HK1023649B

HK1023649B - Method for forming bump and semiconductor device

Info

Publication number: HK1023649B
Application number: HK00102755.1A
Authority: HK
Inventors: 冈本明
Original assignee: Ｎｓｃ株式会社
Priority date: 1996-11-06
Filing date: 1997-10-29
Publication date: 2005-03-18

Description

Method for forming bump and semiconductor device

Technical Field

The present invention relates to a method of forming bumps (bumps) used for connecting 2 substrates (for example, a printed wiring board and a semiconductor chip) on which lands (pads) are formed, such as in the case of mounting by BGA technology or flip chip mounting, and a semiconductor device manufactured using the formed bumps.

Background

One of the technologies for mounting a semiconductor chip on a printed wiring board is a technology called BGA (ball grid array). The BGA technique is a technique of forming lands in both a semiconductor chip and a printed wiring board, and joining these lands by solder balls or gold balls called bumps or the like. By using such a bump, the mounting area can be significantly reduced as compared with a case where a terminal having a lead shape is mounted on a semiconductor chip or a case where COB (chip on board) mounting using a bonding wire is performed.

On the other hand, so-called flip chip mounting, in which a semiconductor chip is mounted on a printed wiring board in a bare chip state without being packaged, has also been widely performed recently. In the case of flip chip mounting, the lands of the bare chip and the lands of the printed wiring board are also bonded by bumps.

As a method for forming bumps used for mounting by BGA technology, flip chip mounting, or the like, 4 types of methods, that is, a normal bump method, a transfer bump method, a ball bump method, and a land bump method, are generally known. In general, the bump method is a method in which the upper surface of a semiconductor wafer except for a bump formation portion is covered with a resist, and the resist is removed after a bump is formed by plating. The transfer bump method is a method in which a bonding bump is transferred to the tip of an inner lead, and the bump is overlapped with an aluminum electrode of a semiconductor chip and then heated and pressed. The ball bump method is a method of mounting a bump on each land using a device for wire bonding, and the mesa bump method is a method of integrally forming a bump at the tip of an inner lead.

Among these 4 methods, the transfer bump method and the mesa bump method are based on the premise of using inner leads, and therefore are not suitable for mounting by BGA technology or flip chip mounting. In the ball-bump method, since bumps are sequentially mounted on the lands, the number of lands increases, which results in a problem that the mounting takes time. On the other hand, since the bump is formed by the plating process, there is a problem that the size and shape of the bump are likely to be discrete.

Disclosure of the invention

The present invention has been made in view of the above problems, and an object thereof is to provide a bump forming method capable of forming a bump having a desired size and shape without requiring a complicated process, and a semiconductor device manufactured using such a bump.

The method for forming the salient point comprises the following steps: the method includes a step of covering the upper surface of the 1 st substrate except for the land forming region with a resist, and a step of ejecting a conductive material from below toward the resist-covered surface of the 1 st substrate with the resist-covered surface facing downward to form a substantially hemispherical bump in the land forming region on the 1 st substrate. By directing the land forming region of the 1 st substrate downward and spraying the conductive material from below, a hemispherical bump can be formed in the land forming region by the action of gravity, and a complicated process is not required to form the bump.

Further, a method for forming a bump of the present invention includes: a step of forming a printing pattern with a predetermined thickness on the periphery of the pad on the 1 st substrate by screen printing and a step of forming the bump in a substantially hemispherical shape by deforming the printing pattern by surface tension. After a print pattern is formed around the lands on the 1 st substrate by screen printing, the print pattern is deformed into a circular shape by surface tension, so that hemispherical bumps can be formed without using any special device or the like.

Further, a method for forming a bump of the present invention includes: the method includes a step of performing screen printing on an upper surface of a 1 st substrate to form a print pattern of a predetermined thickness on a periphery of a land on the 1 st substrate, and a step of placing the 1 st substrate with a surface on which the print pattern is formed facing downward for a predetermined time so that the shape of the print pattern formed on the 1 st substrate becomes substantially hemispherical. Hemispherical bumps can be easily formed by the action of gravity by forming a print pattern on the periphery of the lands on the 1 st substrate by screen printing, and by placing the face on which the print pattern is formed downward for a predetermined time.

