TW201306985A - Copper bonding wire - Google Patents

Abstract

The object of the present invention is to provide a copper bonding wire having high tensile strength, elongation, and small hardness. The method that solves the object of the present invention relates to a copper bonding wire, which is characterized by being formed of a soft low-concentration copper alloy material. The soft low-concentration copper alloy material comprises additive elements selected from the group consisting of Ti, Mg, Zr, Nb, Ca, V, Ni, Mn, and Cr; and the remainder being copper and inevitable impurities. The average size of crystal grains lying from a surface of the copper bonding wire at least to a depth of 20% of a wire diameter is not greater than 20 <mu>m.

Description

Brazing wire

The present invention relates to a novel brazing wire having high tensile strength, elongation, and low hardness.

Conventionally, an Au wire or an Al alloy wire is used for a bonding wire connecting an electrode of a semiconductor element and an external lead. In particular, in the resin element type semiconductor element, an Au line of about 0.025 mm is used from the viewpoint of connection reliability. Further, in recent years, as a welding wire for a power module for an automobile, an Al wire of about 0.3 mm is used.

The Au wire has excellent electrical conductivity, corrosion resistance, and softness, and on the other hand, the cost is very high. Therefore, a welding wire using copper (Cu) as a raw material has been proposed.

Patent Document 1 discloses a copper thin wire for welding which is highly purified to a purity of 99.999 mass% or more by electrolytic refining and zone melting.

Patent Document 2 discloses a brazing wire which is an oxygen-free copper having an unavoidable impurity of 10 ppm or less by repeated purification, and comprising a group selected from the group consisting of Ti, Zr, Hf, V, Cr, Mn, and B. The additive element in the group is composed of a copper alloy of copper, and after hot rolling and cold rolling, it is made to have a diameter of 25 μm by heat treatment at 200 to 300 ° C for 1 to 2 seconds.

Patent Document 3 discloses a brazing wire having an Hv of 41.1 to 49.5, which is an oxygen-free copper having an unavoidable impurity of 10 ppm or less by repeated purification, and comprising a material selected from the group consisting of Mg, Ca, Be, Ge, and Si. The added elements in the group and the remainder are made of a copper alloy of copper. After hot rolling and cold rolling, the surface is made to have a diameter of 25 μm by heat treatment at 200 to 300 ° C for 1 to 2 seconds.

Patent Literatures 4 to 7 show that oxygen-free copper having an unavoidable impurity of 5 ppm or less or 10 ppm or less by repeated purification is composed of an additive element selected from the group consisting of S, Se, Te, and Ag and the rest. In the case of hot rolling and cold rolling, Patent Document 4 uses a surface heat treatment of 250 to 350 ° C for 0.5 to 1.5 seconds to produce a copper wire having a diameter of 25 μm. Patent Document 5 uses 300 to 300. A copper wire having a diameter of 25 μm is produced by heat treatment at 400 ° C for 1 to 2 seconds, and a copper wire having a diameter of 25 μm is produced by heat treatment at 300 to 400 ° C for 1 to 2 seconds in Patent Document 6. In Document 7, a copper wire having a diameter of 25 μm was produced by heat treatment at 250 to 380 ° C for 1.5 seconds.

In the case of a copper core material having a purity of 99.99% by mass or more and less than 99.999% by mass, the copper core material having a purity of 99.99% by mass or more and less than 99.999% by mass is coated with 99.999% by mass or more of copper as a whole. .

Prior art literature

Patent Document 1: Japanese Laid-Open Patent Publication No. 60-244054

Patent Document 2: Japanese Laid-Open Patent Publication No. 61-259558

Patent Document 3: Japanese Laid-Open Patent Publication No. 61-258463

Patent Document 4: Japanese Laid-Open Patent Publication No. 62-22469

Patent Document 5: Japanese Laid-Open Patent Publication No. 61-224443

Patent Document 6: Japanese Patent Laid-Open No. 62-2645

Patent Document 7: Japanese Laid-Open Patent Publication No. 62-94969

Patent Document 8: Japanese Laid-Open Patent Publication No. SHO 63-236338

In Patent Document 1, a welding wire made of OFC (oxygen-free copper) having a purity of 99.99% by mass is made of Cu which is harder than Au. Therefore, if this welding wire is used, for example, it is provided on a semiconductor element (for example, a tantalum wafer). The aluminum pad welding as an electrode pad causes damage to the aluminum pad.

In order to reduce the damage to the aluminum pad, if excessive heat is applied to the aluminum pad to further soften the OFC (oxygen-free copper), since the hardness of the bonding wire is in a relationship with the elongation and tensile strength of the bonding wire, Although the hardness of the weld line is reduced, at the same time, the elongation of the weld line is lowered, and in addition, as the crystal structure (size) of the weld line is coarsened, the tensile strength is also lowered.

That is, if the elongation of the weld line is lowered, the deformability of the weld line itself is lowered, so that it is possible to damage the weld line and the welded object due to the stress generated by the difference in thermal expansion between the weld line and the sealing resin material after the resin sealing after wire bonding. There is a possibility of connection reliability when the connection is reliable, and it is possible to cause curling behavior such as wire curling when the wire is fed from the spool to the welded portion, and the operation characteristics are lowered.

On the other hand, when the tensile strength of the weld line is lowered, in the case of welding, the weld line of the upper portion (the ball neck portion) of the molten ball formed at the time of welding may be reduced in strength and may be broken. Further, if the tensile strength of the weld line is lowered, it is possible to cause the weld line to be broken due to the difference in thermal expansion between the above-described weld line and the sealing resin material when repeatedly subjected to the temperature loop. which is, The fatigue characteristics as a weld line are lowered.

