JPH0564459B2 - - Google Patents

Abstract

PURPOSE:To prevent a metal wire from being oxidized and to contrive to improve the junction strength by a method wherein the wire travelling path between the wire feeding-out part and the point of the wire is brought into an atmosphere of inactive gas, N2 or reducing gas. CONSTITUTION:Hoods 13-15 are provided on parts of the copper wire travelling path between the wire feeding-out part to start after a copper wire 2 passes through a guide 3 and a capillary 6 excluding the parts of clampers 4 and 5. Mixed gas of N2, Ar or H2 is flowed from the inlet 16 of the hood 13, the flow path of the mixed gas is formed along the wire travelling direction and the mixed gas is made to blow off from the wire lead-out port of the capillary 16. The copper wire 2 is led out, a heater 12 is conducted, the mixed gas of H2 is made to flow in 16 and a pole 8 is formed on the point of the copper wire 2 using a torch 7. The pole is pressed by the capillary 6 and a thermocompression bending is performed with ultrasonic waves under a coaction with the heat of the heater 12. In this constitution, an oxidation of the copper wire 2 is prevented, the pole is formed stably on the point of the wire and a firm junction can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a wire bonding method.

[Technical background of the invention and its problems]

Gold wire is used in fully automatic wire bonding for ICs, LSIs, etc. This wire member also becomes a factor in increasing costs as the cost of semiconductor devices decreases, and there is a demand for bonding using a gold substitute wire. Typical examples include attempts to use copper wire or aluminum wire, but these have not been put to practical use.

Especially when using base metal wires such as copper,
Heats the IC work stage and heats the parts to be joined, such as IC pellets and lead frames, to 200℃ to 350℃.
Since it is necessary to raise the temperature to a certain extent, the wire is oxidized by this heat, and this oxidation causes bonding defects.

As a countermeasure against oxidation of wire
As described in No. 26246, it has been proposed to prevent oxidation by spraying an inert gas onto the tip of the wire and forming a ball at the tip of the wire while shielding with the inert gas.

However, even with this proposal, according to the research of the present applicant, the wires in the vicinity above the heater stand are oxidized by the heat of the heater stand built into the work stage. In particular, since the capillary and the wire clamper are also heated, thermal oxidation occurs at the wire clamper portion during the wire travel, and oxidation has already progressed by the time the wire travels near the members to be welded.

Therefore, even if an attempt is made to form a ball by an electric torch method or an oxyhydrogen torch method when the ball is run near the members to be joined, there is a problem in that it is often difficult to form the ball.

[Purpose of the invention]

The present invention has been made in view of the above points, and provides a wire bonding method that prevents oxidation of the wire during running, stabilizes ball formation, and provides high bonding strength.

[Summary of the invention]

That is, when leading out the wire from the wire feeding section and crimping and bonding it to the workpiece, at least a portion of the wire running path from the wire feeding section to the wire tip is placed in an inert gas, nitrogen gas, or reducing gas atmosphere. The present invention provides a wire bonding method characterized in that the inert gas, nitrogen gas, or reducing gas is supplied so as to form a flow path at least along the running direction of the wire.

[Embodiments of the invention]

Next, an embodiment in which the method of the present invention is applied to wire bonding using an electric torch method using copper wire will be described with reference to the drawings.

A fully automatic wire bonding apparatus using an electric torch method is well known to those skilled in the art, so a description thereof will be omitted.

That is, the bonding arm system of the wire bonding apparatus is shown in FIG. A bonding wire, such as a copper wire, is wound around a wire feeding portion, such as a wire spool 1, and installed in a bonding device. The copper wire 2 led out from the wire spool 1 passes through a wire guide 3 and runs through a clamper, for example, a first clamper 4 and a second clamper 5.
A capillary 6, which is a bonding tool, is inserted, and the tip of the copper wire 2 is guided so as to protrude from the capillary 6.

An electric torch rod 7 is installed near the protruding tip of the copper wire 2, and is set relative to the tip of the copper wire 2 so as to generate an electric discharge only when forming a ball at the tip of the copper wire 2. For example, the torch rod 7 is moved to form the ball 8. On this occasion,
The area around the electric torch and wires is covered with an inert gas or reducing gas to prevent oxidation.

Below this ball 8 is a lead frame 10 on which a member to be bonded, such as an integrated circuit (IC) 9, is attached.
A work stage 11 is provided. A heater 12 is built into the work stage 11, and generates a temperature of, for example, 200° C. to promote bonding of the copper wire 2. This heater 12 is heated before the start of bonding and continuously performs heating operation during bonding, and this heating may be performed by either direct current or alternating current.

The bonding arm described above is mounted on an X-Y drive table (not shown) separate from the work stage 11.
Although they are installed above, they are each connected to a linear motor (not shown) without directly engaging a cam mechanism so as to be driven also in the vertical Z-axis direction.

Furthermore, a camera (not shown) for visually recognizing the bonding position is also installed on the table, and the output is input to a computer (not shown), which controls the bonding position.

