JP3500518B2 - Manufacturing method of ultrafine gold alloy wire - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a gold alloy extra fine wire for a semiconductor device, which is used for connecting an IC chip electrode and an external lead, and more specifically, to short-circuiting a gold alloy extra fine wire in a semiconductor device. The present invention relates to a method for manufacturing a gold alloy extra fine wire for semiconductor devices, which is useful for prevention and vibration resistance.

[0002]

2. Description of the Related Art As a method for connecting an electrode of a semiconductor chip such as an IC chip and an external lead, generally, a diameter of 0.0
1-0.1mm gold alloy extra fine wire (bonding wire)
The wire bonding method of connecting with is used.
In the wire bonding method, the tip of a gold alloy fine wire is first bonded to an electrode surface of a semiconductor chip such as an IC chip, the gold alloy fine wire is wired in a loop shape, and then second bonding is performed on an external lead. is there. This kind of wire bonding method is a method that can be mass-produced by a simple device, but when wired in a loop, the gold alloy ultrafine wire bends left and right with respect to the wiring direction and adjacent ultrafine wires contact each other to cause a short circuit. There is a problem that the gold alloy ultrafine wire is broken due to vibration or vibration. As a method for dealing with these problems, conventionally, high purity gold has 1 to 100 ppm by weight.
A corresponding method is used as a gold alloy extra fine wire containing a trace amount of element.

On the other hand, in recent years, ICs have been further enhanced in function and integration, and the number of electrodes has been increasing. In order to cope with this, in the loop formation of the wire bonding method, a long loop (long loop) and a wiring density have become high. Therefore, it has been necessary to further reduce the allowable amount of bending of the gold alloy ultrafine wire (loop) to the left and right with respect to the wiring direction to prevent the above-mentioned short circuit. It has become impossible to adequately meet such demands by means of only containing.

As a method of responding to the above-mentioned demand, Japanese Patent Laid-Open No. 6-
Japanese Patent No. 61292 proposes a cooling device in which a trouble such as a loop abnormality is avoided by immersing a gold alloy wire in a treatment liquid containing a perfluoro tertiary amine or the like for efficient cooling. It is disclosed that the method is effective for improving the unwinding property of the gold alloy ultrafine wire wound on the spool and preventing the occurrence of loop abnormality. However, this method is still insufficient to reduce the essential loop bending caused by the gold alloy ultrafine wire material.

In addition, in order to prevent the gold alloy extra fine wire from being broken due to vibration, which is the second problem described above, reliability has been increasingly demanded in recent years. As described above, in the conventional method, high purity gold is
A gold alloy fine wire containing a trace amount of element of 100 ppm by weight is used. For example, JP-A-5-179375
JP-A No. 2003-242242 proposes that a trace amount of Al, Ca, or the like is contained in high-purity gold to suppress disconnection due to vibration. However, in order to prevent disconnection due to vibration, it is still insufficient to contain a trace amount of element in the high-purity gold, and further improvement in reliability is required.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a gold alloy extra fine wire for wiring an electrode of a semiconductor chip such as an IC chip and an external lead even when a long loop and a high wiring density are provided. The amount by which the ultrafine alloy wire bends in the left-right direction with respect to the wiring direction (loop bend amount) can be reduced to effectively prevent short-circuiting due to contact between adjacent gold alloy ultrafine wires and vibration. It is an object of the present invention to provide a method for manufacturing a gold alloy ultrafine wire for a semiconductor device, which can improve the reliability by reducing the degree of disconnection of the gold alloy ultrafine wire.

[0007]

Means for Solving the Problems As a result of intensive investigations by the present inventors, it was found that a gold alloy ultrafine wire having a uniform central portion and outer peripheral portion is effective for the above problems.
The present invention has been completed. The main points are as follows.

That is, the first invention of the present application is to melt a gold alloy,
In the method of manufacturing a gold alloy extra fine wire for a semiconductor device, which comprises a step of casting to obtain an ingot, a step of performing a roughing process on the ingot, a step of wire drawing using a die, and a step of annealing treatment thereafter. The approach angle of the wire drawing die is 3 to 7 degrees or 8 to 15 degrees. Further, the second invention of the present application is characterized in that the step of obtaining the ingot is a step of cooling the molten metal of the molten gold alloy from the lower end in the crucible to solidify it. Furthermore, the third invention of the present application is characterized in that the hardness ratio between the central portion and the outer peripheral portion of the gold alloy extra fine wire obtained after the step of annealing is 0.9 to 1.0.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A method for manufacturing a gold alloy extra fine wire for a semiconductor device according to the present invention will be described in detail below. The gold alloy used in the present invention may have a gold alloy composition that is usually used as a gold alloy extra fine wire for semiconductor devices. The outline of the method of the present invention is as follows. First, a gold alloy is melted and cast to produce an ingot (ingot), and the ingot is subjected to roughing such as groove roll rolling and then wire drawing to give a predetermined wire. The gold alloy ultrafine wire is manufactured by processing into a diameter and further annealing treatment so as to obtain a predetermined elongation.

In the present invention, in the step of melting and casting a gold alloy to obtain an ingot, an ingot which suppresses the formation of a chill layer during the casting is preferably used. By using the ingot as a starting material, a gold alloy ultrafine wire in which the central portion and the outer peripheral portion of the gold alloy ultrafine wire are more uniform after annealing can be obtained, and the bending of the wiring (loop bending) and vibration, which are the subjects of the present invention, can be obtained. Since it has an extremely excellent effect in preventing disconnection due to, it is preferably used. An example of a method for obtaining an ingot in which the formation of the chill layer is suppressed is shown in FIG.
An explanation will be given using (a). In the figure, reference numeral 11 is a molten gold alloy, 12 is a crucible, and 13 is a high-frequency heating coil. First, the high-frequency heating coil 13 is used to melt the gold alloy in the crucible 12 to obtain the molten metal 11. Next, the high frequency heating coil 13 is moved upward from the lower end of the crucible 12 at a predetermined speed so that the molten metal 11 is solidified in the crucible 12. The solidification rate when solidifying the molten metal 11 is 80 mm / min or less, more preferably 50 mm / min or less. In this way, by cooling the molten gold alloy 11 from the lower end in the crucible 12 and solidifying it, it is possible to suppress the formation of a chill layer on the surface of the ingot, which is preferable. Here, the inner surface shape of the crucible 12 is
It is sufficient that the ingot solidified in the crucible 12 has a shape that facilitates roughing such as groove roll rolling. The inner surface of the crucible 12 preferably has a shape capable of obtaining an ingot longer than twice the radial side of the cross section, and more preferably a cylindrical shape. Graphite is preferably used as the crucible material.

On the other hand, a continuous casting method, which is a method for obtaining a commonly used ingot, will be described with reference to FIG. In the figure, reference numeral 11 is a molten gold alloy, 14 is a tundish, 15 is a graphite mold, 16 is a water cooling pipe for cooling the graphite mold, 17 is a solidified ingot, and the arrow is the ingot drawing direction. First, the molten gold alloy 11 is poured into the graphite mold 15 while adjusting the amount using the tundish 14. The graphite mold 15 is cooled by contacting it with a water cooling pipe 16. Therefore, the molten gold alloy 11 is the graphite mold 1
It is forcibly cooled by 5 and solidifies, and is withdrawn in the direction of the arrow. Conventionally, as a method for obtaining an ingot in the production of a gold alloy ultrafine wire for a semiconductor device, a continuous casting method shown in FIG. This method uses graphite, copper, etc. as the mold material,
The molten metal 11 is solidified at a speed of mm / min or more. By doing so, the melt 11 is forcibly cooled by the mold 15, so that a chill layer is formed on the surface portion of the ingot 17. As shown in FIG. 2 (a), the use of an ingot in which the molten metal 11 is cooled and solidified in the crucible 12 from the lower end is a homogeneous gold alloy extra fine wire with a small difference between the inner surface (center portion) and the outer surface (outer peripheral portion). It is thought that it has a preferable ingot structure for producing

The method for producing a gold alloy ultrafine wire according to the present invention is as follows:
After roughly processing the ingot obtained in the casting step, wire drawing is performed until it becomes an ultrafine wire having a diameter of 0.01 to 0.1 mm. Most commonly, the diameter of the ultrafine wire is 0.02-
It is 0.05 mm. A groove roll rolling method is preferably used for roughing the ingot.

[0013] When wire-drawing the gold alloy extra-fine wire, it has been emphasized in the past that the wire is easily cut because it is an extra-fine wire. Therefore, the number of wire breakages is reduced to increase the production efficiency. . As a method of dealing with this, in the past, the approach angle of the wire drawing die was set to 7.5 ± 0.2 degrees so that the die drawing force would be minimized, and wire breakage was suppressed to improve production efficiency. I have been trying. Here, the cross-sectional shape of the wire drawing die will be described with reference to FIG. In the figure, reference numeral 1 is a wire before wire drawing, 2 is a wire after wire drawing, 3 is a wire drawing die, 4 is a die approach portion, 5 is a die bearing portion, and α is an approach angle. . The wire to be drawn is reduced in the approach portion 4, and the shape of the wire is adjusted in the bearing portion 5. The approach angle α in the present invention is an inclination angle with respect to a reference line L parallel to the die axis, as shown in FIG. 1, and is represented by a half angle of the actual inclination angle of the die 3.

