JPH0825083A - Solder paste - Google Patents

Abstract

PURPOSE:To obtain solder paste which prevents oxidation of solder particles and is capable of dealing with fine circuit patterns by incorporating fine solder particles enclosed in microcaosules into a flux and solvent. CONSTITUTION:The fine particles 3 enclosed in the microcapsuels 4 are incorporated into the flux and solvent 2 of the solder paste for packaging electronic apparatus. A polyamide resin, polyurea resin or a mixture composed thereof is used for the microcapsules 4. Oxidation of the solder particles is, therefore, prevented and the solder particles fused with the plural solder particles 3 are covered by the melt of the microcapsules 4 even after the end of the reflow and consequently, solder migration and the deterioration in the insulation characteristic between the patterns are prevented. The solder paste which substantially prevents oxidation of the solder particles 3 contained therein and are capable of dealing with the fine circuit patterns is thus obtd.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a solder paste,
For example, it is suitable to be applied to a solder paste for mounting an electronic device used when mounting an electronic component (IC chip or the like) on a substrate.

[0002]

2. Description of the Related Art Conventionally, a solder paste is manufactured by mixing solder particles, a flux and a solvent. In this case, as the solder particles mixed in the flux and the solvent, those having a particle size within a predetermined range from the solder particles formed by a predetermined method (for example, the minimum particle size is about 20 [μm]) Select and are using.

[0003]

By the way, in recent years, with miniaturization and high density of electronic parts, circuit patterns formed on a substrate have become finer. Therefore, the solder paste required when mounting these electronic components on the substrate is required to be capable of dealing with a fine circuit pattern. As a practical means of forming such a solder paste, a method of miniaturizing the solder particles mixed in the solder paste can be considered.

However, generally, when the solder particles are miniaturized, they are easily oxidized, and the oxidized solder particles may leave a solder ball after reflow, the solder may not melt, or the solder particles may aggregate. Therefore, when an electronic component having fine pitch between terminals is to be mounted on a board using a solder paste containing such fine solder particles, solder migration and deterioration of insulation characteristics between patterns occur. There was a problem.

On the other hand, as another means for forming the solder paste corresponding to the fine pitch, instead of printing the solder paste on the substrate as described above, electrolytic plating or electroless plating on the substrate side or other methods. Then, a method of forming a preliminary solder layer can be considered. However, according to this method, there are problems that the manufacturing cost of the board is high and the process of mounting the electronic component on the board is complicated.

The present invention has been made in consideration of the above points, and an object thereof is to propose a solder paste which can cope with a fine wiring pattern.

[0007]

In order to solve such a problem, in the present invention, a solder paste (1) is mixed with a flux and a solvent (2) and fine solder particles mixed in the flux and the solvent (2). (3) and the microcapsules (4) surrounding the outer wall of the solder particles (3).

In the present invention, the microcapsules (4) are made of polyamide resin, polyurea resin or a mixture of polyamide resin and polyurea resin.

[0009]

The outer wall of the solder particles (3) mixed in the flux and the solvent (2) is surrounded by the microcapsules (4), so that the solder particles (4) can be prevented from being oxidized.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a solder paste according to the present invention as a whole, which is formed by mixing fine solder particles 3 in a predetermined ratio in a flux and a solvent component 2. In this case, the outer wall of each solder particle 3 is enclosed by a microcapsule 4, so that the solder particles 3 can be prevented from being oxidized.

In the case of this embodiment, the solder particles 3 are the solder particles obtained by spraying the molten solder in a mist in a vacuum and sizing the solidified solder particles, and the particle size is normally used. Only particles with a particle size of 1/10 or less are selected and used. The myrochrome capsules 4 are formed by using a mixture of a polyamide resin and a polyurea resin, which are materials for ordinary microcapsules. Here, the polyamide resin can be obtained by a polycondensation reaction between an acid chloride and an amine. Examples of the acid chloride in this case include adiboyl chloride, sebacoyl chloride, phthalhiyl chloride, 1,4-cyclohexanedicarbonyl chloride, 4,4'-sulfonyldibenzoyl chloride and other diacid halides, and trimesoyl. Mixtures with trifunctional acid chlorides such as chloride can be applied.

When a mixture of two or more amines is used as the amine, a mixture of a bifunctional amine and a trifunctional amine can be applied. In this case, as the bifunctional amine, ethylenediamine, hexamethylenediamine,
4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylether, etc. and their sodium salts can be applied, and as the amine having three or more functional groups, diethylenetriamine, triethylenetetramine, Tetraethylene pentamine or the like can be applied.

The mixing ratio of acid chloride and amine for obtaining these polyamide resins is about 1: 1 to 50 equivalents, preferably 1: 1.1 to 40 equivalents. On the other hand, the polyurea resin can be obtained by a polyaddition reaction of isocyanate and amine. In this case, at least one or both of isocyanate and amine may be a mixture of two or more kinds. In this case, one of them is a difunctional isocyanate and the other is a trifunctional or higher functional isocyanate.

As the bifunctional isocyanate, hexamethylene diisocyanate, itafene diisocyanate or the like can be applied, and as the trifunctional isocyanate, a hexamethylene diisocyanate adduct or a reaction product of toluylene diisocyanate and trimethylolpropane is used. Etc. can be applied. In practice, this solder paste 1 is formed by the following procedure.
That is, first, the solder particles 3 having a particle size of 2 to 3 [μm]
A mixture (hereinafter referred to as the first mixture) is formed by stirring 30 parts, 6 parts of the acid chloride and 14 parts of the isocyanate, and subsequently the first mixture is mixed with the dispersion stabilizer. After being poured into a dispersion medium containing water, the mixture thus obtained (hereinafter referred to as the second mixture) is suspended by a stirrer.

