JP3156483B2 - 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 method for forming a bump on an electrode formed on the surface of an electronic component such as a chip or a substrate.

[0002]

2. Description of the Related Art As a means for increasing the size and density of a chip or a substrate on which the chip is mounted, a large number of electrodes are formed in a matrix on the surface of an electronic component such as a chip or a substrate. A method for forming a protruding electrode is known. Further, as a method of forming a bump, a method is known in which cream solder is applied to an electrode by screen printing means, and then the electronic component is heated in a heating furnace of a reflow device to melt and solidify the cream solder to form a bump. ing.

[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 and the cream solders on the adjacent electrodes are integrated with each other, so that an excessive bump is generated or a bridge in which the bumps on the adjacent electrodes are short-circuited easily occurs. Next, FIG.
The reason will be described in detail with reference to (a), (b), and (c).

FIGS. 2 (a), 2 (b) and 2 (c) are explanatory views of a conventional bump forming method, and show a partial cross section of a substrate on which bumps are formed. First, as shown in FIG. 2A, a cream solder 3 is applied on an electrode 2 formed on a surface of a substrate 1 by screen printing means. Reference numeral 4 denotes a resist film formed between the electrodes 2. The screen printing means for applying the cream solder 3 is disclosed in, for example,
The one described in JP-A-200099 is known.

Next, the substrate 1 is sent to a heating furnace of a reflow apparatus, and the cream solder 3 is heated. As a reflow apparatus, for example, an apparatus described in Japanese Patent Application Laid-Open No. 2-263570 is known. FIG. 2B shows a partial cross section of the substrate 1 during reflow. When the cream solder 3 is heated as shown in the figure, the cream solder 3 is melted and fluidized to the side. The cream solders 3 on the electrodes 2 are connected. Then, the melted cream solder 3 is gradually attracted to the side where the internal pressure of the solder is small (the right side in this example) (see the broken arrow), and as shown by the solid line in FIG. There is a problem that the bumps 3b and the bridges 3c are formed on the electrode 2 as shown in FIG.

However, in recent years, the pitch of electrodes has been gradually narrowed due to the demand for high integration and high density, and the volume of the bumps is required to firmly fix the bumps to the electrodes of the other electronic component to which the bumps are fixed. However, as the electrode pitch becomes narrower and the volume of the bump increases, the above problem becomes more prominent. In addition, the above-described problem similarly occurs when bumps are formed on electrodes of a chip cut out of a wafer in order to form a flip chip.

Accordingly, an object of the present invention is to solve the problems of the conventional method and to provide a bump forming method capable of reliably forming a bump on an electrode of an electronic component such as a chip or a substrate.

[0008]

For this purpose, the present invention provides a method in which cream solder is applied to electrodes formed on the surface of an electronic component by screen printing means, and then the electronic component is turned upside down so that the cream solder is applied. The bumps are formed by heating the electronic component to melt the cream solder, and then cooling and solidifying it to form the bumps.

[0009]

According to the above construction, the electronic component is turned upside down and the cream solder is melted on the lower surface, so that the melted cream solder hangs down due to gravity, so that the melted cream solder flows to the side. Thus, the cream solders are not connected to each other, and the occurrence of bridges is reliably prevented, so that independent bumps can be reliably formed on each electrode.

[0010]

Next, an embodiment of the present invention will be described with reference to the drawings. FIGS. 1A, 1B, 1C, and 1D are explanatory views of a bump forming method according to one embodiment of the present invention.
It is shown in the order of steps. First, as shown in FIG. 1A, a cream solder 3 is applied on an electrode 2 of a substrate 1 by screen printing means.

Next, as shown in FIG. 1 (b), the substrate 1 is turned upside down and sent to a heating furnace of a reflow apparatus with the surface on which the cream solder 3 is applied facing downward, and the substrate 1 is heated. Then, the cream solder 3 gradually melts and gradually becomes spherical due to its own surface tension (see FIG. 1C), but the melted cream solder 3 hangs down due to gravity. Therefore, unlike the conventional example, the melted cream solder 3 does not flow to the side, and the cream solders 3 on the adjacent electrodes 2 are not connected to each other. Next, the substrate 1 is cooled to solidify the cream solder 3, and the substantially spherical bump 3a shown in FIG.
Is completed. The completed bumps 3a are independent without being connected to each other. In the above embodiment, the substrate 1 has been described as an example of an electronic component. However, the present invention can be applied to a method of forming a bump on an electrode of a chip in order to manufacture a flip chip.

[0012]

As described above, according to the present invention, the formation of a bridge is reliably prevented by a very simple method of inverting an electronic component and heating and melting the cream solder on the lower surface so that each of the electrodes can be prevented. A bump having a good shape can be reliably formed on the top.

[Brief description of the drawings]

1A is an explanatory view of a bump forming method according to an embodiment of the present invention; FIG. 1B is an explanatory view of a bump forming method according to an embodiment of the present invention; FIG. (D) is an explanatory view of a bump forming method according to an embodiment of the present invention.

2A is an explanatory view of a conventional bump forming method; FIG. 2B is an explanatory view of a conventional bump forming method; FIG. 2C is an explanatory view of a conventional bump forming method;

[Explanation of symbols]

 1 substrate 2 electrode 3 cream solder 3a bump

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/60 H05K 3/34

Claims (1)

(57) [Claims] 1. A method of forming a bump on an electrode formed on a surface of an electronic component, comprising applying cream solder to the electrode by screen printing means, and then turning the electronic component upside down to obtain the cream. A method for forming a bump, wherein the surface on which solder is applied is a lower surface, the electronic component is heated to melt the cream solder, and then cooled and solidified to form a bump.