JP2013048225A - Copper elemental wire for bonding wire, and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper elemental wire for bonding wire having a low hardness and a high elongation, and further having excellent workability, and to provide a manufacturing method of the copper elemental wire for bonding wire.SOLUTION: The copper elemental wire is used to form a bonding wire having a wire diameter of 180 μm or less. The elemental wire has a diameter between 0.15 mm and 3.0 mm inclusive, and has a composition such that at least one additive element selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Zr, Ti, and rare earth elements is included in a range between 0.0001 mass% and 0.01 mass% inclusive in total, and the balance consists of copper and inevitable impurities. The special grain boundary ratio (Lσ/L), which is a ratio of the length Lσ of a special grain boundary to the length L of all of crystal grain boundaries measured by EBSD method, is 50% or larger.

Description

  The present invention relates to a copper wire for bonding wire used when producing a bonding wire having a wire diameter of 180 μm or less, and a method for producing a copper wire for bonding wire.

  Generally, in a semiconductor device mounted with a semiconductor element, the semiconductor element and the lead are connected by the above-described bonding wire. Conventionally, as a bonding wire, Au wire is mainly used from the viewpoints of drawability and conductivity. However, since Au is expensive, a bonding wire made of Cu is provided as a bonding wire that substitutes for this Au wire.

Here, since Cu is harder than Au, the ball formed at the wire tip during bonding may destroy, for example, an Al wiring film formed on the surface of the Si semiconductor element. Moreover, since Cu has a lower elongation than Au, there is a problem that an appropriate wire loop shape cannot be maintained.
Thus, for example, Patent Documents 1 and 2 propose a Cu bonding wire using ultra-high purity copper (6NCu) having a purity of 99.9999% by mass or more. Patent Document 3 proposes a Cu bonding wire to which a small amount of Ti, Zr, Hf, V, Cr and B is added.

Japanese Patent Laid-Open No. 62-111455 Japanese Patent Laid-Open No. 04-247630 Japanese Examined Patent Publication No. 04-016232

By the way, as described in Patent Documents 1 and 2, when using ultra-high purity copper (6NCu) having a purity of 99.9999% by mass or more, refining treatment is performed to obtain ultra-high purity copper (6NCu). Since a process is required, there is a problem that the manufacturing cost is greatly increased.
Further, the bonding wire described in Patent Document 3 is still harder than Au and has a low elongation, and therefore has insufficient characteristics as a substitute for Au wire.
Furthermore, in recent years, the bonding wire made of Cu wire is required to be thinned, and the copper wire for bonding wire is also required to have workability without disconnection.

  The present invention has been made in view of the above-described circumstances, and has a low hardness, a high elongation, and a process for producing a copper wire for a bonding wire that is excellent in workability. The purpose is to provide.

  In order to solve the above problems, the copper wire for bonding wire of the present invention is a copper wire for forming a bonding wire having a wire diameter of 180 μm or less, and the wire diameter is 0.15 mm or more and 3.0 mm. 1 or more additive elements selected from Mg, Ca, Sr, Ba, Ra, Zr, Ti, and rare earth elements are contained in the range of 0.0001 mass% or more and 0.01 mass% or less in total. And the balance is a special grain boundary ratio (Lσ / L) which is a ratio of the length Lσ of the special grain boundary to the length L of all the grain boundaries measured by the EBSD method. L) is 50% or more.

In the copper wire for bonding wire having this configuration, 0.0001% by mass or more of one or more additive elements selected from Mg, Ca, Sr, Ba, Ra, Zr, Ti, and rare earth elements in total. Since it is contained in the range of 01% by mass or less and the balance is copper and inevitable impurities, S contained in copper reacts with the above-described elements to form a compound. Thereby, the influence of S becomes small, the recrystallization temperature can be lowered, and the hardness can be lowered.
Moreover, since the special grain boundary ratio (Lσ / L), which is the ratio of the special grain boundary length Lσ to the total grain boundary length L measured by the EBSD method, is 50% or more, the hardness is reduced. It is possible to improve elongation and workability while maintaining.

Note that the special grain boundary ratio (Lσ / L) in the present invention is determined by specifying the grain boundaries and special grain boundaries with an EBSD measuring apparatus using a field emission scanning electron microscope, and the length L of all crystal grain boundaries. And the length Lσ of the special grain boundary is obtained.
A crystal grain boundary is defined as a boundary between crystals when the orientation difference between two adjacent crystals is 15 ° or more as a result of two-dimensional cross-sectional observation.
The special grain boundary corresponds to a crystallographically defined Σ value based on CSL theory (Kronberg et al: Trans. Met. Soc. AIME, 185, 501 (1949)) satisfying 3 ≦ Σ ≦ 29. The grain boundary and the inherent corresponding site lattice orientation defect Dq at the corresponding grain boundary is Dq ≦ 15 ° / Σ ^1/2 (DG Brandon: Acta. Metallurgica. Vol. 14, p. 1479, (1966)).

Here, the total content of the additive elements is preferably 0.0003 mass% or more and 0.002 mass% or less.
In this case, the recrystallization temperature can be surely kept low, and the hardness can be lowered.

The contents of Fe, Pb, and S, which are inevitable impurities, are preferably Fe; 0.0001% by mass or less, Pb; 0.0001% by mass or less, and S; 0.005% by mass or less. .
By defining the impurity content as described above, the recrystallization temperature can be surely kept low, and the hardness can be lowered.

The number of acid-insoluble residue having a particle size of 30 μm or more obtained by heating and dissolving 100 g of the copper wire for bonding wire in a nitric acid solution is preferably 1000 or less.
In this case, since the particle size of the acid-insoluble residue present inside the copper wire for bonding wire is small and the number is small, the occurrence of wire breakage during wire drawing when manufacturing a bonding wire is suppressed. It becomes possible to do.

The amount of the acid-insoluble residue obtained by heating and dissolving the copper wire for bonding wire in a nitric acid solution is preferably 0.00015% by mass or less.
In this case, the presence ratio of the acid-insoluble residue present inside the copper wire for bonding wire is reduced, and it is possible to suppress the occurrence of disconnection during wire drawing when manufacturing the bonding wire.

  The method for producing a copper wire for bonding wire according to the present invention is a method for producing the above-described copper wire for bonding wire, wherein the copper raw material having a purity of 99.99 mass% or more and 99.998 mass% or less is coated with Mg, Ca, One or more additive elements selected from Sr, Ba, Ra, Zr, Ti, and rare earth elements are added to produce a molten copper, and the molten copper is used as a belt-wheel continuous casting machine. A continuous casting step for supplying and continuously producing the ingot; and a continuous rolling step for continuously rolling the produced ingot at a condition of an initial temperature of 800 ° C. or more. Yes.

According to the method for manufacturing a copper wire for bonding wire having this structure, since a so-called 4NCu copper raw material having a purity of 99.99 mass% or more and 99.998 mass% or less is used, the bonding wire is compared with the case of using 6NCu. The manufacturing cost of the copper element wire can be greatly reduced.
Furthermore, since the produced ingot is continuously rolled at an initial temperature of 800 ° C. or higher, the special grain boundary ratio (Lσ / L) in the copper wire for bonding wire is 50%. This can be done.

  Moreover, the manufacturing method of the copper strand for bonding wires of this invention is a manufacturing method of the above-mentioned copper strand for bonding wires, Comprising: Mg is added to the copper raw material of purity 99.99 mass% or more and 99.998 mass% or less. One or more additive elements selected from Ca, Sr, Ba, Ra, Zr, Ti, and rare earth elements are added, and a molten copper production process for producing a molten copper, and casting the molten copper into a mold A casting process for producing a lump, an extrusion process for producing an extruded wire by extruding the obtained ingot at an initial temperature of 800 ° C. or more, and a rolling process for the obtained extruded wire. Alternatively, a processing / annealing process in which any one of the wire drawing processes and annealing is repeatedly performed, and a light reduction process in which rolling is performed at a reduction ratio of 5% to 25% to obtain a final wire diameter of 0.15 mm to 3.0 mm. It is characterized by having.

