JP6493604B1 - Cu core ball, solder joint, solder paste and foam solder - Google Patents

Abstract

Provided is a Cu core ball in which a high-sphericity and a low hardness are realized, and a Cu ball in which discoloration is suppressed is coated with a metal layer. A Cu core ball 11A includes a Cu ball 1 and a solder layer 3 that covers the surface of the Cu ball 1, and the Cu ball 1 has a 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, the S content is 0 mass ppm or more and 1.0 mass ppm or less, and the P content is 0 mass ppm or more and less than 3.0 mass ppm. And the balance is Cu and other impurity elements, the purity of the Cu ball 1 is 99.995 mass% or more and 99.9995 mass% or less, the sphericity is 0.95 or more, and the solder layer is made of Sn. , Bi, or Sn and Bi. [Selection] Figure 1

Description

  The present invention relates to a Cu core ball in which a Cu ball is coated with a metal layer, and a solder joint, a solder paste, and a foam solder using the Cu core ball.

  In recent years, with the development of small information devices, electronic components to be mounted are rapidly downsized. In order to meet the demand for downsizing and the reduction of the connection terminals and the reduction of the mounting area, the electronic component uses a ball grid array (hereinafter referred to as “BGA”) in which electrodes are provided on the back surface. .

  An electronic component to which BGA is applied includes, for example, a semiconductor package. In a semiconductor package, a semiconductor chip having electrodes is sealed with a resin. Solder bumps are formed on the electrodes of the semiconductor chip. This solder bump is formed by joining a solder ball to an electrode of a semiconductor chip. A semiconductor package to which BGA is applied is mounted on a printed board by bonding solder bumps melted by heating and conductive lands of the printed board. Further, in order to meet the demand for further high-density mounting, three-dimensional high-density mounting in which semiconductor packages are stacked in the height direction has been studied.

  High-density mounting of electronic components may cause a soft error in which stored contents are rewritten when α rays enter a memory cell of a semiconductor integrated circuit (IC). In recent years, therefore, development of low α-ray solder materials and Cu balls with reduced content of radioisotopes has been carried out. Patent Document 1 discloses a Cu ball containing Pb and Bi and having a purity of 99.9% or more and 99.995% or less and a low α dose. Patent Document 2 discloses a Cu ball that achieves a purity of 99.9% or more and 99.995% or less, a sphericity of 0.95 or more, and a Vickers hardness of 20HV or more and 60HV or less.

  By the way, since the Vickers hardness of Cu balls increases if the crystal grains are fine, durability against external stress is lowered and drop impact resistance is deteriorated. Therefore, Cu balls used for mounting electronic components are required to have a predetermined softness, that is, a Vickers hardness of a predetermined value or less.

  In order to produce soft Cu balls, it is customary to increase the purity of Cu. This is because the impurity element functions as a crystal nucleus in the Cu ball, so that when the impurity element decreases, the crystal grains grow larger, and as a result, the Vickers hardness of the Cu ball decreases. However, when the purity of the Cu ball is increased, the sphericity of the Cu ball is lowered.

  If the sphericity of the Cu ball is low, self-alignment may not be ensured when the Cu ball is mounted on the electrode, and the height of the Cu ball becomes uneven when mounting the semiconductor chip, resulting in poor bonding. May cause.

  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 suitable sphericity and Vickers hardness. ing.

  Further, when the semiconductor package on which the three-dimensional high-density mounting is performed is a BGA and the solder ball is placed on the electrode of the semiconductor chip and reflow processing is performed, the solder ball may be crushed by the weight of the semiconductor package. . If such a thing occurs, the solder may protrude from the electrodes and the electrodes may come into contact with each other, causing a short circuit between the electrodes.

  In order to prevent such a short-circuit accident, a solder bump that is not crushed by its own weight or deformed when the solder melts has been proposed. Specifically, it has been proposed to use a ball molded with a metal or the like as a core and use a core material in which the core is covered with solder as a solder bump.

Japanese Patent No. 5435182 Japanese Patent No. 5585751 Japanese Patent No. 6256616

  However, it has been newly found that a Cu ball containing a predetermined amount or more of S has a problem that it is likely to be discolored by forming sulfide or sulfur oxide during heating. The discoloration in the Cu ball causes the deterioration of wettability, and the deterioration of wettability causes non-wetting and deterioration of self-alignment property. As described above, the Cu ball which is easily discolored is not suitable for coating with the metal layer because the adhesion between the surface of the Cu ball and the metal layer is lowered and the oxidation and reactivity of the metal layer surface are increased. On the other hand, when the sphericity of the Cu ball is low, the sphericity of the Cu core ball in which the Cu ball is covered with the metal layer is also low.

  Therefore, the present invention provides a Cu core ball using a Cu ball that realizes high sphericity and low hardness and suppresses discoloration, and a solder joint, solder paste, and foam solder using the Cu core ball. The purpose is to provide.

The present invention is as follows.
(1) A Cu ball and a solder layer covering the surface of the Cu ball are provided, and the Cu ball has a total content of at least one of Fe, Ag, and Ni of 5.0 mass ppm to 50.0 mass. It is ppm or less, S content is 0 mass ppm or more and 1.0 mass ppm or less, P content is 0 mass ppm or more and less than 3.0 mass ppm, and the balance is Cu and other impurity elements. A Cu core ball containing Sn, Bi, or Sn and Bi, wherein the purity of the Cu ball is 99.995% by mass or more and 99.9995% by mass or less, and the sphericity is 0.95 or more.
(2) The solder layer is made of a (Sn-Bi) -based solder alloy containing Sn and Bi, and the concentration ratio (%) of Bi contained in the solder layer is expressed as concentration ratio (%) = (measured value (mass (mass %) / Target content (mass%) × 100 or concentration ratio (%) = (average value of measurement values (mass%) / target content (mass%)) × 100 The Cu core ball according to the above (1), in which the concentration ratio is within the range of 88.7 to 110.7%.
(3) The solder layer is made of a (Sn-58Bi) -based solder alloy containing Sn and Bi, and the concentration ratio (%) of Bi contained in the solder layer is expressed as concentration ratio (%) = (measured value (mass (mass %) / Target content (mass%) × 100 or concentration ratio (%) = (average value of measurement values (mass%) / target content (mass%)) × 100 The Cu core ball according to (1) above, in which the concentration ratio is within the range of 90.3 to 108.6%.
(4) The solder layer is made of a (Sn-40Bi) -based solder alloy containing Sn and Bi, and the concentration ratio (%) of Bi contained in the solder layer is expressed as concentration ratio (%) = (measured value (mass (mass %) / Target content (mass%) × 100 or concentration ratio (%) = (average value of measurement values (mass%) / target content (mass%)) × 100 The Cu core ball according to (1) above, wherein the concentration ratio is within the range of 96.0 to 102.8%.
(5) The solder layer is made of a (Sn-3Bi) -based solder alloy containing Sn and Bi, and the concentration ratio (%) of Bi contained in the solder layer is expressed as concentration ratio (%) = (measured value (mass (mass %) / Target content (mass%) × 100 or concentration ratio (%) = (average value of measurement values (mass%) / target content (mass%)) × 100 The Cu core ball according to the above (1), in which the concentration ratio is within the range of 88.7 to 110.7%.
(6) The Cu core ball according to any one of (1) to (5), wherein the sphericity is 0.98 or more.
(7) The Cu core ball according to any one of (1) to (5), which has a sphericity of 0.99 or more.
(8) The Cu core ball according to any one of (1) to (7), wherein the α dose is 0.0200 cph / cm ² or less.
(9) The Cu core ball according to any one of (1) to (7), wherein the α dose is 0.0010 cph / cm ² or less.
(10) The metal layer covering the surface of the Cu ball is provided, the surface of the metal layer is covered with a solder layer, and the sphericity is 0.95 or more, according to any one of (1) to (9) Cu core ball.
(11) The Cu core ball according to (10), wherein the sphericity is 0.98 or more.
(12) The Cu core ball according to (10), wherein the sphericity is 0.99 or more.
(13) The Cu core ball according to any one of (10) to (12), wherein the α dose is 0.0200 cph / cm ² or less.
(14) The Cu core ball according to any one of (10) to (12), wherein the α dose is 0.0010 cph / cm ² or less.
(15) The Cu core ball according to any one of (1) to (14), wherein the diameter of the Cu ball is 1 μm or more and 1000 μm or less.
(16) A solder joint using the Cu core ball described in any one of (1) to (15) above.
(17) A solder paste using the Cu core ball according to any one of (1) to (15) above.
(18) Foam solder using the Cu core ball described in any of (1) to (15) above.

According to the present invention, to achieve high sphericity and low hardness of Cu balls, and discoloration of the Cu balls are suppressed. By realizing the high sphericity of Cu balls, the Cu balls can achieve high sphericity of Cu nuclei balls coated with metal layers, ensuring self-alignment property when mounting the Cu nuclei ball on an electrode In addition, variations in the height of the Cu core ball can be suppressed. Further, by realizing the low hardness of the Cu ball, the drop impact resistance can be improved even with a Cu core ball in which the Cu ball is coated with a metal layer. Furthermore, 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, which is suitable for coating with a metal layer, and the wettability is good.

It is a figure showing Cu core ball of a 1st embodiment concerning the present invention. It is a figure showing Cu core ball of a 2nd embodiment concerning the present invention. It is a figure which shows the structural example of the electronic component using the Cu core ball of each embodiment which concerns on this invention. It is a characteristic curve figure when the relationship between Bi density | concentration in the plating solution in a plating process and Bi density | concentration in a solder layer is based on Cu core ball diameter. It is an expanded sectional view of Cu core ball. It is an enlarged view of the surface of Cu core ball. It is a table | surface figure which shows the relationship between a heating time and the brightness which heated the Cu ball | bowl of the Example and the comparative example at 200 degreeC. It is explanatory drawing which shows an example of the method of measuring the density | concentration distribution of Bi of Cu core ball. It is a characteristic curve figure when the relationship between Bi density | concentration in the plating solution in a plating process and Bi density | concentration in a solder layer is based on Cu core ball diameter.

