JP2012089685A - Copper bonding wire and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper bonding wire having high conductivity, soft characteristics, and excellent fatigue characteristics at low cost, and to provide a method of manufacturing the same.SOLUTION: The copper bonding wire contains copper and an additive element selected from a group consisting of Ti, Mg, Zr, Nb, Ca, V, Ni, Mn, and Cr, and the remainder of inevitable impurities. The copper bonding wire has a surface layer where the unprocessed crystal structure has an average crystal grain size of 20 μm or less from the surface down to a depth of 50 μm.

Description

  The present invention relates to a copper bonding wire and a method for manufacturing a copper bonding wire.

  Conventionally, Au wire or Al alloy wire has been used as a bonding wire for connecting an electrode of a semiconductor element and an external lead. In particular, in a resin mold type semiconductor element, Au wire of about φ0.025 mm is used from the viewpoint of connection reliability. In recent years, Al wires having a diameter of about 0.3 mm have been used as bonding wires for automobile power modules.

  The Au wire has excellent conductivity, corrosion resistance, and flexibility, but the cost is very high. Therefore, a bonding wire using copper (Cu) as a material has been proposed. For example, a copper fine wire for bonding containing 0.0005 to 0.2 wt% titanium in pure copper having a purity of 99.99 wt% or more is known (for example, see Patent Document 1).

JP-A-62-130249

  However, since the bonding wire described in Patent Document 1 is made of Cu harder than Au, this bonding wire is used, for example, aluminum as an electrode pad provided on a semiconductor element (for example, a silicon chip). Bonding to the pad may damage the aluminum pad. Although the bonding wire can be softened by setting the purity of Cu constituting the bonding wire to, for example, a high purity of 99.9999% by mass or more, the fatigue characteristics of the bonding wire are lower than those of the Au wire. It becomes difficult to ensure the same reliability as the Au wire.

  Further, when the cost for increasing the purity of Cu constituting the bonding wire is transferred to the bonding wire, the cost of the bonding wire increases. Furthermore, when manufacturing a bonding wire made of high-purity Cu, since the crystal grains are prevented from becoming coarse, the hardness of the bonding wire is increased. Therefore, when such a bonding wire is used, the aluminum pad as the electrode pad provided in the semiconductor element may be damaged. In addition, the conductivity of the bonding wire may decrease due to the mixing of impurities into high purity Cu.

  Accordingly, an object of the present invention is to provide a copper bonding wire and a method for producing the copper bonding wire that are low in cost and have high conductivity, soft properties, and excellent fatigue properties.

  In order to solve the above problems, the present invention includes copper and an additive element selected from the group consisting of Ti, Mg, Zr, Nb, Ca, V, Ni, Mn, and Cr, and the remainder is inevitable. A copper bonding wire having a surface layer having an average crystal grain size of 20 μm or less from the surface to the depth of 50 μm from the surface to the inside thereof. Is provided.

  The copper bonding wire may contain sulfur of 2 mass ppm or more and 12 mass ppm or less, oxygen of more than 2 mass ppm and 30 mass ppm or less, and titanium of 4 mass ppm or more and 55 mass ppm or less.

  The copper bonding wire may have a conductivity of 98% IACS or higher.

In the copper bonding wire, the sulfur (S) and the titanium (Ti) are a compound having a TiO, TiO ₂ , TiS, or Ti—O—S bond, the TiO, the TiO ₂ , the TiS, or It may be included as an aggregate of compounds having the Ti—O—S bond, and the remaining Ti and S may be included as a solid solution.

Further, in the copper bonding wire, a compound or an aggregate in the form of the TiO, the TiO ₂ , the TiS, or the Ti—O—S is distributed in crystal grains, and the TiO has a size of 200 nm or less. The TiO ₂ has a size of 1000 nm or less, the TiS has a size of 200 nm or less, and the compound or aggregate in the form of Ti—O—S has a size of 300 nm or less. 90% or more of particles of 500 nm or less may be used.

  In addition, the present invention aims to solve the above-mentioned problems, and a soft diluted copper alloy material containing an additive element selected from the group consisting of Ti, Mg, Zr, Nb, Ca, V, Ni, Mn, and Cr A molten metal manufacturing process for forming a molten metal at a molten copper temperature of 1100 ° C. or higher and 1320 ° C. or lower, a wire rod manufacturing process for manufacturing a wire rod from the molten metal, and hot rolling at a temperature of 880 ° C. or lower and 550 ° C. or higher on the wire rod There is provided a method for producing a copper bonding wire, comprising: a hot rolling step for applying a wire; and a wire drawing step for drawing the wire rod that has undergone the hot rolling step.

  In the method for producing a copper bonding wire, the additive element is Ti, and the soft dilute copper alloy material is sulfur of 2 mass ppm or more and 12 mass ppm or less, oxygen exceeding 2 mass ppm and oxygen of 30 mass ppm or less, and 4 mass. Titanium of not less than ppm and not more than 55 mass ppm may be included.

  In the method for producing a copper bonding wire, the soft dilute copper alloy material may have a softening temperature of φ2.6 mm and 130 ° C. or more and 148 ° C. or less.

  The copper bonding wire and the method for manufacturing the copper bonding wire according to the present invention are low in cost, and can provide a copper bonding wire and a method for manufacturing the copper bonding wire having high conductivity, soft characteristics, and excellent fatigue characteristics. .

It is a SEM image of TiS particle. It is a figure which shows the analysis result of FIG. SEM images of the TiO ₂ particles. It is a figure which shows the analysis result of FIG. It is a SEM image of Ti-O-S particle. It is a figure which shows the analysis result of FIG. It is a figure which shows the outline | summary of a bending fatigue test. Example 7 produced using a wire rod according to Comparative Example 13 using oxygen-free copper after annealing at 400 ° C. for 1 hour and a soft dilute copper alloy wire obtained by adding Ti to low-oxygen copper It is a figure which shows the result of having measured the bending life with the wire rod which concerns on this. Example 8 produced using a wire rod according to Comparative Example 14 using oxygen-free copper after annealing at 600 ° C. for 1 hour and a soft dilute copper alloy wire obtained by adding Ti to low-oxygen copper It is a figure which shows the result of having measured the bending life with the wire rod which concerns on this. It is a figure which shows the cross-sectional structure | tissue of the width direction of the sample which concerns on the comparative example 14. FIG. FIG. 10 is a diagram showing a cross-sectional structure in the width direction of a sample according to Example 8. It is a schematic diagram of the measuring method of the average grain size in a surface layer.

[Embodiment]
(Composition of copper bonding wire)
The copper bonding wire according to the present embodiment has a thermal conductivity higher than that of aluminum, for example, from the viewpoint of downsizing a power module used in an automobile or the like and / or increasing the current density of current supplied to the power module. Constructed from copper, a high material.

For example, the copper bonding wire according to the present embodiment has an electrical conductivity of 98% IACS (conductivity when the universal annealed copper standard or higher, and a resistivity of 1.7241 × 10 ⁻⁸ Ωm is 100%) Preferably, the soft dilute copper alloy material is used as a soft copper material that satisfies 100% IACS or more, more preferably 102% IACS or more.

  Further, the copper bonding wire according to the present embodiment uses an SCR continuous casting facility, has few scratches on the surface, has a wide manufacturing range, and can be stably produced. The wire rod is made of a material having a softening temperature of 148 ° C. or less at a processing degree of 90% (for example, processing from φ8 mm to φ2.6 mm wire).

  Specifically, the copper bonding wire according to the present embodiment includes copper and an additive element selected from the group consisting of Ti, Mg, Zr, Nb, Ca, V, Ni, Mn, and Cr, with the remainder being It is a copper bonding wire that is an inevitable impurity. The copper bonding wire according to the present embodiment has an average crystal grain size of 20 μm when the crystal structure before processing is a surface layer from the surface of the copper bonding wire to a depth of 50 μm toward the inside of the copper bonding wire. The following crystal grains are included in the surface layer. The reason for selecting an element selected from the group consisting of Ti, Mg, Zr, Nb, Ca, V, Ni, Mn, and Cr as an additive element is that these elements are easily active elements that are easily combined with other elements. This is because S can be trapped because it is easily combined with S, and the copper base material (matrix) can be highly purified. One or more additive elements may be included. Also, other elements and impurities that do not adversely affect the properties of the alloy can be included in the alloy. Further, in the preferred embodiment described below, it is described that the oxygen content is more than 2 and not more than 30 mass ppm, but depending on the addition amount of the additive element and the S content, In the range having the property of, it is possible to include more than 2 and 400 mass ppm.

Further, in the copper bonding wire according to the present embodiment, when the additive element is Ti, sulfur of 2 mass ppm or more and 12 mass ppm or less, oxygen of more than 2 mass ppm and 30 mass ppm or less, and titanium of 4 mass ppm or more and 55 mass ppm or less. Including. Furthermore, sulfur (S) and titanium (Ti) is, _TiO, agglomeration of TiO 2, TiS, or a compound having a TiO-S bond or _TiO, TiO 2, TiS, or a compound having a TiO-S bond It is contained in the copper bonding wire as a product, and the remaining Ti and S are contained in the copper bonding wire as a solid solution. In this embodiment, so-called low oxygen copper (LOC) is targeted because it contains oxygen exceeding 2 mass ppm and not more than 30 mass ppm.

Further, compounds or aggregates in the form of TiO, TiO ₂ , TiS, Ti—O—S are distributed inside the crystal grains constituting the copper bonding wire, and TiO has a size of 200 nm or less, and TiO ₂ has a size of 1000 nm or less, TiS has a size of 200 nm or less, and a compound or aggregate in the form of Ti-O-S has a size of 300 nm or less. Furthermore, the copper bonding wire according to the present embodiment includes 90% or more of particles of 500 nm or less. The “crystal grain” means a copper crystal structure.

(Copper bonding wire manufacturing method)
The method for manufacturing the copper bonding wire according to the present embodiment is as follows. As an example, a case where Ti is selected as an additive element will be described. First, a soft dilute copper alloy material containing Ti as a raw material for a copper bonding wire is prepared (raw material preparation step). Next, this soft dilute copper alloy material is made into a molten metal at a molten copper temperature of 1100 ° C. or higher and 1320 ° C. or lower (melt manufacturing process). Next, a wire rod is produced from the molten metal (wire rod production process). Subsequently, the wire rod is hot-rolled at a temperature of 880 ° C. or lower and 550 ° C. or higher (hot rolling step). Further, the wire rod that has undergone the hot rolling process is subjected to a drawing process (drawing process). Thereby, the copper bonding wire which concerns on this Embodiment is manufactured.

  In addition, for the production of a copper bonding wire, a soft dilute copper alloy material containing 2 mass ppm or more and 12 mass ppm or less of sulfur, 2 mass ppm or more and 30 mass ppm or less of oxygen, and 4 mass ppm or more and 55 mass ppm or less of titanium is used. Specifically, a soft dilute copper alloy material having a softening temperature of 130 ° C. or more and 148 ° C. or less with a size of φ2.6 mm is used.

  Hereinafter, the contents studied by the present inventors in the realization of the copper bonding wire according to the present embodiment will be described.

  First, high-purity copper having a purity of 6N (that is, 99.9999%) has a softening temperature of 130 ° C. at a workability of 90%. Therefore, the present inventor has a soft material having a softening temperature of 130 ° C. or higher and 148 ° C. or lower that enables stable production, and the conductivity of the soft material is 98% IACS or higher, preferably 100% IACS or higher, more preferably 102% IACS or higher. A soft dilute copper alloy material capable of stably producing soft copper and a method for producing the soft dilute copper alloy material were studied.

  Here, high-purity copper (4N) having an oxygen concentration of 1 to 2 mass ppm was prepared, and this Cu was made into a molten Cu using a small continuous casting machine (small continuous casting machine) installed in a laboratory. And several mass ppm of titanium was added to this molten metal. Subsequently, a φ8 mm wire rod was manufactured from the molten metal to which titanium was added. Next, a φ8 mm wire rod was processed to φ2.6 mm (that is, the processing degree was 90%). The softening temperature of the φ2.6 mm wire rod was 160 ° C. to 168 ° C., and the softening temperature was not lower than this temperature. The conductivity of the φ2.6 mm wire rod was about 101.7% IACS. In other words, the oxygen concentration contained in the wire rod is reduced, and the softening temperature of the wire rod cannot be lowered even if titanium is added to the molten metal, and the conductivity of high purity copper (6N) is 102.8% IACS. The inventor has obtained the knowledge that the electrical conductivity is low.

  The reason why the softening temperature could not be lowered and the conductivity was lower than that of 6N high-purity copper was that sulfur (S) of several mass ppm or more as an inevitable impurity was contained during the production of the molten metal. I guessed that. That is, it was speculated that the softening temperature of the wire rod does not decrease due to insufficient formation of sulfides such as TiS between sulfur and titanium contained in the molten metal.

  Therefore, the present inventor has studied the following two measures in order to realize a decrease in the softening temperature of the copper bonding wire and an improvement in the conductivity of the copper bonding wire. And the copper bonding wire which concerns on this Embodiment was obtained by using together the following two measures for manufacture of a copper wire rod.

FIG. 1 is an SEM image of TiS particles, and FIG. 2 shows the analysis result of FIG. FIG. 3 is an SEM image of TiO ₂ particles, and FIG. 4 shows the analysis result of FIG. 5 is an SEM image of Ti—O—S particles, and FIG. 6 shows the analysis result of FIG. In the SEM image, each particle is shown near the center of the figure. FIGS. 1-6 evaluate the cross section of φ8 mm copper wire (wire rod) having the oxygen concentration, sulfur concentration, and Ti concentration shown in the third row from the top in Example 1 of Table 1 by SEM observation and EDX analysis. It is a thing. The observation conditions were an acceleration voltage of 15 keV and an emission current of 10 μA.

First, the first strategy is to prepare a molten Cu in a state where titanium (Ti) is added to Cu having an oxygen concentration exceeding 2 mass ppm. It is considered that TiS and titanium oxide (for example, TiO ₂ ) and Ti—O—S particles are formed in the molten metal. This is a consideration from the SEM image of FIG. 1 and the analysis result of FIG. 2, and the SEM image of FIG. 3 and the analysis result of FIG. 2, 4, and 6, Pt and Pd are metal elements that are vapor-deposited on the observation object when SEM observation is performed.

Next, the second policy aims to facilitate the precipitation of sulfur (S) by introducing dislocations in the copper, and the temperature in the hot rolling process is set to the temperature in the normal copper production conditions (that is, , 950 ° C. to 600 ° C.) lower temperature (880 ° C. to 550 ° C.). By such temperature setting, S can be precipitated on dislocations or by using titanium oxide (for example, TiO ₂ ) as a nucleus. As an example, as shown in FIGS. 5 and 6, Ti—O—S particles and the like are formed together with molten copper.

  By the above first and second measures, sulfur contained in copper crystallizes and precipitates, so that a copper wire rod having a desired softening temperature and a desired conductivity is obtained after cold drawing. be able to.

  Moreover, the copper bonding wire which concerns on this Embodiment is manufactured using SCR continuous casting rolling equipment. Here, the following three conditions were provided as restrictions on the manufacturing conditions when using the SCR continuous casting and rolling equipment.

(1) About composition When obtaining a soft copper material having an electrical conductivity of 98% IACS or more, as pure copper (base material) containing inevitable impurities, 3-12 mass ppm of sulfur, more than 2 and oxygen of 30 mass ppm or less, A soft dilute copper alloy material containing 4-55 mass ppm of titanium is used, and a wire rod (rough drawn wire) is produced from the soft dilute copper alloy material.

  Here, when obtaining a soft copper material having an electrical conductivity of 100% IACS or more, as pure copper (base material) containing inevitable impurities, 2 to 12 mass ppm of sulfur, more than 2 and oxygen of 30 mass ppm or less, A soft dilute copper alloy material containing 4-37 mass ppm titanium is used. Further, when obtaining a soft copper material having an electrical conductivity of 102% IACS or more, as pure copper (base material) containing inevitable impurities, 3 to 12 mass ppm of sulfur, more than 2 and less than 30 mass ppm of oxygen, 4 A soft dilute copper alloy material containing ˜25 mass ppm titanium is used.

  Usually, in the industrial production of pure copper, sulfur is taken into copper when producing electrolytic copper. Therefore, it is difficult to reduce sulfur to 3 mass ppm or less. The upper limit of the sulfur concentration of general-purpose electrolytic copper is 12 mass ppm.

  When the oxygen concentration is low, the softening temperature of the copper bonding wire is difficult to decrease, so the oxygen concentration is controlled to an amount exceeding 2 mass ppm. Further, when the oxygen concentration is high, the surface of the copper bonding wire is likely to be damaged in the hot rolling process, so that it is controlled to 30 mass ppm or less.

(2) Dispersed substance It is preferable that the size of the dispersed particles dispersed in the copper bonding wire is small, and that many dispersed particles are dispersed in the copper bonding wire. The reason is that the dispersed particles have a function as a sulfur precipitation site, and the precipitation site is required to have a small size and a large number.

Sulfur and titanium contained in the copper bonding _wire, TiO, TiO 2, TiS, or compounds or TiO having TiO-S _bond, TiO 2, TiS, or as aggregates of compounds having a TiO-S bond The remaining Ti and S are included as a solid solution. As a soft dilute copper alloy material that is a raw material of a copper bonding wire, TiO has a size of 200 nm or less, TiO ₂ has a size of 1000 nm or less, TiS has a size of 200 nm or less, and Ti—O— A soft dilute copper alloy material in which the compound in the form of S has a size of 300 nm or less and these are distributed in crystal grains is used.

  In addition, since the particle size formed in a crystal grain changes according to the holding | maintenance time of molten copper at the time of casting, and cooling conditions, it is necessary to set casting conditions appropriately.

(3) Casting conditions By SCR continuous casting and rolling, wire rods are produced with an ingot rod working degree of 90% (30 mm) to 99.8% (5 mm). As an example, a condition for manufacturing a wire rod of φ8 mm with a processing degree of 99.3% is adopted. Hereinafter, casting conditions (a) and (b) will be described.

[Casting conditions (a)]
The molten copper temperature in the melting furnace is controlled to 1100 ° C. or higher and 1320 ° C. or lower. When the temperature of the molten copper is high, blowholes increase, and scratches are generated and the particle size tends to increase, so the temperature is controlled to 1320 ° C. or lower. Moreover, although the reason for controlling to 1100 degreeC or more is because copper is hardened easily and manufacture is not stable, molten copper temperature is desirable as low as possible.

[Casting conditions (b)]
As for the temperature of the hot rolling process, the temperature in the first rolling roll is controlled to 880 ° C. or lower, and the temperature in the final rolling roll is controlled to 550 ° C. or higher.

  Unlike normal pure copper production conditions, the temperature of the molten copper and the temperature of the hot metal are reduced for the purpose of reducing the solid solution limit, which is the driving force for the precipitation of sulfur during hot rolling and the crystallization of sulfur. The temperature of the rolling process is preferably set to the conditions described in “Casting conditions (a)” and “Casting conditions (b)”.

  Further, the temperature in the normal hot rolling process is 950 ° C. or less in the first rolling roll and 600 ° C. or more in the final rolling roll, but for the purpose of reducing the solid solution limit, The first rolling roll is set to 880 ° C. or lower, and the final rolling roll is set to 550 ° C. or higher.

  The reason why the temperature in the final rolling roll is set to 550 ° C. or more is that the obtained wire bonding flaws increase at temperatures below 550 ° C., and the manufactured copper bonding wire cannot be handled as a product. The temperature in the hot rolling process is preferably as low as possible while controlling the temperature to 880 ° C. or lower in the first rolling roll and 550 ° C. or higher in the final rolling roll. By setting such a temperature, the softening temperature of the copper bonding wire (softening temperature after being processed to φ8 to φ2.6 mm) can be brought close to the softening temperature of 6N Cu (that is, 130 ° C.).

  The conductivity of oxygen-free copper is about 101.7% IACS, and the conductivity of 6N Cu is 102.8% IACS. In the present embodiment, for example, the conductivity of a wire rod having a diameter of φ8 mm is 98% IACS or more, preferably 100% IACS or more, more preferably 102% IACS or more. In the present embodiment, a soft dilute copper alloy in which the softening temperature of the wire rod of the wire rod (for example, φ2.6 mm) after cold drawing is 130 ° C. or higher and 148 ° C. is manufactured, and this soft dilute copper is manufactured. Alloy wires are used for the production of copper bonding wires.

  In order to use industrially, the electrical conductivity of 98% IACS or more is requested | required as electrical conductivity of the soft copper wire of the purity utilized industrially manufactured from electrolytic copper. Further, the softening temperature is 148 ° C. or less judging from industrial value. Since the softening temperature of 6N high-purity copper is 127 ° C to 130 ° C, the upper limit value of the softening temperature is set to 130 ° C from the obtained data. The slight difference in electrical conductivity and softening temperature between soft copper wire and high-purity copper that are used industrially is due to the presence of inevitable impurities not contained in 6N high-purity copper.

  After the base material copper is melted in the shaft furnace, it is preferably flowed into the trough in a reduced state. That is, in a reducing gas (for example, CO) atmosphere, the wire rod is stably manufactured by casting while controlling the sulfur concentration, titanium concentration, and oxygen concentration of the dilute alloy and rolling the material. It is preferable. In addition, that copper oxide mixes and / or that a particle size is larger than predetermined size will reduce the quality of the copper bonding wire manufactured.

  Here, the reason for adding titanium as an additive to the copper bonding wire is as follows. That is, (a) titanium is easily compounded by bonding with sulfur in molten copper, (b) easier to handle and easier to handle than other additive metals such as Zr, and (c) compared to Nb, etc. This is because it is inexpensive and (d) the oxide is easily deposited as a nucleus.

  As described above, a practical soft dilute copper alloy material having high productivity and excellent conductivity, softening temperature, and surface quality can be obtained as a raw material for the copper bonding wire according to the present embodiment. A plating layer can also be formed on the surface of the soft dilute copper alloy material. For the plating layer, for example, a material mainly containing a noble metal such as palladium, zinc, nickel, gold, platinum, silver, or Pb-free plating can be used. Further, the shape of the soft dilute copper alloy material is not particularly limited, and can be a round cross-section, a rod shape, or a flat conductor.

  In the present embodiment, the wire rod is manufactured by the SCR continuous casting and rolling method, and the soft material is manufactured by hot rolling, but the twin roll type continuous casting rolling method or the Properti type continuous casting and rolling method is adopted. You can also.

