JP2000260806A - Wire bonder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely detect appearance of a metal ball, with a comparatively simple structure, and enable high-speed operation. SOLUTION: A capillary 7 fixed to the top end of a horn 6 and metal ball forming means 10 for melting the top end of a metal wire 8 passing through the capillary 7 and projecting from the lower end of the capillary 7 are provided, thereby forming the metal balls 8a. The metal ball 8a is pushed against a work 1 at the lower end of the capillary 7, and an ultrasonic oscillation is given to the ball while being pressed to connect a metal wire. A means 11 is provided for detecting the appearance of the ball 8a prior to the connection of the metal ball 8a formed at the lower end of the metal wire to the work.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire bonder, and more particularly to a wire bonder for forming a metal ball at the tip of a metal wire and applying the ultrasonic vibration to the metal ball while pressing the metal ball against the object to be bonded at the tip of a capillary. About.

[0002]

2. Description of the Related Art An electronic component such as a semiconductor device electrically connects an electronic component main body and an external electrode such as a lead, and covers a main part including the electronic component main body. When this electronic component is manufactured using a lead frame, metal wires are generally used for electrical connection between the electronic component body and the leads.
In the case of a device having a large number of electrodes, such as a semiconductor integrated circuit device, the leads are arranged on both sides of the electronic component body, and in the case of other electrodes, the leads are arranged around the electronic component body. Therefore, as a bonding tool for connecting the metal wire to the electronic component body and the lead, a capillary having no limitation in the direction in which the metal wire is drawn is used. An example of this type of wire bonder will be described with reference to FIGS. In the drawing, reference numeral 1 denotes a lead frame, which integrally connects an island 1a for mounting an electronic component body 2 such as a semiconductor pellet and a plurality of leads 1b having one end arranged near the island 1a into a frame (not shown). It is a thing.
Reference numeral 3 denotes a guide rail for guiding the lead frame 1, and a feed mechanism (not shown) for intermittently feeding the lead frame 1 is additionally provided. Reference numeral 4 denotes an XY table arranged on the side of the guide rail 3, and reference numeral 5 denotes a bonding head fixed to the XY table 4, and a horn 6 having an ultrasonic vibrator (not shown) fixed at one end to a pivotable shaft. A vertical movement mechanism (not shown) for vertically moving the entire horn 6 is provided.
Reference numeral 7 denotes a capillary fixed to the other end of the horn 6, through which a metal wire 8 is inserted. 9 is an arm connected at one end to the bonding head 5 and extending parallel to the horn 6.
Reference numeral 0 denotes a discharge electrode supported by the arm 9 and reciprocating in a horizontal plane across the lower part of the capillary 7 and applying a high voltage between the lower end of the metal wire 8 protruding from the lower end of the capillary 7 and discharging the wire. 8 to melt the metal ball 8a
To form The operation of this device will be described below. First, the portion to be bonded of the lead frame 1 is connected to the guide rail 3.
Position in the upper fixed position. At the same time, the capillary 7 is moved onto the lead 1b, and the discharge electrode 10 is reciprocated horizontally below the capillary 7 to apply a high voltage. As a result, a metal ball 8a is formed at the lower end of the metal wire 8 protruding from the capillary 7. From this state, the XY table 4 is operated to move the capillary 7 onto an electrode (not shown) of the electronic component body 2. Then, the horn 6 is lowered and the horn 6 is swung to press the metal ball 8a on the electrode at the lower end of the capillary 7 and to apply ultrasonic vibration while applying a load to connect the tip of the metal wire 8 to the electrode. I do. Then, the capillary 7 is moved up while moving out the metal wire 8 and moved on the lead 1b, and the middle part of the metal wire 7 is pressed at the lower end of the capillary 7 and connected to the lead 1b. When this connection is completed, the metal wire 8 is clamped by a clamper (not shown) above the capillary 7 to simultaneously raise the capillary 7 and the clamper to cut the outer position of the wire 8 connected on the lead 1b. Then, the connection between the electrode and the lead on the electronic component body is completed. The above operation is sequentially performed on other electrodes and leads, and the lead frame 1
Is moved at a constant pitch, and the above operation is repeated. In this type of wire bonder, the bonding strength of the wire 8 is important. When the electronic component body 2 is covered with a resin and packaged, external moisture or corrosive gas penetrates from the bonding interface between the lead and the resin and enters the connection portion of the wire. Even if it arrives, corrosion at the bonding interface is unlikely to occur, and in the case of an electronic component that operates repeatedly, moisture that has entered the interior due to the heat generated by the electronic component body 2 is discharged again. Need to be kept high. Further, if the bonding strength is low, the electrical resistance at the bonding portion increases, and there is a risk of local heating and fusing. Therefore, it is necessary to keep the bonding strength high even for a device operated with a large current for stable operation for a long time. By the way, the diameter of the metal ball 8a formed at the tip of the wire 8 is determined by the diameter of the wire 8, and the shape greatly affects the bondability. Therefore, the shape of the discharge electrode 10, the distance from the tip of the wire 8, and the applied voltage are adjusted, and the respective conditions are set so that the shape of the metal ball 8a is optimized.

[0003]

However, the discharge electrode 1
In the case of 0, the polished surface layer evaporates due to the high temperature generated each time the discharge is repeated, and irregularities are formed, and the irregularities are deformed. Then, the discharge condition set to make the shape of the metal ball 8a good changes, and the shape changes to a shape unsuitable for bonding. Further, even when the length of the metal wire 7 protruding from the capillary 7 varies or the protruding wire is bent, the distance from the discharge electrode 10 changes, and the diameter and shape of the metal ball 8a vary. There was a problem of variation. For that reason, for example,
Japanese Unexamined Patent Publication No. 322532 (Prior Art 1) discloses an apparatus for inspecting the state of a connection portion of a metal ball by capturing an image of an electronic component body on which wire bonding has been completed with a television camera. As a result, the shape of the connection part of the metal ball can be observed, but even if there is an inappropriate diameter or shape because it has already been bonded on the lead frame, it is not possible to remove only the inappropriate part. In the post-process, the unsuitable part is packaged together with the non-defective part, and it is impossible to judge the quality after the packaging. It had to be removed in the process. On the other hand, Japanese Patent Application Laid-Open No. 8-250539 (Prior Art 2) discloses that a sensor detects infrared light generated by a discharge between a discharge electrode and a metal wire before wire bonding, and controls a discharge time based on the amount of the infrared light. It is disclosed that the diameter of the metal ball is kept constant.
If the diameter of the ball can be made constant when the metal ball is formed in this way, it is possible to eliminate almost no defective bonding on the electronic component body. However, if the shape of the ball formed by the discharge varies, the amount of infrared rays generated by the discharge also varies, so if the ball shape deviates from the spherical standard state, the diameter is constant even if the discharge time is controlled from the total light amount Could not be. Further, even when the wire surface is contaminated with fat or the like, the amount of generated infrared light varies, and the diameter of the metal ball cannot be kept constant. Also, Japanese Patent Application Laid-Open No. 8-236567 (Prior Art 3) discloses that the tip of a metal wire is imaged using a television camera, and the diameter of a metal ball formed under different discharge conditions is imaged using a television camera. There is disclosed a wire bonder in which the diameter of a metal ball is calculated from a signal, and discharge conditions for forming a metal ball having an arbitrary diameter are determined based on the calculation result. Since this wire bonder can automatically set conditions for determining the diameter of a metal ball, it is effective for forming an initial ball at the start of a bonding operation. However, since it takes time to set the optimum discharge conditions, this apparatus is not suitable for forming metal balls continuously after initial ball formation. After setting the optimal discharge conditions, the TV camera can be operated to image the outer shape of the metal ball formed by the discharge and determine its shape and diameter.However, the TV camera is located near the capillary moving on the electronic component body. However, there is a problem in that there is a restriction in arranging the devices, and there is a problem that the device becomes large.

[0004]

SUMMARY OF THE INVENTION The present invention has been proposed to solve the above-mentioned problems, and includes a horn to which ultrasonic vibration is applied and which moves up and down and horizontally, and a metal fixed to the tip of the horn. A capillary into which the wire is inserted, and ball forming means for forming a metal ball by melting the tip of the metal wire protruding from the lower end of the capillary, and pressing the metal ball against the object to be bonded at the lower end of the capillary to apply pressure. In a wire bonder for connecting a metal wire by applying ultrasonic vibration while providing a means for detecting the appearance of the metal ball prior to connecting the metal ball formed at the lower end of the metal wire to an object to be bonded. A wire bonder characterized by the following.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A wire bonder according to the present invention has means for detecting the appearance of a metal ball before connecting a metal ball formed at the lower end of a metal wire protruding from the lower end of a capillary to an object to be bonded. A light source for irradiating convergent light to a metal ball formed at a wire tip or a light from the light source to a metal ball formed on an oscillating body that oscillates at least on one side below the capillary. An optical sensor for detecting the appearance of the metal ball can be arranged to constitute the metal ball appearance detecting means. In this case, the first and second oscillators move in parallel on both sides below the capillary.
And the first and second optical sensors respectively receiving the light from the respective light sources are arranged at predetermined intervals in the swinging direction, so that the metal ball appearance detecting means can be configured. Place the fixed body on one side below the capillary,
An oscillating body that faces the fixed body via a capillary and is close to and separated from the fixed body is arranged.The light source and the optical sensor are fixed to the fixed body, and a reflecting mirror that reflects light from the light source is fixed to the oscillating body. The light emitted from the light source is reflected by the reflecting mirror, and the reflecting mirror is swung so that the reflected light reaches the optical sensor across the metal ball formed at the tip of the wire.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the figure, the same components as those in FIGS. 7 and 8 are denoted by the same reference numerals, and redundant description will be omitted. Prior to connecting the metal ball 8a formed at the lower end of the metal wire 8 protruding from the lower end of the capillary 7 to an object to be bonded such as an electrode of the electronic component body 2, the wire bonder according to the present invention comprises:
A means 11 for detecting the appearance of the metal ball 8 is provided. In the illustrated example, the ball appearance detecting means 11 is configured by fixing a light source 13 for detecting the metal ball 8a and a sensor 14 to an oscillating body 12 pivotally supported by an arm 9. This rocking body 12 is formed by connecting and integrating one leg piece 12b having a U-shape in plan view with the lower end of a rocking arm 12a having an intermediate portion pivotally supported by the arm 9.
c face each other via the capillary 7, and the light source 1
3 and the sensor 14 are fixed. As the light source 13, a laser light source that can generate a thin light beam is desirable. The oscillating body 12 has bar magnets 1 on both sides along the arm 9 at the upper end.
5 and a spring 16 are fixed, and the spring 16 is provided with a swing arm 12a such that the light source 13 and the sensor 14 fixed to the leg pieces 12b and 12c are located on the opposite side to the discharge electrode 10.
To give an elastic force. One end of the bar magnet 15 is the coil 1
The swinging body 12 reciprocates on the side of the capillary 7 by controlling the energization of the coil 17. The light source 13 is lit at least while the coil 17 is operating and moving below the capillary 7, and the output signal of the sensor 14 is processed by a control unit (not shown).
The table 4 and the bonding head 5 are controlled. The operation of this device will be described below. First, the capillary 7 is raised to slightly protrude the tip of the metal wire 8 from the lower end, and a high voltage is applied to the discharge electrode 10 below the capillary 7 to reciprocate in a horizontal plane. As a result, a discharge is generated between the wire 8 and the discharge electrode 10, and the tip of the wire is heated and melted to form the metal ball 8a. Then, the capillary 7 is slightly lowered to bring the metal ball 8a into close contact with the lower end of the capillary 7. At this time, the height position of the capillary 7 is set at a position crossing the optical axis between the light source 13 and the sensor 14. When the coil 17 is energized, the bar magnet 15 is pulled into the coil 17 against the elastic force of the spring 16,
The swing arm 12a rotates, and the optical axes of the light source 13 and the sensor 14 cross the metal ball 8a. As a result, the light applied to the sensor 14 is interrupted by the metal ball 8a, and this interruption time appears as the pulse width of the output signal of the sensor 14.
By making this pulse width correspond to the actually measured diameter of the metal ball 8a, the diameter of the metal ball 8a can be known based on the pulse width of the output signal of the sensor 14. When the control unit determines that the diameter of the metal ball 8a is out of the predetermined diameter range and is unsuitable for bonding based on the sensor output, the XY table 4 or the bonding head 5 is moved to a preset position to generate an alarm. Notify the operator of the abnormality. In this abnormal state, the capillary 7 is moved to a preset position. At this position, a crimping table or the like for crimping the defective metal ball 8a is arranged, the metal ball 8a is crimped, and the wire 8 is cut. By doing so, the bonding operation can be continued without stopping the apparatus. Further, when the shape defect of the metal ball 8a frequently occurs, it is possible to automatically recover from the defective state by changing the discharge condition according to the diameter of the metal ball 8a. Further, by analyzing the frequency of occurrence, outer shape, and crimping force of the crimped ball crimped on the crimping table or the like, contamination of the wire 8, abrasion of the discharge electrode 10, displacement of the discharge voltage and current, and the like are not shown. It is possible to know the improper adjustment of the wire feed mechanism and the like, and to cope with the problem at an early stage, and prevent a serious accident from occurring. In the embodiment shown in FIG. 1, the light source 13 and the sensor 14 are each described as a single unit. However, as shown in FIG.
And two sensors 14a and 14b that receive light from the light sources 13a and 13b. As a result, pulse signals shown in FIG. 4 are generated at the outputs S1 and S2 of the sensors 14a and 14b. Here, the pulse widths w1 and w2 of the outputs S1 and S2 are substantially equal, and each represents the diameter of the metal ball 8a. On the other hand, the interval T between the rising times of the pulses of the outputs S1 and S2 represents the arrangement interval between the light sources 13a and 13b and the sensors 14a and 14b, and has a known length L
It is. Therefore, the diameter X of the unknown metal ball 8a is (w
T) / L. As a result, even if the speed of the oscillator 12 at the start of the operation changes, the change in the speed on the side of the metal ball 8a can be made extremely small by making the distance L between the optical axes close. Can be detected well. As shown in FIG. 5, a plurality of (three in the illustrated example) light sources are arranged at predetermined intervals from each other (two in the illustrated example).
By arranging a sensor corresponding to each light source, a more accurate outer shape of the metal ball 8a can be known. Further, as shown in FIG. 6, a light source 13 and a sensor 14 are arranged on one leg 12b of the oscillating body 12 at an interval sufficiently larger than the diameter of the metal ball 8a, and light from the light source 13 is applied to the other leg 12c. By arranging the prism 18 that reflects the light to the sensor 14, the same effect as that of the embodiment of FIG. 3 can be obtained with a set of the light source and the sensor.
b, electrical wiring is easy and optical axis alignment is also easy.

