JP2001230272A - Flip chip with lead-free solder multilayer bump and lead-free flip chip assembly - Google Patents

Abstract

(57) Abstract: A flip chip having a lead-free solder multilayer bump formed on an Al electrode and a lead-free flip chip assembly using the same are provided. An Au pedestal is melted on an Al electrode of an IC chip by using a wire bonder.
To form Next, a flip chip having a lead-free solder multilayer bump 10 is formed on the Au pedestal 12 by a lead-free solder bump 13 on which a lead-free solder thin wire melted by a wire bonder is superimposed. Further, the Cu pad 21 arranged on the circuit board 2 and the flip-chip lead-free solder multilayer bump 10 are melt-bonded by an ultrasonic thermocompression bonding method to obtain a lead-free flip-chip assembly. There is no concern about the weakness of the strength due to the Au diffusion at the joints of the assembly, and the lack of precision in the height of the bumps formed by the wire bonder is ensured by ultrasonic thermocompression bonding as bumps of uniform height.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an IC chip mounting technique, and more particularly, to a flip chip bump formation and mounting technique.

[0002]

2. Description of the Related Art The mounting technology of an IC chip having a flip chip structure is based on a bare chip A, which is a post-process of semiconductor manufacturing.
It can be divided into a means for forming a bump on an electrode and processing it into a flip chip, and a means for joining a flip chip and a circuit board in an assembly process of electronic device production.
Flip chips are procured by electronic device manufacturers, who are users of flip chips, by forming a metal thin film layer of Au or the like on the Al electrode of the bare chip purchased by the user by a vacuum process, and then applying a plating method or solder balls on this. It is not common to perform bump processing using a method or the like, and it follows supply from a semiconductor manufacturer. For this reason, the degree of freedom on the user side is restricted, and the cost of the IC chip is unavoidably increased.

Next, a typical means for joining a flip chip to a circuit board will be outlined. As a method of joining the flip chip of the solder bump and the circuit board, a soldering board that has a bonding pad on the circuit board in advance, prints solder paste on the pad of this circuit board, heats and melts the solder, and joins the two together It can be said that this method has the most accumulated technology. However, as IC chips become more highly integrated and finer,
Today, the electrode pitch of the LSI chip is narrowed to the unit of 100 μm, and the printing accuracy of the solder paste is limited. In addition, there is an urgent need to switch to a bonding material that does not contain lead from the viewpoint of protecting the global environment.

As a method of connecting a flip chip of an Au bump and a circuit board, there is a method of using a thermosetting conductive adhesive or an anisotropic conductive film to contact both contacts. The advantage of this method is that it is environmentally friendly because it does not contain lead in the bonding material, and it does not require cleaning to remove the flux after bonding. However, improvements are being made to ensure the uniformity of the height of the Au bumps, the flatness of the circuit board, and the shortening of the thermosetting time.

As a recent construction method, there is a method of bonding a flip chip having an Au bump and a circuit board having an Au pad by an ultrasonic thermocompression bonding method. The joining principle is the same as that of wire bonding, which is a known technique, in which a flip chip is vibrated by ultrasonic waves to apply a load, and an Au bump of the flip chip is joined to an Au pad of the circuit board. This method eliminates the need for lead-free and flux, and can provide stable bonding with low electrical resistance. However, it imposes a load on the production process of applying the Au surface treatment to the pads of the circuit board.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to help lead-free production of electronic equipment.
An object of the present invention is to provide a flip chip having a lead-free solder bump formed on an Al electrode of a chip by a simple method, and a lead-free flip chip assembly using the flip chip having the lead-free solder bump.

[0007]

SUMMARY OF THE INVENTION A first object of the present invention is to provide a flip chip having a lead-free solder bump. The flip chip has an Au pedestal formed on an Al electrode of a bare chip, and is formed so as to overlap with the Au pedestal. The problem is solved by providing a flip chip having a lead-free solder multilayer bump characterized by comprising a lead-free solder bump.

In order to form the above-described lead-free solder multilayer bump, an Au pedestal is formed on the Al electrode of the bare chip using an ultrasonic thermocompression bonding method, and is superposed on the Au pedestal in the same manner as described above. A simple method of forming a lead-free solder multilayer bump, in which a lead-free solder bump is formed by a crimping method, is used.

A second object of the present invention is to provide a lead-free flip-chip assembly, and to provide an assembly structure in which a flip-chip having the above-mentioned lead-free solder multilayer bump is joined to a circuit board using Cu as a wiring conductor. And providing a lead-free flip-chip assembly, wherein a Cu pad arranged at a predetermined position on a circuit board and a lead-free solder multilayer bump of the flip chip mounted on the Cu pad are melt-bonded. To solve the problem.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to FIGS. FIG. 1 shows the general steps of one embodiment of the present invention. FIG. 2 is a schematic diagram showing a process of ultrasonic thermocompression bonding using a wire bonder for forming a lead-free solder multilayer bump on a bare chip according to the first embodiment.

First, a flip chip having a lead-free solder multilayer bump according to claim 1 will be described with reference to FIGS. In the first step of the process (FIG. 1-a), I
An Au pedestal 12 is formed on the Al electrode 11 of the C chip 1.

