Au Alloy Bonding Wire

Abstract

Provided is a thin Au alloy bonding wire having desired strength, good bondability and stability over time, and improved circularity of a squashed ball and sphericity of a melted ball. The Au alloy bonding wire contains, in an Au alloy matrix containing 0.05 to 2 mass % in total of at least one selected from Pd and Pt of high purity in Au of high purity, as trace elements, 10 to 100 ppm by mass of Mg, 5 to 100 ppm by mass of Ce, and 5 to 100 ppm by mass of each of at least one selected from Be, Y, Gd, La, Eu and Si, the total content of Be, Y, Gd, La, Eu and Si being 5 to 100 ppm by mass, or as trace elements, Mg, Be, and at least one selected from Y, La, Eu and Si, or as trace elements, 10 to 100 ppm by mass of Mg, 5 to 30 ppm by mass of Si, 5 to 30 ppm by mass of Be, and 5 to 30 ppm by mass of at least one selected from Ca, Ce and Sn.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to Au alloy bonding wires for wire bonding of semiconductor devices used for connecting external leads of circuit boards to electrodes on semiconductor integrated circuit devices, and more specifically relates to an Au alloy bonding wire according to which the bondability for a first bond and a second bond is improved, and an Au alloy bonding wire according to which the sphericity of a melted ball and the circularity of a squashed ball are improved. [0003] 2. Description of the Related Art [0004] Conventionally, as wires of diameter approximately 25 to 35 μm for connecting external leads to semiconductor chip electrodes used in semiconductor apparatuses, Au alloy bonding wires containing high-purity gold of purity not lower than 99.99 mass % are widely used. Ordinarily, in a method of connecting an Au alloy bonding wire, for a first bond, a combined ultrasonic-thermo compression bonding...

AI Technical Summary

Benefits of technology

[0034] According to the Au alloy of the present invention, even for a fine bonding wire of a diameter not exceeding 23 μm, as in the case that that the diameter is greater than 23 μm, an effect of retarding Au—Al interdiffusion, an effect of improving wedge bondability, an effect of suppressing leaning, an effect of improving the sphericity of the melted ball, and an effect of improving the circularity of a squashed ball can all be attained. In the present invention, it is needless to add the trace elements in an amount exceeding 300 ppm by mass as is conventional, and hence a bonding wire can be realized according to which, even if ball bonding is carried out in air, an oxide film will never be formed on the surface of the fine wire on the melted ball.

Problems solved by technology

However, as the diameter of bonding wires decreases, the absolute rigidity of the wire itself decreases, and hence problems have started to arise that were not a problem with a wire diameter of 25 μm.

For example, if the rigidity decreases as a result of the wire diameter being decreased, then a so-called “leaning” troubles in which wires stringing between the first bond and the second bond fall down sidewise and hence the gap between adjacent wires decreases arises with eventual contacting.

If there is prolonged use in a high-temperature ambience, then growth of an intermetallic compound at the interface between the Au wire and the Al pad at the first bond will proceed rapidly, and as a result the problem of the ball bondability decreasing due to the intermetallic compound produced will become marked.

Furthermore, corrosion under the influence of components contained in the molding resin also becomes a problem.

In the case of adding trace elements to an Au alloy wire, the higher the concentration of the trace elements is made relative to the Au alloy wire, the higher the absolute rigidity of the Au alloy wire becomes, and the better various properties become, but on the other hand, undesirable properties also appear.

An example is that in the case that the loop formability improves, the Au ball formability worsens due to the elements added to the Au alloy matrix.

The wedge bondability may also worsen.

Furthermore, the drawback of the Au alloy ball hardness increasing due to the elements added to the Au alloy matrix may also arise.

There are thus problems such as the melted ball or the squashed ball becoming misshapen, and hence it becomes difficult to carry out ball bonding at a small pitch of spacing, or the rate of chip cracking increasing; trace elements can therefore not be added in large amounts.

For example, in the case that Ca alone is added to secure strength, the Ca may partially deposit out on the surface of the fine wire, the deposited Ca then being oxidized to form a surface oxide film, and as a result there have been problems of the ball shape and bondability for the first bond not being stable, and hence the circularity of the squashed ball becoming poor, and the wedge bondability for the second bond becoming poor.

Moreover, in a complicated case in which many types of elements are added, these elements may function in a complicated manner in the Au alloy and may be deposited out on the surface of the melted ball, whereby good initial bonding cannot be obtained, and there is an increased tendency for it is no longer possible to obtain a reliable first bond and good bondability for the second bond.

Images