JPH10321665A - Adaptability judging method of ball for wire bonding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent imperfect bonding which is to be caused by bonding using a ball having inadequate size, by judging whether the ball is adaptable, on the basis of a voltage between gaps at an instance when a discharge voltage is applied across a wire tip and a discharge electrode. SOLUTION: In a wire bonding equipment 10, a discharge is generated between a wire 11 protruding from a tip of a capillary 15 and a discharge electrode (torch electrode) 18, and a ball 11a is formed at a tip of a wire 11. As to discharge conditions such as a discharge current and a discharge period, a ball 11a having adequate size is formed when the discharge distance between the torch electrode 18 and the tip of the wire 11 is equal to a specified discharge distance L0 . When it is judged that the ball 11a having adequate size is not formed at the tip of the wire 11, the bonding operation of the wire bonding equipment 10 is stopped. As a result, imperfect bonding which is to be caused by bonding using a ball 11a having inadequate size can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for judging the suitability of a ball for wire bonding, which can judge the suitability of the ball.

[0002]

2. Description of the Related Art In a wire bonding apparatus, a discharge is generated between a wire protruding from a capillary at a tip of a bonding arm and a discharge electrode to form a ball at the tip of the wire, and the ball is joined to an electrode of a semiconductor pellet (first electrode). After 1), the capillary is moved onto the lead of the lead frame while the wire is led out, the wire is bonded to this lead (second bonding), and then the wire is cut, and the electrode and the lead are electrically connected by the wire. It is a thing to connect.

[0003] The suitability of the above-mentioned discharge is determined by detecting a discharge current flowing when a discharge is generated between the discharge electrode and the wire. If the discharge current is detected during the discharge time, the discharge is performed. It is determined that the operation was performed normally.

[0004] The discharge conditions such as the discharge current and discharge time, when the discharge distance L between the discharge electrodes and the wire tip is in a predetermined discharge distance L _0, balls proper magnitude is set to be formed ing. Therefore, when the discharge distance L varies, the size of the ball formed at the tip of the wire also varies. In general, the discharge distance L is long and the ball is smaller than the discharge distance L _0, conversely, the discharge distance L is short and tends to ball is larger than the discharge distance L _0.
If the ball is small, a predetermined bonding strength cannot be obtained at the time of bonding, and if the ball is large, a bonding defect may occur such that the ball protrudes from the electrode at the time of bonding and causes a short circuit.

[0005]

However, in the above-described method for determining the suitability of discharge, if the discharge current is flowing during the discharge time, it is determined that the discharge is normal, so that the discharge distance L varies. Even if a ball of an appropriate size cannot be obtained at the tip of the wire, it cannot be detected. As a result, there is a possibility that the bonding may be performed by a ball having an inappropriate size, and the above-described bonding failure may occur.

SUMMARY OF THE INVENTION The object of the present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for judging the suitability of a wire bonding ball which can prevent a bonding failure due to bonding with an unsuitable size ball. To provide.

[0007]

According to a first aspect of the present invention, there is provided a wire for judging the suitability of a ball formed at the tip of a wire when a discharge is generated between the tip of the wire and a discharge electrode. In the method of determining the suitability of a bonding ball, the suitability of the ball is determined based on a voltage between gaps at a moment when a discharge voltage is applied between the tip of the wire and the discharge electrode.

According to a second aspect of the present invention, in the first aspect of the invention, the determination of the suitability of the ball is performed by comparing the detected inter-gap voltage with a reference inter-gap voltage, Is performed depending on whether or not the discharge between them is performed at a predetermined discharge distance.

The invention described in claim 1 or 2 has the following effects. Prior to the wire bonding operation, a discharge is generated between the tip of the wire and the discharge electrode to form a ball at the tip of the wire.
This is performed based on the voltage between gaps at the moment when a discharge voltage is applied between the tip of the wire and the discharge electrode. In general, as the discharge distance increases, the ball formed at the tip of the wire tends to be too small, and as the discharge distance decreases, the ball tends to be too large. Therefore, by determining the length of the discharge distance based on the magnitude of the discharge voltage, it is possible to detect the formation of an inappropriate ball due to the variation in the discharge distance between the tip of the wire and the discharge electrode. As a result, if the apparatus is stopped when an appropriate ball cannot be obtained, it is possible to prevent a bonding failure due to bonding with an inappropriately sized ball.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side view showing one embodiment of a wire bonding apparatus to which the present invention is applied. FIG. 2 is a block diagram of the wire bonding apparatus of FIG. FIG. 3 is an enlarged view showing the wire tip and the torch electrode of FIG.

A wire bonding apparatus 10 shown in FIG.
Is a lead (not shown) of the lead frame 9 on which the semiconductor pellet 8 is mounted in the previous step (second bonding point)
And an electrode (first bonding point) (not shown) of the semiconductor pellet 8 is electrically connected (bonded) by a wire 11.

The wire bonding apparatus 10 has a pair of guide rails 12 for transporting and guiding the lead frame 9 by using a frame feeding mechanism (not shown). An XY table 13 that is movable in the transport direction 9 and in a direction perpendicular to the transport direction is disposed, and a bonding head 14 is mounted on the XY table 13.

A bonding head 14 has a capillary 15 through which a wire 11 is inserted, which is inserted into a head frame 14A.
And a torch electrode 18 serving as a discharge electrode. The bonding arm 16 is vertically swung by an arm driving mechanism (not shown). Also, the torch electrode 1
Reference numeral 8 denotes a torch drive mechanism (not shown) at the time of discharging, the tip of which is located directly below the capillary 15.

A heater block 17 is provided between the pair of guide rails 12 at a bonding position immediately below the capillary 15. With this heater block 17,
The semiconductor pellet 8 and the lead frame 9 which are guided by the guide rail 12 and reach the bonding position are heated,
The first and second bondings described below are performed under a high temperature condition.

The wire bonding apparatus 10 includes a wire 11 protruding from a tip of a capillary 15 and a torch electrode 18.
Between the wire 11 and the ball 1
1a, the bonding arm 16 is rotated downward, and the ball 11a is bonded to the electrode of the semiconductor pellet 8 (first bonding).
6 is moved upward, the capillary 15 is moved onto the lead of the lead frame 8 while the wire 11 is drawn out, and the bonding arm 16 is again rotated downward to join the wire 11 to the lead (second bonding). ). afterwards,
When the bonding arm 16 is rotated upward, the capillary 15 rises while the wire 11 is drawn out. During this ascending, the wire clamper 19 grips the wire 11 at a predetermined timing. Cutting is performed in the vicinity of the joint, and a wire 11 having a predetermined tail length is formed to project from the tip of the capillary 15. Thus, the wire bonding apparatus 10 electrically connects the electrodes of the semiconductor pellet 8 and the leads of the lead frame 9 with the wires 11.

The torch electrode 18 is connected to the high voltage side of the high voltage generator 20, as shown in FIG. Further, the wire 11 inserted into the capillary 15 is connected to the ground side of the high voltage generator 20. Therefore, the high voltage generator 2
0 indicates that a high voltage is applied between the wire 11 inserted into the capillary 15 and the torch electrode 18 to cause discharge, and the wire 1
A ball 11a is formed at the tip of the first. Here, the discharge conditions such as the discharge current and discharge time, as shown in FIG. 3, when the discharge distance between the torch electrode 18 and the wire 11 distal end is in a predetermined discharge distance L _0, an appropriately sized ball 11a Is set to be formed.

The control section 21 controls the generation and stop of the high voltage by the high voltage generation section 20. This control unit 2
1 also controls the XY table 13 and the bonding arm 16 and determines whether or not the discharge is appropriate, as described later.

A voltage detector 22 is provided between the wire 11 inserted in the capillary 15 and the torch electrode 18, and the voltage detector 22 allows the wire 11 inserted in the capillary 15 to be connected to the torch electrode 18. The voltage at the moment when the discharge voltage is applied between the two (at the moment when the discharge occurs), that is, the voltage between the gaps is detected.

The voltage detecting section 22 is connected to the control section 21 via a comparing section 23, and a memory section 24 is connected to the comparing section 23.

The storage section 24 stores a reference gap voltage (V ₀ ± △ V). Gap voltage of the reference (V ₀ ± △ V) is a value measured in advance by experiments or the like, the gap voltage V ₀ which a predetermined discharge distance L ₀ (FIG. 4
(B)) in consideration of the allowable value ΔV.

Further, the comparison unit 23 calculates the actual gap voltage V ₁ at the time of discharge detected by the voltage detection unit 22.
And the reference gap voltage (V
₀ ± △ V) and outputs the comparison result to the control unit 21.

As a result of the comparison by the comparing section 23, the control section 21 determines that the inter-gap voltage V ₁ is within the reference inter-gap voltage (V ₀ ± △ V) as shown in FIG. ,
The discharge is performed at a predetermined discharge distance L ₀ (FIG. 3), and the wire 1
It is determined that the ball 11a of an appropriate size has been formed at the tip of No. 1 and the bonding operation is continued.

Further, as a result of the comparison by the comparing section 23, the control section 21 sets the inter-gap voltage V as shown in FIG.
_{When 1} is larger than the reference gap voltage (V ₀ ± △ V), the discharge is performed at a discharge distance L ₁ (FIG. 3) longer than a predetermined discharge distance L ₀ and is formed at the tip of the wire 11. The ball 11a is too small and has a proper size.
It is determined that a is not obtained, and the XY table 13 and the bonding arm 16 are controlled to stop the bonding operation. Note that the control unit 21 cannot discharge due to a cause such as an excessively large discharge distance, and as shown in FIG.
The gap voltage V ₁ is a reference gap voltage (V ₀ ± △
Even if it becomes extremely larger than V), the wire 1
It is determined that the ball 11a of an appropriate size has not been obtained at the tip of No. 1 (the ball 11a is not formed), and the bonding operation is stopped.

