TW202000936A - Cu core ball, solder head, solder paste and foaming solder material capable of realizing a high spherical property and low hardness and covering a Cu ball with a metal layer for suppressing discoloration - Google Patents

Abstract

An object of the present invention is to provide a Cu core ball capable of realizing a high spherical property and low hardness and covering a Cu ball with a metal layer for suppressing discoloration. To solve the problem, the Cu core ball 11A of the present invention includes: a Cu ball 1; and a solder layer 3 covering the surface of the Cu ball 1, wherein the Cu ball 1 is provided with at least one of Fe, Ag and Ni in a total amount of 5.0 mass ppm or more and 50.0 mass ppm or less, S in an amount of 0 mass ppm or more and 1.0 mass ppm or less, P in an amount of 0 mass ppm or more and 3.0 mass ppm or less, and the balance being Cu and other impurity elements. The purity of the Cu ball 1 is 99.995% by mass or more and 99.9995% by mass or less, and the spherical property thereof is 0.95 or more. The solder layer includes Sn, Bi, or Sn and Bi.

Description

Cu core ball, solder joint, solder paste and foam solder

The invention relates to a Cu core ball covering a Cu ball with a metal layer, and a soldering joint, solder paste and foam solder using the Cu core ball.

In recent years, due to the development of small information equipment, the electronic components loaded have been rapidly miniaturized. For electronic components, in order to meet the requirements of miniaturization and to narrow the pitch of the corresponding connection terminals or the structure area, a ball grid array (hereinafter, referred to as "BGA") in which electrodes are provided on the back side is used.

For electronic parts using BGA, for example, there are semiconductor packages. For semiconductor packaging, the semiconductor wafer with electrodes is sealed with resin. Solder bumps are formed on the electrodes of the semiconductor wafer. The solder bumps are formed by bonding solder balls to the electrodes of the semiconductor wafer. A semiconductor package using BGA is mounted on a printed circuit board by bonding solder bumps heated and melted to conductive pads of the printed circuit board. Furthermore, in order to cope with the requirements of higher-density packaging, there are studies on 3-dimensional high-density packaging in which semiconductor packages are stacked in the height direction.

The high-density packaging of electronic parts sometimes causes soft errors that cause the memory contents to be rewritten due to alpha rays entering the memory cells of semiconductor integrated circuits (ICs). Therefore, in recent years, development of low alpha-ray welding materials and Cu balls for reducing the content of radioisotopes has been carried out. Patent Document 1 discloses a low α-ray Cu ball containing Pb and Bi and having a purity of 99.9% or more and 99.995% or less. Patent Document 2 discloses a Cu ball having a purity of 99.9% or more and 99.995% or less, a true sphericity of 0.95 or more, and a Vickers hardness of 20 HV or more and 60 HV or less.

However, if the crystal grains of the Cu balls are fine, the Vickers hardness becomes large, so the durability against external stress becomes low, and the drop impact resistance becomes poor. Therefore, Cu balls used for electronic component construction require a predetermined degree of flexibility, that is, a Vickers hardness below a predetermined value.

In order to manufacture soft Cu balls, the practice is to increase the purity of Cu. In this system, the impurity element acts as a crystal nucleus in the Cu ball, so if the impurity element is reduced, the crystal grains will grow greatly, and as a result, the Vickers hardness of the Cu ball will become small. However, if the purity of the Cu ball is increased, the true sphericity of the Cu ball will become lower.

When the true sphericity of the Cu ball is low, there is a possibility that the self-alignment when the Cu ball is mounted on the electrode may not be ensured. At the same time, when the semiconductor wafer is mounted, the height of the Cu ball becomes uneven. Causes poor bonding.

Patent Document 3 discloses a Cu ball in which the mass ratio of Cu exceeds 99.995%, the total mass ratio of P and S is 3 ppm or more and 30 ppm or less, and has an appropriate true sphericity and Vickers hardness.

In addition, the semiconductor package for high-density three-dimensional packaging is a BGA. When the solder balls are loaded on the electrodes of the semiconductor wafer for reflow processing, the solder balls may be crushed by the weight of the semiconductor package. If such a situation occurs, it may be considered that the solder will overflow from the electrodes, connecting the electrodes and causing a short circuit.

In order to prevent such a short circuit accident, it has been proposed to use solder that will not be crushed by its own weight or that will not deform when the solder melts. Specifically, it is proposed to use a molded ball of metal or the like as a core, and the core material covered with solder as a solder bump. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 5435182 [Patent Document 2] Japanese Patent No. 5585571 [Patent Document 3] Japanese Patent No. 6256616

[Problems to be solved by the invention]

However, Cu balls containing a certain amount or more of S have a problem that they form sulfides or sulfur oxides when heated and are easily discolored. The discoloration of the Cu ball will cause the deterioration of the wettability, and the deterioration of the wettability will lead to the deterioration of non-wetting or self-alignment. In this way, the Cu balls that are easily discolored are not suitable for being covered with a metal layer because the adhesion between the surface of the Cu balls and the metal layer decreases or the oxidation or reactivity of the surface of the metal layer becomes high. On the other hand, when the true sphericity of the Cu ball is low, the true sphericity of the Cu core ball covered with the metal layer also becomes low.

Therefore, an object of the present invention is to provide a Cu core ball that can realize a high degree of sphericity and a low hardness, and use a Cu ball that suppresses discoloration, and a solder joint, a solder paste, and a foam solder using the Cu core ball. [Means for solving problems]

The invention is as follows. (1) A Cu core ball comprising: a Cu ball; and a solder layer covering the surface of the Cu ball, the Cu ball being at least one of Fe, Ag, and Ni, the total content of which is 5.0 mass ppm or more and 50.0 mass ppm or less, The content of S is 0 mass ppm or more and 1.0 mass ppm or less, the content of P is 0 mass ppm or more and less than 3.0 mass ppm, the balance is Cu and other impurity elements, and the purity of Cu balls is 99.995 mass% or more and 99.9995 Mass% or less, sphericity is 0.95 or more, and contains Sn, Bi, or Sn and Bi. (2) The Cu core ball as described in (1) above, in which the solder layer is composed of (Sn-Bi) based solder alloy containing Sn and Bi, and the concentration ratio (%) of Bi contained in the solder layer is determined by the concentration Ratio (%) = (measured value (mass %) / target content (mass %)) × 100, or concentration ratio (%) = (average value of measured value (mass %) / target content (mass %)) × 100 When expressed, the concentration ratio is in the range of 88.7 to 110.7%. (3) The Cu core ball as described in (1) above, in which the solder layer is composed of (Sn-58Bi)-based solder alloy containing Sn and Bi, and the concentration ratio (%) of Bi contained in the solder layer is calculated as the concentration ratio (%)=(measured value (mass%)/target content (mass%))×100, or concentration ratio (%)=(average value of measured value (mass%)/target content (mass%))×100 means , The concentration ratio is in the range of 90.3~108.6%. (4) The Cu core ball as described in (1) above, in which the solder layer is composed of (Sn-40Bi) solder alloy containing Sn and Bi, and the concentration ratio (%) of Bi contained in the solder layer is based on the concentration ratio (%)=(measured value (mass%)/target content (mass%))×100, or concentration ratio (%)=(average value of measured value (mass%)/target content (mass%))×100 means , The concentration ratio is in the range of 96.0~102.8%. (5) The Cu core ball as described in (1) above, wherein the solder layer is composed of a (Sn-3Bi)-based solder alloy containing Sn and Bi, and the concentration ratio (%) of Bi contained in the solder layer is calculated as the concentration ratio (%)=(measured value (mass%)/target content (mass%))×100, or concentration ratio (%)=(average value of measured value (mass%)/target content (mass%))×100 means , The concentration ratio is in the range of 88.7~110.7%. (6) The Cu core ball according to any one of (1) to (5) above, wherein the true sphericity is 0.98 or more. (7) The Cu core ball according to any one of (1) to (5) above, wherein the true sphericity is 0.99 or more. (8) The Cu core ball according to any one of (1) to (5) above, wherein the amount of α rays is 0.0200 cph/cm ² or less. (9) The Cu core ball according to any one of (1) to (5) above, wherein the amount of α rays is 0.0010 cph/cm ² or less. (10) The Cu core ball as described in (6) above, wherein the amount of α rays is 0.0200 cph/cm ² or less. (11) The Cu core ball according to any one of (1) to (5) above, which has a metal layer covering the surface of the Cu ball, the surface of the metal layer is covered with a solder layer, and the true sphericity is 0.95 or more. (12) The Cu core ball as described in (11) above, wherein the true sphericity is 0.98 or more. (13) The Cu core ball as described in (11) above, wherein the true sphericity is 0.99 or more. (14) The Cu core ball as described in (11) above, wherein the amount of α rays is 0.0200 cph/cm ² or less. (15) The Cu core ball as described in (11) above, wherein the amount of α rays is 0.0010 cph/cm ² or less. (16) The Cu core ball according to any one of (1) to (5) above, wherein the diameter of the Cu ball is 1 μm or more and 1000 μm or less. (17) The Cu core ball as described in (11) above, wherein the diameter of the Cu ball is 1 μm or more and 1000 μm or less. (18) A welding head using the Cu core ball of any one of (1) to (17) above. (19) A solder paste using the Cu core ball of any one of (1) to (17) above. (20) A foam solder using the Cu core ball of any one of (1) to (17) above. [Effect of invention]

According to the present invention, it is possible to achieve high true sphericity and low hardness of Cu balls, and to suppress discoloration of Cu balls. By realizing the high sphericity of the Cu sphere, the high sphericity of the Cu core sphere covered with the metal layer can be achieved, and the self-alignment when the Cu core sphere is mounted on the electrode can be ensured, and at the same time Suppress the height error of Cu core ball. In addition, by achieving the low hardness of the Cu ball, the drop impact resistance of the Cu core ball covered with the metal layer by the metal layer can be improved. In addition, since the discoloration of the Cu ball is suppressed, the adverse effect of the sulfide or sulfur oxide on the Cu ball can be suppressed, and it is suitable for covering with a metal layer and has good wettability.

The present invention will be described in detail below. In this specification, the composition unit (ppm, ppb, and %) of the metal layer of the Cu core ball indicates the ratio to the mass of the metal layer (mass ppm, mass ppb, and mass %) unless otherwise specified. In addition, the units (ppm, ppb, and %) of the composition of the Cu balls indicate the ratio to the mass of the Cu balls (mass ppm, mass ppb, and mass %) unless otherwise specified.

FIG. 1 shows an example of the configuration of the Cu core ball 11A according to the first embodiment of the present invention. As shown in FIG. 1, the Cu core ball 11A according to the first embodiment of the present invention includes: a Cu ball 1; and a solder layer 3 covering the surface of the Cu ball 1.

FIG. 2 shows an example of the configuration of the Cu core ball 11B according to the second embodiment of the present invention. As shown in FIG. 2, the Cu core ball 11B according to the second embodiment of the present invention includes: a Cu ball 1; a layer consisting of one or more elements selected from Ni, Co, Fe, and Pd covering the surface of the Cu ball 1 The above metal layer 2; and the solder layer 3 covering the surface of the metal layer 2.

