JPH06163551A - Bump electrode forming apparatus - Google Patents

Abstract

PURPOSE:To obtain a bump electrode forming apparatus equipped with a capillary for forming a substantially flat bump electrode which allows connection of external lead in stabilized state. CONSTITUTION:A ball 6 at the tip of a wire 5 is bonded onto a semiconductor pellet 7 by means of a wire bonding capellary 1 thus collapsing the ball 6 to form a substantially flat bump electrode. A recessed part 4 having substantially same diameter as the ball 6 and a height smaller than the diameter of the wire 5 is formed concentrically to a wire insertion hole 2 in the flat lower end face 3 of the capillary 1. The ball 6 is collapsed by the flat top surface (m) of the recessed part 4 thus forming a bump electrode having substantially flat top surface while reducing the amount of the ball 6 entering into the wire insertion hole 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for forming bump electrodes on a semiconductor pellet, and more particularly to an apparatus for forming bump electrodes by a ball bonding method using a capillary for bonding a wire such as a gold wire to a semiconductor pellet.

[0002]

2. Description of the Related Art Bump electrodes on a semiconductor pellet to which leads such as a lead frame and a TAB tape are connected by thermocompression bonding are often formed by a ball bonding method which can secure a predetermined height even in a small area. The ball bonding method is a method of forming bump electrodes one by one on a semiconductor pellet by using a wire bonding capillary.
The capillaries used are generally those shown in FIG. 5 or 7.

The capillary (1 ') shown in FIG. 5 has a wire insertion hole (2) at the center of a flat lower end surface (3).
Spool (8) located outside the capillary (1 ')
The wire (5) of the gold wire drawn from the wire freely penetrates the wire insertion hole (2) having an inner diameter sufficiently larger than the wire diameter. The tip of the wire (5) protruding below the wire insertion hole (2) is heated by a discharge torch or the like to form a ball (6) which is a molten metal block. The diameter of the ball (6) is several times the inner diameter of the wire insertion hole (2). The capillary (1 ') is intermittently moved upward, downward, leftward, rightward, forward and backward above the semiconductor pellet (7) to bond the ball (6) onto the semiconductor pellet (7), and the ball (6) to the wire (5).
To cut and separate. The operation procedure is shown in FIGS. 6 (a) and 6 (b).

As shown in FIG. 5, semiconductor pellets (7)
Move the capillary (1 ') directly above. At this time, the ball (6) is held at a position close to the lower end opening of the wire insertion hole (2). Capillary (1 ') to wire (5)
6 (a), the ball (6) is pressed against the semiconductor pellet (7) by the lower end surface (3) of the capillary (1 '), and ultrasonic vibration is applied to the ball (6). On the semiconductor pellet (7). The ball (6) consists of the lower end surface (3) of the capillary (1 ') and the semiconductor pellet (7).
Then, it is flatly crushed to form bump electrodes (6c) having a predetermined height. On the bump electrode (6c), a projection (6d) having the root of the ball (6) embedded in the wire insertion hole (2) of the capillary (1 ') is integrally formed, and the projection (6d) is formed.
A wire (5) extends from above. The height of the protrusion (6d) is
It is determined by the diameter of the ball (6), the inner diameter of the wire insertion hole (2), and the ball bonding conditions.

Next, the capillary (1 ') is attached to the protrusion (6).
The wire (5) is cut by ascending to the position of the chain line in FIG. 6 (b), which is slightly higher than the height of d), and then moving laterally.
At this time, a part of the wire (5) is clamped by a clamper (9) integrally arranged with the capillary (1 ′) above the capillary (1 ′), and the wire (5) is retained by the capillary (1 ′). I'm trying not to let go. When the capillary (1 ') is moved laterally in this state, the edge of the lower end opening of the wire insertion hole (2) will be the protrusion (6) of the wire (5).
Apply stress near d) and tear off the wire (5). The stripped wire rest (6e) is projected on the protrusion (6d) of the bump electrode (6c). After cutting the wire, the capillary (1 ') rises and the capillary (1')
The wire (5) is fed out from the wire (5) to form a ball (6) at the tip of the wire (5), and the capillary (1 ') shifts to the next bump electrode forming operation.

The capillary (1 '') shown in FIG.
A conical tapered concave surface (11) is concentrically formed around the lower end opening of the wire insertion hole (2). The capillary (1 '') presses the ball (6) of the wire (5) against the semiconductor pellet (7) by the tapered concave surface (11) for bonding. The operation of the capillary (1 ″) for this ball bonding is the same as that of the above-mentioned capillary (1 ′).

That is, first, as shown in FIG.
The capillary (1 '') descends and the ball (6) is pressed against the semiconductor pellet (7) by the tapered concave surface (11), and ultrasonic vibration is applied to connect the ball (6) onto the semiconductor pellet (7). The ball (6) is crushed by the tapered concave surface (11) of the capillary (1 ″) and the semiconductor pellet (7) to form a bump electrode (6f) having a chevron cross section. Next, the capillary (1 '') is slightly higher than the height of the bump electrode (6f).
Ascend to the position indicated by the chain line in (b) and then move laterally to cut the wire (5). In this case also, the wire rest (6g) that has been cut off protrudes on the bump electrode (6f).

[0008]

In the capillary (1 ') of FIG. 5, the lower end opening edge of the wire insertion hole (2) of the capillary (1') that cuts the wire (5) after ball bonding has a right-angled cross section. Therefore, the cuttability of the wire (5) is better than that of the capillary (1 ″) of FIG. By the way, since the inner diameter of the wire insertion hole (2) is set to be sufficiently larger than the wire diameter of the wire (5) so that the wire (5) can pass smoothly, the capillary (1 ')
The amount of the ball (6) embedded in the wire insertion hole (2) when the ball (6) is pressed against the semiconductor pellet (7) is increased and the height of the protrusion (6d) of the bump electrode (6c) is increased. Becomes higher. Moreover, since the protrusion (6d) is thick and the wire cannot be cut here, and the portion slightly above the protrusion (6d) of the wire (5) is cut, the protrusion (6d) cannot be cut on the protrusion (6d). The wire remains (6e) occurs at the same height.

Therefore, the bump electrodes (6c) formed on the semiconductor pellets (7) by the capillaries (1 ') are formed on the bump electrodes (6c) shown in FIG.
As shown by the solid line in (a), the flat lead (1
When pressing (0) to perform thermocompression bonding, the protrusion (6d) protruding to the center of the upper surface of the bump electrode (6c) and the wire remainder (6e)
Sometimes tilted the lead (10) as shown by the chain line in FIG. 9 (a). When the lead (10) is tilted on the bump electrode (6c) in this way, the lead (10) is changed to the bump electrode (6c).
And the electromechanical connectivity between the two becomes poor, and the adjacent leads are abnormally close to each other, which causes a poor withstand voltage between the leads.

Further, in the capillary (1 '') of FIG. 7, since the tapered concave surface (11) directly presses the ball (6) of the wire (5) during ball bonding, the wire of the ball (6) is inserted. The amount embedded in the hole (2) is reduced. However, the lower end opening edge of the tapered concave surface (11) of the capillary (1 ″) that cuts off the wire (5) after ball bonding has an obtuse cross-sectional angle, and therefore the wire (5) is not easily cut. Also, the bump electrode (6f) formed on the semiconductor pellet (7) by the capillary (1 '')
Has a chevron cross section, and the wire rest (6g) protrudes on the top surface, so if the flat lead (10) is pressed from directly above as shown by the solid line in FIG. 9
As shown by the chain line in (b), the lead (10) tilts on the side surface of the bump electrode (6f) that tilts downward, and the lead (10) slides sideways.
There is a problem that the electromechanical connectivity between the bump electrode (6f) and the lead (10) and the withstand voltage between adjacent leads deteriorate.

An object of the present invention is to provide a bump electrode forming apparatus provided with a capillary capable of forming a bump electrode having a substantially flat shape, to which external leads are pressed and connected in a stable posture without tilting. To provide.

[0012]

In order to achieve the above-mentioned object, the present invention provides a ball formed by melting a tip of a wire protruding from a wire insertion hole on a flat lower end surface of a capillary under a capillary. In a device for bonding bump electrodes on semiconductor pellets at the end faces to form bump electrodes by the balls on the semiconductor pellets, a wire insertion hole is concentric with the wire insertion hole around the lower end surface of the capillary, and the top surface is the lower end surface of the capillary. It is characterized in that a concave step portion, which is a flat surface at a height equal to or smaller than the wire diameter of the wire, is formed.

[0013]

[Function] The height of the top surface of the concave step portion formed around the wire insertion hole on the flat lower end surface of the capillary from the lower end surface of the capillary is set to be smaller than the wire diameter of the wire, and When a ball of wire is bonded to a semiconductor pellet, the ball is first pressed by the concave step surface to be deformed, and then finally pressed by the lower end surface of the capillary to form a flat bump electrode. At the time of this ball bonding, the ball is deformed and embedded in the concave step surface of the capillary, so that the amount of the ball embedded in the wire insertion hole of the capillary is reduced, and the upper surface of the bump electrode is substantially flat by that amount. The bump electrodes are flattened to form flatter bump electrodes.

[0014]

EXAMPLE An example in which the present invention is applied to the bump electrode forming apparatus of FIG. 5 is shown in FIG. 1 and will be described below. The difference between the bump electrode forming apparatus of FIG. 1 and the conventional apparatus is that the wire insertion hole (2) at the center of the flat lower end surface (3) of the capillary (1) is used.
It is only that the concave step portion (4) is formed in the periphery of, and the same parts as those of the other device in FIG.

The concave step portion (4) of the lower end surface (3) of the capillary (1) is formed concentrically with the wire insertion hole (2) as shown in FIG. The diameter of the concave step (4) is about the diameter of the ball (6) of the wire (5), and the top surface (m) of the concave step (4).
Is a flat surface parallel to the lower end surface (3) of the capillary (1). Concave step (4) from the bottom surface (3) of the capillary (1)
The height h to the top surface (m) of the wire is set to be less than or equal to the wire diameter of the wire (5).