In order to solve such a problem, in Patent Documents 2 and 3, a trace amount (1 to 10 ppm) of an additive element is added to high-purity copper of 99.999 mass% or more, and in Patent Documents 4 to 7, by 99.999 mass% The above-mentioned high-purity copper is added with a small amount (a few ppm) of an additive element to adjust the balance between the elongation of the weld line, the tensile strength, and the hardness of the raw material of the weld line, but the conductor raw material is pulled. The conductor itself after the wire processing and the annealing treatment has a small hardness, and it is impossible to realize a copper conductor which maintains soft characteristics and has high elongation characteristics and tensile strength, and there is still room for improvement.

Further, in Patent Document 8, as in Patent Document 1, a welding wire composed of OFC having a purity of 99.99% by mass is welded to an aluminum pad as an electrode pad provided on a semiconductor element, and the aluminum pad is bonded to the aluminum pad. To destroy.

SUMMARY OF THE INVENTION An object of the present invention is to provide a brazing wire which is low in cost compared with oxygen-free copper and which has high electrical conductivity, tensile strength and elongation, and which is low in hardness.

The present invention relates to a copper bonding wire characterized by being a copper bonding wire composed of a soft low-concentration copper alloy material, and the soft low-concentration copper alloy material (diluted copper alloy material) is selected from the group consisting of Ti, Mg, An additive element in a group consisting of Zr, Nb, Ca, V, Ni, Mn, and Cr, and the balance being copper, and the crystal structure of the brazing wire is from the surface to the inside to a depth of 20% of the wire diameter. The average grain size is 20 μm or less.

Further, the brazing wire of the present invention preferably contains 2 mass ppm or more and 12 mass ppm or less of sulfur, more than 2 mass ppm and 30 mass ppm or less of oxygen, and 4 mass ppm or more and 55 mass ppm or less of titanium.

Further, the brazing wire of the present invention preferably has the same hardness as or less than the oxygen-free copper wire subjected to the annealing treatment, and the average value of the elongation values has an elongation of 1% or more higher than that of the oxygen-free copper wire. value.

Further, it is preferable to have the tensile strength equal to or higher than that of the oxygen-free copper wire subjected to the annealing treatment described above, and the value of the hardness has a value lower than the oxygen-free copper wire by 2 Hv or more.

In addition, the brazing wire of the present invention preferably has an electrical conductivity of 98% IACS or more, and the sulfur (S) and titanium (Ti) comprise TiO, TiO ₂ , TiS or a compound having Ti-OS bonding, or TiO, TiO _{2 .} , TiS or agglomerates of compounds having Ti-OS bonds, the remaining portions of Ti and S may comprise solid solutions.

Further, it is preferred that the compound or aggregate in the form of TiO, TiO ₂ , TiS, or Ti-OS is distributed in the crystal grains, the TiO has a size of 200 nm or less, the TiO ₂ has a size of 1000 nm or less, and the TiS has a size of 200 nm or less. The compound or aggregate in the form of Ti-OS has a size of 300 nm or less, and particles of 500 nm or less are 90% or more.

The brazing wire of the present invention can be produced by a manufacturing method including the following process: comprising a group selected from the group consisting of Ti, Mg, Zr, Nb, Ca, V, Ni, Mn, and Cr a molten metal manufacturing process in which a soft low-concentration copper alloy material with an additive element is formed at a molten copper temperature of 1100 ° C or more and 1320 ° C or less; a wire rod manufacturing process for producing a wire rod from the above molten metal; at 880 ° C The hot rolling process of performing hot rolling on the wire rod at a temperature of 550 ° C or higher; and a wire drawing process for performing wire drawing on the wire rod subjected to the hot rolling process.

In the method for producing a brazing wire according to the present invention, it is preferable that the additive element is Ti of 4 ppm by mass or more and 55 ppm by mass or less, and the soft low-concentration copper alloy material contains 2 ppm by mass or more and 12 ppm by mass or less of sulfur, and more than 2 The mass is ppm and is 30 ppm by mass or less of oxygen.

In the method for producing a brazing wire according to the present invention, it is preferable that the softening temperature of the soft low-concentration copper alloy material is 130 ° C or more and 148 ° C or less in a size of 2.6 2.6 mm.

(Composition of brazing wire) (1) About adding elements

The present invention relates to a soft low-concentration copper alloy material comprising an additive element selected from the group consisting of Ti, Mg, Zr, Nb, Ca, V, Ni, Mn, and Cr, and the balance being copper and unavoidable impurities. A wire bonding process is performed, followed by annealing to form a copper bonding wire.

As an additive element, the reason for selecting an element selected from the group consisting of Ti, Mg, Zr, Nb, Ca, V, Ni, Mn, and Cr is that these elements are active elements that are easily combined with other elements, particularly Since it is easy to combine with S, it is possible to trap S, and it is possible to increase the purity of the copper base material of the substrate and to lower the hardness of the raw material. Further, by trapping S, it is also possible to obtain an effect that high conductivity can be achieved. The additive element contains one type or two or more types. Further, the alloy may contain other elements and impurities which do not adversely affect the properties of the alloy.

(2) About composition ratio

As an additive element, the total content of one or more of Ti, Ca, V, Ni, Mn, and Cr is 4 to 55 ppm by mass, more preferably 10 to 20 ppm by mass, and Mg is 2 to 30. The amount of ppm is more preferably 5 to 10 ppm by mass, and the content of Zr and Nb is 8 to 100 ppm by mass, more preferably 20 to 40 ppm by mass.

Further, in the preferred embodiment to be described later, the oxygen content is more than 2 ppm by mass and is preferably 30 ppm by mass or less, more preferably 5 to 15 ppm by mass, depending on the amount of the added element and the content of S, The range of properties of the alloy may be more than 2 ppm by mass and 400 ppm by mass or less.

The content of S is 2 to 12 ppm by mass, more preferably 3 to 8 ppm by mass.

The brazing wire of the present invention is, for example, higher in thermal conductivity than aluminum from the viewpoint of miniaturization of a power module used in an automobile or the like and/or an increase in current density of a current supplied to the power module. The copper of the material is composed as a main component.

