JPS62126647A - Wire bonding method - Google Patents

Abstract

PURPOSE:To ensure a bonding state even under low temperature conditions, by changing the compressing force of metallic wire to the pad and the lead frame of a semiconductor pellet by a plurality of stages so that the force is small at first and gradually increases thereafter, in bonding work. CONSTITUTION:At first, a control circuit 1 reads compressing data at the first and second stages used at the first bonding B1. Based on the compressing force data, a driving and controlling signal for an actuator 5 required for generating the compressing force is outputted to an amplifier circuit 4. As a result, a driving current having a current value corresponding to said driving and controlling signal is outputted from the amplifier circuit 4 and supplied to the actuator. For example, under the state a metallic wire is contacted with the surface of a pad, a capillary is changed by an amount of displacement (a) corresponding to the compressing force data at the first stage. Then, the compressing force of 30g is applied to the bonding part of the metallic wire. After the compression, the capillary is changed by an amount of displacement (b) corresponding to the compressing force data at the second stage. Then, the compressing force of 50g is applied to the wire bonding part of the metallic wire.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to improvements in wire bonding methods.

[Technical background of the invention]

2. Description of the Related Art In a semiconductor manufacturing process, a wire bonding method is generally used as a method for connecting a semiconductor pellet mounted on a substrate and a lead frame provided on the same substrate. This wire bonding method mainly includes thermocompression bonding method, ultrasonic bonding method, thermosonic bonding method that combines both, and ink method, but all of these methods require heating the substrate to a predetermined temperature. Bonding is performed by pressing a metal wire such as , Au, Cu, or Aρ against a pad or lead frame with a constant pressure. - For example, in the case of ultrasonic bonding, both in the first bonding B1 to the pad and in the second bonding B2 to the lead frame, as shown in FIG.
Bonding is performed by applying a fixed pressure force of, for example, 50 g or 100 g to the bonding point using a capillary. In the figure, PO indicates the change in displacement of the capillary, and TS indicates each bonding B1. B
2 shows the ultrasonic output waveform applied to the metal wire via the capillary.

[Problems with background technology]

However, the conventional wire bonding method that applies such a constant pressing force has the following drawbacks. That is, as mentioned earlier, the substrate is pressurized to a predetermined temperature (for example, 150 to 300 degrees Celsius) during bonding, but depending on the size of the substrate and the placement position of the heater, a temperature distribution may occur on the substrate, and this As a result, if the pressing force is constant, bonding failures tend to occur in areas where the temperature is low. Additionally, wire bonding generally involves detecting the position of the semiconductor plate pad and lead frame prior to bonding, but when bonding is performed by forming a metal ball at the tip of the metal wire, this metal ball Since the wires cool down during the position detection and become difficult to bond, the bonding condition of the bonding of the first wire becomes worse than that of the bonding of the second wire and subsequent wires, and as a result, a connection failure is likely to occur.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a wire bonding method that can obtain a reliable bonding state even under low temperature conditions, thereby reducing the occurrence of connection failures and performing bonding with a high yield.

[Summary of the invention]

In order to achieve the above object, the present invention changes the pressing force of the metal wire to the pad and lead frame of the semiconductor belen 1 in multiple stages such that it is initially small and gradually increases during bonding. It is.

[Embodiments of the invention]

FIG. 1 shows the configuration of a wire bonding drive circuit for carrying out a wire bonding ink method according to an embodiment of the present invention, and this drive circuit includes a control circuit 1. As shown in FIG. This control circuit 1 includes, for example, a microcomputer as a main control section, and is connected via a bus to an input section 2 for setting control data and a memory 3 for storing control data. Further, an actuator 5 and an ultrasonic transducer 7 are connected to the control circuit 1 via an amplifier circuit 4.6. The actuator 5 is connected to the control circuit 1
The capillary is operated by the drive current output from the amplifier circuit 4 in accordance with the drive instruction, and the capillary is displaced by an amount corresponding to the drive current value. Further, the ultrasonic transducer 7 is energized by a drive signal transmitted from the amplifier 6 according to instructions from the control circuit 1, and transmits an ultrasonic wave having an amplitude corresponding to the magnitude of the drive signal to the bonding section for a period of time during which the drive signal is generated. supply to.

Next, the wire bonding method of this embodiment will be explained based on the above configuration. Note that here, each of the first and second bonding B1. For both B2, a case will be explained in which the pressurizing force is set in two stages.

First, before bonding, the operator inputs pressing force data for the first bonding B1 and the second bonding B2 from the input unit 2 by, for example, key operation, and stores this in the memory 3.

For example, for the first bonding B1, the first stage is 3.
Set the second stage to 509 at 0g, while the second stage
Bonding B2 is set so that the first stage is 709 and the second stage is 100 g.

Next, data indicating the application timing of ultrasonic vibration and the magnitude of the amplitude of the ultrasonic wave is stored in the memory 3. For example, here each of the first and second bonding B1.
The application start timing for both B2 is set so that it is not applied in the first stage, but is applied from the second stage, and the amplitude value is set smaller than the normal amplitude value. After setting all the press force data and ultrasonic application control data, the bonding operation is started.

Then, the control circuit 1 first performs the first bonding B1
The first-stage and second-stage pressing force data to be used are read from the memory 3, and based on these pressing force data, a drive control signal for the actuator 5 necessary to generate the pressing force is sent to the amplifier circuit 4. Output. As a result, the amplifier circuit 4 outputs a drive current having a current value corresponding to the drive control signal and supplies it to the actuator 5, whereby the actuator 5 operates to displace the capillary. For example, as shown in Fig. 2, with the metal wire in contact with the pad surface, the capillary is first displaced by a displacement amount a corresponding to the pressure force data of the first stage, thereby applying a pressure force of 30 g to the bonding of the metal wire. applied to the part. After this pressurization is completed, the capillary is displaced by a displacement mb corresponding to the second-stage pressurizing force data, thereby applying a pressurizing force of 50 g to the bonding portion of the metal wire. Also, during this second stage of pressurization, the control circuit 1
outputs an ultrasonic generation control signal to the amplifier circuit 6. As a result, ultrasonic waves are generated from the ultrasonic transducer 7 during the second stage of pressurization as shown in FIG. 2, and are applied to the bonding portion of the metal wire. Thus, the wire bonding in the first bonding B1 is completed.

Similarly, in the second bonding B2, the control circuit 1 drives the actuator 5 so that different pressing forces are applied in the first stage and the second stage according to the pressing force data set in the memory 3, This displaces the capillary. For example, as shown in Figure 2, in the first step, the capillary is displaced by a displacement amount C, thereby applying a pressing force of 70y to the bonding part of the metal wire, and in the second step, the capillary is displaced by a displacement amount d. A pressing force of 100 g is applied to the bonding part. Also, in this second stage, the ultrasonic transducer 7
Ultrasonic vibrations are generated from the metal wire and applied to the bonding portion of the metal wire.

Thus, the wire bonding of the second bonding B2 is completed, thereby completing one cycle of the wire bonding operation.

In this embodiment, the pressure is applied in two stages, both in the first bonding B1 and in the second bonding B2, and the magnitude of the pressure is small in the first stage and is applied in two stages. Since the setting was large in the first step, the metal wire was temporarily joined without applying excessive force to the wire itself, the pad, or the lead frame surface due to the small pressing force in the first step, and in this state, in the second step. The application of a large pressure force and ultrasonic vibration ensures that the metal wire is bonded to the pad or lead frame.

Therefore, even if the heating temperature of the board is lower than the specified temperature or the temperature of the metal ball is low, it is possible to always achieve a high-strength and reliable bond, which reduces the occurrence of connection failures. yield can be significantly increased.

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, the pressing force is changed in two steps, but it may be changed in three or more steps as necessary. Further, in the above embodiment, ultrasonic vibration is applied only during the second stage of pressure application, but if necessary, it can also be applied to the first stage port 19 with a small amplitude as shown in FIG. You can do it like this. Further, although the above embodiments have been explained using the ultrasonic bonding method as an example, other methods such as thermocompression bonding and thermosonic bonding may be applied. in short,
Any method that performs pressure bonding is applicable. In addition, the value of the pressing force at each stage, the structure of the bonding drive circuit, etc. can be modified in various ways without departing from the gist of the present invention.

〔Effect of the invention〕

As detailed above, according to the present invention, during bonding, the pressure applied by the metal wire to the pad of the semiconductor pellet and the lead frame is changed in multiple stages such that it is initially small and then gradually increases.
It is possible to provide a wire bonding method that can obtain a reliable bonding state even under low temperature conditions, thereby reducing the occurrence of connection failures and performing bonding with a high yield.

[Brief explanation of drawings]

1 and 2 are for explaining a wire bonding method according to an embodiment of the present invention, and FIG. 1 is a block diagram showing the configuration of a bonding drive circuit for implementing the method, and FIG. 3 is a diagram showing a change in capillary displacement and an ultrasonic output waveform, and FIG. 3 is a diagram showing a change in capillary displacement and an ultrasonic output waveform for explaining a wire bonding method in another embodiment of the present invention. , and FIG. 4 are diagrams showing changes in capillary displacement and ultrasonic output waveforms for explaining the conventional wire bonding method. 1... Control circuit, 2... Input section, 3... Memory,
4゜6...Amplification circuit, 5...Actuator, 7.
...Ultrasonic transducer, PO...Change in capillary displacement, TS...Ultrasonic output waveform, B1...
1st bonding, B2... 2nd bonding. Applicant's agent Patent attorney Takehiko Suzue Figure 2

Claims (2)

[Claims] (1) In a wire bonding method in which a metal wire is bonded by applying pressure to a pad of a semiconductor pellet and a lead frame provided on a substrate while the substrate is heated, the metal wire is bonded to a pad of a semiconductor pellet and a lead frame provided on the lead frame. A wire bonding method characterized in that the applied force is changed in multiple stages such that it is initially small and gradually increases. (2) In a wire bonding method in which a metal wire is bonded to a pad of a semiconductor pellet and a lead frame provided on a substrate while the substrate is heated and a metal wire is pressurized, the metal wire is bonded to a pad of a semiconductor pellet and a lead frame provided on the lead frame. The applied force is changed in multiple stages such that it is initially small and gradually increases, and ultrasonic vibration is applied to the metal wire such that it is initially zero or is small and gradually increases. Wire bonding method.