JP2653482B2 - IC lead connection method - Google Patents

Description

The present invention relates to a method for connecting a lead such as an inner lead of a film carrier to a chip-like IC.

(B) Conventional Techniques In recent years, mounting techniques for electronic components have been developed in accordance with demands for downsizing and thinning of electronic devices, and various mounting forms have been devised and implemented. For example, TAB (Tape Automated Bondin)
There is a bonding method that connects the IC chip directly to the lead of the circuit board, such as a film carrier method called g). This film carrier method has the following features, and is mainly used in LSIs and VLSIs having a large number of terminals and in fields where small size and thinness are required.

Simultaneous batch bonding can be performed regardless of the number of bonding pads.

Thin mounting with a thickness of about 0.5 to 0.8 mm is possible.

The mechanical strength of the lead is large (more than 5 times the Au wire of 30 μmφ).

A film carrier can be used as a hybrid IC substrate.

The process can flow in a tape between two rolls.

IC operation test can be performed on the film carrier.

In the case of the film carrier method, bumps are generally formed when an IC chip is bonded to leads formed on a carrier film, but are classified into several methods depending on the form. FIGS. 3 to 6 show examples. In these figures, 1 is an IC chip, 2 is a passivation film, and 3 is a bonding pad.

The example shown in FIG. 3 is a so-called chip bump method, in which an Au bump is
11 are formed. In this way, bumps are formed on the IC chip side and bonded to the inner leads 7 of the film carrier. The barrier metal 10 is provided to prevent the generation of an Al-Au intermetallic compound by the bonding pad 3 and the bump 11 and to enhance the adhesion between the two. Generally, it is formed of a two-layer or three-layer metal thin film of Ti / W-Au, Ti-Pt-Au or Cr-Cu-Au. The lowermost layer of each layer is for adhesion and barrier with Al, and the intermediate layer is for barrier and
The uppermost layer is used for the Au plating base, and the uppermost layer is used for the Au plating base.

The example shown in FIG. 4 is based on the so-called BTAB method, in which a bump portion 12a is formed at the tip of a Cu lead 12, and an Au plating film is applied to the surface. In this manner, the bumped leads are bonded to the IC chip bonding pads 3.

The example shown in FIGS. 5 and 6 is based on the so-called transfer bump method, in which a plurality of bumps are arranged and formed in advance on a bump forming substrate, and the bumps on this substrate are
Figure example) or IC bonding pad (Figure 6 example)
Is transferred to a bumped lead or a bumped IC chip. In the example shown in FIG. 5, the leads 7 to which the bumps 13 have been transferred are bonded to the bonding pads 3 of the IC chip. In the example shown in FIG. 6, the leads 7 are bonded to the IC chip to which the bumps 13 have been transferred.

(C) Problems to be Solved by the Invention Each of the bonding methods described above has the following advantages and disadvantages, and the bonding must be performed by a method according to the characteristics.

The chip bump method has high reliability against corrosion since the Al pad (bonding pad) is not exposed. Bumps can be formed on a wafer basis. The permissible displacement is large, for example, the bonding pad pitch can be up to 80 μm. However, such processes as sputter etching for removing an Al oxide film, continuous deposition of two or three layers of barrier metal, and bump annealing at 300 ° C. for 30 minutes are required, and the bump formation process is complicated.

The BTAB method and the transfer bump method do not require a process of forming a bump on the IC chip side, but a part of the Al pad is exposed even after bonding, so there remains a problem in reliability. Also, BTAB
In the method, the cost is increased due to the formation of bumps on the leads, and so-called Si cratering is likely to occur on the IC chip side because of the hard Cu bumps. In the transfer bump method, bonding is performed substantially twice, so that the allowable amount of displacement is small,
For example, the pad pitch cannot be made finer than about 130 μm.

The object of the present invention is that the bonding pads are not exposed, so that the reliability is high, and bumps can be formed on a wafer basis.
It is an object of the present invention to provide an IC lead connection method which has the advantage of the chip bump method that the allowable amount of displacement is large, and eliminates the disadvantage of the chip bump method, which complicates the bump formation process.

(D) Means for Solving the Problems A lead connection method for an IC according to the present invention includes a bump forming step of forming a bump on a bonding pad of the IC via a metal thin film, and heating and pressing between the bump and the lead. A bonding step of thermocompression bonding between the bump and the lead and breaking the metal thin film to alloy-connect the bump to the bonding pad.

(E) Function In the IC lead connection method of the present invention, first, a bump is formed on a bonding pad of the IC via a thin metal film in a bump forming step. Therefore, the bonding pad is covered with this metal thin film. In the subsequent bonding step, the space between the bump and the lead is heated and pressurized, and the space between the bump and the lead is thermocompressed. At the same time, the bumps are plastically deformed, the thin metal film is broken, and the bumps are alloyed and connected to the bonding pads. As described above, the process of forming bumps on the IC chip side is necessary.However, unlike the chip bump method, sputter etching of the Al pad and bump annealing are unnecessary, and only one metal thin film is required. Extremely simplified.

(F) Embodiment FIGS. 1 (A) to 1 (H) and FIG. 2 show a procedure which is an embodiment of a method for connecting leads of an IC according to the present invention. In these figures, 1 is an IC chip, 2 is a passivation film, 3
Is an Al bonding pad, 6 is an Au bump, and 7 is a lead.

First, as shown in FIGS. 1 (A) and 1 (B), a noble metal such as Au or Pt is applied to the entire surface of the IC chip by sputtering or vacuum evaporation to form a thin metal film 4 having a thickness of 1000 to 2000 mm.
To form Subsequently, as shown in FIG. 2C, a photoresist film 5 is applied, and an opening H is formed at a position where a bump is to be formed by photolithography. Then metal thin film 4
Is used as a common electrode, and Au is electroplated at about 5 mA / cm ² to grow Au bumps 6 in the openings. Subsequently, the photoresist film (5) is removed with a solvent as shown in FIG. Thereafter, a photoresist film 8 is first formed on the entire surface as shown in FIG.
An area slightly larger than the opening of the pad 3 is left. Subsequently, as shown in (G) and (H), the metal thin film 4 is etched and the resist film 8 is removed to complete a series of bump forming steps.

FIG. 2 shows a state in which the bumps are formed on the IC chip and the inner leads of the film carrier are bonded to the bumps. In the bonding, the positioning of the leads and the bumps is performed, and the bonding is performed by a heating / pressing head at a constant temperature and a constant load. At this time lead 7
The Au plating film formed on the surface and the Au bump 6 are thermocompression-bonded. Further, the bump 6 is plastically deformed and the metal thin film layer 4 is formed.
And the Au bump 6 and the Al pad 3 are directly alloyed and connected. If an oxide film is formed on the surface of the Al pad, this oxide film is also broken, and the Au bump is directly connected to the Al pad.

(G) Effects of the Invention As described above, according to the present invention, the reliability of the bonding pad against corrosion is enhanced since the bonding pad surface is covered with the metal thin film even after the bonding is completed. In addition, since the number of times of bonding is one, there is a large tolerance for misalignment, and ICs with a fine bonding pad pitch
Also applicable to In addition, only one metal thin film is required. Sputter etching for removing the oxide film on the bonding pad surface and bump annealing for improving the adhesion between the bump and the bonding pad via the barrier metal are required. Is simplified.

[Brief description of the drawings]

1 (A) to 1 (H) and FIG. 2 are views showing a method for connecting leads of an IC according to an embodiment of the present invention. FIGS. 1 (A) to 1 (H) show a bump forming step, and FIG. The figure shows the respective bonding steps. FIG. 3 to FIG.
FIGS. 3A and 3B show a method of connecting leads of an IC, FIG. 3 shows a chip bonding method, FIG. 4 shows a BTAB method, and FIGS. 5 and 6 show a transfer bump method. 1 ... IC chip, 2 ... Passivation film, 3 ... Al pad (bonding pad), 4 ... Metal thin film, 6 ... Au bump, 7 ... Lead.

Claims (1)

(57) [Claims] A bump forming step of forming a bump on a bonding pad of an IC via a metal thin film; heating and pressurizing the bump and the lead to thermocompression-bond the bump and the lead; and breaking the metal thin film. A bonding step of alloying connecting the bump to the bonding pad.