High purity gold bonding wire for semiconductor device

Abstract

Bonding wire for a semiconductor device contains high purity Au or Au alloy as a base metal and 25-10000 atppm of low boiling point element I having a boiling point lower than a melting point of the base metal and soluble in Au, or contains high purity Au or Au alloy as a base metal and 5-500 atppm of low boiling point element II having a boiling point lower than a melting point of the base metal and insoluble in Au, or contains high purity Au or Au alloy as a base metal and 5-10000 atppm of a mixture of low boiling point element I having a boiling point lower than a melting point of the base metal and soluble in Au and low boiling point element II having a boiling point lower than the melting point of the base metal and insoluble in Au under the condition of (content of the low boiling point element I)/25+(content of the low boiling point element II)/5.gtoreq.1.gtoreq.(content of the low boiling point element I)/10000+(content of the low boiling point element II)/500. The low boiling point elements I and II may be replaced by low boiling point element III soluble in Pd and low boiling point element IV insoluble in Pd, respectively.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a bonding wire for a semiconductor device adapted to be used for connection between a chip electrode of the semiconductor device and an external lead, and more particularly to such a bonding wire suitable for a ball bonding process.

It is known that a chip electrode of a semiconductor device is connected through a bonding wire such as Au wire to an external lead by melting a tip of the Au wire depending from an end of a capillary by means of an electrical torch to form a ball at the tip of the Au wire, pressing the ball against the chip electrode to bond together, then leading the Au wire to the external lead so as to form a loop, bonding the loop to the external lead, and finally cutting the Au wire.

In such a conventional bonding wire for a semiconductor device, however, a neck portion formed immediately above the ball is influenced by heat upon formation of the ball to relax a stress accumulated in the wire. Accordingly, the mechanical strength of the neck portion becomes lower than that of the base wire not influenced by heat. As a result, the neck portion is ruptured, or wire falling or wire sagging is generated during bonding work. Furthermore, in temperature cycle life test of products, a stress is generated by heat expansion and contraction due to repeated temperature change, and the stress is concentrated at the neck portion, causing a problem that the rupture of the neck portion is easily generated.

Meanwhile, in recent years, high-density mounting of LSI has accompanied a marked tendency to provide a multiplicity of pins. In this circumstance, it is demanded to reduce a diameter of the bonding wire and thereby reduce a bonding pitch.

However, as the neck portion of the aforementioned bonding wire is easy to rupture, it is impossible to reduce the diameter of the bonding wire, and the above demand cannot accordingly be met.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to make the strength of the neck portion equal to or more than that of the base wire.

According to a first aspect of the present invention achieve the above object, there is provided a bonding wire for a semiconductor device, containing high purity Au or Au alloy as a base metal and 25-10000 atppm of low boiling point element I having a boiling point lower than a melting point of the base metal and soluble in Au, or there is provided a bonding wire for a semiconductor device, containing high purity Au or Au alloy as a base metal and 5-500 atppm of low boiling point element II having a boiling point lower than a melting point of the base metal and insoluble in Au, or there is provided a bonding wire for a semiconductor device, containing high purity Au or Au alloy as a base metal and 5-10000 atppm of a mixture of low boiling point element I having a boiling point lower than a melting point of the base metal and soluble in Au and low boiling point element II having a boiling point lower than the melting point of the base metal and insoluble in Au under the condition of (content of the low boiling point element I)/25+(content of the low boiling point element II/5.gtoreq.1.gtoreq.(content of the low boiling point element I)/10000+(content of the low boiling point element II)/500.

The aforementioned high purity Au contains 99.99% or more of Au and a residual amount of unavoidable impurities.

The aforementioned Au alloy contains the high purity Au and at least one of Pd, Ag (20 at % or less), Pt (10 at % or less), Rh (2 at % or less), Os, Ru (1 at %), Be, Ca, Ge, Y, La, Mg, Zr, Ga, In, Mo, Re, Cu, Fe (1 atppm-8 at %). The use of this Au alloy improves the mechanical strength of the base metal itself at ordinary temperatures and high temperatures to thereby enable high-speed bonding, and also prevents enlargement of crystal grain in the neck portion upon formation of the ball.

The low boiling point element I having a boiling point lower than the melting point of the base metal and soluble in Au contains at least one of Zn, Cd, Hg, Te, etc., while the low boiling point element II having the boiling point lower than the melting point f the base metal and insoluble in Au contains at least one of P, S, As, Se, Rb, Cs, etc.

According to a second aspect of the present invention achieving the above object, there is provided a bonding wire for a semiconductor device, containing high purity Pd or Pd alloy as a base metal and 25-10000 atppm of low boiling point element III having a boiling point lower than a melting point of the base metal and soluble in Pd, or there is provided a bonding wire for a semiconductor device, containing high purity Pd or Pd alloy as a base metal and 5-500 atppm of low boiling point element IV having a boiling point lower than a melting point of the base metal and insoluble in Pd, or there is provided a bonding wire for a semiconductor device, containing high purity Pd or Pd alloy as a base metal and 5-10000 atppm of a mixture of low boiling point element III having a boiling point lower than a melting point of the base metal and soluble in Pd and low boiling point element IV having a boiling point lower than the melting point of the base metal and insoluble in Pd under the condition of (content of the low boiling point element III)/25+(content of the low boiling point element IV)/5.gtoreq.1.gtoreq.(content of the low boiling point element III)/10000+(content of the low boiling point element IV)/500.

The aforementioned high purity Pd contains 99.9% or more of Pd and a residual amount of unavoidable impurities.

The aforementioned Pd alloy contains the high purity Pd and at least one of Au (10 at % or less), Ag (5 at % or less), Pt (20 at % or less), Rh (8 at % or less), Ru, Os, Ir (1 at % or less), Cu, Mo, Fe, Ti (1 atppm-5 at %). The use of this Pd alloy improves mechanical strength of the base metal itself at ordinary temperatures and high temperatures to thereby enable high-speed bonding, and also prevents enlargement of crystal grain in the neck portion upon formation of the ball.

The low boiling point element III having the boiling point lower than the melting point of the base metal and soluble in Pd contains at least one of Zn, Cd, Hg, Li, Be, Mg, Sb, Te, Bi, Yb, etc., while the low boiling point element IV having the boiling point lower than the melting point of the base metal and insoluble in Pd contains at least one of P, S, As, Tl, etc.

The content of each component of the bonding wire for the semiconductor device according to the present invention is limited for the following reasons.

The low boiling point element having the boiling point lower than the melting point of the base metal is vaporized and scattered from the molten ball upon formation thereof. However, the low boiling point element cannot be vaporized from the neck portion, but it tends to be vaporized in the neck portion to generate a stress. Above all, the low boiling point element I soluble in Au is hard to escape from Au. Accordingly, if the content of the low boiling point element I is less than 25 atppm, a satisfactory characteristic cannot be obtained. In contrast, if the content of the low boiling point element I is more than 10000 atppm, embrittlement of the base wire appears to cause difficulty in wire drawing. Moreover, an amount of the element I not scattered from the ball but residing in the ball upon formation of the ball becomes large to excessively harden the ball, causing chip cracking upon bonding. For the above reasons, the content of the low boiling point element I needs to be set in the range of 25-10000 atppm.

On the other hand, the low boiling point element II insoluble in Au is easy to escape from Au. Accordingly, if the content of the low boiling point element II is less than 5 atppm, a satisfactory characteristic cannot be obtained. In contrast, if the content of the low boiling point element II is more than 500 atppm, embrittlement of the base wire appears to cause difficulty in wire drawing. Moreover, an amount of the element II not scattered from the ball but residing in the ball upon formation of the ball becomes large to excessively harden the ball, causing chip cracking upon bonding. For the above reasons, the content of the low boiling point element II needs to be set in the range of 5-500 atppm.

Under the condition of (content of the low boiling point element I)/25+(content of said low boiling point element II)/5.gtoreq.1, if a lower limit of the total content of the low boiling point element I soluble in Au and the low boiling point element II insoluble in Au is less than 5 atppm, a satisfactory characteristic cannot be obtained. Therefore, the lower limit of the total content of both the elements I and II under the above condition needs to be set to 5 atppm.

Further, under the condition of (content of the low boiling point element I)/10000+(content of the low boiling point element II)/500.ltoreq.1, if an upper limit of the total content of the low boiling point element I soluble in Au and the low boiling point element II insoluble in Au is more than 10000 atppm, embrittlement of the base wire appears to cause difficulty in wire drawing. Moreover, an amount of the element I and II not scattered from the ball but residing in the ball upon formation of the ball becomes large to excessively harden the ball, causing chip cracking upon bonding. Therefore, the upper limit of the total content of both elements I and II needs to be set to 10000 atppm.

Consequently, the bonding wire of the present invention contains high purity Au or Au alloy as a base metal and 25-10000 atppm of low boiling point element 1 having a boiling point lower than a melting point of the base metal and soluble in Au, or contains high purity Au or Au alloy as a base metal and 5-500 atppm of low boiling point element II having a boiling point lower than a melting point of the base metal and insoluble in Au, or contains high purity Au or Au alloy as a base metal and 5-10000 atppm of a mixture of low boiling point element I having a boiling point lower than a melting point of the base metal and soluble in Au and low boiling point element II having a boiling point lower than the melting point of the base metal and insoluble in Au under the condition of (content of said low boiling point element I)/25+(content of the low boiling point element II)/5.gtoreq.1.gtoreq.(content of the low boiling point element I)/10000+(content of the low boiling point element II)/500. With this constitution, the low boiling point element in the ball is vaporized and scattered upon formation of the ball to thereby prevent gas absorption peculiar to metal and obtain a ball satisfactory for bonding. On the other hand, the low boiling point element in the neck portion cannot be vaporized from the surface thereof, but it tends to be vaporized in the neck portion to generate a stress. Accordingly, a rupture strength of the neck portion after bonding is improved as compared with that of the base wire generating no stress.

The low boiling point element having a boiling point lower than the melting point of the base metal is vaporized and scattered from the molten ball upon formation thereof. However, the low boiling point element cannot be vaporized from the neck portion, but it tends to be vaporized in the neck portion to generate a stress. Above all, the low boiling point element III soluble in Pd is hard to escape from Pd. Accordingly, if the content of the low boiling point element III is less than 25 atppm, a satisfactory characteristic cannot be obtained. In contrast, if the content of the low boiling point element III is more than 10000 atppm, embrittlement of the base wire appears to cause difficulty in wire drawing. Moreover, an amount of the element III not scattered from the ball but residing in the ball upon formation of the ball becomes large to excessively harden the ball, causing chip cracking upon bonding. For the above reasons, the content of the low boiling point element III needs to be set in the range of 25-10000 atppm.

On the other hand, the low boiling point element IV insoluble in d is easy to escape from Pd. Accordingly, if the content of the low boiling point element IV is less than 6 atppm, a satisfactory characteristic cannot be obtained. In contrast, if the content of the low boiling point element IV is more than 500 atppm, embrittlement of the base wire appears to cause a difficulty of wire drawing. Moreover, an amount of the element IV not scattered from the ball but residing in the ball upon formation of the ball becomes large to excessively harden the ball, causing chip cracking upon bonding. For the above reasons, the content of the low boiling point element IV needs to be set in the range of 5-500 atppm.

Under the condition of (content of said low boiling point element III)/25+(content of said low boiling point element IV)/5.gtoreq.1, if a lower limit of the total content of the low boiling point element III soluble in Pd and the low boiling point element IV insoluble in Pd is less than 5 atppm, a satisfactory characteristic cannot be obtained. Therefore, the lower limit of the total content of both the elements III and IV under the above condition needs to be set to 5 atppm.

Further, under the condition of (content of the low boiling point element III)/10000+(content of the low boiling point element IV)/500.ltoreq.1, if an upper limit of the total content of the low boiling point element III soluble in Pd and the low boiling point element IV insoluble in Pd is more than 10000 atppm, embrittlement of the base wire appears to cause difficulty in wire drawing. Moreover, an amount of the element III and IV not scattered from the ball but residing in the ball upon formation of the ball becomes large to excessively harden the ball, causing chip cracking upon bonding. Therefore, the upper limit of the total content of both the elements III and IV needs to be set to 10000 atppm.

Consequently, the bonding wire of the present invention contains high purity Pd or Pd alloy as a base metal and 25-10000 atppm of low boiling point element III having a boiling point lower than a melting point of the base metal and soluble in Pd, or contains high purity Pd or Pd alloy as a base metal and 5-500 atppm of low boiling point element IV having a boiling point lower than a melting point of the base metal and insoluble in Pd, or contains high purity Pd or Pd alloy as a base metal and 5-10000 atppm of a mixture of low boiling point element III having a boiling point lower than a melting point of the base metal and soluble in Pd and low boiling point element IV having a boiling point lower than the melting point of the base metal and insoluble in Pd under the condition of (content of the low boiling point element III)/25+(content of the low boiling point element IV)/5.gtoreq.1 .gtoreq.(content of the low boiling point element III)/10000+(content of the low boiling point element IV)/500. With this constitution, the low boiling point element in the ball is vaporized and scattered upon formation of the ball to thereby prevent gas absorption peculiar to metal and obtain a ball satisfactory for bonding. On the other hand, the low boiling point element in the neck portion cannot be vaporized from the surface thereof, but it tends to be vaporized in the neck portion to generate a stress. Accordingly, a rupture strength of the neck portion after bonding is improved as compared with that of the base wire generating no stress.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

There will now be described some preferred embodiments of the present invention.

In a first preferred embodiment employing high purity Au or Au alloy as the base metal, various samples were prepared in the following manner. As the base metal were used high purity Au having a purity of 99.999%, Au alloy containing the high purity Au and 20 at % of Pd, Au alloy containing the high purity Au and 10 atppm of Be, Au alloy containing the high purity Au and 0.5 at % of Mo, and Au alloy containing the high purity Au and 8 at % of Cu. Then, at least one of Zn, Cd, Hg, P and Rb was added to the high purity Au and the Au alloys prepared above, and these mixtures were molten to be cast. The castings thus obtained were then subjected to a grooved roll, during which they were annealed. Then, they were subjected to wire drawing, thereby forming base wires each having a diameter of 30 .mu.m. Thereafter, further stress relieving was sufficiently conducted to finally obtain the samples.

The contents of the additional elements in the samples are shown in Table 1. In Table 1, Nos. 1-54 of the samples correspond to the preferred embodiment, and Nos. 55 and 56 of the samples correspond to comparisons departing from the composition range according to the present invention.

TABLE (1)______________________________________SAMPLE ADDITIONAL ELEMENT (at ppm)No. Zn Cd Hg P Rb______________________________________PREFERRED EMBODIMENT 1 20 2 25 3 50 4 500 5 5000 6 10000 7 11000 8 20 9 2510 5011 50012 500013 1000014 1100015 2016 2517 5018 50019 500020 1000021 1100022 323 524 5025 50026 60027 328 529 5030 50031 60032 10 1033 100 10034 1000 100035 5000 500036 6000 600037 10 10 1038 100 100 10039 1000 1000 100040 5000 5000 500041 2 342 5 543 50 5044 100 10045 250 25046 250 30047 10 248 10 10 249 10 2 250 10 250 25051 1000 1000 200 20052 1000 1000 10 200 20053 2000 2000 2000 50 5054 3000 3000 3000 50 50COMPARISON55 Au (99.99)56 Cu (99.9999)______________________________________

By using the above samples, a pull test was carried out given times (n=40), and measurements were carried out for a pull strength, number of times of rupture of the base wire rather than the neck portion, condition of workability, and existence of chip crack. The result of the measurements for the high purity Au and each Au alloy is shown in Table 2.

TABLE (2)__________________________________________________________________________Au Au + Pd (20 at %) Au + Be (10 at ppm) C C C MODE MODE MODESAM- PULL RUP- WORK- PULL RUP- WORK- PULL RUP-PLE STRENGTH TURE ABIL- CHIP STRENGTH TURE ABIL- CHIP STRENGTH TURENO. (g) (n = 40) ITY CRACK (g) (n = 40) ITY CRACK (g) (n__________________________________________________________________________ = 40)PREFERRED EMBODIMENT 1 12.0 4 GOOD UNOB- 21.2 6 GOOD UNOB- 12.2 6 SERVED SERVED 2 12.1 22 GOOD UNOB- 21.3 21 GOOD UNOB- 12.2 20 SERVED SERVED 3 12.2 21 GOOD UNOB- 21.3 25 GOOD UNOB- 12.3 22 SERVED SERVED 4 12.8 30 GOOD UNOB- 21.5 28 GOOD UNOB- 12.9 33 SERVED SERVED 5 13.0 28 GOOD UNOB- 21.6 30 GOOD UNOB- 13.3 33 SERVED SERVED 6 13.4 30 GOOD UNOB- 21.6 33 GOOD UNOB- 13.6 34 SERVED SERVED 7 13.6 31 BAD UNOB- 21.7 32 BAD OB- 13.7 35 SERVED SERVED 8 12.1 7 GOOD UNOB- 21.2 6 GOOD UNOB- 12.2 6 SERVED SERVED 9 12.2 21 GOOD UNOB- 21.3 22 GOOD UNOB- 12.2 21 SERVED SERVED10 12.4 23 GOOD UNOB- 21.3 27 GOOD UNOB- 12.4 25 SERVED SERVED11 12.8 35 GOOD UNOB- 21.5 35 GOOD UNOB- 13.0 35 SERVED SERVED12 13.3 36 GOOD UNOB- 21.7 38 GOOD UNOB- 13.5 37 SERVED SERVED13 13.5 34 GOOD UNOB- 21.7 30 GOOD UNOB- 13.7 36 SERVED SERVED14 13.6 35 BAD UNOB- 21.8 31 BAD OB- 13.7 35 SERVED SERVED15 12.0 9 GOOD UNOB- 21.1 8 GOOD UNOB- 12.3 8 SERVED SERVED16 12.1 26 GOOD UNOB- 21.2 24 GOOD UNOB- 12.4 27 SERVED SERVED17 12.8 33 GOOD UNOB- 21.2 36 GOOD UNOB- 12.5 34 SERVED SERVED18 13.4 40 GOOD UNOB- 21.5 38 GOOD UNOB- 13.1 39 SERVED SERVED19 13.5 38 GOOD UNOB- 21.7 36 GOOD UNOB- 13.4 39 SERVED SERVED20 13.7 35 GOOD UNOB- 21.7 34 GOOD UNOB- 13.7 36 SERVED SERVED21 13.7 36 BAD UNOB- 21.8 37 BAD OB- 13.7 35 SERVED SERVED22 12.0 13 GOOD UNOB- 21.0 12 GOOD UNOB- 12.2 12 SERVED SERVED23 12.0 22 GOOD UNOB- 21.0 20 GOOD UNOB- 12.2 24 SERVED SERVED24 12.2 38 GOOD UNOB- 21.1 35 GOOD UNOB- 12.7 36 SERVED SERVED25 12.5 37 GOOD UNOB- 21.4 37 GOOD UNOB- 13.3 40 SERVED SERVED26 12.7 38 BAD UNOB- 21.5 34 BAD UNOB- 13.4 38 SERVED SERVED27 12.0 12 GOOD UNOB- 21.1 12 GOOD UNOB- 12.3 11 SERVED SERVED28 12.0 22 GOOD UNOB- 21.1 25 GOOD UNOB- 12.3 21 SERVED SERVED29 12.3 35 GOOD UNOB- 21.2 36 GOOD UNOB- 13.0 28 SERVED SERVED30 12.4 37 GOOD UNOB- 21.8 38 GOOD UNOB- 13.5 29 SERVED SERVED31 12.5 38 BAD UNOB- 21.8 38 BAD UNOB- 13.5 30 SERVED SERVED32 12.1 7 GOOD UNOB- 21.2 7 GOOD UNOB- 12.7 6 SERVED SERVED33 12.3 33 GOOD UNOB- 21.4 35 GOOD UNOB- 12.9 37 SERVED SERVED34 13.1 37 GOOD UNOB- 21.6 37 GOOD UNOB- 13.4 38 SERVED SERVED35 13.5 35 GOOD UNOB- 21.7 33 GOOD UNOB- 13.7 35 SERVED SERVED36 13.6 36 BAD UNOB- 21.8 34 BAD OB- 13.7 35 SERVED SERVED37 12.5 28 GOOD UNOB- 21.2 30 GOOD UNOB- 12.3 25 SERVED SERVED38 12.7 36 GOOD UNOB- 21.3 34 GOOD UNOB- 12.6 28 SERVED SERVED39 13.0 30 GOOD UNOB- 21.8 29 GOOD UNOB- 13.3 30 SERVED SERVED40 13.8 35 BAD UNOB- 21.8 30 BAD OB- 13.8 32 SERVED SERVED41 12.0 23 GOOD UNOB- 21.1 27 GOOD UNOB- 12.2 25 SERVED SERVED42 12.1 29 GOOD UNOB- 21.1 31 GOOD UNOB- 12.2 27 SERVED SERVED43 12.4 28 GOOD UNOB- 21.4 35 GOOD UNOB- 12.6 34 SERVED SERVED44 12.4 36 GOOD UNOB- 21.4 38 GOOD UNOB- 12.9 39 SERVED SERVED45 12.5 37 GOOD UNOB- 21.8 36 GOOD UNOB- 13.5 33 SERVED SERVED46 12.4 35 BAD UNOB- 21.8 34 BAD UNOB- 13.5 33 SERVED SERVED47 12.0 12 GOOD UNOB- 21.1 12 GOOD UNOB- 12.2 12 SERVED SERVED48 12.1 23 GOOD UNOB- 21.2 21 GOOD UNOB- 12.3 25 SERVED SERVED49 12.1 27 GOOD UNOB- 21.2 25 GOOD UNOB- 12.3 29 SERVED SERVED50 12.5 36 BAD UNOB- 21.6 33 BAD UNOB- 13.5 35 SERVED SERVED51 13.2 36 GOOD UNOB- 21.6 38 GOOD UNOB- 13.5 39 SERVED SERVED52 13.3 35 BAD UNOB- 21.6 34 BAD UNOB- 13.6 36 SERVED SERVED53 13.5 28 GOOD UNOB- 21.8 35 GOOD UNOB- 13.6 34 SERVED SERVED54 13.7 29 BAD UNOB- 21.8 34 BAD OB- 13.7 37 SERVED SERVEDCOMPARISON PULL STRENGTH (g)55 1256 21__________________________________________________________________________ Au + Mo (0.5 at %) Au + Cu (8 at %) C CAu + Be (10 at ppm) MODE MODESAM- WORK- PULL RUP- WORK- PULL RUP- WORK-PLE ABIL- CHIP STRENGTH TURE ABIL- CHIP STRENGTH TURE ABIL- CHIPNO. ITY CRACK (g) (n = 40) ITY CRACK (g) (n = 40) ITY CRACK__________________________________________________________________________PREFERRED EMBODIMENT 1 GOOD UNOB- 13.0 7 GOOD UNOB- 21.9 5 GOOD UNOB- SERVED SERVED SERVED 2 GOOD UNOB- 13.1 22 GOOD UNOB- 22.0 21 GOOD UNOB- SERVED SERVED SERVED 3 GOOD UNOB- 13.1 24 GOOD UNOB- 22.0 26 GOOD UNOB- SERVED SERVED SERVED 4 GOOD UNOB- 13.5 27 GOOD UNOB- 22.2 32 GOOD UNOB- SERVED SERVED SERVED 5 GOOD UNOB- 13.6 29 GOOD UNOB- 22.3 36 GOOD UNOB- SERVED SERVED SERVED 6 GOOD UNOB- 13.8 29 GOOD UNOB- 22.4 35 GOOD UNOB- SERVED SERVED SERVED 7 BAD UNOB- 13.8 32 BAD OB- 22.5 33 BAD OB- SERVED SERVED SERVED 8 GOOD UNOB- 13.1 8 GOOD UNOB- 22.0 4 GOOD UNOB- SERVED SERVED SERVED 9 GOOD UNOB- 13.2 23 GOOD UNOB- 22.1 22 GOOD UNOB- SERVED SERVED SERVED10 GOOD UNOB- 13.2 26 GOOD UNOB- 22.1 23 GOOD UNOB- SERVED SERVED SERVED11 GOOD UNOB- 13.3 30 GOOD UNOB- 22.2 34 GOOD UNOB- SERVED SERVED SERVED12 GOOD UNOB- 13.5 33 GOOD UNOB- 22.4 36 GOOD UNOB- SERVED SERVED SERVED13 GOOD UNOB- 13.6 31 GOOD UNOB- 22.4 36 GOOD UNOB- SERVED SERVED SERVED14 BAD UNOB- 13.8 34 BAD OB- 22.5 32 BAD OB- SERVED SERVED SERVED15 GOOD UNOB- 13.3 11 GOOD UNOB- 22.0 9 GOOD UNOB- SERVED SERVED SERVED16 GOOD UNOB- 13.3 29 GOOD UNOB- 22.0 27 GOOD UNOB- SERVED SERVED SERVED17 GOOD UNOB- 13.4 30 GOOD UNOB- 22.1 31 GOOD UNOB- SERVED SERVED SERVED18 GOOD UNOB- 13.5 35 GOOD UNOB- 22.3 38 GOOD UNOB- SERVED SERVED SERVED19 GOOD UNOB- 13.7 36 GOOD UNOB- 22.4 36 GOOD UNOB- SERVED SERVED SERVED20 GOOD UNOB- 13.7 35 GOOD UNOB- 22.5 37 GOOD UNOB- SERVED SERVED SERVED21 BAD OB- 13.8 35 BAD OB- 22.5 33 BAD OB- SERVED SERVED SERVED22 GOOD UNOB- 13.2 14 GOOD UNOB- 22.1 10 GOOD UNOB- SERVED SERVED SERVED23 GOOD UNOB- 13.2 25 GOOD UNOB- 22.1 33 GOOD UNOB- SERVED SERVED SERVED24 GOOD UNOB- 13.5 39 GOOD UNOB- 22.2 40 GOOD UNOB- SERVED SERVED SERVED25 GOOD UNOB- 13.7 39 GOOD UNOB- 22.5 39 GOOD UNOB- SERVED SERVED SERVED26 BAD UNOB- 13.7 38 BAD UNOB- 22.5 39 BAD UNOB- SERVED SERVED SERVED27 GOOD UNOB- 13.1 13 GOOD UNOB- 22.1 9 GOOD UNOB- SERVED SERVED SERVED28 GOOD UNOB- 13.1 23 GOOD UNOB- 22.1 30 GOOD UNOB- SERVED SERVED SERVED29 GOOD UNOB- 13.2 37 GOOD UNOB- 22.2 38 GOOD UNOB- SERVED SERVED SERVED30 GOOD UNOB- 13.6 36 GOOD UNOB- 22.4 35 GOOD UNOB- SERVED SERVED SERVED31 BAD UNOB- 13.6 36 BAD UNOB- 22.4 35 BAD UNOB- SERVED SERVED SERVED32 GOOD UNOB- 13.1 7 GOOD UNOB- 22.1 5 GOOD UNOB- SERVED SERVED SERVED33 GOOD UNOB- 13.2 33 GOOD UNOB- 22.1 34 GOOD UNOB- SERVED SERVED SERVED34 GOOD UNOB- 13.4 35 GOOD UNOB- 22.3 35 GOOD UNOB- SERVED SERVED SERVED35 GOOD UNOB- 13.6 22 GOOD UNOB- 22.4 36 GOOD UNOB- SERVED SERVED SERVED36 BAD UNOB- 13.8 36 BAD OB- 22.5 34 BAD OB- SERVED SERVED SERVED37 GOOD UNOB- 13.4 30 GOOD UNOB- 22.2 23 GOOD UNOB- SERVED SERVED SERVED38 GOOD UNOB- 13.5 34 GOOD UNOB- 22.3 30 GOOD UNOB- SERVED SERVED SERVED39 GOOD UNOB- 13.7 37 GOOD UNOB- 22.3 33 GOOD UNOB- SERVED SERVED SERVED40 BAD UNOB- 13.7 35 BAD OB- 22.3 31 BAD OB- SERVED SERVED SERVED41 GOOD UNOB- 13.1 27 GOOD UNOB- 22.1 30 GOOD UNOB- SERVED SERVED SERVED42 GOOD UNOB- 13.3 28 GOOD UNOB- 22.2 34 GOOD UNOB- SERVED SERVED SERVED43 GOOD UNOB- 13.4 38 GOOD UNOB- 22.3 38 GOOD UNOB- SERVED SERVED SERVED44 GOOD UNOB- 13.2 36 GOOD UNOB- 22.1 35 GOOD UNOB- SERVED SERVED SERVED45 GOOD UNOB- 13.6 35 GOOD UNOB- 22.4 33 GOOD UNOB- SERVED SERVED SERVED46 BAD UNOB- 13.6 37 BAD UNOB- 22.4 35 BAD UNOB- SERVED SERVED SERVED47 GOOD UNOB- 13.1 14 GOOD UNOB- 22.1 10 GOOD UNOB- SERVED SERVED SERVED48 GOOD UNOB- 13.0 27 GOOD UNOB- 22.0 33 GOOD UNOB- SERVED SERVED SERVED49 GOOD UNOB- 13.1 31 GOOD UNOB- 22.1 32 GOOD UNOB- SERVED SERVED SERVED50 BAD UNOB- 13.4 37 BAD UNOB- 22.3 32 BAD UNOB- SERVED SERVED SERVED51 GOOD UNOB- 13.6 36 GOOD UNOB- 22.4 35 GOOD UNOB- SERVED SERVED SERVED52 BAD UNOB- 13.5 33 BAD UNOB- 22.3 36 BAD UNOB- SERVED SERVED SERVED53 GOOD UNOB- 13.7 38 GOOD UNOB- 22.4 38 GOOD UNOB- SERVED SERVED SERVED54 BAD UNOB- 13.8 35 BAD OB- 22.5 38 BAD OB- SERVED SERVED SERVEDCOMPARISON C MODE RUPTURE (n = 40)55 256 2__________________________________________________________________________

As apparent from Table 2, it is appreciated that the number of times of C mode rupture in the pull test by using the samples according to the present invention is larger than that by using the samples in the comparisons departing from the composition range according to the present invention, and that the neck portion is stronger than the other portion of the base wire. Accordingly, it is understood that the above-mentioned composition range according to the present invention is optimum.

In a second preferred embodiment employing high purity Pd or Pd alloy as the base metal, various samples were prepared in the following manner. As the base metal were used high purity Pd having a purity of 99.95% Pd alloy containing the high purity Pd and 10 at % of Au, Pd alloy containing the high purity Pd and 5 atppm of Ag, Pd alloy containing the high purity Pd and 0.5 at % of Mo, and Pd alloy containing the high purity Pd and 6 at % of Cu. Then, at least one of Zn, Cd, Hg, P and S was added to the high purity Pd and the Pd alloys prepared above, and these mixtures were molten to be cast. The castings thus obtained were then subjected to a grooved roil, during which they were annealed. Then, they were subjected to wire drawing, thereby forming base wires each having a diameter of 30 .mu.m. Thereafter, further stress relieving was sufficiently conducted to finally obtain the samples.

The contents of the additional elements in the samples are shown in Table 3. In Table 3, Nos. 1-64 of the samples correspond to the preferred embodiment, and Nos. 55 and 56 of the samples correspond to comparisons departing from the composition range according to the present invention.

TABLE (3)______________________________________SAMPLE ADDITIONAL ELEMENT (at ppm)No. Zn Cd Hg P S______________________________________PREFERRED EMBODIMENT 1 20 2 25 3 50 4 500 5 5000 6 10000 7 11000 8 20 9 2510 5011 50012 500013 1000014 1100015 2016 2517 5018 50019 500020 1000021 1100022 323 524 5025 50026 60027 328 529 5030 50031 60032 10 1033 100 10034 1000 100035 5000 500036 6000 600037 10 10 1038 100 100 10039 1000 1000 100040 5000 5000 500041 2 342 5 543 50 5044 100 10045 250 25046 250 30047 10 248 10 10 249 10 2 250 10 250 25051 1000 1000 200 20052 1000 1000 10 200 20053 2000 2000 2000 50 5054 3000 3000 3000 50 50COMPARISON55 Au (99.99)56 Cu (99.9999)______________________________________

By using the above samples, a pull test was carried out given times (n=40), and measurements were carried out for a pull strength, number of times of rupture of the base wire rather than the neck portion, condition of workability, and existence of chip crack. The result of the measurements for the high purity Pd and each Pd alloy is shown in Table 4.

TABLE (4)__________________________________________________________________________Pd Pd + Au (10 at %) Pd + Ag (5 at %) C C C MODE MODE MODESAM- PULL RUP- WORK- PULL RUP- WORK- PULL RUP-PLE STRENGTH TURE ABIL- CHIP STRENGTH TURE ABIL- CHIP STRENGTH TURENO. (g) (n = 40) ITY CRACK (g) (n = 40) ITY CRACK (g) (n__________________________________________________________________________ = 40)PREFERRED EMBODIMENT 1 19.0 4 GOOD UNOB- 21.3 7 GOOD UNOB- 21.5 6 SERVED SERVED 2 19.0 22 GOOD UNOB- 21.3 25 GOOD UNOB- 21.5 22 SERVED SERVED 3 19.2 27 GOOD UNOB- 21.4 29 GOOD UNOB- 21.5 30 SERVED SERVED 4 19.7 35 GOOD UNOB- 21.5 32 GOOD UNOB- 21.6 33 SERVED SERVED 5 19.9 33 GOOD UNOB- 21.6 31 GOOD UNOB- 21.7 34 SERVED SERVED 6 20.1 35 GOOD UNOB- 21.7 34 GOOD UNOB- 21.7 34 SERVED SERVED 7 20.2 30 BAD UNOB- 21.7 35 BAD OB- 21.8 32 SERVED SERVED 8 19.0 5 GOOD UNOB- 21.3 7 GOOD UNOB- 21.5 6 SERVED SERVED 9 19.1 21 GOOD UNOB- 21.3 23 GOOD UNOB- 21.5 21 SERVED SERVED10 19.2 27 GOOD UNOB- 21.4 25 GOOD UNOB- 21.6 27 SERVED SERVED11 19.7 36 GOOD UNOB- 21.5 32 GOOD UNOB- 21.6 33 SERVED SERVED12 20.0 35 GOOD UNOB- 21.5 35 GOOD UNOB- 21.7 37 SERVED SERVED13 20.1 32 GOOD UNOB- 21.6 33 GOOD UNOB- 21.7 34 SERVED SERVED14 20.3 31 BAD UNOB- 21.6 35 BAD OB- 21.8 36 SERVED SERVED15 19.1 4 GOOD UNOB- 21.2 7 GOOD UNOB- 21.4 5 SERVED SERVED16 19.1 23 GOOD UNOB- 21.3 27 GOOD UNOB- 21.5 22 SERVED SERVED17 19.2 30 GOOD UNOB- 21.4 33 GOOD UNOB- 21.6 28 SERVED SERVED18 19.5 38 GOOD UNOB- 21.6 39 GOOD UNOB- 21.7 36 SERVED SERVED19 19.9 37 GOOD UNOB- 21.6 39 GOOD UNOB- 21.7 37 SERVED SERVED20 20.2 38 GOOD UNOB- 21.7 36 GOOD UNOB- 21.7 34 SERVED SERVED21 20.3 33 BAD UNOB- 21.7 35 BAD OB- 21.8 31 SERVED SERVED22 19.0 12 GOOD UNOB- 21.3 10 GOOD UNOB- 21.5 9 SERVED SERVED23 19.1 21 GOOD UNOB- 21.3 21 GOOD UNOB- 21.5 20 SERVED SERVED24 19.3 33 GOOD UNOB- 21.4 29 GOOD UNOB- 21.5 31 SERVED SERVED25 19.6 37 GOOD UNOB- 21.5 35 GOOD UNOB- 21.5 36 SERVED SERVED26 19.7 35 BAD UNOB- 21.6 35 BAD UNOB- 21.6 33 SERVED SERVED27 19.0 10 GOOD UNOB- 21.3 10 GOOD UNOB- 21.5 12 SERVED SERVED28 19.2 22 GOOD UNOB- 21.3 20 GOOD UNOB- 21.5 21 SERVED SERVED29 19.3 30 GOOD UNOB- 21.3 27 GOOD UNOB- 21.5 28 SERVED SERVED30 19.6 36 GOOD UNOB- 21.4 32 GOOD UNOB- 21.6 31 SERVED SERVED31 19.7 37 BAD UNOB- 21.5 36 BAD UNOB- 21.6 35 SERVED SERVED32 19.1 6 GOOD UNOB- 21.3 3 GOOD UNOB- 21.5 3 SERVED SERVED33 19.2 22 GOOD UNOB- 21.4 23 GOOD UNOB- 21.5 24 SERVED SERVED34 19.8 28 GOOD UNOB- 21.5 29 GOOD UNOB- 21.6 30 SERVED SERVED35 20.1 35 GOOD UNOB- 21.6 32 GOOD UNOB- 21.7 33 SERVED SERVED36 20.3 36 BAD UNOB- 21.6 34 BAD OB- 21.8 35 SERVED SERVED37 19.2 27 GOOD UNOB- 21.4 28 GOOD UNOB- 21.5 30 SERVED SERVED38 19.5 38 GOOD UNOB- 21.5 37 GOOD UNOB- 21.6 35 SERVED SERVED39 19.8 37 GOOD UNOB- 21.5 37 GOOD UNOB- 21.6 36 SERVED SERVED40 20.4 33 BAD UNOB- 21.6 36 BAD OB- 21.8 33 SERVED SERVED41 19.1 23 GOOD UNOB- 21.3 21 GOOD UNOB- 21.5 22 SERVED SERVED42 19.3 29 GOOD UNOB- 21.3 32 GOOD UNOB- 21.5 28 SERVED SERVED43 19.4 38 GOOD UNOB- 21.3 37 GOOD UNOB- 21.5 36 SERVED SERVED44 19.5 37 GOOD UNOB- 21.3 35 GOOD UNOB- 21.5 38 SERVED SERVED45 19.6 36 GOOD UNOB- 21.5 34 GOOD UNOB- 21.5 37 SERVED SERVED46 19.7 36 BAD UNOB- 21.5 35 BAD UNOB- 21.5 36 SERVED SERVED47 19.1 6 GOOD UNOB- 21.3 7 GOOD UNOB- 21.5 7 SERVED SERVED48 19.2 20 GOOD UNOB- 21.3 22 GOOD UNOB- 21.5 21 SERVED SERVED49 19.2 24 GOOD UNOB- 21.4 26 GOOD UNOB- 21.5 25 SERVED SERVED50 19.6 37 BAD UNOB- 21.5 37 BAD UNOB- 21.5 36 SERVED SERVED51 19.7 36 GOOD UNOB- 21.6 35 GOOD UNOB- 21.6 36 SERVED SERVED52 19.8 38 BAD UNOB- 21.6 37 BAD UNOB- 21.6 38 SERVED SERVED53 20.1 38 GOOD UNOB- 21.6 38 GOOD UNOB- 21.7 39 SERVED SERVED54 20.2 37 BAD UNOB- 21.7 38 BAD OB- 21.7 37 SERVED SERVEDCOMPARISONPULL STRENGTH (g)55 1256 21__________________________________________________________________________ Pd + Mo (0.5 at %) Pd + Cu (5 at %) C CAu + Be (10 at ppm) MODE MODESAM- WORK- PULL RUP- WORK- PULL RUP- WORK-PLE ABIL- CHIP STRENGTH TURE ABIL- CHIP STRENGTH TURE ABIL- CHIPNO. ITY CRACK (g) (n = 40) ITY CRACK (g) (n = 40) ITY CRACK__________________________________________________________________________PREFERRED EMBODIMENT 1 GOOD UNOB- 20.0 8 GOOD UNOB- 22.0 7 GOOD UNOB- SERVED SERVED SERVED 2 GOOD UNOB- 20.1 26 GOOD UNOB- 22.0 23 GOOD UNOB- SERVED SERVED SERVED 3 GOOD UNOB- 20.1 29 GOOD UNOB- 22.1 27 GOOD UNOB- SERVED SERVED SERVED 4 GOOD UNOB- 20.2 32 GOOD UNOB- 22.1 31 GOOD UNOB- SERVED SERVED SERVED 5 GOOD UNOB- 20.5 34 GOOD UNOB- 22.2 33 GOOD UNOB- SERVED SERVED SERVED 6 GOOD UNOB- 20.6 31 GOOD UNOB- 22.4 35 GOOD UNOB- SERVED SERVED SERVED 7 BAD OB- 20.7 31 BAD OB- 22.4 32 BAD OB- SERVED SERVED SERVED 8 GOOD UNOB- 20.0 8 GOOD UNOB- 22.0 4 GOOD UNOB- SERVED SERVED SERVED 9 GOOD UNOB- 20.0 25 GOOD UNOB- 22.1 23 GOOD UNOB- SERVED SERVED SERVED10 GOOD UNOB- 20.1 34 GOOD UNOB- 22.1 29 GOOD UNOB- SERVED SERVED SERVED11 GOOD UNOB- 20.2 37 GOOD UNOB- 22.2 29 GOOD UNOB- SERVED SERVED SERVED12 GOOD UNOB- 20.6 36 GOOD UNOB- 22.3 34 GOOD UNOB- SERVED SERVED SERVED13 GOOD UNOB- 20.6 33 GOOD UNOB- 22.4 33 GOOD UNOB- SERVED SERVED SERVED14 BAD OB- 20.7 32 BAD OB- 22.4 35 BAD OB- SERVED SERVED SERVED15 GOOD UNOB- 20.0 10 GOOD UNOB- 22.0 6 GOOD UNOB- SERVED SERVED SERVED16 GOOD UNOB- 20.0 26 GOOD UNOB- 22.1 22 GOOD UNOB- SERVED SERVED SERVED17 GOOD UNOB- 20.2 34 GOOD UNOB- 22.1 30 GOOD UNOB- SERVED SERVED SERVED18 GOOD UNOB- 20.3 37 GOOD UNOB- 22.2 38 GOOD UNOB- SERVED SERVED SERVED19 GOOD UNOB- 20.5 36 GOOD UNOB- 22.2 35 GOOD UNOB- SERVED SERVED SERVED20 GOOD UNOB- 20.6 33 GOOD UNOB- 22.4 34 GOOD UNOB- SERVED SERVED SERVED21 BAD OB- 20.7 35 BAD OB- 22.4 36 BAD OB- SERVED SERVED SERVED22 GOOD UNOB- 20.0 13 GOOD UNOB- 22.0 11 GOOD UNOB- SERVED SERVED SERVED23 GOOD UNOB- 20.1 24 GOOD UNOB- 22.0 23 GOOD UNOB- SERVED SERVED SERVED24 GOOD UNOB- 20.2 37 GOOD UNOB- 22.0 32 GOOD UNOB- SERVED SERVED SERVED25 GOOD UNOB- 20.4 38 GOOD UNOB- 22.1 35 GOOD UNOB- SERVED SERVED SERVED26 BAD UNOB- 20.4 36 BAD UNOB- 22.1 33 BAD UNOB- SERVED SERVED SERVED27 GOOD UNOB- 20.0 10 GOOD UNOB- 22.0 9 GOOD UNOB- SERVED SERVED SERVED28 GOOD UNOB- 20.0 22 GOOD UNOB- 22.0 21 GOOD UNOB- SERVED SERVED SERVED29 GOOD UNOB- 20.1 30 GOOD UNOB- 22.0 27 GOOD UNOB- SERVED SERVED SERVED30 GOOD UNOB- 20.3 36 GOOD UNOB- 22.1 32 GOOD UNOB- SERVED SERVED SERVED31 BAD UNOB- 20.4 38 BAD UNOB- 22.1 35 BAD UNOB- SERVED SERVED SERVED32 GOOD UNOB- 20.0 5 GOOD UNOB- 22.0 4 GOOD UNOB- SERVED SERVED SERVED33 GOOD UNOB- 20.1 25 GOOD UNOB- 22.0 22 GOOD UNOB- SERVED SERVED SERVED34 GOOD UNOB- 20.4 33 GOOD UNOB- 22.1 30 GOOD UNOB- SERVED SERVED SERVED35 GOOD UNOB- 20.6 37 GOOD UNOB- 22.4 35 GOOD UNOB- SERVED SERVED SERVED36 BAD OB- 20.7 35 BAD OB- 22.4 33 BAD OB- SERVED SERVED SERVED37 GOOD UNOB- 20.1 31 GOOD UNOB- 22.1 32 GOOD UNOB- SERVED SERVED SERVED38 GOOD UNOB- 20.1 39 GOOD UNOB- 22.1 38 GOOD UNOB- SERVED SERVED SERVED39 GOOD UNOB- 20.3 38 GOOD UNOB- 22.1 37 GOOD UNOB- SERVED SERVED SERVED40 BAD OB- 20.7 38 BAD OB- 22.4 35 BAD OB- SERVED SERVED SERVED41 GOOD UNOB- 20.1 25 GOOD UNOB- 22.0 24 GOOD UNOB- SERVED SERVED SERVED42 GOOD UNOB- 20.0 33 GOOD UNOB- 22.0 30 GOOD UNOB- SERVED SERVED SERVED43 GOOD UNOB- 20.2 38 GOOD UNOB- 22.0 35 GOOD UNOB- SERVED SERVED SERVED44 GOOD UNOB- 20.2 38 GOOD UNOB- 22.0 36 GOOD UNOB- SERVED SERVED SERVED45 GOOD UNOB- 20.4 37 GOOD UNOB- 22.1 37 GOOD UNOB- SERVED SERVED SERVED46 BAD UNOB- 20.3 37 BAD UNOB- 22.1 37 BAD UNOB- SERVED SERVED SERVED47 GOOD UNOB- 20.1 9 GOOD UNOB- 22.0 6 GOOD UNOB- SERVED SERVED SERVED48 GOOD UNOB- 20.1 24 GOOD UNOB- 22.0 23 GOOD UNOB- SERVED SERVED SERVED49 GOOD UNOB- 20.1 28 GOOD UNOB- 22.0 27 GOOD UNOB- SERVED SERVED SERVED50 BAD UNOB- 20.3 38 BAD UNOB- 22.1 37 BAD UNOB- SERVED SERVED SERVED51 GOOD UNOB- 20.4 37 GOOD UNOB- 22.1 37 GOOD UNOB- SERVED SERVED SERVED52 BAD UNOB- 20.4 38 BAD UNOB- 22.1 38 BAD UNOB- SERVED SERVED SERVED53 GOOD UNOB- 20.5 39 GOOD UNOB- 22.2 38 GOOD UNOB- SERVED SERVED SERVED54 BAD OB- 20.6 39 BAD OB- 22.3 39 BAD OB- SERVED SERVED SERVEDCOMPARISONC MODE RUPTURE (n = 40)55 256 2__________________________________________________________________________

As apparent from Table 4, it is appreciated that the number of times of C mode rupture in the pull test by using the samples according to the present invention is larger than that by using the samples in the comparisons departing from the composition range according to the present invention, and that the neck portion is stronger than the other portion of the base wire. Accordingly, it is understood that the above-mentioned composition range according to the present invention is optimum.

In summary, the present invention has the following advantage.

(1) The bonding wire according to the first aspect of the present invention contains high purity Au or Au alloy as a base metal and 25-10000 atppm of low boiling point element I having a boiling point lower than a melting point of the base metal and soluble in Au, or contains high purity Au or Au alloy as a base metal and 5-500 atppm of low boiling point element II having a boiling point lower than a melting point of the base metal and insoluble in Au, or contains high purity Au or Au alloy as a base metal and 5-10000 atppm of a mixture of low boiling point element I having a boiling point lower than a melting point of the base metal and soluble in Au and low boiling point element II having a boiling point lower than the melting point of the base metal and insoluble in Au under the condition of (content of the low boiling point element I)/25+(content of the low boiling point element II)/5.gtoreq.1.gtoreq.(content of the low boiling point element I)/10000+(content of the low boiling point element II)/500. Further, the bonding wire according to the second aspect of the present invention contains high purity Pd or Pd alloy as a base metal and 25-10000 atppm of low boiling point element III having a boiling point lower than a melting point of the base metal and soluble in Pd, or contains high purity Pd or Pd alloy as a base metal and 5-500 atppm of low boiling point element IV having a boiling point lower than a melting point of the base metal and insoluble in Pd, or contains high purity Pd or Pd alloy as a base metal and 5-10000 atppm of a mixture of low boiling point element III having a boiling point lower than a melting point of the base metal and soluble in Pd and low boiling point element IV having a boiling point lower than the melting point of the base metal and insoluble in Pd under the condition of (content of the low boiling point element III)/25+(content of the low boiling point element IV)/5.gtoreq.1.gtoreq.(content of the low boiling point element III)/10000 +(content of the low boiling point element IV)/500. With this constitution, the low boiling point element in the ball is vaporized and scattered upon formation of the ball to thereby prevent gas absorption peculiar to metal and obtain a ball satisfactory for bonding. On the other hand, the low boiling point element in the neck portion cannot be vaporized from the surface thereof, but it tends to be vaporized in the neck portion to generate a stress. Accordingly, a rupture strength of the neck portion after bonding is improved as compared with that of the base wire generating no stress. Accordingly, the strength of the neck portion can be made equal to or more than that of the base wire.

In comparison with the prior art wherein the strength of the neck portion becomes smaller than that of the base wire because of influence of heat upon formation of the ball, the bonding wire of the present invention does not generate a rupture of the neck portion, wire falling or wire sagging during the bonding work. Furthermore, in the temperature cycle life test of products, a stress generated by a repeated temperature change is dispensed to be absorbed in the whole of the base wire. Accordingly, the rupture of the neck portion where the rupture of the bonding wire is most frequently generated can be extremely reduced to thereby improve reliability.

(2) Since the rupture of the neck portion is hard to occur, the bonding wire can be greatly reduced in diameter to thereby enable reduction in bonding pitch and realize high-density mounting of LSI.

Claims

1. A bonding wire for a semiconductor device, said bonding wire consisting essentially of:

high purity Au or Au alloy as a base metal; and

25-10000 atppm of low boiling point element I, said low boiling point element I having a boiling point lower than a melting point of the base metal, being soluble in Au, wherein said element I includes at least one member selected from the group consisting of Zn, Cd and Hg.

2. The bonding wire according to claim 1, wherein said Au alloy contains high purity Au and at least one element selected from the group consisting of Pd, Ag, Pt, Rh, Os, Ru, Be, Ca, Ge, Y, La, Mg, Zr, Ga, In, Mo, Re, Cu and Fe.

3. A bonding wire for a semiconductor device, said bonding wire consisting essentially of:

high purity Au or Au alloy as a base metal; and

5-500 atppm of low boiling point element II, said low boiling point element II having a boiling point lower than a melting point of the base metal, being insoluble in Au, wherein said element II includes at least one member selected from the group consisting of P, S, Se, Rb and Cs.

4. The bonding wire according to claim 3, wherein said Au alloy contains high purity Au and at least one element selected from the group consisting of Pd, Ag, Pt, Rh, Os, Ru, Be, Ca, Ge, Y, La, Mg, Zr, Ga, In, Mo, Re, Cu and Fe.

5. A bonding wire for a semiconductor device, said bonding wire consisting essentially of:

high purity Au or Au alloy as a base metal;

5-10000 atppm of low boiling point element I, said low boiling point element I having a boiling point lower than a melting point of the base metal, being soluble in Au, wherein said element I includes at least one member selected from the group consisting of Zn, Cd and Hg; and

low boiling point element II, said low boiling point element II having a boiling point lower than a melting point of the base metal, being insoluble in Au, comprising at least one member selected from the group consisting of P, S, Se, Rb and Cs, and being present in an concentration so that (content of said low boiling point element I)/25+(content of said low boiling element II)/5.gtoreq.1.gtoreq.(content of said low boiling element I)/10000+(content of said low boiling element II)/500.

6. The bonding wire according to claim 5, wherein said Au alloy contains high purity Au and at least one element selected from the group consisting of Pd, Ag, Pt, Rh, Os, Ru, Be, Ca, Ge, Y, La, Mg, Zr, Ga, In, Mo, Re, Cu and Fe.