JPH11346051A - Forming method of precoating solder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of uniformly and stably forming a precoating solder by the use of solder paste without wasting it. SOLUTION: In a precoating solder forming method where solder paste is applied onto electrodes 2 located on a board 1, and solder contained in the solder paste is soldered by heating to the electrodes 2, a reticulate mask 3 where pattern holes 3d are provided corresponding to a range A around the electrodes 2 is mounted on the board 1, solder paste whose solder content is less than 30 vol.% is fed onto the reticulate mask 3, and a process, where solder paste 4 is printed around the electrodes 2 through the pattern holes 3d and solder contained in the solder paste 4 is melted by heating and soldered to the electrodes 2, is repeatedly carried out a few times. By this setup, solder paste 4 is applied only onto a necessary part to uniformly form a precoating solder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a pre-coated solder by welding a solder to an electrode surface of a work to form a pre-coated solder.

[0002]

2. Description of the Related Art As a method for supplying solder when electrodes of works such as electronic parts and substrates are soldered to each other, a method using pre-coated solder (sometimes called a solder bump) is known. In this method, solder is welded to an electrode surface of a work prior to solder joining. As one of the methods for forming the pre-coated solder, a solder paste containing solder particles is applied to the entire periphery of the work electrode. There is widely used a method in which a so-called solid coating is performed, and then the work is heated to melt the solder in the solder paste and weld it to the electrode surface. In general, when applying a solder paste, conventionally, a stencil mask having a pattern hole formed in an application area is mounted on the upper surface of a work, and the solder paste is filled in the pattern hole.

[0003]

By the way, as the pitch of the electronic parts becomes finer, the thickness of the electrode on which the precoat solder is formed also becomes smaller. Therefore, a stencil mask used for applying a solder paste to a fine pitch work is used. The thickness is as small as tens of microns. For this reason, the stencil mask is very unstable in shape and easily bends, is not stable when mounted on a work, and the applied amount varies in some parts, so that stable application is difficult.

In many cases, the electrodes are formed on a rectangular line along the outer edge of the electronic component. Therefore, the arrangement of the electrodes on the work on which the electronic component is mounted also corresponds to this. Only electrodes are arranged, and there are many patterns in which no electrodes are arranged inside this rectangle. When a pattern hole corresponding to such an arrangement of electrodes is provided in the stencil mask, the entire portion inside the electrode must be formed as one pattern hole. As a result, a large amount of the solder paste is applied to a portion where no electrode is present, and the solder paste is wasted. Also, a large amount of solder paste applied to a position where no electrode exists has a problem that the flow during reflow is unstable, and as a result, the pre-coated solder tends to vary greatly between the electrodes. As described above, the conventional method of forming pre-coated solder has a problem that it is difficult to apply the solder paste stably and without waste, and as a result, it is difficult to form a uniform pre-coated solder.

Accordingly, an object of the present invention is to provide a method for forming a pre-coated solder which can apply a solder paste stably and without waste, and can obtain a uniform pre-coated solder.

[0006]

According to the present invention, there is provided a method for forming a pre-coated solder, comprising: applying a solder paste on an electrode of a work; heating the work; and welding the solder in the solder paste to the surface of the electrode. A method of forming solder, comprising: mounting a mesh mask provided with a pattern hole having a limited opening at a position corresponding to the electrode on the workpiece; and forming a solder content on the mesh mask by volume ratio. Supplying a solder paste of less than 30% by using a squeegee and printing the solder paste around the electrodes through the pattern holes, separating the mesh mask from the work and transferring the solder paste to the work. And melting the solder in the solder paste by heating and welding the solder to the electrode. That the solder coating process was to be repeated several times.

According to the present invention, a solder paste having a solder amount of less than 30% by volume is applied by printing using a mesh mask provided with a pattern hole having a limited opening at a position corresponding to the electrode. By repeating the process of welding the solder to the electrodes by heating and melting a plurality of times, the solder paste can be applied only to the necessary portions to form a pre-coated solder having no variation.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. 1 (a), (b), (c),
2 (a), 2 (a), 2 (b), 2 (c), and 2 (d) are process explanatory views of a method for forming a pre-coated solder according to an embodiment of the present invention, and FIG. 3 (a) is a perspective view of the substrate. FIG. 3B is a perspective view of the mesh mask, and FIG. 3C is a cross-sectional view of the mesh mask.

First, in FIG. 1A, a plurality of electrodes 2 are formed on the upper surface of a substrate 1 which is a work. Electrode 2
Is for soldering an electronic component mounted on the substrate 1, and a precoat solder is formed on the electrode 2 according to the following process before mounting the electronic component. FIG.
As shown in (b), a mesh mask 3 is mounted on the substrate 1, and a solder paste 4 is provided on the mesh mask 3.
Is supplied. Solder paste 4 contains solder particles 4a, and is mixed so that the solder content is less than 30% by volume.

Here, the substrate 1 and the mesh mask 3 will be described with reference to FIG. FIG. 3A shows the arrangement of the electrodes 2 on the substrate 1. The electrodes 2 are formed along the outer edge of the substrate 1 and are arranged in a square shape.
The inside of the square-shaped arrangement is a position (area) where no electrode exists. Therefore, the solder paste for forming the pre-coated solder on the electrode 2 may be applied only to the area A extending around the electrode 2 in a square shape. FIG. 2B shows a mesh mask 3 used for applying the solder paste only in the range A, and the mesh mask 3 includes a mesh plate 3a and mask plates 3b and 3c. .

That is, a rectangular mask plate 3b and a mask plate 3c having a rectangular opening are fixed to the lower surface of the mesh plate 3a, and the openings surrounded by the mask plates 3a and 3b, ie, the pattern holes 3d are shown in FIG. a) corresponds to the range A shown in FIG.
Are opened in a range limited to a position corresponding to the above. As shown in FIG. 2C, the mask plate 3
The thicknesses t1 of b and 3c are extremely thin, about 20 microns, and it is difficult to mount them alone on the upper surface of the substrate 1 in a stable state.

As shown in FIG. 3C, the mask plate 3
The thicknesses t1 of b and 3c are extremely thin, about 20 microns, and it is difficult to mount them alone on the upper surface of the substrate 1 in a stable state.

Therefore, these mask plates 3b, 3b
By fixing c in combination with the mesh plate 3a having a thickness t2 of about 50 microns, the overall rigidity is significantly increased, and it is possible to mount the substrate on the substrate 1 in a stable state. The mesh interval S of the mesh plate 3a is 40 to 50 microns, which is a sufficient interval that does not prevent the filling of the solder particles 4a.

Returning to FIG. 1B, by moving the squeegee 5 horizontally on the mesh mask 3, the solder paste 4 is filled into the pattern holes 3d through the gaps of the mesh plate 3a. By separating the substrate 3 from the substrate 1, the solder paste 4 is applied around the electrode 2 by transfer as shown in FIG. The solder paste 4 filled at this time was
Of these, only the one filled in the pattern hole 3d is peeled off and transferred from the solder paste 4 existing in the gap of the mesh plate 3.

Thereafter, the substrate 1 is sent to a reflow process and heated. As a result, the solder particles 4a in the solder paste 4 are melted and welded to the electrode 2 to form a pre-coated solder 4 'on the upper surface, as shown in FIG. At this time,
Since the content of the solder particles 4a in the solder paste 4 is 30% or less by volume, a portion having a small solder content is apt to be generated partially. In some cases, the amount of solder to be welded is so small that the precoat solder is insufficiently formed.

Therefore, as shown in FIG. 2, the same steps as the above-mentioned solder coating step are repeated and repeated. FIG. 2 (a)
In the above, the pre-coated solder 4 'has already been formed on the electrode 2 of the substrate 1 in the previous solder coating step, but the amount of solder deposited is small due to uneven distribution of the solder in the solder paste 4 on the electrode 2a. Is insufficient, and no precoat solder is formed on the electrode 2b. In order to replenish the electrodes 2a and 2b with pre-coated solder, a mesh mask 3 is mounted on the substrate 1 as shown in FIG. Transcribe Thereby, as shown in FIG. 2C, the solder paste 4 is applied around the electrodes 2 including the electrodes 2a and 2b. At this time, the solder paste 4 does not adhere much on the electrode 2 on which the pre-coated solder 4 'has already been formed in a sufficient amount.

Thereafter, the substrate 1 is sent to a reflow process,
It is heated again. By this, pre-coated solder 4 '
The pre-coated solder 4 'is re-melted on the electrode on which the solder is formed, and the solder particles around it slightly adhere to the pre-coated solder to slightly increase the amount of solder. On the electrode 2a where the amount of solder is small, and no pre-coated solder is formed. On the electrode 2b
The solder particles in the newly applied solder paste 4 are welded to form a new pre-coated solder 4 '. Then, if the pre-coated solder is not formed or the amount of solder is insufficient even after the second reflow process, the same solder coating process is further repeated.

Thereafter, the substrate 1 is sent to a cleaning step, and residues such as flux components in the applied solder paste 4 are removed to complete the formation of the pre-coated solder. Note that the above-described cleaning may be performed each time after each reflow process. By doing so, excess paste is removed prior to solder paste application, and solder particles can be supplied more uniformly.

As described above, by using a mesh mask using a mesh plate when printing the solder paste, even if an extremely thin mask plate corresponding to the electrode of a fine-pitch circuit board is used, necessary electrodes can be formed. The solder paste can be stably transferred only to the portion. Also, by reducing the solder content (30% or less by volume), a sufficient amount of solder paste can be supplied into the pattern holes from the gaps of the mesh plate. Further, by repeating the printing and reflowing of the solder paste a plurality of times, the shortage of the solder amount due to the use of the solder paste having a low solder content can be compensated.

Since the solder coating process including the printing of the solder paste and the reflow process is simple and inexpensive, even if this solder coating process is repeated, the cost does not increase significantly. A large amount of pre-coated solder can be realized stably and at low cost. In the present embodiment, an example is described in which pre-coated solder is formed on an electrode of a substrate. However, the present invention can be applied to a case where pre-coated solder is formed on an electrode of an electronic component.

[0021]

According to the present invention, a solder paste having a solder volume of less than 30% by volume is printed by using a mesh mask provided with a pattern hole having a limited opening at a position corresponding to an electrode portion. By repeating the process of applying and melting the solder to the electrodes by heating and melting a plurality of times,
By applying a solder paste only to a necessary portion, a pre-coated solder having no variation can be formed. Therefore, the precoat solder having a stable amount of solder can be formed on the fine pitch electrodes by a simple and low-cost process of printing and heating the solder paste.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a process explanatory view of a method for forming a pre-coated solder according to an embodiment of the present invention. FIG. 1B is a process explanatory view of a method for forming a pre-coated solder according to an embodiment of the present invention. Process explanatory diagram of a method for forming a precoated solder according to an embodiment (d) Process explanatory diagram of a method for forming a precoated solder according to an embodiment of the present invention

FIG. 2A is an explanatory view showing a step of a method for forming a pre-coated solder according to an embodiment of the present invention. FIG. 2B is an explanatory view showing a step of a method for forming a pre-coated solder according to an embodiment of the present invention. Process explanatory diagram of a method for forming a precoated solder according to an embodiment (d) Process explanatory diagram of a method for forming a precoated solder according to an embodiment of the present invention

FIG. 3A is a perspective view of a substrate according to an embodiment of the present invention. FIG. 3B is a perspective view of a mesh mask according to an embodiment of the present invention. Figure

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Electrode 3 Mesh mask 3a Mesh plate 3b, 3c Mask plate 4 Solder paste 4a Solder particle

Claims (1)

[Claims] 1. A method for forming a pre-coated solder in which a solder paste is applied on an electrode of a work and then the work is heated and a solder in the solder paste is welded to a surface of the electrode, wherein a position corresponding to the electrode is provided. Mounting a mesh mask provided with pattern holes that are limitedly open on the work, supplying a solder paste having a solder content of less than 30% by volume on the mesh mask, and using a squeegee to A step of printing solder paste around the electrodes through pattern holes, a step of separating the mesh mask from a work and transferring the solder paste to the work, and melting solder in the solder paste by heating. Repeating a solder coating step including a step of welding to the electrode a plurality of times. Recoating solder of the formation method.