JP5680773B1 - Cu core ball, solder joint, foam solder and solder paste - Google Patents

Abstract

An object of the present invention is to suppress the occurrence of a soft error while ensuring alignment when mounting a Cu core ball on an electrode. A Cu core ball includes a Cu ball and an Ag plating film formed on the surface of the Cu ball. The Cu ball has a purity of 99.9% or more and 99.995% or less, U content is 5 ppb or less, Th content is 5 ppb or less, Pb or Bi content or Pb and Bi content The total content of both is 1 ppm or more, the sphericity is 0.95 or more, and the α dose is 0.0200 cph / cm 2 or less. The Ag plating film has a film thickness of 5 μm or less. [Selection] Figure 1

Description

  The present invention relates to a Cu core ball, a solder joint, foam solder, and a solder paste with a low α dose.

  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.

  However, when BGA is applied to a semiconductor package on which three-dimensional high-density mounting is performed, the solder balls may be crushed by the weight of the semiconductor package. If such a thing occurs, the solder may protrude from the electrodes, the electrodes may be connected, and a short circuit may occur.

  Therefore, a solder bump for electrically bonding a Cu ball onto an electrode of an electronic component using a solder paste has been studied. Solder bumps formed using Cu balls can support the semiconductor package with Cu balls that do not melt at the melting point of the solder even when the weight of the semiconductor package is applied to the solder bumps when the electronic component is mounted on a printed circuit board. it can. Therefore, the solder bump is not crushed by the weight of the semiconductor package. For example, Patent Document 1 is cited as a related technique.

  Here, the Cu ball has a property of being easily oxidized, and an oxide film is formed on the surface of the Cu ball according to the temperature and humidity of the storage environment. When the Cu ball on which the oxide film is formed is mounted on the electrode and then reflowed, a wetting defect may occur between the Cu ball and the solder. As a result, there arises a problem that the mounted solder ball falls off from the electrode, or the solder ball is mounted with being displaced from the center of the electrode.

  6A shows a state in which the Cu ball 210 mounted on the electrode 230 is not displaced, and FIG. 6B shows a state in which the Cu ball mounted on the electrode 230 is displaced. A solder paste 220 is printed on the electrode 230. As shown in FIG. 6B, when a Cu ball 210 partially formed with an oxide film 212 is mounted on the electrode 230 and reflow treatment is performed, wetting failure occurs, and the Cu ball 210 is displaced from the center of the electrode 230. Will be implemented.

  As described above, when the Cu balls are joined while being displaced from the predetermined positions of the electrodes, the heights of the electrodes including the solder bumps vary. An electrode having a high height can be bonded to the land, but an electrode having a low height cannot be bonded to the land. An electronic component in which a Cu ball is displaced from a predetermined position and joined is treated as a defect. Further, when the Cu ball falls off the electrode, it is handled as a bonding failure. Therefore, Cu balls are required to have a high level of alignment.

  Therefore, Patent Document 2 describes using a Cu core ball in which the surface of the Cu ball is coated with Ag plating in order to ensure the alignment of the Cu ball. In addition, Patent Documents 3 and 4 related to Patent Document 2 describe techniques for coating the Cu ball surface with Ag plating. Furthermore, Patent Document 5 describes a technique for evaluating the uniformity of a silver coating layer from the brightness of the silver coating layer coated on a Cu ball.

By the way, in recent years, high-density mounting has been realized along with downsizing of electronic components, but as high-density mounting has progressed, a problem of soft error has been caused. The soft error is that the stored content may be rewritten when α rays enter a memory cell of a semiconductor integrated circuit (hereinafter referred to as “IC”). It is considered that α rays are radiated by α decay of radioactive elements such as U, Th, and ²¹⁰ Po in the solder alloy. In recent years, therefore, development of low α-ray solder materials with reduced content of radioactive elements has been carried out.

  For example, Patent Document 6 is cited as a related document. Patent Document 6 discloses an invention of a Sn ingot with a low α dose, and in order to reduce the α dose, Pb and Bi are not suspended by simply suspending an adsorbent in the electrolytic solution instead of simply performing electrolytic refining. Is adsorbed to reduce the α dose. Patent Document 7 describes Ag and an Ag alloy having a low α dose. Patent Document 8 describes Cu and Cu alloys having a low α dose.

International Publication No. 95/24113 Pamphlet Japanese Patent Laid-Open No. 9-282935 International Publication No. 2006/126527 Pamphlet JP 2013-1917 A Japanese Patent No. 4660701 Japanese Patent No. 4472752 JP 2011-2104040 A International Publication No. 2012/120982 Pamphlet

  However, Patent Documents 1 to 5 do not consider any problem of reducing the α dose of the Cu core ball, and there is a problem that the occurrence of a soft error cannot be suppressed in high-density mounting.

  Patent Documents 6 and 7 describe that, as described above, Pb and Bi in Sn and Ag ingots are removed to reduce the α dose by electrolytic refining performed in a state where the electrolyte and electrodes are stationary. Has been. However, this document does not disclose any method for preventing misalignment or the like when mounting Cu core balls by performing Ag plating on Cu balls. Further, in the electrolytic refining described in the same document, since the electrolytic deposition surface is limited to one direction, it is not possible to form a plating having a uniform film thickness on a micro work such as a Cu ball. Furthermore, Patent Document 6 and Patent Document 7 do not disclose any idea of the present application that realizes a Cu ball having a low α dose and a high sphericity by including Bi or Pb in the Cu ball. Even if both documents are combined, the idea of the present invention cannot be reached. Further, Patent Document 8 does not describe a Cu ball, and does not disclose any relation between the added amounts of Bi and Pb in the Cu ball and the sphericity of the Cu ball.

  Accordingly, in order to solve the above problems, the present invention provides a Cu core ball, a solder joint, foam solder, and solder that can suppress the occurrence of a soft error while ensuring alignment during mounting on an electrode. Provide paste.

