JPH01189131A - Fine lead for wire bonding - Google Patents

Abstract

PURPOSE:To increase a current capacity, to decrease the diameter of a wire, and to preferably connect to an electrode to be connected by providing a metal coating layer mad of aluminum series metal on a metal core made of gold series metal, copper series metal and its alloy. CONSTITUTION:A fine lead 11 is formed of a metal core 12 made of gold, copper or gold-copper alloy, and a metal coating layer 13 formed of aluminum. The current capacity of the fine lead can be increased by the core 12. A preferable wedge bonding is performed similarly to the fine lead made only of the aluminum to the electrode to be connected by the layer 13.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Application -11'- The present invention relates to a thin lead wire, particularly to a thin lead wire for wire bonding, which connects a thin lead wire to an electrode to be connected by pressing it in the radial direction.

Conventional technology In semiconductor devices, etc., aluminum lead thin wires having a wire diameter of about 200 to 350 μm are used to electrically connect electrodes formed on semiconductor elements such as silicon chips and external leads. is publicly known. The ends of this thin lead wire are generally connected to the electrode to be connected and the external lead by the wedge bonding ink method. The wedge bonding method is a method of connecting a lead thin wire to an electrode to be connected by pressing it in the radial direction, and the method of connecting the lead ymm to the electrode to be connected is called wire bonding.

Next, the wedge bonding method will be explained with reference to FIG. As shown in FIG. 3(A), a thin lead m (2) is let out from a hole (1a) provided in a wedge (1) made of silicon carbide. Next, as shown in Figure 3 (B),
The thin lead wire (2) is pressed against the aluminum electrode (5) of the silicon chip (4), which becomes the first electrode to be connected, by the pressurizing part (3) so as to crush it. ) Apply ultrasonic vibrations vibrating on a plane parallel to the surface of the wedge (1). The silicon chip (4) is fixed in advance on the support plate (6) via solder (not shown).
The thin lead wire (2) is pressed on top in the radial direction to form a first punch ink portion (7). Next, as shown in FIG. 3(C), the thin lead wire (2) is let out from the wedge (1), and then the outer lead (8), which is the second connected electrode, is fed out.
) Move the wedge (1) ° to the bonding ink pad. Subsequently, as shown in FIG. 3(D) in the same manner as FIG. 3(B), the thin lead wire (2 ) to form the second punch ink portion (9). Thereafter, the wedge (1) is moved to the right in the drawing, and a cutting blade (not shown) is pressed against the lead wire (2), thereby cutting the lead wire (2).

Therefore, as shown in an enlarged view in FIG. 4, the first bond ink portion (7) is connected with the lead thin fi (2) pressed back against the aluminum electrode (5). . Although not shown enlarged, the second punch ink section (
9) are also connected in a similar manner. In the wedge bonding ink method, in order to obtain sufficient connection strength between the aluminum electrode (5) and the thin lead wire (2), the thickness Q of the connection part must be 1/2 of the wire diameter of the thin lead wire (2). It is necessary to crush it until it is flattened.

Problems to be Solved By the way, with the increasing power consumption of today's electronic devices, electronic components such as semiconductor devices that can withstand large currents are required. important a
It has become a problem.

Therefore, the properties of the thin lead wire are a major factor in determining the WL current capacity of electronic components, and increasing the wire diameter of the thin lead wire can be considered as a simple method for increasing the current capacity of the thin lead wire. This is because increasing the wire diameter improves electrical conductivity and increases current capacity. However, simply increasing the wire diameter of the thin lead II (2) brings about the risk of damaging the silicon chip (4). That is, when the wire diameter of the lead wire (2) is increased and the lead wire (2) is pressed against the aluminum electrode (5), a large pressing force is required to flatten the lead wire (2). Therefore, when applying wire punch ink onto the aluminum electrode (5) of the silicon chip (4), a large pressing force is applied to the silicon chip (4) by the wedge (1). If a large pressing force is applied to the silicon chip (4), which has low mechanical strength, there is a risk that the silicon chip (4) will crack or break. In order to prevent such damage to the silicon chip (4), conventionally a thin lead AIA (2)
The wire diameter of the thin aluminum wire used as the material was limited to about 350 μm.

In order to avoid damage to the silicon chip (4) due to the pressing force of the wedge (1), it can be connected to the electrode to be connected using two thin gold wires with good electrical conductivity. With this method, it is possible to reduce the diameter of each gold wire to reduce the pressing force on the electrode to be connected. However, since two thin lead wires are wire-bonded, the workability is poor, and the area of the electrode to be connected must be increased.

