JP2001284388A - Wire bonding method - Google Patents

Abstract

(57) Abstract: Provided is a wire bonding method capable of suppressing the length of a tail formed on a bump after secondary bonding, increasing the bonding strength of a secondary bonding portion, and reducing the mounting area. In a wire bonding method for connecting two connection electrodes with a wire, a connection electrode (2) on a secondary side is used in advance.
The bumps 7 are formed thereon by a tearing method, and the primary bonding is performed on the connection electrodes 4 on the primary side, and then the secondary bonding is performed on the bumps 7. By performing the secondary bonding position within a distance range W from the center position of the bump 7 to the wire diameter of the wire 5 and not more than the radius of the bump 7, the initial tail 7a is formed on the bottom surface 6b of the capillary 6, and the wire hole is formed. It is prevented from entering the hole 6a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire bonding method for connecting two connection electrodes with a wire.

[0002]

2. Description of the Related Art As shown in FIG.
When connecting the bonding pad 4 of the IC chip 3 mounted on the substrate 1 with the Au wire 5, the primary bonding is performed on the bonding pad 4 and the wiring 2 of the substrate 1 is formed.
Usually, secondary bonding is performed. Conversely, primary bonding may be performed on the wiring 2 of the substrate 1 and secondary bonding may be performed on the bonding pads 4 of the IC chip 3.

However, when the wiring 2 or the bonding pad 4 as the secondary electrode is poor in bonding property, sufficient bonding strength with the wire 5 cannot be obtained, and the wire 5 is separated from the secondary electrode. There is a problem of doing it. Electrodes having poor bonding properties include, for example, Cu, Ni, and flash Au.
Examples of the electrode include an electrode formed of a material having poor bonding properties such as plating, an electrode having a large surface roughness, an electrode having a projection on its surface, and an electrode having a sloped surface.

Therefore, as a method of improving the bonding strength of wire bonding to a secondary electrode having poor bonding properties, as shown in FIG. 2, a bump 7 is formed on the secondary electrode 2 in advance. A method of performing secondary bonding on the bump 7 has been proposed in, for example, Japanese Patent Application Laid-Open No. 3-183139. The method for forming the bumps 7 is shown in FIG.
As shown in (1), after bonding is performed on the electrode 2 using the capillary 6 to form the bump 7, the wire 5 is pulled upward, and the wire 5 is torn off from the bump 7 and cut off. At this time, a tail 7 a is formed on the bump 7.

[0005]

However, in the conventional method, since the secondary bonding is performed at the center position of the bump 7 as shown in FIG. 4, the tail 7a enters the wire hole 6a of the capillary 6 and is joined. There is a problem that a long tail 7b is generated after the next bonding. Also,
The length of the tail 7b varies greatly. Therefore, the long tail 7b causes a short circuit with other wiring, the tail 7b protrudes from the package, and further, the wire is cut in the wire hole 6a of the capillary 6,
In some cases, a failure such as the ball being unable to be formed and the device being stopped may occur.

Therefore, the wire hole 6a of the capillary 6
Wire hole 6a so that the tail 7a does not enter
Japanese Patent Application Laid-Open No. Hei 10-335368 proposes a method of performing secondary bonding by projecting the outside from the bump 7. In this case, it is possible to prevent the tail 7a from entering the wire hole 6a at the time of the secondary bonding, but the bonding strength of the secondary bonding portion is not high, and the mounting area becomes large, which is disadvantageous in miniaturization. There was a disadvantage that it was.

Accordingly, an object of the present invention is to reduce the length of a tail formed on a bump after secondary bonding,
An object of the present invention is to provide a wire bonding method capable of increasing the bonding strength of a next bonding portion and reducing the mounting area.

[0008]

Means for Solving the Problems To achieve the above object, the invention according to claim 1 uses a capillary having a wire hole for leading out a wire and a bottom surface provided around the wire hole, In a wire bonding method for connecting a wire from a primary connection electrode to a secondary connection electrode, a step of forming a bump on the secondary connection electrode in advance by a tearing method using a first wire; Performing a primary bonding using a second wire derived from the capillary on a secondary connection electrode;
Performing a secondary bonding on the bump using the second wire, wherein the secondary bonding is performed by:
A wire bonding method is provided wherein the bottom surface of the capillary is brought into contact with a tail portion formed when the bump is torn, and the center of a wire hole of the capillary is positioned on the bump.

In the secondary bonding, the bottom of the capillary is brought into contact with the tail formed when the bump is torn,
In addition, since the center of the wire hole of the capillary is positioned on the bump, the tail portion remaining on the bump does not enter the wire hole of the capillary and is joined, and a long tail does not occur after the secondary bonding. . Moreover, the tail part formed on the bump contacts the bottom surface of the capillary, and the tail can be crushed by the bottom surface of the capillary to form the bump. In the present invention, the center of the wire hole of the capillary is bumped. Since the secondary bonding is performed so as to be positioned above, the second wire and the bump are securely bonded, and the bonding strength of the secondary bonding portion can be increased. Further, since the capillary does not need to protrude greatly outside the bump, the mounting area can be reduced and the size can be reduced.

It is desirable that the center of the wire hole of the capillary at the time of the secondary bonding be located within a distance range from the center position of the bump to the wire diameter or more and the bump radius or less. In this case, bonding is performed by offsetting the center of the capillary and the center of the bump by the above distance, so that the tail remaining on the bump can be reliably prevented from entering the wire hole of the capillary, and the tail can be securely held at the bottom of the capillary. Can be molded into

As the capillary used in the secondary bonding, it is desirable to use a capillary having a bottom surface having a diameter equal to or larger than the diameter of the bump.
That is, even when the center of the capillary (the center of the wire hole) is at a maximum distance (bump radius) from the center position of the bump, the tail can be reliably formed.

[0012]

5 and 6 show an example of a wire bonding method according to the present invention. In this example, the connection electrodes on the primary side are bonding pads 4 of the IC chip 3,
The connection electrode on the secondary side is the wiring 2 of the substrate 1,
This wiring 2 is an electrode having poor bonding properties. As shown in FIG. 5A, the wire 5 is bonded on the wiring 2 of the substrate 1 by the capillary 6. Then, the capillary 6 is pulled up, and the bump 7 is formed by a tearing method.
(B)). At this time, a tail 7 a is formed on the bump 7. Next, as shown in FIG. 5C, after the primary bonding is performed on the bonding pads 4 of the IC chip 3, the secondary bonding is performed on the bumps 7. At this time, as shown in FIG.
Is performed within a distance range W from the wire line diameter to the bump radius from the center position of. Therefore, the tail 7 a of the bump 7 does not enter the wire hole 6 a of the capillary 6, and the tail 7 a
It is crushed and molded by b. In FIG. 6, the center of the capillary 6 is offset from the center of the bump 7 to the opposite side (right side) to the looped wire 5, but may be offset to the same side (left side) as the looped wire 5. Alternatively, it may be offset in a direction intersecting with the looping. Next, as shown in FIG. 5D, when the capillary 7 is pulled up and the wire 5 is torn, the tail 7b generated after the secondary bonding is short and the length variation is small. Thereafter, discharge is performed between the wire 5 protruding from the tip of the capillary 7 and the torch 9 to form the ball 10. Therefore, the next bump 7 can be formed without stopping the wire bonding apparatus.

FIG. 7 shows the results of an experiment comparing the lengths of the tails during the secondary bonding. In this experiment, the wire diameter of the wire 5 was set to 20 μm, and the radius of the bump 7 was set to 40 μm. The horizontal axis in FIG. 7 indicates the distance between the center position of the bump 7 and the center position of the capillary 6, and the vertical axis indicates the length of the tail 7b generated after the secondary bonding. As is clear from FIG.
When the center position of the bump 7 and the center position of the capillary 6 substantially match (conventional), the length of the tail is about 20
The distance between the center position of the bump 7 and the center position of the capillary 6 is 20 μm.
When the thickness is set to μm to 40 μm (the present invention), the tail 7b
Was 50 μm or less, and no device stoppage occurred. When the distance between the center position of the bump 7 and the center position of the capillary 6 was set to 50 μm or more (Comparative Example), that is, when the secondary bonding was performed at a position separated by more than the radius of the bump 7, the device stopped frequently. As described above, by performing the secondary bonding in the distance range W from the center position of the bump 7 to the wire diameter or more and the bump radius or less, the operation and effect thereof are proved.

FIG. 8 shows the results of an experiment comparing the bonding strength during secondary bonding. Also in this experiment, the diameter of the wire 5 was set to 20 μm, and the radius of the bump 7 was set to 40 μm. FIG.
Is the distance between the center position of the bump 7 and the center position of the capillary 6, and the vertical axis is the bonding strength of the secondary bonding portion. When the center position of the bump 7 substantially coincides with the center position of the capillary 6 (conventional), while the bonding strength is low, the distance between the center position of the bump 7 and the center position of the capillary 6 is 20 μm or less. When the thickness was 40 μm (the present invention), the bonding strength was twice or more that of the related art. Furthermore, when the secondary bonding was performed at a position separated by more than the radius of the bump 7 (comparative example), the bonding strength was reduced to about half as compared with the present invention, and the bonding strength was insufficient. Therefore, the effect of the present invention was also demonstrated in terms of bonding strength.

In FIG. 5, the connection electrode on the primary side is connected to the IC chip 3.
The connection electrode on the secondary side is the wiring 2 on the substrate 1. The connection electrode on the primary side is the wiring 2 on the substrate 1, and the connection electrode on the secondary side is the bonding pad 4 on the IC chip 3. It may be. When a plurality of IC chips 3 are arranged adjacent to each other, the primary connection electrodes may be used as bonding pads of the IC chip, and the secondary connection electrodes may be used as bonding pads of another IC chip. . Further, the present invention can also be used for wire bonding between connection electrodes in the same chip or the same substrate.

In the above embodiment, the first wire for forming the bump and the second wire for looping are made of the same metal (for example, Au-Au, Au alloy-Au alloy, Cu-C
u), and may be a dissimilar metal (Au-Au alloy, Au-Cu, Au alloy-Cu or vice versa). That is, the capillary formed at the time of bump formation and the capillary used for the secondary bonding do not need to be the same capillary. However, when the same kind of metal is used, the bump formation and the bonding can be performed successively with the same capillary. Also, the wiring material and the bonding pad of the IC chip may be the same metal or different metal as the bump material and the wire for looping.

In the present invention, the bottom surface of the secondary bonding capillary may not be flat and may not be parallel to the connection electrode. Further, the bottom surface does not need to be point-symmetrical with respect to the wire hole. At least 2
At the time of the next bonding, it suffices if the bottom of the bump can be pressed and molded at the bottom.

[0018]

As is apparent from the above description, according to the present invention, the secondary bonding on the bump is performed by contacting the bottom surface of the capillary with the tail formed when the bump is torn, and by using the wire of the capillary. Since the center of the hole is located on the bump, the tail generated during the formation of the bump can be reliably prevented from entering the wire hole of the capillary, and the tail can be reliably formed on the bottom surface of the capillary. Therefore, the length of the tail generated after the secondary bonding is suppressed, and the length variation can be reduced. Also, since the secondary bonding was performed such that the bottom surface of the capillary was in contact with the tail portion of the bump and the center of the wire hole of the capillary was located on the bump, an electrode having poor bonding properties, which was difficult only with the secondary bonding, was used. However, there is an effect that wire bonding can be performed with sufficient bonding strength. Further, in the present invention, since the secondary bonding is performed so that the center of the wire hole of the capillary is located on the bump, the capillary does not protrude greatly outside the bump, the mounting area can be reduced, and the size of the device can be reduced. It is advantageous.

[Brief description of the drawings]

FIG. 1 is a diagram of an example of a conventional wire bonding method.

FIG. 2 is a diagram of another example of a conventional wire bonding method.

FIG. 3 is an enlarged view when a bump is formed.

FIG. 4 is an enlarged view at the time of conventional secondary bonding.

FIG. 5 is a process chart of an example of the wire bonding method of the present invention.

FIG. 6 is an enlarged view showing a main part of the wire bonding method of the present invention.

FIG. 7 is a comparison diagram of tail lengths of the present invention, a conventional example, and a comparative example.

FIG. 8 is a comparison diagram of bonding strength between the present invention, a conventional example, and a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Wiring 3 IC chip 4 Bonding pad 5 Wire 6 Capillary 6a Wire hole 6b Bottom surface 7 Bump 7a, 7b Tail

Claims (2)

[Claims] 1. A wire bonding method for connecting a wire from a primary connection electrode to a secondary connection electrode using a capillary having a wire hole for leading a wire and a bottom surface provided around the wire hole. Forming a bump on the secondary connection electrode in advance by a tearing method using a first wire; and forming a bump on the primary connection electrode using a second wire derived from the capillary. A step of performing a secondary bonding and a step of performing a secondary bonding on the bump using the second wire, wherein the secondary bonding is formed when the bottom surface of the capillary is torn off the bump. Wire bonding, wherein the wire bonding is performed by bringing the capillary into contact with a tail portion and positioning the center of a wire hole of the capillary on the bump. Law. 2. The wire according to claim 1, wherein, in the secondary bonding, a center of a wire hole of the capillary is located within a range from a wire center diameter to a bump radius from a center position of the bump. Bonding method.