JP3146844B2 - Method of forming bump - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bump forming method for forming bumps by screen printing means on electrodes formed in a matrix on the surface of an electronic component such as a substrate or a chip.

[0002]

2. Description of the Related Art As means for reducing the size and density of electronic components, it is known that a large number of electrodes are formed in a matrix on the surface of the electronic components and bumps (protruding electrodes) are formed on the electrodes. I have. Further, as a method for forming a bump, a method is known in which cream solder is applied to electrodes by screen printing means, and then the electronic component is heated in a heating furnace to melt and solidify the cream solder to form a bump.

[0003]

According to the screen printing means, there is an advantage that bumps can be formed at low cost and with good workability. However, when the cream solder is melted by being heated in a heating furnace of a reflow apparatus, the melting point is reduced. There is a problem that the cream solder flows to form a bridge and adjacent bumps are likely to be short-circuited.

FIG. 9 is a partial plan view of a conventional electronic component on which bumps are formed. A large number of bumps 6a are formed on the surface of the electronic component 1 in a matrix. As a result, the bridge 2 is generated by the flowing of the cream solder, and the adjacent bumps 6 a are short-circuited by the bridge 2. Such a bridge 2 is more likely to be generated as the pitch of the bumps 6a is reduced in order to reduce the size and density of the electronic component 1.

Accordingly, an object of the present invention is to provide a method for forming a bump which can eliminate the occurrence of a bridge that short-circuits the bumps.

[0006]

Means for Solving the Problems] The present invention To this end, the
After the cream solder is thinned and applied to the electrode on the surface of the electronic component by the first screen printing means, and then the cream solder is melted and solidified by heating the electronic component to form the first bump. , by the second scan <br/> screen printing means cream solder is coated on the remaining electrodes of the surface of the electronic component, and then a second time with the cream solder is melted and solidified by heating the electronic component again
So that the second bump is formed and the second screen
The first printing is performed on the lower surface of the screen mask of the screen printing means.
Are formed with concave portions to which the bumps are fitted .

[0007]

According to the above construction, by forming the bumps in a plurality of times by thinning them out, it is possible to prevent the occurrence of a bridge that short-circuits the bumps when the electronic component is heated and melted.

[0008]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 7 shows a flowchart of a bump forming method according to one embodiment of the present invention. The method of forming the bumps includes four steps of a first screen printing, a first reflow, a second screen printing, and a second reflow, which will be described in the order of each step.

FIG. 1 is a partial sectional view of a screen printing machine for a first screen printing according to an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of the same. In FIG. 1, a cream mask 6 is applied to the electronic component 1 by bringing a screen mask 4a of the screen printing machine close to the upper surface of the electronic component 1 and sliding a squeegee 5 on the screen mask 4a in the direction of the arrow. In FIG. 2, an electrode 7 is provided on the surface of the electronic component 1.
Are formed, and the electrodes 7 of the screen mask 4a are formed.
A pattern hole 8 is opened at a location corresponding to. The pattern holes 8 are formed so that every other electrode 7 is exposed. Therefore, when the squeegee 5 is slid, the cream solder 6 is thinly applied onto every other electrode 7.

After the cream solder 6 is applied to the electronic component 1, the electronic component 1 is taken out of the screen printing machine. FIG. 3 is a plan view of the electronic component on which the first screen printing has been performed according to the embodiment of the present invention. The cream solder 6 applied by the first screen printing is indicated by a + mark. . As shown in the figure, a large number of electrodes 7 are formed in a matrix on the surface of the electronic component 1, and cream solder 6 is thinned and applied on every other electrode 7.

Next, the electronic component 1 is sent to a heating furnace of a reflow apparatus for a first reflow, and is heated to melt the cream solder 6, and then cooled and solidified to form a bump 6a.

Next, the electronic component 1 is sent to the screen printing machine again, and the cream solder 6 is applied to the remaining electrodes 7.
FIG. 4 is a partially enlarged cross-sectional view of a screen printing machine for the second screen printing according to one embodiment of the present invention. On every other electrode 7 of the electronic component 1, bumps 6a in which the cream solder 6 is solidified are formed by performing the first screen printing and reflow. The lower surface of the screen mask 4b is formed with a concave portion 9 into which the bump 6a is fitted, and a pattern hole 8 for applying the second cream solder 6 on the electrode 7 is opened. Therefore, when the squeegee 5 is slid, the cream solder 6 is applied on the remaining electrodes 7. FIG. 5 is a plan view of the electronic component on which the second screen printing is performed according to the embodiment of the present invention. In FIG. 5, the bumps 6a indicated by + and hatching are formed by the above-described first screen printing and reflow.

Subsequently, the electronic component 1 is sent to a heating furnace of a reflow apparatus for the second reflow, and is heated to melt the cream solder 6. At this time, the bump 6a formed at the first time is also melted again.
Does not flow out of the electrode 7 because it adheres to the upper surface of the electrode 7. Accordingly, the bridge with the cream solder 6 melted in the second reflow is less likely to occur. Then, if the melted cream solder 6 is cooled and solidified, the electronic component 1 with bumps is completed. FIG. 6 is a partial sectional view of an electronic component according to one embodiment of the present invention completed as described above.
As described above, in the present method, all the bumps 6a are not formed at the same time, but are formed twice every other one. Therefore, even if the cream solder 6 is heated and melted in a heating furnace, Adjacent melted cream solders 6 are not short-circuited to each other to form a bridge, and bumps 6a can be reliably formed at a narrow pitch. In the above embodiment, the bump 6a is formed in two steps, but may be formed in three or more steps.

FIG. 8 is a partially enlarged sectional view of a screen printing machine for the second screen printing according to another embodiment of the present invention. The screen mask 4c has a dome-shaped upper surface 10 for securing a concave portion 9a in which the bump 6a formed by the first reflow is fitted. Therefore, the thickness of the screen mask 4c can be made smaller than that of the screen mask 4b shown in FIG. 4, and it is possible to prevent the cream solder 6 from being excessively applied to the pattern holes 8.

[0015]

As described above, according to the bump forming method of the present invention, all the bumps are not formed at the same time, but are thinned out in a plurality of times. When the solder is melted, the melted cream solders are short-circuited to each other, so that a bridge is unlikely to be formed, and a narrow pitch bump can be reliably formed.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a first screen printing screen printing machine according to an embodiment of the present invention.

FIG. 2 is a partially enlarged cross-sectional view of a screen printing machine of a first screen printing according to an embodiment of the present invention.

FIG. 3 is a plan view of an electronic component on which first screen printing is performed according to an embodiment of the present invention.

FIG. 4 is a partially enlarged cross-sectional view of a screen printer of a second screen printing according to an embodiment of the present invention.

FIG. 5 is a plan view of an electronic component on which a second screen printing is performed according to an embodiment of the present invention.

FIG. 6 is a partial sectional view of an electronic component according to one embodiment of the present invention.

FIG. 7 is a flowchart of a bump forming method according to an embodiment of the present invention.

FIG. 8 is a partially enlarged cross-sectional view of a screen printing machine for a second screen printing according to another embodiment of the present invention.

FIG. 9 is a partial plan view of a conventional electronic component on which bumps are formed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electronic component 4a, 4b Screen mask 5 Squeegee 6 Cream solder 6a Bump 7 Electrode 8 Pattern hole 9 Depression

Claims (1)

(57) [Claims] 1. A method of forming a bump on an electrode formed in a matrix on the surface of an electronic component, wherein cream solder is applied to the electrode on the surface of the electronic component by first screen printing means. culled by coating, and then after forming the first round of bumps the cream solder is melted and solidified by heating the electronic component, a second time
The eyes of a screen printing means cream solder is coated on the remaining electrodes of the electronic component of the surface and then to form a second round of bumps the cream solder is melted and solidified by heating the electronic component again And before
The screen mask of the second screen printing means
On the lower surface, a recess is formed to fit the first bump
A method for forming a bump, comprising: