Patent Application
20140054277
The present invention relates to a wire bonding apparatus and a wire bonding method and, more specifically, to a wire bonding apparatus and a wire bonding method capable of performing stable wire bonding.
In the related art, examples of a known wire bonding apparatus as illustrated in
As illustrated in
In wire bonding for connecting the pad of the IC chip and the external lead with a wire containing gold, silver, or copper as principal component on the bonding stage 43, a lead frame is placed on a heater plate 46 heated by a heater block 45 having a heater 45a integrated therein, ultrasonic vibrations and a load of the capillary 34 caused by the ultrasonic horn 33 is applied to the pad of the IC chip and the lead to achieve bonding with respect to the wire in a state in which the IC chip 60 and the lead 61 on the lead frame are heated.
However, in heating by the heater block 45, since heat is transmitted from the heater plate 46, a substrate (lead frame), to the chip in this sequence, heat conduction is not good depending on the types or the materials (ceramic, resin, and the like) of the substrate, so that heating to the IC chip takes time and cooling time is also required before feeding to the next step.
Depending on paste and an adhesive agent for fixing the IC chip on the substrate (lead frame) or on the types of the substrate (ceramic, resin, and the like), sufficient heating cannot be achieved in order to avoid change of properties or deformation due to heat and, as a result of depending excessively on the ultrasonic vibrations for securing the bonding property, stable bonding quality might not be obtained.
There is a case where an LED or a chip of a power semiconductor is adhered to a lead frame having a heat sink. In such a lead frame, since heat loss from the heat sink occurs, it takes time for heating with the heater block 45 and the heater plate 46 on the bonding stage 43, and hence the number of products to be produced may be reduced. Furthermore, when a large-sized substrate is bonded, the entire substrate needs to be heated even though the area to be bonded is small. Therefore, not only that the electricity is wasted, but also it takes significant time for heating and cooling before and after the bonding, and hence the productivity is lowered. Although heating is required only at the moment of bonding, the bonding stage 43 and the heater block 45 need to be continuously heated during the operation of the wire bonding apparatus, and hence electricity is consumed wastefully.
The ultrasonic horn 33 is formed of a metal, and is positioned above the bonding stage 43 which is heated by the heater block 45. Therefore, the position of the bonding tool to be held by the ultrasonic horn 33 is changed by thermal expansion caused by heating, and hence the accuracy of bonding position is lowered. Furthermore, the vibration characteristic of the ultrasonic horn 33 is changed by the metal expansion, and hence the amplitude of the ultrasonic vibration is changed, which may result in lowering of the bonding quality.
Since the camera 38 mounted on the bonding head 31 and configured to detect the position of the IC chip or the like is positioned above the bonding stage 43 which is heated by the heater block 45, the accuracy of position detection of the IC chip or the like due to the thermal expansion caused by heating is lowered. Furthermore, the accuracy of the position detection is lowered also by wavering of air between the IC chip and a lens due to heat. The lowering of the accuracy of the position detection may finally lead to the lowering of the accuracy of the bonding position.
In the bonding to a copper frame, the entire bonding stage needs to be maintained in an inert or reducing atmosphere in order to prevent oxidation of the surface of the copper frame caused by heating at the time of bonding.
The surface of a copper wire is oxidized while it is stored. In copper ball bonding, formation of a ball by using electric discharge is performed in the reducing atmosphere. Therefore, the surface of the copper ball to be bonded in a first bonding operation is not oxidized. However, in a second bonding operation, the bonding strength may be lowered due to the oxidization of the surface of the copper wire.
Furthermore, since the substrate (lead frame) is heated entirely on the bonding stage 43, paste and an adhesive agent used for bonding the IC chip to the substrate (lead frame) or chemical substances contained in the substrate is transformed into gas by heat and dispersed in air, so that peripheral mechanism components such as the ultrasonic horn 33, the bonding head 31, the camera 38, the XY stage 40, and a substrate fixing jig or the like on the bonding stage 43 are contaminated, whereby the function of the apparatus may be impaired.