According to the method for manufacturing a copper wire for bonding wire having this structure, since a so-called 4NCu copper raw material having a purity of 99.99 mass% or more and 99.998 mass% or less is used, the bonding wire is compared with the case of using 6NCu. The manufacturing cost of the copper element wire can be greatly reduced.
Furthermore, the final wire diameter is 0.15 mm or more and 3.0 mm or less by rolling at a reduction ratio of 5% or more and 25% or less by repeatedly performing a rolling process or a drawing process and annealing on the extruded wire. The special grain boundary ratio (Lσ / L) in the copper wire for bonding wire can be 50% or more.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the copper strand for bonding wires which has low hardness, is high elongation, and was excellent in workability, and the copper strand for bonding wires can be provided.

It is explanatory drawing of the continuous casting rolling apparatus used when manufacturing the copper strand for bonding wires which is one Embodiment of this invention. It is a flowchart of the manufacturing method of the copper strand for bonding wires which is one Embodiment of this invention. It is a flowchart of the manufacturing method of the copper strand for bonding wires which is other embodiment of this invention. It is a graph which shows the evaluation result of the acid insoluble residue in the example 1 of this invention.

  Below, the manufacturing method of the copper strand for bonding wires which concerns on one Embodiment of this invention, and the copper strand for bonding wires is demonstrated.

The copper wire for bonding wire according to the present embodiment is used as a material for manufacturing wire bonding with a wire diameter of 180 μm or less, more preferably with a wire diameter of 20 μm or more and 180 μm or less.
Moreover, the copper wire for bonding wires according to the present embodiment has a wire diameter of 0.15 mm or more and 3.0 mm or less.

This copper wire for bonding wire has a total of at least one selected from Mg, Ca, Sr, Ba, Ra, Zr, Ti, and rare earth elements in a range of 0.0001 mass% to 0.01 mass%. And the balance is copper and inevitable impurities. Preferably, the total content of at least one selected from Mg, Ca, Sr, Ba, Ra, Zr, Ti, and rare earth elements is 0.0003 mass% or more and 0.002 mass% or less.
The contents of Fe, Pb, and S, which are inevitable impurities, are Fe; 0.0001% by mass or less, Pb; 0.0001% by mass or less, S; 0.005% by mass or less.
Here, the rare earth elements are Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

This copper wire for bonding wire has a special grain boundary ratio (Lσ / L) of 50% or more. Here, the special grain boundary ratio is a ratio of the length Lσ of the special grain boundary to the length L of all the crystal grain boundaries. A grain boundary and a special grain boundary are specified by an EBSD measuring apparatus using a field emission scanning electron microscope, and the length L of all the grain boundaries and the length Lσ of the special grain boundary are calculated. From this calculated length, the special grain boundary ratio is obtained. That is, the copper wire for bonding wire according to the present embodiment has more special grain boundaries than ordinary crystal grain boundaries.
A crystal grain boundary is defined as a boundary between crystals when the orientation difference between two adjacent crystals is 15 ° or more as a result of two-dimensional cross-sectional observation.
The special grain boundary corresponds to a crystallographically defined Σ value based on CSL theory (Kronberg et al: Trans. Met. Soc. AIME, 185, 501 (1949)) satisfying 3 ≦ Σ ≦ 29. The grain boundary and the inherent corresponding site lattice orientation defect Dq at the corresponding grain boundary is Dq ≦ 15 ° / Σ ^1/2 (DG Brandon: Acta. Metallurgica. Vol. 14, p. 1479, (1966)).

Further, the number of acid-insoluble residue having a particle diameter of 30 μm or more obtained by heating and dissolving 100 g of the copper wire for bonding wire according to the present embodiment in a nitric acid solution is 1000 or less. Furthermore, the abundance ratio of the acid-insoluble residue is 0.00015% by mass or less.
The acid-insoluble residue is evaluated according to the following procedure.
First, a predetermined amount (100 g) of a sample is sampled from the bonding wire copper wire whose surface has been cleaned, and is heated and dissolved in a heated nitric acid solution. The solution is cooled to room temperature and then filtered through a filter to collect the residue.
The filter which collected the residue is weighed, and the residue mass of the residue is measured. And the ratio (mass%) of the quantity (residue mass) of the residue with respect to the quantity of a sample (copper strand for bonding wires) is calculated. As described above, the amount (existence ratio) of the acid-insoluble residue obtained by heating and dissolving the copper wire for bonding wire in the nitric acid solution is measured.
Subsequently, the filter which collected the residue is observed with a scanning electron microscope, and an SEM photograph is taken. Image analysis is performed on the SEM photograph, and the size and number of residues are measured. The number of residues having a particle size of 30 μm or more is determined. As described above, the number of acid-insoluble residue having a particle diameter of 30 μm or more obtained by heating and dissolving 100 g of copper wire for bonding wire in a nitric acid solution is measured.

