 4 of the first circuit member 32A.

[0074] After the second circuit member 32B is placed, as shown in Fig. 7(b), the conductive particles 11 are heated and pressurized at a temperature below the melting point of tin or a tin alloy, and the electrodes 34 of the second circuit member 32B are pressed toward the bumps 4. This electrically connects the conductive particles 11 and the electrodes 34 of the second circuit member 32B, thereby obtaining the connection structure 31 shown in Fig. 5. If the insulating resin film F is made of a thermosetting resin, the thermosetting resin hardens as the conductive particles 11 are heated and pressurized, and an insulating resin layer 35 is formed.

[0075] As described above, in the bumped circuit member 1 according to this embodiment, the bumps 4 containing tin or a tin alloy are provided on the electrodes 3, and the bumps 4 are electrically connected to the electrodes 3 via a base layer 5 including an alloy layer 5A with the metal constituting the electrodes 3 and a eutectic solder layer 5B. With this configuration, the presence of the eutectic solder layer 5B in the base layer 5 ensures that the conductive particles 11 are firmly crushed between the electrodes when the bumped circuit member 1 is connected to another circuit member, ensuring sufficient solder spreading. This improves electrical conductivity reliability. Furthermore, in the bumped circuit member 1, the conductive particles 11 are bonded to the electrodes 3 by the base layer 5, which prevents the conductive particles 11 from flowing into the space between the electrodes when the bumped circuit member 1 is connected to another circuit member. This also improves insulation reliability.

[0076] In this embodiment, the conductive particles 11 have a portion P that is in direct contact with the electrode 3 without the base layer 5. In this case, the conductive particles 11 are firmly supported by the base layer 5, which can more reliably improve the conductivity reliability and insulation reliability.

[0077] If the effective amount of the eutectic solder layer 5B in the base layer 5 is less than 5%, this means that most of the base layer 5 is formed of an alloy with a melting point higher than that of the solder layer 14. In this case, when connecting the bumps 4 of the bumped circuit member 1 to the electrodes of another circuit member, the base layer 5 may barely deform, preventing the deformation of the conductive particles 11, which are components of the bumps 4. If the deformation of the conductive particles 11 is prevented, the contact area between the conductive particles 11 and the electrodes of the other circuit member may be insufficient, resulting in increased connection resistance. Furthermore, if an attempt is made to reduce the distance between the bumped circuit member 1 and the other circuit member to stabilize the resistance value, the conductive particles 11 may attempt to deform alone, even though the base layer 5 does not deform, and may be damaged.

[0078] Furthermore, when forming the bumped circuit member 1, the conductive particles 11 having the solder layer 14 are pressed against the electrode 3. However, the pressing force at this time is generally greater than the pressing force when the conductive particles 11 of the bumped circuit member 1 are pressed against the electrode of another circuit member. The shape of the base layer 5 that joins the electrode 3 of the bumped circuit member 1 and the conductive particles 11 is shaped to follow the curvature of the surface of the conductive particles 11, as shown in FIG. 1 . However, when the conductive particles 11 of the bumped circuit member 1 are pressed against the electrode of another circuit member, a force is also applied to the base layer 5 due to deformation of the conductive particles 11. In this case, if the effective amount of the eutectic solder layer 5B in the base layer 5 is less than 5%, the likelihood of deformation of the base layer 5 is low, resulting in damage to the conductive particles 11. It is difficult to increase the contact area between the electrode 3 of the bumped circuit member 1 and the conductive particles 11, making it difficult to reduce the connection resistance.

[0079] When the effective abundance of the eutectic solder layer 5B in the base layer 5 is greater than 95%, the alloy layer 5A of the base layer 5 is almost absent. The alloy layer 5A is composed of an alloy of the metal constituting the electrode 3 and the solder layer 14, and the effective abundance of the alloy layer 5A means that the solder "wet" the electrode surface. Solder contains tin or a tin alloy, which is a relatively soft material among metals. Therefore, when the conductive particles 11 are pressed against the electrode 3, the solder layer 14 may deform, making it appear as if the conductive particles 11 are bonded to the electrode 3. However, if the solder does not wet the electrode surface sufficiently, an interface exists between the electrode 3 and the solder layer 14, and the bonding strength between the electrode 3 and the conductive particles 11 is insufficient. In this case, poor bonding of the conductive particles 11 to the electrode 3 is likely to occur, and the conductive particles 11 may peel off from the electrode 3 after bonding, or may move to an electrode 3 other than the intended electrode 3, resulting in malfunction.