That is, since there are two first bond ink portions of the ball bond ink that require a large connection area, the electrode area must be increased. This makes it difficult to design the device to be smaller. Although a thin gold wire is preferable in that it can increase current capacity, it has the disadvantage of having low mechanical strength and being easily broken. Further, the thick thin gold wire is expensive, leading to an increase in the cost of the device. Furthermore, when a thin gold wire is wire-bonded to an aluminum electrode, intermetallic compounds are likely to be formed between gold and aluminum. When an intermetallic compound of gold and aluminum is formed, the thin gold wire becomes electrically insulated from the electrode to be connected. As described above, the problem of preventing damage to silicon chips during wire bonding remains unsolved, and no practical means to solve this problem has been proposed.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a thin lead wire for wire bonding that has a large current capacity, a small wire diameter, and can be connected well to an electrode to be connected.

Means for Solving Problem A The thin lead wire for wire bonding of the present invention is a thin lead wire for wire punch ink used in the wire punch ink method in which the thin lead wire is pressed in the radial direction to connect the electrode to be connected. has a metal core wire and a metal coating layer covering the metal core wire, the metal core wire is made of a gold-based metal, a copper-based metal, or an alloy of a gold-based metal and a copper-based metal, and the metal coating layer is made of an aluminum-based metal. Made of metal.

Function: A metal core wire made of a gold-based metal, a copper-based metal, or an alloy of a gold-based metal and a copper-based metal has better electrical conductivity than a metal coating layer. Therefore, the metal core wire serves as the first WL current path of the thin lead wire, and has the effect of making it possible to increase the current capacity of the thin lead wire. In addition, the metal coating layer covers the second gland of the lead and ll11 glands.
This serves as a current path, and has both the function of protecting the metal core wire and the function of enabling a good connection to the connected mh.

Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 and 2. The thin lead wire (11) of Example 1 is called an aluminum-clad thin copper lead wire, and has a metal core I formed of thin copper wire.
! 1A (12) and a metal coating layer (13) formed of aluminum on the outer periphery so as to cover the metal core wire (12).
For example, the wire diameter of the metal core wire (12) is about 30
The thickness of the metal coating layer (13) is approximately 30 μm, which is approximately uniform over the entire circumference of the metal core wire (12). Therefore.

The wire diameter of the thin lead M (11) is about 90 μm.

When the thin lead wire (11) is energized, the metal core wire (12), which is a thin copper wire, reaches the first v! of the thin lead wire (11). This becomes the i-flow path. Copper thin wire has better electrical conductivity than aluminum thin wire of the same wire diameter. The metal core wire (12) makes it possible to increase the current capacity of the thin lead wire (11). Metal coating layer (
13) becomes the second current path of the thin lead wire (11).

The fL metal coating layer (13) has both the function of protecting the metal core M (12) and the function of forming a good connection to the electrode to be connected, as will be described later.

The thin lead wire (11) is formed by various processing methods such as cladding method and plating method. As one of the preferred examples, in Example 1, a method was adopted in which a thin aluminum wire was wound in a ring shape around the outer periphery of a thin copper wire and annealed. Similar to the conventional thin lead wire made only of aluminum, the thin lead m (11) is connected to the electrode to be connected by the wedge bonding ink method. The lead thin 1 (11) of the first embodiment has the following effects.

1. Since the metal core wire (12) with excellent electrical conductivity serves as the first current path, the current capacity can be increased compared to a conventional thin lead wire made only of aluminum and having the same wire diameter. In other words, a thin lead wire having a current capacity equivalent to that of the conventional wire can be realized with a thin lead wire having a wire diameter smaller than that of the conventional wire.

Since it has a large current capacity of 2 m and high strength, it can be used in applications with large current capacity with only one thin lead wire. For this reason,
Wire bonding is easy to work with, and it is also advantageous in terms of miniaturizing the device. Further, no mechanical breakage occurs.

3. The connection portion to the electrode to be connected is formed mainly by the aluminum-based metal constituting the metal coating layer (13). Therefore, similar to the conventional thin lead wire made only of aluminum, it is possible to perform wedge bonding to various electrodes to be connected such as aluminum 11 and nickel.

4 Flexible metal covering a layer made of aluminum (1
3) is formed with a sufficient thickness of about 30 μm, so that the pressing force for crushing the thin lead wire can be approximately equal to that of a thin lead wire made only of aluminum with the same wire diameter. Therefore, it is possible to wire-bond a thin lead wire with a large current capacity with high connection strength without increasing the pressing force. Furthermore, since it has great flexibility against bending, it is easy to handle.

5. Since the metal coating layer (13) covers the metal core wire (12), oxidation of the thin copper wire constituting the metal core wire (12) can be prevented. Thereby, poor connection with the connected electrode due to oxidation can be prevented, and mechanical breakage and electrical disconnection of the connection portion can be avoided. Therefore, it becomes possible to put into practical use wire bonding using copper-based thin lead wires, which has heretofore been difficult.

Next, an aluminum clad gold wire, which is a second embodiment of the present invention, will be described below. This Example 2 is Example 1
A thin gold wire is used instead of a thin copper wire constituting the metal core wire (12). The material and layer thickness of the metal coating layer (13) formed on the outer periphery of the thin gold wire are the same as in Example 1.

In addition, metal core 1! The wire diameter of the thin gold wire as I(12) is 3
It is 0 μm. Further, the formation method is also the same as in Example 1.

The lead wire of Example 2 is a metal core wire (1
2) becomes the first electrical path of the thin lead wire (11). Since the thin gold wire has better electrical conductivity than the thin aluminum wire of the same diameter, the metal core wire (12) makes it possible to increase the current capacity as in Example 1. The metal coating layer (13) becomes a second current path for the thin lead wire (11).

The second embodiment has the above-mentioned effects (1) to (4) in the first embodiment.
). Further, the metal coating layer (13) is coated with the metal core wire (12
), the connection part with the electrode to be connected is coated with a metal coating layer (
13), therefore, it is possible to prevent an intermetallic compound made of a gold-aluminum alloy from forming at the connection portion. Therefore, mechanical breakage and electrical disconnection accidents between the connected electrode and the thin lead wire (11) can be prevented.

Here, when a thin copper wire is used as the metal core wire (12) as in Example 1, there is an advantage that the thin lead wire can be manufactured at a lower cost than when a thin gold wire is used as in Example 2. However, since gold mtm has better flexibility, Example 2 is better in terms of reduced pressing force and ease of handling. Although the second embodiment is inferior in terms of cost, it is lower in cost than the conventional connection method in which two thin gold wires are provided. Furthermore, when considering the degree of freedom in designing the semiconductor element, the yield rate, etc., the use of the thin lead wire of Example 2 also has a large cost advantage.

Modifications The wire diameter of the metal core wire (2) and the layer thickness of the metal covering layer (3) shown in the above embodiment can be modified to an appropriate degree in terms of design. In this case, considering that the current capacity can be sufficiently increased compared to the conventional thin lead wire made only of aluminum and that the wire diameter of the thin lead wire can be reduced, the wire diameter of the metal core wire (2) should be 20 μm, preferably 30 μm or more. Good. Further, in consideration of reducing the pressing force, the thickness of the metal coating layer (3) is preferably 30 μm, preferably 50 μm or more. Generally, the diameter of the thin lead wire (1) is preferably 350 μm or less.

Furthermore, the metal core wire (2) may be an alloy of a gold-based metal and a copper-based metal, and the metal coating layer (3) may be an aluminum-based alloy layer.

Effects of the Invention According to the present invention, the wire diameter is small and the current capacity is large;
Furthermore, it is possible to obtain a fine lead wire that can be well connected to the electrode to be connected and is desirable for use in semiconductor devices and the like.

[Brief explanation of the drawing]

Fig. 1 is a side view showing a cross section along the length of a thin lead wire for wire bonding according to the present invention, Fig. 2 is a cross-sectional view, and Fig. 3 is a series of wedge bonding methods for connecting thin lead wires. FIG. 4, which is an explanatory drawing showing the process, is an enlarged cross-sectional view showing the first bonding ink portion. (2), Thin lead wire, (4), Silicon chip, (5), Aluminum electrode (first connected voltage @
A), (7), first bond ink section, (8
),, external lead (second connected wL pole), (9
), second bonding part, (11)0. Thin lead wire, (12), Metal core wire, (13), Metal coating layer, Patent applicant: Sanken Electric Co., Ltd.

Claims (1)

[Claims] A thin lead wire for wire bonding used in a wire bonding method in which a thin lead wire is pressed radially to an electrode to be connected and has a metal core wire and a metal coating layer covering the metal core wire, The core wire is made of gold-based metal, copper-based metal, or an alloy of gold-based metal and copper-based metal,
A thin lead wire for wire bonding, wherein the metal coating layer is made of an aluminum-based metal.