JP3189133B2 - 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 the soldering, in order to make the soldering more reliable, 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 using a so-called cream solder in which the solder fine particles and the flux are mixed is used. Methods such as 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, (2) good solderability (dissolves and removes oxides on the metal surface, wraps the metal surface, and has the surface of molten solder Which lowers the tension),
(3) It is required that there is no stickiness and (4) that it can be easily washed.

[0004] Generally, the cream solder is obtained by mixing powder solder fine particles and a liquid or paste-like flux to form a cream having an appropriate viscosity. The flux generally uses rosin or a derivative thereof as a base, and contains a solvent, an activator, a thixotropic agent, and the like. The composition of the flux is very important because the properties of the cream solder obtained vary slightly depending on the type and mixing ratio of these compounding agents. Of these flux components, the base often affects solder balls, adhesiveness, printability, color of flux, etc., which are important as cream solder, and is particularly important.

It is well known that the base plays a very important role in cream solder as described above. For example, JP-A-59-159298 discloses a method using a distillation product of a hydrogenated rosin, a disproportionated rosin, or a polymerized rosin. However, the method is mainly a lot-to-lot variation of rosin, alteration due to oxidation, etc.,
The present invention relates to quality improvement such as crystallization, and mainly relates to solder containing tin. Therefore, cream solder is not described in detail, and as a result of the study by the present inventors, solder balls frequently occur,
Further, the spreading rate was insufficient. In addition, Japanese Patent Laid-Open No. 1-1
No. 48,488 discloses a method using hydrogenated rosin. However, this method also has the problems that the color of the flux residue after reflow is poor and that solder balls frequently occur. From the above background, there has been a strong demand for a rosin or a derivative thereof capable of producing a cream solder in which the color of the flux residue after reflowing is pale and good, and in which solder balls are hardly generated.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and the color tone of the flux residue after reflow is good, the generation of solder balls is small, and the solderability is low. The purpose is to provide a good cream solder.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a cream solder obtained by mixing a powder solder and a liquid or paste-like flux in a flux obtained by a Diels-Alder reaction between levopimaric acid and acrylic acid in the flux. This can be achieved by a cream solder characterized by containing the product. Hereinafter, the present invention will be described in detail.

The reaction product obtained by the Diels-Alder reaction between levopimaric acid and acrylic acid in the present invention is a dicarboxylic acid obtained by the Diels-Alder reaction between levopimaric acid and acrylic acid. In the Diels-Alder reaction, acrylic acid is added to the conjugated double bond of levopimaric acid, and two types of reaction products can be obtained depending on the orientation of acrylic acid with respect to the conjugated double bond. Of course, in the present invention, these products may be used alone or as a mixture. The raw material levopimaric acid may be used alone, but a mixture containing levopimaric acid such as rosin can also be preferably used. In order to obtain high-purity levopimaric acid, the cost must be considerably high, but rosin can be obtained at a very low price and is particularly preferably used. In general, the content of levopimaric acid in rosin is low, and it is difficult to use rosin as a raw material if only the contained levopimaric acid reacts, but abietic acid, which is the main component of rosin, isomerized during the reaction. It is thought that rosin can be preferably used since the aldehydes are converted to levopimaric acid to obtain the Diels-Alder reaction product of the present invention. Generally, the carboxyl group in rosin is weakly active because it is bonded to a tertiary carbon. On the other hand, the Diels-Alder reaction product of the present invention tends to be more active than rosin, probably because the carboxyl group of acrylic acid added to levopimaric acid is bonded to secondary carbon. for that reason,
If a relatively strong activator such as amine hydrohalide is used as the activator, conventional rosin is not a problem, but the amount of amine salt of hydrohalic acid should be minimized as in non-cleaning type cream solder. When it is necessary to lower the temperature, a relatively low-activity activator must be used.When rosin is used as a base, solder balls are apt to occur frequently, but the Diels-Alder reaction product of the present invention may be used. Thus, the generation of solder balls can be suppressed. In addition, the Diels-Alder reaction product of the present invention has an acid value of 300 (mg KOH / g), which is significantly higher than that of rosin (about 160 mg KOH / g), in addition to the fact that the activity level of the carboxyl group itself is considered to be strong. There is also a merit that it is high.

[0009] The low activity level activators other than amine salts include 2,3-dibromopropanol, 2,3-dibromobutane-1,4-diol, and 2,3-dibromo-2-butene-1,4-diol. , Nonionic bromine compounds such as ethyl 2-bromo-n-butyrate, succinic acid, malonic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, tetradecandioic acid, palmitic acid and stearic acid. Such carboxylic acids or amine salts thereof can be preferably used. In addition, because the Diels-Alder reaction product of the present invention does not have a conjugated double bond, it is possible to produce a cream solder having a very good color tone with less coloring during storage and heating as compared with rosin.

