JPH0919794A - Powdered solder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a powdered solder, which is stable for oxidation, excellent in storage stability and has inert surface, by treating the surface of powdered solder with a specific organic silane compound. SOLUTION: The surface of a material for powdered solder is treated with at least one kind of a silane compound shown by the equation I, equation II, equation III. Where, R1 -R4 in the equations I, II, III are of an alkyl base/aryl base or an aryl base. Further, a hydrogen atom of R1 can be substituted with one piece or more fluorine atoms. A means to coat a silane compound to a material for powdered solder can be either of dry process, wet process, spray process, etc. A concentration of the silane compound for coating is desirable to be below 4% and above 0.007 for the weight of material for powdered solder.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a solder powder protected by a protective film. More specifically, it is possible to prevent the oxidation of solder particles without impairing the reflow characteristics of solder, solderability, and wettability with the metal to be joined, and also promote deterioration in cream solder. The present invention relates to a solder powder provided with a protective film capable of suppressing the reaction between the solder powder and the flux.

[0002]

2. Description of the Related Art In the electronics industry, circuit parts, that is, resistors, capacitors, inductors, VLS
Initially, I, LSI, IC, transistors, etc. were arranged on one side of the printed circuit board, and lead wires from the components penetrated the circuit board and were soldered on the circuit surface on the opposite side.
However, due to the demand for miniaturization of products, a double-sided printed circuit board having the same circuit surface and component mounting surface, that is, surface mounting and using both surfaces of the circuit board, has come into practical use. Solder paste is commonly used to surface mount components. Solder paste is suitable for automation due to its printability and adhesiveness, and its use has been increasing in recent years.
The solder paste is typically 10 to 70 μm of solder powder, rosin or a resin component as an alternative thereto, inorganic acid salts of basic compounds such as organic acids and / or amines and other activators, and thixotropic for improving printability. It usually contains agents and solvents. Generally, the solder paste is quantitatively screen-printed or optionally applied by a dispenser on a printed circuit board, then the component is mounted and the solder paste is reflowed. Reflow means a series of steps in which the solder paste is heated including preheating until the solder is sufficiently melted, and then cooled and solidified.

As a solder powder for the above-mentioned purpose, some attempts have been made to coat the solder powder to protect it from an activator and improve the stability of the solder paste. For example, Japanese Patent Publication No. 5-26598
Discloses a method of coating solder powder with glycerin, and JP-A-1-113197 discloses a method of coating the solder powder with a coating agent which is insoluble or fusible in the solvent of the solder paste. Suitable examples of the latter include silicone oils, silicone-based high molecular weight compounds, fluorinated silicone oils, fluorosilicone resins and fluorinated hydrocarbon-based polymer compounds. Further, in JP-A-3-184698 and JP-A-4-251690, a solder powder is coated with a rosin-based mixture which is incompatible with the flux at room temperature and compatible with the solder temperature, or the flux itself, that is, a resin mainly containing rosin. A method is disclosed. Further, Japanese Unexamined Patent Application Publication
No. 7993 discloses a method of protecting a powder by vacuum-depositing parylene on a solder powder.

[0004]

One of the problems in the industry relating to solder paste is its storage stability, which is that it usually has a shelf life of 1 to 3 months even when it is refrigerated. Further, the life becomes short at a temperature around 25 ° C. which is the actual use temperature. One of the causes of instability of the solder paste is that the thickness of the oxide film on the surface of the solder powder varies depending on the manufacturing method and storage period.The thicker the oxide film, the poorer the wettability of the solder paste and the generation of solder balls during reflow. Cause inconvenience. Further, the solder powder often reacts with an activator coexisting in the paste, which further oxidizes the solder powder and lowers the activity of the flux, and unnecessary reaction causes an increase in the viscosity of the paste to provide proper printing characteristics. Can't be maintained. Japanese Patent Publication No. 5-26598 and Japanese Patent Laid-Open No.
In 113197, a relatively large amount of coating may be effective in suppressing solder powder oxidation, but a large amount of coating material is rather inconvenient for solder reflow, and these coatings are not physically applied. It is considered that the adhesion is very weak when the solder paste is left alone, and there is a strong possibility that the solder paste will be peeled off during the kneading when manufacturing the solder paste, the transfer during use, or the handling such as printing. Further, it is hard to say that the coating agents disclosed in JP-A-3-184698 and JP-A-4-251690 protect the powder by containing a large number of reactive organic acids themselves. Further, although the coating method disclosed in Japanese Patent Laid-Open No. 6-7993 is considered to be effective, there are many problems in reality such as using an expensive device and taking a long time to process. Moreover, since these coats are still only physically on the powder and not chemically bonded to the powder surface, it is considered that they are merely adherent and not strong. An object of the present invention is to provide a solder powder for a solder paste, which is particularly stable against oxidation, has excellent storage stability, has an inert surface, and has excellent reflow characteristics and printing characteristics.

