JP2007044718A - Metallic ball, method for manufacturing metallic ball, plated structure, and soldering method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metallic ball which can keep the soldered strength, and can lower the melting point in soldering. <P>SOLUTION: The metallic ball 10 comprises a core ball 1, a reaction suppressing layer 2, and a plated layer 3. The core ball 1 is made of copper (Cu), and has a diameter within the range from 50 μm to 1,000 μm. The reaction suppressing layer 2 is made of nickel (Ni), and has a film thickness within the range from 0.1 μm to 5 μm. The plated layer 3 is made of tin-indium (Sn-In alloy), and has a film thickness within the range from 0.1 μm to 100 μm. Further, the plated layer 3 is formed by the electroplating in such a manner that the content of tin (Sn) decreases from its innermost periphery toward its outermost periphery, and the content of indium (In) increases from its innermost periphery toward its outermost periphery. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a metal ball used for mounting an electronic component, a method for producing the metal ball, a plated structure, and a soldering method.

  In surface mounting of electronic components, mounting methods such as BGA (Ball Grid Array) and CSP (Chip Scale Package) are used. These mounting methods use solder, copper aluminum, and metal balls such as a copper core and a resin core whose outer layers are covered with solder as connection terminals.

  Conventionally, a composite microball used for an internal connection electrode of a semiconductor element in a semiconductor package is known (Patent Document 1). The composite microball is composed of a core ball, a base layer covering the core ball, and a solder coating layer formed on the base layer.

The core ball is made of copper having a diameter in the range of 30 μm to 120 μm, the underlayer is made of at least one selected from cobalt and nickel, and the solder coating layer is made of an electric solder plating layer having a thickness of 20 μm or more. Become. The material of the electric solder plating layer is lead-tin, and the outer diameter of the composite microball is in the range of 50 μm to 200 μm.
Japanese Patent No. 3314269

  However, since solder is required to be lead-free, alloys having a higher melting point than conventional Sn-Pb alloy systems such as Sn-Ag-Cu alloys, Sn-Ag alloys and Sn-Cu alloys, or Sn Alloys having a lower melting point than conventional Sn—Pb alloy systems such as —Bi alloy, Sn—Zn alloy, Sn—In alloy, Sn—Zn—Bi alloy, and Sn—Ag—Bi—In alloy are used.

  And in the field of solder plating, the same lead-free is required, and plating of Sn, Sn—Ag alloy, Sn—Cu alloy, Sn—Bi alloy, Sn—Zn alloy, Sn—In alloy, etc. is used. As a metal ball used in mounting technology such as BGA and CSP, a copper core ball whose surface is covered with a plating layer made of an Sn—Ag alloy is becoming mainstream.

  However, when a plating layer made of an Sn—Ag alloy is used, there is a problem that the melting point becomes high when soldering the copper core ball.

  On the other hand, since the Sn—Bi alloy has a low melting point, the melting point when soldering the copper core ball can be lowered by covering the copper core ball with a plating layer made of the Sn—Bi alloy.

  However, when the composition ratio of Bi increases, the Sn—Bi alloy becomes brittle, and there is a problem that the soldered copper core ball becomes inappropriate as a bonding material.

  This problem also occurs when a metal ball is soldered to a copper substrate.

  Accordingly, the present invention has been made to solve such a problem, and an object of the present invention is to provide a metal ball that maintains strength when soldering and can lower the melting point when soldering. That is.

  Another object of the present invention is to provide a method for producing a metal ball that retains the strength when soldered and can lower the melting point when soldered.

  Furthermore, another object of the present invention is to provide a plated structure capable of maintaining the strength when soldering and lowering the melting point when soldering.

  Furthermore, another object of the present invention is to provide a soldering method using a plating structure capable of maintaining the strength when soldering and lowering the melting point when soldering.

  The metal ball according to the present invention is a metal ball used for mounting an electronic component, and includes a core ball and a plating layer. The core ball is made of metal. The plating layer is made of first and second metal elements constituting an alloy for soldering and covers the core ball. The composition ratio of the second metal element increases from the first composition ratio to the second composition ratio from the innermost periphery to the outermost periphery of the plating layer. The first composition ratio is a composition ratio that sets the strength of the plating layer when the metal ball is soldered to a reference strength or more. The second composition ratio is a composition ratio that sets the melting point of the plating layer to a temperature lower than the reference melting point. The second metal element constitutes a lead-free plating alloy and is an element other than Bi.

  Preferably, the metal ball further includes a reaction suppression layer. The reaction suppression layer is inserted between the core ball and the plating layer.

  Preferably, the reaction suppression layer is made of any one of Ni, Ni—P alloy, Ni—B alloy, Co, and Pt.

  Preferably, the first metal element is Sn, and the second metal element is In.

  Preferably, the first composition ratio is in the range of 18-20%, and the second composition ratio is in the range of 34-38%.

  Preferably, the core ball is made of Cu.

  Moreover, according to this invention, a plating structure is equipped with a base | substrate and a plating layer. The plating layer is composed of first and second metal elements that constitute an alloy for soldering, and is formed on one main surface of the substrate. The composition ratio of the second metal element increases from the first composition ratio to the second composition ratio from the interface between the plating layer and the substrate toward the surface of the plating layer. The first composition ratio is a composition ratio that sets the strength of the plating layer to be higher than the reference strength when another substance is soldered to the substrate via the plating layer. The second composition ratio is a composition ratio that sets the melting point of the plating layer to a temperature lower than the reference melting point.

  Preferably, the plating structure further includes a reaction suppression layer. The reaction suppression layer is inserted between the substrate and the plating layer.

  Preferably, the reaction suppression layer is made of any one of Ni, Ni—P alloy, Ni—B alloy, Co, and Pt.

  Preferably, the first metal element is Sn and the second metal element is Bi or In.

  Preferably, the first composition ratio is in the range of 2 to 21%, and the second composition ratio is in the range of 30 to 55%.

  Preferably, the substrate is made of a Cu substrate.

  Furthermore, according to the present invention, the method for producing a metal ball is a method for producing a metal ball used for mounting an electronic component. The metal ball includes a core ball and a plating layer. The core ball is made of metal. The plating layer is made of first and second metal elements constituting an alloy for soldering and covers the core ball. The composition ratio of the second metal element increases from the first composition ratio to the second composition ratio from the innermost periphery to the outermost periphery of the plating layer. The first composition ratio is a composition ratio that sets the strength of the plating layer when the metal ball is soldered to a reference strength or more. The second composition ratio is a composition ratio that sets the melting point of the plating layer to a temperature lower than the reference melting point. The second metal element constitutes a lead-free plating alloy and is an element other than Bi.

  The method for producing the metal ball includes the first step of immersing the core ball in a plating bath containing the first and second metal elements, and the composition ratio of the second metal element from the innermost periphery of the plating layer to the highest. And a second step of forming a plating layer so as to increase from the first composition ratio to the second composition ratio toward the outer periphery.

  Preferably, in the second step, a plating layer is formed by electroplating.

  Preferably, in the second step, the dropping amount of the first compound containing the first metal element to the plating bath is decreased, and the dropping amount of the second compound containing the second metal element to the plating bath is reduced. A plating layer is formed by performing electroplating for a predetermined time while increasing or decreasing.

  Preferably, the current density in electroplating is constant for a predetermined time.

  Preferably, the first metal element is Sn, and the second metal element is In.

  Preferably, the first composition ratio is in the range of 18-20%, and the second composition ratio is in the range of 34-38%.

  Preferably, the method for manufacturing a metal ball further includes a third step of forming a reaction suppression layer so as to cover the core ball before the first step.

  Preferably, the third step forms a reaction suppression layer made of any of Ni, NiP alloy, NiB alloy, Co, and Pt.

  Furthermore, according to the present invention, the soldering method is a soldering method in which a plating layer formed on one main surface of the substrate is melted and another substance is soldered to the substrate. The plating layer is composed of first and second metal elements constituting an alloy for soldering. The composition ratio of the second metal element increases from the first composition ratio to the second composition ratio from the interface between the plating layer and the substrate toward the surface of the plating layer. The first composition ratio is a composition ratio that sets the strength of the plating layer when the other substance melts the plating layer and is soldered to the substrate to a reference strength or higher. The second composition ratio is a composition ratio that sets the melting point of the plating layer to a temperature lower than the reference melting point.

  The soldering method includes a first step of immersing the substrate in a plating bath containing the first and second metal elements, and a composition ratio of the second metal element from the interface toward the surface. A second step of forming a plating layer on the base so as to increase from 2 to a second composition ratio, and a third step of melting the plating layer and soldering another substance to the base.

  Preferably, in the second step, a plating layer is formed by electroplating.

  Preferably, in the second step, the dropping amount of the first compound containing the first metal element to the plating bath is decreased, and the dropping amount of the second compound containing the second metal element to the plating bath is reduced. While increasing, a plating layer is formed by performing electroplating for a predetermined time.

  Preferably, the first metal element is Sn, and the second metal element is Bi.

  Preferably, the first composition ratio is in the range of 2 to 21%, and the second composition ratio is in the range of 30 to 55%.

  In the present invention, a plating layer is constituted by a soldering alloy composed of the first and second metal elements, and the composition ratio of the second metal element in the plating layer is plated from the innermost circumference to the outermost circumference. The plating layer is formed by electroplating by changing the composition ratio at which the strength of the layer is set to be higher than the reference strength to the composition ratio at which the melting point when soldering is lower than the reference melting point. Then, when the metal balls are soldered, the plating layer reflows at a melting point lower than the reference melting point, and the metal balls are soldered at a low temperature and the strength after soldering is maintained at or above the reference strength.

  Therefore, according to the present invention, the strength when the metal ball is soldered can be maintained, and the melting point when soldering can be lowered.

  In the present invention, the plating layer is constituted by a soldering alloy composed of the first and second metal elements, and the composition ratio of the second metal element in the plating layer is changed from the innermost circumference to the outermost circumference. Then, the plating layer is formed by electroplating by changing the composition ratio at which the strength of the plating layer is higher than the reference strength to the composition ratio at which the melting point when soldering is lower than the reference melting point. Then, when soldering other materials to the substrate, the plating layer reflows at a melting point lower than the reference melting point, and the other materials are soldered at a low temperature and the strength after soldering is kept above the reference strength. Is done.

  Therefore, according to the present invention, the strength when soldering another substance to the substrate can be maintained, and the melting point when soldering can be lowered.

  Embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Embodiment 1]
1 is a cross-sectional view showing a configuration of a metal ball according to Embodiment 1 of the present invention. Referring to FIG. 1, metal ball 10 according to Embodiment 1 of the present invention includes a core ball 1, a reaction suppression layer 2, and a plating layer 3.

  The core ball 1 is made of copper (Cu) and has a diameter in the range of 50 μm to 1000 μm. The melting point of the core ball 1 is in the range of 600 to 1600 ° C.

  The reaction suppression layer 2 is made of any one of Ni, NiP alloy, NiB alloy, Co, and Pt, and is formed between the core ball 1 and the plating layer 3. And the film thickness of the reaction suppression layer 2 is the range of 0.1 micrometer-5 micrometers. Reaction suppression layer 2 suppresses the reaction between copper constituting core ball 1 and tin (Sn) and indium (In) constituting plating layer 3.

  The plating layer 3 is formed by electroplating and covers the core ball 1 and the reaction suppression layer 2. And the plating layer 3 consists of a Sn-In alloy, and a film thickness is the range of 0.1 micrometer-100 micrometers. In the plating layer 3, the In composition ratio increases from the first composition ratio to the second composition ratio from the innermost periphery to the outermost periphery of the plating layer 3.

  Here, the first composition ratio is a composition ratio that sets the strength of the plating layer 3 when the metal ball 10 is soldered to a reference strength or more, and the second composition ratio is the melting point of the plating layer 3. The composition ratio is set to a temperature lower than the reference melting point.

  Reaction suppression layer 2 and plating layer 3 are formed by electroplating. FIG. 2 is a schematic view of a barrel plating apparatus for producing the metal ball 10 shown in FIG. Referring to FIG. 2, barrel plating apparatus 100 includes plating tank 20, frame plate 30, barrel drum 40, gears 50 and 60, motor 70, cathode 80, anode 90, and nozzles 110 and 120. And a DC power supply 130.

  A plating bath 140 is placed in the plating tank 20. The frame plate 30 holds the barrel drum 40 rotatably in a substantially horizontal state. The barrel drum 40 includes six side plates 41 and six net members 42. The six side plates 41 are assembled in a hexagonal column shape. The six net members 42 are each attached to the six side plates 41. Therefore, the barrel drum 40 has a hexagonal column shape, and accommodates an article to be plated (= core ball 1) therein.

  The gear 50 is connected to the barrel drum 40 via the frame plate 30. The gear 60 is attached to the frame plate 30 so as to mesh with the gear 50. The motor 70 is connected to the gear 60 via the shaft 71.

  The frame plate 30, the barrel drum 40, and the gears 50 and 60 are accommodated in the plating tank 20 so that a part of the frame plate 30 and the barrel drum 40 is immersed in the plating bath 140.

  The motor 70 rotates the barrel drum 40 in the direction of the arrow 21 at a constant rotation speed via the shaft 71 and the gears 60 and 50. The cathode 80 is attached to the frame plate 30 such that the tip thereof is immersed in the plating bath 140 inside the barrel drum 40. The tip of the anode 90 is immersed in the plating bath 140.

  The nozzles 110 and 120 are supported by a support member (not shown) so that the front ends thereof are located on the plating bath 140. The DC power source 130 is connected between the cathode 80 and the anode 90, and allows a current having a constant current density to flow through the plating bath 140 via the cathode 80 and the anode 90.

  As described above, the barrel drum 40 has a structure in which the side plate 41 to which the mesh material 42 is attached is assembled in a substantially hexagonal column shape, and a part thereof is immersed in the plating bath 140. Then, the article to be plated is collected on the side plate 41 immersed in the plating bath 140. Further, the tip of the cathode 80 is disposed in the vicinity of the side plate 41 immersed in the plating bath 140.

  Therefore, the plating bath 140 enters the barrel drum 40 through the immersed mesh material 42 and is electroplated by flowing a current having a constant current density between the cathode 80 and the anode 90 to be plated. Deposits on the surface of the article.

  Further, since the barrel drum 40 is rotated in the direction of the arrow 21 at a constant rotational speed by the motor 70, the side plate 41 immersed in the plating bath 140 is sequentially changed, and the article to be plated in the barrel drum 40 is rotated. While being plated. Thereby, the reaction suppression layer 2 and the plating layer 3 can be uniformly formed on the surface of the spherical core ball 1.

  The plating bath 140 is made of sulfuric acid, tin sulfate, indium sulfate, polyoxyalkylene alkylaryl ether, and pyrocatechol. Polyoxyalkylene alkylaryl ether and pyrocatechol are used as brighteners for the plating layer 3.

  The plating bath 140 includes tin sulfate and indium sulfate, and the core ball 1 on which the reaction suppression layer 2 is formed from tin sulfate and indium sulfate is plated with a solder alloy (Sn—In alloy) made of tin and indium.

  The nozzle 110 is a nozzle that introduces a solution containing tin sulfate into the plating bath 140, and the nozzle 120 is a nozzle that introduces a solution containing indium sulfate into the plating bath 140.

  In this invention, when the plating layer 3 is formed by electroplating, the amount of dropping of the solution containing tin sulfate is gradually decreased, and the amount of dropping of the solution containing indium sulfate is gradually increased or decreased. Thus, the plating layer 3 is formed. That is, in the present invention, the composition ratio of In in the Sn—In alloy constituting the plating layer 3 increases from the first composition ratio to the second composition ratio from the innermost periphery to the outermost periphery of the plating layer 3. Thus, the plating layer 3 is formed by electroplating.

  FIG. 3 is a diagram showing a change in the composition ratio of In in the Sn—In alloy. In FIG. 3, the horizontal axis represents the film thickness direction of the plating layer 3, and the vertical axis represents the In composition ratio. Referring to FIG. 3, the straight line k <b> 1 increases the In composition ratio at a constant increase rate from the first composition ratio at the innermost periphery of the plating layer 3 to the second composition ratio at the outermost periphery of the plating layer 3. Indicates the case where

  The curve k2 indicates that the In composition ratio is increased from the first composition ratio to the second composition ratio while changing the increase rate of the In composition ratio between the innermost periphery and the outermost periphery of the plating layer 3. Indicates the case where

  Further, the curve k3 indicates that the In composition ratio is changed from the first composition ratio to the second while the In composition ratio increase rate is changed between the innermost periphery and the outermost periphery of the plating layer 3 to two increase rates. The case where it increases to the composition ratio of is shown.

  In the present invention, the composition ratio of In is changed according to one of the straight line k1 and the curves k2 and k3. When the In composition ratio is changed according to any of the straight line k1 and the curves k2 and k3, the In composition ratio may be increased stepwise as shown by the curve k4.

  In order to form the plating layer 3 in which the composition ratio of In changes according to any of the straight line k1 and the curves k2 and k3 shown in FIG. 3, the dropping amount of the solution containing tin sulfate is gradually decreased, and indium sulfate is added. The plating layer 3 is formed by electroplating while gradually increasing the dropping amount of the solution containing it.

  FIG. 4 is a flowchart showing a method for producing the metal ball 10 shown in FIG. When the operation for producing the metal ball 10 is started, the core ball 1 made of copper is immersed in a plating bath for nickel plating (step S1). That is, in the barrel plating apparatus 100 shown in FIG. 2, the core ball 1 is immersed in a plating bath 140 made of a predetermined amount of nickel sulfate, a predetermined amount of nickel chloride and a predetermined amount of boric acid.

