JP3565019B2 - Bonding method for electronic components with bumps - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for bonding electronic components with bumps, which bonds the electronic component with bumps to a surface to be compressed such as a substrate.
[0002]
[Prior art]
2. Description of the Related Art A method using ultrasonic pressure welding is known as a method of bonding an electronic component with a bump to a surface to be compressed such as a substrate. In this method, ultrasonic vibration is applied while pressing the bumps of the electronic component against the substrate, and the bonding surfaces are rubbed against each other for bonding. In order to ensure good bondability in this bonding process, it is necessary to press the bump against the electrode of the substrate with an appropriate pressure load value. For this reason, in the conventional method of bonding electronic components with bumps, the bonding head is brought into contact with the electronic component with bumps to start pressing, and after the pressing load reaches a predetermined value, this load value is held for a predetermined time. Has been used to control the bonding of the bumps to the electrodes.
[0003]
[Problems to be solved by the invention]
By the way, factors that cause poor bonding quality after bonding include displacement of electronic components and variations in bump height. When bonding is performed in such a state, the electronic component cannot be pressed in a correct posture, that is, in a state where the bumps are uniformly contacted with the electrodes, and the bumps are partially crushed and crushed, or the bump height is insufficient. This causes various bonding defects, such as generation of bumps that are not sufficiently bonded to the electrodes.
[0004]
However, in the conventional method of bonding electronic components with bumps, although the pressing load is controlled as described above, it is not possible to know whether the bonding process is proceeding normally. For this reason, the product after bonding may be sent to the next step with problems such as insufficient pressing and crushing of bumps, and there has been a problem that reliability after bonding cannot be ensured.
[0005]
Therefore, an object of the present invention is to provide a bonding method of an electronic component with bumps having excellent reliability after bonding.
[0006]
[Means for Solving the Problems]
2. The method for bonding electronic components with bumps according to claim 1, wherein the bonding head presses the bumps of the electronic components with bumps against the electrodes on the surface to be compressed and applies ultrasonic vibration to bond the electronic components with bumps. In the bonding method, in the bonding step, a bonding head descends from a timing at which the bonding head starts pressing the bumped electronic component against the surface to be pressed to a timing at which the pressing is completed , which is indicated by a descending amount of the bonding head. A second index value represented by a first index value, a load reduction value until the pressing load value for pressing the electronic component with bumps by the bonding head reaches a maximum value and decreases to a minimum value, and maximum current value of the drive power of the vibrator for applying sonic vibration, from said vibration application start Monitoring a third index value indicated by any of the time required to reach the large current, the integrated value of the current in the bonding process, or a combination thereof; and the first index value, the second index value, and the third index value. A step of calculating respective deviations between the reference value set for each of the three index values and the first index value, the second index value, and the third index value; and setting these deviations in advance for each index value. Comparing with the allowable value, and outputting a failure judgment for the index value if the deviation exceeds the allowable value.
[0007]
According to the present invention, in the bonding process, three types of index values are set based on the amount of descent of the bonding head, the reduced value of the pressing load, and the driving power of the ultrasonic vibration, respectively, and these index values and a preset reference value are set. By monitoring the deviation from the value and determining the failure if the deviation exceeds the allowable value, reliability after bonding can be ensured.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a front view of a bonding apparatus for an electronic component with bumps according to an embodiment of the present invention, FIG. 2 is a flowchart of a bonding method for the electronic component with bumps, and FIG. FIG. 3B is a graph showing the pressing load in the bonding process, and FIG. 3C is a graph showing the output power of the ultrasonic transducer driving power in the bonding process.
[0009]
First, the overall structure of a bonding device for electronic components with bumps will be described with reference to FIG. Reference numeral 1 denotes a support frame, on the front surface of which is provided a first elevating plate 2 and a second elevating plate 3 so as to be able to move up and down. A cylinder 4 is mounted on the first lifting plate 2, and its rod 5 is connected to the second lifting plate 3. The bonding head 10 is mounted on the second lifting plate 3. On the upper surface of the support frame 1, a Z-axis motor 6 is provided. The Z-axis motor 6 rotates a vertical feed screw 7. The feed screw 7 is screwed into a nut 8 provided on the back of the first lifting plate 2. Accordingly, when the Z-axis motor 6 is driven to rotate the feed screw 7, the nut 8 moves up and down along the feed screw 7, and the first lifting plate 2 and the second lifting plate 3 also move up and down.
[0010]
In FIG. 1, a substrate 32 that is a surface to be pressed is placed on a substrate holder 33, and a substrate holder 34 is placed on a table 35. The table 34 is a movable table, and horizontally moves the substrate 32 in the X direction and the Y direction to position the substrate 32 at a predetermined position. The main control unit 35 controls the Z-axis motor 6 via the motor drive unit 36 and controls the table 34 via the table control unit 37. The cylinder 4 is connected to a main control unit 35 via a load control unit 38, and the projection load of the rod 5 of the cylinder 4, that is, the pressing load for pressing the electronic component 30 with bumps against the substrate 32 by the bonding tool 20 is controlled. You.
[0011]
A holder 12 is connected to a lower end of the main body 11 of the bonding head 10 via a load cell 13. A block 14 is mounted on the holder 12, and a bonding tool 20 is fixed to the block 14. The bonding tool 20 includes an ultrasonic vibrator 21 that generates ultrasonic vibration, and the ultrasonic vibrator 21 is driven by an ultrasonic vibrator driving unit 39. The bonding tool 20 sucks and holds the electronic component 30 on a holding portion provided on the lower surface at the center. The electronic component 30 is bonded to the substrate 32 by lowering the bonding head 10 while holding the electronic component 30 and driving the ultrasonic transducer 21 while pressing the electronic component 30 against the substrate 32.
[0012]
In the bonding process, the following three types of measured values are set as monitoring targets. First, the pressing load at the time of bonding is detected by the load cell 13, read as load data by the load reading unit 42, and transmitted to the main control unit 35. The height position of the bonding head 10 is measured by a linear scale unit 40 provided on the second lifting plate 3, read as height data by a height reading unit 41, and transmitted to the main control unit 35. . At this time, the reference surface serving as a reference for the height measurement is the upper surface of the substrate 32, and a fixed reference surface may be set in advance by assuming a standard reference surface. To eliminate this, the reference surface may be corrected by measuring the height position of the upper surface of the substrate 32 each time the bonding operation is performed.
[0013]
The drive current of the ultrasonic transducer 21 in the bonding process is measured by the current measuring unit 43, and the measurement result is transmitted to the main control unit 35. A display unit 44 is connected to the main control unit 35, and the measured values, that is, the height of the bonding head 10, the pressing load, and the ultrasonic transducer drive output are graphically displayed on a monitor screen of the display unit 44. .
[0014]
This bonding apparatus is configured as described above. Next, the operation will be described with reference to the graph of FIG. 3 along the flow of FIG. The electronic component 30 is vacuum-sucked and held on the suction surface of the bonding tool 20, and the flow of FIG. 2 starts from a state where the electronic component 30 is positioned above the substrate 32. First, at timing t0, the bonding head 10 holding the electronic component 30 is lowered (ST1). Thereafter, at timing t1 when the bonding head 10 is lowered and the bumps of the electronic component 30 contact the upper surfaces of the electrodes of the substrate 32, the cylinder 4 is driven to lower the bonding head 10 further, and the bumps of the electronic component 30 are removed from the substrate 32. (ST2), and the height reading unit 41 monitors the height and the load reading unit 42 monitors the pressing load (ST3). When the pressing load reaches the set value at the timing t2, the driving of the ultrasonic transducer 21 is started (ST4), and from this time, the monitoring of the driving current of the ultrasonic transducer by the current measuring unit 43 is started. (ST5). When the predetermined pressing time has elapsed at the timing t3, the driving of the ultrasonic transducer 21 is stopped (ST6).
[0015]
In the above bonding process, the following three types of index values are monitored to determine whether the progress of the bonding is good or bad. First, as shown in FIG. 3A, the descending amount h of the bonding head 10 from the timing when the bonding head 10 starts pressing the electronic component 30 to the substrate 32 until a predetermined bonding time elapses is the first. Monitored as an index value. By monitoring the descending amount h, it is determined whether or not the gap between the electronic component 30 and the substrate 32 is within an appropriate range at the end of pressing, that is, a poor bonding between the bump and the electrode surface due to insufficient pressing, and a bump due to excessive pressing. It can be estimated whether or not a defect such as collapse has occurred.
[0016]
Next, as shown in FIG. 3B, the pressing load value for pressing the electronic component 30 by the bonding head 10 decreases after reaching the maximum value and reaches the minimum value, and the load reduction value f is the fourth value. Monitored as two index values. By monitoring the load reduction amount f, it is possible to detect a state in which the bonding tool 20 does not normally press the electronic component due to a displacement of the electronic component 30 or an abnormality such as a piece contact due to a variation in bump dimensions. .
[0017]
Further, as shown in FIG. 3C, the maximum current value imax of the driving power supply of the vibrator for applying the ultrasonic vibration, the arrival time Timax required from the start of the vibration application to the maximum current value imax, the bonding process The current integrated value ∫idt is monitored as a third index value. By monitoring these, it is possible to estimate the load state of the ultrasonic vibration applied at the time of bonding, and it is possible to detect a load abnormality caused by a bump contact or bump slippage. It should be noted that any of the maximum current value imax, the arrival time Timax, and the current integrated value 構成 idt that constitute these third index values may be used as the third index value.
[0018]
Each of the first index value, the second index value, and the third index value is set with a reference value as a typical numerical value expected in a normal bonding process. Then, deviations of these reference values and the first index value, the second index value, and the third index value are obtained (ST7), and these deviations are set in advance as a normal variation range for each index value. A comparison is made with an allowable value (ST8). If these deviations exceed the permissible value, a failure judgment for the index value is output (ST9).
[0019]
Thereafter, the bonding head 10 is raised (ST10), and the bonding of the electronic component 30 is completed. At this time, the electronic component 30 for which the failure determination is output is separated after bonding, further inspected, and then subjected to a detailed pass / fail determination. Is performed. As described above, in the bonding process, the index value composed of items closely related to the bonding quality is monitored, and if the index value exceeds the normal range, it is determined to be defective. It is possible to prevent the transmission after the bonding and to secure the reliability after bonding.
[0020]
【The invention's effect】
According to the present invention, in the bonding process, three types of index values are set based on the amount of descent of the bonding head, the reduced value of the pressing load, and the driving power of the ultrasonic vibration, respectively, and these index values and a preset reference value are set. Since the deviation from the value is monitored, and if the deviation exceeds an allowable value, a defect is determined, so that it is possible to sort out electronic components having defective bonding, and to ensure reliability after bonding.
[Brief description of the drawings]
FIG. 1 is a front view of a bonding apparatus for electronic components with bumps according to an embodiment of the present invention; FIG. 2 is a flowchart of a bonding method for electronic components with bumps according to an embodiment of the present invention; (B) Graph showing the height of the bonding head in the bonding process of one embodiment of the present invention (b) Graph showing the pressing load in the bonding process of one embodiment of the present invention (c) Graph of one embodiment of the present invention Graph showing ultrasonic oscillator drive power supply output during bonding process [Description of symbols]
12 Holder 13 Load cell 20 Bonding tool 21 Ultrasonic transducer 30 Electronic component 32 Substrate 35 Main control unit 38 Load control unit 39 Ultrasonic transducer drive unit 40 Linear scale unit 41 Height reading unit 42 Load reading unit 43 Current measuring unit

Claims (1)

A method of bonding electronic components with bumps, wherein a bonding head presses a bump of an electronic component with bumps against an electrode on a surface to be compressed and applies ultrasonic vibration to bond the electrode to the electrode. A first index value indicated by a descending amount of the bonding head from a timing at which the head starts pressing the bumped electronic component against the surface to be crimped to a timing at which the pressing is completed, and the bumped electronic component by the bonding head. A second index value represented by a load reduction value until the pressing load value for pressing the pressure reaches a maximum value and decreases to a minimum value, and a maximum current value of a driving power supply of a vibrator for applying the ultrasonic vibration. , over-arrival time or bonding from vibration application start until reaching the maximum current Monitoring a third index value indicated by any one of the integrated values of the currents or a combination thereof; and a reference value set for each of the first index value, the second index value, and the third index value. Determining a deviation of each of the first index value, the second index value, and the third index value; comparing these deviations with a predetermined allowable value for each index value; Outputting a failure judgment for the index value if the allowable value is exceeded.

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