JP4179273B2 - Part joining method - Google Patents

Description

  The present invention relates to a component bonding method for bonding a component such as a flip chip to a substrate.

Ultrasonic bonding is known as a method for bonding a component such as a flip chip to a substrate. In ultrasonic bonding, by applying ultrasonic vibration while pressing a bump provided on a component against an electrode of a substrate, the bonding surfaces are rubbed against each other to bond the bump to the electrode (see, for example, Patent Document 1). ). In this patent document example, when the components held by the joining tool are lowered with respect to the substrate and the bumps are pressed against the electrodes, at the timing when the pressing load reaches a predetermined load, the strength set in advance is set. The ultrasonic vibration is applied to the component continuously for a predetermined time.
Japanese Patent No. 3539209

  By the way, when vibration is transmitted from the joining tool to the part, the vibration is not necessarily transmitted to the part as it is, and generally a slip occurs on the contact surface between the joining tool and the part. For this reason, in order to transmit a sufficiently strong vibration to the bonding surface between the bump and the electrode to ensure a good bonding quality, the output of the ultrasonic vibration source should be increased after allowing for a transmission loss due to slippage. It was necessary to set or set the vibration application time longer.

  For this reason, a situation in which excessively strong ultrasonic vibrations are continuously applied to the parts to be joined exceeding the vibration strength originally required to obtain an appropriate joined state for an extra time. In some cases, parts are damaged, and extra joining work time is required. In addition, since vibration is applied while there is slippage between the joining tool and the part, the contact surface between the joining tool and the part tends to wear, shortening the life of the joining tool and reducing the cost of consumables. In addition to the increase, there is a case where a defect such as a variation in bonding quality due to a change in wear state of the bonding tool with time is caused.

  Accordingly, an object of the present invention is to provide a component joining method capable of ensuring joining quality, shortening the time required for joining work, and further realizing extending the life of a joining tool.

The component bonding method of the present invention is a component bonding method for bonding a component electrode provided on a component to a substrate electrode provided on a substrate by vibration, and a contact step of bringing the component electrode into contact with the substrate electrode; , and a bonding step of bonding the component electrode by applying vibration by component bonding tool to said component to said substrate electrode, applied in the joining step, the first vibration being determined from the bonding condition of the component of interest A first vibration applying step and a second vibration applying step of applying a second vibration whose vibration intensity is weaker than the first vibration are alternately executed. In the second vibration applying step, the vibrator Is set to an output value at which no slip occurs between the component joining tool and the component .

  According to the present invention, vibrations having different strengths are applied in two unit vibration application steps that are in a preceding / following relationship among a plurality of unit vibration application steps that constitute a joining step of joining a component electrode to a substrate electrode. As a result, the relative slip between the contact surface of the welding tool and the parts can be reduced as much as possible, ensuring the bonding quality, shortening the time required for bonding, and further extending the life of the bonding tool.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an ultrasonic bonding apparatus according to an embodiment of the present invention. FIG. 2 is an operation explanatory diagram of the ultrasonic bonding apparatus according to an embodiment of the present invention. 6 and 7 are explanatory views of an ultrasonic vibration application pattern in the ultrasonic bonding apparatus according to the embodiment of the present invention, and FIG. 8 is an explanatory view of the ultrasonic vibration application pattern in the conventional ultrasonic bonding apparatus.

  First, the structure of the ultrasonic bonding apparatus will be described with reference to FIG. In FIG. 1, a substrate 3 is held by a substrate holder 2 provided on the upper surface of the positioning table 1. The positioning table 1 is driven by a table driving unit 11. A semiconductor chip 4 as a component is mounted on the substrate 3 by ultrasonic bonding. Circuit electrodes 3 a as substrate electrodes are provided on the upper surface of the substrate 3, and bumps 4 a as component electrodes are provided on the lower surface of the semiconductor chip 4. The semiconductor chip 4 is mounted on the substrate 3 by bonding the bumps 4a to the circuit electrodes 3a by ultrasonic vibration.

  A bonding mechanism is disposed above the positioning table 1. The bonding mechanism is configured by mounting a joining tool 7 on the lower surface of a lifting block 6 that moves up and down by a lifting and lowering pressing mechanism 5. The raising / lowering pressing mechanism 5 is driven by the head raising / lowering driving unit 14. The joining tool 7 is mainly composed of a horn 8 that is a rod-shaped member, and a vibrator 10 is attached to one end of the horn 8. By driving the vibrator 10 by the vibrator driving unit 12, ultrasonic vibration is applied to the horn 8.

  A bonding portion 9 is provided at the center of the lower surface of the horn 8, and the lower surface of the bonding portion 9 is a contact surface 9 a that contacts the semiconductor chip 4 to be bonded. The contact surface 9 a is provided at a position corresponding to the antinode of standing wave vibration of the horn 8. A suction hole 8a is provided inside the horn 8, and the suction hole 8a communicates with a suction hole 9b provided in the contact surface 9a. The suction hole 8 a is connected to the suction drive unit 13. By driving the suction drive unit 13, vacuum suction is performed from the suction hole 9b, and the semiconductor chip 4 in contact with the contact surface 9a is held by vacuum suction.

  The table driving unit 11, the vibrator driving unit 12, the suction driving unit 13, and the head lifting / lowering driving unit 14 are controlled by the control unit 15. In addition to an operation program for component bonding operation described later, the storage unit 16 stores data related to a vibration application pattern when the vibrator 10 is driven to apply vibration to the semiconductor chip 4. The input unit 17 is an input unit such as a keyboard or a mouse, and inputs data such as operation commands and vibration application patterns. The display unit 18 is a display panel, and displays an operation screen and a data input screen.

  FIG. 2 shows a component bonding operation by the ultrasonic bonding apparatus. In the component bonding operation, first, the semiconductor chip 4 is held by the bonding portion 9 of the bonding tool 7 and the bumps 4a are aligned with the circuit electrodes 3a of the substrate 3 as shown in FIG. Next, the bonding tool 7 is lowered to bring the bump 4a into contact with the circuit electrode 3a as shown in FIG. 2B (contact process). Next, the vibrator 10 is driven to apply vibration to the semiconductor chip 4 via the bonding action portion 9 as shown in FIG. 2C, and the bump 4a is metal-bonded to the circuit electrode 3a by load and vibration. (Joining process).

Next, with reference to FIG. 3, the vibration application pattern by the vibrator | oscillator 10 in the above-mentioned joining process is demonstrated. FIG. 3 shows the time variation of the voltage value V of the drive current output to the vibrator 10 by the vibrator driving unit 12 in order to oscillate the vibrator 10 in the joining process. Here, the voltage value V is an index indicating the amplitude of the ultrasonic vibration, that is, the strength of the vibration.

  As shown in FIG. 3, in the joining process of the component joining method shown in the present embodiment, a vibration having a constant strength is applied only for a predetermined time instead of continuously applying a vibration having a uniform strength. The unit vibration applying step to be applied is repeated a plurality of times. That is, the first vibration application step US1 for applying the vibration by the first voltage value V1 only during the first application time T1 between the vibration application start timing t1 and the vibration application end timing tn, and the second voltage value. The second vibration application process US2 in which the vibration by V2 is applied only for the second application time T2 is alternately repeated.

  When applying the vibration, first, at timing t1, the vibrator 10 is driven by the first voltage value V1 defined by the bonding condition, thereby causing the horn 8 to vibrate with a strength corresponding to the first voltage value V1 (first voltage value V1). (Vibration) is applied. Then, at the timing t2 when the first application time T1 has elapsed, the voltage value V is switched to the second voltage value V2 that is smaller than the first voltage value V1, and the vibration with the intensity corresponding to the second voltage value V2 (second Vibration). The significance of the second voltage value V2 will be described later. Then, at the timing t3 when the second application time T2 has elapsed, the voltage value V is switched to the first voltage value V1 again to apply the first vibration, and thereafter the vibration application pattern by the same pulse-shaped voltage value switching is repeatedly executed. To do.

  That is, in the bonding process based on the vibration application pattern shown in FIG. 3, vibration is applied to the semiconductor chip 4 by repeating a plurality of unit vibration application processes. Of the plurality of unit vibration application processes that are repeated, two unit vibration application processes that are directly related to each other in time are applied with vibrations having different strengths. In the example shown in FIG. 3, a vibration application mode is performed in which the first vibration application process and the second vibration application process in which the first vibration and the second vibration having different strengths are applied alternately are repeatedly executed. ing.

  The significance of adopting such a vibration application mode in component joining by vibration and load will be described. FIG. 8 shows the vibration transmission behavior from the bonding tool to the semiconductor chip when the semiconductor chip is bonded by the conventional vibration application mode using the same ultrasonic bonding apparatus as in FIG. FIGS. 8A and 8B are graphs showing temporal changes in the pressing load P and the ultrasonic output W in the component joining process. FIG. 8C is a diagram showing the joining tool 7 in the component joining process. The time change of the amplitude of the vibration transmitted to the semiconductor chip 4 is shown in a graph.

  When the component joining operation is started, as shown in FIG. 8A, the pressing load P increases from the timing t0 when the joining tool 7 contacts the semiconductor chip 4, and reaches the specified pressing load P0 at the timing t1. . Then, at this timing t1, as shown in FIG. 7B, driving of the vibrator 10 is started and application of vibration is started. At this time, conventionally, the vibrator 10 is continuously driven at a uniform voltage value V0 corresponding to a prescribed ultrasonic output from a vibration application start timing t1 to a vibration application end timing tn. .

  By driving the vibrator 10 in this way, ultrasonic vibration is transmitted to the bonding tool 7 via the horn 8, and vibration is further transmitted from the bonding action portion 9 to the semiconductor chip 4 via the contact surface 9a. Communicated. FIG. 8C shows the fluctuations of the amplitudes of the bonding action portion 9 and the semiconductor chip 4 at this time by graph lines a and b. As can be seen from these graph lines, the amplitude A at the contact surface 9a of the bonding portion 9 increases with time from the timing t1 when vibration application starts, and after a certain time has elapsed, the amplitude A0 corresponding to the voltage value V0. Converge to.

On the other hand, the amplitude A of vibration transmitted to the semiconductor chip 4 increases substantially following the amplitude of the bonding operation portion 9 for a very short time after the start of vibration application, but has a certain initial time T (several tens of milliseconds). After reaching the extreme value A1 when the degree of...) Has elapsed, it decreases without following the amplitude of the welding tool, and tends to converge to an amplitude Am that is significantly smaller than the amplitude A0 of the bonding action portion 9.

  That is, the vibration generated by the vibrator 10 is transmitted to the bonding action portion 9 according to the vibration transmission characteristics of the horn 8, but the vibration is not transmitted as it is to the semiconductor chip 4 to be bonded. After the time T has elapsed, it can be seen that slip occurs between the bonding operation portion 9 and the semiconductor chip 4. In other words, in the component bonding process in which the bonding action portion 9 is brought into contact with the semiconductor chip 4 and pressed against the substrate, vibration transmission when the vibration transmitted to the bonding action portion 9 is further transmitted to the semiconductor chip 4 is performed. It can be said that it is efficient only within the range of the initial time T from the start of applying the vibration.

  After the initial time T has elapsed, the vibration transmission efficiency to the semiconductor chip 4 is low, and a substantial portion of the vibration energy transmitted to the bonding action portion 9 is wasted due to slippage between the bonding action portion 9 and the semiconductor chip 4. Such time fluctuation of vibration transmission has not been clarified in the past, and was obtained as new knowledge in various trial experiments conducted by the present inventors for the purpose of improving quality and efficiency in ultrasonic bonding. It is. It has been confirmed that the phenomenon shown in FIG. 8C occurs in a wide load range and an ultrasonic output range.

  Due to such low vibration transmission efficiency, excessively strong ultrasonic vibrations have exceeded the vibration strength originally required to obtain an appropriate bonded state in the semiconductor chip to be bonded. There is a case in which a continuous application time is likely to occur for an extra time, which may cause damage to the semiconductor chip and may require an extra joining operation time. In addition, since vibration is applied while there is slippage between the bonding tool and the semiconductor chip, the contact surface between the bonding tool and the semiconductor chip is likely to wear, and the life of the bonding tool is shortened and consumed. In addition to an increase in product cost, there are cases in which problems such as variations in bonding quality due to changes in the wear state of the bonding tool over time have occurred.

  The vibration application pattern shown in FIG. 3 is set in order to realize the efficiency of vibration transmission from the bonding operation portion 9 to the semiconductor chip 4 based on the above knowledge. That is, in FIG. 3, the first voltage value V1 is first determined from the bonding conditions of the target semiconductor chip, and the first vibration application step US1 of the first vibration application step US1 for applying the vibration (first vibration) by the first voltage value V1 is applied. The application time T1 is set to a time corresponding to the initial time T shown in FIG.

  Then, the second voltage value V2 is set to a low output value that falls within an amplitude range where no slippage occurs between the bonding operation portion 9 and the semiconductor chip 4, and vibration (second vibration) due to the second voltage value V2 is set. The second application time T2 of the second vibration application step US2 to be applied is set to a predetermined time. In the present embodiment, an example is shown in which the second application time T2 is set to approximately the same time as the first application time T1, but the junction time is shortened by setting the time as short as possible (for example, about 5 msec.). Desirable for. By adopting such a vibration application pattern, the vibration transmission state within the initial time T as shown in FIG. 8C is repeated, and slipping occurs between the bonding action portion 9 and the semiconductor chip 4. It is possible to minimize vibration transmission loss due to the occurrence of.

By improving the vibration transmission efficiency in this way, a situation in which ultrasonic vibration having an excessive strength exceeding an originally required vibration strength is continuously applied for an extra time does not occur. Therefore, it is possible to prevent the semiconductor chip 4 from being damaged due to excessive vibration, and to reduce the work time by eliminating the extra joining work time. Moreover, since the relative slip between the joining action part 9 and the semiconductor chip 4 is suppressed, the wear of the contact surface 9a of the joining action part 9 can be reduced, and the life of the joining tool 7 can be extended. Bonding action part 9
It is possible to prevent problems such as variations in bonding quality caused by changes in the wear state over time.

  In the above embodiment, the example in which the strength of the first vibration in the first vibration applying step US1 is always constant has been shown. However, as shown in FIG. 4, the strength of the first vibration is changed. A vibration application pattern may be employed. That is, in the example shown in FIG. 4A, the voltage value that gives the first vibration is set at the vibration application start timing t1 in the state where the second voltage value V2 of the first vibration application step US2 electronic component is constant. The first voltage value V1 is set so as to gradually decrease from the first voltage value V1 to the third voltage value V3 at the timing tn when the vibration application ends. That is, in this example, the first vibration is weakened in stages from the start to the end of the joining process.

  In the example shown in FIG. 4B, the voltage value for applying the first vibration is stepwise from the fourth voltage value V4 at the vibration application start timing t1 to the fifth voltage value V5 at the vibration application end timing tn. Set to be strong. That is, in this example, the first vibration is increased stepwise from the start to the end of the joining process. Furthermore, in the example shown in FIG. 4C, the vibration application pattern is a combination of the above two examples, and the voltage value giving the first vibration is changed from the sixth voltage value V6 at the vibration application start timing t1 to the seventh voltage value. After increasing to the voltage value V7, it is set so as to gradually decrease to the eighth voltage value V8 at the timing tn when the vibration application ends. That is, in this example, the first vibration is set so as to increase stepwise from the start to the middle of the joining process and to weaken stepwise from the middle to the end of the joining process.

  FIG. 5 shows an example in which the strength of the second vibration in the second vibration application step US2 is set to substantially zero in the vibration application pattern shown in FIG. That is, the output state of the vibrator drive unit 12 in the second vibration application process US2 is set to the OFF state by setting the second voltage value V2 to zero, and the vibrator 10 is operated only in the first vibration application process US1. In an intermittent drive state. In the example shown in FIG. 6, the strength of the second vibration in the second vibration applying step US2 is substantially reduced to zero in the three examples shown in FIGS. An example of setting is shown.

