JPH02259032A - Gold alloy thin wire for bonding - Google Patents

Abstract

PURPOSE:To obtain the gold alloy thin wire for bonding having improved tensile strength at an ordinary temp. and having drastically reduced vibration fracture rate by incorporating specified amounts of Ge and Ag into high purity gold. CONSTITUTION:By weight, 5 to 50ppm Ge and 5 to 100ppm Ag are incorporated into high purity gold. As the above high purity gold, the one contg. gold of about >=99.99wt.% purity and the balance inevitable impurities is preferably used. The addition of Ge gives strains to the crystal lattices of gold to precipitate Ge into the grain boundaries, by which the strength at an ordinary temp. can be improved. Furthermore, the addition of Ag suppresses the precipitation of Ge into the grain boundaries to improve the toughness. In this way, the gold alloy thin wire for bonding in which mechanical characteristics at an ordinary temp., loop height, ball shape, etc., are suitably maintainable and having low vibration fracture rate can be obtd.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a gold alloy thin wire used for joining electrodes on a semiconductor element and external leads, and more specifically, to This invention relates to a thin gold alloy wire for bonding that greatly reduces wire breakage caused by vibration and impact.

(Prior Art) Conventionally, a thin gold wire has been used as a bonding wire for connecting an electrode on a silicon semiconductor element and an external lead. The reason why thin gold wires have been so widely used is that the gold balls are formed into perfect spherical shapes, have appropriate hardness, and do not damage silicon semiconductor devices due to pressure during bonding. This was because the connection was reliable and extremely reliable. However, when joining a thin gold wire by applying it to an automatic bongo and melting the tip of the thin gold wire to form a gold ball, the thin gold wire lacks tensile strength just above the formation of the gold ball, and the wire may break or become disconnected. There is a problem in that the thin gold wire that is accidentally joined will break due to resin sealing.

In order to solve this problem, we have developed various bonding gold alloy thin wires that have improved breaking strength by adding trace amounts of additive elements to high-purity gold to the extent that the shape and hardness of the gold balls formed during bonding are not impaired. has been announced.

(Problems to be Solved by the Invention) On the other hand, in the field of manufacturing semiconductor devices, the degree of integration has progressed further, and as bonding speeds have increased, gold alloy thin wires with a diameter of 30 to 25 μm are often used. If a gold alloy wire with a diameter of 25 to 20 .mu.m is used even thinner from the viewpoint of the above, there is a problem that the bonding wire undergoes neck breakage after the semiconductor assembly operation after bonding, and the reliability of bonding decreases.

This problem is caused by the neck breakage of the bonding wire due to vibrations during semiconductor assembly work and mechanical vibrations and shocks occurring during the transportation process, increasing the rate of defective connections.

Figures 1 and 2 are explanatory diagrams showing neck breakage. For example, a semiconductor element (2) is mounted on an island (1) on a substrate on which a semiconductor element is mounted using a gold alloy thin wire with a diameter of 20 μm. The electrode (4) on the semiconductor element (2) and the inner lead (5) are fixed by bonding agent (3), and the tip of the bonding wire (6) is melted into a ball shape (7).
When semiconductor assembly work is performed after bonding with the bonding wire (6), the inner lead (5) vibrates upward (5゛) and downward (5'') due to vibration and impact during the process, and the bonding wire (6) Mo-hi (6゛), bottom (6”
) will cause repeated vibrations. As a result, neck breakage occurs in the bonding wire (6) at the coarse crystal grain portion of the recrystallized grain portion (8) formed by heat during formation of the bonding ball (7). In reality, the island (1) also vibrates as the inner lead (5) vibrates, and the bonding wire (6) receives a considerable impact. Such neck breakage becomes a problem in IC packages having multi-pole bins with high-density packaging in which the inner lead width becomes narrower.

In order to reduce neck breakage, the wire diameter of the bonding wire used can be increased, but the economic efficiency of using gold material is not satisfactory. Therefore, there is a demand for a thinner bonding wire with excellent bonding reliability.

The present invention was made in view of the above problems, and improves the tensile strength at room temperature by incorporating the minimum necessary additive elements into high-purity gold, and reduces the vibration rupture rate to 1-11. The object of the present invention is to provide a fine gold alloy wire for bonding that can be used for bonding.

(Means for Solving the Problems) In order to solve the above problems, the present inventors selected germanium as an additive element that improves the room temperature strength of high-purity gold, and added germanium as an additive element that reduces the vibration rupture rate. As a result of extensive research into whether or not it was possible, we discovered that when used as a bonding wire containing a specific proportion of silver in addition to germanium, the ball shape and loop height are appropriate, and the vibration rupture rate can be significantly reduced. Thus, the present invention was completed.

The present invention adds 5 to 50 pp by weight of germanium to high purity gold.
This is a gold alloy thin wire for bonding containing m and silver in a range of 5 to 100 weight ρpm.

The configuration of the present invention will be further explained below.

The high-purity gold used in the present invention is one that contains gold with a purity of 99.99% by weight or more and whose residue consists of unavoidable impurities, particularly one containing less than 5 ppm by weight of silver impurities.

Addition of germanium strains the gold crystal lattice and precipitates germanium at grain boundaries, thereby improving room temperature strength.

When the amount of germanium added is less than 5 ppm by weight, the mechanical strength at room temperature cannot be further improved. On the other hand, if it exceeds 50 ppm by weight, an oxide film will be formed on the ball surface.
Grain boundary fracture occurs due to recrystallization during bonding, resulting in neck breakage and distortion in the ball shape, reducing the reliability of bonding with microelectrodes. The preferred amount added is 5 to 50 ppm by weight.

Addition of silver suppresses grain boundary precipitation of germanium and improves the toughness properties of the bonding wire. The amount of silver added is 5
When the weight is less than pp+n, it lacks the effect of suppressing grain boundary precipitation of germanium, does not exhibit the toughness characteristics of a bonding wire, and has a high vibration rupture rate. Conversely, 100 ppm by weight
If it exceeds 10 to 60 wt pp
It is.

(Example) Examples will be described below.

Using electrolytic gold with a total purity of 99.99% by weight or more, the first
A gold alloy with the chemical composition shown in the table is melted and cast in a high-frequency vacuum melting furnace, the ingot is rolled, and then wire-drawn at room temperature to form a fine gold alloy wire with a final wire diameter of 20 μmψ. Continuous annealing and refining so that the elongation value becomes 4%.

Table 1 shows the results of examining the tensile strength at room temperature, loop height, vibration rupture rate, and ball shape of the rubbed gold alloy thin wire.

The bonding loop height is determined by observing the top height of the formed loop and the electrode surface of the chip using an optical microscope after bonding between the electrode on the semiconductor element and the external lead using a high-speed automatic bonder. Measure its height.

The vibration rupture rate is pLccg when the semiconductor element is mounted 1~
Plate (Bonde Daspa, N: 1mm, Inner Lee l°
4 for IC packages with 68 pins arranged in a square arrangement
2) 10 Ni-Fe alloy substrates (each having 6 pieces per sheet) were stored in a magazine, and the 20〆7 mψ thin gold alloy wire was passed through an automatic high-speed bong to connect the electrodes of the semiconductor element and the inner Connect the lead and store it in the magazine.

Place the magazine on a cart and place it on a cotton sheet steel plate 1- with a length of 4 m.
After forcibly vibrating the wire by making it reciprocate five times at a speed of 4 km/hr, check for neck breakage at the joint.

The shape of the ball uses a high-speed automatic honggu, electric 1.
- Observe the gold alloy poles obtained by the discharge with a scanning electron microscope to identify those where oxides are formed on the pole surface, those where the shape of the ball is irregular, and those that cannot be bonded to the electrode of a semiconductor element in a good shape. Evaluation was made with an X mark, and a good one with an O mark.

As can be seen from the results, the examples according to the present invention can significantly reduce the vibration rupture rate compared to the gold alloy thin wire to which only germanium is added. In Comparative Example 5, the vibration rupture rate cannot be reduced because the amount of silver added is small. In Comparative Example 6, the ball shape was not perfectly spherical due to the large amount of silver added, and in Comparative Example 7, the room temperature tensile strength was low due to the small amount of germanium added.
Since bonding, especially wire breakage, is likely to occur, there is a problem in practical use.

Although not shown in Table 1, the magazines obtained in Example 2 and Comparative Example 2 were placed on a cart and reciprocated three times over a striped steel plate with a length of 4 m to check for neck breakage. The rate was 1.2% for the former and 2.8% for the latter.

(Effects) As explained above, the gold alloy thin wire according to the present invention can maintain the mechanical properties at room temperature, loop height, and ball shape appropriately, and has the highest vibration rupture rate and can be used in automatic high-speed bongoos. This has the advantage that it can be put to practical use as a bonding line for thin packages, and it also greatly contributes to the economics of high-density semiconductor devices.

[Brief explanation of drawings]

Figure 1 is an enlarged explanatory diagram of the bonding wire that connects the electrode on the semiconductor element and the inner lead receiving vibration and impact, and Figure 2 is an enlarged explanatory diagram of the second electrode part of the semiconductor element in Figure 1. The reference numbers in the drawings are as follows. (1)... Island, (2)... Semiconductor element, (3)... Bonding agent, (4)...
... Electrode of semiconductor element-L, (5) ... Inner lead, (6) ... Bonding wire, (7
)... Ball, (8)... Recrystallized grain part.

Claims (1)

[Claims] A gold alloy fine wire for bonding, characterized in that high-purity gold contains germanium in a range of 5 to 50 ppm by weight and silver in a range of 5 to 100 ppm by weight.