For example, the brazing wire of the present invention is used as a conductivity of 98% IACS (International Anneld Copper Standard, and a specific resistance of 1.7241×10 ^-8 Ωm is 100%). Preferably, it is a soft low-concentration copper alloy material of a soft copper material of 100% IACS or more, more preferably 102% IACS or more.

In the case of obtaining a soft copper material having a conductivity of 98% IACS or more, pure copper containing unavoidable impurities as a base material is used as a base material, and 3 to 12 ppm by mass of sulfur is used, and more than 2 ppm by mass is used. A soft low-concentration copper alloy material of 30 ppm by mass or less and 4 to 55 ppm by mass of titanium is used to produce a wire rod (wire blank) from the soft low-concentration copper alloy material.

When a soft copper material having an electric conductivity of 100% IACS or more is obtained, a pure copper containing an unavoidable impurity as a base material is used as a base material, and 2 to 12 ppm by mass of sulfur is used, and more than 2 ppm by mass is used. Further, it is a soft low-concentration copper alloy material of 30 mass ppm or less of oxygen and 4 to 37 mass ppm of titanium.

In addition, when a soft copper material having a conductivity of 102% IACS or more is obtained, pure copper containing unavoidable impurities as a base material is used as a base material, and sulfur containing 3 to 12 ppm by mass and more than 2 ppm by mass are used. It is a soft low-concentration copper alloy material of 30 mass ppm or less of oxygen and 4 to 25 mass ppm of titanium.

In general, in industrial production of pure copper, sulfur enters copper when electrolytic copper is produced, so that it is difficult to make sulfur 3 mass ppm or less. The upper limit of the sulfur concentration of the general electrolytic copper is 12 mass ppm.

Since the brazing wire of the present invention preferably contains more than 2 ppm by mass and 30 ppm by mass or less of oxygen, in this embodiment, so-called low-oxygen copper (LOC) is targeted.

When the oxygen concentration is less than 2 ppm by mass, since the hardness of the brazing wire is not easily lowered, the oxygen concentration is controlled to an amount exceeding 2 ppm by mass. Further, in the case where the oxygen concentration is higher than 30 ppm by mass, since the damage tends to occur on the surface of the brazing wire during the hot rolling pass, the oxygen concentration is controlled to 30 ppm by mass or less.

(3) About the crystal structure of the brazing wire

In the brazing wire of the present invention, the average crystal grain size of the crystal structure from the surface of the brazing wire to at least the inside of the brazing wire to a depth of 20% of the wire diameter is 20 μm or less. Preferably, the surface layer has an average grain size of 5 to 15 μm and an internal average grain size of 50 to 100 μm.

This is because the presence of fine crystal grains having an average crystal grain size of 20 μm or less on the surface layer can be expected to improve the tensile strength and elongation of the material. The reason for this is considered to be a local strain introduced into the vicinity of the grain boundary due to the tensile deformation, and the crystal grain size is reduced to a fine degree to promote the relaxation of the grain boundary stress concentration. Therefore, the grain boundary stress concentration is lowered to suppress the grain boundary fracture.

Further, in the present invention, the effect of the present invention having an average crystal grain size of 20 μm or less from the inside of the brazing wire to the depth of the wire bonding wire of at least 20% of the wire diameter is not excluded. The depth of 20% of the wire diameter and the region closer to the center of the wire have a fine crystal layer.

(4) About dispersed substances

It is preferable that the dispersed particles dispersed in the brazing wire have a small size, and further, it is preferred that the dispersed particles are largely dispersed in the brazing wire. The reason for this is that the dispersed particles have a function as a precipitation site of sulfur, and as a precipitation site, a small size and a large number are required.

Specifically, the sulfur contained in the brazing wire, particularly titanium as an additive element, contains TiO, TiO ₂ , TiS or a compound having Ti-OS bonding, or has TiO, TiO ₂ , TiS or has a Ti-OS bond. The agglomerates of the compounds, the remaining portions of Ti and S may comprise solid solutions. In addition, the other additive elements are also the same as titanium.

The formation of the dispersed particles and the precipitation of sulfur in the dispersed particles increase the purity of the matrix of the copper base material and promote the reduction of the hardness of the material.

(5) About the hardness, elongation and tensile strength of brazing wire

The material for the brazing wire of the present invention is required to have excellent balance between hardness, elongation, and tensile strength. The reason for this is that if the ball formed at the tip of the wire or the wire is hard, the Al wiring film as a solder pad or the Si semiconductor wafer under it is broken. In addition, the reason is, such as When the tensile strength and elongation of the fruit thread itself are small, it is difficult to maintain an appropriate loop, or it is prone to breakage during welding.

In general, since the hardness (softness) and the elongation (height) and the tensile strength (the height) are in a long-term relationship, it is preferable to have these characteristics in balance.

Further, the brazing wire of the present invention has the same hardness as or less than the oxygen-free copper wire subjected to the annealing treatment, and the average value of the elongation values has a value higher than the oxygen-free copper wire by 1% or more. The term "hardness" as used herein refers to the Vickers hardness of the material.

Further, the brazing wire of the present invention has the same or higher tensile strength as the oxygen-free copper wire subjected to the annealing treatment, and the value of the hardness has a value lower than the oxygen-free copper wire by 2 Hv or more.

(Manufacturing method of brazing wire)

The method for producing the brazing wire of the present invention is as follows. As an example, a case where Ti is added to an additive element will be described.

