JP4301095B2 - Dice set - Google Patents

Description

  The present invention relates to wire drawing of a bonding wire, and more particularly to a die set used in a final wire drawing process for finishing a wire diameter to be shipped to a customer.

  In order to electrically connect an electrode pad on a semiconductor element to a lead frame, a resin substrate, and the like, it is widely used to use a bonding wire having a diameter of 20 to 50 μm. The characteristics required for the material used for the bonding wire are that it has excellent spreadability, a relatively low electrical resistance, and excellent corrosion resistance. For this reason, gold is mainly used for the bonding wires.

  The manufacturing process is simply described as follows. First, a very small amount of other elements are added to high-purity gold and melt cast. The reason for adding a trace amount of other elements is that high-purity gold has poor strength. Next, the wire diameter of the bus bar after rough machining is reduced to a predetermined wire diameter using a wire drawing machine. In the process of thinning to a predetermined wire diameter, a plurality of dies (hereinafter, a plurality of dies used for one wire drawing process are referred to as a die set) are drawn through a wire in a wire drawing machine. The wire diameter is reduced. Finally, heat treatment is applied to remove processing strain, and the product is wound on a predetermined spool before shipment.

  However, even if a small amount of other elements are added to gold, which is the main component of the bonding wire, its strength is lower than other wire drawing materials such as copper and stainless steel, and the bonding wire is likely to break in the wire drawing process. .

  For the occurrence of wire breakage in the wire drawing process, the kind and amount of additive elements contained in the bonding wire, the presence or absence of foreign matter mixed in the bonding wire, the presence or absence of surface defects during processing, the base material wound on the spool Various factors such as the unwinding property of the wire, the characteristics of the lubricant for wire drawing, the wire drawing machine and its jig, etc. are influential.

  In order to reduce the number of disconnections, for example, the crystal structure of the busbar is changed to a columnar crystal structure (Japanese Patent Laid-Open No. 9-10898), or the drawing tension with a die and the optimization of the winding tension on the bobbin (Japanese Patent Laid-Open No. 9-98898). 2002-282929) and the like.

  However, according to these conventional technologies, the bonding wire in the wire drawing process is not sufficiently reduced.

Japanese Patent Laid-Open No. 9-10898

JP 2002-282929 A

  This invention is made | formed in view of this problem, Comprising: It aims at reducing the disconnection of the bonding wire in a wire-drawing process.

The first aspect of the die set according to the present invention is that each of a plurality of dies used in a single wire drawing step for making a bonding wire in which a trace amount of other elements are added to gold into a wire diameter of 20 to 50 μm. When the reduction rate of the die other than the leading die and the final die in the wire drawing process is set to a constant value, the reduction rate of the leading die is 20 to 95% of the constant value. It is in the range.

The second aspect of the die set according to the present invention is that each of a plurality of dies used in a single wire drawing step for making a bonding wire in which a trace amount of other elements are added to gold into a wire diameter of 20 to 50 μm. When the reduction rate of the final die is defined as a constant value, the reduction rate of the final die is within a range of 25 to 90% of the constant value. It is characterized by being.

  In a third aspect of the die set according to the present invention, a reduction rate of each of a plurality of dies used in a single wire drawing process of the bonding wire is defined as Equation 1 above, and a leading die and a final die in the wire drawing process are defined. When the reduction rate of the other dies is a constant value, the reduction rate of the leading die is in the range of 20 to 95% of the constant value, and the reduction rate of the final die is in the range of 25 to 90% of the constant value. It is characterized by that.

  The constant value is, for example, in the range of 6 to 10%.

  In a fourth aspect of the die set according to the present invention, each design reduction of each of the plurality of dies is calculated using a calculation formula in which the design reduction rate of each of the plurality of dies decreases at a constant rate from the head toward the rear. When the rate is calculated, the reduction rate of the leading die is 20 to 95% of the calculated design reduction rate, and the reduction rate of the final die is 25 to 90% of the calculated design reduction rate. .

  The calculation formula is, for example, Formula 2 below, where a and b are constants.

  The fifth aspect of the die set according to the present invention uses a calculation formula in which the reduction rate of the design reduction rate with respect to the previous die is higher as the die closer to the head is higher and the design reduction rate is closer to a constant value with the rear die. When the design reduction rate of each of the plurality of dies is calculated, the reduction rate of the leading die is 20 to 95% of the calculated design reduction rate, and the reduction rate of the final die is 25 to 25 of the calculated design reduction rate. 90%.

  The calculation formula is, for example, Formula 3 below, where a, b, c, and d are constants.

  In the sixth aspect of the die set according to the present invention, the design reduction rate of each of the plurality of dies is calculated using a calculation formula in which the reduction rate of the design reduction rate relative to the previous die is higher in the rear die. The reduction rate of the leading die is 20 to 95% of the calculated design reduction rate, and the reduction rate of the final die is 25 to 90% of the calculated design reduction rate.

  The calculation formula is, for example, Formula 4 below, where a and b are constants.

  The design reduction rate is a reduction rate set in design for each die.

  According to the present invention, it is possible to reduce the disconnection rate in the leading die and the final die, which are likely to cause breakage in the wire drawing process of the bonding wire, thereby improving the productivity in wire drawing and the yield of the bonding wire. This makes it possible to reduce the cost of the bonding wire.

  As described above, the occurrence of disconnection in the wire drawing process includes the type and amount of additive elements contained in the bonding wire, the presence or absence of foreign matter mixed in the bonding wire, the presence or absence of surface defects during processing, the spool Various factors such as the unwinding property of the wound base material, the properties of the wire drawing lubricant, the wire drawing machine and its jigs are affected, but the present inventor paid attention to the die among the aforementioned factors. .

  The reason why the present inventor has paid attention to the dice is that the wire is continuously passed through about 10 dies in one drawing process, and the dies at both ends of the die set used in one drawing process, that is, the leading die This is because the disconnection rate between the die and the final die was high.

  If the bonding wire material, wire surface defects, lubricant, and the like are the cause of the disconnection, it is considered that the disconnection is likely to occur as the wire diameter becomes thinner. However, since the disconnection rate at the dies at both ends of the die set was actually high, the inventor found that the unwinding property of the base material and the structure of the wire drawing machine had a high disconnection rate at both ends of the die set. I thought it was a factor.

  However, it is difficult to completely solve the unwinding property. This is because in order to pursue production efficiency, it is necessary to increase the number of rolls. Also, the wire tension in the vicinity of the final die and the wire tension in the other dies are considered to be the cause of the wire breakage near the final die, but this is unavoidable due to the structure of the wire drawing machine. Since it is not, it is difficult to solve by the structural device of the wire drawing machine.

  Accordingly, the present inventor has paid attention to the dice and conducted extensive research to determine whether the disconnection rate at the dice at both ends of the dice set can be reduced by devising the dice diameter of each dice in the dice set.

  In designing a die set, the reduction rate of each die is usually fixed (for example, JP-A-2003-48014), or the reduction rate is reduced as the wire diameter is reduced.

  The reason for designing the reduction rate of each die to be constant is that the wire drawing speed increases as the wire diameter decreases, and that the wire drawing speed changes more when the reduction rate is larger. This is because, when the reduction rate of each die is changed, the balance of the rate of increase of the drawing speed between the front and rear dies is lost, and there is a possibility that the wire may be broken and the wire may be disconnected. When the reduction rate is constant, it is preferable to set the design reduction rate to 6 to 10% in the final wire drawing process for finishing to the wire diameter shipped to the customer. This is because if the design reduction rate is lower than 6%, the reduction amount of the wire diameter in the wire drawing process using one die set is reduced and the production efficiency is deteriorated. In addition, if the design reduction rate is higher than 10%, the disconnection rate is high even in dies other than both ends of the die set.

  On the other hand, the reason why the reduction rate may be designed to gradually decrease as the wire diameter decreases is that the wire tends to be broken more easily as the wire diameter decreases. The design reduction rate is gradually reduced by a method of decreasing the design reduction rate of the n-th die at a constant rate from the head toward the rear as in Equation 2 above, or a die close to the head as in Equation 3 above. A method of increasing the reduction rate of the design reduction rate relative to the previous die and increasing the design reduction rate to a constant value as the rear die, or the rear die that is more likely to break as shown in Equation 4 above, the previous die. There is a method of increasing the reduction rate of the design reduction rate with respect to.

  However, it has been difficult to reduce the disconnection rate at the dies at both ends of the die set only by these design measures.

  In the final die, the present die is wound immediately on a tension cut roll or directly wound on a spool, so that the force from the wire applied to the die and the tension of the wire are compared with other dies. In addition, since the fluctuation states of these forces are different, it is considered that the tendency to break easily occurs in the final die. This is supported by the fact that when only the final die is made independent from the inside of the wire drawing tank, the tension becomes larger and the wire is more easily disconnected.

  As a result, the inventor makes the actual final die reduction rate lower than the design reduction rate of the final die calculated by the same calculation method as when calculating the reduction rate of other dice in the die set. I learned that it would be possible to prevent disconnection.