  The inventors first selected a Cu ball to be used for the Cu core ball. As a result, if the Cu ball does not contain a certain amount of Pb or Bi, or a combination of both Pb and Bi, the sphericity of the Cu ball decreases, and even if Ag plating is performed, It has been found that the sphericity of the resulting Cu core ball is lowered because the plating is performed with the sphericity being low.

  Next, in order to reduce the α dose of the Ag plating film constituting the Cu core ball, intensive studies were conducted by paying attention to the point that the Ag plating film is formed using a plating method. As a result, in order to reduce Pb and Bi in the plating solution and Po generated by the decay of these elements, the present inventors form a plating film on the Cu ball while flowing the Cu ball or the plating solution. However, unexpectedly, these Pb, Bi and Po elements formed salts without suspending the adsorbent. And the knowledge which these elements were not taken in to a plating film and the alpha dose of Ag plating film which comprises Cu core ball reduced was acquired.

Here, the present invention is as follows.
(1) A Cu core ball comprising a Cu ball and an Ag plating film covering the surface of the Cu ball,
The purity of the Cu balls is 99.9% or more and 99.995% or less, the U content is 5 ppb or less, the Th content is 5 ppb or less, the Pb or Bi content or the Pb and Bi content The total content of both is 1 ppm or more, the sphericity is 0.95 or more, the α dose is 0.0200 cph / cm ² or less, and the film thickness of the Ag plating film is 5 μm or less. Cu core ball characterized by being.

(2) The Cu core ball according to (1) above, wherein the α dose is 0.0200 cph / cm ² or less.

(3) The Cu core ball according to (1) above, wherein the α dose is 0.0020 cph / cm ² or less.

(4) The Cu core ball according to (1) above, wherein the α dose is 0.0010 cph / cm ² or less.

(5) The Cu core ball according to any one of (1) to (4), wherein the brightness in the L ^* a ^* b ^* color system is 80 or more.

  (6) The Cu core ball according to any one of (1) to (5), wherein the diameter is 1-1000 μm.

  (7) The Cu ball is any one of the above (1) to (6), which is coated with a plating layer composed of one or more elements selected from Ni and Co before being coated with the Ag plating film. Cu core ball described in 1.

  (8) The Cu core ball according to any one of (1) to (7), wherein the sphericity of the Cu core ball is 0.95 or more.

  (9) The Cu core ball according to any one of (1) to (8), wherein the entire Cu core ball is coated with a flux.

  (10) A solder joint using the Cu core ball according to any one of (1) to (9).

  (11) Foam solder using the Cu core ball described in any one of (1) to (9).

  (12) A solder paste using the Cu core ball according to any one of (1) to (9).

According to the present invention, the α dose of the Cu ball is set to 0.0200 cph / cm ² or less and the thickness of the Ag plating film is set to 5 μm or less. Therefore, when the solder joint is formed using the Cu core ball of the present invention. The occurrence of soft errors can be suppressed. In addition, since the Cu ball surface is coated with an Ag plating film, the formation of an oxide film on the Cu ball surface can be prevented, and as a result, alignment when mounting the Cu core ball on the electrode can be ensured. it can.

FIG. 1 is a view showing a configuration example of a Cu core ball according to the present invention. FIG. 2 is a graph showing the relationship between lightness / yellowness / redness and the immersion time of Cu balls. FIG. 3 is a graph showing an example of the relationship between the distance between the centers of the Cu core balls and the electrodes and the immersion time of the Cu balls. FIG. 4 is an optical micrograph of a solder bump on which a Cu core ball according to the present invention is mounted. FIG. 5 is an optical micrograph of a solder bump on which a Cu core ball is mounted in a comparative example. 6A and 6B are diagrams for explaining a positional shift that occurs when a conventional Cu ball is mounted on an electrode.

  The invention is described in more detail below. In this specification, the unit (ppm, ppb, and%) relating to the composition of the Ag plating film of the Cu core ball represents a ratio (mass ppm, mass ppb, and mass%) to the mass of the Ag plating film 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%) to the mass of the Cu balls unless otherwise specified.

FIG. 1 shows an example of the configuration of a Cu core ball according to the present invention. As shown in FIG. 1, a Cu core ball 11 according to the present invention includes a Cu ball 1 and an Ag plating film 2 that covers the surface of the Cu ball 1, and has the following characteristics. The Cu ball 1 has a purity of 99.9% or more and 99.995% or less, the total content of Pb or Bi or the total content of both Pb and Bi is 1 ppm or more, and the sphericity is 0.00. 95 or more, and the α dose is 0.0200 cph / cm ² or less. The plating film thickness of the Ag plating film 2 is 5 μm or less. According to the Cu core ball 11 of the present invention, the α dose of the solder joint can be reduced by adopting the above conditions.

  Below, the Ag plating film 2 and the Cu ball 1 which are the components of the Cu core ball 11 will be described in detail.

1. Ag plating film First, the Ag plating film 2 which comprises this invention is demonstrated. The Ag plating film 2 functions as a protective film for preventing the surface of the Cu ball 1 from oxidation and realizing good solderability.

-Film thickness of Ag plating film: 5 micrometers or less The film thickness of Ag plating film 2 shown by T of FIG. 1 is 5 micrometers or less. This is because, when the thickness of the Ag plating film 2 is set to 5 μm or less, the Ag plating is formed when the solder joint is formed even if the α dose of the Ag plating itself exceeds 0.0200 cph / cm ^2. Is diffused in the solder (paste) used for bonding between the Cu core ball 11 and the electrode, the α dose of the solder joint becomes 0.0200 cph / cm ² or less. The film thickness of the Ag plating film 2 is preferably 3 μm or less, more preferably 1 μm or less, from the viewpoint of reducing the α dose of the solder joint and suppressing soft errors.

On the other hand, when the film thickness of the Ag plating film 2 exceeds 5 μm, a solder composition with a small amount of Ag is used as the solder (paste) used for joining the Cu core ball 11 and the electrode. This is because when the bumps are to be formed, the Ag content in the solder bumps increases due to the diffusion of Ag in the Ag plating film 2, so that it is difficult to make the solder bump composition uniform. Therefore, it is not appropriate to make the thickness of the Ag plating film 2 too thick. Moreover, since the amount of Ag increases according to the film thickness of the Ag plating film 2, it leads to a cost increase. When the film thickness of the Ag plating film 2 is more than 5 μm, there are problems such as an increase in processing time of Ag plating and dispersion of the sphere diameter distribution, and a plating method is limited. From these viewpoints, when the α dose of the Ag plating film 2 is 0.0200 cph / cm ² or less, the thickness of the Ag plating film 2 is preferably 5 μm or less.

  Moreover, since the film thickness of the Ag plating film 2 has a correlation between the brightness of the Cu core ball 11 described later and the film thickness of the Ag plating film 2, the brightness of the Cu core ball 11 is at least 80 or more. It is necessary to regulate the film thickness of the Ag plating film 2. In addition, it is preferable to form the Ag plating film 2 with a uniform film thickness on the surface of the Cu ball 1 in order to increase the sphericity and increase the accuracy when mounted on the electrode.

-Α dose of Cu core ball: 0.0200 cph / cm ² or less The α dose of Cu core ball 11 according to the present invention is 0.0200 cph / 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 11 according to the present invention is such that the α dose of the Cu ball 1 constituting the Cu core ball 11 is 0.0200 cph / cm ² or less and the thickness of the Ag plating film 2 is 5 μm. Achieved. Therefore, since the Cu core ball 11 according to the present invention is coated with such a Cu ball 1 and the Ag plating film 2 covering the Cu ball 1, it exhibits a low α dose. The α dose is preferably 0.0020 cph / cm ² or less, and more preferably 0.0010 cph / cm ² or less, from the viewpoint of suppressing soft errors in further high-density mounting.

Lightness: 80 or higher The Cu core ball 11 according to the present invention has a lightness of 80 or higher. Here, lightness and is, L ^* a ^* b ^* color system of L ^* value (hereinafter, simply sometimes referred to as L ^* value.) It is. When the brightness is 80 or more, an Ag plating film 2 having a predetermined film thickness is formed on the surface of the Cu ball 1, so that an oxide film can be prevented from being formed on the surface of the Cu ball 1, and as a result, Generation of misalignment during mounting of the Cu core ball 11 can be prevented. In addition, when confirming the defect or misalignment of the Cu core ball 11 with an image taken with a CCD camera or the like, the accuracy of these confirmations is also increased. Further, since there is a correlation between the brightness of the Cu core ball 11 and the film thickness of the Ag plating film 2, the film thickness of the Ag plating film 2 is determined from the brightness of the Cu core ball 11 in the image taken by the imaging means. I can grasp it. That is, the film thickness of the Ag plating film 2 can be defined by an index based on brightness. This eliminates the need for expensive equipment for measuring the thickness of the Ag plating film 2 and shortens the measurement time. Further, when measuring the height variation of the solder bumps with the laser wavelength meter, the measurement accuracy of the height variation is also improved. As a result, the inspection accuracy of the electronic component is improved and the product yield of the electronic component is improved.

On the other hand, if the brightness of the Cu core ball 11 is less than 80, the surface of the Cu ball is exposed or the film thickness of the Ag plating film 2 is reduced, so that the oxide film composed of Cu ₂ O, CuO, or the like. Will be formed on the surface of the Cu ball 1, causing poor wetting with the solder particles in the solder paste and lowering the alignment. For example, when the brightness of the Cu core ball 11 is 50, the film thickness of the Ag plating film 2 becomes thin, and therefore, when the Cu ball 1 is directly joined on the electrode, the occurrence of misalignment becomes significant. End up. When an oxide film is formed on the surface of the Cu ball 1, the Cu ball 1 loses its metallic luster, so that the inspection accuracy of the electronic component using the imaging means deteriorates. Further, the electrical conductivity and thermal conductivity of the Cu ball 1 are lowered by the oxide film on the surface of the Cu ball 1.

-Composition of Ag plating film The composition of the Ag plating film 2 is 100% Ag except for inevitable impurities.

2. Cu Ball Next, the Cu ball 1 constituting the present invention will be described in detail.

  Since the Cu ball 1 constituting the present invention does not melt at the soldering temperature when the Cu core ball 11 is used for a solder bump, the height variation of the solder joint can be suppressed. Therefore, it is preferable that the Cu ball 1 has a high sphericity and a small variation in diameter. Further, as described above, it is preferable that the α dose of the Cu ball 1 is as low as that of the Ag plating film 2. Hereinafter, preferred embodiments of the Cu ball 1 will be described.

U: 5 ppb or less, Th: 5 ppb or less U and Th are radioisotopes, and it is necessary to suppress their contents in order to suppress soft errors. The U and Th contents need to be 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.

-Purity of Cu ball: 99.9% or more and 99.995% or less The Cu ball 1 constituting the present invention preferably has a purity of 99.9% or more and 99.995% or less. When the purity of the Cu ball 1 is within this range, a sufficient amount of crystal nuclei for increasing the sphericity of the Cu ball 1 can be secured in the molten Cu. The reason why the sphericity is increased will be described in detail as follows.

  When the Cu ball 1 is manufactured, the Cu material formed into small pieces of a predetermined shape is melted by heating, and the molten Cu becomes spherical due to surface tension, which solidifies 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. Such a Cu ball 1 has a low sphericity. As the impurity element, Sn, Sb, Bi, Zn, As, Ag, Cd, Ni, Pb, Au, P, S, U, Th, and the like can be considered.