  The invention is described in more detail below. In this specification, the unit (ppm, ppb, and%) related to the composition of the metal layer of the Cu core ball represents a ratio (mass ppm, mass ppb, and mass%) to the mass of the metal layer unless otherwise specified. Further, the units (ppm, ppb, and%) relating to the composition of the Cu balls represent ratios (mass ppm, mass ppb, and mass%) with respect to the mass of the Cu balls 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 11 </ b> A according to the first embodiment of the present invention includes a Cu ball 1 and a solder layer 3 that covers 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 11 </ b> B of the second embodiment according to the present invention is one or more selected from Cu ball 1 and Ni, Co, Fe, and Pd covering the surface of the Cu ball 1. One or more metal layers 2 made of the above elements and a solder layer 3 covering the surface of the metal layer 2 are provided.

  FIG. 3 shows an example of the configuration of an electronic component 60 in which the semiconductor chip 10 is mounted 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, in the Cu core ball 11 </ b> A or the Cu core ball 11 </ b> B, when the flux is applied to the electrode 100 of the semiconductor chip 10, the melted solder layer 3 is wetted and spread on the electrode 100 of the semiconductor chip 10. Has been implemented. In this example, a structure in which the Cu core ball 11A or the Cu core ball 11B is mounted on the electrode 100 of the semiconductor chip 10 is referred to as a solder bump 30. The solder bump 30 of the semiconductor chip 10 is bonded onto the electrode 41 of the printed circuit board 40 via the molten solder layer 3 or the solder in which the solder paste applied to the electrode 41 is melted. In this example, a structure in which the solder bump 30 is mounted on the electrode 41 of the printed circuit board 40 is referred to as a solder joint 50.

  In the Cu core balls 11A and 11B of each embodiment, the Cu ball 1 has a total content of at least one of Fe, Ag, and Ni of 5.0 mass ppm to 50.0 mass ppm, and S The content of P 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 is 4N5 (99.995% by mass) or more and 5N5 (99.9995% by mass) or less, and the sphericity is 0.95 or more.

  In the Cu core ball 11A of the first embodiment according to the present invention, the sphericity of the Cu core ball 11A can be increased by increasing the sphericity of the Cu ball 1 covered with the solder layer 3. it can. Further, the Cu core ball 11B of the second embodiment according to the present invention increases the sphericity of the Cu ball 1 covered with the metal layer 2 and the solder layer 3, thereby increasing the true sphere of the Cu core ball 11B. The degree can be increased. Below, the preferable aspect of the Cu ball | bowl 1 which comprises Cu core ball | bowl 11A, 11B is demonstrated.

-The sphericity of the Cu ball: 0.95 or more In the present invention, the sphericity represents a deviation from the sphere. The sphericity is an arithmetic average value calculated when the diameter of each of the 500 Cu balls is divided by the major axis. The closer the value is to the upper limit of 1.00, the closer to the true sphere. The sphericity is obtained by various methods such as a least square center method (LSC method), a minimum region center method (MZC method), a maximum inscribed center method (MIC method), and a minimum circumscribed center method (MCC method). . In the present invention, the length of the major axis and the length of the diameter refer to a length measured by an ultra quick vision, ULTRA QV350-PRO measuring device manufactured by Mitutoyo Corporation.

  The Cu ball 1 preferably has a sphericity of 0.95 or more, more preferably a sphericity of 0.98 or more from the viewpoint of maintaining an appropriate space between the substrates, and is 0.99 or more. Even more preferably. If the sphericity of the Cu ball 1 is less than 0.95, the Cu ball 1 has an indeterminate shape, so that bumps with non-uniform height are formed during bump formation, and the possibility of poor bonding is increased. If the sphericity is 0.95 or more, the Cu ball 1 does not melt at the soldering temperature, and therefore, variation in height in the solder joint 50 can be suppressed. Thereby, the joining defect of the semiconductor chip 10 and the printed circuit board 40 can be prevented reliably.

・ Purity of Cu ball: 99.995 mass% or more and 99.9995 mass% or less In general, Cu having a lower purity contains impurity elements that become crystal nuclei of Cu ball 1 in Cu than Cu having a higher purity. Since it can be secured, the sphericity increases. On the other hand, the electrical conductivity and thermal conductivity of the Cu ball 1 with low purity deteriorate.

  Therefore, when the Cu ball 1 has a purity of 99.995 mass% (4N5) or more and 99.9995 mass% (5N5) or less, sufficient sphericity can be ensured. If the purity of the Cu ball 1 is 4N5 or more and 5N5 or less, the α dose can be sufficiently reduced, and the deterioration of the electrical conductivity and thermal conductivity of the Cu ball 1 due to the decrease in purity can be suppressed.

  When the Cu ball 1 is manufactured, the Cu material, which is an example of a metal material formed into small pieces of a predetermined shape, is melted by heating, and the molten Cu becomes spherical due to surface tension, which is solidified by rapid cooling to become the Cu ball 1. . In the process where the molten Cu solidifies from the liquid state, crystal grains grow in the spherical molten Cu. At this time, if there are many impurity elements, the impurity elements serve as crystal nuclei and growth of crystal grains is suppressed. Therefore, the spherical molten Cu becomes a Cu ball 1 having a 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 grains grow with a certain direction without being suppressed. As a result, a part of the surface of the spherical molten Cu protrudes and solidifies to lower the sphericity. As the impurity element, Fe, Ag, Ni, P, S, Sb, Bi, Zn, Al, As, Cd, Pb, In, Sn, Au, U, Th, and the like can be considered.

  Below, the content of impurities defining the purity and sphericity of the Cu ball 1 will be described.

-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, in particular, at least of Fe, Ag and Ni The total content of the one kind 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 among Fe, Ag and Ni, When 2 or more types of these are contained, it is preferable that content of 2 or more types is 5.0 mass ppm or more and 50.0 mass ppm or less. Since Fe, Ag, and Ni become crystal nuclei when melted in the manufacturing process of the Cu ball 1, if a certain amount of Fe, Ag, or Ni is contained in Cu, the Cu ball 1 having a high sphericity can be manufactured. it can. Therefore, at least one of Fe, Ag, and Ni is an important element for estimating the content of impurity elements. Further, when 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, discoloration of the Cu ball 1 can be suppressed, and the Cu ball 1 is The desired Vickers hardness can be realized without performing an annealing step of slowly recrystallizing the Cu ball 1 by slowly cooling after heating gently.

-The content of S is 0 mass ppm or more and 1.0 mass ppm or less. Cu ball 1 containing S in a predetermined amount or more easily forms a sulfide or sulfur oxide during heating, so that wettability is reduced. , S content needs to be 0 mass ppm or more and 1.0 mass ppm or less. The Cu ball 1 in which more sulfides and sulfur oxides are formed has a lower brightness on the surface of the Cu ball. Therefore, as will be described in detail later, if the result of measuring the brightness of the Cu ball surface is a predetermined value or less, the formation of sulfides and sulfur oxides is suppressed, and it can be determined that the wettability is good. .

-Content of P is 0 mass ppm or more and less than 3.0 mass ppm P may have a bad influence on Cu ball | bowl 1 by changing to phosphoric acid or becoming Cu complex. Further, since the Cu ball 1 containing a predetermined amount of P has high hardness, the P content is preferably 0 mass ppm or more and less than 3.0 mass ppm, and preferably less than 1.0 mass ppm. More preferred.

Other impurity elements Other than the above-mentioned impurity elements contained in the Cu ball 1, impurity elements such as Sb, Bi, Zn, Al, As, Cd, Pb, In, Sn, Au (hereinafter referred to as “other impurity elements”) It is preferable that the content of each is 0 mass ppm or more and less than 50.0 mass ppm.

  As described above, the Cu ball 1 contains at least one of Fe, Ag, and Ni as an essential element. However, since the Cu ball 1 cannot prevent elements other than Fe, Ag, and Ni from being mixed with the current technology, the Cu ball 1 substantially contains other impurity elements other than Fe, Ag, and Ni. However, when the content of other impurity elements is less than 1 ppm by mass, the effects and influences due to the addition of each element are hardly exhibited. Moreover, when analyzing the element contained in Cu ball | bowl, when content of an impurity element is less than 1 mass ppm, this value is below a detection limit ability depending on an analyzer. Therefore, when the total content of at least one of Fe, Ag, and Ni is 50 ppm by mass, if the content of other impurity elements is less than 1 ppm by mass, the purity of the Cu ball 1 is substantially 4N5 (99.995% by mass). Further, when the total content of at least one of Fe, Ag, and Ni is 5 ppm by mass, if the content of other impurity elements is less than 1 ppm by mass, the purity of the Cu ball 1 is substantially 5N5 (99.9995% by mass).

-Vickers hardness of Cu ball: 55.5 HV or less The Vickers hardness of Cu ball 1 is preferably 55.5 HV or less. When the Vickers hardness is large, durability against external stress is lowered, drop impact resistance is deteriorated, and cracks are easily generated. In addition, when a hard Cu ball is used when an auxiliary force such as pressurization is applied when forming bumps or joints for three-dimensional mounting, there is a possibility of causing electrode collapse or the like. In addition, when the Vickers hardness of the Cu ball 1 is large, the crystal grains become smaller than a certain level, thereby deteriorating electrical conductivity. If the Vickers hardness of the Cu ball 1 is 55.5 HV or less, the drop impact resistance is good and cracks can be suppressed, electrode collapse and the like can be suppressed, and further, electrical conductivity deterioration can be suppressed. In the present embodiment, the lower limit of the Vickers hardness may be more than 0 HV, preferably 20 HV or more.

-Α dose of Cu ball: 0.0200 cph / cm ² or less In order to make the α dose such that soft error does not become a problem in high-density mounting of electronic components, the α dose of Cu ball 1 is 0.0200 cph / cm ² or less. It is preferable that The α dose is preferably 0.0100 cph / cm ² or less, more preferably 0.0050 cph / cm ² or less, and further preferably 0.0020 cph from the viewpoint of suppressing soft errors in further high-density mounting. / Cm ² or less, and most preferably 0.0010 cph / cm ² or less. In order to suppress soft errors due to the α dose, the content of radioisotopes such as U and Th is preferably less than 5 mass ppb.

Discoloration resistance: Brightness of 55 or more The Cu ball 1 preferably has a lightness of 55 or more. Lightness and is a L ^* a ^* b ^* L ^* value of color system. Since the Cu ball 1 on which the sulfide or sulfur oxide derived from S is formed has a low brightness, if the brightness is 55 or more, it can be said that the sulfide or sulfur oxide is suppressed. Further, the Cu ball 1 having a brightness of 55 or more has good wettability during mounting. 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 is not sufficiently suppressed from forming sulfides or sulfur oxides. Sulfides and sulfur oxides adversely affect the Cu ball 1 and also deteriorate the wettability when the Cu ball 1 is directly bonded onto the electrode. Deterioration of wettability causes non-wetting and deterioration of self-alignment property.

-Diameter of Cu ball: 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 ball 1 can be produced stably, and connection short-circuiting when the terminals are at a narrow pitch can be suppressed. Here, for example, when the Cu ball 1 is used for the paste, the “Cu ball” may be referred to as “Cu powder”. When “Cu balls” are used for “Cu powder”, it is generally preferable that the diameter of the Cu balls is 1 to 300 μm.

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

Solder layer The Cu core balls 11A and 11B of the respective embodiments according to the present invention include a solder layer 3 made of a solder alloy made of Sn and unavoidable impurities, a solder layer 3 made of a solder alloy made of Bi and unavoidable impurities, or Sn and The Cu ball 1 is covered with a solder layer 3 made of a solder alloy containing Bi as an essential element. In particular, the Cu core balls 11A and 11B of the respective embodiments according to the present invention are Cu core balls in which the distribution of Bi in the solder layer 3 made of a solder alloy containing Sn and Bi as essential elements is made uniform, and The present invention provides solder joints, solder pastes and foam solders using the same.

  The composition of the solder layer 3 of the embodiment according to the present invention is made of a (Sn—Bi) -based alloy containing Sn and Bi. About content of Sn, it is preferable that it is 40.0 mass% or more with respect to the whole alloy. Regarding the Bi content, if the Bi content with respect to the entire alloy is in the range of 0.1 to 99.8% by mass, the concentration ratio of Bi is controlled within a predetermined range of 88.7 to 110.7%. The Bi distribution in the solder layer 3 can be made uniform.

  For example, when the target value of the Bi content is 58.0% by mass, the allowable range of the Bi content and concentration ratio is 52.39% by mass (concentration ratio 90.3%) to 62.97% by mass. (The concentration ratio is 108.6%), the Bi concentration ratio 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. A solder alloy having a target Bi content of 58.0% by mass is referred to as a (Sn-58Bi) solder alloy.

  Moreover, when the target value of the Bi content is 40.0% by mass, the allowable range of the Bi content and the concentration ratio is 38.41% by mass (concentration ratio 96.0%) to 41.11% by mass. (The concentration ratio is 102.8%), the Bi concentration ratio 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. A solder alloy having a target Bi content of 40.0 mass% is referred to as a (Sn-40Bi) solder alloy.

  Furthermore, when the target value of the Bi content is 3.0% by mass, the allowable range of the Bi content and concentration ratio is 2.66% by mass (concentration ratio 88.7%) to 3.32% by mass. (The concentration ratio is 110.7%), the Bi concentration ratio 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. A solder alloy having a target Bi content of 3.0 mass% is referred to as a (Sn-3Bi) -based solder alloy.

The allowable range means a range in which soldering such as bump formation can be performed without any problem within this range. In addition, the concentration ratio (%) is the measured value (mass%) relative to the target content (mass%), or the ratio of the average value (mass%) of the measured value to the target content (mass%) ( %). That is, the concentration ratio (%) is
Concentration ratio (%) = (Measured value (mass%) / Target content (mass%)) × 100
Or
Concentration ratio (%) = (average value of measurement values (mass%) / target content (mass%)) × 100
Can be expressed as:

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

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

  As described above, the Bi content in the solder layer 3 is 52.39% by mass (concentration ratio: 90.3%) to 62.97% by mass (concentration ratio: 108.%) with respect to the target value of 58% by mass. 6%) is preferable. Moreover, the Bi content in the solder layer 3 is 38.41% by mass (concentration ratio 96.0%) to 41.11% by mass (concentration ratio 102.8%) with respect to the target value of 40% by mass. The degree is preferred. Furthermore, the Bi content in the solder layer 3 is 2.66 mass% (concentration ratio 88.7%) to 3.32 mass% (concentration ratio 110.7%) as an allowable range with respect to 3 mass% of the target value. The degree is preferred.

  Although the thickness of the solder layer 3 varies depending on the particle diameter of the Cu ball 1, it is preferably 100 μm or less on one side in the radial direction in order to ensure a sufficient amount of solder bonding. The solder layer 3 can be formed by known electroplating or electroless plating. However, when the solder layer is formed by hot dipping, the thickness of the solder layer does not become uniform when the grain size of the Cu balls is reduced. The eccentricity of the Cu ball in the Cu core ball and the unevenness on the surface of the solder layer increase, and the sphericity of the Cu core ball decreases. For this reason, the solder layer 3 is formed by an electroplating process.

  As the plating solution, a mixed solution of an organic acid, a Sn compound, a Bi (III) compound and a surfactant is used. Examples of the Sn compound include tin salts of organic sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, 2-propanolsulfonic acid, and p-phenolsulfonic acid, tin sulfate, tin oxide, tin nitrate, tin chloride, tin bromide, iodine 1st tin oxide, tin phosphate, tin pyrophosphate, tin acetate, tin formate, tin citrate, tin gluconate, tin tartrate, tin lactate, tin succinate, tin sulfamate, tin borofluoride, tin fluorosilicate etc. Sn compound is mentioned. Examples of the Bi (III) compound include fluorinated Bi, Bi chloride, Bi bromide, Bi iodide, Bi citrate, Bi methanesulfonate, Bi nitrate, Bi sulfide, Bi oxide, Bi hydroxide and Bi phosphate. Is mentioned. These compounds can be used singly or in combination of two or more.

  When a Sn-Bi solder alloy composition consisting of Sn and Bi is formed by electroplating, Bi is prioritized over Sn and taken into the solder plating layer, so the Bi concentration in the electroplating solution and the solder plating There is a problem that the amount of Bi in the layers does not match, and a solder alloy plating layer having a uniform Bi concentration distribution cannot be formed. Therefore, a predetermined DC voltage is applied between the anode electrode and the cathode electrode so as to satisfy the conditions of FIG. 4, and the Bi concentration in the liquid is adjusted to be uniform while the Cu ball is swung. Perform electroplating.

  The generation process of the solder layer 3 by this plating process will be described in more detail with reference to FIG. FIG. 4 shows the relationship between the Bi concentration (curve Lb) in the plating solution and the Bi concentration (curve La) in the solder layer 3 in the electroplating treatment with the (Sn-58Bi) -based solder alloy. FIG.

  In this example, the initial value of the Cu ball having a particle size of 215 μm is used. The thickness of the solder layer is monitored step by step, and in this example, Cu core balls when the thickness of the solder layer sequentially increases by a predetermined value are collected as a sample each time. The collected sample is washed and dried, and the particle size is measured.

  When the content of Bi in the solder layer when the particle size of the Cu core ball at the measurement timing is the target value was sequentially measured, a result as shown by a curve La in FIG. 4 was obtained. From this result, it can be seen that even if the solder layer is successively increased by a predetermined thickness, the Bi content at that time is almost the same value as the immediately preceding content. In the case of the curve La, the Bi content 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 uniform (equal) with respect to the plating thickness and there is no concentration gradient.

  5 and 6 are enlarged sectional views of the Cu core ball. FIG. 5 shows a Cu core ball 11B in which the Cu ball 1 is covered with a metal layer 2 and the metal layer 2 is covered with a solder layer 3. FIG. 6 is an image taken using FE-EPMA. As is clear from FIG. 5 and FIG. 6 which is an enlarged view of this, it is well understood that the solder layer 3 has grown while Sn and Bi are mixed homogeneously.

  Since the Bi concentration in the solder layer is maintained almost the same even when the thickness of the solder layer grows, it is clear that Bi in the solder layer grows in a substantially homogeneous distribution. became. The plating process is performed in a state in which the Bi concentration in the plating solution is made uniform so that the Bi concentration falls within an intended value. In this example, the Bi content in the solder layer is set to the target value of 58% by mass, so the Bi concentration in the plating solution is controlled to reach the target value.

  In order to keep the concentration distribution of Bi in the solder layer within a predetermined value, plating is performed while controlling the voltage and current. By such a plating process, the distribution of Bi in the solder layer can be maintained at an expected value.

  In addition, in FIG. 4, it shows as the Bi density | concentration in the solder layer shown as the curve La, and the curve Lb. The reason why the Bi concentrations in the plating solution do not match is that Bi in the plating solution is preferentially taken into the solder layer over Sn in the plating solution.

  The Cu core balls 11 </ b> A and 11 </ b> B may constitute the Cu core balls 11 </ b> A and 11 </ b> B of low α rays by using a low α dose solder alloy for the solder layer 3.

  Next, the metal layer 2 that covers the Cu ball 1 in the Cu core ball 11B according to the second embodiment of the present invention will be described.

Metal layer The metal layer 2 is, 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 multiple layers) containing two or more elements of Ni, Co, Fe, and Pd. Become. The metal layer 2 remains unmelted at the soldering temperature when the Cu core ball 11B is used for a solder bump, and contributes to the height of the solder joint. Therefore, the sphericity is high and the variation in diameter is small. Composed. Further, from the viewpoint of suppressing soft errors, the α dose is configured to be low.