First, a soft low-concentration copper alloy material containing Ti as a raw material of a brazing wire is prepared (raw material preparation process). Next, the soft low-concentration copper alloy material is melted at a molten copper temperature of 1100 ° C or more and 1320 ° C or less (melt manufacturing process). Next, a wire rod (a wire rod manufacturing process) is produced from the melt. Next, hot rolling (hot rolling) is performed on the wire rod at a temperature of 880 ° C or lower and 550 ° C or higher. Then, the wire rod subjected to the hot rolling process is subjected to wire drawing processing and heat treatment (wire drawing processing, heat treatment process). As the heat treatment method, mobile annealing using a tubular furnace, electric conduction annealing using resistance heating, or the like can be applied. In addition, it is also possible to perform batch annealing. The brazing wire of the present invention is produced by these processes.

Further, in the production of the brazing wire, it is preferable to contain 2 mass ppm or more and 12 mass ppm or less of sulfur, more than 2 mass ppm and 30 mass ppm or less of oxygen, and 4 mass ppm or more and 55 mass ppm or less of titanium. Concentration copper alloy material.

Therefore, the inventors studied the following two countermeasures in order to reduce the hardness of the brazing wire. Further, by using the following two measures in combination in the production of the copper wire rod, the brazing wire of the present invention is obtained.

First, the first countermeasure is to prepare a molten metal of a soft low-concentration copper alloy material in a state in which titanium (Ti) is added to Cu having an oxygen concentration of more than 2 ppm by mass. It is considered that TiS, titanium oxide (for example, TiO ₂ ) and Ti-OS particles are formed in the melt.

In the second measure, the temperature in the hot rolling pass is set to be higher than the usual copper production conditions for the purpose of facilitating the precipitation of sulfur (S) by introducing dislocations into the soft low-concentration copper alloy material. Temperature (ie, 950 ° C ~ 600 ° C) low temperature (880 ° C ~ 550 ° C). By such a temperature setting, S can be precipitated on dislocations or S is precipitated by using an oxide of titanium (for example, TiO ₂ ) as a crystal nucleus.

Since the sulfur contained in the soft low-concentration copper alloy material is crystallized and precipitated by the first countermeasure and the second countermeasure described above, it is possible to obtain a copper wire rod having better soft characteristics and better electrical conductivity after cold-rolling drawing.

The brazing wire of the present invention uses SCR continuous casting and rolling equipment, has less surface damage, has a wide manufacturing range, and can be stably produced. The wire rod is produced by SCR continuous casting and rolling, and the processing degree of the ingot bar is 90% (30 mm) to 99.8% (5 mm). As an example, a condition in which a wire rod of 8 mm is produced at a working degree of 99.3% is used.

The temperature of the molten copper in the melting furnace is preferably controlled to be 1100 ° C or more and 1320 ° C or less. If the temperature of the molten copper is high, the pores tend to increase, damage occurs, and the particle size increases, so the control is 1320 ° C or lower. Further, the reason why the control is 1100 ° C or more is that the molten copper tends to solidify when the temperature is lower than the temperature, and the production may be unstable, but the molten copper temperature is preferably as low as possible.

The temperature of the hot rolling process is preferably such that the temperature of the first rolling roll is controlled to 880 ° C or lower, and the temperature of the final rolling roll is controlled to 550 ° C or higher.

These casting conditions are different from the usual production conditions of pure copper, and the purpose thereof is to achieve a solid solution limit (solid solution limit, solid solution limit) as a driving force for crystallization of sulfur in molten copper and precipitation of sulfur in hot rolling. The solubility limit is smaller.

Further, the temperature in the usual hot rolling is 950 ° C or lower in the first rolling roll and 600 ° C or higher in the final rolling roll. However, in order to make the solid solution limit smaller, in the present embodiment, it is preferable to initially The rolling roll was set to 880 ° C or lower, and was set to 550 ° C or higher in the final rolling roll.

Further, the reason why the temperature in the final rolling roll is set to 550 ° C or higher is that the damage of the obtained wire rod is increased at a temperature lower than 550 ° C, and the produced brazing wire cannot be handled as a product. The temperature at the time of hot rolling is preferably controlled to a temperature of 880 ° C or lower in the first rolling roll, and is controlled to a temperature of 550 ° C or more in the final rolling roll, and is as low as possible. By such temperature setting, the hardness of the base of the brazing wire can be made close to the hardness of high-purity copper (5N or more). As an effect of sulfur trapping, in addition to a decrease in softening temperature, the matrix is highly purified and the hardness is lowered.

It is preferred to melt the pure copper of the base material in a shaft furnace (shaft kiln) and then flow in the tank in a reduced state. That is, it is preferable to perform casting while controlling the sulfur concentration, the titanium concentration, and the oxygen concentration of the low-concentration alloy in a reducing gas (for example, CO gas) environment, and to stably manufacture the wire rod by subjecting the material to rolling processing. . In addition, the incorporation of copper oxide and/or particle size greater than a specified size results in a decrease in the quality of the fabricated braze wire.

As described above, a soft low-concentration copper alloy material having a good balance of elongation characteristics, breaking strength, and Vickers hardness can be obtained as a raw material of the brazing wire of the present invention.

Alternatively, a plating layer may be formed on the surface of the soft low-concentration copper alloy material. As the plating layer, a material containing a noble metal such as palladium, zinc, nickel, gold, platinum, silver or the like as a main component or a Pb-free plating layer can be used. Further, the shape of the soft low-concentration copper alloy material is not particularly limited, and it may be formed into a circular cross section, a rod shape, or a flat conductor shape.

Further, in the present embodiment, the wire rod is produced by the SCR continuous casting and rolling method, and the soft material is produced by hot rolling. However, a two-roll continuous casting rolling method or a Properzi-type continuous casting rolling method may be employed.

According to the present invention, since a specific additive element such as Ti is contained, the remainder contains copper, and the average grain size of the crystal structure from the surface up to a depth of 20% of the wire diameter is 20 μm or less, so that high tensile strength and elongation can be provided. It is a copper wire with a softness (small hardness).

Hereinafter, embodiments of the present invention will be described, but the following embodiments do not limit the invention according to the claims. Further, it should be noted that all combinations of the features described in the present embodiment are not necessarily required in the method for solving the problems of the present invention.

[Example 1] [Manufacture of soft low-concentration copper alloy material (2.6mm diameter)]

As a test material, a copper wire (wire bar, workability: 99.3%) having a concentration of 7 mass ppm to 8 mass ppm, a sulfur concentration of 5 mass ppm, and a titanium concentration of 13 mass ppm was prepared. ψ 8mm copper wire is produced by hot rolling processing by SCR continuous casting system (South Continuous Rod System). Regarding Ti, the molten copper melted in the shaft furnace is in a reducing gas atmosphere. Flowing in the tank, introducing the copper melt flowing in the tank into the casting kettle of the same reducing gas environment, adding Ti in the casting pot, passing it through the nozzle, and using the mold formed between the casting wheel and the endless belt Made into ingot bars. The ingot bar was subjected to hot rolling to obtain a copper wire of 8 mm. Next, cold drawing processing was performed on each of the experimental materials. Thus, a copper wire having a size of 2.6 mm was produced.

Use this 2.6 mm copper wire to verify the characteristics of the raw materials used in the brazing wire.

[About the soft properties of soft low-concentration copper alloy materials]

Table 1 shows a comparative material 1 using an oxygen-free copper wire and a material 1 using a soft low-concentration copper alloy wire having an oxygen concentration of 7 mass ppm to 8 mass ppm, a sulfur concentration of 5 mass ppm, and a titanium concentration of 13 mass ppm. A table of Vickers hardness (Hv) of materials annealed at different annealing temperatures for 1 hour was verified. According to Table 1, when the annealing temperature was 400 ° C, the Vickers hardness (Hv) of the comparative material 1 and the material 1 was the same level, and the same Vickers hardness (Hv) was exhibited even when the annealing temperature was 600 °C. Therefore, it is understood that the soft low-concentration copper alloy wire of the present invention has sufficient soft characteristics, and has excellent soft characteristics particularly in the region where the annealing temperature exceeds 400 ° C, compared to the oxygen-free copper wire.

[About the crystal structure of soft low-concentration copper alloy materials]

The average grain size in the surface layer of the 2.6 mm diameter of the material 1 and the comparative material 1 was measured. Here, in the method of measuring the average crystal grain size in the surface layer, as shown in Fig. 1, a line having a length of 10 mm from a position of a radial cross section of 2.6 mm in diameter in a depth direction of 10 μm to a depth of 50 μm is measured. The grain size of the range is obtained by averaging the obtained measured values as the average grain size in the surface layer.

As a result of the measurement, the average grain size in the surface layer of the comparative material 1 was 100 μm, whereas the average grain size in the surface layer of the material 1 was 20 μm. Therefore, in the present invention, the average crystal grain size in the surface layer from the surface to the inside up to 20% is set to 20 μm or less.

In the crystal structure of the comparative material 1, crystal grains having the same size from the surface portion to the entire central portion are uniformly arranged, whereas the crystal structure of the material 1 is formed thinly in the vicinity of the surface in the cross-sectional direction of the sample. The grain size in the layer is extremely small compared to the internal grain size.

[Relationship between elongation characteristics and crystal structure of soft low-concentration copper alloy materials]

Fig. 2 shows the comparison of the material 1 using a 2.6 mm diameter oxygen-free copper wire and the use of a low-oxygen copper (oxygen concentration of 7 mass ppm to 8 mass ppm, sulfur concentration of 5 mass ppm) of 2.6 mm diameter. The material 1 of the soft low-concentration copper alloy wire of ppm Ti was used as a sample to verify the change of the value of the elongation (%) of the material which was annealed at different annealing temperatures for 1 hour. The circular symbol shown in Fig. 2 indicates the material 1 and the rectangular symbol indicates the comparative material 1.

As shown in Fig. 2, it was found that the material 1 exhibited excellent elongation characteristics in a wide range from the vicinity of 130 ° C to 900 ° C at an annealing temperature of more than 100 ° C as compared with the comparative material 1 .

Fig. 3 is a view showing a photograph of a radial cross section of the copper wire of the material 1 at an annealing temperature of 500 °C. As shown in Fig. 3, a fine crystal structure is formed in the entire cross section of the copper wire, and it is considered that the fine crystal structure promotes elongation characteristics. On the other hand, the cross-sectional structure of the comparative material 1 at the annealing temperature of 500 ° C was twice recrystallized, and the crystal grains in the cross-sectional structure were coarsened compared with the crystal structure of FIG. 3 , and thus the elongation characteristics were considered to be lowered.

Fig. 4 is a view showing a photograph of a radial cross section of the copper wire of the material 1 at an annealing temperature of 700 °C. It can be seen that the grain size of the surface layer in the cross section of the copper wire is extremely small compared to the grain size inside. Although the internal crystal structure is recrystallized twice, the layer of fine crystal grains in the outer layer remains. In the material 1, the internal crystal structure grows largely, but the layer of the fine crystal remains in the surface layer, and therefore it is considered that the elongation property is maintained.

Thus, by adjusting the annealing temperature and the annealing time, the proportion of the fine crystal layer in the cross section of the wire can be adjusted, and the elongation characteristics of the wire can be adjusted according to the proportion of the fine crystal layer.

Fig. 5 is a view showing the radial cross-sectional structure of the comparative material 1 in a cross-sectional photograph. As shown in Fig. 5, the crystal grains of substantially equal size from the surface to the entire center are uniformly arranged, and recrystallization is performed twice in the entire cross-sectional structure. Therefore, it is considered that the comparative material 1 is 600 ° C or more as compared with the material 1 . The elongation characteristics in the high temperature region are lowered.

According to the above results, in the product using the material 1 as compared with the comparative material 1, the flexibility and electrical conductivity are improved, and the elongation property can be improved.

In the conventional conductor, in order to recrystallize the crystal structure to the size of the material 1, high-temperature annealing treatment is required. However, if the annealing temperature is too high, S will re-dissolve. Further, in the conventional conductor, when recrystallization is performed, there is a problem that it becomes soft and the elongation property is lowered. However, the material 1 has the feature that since it can be recrystallized without forming twin crystals during annealing, The crystal grains of the portion become large and become soft, but on the other hand, since the fine crystal remains in the surface layer, the tensile strength and the elongation property are not lowered. By using such a material in the brazing wire, it is possible to realize a brazing wire which is soft, has high conductivity, is excellent in elongation characteristics, and has excellent tensile strength as described later.

[Embodiment 2] [brass wire]

The same as in the first embodiment of the soft low-concentration copper alloy material described above, when the copper wire of 2.6 mm size was produced. The copper wire was subjected to wire drawing processing until it was 0.9 mm, and was temporarily annealed by a current-annealing furnace and then pulled up to 0.05 mm. Next, the material of the material 2 was produced by performing a moving annealing of 400 ° C to 600 ° C × 0.8 to 4.8 seconds in a tubular furnace. For comparison, N 0.05 mm of 4N copper (99.99% or more, OFC (oxygen-free copper)) was also produced under the same processing heat treatment conditions to obtain a material of Comparative Material 2. The mechanical properties (tensile strength, elongation, hardness) and grain size of these materials were measured.

The average grain size in the surface layer was measured from the grain size in the range of 0.025 mm from the surface of the radial cross section of the 0.05 mm diameter in the depth direction up to a depth of 10 μm.

(The seventh drawing of the brazing wire is the wire rod of the comparative material 2 using the oxygen-free copper wire, and the material 2 made of the soft low-concentration copper alloy wire containing the low-oxygen copper containing 13 mass ppm of Ti. The wire rod was subjected to wire drawing processing from ψ 0.9 mm (annealed material) to ψ 0.05 mm, and the section hardness (Hv) and mechanical after moving annealing (temperature 300 ° C to 600 ° C, time 0.8 to 4.8 seconds) by a tubular furnace were measured. The result of the properties (tensile strength, elongation).

The cross-sectional hardness was a cross section of a ψ 0.05 mm line embedded in the resin by polishing, and was evaluated by the Vickers hardness at the center of the measurement line. The number of measurements was 5 and the average value was taken.

Tensile strength and elongation were measured by performing a tensile test under the conditions of a gauge length of 100 mm and a tensile speed of 20 mm/min. The maximum tensile stress at the time of material fracture is the tensile strength, and the maximum deformation amount (strain) at the time of material fracture is set to elongation.

As shown in Fig. 6, it is understood that when the comparison is performed at substantially the same elongation, the hardness of the material 2 is about 10 Hv smaller than that of the comparative material 2. Compared with the OFC material, the elongation property can be reduced and the hardness can be reduced, so that the brazing wire of the material 2 can reduce the pad damage during welding as compared with the welding wire using the oxygen-free copper.

As shown in Fig. 7, it is understood that when the comparison is performed at substantially the same elongation, the hardness of the material 2 is about 10 Hv smaller than that of the comparative material 2. Compared with oxygen-free copper, it can not reduce the elongation The hardness is reduced, so that, for example, the copper conductor of the second embodiment can reduce the damage of the pad during soldering as compared with the solder wire using the oxygen-free copper.

Table 2 shows the results of comparison between the material 2 and the comparative material 2 in the evaluation results shown in FIG. The example of the upper case of Table 2 shows the mechanical properties of the wire rod of the material 2 from ψ 0.9 mm (annealed material) to ψ 0.05 mm, and subjected to 400 ° C × 1.2 second moving annealing in a tubular furnace. hardness. Similarly, the comparative example of Table 2 shows that the wire rod of the comparative material 2 is subjected to wire drawing processing from ψ 0.9 mm (annealed material) up to ψ 0.05 mm, and mechanical properties at 600 ° C × 2.4 second moving annealing in a tubular furnace and hardness.

As shown in Table 2, even if the material of the same hardness is used, the elongation of the material 2 is 7% or more higher than that of the comparative material 2, so that the connection reliability and the handling characteristics at the time of wire bonding can be greatly improved. Further, since the material 2 has a higher tensile strength than the welding wire of the comparative material 2 which uses the same hardness but uses oxygen-free copper, the strength reliability of the joint portion (ball neck portion) can be greatly promoted.

Here, the connection reliability of the wire bonding portion refers to the resistance to stress generated by the difference in thermal expansion between the copper wire and the resin material after the resin is molded after the wire is welded. In addition, the operability refers to the resistance to stress when the wire is supplied from the spool to the welded portion, and the ease of occurrence of the curling behavior.

Next, according to Fig. 7, it can be seen that when the comparison is performed at substantially the same tensile strength, the hardness of the material 2 is about 10 Hv smaller than that of the comparative material 2. It is possible to reduce the tensile strength and reduce the hardness, so that the welding pad damage of the welding wire of Example 2 at the time of welding can be reduced.

Table 3 shows the results of comparison between the material 2 and the comparative material 2 in which the tensile strength was selected to be substantially equal. The example of the upper case of Table 3 shows the mechanical properties of the wire rod of the material 2 from ψ 0.9 mm (annealed material) to ψ 0.05 mm, and 500 ° C × 4.8 second moving annealing in a tubular furnace. hardness. Similarly, the comparative example of Table 3 shows the mechanical properties of the wire rod of the comparative material 2 from ψ 0.9 mm (annealed material) to ψ 0.05 mm, and subjected to a moving annealing at 600 ° C × 2.4 seconds in a tubular furnace. hardness.