FIG. 3 shows an example of the configuration of the electronic component 60 that mounts the semiconductor wafer 10 on the printed circuit board 40 using the Cu core ball 11A or the Cu core ball 11B according to the embodiment of the present invention. As shown in FIG. 3, the Cu core ball 11A or the Cu core ball 11B is coated on the electrode 100 of the semiconductor wafer 10 by applying flux to wet and expand the molten solder layer 3, and is mounted on the electrode 100 of the semiconductor wafer 10. In this example, the configuration of the Cu core ball 11A or the Cu core ball 11B mounted on the electrode 100 of the semiconductor wafer 10 is referred to as the solder bump 30. The solder bumps 30 of the semiconductor wafer 10 are bonded to the electrodes 41 of the printed board 40 via the molten solder layer 3 or the solder melted with the solder paste applied to the electrodes 41. In this example, the structure in which the solder bump 30 is mounted on the electrode 41 of the printed board 40 is referred to as a solder joint 50.

The total of at least one content of Cu core balls 11A, 11B, Cu balls 1, Fe, Ag, and Ni in each embodiment is 5.0 mass ppm or more and 50.0 mass ppm or less, and the S content is 0 mass ppm or more and 1.0 mass ppm or less, the content of P is 0 mass ppm or more and less than 3.0 mass ppm, the balance is Cu and other impurity elements, and the purity of the Cu ball 1 is 4N5 (99.995 mass%) or more and 5N5 (99.9995 mass%) or less, The true sphericity is above 0.95.

Regarding the Cu core ball 11A according to the first embodiment of the present invention, by increasing the true sphericity of the Cu ball 1 covered with the solder layer 3, the true sphericity of the Cu core ball 11A can be improved. In addition, with regard to the Cu core ball 11B of the second embodiment of the present invention, by increasing the true sphericity of the Cu ball 1 covered with the metal layer 2 and the solder layer 3, the true sphericity of the Cu core ball 11B can be improved. Hereinafter, a preferred aspect of the Cu ball 1 constituting the Cu core balls 11A and 11B will be described.

. Cu sphericity: 0.95 or more In the present invention, the true degree of sphericity means the deviation from the true sphere. The true sphericity is the arithmetic average calculated when the diameters of 500 Cu balls are divided by the quotient of the long diameter. The closer the value is to the upper limit of 1.00, the closer to the true ball. The true sphericity can be obtained by various methods such as the least square center method (LSC method), the minimum zone center method (MZC method), the maximum inscribed center method (MIC method), and the minimum circumscribed center method (MCC method). Get. The length of the major axis and the length of the diameter of the present invention are measured by the ULTRA Quick Vision, ULTRA QV350-PRO measuring device manufactured by Mitutoyo Corporation.

From the viewpoint of maintaining an appropriate space between the substrates, the Cu ball 1 has a true sphericity of 0.95 or more, a true sphericity of 0.98 or more, and more preferably 0.99 or more. When the true sphericity of the Cu ball 1 is less than 0.95, the Cu ball 1 becomes indefinite, and bumps of uneven height are formed when the bumps are formed, thereby increasing the possibility of occurrence of joint failure. If the true sphericity is 0.95 or more, since the Cu ball 1 does not melt at the welding temperature, the height error at the welding head 50 can be suppressed. With this, it is possible to surely prevent the joint failure of the semiconductor wafer 10 and the printed board 40.

. Purity of Cu balls: 99.995 mass% or more and 99.9995 mass% or less In general, Cu with low purity has a higher degree of sphericity because it is more capable of securing an impurity element that can become the nucleus of the Cu sphere 1 in Cu than Cu with higher purity. On the other hand, the Cu ball 1 with low purity deteriorates the electrical conductivity and thermal conductivity.

Therefore, if the purity of the Cu sphere 1 is 99.995 mass% (4N5) or more and 99.9995 mass% (5N5) or less, sufficient sphericity can be ensured. In addition, if the purity of the Cu ball 1 is 4N5 or more and 5N5 or less, in addition to sufficiently reducing the amount of α rays, the deterioration of the electrical conductivity and thermal conductivity of the Cu ball 1 due to the decrease in purity can be suppressed.

When manufacturing the Cu ball 1, a Cu material, which is an example of a small piece of metal material formed in a predetermined shape, is melted by heating, and the molten Cu becomes spherical due to surface tension, and this rapid condensation solidifies the Cu ball 1. In the process of solidification of molten Cu from a liquid state, crystal grains will grow in spherical molten Cu. At this time, if there are many impurity elements, the impurity elements will become crystal nuclei and suppress the growth of crystal grains. Therefore, the spherical molten Cu becomes Cu balls 1 with high sphericity due to the fine crystal grains whose growth is suppressed. On the other hand, when there are few impurity elements, there are relatively few crystal nuclei, and the growth of crystal grains cannot be suppressed and the growth is directional. As a result, a part of the surface of the spherical molten Cu will protrude and solidify, reducing the true sphericity. As the impurity element, Fe, Ag, Ni, P, S, Sb, Bi, Zn, A1, As, Cd, Pb, In, Sn, Au, U, Th, etc. may be considered.

The following describes the content of impurities that determine the purity and true sphericity of Cu balls 1.

. Total content of at least one of Fe, Ag, and Ni: 5.0 mass ppm or more and 50.0 mass ppm or less Among the impurity elements contained in the Cu ball 1, the total content of at least one of Fe, Ag, and Ni is preferably 5.0 mass ppm or more and 50.0 mass ppm or less. That is, when any one of Fe, Ag and Ni is contained, the content of one kind is preferably 5.0 mass ppm or more and 50.0 mass ppm or less, and when two or more kinds of Fe, Ag and Ni are contained, two or more kinds The total content of is preferably 5.0 mass ppm or more and 50.0 mass ppm or less. Fe, Ag, and Ni become crystal nuclei during melting in the manufacturing process of the Cu ball 1, and therefore a certain amount of Fe, Ag, or Ni is contained in Cu, so that the Cu ball 1 with high sphericity can be manufactured. Therefore, at least one of Fe, Ag, and Ni is an important element for estimating the content of impurity elements. In addition, by setting the total content of at least one of Fe, Ag, and Ni to 5.0 mass ppm or more and 50.0 mass ppm or less, in addition to suppressing the discoloration of the Cu ball 1, even if the Cu ball 1 is not slowly heated The slow Vickers hardness can also be achieved by slowly cooling the Cu balls 1 in the annealing step of crystallization.

. The content of S is 0 mass ppm or more and 1.0 mass ppm or less The Cu balls 1 containing a certain amount of S or more form sulfides or sulfur oxides when heated and are easily discolored, and the wettability decreases. Therefore, the content of S needs to be 0 mass ppm or more and 1.0 mass ppm or less. The more Cu balls 1 forming sulfide and sulfur oxides, the brighter the surface of the Cu balls becomes darker. Therefore, as will be described in detail later, as long as the result of measuring the brightness of the surface of the Cu ball is below a predetermined value, it can be judged that the formation of sulfides and sulfur oxides is suppressed and the wettability is good.

. The content of P is 0 mass ppm or more and less than 3.0 mass ppm P can become phosphoric acid or Cu complex, which may adversely affect the Cu ball 1 in some cases. In addition, since the Cu ball 1 containing a certain amount of P has a higher hardness, the content of P is preferably 0 mass ppm or more and less than 3.0 mass ppm, and more preferably less than 1.0 mass ppm.

. Other impurity elements The content of impurity elements such as Sb, Bi, Zn, A1, As, Cd, Pb, In, Sn, Au, etc. (hereinafter, referred to as "other impurity elements") other than the impurity elements contained in the Cu ball 1, respectively It is preferably 0 mass ppm or more and less than 50.0 mass ppm.

In addition, the Cu ball 1 contains at least one of Fe, Ag, and Ni as an essential element as described above. However, since the Cu ball 1 cannot prevent elements other than Fe, Ag, and Ni from being mixed in with the current technology, it substantially contains other impurity elements other than Fe, Ag, and Ni. However, when the content of other impurity elements is less than 1 mass ppm, it is not easy to show the effect or influence of adding each element. In addition, when analyzing the elements contained in the Cu ball, when the content of the impurity element is less than 1 mass ppm, this value is below the sensing limit of the analyzer. Therefore, when the total content of at least one of Fe, Ag, and Ni is 50 mass ppm, and the content of other impurity elements is less than 1 ppm, the purity of the Cu ball 1 is substantially 4N5 (99.995 mass %). In addition, when the total content of at least one of Fe, Ag, and Ni is 5 mass ppm, and the content of other impurity elements is less than 1 ppm, the purity of the Cu ball 1 is substantially 5N5 (99.9995 mass %).

. Vickers hardness of Cu ball: 55.5HV or less The Vickers hardness of the Cu ball 1 is preferably 55.5 HV or less. When the Vickers hardness is large, the durability against external stress becomes low, the drop impact resistance becomes poor, and cracks easily occur. In addition, when an auxiliary force such as pressurization is applied to the three-dimensionally structured bumps or when forming the joint, if a hard Cu ball is used, there is a possibility that the electrode crushes or the like. In addition, when the Vickers hardness of the Cu ball 1 is large, the crystal grains become smaller than a certain range or more, which may cause deterioration in conductivity. When the Vickers hardness of the Cu ball 1 is 55.5 HV or less, the drop impact resistance is good, cracking can be suppressed, electrode crushing, etc. can be suppressed, and further deterioration of conductivity can be suppressed. In this embodiment, the lower limit of the Vickers hardness may exceed 0 HV, preferably 20 HV or more.

. The amount of α ray of Cu ball: 0.0200cph/cm ² or less In order to make the amount of α ray in the high-density structure of electronic parts not to cause soft errors to the extent, the α ray of Cu ball 1 is 0.0200cph/cm ² or less good. α-ray dose from the package as further suppress soft errors in view of a high density, it is preferably 0.0100cph / cm ² or less, more preferably is 0.0050cph / cm ² or less, more preferably is 0.0020cph / cm ² Below, the best is 0.0010cph/cm ² or less. In order to suppress soft errors caused by α rays, the content of radioisotopes such as U and Th is preferably less than 5 mass ppb.

. Discoloration resistance: Brightness above 55 The Cu ball 1 preferably has a brightness of 55 or more. The L* value of the so-called lightness system L*a*b color system. Since the brightness of the Cu balls 1 in which sulfides or sulfur oxides derived from S are formed on the surface becomes low, if the brightness is 55 or more, it can be said that the sulfides and sulfur oxides are suppressed. In addition, Cu balls 1 having a brightness of 55 or more have good wettability during assembly. On the other hand, when the brightness of the Cu ball 1 is less than 55, it can be said that the Cu ball 1 does not sufficiently suppress the formation of sulfides and sulfur oxides. Sulfide or sulfur oxides, in addition to adversely affecting the Cu balls 1, deteriorate the wettability when the Cu balls 1 are directly bonded to the electrodes. When the wettability deteriorates, non-wetting or deterioration of self-alignment occurs.

. The diameter of Cu balls: 1 μm or more and 1000 μm or less The diameter of the Cu ball 1 is preferably 1 μm or more and 1000 μm or less, and more preferably 50 μm or more and 300 μm. Within this range, the spherical Cu balls 1 can be stably manufactured, and the connection short circuit can be suppressed when the terminals have a narrow pitch. Here, for example, when the Cu ball 1 is used as a paste, the “Cu ball” may also be referred to as “Cu powder”. When "Cu ball" is used for "Cu powder", the diameter of the Cu ball is generally 1 to 300 μm.

Next, the solder layer 3 covering the Cu ball 1 in the Cu core ball 11A of the first embodiment of the present invention and the solder layer 3 covering the metal layer 2 in the Cu core ball 11B of the second embodiment will be described.

. Solder layer The Cu core balls 11A and 11B of the various embodiments of the present invention are the solder layer 3 of a solder alloy composed of Sn and inevitable impurities; the solder layer 3 of a solder alloy composed of Bi and inevitable impurities; or containing Sn and Bi The solder layer 3 of the solder alloy as an essential element covers the Cu ball 1. In particular, regarding the Cu core balls 11A and 11B of each embodiment of the present invention, a Cu core ball with uniform distribution of Bi in the solder layer 3 of a solder alloy containing Sn and Bi as essential elements and a solder joint using the same, Solder paste and foam solder.

The composition of the solder layer 3 in the embodiment of the present invention is composed of (Sn-Bi) alloy containing Sn and Bi. The content of Sn is preferably 40.0% by mass or more for the entire alloy. Regarding the content of Bi, as long as the amount of Bi for the entire alloy is in the range of 0.1 to 99.8% by mass, the concentration ratio of Bi can be controlled within a predetermined range of 88.7 to 110.7%, and the Bi distribution in the solder layer 3 can be made uniform.

For example, when the target value of Bi content is 58.0% by mass, the allowable range of Bi content and concentration ratio is 52.39% by mass (concentration ratio 90.3%) to 62.97% by mass (concentration ratio 108.6%), and the concentration ratio of Bi can be controlled Within a predetermined range of 88.7 to 110.7%, the Bi distribution in the solder layer 3 can be made uniform. The solder alloy whose target value of Bi content is 58.0% by mass is called (Sn-58Bi) solder alloy.

In addition, when the target value of Bi content is 40.0 mass%, the allowable range of Bi content and concentration ratio is 38.41 mass% (concentration ratio 96.0%) to 41.11 mass% (concentration ratio 102.8%), and the concentration ratio of Bi can be controlled The control within the predetermined range of 88.7 to 110.7% can make the Bi distribution in the solder layer 3 uniform. The solder alloy whose target value of Bi content is 40.0% by mass is called (Sn-40Bi) solder alloy.

Furthermore, when the target value of Bi content is 3.0% by mass, the allowable range of Bi content and concentration ratio is 2.66% by mass (concentration ratio 88.7%) to 3.32% by mass (concentration ratio 110.7%). Controlled within the predetermined range of 88.7~110.7%, the Bi distribution in the solder layer 3 can be made uniform. A solder alloy whose target value of Bi content is 3.0% by mass is called (Sn-3Bi) solder alloy.

In addition, the allowable range refers to a range in which soldering such as bump formation can be performed without problems as long as it is within this range. In addition, the concentration ratio (%) refers to the ratio (%) of the measured value (mass %) to the target content (mass %), or the average value of the measured value (mass %) to the target content (mass %). That is, the concentration ratio (%) can be calculated as the concentration ratio (%) = (measured value (mass %)/target content (mass %)) × 100 or the concentration ratio (%) = (average value of measured values (mass %)/Target content (mass %))×100.

In addition, in the binary solder layer 3 composed of Sn and Bi, even if other additive elements are added, the concentration ratio of Bi can be controlled within a predetermined range of 88.7 to 110.7%.

As the additive element, one, two or more of Ag, Cu, Ni, Ge, Ga, In, Zn, Fe, Pb, Sb, Au, Pd, Co, etc. may be used.

As described above, the content of Bi in the solder layer 3 is preferably within the range of 52.39 mass% (density ratio 90.3%) to 62.97 mass% (density ratio 108.6%) to the target value of 58 mass%. In addition, the Bi content in the solder layer 3 is 40% by mass of the target value, and the allowable range is preferably 38.41% by mass (density ratio 96.0%) to 41.11% by mass (density ratio 102.8%). Furthermore, the Bi content in the solder layer 3 is 3% by mass of the target value, and the allowable range is preferably about 2.66% by mass (concentration ratio 88.7%) to 3.32% by mass (concentration ratio 110.7%).

Although the thickness of the solder layer 3 varies depending on the particle size of the Cu balls 1, in order to ensure a sufficient solder bonding amount, it is preferable that the single side in the radial direction is 100 μm or less. The solder layer 3 can be formed by conventional electroplating or electroless plating. However, when the solder layer is formed by molten plating, the particle size of the Cu ball becomes smaller, the film thickness of the solder layer cannot be uniform, and the Cu ball is in the Cu core ball The center eccentricity, or the unevenness of the surface of the solder layer becomes larger, and the true sphericity of the Cu core ball decreases. Therefore, the solder layer 3 is formed by electroplating.

As the plating solution, a mixed solution of organic acid, Sn compound, Bi(III) compound and surfactant can be used. Sn compounds include tin salts of organic sulfonic acids such as methanesulfonic acid, ethylsulfonic acid, 2-propanolsulfonic acid, and p-phenolsulfonic acid, tin sulfate, tin oxide, tin nitrate, tin chloride, olfactory Tin oxide, tin iodide, tin phosphate, tin pyrophosphate, tin acetate, tin formate, tin citrate, tin gluconate, tin tartrate, tin lactate, tin succinate, sulfanilic acid, tin borofluoride, silicon fluoride Sub-Sn compounds such as tin. Bi(III) compounds include, for example, Bi fluoride, Bi chloride, Bi olfactory, Bi iodide, Bi citrate, Bi methanesulfonate, Bi nitrate, Bi sulfide, Bi oxide, Bi hydroxide, Phosphate Bi. These compounds may be used alone or in combination of two or more.

When forming a solder plating layer composed of Sn-Bi solder alloy composed of Sn and Bi by electroplating, since Bi will be taken into the plating layer preferentially over Sn, there is a problem that the concentration of Bi in the plating solution is inconsistent with the amount of Bi in the solder plating layer. However, a solder alloy plating layer with a uniform Bi concentration distribution cannot be formed. Therefore, under the conditions shown in FIG. 4, a predetermined DC voltage is applied between the anode electrode and the cathode electrode, and the Cu ball is shaken to uniformly adjust the Bi concentration in the liquid to perform the plating process.

The generation process of the solder layer 3 regarding the plating process will be described in more detail with reference to FIG. 4. Fig. 4 shows the relationship between the Bi concentration (curve Lb) in the plating solution using the (Sn-58Bi) solder alloy plating process and the Bi concentration (curve La) in the solder layer 3, taking the Cu core ball diameter as a reference Time characteristic curve.

In this example, a particle size of 215 μm is used as the initial value of Cu balls. The thickness of the solder layer is monitored one by one, and the thickness of the solder layer is sequentially increased by Cu core balls with predetermined values, and each time a sample is collected. After the collected sample was washed and dried, the particle size was measured.

The particle size of the Cu core ball at the timing of measurement was measured in sequence, and the Bi content of the solder layer at the target value was obtained, and the result of curve La as shown in FIG. 4 was obtained. Even if the solder layer is only sequentially increased by a predetermined thickness, the Bi content at this time can be found to be approximately the same value as the previous content. In the case of curve La, the content of Bi is approximately 58 to 60% by mass. Therefore, it can be understood from the curve La in FIG. 4 that the concentration distribution of Bi is homogeneous (equal) to the plating thickness without a concentration gradient.

5 and 6 are enlarged cross-sectional views of the Cu core ball. FIG. 5 shows a Cu core ball 11B that covers the Cu ball 1 with the metal layer 2 and covers the metal layer 2 with the solder layer 3. In addition, Figure 6 was shot using FE-EPMA. From FIG. 5 and FIG. 6 which further enlarges this, it can be seen that the solder layer 3 is a process in which Sn and Bi are homogeneously mixed and grown.

From the viewpoint that the concentration of Bi in the solder layer is maintained in substantially the same state even if the thickness of the solder layer grows, it can be seen that the Bi in the solder layer grows in a substantially uniformly distributed state. In a state where the Bi concentration in the plating solution is homogenized, the Bi concentration is kept within a desired value, and the plating process is performed. In this example, the Bi content in the solder layer is 58% by mass as the target value, so the Bi concentration in the plating solution is controlled to reach the target value.

In order to bring the Bi concentration distribution in the solder layer into the desired value, the voltage is controlled. The current is plated. With such a plating process, the Bi distribution in the solder layer can be maintained at a desired value.

In addition, the Bi concentration in the solder layer represented by the curve La in FIG. 4 does not match the Bi concentration in the plating solution represented by the curve Lb. Bi in the plating solution is preferentially taken into the layer over Sn in the plating solution.

The Cu core balls 11A and 11B can also be formed of low α-ray Cu core balls 11A and 11B by using a solder alloy with a low α-ray amount in the solder layer 3.

Next, the Cu core ball 11B according to the second embodiment of the present invention will be described with respect to the metal layer 2 covering the Cu ball 1.

. Metal layer The metal layer 2 is composed of, for example, a Ni plating layer, a Co plating layer, an Fe plating layer, a Pd plating layer, or a plating layer (single layer or plural layers) containing two or more elements of Ni, Co, Fe, and Pd. When the Cu core ball 11B is used as a solder bump, the metal layer 2 does not melt and remains at the soldering temperature, but contributes to the height of the solder joint. Therefore, it is configured to have a high sphericity and a small diameter error. In addition, from the viewpoint of suppressing soft errors, it is configured to have a low α-ray dose.

. Composition and thickness of metal layer When the composition of the metal layer 2 is composed of a single Ni, Co, Fe, or Pd, in addition to inevitable impurities, Ni, Co, Fe, and Pd are 100%. In addition, the metal used for the metal layer 2 is not limited to a single metal, and an alloy of two or more elements in combination of Ni, Co, Fe, or Pd may also be used. Furthermore, the metal layer 2 may also be a layer consisting of a single layer of Ni, Co, Fe, or Pd, and a layer of an alloy composed of two or more elements in combination of Ni, Co, Fe, or Pd, and a suitable composition. constitute. The film thickness T2 of the metal layer 2 is, for example, 1 μm to 20 μm.