Brief description of the drawings

Fig. 1 is a diagram illustrating a bump forming method and a semiconductor device manufacturing process;

FIG. 2 is a diagram illustrating the process of FIG. 1(c) in detail;

FIG. 3 is a view showing an example of a bump having a 2-layer structure;

fig. 4 is a schematic view illustrating screen printing; and

fig. 5 is a diagram showing the shape of a print pattern.

Best mode for carrying out the invention

[ embodiment 1 ]

Fig. 1 is a diagram illustrating a bump forming method and a semiconductor device manufacturing process. This figure shows an example of mounting a packaged semiconductor chip on a printed wiring board based on BGA technology, and specifically, an example of bonding a land formed on a package of the semiconductor chip and a land formed on the printed wiring board by bumps. The printed wiring board described above corresponds to the 1 st substrate, and the packaged semiconductor chip corresponds to the 2 nd substrate.

First, as shown in fig. 1(a), lands 2 are formed on a printed wiring board 1 at the same intervals as lands on a semiconductor chip. Next, as shown in fig. 1(b), the upper surface of the printed wiring board 1 except for the land forming region is covered with a resist 3. Next, as shown in fig. 1(c), the face of the printed wiring board 1 covered with the resist 3 is made to face down, and molten solder is sprayed from below thereof to form bumps 4 in the land forming areas.

Fig. 2 is a diagram illustrating the process of fig. 1(c) in detail. As shown in the figure, the printed wiring board 1 is mounted on the belt conveyor 11 with the resist formation surface facing downward. A nozzle 12 for jetting molten solder is provided below the belt conveyor 11. When the belt conveyor 11 starts moving, molten solder is sprayed onto the printed wiring board 1 passing above the nozzle 12. Solder does not adhere to the portion of the printed wiring board 1 covered with the resist 3, and a solder layer is formed only on the land forming surface not covered with the resist 3. The solder layer is formed into a substantially hemispherical shape by the action of gravity, and is used as the bump 4. Since a constant amount of solder is always ejected from the nozzle 12, the size of the bump 4 becomes substantially uniform.

After removing the resist, the printed wiring board 1 on which the bumps 4 are formed is overlapped with the lands 6 of the semiconductor chip 5, as shown in fig. 1(d), and then passed through a high temperature furnace. As a result, as shown in fig. 1(e), the bumps 4 melt, and the semiconductor chip 5 is bonded to the printed wiring board 1 via the bumps 4.

In this way, in the present embodiment, since the land formation surface of the printed wiring board 1 is faced down and molten solder is ejected from the lower side so as to form a solder layer in the land formation region, the solder layer receives the force of gravity and becomes the ideal hemispherical bump 4. Therefore, the hemispherical bump 4 can be formed by a simple process without using a special apparatus or the like.

Further, since the bump forming portion is covered with the resist 3, solder does not adhere to an unnecessary portion. Furthermore, since a constant amount of molten solder is ejected from the nozzle 12 while the printed wiring board 1 is moved at a constant speed, the variation in the size and shape of the bumps can be eliminated. Further, if a plurality of printed wiring boards 1 are placed on the belt conveyor 11 at a constant interval, bumps 4 of the same shape can be formed on the plurality of printed wiring boards 1 in a short time, and the manufacturing efficiency is improved.

The substance ejected from the nozzle 12 is not limited to the molten solder described above, and various substances (e.g., gold) excellent in adhesion and conductivity can be used. Further, the bumps 4 may be formed by ejecting 2 or more substances. Fig. 3 shows an example in which the bump 4 has a two-layer structure, and a solder layer 4a that melts at a low temperature is formed on the upper layer, and a solder layer 4b that melts at a high temperature is formed on the lower layer. With this structure, electrical contact with the semiconductor chip 5 is ensured at the time when the upper solder layer 4a melts, and therefore, the adhesion of the bump 4 can be improved as compared with a structure in which the bump 4 is formed in one layer. When the bumps 4 have a multilayer structure, different materials may be ejected from one nozzle 12, or two or more nozzles 12 may be provided. When the area of the printed wiring board 1 is large, the plurality of nozzles 12 may be arranged in a row, and the same amount of molten solder may be simultaneously ejected from the nozzles 12.