Therefore, the bonding member having a low coefficient of thermal conductivity, for example, in the bonding of a large hybrid substrate or the like having a plurality of IC chips mounted thereon, heating of the IC chips on the pad cannot be performed sufficiently. Therefore, in order to improve this point, a wire bonding apparatus configured to irradiate a thermal beam from above the bonding surface and heat the bonding surface directly is disclosed in Patent Literature 1.
A wire bonding apparatus including heat control means configured to supply hot air to the surface of a semiconductor chip and a mounted member and heat the connected portion; and cooling means configured to supply cold air to the surface of the semiconductor chip and the mounted member to cool the connected portion, wherein the heat control means perform heating for a predetermined time before starting bonding and the bonding is performed after the heating has terminated, and the cooling means performs forced cooling after the bonding has terminated is disclosed in Patent Literature 2.
PTL1 JP-A-10-125712
PTL2 JP-A-2001-110840
In recent years, when bonding a stacked package, an IC chip on a first stage is bonded, then the package is brought back to a previous process step once to stack an IC chip on the second stage, and the package is returned back to the wire bonding apparatus again to bond a new IC chip on the second stage. By repeating this process, the bonding of the IC chips stacked in multistage is performed. At this time, the lower the stage of the chip, the more thermal history associated with bonding is accumulated. Consequently, lowering of the product quality may result. The higher the stage of the chip, the harder the heat from the bonding stage is transferred. Therefore, the bonding temperature is lowered, and securement of the bonding strength becomes difficult. In the case of the IC chip protruded into air, heat is dissipated into air, and hence the bonding strength may further be lowered.
There is an LSI chip including several hundred or more pads (electrodes). In the LSI chip of this configuration, the pads bonded in the early stage are being heated even after having been bonded until bonding of all of the pads is terminated. In contrast, the last pad, being discharged from the bonding stage immediately after the bonding, is heated for a shorter time after the bonding. In the pads after bonding, bonding with the ball advances further by heat even after having been bonded. Therefore, in the same LSI chip, the bonding strength such as peel strength may be significantly different between the pads bonded in the early stage and the pads bonded in the final stage. This appears as an increase in standard deviation in measurement of the peeling strength, and lowering of process capability index Cpk results. In order to compensate the lowering of the process capability index Cpk, securement of the bonding strength more than necessary is required, and setting (adjustment) of bonding conditions becomes difficult.
Between the pad on the IC chip side and the lead on the substrate (lead frame) side, the material and the shape thereof are significantly different, and the bonding conditions such as a load and ultrasonic vibration strength are significantly different in many cases as well. However, in a current system in which the bonding stage is entirely heated, the pad of the IC chip subjected to the first bonding operation and the lead of the lead frame subjected to the second bonding operation are heated to the same temperature on the heater plate, and hence optimal temperatures cannot be set at a first bonding point (pad) and a second bonding point (pad), respectively.
The wire bonding apparatus of Patent Literature 1 employs both heating by the heater plate of the related art positioned on the backside of the substrate and direct heating of the bonding surface by irradiating the thermal beam from above the bonding surface. When the coefficient of thermal conduction of members such as an HIC substrate is low, a heating effect may be expected. However, in a case where a heating state continues for a long time like the bonding of the stacked package or the bonding of a multiple-pin lead frame, unevenness of the bonding strength may occur.
In the wire bonding apparatus disclosed in Patent Literature 2, the bonding is performed after the heating has terminated, and the forced cooling is performed by the cooling means after the bonding has terminated. Therefore, the cooling time in the next step is not necessary, and hence the in-process loss may be reduced. However, since the surfaces of the semiconductor chip and the mounted members are heated uniformly before bonding, optimal temperatures may not be set at the first bonding point (pad) and the second bonding point (pad), respectively.
Accordingly, it is an object of the invention to provide a wire bonding apparatus and a wire bonding method capable of not only improving bonding properties, but also reducing adverse effects in association with heating, and achieving improvement of both of the productivity and the product quality by heating a chip, a substrate (lead frame), a ball, a bonding tool, or a bonding wire by supplying heated air or gas from an extremely compact hot gaseous matter heater mounted on a bonding head or a bonding arm to a limited area and during a limited period required for bonding.