  Therefore, the reduction rate of the final die is set to 25 to 90% of the design reduction rate of the final die calculated in the same way as other dies. The reason why the lower limit is set to 25% of the calculated value is that when the reduction rate is less than 25% of the calculated value, the pulling force applied to the final die is small, so that the vibration is eliminated when the wire is vibrated before and after the final die. This is because an irregular pattern generated by minute wire diameter variation may occur on the wire surface. The reason why the upper limit is 90% of the calculated value is that when the upper limit is exceeded, the effect of lowering the disconnection rate in the final die is hardly exhibited.

  Further, in the leading die, when the bus bar is bitten during unwinding from the wound bus bar, the tension applied to the wire may suddenly increase and the wire breaks. When the winding is unwound, the bus bar is bitten when the winding state of the bus bar is bad. Furthermore, since the die is worn as it is used, the die diameter increases, and the wire diameter of the drawn wire is thick, so that the wire diameter of the base material is often larger than the design value. For this reason, the reduction rate of the leading die may be substantially higher than the design.

  Therefore, the reduction rate of the top die is set to 20 to 95% of the reduction rate of the design top die calculated based on the same concept as other dies. The reason for limiting the numerical value is that if the reduction rate is less than 20%, the tension is low when the wire drawing is in a steady state, and the wire rod tends to get entangled with the capstan of the wire drawing machine. This is because the lowering effect cannot be fully exhibited.

  In addition, the present invention is a wire drawing in which a capstan or a die is submerged in a wire drawing solution in a wire drawing tank, or a wire drawing solution is sprayed on the die or a capstan. It can be applied regardless of the form of the machine. Further, the present invention can be applied regardless of the capstan shape such as a cylindrical straight capstan or a cone type capstan in which the capstan diameter increases as the wire diameter decreases.

  Examples of the present invention will be specifically described below in comparison with comparative examples not belonging to the scope of the present invention.

(Examples 1-6 and Comparative Examples 1-6)
Table 1 shows the die diameter (μm) of each die of the die sets of Examples 1 to 6, and the value in parentheses shows the reduction rate (%) in each die. Table 2 shows the die diameter (μm) of each die of the die sets of Comparative Examples 1 to 6, and the value in parenthesis shows the reduction rate (%) in each die.

  In Examples 1 to 6 and Comparative Examples 1 to 6, an ingot in which 10 mass ppm of calcium and 5 mass ppm of beryllium were added to high-purity gold was prepared, rough processed with a groove roll, and then drawn in a wire drawing step. Wire was produced to produce a wire having a predetermined wire diameter. The die set used for the wire drawing process consists of 12 dies. In the wire drawing process, the bus passes through the leading die, the dies 2 to 11 and the final die in this order, and the wire diameter is reduced to a predetermined wire diameter. In Examples 1-6 and Comparative Examples 1-6, the diameters of the 12 dies were the same except for the final dies. The reduction rate in the design of each die was set to 8.5% in consideration of the disconnection rate in the die set, but the die size was determined based on this value for the leading die and the final die, and the leading die reduction. The rate was changed by changing the bus wire diameter, and the reduction rate of the final die was changed by changing the final wire diameter after wire drawing. The die diameters of the dies 2 to 11 were determined based on the design reduction rate of 8.5%. From the relationship of effective numbers in the wire diameter display, the dies of Examples 1 to 6 and Comparative Examples 1 to 6 were used. The reduction rate in 2 to 11 was in the range of 97% to 104% with respect to 8.5% which is the designed reduction rate.

  Next, the evaluation method of each dice set of Examples 1-6 and Comparative Examples 1-6 is demonstrated. Using each die set, wire drawing is performed until the length of the wire after drawing becomes 1,000,000 m, and the number of wire breaks in the leading die and the final die is measured, and the wire after the drawing process is completed. The appearance of was observed. The appearance was observed from the viewpoint of whether irregular patterns were generated. Table 3 shows the measurement results of the number of disconnections and the results of appearance observation when using each of the die sets of Examples 1 to 6 and Comparative Examples 1 to 6. At the same time, the reduction rate of the leading die and the final die is shown as a ratio with respect to 8.5% which is the design value of the reduction rate of the dies 2 to 11.

  As shown in Table 3, in Examples 1 to 6 within the scope of the present invention, disconnection hardly occurred in the leading die and the final die, and the appearance of the wire after the wire drawing process was good. On the other hand, in Comparative Examples 1, 2, 5, and 6 in which the reduction rate of the leading die was outside the range of the present invention, many disconnections occurred in the leading die. In Comparative Examples 1 and 3 in which the reduction rate of the final die deviates from the upper limit of the present invention, many disconnections occur in the final die, and in Comparative Examples 4 and 5 in which the reduction rate of the final die deviates from the lower limit of the present invention, occurrence of disconnection occurs. However, there was an abnormality in the appearance of the wire after the wire drawing process.

