JP4387265B2 - Method for manufacturing protruding electrode - Google Patents

Description

The present invention relates to a method of manufacturing a protruding electrode formed on a semiconductor substrate or a printed wiring board for electronic component mounting by soldering or the like. In this specification, a semiconductor substrate, a printed wiring board, an interposer substrate, and the like are simply referred to as “substrate”. Further, the bump electrode whose surface is coated with solder is also called “protrusion electrode”, and the portion covered with solder in this case is called “core”.

  An electronic component having a protruding electrode is an FC (flip chip) or BGA (ball grid array), and the FC or BGA is mounted on another substrate via the protruding electrode. On the other hand, there is a technique for mounting a bare electronic component on a substrate provided with a protruding electrode. A conventional general method for manufacturing a protruding electrode is to apply a solder paste on a lower electrode of a substrate by using a screen printing method, a dispensing method, or the like, and heat and reflow the solder paste. Thereby, a protruding electrode made of hemispherical solder is obtained.

  Next, a conventional protruding electrode which is a premise of the present invention will be described (for example, see Patent Document 1). FIG. 4 [1] is a cross-sectional view showing this type of protruding electrode. Hereinafter, description will be given based on this drawing.

  The protruding electrode 80 includes a core 82 provided on the substrate 81 and a spherical solder layer 83 provided on the surface 90 of the core 82. The surface 90 of the core 82 is divided into a side surface 91 in contact with the substrate 81, an upper surface 92 positioned above the side surface 91, and a corner 93 positioned at the boundary between the upper surface 92 and the side surface 91. The core 82 is formed on a lower electrode (not shown) on the substrate 81 by copper plating or the like. The solder layer 83 is formed, for example, by applying a solder paste on the core 82 and reflowing it.

  According to the bump electrode 80, the solder layer 83 is provided on the surface 90 of the core 82 that does not melt during solder reflow. Therefore, the height of the bump electrode 80 is less likely to be deformed by solder reflow than the bump electrode made entirely of solder. There is an advantage that can be increased.

Japanese Patent Laid-Open No. 10-70127 (FIG. 3)

  However, the conventional protruding electrode 80 has the following problems.

  As shown in FIG. 4 [2], the solder layer 83 may be divided into the side surface 91 and the upper surface 92 with the corner portion 93 of the core 82 as a boundary. As a result, particularly when the amount of solder on the upper surface 92 side is small, poor soldering may occur after mounting. This phenomenon becomes more prominent as the amount of solder in the entire solder layer 83 is smaller. On the other hand, if an attempt is made to simply increase the amount of solder in the entire solder layer 83 in order to prevent this, a short circuit occurs between adjacent protruding electrodes 80, making it difficult to cope with fine pitch.

An object of the present invention is to provide a manufacturing method of the bump electrode with improved solder wettability.

  The reason why the solder layer 83 is divided between the side surface 91 and the upper surface 92 at the corner 93 is considered to be because the solder wettability of the corner 93 is poor. FIG. 5 is an explanatory diagram showing solder wetting on the surface of a solid metal. Hereinafter, the reason why the solder wettability is poor in the corner portion 93 of the core 82 will be described with reference to FIGS. 4 and 5.

  FIG. 5 [1] shows the solder wetting of the surface of the flat solid metal 100 and is used for general explanation of soldering. The solder is heated and melted to form a molten solder 101. The molten solder 101 spreads on the solid metal 100 by the action of the liquid flux 102. At this time, it can be seen that the molten solder 101 is wetted by the action of three forces A, B, and C. That is, when the three forces A, B, and C are in an equilibrium state, the molten solder 101 exhibits a certain spread. A acts in a direction in contact with the curved surface of the liquid, and is a force for minimizing the surface tension of the liquid, that is, the surface area of the molten solder 101. B is a force acting on the interface between the solid metal 100 and the liquid flux 102. C represents the interfacial tension between the molten solder 101 and the solid metal 100. C and B work in directions opposite to each other along the surface of the solid metal 100, and A and C are specific to each metal. In general, the quality of wetting between a solid and a liquid is expressed by the following Young's relational expression.

B = C + A cos θ (1)
∴cos θ = (BC) / A (2)
In this formula (1), θ is the contact angle of the molten solder 101, and the smaller the value, the better the solder wettability.

  On the other hand, FIG. 5 [2] shows solder wetting at the origin O when the surface of the solid metal 100 is bent at an angle φ from the plane at the origin O. In this case, the origin O corresponds to the corner 93 of FIG. Further, it is assumed that the magnitudes of the forces A, B, and C are the same as those in FIG. At this time, when the contact angle of the molten solder 101 is θ ′, the following equation is established by Young's relational expression.

Bcosφ = C + Acosθ ′ (3)
∴cos θ ′ = (B cos φ−C) / A (4)
Here, since 0 <cosφ <1, comparing the equations (2) and (4),
θ ′> θ (5)
Is obtained.

  That is, as the angle φ from the plane is larger, the contact angle θ ′ is larger, that is, the solder wettability is worsened. The corner portion 93 in FIG. 4 has very poor solder wettability because the angle φ is close to 90 °. As a result, as shown in FIG. 4 [2], since the molten solder on the side surface 91 cannot get over the corner portion 93, the amount of solder on the upper surface 92 is reduced.

The present invention has been made to improve the solder wettability at the corners of the core based on this finding. Hereinafter, the protruding electrode manufactured by the manufacturing method according to the present invention is simply referred to as “the protruding electrode according to the present invention”. That is, the protruding electrode according to the present invention is composed of a core provided on the substrate and a solder layer covering the surface of the core, and has a hemispherical shape as a whole. The surface of the core includes a side surface in contact with the substrate, an upper surface located on the side not contacting the substrate, and a chamfered surface located at the boundary between the upper surface and the side surface. In the present invention, since the corner portion of the conventional core is processed into a chamfered surface, that is, the angle φ is reduced in FIG. 5 [2], the solder wettability due to the shape is improved. In addition, a corner | angular part is an intersection line of a surface.

  At this time, the chamfered surface is preferably a convex curved surface. The reason will be described with reference to FIG. In FIG. 6, the surface of the solid metal 100 is a cylindrical surface, and the curvature of the cylindrical surface (reciprocal of the radius of curvature) is set to various values. Here, the above-mentioned Young's relational expression is constituted by a tangential force, and therefore is considered to hold regardless of the curvature. Therefore, the contact angle θ of the molten solder 101 is constant with respect to the solid metal 100 having any curvature. That is, making the chamfered surface a convex curved surface is equivalent to setting the angle φ to zero in FIG. 5 [2]. The “convex curved surface” is not limited to a curved surface having a constant curvature, but also includes a smooth curved surface in which the curvature continuously changes.

  The chamfered surface may be a flat surface. At this time, it is preferable that the boundary portion between the upper surface and the chamfered surface and the boundary portion between the chamfered surface and the side surface are respectively convex curved surfaces for the reasons described above.

  The upper surface and the chamfered surface may be integrated with each other. Also at this time, the integral surface is preferably a convex curved surface.

  The protruding electrode may be made of any one of copper, silver, gold, and nickel, and the surface thereof may be subjected to any one of tin plating, gold plating, nickel-gold plating, and solder plating. Specific examples of the material of the protruding electrode are given.

  Further, the protruding electrode according to the present invention may have a surface covered with solder. This solder is, for example, an alloy containing at least one element selected from tin, indium, silver, copper, zinc, bismuth, antimony, germanium, aluminum, nickel, lead, and gold.

The manufacturing method according to the present invention is a method for manufacturing the protruding electrode according to the present invention, and includes a core forming step, a chamfered surface forming step, and a solder layer forming step. In the core formation step, a core is formed on the substrate. In the chamfered surface forming step, a chamfered surface is formed on the core formed in the core forming step. In the solder layer forming step, a solder layer is formed on the surface of the core on which the chamfered surface is formed in the chamfered surface forming step.

In the chamfered surface forming step, the chamfered surface is formed by buffing or barrel polishing the core .

According to the manufacturing method of the bump electrode according to the present invention, by processing a corner portion of the core to the chamfered surface, it can improve the solder wettability when forming the solder layer on the surface of the core. Therefore, it is possible to prevent the solder layer from being divided into the side surface and the top surface of the core, so that the yield of soldering during mounting and the reliability of soldering after mounting can be improved.

  In other words, the molten solder on the side surface of the core wets and spreads on the top surface of the core along the chamfered surface, so that the solder layer does not break at the boundary between the top surface and the side surface, and the minimum amount of solder required This makes it possible to obtain highly reliable solder joints and to handle fine pitches.

  FIG. 1 [1] is a cross-sectional view showing a first embodiment of the bump electrode according to the present invention. Hereinafter, description will be given based on this drawing.

  The protruding electrode 10 of this embodiment includes a core 12 provided on the substrate 11 and a solder layer 13 provided on the surface 20 of the core 12. The surface 12 of the core 12 includes a side surface 21 that contacts the substrate 11, a top surface 22 that is positioned on the side of the side surface 21 that does not contact the substrate 11 (that is, the upper side), and a chamfered surface that is positioned at the boundary between the top surface 22 and the side surface 21. 23.

The substrate 11 is a semiconductor substrate, a printed wiring board, an interposer substrate, or the like, has a lower electrode (not shown) on the surface, and a core 12 is formed on the lower electrode. The core 12 is made of a metal having good conductivity and a melting point higher than that of the solder layer 13, such as copper, silver, gold, or nickel. The shape of the core 12 is cylindrical or prismatic. The solder layer 13 is made of, for example, Sn—Pb (melting point 183 ° C.), Sn—Ag—Cu (melting point 218 ° C.), Sn—Ag (melting point 221 ° C.), Sn—Cu (melting point 227 ° C.), or the like. Chamfered surface 23 is buffed as described later, by barrels polishing or the like, is finished to a convex curved surface.

  According to the protruding electrode 10, since the corner portion of the conventional core is processed into the chamfered surface 23, the solder wettability resulting from the shape can be improved. Therefore, the molten solder on the side surface 21 easily gets over the chamfered surface 23 and spreads to the upper surface 22, so that a sufficient amount of solder is secured on the upper surface 22.

  FIG. 1 [2] is sectional drawing which shows 2nd embodiment of the protruding electrode which concerns on this invention. Hereinafter, description will be given based on this drawing. However, the same parts as those in FIG.

  In the protruding electrode 30 of this embodiment, the chamfered surface 31 is a flat surface. Corner portions 32 and 33 are formed at the boundary portion between the chamfered surface 31 and the side surface 21 and at the boundary portion between the chamfered surface 31 and the upper surface 22, respectively. However, since the corners 32 and 33 are gentler than the corners of the conventional core, the solder wettability is improved. Such a shape is realized, for example, by appropriately setting polishing conditions.

  FIG. 1 [3] is a partially enlarged cross-sectional view showing a third embodiment of the protruding electrode according to the present invention. Hereinafter, description will be given based on this drawing. However, the same parts as those in FIG.

  In the present embodiment, the chamfered surface 34 is constituted by a flat surface portion 35 and curved surface portions 36 and 37. The curved surface portion 36 is located at the boundary portion between the side surface 21 and the flat surface portion 35, and the curved surface portion 37 is located at the boundary portion between the upper surface 22 and the flat surface portion 35. The curved surface portions 36 and 37 are convex curved surfaces. Since the flat surface portion 36 and the side surface 21 and the upper surface 22 are gently connected by the curved surface portions 36 and 37 without generating corner portions, the solder wettability is improved. Such a shape is realized, for example, by appropriately setting polishing conditions.

  FIG. 2 is a cross-sectional view showing a fourth embodiment of the bump electrode according to the present invention and a method for manufacturing the same, and the steps proceed in the order of FIG. 2 [1] to FIG. 2 [3]. Hereinafter, description will be given based on this drawing. However, the same parts as those in FIG.

  First, as shown in FIG. 2 [1], the core 12 is formed on the substrate 11. A corner 24 is formed at the boundary between the side surface 21 and the upper surface 22 of the core 12. For example, a photolithography technique and a copper plating technique are used for the formation process of the core 12, but since it is the same as the conventional technique, detailed description thereof is omitted.

Subsequently, as shown in FIG. 2 [2], the corner portion 24 of the core 12 is removed to form a chamfered surface, and an integrated surface 41 in which the chamfered surface and the upper surface 22 are integrated is formed. At this time, as described later, for example, buffing the core 12, is subjected to barrels polishing or the like, to form an integral surface 41. The integral surface 41 is a convex curved surface. Such a shape is realized, for example, by appropriately setting polishing conditions.

  Finally, the solder layer 13 is formed on the surface 20 of the core 12 on which the integrated surface 41 is formed. The solder layer 13 is formed by using, for example, solder paste application and reflow, dipping in a molten solder bath, and the like, but since it is the same as in the past, detailed description thereof is omitted.

  According to the protruding electrode 40 of the present embodiment, the core 12 is chamfered to form the integrated surface 41 in which the chamfered surface and the upper surface 22 are integrated. Since the connection is made gently without generating solder, the solder wettability is improved.

3 is a cross-sectional view showing a specific example of the chamfered surface forming step of FIG. 2 [2], FIG. 3 [1] is buff polishing, FIG. 3 [2] is electrolytic polishing (reference form) , and FIG. 3 [3]. Is barrel polishing. Hereinafter, description will be given based on this drawing. However, the same parts as those in FIG.

  The buffing shown in FIG. 3 [1] will be described. The buff 40 is made of, for example, cotton cloth or sisal linen and is fixed on the turntable 41. A slurry-like abrasive 42 is placed on the buff 40. Then, the core 12 is pressed together with the substrate 11 onto the abrasive 42, and the buff 40 is rotated at a high speed. At this time, since the corner portion 24 of the core 12 is polished from two surfaces of the upper surface 22 and the side surface 21, the polishing rate is higher than that of the upper surface 22 and the side surface 21, so that the chamfer as shown in FIGS. Easy to obtain surface shape. If the polishing rate of the corner 24 is the same as or smaller than that of the upper surface 22 and the side surface 21, the corner 24 cannot be removed. Further, the substrate 11 side may also be rotated in the direction opposite to the rotation of the buff 40.

Here, the electropolishing shown in FIG. 3 [2] will be described as a reference form . As a pretreatment, a plating electrode 50 made of copper, for example, is formed on the entire surface of the substrate 11 so that all the cores 12 have the same potential. Then, the plating electrode 50 is used as the anode, the electrode plate 51 made of lead or stainless steel is used as the cathode, and these are immersed in the electrolytic solution 52. Here, a voltage is applied to the plating electrode 50 and the electrode plate 51 from a DC power supply 53 (or an AC power supply in combination). At this time, the corner portion 24 of the core 12 is sharper than the upper surface 22 and the side surface 21, so that the electric field is concentrated on the upper surface 22 and the side surface 21. That is, since the corner portion 24 has a higher polishing rate than the upper surface 22 and the side surface 21, it is easy to obtain a chamfered surface shape as shown in FIGS.

  The barrel polishing shown in FIG. 3 [3] will be described. A medium 60, water 61 and a compound (not shown) are put together with the substrate 11 on which the core 12 is formed in a barrel (not shown). The media 60 uses spherical solid abrasive grains. Here, when the barrel is rotated, the core 12 is polished by the medium 60 colliding with the core 12. At this time, the corner portion 24 of the core 12 protrudes into the water 61 rather than the upper surface 22 and the side surface 21, so that the media 60 is more likely to collide with the upper surface 22 and the side surface 21. That is, since the corner portion 24 has a higher polishing rate than the upper surface 22 and the side surface 21, it is easy to obtain the shape of the chamfered surface as shown in FIGS. Here, rotational barrel polishing for rotating the barrel has been described, but vibration barrel polishing for vibrating the barrel, electromagnetic barrel polishing using a magnetic medium and an alternating magnetic field, or the like may be used.

  Needless to say, the above embodiment does not limit the present invention. For example, the solder layer may be made of the specific example of solder described above.

FIG. 1 [1] is a sectional view showing a first embodiment, FIG. 1 [2] is a sectional view showing a second embodiment, and FIG. 1 [3] is a third embodiment. It is a partial expanded sectional view showing an embodiment. It is sectional drawing which shows 4th embodiment of the bump electrode which concerns on this invention, and its manufacturing method, and a process progresses in order of FIG. 2 [1]-FIG. 2 [3]. FIG. 3 is a cross-sectional view showing a specific example of the chamfered surface forming step of FIG. 2 [2], FIG. 3 [1] is buff polishing, FIG. 3 [2] is electrolytic polishing (reference form) , and FIG. 3 [3] is barrel polishing. It is. It is sectional drawing which shows the conventional protruding electrode, FIG. 4 [1] is an ideal state, and FIG. 4 [2] is a problematic state. It is explanatory drawing which shows the solder wetting of the solid metal surface, FIG. 5 [1] is a case where the solid metal surface is flat, and FIG. 5 [2] is a case where the solid metal surface is bent. It is explanatory drawing which shows the solder wetting of the solid metal surface of various curvature.

10, 30, 40 Projected electrode 11 Substrate 12 Core 13 Solder layer 20 Core surface 21 Side surface 22 Upper surface 23, 31, 34 Chamfered surface 41 Integrated surface

Claims (2)

A core forming step of forming a core composed of an upper surface and side surfaces on the substrate;
A chamfered surface forming step of forming a chamfered surface at a boundary between the upper surface and the side surface by buffing the core;
A solder layer forming step of covering all of the side surface, the upper surface and the chamfered surface with a solder layer to form a hemisphere as a whole;
A protruding electrode manufacturing method comprising: A core forming step of forming a core composed of an upper surface and side surfaces on the substrate;
A chamfered surface forming step of forming a chamfered surface at the boundary between the upper surface and the side surface by performing barrel polishing on the core;
A solder layer forming step of covering all of the side surface, the upper surface and the chamfered surface with a solder layer to form a hemisphere as a whole;
A protruding electrode manufacturing method comprising:

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