Next, the manufacturing method of the copper wire for bonding wires which is this embodiment is demonstrated.
The copper wire for bonding wire in which the ratio (Lσ / L) of the total special grain boundary length Lσ of the special grain boundary to the total grain boundary length L of the crystal grain boundary is 50% or more is a continuous casting and rolling method or casting. Manufactured by mass extrusion process.

In the present embodiment, an example using the continuous casting and rolling apparatus 10 shown in FIG. 1 will be described.
A continuous casting and rolling apparatus 10 shown in FIG. 1 includes a melting furnace 11, a holding furnace 12, a casting rod 13, a belt / wheel type continuous casting machine 30, a continuous rolling apparatus 15, and a coiler 18. .

  In this embodiment, a shaft furnace having a cylindrical furnace body is used as the melting furnace 11. A plurality of burners (not shown) are arranged in the circumferential direction at the lower part of the furnace body, and are arranged in multiple stages in the vertical direction. And the electrolytic copper which is a raw material is inserted from the upper part of a furnace main body, an electrolytic copper is melt | dissolved by the combustion of the said burner, and a molten copper is made continuously.

  The holding furnace 12 is for temporarily storing the pure copper molten metal produced in the melting furnace 11 while holding it at a predetermined temperature and sending a certain amount of molten copper to the casting iron 13.

  The cast iron 13 is for transferring the molten copper sent from the holding furnace 12 to the tundish 20 disposed above the belt-wheel continuous casting machine 30. The casting rod 13 is sealed with an inert gas such as Ar or a reducing gas, for example. The cast iron 13 is provided with a stirring means (not shown) for stirring the molten copper with an inert gas.

The tundish 20 is provided with element addition means 21 for adding elements to the transferred molten copper. Further, a pouring nozzle 22 is disposed on the end side of the tundish 20 in the flow direction of the molten copper, and the molten copper in the tundish 20 is passed to the belt-wheel type continuous casting machine 30 via the pouring nozzle 22. Supplied.
The belt-wheel type continuous casting machine 30 includes a cast wheel 31 having a groove formed on the outer peripheral surface, and an endless belt 32 that is circulated so as to be in contact with a part of the outer peripheral surface of the cast wheel 31. The molten copper supplied through the pouring nozzle 22 is poured into the space formed between the groove and the endless belt 32 and cooled to continuously cast the bar-shaped ingot 40. .

  The belt / wheel continuous casting machine 30 is connected to the continuous rolling device 15. The continuous rolling device 15 continuously rolls the bar-shaped ingot 40 produced from the belt-wheel continuous casting machine 30 to produce a copper roughing wire 50 having a predetermined outer diameter. The copper roughing wire 50 produced from the continuous rolling device 15 is wound around the coiler 18 via the cleaning / cooling device 16 and the flaw detector 17.

Next, the manufacturing method of the copper wire for bonding wires using this belt-wheel type continuous casting machine 30 configured will be described with reference to FIGS.
First, a copper raw material (so-called 4NCu) having a purity of 99.99 mass% or more and 99.998 mass% or less is charged into the melting furnace 11 and melted to obtain a molten copper (melting step S01). In this melting step S01, the air-fuel ratio of the plurality of burners of the shaft furnace is adjusted to make the inside of the melting furnace 11 a reducing atmosphere.

The molten copper obtained by the melting furnace 11 is transferred to the tundish 20 through the holding furnace 12 and the casting rod 13.
Here, the molten copper passing through the cast iron 13 sealed with an inert gas or a reducing gas is stirred by the aforementioned stirring means, thereby promoting the reaction between the molten copper and the inert gas or the reducing gas. Is done.

  Next, one or more elements selected from Mg, Ca, Sr, Ba, Ra, Zr, Ti, and rare earth elements are continuously added to the molten copper in the tundish 20 by the element addition means 21. (Element addition step S02). Accordingly, the total content of one or more elements selected from Mg, Ca, Sr, Ba, Ra, Zr, Ti, and rare earth elements is 0.0001% by mass to 0.01% by mass, and more preferably. Produces a molten copper adjusted to 0.0003 mass% or more and 0.002 mass% or less.

  The molten copper whose components have been adjusted in this way is supplied to the belt-wheel continuous casting machine 30 via the pouring nozzle 22, and the bar-shaped ingot 40 is continuously produced (continuous casting step S03). Here, in the continuous casting step S03, since the space formed between the groove formed in the casting wheel 31 and the endless belt 32 has a trapezoidal shape, the bar-shaped ingot 40 having a substantially trapezoidal cross section. Will be produced.

  The rod-shaped ingot 40 is supplied to the continuous rolling device 15 and subjected to roll rolling, and a copper roughing wire 50 having a predetermined outer diameter (in this embodiment, a diameter of 8 mm) is produced (continuous rolling step S04). In this continuous rolling step S04, rolling is performed in the range of 400 to 900 ° C. In the present embodiment, the initial rolling temperature is set to 800 ° C. or higher.

  The copper roughing wire 50 produced from the continuous rolling device 15 is wound around the coiler 18 via the cleaning / cooling device 16 and the flaw detector 17. The cleaning / cooling device 16 cleans and cools the surface of the copper rough wire 50 produced from the continuous rolling device 15 with a cleaning agent such as alcohol. The flaw detector 17 detects a flaw on the copper roughing wire 50 sent from the cleaning / cooling device 16.

Next, wire drawing is performed on the obtained copper roughing wire 50 to obtain a final wire diameter of 0.15 mm to 3.0 mm (diameter 0.9 mm in this embodiment) (drawing step S05). .
Then, after the wire drawing step S05 described above, a recrystallization heat treatment is performed at 150 ° C. or more and 250 ° C. or less (finish heat treatment step S06). In this embodiment, atmospheric heat treatment is performed at 220 ° C. for 2 hours.
By the procedure as described above, the copper wire for bonding wire according to the present embodiment is produced.

  The copper wire for bonding wire according to the present embodiment is further drawn into a thin wire having a diameter of 180 μm or less and used as a bonding wire.

  According to the bonding wire copper wire of the present embodiment configured as described above, one or more additive elements selected from Mg, Ca, Sr, Ba, Ra, Zr, Ti, and rare earth elements are added. It contains in the range of 0.0001 mass% or more and 0.01 mass% or less in total, and the remainder has a composition which is copper and an unavoidable impurity. More preferably, the total content of the additive elements is 0.0003 mass% or more and 0.002 mass% or less. For this reason, S contained in copper forms a compound with the above-mentioned additive element. Therefore, since the influence of S becomes small, the recrystallization temperature can be lowered and the hardness can be lowered.

  Further, the special grain boundary ratio (Lσ / L) of the copper wire for bonding wire according to the present embodiment is set to 50% or more. Note that the grain boundaries and special grain boundaries are specified by an EBSD measuring apparatus using a field emission scanning electron microscope, and the length L of all crystal grain boundaries and the length Lσ of special grain boundaries are calculated. And the special grain boundary ratio is obtained from this calculated length. When this special grain boundary ratio is high, the consistency of crystal grain boundaries in the entire structure is improved, and dislocations are difficult to accumulate. Therefore, it is possible to improve the elongation and workability while maintaining the hardness low.

Further, the number of acid-insoluble residue having a particle diameter of 30 μm or more obtained by heating and dissolving 100 g of the copper wire for bonding wire according to the present embodiment in a nitric acid solution is 1000 or less. Furthermore, the amount (abundance ratio) of the acid-insoluble residue is 0.00015% by mass or less.
Thus, since the particle size of the acid-insoluble residue is small and the number is reduced, and the existence ratio is also suppressed, the copper wire for bonding wire is drawn to the bonding wire. It becomes possible to suppress disconnection at the time of processing.

