JP2872158B2 - Wire bonding method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode pad formed around a rectangular semiconductor chip mounted on a lead frame, and a lead of a lead frame corresponding to the semiconductor chip and arranged around the semiconductor chip. And a wire bonding method for connecting a wire to a hoop by a thin metal wire.

[0002]

2. Description of the Related Art Usually, in a semiconductor device manufacturing process, after a mounting process of mounting a semiconductor chip having a semiconductor element or wiring formed on a surface thereof on a lead frame, an electrode pad of the mounted semiconductor chip and a lead of the lead frame are mounted. And a wire bonding step of connecting the above with a thin metal wire. In this wire bonding step, various problems such as short-circuiting of the thin metal wire to the semiconductor chip due to the mounting position shift of the semiconductor chip in the previous process and contact between adjacent thin metal wires have occurred.

[0003] Japanese Patent Application Laid-Open No. 218195/1990 discloses a technique for solving the problem of wiring due to the displacement of the mounted semiconductor chip. The wire bonding apparatus includes an ITV camera for imaging a relative position between a lead and a semiconductor chip, a recognition device for recognizing a connection position of a semiconductor chip and a connection position of a lead from an imaging signal of the ITV camera, and a connection of the recognized lead. A calculating means for calculating the distance between the position and the connection position of the electrode pad of the semiconductor chip to determine the length of the thin metal wire and correcting the connection position so that the two values are within an allowable value range; and a sequence controller. ing.

The operation of this wire bonding apparatus is as follows. First, the connection position of a semiconductor chip mounted on a lead frame deviated from a reference position and the connection position of the lead are read by an ITV camera and a recognition device, and the mounted semiconductor chip is read. The XY stage determines whether the gap between the connection point of the electrode pad and the connection point of the lead corresponding to the electrode pad satisfies the allowable value, and if the distance is within the allowable value, corrects the deviation amount. Is moved to lower the bonding tool to connect the electrode pads of the semiconductor chip and the corresponding leads with thin metal wires.

As described above, the amount of displacement is corrected for each electrode pad and each lead, the length of the thin metal wire corresponding to the distance between the connection point of the electrode pad and the connection point of the lead is determined, and the length of the thin metal wire having the obtained length is determined. The short circuit between the fine metal wires due to the slack of the fine metal wire sent excessively and the short circuit of the fine metal wire to the semiconductor chip due to a low loop due to insufficient feeding are prevented.

[0006]

In the above-described conventional wire bonding apparatus, although the length of the thin metal wire to be fed is determined in advance in accordance with the two-dimensional distance, the length of the thin metal wire fed from the wire supply unit is reduced. Each time a thin metal wire is detected by the sensor, the stepping motor is rotated at a fixed angle and the thin metal wire is sent in a step shape to supply a desired length.
Due to the timing of the bonding tool ascending and descending and the timing of the sensor, variations occur within the length of the thin metal wire sent in a step-like manner, even if short-circuiting of the thin metal wires and contact of the thin metal wire to the semiconductor chip do not occur. The height of the thin metal wire formed in a hoop shape varies. If the hoop height of the fine metal wire is high, there is a serious defect in quality that the fine metal wire is exposed from a package body surrounding the semiconductor chip in a resin sealing step. Especially in recent years,
The thickness of the package of the semiconductor device is becoming increasingly thinner, and this problem has become a serious problem.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a wire bonding method for joining metal fine wires by aligning the hoop heights of the metal wires connecting the electrode pads of the semiconductor chip and the leads corresponding to the electrode pads.

[0008]

The feature of the present invention is that an electrode pad formed around a rectangular semiconductor chip mounted on a lead frame and a lead of the lead frame corresponding to the semiconductor chip are formed in a hoop shape. A wire bonding method of connecting a lead line and a connection point of the electrode pad in the thin metal wire and an approximate quadratic trajectory curve formed by a hoop height of the thin metal wire. in terms of function curve calculated the length of the thin metal wire, Ru wire bonding method der for joining the leads and the electrode pads by the length of the thin metal wires obtained.

[0009] Other features of the invention, Ru is mounted on the mounting table
And ITV camera for imaging a semiconductor chip mounted on rie de frame and the lead frame, and recognizing device the position of the input to the semiconductor chip and the lead and the electrode pad an imaging signal of the ITV camera, from the recognition device second information and the connection point of the lead obtained by the data of the approximate trajectory curve of the thin metal wires formed by hoop height relative distance and pre Ji because-determined metallic thin wire and a connection point of the electrode pads an arithmetic processing unit in terms of the following function curve determining the length of the thin metal wire, and the wire feed unit for feeding the gold <br/> genus fine line lengths determined by the bonding tool, the bonding tool of the bonding head Up and down movement, the movement of the stage for moving the bonding head in the XY directions, and the control of the wire supply unit. A wire bonding apparatus and a control unit for controlling the sequence operation of the recognition unit and the arithmetic processing unit.