  Thereafter, the motor 70 rotates the barrel drum 40 in the direction of the arrow 21 through the shaft 71 and the gears 60 and 50 at a constant rotational speed, and the DC power source 130 supplies a constant current between the cathode 80 and the anode 90. Pass a current of density. Then, the surface of the core ball 1 is plated with nickel, and the reaction suppression layer 2 is formed so as to cover the core ball 1 (step S2).

  Then, the core ball 1 on which the reaction suppression layer 2 is formed is immersed in a plating bath 140 for tin-indium plating (step S3). That is, in the barrel plating apparatus 100 shown in FIG. 2, the plating bath 140 is made of a predetermined amount of sulfuric acid, a predetermined amount of tin sulfate, a predetermined amount of indium sulfate, a predetermined amount of polyoxyalkylene alkylaryl ether, and a predetermined amount of pyrocatechol. The core ball 1 on which the reaction suppression layer 2 is formed is immersed.

  Thereafter, the motor 70 rotates the barrel drum 40 in the direction of the arrow 21 through the shaft 71 and the gears 60 and 50 at a constant rotational speed, and the DC power source 130 supplies a constant current between the cathode 80 and the anode 90. Pass a current of density. Further, the amount of the solution containing tin sulfate supplied to the plating bath 140 through the nozzle 110 is gradually reduced, and the amount of the solution containing indium sulfate supplied to the plating bath 140 through the nozzle 120 is gradually increased. .

  Then, the plating layer 3 in which the In composition ratio increases from the first composition ratio to the second composition ratio from the innermost circumference toward the outermost circumference is formed on the surface of the reaction suppression layer 2 (step S4). That is, the plating layer 3 in which the In composition ratio increases according to any of the straight line k1 and the curved lines k2 and k3 shown in FIG. Thereby, the production of the metal ball 10 is completed.

  Thus, the metal ball 10 uses the barrel plating apparatus 100 to control the amount of tin sulfate and indium sulfate supplied to the plating bath 140 during electroplating, so that the composition ratio of In changes from the innermost to the outermost. It is produced by forming the plating layer 3 (= Sn—In alloy) increasing toward the surface of the core ball 1.

  FIG. 5 is a diagram showing the relationship between the In concentration in the Sn—In alloy and the state of the Sn—In alloy. In FIG. 5, the horizontal axis represents In concentration, and the vertical axis represents temperature. Referring to FIG. 5, curve k5 indicates the boundary between the solid phase and the liquid phase of the Sn—In alloy at each In concentration. For example, when the In concentration is about 40 [mass%], the Sn—In alloy becomes a liquid phase at a temperature of about 150 ° C.

  The temperature at which Sn with an In concentration of 0 [mass%] becomes a liquid phase (= melting point) is about 230 ° C., and the melting point of the Sn—In alloy decreases as the In concentration added to Sn increases. It becomes the lowest when the In concentration is about 55 [mass%]. The melting point of the Sn—In alloy becomes higher as the In concentration increases in the region where the In concentration is 55 [mass%] or more.

  On the other hand, when the In concentration increases to 50 [mass%] or more, the Sn—In alloy becomes brittle. Therefore, in the present invention, in order to form an Sn—In alloy whose strength is equal to or higher than the reference strength and whose melting point is lower than the reference melting point (= 200 ° C., for example), the In concentration is set at the innermost periphery of the plating layer 3. The range is set to 18 to 20 [mass%], the In concentration is set to the range of 34 to 38 [mass%] at the outermost periphery of the plating layer 3, and the In concentration is further increased from the innermost periphery toward the outermost periphery. While increasing, the plating layer 3 is formed by electroplating.

  That is, the innermost peripheral portion of the plating layer 3 is formed of an Sn—In alloy having a melting point of 200 ° C. or higher, and the outermost peripheral portion of the plating layer 3 is formed of an Sn—In alloy having a melting point lower than 200 ° C. That is, the plating layer 3 is formed of an Sn—In alloy having a composition that maintains strength at the innermost peripheral portion and lowers the melting point at the outermost peripheral portion.

  FIG. 6 is an electron micrograph of metal balls 10 electroplated using the barrel plating apparatus 100 shown in FIG. 2 while increasing the In concentration from the innermost periphery toward the outermost periphery. In FIG. 6, a curve k6 represents a change in the In amount in the depth direction of the plating layer 3, and a curve k7 represents a change in the Sn amount in the depth direction of the plating layer 3. The amount of In and Sn in the depth direction of the plating layer 3 was measured by EDX (Energy Dispersive X-ray Spectrometry) line analysis.

  Referring to FIG. 6, in the plating layer 3, the In amount increases from the innermost periphery to the outermost periphery, the Sn amount decreases from the innermost periphery to the outermost periphery, and the In composition It was confirmed that the metal ball 10 having the plating layer 3 whose ratio increases from the innermost circumference toward the outermost circumference is produced.

  Next, an experimental result of the Sn—In alloy in which the strength is maintained above the reference strength and the melting point is lower than the reference melting point will be described. Two types of metal balls (Examples 1 and 2) were produced as the metal ball 10 according to the present invention, and two types of metal balls (Comparative Examples 1 and 2) were produced as comparative examples.

  Table 1 shows metal balls 10A (Example 1) and metal balls 10B (Example 2) as metal balls 10 according to the present invention, and metal balls 20A (Comparative Example 1) and metal balls 20B (Comparative Example) as comparative examples. 2) shows a plating bath 140 for producing by electroplating.

  When the metal ball 10A (Example 1) is produced by electroplating, the plating bath 140 includes 80 g / L sulfuric acid, 5 g / L polyoxyalkylene alkylaryl ether, 0.1 g / L pyrocatechol, It consists of sulfuric acid Sn whose concentration changes within a predetermined range A1, and sulfuric acid In whose concentration changes within a predetermined range B1.

  The predetermined range A1 is a range from 11 g / L at the start of electroplating to 3 g / L at the end of electroplating, and the predetermined range B1 is from 25 g / L at the start of electroplating to electroplating. The range is up to 22 g / L at the end.

  Further, when the metal ball 10B (Example 2) is produced by electroplating, the plating bath 140 is composed of 80 g / L sulfuric acid, 5 g / L polyoxyalkylene alkylaryl ether, and 0.1 g / L pyrocatechol. And sulfuric acid Sn whose concentration changes within a predetermined range A2 and sulfuric acid In whose concentration changes within a predetermined range B2.

  The predetermined range A2 is a range from 9 g / L at the start of electroplating to 4 g / L at the end of electroplating, and the predetermined range B2 is from 24 g / L at the start of electroplating to electroplating. The range is up to 27 g / L at the end.

When the metal ball 10A (Example 1) and the metal ball 10B (Example 2) are produced by electroplating, a core ball (= Cu ball) having a diameter of 400 μm is provided in the barrel drum 40 shown in FIG. The barrel drum 40 is rotated at a predetermined rotational speed by a motor 70, and a current having a current density of 0.2 A / dm ² is passed through the cathode 80 and the anode 90 to the plating bath 140 by the DC power source 130, and the nozzle The electroplating is performed while changing the concentration of Sn, which is injected into the plating bath 140 through 110, and the concentration of In, which is injected into the plating bath 140 through the nozzle 120, within the ranges shown in Table 1. In this case, the electroplating time is, for example, 4 hours.

  As described above, the metal balls 10A (Example 1) and the metal balls 10B (Example 2) are subjected to electroplating while gradually decreasing the concentration of Sn sulfate and gradually decreasing or increasing the concentration of In sulfate. It is produced by this. And the density | concentration of sulfuric acid Sn and sulfuric acid In changed linearly in the plating time mentioned above. In this case, the metal balls 10A (Example 1) are produced by changing the concentrations of Sn and In sulfate in a relatively large amount, and the metal balls 10B (Practical Example) are produced by changing the concentrations of Sn and In sulfate in a relatively small amount. Example 2) is prepared.

  Note that the metal ball 10A (Example 1) does not have the reaction suppression layer 2, and the metal ball 10B (Example 2) has the reaction suppression layer 2 made of nickel.

  When the metal ball 20A (Comparative Example 1) is produced by electroplating, the plating bath 140 is prepared by using 80 g / L sulfuric acid, 5 g / L polyoxyalkylene alkylaryl ether, and 0.1 g / L pyrocatechol. And 12 g / L of sulfuric acid Sn and 23 g / L of sulfuric acid In. Then, the sulfuric acid Sn and the sulfuric acid In are replenished through the nozzles 110 and 120 so that the concentrations in the plating bath 140 are 12 g / L and 23 g / L, respectively.

  Further, when the metal ball 20B (Comparative Example 2) is produced by electroplating, the plating bath 140 is composed of 80 g / L sulfuric acid, 5 g / L polyoxyalkylene alkylaryl ether, and 0.1 g / L pyrocatechol. And 5 g / L of sulfuric acid Sn and 25 g / L of sulfuric acid In. Then, the sulfuric acid Sn and the sulfuric acid In are replenished through the nozzles 110 and 120 so that the concentrations in the plating bath 140 are 5 g / L and 25 g / L, respectively.

