JPH0837191A - Bump forming method - Google Patents

Abstract

PURPOSE:To prevent the contact between adjacent bumps by substantially completely eliminating the dispersion in height between the bumps formed on pads on a board. CONSTITUTION:After a bump 7 is formed on pads 1 for an IC die 2 by a wire bonding method, the residual part 3a of a metal wire remained integrally with the bump 7 is emitted with laser light ray 9, thereby cutting the part 3a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bump forming method, and is suitable for application to, for example, forming bumps of an integrated circuit with bumps.

[0002]

2. Description of the Related Art Conventionally, when forming bumps on pads of an integrated circuit (IC) die (also called a chip),
The following method, which is an improvement of the wire bonding method, was used.

That is, according to this method, as shown in FIG. 5, an IC die 102 having a plurality of pads 101 is mounted on a heatable predetermined base of a predetermined wire bonding apparatus (not shown). To do. This IC die 102
A capillary 104 through which the gold wire 103 is passed is provided above the. Reference numeral 105 indicates an electrode for spark generation.

Prior to wire bonding, the electrode 1
05 is applied with a predetermined voltage to generate a spark, and the tip of the gold wire 103, which has come out of the capillary 104, is melted into a ball shape, which is then re-solidified so that the gold wire 103 has a gold tip. The ball 106 is formed.

Next, after the gold ball 106 is pressure bonded onto the pad 101 of the IC die 102 by ultrasonic thermocompression bonding, the capillary 104 is pulled up while the gold wire 103 is clamped, and the gold wire 103 is torn off. Thus, as shown in FIG. 6, each pad 10
The bump 107 is formed on the surface 1.

In the bumps 107 thus formed on each pad 101, the remaining portion 1 of the gold wire 103 is formed.
03a remains with this. This remaining portion 103a
Since the height of the bump 107 is usually different for each bump 107, the height of the bump 107 including the remaining portion 103a varies. Therefore, as shown in FIG. 7, a shaping rod 10
8 hit the upper part of the bump 107 with a predetermined pressure to make the height of the bump 107 uniform, or, as shown in FIG. The height of the bumps 107 is made uniform by pulling the gold wires 103 upward and tearing them off.

[0007]

However, in the method of striking the upper portion of the bump 107 with the rod 108 in order to align the heights of the bumps 107 formed on the pads 101 as described above, the bumps 108 are struck by the rod 108. There is a problem that it is not possible to completely eliminate the variation in height between the bumps 107 because the corners of the bumps 107 contacted with the adjacent bumps 107 or the number of taps is insufficient or excessive. .

Further, in the method of laterally shifting the capillaries 104, corners are generated in the bumps 107 at the shifted positions, so that it is not possible to completely eliminate the height variation between the bumps 107, and the adjacent bumps 107 are not formed. There has been a problem such as contact with.

Therefore, an object of the present invention is to almost completely eliminate the height variation between bumps formed on each pad on a substrate and to prevent contact between adjacent bumps. It is to provide a bump forming method.

[0010]

In order to achieve the above object, the present invention forms bumps (7) on a pad (1) provided on one main surface of a substrate (2) by a wire bonding method. In the bump forming method as described above,
A metal ball (6) integrally formed with the metal wire (3) is crimped onto the pad (1) at one end of the metal wire (3), and the metal wire (3) is moved in a direction away from the substrate (2). The metal wire (3) is cut by making the laser beam (9) on the remaining portion (3a) of the metal wire (3) left integrally with the metal ball (6) after cutting.
It is characterized in that the remaining portion (3a) of the metal wire (3) is cut by irradiating with.

In the present invention, the metal ball is preferably formed under the condition that the metal wire is not cut right above the metal ball when the metal wire is cut.

In a preferred embodiment of the present invention,
The substrate is held so that the main surface of the substrate faces downward when the remaining portion of the metal wire is irradiated with the laser beam.

In another preferred embodiment of the present invention, when the remaining portion of the metal wire is irradiated with the laser beam, the substrate is held so that the main surface of the substrate is on the lower side and the laser beam is irradiated. The remaining portion of the metal wire cut by is sucked by the suction means provided below the substrate.

In still another embodiment of the present invention, when the remaining portion of the metal wire is irradiated with the laser beam, the substrate is held so that the main surface of the substrate is on the lower side, and the laser beam is irradiated. The remaining portion of the cut metal wire is gripped by the chuck means and a force in the direction of separating from the substrate is applied. Here, the force applied by the chuck means is such that the remaining portion of the metal wire is not pulled upward when the remaining portion of the metal wire is heated by being irradiated with a laser beam, and the bump does not cause mechanical destruction. Is.

In the present invention, the laser beam is preferably a laser beam generated by a high power laser, specifically, a laser beam generated by, for example, a YAG laser.

In the present invention, the metal wire is a tin wire, a solder wire, a copper wire or the like in addition to a gold wire. Also, the substrate is, for example, an integrated circuit die.

[0017]

According to the bump forming method of the present invention configured as described above, the remaining portion of the metal wire left after the metal wire is cut by pulling the capillary upward while clamping the metal wire is used. Since the remaining portion of the metal wire is cut by irradiating the laser beam, the height of the bump on each pad can be aligned with the same precision as the laser beam irradiation position precision. Therefore, the variation in height between the bumps on each pad can be almost completely eliminated. Further, contact between bumps on each pad can be prevented.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In all the drawings of the embodiments, the same or corresponding parts are designated by the same reference numerals.

1 to 3 show an embodiment of the present invention.
In this embodiment, as shown in FIG. 1, first, an IC die 2 having a plurality of pads 1 is placed on a heatable predetermined base of a predetermined wire bonding apparatus (not shown). A capillary 4 through which a gold wire 3 is passed is provided above the IC die 2. Code 5
Indicates an electrode for generating a spark.

Prior to wire bonding, the electrode 5
A spark is generated by applying a predetermined voltage to the tip of the gold wire 3 that has come out of the capillary 4, and is made into a ball shape. 6 is formed. In this embodiment, a gold wire 3 having a diameter of 30 μm is used, and a spark of 0.1 μs is generated to form the gold ball 6.

Here, if the spark current is increased, the gold ball 6 formed by melting the gold wire 3 becomes larger. Further, if the spark time is lengthened, the remaining portion 3a of the gold wire 3 when the gold wire 3 is torn off becomes longer as described later. In this embodiment, the remaining time 3a of the gold wire 3 is set longer by increasing the spark time when forming the gold ball 6.

Next, after the gold ball 6 formed as described above is pressure bonded onto the pad 1 on the IC die 2 by ultrasonic thermocompression bonding, the capillary 4 is pulled up while the gold wire 3 is clamped. , Tear off the gold wire 3. In this way, bumps 7 are formed on each pad 1, as shown in FIG. In this case, the remaining portion 3a of the gold wire 3 is left above the bumps 7 for a long time.

Next, as shown in FIG. 3, the IC die 2 is turned upside down by a turning mechanism (not shown) so that the bumps 7
Is on the lower side, and the IC die 2 is held in this state. The upside down of the IC die 2 is specifically performed as follows, for example. That is, for example, after the center of the main surface of the IC die 2 on the bump 7 side is attracted by a vacuum chuck and the IC die 2 is turned upside down, the other main surface of the IC die 2 is attached by another vacuum chuck. Adsorb,
After that, the suction of the main surface on the bump 7 side may be released.

Next, the YAG laser 8 provided in the wire bonding apparatus is moved parallel to the side of the IC die 2 as shown by the arrow in FIG. Irradiation is applied to a portion of the bump 7 formed on each pad 1 of the die 2 near the root of the remaining portion 3a of the gold wire 3, and the remaining portion 3a is cut. At this time, the cut remaining portion 3a is
It falls down as it is. Here, the output of the laser beam 9 is 1 W, for example. The YAG laser 8 is moved parallel to the side of the IC die 2 by, for example, a guide (not shown) attached to a base on which the IC die 2 is placed.

FIG. 4 shows the IC die 2 after cutting the remaining portion 3a of the gold wire 3 of each bump 7 as described above. As shown in FIG. 4, the height of each bump 7 is substantially constant regardless of the size of the gold ball 6 used to form the bump 7.

As described above, according to this embodiment, each pad 1 on the IC die 2 is formed by the wire bonding method.
After the bumps 7 are formed on the bumps 7, the remaining portion 3a of the gold wire 3 left integrally with the bumps 7 is cut by irradiating the laser beam 9, so that the height of each bump 7 is adjusted by the laser beam 9. It is possible to align with the same accuracy as the irradiation position accuracy, and thereby it is possible to almost completely eliminate the height variation between the bumps 7. It is also possible to prevent contact between the adjacent bumps 7. Thus, mounting with a high yield can be performed in a post process after bump formation.