In such an apparatus, the method of the present invention is to make the wire running path in the region where the copper wire 2 is oxidized by the heat from the heater 12 be in an inert gas N ₂ gas or reducing gas atmosphere. For example, the copper wire running path from between the guide 3 and the first clamper 4 to the capillary 6 is made into an inert gas or reducing gas atmosphere. That is, the hoods 13, 14, and 15 are installed in a portion of the first clamper 4 excluding the second clamper 5 so as to form a flow path for the gas, and the hood 13 is provided with a gas inlet 16. Nitrogen gas (N ₂ gas) or an inert gas or a reducing gas such as a hydrogen mixed gas is introduced from this gas inlet 16 to form a flow path along the running direction of the wire, and also from the wire outlet of the capillary 6. A gas flow path is formed so as to be blown out, and a hydrogen mixed gas atmosphere is formed on the running path of the copper wire 2. By forming the hydrogen mixed gas flow path in this way, the tip of the copper wire 2 that protrudes from the capillary 6 due to the blown gas is shielded by the hydrogen mixed gas to a large extent depending on its shape, and also has the effect of preventing the rise of hot air flow. be. The hoods 13, 14, and 15 may not be divided, but may be an integrated hood that accommodates the clampers 4 and 5 to form a hydrogen mixed gas atmosphere.

Of course, the hydrogen mixed gas flow path is connected to the lower hood 1.
5 may be provided with a gas inlet to blow out both upward and downward, or a gas inlet may be provided in an intermediate position, for example in the hood 14, to blow out upward and downward, or a separate shielding gas may be provided at the tip of the copper wire. It may also be used in combination with means for spraying.

Instead of the capillary 6 as the gas outlet, one or more annular gas outlets may be provided so that the wire other than the tip of the wire is exposed to a hydrogen mixed gas atmosphere. Further, the air outlet may be provided not only in the capillary 6 but also in the hoods 14 and 15 in the middle. Furthermore, the gas flow rate is constant, e.g. 0.5
The flow rate may be m/sec, but the flow rate may be varied over time, or the flow rate may be adjusted according to the temperature of the heater. Furthermore, the gas may not be continuously blown out, but may be operated intermittently in pulses at appropriate intervals. Further, the hydrogen mixed gas does not necessarily need to create a gas flow in the capillary 6, and the gas may be supplied to the extent that the capillary is filled.

With such a configuration, when performing bonding, the wire 2 is led out prior to bonding, and after setting, the hydrogen mixed gas is controlled to flow in from the gas inlet 16 at the same time as power is turned on to the heater 12.
Program control is performed by the computer to start the bonding operation.
As is well known, the bonding process is carried out by forming a ball 8 on the tip of the copper wire using a torch rod 7, and then pressing the ball 8 at the bonding position with the capillary 6.
Thermocompression bonding using ultrasonic waves is performed by the synergistic action of 2 with heat.

By forming the running path of the copper wire 2 in a hydrogen mixed gas atmosphere in this way, oxidation of the copper wire 2 before bonding can be prevented, a ball can be stably formed at the tip of the copper wire, and ball bonding can be performed firmly. effective. Particularly in wedge bonding after ball bonding, strong bonding could not be obtained with conventional gas shielding only at the tip, but good bonding strength was obtained with this example.

In the above example, an example was explained in which a hydrogen mixed gas was used, but if the wire is an inert gas or a reducing gas that has the effect of shielding the wire from thermal oxidation, such as argon gas or nitrogen gas, the wire can be heated. Shielding from the atmosphere has a similar effect.

Furthermore, in the above embodiment, an example was explained in which copper wire was used as the base metal, but any base metal that can be used in wire bonding may be used, such as copper alloy wire, aluminum wire, aluminum alloy wire, etc.

Furthermore, although the electric torch method was described in the above embodiment, the present invention may also be applied to wire bonding using an oxyhydrogen torch method.

〔Effect of the invention〕

As explained above, according to the present invention, at least a portion of the bonding wire (base metal wire) running path is made to have an inert gas or reducing gas atmosphere, so that the wire is not oxidized when a ball is formed on the tip of the wire. This has the effect that a good ball can be formed and strong bonding can be performed.

Furthermore, in wedge bonding after ball bonding, since the wire (base metal wire) is not oxidized, there are effects such as improved bonding strength between the wire and the surface to be bonded.

[Brief explanation of the drawing]

FIG. 1 is a side view for explaining an embodiment of the method of the present invention. 1... Spool, 2... Wire, 13, 14,
15...Hood, 6...Capillary, 16...Gas inlet.

Claims (1)

[Scope of Claims] 1. When leading out the wire from the wire feeding section and crimping and bonding it to the member to be joined, at least a part of the wire running path from the wire feeding section to the wire tip is filled with inert gas, nitrogen gas, A wire bonding method characterized in that a reducing gas atmosphere is formed, and the inert gas, nitrogen gas, or reducing gas is supplied so as to form a flow path at least along the running direction of the wire. 2. The wire bonding method according to claim 1, wherein the wire is a base metal wire.