KR100873758B1 - Bonding wire - Google Patents

Abstract

Even if the bonding pitch is short, it provides a bonding wire having strong tensile strength and high wire flow so as to suppress the occurrence of leaning failure during wire bonding, and more specifically, for 15 to 25 seconds in a temperature atmosphere of 523K. After heating, the tensile strength (high temperature strength) measured in the temperature atmosphere is continuously adjusted to be higher than 0.2% proof strength measured in a temperature atmosphere of 298K, and in particular, after the tensile strength is set to 200 MPa or more as a nominal stress. By measuring the tensile strength of the upper portion of the ball, the bonding wire can be easily evaluated and managed.

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Description

Bonding wire {BONDING WIRE}

1 is a schematic elevational side view showing a defective wiring of a bonding wire.

Fig. 2 is a schematic elevational view showing a neck-pole defect of the bonding wire.

3 is a graph showing the relationship between tensile strength and high temperature strength at the top of the ball of the bonding wire having a diameter of 25 µm.

※Explanation of symbols for the main parts of the drawing※

1: bonding wires 1a, 1b: upper part of the roof
1c: outer wire 1d: inner wire
2: Ball

3: Upper part of the ball

4: semiconductor device

5: Lead frame

The present invention relates to a bonding wire for a semiconductor element used to electrically connect an electrode (pad) on a semiconductor element and an external electrode such as a package.

Conventionally, a bonding wire connecting an electrode (pad) of a semiconductor device with an external electrode such as a package has been required to have a higher tensile strength at the same time as thinning to cope with the reduction in size of the semiconductor device and the package size.

In general, the semiconductor element is small, and when the distance between the electrode on the semiconductor element and an external electrode such as a lead frame is long, the loop length of the bonding wire becomes long, and a wire flow is likely to occur during resin molding after wire bonding. Lose. It is necessary to increase the tensile strength of the bonding wire in order to prevent contact of the wire by the wire flow.

In addition, as the semiconductor element becomes smaller, the electrode on the semiconductor element also becomes smaller. Therefore, the size of the ball melt-formed at the tip of the wire must be reduced along with the electrode when wire bonding. For this reason, the diameter of the bonding wire must also be refined, and it is necessary to increase the tensile strength per unit area in order to prevent damage to the refined bonding wire.

As the size of the semiconductor device and the package is reduced in size and size, the distance between electrodes installed on the semiconductor device, that is, the bonding pitch, has been shortened from 100 μm to 80 μm since that time, and this pitch is shorter every year. have.

When the bonding pitch was shortened, even if the bonding wire was thinned and high-strength, there was a new problem of frequent leaning of the upright portion of the loop, which was not a problem at all in the bonding pitch of 100 µm or more.

As shown in Fig. 1, when the loop of the bonding wire 1 after wire bonding is viewed in a direction parallel to this loop, the wire portion immediately above the ball 2 to be bonded with the pad of the semiconductor element 4, as shown in FIG. In 3), the bonding wire 1 is inclined to the left or right, so that the upper portion 1a of the loop of the inclined bonding wire 1 is connected to the upper portion 1b of the bonding wire loop adjacent to the inclined bonding wire 1. It comes close.

In this state, an electrical short circuit of the circuit is caused, and thus, a package having a defective lining is treated as a defective product, which significantly degrades the manufacturing yield of the product.

On the other hand, a soft bonding wire having a higher elongation through annealing is less burdened with poor lining. However, if the tensile strength of the soft bonding wire is reduced through annealing, there is a problem that other obstacles of the wire flow frequently occur during the molding process.

In addition, the bonding wire having a low tensile strength such that no lining defect occurs does not occur when the loop of the bonding wire 1 after wire bonding is viewed at a right angle to the loop, as shown in FIG. A so-called neck-fall failure, which is a phenomenon in which the loop in the wire portion 3 falls by being pulled toward the second bonding portion with respect to the lead frame 5, occurs. In addition, if a neck-fall obstacle appears on the outer bonding wire 1c during staggered bonding, it is likely to cause electrical shorting along with a defective lining because it is close to the inner bonding wire 1d.

An object of the present invention is to provide a bonding wire that has high tensile strength and can prevent occurrence of a lining defect during wire bonding even if the bonding pitch is short.

In order to achieve the above object, the bonding wire provided by the present invention is heated for 15-25 seconds in a temperature environment of 523K (250°C), and then the tensile strength measured in the temperature environment is 298K (25°C). It should be higher than the 0.2% proof stress measured in.

In addition, in the bonding wire for a semiconductor device of the present invention, it is preferable that the tensile strength measured in the temperature environment after heating for 15-25 seconds in a temperature environment of 523K (250°C) is 200 MPa or more as a nominal stress.

However, after heating for 15-25 seconds in a temperature environment of 523K (250°C), the tensile strength measured in the same temperature environment is called the high temperature strength or hot strength from the past to estimate the properties of the bonding wire at the time of bonding. It is widely known worldwide as an indicator.

In addition, the 0.2% proof stress is a relationship between a loaded stress and a strain, and refers to a stress at which a permanent deformation of 0.2% remains when the load disappears in the middle. Nominal stress means the value obtained by dividing the external force by the first cross-section before deformation.

