JP2001313307A - Flip chip having multistage bump and flip-chip assembly using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device in which the connection reliability of flip chips and a flip-chip assembly, in which the flip chips are mounted on a circuit board is improved. SOLUTION: On the electrodes 11 of an IC chip 1, the flip chips having multistage bumps 13 each of which is composed of a bump skeleton section 13a, and a bump buffer connecting section 13b are formed by the ball-bonding method. At formation of the flip-chip assembly 3 in which the flip chips are mounted on the circuit board 2, the bumps 13 are aligned with and jointed to the pads 21 of the circuit board 2 by applying a thermosetting insulating adhesive 22 to the circuit board 2 and pressing the chip 1 and board 2 against each other, while the adhesive 22 is being heated. The connection reliability between the bumps 13 and pads 12 is improved, by correcting the uneven heights of the bumps 13 and the insufficient flatness of the board 1 through the deformation of the connection sections 13b caused, when the chip 1 and board 2 are pressed against each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for forming a bump on an electrode of an IC chip by a ball bonding method using a thin metal wire and a technique for mounting a flip chip on a circuit board.

[0002]

2. Description of the Related Art One of the methods for forming bumps on electrodes of an IC chip is a ball bonding method using a wire bonder. This method is widely known as a simple method of forming bumps that can be handled by manufacturers of electronic devices without semiconductor production facilities. First, formation of a bump by a ball bonding method will be described with reference to the schematic diagram of FIG. Next, a conventional technique of forming a flip chip assembly by mounting a flip chip provided with a bump by a ball bonding method on a circuit board will be outlined with reference to a schematic diagram of FIG.

As shown in FIG. 3A, a thin metal wire 44 is passed through a thin tube called a capillary 41 of a wire bonder 4 made of glass or the like. Next, the discharge electrode 4 of the wire bonder 4
2 is applied with a high voltage. This high voltage causes the discharge electrode 42
A discharge current flows between the thin metal wire 44 protruding from the tip of the capillary 41 and the portion of the fine metal wire 44 protruding from the tip of the capillary 41 is melted to form a spherical molten portion 44a shown in FIG.

Next, as shown in FIG. 3C, the capillary 41 is lowered, and the molten portion 44a of the thin metal wire 44 located at the tip of the capillary 41 is pressed against the electrode 11 of the IC chip 1. At the same time, the capillary 41 is vibrated, and the IC chip 1 is heated from below using a hot plate or the like (not shown). As a result, the molten portion 44a of the thin metal wire 44 is joined to the electrode 11 of the IC chip 1.

Subsequently, as shown in FIG. 3D, the capillary 41 is pulled upward by sandwiching the thin metal wire 44 by the clamper 43 of the wire bonder 3. By this operation, the thin metal wire 44 is cut off near the top of the molten portion 44a. The bumps 12 are formed on the electrodes 11 of the IC chip 1 by a series of operations of the wire bonder 4 described above.

A flip chip functions as an electric circuit when mounted on a circuit board. Next, one method of mounting an IC chip having bumps formed by the above-described ball bonding method on a circuit board will be described.

FIG. 4 shows a mounting method using an insulating adhesive. The circuit board 2 is provided with electrodes (hereinafter referred to as pads 21) for bonding to the bumps 12 of the IC chip 1, and the bumps 12 are connected to the pads 21. And press it (FIG. 4-a).
The bumps 12 and the pads 21 are electrically connected by contact with each other, and the electrical connection is mechanically held by an insulating adhesive 22 applied to a gap between the IC chip 1 and the circuit board 2 (FIG. 4). b).

[0008]

Here, a detailed observation of the method of mounting the flip chip on the circuit board using the insulating adhesive shown in FIG. 4 shows that the top of the bump 12 by the ball bonding method is a conventional one. As described above as a technique, it is a terminal portion where the thin metal wire 44 is torn off, and the tip is thin and sharp at an irregular height.

Since electrical connection is achieved by the point contact between the top of the bump 12 having such a shape and the pad 21 of the circuit board 2, the connection of the bumps 12 having irregular heights is uncertain. For this reason, a method has been adopted in which the tops of the bumps are pressed with a metal plate or the like to level the height of the bumps.

[0010] However, the circuit board to be connected also has a warp or the like, and if the flatness of the circuit board is not sufficiently ensured, the connection becomes unreliable and there is a concern about the reliability of flip-chip mounting. become.

The present invention has been made in order to solve such a problem of the electric connection, and a flip chip having bumps for correcting irregular bump heights and flatness of a circuit board, and a flip chip having the same structure. It is an object to provide a semiconductor device with high connection reliability by a flip chip assembly mounted on a circuit board.

[0012]

An IC chip for providing a semiconductor device with high connection reliability is an IC chip having a flip-chip structure.
A flip chip having a multi-staged bump, which is a C chip, comprising a bump pivot portion joined to an electrode of an IC chip and an inverted L-shaped bump buffer connection portion following the bump pivot portion. In forming an electric circuit in which the bump buffer connection portion is brought into contact with an electrode of a circuit board, the bumper has an effect of correcting unevenness in the height of the bumps and insufficient precision in flatness of the circuit board.

[0013] A flip chip assembly that provides higher bonding reliability is an assembly in which the flip chip is mounted on a circuit board, wherein the flip chip and the circuit board are bonded using a thermosetting insulating adhesive. The contact between the bump of the flip chip and the electrode of the circuit board is held by the thermosetting insulating adhesive.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a flip chip having bumps of a multi-stage structure according to the present invention and a flip chip assembly in which the flip chip is mounted on a circuit board will be described with reference to the drawings.

FIG. 1 is a cross-sectional view of a flip chip having a bump having a multi-stage structure according to the present invention (FIG. 1A), and a cross-sectional view (FIG. 1-b to 1-c) are schematically shown. FIG. 2 is a schematic view showing a main part of a process of forming a bump having a multi-stage structure.

FIG. 3 is a schematic view showing a process of forming a bump by a conventional ball bonding method. FIG. 4 schematically shows a main part of a conventional flip chip assembly in which an IC chip formed by a conventional ball bonding method is mounted on a circuit board using an insulating adhesive. In FIGS. 1 and 2, parts corresponding to those shown in FIGS. 3 and 4 are denoted by the same reference numerals.

First, the process of forming the bumps of the flip chip having the bumps of the multistage structure according to the first invention will be described. The first of the steps follows the conventional ball bonding method described above with reference to FIG.
3B, a thin metal wire 44 is passed through the capillary 41, and then a high voltage is applied to the discharge electrode 42.

The discharge generated in the discharge electrode 42 and the thin metal wire 44 protruding from the tip of the capillary 41 causes the thin metal wire 4
4 is melted. Discharge electrode 42 and thin metal wire 44
The melting of the thin metal wire 44 can be controlled by adjusting the interval between the tips and the voltage and application time applied to the discharge electrode 42.

The shape of the molten portion 44a of the thin metal wire 44 changes depending on the product of the applied voltage and time. Metal wire 44
A 20 μm diameter Au thin wire is used for the discharge electrode 42 and the Au
Set the interval between the tips of the fine wires to a predetermined value and set the applied voltage to 2k.
In the embodiment in which the application time is 5 ms, the tip of the Au thin wire is melted into a spherical shape having a diameter of about 60 μm.

In the second step, the fine metal wire 4 described above is used.
4 of the spherical molten portion 44a and the electrode 1 of the IC chip 1
1 and, at the same time, a bump pivot portion 13a which is a lower structure of the bump 13 having a multi-stage structure is formed. As shown in FIG. 2A, the electrode 11 of the IC chip 1 is located immediately below the molten portion 44a.
Is arranged, and the molten portion 44 a is pressed against the electrode 11 by descending the capillary 41.

Further, the capillary 41 is vibrated by ultrasonic waves, and at the same time, the IC chip 1 is heated, so that the thin metal wires 44 are formed.
Is fused to the electrode 11 of the IC chip 1. This fused portion 44a becomes the bump pivot portion 13a that constitutes the bump 13 having the multi-stage structure shown in FIG.

By the pressing of 300 g and the ultrasonic vibration of 60 KHz, the above-mentioned melted portion having a diameter of about 60 μm is shaped into a pivot portion of a bump having a diameter of about 80 μm, and the four sides of 100 μm as a general electrode of an IC chip. It will be suitable for shaped electrodes.

In a third step, the bump pivot 13
A thin metal wire 44 continuing from the top of a is terminated into an inverted L-shape to form a bump buffer connection portion 13b constituting the multi-stage bump 13. This is formed by the fine movement operation of the capillary 41, and this is shown in FIG.

First, the capillary 41 is pulled up to a predetermined position in the vertical direction, and then moves horizontally and stops at a predetermined distance. By this operation, the thin metal wire 44 is drawn out by a length corresponding to the movement of the capillary 41 from the vertical direction to the horizontal direction.

Next, the thin metal wire 44 is sandwiched by the clamper 43, and the capillary 41 is moved again in the extending direction (horizontal direction). By this movement, the inner surface of the tip end of the capillary 41 catches and cuts the thin metal wire 44 to form the bump buffer connection portion 13b.

The amount of movement of the capillary 41 is minute, and the amount of movement in the vertical and horizontal directions is
In the case where the diameter of each of the metal wires 4 is approximately twice as large, the cutting position of the thin metal wire 44 is near the upper portion 13z of the outer edge of the bump pivot 13a. Therefore, there is no fear of contact with the adjacent bump.

In this manner, the bump 13 having a multi-stage structure including the bump pivot portion 13a and the bump buffer connection portion 13b is formed. In the embodiment using a thin Au wire having a diameter of 20 μm, a bump buffer connection portion 13 b having a vertical portion of 40 μm and a horizontal portion of 40 μm is formed on a bump pivot portion having a diameter of 80 μm.

The formation of the flip chip assembly using the multi-stage bumps according to the second invention will be described with reference to FIG. In the first of the assembling steps, a thermosetting insulating adhesive 22 (hereinafter referred to as an adhesive 22) is applied to the circuit board 2. As shown in FIG. 1B, a predetermined amount is applied near the center of the portion where the IC chip is mounted, avoiding the pad 21. Further, multi-point coating may be performed depending on the size of the IC chip and the number of bumps.

In the second part of the assembling step, the first part of the assembling step is performed.
The IC chip 1 (FIG. 1-a) provided with the bumps 13 having a multi-stage structure is disposed face-down directly on the circuit board 1 according to (1). Thereafter, the positions of the electrodes 11 of the IC chip 1 and the pads 21 of the circuit board 2 are aligned, and the IC chip 1 is placed on the circuit board 2 as shown in FIG. Due to this pressing, the adhesive 22 applied in the first step of the assembly process wraps around substantially the entire gap between the IC chip 1 and the circuit board 2.

In the third part of the assembling step, the second part of the assembling step is performed.
To heat the assembly of the IC chip 1 and the circuit board 2.
By curing the adhesive 22, the IC chip 1 and the circuit board 2
Are fixed, and the electrical contact between the bumps 13 of the multi-stage structure of the IC chip 1 and the pads 21 of the circuit board 2 is maintained.

The bump 13 having a multi-stage structure thus formed
The flip-chip assembly 3 using the flip-chip having the above-mentioned structure has a structure in which the bumps 13 of the IC chip 1 are irregular in height or the flatness of the circuit board 2 is distorted. The portion 13y is plastically deformed by pressing and corrected, and the electrode 1 of the IC chip 1 is corrected.
1 and the electrical connection between the pads 21 of the circuit board 2 are ensured.
FIG. 1C schematically shows the correction of the distortion 2z of the circuit board 2 due to the deformation of the vertical portion 13y.

Further, since the horizontal portion 13x of the bump buffer connection portion 13b makes surface contact with the pad 21 of the circuit board 2, a stable electrical connection with low contact resistance can be obtained.

[0033]

As described above in detail, according to the present invention, the unevenness of bump height and the lack of flatness of the circuit board, which is one of the imperfections of the prior art, between the flip chip and the circuit board, are compensated for and the connection is made. A highly reliable semiconductor device can be manufactured. In addition, a stable connection with low contact resistance can be obtained in electrical connection. Furthermore, the effect of compensating for the uneven bump height and the flatness of the circuit board according to the present invention can contribute to increasing the yield of products and reducing costs. The bump having a multi-stage structure, which is a feature of the present invention, can be formed by a simple method that inherits the steps of the conventional ball bonding method, and the flip chip assembly according to the present invention can be formed by a simple method using an adhesive. Therefore, the semiconductor device according to the present invention can be provided without using any particular technology and equipment.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing one embodiment of a flip chip having bumps of a multi-stage structure and a flip chip assembly using the flip chip.

FIG. 2 is a schematic cross-sectional view showing, as an embodiment, a main part of a process of forming a bump having a multi-stage structure.

FIG. 3 is a schematic cross-sectional view showing the formation of a bump by a conventional ball bonding method.

FIG. 4 is a schematic cross-sectional view showing a conventional method of assembling a flip chip assembly using a thermosetting insulating adhesive.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 IC chip 11 Electrode 12 Bump 13 Multi-layer structure bump 13a Bump central part 13b Bump buffer connection part 13x Horizontal part of bump buffer connection part 13b 13y Vertical part of bump buffer connection part 13b 13z Near upper part of outer edge of bump central part 13a 2 Circuit Board 2z Distortion of Circuit Board 21 Pad 22 Thermosetting Insulating Adhesive 3 Flip Chip Assembly with Multi-Stage Bump 4 Wire Bonder 41 Capillary 42 Discharge Electrode 43 Clamper 44 Fine Metal Wire 44a Melted Part

Claims (2)

[Claims] 1. An IC chip having a flip chip structure, comprising: a bump pivot portion joined to an electrode of the IC chip; and an inverted L-shaped bump buffer connection portion continuing from the bump pivot portion. Flip chip with multi-stage bumps. 2. The assembly according to claim 1, wherein the flip chip is mounted on a circuit board, wherein the flip chip and the circuit board are joined using a thermosetting insulating adhesive. A flip chip assembly, wherein contact of electrodes on a substrate is held by the thermosetting insulating adhesive.