JPS60238079A - Production of ultrafine aluminum wire - Google Patents

Abstract

PURPOSE:To produce an ultrafine Al alloy wire having excellent tensile strength and ductility by subjecting the melt of an Al alloy to unidirectional solidification casting then to a heat treatment for homogenization and working plastically the casting to a wire rod having the final wire diameter without subjecting the casting to an annealing treatment in an intermediate stage. CONSTITUTION:The melt of Al or Al alloy is cast into an adiabatic casting mold and is cooled from a prescribed position, by which the melt is unidirectionally solidified. The wire bar consisting of the unidirectionally solidified columnar crystal is heated to the specific temp. meeting the compsn. of the Al or Al alloy and is thereby homogenized. Such wire bar is drawn by a wire drawing machine, continuous wire drawing machine and precision wire drawing machine, by which the bar is drawn to an extra-fine wire having 30mum diameter, etc. as a lead wire or bonding wire for electrical devices such as an acoustic device and semiconductor device. Since the wire is not subjected to the annealing treatment in the midway, the ultrafine Al alloy having excellent tensile strength and ductility is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing an ultra-fine wire made of aluminum or an aluminum alloy (hereinafter collectively referred to as an ultra-fine aluminum wire) for use mainly as a bonding wire for a semiconductor device.

Strain bonding wire is used to electrically connect semiconductors and external terminals, and usually has a diameter of 20 to 20 mm.
It is a very thin ultra-fine wire of about 30 μm. Gold wire has been used as a bonding wire due to its conductivity and corrosion resistance, but in recent years aluminum wire has been used because of its low cost in addition to the above-mentioned properties. The aluminum ultra-fine wire used for this purpose contains 0.5 to 2% S by weight.
An aluminum alloy containing t, an aluminum alloy containing 1 to 4% by weight of Cu, an aluminum alloy containing 0.5 to 2% by weight of Mg, or an aluminum alloy containing 0.5% to 2% by weight of Mg.
It is made of an alloy to which about 4% by weight of Mn, Crs Co, etc. can be added.

As described above, ultrafine aluminum wires having a diameter of about 20 to 30 μm have conventionally been generally manufactured in the following manner.

That is, a wire bar having a diameter of about 5 Qmm is cast from an aluminum alloy material and subjected to homogenization heat treatment. This wire bar is rolled to form a rough drawn wire, which is then wire drawn to form an ultra-fine aluminum wire of a predetermined wire diameter. At an intermediate stage, the wire is drawn while being appropriately annealed, thereby producing an ultrafine aluminum wire with a predetermined wire diameter.

By the way, when ultrafine aluminum wires are used as bonding wires, their tensile strength and ductility greatly affect the reliability and productivity of semiconductor devices. For example, if the tensile strength is too low, it will be easy to break during electrical connection work, and there will be a high risk of softening due to Joule heat generated when semiconductors are used and causing tab shorts.

If the ductility is too low, the bonding force will be low in electrical bonding using ultrasonic bonding technology, and high-speed wiring will be difficult. Therefore, it is required that the tensile strength and ductility be sufficiently large.

However, when manufacturing using the conventional method described above, increasing the degree of processing by wire drawing to increase the tensile strength of the wire leads to a significant decrease in ductility. It is necessary to perform appropriate annealing treatment at each stage. On the other hand, if this annealing treatment is performed, even if ductility can be increased, a decrease in tensile strength is unavoidable. That is, the annealing treatment has contradictory effects on the tensile strength and ductility required for the manufactured ultrafine aluminum wire. For this reason, it is difficult to obtain a product with excellent tensile strength using conventional technology, which requires intermediate annealing treatment to produce ultra-fine aluminum wire (although final annealing produces a product with a compromise in tensile strength due to the compromise with ductility). We had no choice but to be satisfied.This also posed a problem that needed to be solved in the production of even thinner ultra-fine wires.

OBJECTS OF THE INVENTION In view of the above, an object of the present invention is to provide a method for manufacturing an excellent aluminum ultrafine wire having high tensile strength and suitable for use as a bonding wire of a semiconductor device.

The manufacturing method according to the present invention involves unidirectionally solidifying and casting a molten aluminum alloy to form a cast body having a columnar crystal structure;
After the cast body is homogenized and heat treated, it is characterized in that it is processed into a wire rod of the final diameter without annealing at an intermediate stage.

To explain in more detail, first, as a raw material, a molten aluminum alloy produced by a conventional method is supplied to a heating mold or a mold using a heat insulating material such as graphite, and the molten metal is cooled from a desired position to produce a unidirectional Solidification is caused to obtain a cast body. The raw material, that is, the cast body cast by unidirectional solidification in this manner has a columnar crystal structure in which the crystals are aligned and oriented in one direction. The basic feature of the present invention is to use a material, ie, a cast body, made of this columnar crystal structure.

Ultra-fine wires are manufactured by homogenizing and heat-treating a material made of this columnar crystal structure, that is, a cast body, and then drawing it and plastically working it into a wire of the desired diameter. No intermediate annealing is performed between stages. The inventor is
By using a material consisting of a columnar crystal structure, it is possible to draw wires up to ultra-fine wires without intermediate annealing, and as a result, high-strength ultra-fine aluminum wires can be obtained. They have discovered that by appropriately final annealing, it is possible to obtain ultrafine aluminum wires with excellent tensile strength and ductility, as well as excellent curling properties.

The purpose of the homogenization heat treatment of the cast body is to eliminate the heterogeneity caused by intragranular segregation that occurs during casting. It was also observed that this homogenization heat treatment significantly reduced the gas content of the cast body. These effects, in conjunction with the use of a material with a columnar crystal structure, made it possible to draw the wire to the final wire diameter without any intermediate annealing.

The ultrafine aluminum wire produced in this manner can sufficiently satisfy the high tensile strength and ductility required when used as a bonding wire for electrically connecting a semiconductor chip and an external terminal, for example. Furthermore, it is possible to manufacture even more extremely fine wires, and it is also possible to provide thin wires with high strength for various purposes.

EXAMPLE Aluminum with a purity of 99.99% and silicon with a purity of 99.99% were unidirectionally solidified using a heated mold, thereby casting a wire bar with a diameter of 20 mm and a length of 2000 mm. Table 1 shows the chemical composition of this cast body.
Further, Table 2 shows the casting conditions and grain size, respectively.

Table 1 Table 2 The cast bodies were then heat treated under two different conditions for homogenization. Table 3 shows the conditions for the homogenization heat treatment.

In addition, the gas content was measured at the molten metal stage up to the above-mentioned homogenization heat treatment, at the stage after casting, and at the stage after the homogenization heat treatment. The measurement results are shown in Table 4.

As shown in Table 4, it was confirmed that the cast bodies were sufficiently degassed by any of the homogenization heat treatments.

The castings of Example (A) and Example (B), which were cast and homogenized in this way, were drawn to a diameter of 3 mm using a normal single-head wire drawing machine, and then they were drawn to a diameter of 3 mm using a continuous wire drawing machine. The wire was drawn to a diameter of 0.8 mm. Further, this was wire-drawn using a precision wire-drawing machine in which the slip rate of the die, the amount of lubricating oil, etc. were controlled, and finally an ultra-fine wire with a diameter of 30 μm was produced. The wire drawing speed in this final processing is 80mm
The wire drawing process was carried out very smoothly and successfully without any wire breakage.

Test pieces were cut out at each stage of the wire drawing process, and tensile strength and elongation were measured for each of 10 test pieces of the same diameter. A "universal tensile tester manufactured by Toyo Baldwin Co., Ltd." was used as the measuring device. The tensile test conditions were as follows: gauge distance was 50 mm, and tensile speed was Q mm/min. The measurement results are shown in Table 5.

Table 5 Here, the area reduction processing rate is a value calculated from the following formula, where d is the ultrafine wire diameter and D is the cast body diameter.

(1-(d/Dr)x 100 From the above results, according to the method of the present invention, at least 30
The wire drawing process can be carried out without any annealing process during the wire drawing process up to a wire diameter of approximately μm, the wire drawing process can be performed smoothly and well without wire breakage, and the manufactured aluminum It was confirmed that the ultrafine wire has high tensile strength and elongation, and is superior to that produced by conventional methods (tensile strength of about 30 kg/mm2).

In addition, in the wire drawing process from 0.07 mm to 0.03 mm, a decrease in tensile strength (also a decrease in elongation) was observed, but this is presumed to be due to a softening phenomenon during processing.

Moreover, although the above description has been made regarding the wire drawing process up to the final wire diameter, it goes without saying that the final annealing process can be performed appropriately thereafter. Such an annealing treatment makes it possible to obtain ultrafine wires with desired excellent properties. Furthermore, although the composition of the material was not mentioned in detail above, the method according to the present invention can be similarly applied to materials from which a proper columnar crystal structure can be obtained.

Production ■ Shirai ■ Wire drawing to the final wire diameter is achieved without intermediate annealing, improving productivity.

■ The ultra-fine wire obtained by drawing to the final wire diameter has extremely high strength.

■ Therefore, by appropriately final annealing,
It can be made into ultra-fine wire with excellent tensile strength, elongation, curling properties, etc.

■ This is a technology that will enable the production of even finer wires expected in the future.