[ embodiment 2 ]

The embodiment 2 described below is an embodiment in which the bumps 4 are formed by screen printing.

Fig. 4 is a schematic diagram illustrating screen printing. A screen mask 21 for drawing the shape of the bumps 4 is disposed above the printed wiring board 1. Both ends of the screen mask 21 are supported by the screen frame 22, and if the squeegee 23 is pressed on, the screen mask 21 is closely arranged on the upper surface of the printed wiring board 1, and if the squeegee 23 is released, the screen mask 21 is returned to the original position (the dotted line position shown in the figure).

The squeegee 23 is pressed against the screen mask 21 with a conductive paste 24 made of solder, gold, or the like being carried on the upper surface of the screen mask 21, and the squeegee 23 is moved in the direction of the arrow shown in the drawing in this state. The screen mask 21 is closely attached to the printed wiring board 1 only at the portion pressed by the squeegee 23, and the screen mask 21 at the portion passed by the squeegee 23 is separated from the printed wiring board 1. Thereby, the print pattern 25 corresponding to the shape of the pattern of the screen mask 21 is transferred onto the printed wiring board 1.

If the screen printing is finished, the printed pattern 25 is placed face down for a predetermined time before drying. Thereby, the printed pattern 25 is formed into a hemispherical shape by the gravity and cured, and the bump 4 is completed.

Thereafter, the semiconductor chip 5 is mounted on the printed wiring board 1 by performing the same steps as in fig. 1(d) and (e).

In this way, in embodiment 2, the bumps 4 are formed by screen printing, so that the variation in the size of the bumps 4 can be eliminated. Further, unlike embodiment 1, a process for forming lands and a resist on the printed wiring board 1 is not required, and thus the manufacturing process can be further simplified.

Further, when the screen printing is performed, as shown in fig. 5, if the print pattern 25 is formed to be wider and thicker than the size of the bump 4, the area of the print pattern 25 can be substantially the same as that of the bump 4 even if the print pattern 25 is reduced by the surface tension. Further, since the surface tension deforms into a circular shape as shown by the dotted line, it is not necessary to face the printed surface downward, and the manufacturing process can be further simplified. Alternatively, the bumps 4 may be formed using both surface tension and gravity.

In the above-described embodiments 1 and 2, the example of forming the bumps 4 on the printed wiring board 1 has been described, but the bumps 4 may be formed on the lands of the semiconductor chip 5.

In addition, although the above-described embodiments 1 and 2 have been described with respect to the bump forming method in the case of mounting by the BGA technique, the present embodiment is also applicable to the case of forming the bumps 4 used for so-called flip-chip mounting in which the bare chips cut from the semiconductor wafer are mounted on the printed wiring board 1. However, in the case of flip chip mounting, since the size of the bump 4 must be reduced as compared with the case of mounting by BGA technology, it is necessary to change the material ejected from the nozzle 12 or the ejection amount, or to change the pattern shape of the screen mask 21.

Further, aluminum, polysilicon, or the like is generally used as a material for lands to be formed on a die, but since solder is difficult to adhere to these materials, an intermediate metal layer considering adhesion, interdiffusion, and solder wettability needs to be formed on the surface thereof in advance before the step of spraying molten solder. For example, a surface layer of a metal to which solder such as copper or gold is easily attached is formed in advance by plating or vapor deposition. Alternatively, a surface layer of Cr-Cu-Au, TiW-Cu, Ti-Cu-Ni, Al/Ni-Cu, or the like is formed in advance. Such a surface layer is also effective when the bumps 4 are formed on a printed wiring board or the like where lands to which solder or the like is difficult to adhere are formed.

In the case of flip chip mounting, the bumps 4 may be formed on the semiconductor wafer before the semiconductor wafer is cut out, and the individual chips may be cut out after the bumps are formed.

Possibility of industrial utilization

As described above, according to the present invention, since the bump is formed by ejecting the conductive material from below the 1 st substrate toward the resist-covered surface of the 1 st substrate, an ideal hemispherical bump can be formed by the action of gravity. Further, if the conductive material is ejected while the 1 st substrate is conveyed, the conductive material can be uniformly ejected onto the 1 st substrate, and the dispersion of the size and shape of the bump can be suppressed.

Further, if two or more conductive materials are ejected, a bump having a multilayer structure can be easily formed. Therefore, the upper layer side of the bump can be easily melted at a lower temperature than the lower layer side, and the adhesiveness of the bump can be improved.

Claims

1. A bump forming method for forming a bump to be connected to lands formed on both of a 1 st and a 2 nd substrates, comprising:

covering the upper surface of the 1 st substrate except for the bump forming region with a resist; and

and a step of discharging a conductive material by adjusting a discharge amount from a lower side of the resist-covered surface of the 1 st substrate downward toward the resist-covered surface, thereby forming a substantially hemispherical bump in a land forming region on the 1 st substrate.

2. The method for forming a bump as claimed in claim 1, wherein:

the conductive material is sprayed while the first substrate 1 is conveyed.

3. The method for forming a bump as claimed in claim 1, wherein:

and ejecting two or more kinds of the conductive materials to form the bump having a multilayer structure.

4. The method for forming a bump as claimed in claim 3, wherein:

the bump is formed of two or more kinds of the conductive materials, and the upper layer side of the bump is melted at a lower temperature than the lower layer side of the bump.

5. The method for forming a bump as claimed in claim 1, wherein:

one of the 1 st and 2 nd substrates is a printed wiring board, and the other substrate is a semiconductor chip.

6. The method for forming a bump as claimed in claim 5, wherein:

the above semiconductor chip is a bare chip cut from a semiconductor wafer,

the bumps are formed for use in flip-chip mounting the bare chip on the printed wiring board.

7. The method for forming a bump as claimed in claim 6, wherein:

before the semiconductor wafer is cut, the bumps are formed on the entire surface of the semiconductor wafer.

8. A bump forming method for forming a bump to be connected to lands formed on both of a 1 st and a 2 nd substrates, comprising:

forming a print pattern by screen printing so as to include a land forming region on the 1 st substrate and be wider than the land forming region; and

and deforming the printed pattern by at least surface tension to form the substantially hemispherical bump.

9. The method for forming a bump as claimed in claim 8, wherein:

the 1 st substrate is placed with the surface on which the print pattern is formed facing downward until the print pattern is formed into a substantially hemispherical shape.

10. The method for forming a bump as claimed in claim 8, wherein:

11. The method for forming a bump as claimed in claim 10, wherein:

the above semiconductor chip is a bare chip cut from a semiconductor wafer,

12. The method for forming a bump as claimed in claim 11, wherein:

13. A bump forming method for forming a bump to be connected to lands formed on both of a 1 st and a 2 nd substrates, comprising:

a step of screen printing on the upper surface of the 1 st substrate so as to form a print pattern around a land on the 1 st substrate; and

and a step of placing the surface of the 1 st substrate on which the print pattern is formed downward until the print pattern formed on the 1 st substrate has a substantially hemispherical shape.

14. The method for forming a bump as claimed in claim 13, wherein:

15. The method for forming a bump as claimed in claim 14, wherein:

the above semiconductor chip is a bare chip cut from a semiconductor wafer,

16. The method for forming a bump as claimed in claim 15, wherein:

17. A semiconductor device having 1 st and 2 nd substrates, lands formed on both the 1 st and 2 nd substrates being connected by bumps, characterized in that:

the upper surface of the 1 st substrate except for the land forming region is covered with a resist, and the bump is formed by spraying a conductive material with the spraying amount adjusted from below the surface facing downward.