(Effect of embodiment)
The copper bonding wire according to the present embodiment does not require copper purification (99.9999% by mass or more), and can realize high conductivity by an inexpensive continuous casting and rolling method. Can be made. Since the copper bonding wire is formed from a material having a high conductivity, the temperature rise of the semiconductor element can be suppressed by improving the heat dissipation, and the reliability is improved. Since the added titanium (Ti) traps sulfur (S), which is an impurity, the copper matrix (matrix) is highly purified, and the soft properties of the material are improved. For this reason, it is possible to suppress damage to the fragile aluminum pad on the silicon chip during bonding.

  The copper bonding wire according to the present embodiment is a soft dilute copper alloy material containing Ti and the balance of inevitable impurities, and the average crystal grain size in the surface layer from the surface to a depth of 50 μm is 20 μm. Since it is the following, since flexibility is improved by refinement | miniaturization of the crystal grain of a copper wire surface layer, the fatigue characteristic of a wire can be improved and the reliability of a product can be improved.

  In addition, the copper bonding wire according to the present embodiment can be applied as an alternative to an Al bonding wire of about φ0.3 mm for use in an in-vehicle power module, and the module can be downsized due to a decrease in wire diameter due to high thermal conductivity of the material. In addition, a reduction in connection reliability due to an increase in current density can be avoided by improving heat dissipation by improving thermal conductivity.

  Table 1 shows the experimental conditions and results.

  First, as an experimental material, a φ8 mm copper wire (wire rod, workability 99.3%) having the oxygen concentration, sulfur concentration, and titanium concentration shown in Table 1 was prepared. The φ8 mm copper wire is hot rolled by SCR continuous forging. Ti flows the molten copper melted in the shaft furnace into the reed in the reducing gas atmosphere, guides the molten copper flowing in the reed to the casting pot of the same reducing gas atmosphere, and after adding Ti in this casting pot, An ingot rod was made with a mold formed between the cast ring and the endless belt through the nozzle. This ingot rod is hot-rolled to produce a φ8 mm copper wire. Next, cold drawing was applied to each experimental material. Thus, a copper wire having a size of φ2.6 mm was produced. And while measuring the semi-softening temperature and electrical conductivity of a copper wire of φ 2.6 mm size, the dispersed particle size in the copper wire of φ 8 mm was evaluated.

  The oxygen concentration was measured with an oxygen analyzer (Leco (registered trademark) oxygen analyzer), and the concentrations of sulfur and titanium were analyzed by ICP emission spectroscopic analysis.

  The measurement of the semi-softening temperature in the φ2.6 mm size was obtained from the result of quenching in water after holding each temperature at 400 ° C. or lower for 1 hour and conducting a tensile test. The value obtained by using the result of the tensile test at room temperature and the result of the tensile test of the soft copper wire heat-treated at 400 ° C. for 1 hour, and adding the tensile strengths of the two tensile tests and dividing by two. The temperature corresponding to the strength was determined as the semi-softening temperature.

As described in the embodiment, the size of the dispersed particles dispersed in the copper bonding wire is preferably small, and it is preferable that many dispersed particles are dispersed in the copper bonding wire. Therefore, the case where the number of dispersed particles having a diameter of 500 nm or less is 90% or more was regarded as acceptable. Here, the “size” is the size of the compound and means the size of the major axis of the major axis and minor axis of the shape of the compound. The “particles” refer to the TiO, TiO ₂ , TiS, and Ti—O—S. “90%” indicates the ratio of the number of corresponding particles to the total number of particles.

  In Table 1, Comparative Example 1 is the result of trial manufacture of a copper wire having a diameter of 8 mm in an Ar atmosphere in a laboratory, and Ti was added in an amount of 0 to 18 mass ppm to the molten copper. The semi-softening temperature of the copper wire to which Ti was not added was 215 ° C., whereas the softening temperature of the copper wire to which 13 mass ppm of Ti was added decreased to 160 ° C. (the lowest temperature in the experiment). ). As shown in Table 1, as the Ti concentration increased to 15 mass ppm and 18 mass ppm, the semi-softening temperature also increased, and the required softening temperature of 148 ° C. or lower could not be realized. Moreover, although the electrical conductivity requested | required industrially was 98% IACS or more, comprehensive evaluation was disqualified (henceforth, a disqualification is represented as "x").

  Therefore, as Comparative Example 2, a Φ8 mm copper wire (wire rod) having an oxygen concentration adjusted to 7 to 8 mass ppm was prototyped using the SCR continuous casting and rolling method.

  In Comparative Example 2, it was a copper wire having a minimum Ti concentration (that is, 0 mass ppm, 2 mass ppm) among the prototype manufactured by the SCR continuous casting and rolling method, and the conductivity was 102% IACS or more, but the semi-softening temperature. Was 164 ° C. and 157 ° C., and was not less than the required 148 ° C., so the overall evaluation was “x”.

  In Example 1, the oxygen concentration and the sulfur concentration substantially coincide (that is, the oxygen concentration: 7 to 8 mass ppm, the sulfur concentration: 5 mass ppm), and different copper wires are used within the range of the Ti concentration of 4 to 55 mass ppm. Prototype.

  When the Ti concentration is in the range of 4 to 55 mass ppm, the softening temperature is 148 ° C. or lower, the conductivity is 98% IACS or higher and 102% IACS or higher, and the dispersed particle size is 90% or higher for particles of 500 nm or less. there were. Moreover, since the surface of the wire rod was also clean (that is, the surface was smooth) and all satisfied the product performance, the comprehensive evaluation was a pass (hereinafter, the pass was expressed as “◯”).

  Here, the copper wire satisfying an electrical conductivity of 100% IACS or more was a case where the Ti concentration was 4 to 37 mass ppm, and the copper wire satisfying the 102% IACS or more was a case where the Ti concentration was 4 to 25 mass ppm. When the Ti concentration was 13 mass ppm, the conductivity showed a maximum value of 102.4% IACS, and the conductivity was slightly lower around this concentration. This is because, when the Ti concentration is 13 mass ppm, by capturing the sulfur content in the copper as a compound, the conductivity is close to that of high-purity copper (6N).

