JPH0639585A - Cream solder - Google Patents

Abstract

PURPOSE:To provide the cream solder which less generates solder balls has good solderability by incorporating silystinate into the flux of the cream solder consisting of powdery solder and liquid or pasty flux. CONSTITUTION:The cream solder formed by mixing the pasty or pasty flux with the Sn-Pb solder alloy powder having 20 to 60mum diameter in such a manner that its content attains 8 to 12wt.% is used at the time of soldering of microcircuits, etc. The flux is formed by mixing the amine salts of hydrochloric acid and hydrobromic acid of methyl amine, dimethyl amine and others at 0.05 to 0.15wt.% in terms of chlorine based on the weight of the rosin, using 1, 3; 2, 4-dibenzylidene sorbitol as thixotropic agent and further mixing the silystinate, such as methyl silystinate and ethyl silystinate, at 10 to 40wt.% as a flux in a rosin as a base material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cream solder for use in soldering a microcircuit or the like.

[0002]

2. Description of the Related Art Conventionally, soldering has been frequently used when mounting electronic elements on a printed circuit board. In order to achieve more reliable soldering, a method of cleaning the surfaces of the metal to be joined with a liquid flux or a high-viscosity flux before soldering, or a so-called cream solder in which solder fine particles and flux are mixed A method such as a method using is widely used.

The above liquid flux and flux for cream solder are used in order to maintain high product quality and reliability.
(1) High insulation, (2) Non-corrosive, (3) Long-term stability,
(4) It is required that the materials of other parts do not change,
Also, from the soldering work surface, (1) no harmful gas is generated, (2) good solderability (having an action of dissolving and removing oxides on the metal surface and wrapping the metal surface, and That lowers the surface tension that it has),
It is required that (3) it is not sticky, and (4) that it be easily washed when it is washed.

In general, cream solder is prepared by mixing powder solder fine particles with liquid or paste-like flux to form a creamy paste having an appropriate viscosity. The flux generally uses rosin as a base material, and contains a solvent, an activator, a thixotropic agent, and the like. The composition of the flux is very important because the characteristics of the cream solder obtained depending on the type and mixing ratio of these compounding agents are subtly changed. Of these flux components, the solvent is solder ball, adhesiveness, which is important as cream solder.
This is particularly important because it often affects printability and the like. As described above, it is well known that the solvent plays a very important role in cream solder. For example, JP-A-56-154297 discloses that 2-methyl-2,4.
-A method of using pentanediol is disclosed.
However, in this method, since the solvent has a low boiling point and a high hygroscopicity, the resulting cream solder has a slightly higher hygroscopicity, and there are problems such as frequent occurrence of solder balls and reduced adhesiveness. Further, JP-A-1-186300 discloses a method of using phenethyl alcohol. However, this method also has a problem that the tackiness is lowered probably because the boiling point of the solvent is low. From the above background, it has been strongly desired that the cream solder obtained from the above-mentioned background has good tackiness and generates less solder balls.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to provide a cream solder having less solder balls and good adhesiveness and solderability. is there.

[0006]

The object of the present invention is to provide a cream solder obtained by mixing powder solder and a liquid or pasty flux, wherein the flux contains myristic acid ester. Can be achieved by The present invention will be described in detail below.

The myristic acid ester in the present invention is an ester of myristic acid and a monohydric alcohol. Examples of these esters include methyl myristate, ethyl myristate, -n-propyl myristate, isopropyl myristate, -n-butyl myristate, isobutyl myristate, -t-butyl myristate, amyl myristate, myristate. Isoamyl, myristate-n-hexyl, myristate isohexyl, myristate-n-heptyl, myristate-n-octyl, myristate-2-ethylhexyl, myristate-n-nonyl, myristate-n-decyl, myristate Examples include isotridecyl and benzyl myristate. Among these, methyl myristate, ethyl myristate, n-propyl myristate, isopropyl myristate, n-butyl myristate, and isobutyl myristate are particularly preferred. When the molecular weight is large, like isotridecyl myristate, the residue may not be completely evaporated during reflow and may remain sticky after reflow.

The content of myristic acid ester in the flux in the present invention is not particularly limited, but is 10% by weight.
-40% by weight is particularly preferred. If it is less than 10% by weight, the tackiness may decrease, and if it exceeds 40% by weight, the effect of the present invention may be saturated. In the present invention, it is possible to use myristyrene ester in combination with other solvent. The solvent used in combination with myristyrene ester is not particularly limited, but as an example, butyl carbitol, hexyl carbitol, phenyl carbitol, α-terpineol, β-terpineol, tridecyl alcohol, isomyristyl alcohol, isopalmyl. Examples include alcohol, isostearyl alcohol, diisodecyl adipate, dibutyl phthalate, 1-octadecene, and liquid paraffin.

The base material used in the present invention is not particularly limited, but generally used rosin and its derivatives are preferably used. The activator in the flux in the present invention is not particularly limited, but amine salts of hydrochloric acid and / or hydrobromic acid, dicarboxylic acids and / or amine salts thereof and the like can be preferably used. Examples of amine salts of hydrochloric acid or hydrobromic acid include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, n-propylamine, di-n-propylamine, tri-n-propylamine, isopropylamine. Hydrochlorides and / or hydrobromides of amines having a relatively small number of carbon atoms, such as diisopropylamine, triisopropylamine, butylamine, dibutylamine, tributylamine, cyclohexylamine, monoethanolamine, diethanolamine and triethanolamine Etc. The content of these activators is not particularly limited, but is preferably 0.05% by weight to 0.15% by weight in terms of chlorine amount with respect to the rosin in the flux.

The thixotropic agent in the present invention is not particularly limited, and generally used thixotropic agents are preferable and the thixotropic agent is shaken. Examples of these include hydrogenated castor oil, amide compounds, monobenzylidene sorbitol, 1,3; 2,4-
Examples thereof include dibenzylidene sorbitol, 1,3; 2,4-bis (4-methyldibenzylidene) sorbitol, tribenzylidene sorbitol, and the like. It is well known that thixotropic agents generally impart thixotropy by forming a gel or a precipitate in a flux. The cream solder is preheated during reflow to evaporate the solvent to some extent, but if the thixotropic agent dissolves or melts at this time, the cream solder may "drip", causing frequent solder balls and bridges. . In such a case, the boiling point of the solvent should be as low as possible and the preheating temperature should be low, but in such a case, it will be easier to evaporate even at room temperature, so the tackiness may be reduced. In such a case, the adhesiveness tends to be lowered because it easily evaporates even at room temperature. Therefore, it is necessary to use a solvent having a relatively high boiling point to slow down the evaporation rate at room temperature. Therefore, it is preferable to use a thixotropic agent having a relatively high melting point to prevent dissolution or melting during preheating as much as possible. Generally, as a high melting point thixotropic agent, 1,3; 2,4-
Dibenzylidene sorbitol (melting point 250 ° C-260
C.), 1,3; 2,4-bis (4-methyldibenzylidene) sorbitol (melting point 250.degree. C. to 260.degree. C.) and the like. Cream solders to which these thixotropic agents have been added do not easily cause "drip" during preheating, but the tendency of gel formation differs significantly depending on the solvent used, and only unstable gels can be obtained depending on the solvent. There wasn't. Surprisingly, the use of the myristic acid esters according to the invention as solvent results in the above 1,3; 2,4-dibenzylidene sorbitol and / or 1,3; 2,4-bis (4-methyldibenzylidene) sorbitol. About 180
It has been found that it melts at a temperature of 150 ° C. and generates a very good gel at a temperature of 150 ° C. or lower. Therefore, the myristic acid ester of the present invention is 1,3; 2,4-dibenzylidene sorbitol and / or 1,3; 2,4-bis (4-
It is particularly preferable to use it together with methyldibenzylidene) sorbitol.

The solder powder in the present invention is not particularly limited, but the shape may be either spherical or amorphous, and the particle size of the solder powder may be any commonly used one, but in the case of spherical. Those having a diameter of 20 to 60 μm are particularly preferable. Further, the composition of the solder alloy is not particularly limited, but Sn-Pb based alloy, Sn-Pb-Bi
Based alloys, Sn-Pb-Ag based alloys and the like are preferably used. The content of the flux in the cream solder in the present invention is not particularly limited, but is preferably 8% by weight to 12% by weight.

[0012]

EXAMPLES The present invention will be described in detail below with reference to examples. The determination of each characteristic value in the examples was performed according to the following criteria. A: Very good. ◯: Good. Δ: Can be used. ×: defective

Example 1 (1) Preparation of Flux 20 parts of polymerized rosin, 35 parts of hydrogenated rosin, 30 parts of ethyl myristate, 12 parts of α-terpineol, and 1.5 parts of triethylamine HBr salt were placed in a container and dissolved by heating. It was Then, 1.5 parts of 1,3; 2,4-dibenzylidene sorbitol was added and dissolved. (2) Preparation of cream solder In a container, 325-500 mesh Sn / Pb (63 wt.
% / 37 wt% of solder powder and 10 parts of the flux prepared in the item (1) were taken and stirred to obtain a creamy product. (3) Evaluation of cream solder The cream solder obtained in the item (2) was printed according to a conventional method (glass epoxy substrate), adhesive strength (touch tester manufactured by RESCA CORPORATION, left for 8 hours after printing), and preheated. Drip (Galaevo board, 150 ° C x 30 seconds), Solderability (Galaeppo board, 230 ° C reflow), Solder ball (Al ₂ O ₃ plate with cream solder printed on 4 mm diameter and 0.3 mm thickness, 25 C. × 60% RH × 24 hours, then reflowed at 230 ° C. and observed with a stereomicroscope) and cleaning properties (glass epoxy substrate, room temperature CFC113 / ethanol (96/4) mixture, immersion 2 minutes) were evaluated. . The printability and solderability were extremely good, and there was almost no sagging or solder balls when heated, and the adhesive strength was 35 g, which were all very good. The cleanability was at a usable level.

Example 2 A cream solder was prepared and evaluated in the same manner as in Example 1 except that the solvent shown in Table 1 was used instead of ethyl myristate. Table 1 shows the evaluation results
It was shown to. As is clear from Table 1 and Example 1, the case where myristic acid ester is added is well balanced and good overall. It should be noted that although isotridecyl myristate is at a usable level, the residue is softened even after reflow and sticky, so that the field of development is considered to be limited. On the other hand, in the case of Comparative Example 1 in which the myristic acid ester is not added, sagging occurs at the time of heating and solder balls frequently occur, which is not preferable. Although the adhesive strength is at a usable level, it tends to be considerably low.

[0015]

[Table 1]

Example 3 A cream solder was prepared in the same manner as in Example 1 except that a thixotropic agent as shown in Table 2 was used instead of 1,3; 2,4-dibenzylidene sorbitol. And evaluated. The evaluation results are shown in Table 2. As is clear from Table 2 and Example 1, good cream solder can be obtained even if the thixotropic agent is changed. Thixotropic agent 1,3; 2
4-dibenzylidene sorbitol and 1,3; 2,4
Especially good is the case of -bis (4-methyldibenzylidene) sorbitol. The amounts of various thixotropic agents added were corrected by the amount of ethyl myristate.

[0017]

[Table 2]

Claims (3)

[Claims] 1. A cream solder obtained by mixing powdered solder and a liquid or paste-like flux, wherein the flux contains myristic acid ester. 2. The myristate ester according to claim 1, wherein the ester is selected from methyl myristate, ethyl myristate, n-propyl myristate, isopropyl myristate, n-butyl myristate and isobutyl myristate. The cream solder according to claim 1, wherein the cream solder is one or more compounds. 3. The flux according to claim 1 or 2, wherein 1,3; 2,4-dibenzylidene sorbitol and / or 1,3; 2,4-bis (4-methylbenzylidene) sorbitol is contained in the flux. The cream solder according to claim 1, wherein the cream solder is contained.