The capillary (1) in FIG. 1 has a wire (5).
The ball (6) is bonded to the semiconductor pellet (7) as follows. When the capillary (1) and the wire (5) are lowered and the ball (6) is pressed onto the semiconductor pellet (7) by the capillary (1) and ultrasonic vibration is applied,
The ball (6) is deformed flat and bonded as shown in FIG.

That is, first, the ball (6) is crushed by the top surface (m) of the concave step (4) of the capillary (1), and the upper part of the ball (6) bites into the concave step (4). Balls (6)
Embedded in the concave step (4) up to its outer edge,
The lower part of the periphery of the ball (6) is further crushed by the lower end surface (3) of the capillary (1). By embedding the upper part of the ball (6) in the concave step (4) of the capillary (1), the amount of the ball (6) embedded in the wire insertion hole (2) of the capillary (1) is reduced. As a result, the ball (6) after bonding has a substantially flat bump electrode (6a) having a flat surface (n) pressed by the top surface (m) of the concave step portion (4) of the capillary (1). Become.

The flat surface (n) of the bump electrode (6a)
At the center of, the protrusion (6) embedded in the wire insertion hole (2)
As a result of the experiment, it is known that the protrusion (6b) is as low as the trace of the wire insertion hole (2), although b) is formed.

When the ball (6) is crushed by the capillary (1) to form the bump electrode (6a), the capillary (1) is formed.
Moves to the position shown by the chain line in FIG. 3 (b) and then moves laterally to cut the wire (5). The amount of ascent of the capillary (1) at this time depends on the protrusion (6) of the bump electrode (6a).
It is a little over the height of b), and the amount of this rise is shown in FIG.
A minute, which is a fraction of the equipment, is sufficient. By the lateral movement of the capillary (1), the wire (5) is torn and cut at the lower opening edge of the wire insertion hole (2) on the top surface (m) of the concave step (4). The cutting point of the wire (5) is a root portion very close to the bump electrode (6a), and the wire (5) is directly cut at the lower end opening edge of the right-angled cross section of the wire insertion hole (2). Therefore, the wire (5) is easily and surely cut. In addition, since the wire (5) is cut at the root portion that is very close to the bump electrode (6a),
Almost no wire remains on the bump electrode (6a).

The bump electrode (6a) formed by the capillary (1) has a flat lead (1) as shown in FIG.
0) is thermocompression bonded. Most of the upper surface of the bump electrode (6a) is the top surface (m) of the concave step (4) of the capillary (1).
The flat surface (n) formed in step (6) and the central protrusion (6b) of the flat surface (n) is a minute projection, so the lead (10)
Is stably held on the flat surface (n) and is directly thermocompression-bonded to the bump electrode (6a).

[0021]

According to the present invention, when a ball of wire is bonded to a semiconductor pellet by a capillary,
The ball is crushed and embedded in the concave stepped portion of the lower end surface of the capillary, and the amount of the ball embedded in the wire insertion hole of the capillary of the ball is reduced accordingly. Since it serves as an electrode, it is possible to provide a highly reliable bump electrode forming apparatus capable of easily forming a bump electrode having a good shape in which an external lead is pressed and connected in a stable posture without tilting.

[Brief description of drawings]

FIG. 1 is a side view of a main part including a partial cross section showing an embodiment of the present invention.

FIG. 2 is a bottom view of the capillary in the apparatus shown in FIG.

FIG. 3 is a cross-sectional view of the capillaries in the apparatus shown in FIG. 1 during ball bonding operation.
(B) is when the wire is cut.

FIG. 4 is a cross-sectional view of a bump electrode formed by the device of FIG. 1 at the time of lead connection.

FIG. 5 is a side view of a main part including a partial cross section of a conventional bump electrode forming apparatus.

6 is a cross-sectional view of the capillaries in the apparatus shown in FIG. 5 during ball bonding operation, FIG.
(B) is when the wire is cut.

FIG. 7 is a side view including a partial cross section of a capillary in another conventional bump electrode forming apparatus.

FIG. 8 is a cross-sectional view of the capillaries in the apparatus shown in FIG. 7 during ball bonding operation.
(B) is when the wire is cut.

9A is a cross-sectional view of the bump electrode formed by the device of FIG. 5 at the time of lead connection, and FIG. 9B is a cross-sectional view of the bump electrode formed by the device of FIG. 7 at the time of lead connection.

[Explanation of symbols]

 1 Capillary 2 Wire insertion hole 3 Bottom surface 4 Recessed step 5 Wire 6 Ball 6a Bump electrode 7 Semiconductor pellet

Claims (1)

[Claims] 1. A ball formed by melting a tip of a wire protruding from a wire insertion hole on a flat lower end surface of a capillary is bonded onto a semiconductor pellet at the lower end surface of the capillary, and the ball is bonded onto the semiconductor pellet. A device for forming a bump electrode by the ball, which is concentric with the wire insertion hole around the wire insertion hole on the lower end surface of the capillary, and whose top surface is flat with a height equal to or smaller than the wire diameter of the wire from the lower end surface of the capillary. A bump electrode forming apparatus characterized in that a concave step portion that is a surface is formed.