The steps up to this step are carried out at a temperature of room temperature or lower, and subsequently, while the temperature of the stirred second mixture is increased and kept at the reaction temperature, an amine which is a water-soluble monomer is added to these mixtures, Stirring is continued until the reaction of the amine with the acid chloride and isoanede in the second mixture is complete. After that, the solid matter obtained is subjected to furnace separation and dried to obtain encapsulated solder particles. After this, the encapsulated solder particles 3, the flux and the solvent 2 are obtained.
Mix with. Thereby, the solder paste 1 as shown in FIG. 1 can be obtained.

FIGS. 2A to 2C show an example of an electronic component mounting process using the solder paste 1. First, a printing mask having a fine pattern corresponding to the wiring substrate 10 to be processed. 11 is brought into contact with the processed surface 10A of the wiring board 10, the above-mentioned solder paste 1 is supplied onto the printing mask 11, and then the stage 12 is slid on the printing mask 11 to remove the solder paste 1 Printing is performed on the processed surface 10A of the wiring board 10 (printing process,
FIG. 2 (A)). Then, the corresponding terminals 15 of the electronic component 14 are placed on each solder layer 13 formed of the solder paste 1 formed on the wiring board 10 by the above-described printing process (mounting process, FIG. 2B). Further, the wiring board 10 on which the electronic component 14 is mounted is put in the reflow furnace 15,
The solder layer 13 on the wiring board 10 is reflowed by heating (reflow step, FIG. 2C). As a result, the electronic component 14 can be mounted on the wiring board 10.

In this case, in this solder paste 1, the microcapsules 4 covering the solder particles 3 are destroyed by the pressure of the stage 12 in the above-mentioned printing process (FIG. 2A), so that FIG. Thus, the solder particles 3 are exposed. However, with this solder paste 1, as shown in FIG.
As shown in (B), some solder particles 3 including the solder particles 3 exposed from the microcapsules 4 are fused during the reflow step (FIG. 2C), and some solder particles 3 are fused. Since the outer wall of the solder grain 20 formed of the microcapsules 4 is covered again by the fusion body 21, the solder grain 20 can be prevented from coming into contact with the outside air even after the reflow process is completed, and thus the solder grain 20 is oxidized. Can be prevented.

According to an actual experiment, by using this solder paste 1, it is possible to easily perform screen printing on an IC pad of 0.3 [mm] or less, which is difficult with the conventional solder paste, or melt the solder paste. The condition and the joined state of the parts were also good. Further, in terms of reliability, even if the pattern pitch is narrow, the same performance as the conventional product could be obtained.

In the above-mentioned structure, the solder paste 1 has solder particles 3 mixed in the flux and the solvent 2.
Since a fine pattern is used as the pattern, it is possible to print a desired fine pattern on the substrate. Therefore, 0.3 [m
m] QFP (QUAD FLAT PACKAGE) type I below pitch
Even a C chip or a TCP type IC chip can be mounted by a conventional mounting process. Further, in the solder paste 1, since the solder particles 3 mixed in the flux and the solvent 2 are encapsulated in the microcapsules 2, the solder particles 3 are hard to oxidize before use, and a plurality of solder particles are used even after the reflow is completed. Since the fused body 21 of the microcapsules 4 covers the solder particles 20 formed by fusing the particles 3, deterioration of the insulation properties between the solder migration and patterns can be prevented.

Furthermore, when this solder paste 1 is used in the mounting process of the electronic component 14 on the wiring board 10,
The resin forming the microcapsules covers the soldered portion, and this portion is shielded from the external environment. Therefore, the soldered portion can be protected from the outside air, moisture and the like.

According to the above construction, fine solder particles 3 are mixed in the flux and the solvent component 2, and the outer wall of the solder particles 3 is applied to the microcapsule 2.
By wrapping with, it is possible to easily print a fine pattern and prevent oxidation of the solder particles 3.
Thus, it is possible to realize a solder paste in which the contained solder particles 3 are hard to oxidize and which can correspond to a fine circuit pattern.

In the above embodiment, the case where the mixture of the polyamide resin and the polyurea resin is used as the material of the microcapsule 4 is described.
The present invention is not limited to this, and various other materials can be applied.

Further, in the above-described embodiment, as means for obtaining the fine solder particles 3, among the solder particles obtained by spraying molten solder in a mist in a vacuum and sizing the solidified solder particles, , The case where only the particles having a particle diameter of 1/10 or less of the particle diameter that is normally used is selected and used, but the present invention is not limited to this, and for example, the solder obtained by the above-described method is used. Of the particles, those having a larger particle size than the solder particles 3 used in the solder paste 1 of the present invention may be crushed to obtain fine solder particles 3. As means for obtaining fine solder particles, Various other means can be applied.

[0025]

As described above, according to the present invention, the solder paste is formed of the flux and the solvent and the fine solder particles having the outer wall encapsulated by the microcapsules. It is possible to supply the solder paste in a fine desired pattern, and thus to realize a solder paste that can correspond to a fine wiring pattern.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining a structure of a solder paste according to the present invention.

FIG. 2 is a schematic diagram showing an example of an electronic component mounting process using the solder paste of FIG.

FIG. 3 is a schematic diagram showing the behavior of solder particles in a solder paste during the process of FIG.

[Explanation of symbols]

1 ... Solder paste, 2 ... Flux and solvent, 3
...... Solder particles, 4 …… Microcapsules.

Claims (2)

[Claims] 1. A solder paste comprising a flux and a solvent, fine solder particles mixed in the flux and the solvent, and microcapsules enclosing the outer wall of the solder particle. 2. The solder paste, wherein the microcapsules are made of a polyamide resin, a polyurea resin, or a mixture of the polyamide resin and the polyurea resin.