-Composition and film thickness of metal layer The composition of the metal layer 2 is 100% of Ni, Co, Fe, and Pd except for inevitable impurities when the metal layer 2 is composed of a single Ni, Co, Fe, or Pd. It is. Moreover, the metal used for the metal layer 2 is not limited to a single metal, and an alloy in which two or more elements are combined among Ni, Co, Fe, or Pd may be used. Furthermore, the metal layer 2 includes a plurality of layers in which a layer composed of a single Ni, Co, Fe, or Pd and a layer composed of an alloy that combines two or more elements of Ni, Co, Fe, or Pd are appropriately combined. You may comprise. The film thickness T2 of the metal layer 2 is, for example, 1 μm to 20 μm.

Α dose of Cu core ball: 0.0200 cph / cm ² or less The α dose of Cu core ball 11A of the first embodiment and Cu core ball 11B of the second embodiment according to the present invention is 0.0200 cph / It is preferable that it is cm ² or less. This is an α dose that does not cause a soft error in high-density mounting of electronic components. The α dose of the Cu core ball 11A according to the first embodiment of the present invention is achieved when the α dose of the solder layer 3 constituting the Cu core ball 11A is 0.0200 cph / cm ² or less. Therefore, since the Cu core ball 11A of the first embodiment according to the present invention is covered with such a solder layer 3, it exhibits a low α dose. The α dose of the Cu core ball 11B of the second embodiment according to the present invention is achieved when the α dose of the metal layer 2 and the solder layer 3 constituting the Cu core ball 11B is 0.0200 cph / cm ² or less. Is done. Therefore, since the Cu core ball 11B of the second embodiment according to the present invention is covered with such a metal layer 2 and a solder layer 3, it exhibits a low α dose. The α dose is preferably 0.0100 cph / cm ² or less, more preferably 0.0050 cph / cm ² or less, and further preferably 0.0020 cph from the viewpoint of suppressing soft errors in further high-density mounting. / Cm ² or less, and most preferably 0.0010 cph / cm ² or less. The contents of U and Th in the metal layer 2 and the solder layer 3 are each 5 ppb or less in order to make the α dose of the Cu ball 1 0.0200 cph / cm ² or less. Further, from the viewpoint of suppressing soft errors in current or future high-density mounting, the contents of U and Th are preferably 2 ppb or less, respectively.

· Cu nuclei ball sphericity: 0.95 or more Cu first embodiment of the Cu core ball 11A of the ball 1 according to the present invention coated with the solder layer 3, and a metal of Cu balls 1 layer 2 and The sphericity of the Cu core ball 11B of the second embodiment according to the present invention covered with the solder layer 3 is preferably 0.95 or more, and more preferably 0.98 or more. Preferably, it is still more preferably 0.99 or more. If the sphericity of the Cu core balls 11A and 11B is less than 0.95, the Cu core balls 11A and 11B have an indefinite shape. Therefore, when the Cu core balls 11A and 11B are mounted on electrodes and reflow is performed, Cu The core balls 11A and 11B are displaced, and the self-alignment property is also deteriorated. If the sphericity of the Cu core balls 11A and 11B is 0.95 or more, the self-alignment property when the Cu core balls 11A and 11B are mounted on the electrode 100 or the like of the semiconductor chip 10 can be secured. Since the Cu ball 1 has a sphericity of 0.95 or more, the Cu core balls 11A and 11B do not melt at the soldering temperature. The variation of can be suppressed. Thereby, the joining defect of the semiconductor chip 10 and the printed circuit board 40 can be prevented reliably.

-Barrier function of metal layer When Cu of Cu balls diffuses into the solder (paste) used for bonding between the Cu core ball and the electrode during reflow, hard and brittle Cu ₆ Sn in the solder layer and the connection interface ₅ , a large amount of Cu ₃ Sn intermetallic compound is formed, and when subjected to an impact, cracks may develop and the connection portion may be destroyed. Therefore, in order to obtain sufficient connection strength, it is preferable that the diffusion of Cu from the Cu ball to the solder can be suppressed (barrier). Therefore, in the Cu core ball 11B of the second embodiment, the metal layer 2 functioning as a barrier layer is formed on the surface of the Cu ball 1, so that the Cu of the Cu ball 1 is prevented from diffusing into the paste solder. it can.

-Solder paste, foam solder, solder joint Moreover, a solder paste can also be comprised by making Cu core ball 11A or Cu core ball 11B contain in a solder. Foam solder can be configured by dispersing the Cu core ball 11A or the Cu core ball 11B in the solder. The Cu core ball 11A or the Cu core ball 11B can also be used to form a solder joint that joins electrodes.

-Manufacturing method of Cu ball Next, an example of the manufacturing method of Cu ball 1 is explained. As an example of a metal material, a Cu material is placed on a heat-resistant plate such as ceramic (hereinafter referred to as “heat-resistant plate”) and heated in a furnace together with the heat-resistant plate. The heat-resistant plate is provided with a number of circular grooves whose bottoms are hemispherical. The diameter and depth of the groove are appropriately set according to the particle diameter of the Cu ball 1, and are, for example, 0.8 mm in diameter and 0.88 mm in depth. Further, chip-shaped Cu materials obtained by cutting the Cu fine wires are put into the grooves of the heat-resistant plate one by one. The heat-resistant plate in which the Cu material is put in the groove is heated to 1100 to 1300 ° C. in a furnace filled with ammonia decomposition gas and is heated for 30 to 60 minutes. At this time, when the furnace temperature becomes equal to or higher than the melting point of Cu, the Cu material melts and becomes spherical. Thereafter, the inside of the furnace is cooled, and the Cu ball 1 is rapidly cooled in the groove of the heat-resistant plate to be molded.

  As another method, an atomizing method in which molten Cu is dropped from an orifice provided at the bottom of the crucible, and the droplet is rapidly cooled to room temperature (for example, 25 ° C.) to form a Cu ball 1, There is a method in which plasma forms a ball by heating Cu cut metal to 1000 ° C. or higher.

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

  As a Cu material that is a raw material of the Cu ball 1, for example, a nugget 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 preventing the purity of the Cu ball 1 from being lowered too much.

  Thus, when using high purity Cu material, you may lower the holding | maintenance temperature of molten Cu to about 1000 degreeC similarly to the past, without performing the above-mentioned heat processing. Thus, the above-described heat treatment may be omitted or changed as appropriate according to the purity of the Cu material and the α dose. Further, when a Cu ball 1 having a high α dose or a deformed Cu ball 1 is manufactured, the Cu ball 1 may be reused as a raw material, and the α dose can be further reduced.

  As a method for forming the solder layer 3 on the Cu ball 1, the above-described electroplating method or electroless plating method can be employed.

  As a method of forming the metal layer 2 on the Cu ball 1, a known method such as electroplating can be employed. For example, when forming a Ni plating layer, a Ni plating solution is prepared using a Ni metal or a Ni metal salt for a Ni plating bath type, and the Cu ball 1 is immersed in the adjusted Ni plating solution. By depositing, a Ni plating layer is formed on the surface of the Cu ball 1. Further, as another method for forming the metal layer 2 such as a Ni plating layer, a known electroless plating method or the like can be adopted. When the solder layer 3 made of Sn alloy is formed on the surface of the metal layer 2, the above-described electroplating method or electroless plating method can be employed.

  Examples of the present invention will be described below, but the present invention is not limited thereto. Cu balls of Examples 1 to 20 and Comparative Examples 1 to 12 were prepared with the compositions shown in Table 1 and Table 2 below, and the sphericity, Vickers hardness, α dose, and discoloration resistance of the Cu balls were measured. .

  Further, the Cu balls of Examples 1 to 20 described above were coated with the solder layers of the solder alloys of Composition Examples 1 to 3 shown in Table 3 to produce Cu core balls of Examples 1A to 20A. The sphericity of was measured. Further, the Cu balls of Examples 1 to 20 described above were coated with a metal layer and a solder layer of the solder alloys of Composition Examples 1 to 3 shown in Table 4 to produce Cu core balls of Examples 1B to 20B. The sphericity of the nuclear ball was measured.

  Further, the above-described Cu balls of Comparative Examples 1 to 12 were coated with a solder layer made of a solder alloy of Composition Examples 1 to 3 shown in Table 5 to produce Cu core balls of Comparative Examples 1A to 12A. The sphericity of was measured. Further, the Cu balls of Comparative Examples 1 to 12 described above were coated with a metal layer and a solder layer of the solder alloys of Composition Examples 1 to 3 shown in Table 6 to produce Cu core balls of Comparative Examples 1B to 12B. The sphericity of the nuclear ball was measured.

  In the table below, numbers without units indicate mass ppm or mass ppb. Specifically, the numerical values indicating the content ratios of Fe, Ag, Ni, P, S, Sb, Bi, Zn, Al, As, Cd, Pb, In, Sn, and Au in the table represent mass ppm. “<1” indicates that the content ratio of the corresponding impurity element to the Cu balls is less than 1 mass ppm. Moreover, the numerical value which shows the content rate of U and Th in a table | surface represents mass ppb. “<5” indicates that the content ratio of the corresponding impurity element to the Cu balls is less than 5 mass ppb. “Total amount of impurities” indicates the total proportion of impurity elements contained in the Cu balls.

-Preparation of Cu ball The preparation conditions of Cu ball were examined. A nugget material was prepared as a Cu material as an example of a metal material. As the Cu materials of Examples 1 to 13 and 20 and Comparative Examples 1 to 12, those having a purity of 6N were used, and as the Cu materials of Examples 14 to 19, those having a purity of 5N were used. After each Cu material was put into a crucible, the temperature of the crucible was raised to 1200 ° C., heated for 45 minutes to melt the Cu material, and molten Cu was dropped from an orifice provided at the bottom of the crucible to produce. The droplet was rapidly cooled to room temperature (18 ° C.) and formed into a Cu ball. As a result, Cu balls having average particle diameters as shown in the following tables were produced. Elemental analysis can be performed with high accuracy by using inductively coupled plasma mass spectrometry (ICP-MS analysis) or glow discharge mass spectrometry (GD-MS analysis), but in this example, it was performed by ICP-MS analysis. The ball diameter of the Cu balls was 250 μm in Examples 1 to 17, Examples 19 to 20, and Comparative Examples 1 to 12. In Example 18, the thickness was 180 μm.

