JPH06145842A - Bonding gold alloy thin wire - Google Patents

Abstract

(57) [Summary] [Purpose] A gold bonding wire that has a higher breaking strength and a higher loop height than the conventional gold alloy wire that can be made finer. [Constitution] (1) High-purity gold (purity of 99.995% or more)
In addition, a fine gold alloy wire for bonding, containing boron in an amount of 0.05 to 0.2 ppm by weight and beryllium in an amount of 1 to less than 20 ppm by weight, and the balance being inevitable impurities of gold. (2) 1 weight of one or more of calcium, yttrium, lanthanum, and cerium in the component (1) above.
It is contained in the range of ppm to less than 15 weight ppm, and further, (3) 2 to 50 weight of indium is added to the component of (2) above.
Gold alloy fine wire for bonding that contains ppm and the balance is gold and gold unavoidable impurities. [Effect] With the wire diameter of about 18 μm to 30 μm, it is possible to secure the loop height and the bonding strength comparable to the conventional one.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine gold alloy wire having excellent heat resistance, which is used for connecting electrodes on a semiconductor element and external leads, and more specifically, to a wire diameter used by increasing the strength of the fine gold alloy wire. The present invention relates to a gold alloy thin wire capable of achieving a thinner wire and maintaining the same bonding strength as the conventional one despite the thinning.

[0002]

2. Description of the Related Art Conventionally, gold alloy fine wires have been mainly used as bonding wires for connecting electrodes on a semiconductor element and external leads. A thermocompression bonding method is a typical method for bonding gold alloy fine wires. In the thermocompression bonding method, the tip portion of the gold alloy thin wire is heated and melted with an electric torch and a ball is formed by surface tension,
This is a method in which after the ball portion is pressure-bonded to the electrode of the semiconductor element heated within the range of 300 ° C., connection with the external lead side is further performed by ultrasonic pressure-bonding.

In recent years, the number of electrodes on a semiconductor element has increased along with the improvement in the degree of integration of the semiconductor element. For this reason, the distance between the electrodes can be shortened, the ball diameter for ball bonding can be reduced, or the connecting gold alloy wire can be made longer than before (so-called long span). is the current situation. For this purpose, thinning of the gold wire for bonding is effective for shortening the pitch between the electrodes and reducing the ball diameter, and for longer span, the cost is reduced by making it thinner. be able to.

However, the conventional gold alloy fine wire is inevitably deteriorated in mechanical properties, especially breaking strength, due to the thinning of the wire, so that the wire breakage easily occurs when the gold alloy fine wire is attached to the bonder without careful handling. Or, it is easy to break due to vibration due to transportation after bonding, the bonding strength after thermocompression bonding tends to decrease due to the small number of crystal grains per wire diameter due to thinning, The loop height becomes low due to the addition of the element that improves the breaking strength, and the failure rate of the semiconductor device due to the occurrence of a short circuit due to the contact between the ridge of the semiconductor element and the gold alloy thin wire or the contact between the island and the gold alloy thin wire. Therefore, it is difficult for conventional gold alloy thin wires to cope with thinning, and therefore, the mechanical strength is higher than that of conventional gold alloy thin wires, and it is Bonding strength equivalent to the conventional gold alloy wire, and have high gold alloy thin wire loop height is desired for.

As a conventional bonding gold alloy wire,
For example, as disclosed in JP-A-53-112059, a gold alloy fine wire to which beryllium is added in an amount of 1 to 8 ppm by weight, and calcium disclosed in JP-A-58-112060 is included in an amount of 3 to 5 ppm by weight. Including, 5 germanium
There is a gold bonding wire containing one kind or two kinds or more of ˜50 weight ppm and beryllium of 1 to 8 weight ppm. Further, as described in Japanese Patent Application Laid-Open No. 58-154242, which has higher mechanical strength than before, a gold alloy wire composed of rare earth elements such as lanthanum and cerium, calcium, germanium and beryllium has been invented.

However, in the examples of these gold alloy fine wires, the breaking strength at a diameter of 25 μm is 10 to 12 gf, but the breaking strength at a diameter of 20 μm is 6 due to the decrease of the cross-sectional area.
As a result, the recrystallization region at the time of ball formation becomes narrow due to the increase in the bonding strength after bonding and the amount of heat dissipation due to the increase in the specific surface area, resulting in a decrease in the loop height. However, there are problems such as an increase in the defective rate of the semiconductor device due to the occurrence of vibration disconnection and a decrease in reliability. Even if the wire is made thinner, the same mechanical properties as those of conventional gold alloy wires can be obtained, and the bonding strength after thermocompression bonding is the same as that of conventional gold alloy wires and the loop height is high. Is desired from related business fields.

