JPH0530059B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] This invention relates to a non-noble metal wire bonding method.

[Technical background of the invention and its problems]

With the rapid development of the semiconductor industry, process automation is being carried out, and wire bonding has become the mainstream. Most of the wire bonding devices currently in use use gold wire, but when it comes to mass production, the price of the gold wire has a large impact on the cost. Therefore, the development of gold substitute wires has been carried out for a long time. However, at present, a high-speed wire bonder for gold substitute wires with good bonding properties, such as gold wires, has not yet been developed. This problem is caused by the atmosphere during ball formation and the atmosphere during bonding, and many proposals have been made to change these atmospheres to reducing gas or inert gas atmospheres. Japanese Unexamined Patent Publication No. 123198, 1982, U.S. Pat.
-74044, JP-A No. 140062, JP-A-57-
No. 169918, JP-A-58-199563, JP-A-57-
As disclosed in No. 13747, etc.

However, even if non-noble metal wires are bonded using the above technique, stable bonding cannot be obtained, and the yield and reliability are poor, making it impractical. Particularly in the case of bonding using copper (Cu) wire as a non-noble metal wire, the bonding part of the object to be bonded, such as a lead frame or a semiconductor element, is placed on a heater stage and heated to a temperature of, for example, 150°C to 350°C. Because it is necessary to apply pressure and ultrasonic wire bonding, when the Cu wire is exposed to this temperature atmosphere, the surface of the Cu wire, which undergoes a large oxidation reaction, is immediately oxidized.
This was found to be the cause of deteriorating ball formability and bondability. The effects of the high heat generated by the heater may react within the capillary and even on the clamper side. Therefore, even if the oxidized wire is guided to the tip of the capillary and discharged with an electric torch, the tip of the oxidized wire will not easily melt during the discharge in an inert or reducing gas atmosphere, resulting in poor ball-forming properties. It was found that there was significant delamination, resulting in poor bonding. Furthermore, even when wedge bonding is performed in the second bonding process, if the wire surface is oxidized, there is a problem that the bonding strength with the surface to be bonded, such as the silver-plated surface of the lead frame, is low.

[Purpose of the invention]

The present invention has been made in view of the above points, and provides a non-noble metal wire bonding method that allows good and reliable bonding to be obtained using non-noble metal wires.

[Summary of the invention]

That is, in the present invention, when a non-precious metal wire wound around a spool is inserted into a bonding tool and the wire that has passed through the bonding tool is bonded to a position to be bonded,
The present invention provides a non-noble metal wire bonding method characterized in that bonding is performed after subjecting the non-noble metal wire to a reduction action.

[Embodiments of the invention]

Next, embodiments of the method of the present invention will be described with reference to the drawings. Non-noble metal (base metal) wire such as Cu, Al,
And wire bonding using Cu wire among these alloys will be explained.

Bonding tool for the Cu wire 1 travel path For example, when the wire 1 is staying in the capillary 2, a metal ball 3 is made at the tip of the Cu wire 1 with at least the surface reduced, and this metal ball 3 is attached to the bonding section. For example, an embodiment will be described in which ball bonding is performed on the bonding pad 4 of an IC.

i.e. wound on a spool (not shown)
Cu wire 1 is connected to capillary 2 via clamper 5.
is inserted into the This capillary 2 is configured to reduce at least the surface of the Cu wire 1 while the Cu wire 1 is staying in the capillary 2 or for a predetermined period. For example, on the inlet side of the Cu wire 1 of the capillary 2, a reducing gas such as a hydrogen mixed gas heated to a high temperature is applied to the capillary 1.
A nozzle 6 is connected to the side wall of the nozzle 6 to introduce the reducing gas into the capillary 1 at a predetermined flow rate. That is, the reducing gas supplied from the inlet pipe 7 is introduced into the capillary 2 through the nozzle 6, and is appropriately led out from the tip of the capillary 2. When the discharged gas flows downward forcefully, the gas destroys a shield atmosphere 13, which will be described later, in which the metal sphere 3 is formed. Therefore, it is necessary to suppress the flow rate from the inlet pipe 2 so that the atmosphere is so full that almost no gas flows out from the tip of the capillary 2.

