JP3277564B2 - Wire bonding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire bonding method for connecting a connection 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 connected to the connection electrode or the inner lead. The present invention relates to a wire bonding method for crimping.

[0002]

2. Description of the Related Art In a process of assembling a semiconductor device, there is a so-called wire bonding process in which connection electrodes on a semiconductor chip are connected to inner leads arranged around the semiconductor chip for external drawing by wires. There is something called.

In this wire bonding step, first, a ball is formed at the tip of a wire protruding from a bonding tool by discharge energy. Next, the bonding tool is lowered at a high speed, and is switched to a low speed (search speed) as soon as the search level is reached, so that the tip of the bonding tool gently lands 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 between the ball and the connection electrode, whereby the ball is pressed against the connection electrode. As described above, conventionally, the ball formed at the tip of the wire is pressed against the connection electrode with a certain 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 described above, and then the ball is further crushed while applying ultrasonic waves or heat. Therefore, there has been a problem that a large variation occurs in the pressure-bonded diameter of the ball formed by this and the adhesion strength with the connection electrode. For these reasons, conventionally, it has been extremely difficult to reduce the size of the connection electrodes with an increase in the number of terminals, and at the same time, the electrical reliability of the semiconductor device has been reduced.

[0005] The present invention has been made to solve the above problems, and has as its object to provide a wire bonding method capable of reducing variations in the ball pressing 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 to an inner lead disposed around the semiconductor chip by a wire. In the wire bonding method, the tip of the wire protruding from the bonding tool is
After forming the tool, a first load is applied to the bonding tool.
In addition, press the ball against the connection electrode or inner lead
The first step and connecting the ball in this first step
While pressing against the electrode or inner lead,
A second load different from the first load
Switch to load and replace ball with connection electrode or inner lead
And a second step of crimping the pressure.

[0007]

According to the wire bonding method of the present invention,
Adding first load to the bonding tool is pressed against the connection electrodes or the inner leads a <br/> ball on the wire tip, the pressure
While applying the load, apply the load to the bonding tool.
By switching to a second load different from the first load and crimping the ball to the connection electrode or the inner lead, the ball is pressed against the connection electrode or the inner lead in a sufficiently crushed state. This can reduce variations in the ball pressing diameter and the adhesion strength.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a view for explaining the wire bonding method of the present invention, and FIGS. 2 and 3 are views for explaining the wire bonding process. In the present embodiment, one
Wire while said the continuous wire bonding step in order
A description of the bonding method will be added.

First, in a first step, as shown in FIG. 2A, a bonding tool arranged above the semiconductor chip 1 at a predetermined distance, that is, an extremely fine wire 3 is fed out to the tip of a 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 a second step, as shown in FIG. 2B, the capillary 3 is lowered at a high speed, and the height of the capillary 2 with respect to the semiconductor chip 1 is changed to the search level H.
At the same time (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 applied, and when the descent speed is switched to a low speed, the first bonding load (for example, 100 to 12) is applied.
0 gf) is added to the capillary 2. In this way, the vibration of the capillary 2 accompanying the switching of the descending speed can be suppressed.

Subsequently, in a 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 this 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). Crushed.

Next, in a 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. The ball 3a is pressed against a connection electrode (not shown) by applying, for example, ultrasonic waves or heat to the ball 3a.

Here, the third and fourth steps will be further described with reference to FIG. First, at a time T1 when the capillary 2 lands on the semiconductor chip 1, the first capillary 2 serving as a bonding tool is provided.
Is applied. When a predetermined time (usually several msec) elapses and the time T2 is reached while the first bonding load G1 is applied, the capillary 2
Is switched to a second bonding load G2 which is smaller than the first bonding load G1. Further, during a period from time T2 held at the second bonding load G2 to time T3, ultrasonic waves, heat, and the like are applied to the joint portion, and the ball 3a is pressed against the connection electrode.

In the subsequent steps, the capillary 2 is
As shown in (b), it rises to the loop position P, and then moves toward the inner lead 4 as shown in FIG. Here, a capillary 2 depicting a predetermined loop shape
Then, as shown in FIG. 3D, the other end of the wire 3 is joined to the inner lead 4 by lowering. Through the above steps, the connection electrodes (not shown) on the semiconductor chip 1 and the inner leads 4 are connected (connected) by the wires 3. As a means for changing the bonding load, various wire maker's provided with a function for changing the bonding load in existing wire bonding apparatuses may be used.

As described above, the wire bonding of the present embodiment
In the method, firstly the first bonding load G1 pressed the wire 3 leading end of the ball 3a in addition to the capillary 2 to the connecting electrode (not shown), while the pressure state, calibration
The load applied to the pillar 2 is switched to a second bonding load G2 smaller than the first bonding load G1, and the ball 3a is pressed against the connection electrode to thereby form the ball 3a.
Is pressed against the connection electrode in a sufficiently squeezed state, so that the variation in the ball pressing 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 (two-stage switching of the bonding load) and the conventional method (constant bonding load).

[Table 1]

[Table 2] Table 1 shows comparison data of the ball size after crimping. Table 1
As shown in the figure, the vertical and horizontal widths of the ball size conventionally have considerably large deviations of 4.5 μm and 7.3 μm, whereas the present invention has a deviation of 2.2 μm,
The variation is as small as 2.1 μm. Also, the values of the vertical width and the horizontal width are conventionally 14 μm on average.
In contrast, in the case of the present invention, since the average value is the same, the way the entire ball is crushed is also very uniform. Further, the thickness of the ball has a deviation of 1.8 μm conventionally, whereas the thickness of the ball of the present invention is 0.8 μm.
The dispersion is as small as 8 μm.

On the other hand, Table 2 shows comparison data of adhesion strength. As shown in Table 2, the conventional crimp strength has a deviation of 5.28 gf, whereas the present invention has a small deviation of 3.38 gf. Further, when comparing the magnitudes of the crimping strengths, the present invention is superior in any of the maximum, minimum, and average. Table 1
And the data described in Table 2 indicate that the crimping time was about 15 ms.
ec, an ultrasonic setting value of 70, and a wire diameter of 30 μm, and the value varies depending on these conditions or other conditions (heating temperature, wire material, etc.).

In this embodiment, the connection electrode side on the semiconductor chip 1 is described as the first bond. However, the present invention is not limited to this, and the inner lead 4 side is used as the first bond. The same applies to the case of a so-called reverse bonding method.

Also, on the second bond side where the ball 3a is not provided, the first bonding load is applied and then the second bonding load is applied to the bonding tool (capillary 2) in the same manner as in this embodiment. The other end of 3 may be joined. 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 the variations in the ball pressure bonding diameter and the adhesion strength can be made smaller than before, the bonding conditions can be set more appropriately. as a result,
Even if the connection electrode becomes smaller, the ball can be crimped without protruding from the connection electrode, so that the connection electrode can be easily reduced in size as the number of terminals increases. Further, since the variation in the crimping strength is reduced, the connection strength of the wire becomes more stable, and an improvement in the electrical reliability of the semiconductor device can be expected.

[Brief description of the drawings]

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

FIG. 2 is an explanatory view (1) of a wire bonding process.

FIG. 3 is an explanatory view (2) of a step of wire bonding.

[Explanation of symbols]

 Reference Signs List 1 semiconductor chip 2 capillary (bonding tool) 3 wire 4 inner lead

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-235342 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/60

Claims (2)

(57) [Claims] 1. A wire bonding method for connecting a connection electrode on a semiconductor chip and an inner lead arranged around the semiconductor chip by a wire, wherein a ball is attached to a tip of the wire protruding from a bonding tool.
After forming, a first load is applied to the bonding tool.
In addition, the ball is connected to the connection electrode or the inner
A first step of pressing the ball against the connection electrode or the connecting electrode in the first step.
While maintaining the pressure on the inner lead,
A second load different from the first load,
The ball is switched to the connection electrode or
Comprise a second step of bonding the serial inner leads
A wire bonding method characterized by the above-mentioned. (2) The second load is greater than the first load
The wire bond according to claim 1, wherein the wire bond is also small.
Ding method.