JP2001185570A - Bump formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bump formation method which can increase, at a low cost the height of the bump, which serves as the connection between the wiring of the package of an LSI and the main body of a printed board. SOLUTION: This bump formation method can make the height of a bump increase at a low cost, and this has a process of laying a metal mask on the top of a substrate for transfer, such that the recess and the opening may conform to each other, a process of filling the recess and the opening with cream solder, a process of forming a solder ball by heating the substrate for transfer, thereby fusing the cream solder after removing the metallic mask, and a process of registering the substrate for transfer and an LSI and mounting it, so that the formed solder ball and an LSI pad make contact with each other, and a process of forming a solder bump by heating the substrate for transfer and the LSI, thereby causing solder wetting in the LSI pad.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for forming a bump for connecting a wiring of an LSI (integrated circuit device) package to a printed circuit board body, and more particularly to a bump forming method capable of increasing the bump height at low cost. About the method.

[0002]

2. Description of the Related Art Various methods such as plating, vapor deposition, ball mounting, printing, and recently, metal jet are used as a method of forming a bump serving as a connection portion between an LSI (integrated circuit device) package wiring and a printed circuit board body. Proposed. For example, Japanese Patent Application Laid-Open No.
No. 2,649,322. In other words, the prior art described in Japanese Patent Application Laid-Open No. 8-264932 is designed to prevent the solder paste from sliding and moving on the flux due to the contact of the solid content of the flux in the solder paste so that the solder bump formation defect does not occur. A solder bump is formed on a plurality of wiring pads on an insulating substrate by providing a solder material and a flux, respectively, and heating and melting the solder material to form a solder bump on each wiring pad. In the method, a non-soldering member is provided on the insulating substrate so as to be located between the solder material and the flux of each wiring pad and heated together, and the non-soldering member is insulated after the solidification of the solder material starts. This is a method of forming solder bumps that separate from the substrate. Also, a non-soldering member is provided between each wiring pad on the insulating substrate, a screen mask is provided thereon, and a solder paste obtained by adding a solvent to the solder material and the flux through the opening of the screen mask is applied to each wiring. After printing on the pads and removing the screen mask, the insulating substrate provided with a non-soldering member between the solder material and the flux of each wiring pad is heated. According to such a solder bump forming method, there is disclosed an effect that the solid components of the flux are not brought into contact with each other, so that the solder does not move, and the solder bump can be formed without causing a solder bump formation defect. Have been.

[0003]

However, the above-mentioned conventional techniques using plating, vapor deposition, ball mounting, printing, metal jet, and the like are all technically and economically advantageous and disadvantageous. Among these prior arts, the printing method which is the most advantageous in terms of cost is particularly noted, but the bump height is lower than other methods, and the mounting reliability of an LSI (integrated circuit device) is reduced. There was a problem.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a bump forming method capable of increasing the bump height at low cost.

[0005]

The gist of the present invention is to provide a bump forming method capable of increasing the height of a bump at low cost, wherein a concave portion and an opening portion of a metal mask are formed on a transfer substrate. Overlapping step, filling the concave portion and the opening with cream solder containing a high melting point solder as a solder material, filling the concave portion and the opening with cream solder, and removing the metal mask. Then, heating the transfer substrate to melt the cream solder to form a solder ball, and mounting the transfer substrate and the LSI such that the formed solder ball and the LSI pad are in contact with each other. Process and
There is provided a bump forming method comprising a step of heating the transfer substrate and an LSI to cause solder wetting on the LSI pad to form a solder bump. Also,
The gist of the present invention resides in a bump forming method according to claim 1, further comprising a step of performing an inspection after forming the solder ball and mounting an LSI only on a non-defective part. The gist of the invention described in claim 3 is that the shape of the concave portion of the transfer substrate is a conical shape whose center portion gradually becomes deeper. The present invention resides in a bump forming method. The gist of the invention described in claim 4 is that the shape of the concave portion of the transfer substrate is a polygonal pyramid with a center portion gradually becoming deeper. In the method of forming bumps. The gist of the invention described in claim 5 is that the shape of the concave portion of the transfer substrate is a spherical shape with a central portion gradually deeper. The present invention resides in a bump forming method. The gist of the invention described in claim 6 is that the shape of the concave portion of the transfer substrate has an engraved shape in which a bottom surface is conical, a central portion is gradually deepened, and a surface vicinity is cylindrical. 3. The method according to claim 1, wherein
In the bump forming method described in (1). The gist of the invention described in claim 7 is that the shape of the concave portion of the transfer substrate has an engraved shape in which a bottom surface is a polygonal pyramid, a center portion is gradually deepened, and a surface vicinity is a cylindrical shape. 3. The bump forming method according to claim 1 or 2, wherein The gist of the invention described in claim 8 is that the shape of the concave portion of the transfer substrate has an engraved shape in which a bottom surface is a spherical surface, a center portion is gradually deepened, and a surface vicinity is a cylindrical shape. 3. The bump forming method according to claim 1, wherein Further, the gist of the invention according to claim 9 resides in the bump forming method according to claim 1 or 2, wherein the shape of the concave portion of the transfer substrate is a spherical base. The gist of the invention described in claim 10 resides in the bump forming method according to claim 1 or 2, wherein the shape of the concave portion of the transfer substrate is a truncated cone. The gist of the invention described in claim 11 resides in the bump forming method according to claim 1 or 2, wherein the shape of the concave portion of the transfer substrate is a truncated polygonal pyramid. The gist of the invention according to claim 12 is that the surface shape of the concave portion of the transfer substrate,
12. The bump forming method according to claim 1, wherein the shape of the opening of the metal mask has the same area. Claim 1
The gist of the invention described in claim 3 is that the opening area of the concave portion of the transfer substrate has a shape larger than the opening area of the metal mask. In the bump forming method described in (1). Also,
The gist of the invention described in claim 14 is that at least a part of the concave portion of the transfer substrate has a shape arranged outside the opening of the metal mask. 13. The bump forming method according to any one of the thirteenth aspect. The gist of the invention described in claim 15 is that the transfer substrate is a metal plate, and the concave portion is formed by etching the metal plate. In the bump forming method described in (1). The gist of the invention described in claim 16 is that the transfer substrate is ceramic, and the concave portion is formed by processing the ceramic.
4. The bump forming method according to any one of 4. The gist of the invention described in claim 17 is that the transfer substrate is a silicon substrate, and the method further comprises a step of using Si pits formed by etching the silicon substrate as the concave portions. 15. The bump forming method according to any one of the above items 14 to 14. Claim 18
The gist of the invention described in (1) is that a transfer substrate which is one of a transfer jig having a concave portion corresponding to an LSI pad, or a metal mask which is the other of a transfer jig having an opening corresponding to the LSI pad. 18. The bump forming method according to claim 1, wherein at least one of them is coated with a fluorine resin. The gist of the invention described in claim 19 is that the nitriding treatment is performed on the transfer substrate, which is one of the transfer jigs having a concave portion corresponding to the LSI pad. The bump forming method according to any one of the above. The gist of the invention according to claim 20 is that the transfer substrate has the concave portion for one LSI. The method according to claim 1, wherein Exist. The gist of the invention described in claim 21 resides in a bump forming method according to any one of claims 1 to 20, wherein a high melting point solder is included as a solder material.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The features of each embodiment described below are that a bump forming method using a substrate having a concave portion and a metal mask (transfer jig) having an opening increases the volume of solder, As a result, L
Another object of the present invention is to improve the mounting reliability of the SI.
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
FIG. 9 is a process cross-sectional view for describing a first process of the bump forming method according to the embodiment. Referring to FIG. 1, in the bump forming method of the present embodiment, a concave portion 1a is formed in a transfer substrate 2a (transfer jig) by machining or etching. At this time, the arrangement of the concave portions 1a is the same as the arrangement of the electrodes 8 (described later) of the LSI 9, and the size of the concave portions 1a is set to be equal to 0.
17mm, depth 0.05mm, pitch 0.24
mm. Also, a metal mask 4 (transfer jig) is provided with a circular opening 3 having the same arrangement as the concave portion 1a of the transfer substrate 2a (transfer jig). About 0.17mm, 0.068m thick
m.

FIG. 8 is a top view of a transfer substrate 2a (transfer jig) used in the bump forming method of the present invention. Referring to FIG. 8, the transfer substrate 2a (transfer jig) of the present embodiment has a structure (A) capable of simultaneously forming 16 (= 4 × 4) LSI 9 solder balls (solder balls 7 described later). ) Are arranged vertically and horizontally four by four.

FIG. 9A is an enlarged top view of a portion A of the transfer substrate 2a (transfer jig) of FIG. 8, and FIG.
It is sectional drawing which followed the center of the recessed part 1a which comprises the A section of (a). Referring to FIG. 9A, the transfer substrate 2a (transfer jig) of the present embodiment has several tens to
Several hundred concave portions 1a are arranged. Further, in the present embodiment, as shown in FIG. 9B, the cross-sectional shape of the concave portion 1a is a hemisphere.

As the material of the metal mask 4 (transfer jig) of the present embodiment, Ni, NiCo, stainless steel, and those whose surfaces are coated with a fluororesin can be used.

In this embodiment, at least one of the transfer substrate 2a, which is one of the transfer jigs, and the metal mask 4, which is the other of the transfer jigs, is coated with a fluororesin. I have. When the transfer substrate 2a is coated with a fluororesin, the solder balls 7
Is transferred to the LSI 9 to peel off the LSI 9 and the transfer substrate 2a. Further, when the transfer substrate 2a is used repeatedly, there is an effect that the flux attached to the transfer substrate 2a can be easily and completely cleaned. On the other hand, when the metal mask 4 is coated with the fluororesin, the effect of improving the water repellency of the flux of the cream solder 5 is improved, so that the plate removal property is improved and the variation in the printing volume can be reduced.

The material of the solder of the present embodiment is P
An alloy containing a high melting point solder containing at least one of b, Sn, Ag, Bi, In, Sb, Cu, and Au as a solder material is used. The high melting point solder contained in the cream solder 5 has poor wettability to the electrodes 8 (described later) of the LSI 9 due to the properties of the alloy, and the flux contained in the cream solder 5 has a high heat resistance because it uses a resin. Although the solder is low and adheres to the outer peripheral portion of the molten solder, voids are easily generated. However, the effect of the present invention is that the voids can be eliminated.

Next, each step of the bump forming method of the present embodiment will be described with reference to FIGS. FIG. 2 is the first of FIG.
FIG. 3 is a process cross-sectional view for explaining a second process performed after the process. FIG. 3 is a third process performed after the second process in FIG.
FIG. 4 is a process cross-sectional view for explaining a process, FIG. 4 is a process cross-sectional view for explaining a fourth process performed following the third process of FIG. 3, and FIG. 5 is a process performed after the fourth process of FIG. FIG. 14 is a process cross-sectional view for describing a fifth process to be performed. In the present embodiment, first, the first step shown in FIG.
The transfer substrate 2a (transfer jig) having the concave portion 1a arranged in the same arrangement as the electrode 8 (described later) of 9 and the metal mask 4 (transfer jig) having the circular opening 3 arranged in the same arrangement as the concave portion 1a )
After aligning the squeegee 6 with the metal mask 4
The cream solder 5 is filled into the round opening 3 and the concave portion 1a by scanning on a (transfer jig). Note that a large number of recesses 1a for one LSI 9 may be arranged on the transfer substrate 2a (transfer jig). In the present embodiment, the cream solder 5 having a melting temperature of about 314 ° C. is used.

Subsequently, the second step shown in FIG. 2 is performed to separate the metal mask 4 (transfer jig). In addition, when a printing failure occurs, the transfer substrate 2a (transfer jig) can be cleaned and printed again.

At this time, by inspecting whether or not the cream solder 5 is normally printed, it is possible to prevent defective products from flowing in subsequent steps. In addition, the inspection step in the second step includes a step of measuring the volume of the cream solder 5 by three-dimensionally scanning the surface of the cream solder 5 with a laser displacement meter.

Subsequently, a third step shown in FIG. 3 is performed, and the solder ball 7 is formed by heating to a temperature equal to or higher than the melting point of the solder.
At this time, the height variation of the bump 10 (described later) is reduced by inspecting the diameter of the solder ball 7.
In the inspection of the diameter of the solder ball 7, image data of the solder ball 7 taken by using an engineering image visualizing means such as a CCD (solid-state imaging device) camera is two-dimensionally image-processed, and the diameter and height of the solder ball 7 are measured. (A height of the top of the solder ball 7). At this time, the inspection of the diameter of the solder ball 7
Is executed in a cooled state.

Subsequently, a fourth step shown in FIG. 4 is performed. In the case of multi-cavity, the electrodes 8 of the LSI 9 and the transfer substrate 2a are formed.
The solder ball 7 is heated again to a temperature equal to or higher than the melting point of the solder while the solder ball 7 formed on the (transfer jig) is aligned and brought into contact with the solder ball 7. In addition, in the case of the first single-cavity, the positioning may be performed in a state where the solder ball 7 is heated and melted in advance.

After that, to peel off the LSI 9 from the transfer substrate 2a (transfer jig), a solvent such as a flux solvent, a higher alcohol, or isopropyl alcohol (IPA) is applied to the LSI 9 and the transfer substrate 2a (transfer jig). And a method of melting the flux by heating the flux to about 120 to 150 ° C. (flux softening temperature), bending the transfer substrate 2 a (transfer jig) and deforming the LSI 9 , Or a combination of these methods.

At this time, a flux for removing an oxide film is applied to the LSI 9 side in advance. As a result, the wettability between the electrode 8 and the solder ball 7 can be improved, and the adhesion between them can be improved. In the present embodiment, the flux may be applied to the solder ball 7 side.

Subsequently, a fifth step shown in FIG. 5 is executed, and the bumps 10 can be formed by cleaning and separating the transfer substrate 2a (transfer jig) and the LSI 9.

The material of the transfer substrate 2a (transfer jig) of the present embodiment does not easily react with solder and has heat resistance.
Good workability is desirable. For example, stainless steel, ceramic, or the like may be used. In the case of using stainless steel, it is desirable to use etching or machining, while in the case of ceramic, it is desirable to use machining. Transfer substrate 2 shown in the first to fifth steps
As a (transfer jig), it is desirable to use an amber alloy having a linear expansion coefficient matched with that of the LSI 9, for example, Fe ₆₀ Ni ₄₀ , in addition to a stainless steel material processed by etching. Further, the material for coating the transfer substrate 2a (transfer jig) may be Cr, Ta, T
A coating material such as i, TiN, Mo, fluororesin, or a material subjected to nitriding treatment can be used.

In general, when the cream solder 5 is rapidly heated, voids are generated in the solder balls 7, and when the solder is slowly heated, the solder balls are insufficiently melted to form balls. Therefore, it is necessary to obtain optimum heating conditions. Therefore, the transfer substrate 2
In order to improve the thermal conductivity of a (transfer jig), it is good to use a copper or aluminum plate, but it will react with solder,
It is desirable that the surface be plated with Cr, Ta, Ti, TiN, Mo, fluororesin, or the like, or subjected to nitriding.

As described above, according to the first embodiment, the following effects can be obtained. First, the first effect is L
That is, the mounting reliability of the SI 9 can be improved. The reason is that since the transfer substrate 2a (transfer jig) having the concave portion 1a and the metal mask 4 (transfer jig) are used, the volume of solder can be increased, and as a result, the bump 10 can be made higher. This is because the stress applied to the bump 10 when the LSI 9 is mounted can be dispersed.

The second effect is that the height variation of the bumps 10 can be reduced. The reason is the first
As described in the above effect, the volume of the solder can be increased, and as a result, the opening size of the metal mask 4 (transfer jig) can be set to a size that allows easy printing.

The third effect is that the yield of forming the bumps 10 on the LSI 9 can be improved. The reason is that since the solder balls 7 are formed on the transfer substrate 2a (transfer jig) in advance, it is possible to inspect whether the solder balls 7 are normally formed, and the good solder balls 7 are formed. This is because the bumps 10 can be formed by selecting an existing position and mounting the LSI 9.

(Second Embodiment) Next, a second embodiment of the present invention will be described.
An embodiment will be described in detail with reference to the drawings.
FIG. 6 is a process sectional view for explaining a bump forming method according to the second embodiment of the present invention. The same portions as those already described are denoted by the same reference numerals, and duplicate description will be omitted. If the position of the solder ball 7 and the position of the electrode 8 of the LSI 9 are deviated, the problem that the bump 10 is not formed at a normal position occurs.
When the solder is melted, the solder ball 7
The shape of the concave portion 1a is preferably a shape such as a cone or a quadrangular pyramid that becomes thinner toward the bottom so that is positioned. Therefore, in the present embodiment, as shown in FIG. 6, a concave portion 1b having a conical cross section in the substrate thickness direction (vertical direction on the paper surface) is formed on the transfer substrate 2a (transfer jig). It has features.

(Third Embodiment) Next, a third embodiment of the present invention will be described.
An embodiment will be described in detail with reference to the drawings.
FIG. 7 is a process sectional view for explaining a bump forming method according to the third embodiment of the present invention. The same portions as those already described are denoted by the same reference numerals, and duplicate description will be omitted. If the position of the solder ball 7 and the position of the electrode 8 of the LSI 9 are deviated, the problem that the bump 10 is not formed at a normal position occurs.
When the solder is melted, the solder ball 7
The shape of the concave portion 1a is preferably a shape such as a cone or a quadrangular pyramid that becomes thinner toward the bottom so that is positioned. Therefore, in the present embodiment, as shown in FIG. 7, a concave portion 1c having a cylindrical cross section in the substrate thickness direction (vertical direction on the paper surface) is formed on the transfer substrate 2a (transfer jig). It has features. It should be noted that, in place of the cylindrical concave portion 1c, a quadrangular pyramid groove having a quadrangular pyramid cross section in the substrate thickness direction (vertical direction on the paper) is formed on the transfer substrate 2a (transfer jig). The same operation and effect as in the case of the concave portion 1c having the shape can be obtained.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described.
An embodiment will be described in detail with reference to the drawings.
FIG. 10A is a process sectional view for explaining the bump forming method according to the fourth embodiment of the present invention.
FIG. 11B is a top view of FIG. The same portions as those already described are denoted by the same reference numerals, and duplicate description will be omitted. In the present embodiment, the opening diameter of the hemispherical concave portion 1d of the transfer substrate 2a (transfer jig) is φ
0.19 mm, the opening diameter of the round opening 3 of the metal mask 4 (transfer jig) is φ0.17 mm, and the area of the opening of the hemispherical recess 1 d of the transfer substrate 2 a (transfer jig). Is set large. According to the present embodiment, when filling cream solder 5 into hemispherical concave portion 1d of transfer substrate 2a (transfer jig), after cream solder 5 is filled from the center of hemispherical concave portion 1d. Since the filling is performed while the air is gradually expelled toward the outer periphery, the cream solder 5 can be filled in the hemispherical concave portion 1d of the transfer substrate 2a without any gap, and the printing volume can be stabilized. It works.

(Fifth Embodiment) Next, a fifth embodiment of the present invention will be described.
An embodiment will be described in detail with reference to the drawings.
FIG. 11 is a process top view for explaining a bump forming method according to the fifth embodiment of the present invention. The same portions as those already described are denoted by the same reference numerals, and duplicate description will be omitted. In the present embodiment, the dimensions (length × width) of the opening of the rectangular column-shaped recess 1e of the transfer substrate 2a (transfer jig) are 0.15 × 0.15 mm, and the metal mask 4 (transfer jig). The opening diameter of the round opening 3 of φ0.
It is 17 mm, and a part of the opening of the rectangular column-shaped concave portion 1e of the transfer substrate 2a (transfer jig) is projected horizontally from the opening of the metal mask 4 (transfer jig). According to the present embodiment, the same effects as in the fourth embodiment can be obtained.

(Sixth Embodiment) Next, a sixth embodiment of the present invention will be described.
An embodiment will be described in detail with reference to the drawings.
FIG. 12 is a process top view for explaining a bump forming method according to the sixth embodiment of the present invention. The same portions as those already described are denoted by the same reference numerals, and duplicate description will be omitted. In the present embodiment, the dimensions (length and width) of the opening of the rectangular column-shaped recess 1f of the transfer substrate 2a (transfer jig) are 0.15 × 0.15 mm, and the metal mask 4 (transfer jig). Of the rectangular opening 3a of the transfer substrate 2a (transfer jig) having the same opening shape with the dimensions (length × width) of 0.15 × 0.15 mm. The opening is rotated by 45 degrees with respect to the opening of the square opening 3a of the metal mask 4 (transfer jig), and the rectangular recess 3f of the transfer substrate 2a (transfer jig) is formed. Part of the opening is a metal mask 4 (transfer jig)
From the rectangular opening 3a in the horizontal direction. According to the present embodiment, the same effects as the effects described in the fourth embodiment can be obtained. The angle at which the rectangular opening 3a of the rectangular column-shaped recess 1f of the transfer substrate 2a (transfer jig) is arranged depends on the metal mask 4 (transfer jig).
May be arranged at any angle as long as it protrudes in the horizontal direction from the rectangular opening 3a. Further, the rectangular opening 3a of the metal mask 4 (transfer jig) may be arranged by rotation.

Lastly, the technical differences between the present embodiment and the above-described prior art will be described. With respect to the prior art described in the above-mentioned JP-A-8-264932,
In the present invention, first, voids in the solder can be reduced by performing reflow after printing (that is, once melting the cream solder on the transfer jig). The reason is,
When transferring the solder ball 7 to the electrode 8, the solder is applied to the electrode 8.
This is because the wetting proceeds from one point above and the flux can be driven to the outside of the bump 10. Second,
By adopting a shape in which the position of the melted solder ball is determined by contacting the bottom surface or side surface of the concave portion, defects during transfer can be suppressed. Third, L is selectively applied to non-defective parts.
By mounting the SI, it is possible to prevent a bump formation defect due to a printing defect. Fourth, there is an effect that the inspection is easier if the inspection is performed in the state of the ball. On the other hand, in the prior art described in the above-mentioned Japanese Patent Application Laid-Open No. 8-264932, since solder is melted to directly form bumps on LSI electrodes, fine solder particles flow simultaneously from unspecified portions on the electrodes. As a result, the flux tends to be trapped in the bumps.

Another conventional technique is described in, for example, Japanese Patent Application Laid-Open No. 9-270128. However, in the present invention, the cream solder 5 is inserted into the recess 1 a of the transfer substrate (transfer jig) 2 a via the metal mask 4.
Is printed, firstly, the mounting reliability of the LSI 9 can be improved, secondly, the transfer yield can be improved, thirdly, peeling of the LSI 9 after the transfer becomes easy, and fourthly, the solder 9 There is an effect that the amount of voids in the ball 7 can be reduced. The first reason is that bump 1
0 can be made higher, so that L is lower than bumps of lower height.
This is because stress due to a difference in thermal expansion coefficient between the SI 9 and the transfer substrate (transfer jig) 2a can be easily absorbed. The second reason is that the protrusion height of the solder balls 7 on the transfer substrate (transfer jig) 2a can be increased. The third reason is that the LSI 9 and the transfer substrate (transfer jig) 2
This is because it is possible to widen the distance from a, and it is easy for a cleaning agent, a solvent, and the like to penetrate into the gap. The fourth reason is that at the time of transfer, the LSI 9 and the transfer substrate (transfer jig) are used.
This is because it is possible to widen the interval from the second electrode 2a and to secure a passage through which air bubbles escape.

It is apparent that the present invention is not limited to the above embodiments, and that the above embodiments can be appropriately modified within the scope of the technical idea of the present invention. Further, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiment, and can be set to numbers, positions, shapes, and the like suitable for carrying out the present invention. In each drawing, the same components are denoted by the same reference numerals.

[0034]

Since the present invention is configured as described above, the following effects can be obtained. First, the first effect is L
That is, it is possible to improve the mounting reliability of the SI. The reason is that the use of a substrate having a concave portion and a metal mask makes it possible to increase the solder volume. As a result, the bumps can be made high, and the stress applied to the bumps when mounting the LSI can be dispersed. Because.

A second effect is that variations in bump height can be reduced. The reason is that, as described in the first effect, the volume of the solder can be increased, so that the opening size of the metal mask can be set to a size that allows easy printing.

The third effect is that the yield of forming bumps on an LSI can be improved. The reason is that the solder balls are formed on the board in advance, so it is possible to inspect whether the solder balls are formed normally, select a place where a good solder ball is formed, place the LSI, and bump the bump. This is because it can be formed.

[Brief description of the drawings]

FIG. 1 is a process cross-sectional view for describing a first process of a bump forming method according to a first embodiment of the present invention.

FIG. 2 is a process cross-sectional view for describing a second process performed after the first process in FIG.

FIG. 3 is a process cross-sectional view for describing a third process performed after the second process of FIG. 2;

FIG. 4 is a process cross-sectional view for describing a fourth process performed after the third process in FIG. 3;

FIG. 5 is a process cross-sectional view for describing a fifth process performed after the fourth process of FIG. 4;

FIG. 6 is a process cross-sectional view for explaining a bump forming method according to a second embodiment of the present invention.

FIG. 7 is a process cross-sectional view for explaining a bump forming method according to a third embodiment of the present invention.

FIG. 8 is a top view of a transfer substrate (transfer jig) used in the bump forming method of the present invention.

9 is an enlarged view of a portion A of the transfer substrate (transfer jig) of FIG. 8;

FIG. 10 is a process cross-sectional view for describing a bump forming method according to a fourth embodiment of the present invention.

FIG. 11 is a process top view for explaining a bump forming method according to a fifth embodiment of the present invention.

FIG. 12 is a process top view for describing a bump forming method according to a sixth embodiment of the present invention.

[Explanation of symbols]

 1a: concave portion 1b: conical concave portion 1c: cylindrical concave portion 1d: hemispherical concave portion 1e: rectangular column-shaped concave portion 1f: square column-shaped concave portion 2a: transfer substrate (transfer jig) 3. round shape 3a: Square opening 4: Metal mask (transfer jig) 5: Cream solder 6: Squeegee 7: Solder ball 8: Electrode 9: LSI 10: Bump

Claims (21)

[Claims] 1. A bump forming method capable of increasing a bump height at a low cost, comprising: a step of superposing a metal mask on a transfer substrate so that a concave portion and an opening portion coincide; and applying cream solder to the concave portion and the opening portion. Filling the substrate, heating the transfer substrate after removing the metal mask, melting the cream solder to form a solder ball, and transferring the transferred solder ball to an LSI pad. Forming a solder bump by aligning and mounting a transfer substrate and an LSI, and heating the transfer substrate and the LSI to cause solder wetting on the LSI pad. . 2. The bump forming method according to claim 1, further comprising a step of performing an inspection after forming the solder ball and mounting an LSI only on a non-defective part. 3. The bump forming method according to claim 1, wherein the shape of the concave portion of the transfer substrate is a conical shape with a center portion gradually deeper. 4. The bump forming method according to claim 1, wherein the shape of the concave portion of the transfer substrate is a polygonal pyramid with a central portion gradually deeper. 5. The bump forming method according to claim 1, wherein the shape of the concave portion of the transfer substrate is a spherical shape and a center portion is gradually deeper. 6. The shape of the concave portion of the transfer substrate has an engraved shape in which a bottom surface is conical, a central portion is gradually deepened, and a surface vicinity is cylindrical. 3. The bump forming method according to item 2. 7. The shape of the concave portion of the transfer substrate is such that a bottom surface is a polygonal pyramid and a central portion gradually becomes deeper.
3. The bump forming method according to claim 1, wherein the surface has a carved shape having a cylindrical shape near the surface. 8. The shape of the concave portion of the transfer substrate has an engraved shape in which a bottom surface is a spherical surface, a central portion is gradually deepened, and a surface portion is a cylindrical shape. 3. The bump forming method according to item 2. 9. The bump forming method according to claim 1, wherein the shape of the concave portion of the transfer substrate is a spherical base. 10. The bump forming method according to claim 1, wherein the shape of the concave portion of the transfer substrate is a truncated cone. 11. The bump forming method according to claim 1, wherein the shape of the concave portion of the transfer substrate is a truncated polygonal pyramid. 12. The method according to claim 1, wherein a surface shape of the concave portion of the transfer substrate and a shape of the opening of the metal mask have the same area. Bump formation method. 13. The bump according to claim 1, wherein an opening area of the concave portion of the transfer substrate has a shape larger than an opening area of the metal mask. Forming method. 14. The transfer substrate according to claim 1, wherein at least a part of the concave portion of the transfer substrate has a shape arranged outside the opening of the metal mask. 3. The bump forming method according to 1. 15. The bump forming method according to claim 1, wherein the transfer substrate is a metal plate, and the concave portion is formed by etching the metal plate. 16. The bump forming method according to claim 1, wherein the transfer substrate is ceramic, and the concave portion is formed by processing the ceramic. 17. The bump according to claim 1, wherein the transfer substrate is a silicon substrate, and Si pits formed by etching the silicon substrate are used as the concave portions. Forming method. 18. The transfer substrate, which is one of the transfer jigs having a concave portion corresponding to the LSI pad, or the metal mask, which is the other of the transfer jig having an opening corresponding to the LSI pad. The method according to any one of claims 1 to 17, further comprising a coating using a fluororesin on at least one of: 19. The method according to claim 1, wherein a nitriding process is performed on the transfer substrate, which is one of the transfer jigs having a concave portion corresponding to the LSI pad. Bump formation method. 20. The bump forming method according to claim 1, wherein the transfer substrate has the concave portion for one LSI. 21. The bump forming method according to claim 1, comprising a high melting point solder as a solder material.