JPH09135073A - Method of forming solder bump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently form fine bumps in sufficient level and even composition and shape at low cost by providing the three steps as follows, i.e., the first step of forming solder resist having aperture part, the second step of burying creamy solder in the aperture part and the third step of forming solder bumps only on electrode terminals. SOLUTION: A circuit board 5 made of glass epoxy wherein electrode terminals 2 are formed in the aperture part 1 of a solder resist 4 not to be in contact with the two sides of a solder resist 4 is prepared. Next, creamy solder is buried in the aperture part 1 of the solder resist 4 by sliding a squeegee. Next, the melted solder forms protruded electrode on the electrode terminals 2 by the surface tension thereof by heating the circuit board 5 using an infrared reflow furnace in nitrogen atmosphere so as to form solder bumps 3 by cooling down step for solidification. Finally, the electrodes of semiconductor chips and the solder bumps 3 formed on the circuit board 5 are aligned with one another.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming solder bumps on a circuit board for fixing a semiconductor chip on the circuit board.

[0002]

2. Description of the Related Art A flip chip mounting method, in which a semiconductor chip is mounted face down on a circuit board, and at the same time, electrical connection between the semiconductor chip and the circuit board is performed, has high mass productivity and connection reliability. It is known as a highly effective method.

When adopting such a flip chip mounting method, it is necessary to form a large number of solder bumps having a uniform composition and shape on the electrode terminals of the semiconductor chip and the circuit board, and such solder bumps can be manufactured at low cost. Therefore, there is a demand for an efficient method of forming.

As a method of forming solder bumps, a plating method in which component ions of solder are attached to electrode terminals of a semiconductor chip in an electrolytic solution by the principle of electroplating,
Vapor deposition method that evaporates solder component atoms in a vacuum and deposits them on electrode terminals, fusion method that fuses solder wires to electrode terminals using a method similar to wire bonding and then cuts this is known. However, it does not satisfy the above requirements.

On the other hand, the dropping method is known as a method capable of efficiently forming bumps having a uniform composition at low cost by using molten solder (Japanese Patent Laid-Open No. 60-240142).
No.). In this dropping method, as shown in FIG. 5, the solder 13 is melted in a container 12 equipped with a heater 11, and this molten solder is dropped from a nozzle 15 provided on the bottom of the container under the control of a piezo element 14. The solder bumps 16 are formed on the circuit board 17.

[0006]

However, in the dropping method, since the molten solder droplets are dropped from the nozzle onto the circuit board, acceleration is applied to the molten solder droplets and bumps are formed on the circuit board. Becomes a flat shape. Therefore, if you try to secure the height required for connection,
Since the volume becomes large, the area of the electrode terminal cannot be reduced, and it is difficult to increase the density of the circuit.

[0007]

In order to solve the above-mentioned problems, a method of forming a solder bump according to the present invention includes a method of forming a solder bump on a top surface of a circuit board having electrode terminals formed at positions facing the electrode terminals of a semiconductor chip. A step of forming a solder resist that has an opening that is separated for each electrode terminal of the circuit board and that exposes the electrode terminal and the circuit board around the electrode terminal; and a step of embedding cream solder in the opening, After the embedded cream solder is melted and then solidified, the solder bumps are formed only on the electrode terminals by the surface tension of the melted cream solder.

By the above method, it is possible to efficiently form minute bumps having a sufficient height and having a uniform composition and shape at low cost.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention includes an electrode terminal of a semiconductor chip, an electrode terminal formed on the upper surface of the circuit board, and an electrode terminal of the circuit board. And a step of forming a solder resist having an opening for exposing the electrode terminal and the circuit board around it, a step of embedding cream solder in the opening, and the embedded cream solder melted. After that, by solidifying, it comprises a step of forming solder bumps only on the electrode terminals due to its surface tension, and according to the above method, the opening of the solder resist is larger than the electrode terminals inside thereof, The molten solder produces bumps on the electrode terminals due to its surface tension, and the amount of solder supplied is controlled by the size of the opening. Variability without, uniform solder bumps composition and shape can efficiently formed at low cost, nor for bridging between further adjacent bumps.

An embodiment of the invention described in claim 1 of the present invention will be described below with reference to the drawings. FIG.
FIG. 2 is a plan view of a circuit board according to an embodiment of the present invention, FIG. 2 is a cross-sectional view after forming a solder bump on an electrode terminal of the circuit board, and FIG.
-A sectional drawing and FIG.2 (b) have shown BB sectional drawing in FIG.

1 and 2, 1 is an opening of a solder resist, 2 is an electrode terminal, 3 is a solder bump, 4 is a solder resist, and 5 is a circuit board. Here, the solder bump forming step and the flip chip mounting step will be specifically described based on the cross-sectional view taken along the line BB in FIG. 1 shown in FIG.

125 (W) × 170 (D) × 50 (T)
A circuit made of glass epoxy, in which the electrode terminal 2 of 80 (D) × 15 (T) μm is formed so as not to contact the two sides of the solder resist 4 in the opening 1 of the solder resist 4 formed with the dimension of μm. A substrate 5 is prepared (Fig. 4
(A)). Next, the cream solder 7 is embedded on the circuit board 5 by sliding the squeegee 6 into the opening 1 of the solder resist 4 (FIGS. 4A and 4B). The cream solder 7 used this time was 63Sn / 37Pb eutectic solder having an average particle diameter of 30 μmφ or less.

Next, by heating the circuit board 5 in an infrared reflow furnace in a nitrogen atmosphere, the melted solder forms the shape of a protruding electrode on the electrode terminal 2 by its own surface tension, and is solidified by cooling. Solder bumps 3 are obtained (FIG. 4 (c)). In this case, the obtained solder bump 3 has a semi-cylindrical shape so as to follow the electrode terminal 2 in the opening 1 of the solder resist 4, and the top of the solder bump 3 is higher than the solder resist 4 by 15 μm. Was given.

Next, as shown in FIG. 4D, the electrodes 9 of the semiconductor chip 8 and the solder bumps 3 formed on the circuit board 5 are aligned with each other and mounted face down to perform flip chip mounting. You can get the body.

FIG. 3 is a plan view of a circuit board according to another embodiment of the present invention. In FIG. 3, 1 is an opening of a solder resist, 2 is an electrode terminal, 4 is a solder resist, and 5 is a circuit board. Is. In this embodiment,
Although the solder bumps can be formed by the same process as the above, the solder bumps 3 can be formed higher than the above-described embodiment because the area of the electrode terminals 2 is small and is separated from the solder resist 4. It is a thing.

In the above-described embodiment, 63Sn / 37Pb eutectic cream solder is used for forming the solder bump, but the composition is not limited to this composition and the options are extremely wide. Furthermore, in the present embodiment, the electrode 9 on the semiconductor chip 8 has a projection shape, but it does not matter if it is not a projection shape.

[0017]

As described above, according to the present invention, there is no need for a special device, and the composition is uniform on the electrode terminals of the circuit board and has a sufficient height. The bumps can be formed at low cost and efficiently. The solder bumps formed in this way have a shape suitable for flip-chip mounting bonding, and furthermore, solder bumps can be applied even to glass epoxy substrates where flip-chip mounting was difficult due to the large warp and swell. The tolerance for flip-chip mounting is loosened by the height of itself, the mounting yield is improved, and the heat cycle resistance can be improved because the gap between the semiconductor chip and the circuit board is increased.

[Brief description of the drawings]

FIG. 1 is a plan view of a circuit board according to an embodiment of a solder bump forming method of the invention.

FIG. 2 is a sectional view of the circuit board.

FIG. 3 is a plan view of a circuit board according to another embodiment of the present invention.

FIG. 4 is a process sectional view showing an embodiment of a method for forming a solder bump according to the present invention.

FIG. 5 is a sectional view showing a conventional bump forming apparatus.

[Explanation of symbols]

 1 Solder Resist Opening 2 Electrode Terminal 3 Solder Bump 4 Solder Resist 5 Circuit Board 6 Squeegee 7 Cream Solder 8 Semiconductor Chip 9 Electrode

Claims (1)

[Claims] 1. An upper surface of a circuit board having electrode terminals formed at positions facing the electrode terminals of a semiconductor chip, respectively.
A step of forming a solder resist which is separated for each electrode terminal of the circuit board and has an opening exposing the electrode terminal and a circuit board around the electrode terminal; a step of embedding cream solder in the opening; A method of forming solder bumps, which comprises a step of forming solder bumps only on the electrode terminals by melting the solidified cream solder and then solidifying the cream solder.