JP2014224283A - Corrosion resistant aluminum alloy bonding wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit intergranular corrosion of high-purity aluminum wire for connecting semiconductor elements in a high-temperature and high-humidity environment.SOLUTION: Provided is aluminum alloy bonding wire comprising high-purity aluminum of a purity of 99.99 mass% or more to which is added 10 to 200 mass ppm of rhodium (Rh) and/or palladium (Pd). These added elements are forcibly solid-solubilized and forms a dispersed phase of an intermetallic compound in an aluminum matrix, where a crystal grain size of the aluminum matrix is set at 10 to 100 μm. The rhodium (Rh) and palladium (Pd) converts atomic hydrogen generated on the aluminum surface by a catalytic action into Hto prevent hydrogen from diffusing and permeating into the aluminum matrix. Thus, intergranular corrosion is prevented which occurs by Hformed by bonding of atomic hydrogen.

Description

  The present invention relates to an aluminum alloy bonding wire that connects an electrode on a semiconductor element used in a high temperature environment and an external electrode, and more particularly, a semiconductor element used in a high temperature environment such as an aircraft, an electric vehicle, or a ship. In the bonding wire, the intergranular corrosion generated by moisture in the use environment is suppressed, and the durability and reliability are improved.

Aluminum (Al) is mainly used for bonding pads on semiconductor elements such as silicon (Si), silicon carbide (SiC), gallium nitride (GaN), electrodes on a substrate on which these semiconductor elements are mounted, or lead frames. A material such as copper (Cu) or nickel (Ni) is used.
The electrodes on these substrates may be used with precious metal plating such as gold (Au), silver (Ag), or nickel (Ni) plating. This is called “aluminum pad”.
In order to connect the aluminum pads of these semiconductor elements and electrodes such as lead frames by ultrasonic bonding, an aluminum alloy fine wire using high-purity aluminum (Al) having a high conductivity of 60% or more is used.
As these aluminum alloy thin wires, round thin wires having a wire diameter of 50 to 500 μm are generally used, but depending on the application, extra fine wires having a wire diameter of less than 50 μm or those having a wire diameter of more than 500 μm are also used. A crushed flat rectangular wire (tape) may be used.

  When using such an aluminum (Al) alloy fine wire using high-purity aluminum (Al) in a high-temperature, high-humidity environment (atmosphere), it is particularly a wiring material for semiconductor elements used in aircraft, automobiles, ships, etc. When used as, there is a problem that it is difficult to maintain and ensure durability and reliability in these environments.

As such an example, there is an aluminum alloy in which nickel (Ni) is dissolved in the following aluminum (Al) as a wiring material having relatively small specific resistance, relatively high mechanical strength and excellent heat resistance. .
Japanese Patent Laid-Open No. 59-56737 (Patent Document 1 described later) states that “one or two elements of nickel (Ni) and copper (Cu) are contained in high-purity Al, and the content is 0.00. 005 to 0.2 wt%, that is, 0.005 to 0.2 wt% Ni or 0.005 to 0.2 wt% Cu is contained, or the total amount of Ni and Cu is 0.005 to 0.2 wt% It is characterized in that it is contained. ”Aluminum (Al) fine wires for bonding are disclosed.

Regarding the corrosion mechanism in high-purity aluminum with a purity of 99.99% or higher in high-temperature pure water at 150 ° C. or higher, by the chemical reaction between aluminum and water,
2Al + 3H ₂ O = Al ₂ O ₃ + 6H ↑

What should be the problem of this reaction,
“Of the hydrogen generated in this reaction, those that become molecular on the surface of aluminum and escape as H ₂ gas only increase the gas pressure in the container for this purpose. Alumina diffuses and escapes as hydrogen, diffuses and penetrates along the grain boundaries of aluminum, creates H ₂ molecules therein, and pressurizes, thus causing intergranular cracking in the aluminum ground. As the cracks break the alumina coating, new water enters and the reaction between aluminum and water takes place, and atomic hydrogen is generated and further penetrates into it. It is often explained that it finally breaks and collapses from the crystal grain boundary (edited by the Light Metal Association, Aluminum Handbook, Non-Patent Document 1 described later).
With respect to these reaction mechanisms, in the aluminum alloy in which nickel is dissolved as described in Patent Document 1, atomic hydrogen (H), which is easy to move in the crystal structure because nickel acts as a catalyst in the surface layer, is H. to a _2, it is suppressed that atomic hydrogen (H) is penetrating into the aluminum crystal structure is considered to have improved corrosion resistance

In addition, regarding the effect of such nickel (Ni) added to high-purity aluminum, Non-Patent Document 1 states that “If around 2% is added and second-phase NiAl ₃ is present, It is known that the corrosion resistance of the material is improved (middle of page 1278) ", and Patent Document 1 states that" Ni and Cu increase the bonding property and corrosion resistance of Al, respectively. If the content exceeds 0.2 wt%, the Al wire becomes hard and there is a problem that pellet cracking occurs in the ultrasonic bonding method (page 2, lines 2 to 7).

However, in recent years, nickel (Ni) has been picked up as a substance that is concerned about the environmental impact of health, etc., and there are restrictions on the use depending on the application, and the scope of the restriction will be expanded further in the future. Is expected.
On the other hand, aluminum alloy fine wires are required to be used for semiconductors that require heat resistance of 100 to 200 ° C., particularly power semiconductors used in air conditioners, solar power generation systems, hybrid cars, electric cars, etc. Its application range is expected to expand further in the future. Such an operating condition of the power semiconductor is higher than that of a normal semiconductor element. For example, in a power semiconductor used for in-vehicle use, an aluminum alloy fine wire needs to withstand a junction temperature of 100 to 150 ° C. at the maximum. In an apparatus used in such a high temperature environment, a pure aluminum thin wire made only of high-purity aluminum (Al) that is easily softened has not been put into practical use.

  Therefore, in these fields, there has been a demand for the development of an aluminum alloy fine wire that is free of nickel (Ni) and has improved corrosion resistance in a high-temperature and high-humidity environment more than a nickel (Ni) -added aluminum alloy fine wire.

JP 59-56737 A

“Aluminum Handbook” edited by the Japan Institute of Light Metals, Asakura Shoten 2003, p. 1278-1280

  The present invention is soft against a semiconductor chip like a pure aluminum alloy thin wire made only of high-purity aluminum (Al), so that it does not cause chip cracking at the time of wire bonding, and in a high temperature / high humidity environment. It is a technical problem to provide an aluminum alloy fine wire that exhibits corrosion resistance equal to or higher than that of a conventional nickel (Ni) -added aluminum alloy fine wire and does not cause intergranular corrosion cracking.

The present invention is an aluminum alloy bonding wire in which 10 to 200 ppm by mass of rhodium (Rh) and / or palladium (Pd) is contained in high-purity aluminum having a purity of 99.99% by mass or more,
These additive elements are forcibly solid-solved to form a dispersed phase of an intermetallic compound with aluminum in an aluminum matrix,
The crystal grain size of the aluminum matrix is 10-100 μm,
Furthermore, the purity of the high-purity aluminum is 99.998% by mass or more,
The dispersed phase of the intermetallic compound with aluminum is formed by heat treatment at 200 to 300 ° C. after continuous wire drawing,
The bonding wire is to be ultrasonically bonded,
The wire diameter of the bonding wire is 50 to 500 μm,
The said bonding wire is used at 80 to 300 degreeC or 150 to 250 degreeC.

In the alloy of the present invention, rhodium (Rh) and palladium (Pd) added in a small amount are dissolved in an aluminum matrix in a general wire manufacturing process shown in Examples described later, and crystal grains in the aluminum matrix are obtained. A dispersed phase of an intermetallic compound with aluminum is formed as a second phase at the boundary.
The disperse phase of the intermetallic compound with aluminum is forcibly solid-solved in the alloy matrix by heat-treating an ingot that has been melted and solidified after adding a predetermined amount of Rh and Pd at a temperature close to its melting point, and continuous drawing. By precipitating these intermetallic compounds at the grain boundaries in a tempering heat treatment performed after processing, a uniform dispersed phase in the alloy matrix is formed (see FIG. 3).
Regarding the mechanism for preventing corrosion under a high humidity environment by the dispersed phase of this intermetallic compound, the atomic hydrogen (H) generated by the above chemical reaction formula in the surface layer as in the above prior art is converted to H by its catalytic action. _In addition to the action of converting to ₂ to prevent intrusion from the surface layer into the internal matrix,
Furthermore, it is effective that the intermetallic compound dispersed as the second phase in the crystal grain boundary further penetrates into the crystal grain boundary by changing the atomic hydrogen that enters through the crystal grain boundary to H _2. It is thought to prevent.
Refer to FIG. 3 for the state of the intermetallic compound precipitated as the second phase at the grain boundaries in the aluminum alloy matrix.
In addition, the corrosion state in a high-humidity environment in these high-purity aluminum wires that do not contain Rh and Pd is caused by the formation of cracks in the aluminum matrix inside from the alumina film with a large surface as shown in FIG. However, in the case of the embodiment of the present invention, as shown in FIG. 1, a thin and uniform alumina layer is formed on the surface, and the aluminum alloy matrix under the surface is not cracked by corrosion. Not.