The Au wire 3 is passed through a capillary tube 4 made of tungsten carbide or glass, which is called a capillary 4 of a wire bonder. Au coming out of the tip of the capillary 4
The thin wire 3 is discharged from the discharge electrode 5 to melt the Au thin wire 3 (FIG. 2A).

A melted into a ball at the tip of the capillary 4
The u thin wire 31 is guided to the Al electrode 11 of the IC chip 1, and ultrasonic vibration and a load are applied (FIG. 2B). Thereafter, the capillary 4 is moved to cut the Au fine wire 3. By this vibration and pressure, the Au pedestal 1 is placed on the Al electrode 11 of the IC chip 1.
2 is formed (FIG. 2-c).

The Au pedestal 12 is formed by forming the Au fine wire 3
The main parameters are the diameter, the frequency of the ultrasonic vibration and the pressure. In the embodiment of the present invention in which the diameter of the Au thin wire 3 is 40 μm, the frequency of the ultrasonic vibration is 60 KHz, and the pressure is 300 g, a good Au pedestal is used for a 90 μm square Al electrode 11 which is a general IC chip electrode size. 1
2 was formed.

In the second step (FIG. 1-b), the lead-free solder bump 13 is superposed on the Au pedestal 12 formed as described above to form the lead-free solder multilayer bump 10. The formation of the lead-free solder bump 13 is the same except that a thin wire of lead-free solder is used instead of the Au fine wire 3 in the formation of the Au pedestal 12.
The details of the bump formation process are omitted.

The main parameters for forming the lead-free solder bump 13 are the diameter of the lead-free solder fine wire, the frequency of ultrasonic vibration, and the pressure. In the embodiment in which the Sn-3Ag solder fine wire having a diameter of 40 μm is used as the lead-free solder fine wire, the ultrasonic vibration is 60 KHz, and the pressure is 300 g, the lead-free solder bump 13 superposed on the Au pedestal 12 is formed. The formation of a flip chip having solder multilayer bumps 10 has been confirmed.

In the third step (FIG. 1-c), the IC chip 1 is led onto the Cu pad 21 arranged at a predetermined position on the circuit board 2, and the pad 21 and the lead-free solder multilayer bump of the IC chip 1 are formed. Position 10 and place. Although illustration is omitted, a flux is applied to the lead-free solder multilayer bump 10 of the IC chip 1 before mounting.

In the fourth step (FIG. 1-d), the chip 1 is heated and pressed from the die surface. By heating and pressing, the SnAg solder bump 13 at the tip of the lead-free solder multilayer bump 10 is melted, and the IC chip 1 and the circuit board 2 are joined. Finally, the flux residue is washed, and the assembly process of the lead-free flip chip assembly is completed. As a method of heating and pressurizing, the circuit board 2 may be heated with a hot plate or the like, and a load may be applied from the chip 1 side.

In the embodiment in which the die surface of the IC chip 1 is heated at 250 ° C. for 5 seconds and a load of 50 g per bump is applied to the IC chip 1, a stable bonding strength without Au diffusion at the bonding portion and good electric power are obtained. Confirmed assembly structure with resistance.

The lead-free solder multilayer bump 10 described above
Variations in the bump height that occur during the formation process of the multi-layer bump 1 during the bonding of the IC chip 1 and the circuit board 2 described above.
0 is absorbed by melting. IC chip 1
The stress on the joint generated due to the difference in thermal expansion between the substrate and the circuit board 2 can be absorbed by the plastic deformation of the columnar multilayer bump 10 in which the Au pedestal and the SnAg solder are laminated.

[0021]

The present invention has the following effects as described in the embodiment as an example. ADVANTAGE OF THE INVENTION The lead-free flip-chip assembly by this invention does not have the concern of Au diffusion which arises in the solder joint part of a flip chip and a circuit board, and can ensure the intensity | strength of the stable joining. Further, it is possible to compensate for uncertain joining caused by insufficient precision of the bump height formed by using the wire bonder, and to provide a highly reliable assembly structure. Further, the simple method of forming a lead-free solder multilayer bump provided by the present invention is intended to alleviate restrictions when an electronic device manufacturer procures an IC chip.
The range of choice of chips can be widened, which can contribute to lower prices and shorter delivery times. Further mentioning the effects of the present invention,
The lead-free solder multilayer bump flip chip and the lead-free flip chip assembly using the same contribute to the protection of the global environment.

[Brief description of the drawings]

FIG. 1 is a process chart in one embodiment of the present invention.

FIG. 2 is a schematic diagram of forming a lead-free solder multilayer bump using a wire bonder.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 IC chip 10 Lead-free solder multilayer bump 11 Al electrode 12 Au pedestal 13 Lead-free solder bump or SnAg solder bump 2 Circuit board 21 Pad 3 Au thin wire 31 Melted Au thin wire 4 Capillary 5 Discharge electrode

Claims (2)

[Claims] 1. An IC chip having a flip-chip structure, comprising: an Au pedestal formed on an Al electrode of a bare chip; and a lead-free solder bump formed so as to overlap the Au pedestal. Flip chip with solder multilayer bumps. 2. An assembly structure in which a flip chip having a lead-free solder multilayer bump according to claim 1 is joined to a circuit board using Cu as a wiring conductor, wherein the Cu pad is arranged at a predetermined position on the circuit board. And a lead-free solder multilayer bump of the flip chip mounted on the Cu pad, which is fusion-bonded.