JPH09186162A - Formation of metal bump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to form high-density microminiature metal bumps with reliability. SOLUTION: Recesses 12 are formed on the surface of a substrate 10 in a pattern corresponding to the electrode terminals 18 on an electronic component 16. Metal balls 14 are placed in the recesses 12, and the electrode terminals 18 on the electronic component 16 are butted against the metal balls 14 in the recesses 12 in the substrate 10. In this state, the electronic component 16 and the substrate 10 are clamped between magnetic materials 20, 22. At least either of the electronic component 16 and the substrate 10 is heated to a temperature above the melting point of the metal balls 14, and molten metal balls 14 are transferred as metal bumps from the substrate 10 to the electronic component 10. Then the electronic component 16 is removed from the substrate 10 and the magnetic materials 20, 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a metal bump for mounting an electronic component such as a semiconductor chip on a printed circuit board.

[0002]

2. Description of the Related Art In response to recent demands for miniaturization and weight reduction of electronic devices, electronic components such as ICs and LSIs are highly integrated on a semiconductor chip, and input / output terminals (terminal electrodes) thereof. Number has grown to hundreds. As a method of mounting such a multi-terminal electronic component on a circuit board,
A method is known in which a metal bump such as a solder bump is formed in advance on the surface of an electronic component, and the metal bump is welded to the metal bump on the circuit board.

Conventionally, as a method of previously forming a metal bump such as a solder bump on the surface of an electronic component, there is a method of using a substrate for bump transfer. A vacuum suction port is provided at a predetermined position on the substrate.The metal spheres on which the bumps are to be formed are vacuum-sucked into these vacuum suction ports, and after aligning them with the electrode terminals of the flux-coated electronic component, the vacuum is applied. The suction is released, the metal ball is placed on the electrode terminal, and the metal bump is formed by heating the metal ball above the melting point of the metal ball.

The formation of bumps using a substrate having a recess is described in, for example, Japanese Unexamined Patent Publication No. 2-270327. Further, applying pressure or weight when mounting an electronic component to a solder bump on an electrode terminal of a circuit board is described in, for example, Japanese Patent Laid-Open No. 5-3196.

[0005]

When a substrate for bump transfer having a vacuum suction port is used, when the vacuum suction is released and the metal sphere is placed on the electrode terminal, the metal sphere becomes an electronic component due to the adhesive force of the flux. Fixedly held on the electrode terminals of
Electronic components can be heated in a heating furnace. However, if the amount of the flux is too large, the metal spheres may move to the adjacent metal bump forming region at the time of heating and coalesce with the adjacent molten metal spheres to cause a defect.

The flux applied to the electrode terminals forms a film due to the evaporation of the solvent component with the passage of time and loses its adhesive force, so that the metal bumps must be formed within a short time. Therefore, in order to form a metal bump by the conventional technique, a large-scale device having a metal sphere adsorption function, a uniform application function of a small amount of flux, and a quick metal sphere alignment function is required.

Even if such a large-scale device is used, the fixing force of the metal balls due to the flux is small,
In the process of heating the metal spheres above the melting point, there were cases where misalignment occurred due to external factors. An object of the present invention is to provide a method for forming metal bumps that can more reliably form high density minute metal bumps.

[0008]

According to the method of forming a metal bump of the present invention, a metal ball is arranged in a concave portion formed on the surface of a substrate in a pattern corresponding to an electrode terminal of an electronic component,
The electronic component and the substrate are sandwiched by a magnetic material in a state where the electrode terminals of the electronic component are butted against the metal sphere in the recess of the substrate, and at least one of the electronic component and the substrate is heated to a melting point of the metal sphere or higher. The molten metal sphere is transferred from the substrate to the electronic component as a metal bump, and the electronic component is removed from the substrate and the magnetic body.

A metal sphere is arranged in a recess formed on the surface of the substrate, and the electronic component and the substrate are sandwiched by a magnetic material in a state where the electrode terminals of the electronic component are butted against the metal sphere in the recess of the substrate. There is. Therefore, the metal sphere is held at a predetermined position by the magnetic force of the magnetic material regardless of the amount of the flux. In this way, when the metal sphere is melted with the metal sphere held at a predetermined position and the electronic component is removed from the substrate and the magnetic body, the metal sphere is transferred from the substrate to the electronic component and the electrode of the electronic component is removed. Metal bumps are formed on the terminals. In this case, if the electronic component and the substrate are arranged in a vertical relationship, the gravity of the magnetic substance is applied to the electronic component and the substrate.

Preferably, the recess and the metal sphere are formed in such a relationship that the metal sphere inserted into the recess partially projects from the surface of the substrate. By doing so, even if the size of the metal balls varies, the electrode terminals of the electronic component can be more surely brought into contact with the metal balls in the recesses of the substrate.

Preferably, the volume of the recess formed on the surface of the substrate is larger than the volume of the metal sphere. As a result, even when the surface of the electronic component is in close contact with the surface of the substrate, the material of the molten metal sphere does not spill out from the concave portion of the surface of the substrate, and the material of the metal sphere is adjacent to the metal bump. It does not flow into the formation area. Moreover, if the terminal electrode of the electronic component is sized so as to fit into the recess of the substrate, the terminal electrode comes into strong contact with the molten metal ball.

Preferably, one of the magnetic bodies on the outside of the stacked electronic components and the substrate is made of a hard magnetic body, and the other magnetic body is made of a soft magnetic body. As a result, the hard magnetic material generates a strong magnetic force to attract the soft magnetic material and uniformly integrate the electronic component and the substrate. Therefore, the cost is lower than when hard magnetic bodies are arranged on both sides. Moreover, if the hard magnetic body is placed on the upper side, its weight can be utilized.

When the Curie temperature of the hard magnetic material is set to be equal to or higher than the melting point of the metal sphere, more reliable magnetic force can be maintained even when heated. Preferably, the linear expansion coefficient of the substrate on which the metal balls are arranged is ± 15 × 10 ⁻⁶ / ° C. as compared with the linear expansion coefficient of the electronic component on which the electrode terminal is formed. As a result, the metal bump is formed at a predetermined position even if a difference in thermal expansion occurs between the substrate and the electronic component during heating. The main components of the metal sphere are Sn, A
It may be composed of any one of g, Au, Si, Ge, Bi, In, Cu, and Pb, or some combination thereof.

[0014]

1 and 2 are views showing a method of forming a metal bump according to a first embodiment of the present invention. In the method of forming a metal bump according to the present invention, the transfer substrate 10 is used. The substrate 10 is a flat plate, and the recesses 12 are formed in a pattern corresponding to the electrode terminals 18 of the electronic component 16 related to the one surface 10a. That is, the substrate 10 having the recess 12 is prepared. For example, the substrate 10 is made of stainless steel or another material, and the recess 12 is formed by etching or the like. The recess 12 has a rectangular cross section of, for example, several hundred μm. It goes without saying that the recess 12 can be formed in other shapes.

In FIG. 1A, a metal ball 14 to be a metal bump is placed in the recess 12 of the substrate 10. Metal ball 1
No. 4 consists of a solder alloy that is currently widely used to form solder bumps. However, not only the solder alloy but also other metals can be used as long as they can form bumps. That is, the main component of the metal sphere 14 is
Sn, Ag, Au, Si, Ge, Bi, In, Cu, P
It can consist of any one of b or some combination thereof.

In FIG. 1B, after the flux is applied to the metal spheres 14 in the recesses 12 of the substrate 10, the electronic parts 16 are formed.
And the electrode terminal 18 of the electronic component 16
Is aligned with the metal sphere 14 of the recess 12 of the substrate 10. The concave portion 12 of the substrate 10 is a specific electronic component 1
Since they are arranged in a pattern corresponding to the six electrode terminals 18, the electrode terminals 18 correspond one-to-one with the metal balls 14 of the recess 12. The electronic component 16 is composed of, for example, a semiconductor chip configured as an IC or LSI.

Preferably, the recess 12 and the metal ball 18 are
The metal sphere 18 inserted in the recess 12 is the surface 10 of the substrate 10.
It is formed so as to partially project from a. By doing so, the electrode terminals 12 of the electronic component 16 can be more reliably attached to the substrate 10 even if the sizes of the metal balls vary.
The metal balls 14 of the recess 12 can surely make contact.

In FIG. 1C, the electronic component 16 and the substrate 1
0 and the electrode terminals 18 of the electronic component 16 and the metal balls 14 of the recess 12 of the substrate 10 are butted against each other, the electronic component 16 and the substrate 10 are magnetic bodies 20, 22.
Sandwiched by. In the embodiment, the upper magnetic body 20 is a hard magnetic body and the lower magnetic body 22 is a soft magnetic body. By using a hard magnetic material having a large remanent magnetization, a relatively large magnetic force can be obtained with a relatively small magnetic material. Therefore, the hard magnetic material generates a strong magnetic force to attract the soft magnetic material, and the electronic component 16 and the substrate 10 are uniformly integrated. In this case, the cost is lower than when hard magnetic bodies are arranged on both sides. Moreover, if the hard magnetic body is placed on the upper side, its weight can be utilized.

For comparison, the electronic component 16 and the substrate 1
By stacking 0 and 0 in a horizontal posture and placing a simple weight on it, it is possible to obtain a force for integrating the electrode terminal 18 of the electronic component 16 and the metal ball 14 of the recess 12 of the substrate 10 by the weight. . However, in this case, a large weight is required, and particularly when the electronic component 16 is warped, a larger weight is required. When a large weight is used, the weight is inevitably heated in the subsequent heating step, and it becomes necessary to perform extra heating to heat the weight. Further, as a result, the electronic component 16 may be damaged.

The present invention does not have such a problem by using the magnetic bodies 20 and 22. Further, when a simple weight is used, it is difficult to convey the electronic component 16 and the substrate 10 with the electrode terminals 18 and the metal balls 14 abutted against each other without causing positional displacement, but the magnetic body 2 is used.
By using 0 and 22, the electronic component 16 and the substrate 10 can be easily connected to the electrode terminal 18, the electrode terminal 18 and the metal ball 14.
It is possible to convey without causing a positional deviation in a state where and are butted.

Therefore, the electronic component 16 and the substrate 10 are conveyed to a heating furnace while being superposed on each other, and the electronic component 16 and the substrate 10 are heated to a temperature equal to or higher than the melting point of the metal ball 14 as shown in FIG. . Then, the metal ball 14 is melted, the electronic component 16 is more closely attached to the substrate 10 by the magnetic force of the magnetic bodies 20 and 22, the terminal electrode 18 sinks into the recess 12, and the melted metal ball 14 is recessed. The metal bumps 14a are transferred from the substrate 10 to the electronic component 16 while becoming a shape according to the above shape. When the Curie temperature of the hard magnetic body 20 is set to be equal to or higher than the melting point of the metal spheres 14, more reliable magnetic force can be maintained even when heated.

Preferably, the volume of the recess 12 formed on the surface of the substrate 10 is set larger than the volume of the metal sphere 14. As a result, even if the surface of the electronic component 16 is in close contact with the surface of the substrate 10,
The material of the molten metal sphere 14 does not overflow from the recess 12 of the surface 10a of the substrate 10, and the material of the metal sphere 14 does not flow to the adjacent metal bump formation region. Moreover, if the terminal electrode 18 of the electronic component is sized to fit into the recess 12 of the substrate 10, the terminal electrode 18 makes strong contact with the molten metal ball 14.

Therefore, as shown in FIG.
When the electronic component 16 is detached from the substrate 10 and the magnetic bodies 20 and 22, the metal bumps 14 a are connected to the terminal electrode 1 of the electronic component 16.
It becomes the form attached to 8. Preferably, the linear expansion coefficient of the substrate on which the metal balls are arranged is ± 15 × 10 ⁻⁶ / ° C. as compared with the linear expansion coefficient of the electronic component on which the electrode terminal is formed. As a result, the metal bump is formed at a predetermined position even if a difference in thermal expansion occurs between the substrate and the electronic component during heating.

In this way, the metal sphere is inserted into the recess 12 formed on the surface 10a of the substrate 10 and the electronic component 1
Since the electronic component 16 and the substrate 10 are sandwiched between the magnetic bodies 20 and 22 with the electrode terminal 18 of No. 6 butted against the metal sphere 14 of the recess 12 of the substrate 10, the magnetic body 20, regardless of the amount of flux, The magnetic force of 22 holds the metal sphere 14 at a predetermined position. Thus,
The metal sphere 14 is melted in a state where the metal sphere 14 is held at a predetermined position, and the electronic component 16 is mounted on the substrate 10 and the magnetic bodies 20,
When removed from 2, the metal sphere 14 is transferred from the substrate 10 to the electronic component 16, and a metal bump is formed on the electrode terminal 18 of the electronic component 16.

FIG. 3 is a diagram showing that the electronic component 16 having the metal bumps 14a is thereafter attached to the circuit board 24. As shown in FIG. The circuit board 24 has a terminal electrode 26 corresponding to the terminal electrode 18 of the electronic component 16, and the metal bump 14a.
The metal bumps 14a are attached to the terminal electrodes 26 by pressing them against the terminal electrodes 26 in a heated state, whereby the electronic components 16 are electrically and mechanically connected to the circuit board 24.
Connected to.

FIG. 4 is a diagram showing a method for forming metal bumps according to the second embodiment of the present invention. FIG. 4 shows a step corresponding to FIG. 1C in the embodiment shown in FIGS. FIG.
In the above, the transfer substrate 10 is used as the related electronic component 1.
The recesses 12 are formed in a pattern corresponding to the electrode terminals 18 of No. 6. The recess 12 has a round and shallow shape. Other features are similar to those of the previous embodiment, and the second embodiment can also include the same steps as the steps of FIGS. 1 and 2.

In this example, Sn-37 having a diameter of 800 μm is used.
The Pb solder ball 14 is placed in the recess 12 having a depth of 400 μm provided in the stainless steel substrate 10, and is abutted on the electrode terminal 18 of the PBGA package 16.
It is sandwiched between hard magnetic bodies 20 and 22 composed of m-Co magnets, and 2
Heated to 30 ° C. It was possible to form Sn-37Pb solder bumps on the PBGA package 16 without damage.

FIG. 5 is a diagram showing a method for forming metal bumps according to the third embodiment of the present invention. In the previous example, the metal spheres 14 on which the solder bumps were to be formed were provided as solid spheres. In this embodiment, the metal spheres 14 on which solder bumps are to be formed are first made from solder paste 30.

In FIG. 5A, the transfer substrate 10 is prepared. The substrate 10 is a flat plate of silicon, and the recesses 12 are formed in a pattern corresponding to the electrode terminals 18 of the electronic component 16 related to the one surface 10a. Recess 12
Is a quadrangular pyramid formed by etching on the <100> crystal plane of silicon.

The squeegee 30 fills each recess 12 with the solder paste 30. In this case, the recesses 12 act as a measuring tool, and if the volumes of all the recesses 12 are equal, the amounts of the solder paste 30 in all the recesses 12 are also equal. After filling the solder paste 30 with the squeegee 30,
The surface 10a of the substrate 10 is rubbed with the knife edge 32 to make the amount of the solder paste 30 in the recess 12 more uniform.
The solder paste 30 is composed of a metal component as solder and a non-metal component such as flux.

Therefore, as shown in FIG.
When the substrate 10 is heated above the melting point of the solder, the metal component of the solder paste 30 melts and becomes round due to surface tension,
It becomes the metal ball 14. The metal spheres 14 become solid metal spheres at normal temperature, and hence the same state as in FIG.