Moreover, according to the manufacturing method of the copper wire for bonding wires which is this embodiment, since the so-called 4NCu copper raw material having a purity of 99.99 mass% or more and 99.998 mass% or less is used, compared with the case of using 6NCu. Thus, the manufacturing cost of the copper wire for bonding wire can be greatly reduced.
Furthermore, the continuous casting step S03 for continuously producing the bar-shaped ingot 40 using the belt-wheel type continuous casting machine 30, and the produced bar-shaped ingot 40 continuously under the condition of the initial temperature of 800 ° C. or more. And a continuous rolling step S04 for rolling, the special grain boundary ratio (Lσ / L) of the produced copper wire for bonding wire can be 50% or more.

As mentioned above, although embodiment of this invention was described, this invention is not limited to this, It can change suitably in the range which does not deviate from the technical idea of the invention.
In this embodiment, although demonstrated as what manufactures the copper wire for bonding wires using a belt wheel continuous casting machine, it is not limited to this.

For example, as shown in FIG. 3, a special grain boundary is obtained by performing a molten copper production step S11, a casting step S12, a hot extrusion step S13, a processing / annealing step S14, and a light reduction step S15. A copper wire for bonding wire having a ratio (Lσ / L) of 50% or more may be produced.
In the copper melt generation step S11, a copper raw material (so-called 4NCu) having a purity of 99.99 mass% or more and 99.998 mass% or less is selected from Mg, Ca, Sr, Ba, Ra, Zr, Ti, and rare earth elements. One or more additional elements are added to obtain a molten copper.
In the casting step S12, molten copper is poured into a mold to obtain an ingot having a diameter of 200 mm to 400 mm.
In hot extrusion process S13, an ingot is extruded at the temperature of 800 degreeC or more, and an extrusion strand is obtained.
In the processing / annealing step S14, either the rolling process or the wire drawing process and the annealing process are repeatedly performed on the extruded element wire. Annealing is performed every time the cross-section reduction rate reaches 80% or more.
In the light reduction step S15, rolling is performed at a reduction rate of 5% or more and 25% or less, so that the final wire diameter is 0.15 mm or more and 3.0 mm or less.

Below, the result of the evaluation test evaluated about the copper strand for bonding wires which is this embodiment mentioned above is demonstrated.
The copper wire for bonding wires of Examples 1 to 5 and Comparative Examples 1 and 2 was produced by the method shown in the flowchart of FIG. Specifically, the additive elements listed in Table 1 were added to 4NCu to obtain a molten copper. The molten copper was poured into a belt-wheel continuous casting machine and continuously cast and rolled. Further, wire drawing and finish heat treatment were performed, and a copper wire for bonding wire having a diameter of 0.9 mm was produced.
By the method shown in the flowchart of FIG. 3, copper wires for bonding wires of Invention Examples 6 to 10 and Comparative Examples 3 and 4 were produced. Specifically, the additive elements listed in Table 1 were added to 4NCu to obtain a molten copper. An ingot having a diameter of 240 mm was produced using molten copper. The ingot was hot extruded at 800 ° C. to produce an extruded wire having a diameter of 8 mm. The extruded strand was repeatedly rolled and annealed to produce a copper strand having a wire diameter of 1 mm. Thereafter, the copper strand was rolled at a rolling rate of 10%. Next, a final heat treatment was performed at 220 ° C. to produce a copper wire for bonding wire having a diameter of 0.9 mm.
A conventional copper wire for bonding wire was produced by the following method. First, 0.0030 mass% Zr was added to 4NCu to obtain a molten copper. An ingot having a diameter of 240 mm was produced using molten copper. The ingot was hot extruded at 800 ° C. to produce an extruded wire having a diameter of 8 mm. The drawn wire was drawn. Next, a final heat treatment was performed at 220 ° C. to produce a copper wire for bonding wire having a diameter of 0.9 mm.
Further, the obtained copper wires for bonding wires of Invention Examples 1 to 10, Comparative Examples 1 to 4, and Conventional Example were drawn to produce a bonding wire having a diameter of 180 μm.