When producing the metal balls 20A (Comparative Example 1) and the metal balls 20B (Comparative Example 2), a predetermined number of core balls (= Cu balls) having a diameter of 400 μm are placed in the barrel drum 40 shown in FIG. 70, the barrel drum 40 is rotated at a predetermined rotational speed, and a current having a current density of 0.2 A / dm ² is caused to flow to the plating bath 140 through the cathode 80 and the anode 90 by the DC power source 130, and through the nozzle 110. Electroplating is performed while the concentration of Sn Sn injected into the plating bath 140 and the concentration of In Indium sulfate injected into the plating bath 140 through the nozzle 120 are kept constant. In this case, the electroplating time is, for example, 4 hours.

  As described above, the metal ball 20A (Comparative Example 1) and the metal ball 20B (Comparative Example 2) are produced while keeping the concentrations of Sn sulfate and In sulfate in the plating bath 140 constant.

  In this case, a metal ball 20B (Comparative Example 2) was produced by relatively increasing the concentration of sulfuric acid In (= [sulfuric acid In] / ([sulfuric acid Sn] + [sulfuric acid In]); The metal ball 20A (Comparative Example 1) is manufactured with a relatively low concentration of the above.

  The metal balls 20A and 20B do not have the reaction suppression layer 2.

  Table 2 shows In concentrations, melting points, and film thicknesses of the metal balls 10A and 10B and the metal balls 20A and 20B produced using the plating bath 140 shown in Table 1.

  The In concentration is the concentration in the plating layer and was calculated by [In] / ([Sn] + [In]). The melting point temperature is a melting point when the metal balls 10A, 10B, 20A, and 20B are soldered.

  Metal ball 20A (Comparative Example 1) and metal ball 20B (Comparative Example 2) have In concentrations of 14.5% and 35.7%, respectively, and have melting points of 210 ° C. and 157 ° C. Further, the metal ball 20A (Comparative Example 1) and the metal ball 20B (Comparative Example 2) have plating layers having film thicknesses of 10.7 μm and 9.2 μm, respectively.

  Therefore, in the metal balls 20A (Comparative Example 1) and the metal balls 20B (Comparative Example 2) having a plating layer with a constant In concentration, when the In concentration in the plating layer increases, the metal balls 20A and 20B are soldered. When the melting point decreases. And in the metal ball | bowl 20B whose In density | concentration in a plating layer is 35.7%, melting | fusing point when soldering becomes lower than 200 degreeC.

  On the other hand, the metal ball 10A (Example 1) has In concentrations of 18.7% and 38.0% at the innermost periphery and the outermost periphery, respectively, and has an average concentration of In of 25.8%. The metal ball 10A (Example 1) has a melting point of 150 ° C. In the metal ball 10A (Example 1), the thickness of the plating layer 3 (Sn—In alloy) is 11.0 μm.

  Further, the metal ball 10B (Example 2) has In concentrations of 19.8% and 34.0% at the innermost periphery and the outermost periphery, respectively, and has an average concentration of In of 23.9%. The metal ball 10B (Example 2) has a melting point of 150 ° C. In the metal ball 10B (Example 2), the film thickness of the plating layer 3 (Sn—In alloy) is 9.7 μm, and the film thickness of the reaction suppression layer 2 (= Ni) is 2.0 μm. .

  Thus, the metal ball 10A (Example 1) and the metal ball 10B (Example 2) according to the present invention are substantially the same as the metal ball 20A (Comparative Example 1) and the metal ball 20B (Comparative Example 2) which are comparative examples. It has a plating layer (= Sn—In alloy) having a film thickness and has a melting point lower than that of the metal balls 20A and 20B.

  Therefore, by setting the In concentration in the plating layer 3 to the range of 18.0% to 20.0% and the range of 34.0% to 38.0% on the innermost periphery and the outermost periphery, respectively, the metal balls 10A, The melting point of 10B can be significantly lowered to 150 ° C.

  In addition, the pull strength of the metal ball 10A (Example 1), the metal ball 10B (Example 2), the metal ball 20A (Comparative Example 1) and the metal ball 20B (Comparative Example 2) is measured, and the soldered metal ball The peeling modes from the substrates 10A, 10B, 20A, and 20B were analyzed. In addition, pull strength was performed using the bond tester series 4000 made from Dage.

  FIG. 7 is a conceptual diagram for explaining a method of measuring the pull strength. Referring to FIG. 7, the tweezer 11 sandwiches the metal ball 10 from both sides. When measuring the pull strength, the metal ball 10 soldered on the substrate 13 is sandwiched by the tweezers 11 and the tweezers 11 are moved in the direction of the arrow 12. In this case, the force pulling the tweezer 11 in the direction of the arrow 12 is gradually increased until the metal ball 10 peels from the substrate 13. And the force which pulls the tweezer 11 when the metal ball 10 peels from a board | substrate is detected as pull strength.

  FIG. 8 is a conceptual diagram of a peeling mode in which the metal ball 10 peels from the substrate. Referring to FIG. 8, when the soldered metal ball 10 is peeled off from the substrate 13, a mode in which the metal ball 10, the land 14 and the solder 15 are peeled from the substrate 13 integrally (see FIG. 8A), A mode in which the metal ball 10 and the solder 15 are integrally peeled from the land 14 (see FIG. 8B), and a mode in which the solder 15 is broken to form the solders 15A and 15B, and the metal ball 10 is peeled from the substrate 13. (See FIG. 8C).

  The peeling mode shown in FIGS. 8A and 8B is “interface peeling”, and the peeling mode shown in FIG. 8C is “solder tear”.

  FIG. 9 is a photograph showing interfacial peeling and solder tearing. FIG. 9A shows solder breakage, and FIG. 9B shows interface peeling. When the peeling mode is torn solder, the plating layer of the metal ball becomes brittle by soldering, and the diameter of the metal ball is reduced. (See (a) in FIG. 9).

  On the other hand, when the peeling mode is interfacial peeling, the strength of the plating layer of the metal ball is maintained by soldering, and the diameter of the metal ball does not decrease (see FIG. 9B).

  The pull strength of the soldered metal balls 10A, 10B, 20A, and 20B was measured by the method shown in FIG. 7, and the peeling mode of the soldered metal balls 10A, 10B, 20A, and 20B was analyzed.

  FIG. 10 is a diagram illustrating a measurement result of the pull strength. In FIG. 10, the horizontal axis represents the type of metal ball, and the vertical axis represents the pull strength. The pull strength shown in FIG. 10 was measured for the metal balls 10A, 10B, 20A, and 20B soldered at a reflow temperature of 220 ° C. In addition, the number of metal balls 10A, 10B, 20A, and 20B used for the measurement of pull strength is 20.

  The metal ball 20A (Comparative Example 1) has a pull strength in a range of about 90 [gf] to about 220 [gf] (average value: about 135 [gf]), and the metal ball 20B (Comparative Example 2) It has a pull strength in the range of about 400 [gf] to about 1275 [gf] (average value: about 760 [gf]).

  On the other hand, the metal ball 10A (Example 1) has a pull strength in the range of about 540 [gf] to about 1250 [gf] (average value: about 800 [gf]), and the metal ball 10B (Example 2). Has a pull strength in the range of about 670 [gf] to about 1200 [gf] (average value: about 900 [gf]).

  FIG. 11 is a diagram illustrating the analysis result of the peeling mode. In FIG. 11, the horizontal axis represents the type of metal ball, and the vertical axis represents the ratio of the peeling mode. In addition, the peeling mode shown in FIG. 11 was analyzed for the metal balls 10A, 10B, 20A, and 20B soldered at a reflow temperature of 220 ° C.

  Referring to FIG. 11, all of metal balls 20 </ b> A (Comparative Example 1) are in the mode MD <b> 2 of “interface peeling”.

  Further, in the metal ball 20B (Comparative Example 2), the ratio of the mode MD1 in which the peeling mode is “solder breakage” is 25%, and the ratio in which the peeling mode is the mode MD2 of “interface peeling” is 75%. .

  On the other hand, in each of the metal balls 10A (Example 1) and 10B (Example 2), all are in the mode MD2 of “interface peeling”.

  Therefore, by increasing the In composition ratio in the plating layer 3 from the innermost circumference toward the outermost circumference, the metal ball 10 whose peeling mode is all “interfacial peeling” can be produced.

  Further, from the results shown in Table 2, FIG. 10, and FIG. 11, by forming the plating layer 3 by electroplating while increasing the In concentration from the innermost periphery toward the outermost periphery, the pull strength becomes 400 [gf] ( = The reference strength), the metal ball 10 having a melting point lower than 200 ° C. (= reference melting point) and a peeling mode of “interfacial peeling” can be produced.

  In the above description, the plating layer 3 is composed of a Sn—In alloy. However, in the present invention, the present invention is not limited thereto, and the plating layer 3 is composed of a Sn—Zn alloy or a Sn—Cu alloy. Generally, it is sufficient that the lead-free plating alloy is formed and an alloy of Sn and an element other than Bi is used.

  In the present invention, the plating layer 3 is generally composed of the first and second metal elements, and the composition ratio of the second metal element is from the innermost periphery to the outermost periphery of the plating layer 3. Thus, the composition ratio may be increased from the composition ratio that maintains the strength to the reference strength or higher to the composition ratio that lowers the melting point below the reference melting point.

  The method of increasing the composition ratio of the second metal element from the innermost circumference toward the outermost circumference may be a method of increasing according to a straight line or a curve other than the straight line k1 and the curves k2 and k3 shown in FIG. .

  Further, in the above description, the core ball 1 is made of copper. However, the present invention is not limited to this, and the core ball 1 may be made of aluminum (Al).

  Further, in the above description, the reaction suppression layer 2 has been described as being formed by electroplating. However, in the present invention, the present invention is not limited thereto, and the reaction suppression layer 2 may be formed by a sputtering method.

  Furthermore, in the above description, the metal ball 10 is described as including the reaction suppression layer 2, but in the present invention, the present invention is not limited thereto, and the metal ball 10 may not include the reaction suppression layer 2.

  According to the first embodiment, in the metal ball 10, the In composition ratio increases from the composition ratio that maintains the strength at or above the reference strength from the innermost periphery to the outermost periphery, to the composition ratio that lowers the melting point below the reference melting point. Since the plating layer 3 is provided, the strength can be maintained and the melting point can be lowered when the metal ball 10 is soldered.

[Embodiment 2]
FIG. 12 is a sectional view showing a structure of a plated structure according to Embodiment 2 of the present invention. Referring to FIG. 12, plating structure 200 according to the second embodiment of the present invention includes a substrate 201, a wiring 202, a reaction suppression layer 203, and a plating layer 204.

  The wiring 202 formed on the substrate 201 is made of copper (Cu) and has a thickness of 100 μm or less.

  The reaction suppression layer 203 is made of any one of Ni, NiP alloy, NiB alloy, Co, and Pt, and is formed between the wiring 202 and the plating layer 204. In this case, the reaction suppression layer 203 is formed on a part of the surface of the wiring 202 so as to cover the recess 2021 of the wiring 202. And the film thickness of the reaction suppression layer 203 is 5 micrometers or less. The reaction suppression layer 203 suppresses the reaction between copper constituting the wiring 202 and tin (Sn) and bismuth (Bi) constituting the plating layer 204.

  The plating layer 204 is formed on the reaction suppression layer 203 by electroplating. And the plating layer 204 consists of a Sn-Bi alloy, and a film thickness is the range of 5 micrometers-100 micrometers. In the plating layer 204, the Bi composition ratio increases from the first composition ratio to the second composition ratio from the interface 204A between the plating layer 204 and the reaction suppression layer 203 toward the surface 204B.

  Here, the first composition ratio is a composition ratio that sets the strength of the plating layer 204 when the metal layer (not shown) is soldered to the wiring 202 by melting the plating layer 204 to a reference strength or higher. The second composition ratio is a composition ratio that sets the melting point of the plating layer 204 to a temperature lower than the reference melting point.

  The reaction suppression layer 203 and the plating layer 204 are formed by electroplating. FIG. 13 is a schematic view of a plating apparatus for producing the plating structure 200 shown in FIG. Referring to FIG. 13, plating apparatus 300 includes plating tank 310, nozzles 320 and 330, anode 340, cathode 350, and DC power supply 360.

  A plating bath 370 is placed in the plating tank 310. The nozzles 320 and 330 are supported by a support member (not shown) so that the front ends thereof are located on the plating bath 370. The anode 340 is made of a substrate 201 that is a plated product, and is entirely immersed in the plating bath 370. The tip of the cathode 350 is immersed in the plating bath 370.

  The DC power supply 360 is connected between the anode 340 and the cathode 350, and allows a current having a constant current density to flow through the plating bath 370 via the anode 340 and the cathode 350. The plating bath 370 includes a plating bath 370 </ b> A for producing the reaction suppression layer 203 and a plating bath 370 </ b> B for producing the plating layer 204.

  The reaction suppression layer 203 and the plating layer 204 are formed on a part of the wiring 202 (region covering the recess 2021). In this way, the reaction suppression layer 203 and the plating layer 204 are formed on a part of the wiring 202. For this purpose, a resist is applied to the surface of the substrate 201 by spin coating or the like, and the resist is patterned so that the recesses 2021 are exposed.

  Then, the substrate 201 having a patterned resist is immersed in a plating bath 370A as a cathode 350 to form a reaction suppression layer 203 by electroplating, and then immersed in a plating bath 370B to form a plating layer 204 by electroplating. Form. Thereafter, the resist is removed.

  When the reaction suppression layer 203 and the plating layer 204 are formed by electroplating, the reaction suppression layer 203 and the plating layer 204 are also formed on the resist. However, by removing the resist after electroplating, the resist suppression layer 203 and the plating layer 204 are formed on the resist by lift-off. The formed reaction suppression layer 203 and plating layer 204 are also removed.

  As described above, when the resist patterning technique is used, the reaction suppression layer 203 and the plating layer 204 can be formed on a part of the wiring 202 by electroplating.

  The plating bath 370A is made of nickel sulfate, nickel chloride and boric acid. The plating bath 370B is made of sulfuric acid, tin sulfate, bismuth sulfate, polyoxyalkylene alkylaryl ether, and pyrocatechol. Polyoxyalkylene alkylaryl ether and pyrocatechol are used as brighteners for the plating layer 204.

  The plating bath 370B contains tin sulfate and bismuth sulfate, and electroplats the tin sulfate and bismuth sulfate to plate a solder alloy (Sn—Bi alloy) made of tin and bismuth on the wiring 202 on which the reaction suppression layer 203 is formed. .

  The nozzle 320 is a nozzle for introducing a solution containing tin sulfate into the plating bath 370B, and the nozzle 330 is a nozzle for introducing a solution containing bismuth sulfate into the plating bath 370B.

  In the present invention, when the plating layer 204 is formed by electroplating, the amount of dropping of the solution containing tin sulfate is gradually decreased and the amount of dropping of the solution containing bismuth sulfate is gradually increased while plating is performed by electroplating. Layer 204 is formed. In other words, in the present invention, electroplating is performed so that the composition ratio of Bi in the Sn—Bi alloy constituting the plating layer 204 increases from the first composition ratio to the second composition ratio from the interface 204A toward the surface 204B. A plating layer 204 is formed. When the composition ratio of Bi in the Sn—Bi alloy is increased from the first composition ratio to the second composition ratio from the interface 204A toward the surface 204B, the composition ratio of Bi is a straight line k1 and a curve shown in FIG. Increased according to either k2 or k3. When the Bi composition ratio is increased according to any of the straight line k1 and the curves k2 and k3, the Bi composition ratio may be increased stepwise as indicated by the curve k4.

  In order to form the plating layer 204 in which the composition ratio of Bi changes according to any of the straight line k1 and the curves k2 and k3 shown in FIG. 3, the dropping amount of the solution containing tin sulfate is gradually decreased, and bismuth sulfate is added. The plating layer 204 is formed by electroplating while gradually increasing the dropping amount of the solution containing it.

  FIG. 14 is a flowchart showing a method for producing the plated structure 200 shown in FIG. When the operation for producing the plating structure 200 is started, a resist is applied to the substrate 201 by spin coating or the like (step S11), and the applied resist is patterned into a predetermined pattern (step S12). As a result, the recess 2021 of the wiring 202 formed on the substrate 201 is exposed.

  Thereafter, the substrate 201 having the patterned resist is immersed in a plating bath for nickel plating (step S13). That is, in the plating apparatus 300 shown in FIG. 13, the substrate 201 is immersed as a cathode 350 in a plating bath 370 </ b> A composed of a predetermined amount of nickel sulfate, a predetermined amount of nickel chloride, and a predetermined amount of boric acid.

  Thereafter, the DC power supply 360 causes a current having a constant current density to flow between the anode 340 and the cathode 350. Then, the surface of the substrate 201 is plated with nickel, and the reaction suppression layer 203 is formed on the recess 2021 and the resist (step S14).

  And the board | substrate 201 with which the reaction suppression layer 203 was formed is immersed in the plating bath 370B for tin-bismuth plating (step S15). That is, in the plating apparatus 300 shown in FIG. 13, a plating bath 370B made of a predetermined amount of sulfuric acid, a predetermined amount of tin sulfate, a predetermined amount of bismuth sulfate, a predetermined amount of polyoxyalkylene alkylaryl ether and a predetermined amount of pyrocatechol is added. The substrate 201 on which the reaction suppression layer 203 is formed is immersed as the cathode 350.

  Thereafter, the DC power supply 360 causes a current having a constant current density to flow between the anode 340 and the cathode 350. Further, the amount of the solution containing tin sulfate supplied to the plating bath 370B through the nozzle 320 is gradually decreased, and the amount of the solution containing bismuth sulfate supplied to the plating bath 370B through the nozzle 330 is gradually increased. .

  Then, the plating layer 204 whose Bi composition ratio increases from the first composition ratio to the second composition ratio from the interface 204A between the plating layer 204 and the reaction suppression layer 203 toward the surface 204B is formed on the surface of the reaction suppression layer 203. It is formed (step S16). That is, the plating layer 204 in which the Bi composition ratio increases according to any of the straight line k1 and the curved lines k2 and k3 shown in FIG. Then, the resist is removed (step S17). Thereby, the production of the plating structure 200 is completed.

  In this way, the plating structure 200 uses the plating apparatus 300 to control the amount of the solution containing tin sulfate and the solution containing bismuth sulfate supplied to the plating bath 370 during electroplating, so that the composition ratio of Bi is the interface. It is produced by forming on the surface of the substrate 201 a plating layer 204 (= Sn—Bi alloy) that increases from 203A toward the surface 203B.

  FIG. 15 is a diagram showing the relationship between the Bi concentration in the Sn—Bi alloy and the state of the Sn—Bi alloy. In FIG. 15, the horizontal axis represents Bi concentration, and the vertical axis represents temperature. Referring to FIG. 15, curve k8 shows the boundary between the solid phase and the liquid phase of the Sn—Bi alloy at each Bi concentration. For example, when the Bi concentration is about 60 [mass%], the Sn—Bi alloy becomes a liquid phase at a temperature of about 150 ° C.

  The temperature at which Sn with a Bi concentration of 0 [mass%] becomes liquid phase (= melting point) is about 230 ° C., and the melting point of the Sn—Bi alloy decreases as the Bi concentration added to Sn increases. It becomes the lowest when the Bi concentration is about 60 [mass%]. The melting point of the Sn—Bi alloy becomes higher as the Bi concentration increases in the region where the Bi concentration is 60 [mass%] or more.

  On the other hand, when the Bi concentration increases, the Sn—Bi alloy becomes brittle. Therefore, in the present invention, in order to form an Sn—Bi alloy whose strength is equal to or higher than the reference strength and whose melting point is lower than the reference melting point (= 200 ° C., for example), the interface between the plating layer 204 and the reaction suppression layer 203 In 204A, the Bi concentration is set in the range of 2 to 21 [mass%], the Bi concentration is set in the range of 30 to 55 [mass%] on the surface 204B of the plating layer 204, and further from the interface 204A to the surface 204B. Then, the plating layer 204 is formed by electroplating while increasing the Bi concentration.

  That is, the innermost part (= interface 204A) of the plating layer 204 is formed of an Sn—Bi alloy having a melting point of 200 ° C. or higher, and the outermost part (= surface 204B) of the plating layer 204 is Sn— whose melting point is lower than 200 ° C. It is made of Bi alloy. That is, the plating layer 204 is formed of an Sn—Bi alloy having a composition that maintains strength at the innermost portion (= interface 204A) and lowers the melting point at the outermost portion (= surface 204B).

  Next, an experimental result of the Sn—In alloy in which the strength is maintained above the reference strength and the melting point is lower than the reference melting point will be described. In this experiment, the pull strength when the metal ball was soldered to the plating structure 200 was measured, and the peeling mode of the metal ball was analyzed.

  FIG. 16 is a diagram for explaining a sample for measuring the pull strength and analyzing the peeling mode. Referring to FIG. 16, metal ball 220 includes core ball 221 and plating layers 222 and 223.

  The core ball 221 is made of copper. The plating layer 222 covers the core ball 221 and is made of nickel plating. The plating layer 223 covers the plating layer 222 and is made of gold (Au) plating.

  The plated layer 204 of the plated structure 200 was melted and the metal balls 220 were soldered to the substrate 201, and the pull strength was measured using the pull strength measuring method described in FIG.

  Further, the analyzed peeling mode is as described in FIG.

  In the experiment, two kinds of plating structures (Examples 3 and 4) were produced as the plating structure 200 according to the present invention, and two kinds of plating structures (Comparative Examples 3 and 4) were produced as comparative examples.

  Table 3 shows a plated structure 200A (Example 3) and a plated structure 200B (Example 4) as a plated structure 200 according to the present invention, and a plated structure 210A (Comparative Example 3) and a plated structure as a comparative example. The plating bath 370B when producing the product 210B (Comparative Example 4) by electroplating is shown.

  When the plating structure 200A (Example 3) is produced by electroplating, the plating bath 370B includes 80 g / L sulfuric acid, 5 g / L polyoxyalkylene alkylaryl ether, 0.1 g / L pyrocatechol and The sulfuric acid Sn whose concentration changes within a predetermined range A3 and the sulfuric acid Bi whose concentration changes within a predetermined range B3.

  The predetermined range A3 is a range from 24 g / L at the start of electroplating to 18 g / L at the end of electroplating, and the predetermined range B3 is from 0.5 g / L at the start of electroplating to electric The range is up to 6 g / L at the end of plating.

  When the plating structure 200B (Example 4) is produced by electroplating, the plating bath 370B is composed of 80 g / L sulfuric acid, 5 g / L polyoxyalkylene alkylaryl ether, and 0.1 g / L pyrol. It consists of catechol, sulfuric acid Sn whose concentration changes within a predetermined range A4, and sulfuric acid Bi whose concentration changes within a predetermined range B4.

  The predetermined range A4 is a range from 19 g / L at the start of electroplating to 17 g / L at the end of electroplating, and the predetermined range B4 is from 3 g / L at the start of electroplating to electroplating. The range is up to 10 g / L at the end.

When the plating structure 200A (Example 3) and the plating structure 200B (Example 4) are produced by electroplating, the substrate is placed in the plating apparatus 300 shown in FIG. 13 and 0.2 A / dm ² is supplied from the DC power supply 360. A current composed of a current density is passed through the anode 340 and the cathode 350 to the plating bath 370B, Sn of sulfuric acid injected into the plating bath 370B through the nozzle 320, and Bi sulfate injected into the plating bath 370B through the nozzle 330. Electroplating is performed while changing the concentration within the range shown in Table 3. In this case, the electroplating time is, for example, 4 hours. This plating is repeated a predetermined number of times to produce a predetermined number of plating structures 200A (Example 3) and plating structures 200B (Example 4).

  Thus, the plating structure 200A (Example 3) and the plating structure 200B (Example 4) are subjected to electroplating while gradually decreasing the concentration of Sn sulfate and gradually increasing the concentration of Bi sulfate. It is produced by. And the density | concentration of the sulfuric acid Sn and the sulfuric acid Bi was changed linearly in the plating time mentioned above.

  The plating structure 200A (Example 3) and the plating structure 200B (Example 4) do not include the reaction suppression layer 203.

  When the plating structure 210A (Comparative Example 3) is produced by electroplating, the plating bath 370B is composed of 80 g / L sulfuric acid, 5 g / L polyoxyalkylene alkylaryl ether, and 0.1 g / L pyrol. It consists of catechol, 20 g / L Sn sulfate, and 3 g / L Bi sulfate. Then, the sulfuric acid Sn and the sulfuric acid Bi are replenished through the nozzles 320 and 330 so that the concentrations in the plating bath 370B are 20 g / L and 3 g / L, respectively.

  Further, when the plating structure 210B (Comparative Example 4) is produced by electroplating, the plating bath 140 is composed of 80 g / L sulfuric acid, 5 g / L polyoxyalkylene alkylaryl ether, and 0.1 g / L pyrol. It consists of catechol, 15 g / L Sn sulfate and 7 g / L Bi sulfate. Then, the sulfuric acid Sn and the sulfuric acid Bi are replenished through the nozzles 320 and 330 so that the concentrations in the plating bath 370B are 15 g / L and 7 g / L, respectively.

When producing the plating structure 210A (Comparative Example 3) and the plating structure 210B (Comparative Example 4), the substrate is placed in the plating apparatus 300 shown in FIG. 13, and the current density of 0.2 A / dm ² is applied by the DC power supply 360. Is supplied to the plating bath 370B through the anode 340 and the cathode 350, and the concentration of sulfuric acid injected into the plating bath 370B through the nozzle 320 and the concentration of sulfuric acid Bi injected into the plating bath 370B through the nozzle 330. The electroplating is performed while keeping the constant. In this case, the electroplating time is, for example, 4 hours. Then, this plating is repeated a predetermined number of times to produce a predetermined number of plating structures 210A (Comparative Example 3) and plating structures 210B (Comparative Example 4).

  As described above, the plating structure 210A (Comparative Example 3) and the plating structure 210B (Comparative Example 4) are produced while keeping the concentrations of Sn sulfate and Bi sulfate in the plating bath 370B constant.

  The plating structure 210A (Comparative Example 3) and the plating structure 210B (Comparative Example 4) do not have the reaction suppression layer 2.

  Table 4 shows the Bi concentration, the melting point, and the film thickness of the plating structures 200A and 200B produced using the plating bath 370B shown in Table 3 and the plating structures 210A and 210B.

  The Bi concentration is a concentration in the plating layer and was calculated by [Bi] / ([Sn] + [Bi]). Moreover, melting | fusing point temperature is melting | fusing point when soldering plating structure 200A, 200B, 210A, 210B.

