JPS6361776B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wire bonding stop circuit, and more particularly to a wire bonding stop circuit for an automatic wire bonding apparatus using spark discharge.

In the manufacturing of semiconductor integrated circuit (IC) parts,
Speeding up the bonding process, in which metal lead wires are used to connect the bonding pads of IC chips and pin terminals of lead frames, is an extremely important issue for the mass production of IC components.

To solve this problem, automatic wire bonding equipment has recently been widely adopted in IC manufacturing lines. In this bonding process, the tip of a metal lead wire, such as a gold wire, is melted and
It is essential to form a 110 μm gold ball, and for this reason, a method of forming a gold ball using an electrical spark discharge between a gold wire and a spark electrode is widely practiced. This gold ball is used to increase the surface area for thermocompression bonding with the bonding pad of the IC chip, and as a buffer to prevent cracks from occurring in the pad due to mechanical impact during wire bonding. work.

One bonding cycle of the automatic wire bonding apparatus consists of the following first to third main steps.

(1) Send out a specified length of gold wire from the tip of the capillary. (Gold wire delivery process) (2) After placing the spark electrode at the tip of the gold wire, the tip of the gold wire is melted by spark discharge to form a gold ball of a predetermined diameter. (Gold ball forming process) (3) After placing the capillary on the pad part of the IC chip, the pad part and the gold ball part are bonded by thermocompression.
(Thermocompression bonding process) Conventional automatic wire bonding equipment using spark discharge performs bonding work at a bonding speed of about 0.2 to 0.4 seconds/bonding cycle, but the amount of gold wire delivered from the capillary exceeds the set value. When the length was too long, the spark electrode and the gold wire were short-circuited, and a gold ball was often not formed at the tip of the gold wire.

Conventional bonding equipment does not have a function to detect short-circuit conditions between the gold wire and the spark electrode, so the thermocompression bonding process is started before a gold ball of a specified diameter is formed at the tip of the gold wire, and the tip of the capillary is directly attached to the pad. Since the pad is "dry-struck", bonding defects are continuously detected while causing cracks in the pad.
There was a problem in manufacturing IC parts.

The present invention solves these drawbacks by providing a wire bonding stop circuit that stops the thermocompression bonding process when the gold wire comes into contact with the spark electrode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention shown in FIGS. 1 to 3 will be described in detail below.

The wire bonding stop circuit according to the embodiment of the present invention includes a discharge current detection circuit 1, a delay circuit 2, a signal comparison circuit 3, and an inhibition signal generation circuit 4. The discharge current detection circuit 1 is a spark discharge circuit 5
This circuit detects the presence or absence of current flowing through the circuit and converts it into a pulse signal. The discharge current circuit 5 is formed of a high voltage DC power source (for example, 550V) 6, a switch 7, a resistor 8, a wire clamping means 9, a gold wire 10, and a spark electrode 11.

The gold wire 10 is fed out vertically (in the Z-axis direction) from the wire reel 12 and guided into the needle hole of the capillary 13. The capillary 13 is integrated with the bonding arm 14 and is moved in the Z-axis direction by the output signal (K) of the drive circuit 15. The wire clamping means 9 temporally clamps the gold wire 10 by a drive circuit 16,
It also acts as a switch for the discharge circuit 5.

The spark electrode 11 is rotated around the Z axis by a drive circuit 17 and is placed directly below the capillary 13 . The offset l ₁ between the tip of the capillary 13 and the spark electrode 11 is accurately determined to a set value (1.2 mm in this embodiment).

The discharge current detection circuit 1 is, for example, a photocoupler circuit 1.
8 and a waveform shaping circuit 19. The photocoupler circuit 18 includes a light emitting element 20 and a light receiving element 21, and the voltage dropped across the resistor 8 causes the light emitting element 20 to
emits light and enters the light receiving element 21. The waveform shaping circuit 19 includes, for example, a transistor 22 and an inverter 23, and amplifies and shapes the waveform of the signal input from the light receiving element 21.