[0080] To address this problem, in this embodiment, the effective amount of eutectic solder layer 5B in base layer 5 is set to 5% to 95%. By setting the effective amount of eutectic solder layer 5B in base layer 5 to 5% or more, the conductive particles 11 can be sufficiently deformed together with base layer 5 when connecting circuit member 1 with bumps to another circuit member. This reduces the connection resistance and stabilizes the resistance value. By setting the effective amount of eutectic solder layer 5B in base layer 5 to 95% or less, the bonding strength of conductive particles 11 to electrode 3 can be sufficiently ensured. This improves the stability of the connection.

[0081] In this embodiment, the conductive particles 11 have a base particle 12 and a metal layer 13 covering the base particle 12, and the melting point of the metal constituting the metal layer 13 is higher than the melting point of tin or a tin alloy. This makes it possible to suppress melting of the metal layer 13 when joining the conductive particles 11 to the electrode 3. Therefore, the conductive particles 11 and the electrode 3 can be firmly joined by the solder layer 14 melted at a predetermined position on the surface of the electrode 3, while the state in which the metal layer 13 covers the base particle 12 is sufficiently maintained, resulting in excellent connection reliability when the bumped circuit member 1 is connected to another circuit member.

[0082] Furthermore, in the method for manufacturing a bumped circuit member according to this embodiment, conductive particles 11 are bonded to electrodes 3 at a temperature below the melting point of tin or a tin alloy, forming a base layer 5 including an alloy layer 5A with the metal constituting the electrode 3 and a eutectic solder layer 5B. In the bumped circuit member 1 obtained by this method for manufacturing a bumped circuit member, the presence of the eutectic solder layer 5B in the base layer 5 ensures that the conductive particles 11 are firmly crushed between the electrodes when the bumped circuit member 1 is connected to another circuit member, allowing for sufficient solder spreading. This improves electrical conductivity reliability. Furthermore, because the conductive particles 11 are bonded to electrodes 3 by the base layer 5, the conductive particles 11 are prevented from flowing into the space between the electrodes when the resulting bumped circuit member 1 is connected to another circuit member. This also improves insulation reliability.

[0083] 8 is a diagram showing the results of a conductivity reliability test of the circuit member with bumps according to the present disclosure. This conductivity reliability test was performed by conducting a high-temperature, high-humidity test on a connection structure (comparative example) in which a circuit member with bumps obtained by bonding conductive particles to electrodes at a temperature higher than the melting point of tin or a tin alloy was connected to another circuit member, and a connection structure (example) in which a circuit member with bumps obtained by bonding conductive particles to electrodes at a temperature higher than the melting point of tin or a tin alloy was connected to another circuit member, and measuring the change over time in the connection resistance of each.

[0084] In the examples and comparative examples, the solder layer was made of Sn-Bi58 (melting point 139°C). In the examples, the temperature when bonding the conductive particles and electrodes was 135°C, and in the comparative examples, the temperature when bonding the conductive particles and electrodes was 170°C. The high-temperature, high-humidity test was carried out at a temperature of 85°C and a humidity of 85% RH for 250 hours.

[0085] 8, in the comparative example, the initial connection resistance was about 4 Ω, but after 250 hours the connection resistance increased to about 6 Ω (about 1.5 times the initial connection resistance). In contrast, in the example, the initial connection resistance was about 2.6 Ω, but after 250 hours the connection resistance was about 2.9 Ω (about 1.1 times the initial connection resistance). From these results, it was confirmed that the method of joining conductive particles to electrodes at a temperature higher than the melting point of tin or a tin alloy, as disclosed herein, contributes to improving the electrical conductivity reliability.

[0086] 9 is a diagram showing the results of an insulation reliability test on a circuit member with bumps according to the present disclosure. This insulation reliability test was conducted by observing the locations of conductive particles between the electrodes of a connection structure (comparative example) in which the electrodes of two circuit members were connected together using a general anisotropic conductive film, and a connection structure (example) in which a circuit member with bumps obtained by bonding conductive particles to electrodes at a temperature higher than the melting point of tin or a tin alloy was connected to another circuit member.

[0087] In the insulation reliability test, evaluation was performed using a glass substrate with a transparent electrode (with ITO) and a sapphire chip with an Au electrode. The connection structures obtained in the examples and comparative examples were placed on the stage of a differential interference microscope (ECLIPSEL200N, manufactured by Nikon), and the periphery of the electrodes was observed in transmitted light mode at magnifications of 500x and 1000x.

[0088] As shown in Figure 9, in the comparative example, multiple conductive particles are located in the space between adjacent electrodes. On the other hand, in the example, the conductive particles do not protrude into the space between adjacent electrodes, and the electrodes are firmly separated. From these results, it was confirmed that the method of bonding conductive particles to electrodes at a temperature higher than the melting point of tin or tin alloy, as disclosed herein, contributes to improving insulation reliability.

[0089] 1...circuit member with bumps, 2...substrate, 2a...one surface, 3...electrode, 4...bump, 5...base layer, 5A...alloy layer, 5B...eutectic solder layer, 11...conductive particles, 32A...first circuit member (circuit member with bumps), 32B...second circuit member, 34...electrode.

Claims

1. A circuit component with bumps comprising: a substrate; an electrode provided on one surface of the substrate; and a bump provided on the electrode, wherein the bump has conductive particles and a base layer containing tin or a tin alloy and electrically connecting the conductive particles to the electrode while covering at least a portion of the conductive particles, the base layer being composed of an alloy layer with a metal constituting the electrode and a eutectic solder layer.

2. The circuit member with bumps according to claim 1, wherein the conductive particles have portions that directly contact the electrodes without the intermediation of the base layer.

3. The circuit member with bumps according to claim 1 or 2, wherein the effective amount of the eutectic solder layer in the base layer is 5% to 95%.

4. A circuit member with bumps according to any one of claims 1 to 3, wherein the conductive particles have a base particle and a metal layer covering the base particle, and the melting point of the metal constituting the metal layer is higher than the melting point of the tin or tin alloy.

5. A method for manufacturing a circuit member with bumps, comprising: a preparation step of preparing a circuit member having an electrode on one surface of a substrate, and conductive particles at least partially covered with a solder layer containing tin or a tin alloy; and a formation step of forming bumps from the conductive particles on the electrode, in which the conductive particles are joined to the electrode at a temperature below the melting point of the tin or tin alloy, and a base layer including an alloy layer with a metal constituting the electrode and a eutectic solder layer is formed, thereby electrically connecting the conductive particles to the electrode.

6. A connection structure in which a first circuit member constituted by the circuit member with bumps as set forth in any one of claims 1 to 4 and a second circuit member having electrodes corresponding to the electrodes of the first circuit member are electrically connected via the bumps, the bumps having conductive particles and a base layer containing tin or a tin alloy, electrically connecting the conductive particles to the electrodes of the first circuit member while covering at least a portion of the conductive particles, the base layer being constituted by including an alloy layer with the metal constituting the electrodes and a eutectic solder layer.

7. A method for manufacturing a connection structure comprising: a preparation step of preparing a circuit member with bumps as defined in any one of claims 1 to 4 as a first circuit member, and preparing a second circuit member having electrodes corresponding to the electrodes of said first circuit member; and a connection step of opposing said electrodes of said second circuit member to said bumps of said first circuit member, and heating said conductive particles to a temperature higher than the melting point of said tin or tin alloy, thereby electrically connecting said conductive particles to said electrodes of said second circuit member.

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