JP2008254056A - Method for producing base material for bonding wire, and bonding wire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bonding wire in which the generation of a defect in cleaning and a defect in eccentric balls in the case of a wire bonding can be suppressed even in a narrow bonding pitch. <P>SOLUTION: A crucible charged with a metal as the main component and Pd is arranged at a heating space. The molten metal is heated at 1,350 to 1,500°C, thereafter, the crucible is drawn from the heating space toward the lower part in such a manner that the crucible is successively annealed from the lower part to the upper part, and the molten metal in the crucible is solidified, so as to cast an ingot. The obtained ingot and a prescribed additional element other than Pd are charged to a continuous casting furnace and is heated in the continuous casting furnace. The molten metal in the continuous casting furnace is heated at 1,350 to 1,500°C, is held for 10 to 15 min at the temperature of the molten metal, and is successively drawn from the lower part of the continuous casting furnace through a water cooling type die, so as to be solidified. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a bonding wire used for electrically connecting a chip of a semiconductor element and an external lead, and a method for manufacturing a bonding wire base material.

  In order to manufacture a bonding wire used to connect an electrode on a semiconductor element and a lead, first, an ingot of a predetermined composition is cast, and then the obtained ingot is subjected to intermediate processing by roll processing or direct die processing. Processing up to wire diameter. The obtained wire having an intermediate wire diameter is subjected to wire drawing with a diamond die or the like to a predetermined wire diameter of, for example, 15 μm or 30 μm, and further, the processing strain is removed by final annealing to obtain a bonding wire.

  As a method for manufacturing an ingot for a bonding wire, an element that is a main component, for example, Au, and an additive element are charged into a container that contains molten metal, for example, a crucible, and the crucible is heated by a heating device. And the method of drawing the crucible downward from the heating space and solidifying the molten metal in the crucible so that the crucible is gradually cooled from the lower part to the upper part in order. is there.

  FIG. 1 is a longitudinal sectional view showing a casting furnace for casting such an ingot.

  As shown in the drawing, the crucible (1) is gradually cooled from the lower part to the upper part by pulling the crucible (1) downward from the heating space formed by the heating device (2), and the molten metal in the crucible (1). (3) also solidifies from the lower surface to the upper surface. Thereby, the ingot without a shrinkage nest (cavity) is cast. In this case, the drawing speed is 10 to 40 mm / min.

  As described above, the obtained ingot is processed to the bonding wire through the intermediate wire diameter.

  Further, there is a continuous casting method including a step of charging a raw material into a melting furnace and heating it to about 1200 to 1250 ° C., and then drawing the molten metal from a lower part of the melting furnace through a water-cooled die and solidifying it.

  FIG. 2 is a longitudinal sectional view showing a continuous casting furnace. In the continuous casting method, as shown in the figure, molten metal (6) is poured into a furnace (4) installed in a heating device (5), and the molten metal (6) is poured into a die (7) cooled by a water cooling jacket. By passing 6) and solidifying, a wire rod (9) corresponding to the die wire diameter is cast. In this case, the drawing speed is 10 to 300 mm / min.

  Thereafter, the obtained wire is drawn to a predetermined wire diameter, and further, the processing strain is removed by final annealing to obtain a bonding wire.

  The obtained bonding wire is subjected to wire bonding, for example, as shown in a perspective view in FIG. 3, to obtain a semiconductor element.

  In recent years, in order to cope with the reduction in size and size of semiconductor elements and packages, in the wire loop (10) obtained by wire bonding, the wire interval (bonding pitch) is narrowed, and the loop length of the wire loop (10) is also It is getting longer like 4mm and 5mm. For this reason, if there is an extremely small bend or leaning failure in an angle, adjacent wire loops (10) are likely to come into contact with each other, resulting in frequent short-circuit failures.

  Specifically, the leaning failure is inclined laterally with respect to the direction in which the wire loop (10) extends, immediately above the ball, which is a portion immediately above the ball (12) bonded to the pad of the semiconductor element. The state where the upper part of the inclined wire loop (10) is close to the upper part of the adjacent wire loop (10) is said. Leaning defects increase the risk of electrical shorts in resin sealing in the next process, so that a package in which a leaning defect has occurred is treated as a defective product, which is a factor that greatly reduces the product yield.

  Furthermore, there is also a problem of eccentric ball failure in which the roundness of the ball (12) bonded to the pad of the semiconductor element is lowered.

  Specifically, the eccentric ball defect means that the long side becomes longer than the specified dimension, so that the risk of contact with an adjacent ball is increased, which in turn causes an electrical short circuit. A package in which a core ball defect has occurred is processed as a defective product, which is a factor that greatly reduces the product yield.