(Special grain boundary ratio)
The special grain boundary ratio (Lσ / L) was measured by the following method for the obtained inventive copper inventive wires 1 to 10, comparative examples 1 to 4, and conventional copper wires for bonding wires.
Each sample was mechanically polished using water-resistant abrasive paper and diamond abrasive grains. Next, finish polishing was performed using a colloidal silica solution.
Then, by using an EBSB measuring apparatus (HITACHI S4300-SEM, EDAX / TSL OIM Data Collection) and analysis software (EDAX / TSL OIM Data Analysis ver. 5.2), grain boundaries and special grain boundaries. And the length L of all crystal grain boundaries and the length Lσ of special grain boundaries were calculated. This analyzed the average crystal grain size and the special grain boundary length ratio. Details of the measurement method are shown below.
First, using a scanning electron microscope, each measurement point within the measurement range on the sample surface was irradiated with an electron beam, and the sample surface was scanned in two dimensions. By orientation analysis by backscattered electron beam diffraction, the crystal grain boundary was defined between the measurement points where the orientation difference between adjacent measurement points was 15 ° or more.
The total grain boundary length (length of all crystal grain boundaries) L of the grain boundaries in the measurement range was measured. Further, the position of the crystal grain boundary where the interface between adjacent crystal grains is a special grain boundary was determined, and the total grain boundary length (length of all special grain boundaries) Lσ of the special grain boundary was measured. Then, the ratio Lσ / L of the length Lσ of the special grain boundary to the total grain boundary length L of the crystal grain boundary measured above was determined and used as the special grain boundary ratio (Lσ / L).

(Hardness test)
Next, the hardness of the obtained copper wires for bonding wires of Examples 1 to 10 of the present invention, comparative examples 1 to 4 and conventional examples, and bonding wires produced from the copper wires for bonding wires were measured. It was measured.
In addition, the hardness test was implemented based on JISZ2241 using the micro Vickers tester MVK-700 made from AKASHI.

(Elongation)
Next, with respect to the obtained copper wires for bonding wires of the present invention examples 1 to 10, comparative examples 1 to 4 and conventional examples, and bonding wires produced from these copper wires for bonding wires, AKASHI made A tensile test was carried out using an Amsler type vertical tensile tester, and the elongation was evaluated.

(Processability)
The obtained copper wires for bonding wires of the present invention examples 1 to 10, comparative examples 1 to 4, and the conventional example were further drawn to produce a wire having a diameter of 87 μm, 50 μm, or 20 μm. . The number of wire breaks during wire drawing was evaluated.

  Table 1 shows the evaluation results of the special grain boundary ratio (Lσ / L), hardness, and elongation of the bonding wire, the hardness and elongation of the bonding wire, and the number of wire breaks during wire drawing.

In Invention Examples 1 to 10, it is confirmed that the special grain boundary ratio (Lσ / L) is 50% or more. On the other hand, in Comparative Examples 1 to 4 and the conventional example, the special grain boundary ratio (Lσ / L) was less than 50%. When the inventive examples 6 to 10 are compared with the conventional examples, the special grain boundary ratio (Lσ) is obtained by performing the processing at a rolling rate of 10% before performing the finish heat treatment on the strand having the final wire diameter. It is confirmed that it is possible to increase / L).
In the inventive examples 1 to 10 in which the special grain boundary ratio (Lσ / L) is 50% or more, it is confirmed that the hardness is as low as 40 Hv in the wire bonding state with a wire diameter of 180 μm.
Moreover, in the inventive examples 1 to 10, it is confirmed that the wire breakage during wire drawing is suppressed as compared with the comparative example, and the wire can be drawn to a small diameter.

Next, the residue amount and the particle size distribution of the acid-insoluble residue were evaluated using the copper wires for bonding wires from Invention Example 1 to Invention Example 10.
The sample was etched with nitric acid to remove impurities adhering to the surface. A 100 g sample was then weighed. This sample was dissolved by heating in a nitric acid solution. The heating temperature was 60 ° C. This operation was repeated.
Then it was cooled to room temperature and filtered through a filter to collect the residue.
Here, it filtered using the polycarbonate filter (pore diameter 0.4 micrometer). The residue mass of the residue was measured for the polycarbonate filter which collected this residue using the electronic balance in the clean room.