FIG. 5 shows the relationship between the approach angle α and the drawing force of the gold alloy wire. The horizontal axis represents the approach angle α, and the vertical axis represents the pulling force. As is clear from FIG. 5, the pulling-out force becomes minimum when the approach angle α is 7.5 degrees. In contrast to the above situation, in the present invention, the approach angle α
Should be set to 3.0 to 7.0 degrees or 8.0 to 15.0 degrees. Approach angle α of wire drawing die
In the case of the angle according to the present invention, the gold alloy ultrafine wire that has undergone the annealing step that is the next step, when used for the wiring of the semiconductor device, can reduce the amount of bending in the left-right direction, and can reduce the amount of vibration due to vibration. It has an excellent effect that it is possible to reduce the degree of disconnection of the ultrafine alloy wire. A more preferable approach angle α is 4.0 to 7.0 degrees or 8.0 to 12.5 degrees. At this angle, the gold alloy ultrafine wire that has undergone the annealing step has a more excellent effect on the above-mentioned problems of the present invention.

When the approach angle α is less than 3.0 degrees and more than 15.0 degrees, the number of wire breakages remarkably increases. Therefore, the lower limit value of the approach angle α of the present invention is 3.0 degrees and the upper limit value is 15. It was 0 degree. Further, when the approach angle α is 7.1 to 7.9 degrees including 7.5 ± 0.2 degrees which is conventionally used, the gold alloy ultrafine wire after the annealing step bends in the left and right direction at the time of wiring. Is large and the gold alloy ultrafine wire is easily broken due to vibration. Therefore, the approach angle α is set within the above range.

Further, the step of obtaining an ingot is a step of solidifying by cooling from the lower end in the crucible, and by using the ingot thus obtained, the number of wire breakages at the time of wire drawing can be reduced, and at the same time, according to the present invention. With respect to the problem, the gold alloy fine wire wired in a loop shape is more effectively exhibited against the bending in the left-right direction and the disconnection due to vibration.

The gold alloy ultrafine wire drawn as described above is annealed for refining. Usually, annealing is performed so that the elongation rate becomes 4%. As the annealing method, a continuous annealing method is preferred in which the ultrafine wires are sequentially passed through the furnace and annealed. The annealing temperature of the present invention is 350 to 65.
0 ° C. is used depending on the type of gold alloy. The residence time in the furnace is preferably 0.4 to 3.0 seconds.

By the method of the present invention, that is, by performing wire drawing using a wire drawing die in which the approach angle α is set to 3.0 to 7.0 degrees or 8.0 to 15.0 degrees, More preferably, by using the ingot obtained in the step of cooling and solidifying from the lower end in the crucible, the hardness ratio between the central part and the outer peripheral part of the gold alloy ultrafine wire after annealing shown by the following formula is close to 1.0. It becomes a value. It is considered that the homogeneity of the central portion and the outer peripheral portion of such a gold alloy extra fine wire exhibits an excellent effect on the problem of the present invention. The hardness ratio is preferably in the range of 0.9 to 1.0.

Here, the hardness ratio according to the present invention will be described with reference to FIG. FIG. 3 shows a vertically split state of the gold alloy ultrafine wire after the annealing. In the figure, the hardness of the central portion of the ultrafine wire indicated by ○ and the outer peripheral portion of the ultrafine wire indicated by × are measured at 5 points each, and an average value of the hardness of the central portion and the outer peripheral portion is obtained. The hardness ratio is calculated from the formula <Equation 1>.

[Equation 1]

Thus, it is not clear why the gold alloy ultrafine wire obtained by the method of the present invention has an excellent effect on the problems of the present invention, but the central portion and outer circumference of the gold alloy ultrafine wire are not clear. It is possible to improve the homogeneity of the part, so that when wiring to a semiconductor device, there is no built-in complicated strain, so the loop bending is small, and when exposed to an environment subject to vibration, the gold alloy ultrafine wire It is considered that the gold alloy ultrafine wire, which is strong against vibration, can be obtained because the weak spots are less likely to occur on the surface part of.

[0021]

The present invention will be described in more detail based on the following examples. (Example 1) Containing 5 ppm by weight of Be and the balance of 5N
(99.999 wt%) high-purity gold alloy with an inner diameter of 30 m
It was melted by high frequency heating in a graphite crucible having a length of m and a length of 300 mm. Next, the high-frequency heating coil was moved upward from the lower end of the crucible at a speed of 50 mm / min to cool and solidify the molten metal in the crucible and cast it into an ingot. After rolling the ingot with a groove roll, wire drawing is performed,
A gold alloy ultrafine wire having a diameter of 25 μm was finished. The die used for wire drawing had an approach angle of 3 degrees. The ultrafine wire was passed through an annealing furnace so as to have an elongation of 4% and annealed. During this time, the number of wire breakages per unit weight during wire drawing was measured. The hardness ratio, the amount of loop bending, and the number of vibrations until breakage were measured using an ultrafine wire after annealing. The above-mentioned manufacturing conditions and measurement results are shown in Tables 1 and 2.

The measuring method was as follows. (Hardness ratio) As described above, the hardness of the central portion of the ultrafine wire indicated by a circle in FIG. 3 and the outer peripheral portion of the ultrafine wire indicated by a cross in FIG. Obtain the average hardness value,
Further, the hardness ratio is obtained from the above formula <Equation 1>. The hardness ratio was obtained at 10 points in the length direction of the ultrafine wire, and the average value thereof was used as the measured value. (Bending amount of loop) As a loop forming method, a 50 type bonder manufactured by Shinkawa Co., Ltd. was used, and wire bonding was performed between the IC chip electrode and the external terminal. After the first ball bonding was performed on the IC chip electrode, the capillary was once moved in the direction opposite to the loop formation, reverse deformation was performed, and then a regular loop was formed. Bonding condition is loop height: 2
The distance between the chip electrode and the external terminal was 5 mm. The loop was formed in this manner, and the distance at which the loop was most distant from the straight line connecting the connection point of the chip electrode and the external terminal was measured, and the average value of 100 loops was taken as the loop bending amount. (Number of vibrations until breaking) An outline of the test method is shown in FIG. A gold alloy fine wire 22 having a length of 10 cm was ball-bonded on a silver-plated lead frame (5 mm × 5 mm) 21 to obtain a vibration test material. Using the vibration test machine 23,
A vibration test was carried out under the following conditions in which the ultrafine wire 22 was held by a clamp 24 and vibrated to the left and right around a shaft 25, and the number of vibrations until breakage was measured. Span distance (L ₁ ): 150 μm Bilateral amplitude L ₂ : 26 μm Vibration frequency: 40 Hz (40 times per second) The same test was repeated 3 times, and the obtained average value was displayed as the number of vibrations until breakage.

(Examples 2 to 14 / Comparative Examples 1 to 9) Table 1 shows the types of gold alloys as production conditions, solidification method and rate in the casting process, and die approach angle in the wire drawing process.
A gold alloy ultrafine wire was manufactured and measured in the same manner as in Example 1 except that the description was made therein. Manufacturing conditions and measurement results are shown in Tables 1 and 2.

[0024]

[Table 1]

[0025]

[Table 2]

From the above measurement results, there are Examples 1 to 14 in which the die approach angle α is within the range of the present invention, and Comparative Examples 3, 6 and 8 in which the conventional die angle is 7.5 ± 0.2 degrees. From the comparison of, the following can be understood. When an ingot obtained by the solidification method in the crucible was used, the hardness ratio was 0.77 to
0.78, whereas in the embodiment 0.96 to 0.98
In the comparative example, the amount of loop bending is 36 μm, whereas in the example, it is improved to 15 to 18 μm, and the vibration frequency is 9.7 to 9.8 × 10 ³ in the comparative example. Then, it has improved to 13.0 × 10 ³ or more. When an ingot obtained by the continuous casting method is used, the hardness ratio is 0.55 in the comparative example, but 0.90 to 0.91 in the example.
The loop bending amount is 55 μm in the comparative example, while it is improved to 23 to 24 μm in the example, and the vibration frequency is 1 in the example, while it is 7.9 × 10 ^3.
It has improved to 1.9 to 12.1 × 10 ³ or more.

Comparative examples 2, 4, 7 and 9 in which the die approach angle α is between the range of the present invention and the conventional angle.
Although the hardness ratio, the amount of loop bending, and the number of vibrations are improved as compared with the conventional examples, it is inferior to the examples of the present invention, and it is understood that the object of the present invention cannot be satisfied.

Further, from comparison between Comparative Examples 1 and 5 and Examples of the present invention, even if the hardness ratio is within the range of 0.9 to 1.0,
When the die approach angle α is less than the lower limit value or more than the upper limit value of the present invention, the number of wire breakages during wire drawing is 10 times or more as compared with the conventional one, and it was confirmed that it cannot be put to practical use.

Further, from the comparison between Examples 1, 3, 4, 9 to 11 and Examples 12 to 14, even if the die approach angle α is the same, the step of obtaining the ingot is the lower end of the molten metal in the crucible. It is understood that when the in- crucible solidification method of cooling and solidifying is adopted, the loop bending amount becomes further smaller, and the number of breaks by the vibration test is further increased.

When the number of wire breaks during wire drawing is compared, Comparative Example 3, which is a conventional die approach angle, is used.
It was confirmed that the examples of the present invention were equivalent or slightly inferior to those of Examples 6 and 8, but they were not practically applicable, and that there were some effects as described above.

[0031]

As described above, according to the method for producing a gold alloy ultrafine wire of the present invention, the approach angle is 3 to 7 after the ingot obtained by melting and casting the gold alloy is rough processed. Since a new method is used in which wire drawing is performed using a die having a temperature of 8 to 15 degrees, and then annealing treatment is performed so that a predetermined elongation is obtained. Characteristics, and when wiring to a semiconductor device, complicated distortion is not built in, so loop bending is reduced, and when exposed to an environment subject to vibration, weak spots are less likely to occur on the surface of ultrafine wires. Therefore, a gold alloy extra fine wire that is strong against vibration can be obtained. Therefore, when the chip electrode and the external lead are wired, it is possible to effectively prevent a short circuit due to contact between adjacent ultrafine wires even if the wire length is long and the wiring density is high, and the ultrafine wires are vibrated by vibration. It is possible to reduce the degree of disconnection and improve reliability, and it is possible to manufacture a gold alloy ultrafine wire useful for highly functional and highly integrated semiconductor devices.

When the step of obtaining the ingot is the step of cooling the molten metal of the molten gold alloy from the lower end in the crucible to solidify it, generation of a chill layer on the surface of the ingot is suppressed, A more preferred ingot structure for producing a homogeneous gold alloy extra fine wire, the amount of loop bending of the extra fine wire obtained after the annealing step is further reduced,
The number of breaks by the vibration test can be further increased, and the above-mentioned effects can be made more effective.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an outline of wire drawing by a wire drawing die.

FIG. 2 is a cross-sectional view showing a process of obtaining an ingot, where (a) shows a solidification method in a crucible and (b) shows a continuous casting method.

FIG. 3 is a sectional view showing an outline of a method for measuring the hardness ratio of a gold alloy ultrafine wire.

FIG. 4 is a cross-sectional view showing an outline of a method of testing the number of vibrations until breaking.

FIG. 5 is a graph showing the relationship between the die approach angle and the gold alloy wire drawing force.

[Explanation of symbols]

1: Gold alloy wire before wire drawing 2: Gold alloy wire after wire drawing 3: Die for wire drawing 4: Approach section 5: Bearing part α: Approach angle 11: Gold alloy melt 12: crucible 13: High frequency heating coil 14: Tundish 15: Mold 16: Water cooling pipe 17: Ingot 21: Lead frame 22: Gold alloy extra fine wire 23: Vibration tester

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A 63-34934 (JP, A) JP-A 6-154840 (JP, A) JP-A 6-328124 (JP, A) JP-A 48- 34060 (JP, A) JP 4-210814 (JP, A) JP 63-299810 (JP, A) JP 6-226328 (JP, A) JP 6-277745 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/60 301 B21C 3/02

Claims (3)

(57) [Claims] 1. A gold alloy for a semiconductor device, comprising: a step of melting and casting a gold alloy to obtain an ingot; a step of rough-working the ingot; then a wire drawing step; and a step of annealing. A method for manufacturing a gold alloy ultrafine wire for a semiconductor device, wherein an approach angle of the wire drawing die is 3 to 7 degrees or 8 to 15 degrees. 2. The gold alloy extra fine wire for a semiconductor device according to claim 1, wherein the step of obtaining the ingot is a step of cooling the molten metal of the molten gold alloy from the lower end in the crucible and solidifying the molten alloy. Manufacturing method. 3. The hardness ratio between the central portion and the outer peripheral portion of the gold alloy ultrafine wire obtained after the step of performing the annealing treatment is 0.9 to 1.0, wherein the hardness ratio is 0.9 to 1.0. Manufacturing method of gold alloy ultrafine wire for semiconductor device.