-Production of Cu Core Ball Using the Cu balls of Examples 1 to 20 described above, Examples 1A to 17A and Examples 19A to 20A were made of the solder alloys of Composition Examples 1 to 3 with a thickness of 23 μm on one side. A solder layer was formed by electroplating to prepare Cu core balls of Examples 1A to 17A and Examples 19A to 20A. For the Cu core ball of Example 18A, a solder layer was formed by electroplating using the solder alloys of Composition Examples 1 to 3 with a thickness of 33 μm on one side to prepare the Cu core ball of Example 18A.

  Moreover, using Examples 1-20 Cu ball | bowl mentioned above, about Example 1B-17B and Example 19B-20B, a Ni plating layer is formed by the thickness of 2 micrometers on one side as a metal layer, and also one side Cu core balls of Examples 1B to 17B and Examples 19B to 20B were prepared by forming a solder layer by electroplating using the solder alloys of Composition Examples 1 to 3 with a thickness of 23 μm. For 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 a solder layer formed by electroplating with the solder alloys of Composition Examples 1 to 3 was formed with a thickness of 33 μm on one side. Thus, a Cu core ball of Example 18B was produced.

  Furthermore, using the Cu balls of Comparative Examples 1 to 12 described above, a solder layer made of the solder alloy of Composition Examples 1 to 3 was formed with a thickness of 23 μm on one side to prepare Cu core balls of Comparative Examples 1A to 12A. . Moreover, using the Cu ball | bowl of the comparative examples 1-12 mentioned above, Ni plating layer is formed by the thickness of 2 micrometers on one side as a metal layer, and also by the solder alloy of the composition examples 1-3 by thickness of 23 micrometers on one side. A solder layer was formed to prepare Cu core balls of Comparative Examples 1B to 12B.

  Below, each evaluation method of the sphericity of Cu ball | bowl and Cu nucleus ball | bowl, alpha dose of Cu ball | bowl, Vickers hardness, and discoloration resistance is explained in full detail.

-Sphericality The sphericity of Cu balls and Cu core balls was measured with a CNC image measurement system. The apparatus is Ultra Quick Vision, ULTRA QV350-PRO, manufactured by Mitutoyo Corporation.

[Evaluation criteria for sphericity]
In the following tables, the evaluation criteria for the sphericity of Cu balls and Cu core balls are as follows.
○○○: The sphericity was 0.99 or more ○○: The sphericity was 0.98 or more and less than 0.99 〇: The sphericity was 0.95 or more and less than 0.98 X: The sphericity was less than 0.95

-Vickers hardness The Vickers hardness of the Cu ball was measured according to "Vickers hardness test-test method JIS Z2244". As the apparatus, a micro Vickers hardness tester manufactured by Akashi Seisakusho Co., Ltd. and AKASHI micro hardness tester MVK-F 12001-Q were used.

[Vickers hardness evaluation criteria]
In the following tables, the evaluation criteria for the Vickers hardness of Cu balls were as follows.
○: Over 0 HV and below 55.5 HV ×: Over 55.5 HV

・ Α Dose The method of measuring the α dose of Cu balls is as follows. For measuring the α dose, an α ray measuring device of a gas flow proportional counter was used. The measurement sample is a 300 mm × 300 mm flat shallow container in which Cu balls are spread until the bottom of the container is not visible. This measurement sample was placed in an α-ray measuring apparatus and allowed to stand for 24 hours in a PR-10 gas flow, and then the α dose was measured.

[Evaluation criteria for alpha dose]
In the following tables, the evaluation criteria for the α dose of Cu balls were as follows.
○: α dose was 0.0200 cph / cm ² or less ×: α dose exceeded 0.0200 cph / cm ²

  In addition, PR-10 gas (argon 90% -methane 10%) used for the measurement has passed three weeks or more after the gas cylinder was filled with PR-10 gas. The cylinder that was used for more than 3 weeks was used because the JEDEC STANDARD-Alpha Radiation Measurement Measurement was established by JEDEC (Joint Electron Engineering Engineering Coil) so that alpha rays would not be generated by radon in the atmosphere entering the gas cylinder. This is because JESD221 is followed.

・ Discoloration resistance In order to measure the discoloration resistance of Cu balls, the Cu balls were heated for 420 seconds at a setting of 200 ° C. using a thermostatic chamber in an air atmosphere, and the change in lightness was measured. It was evaluated whether it was a Cu ball that could withstand. The lightness is measured using a Konica Minolta CM-3500d spectrophotometer, with a D65 light source and a 10-degree field of view, in accordance with JIS Z 8722 “Color Measurement Method-Reflection and Transmission Object Color”. And obtained from the color values (L ^* , a ^* , b ^* ). (L ^* , a ^* , b ^* ) are defined in JIS Z 8729 “Color Display Method-L ^* a ^* b ^* Color System and L ^* u ^* v ^* Color System”. It is. L ^* is lightness, a ^* is redness, and b ^* is yellowness.

[Evaluation criteria for discoloration resistance]
In the following tables, the evaluation criteria for the discoloration resistance of Cu balls were as follows.
○: The brightness after 420 seconds was 55 or more. X: The brightness after 420 seconds was less than 55.

・ Comprehensive evaluation In all of the evaluation methods and evaluation criteria described above, Cu balls that were ○, ○○, or ○○○ in any of sphericity, Vickers hardness, α dose, and discoloration resistance were did. On the other hand, Cu balls in which any one of sphericity, Vickers hardness, α dose and discoloration resistance was x were evaluated as x in the comprehensive evaluation.

  Further, Cu core balls having a sphericity of ◯, OO or OO in the evaluation method and evaluation criteria described above were evaluated as ◯ in the overall evaluation together with the evaluation in the Cu balls. On the other hand, a Cu core ball having a sphericity of x was evaluated as x in the overall evaluation. In addition, even if the sphericity is ◯, OO or OO in the evaluation of the Cu core ball, any one of sphericity, Vickers hardness, α dose, and discoloration resistance in the evaluation of the Cu ball. For Cu core balls that were marked with x, the overall evaluation was x.

  In addition, since the Vickers hardness of Cu core ball depends on the Ni plating layer which is an example of a solder layer and a metal layer, the Vickers hardness of Cu core ball is not evaluated. However, in the Cu core ball, if 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 and can suppress cracks, and the electrode collapses. In addition, it is possible to suppress deterioration of electrical conductivity.

  On the other hand, when the Vickers hardness of the Cu ball is larger than the range specified by the present invention in the Cu core ball, durability against external stress is lowered, drop impact resistance is deteriorated and cracks are generated. The problem of being easy to do cannot be solved.

  For this reason, since the Cu core ball using the Cu ball of Comparative Examples 8 to 11 having a Vickers hardness exceeding 55.5 HV is not suitable for the evaluation of the Vickers hardness, the overall evaluation is x.

  Moreover, since 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, the discoloration resistance of the Cu core ball is not evaluated. However, if the brightness of the Cu ball is within the range specified in the present invention, sulfides and sulfur oxides on the surface of the Cu ball are suppressed, and the coating with a metal layer such as a solder layer or a Ni plating layer is possible. Is suitable.

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

  For this reason, since the Cu core ball using the Cu balls of Comparative Examples 1 to 6 whose lightness after 420 seconds was less than 55 is not suitable for the evaluation of discoloration resistance, the overall evaluation is x.

  The α dose of the Cu core ball depends on the composition of the plating solution raw material constituting the solder layer covering the Cu ball and each element in the composition. When the Ni plating layer which is an example of the metal layer which coat | covers Cu ball | bowl is provided, it depends also on the plating solution raw material which comprises Ni layer.

  When the Cu ball has a low α dose defined in the present invention, if the plating solution raw material constituting the solder layer and the Ni plating layer is a low α dose defined in the present invention, the Cu core ball is also defined in the present invention. Resulting in a low alpha dose. In contrast, if the plating solution raw material constituting the solder layer and the Ni plating layer is a high α dose exceeding the α dose prescribed in the present invention, even if the Cu ball has the low α dose described above, the Cu nucleus The ball also has a high α dose exceeding the α dose prescribed in the present invention.

  In addition, even when the α dose of the plating solution raw material constituting the solder layer and the Ni plating layer shows an α dose slightly higher than the low α dose prescribed in the present invention, impurities should be removed in the above-described plating process. Thus, the α dose is reduced to the low α dose range defined in the present invention.

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

  Hereinafter, the details of the evaluation will be described. As in Examples 1 to 12 and 19, a Cu ball having a purity of 4N5 or more and 5N5 or less and containing Fe, Ag or Ni of 5.0 to 50.0 ppm by mass. Gave good results in a comprehensive evaluation of sphericity, Vickers hardness, alpha dose and resistance to discoloration. As shown in Examples 13 to 18 and 20, Cu balls having a purity of 4N5 or more and 5N5 or less and containing Fe, Ag and Ni in a total of 5.0 mass ppm or more and 50.0 mass ppm or less are also sphericity, Vickers hardness In addition, good results were obtained in a comprehensive evaluation of α dose and discoloration resistance. 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, and the Ag content is 0 ppm or more and less than 5.0 mass ppm. The Cu ball having a Ni content of 0 mass ppm or more and less than 5.0 mass ppm and the total of Fe, Ag and Ni being 5.0 mass ppm or more is also sphericity, Vickers hardness, α dose In addition, good results were obtained in the comprehensive evaluation of discoloration resistance.

  Further, as shown in Example 19, Fe, Ag, or Ni is contained in an amount of 5.0 ppm to 50.0 ppm by mass, and other impurity elements Sb, Bi, Zn, Al, As, Cd, Pb are contained. Also, the Cu balls of Example 19 in which each of In, Sn, and Au was 50.0 mass ppm or less gave good results in comprehensive evaluation of sphericity, Vickers hardness, α dose, and discoloration resistance.