In order to achieve the above-described object, there is provided a wire bonding apparatus of the present invention configured to connect an electrode (pad) on a semiconductor chip as a bonding point and an external terminal (lead) with a wire by a bonding tool, including: a nozzle-shaped casing including a heater formed of a metal having a large coefficient of resistance temperature which can be heated instantaneously in the interior thereof, an outlet port for blowing out hot gaseous matter from a distal end thereof to a bonding member including the bonding point, and an inlet port for allowing entry of compressed gaseous matter into the other end; heat control means configured to heat the heater; and compressed gaseous matter supply control means configured to perform supply and block of the compressed gaseous matter into the casing, wherein control is performed to provide a period in which the hot gaseous matter is not supplied from the casing to the bonding member in at least any one of periods when the bonding tool is not landed on the bonding point during the bonding operation.
The wire bonding apparatus of the invention is characterized in that the heat control means and the compressed gaseous matter supply control means are configured to vary the temperature of the hot gaseous matter and the blowing timing of the hot gaseous matter for each of the bonding points.
The wire bonding apparatus of the invention is also characterized in that the heat control means is configured to control a heat generating temperature of the heater without using a temperature sensor by controlling the value of resistance of the heater to maintain a predetermined value by electricity distribution.
In order to achieve the above-described object, there is provided a wire bonding apparatus of the present invention configured to connect an electrode (pad) on a semiconductor chip as a bonding point and an external terminal (lead) with a wire by a bonding tool, including: a nozzle-shaped casing including a heater formed of a metal having a large coefficient of resistance temperature which can be heated instantaneously in the interior thereof, an outlet port for blowing out hot gaseous matter from a distal end thereof to a bonding member including the bonding point, and an inlet port for allowing entry of compressed gaseous matter into the other end; heat control means configured to heat the heater; and compressed gaseous matter supply control means configured to perform supply and block of the compressed gaseous matter into the casing, wherein control is performed to provide a period in which the hot gaseous matter is not supplied from the casing to the bonding member by the heat control means and the compressed gaseous matter supply control means in at least any one of periods when the bonding tool is not landed on the bonding point during the bonding operation.
According to the invention, an optimal heating may be performed only during a minimum time required for bonding by controlling to provide a period during which the hot gaseous matter is not provided in at least any one of periods when the bonding tool is not landed on the bonding point during the bonding operation.
Consequently, selective heating of only part contributing to the bonding such as the surface of the electrode, the bonding wire, and the distal end of the bonding tool is achieved while avoiding penetration of heat to the member or diffusion of the heat to the peripheral portion.
In addition, since the heating temperature may be variably set at each of the bonding points such as the first bonding point and the second bonding point, the bonding may be performed at an optimal heating temperature.
In the bonding of the stacked package, since the surface of the electrode can reliably be heated because the apparatus employs a top heating system, and the penetration of heat into the chip is suppressed because the apparatus employs an instantaneous heating system, so that the accumulation of the thermal history to the chip on the lower layer may be prevented.
In addition, since the heating control means is configured to control so that the value of resistance of the heater in the casing is maintained at the predetermined value by electricity distribution, control of the heat generating temperature of the heater is enabled without using the temperature sensor, and hence a sensor for detecting the temperature of the heater is not necessary, so that the configuration in the casing may be simplified.
Referring now to the drawings, embodiments for implementing a wire bonding apparatus and a wire bonding method according to the invention will be described below. The invention is configured to be capable of improving bonding properties by supplying heated air or gas to a heating area required for bonding for a limited time by heating a chip, a substrate (lead frame), a ball, a bonding tool, or a bonding wire with gaseous matter such as heated air or gas from an extremely compact hot gaseous matter heater mounted on a bonding head or a bonding arm, alleviating adverse effect in association with heating by a heater plate of the related art, and achieving improvement of the productivity and the quality.
As illustrated in
A microcomputer as the control unit 30 includes a program configured to perform control such as bonding operation of the wire bonding apparatus 1 integrated therein, and the microcomputer is configured to perform control of various operations including an operation of the hot gaseous matter heater 5 of the wire bonding apparatus 1 by executing the program.
A supporting member 8 provided on the outer periphery of the casing 7 is configured to mount the hot gaseous matter heater 5 on the bonding head 31 or the bonding arm 32, and is mounted via a mounting bracket 28 so that the hot gaseous matter outlet port 7b is positioned in the direction of a pad of the IC chip as a bonding point, a lead of the substrate (lead frame), the ball at a distal end of the bonding tool, or the bonding wire.
When the hot gaseous matter heater 5 is mounted on the bonding head 31 by using the mounting bracket, the hot gaseous matter heater 5 always moves integrally with the bonding head 31 by the XY stage. If a target position of the hot gaseous matter blowing out from the hot gaseous matter heater 5 is adjusted to a landing point of the bonding tool, the IC chip, the substrate (lead frame), the ball, and the bonding tool may be heated at the time of bonding by supplying hot gaseous matter with timing of bonding.
When the hot gaseous matter heater 5 is mounted on the bonding arm 32 by using the mounting bracket, the hot gaseous matter heater not only moves integrally with the bonding head 31 by the XY stage, but also moves upward and downward together with the bonding arm 32. If the target position of the hot gaseous matter blowing out from the hot gaseous matter heater 5 is adjusted to near a distal end of a bonding tool 34, the IC chip, the substrate (lead frame), the ball, and the bonding tool may be heated at the time of bonding by supplying hot gaseous matter with timing of bonding. In this case, a stress in association with shaping of the wire may be reduced by further heating and softening the bonding wire by hot gaseous matter at the time of looping operation.
Subsequently, with reference to
The bridge circuit 16 is composed of a resistance resistance 17 (a value of resistance is R1) connected in series, and the filament heater 6 (filament is formed of white gold having a positive coefficient of resistance temperature and has a value of resistance of Rh), a resistance 18 (a value of resistance is R2) connected in series, a resistance 19 (a value of resistance is R3), and a digital potentiometer 20 (a selected value of resistance is VR1). The digital potentiometer 20 includes a plurality of resistances integrated therein, and is configured to output a figure corresponding to the value of resistance from the external control unit 30 and specify a specific value of resistance.
A connecting point between the resistance 17 and the heater 6 is input to a − (minus) terminal of the differential amplifier 14 via a resistance 23, and a connecting point between the resistance 18 and the resistance 19 is input to a + (plus) terminal of the differential amplifier 14 via a resistance 24. An output from the differential amplifier 14 is input to a + (plus) terminal of the comparator 15. A − (minus) terminal of the comparator 15 is connected to GND. An output from the comparator 15 is of a general open collector type of an NPN transistor, and when the output from the comparator 15 is at a high level, the high-voltage drive circuit 12 and the low-voltage drive circuit 13 are configured to be turned ON by a pull-up voltage of a command input voltage as a control signal. In this manner, the output from the comparator 15 functions as a signal configured to control the high-voltage drive circuit 12 and the low-voltage drive circuit 13 when the control signal is input.
The heater drive circuit 11 is provided with the high-voltage drive circuit 12 and the low-voltage drive circuit 13, and the high-voltage drive circuit 12 controls a high-voltage power source 12a by FETs 12b and 12c and applies the high-voltage power source 12a to the bridge circuit 16. The low-voltage drive circuit 13 is configured to control a low-voltage power source 13a by FETs 13b and 13c and apply the low-voltage power source 13a to the bridge circuit 16.
Power sources of the high-voltage drive circuit 12 and the low-voltage drive circuit 13 are both connected to the bridge circuit 16 including the heater 6, and a protective diode 25 is inserted in series in the forward direction in order to prevent a reverse voltage to the respective circuits.
By passing a current to the heater 6 of the hot gaseous matter heater 5, the heater 6 is heated by generated Joule heat and the temperature is increased. The heater 6 is increased in temperature and the value of resistance of the heater 6 by itself is also increased. Since the relationship between the value of resistance and the temperature of the heater 6 is linear, the temperature of the heater 6 may be set to be constant by maintaining the value of resistance of the heater 6 constant. When setting the temperature of the surface of the heater 6 to be high, a value of resistance of the digital potentiometer 20 is selected so that the value of resistance of the heater 6 is increased.
