JP3307262B2 - Method of forming solder bumps - 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 solder bump on an aluminum electrode of a chip.

[0002]

2. Description of the Related Art In recent years, in order to solder an electrode of a chip to a circuit pattern of a substrate, a solder bump is formed on the electrode of the chip in advance.

[0003]

However, when the electrode of the chip is an aluminum electrode, it is difficult to form a solder bump on the aluminum electrode because aluminum has poor solder wettability. Therefore, conventionally, in a semiconductor wafer process before forming solder bumps, a metal layer such as copper having good solder wettability is formed as a barrier layer on the surface of the chip, and portions of this metal layer other than the aluminum electrode are etched. To form an electrode. However, such a method requires a new step of forming a metal layer on the surface of the chip or removing the metal layer by etching to form an electrode.
There is a problem that the process is troublesome, the productivity is not increased, and the cost is increased.

When a flip chip or the like is bonded to a substrate by bumps, it is desired that the height of the bumps be higher. This is because the higher bumps can more easily absorb the thermal deformation caused by the difference in thermal expansion between the substrate and the chip after bonding, and can more effectively absorb the difference in elevation due to the undulation of the substrate.

In some cases, solder bumps are formed as bumps. As a method of forming solder, which is a material of a solder bump, on an electrode, a method of applying cream solder on the electrode by screen printing is widely used. When cream solder is applied on an electrode by screen printing to form a solder bump on the electrode, a larger amount of cream solder must be applied on the electrode to increase the height of the solder bump.

For this purpose, it is necessary to increase the thickness of the print mask to increase the amount of cream solder filled in the pattern holes. However, when the thickness of the print mask is increased, the cream solder from the pattern holes is increased. There was a limit to the thickness of the print mask due to poor plate-out performance. Therefore, in the screen printing method, it was difficult to form a high solder bump by applying a large amount of cream solder on the electrode.

Further, when a solder bump is formed on an electrode covered with a metal layer such as copper, there is a problem that the height of the solder bump varies depending on the size of the electrode as described below. . That is, depending on the chip, electrodes of different sizes may be formed on the same chip,
Alternatively, the size of each electrode may vary due to an error in the manufacturing process. In general, when cream solder of the same thickness is applied on electrodes and solder bumps are formed by melting and solidifying, the bottom shape and bottom area of the solder bumps are determined by the size of the electrode to which they are attached. The height of the formed solder bump is lower than the height of the solder bump formed on the small electrode. For this reason, when electrodes having different sizes are formed on the same chip, the height of the solder bumps differs depending on the size of the electrodes, and there has been a problem that a failure occurs in mounting.

Accordingly, an object of the present invention is to provide a solder bump forming method capable of forming a solder bump having a high height and a uniform height on an aluminum electrode of a chip.

[0009]

According to the present invention, there is provided a method of forming a solder bump, comprising the steps of forming a copper bump having a tail projecting upward by wire bonding on an aluminum electrode of a chip, and adjusting the position of the electrode. The printing mask having a plurality of pattern holes formed thereon is overlaid on a chip, a squeegee is slid over the printing mask to fill the pattern holes with cream solder, and then the printing mask is separated from the chip by removing the copper from the chip. a step of the cream solder to the coating fabric for covering the copper bumps and the electrode bump as a core, the photoelectrically by heating the chips to melt the solder paste
The cream solder melted on the extreme is sucked onto the copper bump.
It was followed and forming a solder bump on the electrode by cooling and solidifying.

[0010]

According to the present invention having the above-mentioned structure, a tail which projects upward on the aluminum electrode of the chip is provided.
Since the copper solder is formed and cream solder is applied by a print mask so as to cover the copper bump, even if the thickness of the print mask is increased and the amount of applied cream solder is increased, the cream solder is It adheres firmly to the surface of the copper bump on the electrode. In addition, in this case, the shape of the copper bump is spherical and its surface area is large, so that the cream solder adheres very firmly to the surface of the copper bump, and as a result, the cream solder is easily removed from the electrode and is not deformed on the electrode. Can be applied to In addition, the volume of the solder bump on the electrode is the sum of the volume of the copper bump and the volume of the cream solder, so that a solder bump having a high height and a uniform height can be formed.

Next, an embodiment of the present invention will be described with reference to the drawings. 1, 2, 3, 4, 5, and 6 are:
FIG. 4 is a process explanatory view of a method for forming a solder bump according to one embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a chip, on which an aluminum electrode 2 is formed. Also,
On a portion other than the electrode 2 on the upper surface of the chip 1, a protective film 3 containing SiO2 or the like as a component is formed. Reference numeral 4 denotes a capillary tool of a wire bonder, through which a wire 5 is inserted. The wire bonder brings the torch (electrode) close to the lower end of the wire 5 drawn out from the lower end of the capillary tool 4 to generate an electric spark between the wire bonder and the torch. The ball 5a is pressed against the electrode 2 of the chip 1 on the lower surface of the capillary tool 4 for bonding (FIG. 1), and then the capillary tool 4 is raised and the wire 5 is pulled up to cut the wire 5.

FIG. 2 shows a state in which copper bumps (balls) 5a are formed on the electrodes 2 in this manner. 5 'is a cut end (hereinafter, referred to as "tail") of the wire 5 generated by cutting the wire.

Next, the cream solder 10 is applied on the electrode 2 on which the copper bumps 5a are formed as follows. FIG.
In the figure, reference numeral 6 denotes a printing mask, in which a plurality of pattern holes 7 are provided in accordance with the positions of the electrodes 2. The print mask 6 is positioned and overlapped on the chip 1, and cream solder 10 is supplied to the upper surface of the print mask 6. As shown in FIG. 4, by sliding the squeegee 9 rightward on the print mask 6, the cream solder 10 is filled in the pattern holes 7 so as to cover the copper bumps 5a.

Next, as shown in FIG. 5, the print mask 6 is separated from the chip 1, and the cream solder 10 in the pattern hole 7 is applied on the electrode 2. In this case, the cream solder 10 applied to the electrode 2 adheres to the surface of the spherical copper bump 5a having a large surface area and the surface of the tail 5 'projecting upward therefrom.
It can be transferred to the side and can be applied on the electrode 2 without deformation. For this reason, the thickness of the print mask 6 can be made thicker than before, and a larger amount of cream solder 10 can be applied.

Thereafter, the chip 1 is sent to a reflow process. Then, the cream solder 10 is heated and melted, becomes spherical on the electrode 2 by its surface tension, and then cooled and solidified to form a solder bump 10 a on the electrode 2. FIG. 6 shows a state where the solder bumps 10a are formed. In this case, since aluminum as a material of the electrode 2 has poor solder wettability, the cream solder melted by reflow is repelled from the upper surface of the electrode 2 and is attracted to the copper bump 5a having good wettability. That is, the shape of the bottom surface of the solder bump 10a is determined by the shape of the bottom surface of the copper bump 5a, and is not affected by the size or shape of the electrode 2. Therefore, if the copper bumps 5a are formed uniformly, the solder bumps 10a having a uniform height and volume are always formed regardless of the variation in the size of the electrodes 2.

[0017]

According to the present invention, the electrode projects upward on the electrode.
Since the cream solder is applied by the print mask after forming the copper bump with the tail , the cream solder adheres to the surface of the copper bump on the electrode, and thus the printing mask is removed from the pattern hole of the print mask. It has good properties and can apply cream solder on electrodes with sufficient thickness without shape loss. In addition, since the shape of the copper bump is spherical with a large surface area, and the copper bump generally has a tail protruding upward, the cream solder adheres very firmly to the surface of the copper bump. It can be applied to electrodes with good removability. Since the volume of the bump formed on the electrode is the sum of the volume of the copper bump and the volume of the cream solder, the volume of the bump can be increased to form a high-height solder bump. Also, when the cream solder is heated and melted, the melted cream solder is repelled by the poorly wettable aluminum electrode and attracted to the wettable copper bump, so the bottom area of the bump is the size of the aluminum electrode. Therefore, even if the size of the aluminum electrode varies, a bump having no variation in height can be formed. Furthermore, since expensive facilities such as a facility for forming a metal film as a barrier layer and an etching facility that are conventionally required are not required, costs can be reduced and productivity can be increased.

[Brief description of the drawings]

FIG. 1 is a process explanatory view of a method for forming a solder bump according to an embodiment of the present invention;

FIG. 2 is a process explanatory view of a method for forming a solder bump according to an embodiment of the present invention;

FIG. 3 is a process explanatory view of a method for forming a solder bump according to an embodiment of the present invention;

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

FIG. 5 is a process explanatory view of a method for forming a solder bump according to an embodiment of the present invention;

FIG. 6 is a process explanatory view of a method for forming a solder bump according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 chip 2 electrode 3 protective film 4 capillary tool 5 wire 5a copper bump 5 'tail 6 print mask 9 squeegee 10 cream solder 10a solder bump

Claims (1)

(57) [Claims] A step of forming a copper bump having a tail protruding upward by wire bonding on an aluminum electrode of the chip; and forming a print mask having a plurality of pattern holes in accordance with the position of the electrode on the chip. , A squeegee is slid over the print mask to fill the pattern holes with cream solder, and then the print mask is separated from the chip to cover the copper bumps and the electrodes with the copper bumps as cores. a step of coating the fabric solder, said heated tip is melted cream solder
Suck cream solder melted on the electrodes onto the copper bumps
Asked, then the method of forming the solder bump, characterized in that it comprises a step of forming a solder bump on the electrode by cooling and solidifying.