JPH0689928A - Ball crimping method in wire bonding - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a ball crimping method in wire bonding capable of reducing variations in ball crimping diameter and adhesion strength. In wire bonding for connecting a connection electrode on a semiconductor chip and an inner lead with a wire, first, a ball is formed at the tip of the wire protruding from a bonding tool. Next, the bonding tool is lowered at a predetermined speed, and a first bonding load G1 is applied to the bonding tool to press the ball into contact with the connection electrode or the inner lead. Then, a second bonding load G2 smaller than the first bonding load G1 is applied to the bonding tool to press the ball onto the connection electrode or the inner lead.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wire bonding for connecting a connecting electrode on a semiconductor chip and an inner lead with a wire, and in particular, a ball formed at the tip of the wire is crimped to the connecting electrode or the inner lead. The present invention relates to a ball crimping method in wire bonding for the purpose.

[0002]

2. Description of the Related Art In the process of assembling a semiconductor device, there is a so-called wire bonding process in which a connecting electrode on a semiconductor chip and an inner lead arranged around the semiconductor chip for external extraction are connected by a wire. There is something called.

In this wire bonding process, first, a ball is formed at the tip of the wire protruding from the bonding tool by discharge energy. Next, the bonding tool is lowered at a high speed, and at the same time as reaching the search level, it is switched to a low speed (search speed) to gently land the tip of the bonding tool on the semiconductor chip. At this time, a predetermined bonding load (usually 50 to 60 gf) is applied to the bonding tool, and the ball is pressed against the connection electrode while keeping the bonding load constant. Further, ultrasonic waves and / or heat are applied to the joint portion between the ball and the connecting electrode, whereby the ball is pressure-bonded to the connecting electrode. As described above, conventionally, the ball formed at the tip of the wire is pressure-bonded to the connection electrode with a constant bonding load.

[0004]

However, in the conventional method, the ball formed at the tip of the wire cannot be sufficiently crushed only by the bonding load, and then the ball is further crushed while applying ultrasonic waves or heat. Therefore, there is a problem in that the pressure bonding diameter of the ball formed by this and the adhesion strength with the connection electrode greatly vary. For this reason, conventionally, it has become extremely difficult to reduce the size of the connection electrode as the number of terminals increases, and at the same time, the electrical reliability of the semiconductor device is reduced.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a ball crimping method in wire bonding which can reduce variations in ball crimping diameter and adhesion strength.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, and connects a connection electrode on a semiconductor chip and an inner lead arranged around the semiconductor chip with a wire. In wire bonding,
First, a ball is formed at the tip of the wire protruding from the bonding tool, then the bonding tool is lowered at a predetermined speed, and a first bonding load is applied to the bonding tool to press the ball to the connection electrode or the inner lead, Then, a ball bonding method in wire bonding in which a second bonding load smaller than the first bonding load is applied to the bonding tool to bond the ball to the connection electrode or the inner lead.

[0007]

In the ball-bonding method for wire bonding of the present invention, the first bonding load is applied to the bonding tool to press the ball formed at the tip of the wire against the connection electrode or the inner lead, and then the first bonding load is applied. By applying a smaller second bonding load to the bonding tool and crimping the ball to the connection electrode or the inner lead, the ball comes to be crimped to the connection electrode or the inner lead in a sufficiently crushed state. This makes it possible to reduce variations in ball pressure bonding diameter and adhesion strength.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a diagram for explaining a ball pressure bonding method in wire bonding of the present invention, and FIGS. 2 and 3 are process explanatory diagrams of wire bonding. In this embodiment, the ball pressure bonding method will be described while sequentially describing the wire bonding steps.

First, in the first step, as shown in FIG. 2A, a bonding tool arranged above the semiconductor chip 1 at a predetermined distance, that is, an ultrafine wire 3 is fed to the tip of the capillary 2. Next, a ball 3a having a predetermined size is formed at the tip of the wire 3 protruding from the capillary 2 by the discharge energy of a ball forming device such as an electric torch.

Next, in the second step, as shown in FIG. 2B, the capillary 3 is lowered at a high speed so that the height of the capillary 2 with respect to the semiconductor chip 1 is the search level H.
At the same time as reaching (normally 50 to 200 μm), the descending speed of the capillary 2 is switched from high speed to low speed. Until the descending speed of the capillary 2 is switched from high speed to low speed, a considerably large load (for example, 200 to 300) is applied to the capillary 2 itself.
gf) is added, and when the descending speed is switched to a low speed, the first bonding load (for example, 100 to 12) is applied.
0 gf) is added to capillary 2. In this way, the vibration of the capillary 2 due to the switching of the descending speed can be suppressed.

Subsequently, in the third step, as shown in FIG. 3A, the tip of the capillary 2 is gently landed on the semiconductor chip 1 while lowering the capillary 2 at a low speed, and at the same time, the first bonding is performed. The ball 3a at the tip of the wire 3 is pressed against a connection electrode (not shown) on the semiconductor chip 1 with a load. In the present embodiment, the first bonding load (for example, 100 to 120 gf) is set to be larger than the normal bonding load (for example, 50 to 60 gf), so that the ball 3a at the tip of the wire 3 is sufficiently set on the connection electrode. Crushed.

Next, in the fourth step, a second bonding load (for example, 50 to 60 gf) smaller than the first bonding load is applied to the capillary 2 in the state shown in FIG. For example, ultrasonic waves or heat is applied to press the ball 3a to the connection electrode (not shown).

Here, the third and fourth steps will be further described with reference to FIG. First, at time T1 when the capillaries 2 land on the semiconductor chip 1, the capillaries 2 as bonding tools are first
Bonding load G1 is applied. When a certain time (usually several msec) elapses with the first bonding load G1 applied and time T2 is reached, the capillary 2
The bonding load applied to the second bonding load G2 is switched to the second bonding load G2 which is smaller than the first bonding load G1. Further, during the period from the time T2 when the second bonding load G2 is held to the time T3, ultrasonic waves or heat is applied to the joint portion and the ball 3a is pressure-bonded to the connection electrode.

In the subsequent steps, the capillary 2 is shown in FIG.
As shown in (b), it rises to the loop position P, and then moves toward the inner lead 4 as shown in FIG. 3 (c). Here, the capillary 2 that draws a predetermined loop shape
Further descends as shown in FIG. 3D to join the other end of the wire 3 onto the inner lead 4. Through the above steps, the connection electrodes (not shown) on the semiconductor chip 1 and the inner leads 4 are connected (wired) by the wires 3. As a means for varying the bonding load, existing wire bonding apparatuses having a function of varying the bonding load are provided by various manufacturers, and therefore, this may be used.

As described above, in the ball pressure bonding method according to the present embodiment, first, the first bonding load G1 is applied to the capillary 2 so that the ball 3a formed at the tip of the wire 3 is pressure-contacted to the connection electrode (not shown). By applying a second bonding load G2 smaller than the first bonding load G1 to the capillary 2 and crimping the ball 3a to the connection electrode, the ball 3a is sufficiently crushed to be crimped to the connection electrode. As a result, variations in the ball pressure bonding diameter and the adhesion strength can be made smaller than before.

Tables 1 and 2 show comparison data between the method according to the present invention (switching the bonding load in two steps) and the conventional method (constant bonding load).

[Table 1]

[Table 2] Table 1 shows comparative data of ball sizes after pressure bonding. Table 1
As shown in FIG. 5, the deviations of the ball size in the vertical and horizontal directions are 4.5 μm and 7.3 μm, respectively, which are considerably large in the conventional case, whereas in the case of the present invention, the deviation is 2.2 μm.
The variation is as small as 2.1 μm. Also, regarding the width and width values, the average value is 14 μm in the past.
However, in the case of the present invention, since the average values are the same, the crushing of the entire ball is also very uniform. Further, the deviation of the ball thickness is 1.8 μm in the related art, whereas the deviation is 0.
The variation is as small as 8 μm.

On the other hand, Table 2 shows comparative data of adhesion strength. As shown in Table 2, with respect to the pressure bonding strength as well, the conventional deviation is 5.28 gf, whereas in the present invention, the deviation is small with 3.38 gf. Moreover, when comparing the magnitudes of the pressure bonding strength, the present invention is higher than the maximum, the minimum, and the average. By the way, Table 1
And the data shown in Table 2 shows that the crimping time is about 15 ms.
ec, the ultrasonic set value 70, and the wire diameter of 30 μm, and the value varies depending on these conditions or other conditions (heating temperature, wire material, etc.).

In the description of this embodiment, the connection electrode side on the semiconductor chip 1 is described as the first bond, but the present invention is not limited to this, and the inner lead 4 side is the first bond. The same can be applied to the so-called reverse bond method.

Also on the second bond side where the ball 3a is not provided, as in the case of the present embodiment, the second bonding load is applied to the bonding tool (capillary 2) after applying the first bonding load. You may make it join the other end of 3. Incidentally, the bonding load on the second bond (stitch bond) side is usually set to be slightly larger than that on the first bond (ball bond) side.

[0020]

As described above, according to the present invention,
Since variations in the ball pressure bonding diameter and the adhesion strength can be made smaller than before, it is possible to set more appropriate bonding conditions accordingly. as a result,
Even if the connection electrode becomes smaller, the balls can be crimped without sticking out of the connection electrode, so that the connection electrode can be easily downsized as the number of terminals increases. Further, since the variation in the pressure bonding strength is reduced, the wire connection strength becomes more stable, and the electrical reliability of the semiconductor device can be expected to improve.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a ball pressure bonding method in wire bonding of the present invention.

FIG. 2 is an explanatory view (No. 1) of steps of wire bonding.

FIG. 3 is a diagram (No. 2) for explaining the wire bonding process.

[Explanation of symbols]

 1 Semiconductor chip 2 Capillary (bonding tool) 3 Wire 4 Inner lead

Claims (1)

[Claims] 1. In wire bonding for connecting a connecting electrode on a semiconductor chip and an inner lead arranged around the semiconductor chip with a wire, first, a ball is formed at a tip of the wire protruding from a bonding tool, and then a ball is formed. While lowering the bonding tool at a predetermined speed, a first bonding load is applied to the bonding tool to press the ball against the connection electrode or the inner lead, and then the bonding tool is applied with the first bonding load from the first bonding load. A ball crimping method in wire bonding, wherein the ball is crimped to the connection electrode or the inner lead by applying a second bonding load having a small value.