  One method of reducing leaning defects and eccentric ball defects is to homogenize materials. However, since there are a wide variety of additive elements that are important in manufacturing a bonding wire and the total amount of additives tends to increase, there is a problem that it is difficult to ensure homogenization.

In particular, in bonding wires, elements that dissolve in Au, such as Pd and Pt, can be added at a higher concentration than other elements that do not dissolve, so that they are effective in improving strength, In order to improve the reliability of the bonding portion, bonding wires added with Pd and Pt obtained by a conventional manufacturing method may be homogeneously distributed because their melting points are higher than those of Au. This was considered difficult, and this was considered to be the cause of frequent defects in leaning and eccentric balls.
JP 2005-138113 A

  The present invention provides a method for manufacturing an ingot or wire rod for bonding wire capable of uniformly dispersing an additive element, and by using the ingot or wire rod to which the additive element is uniformly added as a base material, narrow bonding is achieved. It is an object of the present invention to provide a bonding wire that can suppress the occurrence of leaning defects and eccentric ball defects during wire bonding even with a pitch.

  The method for manufacturing an ingot for a bonding wire according to the present invention includes a bonding wire in which 0.1% by mass or more of Au and an additive element having a melting point of 300 ° C. or higher than Au are added. The above elements are charged in the crucible, the crucible is placed in the heating space, and the molten metal in the crucible is heated to 1350 ° C. or higher and 1500 ° C. or lower, and then the crucible is gradually cooled from the bottom to the top. Then, the molten metal is drawn downward from the heating space, and the molten metal is solidified to produce an ingot, which is then charged into a continuous casting furnace, the continuous casting furnace is heated, and the molten metal in the continuous casting furnace is heated to 1350 ° C. or more, 1500 After the temperature of the molten metal is maintained at 10 ° C. or lower for 10 to 15 minutes, the molten metal is drawn out from the lower part of the continuous casting furnace through a water-cooled die and solidified.

  In addition, when further adding a predetermined additive element other than an element having a melting point of 300 ° C. or higher than Au, these additive elements are charged into a continuous casting furnace together with the bonding wire ingot.

  The bonding wire according to the present invention is obtained by processing an ingot or wire obtained using any of the above-described manufacturing methods to a predetermined wire diameter, contains at least Pd or Pt, and is a total of Pd or Pt. Content is 0.1-2.0 mass%, It is characterized by the above-mentioned.

  According to the present invention, in the process of casting a bonding wire ingot or wire, the additive element is uniformly dispersed, thereby providing a bonding wire in which the occurrence of leaning defects and eccentric ball defects is suppressed. Miniaturization and high density can be achieved.

  For the purpose of improving various characteristics required for bonding wires, various additive elements are added to Au as a main component for bonding wires to form alloys. As these additive elements, Pd and Pt may be added in an amount of about 0.1 to 2.0% by mass for the purpose of improving strength and reliability.

  When the present inventors add 0.1 to 2.0% by mass of an additive element such as Pd to the metal as the main component of the bonding wire, the segregation of Pd occurs when the melting temperature is low. As a result, it was assumed that uniform dispersion of Pd and the like could be impaired and problems such as leaning failure and eccentric ball failure could occur.

  As a result of repeating various experiments based on such knowledge, Au added with a high melting point element from Au such as Pd was melted at 1350 ° C. or more and 1500 ° C. or less, and an element having a higher melting point than Au such as Pd was uniformly distributed in Au. Further, by adopting means for dispersing and re-melting the ingot in a continuous casting furnace set to 1350 ° C. or higher and 1500 ° C. or lower, the above-mentioned leaning defects and eccentric ball defects were reduced. The inventors have obtained knowledge that a wire for bonding wire, which is considered to have a higher melting point element dispersed more uniformly in Au, can be obtained by a continuous casting method manufactured by an appropriate working method.

  When casting a bonding wire ingot or wire containing 0.5 to 1.5% by mass of Pd under the condition where the furnace temperature is about 1200 ° C, it is completely related to the melting point of Pd (around 1550 ° C). It is considered that Pd is clustered and remains in the Au bulk without melting, and in the obtained ingot or wire rod, Pd is not uniformly dispersed and segregated.

  Since such a phenomenon is limited to a minute region, it has not been proved by EPMA analysis or the like. It is considered that in the bonding wire having the final wire diameter obtained by processing and annealing, a leaning defect and an eccentric ball defect are caused.