The corrosion-resistant aluminum alloy bonding wire to which rhodium (Rh) and / or palladium (Pd) in the aluminum alloy matrix of the present invention is added is an atomic hydrogen (H) formed by reacting with aluminum in a high temperature / high humidity environment. ) Is prevented from entering and diffusing into the alloy matrix to prevent intergranular corrosion in the matrix.
For this reason, while exhibiting the corrosion resistance in a high temperature and high humidity environment, the alloy composition suppresses the hardness of the wire to prevent chip cracking, and maintains the same conductivity as that of high purity aluminum.

FIG. 1 shows a cross section of the aluminum alloy fine wire of Example 3 of the present invention after a corrosion resistance test. FIG. 2 shows a cross section of the aluminum alloy fine wire of Comparative Example 1 after a corrosion resistance test. FIG. 3 is a TEM observation photograph showing an intermetallic compound (arrow) precipitated at a crystal grain boundary of an aluminum alloy fine wire cross section of Example 8 of the present invention.

As an example and a comparative example of the present invention, an aluminum alloy having a composition shown in Table 1 was melted, and an aluminum alloy ingot having a diameter of 300 mm was prepared by continuous casting. An aluminum alloy wire was prepared.
Subsequently, this strand was continuously drawn in water to a predetermined wire diameter, and finally heat-treated at 200 ° C. to 300 hours for 1 hour to perform temper annealing to obtain a bonding wire having a predetermined wire diameter. By this heat treatment of temper annealing, rhodium (Rh) and palladium (Pd), which are forcibly dissolved, precipitate as intermetallic compounds with aluminum as the second phase of the alloy matrix at the grain boundaries, and in the aluminum alloy matrix A dispersed phase is formed.
An Al-50 ppm Ni alloy wire prepared in the same manner as a conventional example was employed.
In these wire drawing steps, an intermediate heat treatment may be performed as necessary, and may be appropriately adjusted in consideration of the properties of the wire and the formation conditions of these intermetallic compounds.

With respect to the bonding wires prepared in the above-described steps and below, properties such as corrosion resistance under a high temperature / high humidity environment were confirmed under the following conditions.
(Ultrasonic bonding conditions)
The wire diameters of the aluminum alloy thin wires were 0.05 mm, 0.3 mm, and 0.5 mm, the loop length was 8 mm, and the loop height was 1.3 mm.
Using a REBO-7 type fully automatic bonder manufactured by Ultrasonic Industry Co., Ltd., an aluminum alloy fine wire was ultrasonically bonded onto an Al-1.0% Si film (thickness 3 μm) on a Si chip (thickness 0.2 mm). Carried out.
The bonding conditions were a frequency of 130 kHz, and the load and ultrasonic conditions were adjusted so that the crush width of the first bonded portion was 1.3 times the wire diameter. And the second bond ultrasonic bonding was carried out. The carbide tool and the bonding guide used were those manufactured by Ultrasonic Industry Co., Ltd. that matched the wire.

(Chip crack observation test)
The sample after bonding was dissolved in an Al-1.0Si pad with a 20% NaOH solution, and the presence or absence of chip cracking was observed at a magnification of 100 using an optical microscope (Olympus measuring microscope, STM6). When 100 chip observations were made and no chip cracking occurred, it was determined to be OK. When chip cracking was observed at one or more spots, NG was determined.

(Crystal grain size observation)
A cross-section milling device (Hitachi High-Technologies Model IM-4000) was used to produce a wire cross-section, and a focused ion beam processing observation device (JEOL Ltd. Model JIB-4000) was used for tissue observation. A cross-sectional method was used to measure the crystal grain size.

