JPH10242632A - Forming method for solder bump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a solder bump for forming the higher bump by eliminating occurrence of a solder bridge. SOLUTION: A print mask in which a pattern hole is opened is superposed on an upper surface of a chip 1, and an electrode of the chip 1 is coated with cream solder. When the coated cream solder 5 is heated by reflowing, the solder 5 is melted, but the solder 5 coating the adjacent electrodes is burred reversely to one another. Accordingly, the solders 5 on the adjacent electrodes do not generate a solder bridge due to combining. Further, the solder 5 is burred from above the electrode to coat in a large quantity, melted and sucked onto the electrode, thereby forming a solder bump with a high height.

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 solder bumps on a work.

[0002]

2. Description of the Related Art A flip chip or a BGA (Ball G
As a method of forming a bump of an electronic component with a bump such as a lid array, it is known to form a solder bump on an electrode of a chip or a work of a substrate. As a method of forming solder bumps, it is known that cream solder is applied to electrodes of a work by screen printing, and then the cream solder is reflowed to form solder bumps on the electrodes.

[0003] When the solder bumps thus formed are soldered to a substrate, it is desired that the height of the solder bumps be higher. This is because the higher solder bumps are easier to absorb the thermal deformation caused by the difference in thermal expansion between the board and the chip during reflow or after soldering, and also better absorb the height difference of the board surface due to warpage or undulation of the board. Then, all the solder bumps can be firmly soldered to the electrodes of the substrate.

For this reason, it has been practiced to increase the amount of cream solder applied on the electrodes of the work as much as possible to increase the height of the solder bumps.

Hereinafter, a conventional bump forming method will be described with reference to the drawings. 9, 10, 11, 12, and 1
3, FIG. 14 is a process explanatory view of a conventional bump forming method,
FIGS. 15A and 15B are partial plan views of the same chip.
In FIG. 9, reference numeral 1 denotes a chip, on the surface of which are formed electrodes 2 for connection to electrodes of a circuit pattern on a substrate. A solder bump is formed on the electrode 2 by a process described below.

In FIG. 10, reference numeral 3 denotes a printing mask for cream solder printing, in which pattern holes 4 are provided in accordance with the electrodes 2 of the chip 1. The pattern hole 4 is rectangular,
The short side is almost the same as the width of the electrode 2, but the long side is longer than the length of the electrode 2 in order to increase the amount of cream solder applied on the electrode 2 as much as possible.

[0007] Next, as shown in FIG.
On the chip 1, and as shown in FIG.
The squeegee 6 is slid to the right to fill the pattern holes 4 with the cream solder 5. Next, when the print mask 3 is separated from the chip 1, the electrodes of the chip 1 are placed on the electrodes of FIG.
As shown in FIG. 7, the cream solder 5 is applied.

Thereafter, the chip 1 is sent to a reflow device, where it is heated, whereby the cream solder 5 is melted and cooled and solidified to form solder bumps 5a on the electrodes 2 as shown in FIG.

[0009]

FIG. 15 (a) is a view similar to FIG.
FIG. 4 is a partial plan view of the chip 1 to which the cream solder 5 shown in FIG. 3 is applied. As described above, since the length of the pattern hole 4 of the print mask 3 is increased, the cream solder 5 is applied long from the electrode 2 of the chip 1. FIG.
FIG. 5B is a partial plan view of the chip 1 after the reflow shown in FIG. When the cream solder 5 is heated and melted by reflow, the melted cream solder 5 is attracted to the electrode 2, and a substantially spherical bump 5 a is formed on the electrode 2 by the surface tension.

However, the behavior of the cream solder 5 in a flowing state is unstable, and the cream solder 5 on the adjacent electrodes 2 merges to form a solder bridge 5b between the electrodes 2 as shown in FIG. It was easy to occur.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for forming a solder bump which can eliminate the occurrence of a solder bridge and can form a higher solder bump.

[0012]

According to the present invention, a print mask is placed on the upper surface of a work, and a squeegee is slid on the print mask, so that the pattern is formed on the upper surface of the work through a pattern hole formed in the print mask. A method of forming solder bumps, in which cream solder is screen-printed and applied on the side-by-side electrodes, and the cream solder is heated and melted and solidified by a reflow process to form solder bumps on the electrodes. In the screen printing, cream solder was applied to the electrodes adjacent to each other in a direction opposite to each other to prevent solder bridges from being generated in the reflow process.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention having the above-mentioned structure, the cream solder applied on the electrodes of the work is melted when heated by the reflow process, but the cream solder applied on the adjacent electrodes is not melted. Since they protrude in the opposite direction, the cream solders on the adjacent electrodes do not merge to form a solder bridge. In addition, a large amount of cream solder is laid out on the electrode and applied, melted and sucked onto the electrode, whereby a high-height solder bump 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. 7 is a process explanatory view of a bump forming method according to an embodiment of the present invention, FIG. 7 is a partially enlarged view of a print mask and a chip of the bump forming method, and FIGS. FIG. 4 is a partial cross-sectional view of the chip of FIG. The same elements as those in the conventional method are denoted by the same reference numerals.