[0007]

As described above, the wire bonder according to the present invention can reliably detect the outer shape of the metal ball with a relatively simple structure, and can operate at high speed. Therefore, it is possible to detect the external shape abnormality of all the formed metal balls before bonding without lowering the bonding speed compared to the device using a TV camera, and to bond only good metal balls. Electronic components with high reliability can be manufactured.

[Brief description of the drawings]

FIG. 1 is a perspective view of a main part of a wire bonder showing an embodiment of the present invention.

FIG. 2 is a plan view of the apparatus in FIG. 1;

FIG. 3 is a plan sectional view showing another embodiment of the metal ball appearance detecting means of the apparatus of the present invention.

FIG. 4 is a sensor output signal waveform diagram of the metal ball appearance detecting means of FIG. 3 embodiment.

FIG. 5 is a side view showing another embodiment of the metal ball appearance detecting means of the apparatus of the present invention.

FIG. 6 is a plan sectional view showing another embodiment of the metal ball appearance detecting means of the apparatus of the present invention.

FIG. 7 is a side view showing an example of a wire bonder.

8 is a front view of a main part of the apparatus in FIG. 7;

[Explanation of symbols]

 2 Bonded object (electronic component body) 6 Horn 7 Capillary 8 Metal wire 8a Metal ball 10 Ball forming means (discharge electrode) 11 Metal ball appearance detecting means

Claims (4)

[Claims] 1. A horn to which ultrasonic vibration is applied and which moves vertically and horizontally, a capillary fixed to a tip of the horn, through which a metal wire is inserted, and a tip of the metal wire protruding from a lower end of the capillary are melted. Ball forming means for forming a metal ball by pressing the metal ball against the object to be bonded at the lower end of the capillary, applying ultrasonic vibration while applying pressure to connect the metal wire, the wire bonder, A wire bonder comprising means for detecting the appearance of a metal ball prior to connecting the metal ball formed at the lower end to an object to be bonded. 2. A light source for irradiating convergent light to a metal ball formed at the tip of a wire or a light from the light source is applied to an oscillating body that oscillates at least on one side below the capillary, and detects the appearance of the metal ball. 2. The wire bonder according to claim 1, wherein an optical sensor is provided to form a metal ball appearance detecting means. 3. An oscillating body that moves in parallel on both sides below a capillary includes first and second light sources and first and second optical sensors respectively receiving light from the respective light sources in the oscillating direction. 3. The wire bonder according to claim 2, wherein the metal ball appearance detecting means is arranged at predetermined intervals. 4. A fixed body is disposed on one side below the capillary, and an oscillating body facing the fixed body via the capillary and spaced close to and away from the fixed body is provided. Is fixed, and a reflector that reflects the light from the light source is fixed to the oscillator, and the light emitted from the light source is reflected by the reflector,
3. The wire bonder according to claim 2, wherein the reflecting mirror is swung so that the reflected light crosses the metal ball formed at the tip of the wire and reaches the optical sensor.