JP4344977B2 - Ultrasonic wire bonder - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic wire bonder for fixing a bonding wire to a semiconductor chip using ultrasonic vibration in an assembly process of a semiconductor device.
[0002]
[Prior art]
As a method for wiring from a semiconductor chip of a power device such as an IGBT to an external lead-out terminal, it is known to connect with a bonding wire. An ultrasonic wire bonder is generally used as an apparatus for fixing the bonding wire to the semiconductor chip.
[0003]
FIG. 4 is a configuration diagram of a main part of a conventional ultrasonic wire bonder. This ultrasonic wire bonder supplies a wire 56 to a bonding tool 57 via a wire clamp 54 and a wire holder 55 from a wire supply unit (not shown).
Next, the wire 56 is pressed against the semiconductor chip 71 and pressed using the bonding tool 57. Further, ultrasonic vibration is applied (transmitted) to the bonding tool 57 via the ultrasonic horn 2 and the bonding tool holder 58 from an ultrasonic vibration generation unit (ultrasonic vibration generator) (not shown).
[0004]
In this manner, the wire 56 is fixed to the bonding pad of the semiconductor chip 71 by applying ultrasonic vibration to the wire 56 using the bonding tool 57.
Next, while supplying the wire 56, the wire 56 is moved to the upper part of the external lead-out terminal 72, the same bonding is performed on the external lead-out terminal 72, and the semiconductor chip 71 and the external lead-out terminal 72 are connected by the wire 56.
[0005]
The rear part of the bonding tool 57 includes a wire clamp 54 for fixing the wire 56, a wire holder 55 for holding the wire 56, and a wire cutter 53 for cutting the wire 56.
Moreover, the bonding tool 57 and the table 74 have an elevating mechanism and a moving mechanism in a horizontal plane, and the bonding tool 57 and the table 74 can be moved up and down and horizontally relatively. Some apparatuses have a rotation mechanism.
[0006]
In ultrasonic wire bonding, the bonding conditions are optimized by applying pressure to the wire 56 of the bonding tool 57, applying ultrasonic vibration, and applying time and application time. For example, when the diameter of the wire 56 is 300 μm, the applied pressure is 0.6 N and the time is about 250 ms.
[0007]
[Problems to be solved by the invention]
When the pressing force of the bonding tool 57 is large, damage to the semiconductor chip 71 increases, so it is desirable to optimize the bonding conditions by reducing the pressing force as much as possible. However, when the applied pressure of the bonding tool 57 is reduced, the front end of the wire 56 is a free end, and the rear end of the wire 56 is constrained by the wire 56. Therefore, at the bonding surface between the wire 56 and the semiconductor chip 71, The restraint conditions of the front side and the rear side of the wire 56 are different.
[0008]
When ultrasonic wire bonding is performed in a state where the constraint conditions are different, the wire 56 is subjected to a force drawn toward the wire holder 55 by ultrasonic vibration. Since the pulling force and the rear side are constrained, the stress concentration in the bonding surface of the wire 56 becomes larger on the front side than on the rear side, and a large damage is given to the front side. Further, when the pull-in amount is large, it becomes the leading end of the wire 56 as pressed by the wire holders 55, can not be successful bonding.
[0009]
5A and 5B are diagrams in which a crack is generated in the semiconductor chip. FIG. 5A is a view of a bonding portion, FIG. 5B is a view showing a bonding surface A of FIG. It is an enlarged view of the joining location B of the same figure (a).
In FIG. 6A, the front side 61 of the wire 56 is a free end, and the rear side 62 is constrained by the wire. Although cracks 65 are generated on the front side 63 (toe side) and the rear side 64 (heel side) of the joint surface A in FIG. 5B, as described above, the rate of occurrence of the cracks 65 is higher on the front side. FIG. 3C is an enlarged view of a portion where the crack 65 is generated. The upper structure of the semiconductor chip 90 includes a gate oxide film 84, a gate electrode 85 formed of a polysilicon film, an interlayer insulating film 86 formed of a BPSG film, and an emitter electrode 87 formed of an Al-Si film. The location where the crack 65 is generated is the terrace portion 84a (location having a convex shape). In addition, a well region 82 and an emitter region 83 are formed in the semiconductor substrate 81.
[0010]
As described above, when the crack 65 is generated, the electrical characteristics (gate breakdown voltage characteristics, etc.) of the semiconductor chip 90 deteriorate at this location, and the wire 65 is peeled off from the semiconductor chip 90.
An object of the present invention is to solve the above-described problems and to supply an ultrasonic wire bonder that is less likely to cause stress concentration on a joint surface.
[0011]
[Means for Solving the Problems]
To achieve the above object, a bonding tool that presses a bonding wire against a metal film, an ultrasonic horn that transmits ultrasonic vibration to the bonding tool, and an ultrasonic vibration that transmits ultrasonic vibration to the ultrasonic horn. An ultrasonic wire bonder that welds the bonding wire and the metal film by ultrasonic vibration, and includes a pull-in prevention tool for fixing the bonding wire adjacent to the bonding tool, and a free end of the bonding wire. The side is configured to be pressed and fixed to the metal film with the pull-in prevention tool .
[0012]
The bonding wire may be fixed by piercing the bonding wire with the tip of the pull-in prevention tool or by crushing the bonding wire with the tip of the pull-out prevention tool .
The pull-in prevention tool may have a spring mechanism, and the bonding wire may be pressed and fixed to the metal film with the spring mechanism.
The pull-in prevention tool moves in conjunction with the bonding tool, the bonding tool presses the bonding wire before the pull-in prevention tool, and then the pull-in prevention tool fixes the free end side of the bonding wire. Good.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing the principal part of an ultrasonic wire bonder according to a first embodiment of the present invention.
The wire clamp 4 is fixed to the arm 1, the wire holder 5 is fixed to the wire clamp 4, the bonding tool holder 8 is fixed to the ultrasonic horn 2, and the bonding tool 7 is fixed to the bonding tool holder 8. An aluminum wire 6 is supplied via the wire holder 5. Further, the pull-in preventing tool holder 9 is fixed to the tip of the arm 1, and the pull-in preventing tool 10 is fixed to the tip of the pull-in preventing tool holder 9. On the table 24, a substrate 23 to which the semiconductor chip 21 and the external lead-out terminal 22 are fixed (for example, an insulating substrate to which a patterned conductive foil is fixed) is set.
[0014]
A wire 6 supplied from a wire supply unit (not shown) is supplied to the bonding tool 7 via the wire clamp 4 and the wire holder 5, and the bonding tool 7 and the anti-retraction tool 10 are lowered simultaneously, or the table 24 , The wire 6 is pressurized with the bonding tool 7, and the free end side of the wire 6 is fixed with the pull-in prevention tool 10.
[0015]
Next, ultrasonic vibration is applied to the wire 6 from the ultrasonic vibration generating unit (not shown) via the ultrasonic horn 2, the bonding tool holder 8, and the bonding tool 7, thereby bonding the wire 6 and the semiconductor chip 21. . Next, while supplying the wire 6, it moves to the upper part of the external lead-out terminal 22, performs the same bonding to the external lead-out terminal 22, and the semiconductor chip 21 and the external lead-out terminal 22 are electrically connected by the wire 6. Further, at the rear part of the bonding tool 7, a wire clamp 4 for fixing the wire 6 and a wire cutter 3 for cutting the wire 6 are provided. Moreover, the bonding tool 7 or the table 24 has an elevating mechanism and a moving mechanism in a horizontal plane, and can move relatively up and down and left and right. Some apparatuses have a rotation mechanism.
[0016]
The pull-in prevention tool 10 described above is a needle as shown in FIG. 2A or a thin plate as shown in FIG.
The method of fixing the free end side of the wire 6 can be achieved by piercing the tip of the needle in FIG. 2A into the wire 6 and making a needle-like hole in the wire 6 to fix it, or by fixing the tip of the thin plate in FIG. Then, the wire 6 is crushed and fixed. In order to reduce damage to the semiconductor chip 21 by the pull-in preventing tool 10, the contact area between the pull-in preventing tool 10 formed of a needle or a thin plate and the wire 6 is made smaller than the contact area between the bonding tool 7 and the wire 6. .
[0017]
Also, the wire 6 is pressed by the pull-in prevention tool 10 and the bonding tool 7 by moving the ultrasonic horn 2 moving in conjunction with the arm 1 up and down through the arm 1 and a portion not shown. In that case, the bonding tool 7 is adjusted so as to press the wire 6 ahead of the pull-in prevention tool 10. In this way, by the tip of the prevention tools 10 pull the tip of bonderized I ring tool 7 moves while holding the relative position, securely fixed to the free end of the wire 6 by preventing tool 10 retracted, and The damage to the semiconductor chip 21 can be reduced.
[0018]
Thus, by fixing the free end of the wire 6, that Ki constraints on front and rear sides of the wires 6 out be equal. Further, ultrasonic vibration, that the wire 6 is moved so as child prevented in the direction of the wire holder 5. As a result, the stress of the joint surface can be made uniform on the front side and the rear side, and stress concentration is suppressed. By suppressing the stress concentration, it is possible to prevent cracks from being introduced into the semiconductor chip 21.
[0019]
FIG. 3 is a block diagram showing the principal part of an ultrasonic wire bonder according to a second embodiment of the present invention.
The difference from FIG. 1 is that a spring mechanism 11 is provided on the upper part of the pull-in prevention tool holder 9 and the wire 6 is pressed and fixed by the force of the spring. In this case, there is an advantage that the pressure applied to the wire 6 of the pull-in prevention tool 10 can be set to an arbitrary magnitude. The effect is the same as that of the first embodiment.
[0020]
【The invention's effect】
According to the present invention, by fixing the free end of the wire with the pull-in prevention tool, the pressure applied by the bonding tool can be reduced and damage to the semiconductor chip can be reduced. In addition, by making the restraining conditions of the front side and the rear side equal on the bonding surface between the wire and the semiconductor chip, stress can be dispersed and damage to the semiconductor chip can be reduced.
[0021]
Further, by using the ultrasonic wire bonder of the present invention, a highly reliable semiconductor device that can withstand severe power cycles can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing the configuration of the main part of an ultrasonic wire bonder according to a first embodiment of the present invention. FIG. 2 is a diagram showing the shape of a retracting tool, in which FIG. ) Is a plate-like view. FIG. 3 is a block diagram of the main part of an ultrasonic wire bonder according to a second embodiment of the present invention. FIG. 4 is a block diagram of a main part of a conventional ultrasonic wire bonder. In the figure which occurred, (a) is a diagram of the bonding location, (b) is a diagram showing the bonding surface A of (a), (c) is an enlarged view of the bonding location B of (a)
DESCRIPTION OF SYMBOLS 1 Arm 2 Ultrasonic horn 3 Wire cutter 4 Wire clamp 5 Wire holder 6 Wire 7 Bonding tool 8 Bonding tool holder 9 Retraction prevention tool holder 10 Retraction prevention tool 21 Semiconductor chip 22 External lead-out terminal 23 Substrate 24 Table

Claims (5)

A bonding tool that presses a bonding wire against a metal film; an ultrasonic horn that transmits ultrasonic vibration to the bonding tool; and an ultrasonic vibration generator that transmits ultrasonic vibration to the ultrasonic horn. In an ultrasonic wire bonder that welds the metal film with ultrasonic vibration,
A drawing-in prevention tool fixed adjacent to the bonding tool and fixing the free end side of the bonding wire; and a table that moves relative to the bonding tool,
An ultrasonic wire bonder, wherein a free end side of the bonding wire is pressed and fixed to the table side with the pull-in prevention tool. The ultrasonic wire bonder according to claim 1, wherein the bonding wire is fixed by piercing the tip of the pull-in prevention tool into the bonding wire. The ultrasonic wire bonder according to claim 1, wherein the bonding wire is fixed by crushing the bonding wire with a tip of the pull-in prevention tool. The ultrasonic wire bonder according to claim 1, wherein the pull-in prevention tool has a spring mechanism, and the bonding wire is pressed and fixed by the spring mechanism. The pull-in prevention tool moves in conjunction with the bonding tool, the bonding tool presses the bonding wire before the pull-in prevention tool, and then the pull-in prevention tool fixes the free end side of the bonding wire. The ultrasonic wire bonder according to claim 1.

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