JP2770041B2 - Bump forming method and semiconductor element connecting method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for connecting a semiconductor element represented by a semiconductor chip to a mounting board.

[Prior Art] FIG. 4 shows a schematic structure of a conventional method of connecting a semiconductor element by bumps. 1 is a semiconductor element, 2 is a mounting board, 3 is a semiconductor element or a solder bump formed on the mounting board,
Reference numeral 4 denotes electrodes of the semiconductor element 1 and the mounting substrate 2, which are AA '.
Indicates the center of the semiconductor element.

The connection is performed by heating and melting the solder bumps 3 and is a batch connection, so that the workability is superior to the wire connection method, and the wire connection and TAB (Tape Automate) are performed.
It has the feature that the number of connection terminals can be greatly increased as compared with the case where the electrode arrangement is limited to the periphery of the IC chip as in the d bonding method.

However, in this method, due to the temperature change, the fifth
As shown in the figure, a dimensional deviation B due to a difference in thermal expansion between the semiconductor element 1 and the mounting substrate 2 occurs, causing a shear strain in the solder bump 3 and lowering the connection reliability. Since the shear strain increases with an increase in the distance between the solder bump 3 and the center of the semiconductor element 1, the area where the solder bump 3 can be arranged is limited due to the allowable shear strain of the solder bump 3, so that the number of terminals is increased and the area is increased. Is difficult to apply to semiconductor devices.

As a means for reducing the shear strain of the solder bumps, a method using a wiring board having a thermal expansion coefficient close to that of the semiconductor element can be considered. However, since the material of the mounting substrate is limited, a semiconductor element having a different thermal expansion coefficient is used. There are drawbacks such as the inability to mix. On the other hand, means for increasing the height of the solder bump to reduce shear strain has been proposed. As this means, there is a method of forming a multi-stage bump by laminating solder bumps supported by a polyimide film (Japanese Patent Application Laid-Open No. 62-293730). There is a disadvantage that the price increases due to an increase in the number of manufacturing steps.

FIG. 6 shows a semiconductor element structure in which solder bumps are brought into contact with each other by pressure to obtain electrical connection. In FIG. 6, solder bumps 3 are formed on respective electrodes 4 of the semiconductor element 1 and the mounting substrate 2. Pressure is applied to the solder bumps 3 by the shrinkage force of the resin 5 at the time of curing, and the solder bumps 3 are brought into mechanical contact to establish electrical connection.

However, in this connection structure, if the height of the solder bumps 3 varies, there are places where electrical connection cannot be obtained.
In addition, since the expansion coefficient of the resin 5 is larger than that of the solder bumps, when a temperature change occurs, the pressure is weakened, and the contact of the solder bumps 3 becomes unstable.

[Problems to be Solved by the Invention] It is an object of the present invention to provide a bump connection method which is highly reliable even when the thermal deformation strain as described above is generated and which enables fine connection. An object of the present invention is to easily and surely connect without using an equal connection medium.

Means and Action for Solving the Problems According to the present invention, at least one of an electrode of a semiconductor element and an electrode of a mounting substrate is provided with a protruding electrode (bump) made of a superelastic alloy.
Forming a bump by heating ultrasonic method, and heating the electrode of the semiconductor element and the electrode of the mounting board via the protruding electrode (bump) made of the superelastic alloy formed by the above-described method. This is a method for connecting semiconductor elements, which is joined by an acoustic method.

In connecting the semiconductor element and the mounting board, a protruding electrode (bump) made of a superelastic alloy may be formed on one of the electrode of the semiconductor element and the electrode of the mounting board, or both may be made of a superelastic alloy. After the projection electrodes (bumps) are formed, they may be joined together.

 The heating ultrasonic method is performed as follows.

Ultrasonic waves are input into a mounting substrate or a semiconductor element using a columnar ceramic or the like as an input medium. In a heating furnace, when an ultrasonic wave is input by applying pressure so that the electrode and the bump and the bump contact each other, the ultrasonic wave is transmitted to the superelastic bump through the mounting substrate or the semiconductor element and the electrode. Ultrasonic vibration energy is converted to friction energy at the interface between the electrode and the bump and between the bumps,
Each is ultrasonically pressed. By inputting ultrasonic waves in a heating furnace, the temperature can be raised to a temperature equal to or higher than the temperature set in the heating furnace at the bumps or at the interface between the bumps and the metal electrodes, and the joining efficiency can be increased. When joining the bumps, the bumps may have the same composition or different compositions. In particular, when the component of the bump on the other side contains an element that easily diffuses in the bump on the other side, the ultrasonic bonding may be further facilitated.

As the superelastic alloy that can be connected by the heating ultrasonic method used in the present invention, an alloy having a relatively low melting point (500 to 800 ° C.) such as Au—Cd, Au—Cu—Zn, or Cu—Zn—Sn is used. Suitable, but high melting point (1000 ℃ or higher) superelastic alloy such as Ti-Ni, Cu-Al-Ni alloy, or low melting point (300 ℃ or lower) such as In-Tl, In-Cd, In-Pb Can also be used.

As described above, the protruding electrodes (bumps) made of a superelastic alloy are formed on the electrodes of the semiconductor element or the mounting board by the heating ultrasonic method, and the bumps or one bump and the other electrode are formed by the heating ultrasonic method. By implementing the connection structure for joining, connection can be easily performed without using a connection medium such as solder. Also, because it uses a superelastic alloy,
Thermal deformation distortion can be compensated only by elastic deformation including superelastic deformation, and a highly reliable connection in which the bump material is not broken by flexibly following external distortion can be realized.

[Examples] Next, the present invention will be described based on examples shown in the drawings.

Example 1 FIG. 1 shows a cross section of a semiconductor device having connection bumps. In the figure, 1 is a semiconductor element, 2 is a mounting substrate, 4 is an Al electrode, and 6 is a superelastic bump.

 The connection bump forming method of the present invention will be described.

A columnar super-elastic bump 6 made of a Au-Cd alloy is bonded on the Al electrode 4 of the semiconductor element by a heating ultrasonic method. 200
Ultrasonic waves (output: 0.2 W) are input from the superelastic bump side through the ceramic chip 10 while applying pressure to the semiconductor element in the vertical direction in a heating furnace at ℃, and the Al electrode 4 of the semiconductor element and Au
-Join the Cd alloy superelastic bump. Then, the mounting substrate 2
The electrodes 4 are aligned with the superelastic bumps 6 formed on the semiconductor element 1, and the mounting substrate and the semiconductor element are pressed in a heating furnace at 200 ° C. in a direction perpendicular to the mounting substrate. Ultrasonic waves (0.2 W) are input from the side through the ceramic chip 10 to join the superelastic bumps 6 and the electrodes 4 of the mounting substrate 2. The composition of the Au-Cd alloy is selected to be Au-49.5 at% Cd which exhibits superelasticity at a temperature higher than room temperature. With such a structure, the superelastic bump of this example had an elastic strain of 7%, and the electrical contact was maintained even when the temperature cycle of 0 to 150 ° C. was repeated 1,000 times.

Embodiment 2 FIG. 2 shows an embodiment in which connection bumps are formed on both electrodes of a semiconductor element and electrodes of a mounting substrate.
1 is a semiconductor element, 2 is a mounting substrate, 4 is an Al electrode, and 7 is a superelastic bump. On the Al electrode 4 of the semiconductor element 1, a spherical Au-Cu
The superelastic bump 7 made of -Zn alloy is put together in a heating furnace at 180 ° C. while applying pressure in a direction perpendicular to the semiconductor element.
Ultrasonic waves (0.3 W) are input from the superelastic bump side through the ceramic chip 10, and the electrode 4 of the semiconductor element and the Au-Cu-Zn
Join and form super elastic bumps. The composition of Au-Cu-Zn alloy is Au-27at% Cu-47at which shows superelasticity at room temperature or higher.
% Zn is selected. Also, the superelastic bumps 7 of the same component are bonded and formed on the Al electrode 4 of the mounting substrate 2 in the same manner by inputting ultrasonic waves from the mounting substrate side, and then the two superelastic bumps are connected to each other from the mounting substrate side. Bonding is performed by inputting ultrasonic waves (0.2 W) through the ceramic chip 10. With such a structure, the present superelastic bump has an elastic strain of 6%, and the electrical contact is maintained even when the temperature cycle of 0 to 150 ° C. is repeated 1000 times.

Third Embodiment FIG. 3 shows an embodiment in which different types of superelastic bumps are respectively formed on electrodes of a semiconductor element and electrodes of a mounting substrate. 1 is a semiconductor element, 2 is a mounting board, 4 is
Al electrodes 8, 9 are superelastic bumps. Al of semiconductor element 1
A superelastic bump 8 made of a columnar Cu-Zn-Sn alloy is placed on the electrode 4 in a heating furnace at 200 ° C while applying pressure in a direction perpendicular to the semiconductor element from the superelastic bump side to the ceramic chip.
Ultrasonic waves (0.2 W) are input through 10 and joined to the electrodes 4 of the semiconductor element 1. As the composition of the Cu-Zn-Sn alloy, Cu-34.7wt% Zn-3.0wt% Sn which exhibits superelasticity at a temperature higher than room temperature is selected. Also, a columnar Au-Cu-Zn alloy superelastic bump 9 is bonded and formed on the Al electrode 4 of the mounting substrate 2 in the same manner by inputting ultrasonic waves (0.2 W) from the mounting substrate side. The two superelastic bumps are joined by inputting ultrasonic waves (0.3 W) through the ceramic chip 10 from the mounting substrate side. As the composition of the Au-Cu-Zn alloy, Au-27at% Cu-47at% Zn, which exhibits a superelastic effect at a temperature higher than room temperature, is selected.

With such a structure, the Cu-Zn-Sn superelastic bump has 2% elastic strain, and the Au-Cu-Zn superelastic bump has 6% elastic strain.
The electrical connection was maintained even when the temperature cycle of 0 to 150 ° C. was repeated 1000 times.

[Effects of the Invention] As described above, the present invention uses a superelastic alloy as a bump for connecting a semiconductor element, and heats the bonding between the mounting substrate and the superelastic bump, the semiconductor element and the superelastic bump, and the bonding between the superelastic bumps. It is characterized by using an ultrasonic method. By using this superelastic bump, heating and ultrasonic waves are jointly used to join the semiconductor element and the mounting board, it is possible to join at a low temperature that does not have a thermal effect on the semiconductor element, and it is caused by a temperature change Flip-chip bonding with high reliability against distortion and variations in bump height due to thermal stress was easily realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a state in which a semiconductor element and electrodes of a mounting board are connected by a heating ultrasonic method via columnar Au-Cd superelastic bumps. FIG. 2 is a cross-sectional view in which spherical Au—Cu—Zn superelastic bumps formed on the electrodes of the semiconductor element and the electrodes of the mounting board are connected by a heating ultrasonic method. FIG. 3 shows a columnar Cu—Zn—
Au-Cu- composed of Sn superelastic bumps and electrodes on the mounting board
It is sectional drawing which connected Zn super elastic bump by the heating ultrasonic method. 4 to 6 are cross-sectional views of a conventional semiconductor device and a mounting board connected by solder bumps. FIG. 4 shows a normal state, and FIG. 5 shows a mounting board due to a temperature change. FIG. 6 is a view showing a state in which the solder bumps are expanded and shear strain is introduced into the bumps. FIG. 6 is a view showing a semiconductor element structure in a case where the solder bumps are brought into contact with each other by pressure and solidified with a resin. DESCRIPTION OF SYMBOLS 1 ... Semiconductor element, 2 ... Mounting board, 3 ... Solder bump, 4
... Metal electrode, 5 ... Resin, 6 ... Au-Cd superelastic bump (columnar), 7 ... Au-Cu-Zn superelastic bump (spherical), 8 ... Cu-
Zn-Sn superelastic bump (columnar), 9 ... Au-Cu-Zn superelastic bump (columnar), 10 ... ceramic chip.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoshio Ozeki 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture New Nippon Steel Corporation 1st Technical Research Institute (72) Inventor Keisuke Watanabe 1-7-7 Toranomon, Minato-ku, Tokyo No. 12 Oki Electric Industry Co., Ltd. (72) Inventor Takashi Kanamori 1-7-1, Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd. (72) Inventor Yasuo Iguchi 1-7-7 Toranomon, Minato-ku, Tokyo No. 12 Oki Electric Industry Co., Ltd. (56) Reference JP-A-2-58346 (JP, A) JP-A 64-81264 (JP, A) JP-A 63-106979 (JP, A) JP 62-258675 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 21/60 H01L 21/321

Claims (2)

(57) [Claims] 2. A bump forming method, comprising: forming a projecting electrode (bump) made of a superelastic alloy on at least one of an electrode of a semiconductor element and an electrode on a surface of a mounting substrate by a heating ultrasonic method. 2. The method according to claim 1, wherein the electrodes of the semiconductor element and the electrodes of the mounting board are joined by a heating ultrasonic method via bumps (bumps) made of a superelastic alloy formed by the method of claim 1. How to connect semiconductor elements.