Therefore, in the present invention, when melting a high melting point element such as Au and Pd, the molten metal is heated to 1350 ° C. or higher and 1500 ° C. or lower. If the molten metal is less than 1350 ° C., segregation of high melting point elements becomes larger than Au such as Pd. On the other hand, if the molten metal exceeds 1500 ° C., the manufacturing cost also increases, and the concentration of the additive element varies from production to production. The crucible is drawn downward from the heating space to a position where the upper part of the crucible remains in the heating space at a drawing speed of 10 to 40 mm / min, and the molten metal in the crucible is solidified from the lower surface to the upper surface, and then the heating space The heating in is stopped and the upper part of the molten metal is solidified. Thereby, an ingot without a shrinkage nest is cast. Ingots without shrinkage are produced because there is a possibility that slag separated from the ingot may fall into the shrinkage and be taken into the molten metal in the next continuous casting. It is necessary to make the pulling speed as slow as possible to prevent shrinkage. On the other hand, if the drawing speed at the time of solidification is too slow, a concentration gradient is generated in the solidification process, and the added element may be segregated to one side, which must be avoided. In consideration of the above, the pulling speed during solidification is suitably 10 to 40 mm / min. In this ingot production, the object is to add a high melting point element from Au and dissolve and disperse it in Au. However, it takes some time for the high melting point element to dissolve in Au. It is also necessary to set the retention time at. However, since the time until solid solution varies depending on the type and amount of the additive element and the presence / absence of forced stirring, the retention time must be appropriately set according to them. Considering, at least 5 minutes or more is necessary. Stirring is effective for shortening the holding time, and may be carried out.

  In the present invention, an ingot to which a high melting point element such as Pd is added is cast in advance, and the ingot is remelted. It is considered that segregation of clusters of refractory elements such as Pd can be further avoided by performing dissolution stepwise in this way.

  In particular, in the present invention, the wire for bonding wire in which the high melting point element such as Pd is more uniformly dispersed in Au is obtained by re-melting the ingot in a continuous casting furnace. Remelting is performed in a continuous casting furnace because continuous casting is solidified at a high cooling rate, and it is considered that the uniformity of the additive element is improved.

  The operation of the continuous casting method is the same as the conventional one except for the heating temperature. That is, after maintaining the temperature of the molten metal at the above temperature for 10 to 15 minutes, the molten metal is solidified by being pulled out from the lower part of the continuous casting furnace through a water-cooled die.

  In addition to the high melting point element such as Pd, a predetermined additive element is added to the bonding wire to Au in order to improve various characteristics of the bonding wire. When adding a predetermined additive element other than these high melting point elements such as Pd, the ingot is charged at the same time when it is charged into the continuous casting furnace. Predetermined additional elements other than these high melting point elements such as Pd have a melting point that is not as high as Pd, so if the furnace temperature is 1350 ° C. or higher, they are uniformly dispersed in Au by melting once. Because it is possible. Further, when a predetermined additive element other than these high melting point elements such as Pd is added in the casting process of the ingot, these additional elements evaporate due to a relatively high melting temperature.

  Further, Be (melting point: 1287 ° C.), Ca (melting point: 843 ° C.), rare earth elements, and the like are added in addition to the above-described high melting point elements such as Pd and Pt. In addition, as for these content, less than 0.01 mass% is mainstream as a whole.

  By processing the ingot or wire obtained by the above manufacturing method to a predetermined wire diameter, it contains at least Pd and Pt as additive elements, and the content of Pd and Pt is 0.1 to 2.0% by mass. In the Au bonding wire, an Au bonding wire in which Pd and Pt are extremely uniformly dispersed can be obtained. In the wire loop obtained by bonding using the Au bonding wire according to the present invention, the occurrence of leaning defects and eccentric ball defects is suppressed.

Example 1
1 was charged into a crucible (1) having an inner diameter of 25 mmφ and a length of 300 mm using a casting furnace having a crucible raising / lowering function shown in FIG. 1 and having a purity of 99.999% (5N). The crucible (1) was heated to 1400 ° C. in a casting furnace, Au was melted, and Pd was added so that the final bonding wire was 0.8% by mass. The actual addition amount of Pd is appropriately determined according to the operating conditions. Then, after maintaining at 1400 ° C. for 10 minutes, the molten Pd was pushed into the bottom of the crucible using a stir bar, and the mixture was uniformly dispersed and stirred for 2 minutes. After that, after holding for 1 minute and self-diffusion, the crucible is drawn from the lower part of the heating part of the casting furnace at a drawing speed of 20 mm / min so that the upper part 100 mm remains in the heating part, and then heated. By stopping, the molten metal was solidified from below. The ingot obtained by casting was 25 mmφ.

  Thereafter, the obtained ingot and Ca were charged into a continuous casting furnace whose longitudinal sectional view is shown in FIG. In addition, in the bonding wire finally obtained, the added amount of Ca is an amount determined to be 0.002% by mass. The melting temperature was set to 1400 ° C., and after confirming re-melting of the ingot, the added element was self-diffused by holding at the set temperature for 10 minutes.

  From that state, a wire having an intermediate wire diameter (similar to the inner diameter of the die) was drawn at a drawing speed of 100 mm / min through a die having an inner diameter of 8 mmφ at the bottom of the furnace and provided with a water-cooled jacket around it. The wire rod is subjected to reduced diameter drawing and intermediate annealing to make the final wire diameter 25 μmφ, and then final annealing (continuous annealing) so that the elongation at room temperature is 4 to 6%. To obtain a bonding wire.

  The obtained bonding wire was subjected to 7200 wire bonding using a capillary having an inner diameter of 30 μmφ at a wire interval of 90 μm, a loop length of 5 mm, and a loop height of 500 μm. (Olympus Co., Ltd.) was observed, and the case where the distance between the upper portions of adjacent wire loops was 40 μm or less was judged as a leaning defect. Further, the long side and the short side of the ball at the pad-side bonded portion were measured, and the case where the difference between the long side and the short side was 5 μm or more was judged as an eccentric ball defect. The evaluation results are shown in Table 1.

(Example 2)
The addition of Pd was 0.5 mass% in the finally obtained bonding wire, the addition of Ca was the addition of Ca and Be, and the added amount of Ca in the finally obtained bonding wire A bonding wire was produced by the same manufacturing method as in Example 1 except that the amount of Be was 0.0005 mass% and the addition amount of Be was 0.001 mass%, and the same evaluation was performed.

(Comparative Example 1)
The additive elements were simultaneously charged into the continuous casting furnace so that the final content of the bonding wire in Au was 0.8 mass% Pd and 0.002 mass% Ca, respectively. The melting temperature was set to 1250 ° C., and after confirming the melting of the charge, the additive element was self-diffused into Au by holding at the set temperature for 10 minutes.

  From that state, a wire with an intermediate wire diameter was drawn out at a drawing speed of 100 mm / min, and the obtained wire was subjected to reduced diameter drawing and intermediate annealing to a final wire diameter of 25 μmφ, and then at room temperature. Final annealing (continuous annealing) was performed so that the elongation percentage of the film became 4 to 6%, and a bonding wire was obtained.

  The obtained bonding wire was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

  As can be seen from Table 1, in Example 1 and Example 2 of the present invention, the number of leaning defects is reduced by 30% or more compared to Comparative Example 1, and the present invention may be effective in suppressing leaning defects. I understand.

  Further, the eccentric ball defects tended to occur discontinuously and frequently in Comparative Example 1, but were not observed at all in Examples 1 and 2.

It is the longitudinal cross-sectional view which showed the casting furnace which casts an ingot. It is the longitudinal cross-sectional view which showed the continuous casting furnace. It is a perspective view which shows the bonding wire obtained by wire bonding.

Explanation of symbols

1 crucible 2, 5 heating device 3, 6 molten metal 4 crucible for continuous casting furnace 7 water-cooled die 8 starting rod 9 bonding wire 10 wire loop 11 substrate 12 ball

Claims (3)

  In a bonding wire in which Au and an additive element having a melting point of 300 ° C. or higher than Au are added by 0.1% by mass or more, an element having a melting point of 300 ° C. or more higher than Au is added to the crucible. After placing in the heating space and heating the molten metal in the crucible to 1350 ° C. or higher and 1500 ° C. or lower, the crucible is gradually cooled from the lower part to the upper part in order to draw down the molten metal from the heating space. After solidifying and producing an ingot, it is charged into a continuous casting furnace, the continuous casting furnace is heated, the molten metal in the continuous casting furnace is set to 1350 ° C. or higher and 1500 ° C. or lower, and the temperature of the molten metal for 10 to 15 minutes. After holding, after the molten metal is drawn out from the lower part of the continuous casting furnace through a water-cooled die, it is solidified.   2. The method for producing a bonding wire according to claim 1, wherein the element not added at the time of producing the ingot is charged into a continuous casting furnace together with the bonding wire ingot.   It is obtained by processing the wire after continuous casting obtained by the production method according to claim 1 or 2 to a predetermined wire diameter, and the total content of Pd or Pt is 0.1 to 2.0% by mass. There is a bonding wire.

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