The Diels-Alder reaction product of levopimaric acid and acrylic acid in the present invention may be used alone or in combination with a conventionally known rosin or a derivative thereof. When mixed and used, the rosin to be mixed is not particularly limited, but polymerized rosin, hydrogenated rosin, disproportionated rosin and the like are particularly preferred. Even when used in combination with other rosin, the amount of the Diels-Alder reaction product of the present invention is 10% by weight to 50% by weight in the flux.
% By weight. If the amount is less than 10% by weight, solder balls may occur frequently, and if the amount exceeds 50% by weight, the effect of suppressing solder balls may be saturated.

The solvent, thixotropic agent and the like in the flux in the present invention are not particularly limited, and conventionally known ones can be preferably used. Although the solder powder in the present invention is not particularly limited, the shape may be a true sphere or an irregular shape, or the particle size of the solder powder may be any commonly used one. Those having a thickness of 60 μm are particularly preferred. Furthermore, although the composition of the solder alloy is not particularly limited, 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]

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 25 parts of an acrylic acid addition reaction product of levopimaric acid, 10 parts of disproportionated rosin, 5 parts of polymerized rosin, 20 parts of α-terpineol, 10 parts of dibutyl phthalate, butyl carbyl 10 parts of tall, trans-2,3-dibromo-2-butene-
5 parts of 1,4-diol, 4 parts of glutaric acid, 5 parts of stearic acid amide and 6 parts of hydrogenated castor oil were charged into a container and dissolved by heating. Then, 1.5 parts of 1,3; 2,4-dibenzylidenesorbitol was added and dissolved. (2) Preparation of cream solder 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 the section (2) was printed according to a conventional method (glass epoxy substrate) and solderability (glass epoxy substrate, 2).
30 ° C reflow), solder balls (Al ₂ O ₃ board, cream solder printed to 4 mm in diameter and 0.3 mm in thickness.
After standing at 5 ° C. × 60% RH × 24 hours, the sample was reflowed at 230 ° C. and observed with a stereoscopic microscope), and the color of the reflow residue (sample for evaluating solder balls) was evaluated. The printability and the solderability were very good, the number of solder balls was very small, and the color of the reflow residue was very small, and both were good.

Example 2 A cream solder was prepared and evaluated in the same manner as in Example 1, except that the solvents shown in Table 1 were used. When the amount of the substrate was changed, the correction was made with the amount of the solvent (the mixing ratio of each solvent was constant). Table 1 shows the evaluation results.

[0015]

[Table 1]

As is clear from Table 1 and Example 1,
When the Diels-Alder reaction product of the present invention is added as the base material, the overall balance is good and good. On the other hand, in the case of Comparative Example 1, which is out of the range of the present invention, solder balls frequently occur, and the reflow residue is not easily colored.

Example 3 A cream solder was prepared and evaluated in the same manner as in Example 1 except that the activator was changed as shown in Table 2. When the total amount of the activator was changed, the correction was made with the amount of the solvent (the mixing ratio of each solvent was constant). Table 2 shows the evaluation results.

[0018]

[Table 2]

Even if the activator is changed as shown in Table 2, the performance of the cream solder is well balanced and good. 2,3 without adding the amine hydrohalide
-Dibromopropanol, 2,3-dibromobutane-
1,4-diol and 2,3-dibromobutene-1,
Particularly preferred is the case where 4-diol is added.

Example 4 In Example 1, a Diels-Alder of water white rosin and acrylic acid was used in place of 25 parts of the acrylic acid addition reaction product of levopimaric acid, 10 parts of disproportionated rosin, and 5 parts of polymerized rosin, for a total of 40 parts. 40 parts of reaction product (acid value 2
Example 1 using 46 mg KOH / g, conversion 60%)
A cream solder was prepared and evaluated in the same manner as described above. The printability and the solderability were very good, the number of solder balls was very small, and the color of the reflow residue was very small, and both were good.

[0021]

According to the present invention, a cream solder having less solder balls, less coloring of reflow residues, and excellent printability and solderability can be produced as compared with the conventionally known technology.

──────────────────────────────────────────────────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 obtained by mixing a powder solder and a liquid or paste-like flux, wherein the flux contains a reaction product obtained by a Diels-Alder reaction between levopimaric acid and acrylic acid. Cream solder. 2. The flux according to claim 1, wherein 2,3-dibromopropanol, 2,3
-Dibromobutane-1,4-diol, and 2,3-
2. The cream solder according to claim 1, comprising at least one bromine compound selected from dibromo-2-butene-1,4-diol. 3. The flux according to claim 1, wherein the content of a reaction product obtained by a Diels-Alder reaction between levopimaric acid and acrylic acid is 10% by weight.
3 to 50% by weight.
The cream solder described.