The delay circuit 2 is formed from monostable multivibrator circuits 24 and 25 having time constant circuits 26 and 27, respectively, and the signal output from the inverter 23 causes a time T ₁ corresponding to the pulse width of this output signal.
After , a pulse signal is output. Time constant circuit 2
6 has a time constant T ₂ that is greater than the pulse width of the output signal output from the inverter 23 .

The signal comparison circuit 3 is composed of an inverter 28 and an AND logic circuit 29, and outputs a pulse signal when the inverter 23 outputs a pulse signal having a predetermined pulse width.

Inhibition signal generation circuit 4 is JK flip-flop 3
0, a gate circuit 31, and a delay circuit 32, and outputs an inhibition signal for stopping the bonding operation of the capillary 13 in response to the output signal of the comparison circuit 3. The JK flip-flop 30 receives a timing signal from the timing signal generation circuit 33 through the delay circuit 32, and periodically resets its output terminal to the "H" level.

Next, the operation according to the embodiment of the present invention will be explained with reference to the timing diagram of FIG.

First, when the timing signal A is output from the timing signal generation circuit 33, the wire clamp means 9 clamps the gold wire 10 by the drive circuit 16.
(FIG. 2A) Next, when the timing signal B is output from the timing signal generation circuit 33, the drive circuit 17
The spark electrode 11 is placed directly below the capillary 13. (FIG. 2B) Usually, a gold wire 10 with a diameter of 20 to 30 μm is used as the bonding wire, and the distance l ₁ between the tip of the capillary 13 and the spark electrode 11 is set to, for example, about 1 to 2 mm. Further, when the DC power source 6 of the discharge circuit 5 is about 550V, the spark gap _l3 between the tip of the gold wire 10 and the spark electrode 11 is, for example,
It is set at about 0.15 to 0.2 mm.

Since the LK flip-flop 30 is reset by the timing signal C of the timing signal generating circuit 33 during the previous bonding cycle, the output terminal is held at the "H" level state. or,
One input terminal of the AND logic circuit 34 is held at the "L" level state until the next timing signal is generated.

Next, when the timing signal E is output from the timing signal generation circuit 33, the switch 7 changes from 20 to 20, for example.
The discharge circuit 5 is completed by closing for 30 milliseconds. This generates a spark discharge in the gap _l3 , melting the tip of the gold wire 10. The molten gold wire becomes a ball 10a at a height where spark discharge does not continue due to surface tension.
It will rise to l ₂ (e.g. about 0.5mm) and stop. In this normal spark state, the waveform shaping circuit 19 remains “H” for a predetermined period T ₁ (for example, 2.5 to 3.0 milliseconds).
Outputs a level signal. (FIG. 2F) The output signal output from the inverter 23 is input to the delay circuit 2, and the time T ₂ is longer than the period T ₁ and shorter than the control signal E of the switch 7.
Afterwards, a pulse signal G is output. (FIG. 2G) The states of the pulse signals G and F are compared, and if the pulse width of the output signal F of the waveform shaping circuit 19 is within the normal spark period _T1 , an "H" level signal is output. (FIG. 2H) When the "H" level signal is input to the JK flip-flop 30, the output signal I at the output terminal changes to the "L" level state and is input to the AND logic circuit 34. (FIG. 2 I) Therefore, the output signal J of the gate circuit 34 becomes "L" level, and the drive circuit 15 operates normally and the bonding arm 14
drive. (FIG. 2 J, K) Therefore, the thermocompression bonding process to the pad portion is performed.

