JP3189134B2 - Cream solder - Google Patents

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 microcircuits and the like.

[0002]

2. Description of the Related Art Conventionally, when electronic elements are mounted on a printed circuit board, soldering has been frequently used. In order to make the soldering more reliable in the soldering, a method of cleaning the surface of the metal to be joined with a liquid flux or a high-viscosity flux and then soldering, or a so-called cream solder in which solder particles are mixed with a flux. And other methods are widely used.

[0003] The above-mentioned liquid flux and flux for cream solder are used to maintain high product quality and reliability.
(1) high insulation, (2) non-corrosive, (3) long-term stability,
(4) It is required that the material of other parts does not change,
In addition, from the soldering work surface, (1) no harmful gas is generated, and (2) good solderability (has an action of dissolving and removing oxides on the metal surface and wrapping up the metal surface, and further has a function of melting solder. Which lowers the surface tension)
(3) It is required that there is no stickiness and (4) that it can be easily washed.

[0004] In general, cream solder is prepared by mixing fine particles of powdered solder with a liquid or paste-like flux to form a cream 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 vary slightly depending on the type and the mixing ratio of these compounding agents. Among these flux components, the solvent is solder ball, which is important as cream solder, tackiness,
It often affects printability and the like, and is particularly important. It is well known that solvents play a very important role in cream solder as described above. For example, JP-A-56-154297 discloses 2-methyl-2,4
-A method 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 has problems such as frequent occurrence of solder balls and a decrease in tackiness. Japanese Patent Application Laid-Open No. 1-186300 discloses a method using phenethyl alcohol. However, this method also has a problem that the tackiness is reduced, probably because the boiling point of the solvent is low. Solvents having good tackiness and low solder ball generation from the above-described background have been strongly desired.

[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 few solder balls and good adhesiveness and solderability. is there.

[0006]

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

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, and amyl myristate. Isoamyl, n-hexyl myristate, isohexyl myristate, n-heptyl myristate, n-octyl myristate, 2-ethylhexyl myristate, n-nonyl myristate, n-decyl myristate, n-decyl myristate, myristic acid Examples include isotridecyl and benzyl myristate. Of these, methyl myristate, ethyl myristate, n-propyl myristate, isopropyl myristate, n-butyl myristate, and isobutyl myristate are particularly preferred. If the molecular weight is large like isotridecyl myristate, it will not completely evaporate during reflow and will remain, and the residue may become sticky after reflow.

[0008] In the present invention, the content of myristic acid ester in the flux is not particularly limited, but 10 wt%
-40% by weight is particularly preferred. If the amount is less than 10% by weight, the tackiness may decrease. If the amount exceeds 40% by weight, the effect of the present invention may be saturated. In the present invention, it is also possible to use myristenic acid ester and another solvent in combination. The solvent used in combination with the myristenic acid ester is not particularly limited. Examples include alcohol, isostearyl alcohol, diisodecyl adipate, dibutyl phthalate, 1-octadecene, and liquid paraffin.

The substrate 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 an amine salt of hydrochloric acid and / or hydrobromic acid, a dicarboxylic acid and / or an amine salt thereof 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 Hydrochloride and / or hydrobromide of amine having relatively small carbon number such as diisopropylamine, triisopropylamine, butylamine, dibutylamine, tributylamine, cyclohexylamine, monoethanolamine, diethanolamine, triethanolamine, etc. And the like. The content of these activators is not particularly limited, but is particularly preferably 0.05% by weight to 0.15% by weight in terms of chlorine based on the rosin in the flux.

