JPH08293664A - Forming method for solder ball - Google Patents

Abstract

PURPOSE: To make the shape uniform and to improve the yield by coating the semispherical recess formed on a non-solder bondable base surface with solder paste, heating it to the melting temperature and then cooling it. CONSTITUTION: A plurality of semispherical recesses 1a, 1b, 1c and 1d for forming solder ball is formed on the surface of a non-solder bondable metal base 1 made, for example, iron or aluminum material. Then, the recessed 1a, 1b, 1c and 1d of the base 1 are coated with solder pastes 2a, 2b, 2c and 2d by screen printing method. The entire base 1 is introduced into a solder reflow furnace, and heated to the melting temperature. Thereafter, the pastes in the recesses 1a, 1b, 1c, 1d become molten solder 3a, 3b, 3c and 3d, which are naturally cooled without being bonded to the base 1. Thus, the molten solder is solidified to form solder balls 4a, 4b, 4c and 4d by the surface tension.

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 a solder ball used for connecting an electronic component such as a semiconductor chip or a ceramic substrate to a printed board via a solder ball.

[0002]

2. Description of the Related Art A joining structure for joining an electronic component such as a semiconductor chip or a ceramic substrate to a printed circuit board by using solder balls is shown in FIG.
To the terminals 6a, 6b, 6c of the solder balls 4a,
4b, 4c are placed, and an electronic component 7 such as a semiconductor chip or a ceramic substrate is further mounted thereon, and the connection terminals 8a, 8b, 8c of the electronic component 7 are connected to the solder balls 4a, 4c.
It is placed at a predetermined position so as to come into contact with b and 4c, and all of them are put in a solder reflow furnace and heated to the melting temperature of solder. According to the above bonding structure, the solder balls 4a, 4b, 4
The shape of c must have a uniform diameter close to a true sphere, and if it has a non-uniform diameter, the electronic component 5 tilts when placed in a solder reflow furnace and heated to the melting temperature of the solder,
For this reason, a solder bridge occurs in the adjacent terminal. Therefore, strict shape management is required to form the solder balls 4a, 4b, 4c and the like. Conventionally, as a method for forming such a solder ball, for example, as in the atomization method, each of the small droplets of the molten solder sprayed in the vacuum container together with nitrogen gas falls into a spherical shape due to the surface tension and falls from a predetermined shape. There is a method of selecting ones in the shape of.
However, such a method not only requires a large-scale manufacturing apparatus, but also has a diameter of, for example, 0.76 ± 0.1 m among solder balls formed by the manufacturing apparatus.
It is very difficult to select a solder ball having a substantially spherical shape of m, and there is a problem that fractionation is poor.

[0003]

The solder ball obtained by the conventional method for forming a solder ball described above has a problem in that the manufacturing apparatus is large-scaled, and the shape of the obtained solder ball is non-uniform and the fractionation is poor. I had one. The present technology has been made in view of the above problems, and an object thereof is to provide a method for forming a solder ball that has a simple manufacturing apparatus and has a uniform shape of the obtained solder ball and good fractionation.

[0004]

In order to solve the above-mentioned problems, the present invention forms a hemispherical recess having a required inner diameter on the surface of a base made of a non-solder-bonding material, and the recess is formed in the recess. It is characterized in that it is formed into a solder ball shape by applying a solder paste, heating it to a solder melting temperature, and then cooling it. Also, the diameter of the solder ball can be set by changing the inner diameter of the recess. Further, the base is made of iron. Furthermore, the base is made of aluminum.

[0005]

With the above structure, the solder in the solder paste applied to the surface of the base is melted by heating, and the solder that is melted in the portion outside the recess is bonded to the surface of the base. Without doing so, the portion that melts inside the concave portion is solidified into a ball shape by the surface tension of the molten solder to form a solder ball.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a solder ball forming method according to the present invention will be described below in detail with reference to the drawings. The same reference numerals as those in the conventional example are used in the figure.

In FIG. 1, reference numeral 1 is a base made of a non-solderable metal such as iron or aluminum, and a hemisphere for forming solder balls on the surface of the base 1 as shown in FIG. -Shaped recesses 1a, 1b, 1c, 1 having a diameter d
d is formed.

Next, as shown in FIG. 2, the solder pastes 2a, 2b, 2b, 2b, 2b,
Apply 2c and 2d.

Then, the entire base 1 is put in a solder reflow furnace as shown in FIG. 3 and heated to the melting temperature of the solder. Then, the solder paste in the recesses 1a, 1b, 1c, 1d becomes the molten solders 3a, 3b, 3c, 3d,
The molten solders 3a, 3b, 3c, and 3d are not bonded to the base 1 and are naturally cooled as they are naturally cooled, and are solidified into balls by the surface tension of the molten solder, as shown in FIG. 4c, 4d can be formed.

Each of the solder balls 4a, 4b, 4c, 4d
The diameter H at is equal to
It can be arbitrarily set by changing the inner diameter d of.

[0011]

As described above, according to the solder ball forming method of the present invention, a plurality of solder balls can be formed by simply applying solder paste on the surface of a base having a plurality of recesses on the surface and then heating. Since the solder balls can be formed, the manufacturing apparatus of the solder balls is simple, the shape is uniform, and the yield is good, and the manufacturing cost of the solder balls can be significantly reduced.

[Brief description of drawings]

FIG. 1 is an enlarged vertical sectional front view of a base of a solder ball forming method according to the present invention.

FIG. 2 is an enlarged vertical sectional front view of the solder ball forming method according to the present invention in which a solder paste is applied to the surface of the base in FIG.

FIG. 3 is a vertical sectional front view of a solder paste applied to the surface of the base in FIG. 2 of the method for forming a solder ball according to the present invention, which is obtained by melting the solder paste.

FIG. 4 is a vertical sectional front view of the solder paste applied to the surface of the base in FIG. 3 of the method for forming a solder ball according to the present invention, which is cooled.

FIG. 5 is an enlarged vertical sectional front view of an essential part for joining an electronic component to a printed board by a conventional solder ball forming method.

[Explanation of symbols]

 1 Base 1a Recess 1b Recess 1c Recess 1d Recess 2 Solder Paste 3 Molten Solder 4 Solder Ball

Claims (4)

[Claims] 1. A hemispherical recess having a required inner diameter is formed on the surface of a base made of a non-solder-bonding material, solder paste is applied to the recess, and the mixture is heated to a solder melting temperature and then cooled. A method of forming a solder ball, which is characterized in that the solder ball is formed into a solder ball shape. 2. The method for forming a solder ball according to claim 1, wherein the diameter of the solder ball can be set by changing the inner diameter of the recess. 3. The method of forming solder balls according to claim 1, wherein the base is made of iron. 4. The method of forming solder balls according to claim 1, wherein the base is made of aluminum.