JPH02228437A - Gold alloy thin wire for bonding - Google Patents

Abstract

PURPOSE:To manufacture the thin wire for bonding having drastically reduced disconnection caused by vibration and impact by using the one of which specified ratios of Be and silver are added to high purity gold as a gold alloy thin wire bonding the electrode on a semiconductor element with an external lead. CONSTITUTION:A gold alloy thin wire used for bonding the electrode on a semiconductor element with an external lead is formed by incorporating, by weight, 1 to 10ppm (preferably 1 to 6ppm) Be and 5 to 100ppm (preferably 10 to 60ppm) silver into high purity gold (having about >=99.99% purity). In this way, the disconnection of the thin wire caused by vibration and impact can drastically be reduced in the working for assembling a semiconductor after bonding.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a gold alloy fine wire with excellent heat resistance used for joining electrodes on a semiconductor element and external leads, and more specifically, to This invention relates to a gold alloy thin wire for bonding that greatly reduces wire breakage due to vibration fatigue during semiconductor assembly work.

(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 its reliability was extremely high. However, when bonding is performed by applying a thin gold wire to an automatic bongo and melting the tip of the thin gold wire to form a gold ball, the thin gold wire has a low recrystallization temperature and lacks heat resistance, so Wire breakage may occur due to insufficient tensile strength, or thin gold wires that have been joined to avoid breakage may break due to resin sealing, and if semiconductor elements are protected with sealing resin, wire flow may occur and short circuits may occur. There is a problem.

To solve this problem, we have developed a variety of bonding products that improve breaking strength and heat resistance 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 affected. Gold alloy thin wire has been announced.

(Problems to be Solved by the Invention) On the other hand, in the field of manufacturing semiconductor devices, the density of integration has progressed further, and as well as increasing the speed of bonding, heat-resistant thin gold alloy wires with a diameter of 25 μm are being used. If a thinner heat-resistant gold alloy wire with a diameter of 20 μm is used from an economic point of view, there is a problem in that the bonding wire undergoes neck breakage after bonding and semiconductor assembly work, reducing the reliability of bonding. This problem is caused by vibrations during semiconductor assembly work and fatigue caused by mechanical vibrations and shocks occurring during the transportation process, which causes the bonding wire to break, resulting in an increase in the rate of defective connections. Figures 1 and 2 are explanatory diagrams showing neck disconnection. For example, a semiconductor element (2) is mounted on an island (1) on a substrate on which a semiconductor element is mounted using a heat-resistant gold alloy thin wire with a diameter of 20 μm. ) is fixed with bonding agent (3), and the tip of the bonding wire (6) is tied into a pole shape (7
), and after bonding the electrode (4) on the semiconductor element (2) and the inner lead (5) with the bonding wire (6), when semiconductor assembly work is performed, the inner lead is exposed to vibration and impact during the process. Lead (5) is above (5'), below (5')
”), and the bonding wire (6) also vibrates upward (6).
“) and downward (6”) vibrations will be repeated. Therefore, in the bonding wire (6), strain concentrates at the boundary between the recrystallized grain part (8), which is formed by the heat during the formation of the bonding ball (7), and the fiber structure part (9), where wire drawing strain remains. This can lead to neck breakage due to fatigue. In reality, as the inner lead (5) vibrates, the island (1) also vibrates, accelerating fatigue due to strain. However, such neck breakage occurs when the inner lead width is narrower and the inner lead width is narrower, resulting in higher density mounting. An IC package with pins is a problem. 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-mentioned problems, and it is possible to improve the tensile strength at room temperature and significantly reduce the vibration rupture rate by incorporating the minimum necessary additive elements into high-purity gold. 2
The object of the present invention is to provide a gold alloy thin wire for bonding with a diameter of 5 to 20 μm.

(Means for Solving the Problems) In order to solve the above problems, the present inventors selected beryllium as an additive element that improves the heat resistance of high-purity gold, and added beryllium as an additive element that reduces the vibration rupture rate. As a result of intensive research into whether or not this was possible, we discovered that by using a bonding wire containing a specific proportion of silver in addition to the addition of beryllium, the ball shape and loop height would be appropriate, and the vibration rupture rate could be significantly reduced. Thus, the present invention was completed.

The present invention combines 1 to 10 ppf of beryllium to high-purity gold.
This is a gold alloy thin wire for bonding containing fI and silver in a range of 5 to 100 ppm by weight.

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

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

Addition of beryllium strains the gold crystal lattice, increases the recrystallization temperature, precipitates beryllium at grain boundaries, and improves room temperature and heat resistance.

When the amount of beryllium added is less than 1 ppm by weight,
Mechanical strength at room temperature cannot be further improved.

On the other hand, if it exceeds 10 weight ppn+, in addition to coarsening of crystal grains due to recrystallization during bonding, box-shaped joints will occur and neck breakage will occur, and the ball shape will be distorted, making it difficult to bond with microelectrodes. reduce the reliability of The preferred amount added is 1 to 6 ppm by weight.

Addition of silver suppresses grain boundary precipitation of beryllium and improves the toughness properties of the bonding wire.

When the amount of silver added is less than 5 ppm by weight, it lacks the effect of suppressing grain boundary precipitation of beryllium, does not exhibit the toughness characteristics of the bonding wire, and has a high vibration rupture rate. 100 on the contrary
If it exceeds Mppm, the shape of the ball deteriorates and the reliability of the bonding decreases. Its preferable addition amount is 10 to 60 ppm by weight.

(Example) Examples will be described below.

Using electrolytic gold with a gold 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 produce a fine gold alloy wire with a final wire diameter of 2011 mφ, which is continuous in the atmosphere. It is annealed and tempered so that the elongation value becomes 4%.

Table 1 also shows the results of examining the tensile strength at room temperature, loop height, vibration rupture rate, and ball shape of the obtained 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 was determined by the PLCC board on which the semiconductor element is mounted (bond span: 11, inner lead bin: 6).
42Ni for IC packages arranged in 8 squares
68 Fe alloy substrates (each having 6 pieces per sheet) were stored in a cassette, and the 20 μmφ thin gold alloy wire was applied to an automatic high-speed bonder to bond the electrodes on the semiconductor element and the inner leads, and then stored in the cassette. do.

Place the cassette on a cart and roll it over a 4m long striped steel plate.
After forcibly applying vibration by making it reciprocate 4 times at a speed of km/hr, check for neck breakage at the joint.

The shape of the ball is determined by observing the gold alloy ball obtained by electric torch discharge using a high-speed automatic bonder with a scanning electron microscope. Those that could not be bonded to the electrode in a good shape were marked with an x mark, and those that were good were marked with an ○ 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 helium is added. In Comparative Example 4, the vibration rupture rate could not be reduced because the amount of silver added was small. In Comparative Example 5, the ball shape did not become true spherical due to the large amount of silver added, and in Comparative Example 6, the room temperature tensile strength was low due to the small amount of beryllium added, and wire breakage occurred during bonding, making it impossible to put it into practical use. do not have.

Although not shown in Table 1, the necks and throats obtained in Example 3 and Comparative Example 2 were placed on a cart and moved back and forth three times over a striped steel plate with a length of 4 m to check for neck breakage. The vibration rupture rate was 1.4% 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 appropriate mechanical properties, loop height, and ball shape at room temperature and high temperature, and can be used in automatic high-speed bonders, and has a high vibration rupture rate. Since the width can be reduced, it has the advantage that it can be used practically as a bonding wire for thin puff cages.
It also greatly contributes to the economic aspect of high-density semiconductor devices.

[Brief explanation of the drawing]

FIG. 2 is an enlarged explanatory view of the electrode portion on the semiconductor element in FIG. 1, and the reference numbers in the drawings are as follows. be. (1)... Island, (2)... Semiconductor element, (3)... Bonding agent, (4)...
...electrode on semiconductor element, (5) ...inner lead, (6) ...bonding wire, (7)
... Ball, (8) ... Recrystallized grain part,
(9)...Fib tissue part.

Claims (1)

[Claims] A gold alloy thin wire for bonding, characterized in that high-purity gold contains beryllium in a range of 1 to 10 weight ppm and silver in a range of 5 to 100 weight ppm.