1 Procedural amendment (voluntary) 2. Name of the invention Method for producing ultra-fine aluminum wire 3. Person making the amendment Relationship to the case Name of patent applicant (474) Nippon Light Metal Co., Ltd. 4. Agent Address: 164 5. Subject of amendment Full text of the specification 6, contents of amendments as per attached sheet 2 Specification 1, Title of the invention Method for manufacturing ultra-fine aluminum wire 2, Claims Aluminum or molten aluminum base metal is unidirectionally solidified and cast to have a columnar crystal structure. An ultra-fine aluminum wire with excellent tensile strength characterized by casting a cast body, subjecting the cast body to homogenization heat treatment, and then subjecting it to mulch processing to the final wire diameter without annealing at an intermediate stage. Production method.

3. Detailed description of the invention Technical field Various wires, ultra-fine wires made of aluminum or aluminum alloys (hereinafter collectively referred to as aluminum ultra-fine wires) for use as lead wires and bonding wires for electrical devices such as audio equipment and semiconductor devices. ).

BACKGROUND OF THE INVENTION Bonding wires used in semiconductor devices, for example, are used to electrically connect semiconductors and external terminals, and are usually very thin wires with a diameter of about 20 to 30 ttm. Gold wire has been used as a bonding wire due to its conductivity and corrosion resistance, but in recent years aluminum wire has been used because of its low cost in addition to the above-mentioned properties. The ultra-fine aluminum wire used for this purpose is an aluminum alloy containing 0.5 to 2% Si, an aluminum alloy containing 1 to 4% Cu, and 0.5 to 2% Mg. Aluminum alloys containing o, about 4% by weight of Mn,
It is made from an alloy containing added Cr, Co, etc.

As described above, ultrafine aluminum wires having a diameter of about 20 to 30 pm have been generally manufactured in the following manner.

That is, a wire par with a diameter of about 50 mm is cast from an aluminum alloy material and subjected to homogenization heat treatment. This wire bar is rolled to form a rough drawn wire, which is then wire drawn to form an ultra-fine aluminum wire of a predetermined wire diameter. At an intermediate stage of processing, the wire is drawn while being appropriately annealed, thereby producing ultra-fine aluminum wire with a predetermined wire diameter.

By the way, when ultrafine aluminum wires are used, for example, as bonding wires, their tensile strength and ductility greatly affect the reliability and productivity of semiconductor devices.

That is, if the tensile strength is too low, it will be easy to break during electrical connection work, and there will be a high risk of softening due to Joule heat generated when semiconductors are used and causing tab shorts.

If the ductility is too low, the bonding force will be low in electrical bonding using ultrasonic bonding technology, and high-speed wiring will be difficult. Therefore, it is required that the tensile strength and ductility be sufficiently large.

However, when manufacturing using the conventional method described above, increasing the degree of processing by wire drawing to increase the tensile strength of the wire leads to a significant decrease in ductility. It is necessary to perform appropriate annealing treatment at each stage. On the other hand, if this annealing treatment is performed, even if ductility can be increased, a decrease in tensile strength is unavoidable. That is, the annealing treatment has contradictory effects on the tensile strength and ductility required for the manufactured ultrafine aluminum wire. For this reason, it is difficult to obtain a product with excellent tensile strength using conventional technology, which requires intermediate annealing treatment to produce ultra-fine aluminum wire (although final annealing produces a product with a compromise in tensile strength due to the compromise with ductility). This posed a problem that needed to be solved in manufacturing ultrafine wires with high tensile strength.

Purpose of the Invention In view of the above, the purpose of the present invention is to provide an excellent ultra-fine aluminum wire with high tensile strength and suitable for use in various wires, lead wires and bonding wires of electrical devices such as audio equipment and semiconductor devices. An object of the present invention is to provide a manufacturing method.

The manufacturing method according to the present invention involves unidirectional solidification casting of aluminum or molten aluminum alloy to cast a cast body having a columnar crystal structure, homogenization heat treatment of the cast body, and then annealing treatment at an intermediate stage. It is characterized by plastic working to the final diameter of the wire rod without any additional processing.

To explain in more detail, first, as a raw material, aluminum or aluminum alloy molten metal produced by a conventional method is supplied to a heating mold or a mold using a heat insulating material such as graphite, and the molten metal is cooled from a required position. A cast body is obtained by causing directional solidification. The raw material, that is, the cast body cast by unidirectional solidification in this manner has a columnar crystal structure in which the crystals are aligned and oriented in one direction. The basic feature of the present invention is to use a material, ie, a cast body, made of this columnar crystal structure.

Ultra-fine wires are manufactured by homogenizing and heat-treating a material made of this columnar crystal structure, that is, a cast body, and then drawing it and plastically working it into a wire of the desired diameter. No intermediate annealing is performed between stages. The inventor is
By using a material consisting of columnar crystal U-weave, it is possible to draw up to ultra-fine wire without intermediate annealing, and this results in high-strength ultra-fine aluminum wire, and this can be done depending on the application. By appropriately final annealing, an ultrafine aluminum wire with excellent tensile strength and ductility can be obtained.Furthermore, the ultrafine wire produced in this way has excellent curling properties when used as a bonding wire for semiconductor devices. I discovered that.

The purpose of the homogenization heat treatment of the cast body is to eliminate the heterogeneity caused by intragranular segregation that occurs during casting. It was also observed that this homogenization heat treatment significantly reduced the gas content of the cast body. These effects, in conjunction with the use of a material with a columnar crystal structure, made it possible to draw the wire to the final wire diameter without any intermediate annealing.

The ultra-fine aluminum wire manufactured in this way has excellent tensile strength, so it has sufficient tensile strength and ductility required when used, for example, as a bonding wire to electrically connect a semiconductor chip and an external terminal. In addition, it can be used as various wires and wires for electrical equipment such as audio equipment, improving workability and reliability of the equipment. It also makes it possible to manufacture ultra-fine wires that are thinner than ever before, and to provide thin wires with high strength for a variety of purposes.

99% purity, 99% aluminum and 99°99 purity
% silicon and unidirectionally solidified using a heated mold, thereby casting a wire bar with a diameter of 20 mm and a length of 2000 mm. Table 1 shows the chemical composition of this cast body, and Table 2 shows the casting conditions and grain size.

Table 1 This casting was then heat treated under two different conditions for homogenization. Table 3 shows the conditions for the homogenization heat treatment.

Table 3 Gas contents were also measured at the molten metal stage up to the homogenization heat treatment mentioned above, at the stage after casting, and at the stage after the homogenization heat treatment. The measurement results are shown in Table 4.

As shown in Table 4, it was confirmed that the cast bodies were sufficiently degassed by any of the homogenization heat treatments.

The castings of Example (A) and Example (B), which were cast and homogenized in this way, were drawn to a diameter of 3 mm using a normal single-head wire drawing machine, and then they were drawn to a diameter of 3 mm using a continuous wire drawing machine. The wire was drawn to a diameter of 0.8 mm. Further, this was wire-drawn using a precision wire-drawing machine in which the die slip rate and lubricating oil were controlled, and finally an ultra-fine wire with a diameter of 30 μm was produced. The wire drawing speed in this final processing is 80mm
It was Z minutes, and we were able to carry out extremely smooth and good wire drawing without any wire breakage.

Test pieces were cut out at each stage of the wire drawing process, and tensile strength and elongation were measured for each of 10 test pieces of the same diameter. A "universal tensile tester manufactured by Toyo Baldwin Co., Ltd." was used as the measuring device. The tensile test conditions were a gage distance of 50 mm and a tensile speed of 10 mm/min. The measurement results are shown in Table 5.

Here, in Table 5, the area reduction processing rate and the ultra-fine wire diameter are d
, is a value calculated from the following equation, where D is the diameter of the cast body.

(1-(d/D)21X 100 From the above results, according to the method of the present invention, the amount of
It is possible to draw wires up to a wire diameter of approximately μm without any annealing during the wire drawing process, and that this wire drawing process can be carried out smoothly and in good condition without causing wire breakage. It was confirmed that the produced ultra-fine aluminum wire had high tensile strength and elongation, and was superior to that produced by conventional methods (tensile strength of about 30 kg/mm2).

In addition, in the wire drawing process from 0.07 mm to 0.03 mm, a decrease in tensile strength (also a decrease in elongation) was observed, but this is presumed to be due to a softening phenomenon during processing.

Moreover, although the above description has been made regarding the wire drawing process up to the final wire diameter, it goes without saying that the final annealing process can be performed appropriately thereafter. Such an annealing treatment makes it possible to obtain ultrafine wires with desired excellent properties. Although the composition of the material was not mentioned in detail above, the method according to the present invention can be similarly applied to materials that can obtain a proper columnar crystal structure. It goes without saying that the present invention can also be applied to the production of thin wires of various diameters, such as diameters of 0.1 mm and 1 mm.

Hikari Shokyadama ■ Wire drawing to the final wire diameter can be achieved without intermediate annealing, improving productivity.

■ The ultra-fine wire obtained by drawing to the final wire diameter has extremely high strength.

1. Therefore, by final annealing this wire to jmη:, it is possible to obtain an ultra-fine wire with excellent tensile strength, elongation, curling properties, etc.

■ This is a technology that will make it possible to manufacture ultra-fine wires in the future.

Claims (1)

[Claims] Molten aluminum alloy is unidirectionally solidified and cast to form a cast body with a columnar crystal structure, and after the cast body is homogenized and heat treated, it is plastically worked to the final wire diameter without annealing at an intermediate stage. A method for producing ultrafine aluminum wire, characterized by: