JP3385942B2 - Inspection method for wire bonding - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wire bonding in which a pad of a chip mounted on a substrate and an electrode of the substrate are connected by a wire, and the wire is bonded to the pad or the electrode. The present invention relates to a method for inspecting wire bonding for inspecting whether or not the above has been performed. In wire bonding, a ball at the lower end of a wire inserted through a capillary tool is bonded to a pad of a chip mounted on a substrate such as a lead frame or a printed circuit board, and then the wire is bonded to an electrode of the substrate. It is supposed to be bonded to. The former is called 1st (first) bonding, and the latter is called 2nd (second) bonding. Wire bonding is not always successful, and non-bonding may occur due to external factors such as device defects, substrate contamination and dust adhesion. So conventionally,
Perform 1st bonding while passing current through the wire,
Whether the wire is attached or not is determined by determining the magnitude of the voltage at that time. However, in the prior art,
During wire bonding, a current was constantly applied to the wire, and as a result of the 1st bonding, the tip of the ball was easily damaged when the ball at the lower end of the wire was connected to the pad of the chip. It was. For 2nd bonding, wire attachment /
There was a situation where non-delivery inspection was not conducted. Accordingly, it is an object of the present invention to provide a wire bonding inspection method capable of determining whether a wire is attached or not without damaging a chip. [0006] [0007] [0008] wire bonding of SUMMARY OF THE INVENTION The present invention
In the inspection method, the ball at the lower end of the wire inserted into the capillary tool is first bonded to the pad of the chip mounted on the substrate, and then the capillary tool is moved above the electrode on the substrate to connect the wire to this electrode. In wire bonding in which the wire is cut from the bonding point to this electrode by performing 2nd bonding, then closing the clamper, clamping the wire, and pulling the wire up, after the 2nd bonding, the clamper is open In addition, a current is passed through the wire twice before and after the clamper is closed, and whether the wire is attached or not is determined from the magnitude of each voltage. According to inventions having the above configuration, after the wire is in contact with the pad and the substrate electrode of the chip, the voltage was measured by applying a spot electric current to the wire, the magnitude of the voltage, wire wear of・ Non-delivery can be accurately determined. DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of a wire bonding apparatus according to an embodiment of the present invention. FIG. 2 is an electric circuit diagram for inspection of wire attachment / non-attachment of the wire bonding apparatus.
3, 4, 5, 6, 7, and 8 are explanatory diagrams of the wire bonding inspection method. First, the structure of the wire bonding apparatus will be described with reference to FIG. In FIG. 1, a chip 2 is mounted on a substrate 1. An electrode 3 is formed on the upper surface of the substrate 1, and a pad 4 (described later) is formed on the upper surface of the chip 2. The substrate 1 is placed on the table 5. A mask plate 6 that exposes only the wire bonding area is mounted on the substrate 1 on which wire bonding is performed. The mask plate 6 has a cylinder 7
When the rod 8 projects and sinks, it moves up and down. A horn 10 extends above the substrate 1. A capillary tool 11 is held at the tip of the horn 10, and a wire 12 is inserted through the capillary tool 11. The wire 12 is wound around the spool 13 and is led out from the spool 13. The base end portion of the horn 10 is supported by the drive unit 14, and when the drive unit 14 is driven, the horn 1
0 swings up and down, and ultrasonic energy (US) energy is applied to the capillary tool 11. The drive unit 14 is provided inside the cover case 15. An arm 16 extends from the cover case 15, and a torch 17 is held at the tip of the arm 16. An arm 18 extends from the drive unit 14, and a clamper 19 that clamps the wire 12 is attached to the tip of the arm 18. The drive unit 14 and the cover case 15 are installed on the movable table 20. 21 is an X-axis motor, 22
Is a Y-axis motor. When the movable table 20 is driven,
The capillary tool 11 moves horizontally in the X and Y directions,
Stop at a predetermined bonding position. Therefore, the capillary tool 11 moves up and down to perform 1st bonding and 2nd bonding. Next, an electric circuit will be described with reference to FIG. The wire 12 inserted into the capillary tool 11 is
The first power supply 31 and the second power supply 32 are connected via the analog switch 30. An intermediate point between the first power supply 31 and the second power supply 32 is grounded to the ground portion 33. Therefore, by switching the analog switch 30, the wire 1
2 can pass a positive current Ia and a reverse current Ib. The switching between the positive current Ia and the reverse current Ib is useful when the chip 2 has a voltage-current characteristic that differs depending on the current flow direction, such as a diode. The wire 12 is connected to the first of the comparator 34.
It is connected to the input terminal 35. The comparator 34
The second input terminal 36 receives the threshold voltage VTH. The output terminal of the comparator 34 is connected to the determination circuit 3
7 is connected. As will be described later, the voltage VDC of the wire 12 is compared with the threshold voltage VTH, and the wire 12
Judge whether or not you are This wire bonding apparatus is constructed as described above. Next, a wire bonding inspection method will be described with reference to FIGS. There are various patterns of wire bonding. Therefore, each pattern is shown in FIG. 3 to FIG.
The inspection method will be described with reference to these in order. 3 to 8, (a) is the trajectory of the capillary tool, (b)
Is a timing chart for applying ultrasonic energy to a capillary tool and bonding the wire to a pad or an electrode, (c) is a timing chart of a detection time for applying a positive current to the wire, and (d) is a detection time for applying a reverse current to the wire. (E) shows the opening / closing timing chart of the clamper, and (f) shows the detection voltage VDC. Lead is an electrode of the substrate 1, and Pad is a pad of the chip 2. First, referring to FIG. 3, the case where the pad is completely attached will be described. In FIG. 3A, Q indicates the locus of the capillary tool 11. The wire bonding operation will be described with reference to the locus Q. By bringing the torch 17 close to the lower end portion of the wire 12 led out from the lower end portion of the capillary tool 11 and applying a voltage to the torch 17, a ball 12a is formed at the lower end portion of the wire 12 by electric spark. Next, the capillary tool 11
Is lowered and the ball 12a is pressed against the pad 4 of the chip 2 for 1st bonding (t in FIG. 3B).
1). Next, the capillary tool 11 moves upward above the electrode 3 of the substrate 1 while moving up, then descends and presses the wire 12 against the electrode 3 to perform 2nd bonding (t2 in FIG. 3B). When performing 1st bonding and 2nd bonding, the capillary tool 11 includes:
Ultrasonic (US) energy is applied (t1 and t2 in FIG. 3B). During the above operation, the clamper 19 is open, but after the end of the 2nd bonding, when the capillary tool 11 is raised by a predetermined amount, the clamper 19 is closed (t3 in FIG. 3E), and the wire 12 is clamped. Furthermore, the capillary tool 11 is raised and the clamper 19
Pulls up the wire 12 so that the wire 12 becomes 2
Cutting at the nd bonding point. t4 is a cutting start timing. Thereafter, the capillary tool 11 is raised and returned to the original position, and one cycle of wire bonding is completed. By repeating the above operation, the substrate 1
Electrode (Lead) 3 and chip 2 pad (Pad) 4
Are connected one after another by wires 12. Now, during the transition from 1st bonding to 2nd bonding, positive current Ia (FIG. 2) is applied to wire 1.
2 is spot-flowed (timing t11 at detection time 1 in FIG. 3C), and the reverse current Ib is spot-flowed through the wire 12 (timing t12 at detection time 2 in FIG. 3D). V11 and V12 in FIG. 3 (f) are the voltages of the wire 12 at this time. This chip 2 is a diode, and in the case of the positive current Ia, the voltage is small (V1
1) In the case of the reverse current Ib, the voltage is large (V12). Therefore, the threshold voltage VTH is set and V11 <
If VTH, the positive current Ia is flowing normally, and if V12> VTH, the reverse current Ib is flowing normally, so that the wire 12 is correctly 1st bonded (completely attached) to the pad 4. It turns out. Next, the case where the pad is not attached will be described with reference to FIG. In FIG. 4A, 1st for the pad 4
Bonding fails and the ball 12a remains attached to the lower end of the wire 12 after the first bonding.
4B to 4E are the same as FIGS. 3B to 3E. In FIG. 4 (f), since the ball 12a is away from the pad 4, the circuit is open, and therefore the wire 1
2 even if a positive current Ia and a reverse current Ib are passed through, V11 = V12
V11> VTH, V12> VTH, and
Therefore, it turns out that it is non-delivery. Next, a method for detecting non-sticking on the electrode side of the substrate 1 will be described. The feature of this method is a clamper 1 for cutting.
9, detection times t21 and t22 for checking non-delivery are provided before and after the operation 9, and the comparator 3 corresponds to this.
4 VTH is switched to VTH1 and VTH2. Then, when VDC exceeds VTH, it is turned ON, and when it does not exceed VTH, it is turned OFF.
From the combination of N and OFF, as shown in (Table 1), complete / non-attachment is determined. [Table 1] Next, the case where both the pad 4 and the electrode 3 are completely attached will be described with reference to FIG. The 1st bonding is the same as in the case of FIG. As for electrode non-stick detection, detection times t21, t so that non-stick can be detected before and after the clamper operation.
t22 is provided, and the threshold voltage VTH is set to V corresponding to this.
It is switched to TH1 and VTH2. After the 2nd bonding, the clamper 19 is closed at time t3 to clamp the wire 12, and the wire 12 is cut from the 2nd bonding point by pulling up the wire 12 (timing t4). At timing t21 immediately after the 2nd bonding, a current is allowed to flow through the wire 12 in a spot manner. At this time, since the wire 12 is electrically connected to the electrode 3, V21 = 0 and V21 <VTH1. In addition, at a timing t22 immediately after cutting, a current is passed through the wire 12 in a spot manner. At this time, since the wire 12 has already been cut at the 2nd bonding point and the circuit is open, V22> VTH2. From the above, t21 is OF
Since F and t22 are ON, it is found that the 2nd bonding is completed. The direction of current at timing t21 and timing t22 is the same direction. Next, the case where the electrode 3 is not attached will be described. 6 to 8 show three patterns when the electrode 3 is not attached. First, the first pattern will be described with reference to FIG. It is assumed that the first bonding is complete. In FIG. 6A, the capillary tool 11 fails in the 2nd bonding, and the wire 12 is separated from the electrode 3. In this case, the wire 12 is connected to the chip 2 via the 1st bonding point, so that 2
After the nd bonding, if a positive current is applied in spots at timings t21 and t22, the current flows through the first bonding point of the chip 2 in any case, and V2
1, V22 is detected. In this case, V21 = V22 and V21> VTH1, V22 <VTH2. Therefore, t21 is ON and t22 is OFF.
It turns out that the nd bonding point is not attached. Next, the second pattern will be described with reference to FIG. In FIG. 7A, when the wire 12 is once attached to the electrode 3 at the time of 2nd bonding, the capillary tool 11 is raised, and when the wire 12 is pulled up by the clamper 19 and the wire 12 is cut at timing t4, The wire 12 is peeled off from the 2nd bonding point. In this case, since the wire 12 is in contact with the electrode 3 at the ting t21, V21> VTH1,
At timing t22, since the wire 12 is away from the 2nd bonding point, no current flows through the wire 12, and V
22> VTH2. From the above, it is found that the 2nd bonding is not attached. Next, the third pattern will be described with reference to FIG. In FIG. 8A, after 2nd bonding,
When the clamper 19 clamps and pulls up the wire 12, the wire 12 is peeled off from the electrode 3. In this case, V21 = 0 at timing t21, and V21 <
VTH1 is reached, and at timing t22, the current is 1 s.
Since it flows through the t-bonding point, the voltage V22 is detected, V22 = V11, and V22 <VTH2. From the above, it is found that the 2nd bonding is not attached. In this embodiment, the diode is described as an example of the chip, but this inspection method can be applied to a chip other than the diode. According to the present invention, after the wire comes into contact with the chip pad or the electrode on the substrate, the current is spotted to the wire to measure the voltage, so that the chip is damaged. It is possible to accurately determine whether or not a wire is attached or not without giving a wire.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a wire bonding apparatus according to an embodiment of the present invention. FIG. 2 is an electric for inspecting wire attachment / non-bonding of the wire bonding apparatus according to an embodiment of the present invention. FIG. 3 is an explanatory diagram of a wire bonding inspection method according to an embodiment of the present invention. FIG. 4 is an explanatory diagram of a wire bonding inspection method according to an embodiment of the present invention. FIG. 6 is an explanatory diagram of a wire bonding inspection method according to an embodiment. FIG. 6 is an explanatory diagram of a wire bonding inspection method according to an embodiment of the invention. FIG. 8 is an explanatory diagram of a wire bonding inspection method according to an embodiment of the present invention. [Explanation of Symbols] 1 Substrate 2 Chip 3 Electrode 4 Pad 10 Horn 11 Capillary tool 12 Wire 19 Clamper

Continued from front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/60

Claims (1)

(57) [Claims] [Claim 1] A ball at the lower end of a wire inserted through a capillary tool is applied to a pad of a chip mounted on a substrate for 1 s.
After t-bonding, move the capillary tool above the substrate electrode to bond the wire to this electrode 2nd, then close the clamper to clamp the wire,
In wire bonding in which the wire is cut from the bonding point to the electrode by pulling up the wire, after the 2nd bonding, when the clamper is opened and when the clamper is closed, the wire is spotted twice. A method for inspecting wire bonding, characterized in that a current is passed through the wire and whether or not a wire is attached or not is determined from the magnitude of each voltage.