The thixotropic agent in the present invention is not particularly limited, and generally used thixotropic agents are preferable and are rocked. Examples of these are hydrogenated castor oil, amide compounds, monobenzylidene sorbitol, 1,3; 2,4-
Dibenzylidene sorbitol; 1,3; 2,4-bis (4-methyldibenzylidene) sorbitol, tribenzylidene sorbitol, and the like. It is well known that thixotropic agents generally impart thixotropic properties by forming a gel or forming a precipitate in the flux. The cream solder is pre-heated during reflow and evaporates the solvent to some extent.At this time, if the thixotropic agent is dissolved or melted, the cream solder may cause "sagging", causing solder balls to be frequently generated and bridges to be generated. . In such a case, the boiling point of the solvent should be as low as possible, and the preheating temperature should be lowered.In such a case, it is easy to evaporate even at room temperature. In such cases, the composition tends to evaporate even at room temperature, so that the tackiness tends to decrease. Therefore, it is necessary to use a solvent having a relatively high boiling point and to reduce 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, high melting point thixotropic agents are 1,3; 2,4-
Dibenzylidene sorbitol (melting point 250 ° C. to 260
° C), 1,3; 2,4-bis (4-methyldibenzylidene) sorbitol (melting point: 250 ° C to 260 ° C). The cream solder to which these thixotropic agents are added is not likely to cause dripping during preheating, but the tendency of gel formation differs significantly depending on the solvent used, and only unstable gels are obtained depending on the solvent used. Did not. Surprisingly, the use of the myristic esters according to the invention as solvents provides the above 1,3; 2,4-dibenzylidenesorbitol and / or 1,3; 2,4-bis (4-methyldibenzylidene) sorbitol. About 180
It turned out that it melts at a temperature of 150 ° C. and generates a very good gel at a temperature of 150 ° C. or less. Therefore, the myristic esters of the present invention are 1,3; 2,4-dibenzylidenesorbitol and / or 1,3; 2,4-bis (4-
It is particularly preferred to use in combination with (methyldibenzylidene) sorbitol.

Although the solder powder in the present invention is not particularly limited, the shape may be a true sphere or an irregular shape. The particle size of the solder powder may be any commonly used one. Those having a diameter of 20 to 60 μm are particularly preferred. Furthermore, although the composition of the solder alloy is not particularly limited, Sn-Pb-based alloys, Sn-Pb-Bi
Alloys, Sn-Pb-Ag 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]

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: Available. ×: 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 charged into a container, and dissolved by heating. Was. Then, 1.5 parts of 1,3; 2,4-dibenzylidenesorbitol 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 item (1), and stirred to obtain a cream. (3) Evaluation of cream solder The cream solder obtained in (2) was printed according to a conventional method (glass epoxy substrate), adhesive strength (Touchness tester manufactured by Resca Co., Ltd., left for 8 hours after printing), and preheated (Galaevo substrate, 150 ° C. × 30 seconds), solderability (Galaepo substrate, 230 ° C. reflow), solder ball (Al ₂ O ₃ plate with cream solder printed to 4 mm in diameter and 0.3 mm in thickness, 25 After leaving for 24 hours at a temperature of 60 ° C. × 60% RH, reflow was performed at 230 ° C. and observed with a stereoscopic microscope) and cleanability (glass epoxy substrate, mixed solution of Freon 113 / ethanol (96/4) at room temperature, immersion for 2 minutes) was evaluated. . The printability and the solderability were very good, the sagging and the solder balls were hardly generated, and the adhesion was 35 g, which was very good. Further, the cleaning property 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 the myristic acid ester was added was balanced and overall good. It should be noted that, although isotridecyl myristate is at a usable level, the residue is softened and sticky even after reflow, so that the development field is considered to be limited. On the other hand, in the case of Comparative Example 1 in which the myristic acid ester was not added, sagging at the time of heating occurred and solder balls frequently occurred, which is not preferable. Also, the adhesive strength tends to be quite low, even at a usable level.

[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-dibenzylidenesorbitol. And evaluated. Table 2 shows the evaluation results. As is clear from Table 2 and Example 1, even when the thixotropic agent is changed, a good cream solder can be obtained. Thixotropic agents 1,3; 2
4-dibenzylidene sorbitol and 1,3; 2,4
-Bis (4-methyldibenzylidene) sorbitol is particularly good. In addition, the thing to which the addition amount of various thixo agents was different was corrected by the amount of ethyl myristate.

[0017]

[Table 2]

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B23K 35/22-35/26 B23K 35/363

Claims (3)

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