JPH0766210A - Method of forming bump - Google Patents

Abstract

PURPOSE:To provide a method of forming bumps, in which a screen is easily released. CONSTITUTION:Bumps 51 of conductive bonding agent 5, which increases its bonding power by heat, are attached to the upper surface of a substantially flat plate 1 coated with adhesive 2. A semiconductor chip 10, heated, is placed and pressed against the bumps so that they can be bonded. Then, the adhesive 2 is removed by organic solvent, for example, isopropyl alcohol, before the plate 1 is separated from the bumps. The adhesive 2 may also be of the type that increases its adhesiveness by heat.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming bump electrodes for electrically connecting semiconductor elements.

[0002]

2. Description of the Related Art Wire bonding using a gold wire or the like is generally used to electrically connect a wiring substrate, such as a lead frame or a printed wiring board, to a chip-shaped semiconductor element. In order to cope with the increase in the number of devices and the narrowing of pitches, a device that is connected to a semiconductor element via a bump electrode that is electrically connected is used.

Conventionally, the method of forming such bump electrodes includes a method of directly forming bumps on electrode pads of a semiconductor element, and a method of forming bumps on a base such as ceramics from the viewpoint of mass productivity. A method of transferring this bump to a semiconductor element is used.

In the method of transferring bumps to a semiconductor element, first, a metallic screen is placed on a base such as ceramics, and a bump material made of silver paste or the like is printed on the base through the screen. . The screen is provided with openings corresponding to the positions of the bumps to be formed in advance, and the material of the bumps is printed on the base through the openings.

Then, after forming the bumps on the base, the substrate on which the semiconductor elements are formed is mounted on the bumps to connect the bumps to the electrode pads of the semiconductor element. As a result, the bumps are transferred onto the electrode pads of the semiconductor element, and by curing the bumps, bump electrodes that are electrically connected to the semiconductor element are formed.

[0006]

However, such a bump electrode forming method has the following problems. That is, the bumps are printed on the base using a screen,
After that, when the screen is separated from the base, the viscosity of the bump material causes the bump to peel off together with the screen, which is a problem of deterioration of so-called plate printing. This deterioration of the print area becomes more remarkable as the diameter of the bump becomes smaller, and it becomes difficult to deal with the case where the number of electrodes is large or the pitch is narrow.

Further, if the bumps formed on the semiconductor element are not uniform in height, the contact with a wiring substrate such as a lead frame or a printed wiring board will be adversely affected. Therefore, it is necessary to make the height uniform by performing ultrasonic grinding or the like. However, performing such a process causes breakage or peeling of the bump.

[0008]

The present invention is a method of forming a bump electrode, which has been made to solve such a problem. That is, in this bump electrode forming method, first, a temporary fixing adhesive is applied to the upper surface of a substantially flat base to form a plurality of bumps made of a resin that has conductivity and whose adhesive force increases by heating. The semiconductor element and the bumps are bonded by bonding them on a fixing adhesive, and then the substrate on which the semiconductor element is formed is heated to press the substrate on the bump, and then the temporary fixing adhesive is applied with an organic solvent. It is used to dissolve and separate the base and the bump. Further, it is also a method of forming bump electrodes using an adhesive for temporary fixing whose adhesive force increases by heating.

[0009]

The bonding force between the bumps and the base is increased by bonding the bumps with the temporary adhesive applied to the upper surface of the base. For example, when bumps are printed using a screen and then the screen is released, the bumps are in close contact with the base, which improves the printability. Further, by pressing the substrate onto the bumps to connect the semiconductor element and the bumps, and then dissolving the temporary fixing adhesive with an organic solvent, the base and the bumps are easily separated from each other. The bump electrode is connected to.

Also, by using a temporary fixing adhesive whose adhesive strength increases by heating, the adhesive strength of the temporary fixing adhesive can be increased only when the bumps are connected to the base. become. Furthermore, by using a resin having conductivity as the material of the bump, the bump can be made to have elasticity, and the difference can be absorbed even if the height of the bump is uneven.

[0011]

EXAMPLE An example of a method of forming a bump electrode according to the present invention will be described below with reference to the drawings. 1 to 3 are cross-sectional views illustrating a method of forming a bump electrode according to the present invention in the order of steps,
In this forming method, after the bumps 51 are formed on the base 1, the bumps 51 are transferred to the side of the substrate 10 on which the semiconductor element is formed.

First, as the application of the temporary fixing adhesive shown in FIG. 1A, the temporary fixing adhesive 2 is applied to the upper surface of a substantially flat base 1 made of ceramics or the like. Adhesive 2 for temporary fixing
For example, a so-called thermo-viscous resin whose adhesive force increases by heating is used and is applied to a thickness of about 100 μm.

Next, as the evaporation of the solvent shown in FIG. 1 (b), the base 1 coated with the temporary fixing adhesive 2 is mounted on the hot plate 3 and the temperature is 70 ° C. to 85 ° C. for 5 minutes to 10 minutes. It is heated for a minute to evaporate the solvent contained in the temporary fixing adhesive 2. As a result, the temporary fixing adhesive 2 is cured on the base 1.

Next, as the printing shown in FIG. 1C, the screen 4 is formed on the upper surface of the temporary fixing adhesive 2 applied to the base 1.
Then, the conductive adhesive 5 is printed. That is, the screen 4 is provided with an opening 41 in advance corresponding to a position where a bump (see FIG. 2) is desired to be formed, and the conductive adhesive 5 applied on the screen 4 is spread by a squeegee 6. The conductive adhesive 5 is printed on the temporary adhesive 2 through the opening 41.

When this printing is performed, the base 1 is heated by the hot plate 3 and the adhesive 2 for temporary fixing is set to 100 for example.
Heat at 5 ° C to 120 ° C for 5 seconds to 25 seconds. By this heating, the adhesive force of the temporary adhesive 2 is increased so that the conductive adhesive 5 printed from the opening 41 can be brought into close contact with the temporary adhesive 2.

After the printing of the conductive adhesive 5 is completed, as shown in FIG.
As the screen raising shown in (a), the screen 4 is raised so as to be separated from the base 1. The surface of the screen 4 is previously coated with a fluororesin or the like, and the adhesive force between the temporary adhesive 2 and the screen 4 is not great. That is, the conductive adhesive 5 adheres to the temporary adhesive 2 with a large adhesive force, but the screen 4 adheres to the temporary adhesive 2 with an adhesive force much smaller than the adhesive force. It will be.

For this reason, when the screen 4 is separated from the base 1, the conductive adhesive 5, that is, the bumps 51 are removed from the screen 4.
At the same time, it does not peel off, and the bumps 51 can be neatly left on the base 1.

Next, as the bump connection shown in FIG. 2 (b), the substrate 10 on which a semiconductor element (not shown) is formed is bumped from the bumps 51 formed on the base 1 via the temporary bonding adhesive 2. The semiconductor element and the bump 51 are connected by pressing. At this time, the substrate 10 is heated to, for example, 170 ° C., and the bumps 51 are heated at the time of connection so that the bumps 5
The adhesive force of 1 is increased to ensure that the substrate 10 and the bump 51 are adhered. As a result, the semiconductor element and the bump 51 are electrically connected. The substrate 10 to which the bumps 51 are connected may be chip-shaped or wafer-shaped.

Next, as a temporary fixing adhesive solution shown in FIG. 2C, the base 1 and the substrate 10 connected via the bumps 51 are immersed in an organic solvent such as isopropyl alcohol 7 to temporarily fix them. Adhesive 2 for adhesive is dissolved. For example, the adhesive 2 for temporary fixing is dissolved by using isopropyl alcohol 7 having a concentration of 70%, and the bump 51 and the base 1 are separated. The organic solvent is not limited to isopropyl alcohol 7 as long as it can dissolve only the adhesive 2 for temporary fixing.

Due to this separation, the substrate 1 as shown in FIG.
The bump electrode 5 is in a state in which only the bump 51 remains at 0, and is electrically connected to a semiconductor element (not shown) formed on the substrate 10.
1a is formed.

FIG. 4 is a sectional view for explaining the bonding of the substrate 10 having the bump electrodes 51a formed thereon. That is, the substrate 10 is mounted so that the bump electrodes 51a are in contact with the wiring substrate including the lead frame 9 and the like,
The substrate 10 is pressed while being heated to, for example, 250 ° C. to 300 ° C. by using the bonding tool 8. The adhesive force of the bump electrode 51a is increased by heating, and the bump electrode 51a is bonded in a state of being aligned with a predetermined connection position of the lead frame 9. Thereby, the bump electrode 51a
The semiconductor element (not shown) formed on the substrate 10 and the lead frame 9 are electrically connected via the.

Further, since the bump electrode 51a of the present invention is made of the conductive adhesive 5, it has a predetermined elasticity, and even if the height of the formed bump electrode 51a is not uniform, the bonding tool is formed. By the pressing force of 8, the bump electrodes 51a are slightly contracted so that all the bump electrodes 51a can come into contact with the lead frame 9. Further, the elasticity of the bump electrode 51a can absorb the warp of the wiring substrate formed of the lead frame 9, so that the stress after bonding can be relaxed.

The temporary fixing adhesive 2 described in this embodiment is not limited to the thermo-viscous adhesive, and the bumps 51 can be temporarily fixed to the base 1 and the bumps 51 are connected to the substrate 10. Anything that can be easily peeled off later may be used.

[0024]

As described above, the bump electrode forming method of the present invention has the following effects. That is, even when the bumps are printed on the base using the screen, the bumps are not peeled off together with the screen, and the bumps can be reliably transferred to the substrate on which the semiconductor element is formed. Therefore, bump electrodes can be reliably formed even if the number of electrodes of the semiconductor element is large or the pitch is narrow.

Further, since reliable electrical connection can be obtained even if the bump electrodes have uneven heights, it is possible to manufacture a highly reliable semiconductor device.

[Brief description of drawings]

FIG. 1 is a cross-sectional view (No. 1) illustrating a method for forming bump electrodes according to the present invention, in which (a) is an adhesive application for temporary fixing, and (b) is a sectional view.
Indicates evaporation of the solvent, and (c) indicates printing.

FIG. 2 is a cross-sectional view (part 2) for explaining the method for forming bump electrodes of the present invention, (a) showing a screen rise, (b) showing bump connection, and (c) showing dissolution of a temporary fixing adhesive. is there.

FIG. 3 is a sectional view (No. 3) for explaining the bump electrode forming method of the invention.

FIG. 4 is a cross-sectional view illustrating bonding.

[Explanation of symbols]

 1 Base 2 Temporary Fixing Adhesive 3 Hot Plate 4 Screen 5 Conductive Adhesive 10 Substrate 51 Bump 51a Bump Electrode

Claims (2)

[Claims] 1. A method of forming a bump electrode electrically connected to a semiconductor element on a substrate on which a semiconductor element is formed, the method comprising: applying a temporary fixing adhesive to the upper surface of a substantially flat base; And a step of adhering a plurality of bumps made of a resin whose adhesive strength increases by heating on the temporary fixing adhesive, and pressing the substrate on the bump with the substrate on which the semiconductor element is formed being heated. Forming a bump electrode, which comprises a step of connecting the semiconductor element and the bump, and a step of dissolving the adhesive for temporary fixing with an organic solvent to separate the base and the bump. Method. 2. The bump electrode forming method according to claim 1, wherein the adhesive for temporary fixing has an adhesive strength increased by heating.