  Moreover, the particle size distribution of the acid-insoluble residue was measured. The filter which collected the above-mentioned residue was observed with the scanning electron microscope, and the SEM image was image | photographed. The image was taken into a personal computer, and the image was analyzed for binarization using image analysis software (WinRoof software). Then, the projected area of the residue was measured, and the diameter (circle equivalent diameter) of a circle having the same area as this projected area was calculated. This equivalent circle diameter was used as the particle size of the residue. Further, the number of residues was measured. A graph of particle size distribution was created from the data calculated using Example 1 of the present invention. The result is shown in FIG.

  As a result of WinRoof software image analysis, when 100 g of the inventive samples 1 to 10 (copper wire for bonding wire) were heated and dissolved in a nitric acid solution, the number of acid-insoluble residue having a particle size of 30 μm or more was 1000 It was confirmed that it was less than the number. Moreover, as a result of measuring the residue mass of the residue by the above-mentioned method, the mass ratio of the acid-insoluble residue in the samples of Invention Examples 1 to 10 was confirmed to be 0.00015% by mass or less. .

30 belt-wheel type continuous casting machine

Claims (7)

A copper wire for forming a bonding wire having a wire diameter of 180 μm or less,
The wire diameter is 0.15 mm or more and 3.0 mm or less,
Contains one or more additive elements selected from Mg, Ca, Sr, Ba, Ra, Zr, Ti, and rare earth elements in a total range of 0.0001 mass% to 0.01 mass%, with the balance being Having a composition that is copper and inevitable impurities;
A bonding wire having a special grain boundary ratio (Lσ / L), which is a ratio of the length Lσ of the special grain boundary to the length L of all the grain boundaries measured by the EBSD method, of 50% or more. Copper wire for use.   2. The copper wire for bonding wire according to claim 1, wherein the total content of the additive elements is 0.0003 mass% or more and 0.002 mass% or less.   The contents of Fe, Pb, and S, which are inevitable impurities, are Fe; 0.0001% by mass or less, Pb; 0.0001% by mass or less, and S; 0.005% by mass or less. The copper strand for bonding wires according to claim 1 or 2.   4. The number of acid-insoluble residue having a particle size of 30 [mu] m obtained by heating and dissolving 100 g of the copper wire for bonding wire in a nitric acid solution is 1000 or less. The copper wire for bonding wires according to one item.   The amount of the acid-insoluble residue obtained by heating and dissolving the copper wire for bonding wire in a nitric acid solution is 0.00015% by mass or less. Copper wire for bonding wire as described in 1. It is a manufacturing method of the copper wire for bonding wires according to any one of claims 1 to 5,
One or more additive elements selected from Mg, Ca, Sr, Ba, Ra, Zr, Ti, and rare earth elements are added to a copper raw material having a purity of 99.99 mass% or more and 99.998 mass% or less, and a molten copper A molten copper production process for producing
Supplying the copper melt to a belt-wheel type continuous casting machine and continuously producing an ingot; and
And a continuous rolling step of continuously rolling the produced ingot at an initial temperature of 800 ° C. or more. A method for producing a copper wire for bonding wire, comprising: It is a manufacturing method of the copper wire for bonding wires according to any one of claims 1 to 5,
One or more additive elements selected from Mg, Ca, Sr, Ba, Ra, Zr, Ti, and rare earth elements are added to a copper raw material having a purity of 99.99 mass% or more and 99.998 mass% or less, and a molten copper A molten copper production process for producing
A casting process in which the molten copper is poured into a mold to produce an ingot;
An extrusion process in which the obtained ingot is extruded under conditions of an initial temperature of 800 ° C. or more to produce an extruded wire;
For the obtained extruded wire, either a rolling process or a wire drawing process and an annealing process for repeatedly performing annealing, and
A light reduction step of rolling at a reduction rate of 5% to 25% to obtain a final wire diameter of 0.15 mm to 3.0 mm, and a method for producing a copper wire for bonding wires.

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