(Examples 7 and 8 and Comparative Example 7)
Table 4 shows the die diameter (μm) of each die of Examples 7 and 8 and Comparative Example 7, and the value in parentheses shows the reduction rate (%) in each die. .

  In Examples 1 to 6 and Comparative Examples 1 to 6, the reduction rate in design of each die was set to a constant value (8.5%), but in Examples 7 and 8 and Comparative Example 7, n from the top The design reduction rate (%) of the second die was calculated from Equation 5 below. Formula 5 is a formula in Formula 3 where a = 3.75, b = 1, c = 0.03, and d = 0.

  For the dies 2 to 11, the die diameter was determined based on the design reduction rate obtained from Equation 5. For the first die and the final die, the die diameter is not determined based on the design reduction rate obtained from Equation 5, and the final die reduction rate is changed by changing the final wire diameter after drawing. I let you.

  In Examples 7 and 8 and Comparative Example 7, as in Examples 1 to 6 and Comparative Examples 1 to 6, an ingot was prepared by adding 10 mass ppm of calcium and 5 mass ppm of beryllium to high-purity gold. Then, sequential processing was performed to prepare a wire having a predetermined wire diameter.

  As shown in Table 4, the die diameter of each die of Examples 7 and 8 and Comparative Example 7 was unified for each die except for the final die. In Examples 7 and 8 and Comparative Example 7, since the same base material was used, the reduction rate of the leading die was the same in Examples 7 and 8 and Comparative Example 7. The reduction rate of the final die was changed by changing the final wire diameter after wire drawing.

  Table 5 shows the ratio of the reduction rate of the leading die and the final die to the design value, the number of disconnections, and the appearance observation results of the wire after the drawing process for Examples 7 and 8 and Comparative Example 7. . In Examples 7 and 8, since the reduction rate of both the leading die and the final die is within the range of the present invention, disconnection hardly occurs and no abnormality is observed in the appearance. On the other hand, in Comparative Example 7, the reduction rate of the final die was below the lower limit of the present invention, and thus an abnormality was observed in the appearance of the wire after the drawing process.

Claims (10)

The reduction rate of each of a plurality of dies used in a single wire drawing process for making a bonding wire in which a trace amount of other elements are added to gold into a wire diameter of 20 to 50 μm.

Dies characterized in that when the reduction rate of the die other than the first die and the final die in the wire drawing process is a constant value, the reduction rate of the first die is in the range of 20 to 95% of the constant value. set. The reduction rate of each of a plurality of dies used in a single wire drawing process for making a bonding wire in which a trace amount of other elements are added to gold into a wire diameter of 20 to 50 μm.

Dies characterized in that the reduction rate of the final die is in the range of 25 to 90% of the constant value when the reduction rate of the die other than the first die and the final die in the wire drawing process is a constant value. set. The reduction rate of each of a plurality of dies used in a single wire drawing process

When the reduction rate of the die other than the first die and the final die in the wire drawing process is a constant value, the reduction rate of the first die is in the range of 20 to 95% of the constant value, and the reduction rate of the final die. Is in a range of 25 to 90% of the predetermined value.   The die set according to any one of claims 1 to 3, wherein the constant value is in a range of 6 to 10%. The reduction rate of each of a plurality of dies used in a single wire drawing process

When the design reduction rate of each of the plurality of dies is calculated using a calculation formula in which the design reduction rate of each of the plurality of dies decreases at a constant rate from the beginning to the back, A die set, wherein the reduction rate is 20 to 95% of the calculated design reduction rate, and the reduction rate of the final die is 25 to 90% of the calculated design reduction rate. The reduction rate of each of a plurality of dies used in a single wire drawing process

The reduction rate of the design reduction rate with respect to the previous die is higher as the die closer to the head is higher, and the design reduction of each of the plurality of dies is calculated using a calculation formula in which the design reduction rate approaches a constant value as the rear die is closer. When the rate is calculated, the reduction rate of the leading die is 20 to 95% of the calculated design reduction rate, and the reduction rate of the final die is 25 to 90% of the calculated design reduction rate. Dice set. The reduction rate of each of a plurality of dies used in a single wire drawing process

When the calculation reduction rate of each of the plurality of dies is calculated using a calculation formula in which the reduction rate of the design reduction rate with respect to the previous die is higher in the rear die, the reduction rate of the first die is calculated. A die set, wherein the reduction rate of the final die is 20 to 95%, and the reduction rate of the final die is 25 to 90% of the calculated design reduction rate. In the calculation formula, when a and b are constants,

The die set according to claim 5, wherein: In the calculation formula, when a, b, c, and d are constants,

The die set according to claim 6, wherein: In the calculation formula, when a and b are constants,

The die set according to claim 7, wherein: