JPH0339429A - Gold wire for bonding in semiconductor device - Google Patents

Abstract

PURPOSE:To obtain the gold wire for bonding in a semiconductor device free from disconnection caused by stress concentration directly upon a gold ball by limiting its grain size by the relationship between the grain size in the heat affected zone and the initial grain size in the wire. CONSTITUTION:As for the grain size of a gold wire having about >=99% high purity, the ratio of 1<(the average grain size in the heat affected zone)/(the initial grain size in the wire) <=2.5 times is regulated. The above crystals can be formed by controlling the heat treatment and wire drawing. In this way, the gold wire in which external stress is uniformly dispersed and the disconnection caused by stress concentration directly upon a gold ball is prevented can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a bonding gold wire used for connecting semiconductor chip electrodes and external lead portions.

(Prior Art J3 and Problems) Gold has conventionally been used as a gold wire for bonding semiconductor devices because it has corrosion resistance, good malleability, and excellent bonding properties.

The thermocompression bonding method and the ultrasonic thermocompression bonding method are adopted as typical methods of wire bonding technology, and the tip of the gold wire hanging from the tip of the capillary is melted using an electric discharge device to form a gold ball. is applied to a semiconductor chip electrode and then adhesively discharged, and then guided in a loop to an external lead portion, crimped and cut to the external lead portion, and the chip electrode and external lead portion are connected.

By the way, the gold wire used has a diameter of about 10 to 100 μm, and there is a large difference in the crystal grain size of the gold wire between the upper part of the heat affected zone and the outer lead part side. The reason for this is that during the gold ball formation process during wiring, the crystal grain size directly above the gold ball varies depending on the type, and recrystallization occurs under the influence of heat during heating, and the recrystallization length also varies. It can be determined that there is a significant difference in mechanical strength directly above.

Furthermore, since the loop portion is shaped like an arc, stress tends to concentrate directly above the gold ball.

As a result, it is thought that a wire breakage occurs directly above the gold ball due to the synergistic effect of weakening due to coarsening of the crystal grain size and stress concentration.

However, the loop shape problem cannot be changed due to the design of the semiconductor device.

Therefore, the inventor of the present invention conducted intensive research to avoid stress concentration, which is presumed to be the cause of wire breakage accidents.
Noting that the crystal grain size was significantly different between directly above the gold ball and other loop parts, the crystal grain size was determined in advance to be almost the same as the grain size directly above the heat-affected zone, that is, the gold ball. The present invention has been completed based on the discovery that the number of disconnection accidents directly above the gold ball can be reduced in this case.

(Objective of the Invention) The present invention provides a useful gold wire in which stress is dispersed without concentration by setting the crystal grain size to an appropriate value, and there is no breakage due to stress concentration directly above the gold ball. The porpose is to do.

(J and A of Invention) In the gold wire of the present invention, The crystal grain size is It is characterized by:

More specifically, the gold wire is made of high purity gold of 99% or more.

If the crystal grain size is larger than 2.5 times, stress concentration will occur in the heat affected zone, which is inappropriate.

(Function) Since the crystal grain size is less than 2.5 times that of the entire wire, external stress is evenly received and wire breakage does not occur.

(Example) An example of implementing the present invention will be described in detail below.

Gold wire is made by melt-casting high-purity gold (99,995%) with various elements added to it, then subjected to groove roll processing, and then heat-treated and wire-drawn in the middle to form a wire with a diameter of 10 to 100μ. The wire is drawn into an ultra-fine gold wire having a desired final wire diameter in the range of , and crystal grains in the range of . Specifically, the final wire diameter is 30 μmφ, and the crystal grain size is large.

The following table shows the results of measuring the presence or absence of stress concentration directly above the gold ball and the occurrence of wire breakage for the product according to the present invention and a comparative product whose crystal grain size is greater than or equal to the magnification of the present invention.

O Comparative amount 1 caused stress concentration directly above the gold ball, resulting in wire breakage (neck breakage), whereas products 2 and 3 of the present invention did not cause stress concentration and did not break.

(Effect of the invention) Therefore, the present invention has the following advantages.

■ Since the external pressure is received evenly over the wire directly above the gold ball and throughout the loop portion, stress concentration does not occur and there is no disconnection directly above the gold ball.

(2) There is no neck breakage, and it is possible to securely connect the semiconductor chip electrode to the external lead part.

Claims (1)

[Scope of Claims] A gold wire for bonding semiconductor devices, characterized in that the crystal grain size is 1<average crystal grain size of heat-affected zone/initial crystal grain size of wire≦2.5 times.