JPH11266073A - Forming and mounting method of solder bump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming and mounting solder bumps of high bonding reliability. SOLUTION: A solder ball 15 is soldered to a circuit electrode 13 via a through-hole 12 provided to an insulating board 11 for forming a solder bump 16 on the surface of the insulating board 11 opposite to its other surface which confronts the circuit electrode 13. In this case, the solder ball 15 is mounted on the through-hole 12, whose diameter is smaller than that of the solder ball 15 after a cream soldery 14 whose liquidus line temperature is higher than that of the solder ball 15 is fed into the through-hole 12. Then, the insulating board 11 is heated to melt the solder ball 15 and to evaporate a solvent component of the flux inside the through-hole 12 at the same time. With this setup, dispersing of solvent vapor contained in flux is facilitated, whereby voids can be prevented from being formed due to the solvent vapor staying in melted solder, while a solder bonding operation is being carried out.

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 a solder bump on a circuit electrode of an electronic component or a substrate and a method of mounting a solder bump on an electronic component or a substrate. .

[0002]

2. Description of the Related Art As a method for mounting electronic components, a method using solder bumps is known. In this method, a solder bump, which is a protruding electrode of solder, is previously formed on a circuit electrode of an electronic component, and the solder bump is soldered to a circuit electrode such as a substrate. As a method of forming a solder bump, a method of mounting a solder ball on a circuit electrode such as an electronic component has been conventionally known.

[0003] By the way, CSP (Chip Size P)
In some cases, the surface on which the circuit electrodes are formed and the surface on which the solder bumps are formed are not the same surface of the substrate. That is, circuit electrodes are formed on one surface of a tape-shaped substrate constituting a package, and solder balls are mounted on the opposite side of the surface on which the circuit electrodes are formed. Then, the solder ball is melted, and the molten solder is conducted to the circuit electrode through a through hole of the substrate provided at the position of the circuit electrode to form a solder bump. Here, the through-hole of the front hole is also reduced due to the fine pitch of the circuit electrodes accompanying the miniaturization of electronic components, and the use of a through-hole smaller than the diameter of the solder ball to be mounted is increasing.

A conventional solder bump forming method in such a case will be described below with reference to the drawings. FIG.
(A), (b), (c) is a partial sectional view of a conventional tape-shaped substrate. In FIG. 3A, a circuit electrode 2 is formed on a lower surface of a tape-shaped insulating substrate 1. Insulating substrate 1
A through-hole 3 is provided at the position of the circuit electrode 2 in which the cream solder 4 in which the solder particles 4a and the flux are mixed is supplied into the through-hole 3. A solder ball 5 is mounted on the through hole 3. Here, the diameter of the through hole 3 is smaller than the diameter of the solder ball 5 to be mounted, and the solder ball 5 blocks the upper portion of the through hole 3 without entering the inside of the through hole 3.

As the solder particles contained in the cream solder 4, a eutectic type of lead and tin having a liquidus temperature of 183 ° C. is used, whereas the solder forming the solder balls 5 is In addition, a material having a high liquidus temperature that does not melt in a heating step at the time of forming a bump has been used. This is to prevent the solder balls 5 from melting in the heating step in order to ensure the bump height after forming the solder bumps as high as possible.

[0006] Thereafter, the cream solder 4 is heated by sending the insulating substrate 1 to reflow and heating. At this time, the solvent component of the flux in the cream solder 4 evaporates as the temperature rises and bubbles 4b are generated. Occurs (Fig. 3
(B)). After the solder particles 4a are melted, the bubbles 4b are aggregated in the molten solder to form bubbles of a certain size, rise in the molten solder and are radiated to the outside.

[0007]

Here, the solder ball 5
Is not melted in this heating step, so that the upper portion of the through hole 3 is closed. However, since the bubbles 4b of the solvent vapor are trapped in the molten solder while maintaining a certain size due to surface tension, they cannot escape from the gap between the solder ball 5 above the through hole 3. As a result, the solvent vapor 4c in a bubble state remains in the molten solder 4a '(FIG. 3C), and after solidification of the molten solder 4a', voids formed by these solvent vapors form voids in the solder joint. As a residue. Such voids are serious defects that greatly impair the reliability of the solder joints and are unacceptable in quality.

However, in the above-mentioned conventional solder bump forming method, the above-mentioned serious defects cannot be prevented due to the combination of the material types of the solder ball 5 and the cream solder 4, and a solder bump having high joining reliability is formed. There was a problem that it was not possible. Further, the above problem is caused when a spherical solder bump is mounted on a circuit electrode of a substrate, that is, a through hole smaller than the diameter of the solder bump is provided in a resist covering the circuit electrode, and cream solder is supplied into the through hole. This is also common when mounting spherical solder bumps.

Accordingly, an object of the present invention is to provide a method for forming a solder bump having high bonding reliability and a method for mounting a solder bump.

[0010]

According to a first aspect of the present invention, there is provided a method of forming a solder bump, comprising: soldering a solder ball to a circuit electrode via a through hole provided in an insulating substrate; A method of forming a solder bump on a surface, wherein a temperature of a liquidus temperature of a first solder, which is a material of the solder ball, is higher in a through hole provided with a smaller diameter than the solder ball. Supplying a second solder and a flux having a liquidus temperature, mounting the solder balls on the through holes, heating the insulating substrate to melt the first solder, and Evaporating the solvent component of the flux in the holes, and further heating the insulating substrate to melt the second solder, thereby structurally integrating the first solder and the second solder to form the circuit. On the electrode And a step of fields joined.

According to a second aspect of the present invention, there is provided a method of forming a solder bump.
The method for forming a solder bump according to claim 1, wherein the second solder is tin, lead, zinc, gold, silver, copper, antimony,
Solder particles containing either indium or bismuth, and supplied in the form of cream solder mixed with a flux containing a solvent.

According to a third aspect of the present invention, there is provided a method of forming a solder bump.
The method for forming a solder bump according to claim 1, wherein the second solder is tin, lead, zinc, gold, silver, copper, antimony,
It contains either indium or bismuth, and is supplied after being precoated on the circuit board.

According to a fourth aspect of the present invention, there is provided a method of mounting a solder bump.
A solder bump mounting method of soldering a solder bump formed on an electronic component to the circuit electrode via a through hole provided in an insulating film covering a circuit electrode of the board, and mounting the solder bump on the board. Supplying a second solder and a flux having a liquidus temperature higher than the liquidus temperature of the first solder, which is the material of the solder bump, into the through hole provided with a smaller diameter than the solder bump. Performing the step of mounting the solder bumps on the through-holes, heating the substrate to melt the first solder, and vaporizing a solvent component of the flux in the through-holes; Is further heated to melt the second solder, so that the first solder and the second solder are structurally integrated and soldered to the circuit electrode.

According to a fifth aspect of the present invention, there is provided a method of mounting a solder bump, comprising:
5. The method of claim 4, wherein the second solder is tin, lead, zinc, gold, silver, copper, antimony,
Solder particles containing either indium or bismuth, and supplied in the form of cream solder mixed with a flux containing a solvent.

According to a sixth aspect of the present invention, there is provided a method of mounting a solder bump, comprising:
5. The method of claim 4, wherein the second solder is tin, lead, zinc, gold, silver, copper, antimony,
It contains either indium or bismuth, and is supplied after being precoated on the circuit board.

According to the present invention, the liquidus temperature of the second solder supplied into the through-hole for solder-bonding the solder ball or the solder bump to the circuit electrode is set to the solder which is the first solder. By combining the first and second types of solder so as to be higher than the liquidus temperature of the ball or the solder bump, it is easy to dissipate the solvent vapor in the flux in the heating process, and the solvent The generation of voids due to the vapor remaining in the molten solder can be prevented.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIG.
(B), (c), (d), (e), and (f) are process explanatory diagrams of the method of forming a solder bump according to the first embodiment of the present invention, and show the method of forming a solder bump in the order of processes. It is.
In FIG. 1A, an insulating substrate 11 is made of an insulating material such as a polyimide tape or glass epoxy resin.
Is formed with a through hole 13. The through-hole 13 is provided corresponding to the position of the circuit electrode 12 formed on the lower surface of the insulating substrate 11, and a solder bump is formed on the surface of the insulating substrate 11 opposite to the circuit electrode 12 (the surface on the side of the through-hole 13 in FIG. 1). It is for forming. Here, the diameter of the through hole 13 is
The diameter is reduced due to the narrow pitch, and is smaller than the diameter of the solder ball mounted for forming the solder bump.

Next, as shown in FIG.
The cream solder 14 as the second solder is supplied into the inside.
The cream solder 14 is obtained by mixing solder particles 14a of eutectic solder of silver and tin in a flux containing a solvent component,
The liquidus temperature is 220 ° C. Thereby, the second solder and the flux are simultaneously supplied into the through-hole 12.

Next, as shown in FIG. 1C, a solder ball 15 is mounted on the through hole 13 to which the cream solder 14 has been supplied. As described above, the diameter of the solder ball 15 is
And the solder ball 15 does not enter the bottom of the through hole 13 until it comes into contact with the circuit electrode 12.
3 is closed. The material of the solder ball 15 is eutectic solder of lead and tin, which is the first solder, and its liquid crystal point temperature is 183 ° C. That is, the liquidus temperature of the second solder is higher than the liquidus temperature of the first solder.

Thereafter, the insulating substrate 11 is sent to a reflow step and heated. As the temperature rises, the solvent component of the flux in the cream solder 14 starts to evaporate, and when the heating temperature exceeds 183 ° C., which is the liquidus temperature of the solder ball 15, the solder becomes as shown in FIG. The ball 15 melts,
It becomes molten solder 15 '. As a result, the solvent vapor 14b vaporized in the through-hole 12 rises inside the through-hole 13 without being melted, that is, without forming bubbles in the molten solder, and is diffused to the outside. At this time, the molten solder 15 'that has closed the upper portion of the through hole 13 is deformed by a slight force because the molten solder 15' is simply kept in a spherical shape by surface tension. Therefore, the solvent vapor 14b in the through hole 13
Is dissipated to the outside while easily removing the molten solder 15 'in the gap between the upper end of the through hole 13 and the molten solder 15'.

Thereafter, when the temperature further rises and exceeds the liquidus temperature of the second solder of 220 ° C., the solder particles in the cream solder 14 melt. As a result, as shown in FIG. 1E, the molten solder 15 'and the molten solder 14' in which the cream solder 14 is melted are structurally integrated and soldered to the circuit electrode 12, and then solidified, thereby obtaining As shown in (f), the solder bumps 16 are formed. At this time, as described above, after the solder ball 15 is melted and before the cream solder 14 is melted, the cream solder 14 in the through-hole 13 is melted.
Is vaporized and dissipated without being disturbed by the solder balls 15, so that the occurrence of voids in the joints due to the solvent vapor remaining in a bubble state is prevented, and a highly reliable solder bump is formed. It is formed. It is the solvent component in the flux that is vaporized and emitted,
Since the active component in the flux remains as it is, the effect of the flux at the time of soldering is not impaired.

(Embodiment 2) FIGS. 2 (a), (b),
(C), (d), and (e) are process explanatory diagrams of the solder bump mounting method according to the second embodiment of the present invention, and show the solder bump mounting method in the order of processes.

In FIG. 2A, a circuit electrode 22 is formed on a surface of a substrate 21. A solder resist 23 as an insulating film made of a resin material such as epoxy or acrylic is formed so as to cover the substrate 21 and the circuit electrodes 22. A through hole 24 is provided at a position corresponding to the circuit electrode 22 of the solder resist 23. Here, the diameter of the through hole 24 is reduced by narrowing the pitch of the circuit electrode 22,
The diameter is smaller than the diameter of the solder bump to be mounted. Next, as shown in FIG.
Is supplied. The cream solder 25 is similar to the cream solder 14 in the first embodiment.

Next, as shown in FIG. 2C, an electronic component 27 having a spherical solder bump 26 formed on the substrate 21 is mounted. As mentioned above, the diameter of the solder bump 26 is
Is larger than the diameter of the solder bump 26, so that the solder bump 26
4 does not enter into the position where it contacts the circuit electrode 22 at the bottom, but is closed at the top. The material of the solder bump 26 is the first solder, which is the same as that of the solder ball 15 in the first embodiment.

Thereafter, the substrate 21 is sent to a reflow process,
Heated. As a result, as shown in FIG. 2D, the solder bumps 26 are first melted into molten solder 26 ', and the flux solvent component in the cream solder 25 is vaporized. By further heating, the cream solder 25 is melted as shown in FIG.
6 ′ and 25 ′ are structurally integrated and soldered to the circuit electrode 22, whereby the solder bumps 26 are mounted on the substrate 21. At this time, as in the first embodiment, in the heating step, the dissipation of the solvent component in the cream solder 25 is not hindered by the solder bumps 26, and the generation of voids in the joints is prevented so that a highly reliable solder can be obtained. Mounting of bumps can be performed.

In each of the above embodiments, an example is shown in which the second solder is supplied together with the flux as a cream solder. However, other methods, such as first pre-coating the solder on the circuit electrode and then applying the solvent, May be supplied onto the pre-coated solder. As the second solder, a solder containing components such as tin, lead, zinc, gold, silver, copper, indium, and bismuth in addition to the eutectic solder of silver and tin may be used.

[0027]

According to the present invention, the liquidus temperature of the second solder supplied into the through-hole for solder-joining the solder ball or the solder bump to the circuit electrode is adjusted by the solder which is the first solder. Since the first and second solder types are combined so as to be higher than the liquidus temperature of the balls or the solder bumps, it is easy to dissipate the solvent vapor in the flux in the heating step and to perform solder bonding. The generation of voids due to residual solvent vapor can be prevented. Therefore, it is possible to form a solder bump with high reliability and mount the solder bump while preventing the occurrence of a defect in the solder joint.

[Brief description of the drawings]

FIG. 1A is a process explanatory view of a solder bump forming method according to a first embodiment of the present invention. FIG. 1B is a process explanatory view of a solder bump forming method according to a first embodiment of the present invention. Process description diagram of the solder bump forming method of the first embodiment (d) Process description diagram of the solder bump forming method of the first embodiment of the present invention (e) Method of forming the solder bump of the first embodiment of the present invention (F) Process explanatory diagram of the method for forming a solder bump according to the first embodiment of the present invention

FIG. 2A is a process explanatory view of a solder bump mounting method according to a second embodiment of the present invention. FIG. 2B is a process explanatory view of a solder bump mounting method according to a second embodiment of the present invention. Process description diagram of solder bump mounting method according to Embodiment 2 (d) Process description diagram of solder bump mounting method according to Embodiment 2 of the present invention (e) Method of mounting solder bump according to Embodiment 2 of the present invention Process description diagram

3A is a partial cross-sectional view of a conventional tape-shaped substrate. FIG. 3B is a partial cross-sectional view of a conventional tape-shaped substrate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 11 Insulating substrate 2, 12, 22 Circuit electrode 3, 13, 24 Through-hole 4, 14, 25 Cream solder 5, 15 Solder ball 16, 26 Solder bump 21 Substrate 23 Solder resist 27 Electronic component

Claims (6)

[Claims] 1. A method of forming a solder bump, comprising: soldering a solder ball to a circuit electrode via a through hole provided in an insulating substrate to form a solder bump on a surface of the insulating substrate opposite to the circuit electrode; A step of supplying a second solder and a flux having a liquidus temperature higher than the liquidus temperature of the first solder, which is the material of the solder ball, into the through hole provided with a smaller diameter than the solder ball; Mounting the solder ball on the through-hole, heating the insulating substrate to melt the first solder, and vaporizing a solvent component of the flux in the through-hole; Is further heated to melt the second solder,
A step of structurally integrating the first solder and the second solder and joining them to the circuit electrode by soldering. 2. The method according to claim 2, wherein the second solder is tin, lead, zinc, gold,
2. The method of claim 1, wherein the solder bumps are solder particles containing any of silver, copper, antimony, indium, and bismuth, and are supplied in the form of cream solder mixed with a flux containing a solvent. . 3. The method of claim 2, wherein the second solder is tin, lead, zinc, gold,
2. The method for forming a solder bump according to claim 1, wherein the circuit board is provided with one of silver, copper, antimony, indium, and bismuth and is precoated on the circuit board. 4. A solder bump for mounting a solder bump on a substrate by soldering a solder bump formed on an electronic component to the circuit electrode via a through hole provided in an insulating film covering the circuit electrode on the substrate. Wherein the second soldering material has a liquidus temperature higher than the liquidus temperature of the first solder, which is the material of the solder bump, in the through hole provided with a smaller diameter than the solder bump. Supplying solder and flux, mounting the solder bump on the through-hole, heating the substrate to melt the first solder, and vaporizing a solvent component of the flux in the through-hole. And a step of further heating the substrate to melt the second solder, thereby structurally integrating the first solder and the second solder and solder-joining to the circuit electrode. And half Implementation of the bump. 5. The method according to claim 1, wherein the second solder is tin, lead, zinc, gold,
5. The solder bump mounting method according to claim 4, wherein the solder bumps are solder particles containing any of silver, copper, antimony, indium and bismuth, and are supplied in the form of cream solder mixed with a flux containing a solvent. . 6. The method according to claim 1, wherein the second solder is tin, lead, zinc, gold,
5. The solder bump mounting method according to claim 4, wherein the circuit board is supplied by containing one of silver, copper, antimony, indium, and bismuth and pre-coated on the circuit board.