  The lower limit value of the purity is not particularly limited, but is preferably 99.9% or more from the viewpoint of suppressing the α dose and suppressing deterioration of the electrical conductivity and thermal conductivity of the Cu ball 1 due to the decrease in purity.

Here, the higher the purity of the Ag plating film 2 can reduce the α dose, whereas the Cu ball 1 can reduce the α dose without increasing the purity more than necessary. Cu has a higher melting point than Sn, and the heating temperature during production is higher for Cu. In the present invention, when the Cu ball 1 is manufactured, since a heat treatment not conventionally performed is performed on the Cu material as described later, radioactive elements represented by ²¹⁰ Po, ²¹⁰ Pb, and ²¹⁰ Bi are volatilized. In particular, ²¹⁰ Po tends to volatilize among these radioactive elements.

Α dose: 0.0200 cph / cm ² or less The α dose of the Cu ball 1 constituting the present invention is preferably 0.0200 cph / cm ² or less. This is an α dose that does not cause a soft error in high-density mounting of electronic components. In this invention, in addition to the process normally performed in order to manufacture Cu ball | bowl 1, it heat-processes again. For this reason, ²¹⁰ Po slightly remaining in the Cu raw material volatilizes, and the Cu ball 1 shows a lower α dose than the Cu raw material. The α dose is preferably 0.0020 cph / cm ² or less, and more preferably 0.0010 cph / cm ² or less, from the viewpoint of suppressing soft errors in further high-density mounting.

-The content of Pb or Bi or the combined content of both Pb and Bi is 1 ppm or more in total. The Cu balls 1 constituting the present invention are Sn, Sb, Bi, Zn, As, Ag, Cd, Ni, Pb, Au, P, S, U, Th and the like are contained, but it is particularly preferable that the content of Pb or Bi or the combined content of both Pb and Bi is 1 ppm or more in total. In the present invention, even when the Cu ball 1 is exposed during the formation of the solder joint, the Pb or Bi content of the Cu ball 1 or the combined content of both Pb and Bi is used to reduce the α dose. There is no need to reduce it to the limit. This is due to the following reason.

²¹⁰ Pb and ²¹⁰ Bi change to ²¹⁰ Po by β decay. In order to reduce the α dose, it is preferable that the contents of impurity elements Pb and Bi are as low as possible.

However, the content ratio of ²¹⁰ Pb and ²¹⁰ Bi contained in Pb and Bi is low. If the contents of Pb and Bi are reduced to some extent, it is considered that ²¹⁰ Pb and ²¹⁰ Bi are almost removed. The Cu ball 1 according to the present invention is manufactured by setting the melting temperature of Cu to be slightly higher than before, or by subjecting the Cu material and / or the granulated Cu ball 1 to heat treatment. Even if this temperature is lower than the boiling point of Pb or Bi, vaporization occurs and the amount of impurity elements is reduced. In order to increase the sphericity of the Cu ball 1, it is preferable that the content of the impurity element is high. Therefore, in the Cu ball 1 of the present invention, the total content of Pb or Bi or the total content of both Pb and Bi is 1 ppm or more. When both Pb and Bi are included, the total content of Pb and Bi is 1 ppm or more.

  Thus, since at least one of Pb and Bi remains to a certain extent even after the Cu ball 1 is manufactured, the content measurement error is small. Further, as described above, since Bi and Pb become crystal nuclei when melted in the manufacturing process of the Cu ball 1, if a certain amount of Bi or Pb is contained in Cu, the Cu ball 1 having high sphericity can be manufactured. Can do. Therefore, Pb and Bi are important elements for estimating the content of impurity elements. Also from such a viewpoint, the total content of Pb or Bi or the total content of both Pb and Bi is preferably 1 ppm or more. The content of Pb or Bi or the combined content of both Pb and Bi is more preferably 10 ppm or more in total. The upper limit is not particularly limited, but from the viewpoint of suppressing the deterioration of the electrical conductivity of the Cu ball 1, more preferably the content of Pb or Bi or the content of both Pb and Bi is less than 1000 ppm in total. More preferably, it is 100 ppm or less. The content of Pb is more preferably 10 ppm to 50 ppm, and the content of Bi is more preferably 10 ppm to 50 ppm.

Cu ball sphericity: 0.95 or more Cu ball 1 constituting the present invention has a sphericity of 0.95 or more from the standpoint of controlling the standoff height. 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. Further, when the Cu core ball 11 is mounted on the electrode and reflow is performed, the Cu core ball 11 is displaced, and the self-alignment property is also deteriorated. The sphericity is more preferably 0.990 or more. In the present invention, the sphericity represents a deviation from the 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). . Specifically, the sphericity is an arithmetic average value calculated when the diameter of each of the 500 Cu balls or each of the Cu core balls is divided by the major axis. The closer the value is to the upper limit of 1.00, the more true the sphericity is. Represents close to a sphere. In the present invention, the length of the major axis and the length of the diameter refer to the length measured by an ultra quick vision, ULTRA QV350-PRO measuring device manufactured by Mitutoyo Corporation.

・ Cu ball diameter: 1-1000 μm
It is preferable that the diameter of the Cu ball | bowl 1 which comprises this invention is 1-1000 micrometers. 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 diameter of the Cu core ball 11 according to the present invention is about 1 to 300 μm, the aggregate of “Cu core balls” may be referred to as “Cu core powder”. Here, the “Cu core powder” is an aggregate of a large number of Cu core balls 11 in which the individual Cu core balls 11 have the above-described characteristics. For example, it is distinguished from the single Cu core ball 11 in the form of use, such as being blended as a powder in a solder paste. Similarly, when used for forming solder bumps, the “Cu core powder” used in such a form is distinguished from the single Cu core ball 11 because it is normally handled as an aggregate.

