JP3121464B2 - Bump forming method and bump manufacturing apparatus - 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, which are metal protrusions provided for connection to external leads, on electrode pads provided on a peripheral portion of a substrate such as a semiconductor chip. And a bump manufacturing apparatus. More specifically, the present invention relates to a bump forming method using screen printing and a bump manufacturing apparatus.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of electronic equipment, semiconductor devices incorporating integrated circuits (ICs) and the like do not have lead wires derived by molding with resin, but COB, COB.
Semiconductor chips (so-called bare chips), such as G or TAB, in which bumps, which are metal projections for external connection, are formed directly on electrode pads of the semiconductor chip are used. Since this type of semiconductor chip is used by directly connecting to a wiring lead of a printed circuit board or the like (so-called wireless bonding), it advantageously contributes to downsizing of electronic devices.

FIG. 4 shows a bump portion of such a semiconductor chip.
This will be described with reference to the cross-sectional view shown in FIG. The electrode terminals for external connection of the semiconductor circuit of the semiconductor substrate 1 are led out to the periphery of the semiconductor chip by aluminum wiring or the like, and the electrode pads 11 are formed. A metal bump 14b is formed on the electrode pad 11. However, in many cases, the aluminum constituting the electrode pad 11 and the solder constituting the bump 14b do not adhere to each other and do not adhere to each other.
A bump 14b is formed thereon with the interposition of 12, and a portion where no bump is formed is covered with a passivation film 13 made of a silicon oxide film, a silicon nitride film, or the like.

Conventionally, such bumps 14b are generally formed by electrolytic plating. In addition, methods such as screen printing, transfer and vapor deposition have been studied. When bumps are formed by a screen printing method, it is necessary to dry and fire the printed metal paste molded body, and drying and firing are usually performed in an oven or the like.

[0005]

However, when the bumps are dried in an oven, the drying starts from the surface of the bumps, so that the solvent or gas inside the bumps is not released and remains in the bumps. There is a problem that it is brittle and has a high electrical resistance and does not fulfill the function of a bump.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a bump forming method and a bump manufacturing apparatus capable of solving such a problem and forming a bump easily by screen printing without generating a gap in the bump.

[0007]

According to the bump forming method of the present invention, a mask having holes corresponding to electrode pads provided on a substrate is provided on the substrate, and a metal paste is applied from the mask by screen printing. Printing, heating from under the substrate, drying the metal paste, then the
The method is characterized in that the metal paste is baked by an apparatus different from drying .

[0008] Further, the bump manufacturing apparatus of the present invention comprises a drier for heating the substrate on which the metal paste is printed by screen printing from below, and a baking device for firing the substrate dried by the drier. And a transfer device for transferring the substrate, wherein drying and firing are continuously performed while the substrate is transferred by the transfer device.

[0009]

According to the bump forming method of the present invention, bumps can be easily formed in a short time by screen printing, and the gas in the bumps is completely removed by heating and drying from the lower side of the substrate, thereby improving the strength. And a bump having a low electric resistance can be formed. Moreover, according to the bump manufacturing apparatus of the present invention, the processes from screen printing to drying and baking of the bump can be continuously performed, and automation can be performed.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is a cross-sectional view of a bump portion for explaining a bump forming method of the present invention in order, 1 is a substrate such as a semiconductor substrate or a circuit board, 2 is an electrode pad, 5 is a metal mask, and 6 is a metal mask. The electrode pad 2 is exposed at the periphery of the substrate 1, and the hole 6 is formed at a position corresponding to the electrode pad 2 on the metal mask 5.

Here, the metal mask 5 is made of a thin film of stainless steel, nickel, tungsten or the like, and has holes 6 corresponding to the electrode pads 2 provided on the substrate 1 on which bumps are to be formed. This metal mask 5 is usually 50-30
It is formed with a thickness of 0 μm. Hole 6 if too thick
Is not formed vertically, and if it is too thin, the height of the bumps becomes low, and it becomes impossible to protrude from other films or the like.

As shown in FIG. 1A, first, the substrate 1 is placed on a fixing jig 3 and aligned, and then the substrate 1 is removed from a suction hole 4 opened on the upper surface of the fixing jig 3. Vacuum,
The substrate 1 is securely placed on the fixing jig 3.

Next, as shown in FIG. 1B, a metal paste 9 is printed by a screen printing machine. As the metal paste 9, a material is selected according to the purpose of the bump to be formed. For example, a silver paste, a solder paste, a gold paste, a copper paste, or the like is used. The silver paste is a mixture of silver powder and glass powder in a solvent butyl carbitol acetate (BCA) to form a paste. The solder paste is a mixture of eutectic solder powder mixed with a flux to form a paste. . As a specific example, after firmly aligning the hole 6 of the metal mask 5 so as to be over the electrode pad 2, the metal mask 9 is fixed from all three directions with the fixture 7, the metal paste 9 is embedded in the hole 6 with the squeegee 8, This is referred to as a paste molded body 14. At this time, the metal paste 9 is not left on the metal mask 5.
If the metal mask 5 is removed when drying and firing, the metal paste 9 may remain on the metal mask 5.

Next, as shown in FIG.
Then, the metal mask 5 is removed from the screen printing machine and heated from below by a heater 10 such as a hot plate. Then, the metal paste molded body 14 starts drying from the lower side facing the substrate 1, the solvent in the metal paste molded body 14 evaporates from the open upper side, and is dried sequentially from the lower side. After that, the metal mask 5 is removed, and FIG.
As shown in (d), bumps are formed on the electrode pads 2 of the substrate 1.
14a is formed.

In FIG. 1C, since the metal mask 5 is for preventing the metal paste molded body 14 from sagging, the metal paste molded body 14 having a certain viscosity is used.
When using, the metal mask 5 may be removed and drying may be performed.

After drying as described above, it is preferable to produce the bumps 14a by firing the metal paste molded body 14 using, for example, an RTA (Rapid Thermal Anneal) device 15 as shown in FIG. . Here, the RTA apparatus is, for example, a light lamp such as a halogen lamp, a xenon lamp, an arc lamp or a discharge lamp, a laser beam,
A device capable of performing heat treatment in a short time (usually within 10 ns to several minutes) from an irradiated surface by irradiating light, heat ray, beam, or the like as a heat source such as an electron beam (EB) or a carbon heater. According to this RTA apparatus, the surface is irradiated with light or a beam and heated, and the temperature rises. Further, when there is a difference between transmittance and absorptivity depending on a material to be irradiated with light or the like, light received by a material having good absorptivity is converted into heat, and the temperature rises.

This firing is for improving the electrical conductivity by improving the contact between the metal powders of the metal paste compact. Therefore, for eutectic solder bumps, for example, 210
It is baked by heating at about 220 ° C. for about 1 to 60 seconds, completely melted (melting point of eutectic solder is 183 ° C.), and then cooled and solidified to form a lump of solder. Good electrical conduction. On the other hand, silver bumps are baked by heating at, for example, about 350 to 450 ° C. for about 5 to 120 seconds. At this temperature, the silver powder does not reach a molten state, but the solvent formed into a paste evaporates.
The surfaces between the powders are connected to improve the electrical conductivity of the bumps 14a.

The RTA device 15 includes a SUS chamber 16 which is a sealable box having a lid 16a, a halogen lamp 21 provided inside the SUS chamber 16, and further inside the halogen lamp 21 toward the lid 16a. A first supply pipe 18 is provided on the lid 16a, a temperature measurement opening pipe 19 on the back surface of the substrate below the quartz susceptor 17, and a quartz susceptor 17 on the side opposite to the open end. Exhaust pipe
20 are provided. With this apparatus, the lid 16a is opened, the substrate 1 is placed on the quartz wafer susceptor 22, and the lid 16a is closed so that the substrate 1 is located inside the quartz susceptor 17. After that, the halogen lamp 21 is turned on, the temperature of the metal paste molded body 14 is set to a firing temperature suitable for the metal material, and firing is performed to form bumps.

As a specific example, a silver paste is used as the above-mentioned metal paste 9, for example, placed on a hot plate at about 150 ° C. for about 1 to 3 minutes, dried, and then RTA.
For example, it was baked at about 350 ° C. for about 1 to 60 seconds.

Next, a bump manufacturing apparatus for forming the above-mentioned bump will be described with reference to FIG. In FIG. 3, reference numeral 30 denotes a heat-resistant transfer device made of, for example, an endless belt; 31, a screen printing machine; 32, a dryer made of a heater 10;
This is a firing device which is loaded on 22 and fires by closing the lid 16a.

The substrate 1 on which the metal paste 9 is printed by the screen printing machine 31 and the metal paste molded body 14 is formed is sent to the dryer 32 by the transfer device 30. Dryer
At 32, the substrate 1 is heat-treated from below by the heater 10,
The solvent and gas in the bump 14a are sufficiently released to the outside and dried. At this time, if there is a possibility that the metal paste 9 flows out, the metal paste 9 may be dried while being covered with the metal mask 5 as shown in FIG.

Further, the substrate 1 is transported by the transport device 30 to the baking device 33, and the substrate 1 is transferred onto the protruding plate of the lid 16a and the quartz wafer susceptor 22 located in the depth direction of the drawing by a feeding device not shown. The lid 16a is closed and firing is performed as described above.
After that, the cover 16a is opened, and the substrate 1 is returned to the transporting device in the front direction of the drawing by a feeding device (not shown), and is carried out as a finished product.

If there is a possibility that the metal paste 9 flows out, drying and baking are performed with the metal mask 5 as shown in FIG. .

In the above embodiment, the bumps formed on the semiconductor chip are formed in the state of the semiconductor wafer. However, the bumps are not limited to the semiconductor chip, but the leadless resistors, capacitors, and wirings connected to a circuit board or the like in a leadless manner. The present invention can be applied to other electronic components. Further, there are cases where bumps are formed not only on electronic components but also on connection portions of a circuit board or the like, and the present invention can be applied to any case of forming bumps.

[0025]

According to the bump forming method of the present invention, since the metal paste molded body is heated and dried from the lower side of the substrate, the metal paste starts drying from the bottom portion which is in contact with the substrate, The solvent in the molded body is completely removed to the outside from the non-contact open portion, and is not left as a void in the bump. Therefore, the strength of the bump is enormous, and the electrical resistance is reduced, so that a good bump can be obtained. Further, by using screen printing, a large amount of sintered body of metal paste can be easily formed in a short time.
Further, according to the bump manufacturing apparatus of the present invention, processes from screen printing to drying and baking of the bump can be continuously performed by automation. As a result, manufacturing costs are reduced, which contributes to cost reduction of electronic components.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view of a bump portion for explaining a bump forming method of the present invention in order.

FIG. 2 shows R used in a firing step of the bump forming method of the present invention.
FIG. 3 is an explanatory cross-sectional view of an example of a TA device.

FIG. 3 is a configuration diagram of a bump manufacturing apparatus of the present invention.

FIG. 4 is an explanatory sectional view of a bump portion formed on a substrate.

[Description of Signs] 1 Substrate 2 Electrode pad 5 Metal mask 6 Hole 9 Metal paste 14 Metal paste molded body 14a Bump

Claims (2)

(57) [Claims] 1. A mask having holes corresponding to electrode pads provided on a substrate is provided on the substrate, a metal paste is printed on the mask by screen printing, and the metal paste is heated from below the substrate. Drying the metal paste,
Then , the metal paste is fired by an apparatus different from the drying method. 2. A dryer for heating the substrate on which the metal paste is printed by screen printing from below, a baking unit for baking the substrate dried by the dryer, and a transport for transporting the substrate. A bump manufacturing apparatus, comprising: an apparatus for continuously drying and firing while transporting the substrate by the transport apparatus.