In FIG. 1, reference numeral 1 denotes a chip, on the surface of which are formed a large number of electrodes 2 for connection to electrodes of a circuit pattern on a substrate. A solder bump is formed on the electrode 2 by a process described below.

In FIG. 2, reference numeral 13 denotes a print mask for cream solder printing, in which pattern holes 14 are provided in accordance with the electrodes 2 of the chip 1. The pattern hole 14 has a rectangular shape, and the short side is almost the same as the width of the electrode 2, but the long side is longer than the length of the electrode 2 in order to increase the amount of cream solder applied on the electrode 2 as much as possible. . Here, FIG.
As shown in FIG. 7, the pattern holes 14 are formed to be long in the direction in which adjacent electrodes 2 alternately protrude from the electrodes 2 in the opposite direction, and are arranged in a staggered shape as a whole.

Next, as shown in FIG.
The squeegee 6 is slid to the right on the print mask 3 to fill the pattern holes 4 with the cream solder 5 as shown in FIG. Next, when the print mask 3 is separated from the chip 1, the cream solder 5 is applied on the electrodes 2 of the chip 1 as shown in FIG. The cream solder 5 applied in this manner protrudes alternately in the opposite direction (see also FIG. 7).

Thereafter, the chip 1 is sent to a reflow device, where the cream solder 5 is heated and melted, and then cooled and solidified to form a solder bump 5a.
FIG. 6 shows a chip on which the solder bumps 5a are formed as described above.

FIGS. 8A and 8B show a process of forming the solder bump 5a at the time of reflow. As shown in FIG. 8A, the cream solder 5 applied on the electrode 2 is melted by heating, and is attracted to the electrode 2 side on the chip 1 (see arrow a). The sucked cream solder 5 is applied to the electrode 2 having good solder wettability as shown in FIG.
The solder bumps agglomerate on each other to form a substantially spherical solder bump 5a due to surface tension. In FIG. 8B, the cream solder 5 indicated by a dashed line shows a state in the middle of aggregation. In the melting process of the cream solder 5, the cream solder 5 applied on the adjacent electrodes 2 has the protruding directions opposite to each other and is separated from each other, so that the cream solder 5 may merge. No solder bridges.

[0020]

According to the present invention, when the cream solder applied on the electrode of the work is heated by the reflow treatment, the cream solder is melted, but the cream solder applied on the adjacent electrodes protrudes in opposite directions. Therefore, the cream solders on the adjacent electrodes do not merge to form a solder bridge. In addition, a large amount of cream solder is laid out on the electrode and applied, melted and sucked onto the electrode, whereby a high-height solder bump can be formed.

[Brief description of the drawings]

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

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

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

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

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

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

FIG. 7 is a partially enlarged view of a print mask and a chip in a bump forming method according to an embodiment of the present invention.

8A is a partial cross-sectional view of a chip in a bump forming method according to one embodiment of the present invention; FIG. 8B is a partial cross-sectional view of a chip in a bump forming method according to one embodiment of the present invention;

FIG. 9 is a process explanatory view of a conventional bump forming method.

FIG. 10 is a process explanatory view of a conventional bump forming method.

FIG. 11 is a process explanatory view of a conventional bump forming method.

FIG. 12 is a process explanatory view of a conventional bump forming method.

FIG. 13 is a process explanatory view of a conventional bump forming method.

FIG. 14 is a process explanatory view of a conventional bump forming method.

FIG. 15A is a partial plan view of a chip in a conventional bump forming method. FIG. 15B is a partial plan view of a chip in a conventional bump forming method.

[Explanation of symbols]

 Reference Signs List 1 chip 2 electrode 3 print mask 4 pattern hole 5 cream solder 5a solder bump 6 squeegee 13 print mask 14 pattern hole

Claims (1)

[Claims] 1. A print mask is placed on the upper surface of a work, and a squeegee is slid on the print mask, so that cream is applied to electrodes arranged side by side on the upper surface of the work through pattern holes formed in the print mask. A method of forming solder bumps in which solder is screen-printed and applied, and the cream solder is heated and melted and solidified by a reflow process to form a solder bump on an electrode, wherein the solder bumps are adjacent to each other in the screen printing. A method of forming solder bumps, wherein cream solder is applied to electrodes in a direction opposite to each other to prevent solder bridges from being generated in the reflow process.