JPH0425337B2 - - Google Patents

Abstract

PURPOSE:To obtain a bonding wire made of high purity gold having superior mechanical properties and heat resisting strength, by incorporating, in specified trace amounts, Ca, Be, and at least one kind among Ti, Zr, Hf and Nb to high purity Au. CONSTITUTION:The fine wire of Au is manufactured by incorporating by weight, 0.0001-0.001wt% Ca, 0.0001-0.001wt% Be, and 0.0005-0.005wt% at least one kind among Ti, Zr, Hf and Nb to >=99.99wt% high purity Au. This wire is fit for use as bonding wire for connecting a chip electrode of a semiconductor device to an external lead wire. The bonding wire having mechanical and heat resisting strength superior enough to cope with a high-speed bonder can be obtained.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a bonding wire used for connecting chip electrodes and external leads of a semiconductor device. [Prior Art] Conventionally, thin gold wires have been used as bonding wires in many connections between chip electrodes and external leads of semiconductor devices such as transistors, ICs, and LSIs. On the other hand, with the recent improvements in bonding technology resulting in higher speeds and higher integration of semiconductor devices, requirements regarding the mechanical properties and bonding properties of wires used in these devices are becoming stricter year by year. To summarize the characteristics required for bonding wire: 1. A good ball shape can be stably obtained. 2. Good bondability and stable bonding strength between the chip electrode and the gold ball. 3. A good wire loop shape can be obtained and the necessary loop height can be stably obtained. 4. Must have mechanical and heat-resistant strength that can support high-speed bonders. 5. Must be able to withstand resin flow, expansion, and contraction during resin molding. In order to meet these demands, conventional methods have been used to improve the mechanical and heat-resistant strength of wires by adding other metal elements to high-purity gold (99.99% or higher). However, with the additive elements and their combinations that are currently in practical use, it is not possible to obtain a wire that satisfies all of the above requirements. For example, a wire made of high-purity gold with Ca added (for example, JP-A-53-
105968) improves the mechanical and heat-resistant strength of the wire and can sufficiently handle the high-speed bonder, but because the recrystallization temperature of gold increases, hydrogen flame or arc discharge is not used in the bonding process. Crystal growth is inhibited even at the heating temperature applied when the tip of the wire is melted and formed into a ball, resulting in a lower wire loop height and a disadvantage in that it causes shot defects. In addition, wires in which Be is added to high-purity gold (e.g., Japanese Patent Laid-Open No. 112059/1983) have the effect of improving the mechanical strength of the wire, but the effect of improving heat resistance strength is small, and as a result, the wire is not affected during ball formation. Although crystal growth progresses at the heating temperature and the necessary loop height can be obtained sufficiently, the Ca-added wire causes coarsening of the crystal grains directly above the ball and decreases the wire strength at the ball neck, making it more likely to break at the ball neck. It has contradictory drawbacks. Furthermore, by adding a combination of Ca and Be, we developed a wire that took advantage of the characteristics of both (for example, Japanese Patent Application Laid-Open No. 112060/1983).
However, even with these combined additions, it is not possible to prevent the coarsening of crystal grains and the decrease in the wire strength of the ball neck due to the heating temperature during ball formation. Due to these problems, conventional gold alloy wires have not been able to provide sufficient bonding performance, and there has been a strong demand for the development of wires that improve these drawbacks. [Problems to be Solved by the Invention] The present invention overcomes the conventional drawbacks, has mechanical and heat-resistant strength sufficient to cope with high-speed bonders, and furthermore, can be used directly above the ball even at the heating temperature applied during ball formation. It is an object of the present invention to provide a bonding wire that maintains a stable loop height by preventing coarsening of the crystal grains and reduction in wire strength at the ball neck portion. [Means for solving the problem] That is, the bonding wire of the present invention has a purity
Gold of 99.99% by weight or more, calcium 0.0001~
The gold alloy wire contains 0.001% by weight of beryllium, 0.0001 to 0.001% by weight of beryllium, and 0.0005 to 0.005% by weight of at least one selected from the group of elements consisting of titanium, zirconium, hafnium, and niobium. . [Function] The higher the calcium content, the better the mechanical and heat resistance strength of the wire, but if it exceeds 0.001% by weight, the recrystallization temperature of the wire will become too high, making it impossible to obtain the required loop height of the wire.
It must be 0.001% by weight or less. Also, if the calcium content is less than 0.0001% by weight, there is almost no strength improvement effect, so the calcium content should be
It needs to be 0.0001 to 0.001% by weight. The higher the beryllium content, the higher the wire loop height in the bonding process, but
If it is less than 0.001% by weight, it will not be effective, and if it exceeds 0.001% by weight, the crystal grains will become coarser and the wire strength at the ball neck will decrease.
It needs to be 0.0001 to 0.001% by weight. Furthermore, it is preferable to add one or more of the elements consisting of titanium, zirconium, hafnium, and niobium; however, the higher the content of these elements, the more the coarsening of crystal grains and ball necks that occur under the influence of heating during ball formation are reduced. It is possible to control the decrease in wire strength at the end of the wire. However, if the total amount of these elements is less than 0.0005% by weight, there is no effect, and if it exceeds 0.005% by weight, ball deformation and bondability with the chip electrode will deteriorate.
It needs to be 0.0005 to 0.005% by weight. [Example] Using high-purity gold with a purity of 99.999% by weight as a raw material, calcium, beryllium, titanium, zirconium, hafnium, and niobium were added in various proportions to melt and cast a gold alloy with the composition shown in Table 1. , then swaging and then wire drawing to make the diameter
Wire drawing was carried out to 0.03mm. Next, this wire was heat treated so that the elongation at break at room temperature was 6%, and then subjected to a tensile test at room temperature and temperature =
A high temperature tensile test was conducted at 250°C and holding time = 30 seconds. In addition, bonding is performed with a wire bonder with the semiconductor element surface and the lead frame surface at the same height, and the height from the lead frame surface to the highest part of the wire loop after bonding and the crystal grain size directly above the gold ball are measured. Measurements were made. In addition, a gold ball is formed by arc discharge, the bottom of the ball neck is passed through a perforated block, the other end is held, and the length from the bottom of the ball neck to the part that enters the holding part is 100 mm, and the perforated block is set. Measure the tension and wire strength of the ball neck part,
The shape of the ball was observed. The ball diameter was 80-90 μm. Furthermore, the bonding strength between the chip electrode and the wire was measured. These results are shown in Tables 1 and 2.

【table】

〔Effect of the invention〕

As can be seen from Tables 1 and 2, the bonding wires of the present invention both have mechanical and heat-resistant strength sufficient to withstand high-speed wire bonding, and also have coarsening of crystal grains directly above the gold balls, which is a feature of the present invention. It can be seen that a stable loop height can be obtained without reducing the wire strength at the ball neck portion. From the above results, the bonding wire according to the present invention eliminates the drawbacks of conventional bonding wires and makes it possible to improve yield and reliability in the bonding process.

Claims (1)

[Claims] 1. Containing 0.0001 to 0.001% by weight of calcium, 0.0001 to 0.001% by weight of beryllium, and 0.0005 to 0.005% by weight of at least one selected from the group of elements consisting of titanium, zirconium, hafnium, and niobium. Remaining purity
Bonding wire made of high purity gold of 99.99% by weight or more.