JPH10107037A - Method of forming bump electrodes - Google Patents

Abstract

(57) Abstract: A fine pitch can be achieved even when the height of a substantially spherical protruding electrode made of solder is increased. SOLUTION: First and second plating resist layers 16 and 18 are formed on a base metal layer 15, and electrolytic plating of solder is performed. Then, the opening 19 of the second plating resist layer 18 is formed.
Is larger than the opening 17 of the first plating resist layer 16, so that solder plating is isotropically deposited in the opening 19 of the second plating resist layer 18, as shown by a dotted line in FIG. Next, by continuing this isotropic deposition, the first and second plating resist layers 16,
The upper portions of the projecting electrodes 20 formed in the openings 17 and 19 of the 18 will rise above the openings 19 of the second plating resist layer 18. In this case, the periphery of the mushroom-shaped umbrella portion indicated by the dotted line in FIG. 1B is further restricted by the inner wall of the opening 19 of the second plating resist layer 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a substantially spherical protruding electrode made of a low melting point metal such as solder.

[0002]

2. Description of the Related Art For example, in a semiconductor chip mounting technique called a flip chip method, a substantially spherical projecting electrode made of a low melting point metal such as solder formed on a connection pad of a semiconductor chip is connected to a connection formed on a circuit board. The solder is placed on the pad and subjected to heat treatment to reflow the solder.
w) to perform bonding. Therefore, it is necessary to form a substantially spherical protruding electrode made of a low melting point metal such as solder on the semiconductor chip.

Next, a conventional method for forming such a bump electrode will be described with reference to FIG. First, FIG.
As shown in (A), a connection pad 2 is formed on a silicon substrate 1.
And a protective film 3 is formed on the upper surface except for the central portion of the connection pad 2, and the central portion of the connection pad 2 is exposed through a circular opening 4 formed in the protective film 3. Prepare Next, as shown in FIG.
A base metal layer 5 is formed on the entire upper surface. Next, a plating resist layer 6 is formed on the upper surface of the base metal layer 5, and a circular opening 7 is formed in a portion of the plating resist layer 6 corresponding to the connection pad 2.

[0004] Next, by using the base metal layer 5 as a plating current path and performing electrolytic plating of solder, a bump electrode 8 made of solder is formed on the upper surface of the base metal layer 5 in the opening 7 of the plating resist layer 6. . In this case, solder plating is isotropically deposited on the plating resist layer 6. For this reason, the shape of the bump electrode 8 at this stage becomes a mushroom shape. At this stage, the mushroom shape of the protruding electrode 8 has a limit in the thickness of the plating resist layer 6, and even if the upper limit is, for example, about 50 μm, the thickness exceeds the thickness of the plating resist layer 6. This is because the volume of the plating metal is increased by deposition, and thereby the height of the final protruding electrode described later is further increased. Next, the plating resist layer 6 is peeled off. Next, unnecessary portions of the base metal layer 5 are removed by etching using the bump electrodes 8 as a mask, and the base metal layer 5 remains only under the bump electrodes 8 as shown in FIG. Next, as shown in FIG. 8 (D), when heat treatment is performed, the mushroom-shaped protruding electrode 8 is melted and then rounded due to surface tension to become substantially spherical. 8a are formed. At this time, since the bump electrode 8a becomes substantially spherical by the heat treatment, the height of the bump electrode 8a increases as the volume of the plating metal increases.

[0005]

By the way, in such a conventional method of forming a protruding electrode, a substantially spherical protruding electrode 8 is used.
When the height of a is to be increased, the height of the umbrella portion of the mushroom-shaped protruding electrode 8 is increased to increase the plating volume. However, when the height of the umbrella portion of the mushroom-shaped protruding electrode 8 is increased, the spread of the umbrella portion also becomes larger. There has been a problem that it is necessary to increase the interval, and it is difficult to achieve a fine pitch. An object of the present invention is to make it possible to achieve a fine pitch even if the height of the protruding electrode is further increased.

[0006]

According to the present invention, a first plating resist layer having an opening at a portion corresponding to the connection pad is formed on a substrate having a connection pad formed on an upper surface thereof. On the resist layer, a second plating resist layer having an opening larger than the opening is formed at a portion corresponding to the opening of the first plating resist layer, and the openings of the first and second plating resist layers are formed. A protruding electrode made of a low melting point metal is formed in the portion by plating, the first and second plating resist layers are peeled off, and the shape of the protruding electrode is made substantially spherical by heat treatment.

According to the present invention, since the size of the opening of the second plating resist layer is larger than the size of the opening of the first plating resist layer, plating is isotropic in the opening of the second plating resist layer. And the periphery of the mushroom-shaped umbrella portion is further restricted by the inner wall of the opening of the second plating resist layer, so that the height of the protruding electrode is increased. However, fine pitch can be achieved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1A to 1D show respective steps of forming a bump electrode according to a first embodiment of the present invention. Therefore, a method for forming the bump electrodes in the first embodiment will be described with reference to these drawings in order.

First, as shown in FIG. 1A, a connection pad 12 is formed on a silicon substrate 11, and a protective film 13 is formed on the upper surface of the connection pad 12 except for a central portion thereof. The one whose central portion is exposed through a circular opening 14 formed in the protective film 13 is prepared. Next, as shown in FIG. 1B, a base metal layer 15 is formed on the entire upper surface. Next, a negative first plating resist layer 16 is formed on the upper surface of the base metal layer 15, and a circular opening 17 is formed in a portion of the first plating resist layer 16 corresponding to the connection pad 12. Next, a negative type second plating resist layer 18 is formed on the upper surface of the first plating resist layer 16, and a portion corresponding to the opening 17 of the first plating resist layer 16 is formed on the second plating resist layer 18. A circular opening 19 larger than the opening 17 by a predetermined amount is formed.

Next, electrolytic plating of solder (low melting point metal) is performed using the underlying metal layer 15 as a plating current path. Then
First, solder plating is deposited on the upper surface of the base metal layer 15 in the opening 17 of the first plating resist layer 16. next,
The size of the opening 19 of the second plating resist layer 18 is the first size.
Since the size of the opening 17 of the plating resist layer 16 is larger than that of the opening 17, solder plating is isotropically deposited in the opening 19 of the second plating resist layer 18 as shown by a dotted line in FIG. Next, by continuing this isotropic deposition, the first and second plating resist layers 1 are formed.
Protruding electrode 2 formed in openings 17, 19 of 6, 18
Thus, the upper portion of the ridge 0 rises above the opening 19 of the second plating resist layer 18. In this case, when the solder plating is isotropically deposited in the opening 19 of the second plating resist layer 18, the periphery of the mushroom-shaped umbrella portion indicated by the dotted line in FIG. 18
The further expansion is regulated by the inner wall of the opening 19. Therefore, the shape of the protruding electrode 20 at this stage is slightly different from the conventional case shown in FIG.

Next, the second plating resist layer 18 and the first
The plating resist layer 16 is peeled off. Next, the projecting electrode 20
When unnecessary portions of the base metal layer 15 are removed by etching using the mask as a mask, the base metal layer 15 remains only under the bump electrodes 20, as shown in FIG. Next, FIG.
As shown in (D), when the heat treatment is performed, the mushroom-shaped protruding electrode 20 is melted and then rounded due to surface tension to become substantially spherical. By solidifying in this state, a substantially spherical protruding electrode 20a is formed. .

In FIG. 1B, the first plating resist layer 1 is provided without the second plating resist layer 18.
When only 6 are provided, the protruding electrodes indicated by the dotted lines in FIG. 1B are formed as in the conventional case shown in FIG. On the other hand, when the second plating resist layer 18 is provided, the height of the mushroom-shaped umbrella portion indicated by a dotted line in FIG. 1B is equivalent to the thickness of the second plating resist layer 18. Can only be higher.
Moreover, when the solder plating is isotropically deposited in the opening 19 of the second plating resist layer 18, the solder plating shown in FIG.
The area around the mushroom-shaped umbrella portion indicated by the dotted line
Further expansion is regulated by the inner wall of the opening 18 of the plating resist layer 18. Thus, FIG.
In the case of the protruding electrode 20 shown in (B), even if the height of the mushroom-shaped umbrella portion is increased in order to increase the volume of the plating metal, the umbrella portion should not be unnecessarily spread. Therefore, a short circuit between the adjacent protruding electrodes 20 can be reliably prevented. As a result, even if the height of the protruding electrode 20a shown in FIG. 1D is further increased, a fine pitch can be achieved while avoiding a short circuit.

In the first embodiment, FIG.
As described above, the case where the first plating resist layer 16 and the second plating resist layer 18 have substantially the same thickness has been described, but the present invention is not limited to this. For example,
As in the second embodiment shown in FIG. 2, the thickness of the first plating resist layer 16 may be reduced. Even in this case, if the thickness of the second plating resist layer 18 is the same as the thickness of the plating resist layer 6 in the conventional example shown in FIG.
The volume of the projecting electrode 20 is increased, and the height of the substantially spherical projecting electrode can be further increased. In this case, an inexpensive low-viscosity resist can be used as the material of the first plating resist layer 16 having a small thickness. When the first and second plating resist layers 16 and 18 are made of materials having different viscosities, materials, and the like, it is preferable to use materials that are peeled by the same peeling liquid. Also, for example, FIG.
As in the third embodiment shown in FIG.
8 are two plating resist layers 18a, 1
8b. In this case, 2
Openings 19a, 19b of the same size are formed in the plating resist layers 18a, 18b.

Referring to FIG. 1D, the semiconductor chip having the protruding electrodes is formed by arranging a plurality of protruding electrodes 20a around one predetermined surface of a rectangular parallelepiped silicon substrate 11. Has a structure in which a protective film 13 is provided on another portion of one surface. Therefore,
For example, the predetermined surface of the silicon substrate 11 in a state where only the first plating resist layer 16 is formed on the base metal layer 15 in the step shown in FIG.
It becomes as shown in. Further, one predetermined surface of the silicon substrate 11 in a state where the second plating resist layer 18 is formed is as shown in FIG. However, in FIG. 5, the opening 17 of the first plating resist layer 16 is omitted.
Here, an example of the dimensions will be described.
The pitch A of 19 (that is, the pitch of the protruding electrodes 22a) is about 150 to 250 μm. The diameter B of the opening 17 is about 50 μm. The diameter of the opening 19 is
The distance C between them is about 50 μm.

As shown in FIG. 5, the opening 19 of the second plating resist layer 18 has a circular shape, but is not limited to this. For example, as in the fourth embodiment shown in FIG. 6, the shape of the opening 19 of the second plating resist layer 18 may be a square. In this case, since the volume in the square opening 19 is larger than that in the case of a circular shape, the height of the protruding electrode 22a can be further increased. Further, as in the fifth embodiment shown in FIG. 7, the shape of the opening 19 of the second plating resist layer 18 may be a rectangle extending in the direction orthogonal to the arrangement direction of the openings 19 and inside the chip. . In this case, the length of the long side of the opening 19 and the interval between the openings 19 are
When a substantially spherical protruding electrode is formed by heat treatment, it may be determined on condition that adjacent protruding electrodes are not in contact with each other.

[0016]

As described above, according to the present invention, when the plating is isotropically deposited in the opening of the second plating resist layer, the periphery of the mushroom-shaped umbrella portion is formed by the second plating resist. Since further expansion is regulated by the inner wall of the opening of the layer, fine pitch can be achieved even if the height of the protruding electrode is further increased.

[Brief description of the drawings]

FIGS. 1A to 1D are cross-sectional views showing respective steps of forming a bump electrode according to a first embodiment of the present invention.

FIG. 2 is a sectional view similar to FIG. 1B in a second embodiment of the present invention.

FIG. 3 is a sectional view similar to FIG. 1B in a third embodiment of the present invention.

FIG. 4 is a plan view showing a state where only a first plating resist layer is formed on a base metal layer in the step shown in FIG. 1 (B).

FIG. 5 is a plan view showing a state where a second plating resist layer is formed in the step shown in FIG. 1 (B).

FIG. 6 is a plan view similar to FIG. 5 according to a fourth embodiment of the present invention.

FIG. 7 is a plan view similar to FIG. 5 according to a fifth embodiment of the present invention.

8 (A) to 8 (D) are cross-sectional views showing respective steps of forming a conventional bump electrode.

[Explanation of symbols]

 Reference Signs List 11 silicon substrate 12 connection pad 13 protective film 14 opening 15 base metal layer 16 first plating resist layer 17 opening 18 second plating resist layer 19 opening 20, 20a projecting electrode

Claims (6)

[Claims] 1. A first plating resist layer having an opening at a portion corresponding to the connection pad is formed on a substrate having a connection pad formed on an upper surface, and the first plating resist layer is formed on the first plating resist layer. Forming a second plating resist layer having an opening larger than the opening at a portion corresponding to the opening of the plating resist layer, and plating the low melting point metal in the openings of the first and second plating resist layers by plating. A method of forming a protruding electrode, comprising: forming a protruding electrode formed on the substrate; removing the first and second plating resist layers; and heat-treating the protruding electrode into a substantially spherical shape. 2. A connection pad is formed on a substrate, and a protective film having an opening at a portion corresponding to a predetermined part of the connection pad is formed on an upper surface of the substrate, whereby a predetermined portion of the connection pad is formed. After preparing a part of which is exposed through the opening of the protective film, a base metal layer is formed on the entire upper surface thereof, and a part corresponding to the opening of the protective film is formed on the base metal layer. Forming a first plating resist layer having an opening, and forming a second plating on the first plating resist layer at a portion corresponding to the opening of the first plating resist layer, the opening being larger than the opening; Forming a resist layer, forming a protruding electrode made of a low-melting-point metal in an opening of the first and second plating resist layers by plating, peeling the first and second plating resist layers, and masking the protruding electrode. As the etching An unnecessary part of the base metal layer is removed by performing the method, and the shape of the projecting electrode is made substantially spherical by heat treatment. 3. The method according to claim 1, wherein
A method of forming a projecting electrode, wherein upper portions of the projecting electrodes formed by plating in the openings of the first and second plating resist layers are raised above the openings of the second plating resist layer. 4. The method according to claim 1, wherein said second plating resist layer comprises a plurality of plating resist layers. 5. The method according to claim 1, wherein the first plating resist layer is formed of a thinner layer than the second plating resist layer. 6. The invention according to claim 1, wherein the shape of the opening of the first plating resist layer is circular, and the shape of the opening of the second plating resist layer is circular or square. A method for forming a protruding electrode, the method comprising: