JPH0236064B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a wire bonding method for connecting a plate and a lead on a lead frame with a wire, for example, in the assembly process of a semiconductor device.

[Technical background of the invention and its problems]

In the assembly process of semiconductor devices, a bonding apparatus shown in FIG. 1 is generally used as a means for connecting pellets and lead frames with wires. Reference numeral 1 in FIG. 1 is a bonding head main body, and a wire spool 2 is provided on the upper part of this main body 1. A wire guide 4 for guiding the wire 3 is provided on the wire feeding side of the main body 1. Further, a curved portion 8 for guiding the wire 3 downward is formed at the free end of the wire guide 4. An upper clamp 9 for clamping and releasing the introduced wire 3 is provided at the lower part of the curved portion 8 of the wire guide 4. The upper clamp 9 is supported by an arm 9a projecting from the side of the main body 1, and is opened and closed by a solenoid (not shown) to clamp and release the wire 3. Another role of the upper clamp 9 is to hold the ball at the tip of the bonding tool and provide back tension to the wire as it descends to the first connection point. The lower clamp 11 is provided at the tip of the swing bracket 12, and is opened and closed by a solenoid (not shown) to clamp and release the wire 3. A bonding arm 13 is provided below the swing bracket 12 and is substantially parallel to the swing bracket 12. A capillary 14 serving as a bonding tool through which the wire 3 is inserted is provided at the tip of the bonding arm 13. The bonding arm 13 is held by the swing bracket via a plate spring 13a and a tension spring 13b, and is configured to rotate vertically about a rotation shaft 15 that supports the base end of the swing bracket 12. It's getting old. That is, the lower clamp 11 and the capillary 14 are configured to move together in the vertical direction.
Note that a torch 16 or a spark electrode is provided below the capillary 14.
The tip of the wire 3 protruding downward from the wire 4 is heated to form a ball 17. However,
A pellet 18 and a lead frame 19 are arranged below the capillary 14, and the ball 17 is bonded to the first connection point _P1 of the pellet 18, and then the wire 3 is bonded to the second connection point _P2 of the lead frame 19. Bonding is then performed by connecting pellet 18 and lead frame 19.

This conventional bonding method will be explained in more detail with reference to FIG. A shows the state before the start of the bonding operation, and a ball 17 is formed at the tip of the wire 3. From this state, the capillary 14 descends and bonding is performed in state b. When the capillary 14 descends, the wire 3 is let out from the wire spool 2. Further, the upper clamp 9 is closed to clamp the wire 3 with a weak clamping force to provide back tension. b shows the state in which the pellet 18 is bonded to the electrode. At this point, the upper clamp 9 is opened. 3c shows a state in which the capillary 14 is raised and moved toward the lead frame 19 in the middle. At this time as well, the wire 3 is fed out by the horizontal movement of the capillary 14. d shows a state in which the capillary 14 has started descending again. At this time, the capillary 14 continues to move in the XY directions, so the wire 3 continues to be fed out.
e and f indicate the state in which the capillary 14 has finished moving in the XY directions and continues to descend. In this state, a phenomenon occurs in which the wire 3 moves inside the capillary 14 in the opposite direction, that is, from the bottom to the top. The smooth movement of this wire 3 from the bottom to the top is an important condition for forming a loop in the wire 3. f indicates a state in which the wire contacts the lead frame before the capillary 14 does. g is the second connection point P ₂ of the lead frame 19
This shows the bonded state. At h, the capillary 14 stops rising and the lower clamp 11 closes and the wire 3
Shows the state immediately before being torn off. i shows a state in which the tip of the torn wire 3 is heated to form a ball 17 and returned to the initial position, and wire bonding was performed in the above order.

By the way, Fig. 3 shows a good example a and typical bad examples b and c of the shape of the wire loop of the wire 3 after being connected to the first connection point _P1 . The wire 3 is in contact with the lead frame 19 and is determined to be defective. Also, b, c
Even if the wire 3 does not contact the lead frame 19, if the height H of the wire loop is low, it will short circuit when molded for resin sealing in the next process, resulting in a defective product, resulting in a decrease in product yield. . In this way, defects b and c occur as shown in Fig. 2 c and d.
For example, when the wire 3 is fed out in this state, the friction between the upper clamp 9 and the wire 3 becomes abnormally large.
As a result of the large tensile force acting horizontally on the connecting portion of the ball 17, the height of the wire loop L is reduced.

In addition, the defect c is caused by the fact that when the wire 3 that has been unwound in excess moves upward inside the capillary 14 from below in FIGS. This occurs when this is not done, resulting in slack in the wire. Product defects due to defects in the shape of these wire loops are caused by increased friction due to dust and oil adhesion in the wire path and the clamper, or increased friction due to clogging of the capillary 14, and are difficult to prevent. This not only reduces the product yield, but also reduces the operating rate of the device due to frequent replacement of the capillary 14.

[Purpose of the invention]

This invention was made by paying attention to the above circumstances, and its purpose is to connect the first connection point and the second connection point.
It is an object of the present invention to provide a wire bonding method in which the length of the wire connecting the connection point is kept constant, the shape of the wire loop can always be controlled to a normal (ideal) state, and reliability can be improved.

[Summary of the invention]

This invention involves bonding a wire to a first connection point on a pellet, and then raising a capillary as a bonding tool to connect the wire from the tip of the capillary to the lead frame whose length extends from the first connection point to the next bonding point. The wire is let out until it is equal to the normal length of the wire loop up to the second connection point, and then fixed with a lower clamp that moves up and down as one with the capillary to prevent the wire from being let out again.The wire is then let out from the tip of the capillary. After making the length constant, the capillary is moved to the second connection point and the wire is bonded to the lead frame.The shape of the wire loop above the first connection point is kept constant, and reliability is improved. , product yield can be improved.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 4 to 7, in which the same components as in FIG. 1 are given the same reference numerals. 20 in FIG. 4 is a bonding head frame. This bonding head frame 20 is installed on an XY table 21, and includes an X-axis motor 22 having an encoder 22a on the same axis and a Y-axis motor 2 having an encoder 23a on the same axis.
3 to move in the XY directions. In addition, the bonding head frame 2
0, a capillary arm 13 having a capillary 14 as a bonding tool at its tip is driven by a Z-axis motor 24 having an encoder 24a provided on the side wall of the bonding head frame 20, and rotates with the rotation axis 15 shown in FIG. Similarly, it is swingably supported on a rotating shaft. In addition, the X-axis motor 22 is connected to the CPU via an X-axis servo driver 25 and an X-axis servo controller 26.
It is connected to a capillary position calculation control device 27 as a control circuit composed of RAM, POM, and PIO. The Y-axis motor 23 includes a Y-axis servo driver 28 and a Y-axis servo controller 2.
9, the capillary position calculation control device 2
7 is connected. In addition, the Z-axis motor 24
is connected to the capillary position calculation and control device 27 via a Z-axis servo driver 30 and a Z-axis servo controller 31. Further, each of the encoders 22a, 23a, 24a is connected to a capillary position calculation control device 27 via each servo controller 26, 29, 31. The capillary position calculation control device 27 is connected to the bonder control device 32, and controls the movement of the capillary 14 in the X, Y, and Z directions, as well as the opening and closing of the clamp device. 33 is pellet 18
This is a lead frame equipped with...

Next, the operation of the wire bonding apparatus constructed as described above will be explained with reference to FIGS. 5 and 6. In FIG. 5, a and b are exactly the same as in the conventional example. That is, the upper clamp 9 is closed and the lower clamp 11 is open. The closed upper clamp 9 acts to provide back tension when the wire 3 is fed out. In Fig. 5c, l has coordinates (x ₁ ,
y ₁ , z ₁ ), the first and second connection points P ₁ of (x ₂ , y ₂ , z ₂ ),
The wire length required to bond P ₂ with a normal wire loop is shown. The length of this wire 3 is calculated by the capillary position calculation control device 27 and the bonder control device 32, and the capillary 14 is Raise it to point ₁ so that its lower end is at height l. The capillary 14 has a height l.
When it rises to point _Q1 , the lower clamp 11 is closed and the length of the wire 3 held at the lower end of the capillary 14 is fixed. The lower clamp 11 moves up and down together with the capillary 14 while remaining closed. Then, as shown in FIG. 5d, the capillary 14 moves in the opposite direction to the second connection point _P2 , and the wire 3
The capillary 14 is lowered at the same time to prevent it from being cut. As a result, the connecting portion of the ball 17 is deformed in the opposite direction to the second connecting point _P2 . Next, make _sure that the wire 3 at the lower end of the capillary 14 has an appropriate amount of slack by adjusting
Move to the point. At this time, the lower end of the capillary 14 is at a distance l' from the first connection point _P1 . and,
In experiments, this l' was optimally about 70% of the straight-line distance d between the first connection point _P1 and the second connection point _P2 .
Then, it moves almost linearly from the _Q2 point to the _Q3 point. On the way, point Q ₂ ' is directly above the first connection point. This is shown in Figure 5e. At the position shown in e, the wire 3 near the lower end of the capillary 14 is deformed in the direction opposite to the second connection point _P2 and bent into a dogleg shape. FIG. 5f shows the state in which the capillary 14 continues to move toward the second connection point _P2 , and the capillary 14 is located near the lead frame 19.
When approaching point Q ₃ , the wire 3 contacts the lead frame 19 before the capillary 14. FIG. 5g shows this state. However, compared to the conventional method, the wire 3 at the tip of the capillary 14 is bent at about 90 degrees, so the second connection point is
No abnormal sagging occurs in _P2 . When the capillary 14 approaches the lead frame 19,
direction, and come directly above the second connection point _P2 . FIG. 5h shows a state in which the capillary 14 is lowered directly above the second connection point _P2 and bonding is performed at a predetermined pressure. When bonding is completed, the lower clamp 11 opens and the capillary 1
4 is raised to a predetermined height as shown in FIG. 5i, the lower clamp 11 is closed and the wire 3 is torn off. Then, a ball 17 is formed at the tip of the wire 3, and the capillary 14 returns to its initial position, completing one cycle.

Next, the functions of the capillary position calculation control device 27 and the bonder control device that control the operations of the capillary 14, upper clamp 9, and lower clamp 11 will be explained.

The coordinates (x _{1 ,}
y ₁ , z ₁ ) and the coordinates (x ₂ , y ₂ , z ₂ ) of the second connection point P ₂ . As a result, the capillary position calculation control device 27 calculates the linear distance between the first connection point P ₁ and the second connection point P ₂ , the normal length l of the wire 3, and the distance between the capillary 14 from the first connection point P ₁ to Q ₁ , Q ₂ , second connection point via Q ₃
Calculate the route to move continuously and smoothly to P ₂ . The calculation results are stored in memory each time and then given as position command pulses to the X, Y, and Z axis servo controllers 26, 29, and 31 every 1 ms. Each servo controller 26, 29, 31 counts the position command pulse, and each driver 25, 28, 30 counts the position command pulse so that the current position and the command position are equal.
Give a motor drive command to. Each motor 22, 23
and 24 rotates, the encoders 22a, 23
Pulses proportional to the amount of rotation are generated from a and 24a, and the pulses are sent to the servo controllers 26 and 2.
9 and 31 are counted and the current position of the capillary 14 is known. The capillary position calculation control device 27 sends a signal to drive the upper clamp 9 and lower clamp 11 in synchronization with the position of the capillary 14.

After bonding at the first connection point as in the above embodiment, the bonding tool is raised to feed out the necessary length of wire, and the connection part at the first connection point is deformed in the opposite direction to the second connection point. Even if the wire 3 is bonded to the second connection point while being clamped by the lower clamp 11, the wire can be stretched stably with a high loop. wire 3
The height of the loop is the height of the capillary 14 in Figure 5.
It can be freely set by controlling the length l to the lower end. In addition, the normal length of the wire 3 is automatically calculated from the distance between the first connection point and the second connection point, and the wire of that length is accurately fed out, making it possible to create a very accurate ideal loop. can be formed. In addition, since the wire 3 inside the capillary 14 does not return in the vicinity of the second connection point as in the conventional case, the wire 3 inside the capillary 14
Another advantage is that the shape of the loop is not affected by wire scraps or the like attached to the loop.

Next, other embodiments will be described.

FIG. 7 shows a partially modified version of FIG. 1 so that the lower clamp can be rotated about a rotational fulcrum 40. The power source is the actuator 41 shown in the figure.
and this actuator is the bonder control device 32.
Driven by. With this mechanism, the lower clamp 11
can be moved up and down by about 1 mm.

Next, a method for performing bonding using this apparatus will be explained. The purpose of this is to help the wire at the tip of the capillary to be bent to about 90 degrees in the section of FIGS. 5f to g. That is, in FIG. 5g, the length of the wire that contacts the lead frame 19 before the capillary 14 is made as short as possible to create a stable wire loop.

For this purpose, it is necessary to make some modifications to the operation shown in FIG. That is, in Fig. 5c, the wire length l is increased by about 0.5 mm to l ₁ (l ₁ = l +
α) This added α then raises the lower clamp 11 by +α in FIG. 5g. By this operation, the length of the wire loop becomes l, which is the same as in the previous embodiment. In this embodiment, since the wire is pulled up by α in FIG. 5g, the time when the wire comes into contact with the lead frame 19 is delayed, and the occurrence of slack in the wire loop is reduced by that much, resulting in a better loop.

In each of the above embodiments, ball bonding using a capillary 14 with a wire 13 inserted through the center as a bonding tool was explained, but it is clear that the present invention can also be applied to bonding using a wedge, which is generally known as ultrasonic bonding. be.

Note that gold wire, aluminum wire, copper wire, etc. can also be used as the wire.

〔Effect of the invention〕

As explained above, in this invention, the length of the wire between the tip of the bonding tool and the first connection point is fed out until it becomes approximately equal to the length of the wire connecting the first connection point and the second connection point. Since the wire is then clamped and the capillary is moved to the second connection point, the shape of the wire loop can be reliably controlled.

[Brief explanation of drawings]

Fig. 1 is a side view showing a general wire bonding device, Fig. 2 is an explanatory diagram of the operation in a conventional wire bonding method, and Fig. 3 is a side view showing a comparison of good and bad wire loop shapes. , FIG. 4 is a perspective view showing the main parts of a bonding apparatus used in an embodiment of the present invention, FIG. 5 is an explanatory diagram of the operation in the method of the present invention, and FIG. 6 is an explanatory diagram of the operation in the method of the present invention. , FIG. 7 is a side view of a bonding apparatus used in another embodiment. 2... wire spool, 3... wire, 4...
Wire guide, 9... Upper clamp, 11... Lower clamp, 14... Capillary, P ₁ ... First connection point, P ₂ ... Second connection point, 27... Capillary position calculation control device (control circuit) , 26, 29, 31
...X, Y, Z servo controller.

Claims (1)

[Claims] 1. A wire that is passed through a wire guide, a clamp, and a bonding tool from a spool around which the wire is wound is bonded to a first connection point by lowering the bonding tool; In a wire bonding method in which the tool is moved upward and in the XY direction, the wire is fed out, bonded to a second connection point, and then the wire is torn off, the wire is bonded to the first connection point, and then from the tip of the bonding tool to the first connection point. Raise the bonding tool until the length of the wire between them is approximately equal to the length of the normal loop (=l) connecting the first and second connection points, and then lower the bonding tool. The clamper, which has a structure that moves together, is closed to stop the wire from being fed out from now on. Next, while lowering the bonding tool, move it in the opposite direction to the direction of the second connection point to remove the slack in the wire. Then move the wire directly above the first connection point again while holding this slack, make the wire buckle in the opposite direction of the second connection point, cause plastic deformation, and make the second connection while forming the wire. A wire bonding method that moves, lowers, and bonds to a point. 2 Calculate based on the coordinates of the first and second connection points and the required height of the wire loop, automatically calculate the required wire length (=l), and raise it above the first connection point. 2. The wire bonding method according to claim 1, wherein the height of the tool when clamping the wire is set to the above l. 3. In the method according to claim 1, the clamper is provided with a function of moving up and down relative to the bonding tool, and the bonding tool
The height of the bonding tool when it rises above the first connection point and then clamps the wire with the clamper is set equal to a length (=l+α) that is slightly larger than the required wire length (=l), and this slightly The wire bonding method is characterized in that the wire bonding tool is pulled up by a slight length (=α) above the bonding tool using a clamper before the bonding tool bonds to the second connection point.