  Regarding the Cu core ball, as shown in Tables 3 and 4, it is a solder layer made of the solder alloy of Composition Example 1 containing 58.0% by mass of Bi and the balance being Sn. Cu core balls of Examples 1A to 20A coated with Cu balls, Cu balls of Examples 1 to 20 coated with a Ni plating layer, and further coated with a solder layer of the solder alloy of Composition Example 1 Even with a 20B Cu core ball, good results were obtained in the overall evaluation of sphericity.

  A 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 being Sn. Examples 1A to 1A in which Cu core balls of Examples 1A to 20A coated with Cu balls and Cu balls of Examples 1 to 20 were coated with a Ni plating layer and further coated with a solder layer of a solder alloy of Composition Example 2 Even with a 20B Cu core ball, good results were obtained in the overall evaluation of sphericity.

  A solder layer made of the solder alloy of Composition Example 3 containing 3.0% by mass of Ag, 0.8% by mass of Cu and 3.0% by mass of Bi, and the balance being Sn. Examples 1A to 1A in which Cu core balls of Examples 1A to 20A coated with Cu balls and Cu balls of Examples 1 to 20 were coated with a Ni plating layer, and further coated with a solder layer of a solder alloy of Composition Example 3 Even with a 20B Cu core ball, good results were obtained in the overall evaluation of sphericity.

  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, and the Ag content is 0 ppm or more and less than 5.0 mass ppm. A Cu ball in which the content of Ni is changed to 0 mass ppm or more and less than 5.0 mass ppm and the total of Fe, Ag and Ni is 5.0 mass ppm or more is any one of Composition Examples 1 to 3. A Cu core ball coated with a solder layer of the above solder alloy, or a Cu core ball coated with a solder layer of any one of Composition Examples 1 to 3 after coating the Cu ball with a Ni plating layer. Good results were obtained in the overall evaluation of sphericity.

  On the other hand, in the Cu ball of Comparative Example 7, the total content of Fe, Ag and Ni is less than 5.0 mass ppm, U and Th are less than 5 mass ppb, and other impurity elements are also 1 mass ppm. The Cu core ball of Comparative Example 7A in which the Cu ball of Comparative Example 7 and the Cu ball of Comparative Example 7 were coated with the solder layer of the solder alloy of each composition example, and the Cu ball of Comparative Example 7 were Ni The Cu core ball of Comparative Example 7B covered with the plating layer and further covered with the solder layer of the solder alloy of each composition example had a sphericity of less than 0.95. Moreover, even if it contains an impurity element, the Cu ball of Comparative Example 12 and the Cu ball of Comparative Example 12 in which the total content of at least one of Fe, Ag and Ni is less than 5.0 ppm by mass, Comparison of Comparative Example 12A Cu Core Ball Coated with Solder Layer of Solder Alloy of Each Composition Example and Cu Ball of Comparative Example 12 Covered with Ni Plating Layer, and further Coated with Solder Layer of Solder Alloy of Each Composition Example The Cu core ball of Example 12B also had a sphericity of less than 0.95. From these results, Cu balls in which the total content of at least one of Fe, Ag, and Ni is less than 5.0 ppm by mass, and the Cu balls covered with the solder layer of the solder alloy of each composition example are Cu balls. It can be said that the core ball and the Cu core ball in which the Cu ball is coated with a Ni plating layer and further coated with a solder layer made of a solder alloy of each composition example cannot achieve high sphericity.

  Further, the Cu ball of Comparative Example 10 has a total content of Fe, Ag and Ni of 153.6 ppm by mass and the content of other impurity elements is 50 ppm by mass or less, respectively, but the Vickers hardness is 55.5 HV. As a result, good results could not be obtained. Further, the Cu ball of Comparative Example 8 has a total content of Fe, Ag and Ni of 150.0 ppm by mass, and the content of other impurity elements, particularly Sn of 151.0 ppm by mass, The Vickers hardness exceeded 55.5 HV, and good results were not obtained. Therefore, even if the Cu ball has a purity of 4N5 or more and 5N5 or less, a Cu ball having a total content of at least one of Fe, Ag and Ni exceeding 50.0 ppm by mass has a large Vickers hardness. Therefore, it can be said that low hardness cannot be realized. As described above, when the Vickers hardness of the Cu ball is larger than the range specified in the present invention, durability against external stress is reduced, drop impact resistance is deteriorated, and cracks are easily generated. This problem cannot be solved. Furthermore, it can be said that other impurity elements are preferably contained within a range not exceeding 50.0 ppm by mass.

  From these results, Cu balls having a purity of 4N5 or more and 5N5 or less and containing a total content of at least one of Fe, Ag and Ni of 5.0 ppm to 50.0 ppm by mass are highly spherical. It can be said that a high degree of hardness and low hardness are achieved and discoloration is suppressed. Cu core balls in which such Cu balls are coated with a solder layer made of a solder alloy of each composition example, such Cu balls are coated with a Ni plating layer, and further Cu cores covered with a solder layer made of a solder alloy of each composition example The ball achieves high sphericity, and the Cu ball achieves low hardness, so that the Cu core ball can also have good drop impact resistance and can suppress cracks, and can suppress electrode crushing, Deterioration of electrical conductivity can also be suppressed. Furthermore, since the discoloration of the Cu ball is suppressed, it is suitable for coating 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 having the same composition as these examples and a sphere diameter of 1 μm or more and 1000 μm or less are all good in comprehensive evaluation of sphericity, Vickers hardness, α dose and discoloration resistance. The result was obtained. From this, it can be said that the spherical 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.

  In the Cu ball of Example 20, the total content of Fe, Ag, and Ni is 5.0 mass ppm or more and 50.0 mass ppm or less, and P is contained in 2.9 mass ppm. Good results were obtained in a comprehensive evaluation of Vickers hardness, α dose and discoloration resistance. A Cu core ball in which the Cu balls of Example 20 were coated with a solder layer of a solder alloy of each composition example, a Cu ball of Example 20 was coated with a Ni plating layer, and further coated with a solder layer of a solder alloy of each composition example Even with a Cu core ball, good results were obtained in the overall evaluation of sphericity. The Cu ball of Comparative Example 11 had a total content of Fe, Ag and Ni of 50.0 ppm by mass or less, similar to the Cu ball of Example 20, but the Vickers hardness exceeded 5.5 HV. Results were different from the Cu balls of Example 20. Further, in Comparative Example 9, the Vickers hardness exceeded 5.5 HV. This is considered to be because the P content in Comparative Examples 9 and 11 is remarkably high. From this result, it can be seen that the Vickers hardness increases as the P content increases. Therefore, the P content is preferably less than 3 ppm by mass, and more preferably less than 1 ppm by mass.

In the Cu ball of each example, the α dose was 0.0200 cph / cm ² or less. Therefore, in the solder alloys of Composition Examples 1 to 3 that cover the Cu balls of Examples 1 to 20, the Cu nuclei of Examples 1A to 20A are obtained because each element has a low α dose defined in the present invention. The ball also has a low α dose defined in the present invention. In addition, in the case where a Ni plating layer which is an example of a metal layer covering a Cu ball is provided, in addition to the solder alloy, each element constituting the Ni plating layer has a low α dose defined in the present invention. The Cu core balls of Examples 1B to 20B also have a low α dose defined in the present invention.

  Further, in the plating process for forming the solder layer and the Ni plating layer, impurities that emit α rays contained in the alloy are removed, so that the α dose of the alloy before plating is low α defined in the present invention. Even when the α dose is slightly higher than the dose, the α dose after plating is reduced to the low α dose range defined in the present invention.

  As a result, when the Cu core ball of each example is used for high-density mounting of electronic components, the raw material constituting the solder layer and the Ni plating layer has a low α dose defined in the present invention, so that a soft error occurs. Can be suppressed.

  In the Cu ball of Comparative Example 7, good results with discoloration resistance were obtained, while in Comparative Examples 1 to 6, good results with discoloration resistance were not obtained. When the Cu balls of Comparative Examples 1 to 6 and the Cu ball of Comparative Example 7 are compared, the difference in these compositions is only the S content. Therefore, it can be said that the content of S needs to be less than 1 ppm by mass in order to obtain good results with discoloration resistance. In all the Cu balls of the examples, since the S content is less than 1 ppm by mass, it can be said that the S content is preferably less than 1 ppm by mass.

  Subsequently, in order to confirm the relationship between the S content and the color fastness, the Cu balls of Example 14, Comparative Example 1 and Comparative Example 5 were heated at 200 ° C., before heating, after 60 seconds of heating, 180 After 2 seconds, a photo after 420 seconds was taken and the brightness was measured. Table 7 and FIG. 7 are graphs showing the relationship between the time when each Cu ball is heated and the brightness.

  From this table, comparing the brightness before heating and the brightness after 420 seconds after heating, the brightness of Example 14 and Comparative Examples 1 and 5 were close to 64 and 65 before heating. After 420 seconds after heating, the brightness of Comparative Example 5 containing 30.0 ppm by mass of S was the lowest, followed by Comparative Example 1 containing 10.0 ppm by mass of S, and the content of S was 1 ppm by mass. It became the order of less than Example 14. From this, it can be said that the lightness after heating becomes low, so that there is much content of S. Since the brightness of the Cu balls of Comparative Examples 1 and 5 was less than 55, it can be said that the Cu balls containing 10.0 mass ppm or more of S are likely to be discolored by forming sulfides or sulfur oxides upon heating. Moreover, if content of S is 0 mass ppm or more and 1.0 mass ppm or less, it can be said that formation of sulfide or sulfur oxide is suppressed and wettability is good. In addition, when the Cu ball | bowl of Example 14 was mounted on the electrode, favorable wettability was shown.

  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. In the Cu balls of the present example in which the P content is 0 mass ppm or more and less than 3.0 mass ppm, the sphericity is 0.95 or more. High sphericity was achieved. By realizing high sphericity, the self-alignment property when the Cu ball is mounted on an electrode or the like can be secured, and variations in the height of the Cu ball can be suppressed. The same effect can be obtained with a Cu core ball in which the Cu ball of this embodiment is coated with a solder layer, and a Cu core ball in which the Cu ball of this embodiment is coated with a metal layer and the metal layer is further coated with a solder layer.

  Moreover, in the Cu ball | bowl of a present Example, since all had Vickers hardness 55HV or less, low hardness was realizable. By realizing the low hardness, the drop impact resistance of the Cu ball can be improved. Since the Cu ball achieves low hardness, a Cu core ball in which the Cu ball of this example is coated with a solder layer, a Cu ball of this example is coated with a metal layer, and the metal layer is further coated with a solder layer. Even with a nuclear ball, the drop impact resistance is good, cracks can be suppressed, electrode crushing and the like can be suppressed, and furthermore, deterioration of electrical conductivity can be suppressed.

  Moreover, discoloration was suppressed in any of the Cu balls of this example. By suppressing the discoloration of the Cu ball, adverse effects on the Cu ball due to sulfides and sulfur oxides can be suppressed, and wettability when the Cu ball is mounted on the electrode is improved. By suppressing the discoloration of the Cu ball, it is suitable for coating with a metal layer such as a solder layer or a Ni plating layer.

  In addition, as the Cu material of this example, a Cu nugget material having a purity of 4N5 to 6N or less was used to produce a Cu ball having a purity of 4N5 or more and 5N5 or less. Even when Cu was used, good results were obtained in comprehensive evaluation for both Cu balls and Cu core balls.

  Next, in the Cu core ball in which the surface of the Cu ball is covered with a solder layer made of an Sn-based solder alloy, the distribution of elements other than Sn in the solder layer will be described. As a solder layer covering Cu balls, as shown in Japanese Patent Application Laid-Open No. 2007-44718 (referred to as Patent Document 4) and Japanese Patent No. 5367924 (referred to as Patent Document 5), a solder alloy containing Sn as a main component Is used.

  In Patent Document 4, the surface of a 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 relatively low melting temperature of 130 to 140 ° C., and is referred to as a low temperature solder.

  In Patent Document 4, the content of Bi contained in the solder layer is plated with a concentration gradient such that the inner side (inner peripheral side) is thin and the outer side (outer peripheral side) is thicker.

  Patent Document 5 also discloses a solder bump obtained by plating a Cu ball with a Sn-based solder alloy composed of Sn and Bi. The content of Bi contained in the solder layer in Patent Document 5 is plated with a concentration gradient such that the inner side (inner peripheral side) is thicker and the outer side (outer peripheral side) becomes thinner.

  The technique of Patent Document 5 has a concentration gradient completely opposite to that of Patent Document 4. This is considered to be because the density control according to Patent Document 5 is simpler and easier to make than the case according to Patent Document 4.

  As described above, when reflow treatment is performed by placing a Cu core ball obtained by plating the surface of a Cu ball with two or more Sn-based solder alloys obtained by adding other elements to Sn on the surface of the semiconductor chip. In Patent Documents 4 and 5 in which the above elements have a concentration gradient in the solder layer, the following problems are caused.

  The technique disclosed in Patent Document 4 is a solder layer having a concentration gradient in which the Bi concentration is thin on the inner peripheral side and thicker on the outer peripheral side, but such a concentration gradient (the inner side is thin and the outer side is thick). ), There is a possibility that the timing of Bi melting slightly shifts between the inner peripheral side and the outer peripheral side.

  When a deviation occurs in the melting timing, even if the outer surface of the Cu core ball starts to melt, partial melting that does not yet occur in the region on the inner peripheral surface side is mixed, resulting in the core material. Causes a slight misalignment on the melted side. In high-density mounting with a pinch pitch, solder processing due to this misalignment may be a fatal defect.

  In Patent Document 5, the concentration gradient of Bi is opposite to that of Patent Document 1. Even in this case, heat treatment by reflow is performed to connect the semiconductor packages. As in Patent Document 5, when the Bi concentration in the solder layer is high on the inner peripheral side and is heated and melted in a state where the outer peripheral side is thin, the Bi density on the inner peripheral side is high, so the solder starts to melt from the Bi region on the inner peripheral side. . Even if the Bi region on the inner peripheral side melts, the Bi region on the outer peripheral side has not yet started to melt, so that the volume expansion on the Bi region side on the inner peripheral side occurs quickly.

  Due to the slow speed on the inner and outer peripheral sides of this volume expansion, a pressure difference occurs between the inner peripheral side and the outer peripheral side (outside air) of Bi, and when the outer peripheral side of Bi begins to melt, A situation occurs in which the Cu ball that is formed is hopping off. Such a situation must be avoided.

  Thus, the Cu core ball having the solder layer made of the Sn-based solder alloy made of Sn and Bi had a defect when there was a concentration gradient in Bi in the solder layer.

Then, the effect of the uniform distribution of Bi in the solder layer 3 will be described. In order to confirm that the concentration distribution of Bi in the solder layer 3 is a value corresponding to the target value, the following experiment was conducted.
(1) A Cu core ball 11B in which the composition of the solder layer 3 is (Sn-58Bi) under the following conditions was prepared. In the following examples, Cu balls having the composition of Example 17 shown in Table 1 were used.
-Diameter of the Cu ball 1: 250 μm
・ Metal layer (Ni plating layer) 2 thickness: 2 μm
-Solder layer 3 film thickness: 23 μm
-Diameter of the Cu core ball 11B: 300 μm

  In order to facilitate the measurement of the experimental results, a Cu core ball having a relatively thin solder layer was prepared as the Cu core ball 11B.

The plating method was prepared by the electroplating method so as to satisfy the above-described conditions of FIG.
(2) As samples, ten Cu core balls 11B on which solder layers of (Sn-58Bi) solder alloy having the same composition were formed were prepared. These were used as Sample A.
(3) Ten samples A are sealed with resin.
(4) Each sealed sample A is polished together with the resin, and the cross section of each sample A is observed. The observation equipment used was FE-EPMAJXA-8530F made by JEOL.

  FIG. 8 is an explanatory diagram showing an example of a method for measuring the Bi concentration distribution of the Cu core ball. The solder layer 3 is divided into an inner layer 16a, an intermediate layer 16b, and an outer layer 16c from the surface side of the Cu ball 1 for convenience. The inner layer 16a is 9 μm from the surface of the Cu ball 1, 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. The inner layer region 17a, the intermediate layer region 17b, and the outer layer region 17c each having a width of 5 μm and a width of 40 μm were cut out, and the concentration of Bi was measured by qualitative analysis using each region as a measurement region. This operation was performed for each of the inner layer 16a, the intermediate layer 16b, and the outer layer 16c for a total of 10 fields of view.

  Such measurement work was similarly performed on samples B to D prepared separately from the sample A. For Samples B to D, for example, 10 Cu core balls 11B on which a solder layer of (Sn-58Bi) -based solder alloy having the same composition was formed were used.

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

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

  As described above, Samples A to D measure the concentration of Bi in the inner layer, the intermediate layer, and the outer layer for each of the 10 Cu core balls. For samples A to D, the measured values of the concentration of Bi in the inner layer, the intermediate layer, and the outer layer of each of the 10 Cu core balls are not shown in Table 8.

Samples A to D have a target Bi content (target value) of 58 mass%. In this case, the concentration ratio (%) of Bi in each of the 10 Cu core balls in the samples A to D can be obtained by the following equation (1) from the measured value of Bi concentration.
Concentration ratio (%) = (measured value / 58) × 100 (1)

Further, the average value of the Bi concentration can be obtained by the following equation (2) when the number of Cu core balls used as a sample is ten.
Average value of Bi concentration = total value of 10 measured values / 10 (2)

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

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

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

  Further, for sample C, the average value of the Bi concentration in the inner layer region 17a is 62.97% by mass and the concentration ratio is 108.6%, and the average value of the Bi concentration in the intermediate layer region 17b is 57.63% by mass. The concentration ratio was 99.4%, the average concentration of Bi in the outer layer region 17c was 58.67% by mass, and the concentration ratio was 101.2%.

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

  Thus, in each of the inner layer region 17a, the intermediate layer region 17b, and the outer layer region 17c, the concentration of Bi in the solder layer is within the allowable range of 52.39% by mass to 62.97% by mass. It can be seen that the density ratio of Bi is almost the target value.

  Then, for example, 10 Cu core balls manufactured in the same lot as those of Samples A to D were extracted, and each was bonded to the substrate by a normal reflow process. The joining results are also shown in Table 8.

  As for the bonding results, “no good” means that no bonding failure was measured in all the samples. Even if one sample was misaligned during bonding, and even in one sample, the Cu core ball 11B was not bonded. What was blown off was judged as “bad”.

  In either case, the inner peripheral side melts earlier than the outer peripheral side, causing a difference in volume expansion between the inner peripheral side and the outer peripheral side, so that the Cu core ball 11B is not repelled. Since melting is performed almost uniformly, there is no position shift of the nuclear material that is expected to occur due to a shift in melting timing, so there is no possibility of short-circuiting between electrodes due to position shift. Therefore, a good result was obtained in which no bonding failure occurred, and thus it was determined as “good”.

  As described above, in the case of (Sn-58Bi) based solder alloy, from the results of Table 8, 52.39 mass% (concentration ratio 90.3%) to 62.97 mass% (concentration ratio 108.6%). It was found that it was acceptable up to the range.

Next, the same measurement is performed when the quaternary Sn-based solder alloy solder layer 3 including Cu, Ni and Bi (Sn-40Bi-0.5Cu-0.03Ni) is formed. It was. The distribution of Bi at this time is 40% by mass as a target value, but the allowable range is 38.41% by mass (concentration ratio 96.0%) to 41.11% by mass (concentration ratio 102.8%). is there. In the following examples, Cu balls having the composition of Example 18 shown in Table 1 were used.
-Diameter of Cu ball 1: 180 μm
・ Metal layer (Ni plating layer) 2 thickness: 2 μm
-Solder layer 3 film thickness: 33 μm
-Diameter of the Cu core ball 11B: 250 μm

  The method for producing the Cu core ball is such that the Bi concentration in the plating solution is uniform under the same electroplating conditions as in the examples of the samples A to D using the Cu core ball using the solder alloy of (Sn-58Bi) described above. I went like that.