Although one embodiment of the present invention has been specifically described above, the present invention is not limited to the above embodiment, and various modifications can be made based on the technical idea of the present invention. .

For example, in the above-described embodiment, the IC
By turning the die 2 upside down and irradiating and cutting the remaining portion 3a of the gold wire 3 with the laser beam 9 in a state where the bump 7 is on the lower side, the remaining portion 3a does not drop onto the IC die 2. However, without turning the IC die 2 upside down, the remaining portion 3a of the gold wire 3 is cut by irradiation of the laser beam 9, and the remaining portion 3a falling on the IC die 2 is blown off by, for example, air blow. Good.

Further, the cutting of the remaining portion 3a of the gold wire 3 by the irradiation of the laser beam 9 does not necessarily have to be performed in the wire bonding apparatus. For example, after the bump 7 is formed in the wire bonding apparatus, I
The C die 2 may be moved to a predetermined laser beam irradiation device different from the wire bonding device, and the remaining portion 3a of the gold wire 3 may be cut by the irradiation of the laser beam in this laser beam irradiation device.

[0030]

As described above, according to the present invention,
Since the remaining part of the metal wire left integrally with the metal ball is irradiated with a laser beam to cut it,
Height variations between bumps on each pad can be almost completely eliminated, and contact between adjacent bumps can be prevented.

[Brief description of drawings]

FIG. 1 is a perspective view illustrating a bump forming method according to an embodiment of the present invention.

FIG. 2 is a perspective view illustrating a bump forming method according to an embodiment of the present invention.

FIG. 3 is a perspective view illustrating a bump forming method according to an embodiment of the present invention.

FIG. 4 is a schematic diagram showing a bump formed by a bump forming method according to an embodiment of the present invention.

FIG. 5 is a perspective view for explaining a conventional bump forming method.

FIG. 6 is a perspective view for explaining a conventional bump forming method.

FIG. 7 is a perspective view for explaining a conventional bump forming method.

FIG. 8 is a perspective view for explaining a conventional bump forming method.

[Explanation of symbols]

 1 Pad 2 IC Die 3 Gold Wire 3a Remaining Part 4 Capillary 6 Gold Ball 7 Bump 8 YAG Laser 9 Laser Beam

Claims (9)

[Claims] 1. A bump forming method in which a bump is formed on a pad provided on one main surface of a substrate by a wire bonding method, wherein a metal ball integrally formed with the metal wire is provided at one end of the metal wire. Crimping onto the pad, cutting the metal wire by moving the metal wire in a direction away from the substrate, and irradiating the remaining portion of the metal wire left integrally with the metal ball after the cutting with a laser beam. The bump forming method is characterized in that the remaining portion of the metal wire is cut by doing so. 2. The bump forming method according to claim 1, wherein, when the metal wire is cut, the metal ball is formed under the condition that the metal wire is not cut right above the metal ball. 3. The substrate is held so that the main surface of the substrate faces downward when the remaining portion of the metal wire is irradiated with the laser beam. The method for forming bumps as described above. 4. The substrate is held so that the main surface of the substrate faces downward when the remaining portion of the metal wire is irradiated with the laser beam, and is cut by irradiating the laser beam. The bump forming method according to claim 1 or 2, wherein the remaining portion of the metal wire is sucked by a suction means provided below the substrate. 5. The substrate is held by holding the substrate so that the main surface of the substrate faces downward when the remaining portion of the metal wire is irradiated with the laser beam, and is cut by irradiating the laser beam. 3. The bump forming method according to claim 1, wherein the remaining portion of the metal wire is gripped by chucking means to apply a force in a direction away from the substrate. 6. The bump forming method according to claim 1, wherein the laser beam is a laser beam generated by a high-power laser. 7. The bump forming method according to claim 6, wherein the laser is a YAG laser. 8. The bump forming method according to claim 1, wherein the metal wire is a gold wire, a tin wire, a solder wire or a copper wire. 9. The bump forming method according to claim 1, wherein the substrate is an integrated circuit die.