. The amount of α rays of the Cu core ball: 0.0200 cph/cm ² or less The amount of α rays of the Cu core ball 11A of the first embodiment and the Cu core ball 11B of the second embodiment is preferably 0.0200 cph/cm ² or less . This is the amount of alpha rays to the extent that high-density packaging of electronic parts does not make soft errors a problem. The α-ray amount of the Cu core ball 11A according to the first embodiment of the present invention can be achieved by the α-ray amount of the solder layer 3 constituting the Cu core ball 11A being 0.0200 cph/cm ² or less. Therefore, the Cu core ball 11A according to the first embodiment of the present invention is covered with such a solder layer 3, and therefore shows a low amount of α rays. The α-ray amount of the Cu core ball 11B according to the second embodiment of the present invention can be achieved by the α-ray amount of the metal layer 2 and the solder layer 3 constituting the Cu core ball 11B being 0.0200 cph/cm ² or less. Therefore, the Cu core ball 11B according to the second embodiment of the present invention is covered with such a metal layer 2 and a solder layer 3, and therefore shows a low amount of α rays. α-ray dose, suppressing the package as a soft error in the viewpoint of a higher density, is preferably 0.0100cph / cm ² or less, more preferably is 0.0050cph / cm ² or less, more preferably is 0.0020cph / cm ² Below, the best is 0.0010cph/cm ² or less. In order to make the amount of α rays of the Cu ball 1 to be 0.0200 cph/cm ² or less, the U and Th contents of the metal layer 2 and the solder layer 3 are respectively 5 ppb or less. In addition, from the viewpoint of suppressing soft errors in the present or future high-density packaging, the contents of U and Th are preferably 2 ppb or less, respectively.

. Cu core ball's true sphericity: 0.95 or more The Cu core ball 11A of the first embodiment of the present invention covering the Cu ball 1 with the solder layer 3 and the Cu core ball 11B of the second embodiment of the present invention covering the Cu ball 1 with the metal layer 2 and the solder layer 3 The true sphericity is preferably 0.95 or more, the true sphericity is more preferably 0.98 or more, and further preferably 0.99 or more. If the true sphericity of Cu core balls 11A and 11B is less than 0.95, the Cu core balls 11A and 11B will become indefinite in shape. When the Cu core balls 11A and 11B are placed on the electrodes for reflow, the Cu core balls 11A , 11B's position shift, and self-alignment will also deteriorate. When the Cu core balls 11A and 11B have a true sphericity of 0.95 or more, the self-alignment when the Cu core balls 11A and 11B are mounted on the electrode 100 of the semiconductor wafer 10 or the like can be ensured. Then, by setting the Cu sphere 1 to a true sphericity of 0.95 or more, the Cu spheres 11A and 11B do not melt the Cu sphere 1 and the metal layer 2 at the welding temperature, so that the height error of the welding head 50 can be suppressed. With this, it is possible to surely prevent the joint failure of the semiconductor wafer 10 and the printed board 40.

. The barrier function of the metal layer When reflowing, the Cu of the Cu ball diffuses into the solder (paste) used to join the Cu core ball and the electrode, and a large amount of hard and brittle Cu ₆ Sn is formed in the solder layer and the connection interface _5. The intermetallic compound of Cu ₃ Sn, when it is impacted, the crack will become serious, and there is a possibility of damage to the connection part. Therefore, in order to obtain sufficient connection strength, it is preferable to suppress (block) the diffusion of Cu from the Cu ball to the solder. Therefore, in the Cu core ball 11B of the second embodiment, since the metal layer 2 functioning as a barrier layer is formed on the surface of the Cu ball 1, it is possible to suppress the Cu of the Cu ball 1 from diffusing into the solder paste.

. Solder paste, foam solder, solder joint In addition, the solder paste may be constituted by including Cu core balls 11A or Cu core balls 11B in the solder. By dispersing the Cu core ball 11A or the Cu core ball 11B in the solder, a foam solder can be constituted. The Cu core ball 11A or the Cu core ball 11B can also be used to form a welded joint between bonding electrodes.

. Cu ball manufacturing method Next, an example of a method of manufacturing Cu balls 1 will be described. As an example of a metal material, Cu material is placed on a heat-resistant plate such as ceramic (hereinafter referred to as "heat-resistant plate"), and heated together with the heat-resistant plate in a furnace. The heat-resistant plate is provided with a plurality of circular grooves whose bottoms are hemispherical. The diameter and depth of the groove can be appropriately set according to the particle diameter of the Cu ball 1, for example, the diameter is 0.8 mm and the depth is 0.88 mm. In addition, small pieces of Cu material obtained by cutting Cu thin wires are put into the grooves of the heat-resistant plate one by one. A heat-resistant plate of Cu material was put into the trench, and the temperature was raised to 1100 to 1300°C in a furnace filled with ammonia decomposition gas, and heat treatment was performed for 30 to 60 minutes. At this time, if the temperature in the furnace is above the melting point of Cu, the Cu material will melt into a spherical shape. After that, it is cooled in the furnace, and is formed by rapidly cooling the Cu balls 1 in the grooves of the heat-resistant plate.

In addition, as another method, there is a spray method in which molten Cu is dropped through a small hole provided at the bottom of the crucible, and the droplet is quenched to room temperature (for example, 25° C.) to pelletize the Cu ball 1, or the Cu is cut with a thermal plasma. A method of making balls by heating metal to above 1000°C.

In the manufacturing method of the Cu ball 1, before the Cu ball 1 is pelletized, the Cu material of the raw material of the Cu ball 1 may be heat-treated at 800 to 1000°C.

As the Cu material that is the raw material of the Cu ball 1, for example, a block material, a wire material, a plate material, or the like can be used. The purity of the Cu material may be more than 4N5 and 6N or less from the viewpoint of not excessively reducing the purity of the Cu ball 1.

When using a high-purity Cu material in this way, the holding temperature of molten Cu may be reduced to about 1000° C. as before, without performing the above-mentioned heat treatment. In this way, the above heat treatment can be appropriately omitted or changed according to the purity of the Cu material and the amount of α rays. In addition, when a Cu ball 1 having a high α-ray amount or a shaped Cu ball 1 is manufactured, these Cu balls 1 may be reused as a raw material to reduce the α-ray amount.

As a method of forming the solder layer 3 on the Cu ball 1, the above-mentioned electroplating method or electroless plating method can be used.

As a method of forming the metal layer 2 on the Cu ball 1, a conventional plating method or the like can be used. For example, when forming the Ni plating layer, adjust the Ni plating solution using a Ni metal block or a Ni metal salt for the Ni plating bath, and immerse the Cu ball 1 in the adjusted Ni plating solution by precipitation on the surface of the Cu ball 1 Ni plating is formed. In addition, as another method of forming the metal layer 2 such as a Ni plating layer, a conventional electroless plating method or the like can also be used. When the solder layer 3 of Sn alloy is formed on the surface of the metal layer 2, the above-mentioned electroplating method or electroless plating method can be used. [Example]

The following describes embodiments of the present invention, but the present invention should not be limited to these. The Cu spheres of Examples 1 to 20 and Comparative Examples 1 to 12 were prepared with the compositions shown in Tables 1 and 2 below, and the sphericity, Vickers hardness, α-ray amount, and discoloration resistance of the Cu spheres were measured.

In addition, the Cu balls of the above Examples 1 to 20 were covered with the solder layers of the solder alloys of Composition Examples 1 to 3 shown in Table 3 to prepare the Cu core balls of Examples 1A to 20A, and the true sphericity of the Cu core balls was measured . Furthermore, the Cu spheres of the above Examples 1-20 were covered with the metal layer and the solder layer of the solder alloy of the composition examples 1-3 shown in Table 4 to prepare the Cu core balls of Examples 1B-20B, and the Cu core balls were measured True sphericity.

In addition, the Cu balls of Comparative Examples 1 to 12 above were covered with the solder layers of the solder alloys of Composition Examples 1 to 3 shown in Table 5 to prepare Cu core balls of Comparative Examples 1A to 12A, and the true sphericity of the Cu core balls was measured . In addition, the Cu balls of Comparative Examples 1 to 12 were covered with a metal layer and the solder layers of the solder alloys of Composition Examples 1 to 3 shown in Table 6 to prepare Cu core balls of Comparative Examples 1B to 12B, and the Cu core balls were measured. True sphericity.

In the following table, there is no unit number, which means mass ppm or mass ppb. Specifically, the numerical values in the table indicating the content ratios of Fe, Ag, Ni, P, S, Sb, Bi, Zn, Al, As, Cd, Pb, In, Sn, and Au represent mass ppm. ">1" means that the content ratio of the impurity element to the Cu ball is less than 1 mass ppm. In addition, the values in the table showing the content ratio of U and Th represent the mass ppb. ">5" means that the content ratio of the impurity element to the Cu ball is less than 5 mass ppb. "Total Impurity" means the total proportion of impurity elements contained in Cu balls.

. Production of Cu balls The production conditions of Cu balls were studied. As an example of a metal material, Cu material is prepared as a bulk material. The Cu materials with a purity of 6N were used as Examples 1 to 13, 20, and Comparative Examples 1 to 12, and the Cu materials with a purity of 5N were used as Examples 14 to 19. After putting each Cu material into the crucible, the temperature of the crucible was raised to 1200°C, heated for 45 minutes to melt the Cu material, the molten Cu was dripped from the hole provided at the bottom of the crucible, and the generated droplets were quickly cooled to room temperature (18 ℃) Pellets into Cu balls. With this, Cu spheres having an average particle diameter of the values shown in the following tables were produced. Elemental analysis, using inductively coupled plasma mass spectrometry (ICP-MS analysis) or glow discharge mass spectrometry (GD-MS analysis) enables high-precision analysis, but in this case ICP-MS analysis was used. The ball diameters of Cu balls were 250 μm in Examples 1 to 17, Example 19 to Example 20, and Comparative Examples 1 to 12. Example 18 is 180 μm.

. Cu core ball production For Examples 1A to 17A and Examples 19A to 20A, using the Cu balls of Examples 1 to 20 above, the solder alloys of Examples 1 to 3 were electroplated to form a solder layer with a thickness of 23 μm on one side to produce Example 1A. ~17A, Cu core balls of Examples 19A~20A. Regarding the Cu core balls of Example 18A, the solder alloys of Composition Examples 1 to 3 were formed into a solder layer with a thickness of 33 μm on one side by an electroplating method to produce Cu core balls of Example 18A.

In addition, regarding Examples 1B to 17B and Examples 19B to 20B, the Cu balls of the above Examples 1 to 20 were used to form a Ni plating layer with a thickness of 2 μm on one side as a metal layer, and further the solder alloys of Composition Examples 1 to 3 were used: A solder layer with a thickness of 23 μm on one side was formed by electroplating to produce Cu core balls of Examples 1B to 17B and Examples 19B to 20B. Regarding the Cu core ball of Example 18B, a Ni plating layer was formed as a metal layer with a thickness of 2 μm on one side, and further the solder alloy of Compositions 1 to 3 was formed by a plating method to form a solder layer with a thickness of 33 μm on one side to produce a Cu core of Example 18B ball.

Furthermore, using the Cu balls of Comparative Examples 1 to 12 above, the solder alloys of Composition Examples 1 to 3 were used to form a solder layer with a thickness of 23 μm on one side, to produce Cu core balls of Comparative Examples 1A to 12A. In addition, using the Cu balls of the above Comparative Examples 1 to 12, a Ni plating layer was formed as a metal layer with a thickness of 2 μm on one side, and the solder alloy of Composition Examples 1 to 3 was further formed into a solder layer with a thickness of 23 μm on one side. Production Example Comparative Example 1B ~12B Cu core ball.

Each evaluation method of the true sphericity of Cu balls and Cu core balls, the α-ray amount of Cu balls, Vickers hardness, and discoloration resistance will be described in detail below.

. True degree The true sphericity of Cu spheres and Cu core spheres is measured by CNC image measuring system. The device is ULTRA QUICK VISION, ULTRA QV350-PRO manufactured by MITSUTOYO.

[Evaluation criteria of true sphericity] In the following tables, the evaluation criteria for the sphericity of Cu balls and Cu core balls are as follows. ○○○: Sphericality is 0.99 or more ○○: Sphericality is 0.98 or more and less than 0.99 ○: The true sphericity is 0.95 or more and less than 0.98 ×: The true sphericity is less than 0.95

. Vickers hardness . The Vickers hardness of the Cu ball is measured in accordance with "Vickers hardness test-test method JIS Z2244". The device uses a micro Vickers hardness tester made by Akashi, AKASHI micro hardness tester MVK-F 1200l-Q.

[Vickers hardness evaluation criteria] In the following tables, the evaluation criteria of the Vickers hardness of Cu balls are as follows. ○: More than 0HV and less than 55.5HV ×: More than 55.5HV

. Alpha dose The method of measuring the α-ray amount of Cu balls is as follows. For the measurement of the amount of α rays, an α-ray measuring device of a ventilation ratio counter was used. The measurement sample is covered with Cu balls on a flat shallow bottom container of 300 mm×300 mm so that the bottom of the container cannot be seen. This measurement sample was placed in an α-ray measuring apparatus, and after being left under PR-10 ventilation for 24 hours, the amount of α-ray was measured.

[Evaluation Criteria of α-Ray Quantity] In the following tables, the evaluation criteria of the α-ray quantity of Cu balls are as follows. ○: The amount of α rays is 0.0200cph/cm ² or less ×: The amount of α rays exceeds 0.0200cph/cm ²

In addition, the PR-10 gas (90% argon-10% methane) used for measurement is filled with PR-10 gas for more than 3 weeks. The use of gas cylinders for more than 3 weeks is to comply with JEDEC STANDARD-Alpha Radiation Measurement prescribed by JEDEC (Joint Electron Device Engineering Council) in order to prevent radon in the atmosphere from entering the gas cylinder to generate alpha rays. in Electronic Materials JESD221.

. Discoloration resistance In order to measure the discoloration resistance of Cu balls, the Cu balls were heated in a constant temperature bath at 200° C. for 420 seconds in an atmospheric atmosphere, the change in lightness was measured, and it was evaluated whether the Cu balls were sufficiently resistant to changes with time. Brightness, using Konica Minolta CM-3500d spectrophotometer, D65 light source, 10˚ field of view, in accordance with JIS Z 8722 "Color measurement method-reflection and penetrating object color", to determine the spectral transmittance, Obtained from the color values (L*, a*, b*). Furthermore, (L*,a*,b*) is in accordance with JIS Z 8729 "Color Representation-L*a*b* Color System and L*u*v* Color System". L* is lightness, a* is redness, b* is yellowness.

[Evaluation criteria for discoloration resistance] In the following tables, the evaluation criteria for the discoloration resistance of Cu balls are as follows. ○: The brightness after 420 seconds is above 55 ×: The brightness after 420 seconds is less than 55.

. Overview In the above evaluation methods and evaluation criteria, Cu balls having all sphericity, Vickers hardness, α-ray amount, and discoloration resistance were ○, ○○, or ○○○, and the overall evaluation was ○. On the other hand, Cu balls with any of the true sphericity, Vickers hardness, α-ray amount, and discoloration resistance as × were evaluated as × in a comprehensive manner.

In addition, in the above evaluation method and evaluation criteria, Cu core balls with a true sphericity of ○, ○○, or ○○○, together with the evaluation of Cu balls, were evaluated as ○. On the other hand, a Cu core ball with a true sphericity of × is × in a comprehensive evaluation. In addition, even in the evaluation of the Cu core ball, the true sphericity is ○, ○○, or ○○○, and in the evaluation of the Cu ball, any one of the true sphericity, Vickers hardness, α-ray amount, and discoloration resistance is The × Cu core ball is × in the overall evaluation.

In addition, the Vickers hardness of the Cu core ball depends on the Ni plating layer which is an example of the solder layer and the metal layer, so the Vickers hardness of the Cu core ball is not evaluated. However, in the Cu core ball, as long as the Vickers hardness of the Cu ball is within the range specified by the present invention, even the Cu core ball has good drop impact resistance, cracks can be suppressed, electrode crushing, etc., and It is also possible to suppress the deterioration of conductivity.

On the other hand, when the V core hardness of the Cu core ball and the Cu ball is larger than the range specified by the present invention, the durability against external stress becomes lower, the drop impact resistance becomes worse, and it easily occurs. Crack subject.

Therefore, the Cu core balls using the Cu balls of Comparative Examples 8 to 11 whose Vickers hardness exceeds 55.5 HV are not suitable for the evaluation of Vickers hardness, so the overall evaluation is ×.

In addition, the discoloration resistance of the Cu core ball depends on the Ni plating layer which is an example of the solder layer and the metal layer, and therefore the discoloration resistance of the Cu core ball is not evaluated. However, as long as the brightness of the Cu ball is within the range specified by the present invention, the sulfide or sulfur oxide on the surface of the Cu ball can be suppressed, so it is suitable to be covered with a metal layer such as a solder layer or a Ni plating layer.

On the other hand, when the brightness of the Cu ball is lower than the range specified by the present invention, the sulfide or sulfur oxide on the surface of the Cu ball is not suppressed, so it is not suitable for coating with a metal layer such as a solder layer or a Ni plating layer.

Therefore, the Cu core balls using the Cu balls of Comparative Examples 1 to 6 whose brightness after 420 seconds was less than 55 were not suitable for the evaluation of discoloration resistance, so the overall evaluation was ×.

In addition, the amount of α rays of the Cu core ball depends on the composition of the plating solution material constituting the solder layer covering the Cu ball and each element in the composition. When an Ni plating layer which is an example of a metal layer covering the Cu balls is provided, it also depends on the raw material of the plating solution constituting the Ni layer.

When the Cu ball is the low α-ray amount prescribed by the present invention, as long as the plating solution material constituting the solder layer and the Ni plating layer uses the low α-ray amount prescribed by the present invention, the Cu core ball may also become the low α-ray prescribed by the present invention Ray volume. On the other hand, if the solder layer and the plating solution material constituting the Ni plating layer have a high α-ray amount exceeding the predetermined α-ray amount of the present invention, even if the Cu ball has the above-mentioned low α-ray amount, the Cu core ball will become more than the present invention. High alpha radiation with a prescribed alpha radiation.

Furthermore, even if the α-ray amount of the plating solution material constituting the solder layer and the Ni plating layer shows a slightly higher α-ray amount than the low α-ray amount prescribed by the present invention, impurities can be removed by the above-mentioned plating process. The amount of α rays is reduced to the range of low α rays prescribed by the present invention.

[Table 1]

[Table 2]

[table 3]

[Table 4]

[table 5]

[Table 6]

As shown in Table 1, the Cu balls of each example with a purity of 4N5 or more and 5N5 or less obtained good results in the comprehensive evaluation. From this, it can be said that the purity of the Cu balls is preferably 4N5 or more and 5N5 or less.

The details of the evaluation will be described below. As in Examples 1 to 12, 19, Cu spheres with a purity of 4N5 or more and 5N5 or less, containing Fe, Ag, or Ni of 5.0 mass ppm or more and 50.0 mass ppm or less, true sphericity, The comprehensive evaluation of the Vickers hardness, the amount of α rays and the discoloration resistance yielded good results. As shown in Examples 13 to 18, 20, Cu balls with a purity of 4N5 or more and 5N5 or less, containing Fe, Ag, or Ni in a total amount of 5.0 mass ppm or more and 50.0 mass ppm or less, also have true sphericity, Vickers hardness, The comprehensive evaluation of the α-ray amount and the discoloration resistance results in good results. In addition, although not shown in the table, from Examples 1, 19, and 20, the Fe content is 0 mass ppm or more and less than 5.0 mass ppm, the Ag content is 0 ppm or more and less than 5.0 mass ppm, and Ni Cu balls with a content of 0 mass ppm or more and less than 5.0 mass ppm, and a total of Fe, Ag, and Ni of 5.0 mass ppm or more are also obtained in the comprehensive evaluation of true sphericity, Vickers hardness, α-ray amount, and discoloration resistance Good result.

In addition, as shown in Example 19, Sb, Bi, Zn, A1, As, Cd, Pb, In, Sn containing Fe, Ag, or Ni of 5.0 mass ppm or more and 50.0 mass ppm or less, and other impurity elements The Au balls of Example 19 with Au and 50.0 mass ppm or less, respectively, also obtained good results in the comprehensive evaluation of true sphericity, Vickers hardness, α-ray amount, and discoloration resistance.

Regarding the Cu core balls, as shown in Tables 3 and 4, the solder layer of the solder alloy of Composition Example 1 containing 58.0% by mass of Bi and the balance being Sn was used to cover the Cu balls of Examples 1 to 20. For the Cu core balls of Examples 1A-20A, the Cu balls of Examples 1-20 were covered with Ni plating, and the Cu core balls of Examples 1B-20B were further covered with the solder layer of the solder alloy constituting Example 1, in the true Comprehensive evaluation of sphericity yielded good results.

The solder layer of the solder alloy of Composition Example 2 containing 40.0% by mass of Bi, 0.5% by mass of Cu, 0.03% by mass of Ni, and the balance of Sn is Example 1A covering the Cu balls of Examples 1 to 20 ~20A Cu core ball, covering the Cu balls of Example 1~Example 20 with Ni plating, and further covering the Cu core balls of Examples 1B~20B with the solder layer of the solder alloy of Composition Example 2, in true sphericity The comprehensive evaluation obtained good results.

The solder layer of the solder alloy of Composition Example 3 containing 3.0% by mass of Ag, 0.8% by mass of Cu, 3.0% by mass of Bi, and the balance of Sn is Example 1A covering the Cu balls of Examples 1 to 20 ~20A Cu core balls, covering the Cu balls of Example 1~Example 20 with Ni plating, and further covering the Cu core balls of Examples 1B~20B with the solder layer of the solder alloy constituting Example 3, in true sphericity The comprehensive evaluation obtained good results.

In addition, although not shown in the figure, from Examples 1, 19, and 20, the Fe content was changed to 0 mass ppm or more and less than 5.0 mass ppm, and the Ag content was 0 mass ppm or more and less than 5.0 mass ppm. , The content of Ni is 0 mass ppm or more and less than 5.0 mass ppm, Cu balls of Fe, Ag or Ni totaling 5.0 mass ppm or more, Cu covered with the solder layer of any one of the solder alloys of Composition Example 1 to Composition Example 3 For the core ball, the same Cu ball is covered with a Ni plating layer, and further the Cu core ball covered with the solder layer of any one of the solder alloys of Composition Example 1 to Composition Example 3, and good results are obtained in the comprehensive evaluation of the true sphericity.

On the other hand, in the Cu ball of Comparative Example 7, not only the total content of Fe, Ag, and Ni was less than 5.0 mass ppm, but U and Th were less than 5 mass ppb, and other impurity elements were less than 1 mass ppm. Comparative Example 7 Cu balls of Comparative Example 7, Cu balls of Comparative Example 7A covered with the solder layer of the solder alloy of each composition example, and Cu balls of Comparative Example 7 covered with Ni plating of the Cu balls of Comparative Example 7, further with each composition example The Cu core ball of Comparative Example 7B covered by the solder layer of the solder alloy did not have a full sphericity of 0.95. In addition, even if the impurity element contains at least one of Fe, Ag, and Ni, the total content of the Cu balls of Comparative Example 12 is less than 5.0 mass ppm, and the Cu balls of Comparative Example 12 are solder layers of the solder alloy of each composition example. The Cu core balls of Comparative Example 12A, and the Cu balls of Comparative Example 12 were covered with Ni plating, and the Cu core balls of Comparative Example 12B, which were further covered with the solder layers of the solder alloys of the respective composition examples, also had a true sphericity of less than 0.95. From these results, Cu balls with a total content of at least one content of Fe, Ag, and Ni less than 5.0 mass ppm, Cu core balls covered with Cu layers by the solder layer of the solder alloy of each composition example, and Cu balls It can be said that the Cu core ball covered with the Ni plating layer and further covered with the solder layer of the solder alloy of each composition example cannot achieve high sphericity.

In addition, in the Cu ball of Comparative Example 10, the total content of Fe, Ag, and Ni is 153.6 mass ppm, and the content of other impurity elements is 50 mass ppm or less, respectively, but the Vickers hardness exceeds 55.5 HV, and good results are not obtained. . Furthermore, in the Cu ball of Comparative Example 8, not only the total content of Fe, Ag, and Ni is 150.0 mass ppm, but also the content of other impurity elements, especially Sn is 151.0 mass ppm, which greatly exceeds 50.0 mass ppm, and the Vickers hardness More than 55.5HV without good results. Therefore, even for Cu balls with a purity of 4N5 or more and 5N5 or less, Cu balls having a total content of at least one of Fe, Ag, and Ni exceeding 50.0 mass ppm increase the Vickers hardness, and it can be said that low hardness cannot be achieved. In this way, when the Vickers hardness of the Cu ball is larger than the range specified by the present invention, it cannot solve the problem that the durability against external stress becomes low, the drop impact resistance becomes poor, and cracks easily occur. Furthermore, it can be said that other impurity elements are preferably contained in a range not exceeding 50.0 mass ppm.

From these results, Cu balls with a purity of 4N5 or more and 5N5 or less and a total content of at least one of Fe, Ag, and Ni of 5.0 mass ppm or more and 50.0 mass ppm or less can be said to achieve high sphericity and Low hardness, and can inhibit discoloration. The Cu core ball of such a Cu ball is covered with the solder layer of the solder alloy of each composition example, and the Cu core ball is covered with the Ni plating layer, and the Cu core ball covered with the solder layer of the solder alloy of each composition example can achieve high The sphericity, in addition, by achieving the low hardness of the Cu ball, even if the Cu core ball is made, the drop impact resistance is good, cracks can be suppressed, electrode crushing, etc. can be suppressed, and deterioration in conductivity can be suppressed. Furthermore, by suppressing the discoloration of Cu balls, it is suitable to be covered with a metal layer such as a solder layer or a Ni plating layer. The content of other impurity elements is preferably 50.0 ppm by mass or less.

Although not shown in the table, Cu balls with a ball diameter of 1 μm or more and 1000 μm or less with the same composition as those of the examples are all good in the comprehensive evaluation of true sphericity, Vickers hardness, α-ray amount, and discoloration resistance the result of. From this, it can be said that the ball diameter of the Cu ball is preferably 1 μm or more and 1000 μm or less, and more preferably 50 μm or more and 300 μm or less.

The Cu ball of Example 20 has a total content of Fe, Ag, and Ni of 5.0 mass ppm or more and 50.0 mass ppm or less, and contains P of 2.9 mass ppm, in terms of true sphericity, Vickers hardness, α-ray amount, and discoloration resistance The comprehensive evaluation obtained good results. The Cu core ball of the Cu ball of Example 20 was covered with the solder layer of the solder alloy of each composition example, the Cu ball of Example 20 was covered with the Ni plating layer, and the Cu core ball of the solder layer of the solder alloy of each composition example was further covered The comprehensive evaluation of the true sphericity yielded good results. The total content of Fe, Ag, and Ni of the Cu ball of Comparative Example 11 is 50.0 mass ppm or less as in the Cu ball of Example 20, but the Vickers hardness exceeds 5.5 HV, which is different from the Cu ball of Example 20. . In addition, in Comparative Example 9, the YVickers hardness exceeds 5.5 HV. This is considered to be because the P content in Comparative Examples 9 and 11 is significantly higher. From this result, it is understood that as the P content increases, the Vickers hardness increases. Therefore, it can be said that the content of P is preferably less than 3 mass ppm, and more preferably less than 1 mass ppm.

The amount of α rays of the Cu balls in each example was 0.0200 cph/cm ² or less. Therefore, in the solder alloy covering the composition examples 1 to 3 of the Cu balls of each of Examples 1 to 20, the Cu core balls of each of the Examples 1A to 20A are obtained by making each element at a low α-ray amount prescribed by the present invention. It also exhibits the low α-ray dose prescribed by the present invention. In addition, when the Ni plating layer as an example of the metal layer covering the Cu balls is provided, in addition to the solder alloy, each element constituting the Ni plating layer is a low α-ray amount prescribed by the present invention, and the Cu core balls of each of Examples 1B to 20B It also becomes a low α-ray amount prescribed by the present invention.

Furthermore, during the plating process of forming the solder layer and the Ni plating layer, impurities including alpha rays radiated from the alloy are removed, and the amount of alpha rays of the alloy before plating shows a lower alpha ray than that specified by the present invention When the amount of α rays is slightly higher, the amount of α rays after plating can be reduced to the range of low α rays prescribed by the present invention.

Thus, when the Cu core balls of the examples are used for high-density packaging of electronic parts, by making the raw materials constituting the solder layer and the Ni plating layer a low α-ray amount prescribed by the present invention, soft errors can be suppressed.

In the Cu ball of Comparative Example 7, the results of good discoloration resistance were obtained, but in Comparative Examples 1 to 6, the results of good discoloration resistance were not obtained. Comparing the Cu balls of Comparative Examples 1 to 6 with the Cu balls of Comparative Example 7, the difference in these compositions is only the S content. Therefore, in order to obtain a good result of discoloration resistance, it can be said that the content of S needs to be less than 1 mass ppm. In the Cu balls of each example, since the S content is less than 1 mass ppm, it can be said that the S content is preferably less than 1 mass ppm.

Next, in order to confirm the relationship between the S content and the discoloration resistance, the Cu balls of Example 14, Comparative Example 1 and Comparative Example 5 were heated at 200° C., before the heating, after 60 seconds of heating, after 180 seconds, after 420 seconds After the photos, measure the brightness. Table 7 and FIG. 7 are tables showing the relationship between the time for heating each Cu ball and the brightness.

[Table 7]

From this table, comparing the brightness before heating and the brightness after 420 seconds of heating, the brightness of Example 14, Comparative Examples 1, and 5 before heating is a value near 64 or 65. After heating for 420 seconds, the brightness of Comparative Example 5 containing 30.0 mass ppm of S became the lowest, and then, in order, the comparative example 1 containing 10.0 mass ppm of S, and the S content was less than 1 mass ppm 14. From this, it can be said that the greater the content of S, the lower the brightness after heating becomes. Since the Cu balls of Comparative Examples 1 and 5 have a brightness of less than 55 and contain 10.0 mass ppm or more of S, it can be said that sulfides or sulfur oxides are easily formed and change color when heated. In addition, if the content of S is 0 mass ppm or more and 1.0 mass ppm or less, the formation of sulfides or sulfur oxides can be suppressed, and it can be said that the wettability is good. Furthermore, the Cu balls of Example 14 were constructed on the electrode, and showed good wettability.

As described above, the purity is 4N5 or more and 5N5 or less, the total content of at least one of Fe, Ag, and Ni is 5.0 mass ppm or more and 50.0 mass ppm or less, and the S content is 0 mass ppm or more and 1.0 mass ppm or less, P The Cu spheres of the present example having a content of 0 mass ppm or more and less than 3.0 mass ppm have a true sphericity of 0.95 or more, so that a high true sphericity can be achieved. By achieving a high degree of sphericity, the self-alignment of the Cu balls when mounted on the electrodes can be ensured, and the height errors of the Cu balls can be suppressed. The same effect can also be obtained by covering the Cu core ball of the present embodiment with a Cu core ball covered with a solder layer, covering the Cu ball of the present embodiment with a metal layer, and further covering the Cu core ball with a solder layer on the metal layer.

In addition, the Cu balls of the present embodiment can achieve a low hardness because the Vickers hardness is 55 HV or less. By realizing low hardness, the impact resistance of Cu balls can be improved. Due to the low hardness of the Cu ball, the Cu ball of this embodiment is covered with a solder layer, the Cu ball of this embodiment is covered with a metal layer, and the Cu core ball of the metal layer is further covered with a solder layer, which is resistant to falling impact The properties are also good and cracks can be suppressed, electrode crushing, etc. can be suppressed, and the deterioration of conductivity can also be suppressed.

In addition, in the Cu balls of this example, discoloration was suppressed. By suppressing the discoloration of the Cu balls, the adverse effects of sulfides or sulfur oxides on the Cu balls can be suppressed, and at the same time, the wettability when mounting the Cu balls on the electrode can be improved. Since the discoloration of Cu balls is suppressed, it is suitable to be covered with a metal layer such as a solder layer or a Ni plating layer.

In addition, in the Cu material of this embodiment, Cu blocks with a purity exceeding 4N5 and below 6N are used to produce Cu balls with a purity of above 4N5 and below 5N5, but using wire or plate material exceeding 4N5 and below 6N, in the Cu Both the ball and the Cu core ball also achieved good results in the comprehensive evaluation.

Next, the Cu core ball on the surface of the Cu ball is covered with the solder layer of the Sn-based solder alloy, and the element distribution other than Sn in the solder layer will be described. As the solder layer covering the Cu balls, a solder alloy mainly composed of Sn, as shown in Japanese Patent Laid-Open No. 2007-44718 (referred to as Patent Document 4) and Japanese Patent No. 5367924 (referred to as Patent Document 5), can be used.

In Patent Document 4, the surface of the Cu ball is covered with a Sn-based solder alloy composed of Sn and Bi to form a solder layer. The Sn-based solder alloy containing Bi has a melting temperature of 130 to 140°C and a relatively low temperature, and is called a low-temperature solder.

In Patent Document 4, the content of Bi contained in the solder layer is a concentration gradient plating process in which the inner side (inner peripheral side) is lighter and the outer side (outer peripheral side) is thicker.

Patent Document 5 also discloses a solder bump of a Sn-based solder alloy composed of Sn and Bi by plating a Cu film. In Patent Document 5, the content of Bi contained in the solder layer is a concentration gradient plating process that is thicker on the inner side (inner peripheral side) and lighter toward the outer side (outer peripheral side).

The technique of Patent Document 5 has a completely opposite concentration gradient from that of Patent Document 4. This is the concentration control of Patent Document 5, which is simpler than the case of Patent Document 4, and is considered to be easier to do.

As described above, when a Sn-based solder alloy in which two or more elements are added to Sn is added, and the Cu core balls coated on the surface of the Cu balls are placed on the electrode of the semiconductor wafer for reflow processing, the added elements are in the solder layer Patent documents 4 and 5 having a concentration gradient cause the following problems.

The technology disclosed in Patent Document 4 is a solder layer in which the Bi concentration is lighter on the inner peripheral side and becomes thicker on the outer peripheral side. With such a concentration gradient (the inner side is lighter and the outer side is thicker), the timing of Bi melting There may be a slight deviation between the inner peripheral side and the outer peripheral side.

When the melting timing shifts, even if the outer surface of the Cu core ball starts to melt, the region on the inner peripheral surface side has not melted, but the mixed part melts, and as a result, the position of the core material shifts slightly to the melting side. In a high-density package with a narrow pitch, this position shift may cause fatal defects in solder processing.

In Patent Document 5, the concentration gradient of Bi is opposite to that of Patent Document 1. At this time, in order to connect the semiconductor package, a heat treatment for reflow is required. When the Bi concentration of the solder layer as in Patent Document 5 is concentrated on the inner peripheral side and heated and melted in a state where the outer peripheral side is light, the Bi density on the inner peripheral side is high, and the solder starts to melt from the Bi region on the inner peripheral side. Even if the Bi region on the inner peripheral side has melted, the Bi region on the outer peripheral side has not yet begun to melt, so volume expansion of the Bi region on the inner peripheral side occurs earlier.

Due to the speed of volume expansion on the inner and outer peripheral sides, a pressure difference occurs between the inner and outer peripheral sides of Bi (outside air), and the outer peripheral side of Bi begins to melt, then the core Cu ball will be affected by the pressure difference of the volume expansion of the inner peripheral side. A bounce situation has occurred. Such a situation must be avoided.

In this way, Cu core balls having a solder layer composed of a Sn-based solder alloy composed of Sn and Bi, if Bi in the solder layer has a concentration gradient, defects will occur.

Therefore, the effect of the uniform distribution of Bi in the solder layer 3 will be described next. In order to confirm that the concentration distribution of Bi in the solder layer 3 has a corresponding target value, the following experiment was performed. (1) Under the following conditions, a Cu core ball 11B having a composition of the solder layer 3 (Sn-58Bi) was produced. In the following examples, Cu balls having the composition of Example 17 shown in Table 1 were used. . Cu ball 1 diameter: 250 μm . Film thickness of metal layer (Ni plating) 2: 2 μm . Film thickness of solder layer 3: 23 μm . The diameter of the Cu core ball 11B: 300 μm

In order to easily measure the experimental results, a Cu core ball having a thin solder layer was produced as the Cu core ball 11B.

The plating method is produced by the electroplating method under the conditions of FIG. 4 described above. (2) As a sample, ten Cu core balls 11B forming a solder layer of a (Sn-58Bi)-based solder alloy of the same composition were prepared. These were used as Sample A. (3) Ten samples A were sealed with resin. (4) The sealed samples A were polished for each resin to observe the cross section of the samples A. Observation equipment used FE-EPMAJXA-8530F manufactured by JEOL.

FIG. 8 is an explanatory diagram showing an example of a method of measuring the Bi concentration distribution of Cu core balls. The solder layer 3 is expediently divided into an inner layer 16a, an intermediate layer 16b, and an outer layer 16c from the surface side of the Cu ball 1. Then, the inner layer 16a is the surface of the Cu ball 1 to 9 μm, the intermediate layer 16b is 9 to 17 μm, and the outer layer 16c is 17 to 23 μm. From the inner layer 16a, the intermediate layer 16b and the outer layer 16c, as shown in FIG. 8 in this example, The inner layer region 17a, the middle layer region 17b, and the outer layer region 17c were cut out with a thickness of 5 μm and a width of 40 μm, and the Bi concentration was measured by qualitative analysis using each region as a measurement region. This operation is performed for 10 views of each of the inner layer 16a, the middle layer 16b, and the outer layer 16c.

With regard to the preparation of the samples B to D separately from the sample A, the same measurement operation is also carried out. For samples B to D, as in sample A, 10 Cu core balls 11B were prepared in which a solder layer of (Sn-58Bi)-based solder alloy having the same composition was prepared.

Table 8 below shows the concentration ratio of each layer obtained by measuring the Bi concentration of the inner layer, the intermediate layer, and the outer layer of the solder layer.

Table 8 shows the Bi concentration ratio when the average Bi concentration of each layer of the solder layer was measured with 10 Cu core balls in samples A to D, and the target Bi content (target value) was 58% by mass.

For samples A to D, as described above, for 10 Cu core balls, the Bi concentration of the inner layer, the middle layer, and the outer layer was measured. Regarding samples A to D, the measured values of the Bi concentrations of the inner layer, the middle layer, and the outer layer of the ten Cu core balls are not shown in Table 8.

For samples A to D, the target Bi content (target value) was 58% by mass. At this time, the Bi concentration ratio (%) of each of the 10 Cu core spheres in samples A to D was obtained from the measured value of the Bi concentration using the following formula (1). Concentration ratio (%)=(measured value/58)×100…(1).

In addition, the average value of the Bi concentration is obtained by the following formula (2) when the number of Cu core balls as a sample is 10 pieces. The average value of Bi concentration = the sum of 10 measured values/10... (2)

In addition, when the target Bi content (target value) is 58% by mass, the concentration ratio (%) of the samples A to D is obtained from the average value of the measured values of the Bi concentration, and the following (3). Concentration ratio (%) = (average of measured values/58) × 100. . . (3)

[Table 8]

As shown in Table 8, regarding the sample A, the average Bi concentration in the inner layer region 17a is 58.10 mass% and the concentration ratio is 100.2%, and the average Bi concentration in the intermediate layer region 17b is 57.22 mass% and the concentration ratio It is 98.7%, the average value of the Bi concentration in the outer layer region 17c is 58.08% by mass, and the concentration ratio is 100.1%.

In addition, regarding Sample B, the average Bi concentration in the inner layer region 17a is 57.82 mass%, the concentration ratio is 99.7%, and the average Bi concentration in the intermediate layer region 17b is 56.47 mass%, the concentration ratio is 97.4%, The average value of the Bi concentration in the outer layer region 17c is 56.61% by mass, and the concentration ratio is 97.6%.

In addition, regarding sample C, the average Bi concentration in the inner layer region 17a is 62.97 mass%, the concentration ratio is 108.6%, and the average Bi concentration in the intermediate layer region 17b is 57.63 mass%, the concentration ratio is 99.4% The average Bi concentration in the outer layer region 17c is 58.67% by mass, and the concentration ratio is 101.2%.

In addition, regarding sample D, the average Bi concentration in the inner layer region 17a was 58.02 mass%, the concentration ratio was 100.0%, and the average Bi concentration in the intermediate layer region 17b was 52.39 mass%, and the concentration ratio was 90.3%, The average value of the Bi concentration in the outer layer region 17c is 57.84% by mass, and the concentration ratio is 99.7%.

In this manner, the Bi concentration in the solder layer in the inner layer region 17a, the intermediate layer region 17b, and the outer layer region 17c is within the allowable range of 52.39% by mass to 62.97% by mass, and it is known that the Bi concentration ratio is approximately at the target value.

Then, for example, 10 Cu core balls manufactured in the same batch as the samples A to D are respectively extracted, and they are joined on the substrate by a normal reflow process. The results of joining are also shown in Table 8.

Regarding the joining results, the determination of any joint failure for all samples was determined to be "good", as long as one sample had a positional shift at the time of joining, and as long as one sample had the Cu core ball 11B bounced off at the time of joining Is judged as "bad".

None of the inner peripheral side melted earlier than the outer peripheral side, and there was a difference in volume expansion between the inner peripheral side and the outer peripheral side, and the Cu core ball 11B was flicked, etc. In addition, the entire solder layer 3 can be melted substantially uniformly, and There is no possibility that the position of the core material is shifted due to the shift of the melting timing, so there is no risk of short-circuiting between the electrodes due to displacement or the like. Therefore, a good result was obtained in which no joint failure occurred at all, so it was judged as "good".

As described above, when using a (Sn-58Bi) solder alloy, the results in Table 8 show that the range of 52.39 mass% (density ratio 90.3%) to 62.97 mass% (density ratio 108.6%) is acceptable.

Next, the same measurement was performed for the case of forming the solder layer 3 of a quaternary Sn-based solder alloy composed of Cu and Ni and containing Bi (Sn-40Bi-0.5Cu-0.03Ni). At this time, the distribution of Bi takes 40 mass% as the target value, but the allowable range is 38.41 mass% (concentration ratio 96.0%) to 41.11 mass% (concentration ratio 102.8%). In the following examples, Cu balls having the composition of Example 18 shown in Table 1 were used. . Cu ball 1 diameter: 180μm . Film thickness of metal layer (Ni plating) 2: 2 μm . Film thickness of solder layer 3: 33 μm . The diameter of the Cu core ball 11B: 250 μm

The production method of the Cu core ball is carried out under the same plating conditions as in the case of the examples A to D of the Cu core ball using the (Sn-58Bi) solder alloy described above, so that the Bi concentration in the plating solution is uniform.

Regarding the experimental method, the inner layer 16a is made from the surface of the Cu ball to 11 μm, the intermediate layer 16b is 11 to 22 μm, and then the outer layer 16c is other than 22 to 33 μm, and the Cu core ball using (Sn-58Bi) solder alloy The examples of samples A to D have the same conditions.

The results are shown in samples E to H in Table 8. At this time, the target value of Bi is 40% by mass, so as shown in samples E~H, 38.41~41.11% by mass (all are the average of 10 measurements of the same sample), although there are some errors (the minimum value of the average value is 38.41 % (Concentration ratio 96.0%) to a maximum of 41.11 mass% (concentration ratio 102.8%), but within the allowable range. Therefore, it can be seen that it is in the range of 38.41 mass% (concentration ratio 96.0%) to 41.11 mass% (concentration ratio 102.8%). The judgment was the same as the examples of Samples A to D. Since a good result was obtained in which no joint failure occurred at all, it was judged as "good".

The target Bi content (target value) of the samples E to H was 40 (mass %). Therefore, the concentration ratio (%) of the samples E to H in Table 8 is obtained by the following formula (4). Concentration ratio (%)=(average of measured values/40)×100…(4)

Fig. 9 is the characteristic curve of the relationship between the Bi concentration (curve Lc) and the Bi concentration of the solder layer (curve Ld) in the plating solution of the (Sn-40Bi) solder alloy plating process, taking the Cu core ball diameter as a reference Figure.

In this example, a particle size of 250 μm is used as the initial value of Cu balls. The thickness of the solder layer is monitored one by one, and the thickness of the solder layer is sequentially increased by Cu core balls with predetermined values, and each time a sample is collected. After the collected sample was washed and dried, the particle size was measured.

The particle size of the Cu core ball at the measurement timing was measured in sequence, and the Bi content of the solder layer at the target value was obtained, and the result as shown in the curve Lc in FIG. 9 was obtained. Even if the solder layer is only sequentially increased by a predetermined thickness, the Bi content at this time can be found to be approximately the same value as the previous content. In the case of curve Lc, the content of Bi is approximately 40 to 42% by mass. As in the curve Lc, it can be understood that the concentration distribution of Bi is homogeneous (equal) to the plating thickness without a concentration gradient. The difference between the Bi concentration in the solder layer (curve Lc) and the Bi concentration in the plating solution (curve Ld) is the same as in FIG. 4 because Bi in the plating solution is preferentially taken into the layer over Sn in the plating solution.

Next, the same measurement was performed for the case where the solder layer 3 of a quaternary Sn-based solder alloy composed of (Sn-3Ag-0.8Cu-3Bi) containing Ag and Cu and Bi was formed. At this time, the target value of the Bi distribution is 3% by mass, but the allowable range is 2.66% by mass (concentration ratio 88.7%) to 3.32% by mass (concentration ratio 110.7%). The production method of the Cu core ball is the same as the case of the examples A to D of the Cu core ball using the (Sn-58Bi) solder alloy described above.

The specifications of the diameters of the Cu balls and Cu core balls used, the thickness of the metal layer (Ni plating) and the solder layer, and the experimental conditions are the same as those of the samples A to D except for the composition of the solder layer.

The results are shown as samples I~L in Table 8. Since the target value of Bi at this time is 3% by mass, as shown in samples I to L, 2.66 to 3.32% by mass (all are the average of 10 measurements on the same sample), although there are some errors (the minimum value of the average is 2.66 Mass% (concentration ratio 88.7%) to maximum 3.32 mass% (concentration ratio 110.7%), but within the allowable range. Therefore, it can be seen that it is in the range of 2.66 mass% (concentration ratio 88.7%) to 3.32 mass% (concentration ratio 110.7%). The joint determination was the same as the examples of samples A to D, and since a good result was obtained in which joint failure did not occur at all, it was determined as "good".

The target Bi content (target value) of samples I~L is 3 (mass %). Therefore, the concentration ratio (%) of the samples I to L in Table 8 is obtained by the following formula (5). Concentration ratio (%)=(average of measured values/3)×100…(5)

The results of Examples A to D, Examples E to H, and Examples I to L are summarized in Table 9. The concentration ratio of Bi is 88.7 to 110.7 mass%. Here, the sphericity of the Cu core balls produced by the examples of samples A to D, the examples of samples E to H, and the examples of samples I to L were measured, and the results were all 0.99 or more and satisfies 0.95 or more.

[Table 9]

The concentration ratio (%) in Table 9 is obtained by the following formula (6). Concentration ratio (%)=(measured value/target value)×100…(6)

In addition, Table 8 shows the experimental results when the Bi distribution in the solder layer has a concentration gradient as a comparative example. The ball diameters of the Cu balls and Cu core balls used, the film thickness of the solder layer of the metal layer (Ni plating), etc., and the experimental conditions, in addition to the following electroplating methods, are similar to the examples of samples A to D and samples I to L The example of is the same condition.

In Comparative Example A, the plating solution is electroplated with a plating solution containing a Sn compound, an organic acid, and a surfactant. Then, at a stage where the plating film thickness is half of the target value, only the Bi(III) compound is further added. With this, the concentration of the Bi(III) compound is increased while reducing the concentration of the Sn compound in the plating solution, and plating is performed.

As a result, even if a 58 mass% solder layer with a Bi content as a target value is formed over the entire solder layer, the Bi concentration in the solder layer is lighter on the inner side, and becomes denser toward the outer side (inner layer 0 mass%, 54.71% by mass in the middle layer and 100% by mass in the outer layer).

In Comparative Example B, electroplating was performed with a plating solution containing Sn compound, Bi(III) compound, organic acid, and surfactant. From the beginning of plating, a predetermined DC voltage is applied between the anode electrode and the cathode electrode, and the Cu ball is shaken while performing the plating process.

As a result, even if the entire solder layer forms a 58 mass% solder layer with a Bi content as a target value, the Bi concentration of the solder layer becomes denser on the inner side, and becomes thinner toward the outer side (inner layer 82.10 mass %, middle layer) 38.10 mass%, outer layer 4.10 mass%). In addition, in Comparative Examples A and B, the content of Bi is 58 (mass %) of the target value, and the concentration ratio (%) is obtained by formula (3).

As a result, in Comparative Example A, a positional shift occurred during joining, and in Comparative Example B, the Cu core ball was bounced, and therefore all were judged to be "bad". Here, the sphericity of the Cu core balls produced in the above Comparative Examples A and B was measured, and the results were all less than 0.95.

When the Bi concentration in the solder layer 3 is changed in this way, a phenomenon such as positional deviation or flying of the Cu core ball 11B occurs.

As described above, in each of Examples A to L, since Bi in the solder layer is homogeneous, the film thickness of Bi to the solder layer is within a predetermined range of the Bi concentration ratio in the entire region including the inner peripheral side and the outer peripheral side . Therefore, the Bi of the solder layer is the homogeneous Cu core ball of the present invention, and the inner peripheral side does not melt earlier than the outer peripheral side, but the difference in volume expansion occurs between the inner peripheral side and the outer peripheral side, and the Cu core ball is bounced. situation.

In addition, since the Bi of the solder layer is homogeneous, and the Cu core balls can be melted substantially uniformly over the entire surface, there is almost no time difference in the timing of melting in the solder layer. As a result, since the positional deviation of the Cu core ball due to the deviation of the melting timing does not occur, there is no risk of short-circuiting between the electrodes due to the positional deviation or the like. Therefore, high-quality solder joints can be provided by using this Cu core ball.

1‧‧‧Cu ball 11A, 11B‧‧‧Cu core ball 2‧‧‧Metal layer 3‧‧‧ solder layer 10‧‧‧Semiconductor chip 100、41‧‧‧electrode 30‧‧‧Solder bump 40‧‧‧ printed circuit board 50‧‧‧welding head 60‧‧‧Electronic parts

FIG. 1 is a diagram showing a Cu core ball according to the first embodiment of the present invention. 2 is a diagram showing a Cu core ball according to a second embodiment of the present invention. 3 is a diagram showing a configuration example of an electronic component using Cu core balls according to each embodiment of the present invention. FIG. 4 is a characteristic curve diagram showing the relationship between the Bi concentration in the plating solution of the plating process and the Bi concentration of the solder layer, based on the Cu core ball diameter. Fig. 5 is an enlarged cross-sectional view of a Cu core ball. Fig. 6 is an enlarged view of the surface of the Cu core ball. Fig. 7 is a graph showing the relationship between the heating time and the brightness of the Cu balls of Examples and Comparative Examples heated at 200°C. 8 is an explanatory diagram showing an example of a method of measuring the Bi concentration distribution of Cu core spheres. FIG. 9 is a characteristic curve diagram showing the relationship between the Bi concentration in the plating solution of the plating process and the Bi concentration in the solder layer, using the Cu core ball diameter as a reference.

1‧‧‧Cu ball

3‧‧‧ solder layer

11A‧‧‧Cu nuclear ball

Claims (20)

A Cu core ball with: Cu balls; and The solder layer covering the surface of the above Cu ball, The Cu balls are Fe, Ag and Ni. The total content of at least one content is 5.0 mass ppm or more and 50.0 mass ppm or less, The content of S is 0 mass ppm or more and 1.0 mass ppm or less, The content of P is 0 mass ppm or more and less than 3.0 mass ppm, The balance is Cu and other impurity elements. The purity of the Cu balls is 99.995% by mass or more and 99.9995% by mass or less. The true sphericity is above 0.95, The solder layer contains Sn, Bi, or Sn and Bi. For example, the Cu core ball of claim 1, the above solder layer is composed of (Sn-Bi) solder alloy containing Sn and Bi, The concentration ratio (%) of Bi contained in the above solder layer is Concentration ratio (%) = (measured value (mass %)/target content (mass %)) × 100, or Concentration ratio (%) = (average of measured values (mass %)/target content (mass %)) × 100, The above concentration ratio is in the range of 88.7 to 110.7%. For example, the Cu core ball of patent application item 1, wherein the above solder layer is composed of (Sn-58Bi) solder alloy containing Sn and Bi, The concentration ratio (%) of Bi contained in the above solder layer is Concentration ratio (%) = (measured value (mass %)/target content (mass %)) × 100, or Concentration ratio (%) = (average of measured values (mass %)/target content (mass %)) × 100, The above concentration ratio is in the range of 90.3 to 108.6%. For example, the Cu core ball of the first patent application, wherein the above solder layer is composed of (Sn-40Bi) solder alloy containing Sn and Bi, The concentration ratio (%) of Bi contained in the above solder layer is Concentration ratio (%) = (measured value (mass %)/target content (mass %)) × 100, or Concentration ratio (%) = (average of measured values (mass %)/target content (mass %)) × 100, The above concentration ratio is in the range of 96.0 to 102.8%. For example, the Cu core ball of the first patent application, in which the above solder layer is composed of (Sn-3Bi) solder alloy containing Sn and Bi, The concentration ratio (%) of Bi contained in the above solder layer is Concentration ratio (%) = (measured value (mass %)/target content (mass %)) × 100, or Concentration ratio (%) = (average of measured values (mass %)/target content (mass %)) × 100, The above concentration ratio is in the range of 88.7 to 110.7%. If the Cu core ball of any one of the items 1 to 5 of the patent application range, the true sphericity is more than 0.98. If the Cu core ball of any one of the items 1 to 5 of the patent application range, the true sphericity is more than 0.99. For example, the Cu core ball of any one of the items 1 to 5 of the patent application range, in which the amount of α rays is 0.0200 cph/cm ² or less. For example, the Cu core ball according to any one of the items 1 to 5 of the patent application, in which the amount of α rays is 0.0010 cph/cm ² or less. For example, the Cu core ball in the 6th scope of the patent application, in which the amount of α rays is 0.0200cph/cm ² or less. For example, the Cu core ball according to any one of claims 1 to 5 has a metal layer covering the surface of the Cu ball, and the surface of the metal layer is covered with the solder layer, and the true sphericity is 0.95 or more. For example, the Cu core ball in the 11th range of patent application, the true sphericity is above 0.98. For example, the Cu core ball in the 11th range of patent application, the true sphericity is more than 0.99. For example, the Cu core ball of the 11th range of patent application, in which the amount of α rays is 0.0200cph/cm ² or less. For example, the Cu core ball of claim 11 of the patent application, in which the amount of α rays is 0.0010cph/cm ² or less. For example, a Cu core ball according to any one of the items 1 to 5 of the patent application range, wherein the diameter of the Cu ball is 1 μm or more and 1000 μm or less. For example, the Cu core ball of claim 11 of the patent application, wherein the diameter of the Cu ball is 1 μm or more and 1000 μm or less. A welding head, which uses Cu core ball according to any one of patent application items 1 to 17. A solder paste that uses Cu core balls according to any one of patent application items 1 to 17. A foam solder, which uses Cu core balls according to any one of patent application items 1 to 17.

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