[0007]

DISCLOSURE OF THE INVENTION The inventors of the present invention have studied various conventionally proposed gold alloy fine wires for bonding, and as a result, when the breaking strength of the gold alloy fine wires is 5 to 6 gf or less, the gold to be bonded to the bonder is reduced. Since it is necessary to take sufficient care in handling such as mounting fine alloy wires, it will be difficult to handle the same as conventional fine gold alloy wires. Therefore, it is desirable that the breaking strength be at least 6 gf. In the case of fine wires, increasing the amount of additional elements that increase the mechanical strength for thinning (less than 25 μm) shortens the recrystallized region during ball formation, and the height of the loop after bonding is low due to the reasons described above. As a result, the pull strength tended to decrease. In addition, excessive addition of an alloy element causes an oxide layer to be formed on the surface of the ball by oxidation of the additional element during ball formation, resulting in insufficient bonding during thermocompression bonding with the electrode, resulting in a decrease in bonding strength. If the hardness is increased, the deformation rate is reduced during pressure bonding, and the shear strength is reduced or is extremely large, the semiconductor element may be damaged. Further, it has been found that a contraction hole is easily formed at the tip of the ball, and the bonding area after the thermocompression bonding is reduced due to the reduction of the bonding area.

[0008]

Means for Solving the Problems The present inventors have conducted various studies in order to clarify the above-mentioned problems, and as a result, by adding beryllium and a very small amount of boron, mechanical properties,
In particular, it has been found that there is an effect of significantly increasing the breaking strength, expanding the recrystallized region during ball formation, and increasing the loop height. Regarding the gold alloy fine wire to which boron is added, the proposal of Japanese Patent Application Laid-Open No. 59-65440 has already been known. However, when the content of boron is less than the content described in the publication, beryllium and other second group, It was found that the coexistence with the elements of the third group has a more sufficient effect. Further, even if the wire is thinned, the strength of the ball neck portion is high, and the variation is small, and in order to obtain a gold alloy thin wire for bonding with fine graining of the ball neck portion, the content of boron is particularly required. It has been discovered that by controlling the amount within a very small range, a gold alloy thin wire for bonding suitable for thinning can be industrially easily manufactured and the above-mentioned various problems can be solved.

That is, the present invention is based on the above findings and has the following structures. (1) High-purity gold (purity 99.995% or more), weight pp
A fine gold alloy wire for bonding, wherein boron is contained in a range of 0.05 to 0.2 ppm and beryllium is contained in a range of 1 to less than 20 ppm as m, and the balance is inevitable impurities of gold. (2) The above component (1) contains one or more of calcium, yttrium, lanthanum, and cerium in a range of 1 to less than 15 ppm by weight, and the balance is composed of gold and gold unavoidable impurities. Gold alloy fine wire. (3) 1 weight of indium is added to the component of (2) above.
A fine gold alloy wire for bonding, containing ~ 50ppm, and the balance being gold and inevitable impurities of gold.

The structure of the present invention will be further described below. The high-purity gold used in the present invention is gold having a purity of at least 99.995% by weight and the balance being inevitable impurities. If the purity is less than 99.995% by weight, it will be affected by the impurities contained therein. In particular, in the case of a gold alloy fine wire for a high loop, which has a relatively small addition amount, the effect of the content of the present invention cannot be sufficiently exerted.

Boron has a small solid solubility in gold and is known to be effective in improving mechanical strength. Although the conventionally known boron content in gold is 1 ppm by weight or more, the present inventors have found that when adding a plurality of elements,
In particular, it has been found that the optimum boron content for gold alloy fine wires is in the trace amount range of less than 0.2 ppm by weight when coexisting with beryllium. That is, the boron content is 0.2 weight
Above ppm, the hardness of the ball becomes high, and the amount of plastic deformation of the ball is small at the time of pressure bonding with the electrode on the semiconductor element,
In addition to making it difficult to obtain sufficient bonding strength or producing fine cracks in a semiconductor element, it has the drawback that it is difficult to form a true sphere when forming gold balls due to the influence of other coexisting elements. The problem of not being a true sphere is that when the electrode area on the semiconductor element is reduced, a part of the gold ball that is plastically deformed when the ball is crushed by the capillary protrudes from the electrode, causing a short circuit between the electrodes. If there is no gold alloy thin wire at the center of the ball, the loop bends during bonding, impairing the linearity. On the other hand, 0.05 weight pp
If it is less than m, the distribution of boron in the gold becomes non-uniform, resulting in local variations in mechanical strength even within the same gold alloy thin wire, resulting in increased variations in loop height, variations in bonding strength, etc. Will cause defects. Therefore, the boron content should be 0.05 ppm by weight or more and 0.2 weight
The range was ppm.