On the other hand, while the switch signal E is at the "H" level, the timing signal C is input from the timing signal generating circuit 33 to the delay circuit 32, and after a predetermined time has elapsed, the output terminal of the JK flip-flop 30 is reset to the "H" level. (FIGS. 2C and D) Next, considering the case where the gold wire 10 comes into contact with the spark electrode 11, a short circuit current flows through the discharge circuit 5 while the switch 7 is on. Therefore, waveform shaping circuit 1
The output signal F of 9 outputs an "H" level signal for the _T1 period or more. (Figure 2 F dotted line waveform) Delay circuit 2
always outputs a pulse signal after a period of _T2 when a signal is input. For this reason, the comparison circuit 3 uses the switch signal E.
is held at the "L" level during the "H" level period, and accordingly, the state of the output terminal of the JK flip-flop circuit 30 is also held at the "H" level.

Next, an "H" level signal is input from the timing signal generation circuit 33 to one input terminal of the AND logic circuit 34, so that the AND logic circuit 34 outputs an "H" level inhibition signal to the drive circuit 15. Therefore, the bonding arm 14 stops operating, and the process of thermocompression bonding of the IC component to the pad portion is completely prevented. The drive circuit 15 maintains its state until the release signal O is input. After the AND logic circuit 34 outputs the prohibition signal, one input terminal becomes the "L" level state, and the output terminal of the AND logic circuit 34 returns to the "L" level state again.

Next, there is an I ₂ between the tip of the gold wire 10 and the spark electrode 11.
Considering the above case, no spark discharge occurs during the ON period of the switch 7, and no discharge current flows through the discharge circuit 5. Output signal F of waveform shaping circuit 19
is held at the "L" level, and the output signal G of the delay circuit 2 is also held at the "L" level. Therefore, the output signal H of the comparator circuit 3 also becomes "L" level, and the signal of the JK flip-flop 30 goes "H".
Do not change level status. After that, when the timing signal C is input from the timing signal generation circuit 33 to one input terminal of the AND logic circuit 34,
The AND logic circuit 34 outputs an "H" level inhibition signal to the drive circuit 15, and the bonding arm 14
stop the operation. Thereafter, a reset signal D is output from the delay circuit 32, and the output terminal of the JK flip-flop 30 is held at the "H" level, waiting for a signal to be input to the clock terminal CK in the next bonding cycle.

In the embodiment of the present invention, each timing signal is generated by a timing signal generation circuit 3 using a digital circuit.
3 has been considered, but it is also possible to generate it by mechanical means having a control disk with a slit and a detector mounted on the rotating shaft.

As explained above, the wire bonding stop circuit according to the present invention similarly detects a gold wire short-circuit condition between the capillary tip and the spark electrode and a condition in which the amount of gold wire delivered from the capillary tip is small, and operates the bonding arm. This completely prevents the tip of the capillary from directly hitting the bonding pad of the semiconductor electronic component.

Therefore, the automatic bonding operation is performed without a gold ball being formed at the tip of the gold wire, and the accident of continuously manufacturing defective IC parts is eliminated.
The wire bonding stop circuit according to the present invention can be used in fully automatic bonding equipment operating at high speeds to enable wire bonding operations with very high manufacturing yields.

[Brief explanation of drawings]

FIG. 1 is an embodiment of a wire bonding stop circuit according to the present invention. FIG. 2 is an operational timing diagram for an embodiment of the present invention. 1...Discharge current detection circuit, 2...Delay circuit, 3
...Comparison circuit, 4...Prohibition signal generation circuit.

Claims (1)

[Scope of Claims] 1. A discharge current detection circuit that outputs a first pulse signal corresponding to a discharge period when a discharge current flows between the spark electrode and the bonding metal wire;
a delay circuit that outputs a second pulse signal after a predetermined time has elapsed from generation of the pulse signal; a comparison circuit that compares the pulse width of the first pulse signal with the delay time; and a response to the output signal of the comparison circuit. A wire bonding stop circuit including a prohibition signal generating circuit that outputs a signal to stop a thermocompression bonding process between a pad portion of a semiconductor element and the metal wire for bonding. 2. Claim 1, wherein the delay circuit comprises a plurality of monostable multivibrators.
Wire bonding stop circuit described in section. 3. The wire bonding stop circuit according to claim 1, wherein the delay time is 3 milliseconds or more.