As shown in Table 3, even in the case of the material having the same tensile strength, the elongation of Example 2 was 5% higher than that of Comparative Material 2, so that the connection reliability and the handling characteristics at the time of wire bonding can be greatly improved. Further, although the material having the same tensile strength was used, the hardness of the material 2 was extremely small as compared with Comparative Example 2, so that the damage of the pad during wire bonding can be reduced.

Here, the connection reliability of the wire bonding portion refers to resistance (resistance) to stress generated by a difference in thermal expansion between the copper wire and the resin material after the resin is molded after the wire is welded. In addition, the operability refers to the resistance to stress when the wire is supplied from the spool to the welded portion, and the ease of occurrence of the curling behavior.

The balance of the hardness, the elongation, and the tensile strength is slightly different depending on the specifications required for the product. As an example, according to the present invention, when the tensile strength is emphasized, the tensile strength of 270 MPa or more and the elongation of 7% can be supplied. Above the line with a hardness of 65Hv or less.

Further, when the importance is small, a conductor having a tensile strength of 210 MPa or more and less than 270 MPa, an elongation of 15% or more, and a hardness of 63 Hv or less can be supplied.

(About the crystal structure of a 0.05 mm diameter copper wire)

Fig. 8 is a view showing a radial cross-sectional structure of a brazing wire of the comparative material 2 in a cross-sectional photograph, and Fig. 9 is a view showing a radial cross-sectional structure of a brazing wire of the material 2 in a cross-sectional photograph. As shown in Fig. 8, it is understood that in the crystal structure of the comparative material 2, crystal grains having the same size from the surface to the entire center are uniformly arranged. On the other hand, in the crystal structure of the material 2, the size of the crystal grains as a whole is sparse, and the grain size in the layer formed thinly in the vicinity of the surface in the cross-sectional direction of the sample is extremely small as compared with the internal crystal grain size. .

The inventors believe that the fine crystal grain layer which is not formed in the surface layer 2 which is not formed in the surface layer has soft properties in Example 2, and promotes both tensile strength and elongation characteristics.

In general, it is understood that when the heat treatment for the purpose of softening is performed, crystal grains which are uniformly coarsened are formed by recrystallization as in the comparative material 2. However, in the material 2, even if the annealing treatment for forming coarse crystal grains inside is performed, the fine crystal grain layer remains in the surface layer. Therefore, it is considered that the implement 2 obtains a soft low-concentration copper alloy material which is a soft copper material but is excellent in tensile strength and elongation.

Further, based on the cross-sectional photograph of the crystal structure shown in FIGS. 8 and 9, the comparative material 2 is measured. And the average grain size in the surface layer of the sample of the material 2 was measured.

Fig. 10 is a view showing an outline of a method of measuring the average grain size in the surface layer. As shown in Fig. 10, the crystal grain size was measured in a range of 20% of the wire diameter from the surface of the cross section of the 0.05 mm diameter in the width direction at a depth of 5 μm to a depth of 10 μm in the depth direction. Then, the average value was obtained from each measured value (actual measurement value), and this average value was made into the average crystal grain size.

As a result of the measurement, the average grain size in the surface layer of the comparative material 2 was 22 μm, whereas the average grain size in the surface layer of the material 2 was up to 7 μm up to the depth of 5 μm and up to 5 μm inside. The surface layer of ~10 μm is 15 μm, which is different from the surface layer of the comparative material 2. It is considered that one of the reasons why the average grain size of the surface layer is fine is that high tensile strength and elongation are obtained. In addition, if the grain size is large, the crack progresses along the crystal grain boundary. However, if the grain size in the surface layer is small, the progress is suppressed because the progress direction of the crack changes. Therefore, it is considered that the fatigue properties of the material 2 are superior to those of the comparative material 2. Therefore, in order to achieve the effect of the present embodiment, the average grain size of the surface layer is preferably 15 μm or less.

The term "fatigue property" refers to the number or time of stress application cycles until the material breaks when subjected to repeated stress.

[Example 3] (The crystal structure of a 0.26 mm diameter brazing wire at an annealing temperature of 600 ° C)

Fig. 11 is a cross-sectional photograph showing the radial cross-sectional structure of the sample of the material 3 having the same composition as that of the material 1, and the sample of the material 3 was subjected to an annealing temperature of 600 ° C using a wire having a diameter of 0.26 mm. The hour-annealed material, Fig. 12 is a view showing a cross-sectional photograph of the radial cross-sectional structure of the comparative material 3.

As shown in Fig. 11 and Fig. 12, it is understood that crystal grains having the same size from the surface portion to the entire central portion are uniformly arranged in the crystal structure of the comparative material 3. On the other hand, in the crystal structure of the material 3, the size of the crystal grains as a whole is sparse, and the crystal grain size and the inner crystal in the layer formed thinly in the vicinity of the surface in the cross-sectional direction of the sample should be particularly specified. The particle size is extremely small.

In the case of the present invention, it is understood that, in the case of the present invention, it is understood that if the annealing treatment is performed at an annealing temperature of 600 ° C for 1 hour, the crystal grains which are uniformly coarsened are formed by recrystallization as in the comparative material 3, but in the case of the present invention, Even if the annealing treatment is performed at an annealing temperature of 600 ° C for 1 hour, the fine crystal grain layer remains on the surface layer. Therefore, it is possible to obtain a soft copper material, but it is possible to achieve good tensile strength and elongation properties of the brazing wire to be described later. Soft low concentration copper alloy material.

Further, based on the cross-sectional photographs of the crystal structures shown in Figs. 11 and 12, the average grain size in the surface layer of the sample of the material 3 and the comparative material 3 was measured. In the method of measuring the average crystal grain size in the surface layer, as shown in Fig. 1, a line having a length of 1 mm from a position of a cross section of a 0.26 mm diameter in the width direction at a depth of 10 μm to a depth of 50 μm in the depth direction is measured. The grain size of the range is obtained by averaging the obtained measured values as the average grain size in the surface layer.