It can be seen that during wire bonding, plastic deformation occurs due to the capillary action for forming the loop of the bonding wire on the wire portion directly above the ball, and accordingly, the lining disturbance is associated with the tensile strength of the wire portion immediately above the ball. So, the present inventors heated for 15-25 seconds in a temperature environment of 523K (250° C.), and then continuously measured in the temperature atmosphere, the tensile strength (hereinafter referred to as “high temperature strength”) and the tension at the top of the ball after wire bonding. As a result of investigating the relationship with the intensity, it was found that the relationship between the two has a substantially positive positive correlation, as shown in FIG.

In addition, the present inventors examined the relationship between the high temperature strength and the failure in more detail, and as a result of the bonding wire, when having a high temperature strength higher than 0.2% yield strength measured in a temperature environment of 298K (25°C), the failure in the listening It has been found that this is greatly reduced, and the present invention has been completed. In addition, it was also found that a bonding wire having such a high temperature strength and having a high temperature strength of 200 MPa or more as a nominal stress is more preferable. The above characteristics required for the bonding wire of the present invention can be obtained by appropriately adjusting the composition of the bonding wire or the heat treatment conditions during the wire manufacturing process.

That is, the composition of the wire or the heat treatment conditions of the wire manufacturing process are adjusted so that the high temperature strength of the bonding wire is higher than the 0.2% yield strength measured in a temperature environment of 298K (25°C).

Regarding the composition of the bonding wire, a wire containing gold as a main component is preferable. Particularly, trace components such as Be, Ca, Ce, and La added to gold may improve the wire strength according to an increase in the amount of addition, but if too much is added, there is a problem of bonding defects during the bonding process. Therefore, it is preferable to appropriately adjust the amount of addition. Specifically, it is preferable to adjust Be to a range of 2-10 wt ppm and Ca to a range of 10-35 wt ppm.

In the bonding wire manufacturing process, when adjusting the heat treatment conditions during the wire drawing step, when the diameter of the wire is about 3.5 mm to about 5.0 mm depending on the wire composition, the Vickers Hardness of the wire surface after annealing is about 60 before annealing It is preferable to continuously anneal such that the elongation is about 3% to 10% at a point in time between% to 75% or when the wire diameter is 0.20 mm to 0.40 mm. In particular, it is more preferable to perform both annealing and continuous annealing for the above-mentioned hardness adjustment because the strength of the wire tends to increase as the amount of elements such as Ca and Be added increases.

By performing this treatment, the high-temperature strength of the bonding wire is higher than the 0.2% proof stress measured in a temperature environment of 298K, so that the wire can be normally deformed without any break immediately above the ball. Therefore, even in the case of a severe capillary operation for forming a loop, the loop is correctly followed by the capillary, thereby preventing a defective lining. Moreover, by combining the composition of the wires as described above and the heat treatment conditions in the drawing process during the wire manufacturing process, adjusting the nominal stress for the high-temperature strength of the bonding wire to be 200 MPa or more can prevent a defective lining, and also a neck- Poor defects or resin molding can reduce wire flow.

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As described above, instead of measuring the tensile strength of the wire portion located immediately above the ball after wire bonding, the present invention is based on a high-temperature strength that can be easily measured from the bonding wire itself, and provides a bonding wire that does not cause a lining obstacle. It can be easily evaluated and managed.

Example

Purity of 99.999% by weight or more of high purity Au and a predetermined amount of additives such as Be, Ca, Ce, and La are dissolved in a high frequency induction heating furnace to obtain a lump of a synthetic cast alloy having the composition shown in Table 1 below. The cast alloy body is rolled with a grooved rule to form a line, and then subjected to intermediate annealing under the conditions described later in the process during wire drawing to obtain an ultrafine wire having a final diameter of 28 µm.
Subsequently, each ultrafine wire is continuously annealed at a room temperature from 5% to 10% to obtain a bonding wire.

Table 1
                Composition (ppm weight)  Intermediate annealing conditions sample Ca Be Other One 20 3 Up to 50 Condition 2 2 30 3 Up to 50 Condition 2 3 20 6 Up to 50 Condition 1 4* 20 6 Up to 50 Condition 4 5＊ 30 3 Up to 50 Condition 1 6＊ 6 6 Up to 50 Condition 3 7＊ 6 6 Up to 50 Condition 4

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In the above table, the sample marked with ＊ is a comparative example.

The annealing conditions during processing during the drawing process are as follows.

① Condition 1: When the wire diameter is 4.0 mm, annealing is performed so that the Vickers hardness of the wire surface after annealing becomes 70% before annealing.

② Condition 2: When the wire diameter is 4.0 mm, annealing is performed so that the Vickers hardness of the wire surface after annealing becomes 70% before annealing, and then continuously annealing so that the elongation becomes 10% when the wire diameter is 0.3 mm.

③ Condition 3: Continuous annealing so that the elongation is 5% when the wire diameter is 0.3 mm.

④ Condition 4: No annealing was performed during processing until the final wire diameter.

For the bonding wire obtained as described above, 0.2% proof stress in a temperature atmosphere of 298 K, tensile strength and elongation at the same temperature were measured, heated for 15-25 seconds in a temperature atmosphere of 523 K, and then continued in the same temperature atmosphere. Tensile strength (high temperature strength) was measured and the nominal stress was obtained. The obtained results are shown in Table 2 below.

Table 2

               298K             523K sample Tensile strength (cN) Tensile rate (%) 0.2% proof stress (cN) High temperature strength (cN) Nominal stress (MPa) One 14.0 7.0 12.2 12.8 208 2 14.8 7.7 13.0 13.3 216 3 13.9 10.2 12.1 12.8 208 4* 16.0 6.0 14.0 13.9 226 5＊ 15.9 5.3 14.5 14.3 232 6＊ 16.2 4.6 14.3 13.1 213 7＊ 15.1 7.0 12.6 12.2 198

In the above table, the sample marked with ＊ is a comparative example.

As can be seen from the above results, Samples 1 to 3 of the present invention are adjusted so that the high temperature strength (523K) is higher than the 0.2% proof stress measured in a temperature atmosphere of 298K, and the nominal stresses are both 200 MPa or more. On the other hand, in Comparative Examples 4 to 7, the high temperature strength (523K) is lower than the 0.2% yield strength, and in particular, the high temperature strength (523K) is significantly lower in Sample 7 compared to the tensile strength (298K), and the nominal stress is 200 MPa or less.

Next, using the bonding wire of each sample, a "UTC-300 type" bonder manufactured by Shinkawa Co., Ltd. of Japan was applied to obtain 6240 copies at a loop height of 200µm and a loop length of 5mm at 80µm pitch, respectively. Bonding was done in parallel. Using a measuring microscope, observation was performed in a direction parallel to the loop, and wires inclined to the left and right were observed as poor lining until the gap between the upper portions of the loops was 35 µm or less, and the number of their measurements was measured. In addition, by observing from the direction perpendicular to the loop, the number of bonding wires having a neck-pole failure was measured. Table 3 shows the total number of defects and the total defect rates of the bonding defects and neck-pole obstacles thus obtained.

In addition, as described above, for each sample bonded with a loop height of 200 μm and a loop length of 5 mm, resin molding was applied to the loop under normal conditions in the normal direction, and then the flow rate of the wire was measured. For the wire flow rate, the maximum distance displaced from the position before the mold for the loop where the resin flowed and curved was determined as the loop length, and the average value of 5 points was expressed as %. Table 3 shows the obtained flow rates of the wires.

Table 3

 sample The number of bad living The neck-pocket defect Total defective rate (%) Wire flow rate (%) One One 0 0.02 2.9 2 4 0 0.06 2.6 3 6 0 0.10 2.9 4* 85 0 1.36 2.5 5＊ 188 0 3.01 2.4 6＊ 168 0 2.69 2.8 7＊ 5 997 16.06 5.6

The sample marked with * in the above table is a comparative example.

From the above results, the bonding wire of Sample 1-3 of the present invention has a high temperature strength (523K) higher than 0.2% proof stress (298K), and a high nominal stress (523K) exceeding 200 MPa, It can be seen that, compared to Samples 1 to 3 of the corresponding comparative example, the defective lining was reduced to 1/10 to 1/100 or less.
In addition, the occurrence of a neck pole failure in which conventional lining defects are small as in Sample 7 can be eliminated by Samples 1 to 3 of the present invention, and at the same time, the flow rate of the wire is maintained at 3% or less, which can be said to be generally good You can.

According to the present invention, after heating for 15-25 seconds in a temperature atmosphere of 523K, the tensile strength (high temperature strength) measured in the temperature atmosphere is continuously adjusted to prevent poor wiring or neck-pole failure during wire bonding. It is possible to suppress the occurrence, and in particular, to provide a bonding wire having strong mechanical strength in wire flow.

In addition, in the present invention, even after the wire bonding, even if the tensile strength of the upper portion of the ball is not measured, it is easy to evaluate and manage the wire that does not cause a defect in lining based on the high temperature strength that can be easily measured from the bonding wire before wire bonding. You can.

 Therefore, even with a narrow bonding pitch of 100 µm or less due to the small and reduced size of the semiconductor device and package size, it is possible to reduce the defect rate occurring in the bonding process of the wire and to improve the product yield and reliability in the assembly process of the semiconductor device. There will be.

Claims (3)

Au as a main component, and further comprises any one or more selected from the group consisting of Be, Ca, Ce, and La, and after heating for 15-25 seconds in a temperature atmosphere of 523K, tensile strength continuously measured in the temperature atmosphere A bonding wire characterized in that it is higher than the 0.2% yield strength measured in a temperature atmosphere of 298K. According to claim 1, Bonding wire characterized in that the tensile strength measured in the temperature atmosphere after heating for 15-25 seconds in a temperature atmosphere of 523K is 200 MPa or more at a nominal stress. According to claim 1 or claim 2, The Be is 2ppm to 10ppm by weight, Ca is 10ppm to 35ppm by weight, characterized in that the bonding wire is included.

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