The heater drive circuit 11 is configured to control the heat generating temperature of the heater by controlling the value of resistance of the heater integrated in the bridge circuit 16 to be maintained at a predetermined value. The control of the value of resistance of the heater 6 detects the voltage difference of the contact point of the bridge circuit 16 by the differential amplifier 14, and distribute high voltage from the high-voltage drive circuit 12 to the bridge circuit 16 so that the voltage difference detected by the differential amplifier 14 becomes zero. Accordingly, the value of resistance of the heater 6 is maintained to a predetermined value, and the heat generating temperature of the heater 6 is maintained to be constant.
As illustrated in
The high-voltage drive circuit 12 has a configuration of a high-side switch using a P-channel MOS for an output. An N-channel MOS is used for the gate drive of the output P-channel MOS for the purpose of achieving a quicker response. When the high-voltage power source is turned ON by the high-voltage drive circuit 12, a high voltage is applied to the bridge circuit 16 including the heater 6, and current flows to the heater 6, whereby heat is generated by Joule heat. The voltage of the high-voltage power source 12a of the high-voltage drive circuit 12 is set to allow a current as high as several times the rating, preferably, as high as dozens of times the rating to flow to the heater 6 by turning the high-voltage drive circuit 12 ON. Accordingly, as illustrated in
In contrast, when the heater 6 abruptly generates heat and the temperature is increased and also the value of resistance of the heater 6 is increased, and consequently a voltage difference at the differential amplifier 14 between the voltage Vin1 generated in the heater 6 and the voltage Vin2 at the connecting point between the resistance 18 and the resistance 19 in the bridge circuit 16 is Vin2<Vin1, that is, (R3+VR1)/(R2+R3+VR1)<Rh/(R1+Rh) is satisfied, the differential amplifier 14 outputs a negative voltage (during a period from t3 to t5) and the output from the comparator 15 is in a low level. Therefore, the high-voltage drive circuit 12 is turned OFF. Accordingly, the heat generation of the heater 6 is stopped and the temperature of the heater 6 is lowered, so that the value of resistance of the heater 6 is reduced. While the heater drive circuit 11 is operated (while the command input voltage is in the ON state), a minimum required voltage is applied to the bridge circuit including the heater 6 in order to maintain an output voltage from the differential amplifier 14. The voltage applied to the bridge circuit 16 is set to be sufficiently low so that the heater 6 does not increase in temperature beyond the set temperature, and is supplied by the low-voltage drive circuit 13. The reason is that if the voltage is not applied to the bridge circuit 16 including the heater 6, the output voltage from the differential amplifier 14 becomes zero irrespective of the resistance of the heater 6, that is, the temperature, and hence the temperature control is prevented from becoming disabled. The low-voltage drive circuit 13 has a configuration of the high-side switch with the P-channel MOS which is similar to the high-voltage drive circuit 12, and turns the low-voltage power source 13a ON while the command voltage input is in the high level.
From then onward, while the command voltage input is in the high level, the magnitudes of the voltage Vin1 generated at the heater 6 and the voltage Vin2 at the connecting point between the resistance 18 and the resistance 19 in the bridge circuit 16 at the differential amplifier 14 is switched alternately, and ON/OFF control of the high-voltage drive circuit 12 is repeated.
Subsequently, the bonding operation in the wire bonding apparatus configured as described above will be described with reference to
First of all, as illustrated in
After the calculation of the bonding position has performed, the XY stage 40 having the bonding head 31 mounted thereon is moved to the first bonding position. The capillary 34 as the bonding tool 34 is controlled to be lowered to immediately above the first bonding point (Step S3).