  Plating structure 210A (Comparative Example 3) and plating structure 210B (Comparative Example 4) have Bi concentrations of 20.1% and 43.2%, respectively, and have melting points of 203 ° C and 142 ° C. The plating structure 210A (Comparative Example 3) and the plating structure 210B (Comparative Example 4) have plating layers having film thicknesses of 23.2 μm and 22.4 μm, respectively.

  Therefore, in the plating structure 210A (Comparative Example 3) and the plating structure 210B (Comparative Example 4) having a plating layer with a constant Bi concentration, when the Bi concentration in the plating layer increases, the plating structures 210A and 210B are The melting point when soldering is lowered. And in the plating structure 210B whose Bi density | concentration in a plating layer is 43.2%, melting | fusing point when soldering becomes lower than 200 degreeC.

  On the other hand, the plating structure 200A (Example 3) has Bi concentrations of 2.0% and 30.2% in the innermost portion (= interface 204A) and outermost portion (= surface 204B), respectively, and 23.8% Having an average concentration of Bi. The plating structure 200A (Example 3) has a melting point of 150 ° C. In the plating structure 200A (Example 3), the thickness of the plating layer 204 (Sn—Bi alloy) is 23.5 μm.

  Further, the plating structure 200B (Example 4) has Bi concentrations of 20.5% and 55.0% in the innermost portion (= interface 204A) and the outermost portion (= surface 204B), respectively, and 29.5%. Having an average concentration of Bi. Moreover, the plating structure 200B (Example 4) has a melting point of 140 ° C. In the plating structure 200B (Example 4), the thickness of the plating layer 204 (Sn—Bi alloy) is 25.3 μm.

  As described above, the plating structure 200A (Example 3) and the plating structure 200B (Example 4) according to the present invention include a plating structure 210A (Comparative Example 3) and a plating structure 210B (Comparative Example 4) which are comparative examples. ) And a melting point equivalent to or lower than the melting point of the plating structures 210A and 210B.

  Therefore, by setting the Bi concentration in the plating layer 204 to the range of 2.0% to 21.0% and the range of 30.0% to 55.0% at the innermost and outermost parts, respectively, the plated structure 200A, The melting point of 200B can be greatly reduced to 140 ° C.

  In addition, the pull strength of the plating structure 200A (Example 3), the plating structure 200B (Example 4), the plating structure 210A (Comparative Example 3) and the plating structure 210B (Comparative Example 4) is measured and soldered. The peeling mode of the attached plating structures 200A, 200B, 210A, 210B from the substrate 201 was analyzed. The pull strength was measured using a bond tester series 4000 manufactured by Dage as in the first embodiment.

  The pull strength of the plated structures 200A, 200B, 210A, 210B soldered with the metal balls 220 is measured by the method shown in FIG. 7, and the plated structures 200A, 200B, 210A, 210B soldered with the metal balls 220 are peeled off. The mode was analyzed.

  FIG. 17 is a diagram illustrating a measurement result of the pull strength. In FIG. 17, the horizontal axis represents the type of plating structure, and the vertical axis represents the pull strength. Note that the pull strength shown in FIG. 17 was measured for the plated structures 200A, 200B, 210A, and 210B in which the metal balls 220 were soldered at a reflow temperature of 220 ° C. The number of plating structures 200A, 200B, 210A, 210B used for the measurement of pull strength is 20.

  The plated structure 210A (Comparative Example 3) has a pull strength in the range of about 360 [gf] to about 960 [gf] (average value: about 570 [gf]), and the plated structure 210B (Comparative Example 4). Has a pull strength in the range of about 790 [gf] to about 1560 [gf] (average value: about 1180 [gf]).

  On the other hand, the plating structure 200A (Example 3) has a pull strength in the range of about 800 [gf] to about 1650 [gf] (average value: about 1230 [gf]), and the plating structure 200B (Example). 4) has a pull strength in the range of about 740 [gf] to about 1500 [gf] (average value: about 1190 [gf]).

  FIG. 18 is a diagram illustrating the analysis result of the peeling mode. In FIG. 18, the horizontal axis represents the type of plating structure, and the vertical axis represents the ratio of the peeling mode. In addition, the peeling mode shown in FIG. 18 was analyzed for the plating structures 200A, 200B, 210A, and 210B in which the metal balls 220 were soldered at a reflow temperature of 220 ° C.

  Referring to FIG. 18, in plating structure 210 </ b> A (Comparative Example 3), all are in mode MD <b> 2 of “interface peeling”.

  In the plating structure 210B (Comparative Example 4), the ratio of the mode MD1 in which the peeling mode is “solder tear” is 55%, and the ratio in which the peeling mode is the mode MD2 of “interface peeling” is 45%. is there.

  On the other hand, in each of the plated structures 200A (Example 3) and 200B (Example 4), all are in the mode MD2 of “interface peeling”.

  Therefore, by increasing the Bi composition ratio in the plating layer 204 from the innermost side toward the outermost side, the plating structure 200 in which all the peeling modes are “interfacial peeling” can be produced.

  Further, from the results shown in Table 4, FIG. 17 and FIG. 18, by forming the plating layer 204 by electroplating while increasing the Bi concentration from the innermost to the outermost, the pull strength is 600 [gf] (= It is possible to produce a plated structure 200 that is equal to or higher than (reference strength), has a melting point lower than 200 ° C. (= reference melting point), and has a peeling mode of “interface peeling”.

  Thus, when the metal ball 220 is soldered to the substrate 201, the plating layer 204 whose Bi composition ratio increases from the innermost (= interface 204A) to the outermost (= surface 204B) is formed on the surface of the substrate 201. By forming, the holding strength of the metal ball 220 can be improved to a holding strength equal to or higher than the reference strength, the melting point when soldering can be lowered to a melting point lower than the reference melting point, and the peeling mode of the metal ball 220 can be changed. It can be set to the peeling mode of interface peeling.

  Therefore, the plating structure 200 is suitable for soldering an electronic component to a Cu substrate or the like.

  FIG. 19 is a flowchart for explaining a soldering method when the metal ball 220 is soldered to the substrate 201 using the plating structure 200. When a series of operations is started, the reaction suppression layer 203 is formed on the substrate 201, and the plating layer 204 is formed on the formed reaction suppression layer 203 by gradient plating (step S21).

  The detailed operation of step S21 is executed according to the flowchart shown in FIG.

  After step S21, the plating layer 204 is melted and the metal ball 220 is soldered to the substrate 201 (step S22). Thereby, a series of operation | movement is complete | finished.

  In the above description, the plating layer 204 has been described as being composed of a Sn—Bi alloy. However, the present invention is not limited thereto, and the plating layer 204 may be composed of a Sn—In alloy. As shown in FIG. 5, the changing tendency of the melting point of the Sn—In alloy with respect to the In concentration is substantially the same as the changing tendency of the melting point of the Sn—Bi alloy with respect to the Bi concentration. Therefore, as described above, the plating layer 204 is replaced with a Sn—In alloy, and the In composition ratio in the plating layer 204 is increased from the innermost portion (= interface 204A) toward the outermost portion (= surface 204B). A plated structure 200 in which the strength of the layer 204 is maintained at or above the reference strength and the melting point is lower than the reference melting point can be produced.

  In the present invention, the plating layer 204 is generally composed of the first and second metal elements, and the composition ratio of the second metal element is determined from the innermost portion (= interface 204A) of the plating layer 204. What is necessary is just to increase from the composition ratio which keeps intensity | strength more than a reference | standard intensity | strength toward the outermost part (= surface 204B) to the composition ratio which makes melting | fusing point lower than a reference | standard melting | fusing point.

  The method of increasing the composition ratio of the second metal element from the innermost circumference toward the outermost circumference may be a method of increasing according to a straight line or a curve other than the straight line k1 and the curves k2 and k3 shown in FIG. .

  Further, in the above description, the wiring 202 is made of copper. However, the present invention is not limited to this, and the wiring 202 may be made of aluminum (Al).

  Furthermore, in the above description, the reaction suppression layer 203 has been described as being formed by electroplating. However, the present invention is not limited to this, and the reaction suppression layer 203 may be formed by a sputtering method.

  Furthermore, in the above description, the plating structure 200 is described as including the reaction suppression layer 203. However, in the present invention, the present invention is not limited thereto, and the plating structure 200 may not include the reaction suppression layer 203. .

  Further, in the above description, the case where the metal ball 220 is soldered to the substrate 201 has been described. However, the present invention is not limited to this, and an electronic component other than the metal ball 220 may be soldered to the wiring 202. The wiring 202 is not limited to the Cu substrate, and may be a printed board, and various electronic components may be soldered to the printed board using the plating structure 200 formed on the printed board.

  Furthermore, in the present invention, when two substances A and B are soldered, a plating layer 204 is formed on the surface of the substance A to produce a plating structure 200, and the substance is produced using the produced plating structure 200. B may be soldered to substance A.