  In the Cu core ball 11 according to the present invention, the surface of the Cu ball 1 may be previously coated with another metal plating layer before the Ag plating film 2 is formed. In particular, if the surface of the Cu ball 1 is previously coated with a Ni plating layer, a Co plating layer, or the like, it is possible to reduce the diffusion of Cu into the solder at the time of bonding to the electrode. It becomes possible to suppress biting. Moreover, the metal which comprises a plating layer is not restricted to a single metal, The alloy which combined 2 or more elements from Ni, Co, etc. may be sufficient.

  The sphericity of the Cu core ball 11 according to the present invention is preferably 0.95 or more. When the sphericity of the Cu core ball 11 is low, when the Cu core ball 11 is mounted on an electrode and reflowing is performed, the Cu core ball 11 is displaced and the self-alignment property is also deteriorated. The sphericity is more preferably 0.990 or more.

  Furthermore, the entire Cu core ball 11 according to the present invention can be covered with a flux. Moreover, it can be set as foam solder by disperse | distributing Cu core ball 11 concerning the present invention in solder. Moreover, it can also be set as the solder paste containing Cu core ball 11 concerning the present invention. The Cu core ball 11 according to the present invention can also be used for forming a solder joint for joining terminals of an electronic component.

An example of a method for manufacturing the Cu core ball 11 according to the present invention will be described.
A Cu material as a material is placed on a heat-resistant plate such as ceramic (hereinafter referred to as “heat-resistant plate”), and is heated together with the heat-resistant plate in a furnace. 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 for example, the diameter is 0.8 mm and the depth is 0.88 mm. In addition, chip-shaped Cu material (hereinafter referred to as “chip material”) obtained by cutting the Cu thin wire is put into the groove of the heat-resistant plate one by one. The heat-resistant plate in which the chip material is put in the groove is heated to 1100 to 1300 ° C. in a furnace filled with ammonia decomposition gas and subjected to heat treatment for 30 to 60 minutes. At this time, if the furnace temperature becomes equal to or higher than the melting point of Cu, the chip material melts and becomes spherical. Thereafter, the inside of the furnace is cooled, and the Cu ball 1 is formed in the groove of the heat-resistant plate. After cooling, the molded Cu ball 1 is subjected to heat treatment again at 800 to 1000 ° C., which is a temperature lower than the melting point of Cu.

  As another method, molten Cu is dripped from an orifice provided at the bottom of the crucible, and the droplet is cooled to granulate the Cu ball 1. There is a method of granulating by heating to above ℃. The Cu balls 1 thus granulated may be reheated at a temperature of 800 to 1000 ° C. for 30 to 60 minutes.

  In the method for manufacturing the Cu core ball 11 of the present invention, 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 granulated.

  As a Cu material that is a raw material of the Cu ball 1, for example, a pellet, a wire, a pillar, or the like can be used. The purity of the Cu material may be 99.9 to 99.99% from the viewpoint of preventing the purity of the Cu ball 1 from being lowered too much.

  Further, when a high-purity Cu material is used, the above-described heat treatment may not be performed, and the molten Cu holding temperature may be lowered to about 1000 ° C. as in the conventional case. 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 can be reused as a raw material, and the α dose can be further reduced. .

  Moreover, as a method of forming the Ag plating film 2 on the Cu ball 1 produced as described above, there are known methods such as an electroless plating method.

  The Ag plating solution includes, for example, silver ions, 3,5-dinitrosalicylic acid as the first complexing agent, and one kind selected from aminocarboxylic acid compounds, hydroxycarboxylic acid compounds, and triazole compounds as the second complexing agent. The thing containing the above can be used. The pH of the silver plating solution is preferably in the range of 0.2-2.

When the Cu ball 1 is immersed in the plating solution, Cu atoms of the Cu ball 1 are dissolved into the plating solution as Cu ²⁺ ions, and the electrons generated at that time react with Ag ⁺ ions in the plating solution to cause Cu and Ag. And are replaced. At this time, in order to reduce Pb and Bi in the plating solution and Po generated by the decay of these elements, the Ag plating film 2 can be formed on the Cu ball 1 while flowing the Cu ball 1 or the plating solution. preferable. As a result, it is possible to form salts of the elements Pb, Bi, and Po without suspending the adsorbent. As a result, the Cu core balls 11 can be formed without incorporating these elements into the Ag plating film 2. The α dose of the Ag plating film 2 to be configured can be reduced. In this way, the Ag plating film 2 is formed on the surface of the Cu ball 1. After the plating treatment, the Cu core ball 11 according to the present invention can be obtained by drying in the air or N ₂ atmosphere. After the plating treatment, the surface of the Cu core ball 11 may be washed with (ion exchange) water or an organic solvent as necessary.

In addition, in the said Example, although Ag plating film 2 was formed by the electroless-plating method, it is not limited to this. For example, the Ag plating film 2 can be formed by an electrolytic plating method such as barrel plating. When performing barrel plating, as an Ag plating solution, one having a composition of silver cyanide: 15 to 25 g / l, potassium cyanide: 43 to 73 g / l, and potassium carbonate: 10 g / l can be used. The cathode current density is preferably 0.5 A / m ² and the temperature is preferably set to 20 to 30 ° C.

  Examples of the present invention will be described below, but the present invention is not limited thereto. In this example, a Cu ball having a high sphericity was produced, an Ag plating film was formed on the surface of the Cu ball, and the α dose was measured.

-Production of Cu ball The production conditions of a Cu ball having a high sphericity were investigated. A Cu pellet having a purity of 99.9%, a Cu wire having a purity of 99.995% or less, and a Cu plate having a purity exceeding 99.995% were prepared. After putting each into the crucible, the temperature of the crucible is raised to 1200 ° C., heat treatment is performed for 45 minutes, molten Cu is dropped from the orifice provided at the bottom of the crucible, and the generated droplet is cooled to form Cu. Granulated into balls. Thereby, Cu balls having an average particle diameter of 250 μm were produced. Table 1 shows the elemental analysis results and sphericity of the produced Cu balls. Elemental analysis was performed by inductively coupled plasma mass spectrometry (ICP-MS analysis) for U and Th, and by inductively coupled plasma emission spectroscopy (ICP-AES analysis) for the other elements. Below, the measuring method of sphericity is explained in full detail.

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

  The measuring method of alpha dose is as follows.

・ Α dose An α ray measurement device of a gas flow proportional counter was used to measure α dose. 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.

  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.

  Table 1 shows the elemental analysis results and α dose of the produced Cu balls.

  As shown in Table 1, the Cu balls using Cu pellets with a purity of 99.9% and Cu wires of 99.995% or less exhibited a sphericity of 0.990 or more. On the other hand, as shown in Table 1, the sphericity of Cu balls using a Cu plate with a purity exceeding 99.995% was less than 0.95.

-Example 1-1
Next, an Ag plating film was formed on the surface of a Cu ball made of 99.9% pure Cu pellets to produce a Cu core ball. Specifically, 70 cc SSP-700M (manufactured by Shikoku Kasei Kogyo Co., Ltd.) was put as a Ag plating solution in a 100 cc glass bottle. The α dose of the Ag tip material, which is the raw material for the Ag plating solution, was 0.0053 cph / cm ² . Subsequently, 1 g of a Cu ball having a diameter of 250 μm was added to the glass bottle, the cap was quickly covered, and the glass bottle was stirred for 3 minutes. After a predetermined time, the precipitated Cu balls were separated by suction filtration, and the separated Cu balls were washed with ion-exchanged water. Note that the Cu balls may be washed using an organic solvent (for example, isopropyl alcohol) that is easy to dry instead of ion-exchanged water. Thereafter, drying was performed at 100 ° C. for 1 minute to obtain a Cu core ball in which Ag plating was uniformly coated on a Cu ball surface having a diameter of 250 μm.

  The α dose of the Cu core ball was measured in the same manner as the Cu ball described above. The sphericity of the Cu core ball was also measured under the same conditions as the Cu ball. These measurement results are shown in Table 2.

Examples 1-2 and 1-3
In Example 1-2, Ag plating treatment was performed in the same manner as in Example 1-1 using Cu balls using Cu wires with a purity of 99.995% or less shown in Table 1, and the surface of the Cu balls A Cu core ball having an Ag plating film formed thereon was prepared, and the same evaluation as in Example 1-1 was performed. About the produced Cu nucleus ball | bowl, alpha dose and sphericity were measured similarly to Example 1-1. The measurement results are shown in Table 2.

  In Example 1-3, Ag plating treatment was performed in the same manner as in Example 1-1 using Cu balls using a Cu plate having a purity exceeding 99.995% shown in Table 1, and the surface of the Cu balls A Cu core ball having an Ag plating film formed thereon was prepared, and the same evaluation as in Example 1-1 was performed. About the produced Cu nucleus ball | bowl, alpha dose and sphericity were measured similarly to Example 1-1. The measurement results are shown in Table 2.

As shown in Table 2, the α dose of the Cu core ball of Example 1-1 was less than 0.0010 cph / cm ² . From this result, it was proved that the α dose was reduced as a whole Cu core ball even when an Ag plating film was coated on the surface of the Cu ball by the electroless plating method. Further, although the α dose of the Cu core ball prepared in Example 1-1 is not shown in Table 2, no increase in α rays was observed even after one year from the preparation.

Similarly, also in the Cu core balls of Examples 1-2 and 1-3, the α dose was less than 0.0010 cph / cm ² . From this result, it was proved that the α dose was reduced as a whole Cu core ball even when an Ag plating film was coated on the surface of the Cu ball by the electroless plating method. Moreover, although the alpha dose of Cu core ball produced in Examples 1-2 and 1-3 is not shown in Table 2, even if it passed 1 year after production, the raise of alpha rays was not seen.

  Next, the α dose of the solder portion of the solder joint using the Cu core ball according to the present invention was calculated. In this example, a solder joint structure was assumed in which a substrate on which a solder paste was printed on an electrode was used, and the upper and lower sides of the Cu core ball according to the present invention were sandwiched between the electrodes of the substrate. Further, it was assumed that the Cu ball was not melted by reflow and that bumps were formed in which Ag was uniformly diffused in the solder. Further, depending on the ratio, the so-called solid solubility limit may be exceeded so that Ag and Sn cannot form an alloy layer. However, a form in which Ag is uniformly diffused throughout the solder portion has the highest α-ray.

Here, the opening diameter of the electrode provided on the substrate was 240 μm, and the print thickness of the solder paste was 100 μm (+ resist height 15 μm, total 115 μm). The solder weight in the solder paste was 50% (flux weight was 50%). The solder powder composition in the solder paste was Sn 100%, the specific gravity was 7.365 g / cm ^3, and the total solder weight of the upper and lower solder pastes was 3.83 × 10 ⁻⁸ g.

First, the Ag weight in the Cu core ball was calculated. In Example 2-1, Cu plating was performed by the same method as in Example 1-1, and an Ag plating film having a film thickness (T in FIG. 1) of 0.3 μm was formed on a Cu ball having a diameter of 300 μm. A nuclear ball was assumed. In this case, if the specific gravity of Ag is 10.490 g / cm ³ , the Ag weight plated in the Cu core ball is 8.92 × 10 ⁻¹⁰ g.

In Comparative Example 2-1, an Ag plating treatment was performed in the same manner as in Example 1-1, and a Cu ball having a diameter (T in FIG. 1) of Cu plating having a thickness of 6.0 μm formed on a 300 μm diameter Cu ball. A nuclear ball was assumed. In this case, when the specific gravity of Ag is 10.490 g / cm ³ , the Ag weight plated in the Cu core ball is 1.53 × 10 ⁻⁸ g.

  Then, the average alpha ray of the solder part in the solder joint of Example 2-1 and Comparative Example 2-1 was calculated. The average α dose of the solder part was calculated by the following formula (1). It is assumed that there is no change in the volume of the metal part or change in α rays due to the diffusion of Ag.

(Average α dose) = {(Ag weight) × (Ag α dose) + (Sn weight) × (Sn α dose)} / {(Ag weight) + (Sn weight)} (1)
In the above formula (1), the α dose of Sn was assumed to be 0.0000 cph / cm ^2, and the α dose of Ag was assumed to be 0.0700 cph / cm ² . The calculation result of the formula (1) is shown in Table 3 below.

As shown in Example 2-1 of Table 3, even when the α dose of Ag plating is 0.0700 cph / cm ² , if the film thickness T of the Ag plating film is 5 μm or less, the solder of the solder joint It was found that the α dose of the portion was 0.0200 cph / cm ² or less. This is because if the thickness of the Ag plating film is 5 μm or less, the volume ratio of Ag plating diffused in the solder to the solder becomes small, and the α dose of the solder portion becomes low.

On the other hand, as shown in Comparative Example 2-1 in Table 3, when the α dose of Ag plating is 0.0700 cph / cm ² and the film thickness of the Ag plating film exceeds 5 μm, the Ag plating is soldered. Even if it diffuses in (Sn), the volume ratio of Ag plating diffused in the solder to the solder becomes large (the content increases), so that the α dose of the solder portion exceeds 0.0200 cph / cm ^2. I understood it.

  Next, in order to investigate the relationship between the brightness of the Cu core ball and the positional deviation when the Cu core ball is mounted on the electrode, the alignment of various Cu core balls having different brightness immediately after manufacture was examined. In the following examples and comparative examples, various investigations were performed using Cu balls made of a Cu wire material having a purity of 99.995% or less shown in Table 1.

・ Measurement of brightness The brightness is measured by using SPECTROTOPOMETER CM-3500d made by MINOLTA and measuring the spectral transmittance according to JIS Z 8722 “Color measurement method-reflection and transmission object color” with a D65 light source and a 10-degree field of view. L ^* , a ^* , b ^* ). The brightness was measured within 1 hour. (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 of alignment property In this example, when each of a plurality of Cu core balls immersed in an Ag plating solution for different times is mounted on an electrode and reflowed, how much the position of the Cu core ball is displaced with respect to the electrode. Measured. The positional deviation of the Cu core ball with respect to the electrode was performed by measuring the distance between the centers. Inter-center distance measurement means that the circumference of the Cu core ball is plotted at three points and the circumference of the electrode is plotted at three points, the center point of the three points plot of the Cu core ball and the center of the plot of the three points of the electrode It measures the distance between points (distance between circle centers). The number of plots is not limited to 3 points. A VH-S30 manufactured by KEYENCE was used for the measurement of the distance between the circle centers.

  In this example, the average value of the distance between the plurality of circles obtained by the measurement was used as the final circle distance. Specifically, first, 10 solder bumps were created using 10 Cu core balls created under exactly the same conditions. Next, the distance between the circle centers of one solder bump is measured five times, and X is calculated for each of the ten solder bumps using a method of calculating the average value X. Y, which is the average value of X, was defined as the distance between the centers. The above operation was performed for each example and comparative example, and the distance between each center was calculated. And alignment property was evaluated based on the calculated distance between circle centers.

-About Examples 3-1 to 3-5 and Comparative Example 3-1, First, in Examples 3-1 to 3-5, the Ag plating treatment is the same method as Example 1-1, but Cu balls were used. The brightness, redness, and yellowness of the Cu core ball formed by immersion in the Ag plating solution for different times were measured. Subsequently, the Cu core ball formed in each of Examples 3-1 to 3-5 was put into the petri dish, and the petri dish was placed in a thermostatic bath and heated at 200 ° C. for 10 minutes, whereby the Cu core ball was intentionally oxidized. Conditions that make it easy to do. Thereafter, each Cu core ball is taken out from the thermostatic bath, and each Cu core ball is mounted on an electrode on which a solder paste (manufactured by Senju Metal Industry Co., Ltd .: M705-GRN360-K2-V) is printed with a metal mask having a thickness of 100 μm. Then, the reflow (heating) was performed, and the alignment property of each Cu core ball with respect to the electrode was evaluated. As the substrate, a substrate having an opening diameter of 240 μm and a resist thickness of 15 μm, which was obtained by subjecting a Cu electrode to a surface treatment of water-soluble preflux (OSP: Organic Solderability Preservative), was used. For reflow heating, the peak temperature was 245 ° C. in an N ₂ atmosphere, preheating was performed at 140 to 160 ° C. for 20 seconds, and main heating was performed at 220 ° C. or more for 40 seconds.

  In Comparative Example 3-1, the brightness, redness, and yellowness of Cu balls immediately after production when Ag plating was not performed were measured. Subsequently, a Cu core ball was placed in the petri dish, and the petri dish was placed in a thermostatic bath and heated at 200 ° C. for 10 minutes to easily oxidize the Cu core ball intentionally. Thereafter, evaluation of the alignment property of the Cu core ball with respect to the electrode was performed when the Cu core ball formed in Comparative Example 3-1 was mounted on the electrode and reflowed under the same conditions as in Examples 3-1 to 3-5. It was.