[0010]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a plan view, an AA sectional view, and a BB sectional view showing a relative position between an electrode pad and a lead of a semiconductor chip for explaining a wire bonding method according to an embodiment of the present invention. To explain the process leading to the present invention, first, as shown in FIG. 1A, the leads 15a and 15b to be connected to the electrode pads 16a and 16b of the semiconductor chip 14 are arranged so as to correspond to each other.
Then, looking at the relative distance in two dimensions, the electrode pad 16
The distance between the connection point of the electrode pad 16b and the connection point of the lead 15b is longer than the distance between the connection point of a and the connection point of the lead 15a. Further, as shown in FIGS. 1B and 1C, if the ascending limit point of the bonding tool 18 is h, the trajectory curves of the short metal wire 17a and the long metal wire 17b having a short distance in two dimensions are as follows. Although the smoothness is different due to the difference in the length of the thin metal wires 17a and 17b, the locus curves formed by the thin metal wires 17a and 17b are almost similar to quadratic function curves.

Therefore, the thin metal wires 17a and 17b are so small that the thin metal wires 17a and 17b do not contact the semiconductor chip 14.
If the minimum height h of the hoop of 7b is set and the length of the thin metal wire that draws the trajectory curve is set according to the length of the relative distance between the two-dimensional connection points and sent, the excess or deficiency of the sent thin metal wire results. The above-mentioned problem will be solved.

In order to determine the length of the locus curve of the thin metal wire, if the locus curve of the thin metal wire is Y = -K (X + R) ² , for example, the quadratic function curve is given by the following equation. This is a value that determines smoothness, and is determined by a ratio of a two-dimensional distance L between a connection point between the electrode pads 16a and 16b and a connection point between the leads 15a and 15b. For example, when the relative distance is short such as the lead 15a and the electrode pad 16a, for example, K
Assuming that h is constant, the trajectory of the lead 15b having a long relative distance and the thin metal wire of the electrode pad is, for example, as follows:
A slightly gentle locus curve is obtained, such as K = 1 / 1.3.

Next, in order to determine the length of the thin metal wire, FIG.
A vertical plane including the cross section line AA or BB in FIG. 1B and FIG. 1C is defined as an XY coordinate plane, and the lengths of the thin metal wires 17a and 17b having the locus curves on the XY coordinate plane are determined. For this, R is the position coordinate of the bonding tool 18, K is a constant, the connection point between the electrode pads 16 a and 16 b of the semiconductor chip 14 and the leads 15 a and 1
The coordinate value of the connection point 5b is input to the arithmetic processing unit, and a quadratic function curve to be converted is obtained. Then, a tangent at each point is obtained from the quadratic function curve, and a length of the oblique line is obtained from a small right triangle having the tangent as an oblique line.
5b to the electrode pads 16a and 16b, the sum of the lengths of the oblique lines at each of the finely divided points is calculated.
Find the length of 7b.

Further, the locus curve of the thin metal wire is not only a quadratic function curve but also a hoop-shaped curved portion is a quadratic function curve, and the connection points between the electrode pads and the leads of the remaining semiconductor chip are converted into a linear line. May be. The choice between them is determined by whether the material of the thin metal wire is gold or aluminum.

FIG. 2 is a block diagram for explaining a wire bonding apparatus according to one embodiment of the present invention. As shown in FIG. 1, this wire bonding apparatus includes an ITV for imaging a lead frame mounted on a mounting table 11 and a semiconductor chip 12 mounted on the lead frame.
A camera 5, a monitor television 4 for displaying a captured image based on an image signal of the ITV camera 5, a recognition device 2 for inputting an image signal of the ITV camera and recognizing connection positions of the semiconductor chip 12, the leads, and the electrode pads; Set in advance the constants that determine the waveforms of the quadratic function curves that approximate the locus curves of the hoop-shaped metal wires formed by connecting the positions to be connected and the electrode pads, and the leads and electrode pads that connect these leads and electrode pads. A setting unit 3a, an arithmetic processing unit 3 for calculating the length of the thin metal wire from the position information from the recognition device 2, a trajectory curve and a waveform constant taken from the setting unit 3a, and a length determined by a signal from the arithmetic processing unit 3 Supply control unit 1 for instructing the thin metal wire supply unit to feed the thin metal wire
And a control unit 6 for controlling the vertical movement of the bonding tool of the bonding head 7 and the movement of the XY stage 9 and for controlling the sequence operation of the apparatus.

When the length of the metal wire to be fed is determined, the clamper immediately before the lowering of the bonding tool holds and fixes the metal wire, and at the same time, rotates the stepping motor of the wire supply unit 8 to start supplying the metal wire. Then, the metal wire is bonded to the first lead or the electrode pad, and the metal wire is bonded to the next electrode pad or the lead. And XY
It is desirable to set so that the moving speed of the stage matches.

FIG. 3 is a flowchart for explaining the operation of the wire bonding apparatus of FIG. First, FIG.
In step A, the coordinates of the leads of the lead frame on which the semiconductor chip to be wired is to be mounted, the electrode pads corresponding to the leads, the locus curve, and the multiplier K are registered in the setting unit 3a of FIG.

Next, in step B, the lead frame on which the semiconductor chip is mounted is positioned and mounted on the mounting table 11 of FIG. Next, in step C, the ITV camera 5 of FIG. 2 images the electrode pads to be wired to the semiconductor chip and the leads corresponding to the electrode pads, and the recognition device 2 of FIG.
Then, the position coordinates of the electrode pad and the lead are recognized. Next, in step D, the comparison unit in the control unit 6 of FIG. 2 compares the position coordinates stored in the setting unit 3a with the position coordinates recognized by the recognition device 2 to determine whether the position deviation is within an allowable range. Is determined.

If the positional deviation exceeds the allowable range, the lead frame is removed from the mounting table 11 in step I, and the process returns to step B to mount a new lead frame. If the positional deviation is within the allowable range, step E
To determine whether it is necessary to correct the positional deviation. Here, the determination value of whether or not to perform the correction depends on the movable resolution of the XY stage in FIG.

Next, if correction is necessary, the arithmetic processing unit 3 in FIG. 2 calculates and corrects the deviation between the position coordinates of the lead and the electrode pad, and corrects the position coordinates stored in the setting unit 3a in FIG. . Next, in step G, even when the positional deviation is corrected or not corrected, the position coordinate information and the locus curve data are taken out from the setting unit 3a in FIG. 2 and taken into the arithmetic processing unit 3 in FIG. Then, the length data information is set in the buffer memory of the wire supply control unit 1 shown in FIG.

Next, in step H, the control unit 6
The data of “a” is taken in, and at the same time the operations of the XY stage 9 and the bonding head 10 in FIG. 2 are controlled, the wire supply control unit 1 operates the wire supply unit 8 to connect the electrode pads and the leads corresponding to the electrode pads with thin metal wires. . Then, returning to step C, the position coordinates of the next electrode pad and the lead corresponding to this electrode pad are recognized. By repeating such an operation, the connection of each electrode pad of the semiconductor chip and the lead corresponding to each electrode pad by the thin metal wire is completed.

[0023]

As described above, according to the present invention, even when a positional shift occurs between the electrode pad and the lead, the relative distance between the electrode pad and the corresponding lead and the height of the hoop of the metal wiring to be connected each time the position shift occurs. By calculating the length including the metal wire and supplying the calculated length of the metal wire, the hoop height of the metal wire can be made constant, so that there is no contact between the metal wire or the semiconductor chip and the post-process. There is an effect that a stable quality of the package body can be obtained without exposing the fine metal wires to the package body by the resin sealing.

[Brief description of the drawings]

FIG. 1 is a plan view showing a relative position between an electrode pad and a lead of a semiconductor chip for explaining a wire bonding method according to an embodiment of the present invention; FIG.
It is B sectional drawing.

FIG. 2 is a block diagram illustrating a wire bonding apparatus according to one embodiment of the present invention.

FIG. 3 is a flowchart illustrating an operation of the wire bonding apparatus of FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wire supply control part 2 Recognition device 3 Arithmetic processing part 3a Setting part 4 Monitor television 5 ITV camera 6 Control part 7 Bonding head 8 Wire supply part 9 XY stage 10 Bonding tool 11 Loading table 12 Semiconductor chip

Claims (2)

(57) [Claims] 1. A wire bonding method for connecting an electrode pad formed around a square semiconductor chip mounted on a lead frame and a lead of the lead frame corresponding to the semiconductor chip by a thin metal wire in a hoop shape. The locus curve formed by the relative distance between the connection point of the lead and the connection point of the electrode pad in the thin metal wire and the hoop height of the thin metal wire is converted into an approximate quadratic function curve, and the A wire bonding method comprising: determining a length; and bonding the electrode pad and the lead with the metal wire having the determined length. A lead frame mounted on a mounting table;
I for imaging a semiconductor chip mounted on a lead frame
Before inputting the TV camera and the imaging signal of this ITV camera
Position of semiconductor chip and lead and electrode pad
Recognition device that recognizes and information data from the recognition device
Of the electrode pad and the connection point of the lead obtained by
The relative distance to the connection point and the
The trajectory curve of the thin metal wire formed at the
Calculation to calculate the length of the metal wire by converting to the following function curve
Processing part and bondin the metal wire of the required length
Wire feeding section for feeding
Up and down movement of the bonding tool and
Stage movement to move the loading head in the X and Y directions
Controls the operation and the wire feeder and
Controls the sequence operation of the recognition device and the arithmetic processing unit
A wire bonder, comprising:
Device.