  The substrate 201 constitutes a “base”. Therefore, the plating structure according to the present invention generally includes a base and a plating layer formed on the surface of the base.

  According to the second embodiment, the plated structure 200 has a composition in which the Bi composition ratio or the In composition ratio makes the melting point lower than the reference melting point from the composition ratio that keeps the strength at or above the reference strength from the innermost to the outermost. Since the plating layer 204 increases up to the ratio, when the metal ball 220 is soldered to the substrate 201 through the plating layer 204, the strength can be maintained and the melting point can be lowered.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

The present invention is applied to a metal ball that maintains strength when soldered and can lower the melting point when soldering. In addition, the present invention is applied to a method for producing a metal ball that retains the strength when soldering and can lower the melting point when soldering. Furthermore, the present invention is applied to a plated structure that maintains the strength when soldering and can lower the melting point when soldering. Furthermore, the present invention is applied to a soldering method using a plating structure capable of maintaining the strength when soldering and lowering the melting point when soldering.

It is sectional drawing which shows the structure of the metal ball by Embodiment 1 of this invention. It is the schematic of the barrel plating apparatus which produces the metal ball | bowl shown in FIG. It is a figure which shows the change of the composition ratio of In in a Sn-In alloy. It is a flowchart which shows the preparation methods of the metal ball | bowl shown in FIG. It is a figure which shows the relationship between In density | concentration in a Sn-In alloy, and the state of a Sn-In alloy. It is an electron micrograph of the metal ball electroplated using the barrel plating apparatus shown in FIG. 2 while increasing the In concentration from the innermost circumference toward the outermost circumference. It is a conceptual diagram for demonstrating the method to measure pull intensity | strength. It is a conceptual diagram of peeling mode in which a metal ball peels from a board | substrate. It is a photograph which shows interface peeling and solder tearing. It is a figure which shows the measurement result of a pull intensity | strength. It is a figure which shows the analysis result of peeling mode. It is sectional drawing which shows the structure of the plating structure by Embodiment 2 of this invention. It is the schematic of the plating apparatus which produces the plating structure shown in FIG. It is a flowchart which shows the preparation methods of the plating structure shown in FIG. It is a figure which shows the relationship between Bi density | concentration in a Sn-Bi alloy, and the state of a Sn-Bi alloy. It is a figure for demonstrating the sample which measures a pull intensity | strength and analysis of peeling mode. It is a figure which shows the measurement result of a pull intensity | strength. It is a figure which shows the analysis result of peeling mode. It is a flowchart for demonstrating the soldering method when soldering a metal ball to a board | substrate using a plating structure.

Explanation of symbols

  1,221 core ball, 2,203 reaction suppression layer, 3,204,222,223 plating layer, 10,220 metal ball, 11 tweezer, 12,21 arrow, 13 substrate, 14 land, 15, 15A, 15B solder, 20,310 plating tank, 30 frame plate, 40 barrel drum, 41 side plate, 42 mesh material, 50, 60 gear, 70 motor, 71 shaft, 80, 350 cathode, 90, 340 anode, 100 barrel plating device, 111 opening 110, 120, 320, 330 nozzle, 130, 360 DC power supply, 140, 370 plating bath, 200 plating structure, 201 substrate, 202 wiring, 204A interface, 204B surface, 300 plating apparatus, 2021 recess.

Claims (25)

A metal ball used for mounting electronic components,
A core ball made of metal,
Consisting of first and second metal elements constituting an alloy for soldering, and comprising a plating layer covering the core ball,
The composition ratio of the second metal element increases from the first composition ratio to the second composition ratio from the innermost periphery to the outermost periphery of the plating layer,
The first composition ratio is a composition ratio that sets the strength of the plating layer when the metal ball is soldered to a reference strength or more,
The second composition ratio is a composition ratio for setting the melting point of the plating layer to a temperature lower than a reference melting point,
The second metal element is a metal ball constituting a lead-free plating alloy and being an element other than Bi.   The metal ball according to claim 1, further comprising a reaction suppression layer inserted between the core ball and the plating layer.   The metal ball according to claim 2, wherein the reaction suppression layer is made of any one of Ni, Ni—P alloy, Ni—B alloy, Co, and Pt. The first metal element is Sn;
The metal ball according to any one of claims 1 to 3, wherein the second metal element is In. The first composition ratio is in a range of 18 to 20%,
The metal ball according to claim 4, wherein the second composition ratio is in a range of 34 to 38%.   The metal ball according to any one of claims 1 to 5, wherein the core ball is made of Cu. A substrate;
Consisting of first and second metal elements constituting an alloy for soldering, and comprising a plating layer formed on one main surface of the substrate,
The composition ratio of the second metal element increases from the first composition ratio to the second composition ratio from the interface between the plating layer and the substrate toward the surface of the plating layer,
The first composition ratio is a composition ratio that sets the strength of the plating layer when other substances are soldered to the base via the plating layer to be equal to or higher than a reference strength.
Said 2nd composition ratio is a plating structure which is a composition ratio which sets the melting | fusing point of the said plating layer to temperature lower than a reference | standard melting | fusing point.   The plating structure according to claim 7, further comprising a reaction suppression layer inserted between the base and the plating layer.   The plating structure according to claim 8, wherein the reaction suppression layer is made of any one of Ni, Ni-P alloy, Ni-B alloy, Co, and Pt. The first metal element is Sn;
The plated structure according to any one of claims 7 to 9, wherein the second metal element is Bi or In. The first composition ratio is in the range of 2 to 21%;
The plated structure according to claim 10, wherein the second composition ratio is in a range of 30 to 55%.   The plating structure according to claim 7, wherein the base is made of a Cu substrate. A method for producing a metal ball used for mounting electronic components,
The metal ball is
A core ball made of metal,
Consisting of first and second metal elements constituting an alloy for soldering, and comprising a plating layer covering the core ball,
The composition ratio of the second metal element increases from the first composition ratio to the second composition ratio from the innermost periphery to the outermost periphery of the plating layer,
The first composition ratio is a composition ratio that sets the strength of the plating layer when the metal ball is soldered to a reference strength or more,
The second composition ratio is a composition ratio for setting the melting point of the plating layer to a temperature lower than a reference melting point,
The second metal element constitutes a lead-free plating alloy and is an element other than Bi,
The production method is as follows:
A first step of immersing the core ball in a plating bath containing the first and second metal elements;
A second step of forming the plating layer such that the composition ratio of the second metal element increases from the first composition ratio to the second composition ratio from the innermost periphery to the outermost periphery of the plating layer; A method for producing a metal ball.   The method for producing a metal ball according to claim 13, wherein in the second step, the plating layer is formed by electroplating.   In the second step, the dropping amount of the first compound containing the first metal element to the plating bath is decreased, and the dropping amount of the second compound containing the second metal element to the plating bath is reduced. The method for producing a metal ball according to claim 14, wherein the plating layer is formed by performing the electroplating for a predetermined time while increasing or decreasing.   The method for producing a metal ball according to claim 15, wherein a current density in the electroplating is constant for the predetermined time. The first metal element is Sn;
The method for producing a metal ball according to any one of claims 13 to 16, wherein the second metal element is In. The first composition ratio is in a range of 18 to 20%,
The method for producing a metal ball according to claim 17, wherein the second composition ratio is in a range of 34 to 38%.   The method for producing a metal ball according to any one of claims 13 to 18, further comprising a third step of forming a reaction suppression layer so as to cover the core ball before the first step.   The method for producing a metal ball according to claim 19, wherein the third step forms the reaction suppression layer made of any one of Ni, NiP alloy, NiB alloy, Co, and Pt. A soldering method for melting a plating layer formed on one main surface of a substrate and soldering another substance to the substrate,
The plating layer is composed of first and second metal elements constituting an alloy for soldering,
The composition ratio of the second metal element increases from the first composition ratio to the second composition ratio from the interface between the plating layer and the substrate toward the surface of the plating layer,
The first composition ratio is a composition ratio that sets the strength of the plating layer when the other substance melts the plating layer and is soldered to the substrate to a reference strength or higher.
The second composition ratio is a composition ratio for setting the melting point of the plating layer to a temperature lower than a reference melting point,
The soldering method is:
A first step of immersing the substrate in a plating bath containing the first and second metal elements;
A second step of forming the plating layer on the substrate such that the composition ratio of the second metal element increases from the first composition ratio to the second composition ratio from the interface toward the surface;
A third step of melting the plating layer and soldering the other substance to the substrate.   The soldering method according to claim 21, wherein in the second step, the plating layer is formed by electroplating.   In the second step, the dropping amount of the first compound containing the first metal element to the plating bath is decreased, and the dropping amount of the second compound containing the second metal element to the plating bath is reduced. The soldering method according to claim 22, wherein the plating layer is formed by performing the electroplating for a predetermined time while increasing the thickness. The first metal element is Sn;
The soldering method according to any one of claims 21 to 23, wherein the second metal element is Bi. The first composition ratio is in the range of 2 to 21%;
The soldering method according to claim 24, wherein the second composition ratio is in a range of 30 to 55%.