  Table 4 below shows the measurement results of lightness, redness, and yellowness immediately after the production of each Cu core ball of Examples 3-1 to 3-5 and Comparative Example 3-1. Further, the relationship between the immersion time of the Cu balls in the Ag plating solution and the brightness, redness, and yellowness of the Cu core balls shown in Table 4 is shown in the graph of FIG.

  Next, Table 5 below shows the distance between the centers and the alignment when each Cu core ball of Examples 3-1 to 3-5 and Comparative Example 3-1 is mounted on the electrode and reflowed. In Table 5, when the distance between the centers of the Cu core balls is 15 μm or less, it is indicated as “◯” because the alignment is good, and when the distance between the centers of the Cu core balls is more than 15 μm, the alignment is performed. It is indicated by “x” because the property is poor. Moreover, the relationship between the immersion time of Cu ball | bowl shown in Table 4 and the distance between the circle centers between Cu core ball | bowl and an electrode shown in Table 5 is shown in the graph of FIG.

  In Examples 3-1 to 3-5, as shown in Table 4 and FIG. 2, the lightness of the Cu ball was formed by immersing the Cu ball in the Ag plating solution for a predetermined time to form an Ag coating on the surface of the Cu ball. Became over 80. Moreover, as shown in Table 5 and FIG. 3, in Example 3-1, in which the brightness is 80 or more, the average positional deviation of the Cu core balls was 15 μm or less, and all the alignment properties were “◯”. In FIG. 4, the photograph which image | photographed the state of the solder bump at the time of mounting Cu core ball 11 of Example 3-1 on the electrode 13 with the optical microscope is shown. As is clear from FIG. 4, the Cu core ball 11 is mounted at the center of the electrode 13 of the semiconductor chip 10, and it can be seen that the Cu core ball 11 is not displaced on the electrode 13.

  Also in Examples 3-2 to 3-5, as shown in Table 4 and FIG. 2, the distance between the circle centers was 15 μm or less, and the alignment properties were all “◯”. In addition, the state of the solder bump when the Cu core balls of Examples 3-2 to 3-5 are mounted on the electrodes is substantially the same as that of Example 3-1, and is omitted for convenience. doing.

  On the other hand, in Comparative Example 3-1, as shown in Table 4 and FIG. 2, the Ag film was not formed on the surface of the Cu ball, so the brightness was less than 80. Moreover, as shown in Table 5 and FIG. 3, in Comparative Example 3-1, in which the lightness is less than 80, the average positional deviation of Cu balls exceeded 15 μm, and the alignment property was “x”. In FIG. 5, the photograph which image | photographed the state of the solder bump at the time of mounting Cu core ball 21 of the comparative example 3-1 on the electrode 23 with the optical microscope is shown. As is clear from FIG. 5, it can be seen that the Cu core ball 21 is displaced from the center of the electrode 23 when the Ag plating film is not formed.

  From the above, the correlation between brightness and alignment was shown, and it became clear that the alignment of Cu core balls can be determined using brightness.

  Next, it was examined whether or not the degree of coating of the Cu core ball with the Ag plating can be determined by the redness. As shown in Examples 3-1 to 3-5 in Table 4, when Cu balls are immersed in an Ag plating solution for a predetermined time, an Ag plating film having a predetermined film thickness is formed on the surface of the Cu balls, and Cu nuclei are formed. The whole ball changed from red to white. Thereby, redness showed the value of 10 or less when immersion time became 0.5 minutes or more. When the redness was 10 or less, as shown in Table 5, the distance between the circle centers was 15 mm or less, and the alignment property was “◯”. Therefore, the correlation between the redness and the alignment is also shown in the redness, and it has become clear that the alignment of the Cu core ball can be determined using the redness.

  Furthermore, it was examined whether or not the degree of coating of the Cu core ball with the Ag plating can be determined by the yellowness. As shown in Examples 3-1 to 3-5 in Table 4, when Cu balls are immersed in an Ag plating solution for a predetermined time, an Ag plating film having a predetermined film thickness is formed on the surface of the Cu balls, and Cu nuclei are formed. The entire ball changed from yellow to white. Thereby, yellowness showed the value of 14 or less, when immersion time became 0.5 minutes or more. When the yellowness was 14 or less, as shown in Table 5, the distance between the circle centers was 15 mm or less, and the alignment property was “◯”. Therefore, the correlation between the yellowness and the alignment was also shown in the yellowness, and it became clear that the alignment of the Cu core ball can be determined using the yellowness.

  It should be noted that the technical scope of the present invention is not limited to the above-described embodiments, and includes those in which various modifications are made to the above-described embodiments without departing from the spirit of the present invention.

Claims (12)

A Cu core ball comprising a Cu ball and an Ag plating film covering the surface of the Cu ball,
The purity of the Cu balls is 99.9% or more and 99.995% or less, the U content is 5 ppb or less, the Th content is 5 ppb or less, the Pb or Bi content or the Pb and Bi content The total amount of the combined content is 1 ppm or more, the sphericity is 0.95 or more, the α dose is 0.0200 cph / cm ² or less,
A Cu core ball in which the film thickness of the Ag plating film is 5 μm or less. 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 0.0020 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 Cu core ball according to any one of claims 1 to 4, wherein the lightness in the L ^* a ^* b ^* color system is 80 or more.   Cu core ball given in any 1 paragraph of Claims 1-5 whose diameter is 1-1000 micrometers.   The Cu core according to any one of claims 1 to 6, wherein the Cu ball is coated with a plating layer made of at least one element selected from Ni and Co before being coated with the Ag plating film. ball.   The Cu core ball according to any one of claims 1 to 7, wherein the sphericity of the Cu core ball is 0.95 or more.   The Cu core ball according to claim 1, wherein the entire Cu core ball is coated with a flux.   A solder joint using the Cu core ball according to claim 1. Foam solder using the Cu core ball according to any one of claims 1 to 9 .   Solder paste using the Cu core ball according to any one of claims 1 to 9.

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