(Corrosion resistance test)
The test was conducted up to 1000 hours at 121 ° C. under the condition of 100% RH (unsaturated) using an unsaturated hyperaccelerated life test apparatus (HASTEST model IPAC-R8D) manufactured by Hirayama Seisakusho. Corrosion layer thickness is measured by using a cross-section milling device (Hitachi High-Technologies Model IM-4000) to produce a wire cross-section and then using FE-SEM (JEOL Model JSM-7800F). The layer was observed.

The above test results are listed in Table 1.
The nickel alloy wire of the conventional example has satisfactory results with respect to corrosion resistance and chip crack suppression.
The present invention relates to a conventional nickel alloy for corrosion resistance and chip cracking suppression in a high-temperature and high-humidity environment within a content range of 10 to 200 ppm by mass, regardless of whether rhodium (Rh) or palladium (Pd) is contained. A suitable effect equivalent to or better than that of a wire is achieved.
Similar results were obtained even when these rhodium (Rh) and palladium (Pd) were contained in a total of 10 mass ppm (No. 5) or 200 mass ppm (No. 6).
On the other hand, when rhodium (Rh) and palladium (Pd), which are comparative examples of 5 mass ppm, which is less than 10 mass ppm, did not cause chip cracking, the thickness of the corrosion layer increased remarkably. Moreover, when these contents exceeded 200 ppm by mass and 250 ppm by mass, the corrosion resistance was good, but the hardness was large and chip cracking occurred.
As the rhodium (Rh) and palladium (Pd) contents increase, the crystal grain size tends to decrease, and the mechanical strength and hardness tend to increase. As a result, chip cracking occurs, and the limit is expressed as the crystal grain size is lower than the lower limit of the range of the present invention together with the content.

FIGS. 1 and 2 are photographs of the wire cross sections of the inventive examples and comparative examples subjected to the corrosion resistance test, and FIG. 1 is the cross section of the aluminum alloy wire of the third embodiment of the present invention, which is a light-colored aluminum layer. A dark gray thin layer on the cross section is an alumina layer formed on the wire surface, and the uniform and thin alumina layer covers the surface of the aluminum alloy, and the inner alloy matrix is not cracked. Absent.
On the other hand, in the case of Comparative Example 1 in FIG. 2, a cross section of a high-purity aluminum wire subjected to a corrosion resistance test under the same conditions as in the example was photographed, and the surface was uneven and thick. It can be seen that a corrosion layer is formed and a crack is formed deeply from the corrosion layer into the alloy matrix.

  The aluminum alloy thin wire of the present invention suppresses chip cracking in ultrasonic bonding, exhibits corrosion resistance under high temperature and high humidity environment, and has high conductivity, so it can be applied to a wide range of applications such as aircraft, automobiles or ships. In addition, its good bondability is expected to be widely used for these applications and can contribute to the industry.

Claims (7)

An aluminum alloy bonding wire in which rhodium (Rh) and / or palladium (Pd) is contained in high-purity aluminum having a purity of 99.99% by mass or more, comprising 10 to 200 ppm by mass,
These additive elements are forcibly dissolved to form a dispersed phase of an intermetallic compound with aluminum in an aluminum matrix, and the crystal grain size of the aluminum matrix is 10 to 100 μm,
High corrosion resistance aluminum alloy bonding wire.   The high-corrosion-resistant aluminum alloy bonding wire according to claim 1, wherein the purity of the high-purity aluminum is 99.998% by mass or more.     2. The high corrosion resistance aluminum alloy bonding wire according to claim 1, wherein the crystal grain size of the aluminum alloy matrix is 10 to 100 [mu] m.     2. The high corrosion resistance aluminum alloy bonding wire according to claim 1, wherein the dispersed phase is formed by heat treatment at 200 to 300 [deg.] C. after continuous wire drawing.   2. The highly corrosion-resistant bonding wire according to claim 1, wherein the bonding wire is ultrasonically bonded.   2. The high corrosion resistance aluminum alloy bonding wire according to claim 1, wherein the bonding wire has a diameter of 50 to 500 [mu] m. The high corrosion resistance aluminum alloy bonding according to claim 1, wherein the bonding wire is used at 80 to 300 ° C or 150 to 250 ° C.