After the lowering of a capillary 34 has started, whether or not the capillary 34 has reached a search height (the position of P1 at t10 illustrated in
When the capillary 34 reaches the search height (Yes in Step S4), the capillary 34 is lowered at a search speed as a constant low speed and the heater drive unit 11 selects the value of resistance of the digital potentiometer 20, sets heating conditions such as the temperature of the hot gaseous matter heater 5, starts heating of the hot gaseous matter heater 5, and starts supply of gaseous matter to the gaseous matter inlet port 7a of the hot gaseous matter heater 5 (Step S5). Accordingly, hot gaseous matter is blown out from the hot gaseous matter outlet port 7b of the hot gaseous matter heater 5 and heats an area in the vicinity of the bonding point.
Subsequently, whether or not the ball locked to the distal end of the capillary 34 comes into contact with the pad at the first boding point is checked (Step S6). After the fact that the distal end of the capillary 34 comes into contact (P2 illustrated in
Subsequently, the capillary 34 is controlled to be lowered to immediately above the second bonding point (Step S11). Whether or not the capillary 34 reaches the search height (the position of P3 at t12 illustrated in
After the fact that the distal end of the capillary 34 comes into contact(P4 illustrated in
Whether or not the bonding for all the wires is completed is checked (Step S18). When the bonding of all of the wires is not completed (No in Step S18), the capillary 34 is moved upward, the ball is formed at the distal end of the capillary 34, and then the procedure goes to Step S3 to continue the remaining bonding. In contrast, when the bonding of all the wires is completed (Yes in Step S18), the capillary 34, and the XY stage are moved to their original points and end the bonding operation is terminated (Step 19).
In this manner, the wire bonding apparatus of the invention is configured to control to provide a period during which hot gaseous matter is not supplied in at least any one of periods when the capillary 34 is not landed on the bonding point during the bonding operation. In the bonding operation illustrated in
As described above, according to the invention, an optimal heating may be performed only during a minimum period required for bonding by controlling to provide a period in which the hot gaseous matter is not provided in at least any one of periods when the bonding tool is not landed on the bonding point during the bonding operation. Consequently, selective heating of only part contributing to the bonding such as the surface of the electrode, the bonding wire, and the distal end of the bonding tool is achieved while avoiding penetration of heat to the member or diffusion of the heat to the peripheral portion.
In addition, since the heating temperature may be variably set at each of the bonding points such as the first bonding point and the second bonding point, the bonding may be performed at an optimal heating temperature.
In the bonding of the stacked package, since the surface of the electrode may reliably be heated because the apparatus employs a top heating system, and the penetration of heat into the IC chip is suppressed because the apparatus employs an instantaneous heating system, the accumulation of the thermal history to the chip on the lower layer may be prevented.
In addition, since the heating control means is configured to control the value of resistance of the heater in the casing so as to be maintained at the predetermined value by electricity distribution, control of the heat generating temperature of the heater is enabled without using the temperature sensor, and hence a sensor for detecting the temperature of the heater is not necessary and hence the configuration in the casing may be simplified.
The invention may be embodied in various modes without departing the essential characteristics. Therefore, needless to say, the embodiment described above is given only for description and does not limit the invention.
1, 30 wire bonding apparatus
5 hot gaseous matter heater
6 heat-generating member (heater), filament (white gold)
6
a lead wire
7 casing
7
a gaseous matter inlet port
7
b hot gaseous matter outlet port
8 Supporting member
10 hot gaseous matter heater drive unit
11 heater drive circuit
12 high-voltage drive circuit
12
a high-voltage power source
12
b, 12bc FET
13 low-voltage drive circuit
13
a low-voltage power source
13
b, 13c FET
14 differential amplifier
15 comparator
16 bridge circuit
17, 18, 19 resistance (for bridge circuit)
20 digital potentiometer
23, 24 resistance
25 diode
26 electromagnetic opening and closing valve
27 throttle valve
28 mounting bracket
31 bonding head
32 bonding arm
33 ultrasonic horn
34 bonding tool (capillary)
35 encoder
36 supporting shaft
37 rear motor
38 camera
39, 43 bonding stage
40 XY stage
45 heater block
45
a heater
46 heater plate
30, 50 control unit
55 drive unit
60 IC chip
61 lead
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-285197 | Dec 2011 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2012/075630 | 10/3/2012 | WO | 00 | 10/8/2013 |