When the amount of beryllium to be coexisted is less than 1 ppm by weight, the combined effect is insufficient and the breaking strength does not increase. On the other hand, when the amount of beryllium exceeds 20 ppm by weight, the aluminum electrode on the semiconductor element and the gold alloy fine wire are not uniformly diffused, so-called Kirkendall voids are easily generated, and as a result, the joint reliability is deteriorated. From 20
Weight ppm or less. The preferred range for obtaining high strength and high loop is that the boron content is 0.07 to 0.1 ppm by weight.
, And beryllium are 6 to 12 ppm by weight.

The purpose of adding the second group element is to further improve the mechanical strength as compared with the gold alloy fine wire made of boron and beryllium, and to prevent the crystal grains of the gold alloy fine wire from becoming coarse due to the heat effect during ball formation. , To improve the strength of the ball neck portion. Calcium is disclosed in JP-A-53-105.
As described in Japanese Patent No. 968, it is known that the heat resistance of the gold alloy wire and the mechanical strength of the gold alloy wire are increased. It has been found that when boron and beryllium are contained within the above range, the addition of calcium alone has the effect of further improving the mechanical strength. However, if the calcium content exceeds 15 ppm by weight, a contraction hole is formed at the tip of the ball, the ball does not become a true sphere, and the bonding strength after ball bonding is reduced. The upper limit was set to 15 ppm by weight. When the content of calcium is less than 1 ppm by weight, the joint effect of boron, beryllium and calcium is unstable,
The combined effect of improving mechanical strength is also insufficient. Therefore, the calcium content is from 1 ppm by weight to 15 ppm by weight.
m.

Lanthanum, cerium and yttrium are elements having the same tendency effect as calcium as described in German Patent No. 1608161, and as a result of studying the combined addition effect of boron and beryllium, similar to calcium. It was found to be effective. All elements are 1
If the content is less than ppm by weight, sufficient mechanical strength cannot be obtained due to the combined effect of boron and beryllium, resulting in large variation in strength within the gold alloy thin wire. On the other hand, if it is added in excess of 15 ppm by weight, the ball does not become a true sphere and a contraction hole is formed at the tip of the ball, and the bonding strength after ball bonding decreases, so the upper limit of the content is set. 15 weight
It was set to ppm. Even if two or more of calcium, lanthanum, cerium, and yttrium are added to boron and beryllium, if the amount is less than 1 ppm by weight, the effect of addition is small and the variation in strength in the fine gold alloy wire becomes large, resulting in 15 ppm by weight.
If the amount of addition exceeds 5, the ball does not become a true sphere, and a contraction hole is formed at the tip of the ball, so the bonding strength after ball bonding decreases, so the upper limit of the content is 15
Weight ppm was used. The preferred range for obtaining high strength and high loop is 2 to 5 ppm by weight.

The third group of indium is disclosed in JP-A-63-14.
As described in Japanese Patent No. 5729, the effect of increasing the loop height is recognized. When calcium, lanthanum, cerium, or yttrium is added to boron and beryllium, the loop height becomes lower than that of boron and beryllium, so that it was included in order to make the loop higher. However, if the indium content is less than 1 wtppm, the effect of raising the loop is small, and if it exceeds 50 wtppm, the ball neck strength decreases, so the content was made 1 to 50 wtppm. As a result of the experiment, the desirable content range of indium was 10 to 30 ppm by weight.

[0016]

EXAMPLES Examples will be described below. Gold purity is 9
Using 9.995% by weight or more of electrolytic gold, the master alloys containing the above-mentioned additive elements were individually melt-cast in a high frequency vacuum melting furnace to melt the master alloys. A gold alloy having the chemical composition shown in Table 1 was melt-cast in a high-frequency vacuum melting furnace with a predetermined amount of the mother alloy of each additive element thus obtained and electrolytic gold having a gold purity of 99.995% by weight or more. After rolling the ingot, drawing is performed at room temperature, an intermediate annealing step of the gold alloy fine wire is added if necessary, and further drawing is continued to obtain a gold alloy fine wire having a final wire diameter of 20 μmφ, Continuous annealing was performed in the air atmosphere so that the elongation value of the gold alloy thin wire was adjusted to about 4%.

Table 1 also shows the results of examining the tensile strength at room temperature, loop height, ball shape and bonding strength of the obtained gold alloy thin wire. As for the loop height, after joining the electrode on the semiconductor element and the external lead using a high-speed automatic bonder, the top height of each loop formed and the electrode surface of the semiconductor element are 100 with an optical microscope. The measurement was performed, and the difference in distance between the two was used as the loop height. For the ball shape, using a high-speed automatic bonder, observing a gold alloy ball obtained by arc discharge with an electric torch with a scanning electron microscope, the ball shape is abnormal, excessive oxide is generated on the ball surface, etc. Those that could not be bonded to the electrodes on the semiconductor element in a good shape were evaluated as x, and those that were good were evaluated as o. The bonding strength was determined by fixing the lead frame and the semiconductor element to be measured after high-speed automatic bonding with a jig, and then pulling the central portion of the gold alloy thin wire after bonding, and measuring the tensile strength at the time of breaking 100 of the fine wire and the pull strength. It was evaluated by variation. In addition, a shear strength was measured by moving a jig parallel to the semiconductor element at a position 3 μm above the electrode of the semiconductor element that was also fixed to bond and bond the gold balls to shear, and measure the maximum load during peeling to 100 pieces. It was judged based on the result of obtaining the variation.

Table 1 shows the evaluation results of the gold alloy fine wire produced with the present constituents, and Table 2 shows the case where the wire diameter is changed with the same composition.
Table 3 shows the evaluation results of the gold alloy fine wire including the addition amount deviating from the constituents. In addition, Table 4 shows the results of examining the influence particularly when the purity of the original charge is less than 99.995%.

In comparison of the pull strengths of the gold alloy wires having almost the same loop heights in Tables 1 and 3, the loop height variation in Table 1 is smaller than that in Table 3, or the pull strengths in Table 1 are both. The results are larger than the values in Table 3 and smaller than the values shown in Table 3, or the results show that the shear strength and the fluctuations are small, and the components of the present invention are all better when judged comprehensively. It is the result. In addition, when the amount of alloying element exceeding the range of the present invention was added, the ball shape was not normal in all cases, and the shear strength was lowered and the variation was large.

Regarding the shear strength, it is generally considered that there is no problem in the case of a gold alloy fine wire of 25 μm if the average value is 50 g or more. As a result of trial calculation of the shear strength of the gold alloy thin wire of 20 μm from the shape after bonding, the value is about 30 g. In the case of Table 1, all of them satisfy the value of 30 g or more, but in the case of Table 3, there are many cases of 30 g or less, which is not sufficient as a gold alloy fine wire for bonding.

In the evaluation of the ball shape, all the components within the scope of claims of Table 1 formed normal balls.
In the comparative example of Table 3, there are some balls which have abnormal balls such as shrinkage holes at the tip of the ball.

As described above, when the upper limit of this component is deviated, the loop height is low, the joining strength between the pull strength and the shear strength is insufficient, and the variation is large, resulting in the reliability of the semiconductor device. It is clear that If the lower limit of the configuration of the present invention is not satisfied,
Although the mechanical strength is reduced and the loop height can be maintained,
The variation is large, resulting in a large variation in pull strength and a large variation in shear strength. The same results are shown in Table 4 where the purity of the original fee is low.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

[Table 4]

[0027]

The gold alloy fine wire of the present invention has sufficient mechanical strength, the loop height after bonding is high and its variation is small, and the bonding strength is high and its variation is small.
Since the ball shapes are all normal and stable bonding is possible, and a similar effect was obtained even when the wire diameter was 18 to 30 μm, it has industrially useful characteristics.

Claims (3)

[Claims] 1. High-purity gold (purity of 99.995% or more)
In addition, a fine gold alloy wire for bonding, containing boron in an amount of 0.05 to 0.2 ppm and beryllium in an amount of 1 to less than 20 ppm as the weight ppm, and the balance being inevitable impurities of gold. 2. The bonding according to claim 1, containing 1 or 2 or more of calcium, yttrium, lanthanum, and cerium in a range of 1 to less than 15 ppm by weight, and the balance being gold and inevitable impurities of gold. Gold alloy fine wire for use. 3. A gold alloy thin wire for bonding, which contains 1 to 50 ppm by weight of indium as a component of claim 2 and the balance is gold and inevitable impurities of gold.