Therefore, in FIG. 5C, after the flux is applied to the metal spheres 14 in the recesses 12 of the substrate 10, the electronic component 16 is superposed on the substrate 10, and the electrode terminals 18 of the electronic component 16 are placed on the substrate 10. The metal ball 14 of the concave portion 12 is butted. Further, the electrode terminal 18 of the electronic component 16 and the substrate 10
With the metal sphere 14 of the recess 12 of the
The electronic component 16 and the substrate 10 are sandwiched by the magnetic bodies 20 and 22.

In this way, the electronic component 16 and the substrate 10 are overlapped with each other in the state where the electronic component 16 and the substrate 10 are superposed on each other.
Heat to above the melting point of 4. Then, the metal balls 14 are melted, and the electronic component 16 is more closely attached to the substrate 10 by the magnetic force of the magnetic bodies 20 and 22. Therefore, as shown in FIG. 5D, the electronic component 16 is mounted on the substrate 10 and the magnetic body 2.
When removed from Nos. 0 and 22, the metal bumps 14a become a form in which they are attached to the terminal electrodes 18 of the electronic component 16.

In this example, Pb-5S having a diameter of 110 μm is used.
The n solder balls 14 are placed in the recesses 12 having a depth of 120 μm provided in the silicon substrate 10 and abutted on the electrode terminals 18 of the bare chip 16, and then the hard magnetic body 20 made of an Sm—Co magnet and the soft magnetic body made of an iron plate are arranged. It was sandwiched with the body 22 and heated to 350 ° C. Solder bumps could be formed on the bare chip 16 without any damage.

[0035]

As described above, according to the present invention,
It is possible to more reliably form high-density minute metal bumps.

[Brief description of the drawings]

FIG. 1 is a diagram showing a method for forming a metal bump according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a step that follows FIG.

FIG. 3 is a view showing how an electronic component having metal bumps is attached to a circuit board.

FIG. 4 is a diagram showing a method of forming a metal bump according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a method of forming a metal bump according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Substrate 12 ... Recess 14 ... Metal ball 16 ... Electronic component 18 ... Terminal electrode

Claims (7)

[Claims] 1. A metal ball (14) is arranged in a recess (12) formed in the surface of a substrate (10) in a pattern corresponding to an electrode terminal (18) of the electronic component (16), and an electrode of the electronic component is provided. The electronic component and the substrate are sandwiched by magnetic bodies (20, 22) in a state in which the terminals are abutted against the metal balls in the concave portion of the substrate, and at least one of the electronic component and the substrate is heated to the melting point of the metal ball or higher. A method of manufacturing a metal bump, comprising: transferring a molten metal ball from the substrate to the electronic component as a metal bump, and removing the electronic component from the substrate and the magnetic body. 2. The recess (12) and the metal sphere (14) are formed in such a relationship that the metal sphere inserted into the recess partially projects from the surface of the substrate. The method of manufacturing a metal bump according to claim 1. 3. A recess (1) formed on the surface of a substrate.
The method of manufacturing a metal bump according to claim 1 or 2, wherein the volume of 2) is larger than the volume of the metal sphere (14). 4. The magnetic body (20) on the outer side of the stacked electronic component (16) and the substrate (10) is made of a hard magnetic body, and the other magnetic body (22) is made of a soft magnetic body. The method for manufacturing a metal bump according to any one of claims 1 to 3, wherein: 5. The method of manufacturing a metal bump according to claim 1, wherein the Curie temperature of the hard magnetic body (20) is equal to or higher than the melting point of the metal sphere (14). 6. A substrate (10) on which metal balls (14) are arranged.
Coefficient of linear expansion is ± 15 × 10 ^{−6 as} compared with the coefficient of linear expansion of the electronic component (16) on which the electrode terminal (18) is formed.
/ ° C. 6. The method for manufacturing a metal bump according to claim 1, wherein the temperature is / ° C. 7. The main component of the metal sphere (14) is Sn,
7. Manufacture of a metal bump according to any one of claims 1 to 6, characterized in that it comprises any one of Ag, Au, Si, Ge, Bi, In, Cu, Pb or some combination thereof. Method.