  Therefore, by increasing the oxygen concentration and adding Ti, both the semi-softening temperature and the conductivity can be satisfied.

  In Comparative Example 3, a copper wire having a Ti concentration of 60 mass ppm was prototyped. Although the copper wire which concerns on the comparative example 3 satisfy | fills a request | requirement, semi-softening temperature is 148 degreeC or more, and did not satisfy | fill product performance. Furthermore, there are many scratches on the surface of the wire rod, making it difficult to adopt as a product. Therefore, it was shown that the addition amount of Ti is preferably less than 60 mass ppm.

  In the copper wire which concerns on Example 2, while setting sulfur concentration to 5 mass ppm and controlling Ti concentration in the range of 13-10 mass ppm, the influence of oxygen concentration was examined by changing oxygen concentration.

  Regarding the oxygen concentration, copper wires having greatly different concentrations from 2 mass ppm to 30 mass ppm were prepared. However, since copper wires with an oxygen concentration of less than 2 mass ppm are difficult to produce and cannot be stably manufactured, the overall evaluation is “△” (“△” is an intermediate evaluation between “○” and “×”) .) Further, even when the oxygen concentration was 30 mass ppm, both the semi-softening temperature and the conductivity met the requirements.

  In Comparative Example 4, when the oxygen concentration was 40 mass ppm, there were many scratches on the surface of the wire rod, and the product could not be used as a product.

  Therefore, by setting the oxygen concentration in the range of more than 2 and 30 mass ppm or less, all the characteristics of the semi-softening temperature, the electrical conductivity of 102% IACS or more, and the dispersed particle size can be satisfied. It was shown to be clean and satisfy product performance.

  Example 3 is a copper wire in which the oxygen concentration and the Ti concentration are set close to each other and the sulfur concentration is changed within a range of 4 to 20 mass ppm. In Example 3, a copper wire having a sulfur concentration of less than 2 mass ppm could not be realized due to restrictions on raw materials. However, by controlling the Ti concentration and the sulfur concentration, the requirements for both the semi-softening temperature and the conductivity could be satisfied.

  In Comparative Example 5, when the sulfur concentration was 18 mass ppm and the Ti concentration was 13 mass ppm, the semi-softening temperature was as high as 162 ° C., and the required characteristics were not satisfied. In particular, the surface quality of the wire rod was poor and it was difficult to produce a product.

  From the above, when the sulfur concentration is in the range of 2 to 12 mass ppm, the semi-softening temperature, the conductivity of 102% IACS or more, and the dispersed particle size can be satisfied, and the surface of the wire rod is also clean. It was shown that the product performance can be satisfied.

  Comparative Example 6 is a copper wire using 6N high-purity copper. In the copper wire according to Comparative Example 6, the semi-softening temperature was 127 ° C. to 130 ° C., the conductivity was 102.8% IACS, and no particles having a dispersed particle size of 500 nm or less were observed.

  Table 2 shows the temperature of molten copper and the rolling temperature as production conditions.

  In Comparative Example 7, a wire rod having a molten copper temperature of 1330 ° C. to 1350 ° C. and a rolling temperature of 950 to 600 ° C. and a diameter of 8 mm was produced. Although the wire rod according to Comparative Example 7 satisfies the requirements for the semi-softening temperature and the electrical conductivity, there are about 1000 nm of particles with respect to the dispersed particle size, and more than 10% of the particles are over 500 nm. . Therefore, the wire rod according to Example 7 was determined to be inappropriate.

  In Example 4, the molten copper temperature was controlled in the temperature range of 1200 ° C. to 1320 ° C., and the rolling temperature was controlled in the temperature range of 880 ° C. to 550 ° C. to produce a φ8 mm wire rod. The wire rod according to Example 4 had good wire rod surface quality and dispersed particle size, and the overall evaluation was “◯”.

  In Comparative Example 8, the molten copper temperature was controlled to 1100 ° C., and the rolling temperature was controlled to a temperature range of 880 ° C. to 550 ° C. to produce a φ8 mm wire rod. The wire rod according to Comparative Example 8 was not suitable as a product because there were many scratches on the surface of the wire rod because the molten copper temperature was low. This is because, since the molten copper temperature is low, scratches are likely to occur during rolling.

  In Comparative Example 9, the molten copper temperature was controlled to 1300 ° C. and the rolling temperature was controlled to a temperature range of 950 ° C. to 600 ° C. to produce a φ8 mm wire rod. The wire rod according to Comparative Example 9 has a high quality in the surface of the wire rod because the temperature in the hot rolling process is high, but the dispersed particle size includes a large size, and the overall evaluation is “x”. It was.

  In Comparative Example 10, the molten copper temperature was controlled to 1350 ° C., and the rolling temperature was controlled to a temperature range of 880 ° C. to 550 ° C. to produce a φ8 mm wire rod. The wire rod according to Comparative Example 10 had a large dispersed particle size due to the high molten copper temperature, and the overall evaluation was “x”.

(Soft characteristics of soft dilute copper alloy wire)
Table 3 shows the wire rod according to Comparative Example 11 using an oxygen-free copper wire, and the wire rod according to Example 5 made from a soft dilute copper alloy wire containing 13 mass ppm Ti in low oxygen copper. The result of having measured the Vickers hardness (Hv) after annealing for 1 hour at different annealing temperatures is shown.

  The wire rod according to Example 5 has the same alloy composition as the alloy composition described in Example 1 of Table 1. As a sample, a 2.6 mm diameter sample was used. Referring to Table 3, when the annealing temperature was 400 ° C. and 600 ° C., it was shown that the Vickers hardness of the wire rod according to Comparative Example 11 and the wire rod according to Example 5 was at the same level. . Therefore, the wire rod according to Example 5 has sufficient soft characteristics, and also shows excellent soft characteristics in the temperature range where the annealing temperature exceeds 400 ° C. in comparison with the oxygen-free copper wire. It was done.

(Examination of yield strength and bending life of soft dilute copper alloy wire)
Table 4 shows a wire rod according to Comparative Example 12 using an oxygen-free copper wire, and a wire rod according to Example 6 manufactured using a soft dilute copper alloy wire containing 13 mass ppm Ti in low oxygen copper. Shows the results of measuring the transition of 0.2% proof stress after annealing for 1 hour at different annealing temperatures. As a sample, a 2.6 mm diameter sample was used. Further, the wire rod according to Example 6 has the same alloy composition as the alloy composition described in Example 1 of Table 1.

  Referring to Table 4, when the annealing temperature is 400 ° C. and 600 ° C., it is shown that the 0.2% proof stress value of the wire rod according to Comparative Example 12 and the wire rod according to Example 6 is at the same level. It was.

  FIG. 7 shows an outline of the bending fatigue test, and FIG. 8 shows a wire rod according to Comparative Example 13 using oxygen-free copper after annealing at 400 ° C. for 1 hour, and low oxygen copper with Ti. The result of having measured the bending life with the wire rod which concerns on Example 7 produced using the soft dilute copper alloy wire which added Si is shown.

  As a sample, a sample obtained by annealing a 0.26 mm diameter wire rod at an annealing temperature of 400 ° C. for 1 hour, the wire rod according to Comparative Example 13 has the same component composition as the wire rod according to Comparative Example 11. And the wire rod according to Example 7 has the same component composition as the wire rod according to Example 5.

  The bending life was measured using a bending fatigue test. The bending fatigue test is a test in which a load is applied to a sample and repeated bending strains of tension and compression are applied to the sample surface. Specifically, first, as shown in FIG. 7A, the sample 20 is fixed to the clamp 12 included in the bending head 14, and the sample 20 is set between the bending jigs (that is, the ring 10). Then, a load is applied to the sample 20 by the weight 16. Next, the sample 20 is bent by rotating the ring 10 by 90 degrees as shown in FIG. By this operation, compressive strain is generated on the surface of the sample 20 in contact with the ring 10, and tensile strain is generated on the surface opposite to the surface where the compressive strain is generated.

  Thereafter, the sample 20 returns to the state shown in FIG. 7A (that is, the sample 20 is not bent). Subsequently, as shown in FIG. 7C, the sample 20 is bent by rotating the ring 10 by 90 degrees in the opposite direction to that in FIG. 7B. By this operation, compressive strain is generated on the surface of the sample 20 in contact with the ring 10, and tensile strain is generated on the surface opposite to the surface where the compressive strain is generated. Then, the sample 20 returns to the state shown in FIG. One cycle of this bending fatigue (Note that the state of (A) in FIG. 7 is changed to the state of (B), the state of (B) is returned to the state of (A), and the state of (A) is changed to the state of (C). The time required to enter the state and return from the state (C) to the state (A) is defined as one cycle).

  The surface bending strain is calculated from “surface bending strain (%) = r / (R + r) × 100 (%)”. “R” is the strand bending radius (30 mm), and “r” is the strand radius.

  As shown in FIG. 8, the wire rod according to Example 7 showed higher flex life characteristics than the wire rod according to Comparative Example 13.

  FIG. 9 is produced using a wire rod according to Comparative Example 14 using oxygen-free copper after annealing at 600 ° C. for 1 hour and a soft dilute copper alloy wire obtained by adding Ti to low-oxygen copper. The result of having measured the bending life with the wire rod which concerns on Example 8 was shown.

  As a sample, a sample obtained by annealing a 0.26 mm diameter wire rod at an annealing temperature of 600 ° C. for 1 hour, the wire rod according to Comparative Example 14 has the same component composition as the wire rod according to Comparative Example 11. And the wire rod according to Example 8 has the same component composition as the wire rod according to Example 5. Further, the bending life was measured in the same manner as the measuring method shown in FIG. As a result, the wire rod according to Example 8 exhibited higher bending life characteristics than the wire rod according to Comparative Example 14.

  The results of the bending life measurement of the wire rods according to Example 7, Example 8, Comparative Example 13, and Comparative Example 14 are the results of the wire rods according to Example 7 and Example 8 under any annealing conditions. It can be understood that the 0.2% proof stress value is larger than that of the wire rods according to Comparative Example 13 and Comparative Example 14.

(Examination on crystal structure of soft dilute copper alloy wire)
11 shows a cross-sectional structure in the width direction of the sample according to Comparative Example 14, and FIG. 10 shows a cross-sectional structure in the width direction of the sample according to Example 8.

  Referring to FIG. 10, it can be seen that in the crystal structure of Comparative Example 14, crystal grains having the same size are arranged uniformly from the surface portion to the center portion. On the other hand, in the crystal structure of Example 8, the size of the crystal grains is sparse as a whole, and the crystal grain size in the layer formed thin near the surface in the cross-sectional direction of the sample is smaller than the internal crystal grain size. It is extremely small.

  The inventor believes that the fine crystal grain layer that appears in the surface layer that is not formed in Comparative Example 14 contributes to the improvement of the bending characteristics of Example 8.

  Usually, it is understood that if an annealing process is performed at an annealing temperature of 600 ° C. for 1 hour, crystal grains uniformly coarsened by recrystallization as in Comparative Example 14 are formed. However, in this example, even if an annealing process is performed at an annealing temperature of 600 ° C. for 1 hour, a fine crystal grain layer remains on the surface layer. Therefore, in the present Example, it is thought that the soft dilute copper alloy material which was a soft copper material and was excellent in the bending characteristic was obtained.

  In addition, based on the cross-sectional photographs of the crystal structure shown in FIGS. 10 and 11, the average crystal grain size in the surface layer of the samples according to Example 8 and Comparative Example 14 was measured.

  FIG. 12 shows an outline of a method for measuring the average grain size in the surface layer.

  As shown in FIG. 12, the crystal grain size was measured in a range of 1 mm in length from the surface of the cross section in the width direction of 0.26 mm diameter to the depth of 50 μm at 10 μm intervals in the depth direction. And the average value was calculated | required from each measured value (actually measured value), and this average value was made into the average crystal grain size.

  As a result of the measurement, the average crystal grain size in the surface layer of Comparative Example 14 was 50 μm, whereas the average crystal grain size in the surface layer of Example 8 was 10 μm, which was greatly different. It is thought that the growth of cracks in the bending fatigue test was suppressed due to the fine average grain size of the surface layer, and the bending fatigue life was extended (in addition, if the grain size is large, cracks propagate along the grain boundaries) However, if the crystal grain size is small, the direction of crack growth changes, so the growth is suppressed.) As described above, this is considered to be the reason for the great difference in the bending characteristics between the comparative example and the example.

  The average crystal grain size in the surface layer of Example 6 and Comparative Example 12 having a diameter of 2.6 mm is 10 mm in length at a depth of 50 μm in the depth direction from the surface of the cross section in the width direction of 2.6 mm diameter. The grain size in the range was measured.

  As a result of the measurement, the average crystal grain size in the surface layer of Comparative Example 12 was 100 μm, whereas the average crystal grain size in the surface layer of Example 6 was 20 μm.

  In order to achieve the effect of the present embodiment, the upper limit value of the average grain size of the surface layer is preferably 20 μm or less. In consideration of the manufacturing limit, the average grain size is preferably 5 μm or more.

(Application example of copper bonding wire)
The third material (φ2.6 mm) from the top of Example 1 shown in Table 1 was annealed at 300 ° C. for 1 hour, then drawn to φ0.025 mm, and at 400 ° C. for 10 to 60 seconds. Travel annealing was performed. By this step, a copper bonding wire was produced.

  Further, the third material (φ2.6 mm) from the top in Example 1 shown in Table 1 was drawn to φ0.9 mm, and then annealed at 300 ° C. for 1 hour, and then φ0.025 mm. The wire was further drawn until it was annealed at 400 ° C. for 10 to 60 seconds. By this step, a copper bonding wire was produced.

  In addition, in the manufacturing method of these copper bonding wires, the raw material is made into a φ8 mm wire rod at a molten copper temperature of 1320 ° C. and a rolling temperature of 880 ° C. to 550 ° C. The wire drawing material is used.

(Application example of copper bonding wire to semiconductor devices)
After mounting the semiconductor element on the frame (die) through the connecting material and connecting the electrode of the semiconductor element to the inner lead using the copper bonding wire according to the embodiment, the semiconductor element, the frame, the inner lead, and The wire was resin-sealed with resin to manufacture a semiconductor device.

  While the embodiments and examples of the present invention have been described above, the embodiments and examples described above do not limit the invention according to the claims. It should be noted that not all combinations of features described in the embodiments and examples are necessarily essential to the means for solving the problems of the invention.

10 Ring 12 Clamp 14 Bending head 16 Weight 20 Sample

Claims (8)

A copper bonding wire comprising copper and an additive element selected from the group consisting of Ti, Mg, Zr, Nb, Ca, V, Ni, Mn, and Cr, the balance being inevitable impurities,
The said copper bonding wire is a copper bonding wire which has the surface layer whose average crystal grain size to the depth of 50 micrometers is 50 micrometers or less from the surface to the inside in the crystal structure before a process.   The copper bonding wire of Claim 1 containing 2 mass ppm or more and 12 mass ppm or less sulfur, 2 mass ppm or more and 30 mass ppm or less oxygen, and 4 mass ppm or more and 55 mass ppm or less titanium.   The copper bonding wire according to claim 2, wherein the electrical conductivity is 98% IACS or more. The sulfur (S) and the titanium (Ti) are TiO, TiO ₂ , TiS, or a compound having a Ti—O—S bond, or the TiO, the TiO ₂ , the TiS, or the Ti—O—S bond. The copper bonding wire according to claim 3, wherein the copper bonding wire is contained as an agglomerate of a compound having the remaining Ti and S as a solid solution. The TiO, the TiO ₂ , the TiS, the compound of Ti—O—S or the aggregates are 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;
The TiS has a size of 200 nm or less;
The compound or aggregate in the form of Ti-O-S has a size of 300 nm or less,
The copper bonding wire according to claim 4, wherein the particle size of 500 nm or less is 90% or more. Molten metal that melts a soft dilute copper alloy material containing an additive element selected from the group consisting of Ti, Mg, Zr, Nb, Ca, V, Ni, Mn, and Cr at a molten copper temperature of 1100 ° C. or higher and 1320 ° C. or lower. Manufacturing process,
A wire rod production step of producing a wire rod from the molten metal;
A hot rolling step of hot rolling the wire rod at a temperature of 880 ° C. or lower and 550 ° C. or higher;
A method for producing a copper bonding wire, comprising: a wire drawing process for drawing the wire rod that has undergone the hot rolling process.   The additive element is Ti, and the soft dilute copper alloy material includes sulfur of 2 mass ppm to 12 mass ppm, oxygen of more than 2 mass ppm to 30 mass ppm and titanium, and titanium of 4 mass ppm to 55 mass ppm. Item 7. A method for producing a copper bonding wire according to Item 6.   The method for producing a copper bonding wire according to claim 7, wherein a softening temperature of the soft dilute copper alloy material is 130 ° C. or more and 148 ° C. or less in a size of φ2.6 mm.