  As described above, in the vibration application pattern according to the present invention, vibration is applied to the semiconductor chip 4 by repeating a plurality of unit vibration application steps in the bonding step, and the temporal advance directly among the plurality of unit vibration application steps. In the two unit vibration application steps in the subsequent relationship, vibrations having different strengths are applied. Accordingly, it is possible to improve the vibration transmission efficiency by suppressing the relative slip between the bonding action portion 9 and the semiconductor chip 4 caused by continuously applying the vibration with the same strength.

  In the vibration application patterns shown in FIGS. 3 to 6, when the first vibration application process US1 and the second vibration application process US2 are alternately repeated, the vibrations from the first vibration application process US1 having a strong vibration strength are generated. Although the example of starting the application has been shown, the application of vibration may be started from the second vibration application process US2 in which the intensity of vibration is weak.

  In the vibration application patterns shown in FIGS. 3 to 6, an example in which the intensity of the first vibration and the second vibration is set to a constant value or a regularly varying value that regularly changes is shown in FIG. 7. As shown, in a plurality of unit vibration application processes, voltage values may be set randomly for each unit vibration application process so that vibrations of the same strength are not continuously applied. Also in this example, in the two unit vibration application steps that are in direct preceding / following relationship in time, the pattern is such that vibrations of different strengths are applied, and vibration application is continuously performed with the same strength. The similar effect is obtained by suppressing the relative slip between the bonding operation part 9 and the semiconductor chip 4 due to the above.

  The component joining method of the present invention reduces the relative slip between the contact surface of the joining tool and the part as much as possible, ensures joining quality, shortens the time required for joining, and realizes a longer life of the joining tool. It is useful in the field of component mounting in which electronic components are mounted by load and vibration, such as flip chip.

The block diagram which shows the structure of the ultrasonic bonding apparatus of one embodiment of this invention Operation | movement explanatory drawing of the ultrasonic bonding apparatus of one embodiment of this invention Explanatory drawing of the ultrasonic vibration application pattern in the ultrasonic bonding apparatus of one embodiment of this invention Explanatory drawing of the ultrasonic vibration application pattern in the ultrasonic bonding apparatus of one embodiment of this invention Explanatory drawing of the ultrasonic vibration application pattern in the ultrasonic bonding apparatus of one embodiment of this invention Explanatory drawing of the ultrasonic vibration application pattern in the ultrasonic bonding apparatus of one embodiment of this invention Explanatory drawing of the ultrasonic vibration application pattern in the ultrasonic bonding apparatus of one embodiment of this invention Illustration of ultrasonic vibration application pattern in conventional ultrasonic bonding equipment

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 Substrate 3a Circuit electrode 4 Semiconductor chip 4a Bump 7 Joining tool 9 Joining action part 10 Vibrator US1 1st vibration application process US2 2nd vibration application process

Claims (5)

A component joining method for joining a component electrode provided on a component to a substrate electrode provided on a substrate by vibration,
The includes a contact step of bringing the component electrode in contact with the substrate electrode, and a bonding step of bonding the component electrode by applying vibration by component bonding tool to said component on the substrate electrode,
In the joining step, a first vibration applying step for applying a first vibration determined from bonding conditions of a target component, and a second vibration for applying a second vibration whose vibration intensity is weaker than the first vibration. Two vibration application steps are alternately and repeatedly executed, and the voltage value of the drive current output to the vibrator in the second vibration application step is set to an output value that does not cause a slip between the component joining tool and the component. A method for joining parts, characterized by comprising:   The component joining method according to claim 1, wherein in the joining step, the first vibration is increased stepwise from the start to the end of the joining step.   The component joining method according to claim 1, wherein in the joining step, the first vibration is weakened in a stepwise manner from the start to the end of the joining step.   The said joining process WHEREIN: The said 1st vibration is strengthened in steps until it reaches the middle from the start of a joining process, It weakens in steps until it reaches the completion | finish of a joining process from the middle. Parts joining method.   The component joining method according to claim 1, wherein the second vibration has substantially zero intensity.

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