As a result of the measurement, the average grain size in the surface layer of the comparative material 3 was 50 μm, whereas the average grain size in the surface layer of the material 3 was 10 μm, which was greatly different in this point. It is considered that since the average grain size of the surface layer is small, good tensile strength and elongation characteristics of the brazing wire to be described later are achieved.

[Example 4] (The crystal structure of a 0.26 mm diameter brazing wire at an annealing temperature of 400 ° C)

Fig. 13 is a view showing a cross-sectional structure in the width direction of the sample of the material 4 in a cross-sectional photograph, and Fig. 14 is a view showing a cross-sectional structure in the width direction of the comparative material 4 in the cross-sectional photograph.

The material 4 was a 0.26 mm diameter low-concentration copper alloy wire having an oxygen concentration of 7 ppm by mass to 8 ppm by mass, a sulfur concentration of 5 ppm by mass, and a titanium concentration of 13 ppm by mass, and was produced by annealing at an annealing temperature of 400 ° C for 1 hour. The comparative material 4 was a 0.26 mm diameter wire made of oxygen-free copper (OFC), and was annealed at an annealing temperature of 400 ° C for 1 hour.

As shown in Fig. 13 and Fig. 14, it is understood that in the crystal structure of the comparative material 4, crystal grains having the same size from the surface portion to the entire central portion are uniformly arranged. On the other hand, the crystal structure of the material 3 differs in the size of the crystal grains in the surface layer and the inside, and the internal crystal grain size is extremely larger than the grain size in the surface layer.

When the copper is annealed to recrystallize the crystal structure, the material 4 is easily recrystallized, and the internal crystal grains are greatly grown.

Next, Table 4 shows the electrical conductivity of the implement 4 and the comparative material 4.

As shown in Table 4, the electrical conductivity of the material 4 was higher than that of the comparative material 4, and was substantially equal. As a welding line can be satisfied.

The brazing wire of the above embodiment is a soft low-concentration copper alloy material containing Ti or the like and containing the unavoidable impurities in the remaining portion, wherein the average grain size of the surface layer of the crystal structure from the surface to a depth of 20% of the wire diameter When the thickness is 15 μm or less, the average grain size inside is larger than the average grain size of the surface layer, so that the grain size of the surface layer of the copper wire can be combined to have high tensile strength and elongation, thereby improving the connection of the article. reliability.

Further, similarly to the added Ti, sulfur (S) as an impurity is also trapped in an additive element selected from the group consisting of Mg, Zr, Nb, Ca, V, Ni, Mn, and Cr, and thus The copper matrix phase of the matrix is highly purified, thereby improving the soft properties of the raw materials. Therefore, it was confirmed that an effect of suppressing damage to the fragile aluminum pad on the germanium wafer during soldering can be obtained.

Further, the brazing wire of the present embodiment does not require high-purity (99.999 mass% or more) treatment of copper, and high electrical conductivity can be achieved by a low-cost continuous casting and rolling method, so that cost can be reduced.

Further, the brazing wire of the present embodiment can be suitably used as an alternative to an Al welding wire of about 0.3 mm for use in a vehicle power module, and can avoid the following problems: due to high thermal conductivity caused by the raw material. The miniaturization of the module due to the reduction in the wire diameter and the heat dissipation due to the improvement in thermal conductivity are improved, and the connection reliability is lowered because the current density is increased.

Fig. 1 is a view for explaining a method of measuring an average crystal grain size in a surface layer of a sample; and Fig. 2 is a view showing a relationship between different annealing temperatures and elongation of the material 1 and the comparative material 1; The figure shows a photograph of a radial cross section of the material 1 at an annealing temperature of 500 ° C; FIG. 4 is a diagram showing a radial cross section of the material 1 at an annealing temperature of 700 ° C; and FIG. 5 shows a comparative material 1 FIG. 6 is a view showing the relationship between the elongation and the hardness of the material 2 and the comparative material 2; and FIG. 7 is a graph showing the relationship between the elongation of the material 2 and the comparative material 2 and the hardness of the comparative material 2; FIG. 8 is a view showing a cross-sectional photograph of the weld line of the comparative material 2 having a diameter of 0.05 mm in the width direction; and FIG. 9 is a view showing the width of the weld line of the material 2 having a diameter of 0.05 mm. a photograph of a cross-sectional photograph of the direction; Figure 10 is a schematic illustration of a method of determining the average grain size in the surface layer.

Fig. 11 is a view showing a photograph of a cross section in the width direction of the material 3 having a diameter of 0.26 mm; Fig. 12 is a view showing a photograph of a cross section in the width direction of the comparative material 3 having a diameter of 0.26 mm; and Fig. 13 is a view showing a diameter of 0.26 mm. FIG. 14 is a view showing a cross-sectional photograph of the comparative material 4 having a diameter of 0.26 mm in the width direction.

Claims (5)

A copper bonding wire, wherein the brazing wire is characterized by: a soft low-concentration copper alloy material comprising: selected from the group consisting of Ti, Mg, Zr, Nb, Ca, V, Ni, Mn, and The additive element in the group consisting of Cr and the remainder is copper, and the crystal grain structure of the brazing wire has an average grain size of at least 20 μm from the surface to the inside to a depth of 20% of the wire diameter. The copper wire according to the first aspect of the invention, which contains oxygen in an amount of more than 2 ppm by mass, and contains 2 ppm by mass or more and 12 ppm by mass or less of sulfur. The brazing wire according to the first or second aspect of the invention, wherein the tensile strength is 210 MPa or more, the elongation is 15% or more, and the Vickers hardness is 65 Hv or less. The brazing wire according to any one of claims 1 to 3, wherein the electrical conductivity is 98% IACS or more. The brazing wire according to any one of the above-mentioned items, wherein the additive element is 4 mass ppm or more and 55 mass ppm or less of Ti and contains more than 2 mass ppm and is 30 mass ppm or less. Oxygen.