Further, as a result of the comparison by the comparing section 23, the control section 21 sets the voltage V between the gaps as shown in FIG.
_{When 1} is smaller than the reference gap voltage (V ₀ ± △ V), discharge is performed at a discharge distance L ₂ (FIG. 3) smaller than a predetermined discharge distance L ₀ , and formed at the tip of the wire 11. It is determined that the ball 11a is too large and an appropriate ball 11a has not been obtained, and the XY table 13 and the bonding arm 16 are controlled to stop the bonding operation.

Therefore, according to the above embodiment, the voltage detector 22 detects the gap voltage V ₁ at the moment when a discharge voltage is applied between the tip of the wire 11 and the torch electrode 18, and the comparator 23 detects And the gap voltage V ₁ is stored in the storage unit 2.
4, the controller 21 compares the reference gap voltage (V ₀ ± △ V) stored in 4 with the control unit 21, and based on the comparison result by the comparison unit 23, discharge performed between the tip of the wire 11 and the torch electrode 18. determines whether made under the predetermined discharge distance L _0. If the discharge is not performed at the predetermined discharge distance L ₀ , the control unit 21 determines that the ball 11 a having an appropriate size is not formed at the tip of the wire 11, and the bonding of the wire bonding apparatus 10 is performed. Since the operation is stopped, it is possible to prevent a bonding failure due to bonding with the ball 11a having an inappropriate size.

In the above embodiment, the ball 1 having an improper size due to a variation in the discharge distance.
Although the case where the formation of the ball 1a is determined has been described, the formation of the improperly sized ball 11a (non-formation of the ball 11a) due to the discharge being performed between members other than the wire 11 may be determined. . That is, when the torch electrode is arranged at the discharge position, a member such as a metal having a possibility of generating a discharge with the discharge electrode 18, for example, a lead frame presser or the like, has a predetermined discharge distance L The discharge position of the torch electrode 18 is set so as to be located away from ₀ . Then, in forming the ball 11a, the wire 11 tip and discharge voltage detecting the gap voltage V ₁ of the moment of applying between the torch electrode 18, the gap voltage V ₁ and the reference of the gap voltage (V ₀ ± △ V) in the comparison unit 23, and as a result of this comparison, the gap voltage V
_{When 1} is a reference gap voltage (V ₀ ± △ V), it is determined that an appropriate size ball 11a is formed at the tip of the wire 11 by discharging the wire 11 and bonding. Continue operation. When the gap voltage V ₁ is larger than the reference gap voltage (V ₀ ± △ V), discharge occurs between members other than the wire 11, and the ball 11 a is not formed at the tip of the wire 11. And the bonding operation is stopped. As a result, even when the discharge is performed between members other than the wire 11 and the ball 11a is not formed at the tip of the wire 11, this can be reliably detected, and the ball 1 having an inappropriate size is not detected.
It is possible to prevent a bonding failure due to bonding with 1a (the wire 11 on which the ball 11a is not formed).

In the above embodiment, the torch electrode 18
Has been described as a movable torch electrode, but may be a fixed torch electrode.

[0028]

As described above, according to the present invention, it is possible to prevent a bonding failure due to bonding with an inappropriately sized ball.

[Brief description of the drawings]

FIG. 1 is a side view showing one embodiment of a wire bonding apparatus applied to the present invention.

FIG. 2 is a block diagram of the wire bonding apparatus of FIG. 1;

FIG. 3 is an enlarged view showing a wire tip and a torch electrode of FIG. 1;

FIG. 4 is a graph showing a voltage between gaps.

[Explanation of symbols]

REFERENCE SIGNS LIST 10 wire bonding apparatus 11 wire 11 a ball 15 capillary 18 torch electrode (discharge electrode) 21 control unit 22 voltage detection unit 23 comparison unit 24 storage unit V ₀ , V ₁ gap voltage V ₀ ± ΔV Reference gap voltage L ₀ , L ₁ , L ₂ discharge distance

Claims (2)

[Claims] 1. A method for judging the suitability of a ball formed on the tip of a wire when a discharge is generated between the tip of the wire and a discharge electrode. A wire bonding method, wherein the suitability of the ball is determined based on a gap voltage at a moment when a discharge voltage is applied to the discharge electrode. 2. The method according to claim 1, wherein the determination of the suitability of the ball is performed by comparing the detected gap voltage with a reference gap voltage, and determining whether the discharge between the tip of the wire and the discharge electrode has been performed at a predetermined discharge distance. The method for judging suitability of a ball for wire bonding according to claim 1, wherein the method is carried out by: