JP2015076559A - Copper elemental wire for bonding wire use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper elemental wire for bonding wire use which has good processability, and is less likely to cause disconnection even when it is formed into a fine wire; and a method for manufacturing such a copper elemental wire for bonding wire use.SOLUTION: A copper elemental wire for bonding wire use is for forming a bonding wire. The copper elemental wire is made of high-purity copper having a purity of 99.9999 mass% or more, of which the wire diameter is 0.5-3.5 mm; the areal percentage of (001) plane in a section perpendicular to a wire-drawing direction is 15-30%.

Description

  The present invention relates to a bonding wire copper wire for forming a bonding wire.

  Generally, in a semiconductor device on which a semiconductor element is mounted, the semiconductor element and the lead are connected by a bonding wire. Conventionally, as a bonding wire, Au wire is mainly used from the viewpoints of drawability and conductivity. However, since Au is expensive, a bonding wire made of a Cu wire is provided as a bonding wire that replaces the Au wire.

  For example, a bonding wire made of Cu wire is obtained by drawing a cast material having a wire diameter of 4 mm to 8 mm to 0.5 mm to obtain a copper wire for bonding wire, and further drawing the copper wire for bonding wire. It is manufactured by processing to a wire diameter of 30 μm to 50 μm. For example, Patent Documents 1 and 2 propose bonding wires made of Cu wire of high-purity copper (so-called 6NCu) having a purity of 99.9999% by mass or more. Since this bonding wire has high purity, its strength is low, and it becomes easy to form a loop shape of the wire and the reliability is improved. Moreover, since there is high purity, there are few inclusions and it can suppress that a disconnection arises at the time of wire drawing.

Japanese Patent Laid-Open No. 62-111455 Japanese Patent Laid-Open No. 04-247630

  By the way, in recent years, in order to reduce the size and cost of a semiconductor device, the bonding wire is required to be thinned. In the future, the wire diameter of the bonding wire is expected to advance to, for example, 10 μm or less. Therefore, the copper wire for bonding wire for forming the bonding wire is required to have a workability that does not break during the wire drawing even if the wire is thinned.

  However, when the bonding wires shown in Patent Documents 1 and 2 are manufactured, if the copper wire for bonding wires is drawn and processed to, for example, a wire diameter of 10 μm, the elongation of the wires becomes insufficient, and frequently occurs. Wire breakage will occur. Thus, when a wire breakage occurs when the copper wire for bonding wires is drawn, there arises a problem that the productivity is significantly reduced.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a copper wire for a bonding wire that has good workability and is less likely to be disconnected even if it is thinned.

As a result of studying to solve the above-described problems, the inventors of the present invention have made a copper wire for bonding wire drawn to produce a bonding wire, and the copper wire for bonding wire is perpendicular to the wire drawing direction. It was found that by controlling the area ratio of the (001) plane in a simple cross section to a specific range, the workability of the copper wire for bonding wire can be improved and the disconnection during wire drawing can be suppressed.
The present invention has been completed based on the above findings, and the gist thereof is as follows.

  That is, the copper wire for bonding wire of the present invention is a copper wire for bonding wire for forming a bonding wire, and is made of high-purity copper having a purity of 99.9999% by mass or more, and the wire diameter is 0.00. The area ratio of the (001) plane is 15% or more and 30% or less in a cross section perpendicular to the wire drawing direction.

According to the copper wire for bonding wire of the present invention, the area ratio of the (001) plane in the cross section perpendicular to the drawing direction is 15% or more and 30% or less, so that workability can be improved. The occurrence of disconnection during wire drawing can be suppressed.
When the area ratio of the (001) plane is less than 15% in the cross section perpendicular to the wire drawing direction, other orientations including the (111) plane increase, the strength decreases, and the wire breaks during wire drawing. It tends to occur. Further, when the area ratio of the (001) plane is more than 30% in a cross section perpendicular to the wire drawing direction, the elongation is lowered, and breakage is likely to occur during the wire drawing. Therefore, the area ratio of the (001) plane is set in the above range.
Further, since the copper wire for bonding wire is made of high-purity copper having a purity of 99.9999% by mass or more, the strength of the bonding wire using the copper wire for bonding wire is sufficiently lowered, and the reliability of the bonding wire is improved. Can be improved. Moreover, since high purity copper with a purity of 99.9999% by mass or more has few inclusions, it is possible to suppress the occurrence of disconnection due to the inclusions during wire drawing.

  According to the present invention, it is possible to provide a copper wire for a bonding wire that has good workability and hardly breaks even if it is thinned.

It is a flowchart of the manufacturing method of the copper strand for bonding wires which concerns on embodiment of this invention.

  Below, the copper strand for bonding wires which concerns on embodiment of this invention, and the manufacturing method of the copper strand for bonding wires are demonstrated.

  The copper wire for bonding wires according to the present embodiment is used as a wire when manufacturing a bonding wire having a wire diameter of 80 μm or less, preferably 5 μm or more and 50 μm or less. The copper wire for bonding wire has a wire diameter of 0.5 mm to 3.5 mm.

The copper wire for bonding wires is made of high-purity copper (6NCu) having a purity of 99.9999% by mass or more.
The copper wire for bonding wire has an area ratio of (001) plane of 15% to 30% in a cross section perpendicular to the drawing direction. In the present embodiment, the cross section perpendicular to the wire drawing direction is a cross section including the central axis of the copper wire for bonding wires. In the present embodiment, in the cross section perpendicular to the wire drawing direction, the total area ratio of crystal faces within a deviation angle of 15 ° with respect to the (001) plane is defined as the area ratio of the (001) plane.

Here, when the area ratio of the (001) plane is less than 15% in the cross section perpendicular to the wire drawing direction, other orientations including the (111) plane increase, the strength decreases, and the wire drawing is performed. Sometimes breakage tends to occur. Further, when the area ratio of the (001) plane is more than 30% in a cross section perpendicular to the wire drawing direction, the elongation is lowered, and breakage is likely to occur during the wire drawing.
For these reasons, the area ratio of the (001) plane in the cross section perpendicular to the drawing direction is set in the above range.

  The area ratio of the (001) plane in the cross section perpendicular to the wire drawing direction can be measured by an electron back scatter diffraction patterns method (EBSD method). In this EBSD method, an EBSD detector is connected to an SEM (scanning electron microscope) to analyze the orientation of individual crystal diffraction images (EBSD) generated when a focused electron beam is irradiated onto the sample surface, and to measure the orientation data and measurement. This is a method of measuring the crystal orientation of a material from point position information.

  Next, the manufacturing method of the copper wire for bonding wires which concerns on this embodiment is demonstrated. As shown in FIG. 1, for example, the method for manufacturing a copper wire for bonding wire includes a hot working step S1, a wire drawing step S2, and a heat treatment step S3. Details of each step will be described below.

(Hot processing step S1)
First, a billet (ingot) having a diameter of 250 mm and a length of 700 mm made of high-purity copper having a purity of 99.9999% by mass or more is prepared.
Then, the billet is heated to a temperature range of 700 ° C. or more and 900 ° C. or less, and hot-extruded in a range of 99% or more and 99.9% or less in area reduction to produce a strand of 6 mm to 20 mm. In this hot working step S1, in order to destroy the cast structure of the billet (ingot) and make a fine and uniform hot worked structure as compared with the cast structure, in the above temperature range and area reduction rate. Hot extrusion is performed.
In this embodiment, heating was performed at 800 ° C., and hot extrusion was performed under the condition of a surface reduction rate of 99.9% to produce an 8 mm strand.

(Wire drawing process S2)
The wire produced in the hot working step S1 described above is drawn (cold drawing) within a range of the area reduction rate of 80% or more and 99.6% or less, and the wire diameter is 0.5 mm or more and 3 Process to 5mm or less. Here, the wire drawing may be performed in one pass, but is preferably performed in a plurality of passes. In this wire drawing process S2, the hot work structure (crystal grains) formed in the hot work process S1 extends in the wire drawing direction to form a fibrous metal structure.
In this embodiment, machining is performed from 8 mm to 1 mm in diameter in 15 passes, and the area reduction rate is 98%.
In the wire drawing step S2, a peeling wire drawing process may be performed.

(Heat treatment step S3)
The element wire drawn in the wire drawing step S2 is subjected to heat treatment within a range of 200 ° C. to 260 ° C. and 30 minutes to 300 minutes. Here, the heat treatment step S3 is performed in a batch annealing furnace having a reducing atmosphere. In this heat treatment step S3, a part of the metal structure made fibrous in the wire drawing step S2 is recrystallized, and a metal structure in which a fibrous metal structure and an equiaxed recrystallized structure coexist. It has become.
In the present embodiment, the wire is heat-treated in a reducing gas atmosphere by a batch-type annealing furnace at 220 ° C. for 60 minutes.

As described above, the copper wire for bonding wire according to the present embodiment is manufactured.
In addition, when processing this copper wire for bonding wires into a bonding wire, it is set as a 20-micrometer bonding wire, for example by drawing at a surface reduction rate of 99.96%.

  According to the copper wire for bonding wire according to the present embodiment configured as described above, the area ratio of the (001) plane is 15% or more and 30% or less in the cross section perpendicular to the drawing direction. The workability can be improved and the occurrence of disconnection at the time of wire drawing can be suppressed.

  Further, since the copper wire for bonding wire is made of high-purity copper having a purity of 99.9999% by mass or more, the strength of the bonding wire using the copper wire for bonding wire is sufficiently lowered, and the reliability of the bonding wire is improved. Can be improved. Moreover, since high purity copper with a purity of 99.9999% by mass or more has few inclusions, it is possible to suppress the occurrence of disconnection due to the inclusions during wire drawing.

  Further, according to the method for manufacturing a copper wire for bonding wire according to the present embodiment, a hot working step S1 for hot-working an ingot made of high-purity copper to produce a wire, and the number of wires are reduced. A wire drawing step S2 for drawing in an area ratio of 80% or more and 99.6% or less, and 200 to 260 ° C. for 30 to 300 minutes with respect to the drawn wire. In the cross section perpendicular to the wire drawing direction, the (001) plane area ratio is 15% or more and 30% or less. Copper wire can be manufactured.

  When the wire drawing step S2 is performed within the range of the area reduction rate of 80% or more and 99.6% or less with respect to the strand produced in the hot working step S1, the crystal grains become fibrous in the drawing direction. An elongated metal structure is formed, and the (001) plane increases in a cross section perpendicular to the drawing direction. When the metal structure stretched in the form of fibers is further drawn, the elongation may be low and breakage may occur. Therefore, by performing the heat treatment step S3 under the above-described conditions, a part of the metal structure elongated in a fibrous form is recrystallized to improve the elongation by controlling the area ratio of the (001) plane to a predetermined range, This improves the workability during wire drawing.

  In addition, in the heat treatment step S3, the wire drawn in the wire drawing step S2 is subjected to a heat treatment within a range of 200 ° C. to 260 ° C. and 30 minutes to 300 minutes by a batch annealing furnace. Therefore, the area ratio of the (001) plane in the cross section perpendicular to the drawing direction can be reliably controlled to 15% or more and 30% or less.

  In the heat treatment step S3, when the heating temperature is less than 200 ° C., recrystallization does not occur sufficiently, and it becomes difficult to control the area ratio of the (001) plane to 30% or less, and the elongation decreases and during wire drawing. There is a risk of breakage. In addition, when the heating temperature exceeds 260 ° C., recrystallization progresses too much, and it becomes difficult to control the area ratio of the (001) plane to 15% or more, the strength is lowered, and it is easy to break during wire drawing. End up.

In the heat treatment step S3, when the heating time is less than 30 minutes, recrystallization does not occur sufficiently, and it becomes difficult to control the area ratio of the (001) plane to 30% or less. When the heating time exceeds 300 minutes, recrystallization proceeds excessively, and it becomes difficult to control the area ratio of the (001) plane to 15% or more.
For the above reasons, the heat treatment conditions of the heat treatment step are set in the range of 200 ° C. to 260 ° C. and 30 minutes to 300 minutes.

  For example, in a high-temperature short-time heat treatment such as current annealing, a recrystallized structure cannot be stably formed in a fibrous structure formed by wire drawing, and in a cross section perpendicular to the wire drawing direction. It becomes difficult to control the area ratio of the (001) plane within the above range. On the other hand, in this embodiment, the area ratio of the (001) plane can be stably controlled within the above range by performing the heat treatment under the above heating conditions using a batch annealing furnace.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this, It can change suitably in the range which does not deviate from the technical idea of the invention.

  In addition, there is no limitation in the shape and size of the ingot which consists of high purity copper with a purity of 99.9999 mass% or more, and it is not limited to this embodiment.

Below, the result of the confirmation experiment performed in order to confirm the effectiveness of this invention is demonstrated.
(Invention Examples 1 to 5)
First, a billet having a diameter of 250 mm and a length of 700 mm made of high-purity copper having a purity of 99.9999% by mass or more was prepared. The billet was heated to 800 ° C. and subjected to hot extrusion to produce a strand having a diameter of 8 mm.
Next, a wire having a diameter of 1 mm was drawn to a diameter of 1 mm, including cold peel drawing. In this wire drawing, the area reduction rate was 98%, and the number of passes was 15.
Next, the drawn wire was placed in a batch annealing furnace, and heat treatment was performed at the heating temperature and heating time shown in Table 1. The atmosphere of the batch type annealing furnace was a reducing atmosphere.
As described above, copper wires for bonding wires according to Invention Examples 1 to 5 were manufactured.

(Comparative Example 1)
In Comparative Example 1, a copper wire for bonding wire was manufactured without performing heat treatment after wire drawing. That is, a copper wire for bonding wire of Comparative Example 1 was manufactured in the same manner as the above-described example of the present invention except that the heat treatment after the wire drawing was not performed.

(Comparative Example 2)
First, an ingot made of high-purity copper having a purity of 99.9999% or more was prepared. Using this ingot as a raw material, a strand having a diameter of 8 mm was cast.
Next, a wire having a diameter of 1 mm was drawn to a diameter of 1 mm, including cold peel drawing. In this wire drawing, the area reduction rate was 98%, and the number of passes was 15.
Thus, the copper wire for bonding wires of Comparative Example 2 was produced. In addition, also in the comparative example 2, the heat processing after a wire drawing process are not performed.

In the copper wire for bonding wire manufactured as described above, EBSD measurement was performed on a cross section perpendicular to the drawing direction, and the area ratio of the (001) plane was measured.
The EBSD measurement procedure will be described below. First, a copper wire for bonding wire was mechanically polished using water-resistant polishing paper and diamond abrasive grains, and then finish-polished using a colloidal silica solution. And the EBSD measuring device (HITACHI S4300-SEM, EDAX / TSL OIM Data Collection) and analysis software (EDAX / TSL OIM Data Analysis ver.5.2) The crystal orientation of the cross section perpendicular to the drawing direction was measured. Specifically, each measurement point in the measurement range on the sample surface was irradiated with an electron beam, the electron beam was scanned two-dimensionally on the sample surface, and orientation analysis by backscattered electron beam diffraction was performed.
In the section of the copper wire for bonding wire measured by EBSD, the area ratio of the (001) plane was evaluated with the crystal plane having a deviation angle of 15 ° or less with respect to the (001) plane as the (001) plane.

Further, the manufactured copper wire for bonding wire was further drawn to a diameter of 5 μm. Specifically, the wire was drawn from 1 mm (1000 μm) in diameter to 100 μm, and further drawn in the order of 100 μm → 50 μm → 25 μm → 10 μm → 5 μm. At this time, the number of breaks that occurred when processing each diameter from 100 μm to 5 μm was measured. In addition, this wire drawing process was implemented so that the wire of 100 m of full length might be obtained in the step processed to 5 micrometers.
In addition, about the comparative example 1, in the wire drawing process, since disconnection occurred frequently, manufacture was stopped on the way.
The measurement results are shown in Table 1.

  As shown in Table 1, Invention Examples 1 to 5 were confirmed to have good workability because the number of wire breakage was small even when wire drawing was performed from 100 μm to 5 μm. In other words, it was confirmed that Examples 1 to 5 of the present invention are copper wires for bonding wires that are less likely to be broken even if they are thinned.

In Comparative Example 1, since the heat treatment was not performed after the wire was drawn to a diameter of 1 mm, the area ratio of the (001) plane was over 30%, and the number of disconnections was increased compared to the inventive example.
In Comparative Example 2, an element wire having a diameter of 8 mm is cast, and the element wire is drawn to a diameter of 1 mm. The area reduction rate of the drawing process to a diameter of 1 mm is insufficient as compared with the example of the present invention. For this reason, the area ratio of the (001) plane was less than 15%, and the number of disconnections increased compared to the inventive example.

S1 Hot working process S2 Wire drawing process S3 Heat treatment process

Claims (1)

A copper wire for bonding wire for forming a bonding wire,
It consists of high-purity copper with a purity of 99.9999% by mass or more,
The wire diameter is 0.5 mm or more and 3.5 mm or less,
A copper wire for bonding wire, wherein the area ratio of the (001) plane is 15% or more and 30% or less in a cross section perpendicular to the drawing direction.

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