As the hydrogen mixed gas, for example, a gas obtained by heating an argon (Ar) mixed gas containing 10% hydrogen concentration to a temperature of, for example, 300° C. is used. This high-temperature gas only needs to be formed within the capillary 2; for example, by supplying room-temperature gas from the inlet pipe 7 and heating the capillary 2, the temperature of the capillary 2 makes the reducing gas within the capillary 2 high-temperature. It may be a method. It is preferable to configure the flow rate of the reducing gas and the structure of the tip of the capillary 2 so that the reducing gas supplied to the capillary 1 flows out from the tip of the capillary 1 and air does not flow into the ball forming portion and the bonding portion. Furthermore, during wire bonding, the Cu wire 1 moves in and out of the capillary 2, and due to the forward and backward movement of the Cu wire, reducing gas is supplied to prevent air from entering through the thin hole at the tip of the capillary 2.
A torch rod 8 of an electric torch for forming a metal sphere 3 is installed near the tip of the Cu wire 1 protruding from the tip of the capillary 2, and as is well known, this torch rod 8 connects the metal ball 3 to the tip of the Cu wire 1. When forming the Cu wire 1, it is operated according to a pre-stored program so as to be located near the tip of the Cu wire 1. The atmosphere that forms this metal sphere 3, especially from the lower end of the capillary
A nozzle 9 is provided so that the atmosphere up to the tip of the Cu wire 1 is at least one of an inert gas and a reducing gas. This atmosphere is completely isolated from the atmosphere by the shielding gas, but if air is involved, it becomes difficult to form a spherical metal ball 3, the surface is oxidized, and the bondability is significantly reduced. If the shielding gas flows out forcefully, it will not be possible to form the metal sphere 3 even if it is sparked, so there is an optimum (flow rate) range. Further, an IC 12 fixed to a lead frame 11 is provided on the heater stage 10 so as to maintain the bonding pad 4 at a temperature of, for example, 150° C. to 350° C. during bonding. That is, at least the surface of the Cu wire 1 is reduced in the capillary 2, and the Cu wire with the active surface protrudes from the tip of the capillary 1, and the torch rod 8 is at this position.
A high voltage pulse is applied to the tip of the Cu wire 1, and a discharge occurs between the torch rod 8 and the tip of the Cu wire 1, forming a metal ball 3. This atmosphere is maintained as an inert gas atmosphere from the nozzle 9 as described above, and a good metal ball 3 is formed, and in this state, the metal ball 3 is bonded onto the bonding pad 4. Since the surface of the metal ball 3 is not oxidized, good bonding can be stably obtained. After bonding the metal ball 3, second bonding is performed at a predetermined bonding position on the lead frame 11. In this case as well, capillary 2
Since the wedge bonding is performed in an inert gas atmosphere using the Cu wire 1 which has been reduced and activated, good bonding can be stably obtained in this bonding as well.

In the above embodiment, an example was described in which the non-noble metal wire was reduced using a bonding tool, but the same effect can be obtained by forming a reducing atmosphere at a position including the clamper as long as the wire travels. Good effects can also be obtained in wedge bonding of non-noble metal wires without forming a ball at the tip of the wire.

Further, in the above embodiment, a Cu wire was described, but any non-noble metal wire such as an alloy wire containing Cu, an Al wire, an alloy wire containing Al, etc. may be applied to wire bonding.

〔Effect of the invention〕

As explained above, according to the method of the present invention, it is possible to obtain a bonding method in which a metal sphere is formed after applying a reducing action to a non-precious metal wire, so that a good metal sphere can be formed and the reduced wire Since the surface is bonded, stable and strong ball bonding and wedge bonding can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining an embodiment of the method of the present invention, and FIG. 2 is an explanatory diagram showing an enlarged view of the capillary section in FIG. 1. 1... Non-precious metal wire, 2... Capillary, 3
...Metal ball, 6,9...Nozzle, 7...Inlet pipe,
8...Torch stick.

Claims (1)

[Scope of Claims] 1 A non-precious metal wire wound around a spool is passed through a bonding tool, and when the wire that has passed through the bonding tool is bonded to a bonding target position, a reducing action is applied to the non-precious metal wire. A non-precious metal wire bonding method characterized by post-bonding. 2. The non-noble metal wire according to claim 1, wherein the means for applying a reducing action to the non-noble metal wire is a heated reducing gas atmosphere formed in the running path of the non-noble metal wire. Bonding method. 3. The non-noble metal wire bonding method according to claim 1, wherein the means for applying the reducing action to the non-noble metal wire is carried out while the non-noble metal wire is running within the bonding tool.