  Regarding the experimental method, a Cu core using a solder alloy of (Sn-58Bi), except that the inner layer 16a is 11 μm from the surface of the Cu ball, the intermediate layer 16b is 11 to 22 μm, and the outer layer 16c is 22 to 33 μm. The conditions are the same as those of the samples A to D using the balls.

  The results are shown as Samples E to H in Table 8. In this case, Bi, which is the target value, is 40% by mass, and therefore, as shown in Samples E to H, 38.41 to 41.11% by mass (both average values measured 10 times for the same sample) and Some variation (minimum 38.41% by mass (concentration ratio 96.0%) to 41.11% by mass (concentration ratio 102.8%) of the average value is acceptable, but 38. It can be seen that it is within the range of 41 mass% (concentration ratio 96.0%) to 41.11 mass% (concentration ratio 102.8%). Since a good result that did not occur was obtained, it was judged as “good”.

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

  FIG. 9 shows the relationship between the Bi concentration in the plating solution (curve Lc) and the Bi concentration in the solder layer (curve Ld) in the electroplating process with the (Sn-40Bi) solder alloy, and the Cu core ball diameter. It is a characteristic curve figure when it is set as a standard.

  In this example, the initial value of the Cu ball having a particle diameter of 250 μm is used. The thickness of the solder layer is monitored step by step, and in this example, Cu core balls when the thickness of the solder layer sequentially increases by a predetermined value are collected as a sample each time. The collected sample is washed and dried, and the particle size is measured.

  When the content of Bi in the solder layer when the particle size of the Cu core ball at the measurement timing is the target value was sequentially measured, a result as shown by a curve Lc in FIG. 9 was obtained. From this result, it can be seen that even if the solder layer is successively increased by a predetermined thickness, the Bi content at that time is almost the same value as the immediately preceding content. In the case of the curve Lc, the Bi content is approximately 40 to 42% by mass. As can be seen from the curve Lc, the concentration distribution of Bi is uniform (equal) with respect to the plating thickness, and there is no concentration gradient. The Bi concentration in the solder layer (curve Lc) and the Bi concentration in the plating solution (curve Ld) do not coincide with each other because the Bi in the plating solution has priority over the Sn in the plating solution as in FIG. This is because it is incorporated in the layer.

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

  The diameters of the Cu balls and Cu core balls used, the specifications such as the thickness of the metal layer (Ni plating layer) 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 to L in Table 8. In this case, Bi as the target value is 3% by mass, and therefore, as shown in Samples I to L, 2.66 to 3.32% by mass (both average values measured 10 times for the same sample) and However, there is some variation (minimum 2.66% by mass (concentration ratio 88.7%) to 3.32% by mass (concentration ratio 110.7%) of the average value, but this is acceptable. It can be seen that it is within the range of 66% by mass (concentration ratio 88.7%) to 3.32% by mass (concentration ratio 110.7%). Since a good result that did not occur was obtained, it was judged as “good”.

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

  Table 9 summarizes the results of the samples A to D, the samples E to H, and the samples I to L described above. The concentration ratio of Bi is 88.7 to 110.7% by mass. Here, when the sphericity was measured for the Cu core balls created in the examples of samples A to D, the examples of samples E to H, and the examples of samples I to L, all were 0.99 or more, Satisfies 0.95 or more.

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

  As a comparative example, the experimental results when the distribution of Bi in the solder layer has a concentration gradient are shown in Table 8 described above. Regarding the used Cu balls, the diameter of the Cu core balls, the film thickness of the metal layer (Ni plating layer) and the solder layer, and the experimental conditions, other than the following electroplating method, Examples of Samples A to D, Sample I The conditions are the same as in the examples of ~ L.

  In Comparative Example A, the plating solution is electroplated with a plating solution containing a Sn compound, an organic acid, and a surfactant. Then, only the Bi (III) compound is added at a stage where the plating film thickness is half of the target value. Thus, the electroplating process was performed while increasing the concentration of the Bi (III) compound while decreasing the concentration of the Sn compound in the plating solution.

  As a result, even if a solder layer having a Bi content of 58 mass% is formed as a whole solder layer, the Bi concentration in the solder layer is thin on the inner side and becomes a concentration gradient (inner layer) 0 mass%, middle layer 54.71 mass%, outer layer 100 mass%).

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

  As a result, even if a solder layer having a Bi content of the target value of 58% by mass is formed as the entire solder layer, the Bi concentration in the solder layer is higher on the inner side and lowers toward the outer side (inner layer). 82.10 mass%, middle layer 38.10 mass%, outer layer 4.10 mass%). In Comparative Examples A and B, the target Bi content is 58 (mass%), and the concentration ratio (%) is obtained by the equation (3).

  As a result, in Comparative Example A, a displacement occurred during bonding, and in Comparative Example B, the Cu core ball was repelled, so both were determined to be “defective”. Here, when the sphericity of the Cu core balls prepared in Comparative Example A and Comparative Example B was measured, both were below 0.95.

  In this way, when the Bi concentration in the solder layer 3 was changed, phenomena such as misalignment and blow-off of the Cu core ball 11B occurred.

  As described above, in each of Examples A to L, Bi in the solder layer is homogeneous, and therefore the Bi concentration over the entire region including the inner and outer peripheral sides of Bi with respect to the film thickness of the solder layer. The ratio is within a predetermined range. For this reason, in the Cu core ball of the present invention in which Bi in the solder layer is homogeneous, the inner peripheral side melts earlier than the outer peripheral side, resulting in a difference in volume expansion between the inner peripheral side and the outer peripheral side, and the Cu core ball becomes There is no such thing as being blown away.

  Further, since Bi in the solder layer is homogeneous, it melts almost uniformly over the entire surface of the Cu core ball, so that there is almost no time difference in the melting timing in the solder layer. As a result, there is no possibility of a short circuit between the electrodes due to a positional shift or the like because there is no positional shift of the Cu core ball that occurs due to a shift in melting timing. Therefore, a high quality solder joint can be provided by using this Cu core ball.

DESCRIPTION OF SYMBOLS 1 ... Cu ball | bowl, 11A, 11B ... Cu nucleus ball | bowl, 2 ... Metal layer, 3 ... Solder layer, 10 ... Semiconductor chip, 100, 41 ... Electrode, 30 ... Solder bump, 40 ... printed circuit board, 50 ... solder joint, 60 ... electronic component

Claims (18)

Cu balls,
A solder layer covering the surface of the Cu ball,
The Cu ball is
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,
S content is 0 mass ppm or more and 1.0 mass ppm or less,
The P content 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 balls is 99.995% by mass or more and 99.9995% by mass or less,
The sphericity is 0.95 or more,
The solder layer contains Sn, Bi, or a Cu core ball containing Sn and Bi. The solder layer is made of (Sn—Bi) based solder alloy containing Sn and Bi,
The concentration ratio (%) of Bi contained in the solder layer is
Concentration ratio (%) = (measured value (mass%) / target content (mass%)) × 100,
Or
When expressed as concentration ratio (%) = (average value of measured values (mass%) / target content (mass%)) × 100,
The Cu core ball according to claim 1, wherein the concentration ratio is in a range of 88.7 to 110.7%. The solder layer is made of (Sn-58Bi) based solder alloy containing Sn and Bi,
The concentration ratio (%) of Bi contained in the solder layer is
Concentration ratio (%) = (measured value (mass%) / target content (mass%)) × 100,
Or
When expressed as concentration ratio (%) = (average value of measured values (mass%) / target content (mass%)) × 100,
The Cu core ball according to claim 1, wherein the concentration ratio is in a range of 90.3 to 108.6%. The solder layer is made of (Sn-40Bi) based solder alloy containing Sn and Bi,
The concentration ratio (%) of Bi contained in the solder layer is
Concentration ratio (%) = (measured value (mass%) / target content (mass%)) × 100,
Or
When expressed as concentration ratio (%) = (average value of measured values (mass%) / target content (mass%)) × 100,
The Cu core ball according to claim 1, wherein the concentration ratio is in a range of 96.0 to 102.8%. The solder layer is made of (Sn-3Bi) based solder alloy containing Sn and Bi,
The concentration ratio (%) of Bi contained in the solder layer is
Concentration ratio (%) = (measured value (mass%) / target content (mass%)) × 100,
Or
When expressed as concentration ratio (%) = (average value of measured values (mass%) / target content (mass%)) × 100,
The Cu core ball according to claim 1, wherein the concentration ratio is in a range of 88.7 to 110.7%.   The Cu core ball according to any one of claims 1 to 5, wherein the sphericity is 0.98 or more.   The Cu core ball according to any one of claims 1 to 5, wherein the sphericity is 0.99 or more. The Cu core ball according to claim 1, wherein the α dose is 0.0200 cph / cm ² or less. The Cu core ball according to claim 1, wherein the α dose is 0.0010 cph / cm ² or less.   The metal layer which coat | covers the surface of the said Cu ball | bowl, the surface of the said metal layer is coat | covered with the said solder layer, and sphericity is 0.95 or more, The any one of Claims 1-9. Cu core ball.   The Cu core ball according to claim 10, which has a sphericity of 0.98 or more.   The Cu core ball according to claim 10, which has a sphericity of 0.99 or more. The Cu core ball according to any one of claims 10 to 12, wherein the α dose is 0.0200 cph / cm ² or less. The Cu core ball according to any one of claims 10 to 12, wherein the α dose is 0.0010 cph / cm ² or less. The Cu core ball according to claim 1, wherein a diameter of the Cu ball is not less than 1 μm and not more than 1000 μm.   A solder joint using the Cu core ball according to claim 1.   Solder paste using the Cu core ball according to any one of claims 1 to 15.   Foam solder using the Cu core ball according to any one of claims 1 to 15.