[0005]

Means for Solving the Problems The inventor of the present invention has made intensive efforts to achieve the above-mentioned object, and as a result of various studies, have found the present invention. That is,

Embedded image Of the solder powder (wherein R _{1 to} R ₄ are an alkyl group, an aryl group or an aralkyl group) and the hydrogen atom of R ₁ is 1 or more. The above-mentioned solder powder substituted with the fluorine atom of was found.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The solder raw material powder to be surface-treated in the present invention is a method in which ordinary molten solder is dropped and an inert gas is sprayed on the way, or molten solder is sprayed from a rotary slit in the inert gas. It is manufactured by atomizing method. The particle size depends on the purpose of use, but is, for example, 5 to 30 μm, 20 to 50 μm, 30 to 70 μm,
100 μm or the like is used. Its composition is, for example, 63 Eu / 37Pb eutectic solder composition
2Sn / 36Pb / 2Ag, 60Sn / 40Pb, 50
Sn / 50Pb, 30Sn / 70Pb, 25Sn / 75
Pb, 10Sn / 88Pb / 2Ag, 46Sn / 8Bi
/ 46Pb, 57Sn / 3Bi / 40Pb, 42Sn /
42Pb / 14Bi / 2Ag, 45Sn / 40Pb / 1
5Bi, 50Sn / 32Pb / 18Cd, etc. are mentioned. Further, from the viewpoint of recent Pb elimination, Pb is not included, for example, 48Sn / 52In, 43Sn / 57Bi, 97I.
n / 3Ag, 58Sn / 42In, 95In / 5Bi,
60Sn / 40Bi, 91Sn / 9Zn, 96.5Sn
/3.5Ag, 99.3Sn / 0.7Cu, 95Sn /
5Sb, 20Sn / 80Au, 90Sn / 10Ag, 9
7Sn / 3Cu, 99Sn / 1Ge, 92Sn / 7.5
Bi / 0.5Cu, 97Sn / 2Cu / 0.8Sb /
0.2Ag, 95.5Sn / 3.5Ag / 1Zn, 9
Examples include 5.5Sn / 4Cu / 0.5Ag. Further, a mixture of metal powders having two or more compositions may be used.

In the present invention, these solder raw material powders are

Embedded image Surface treatment with at least one compound (wherein R _{1 to} R ₄ are alkyl groups, aryl groups or aralkyl groups) or a compound in which one or more hydrogen atoms of R ₁ of the above compound is substituted with a fluorine atom. To do. Examples of the compound of the former group, methyltrimethoxysilane, methyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, octadecyltrimethoxysilane, octadecyltriethoxysilane, octadecylmethyldimethoxysilane, phenyltrimethoxysilane,
Phenyltriethoxysilane and the like can be mentioned, and particularly preferably, R ₁ has 6 or more carbon atoms. If it is less than 6, the chain length is short and the coating action is somewhat insufficient, which is not preferable. Also R
₁ , dimethyl siloxane group, diphenyl siloxane group,
A compound containing one or more methylphenylsiloxane groups and diethylsiloxane groups can also be suitably used.

Further examples of the latter group of compounds substituted with a fluorine atom include, for example, heptadecafluorodecylmethyldimethoxysilane, heptadecafluorodecyltrimethoxysilane, tridecafluorooctyltrimethoxysilane and trideca. Examples thereof include fluorooctyltriethoxysilane and heptadecafluorodecyltriethoxysilane. The surface-treating compound of the present invention is characterized by having a functional group highly reactive to the solder raw material powder at the terminal of the molecule, and in addition to the reactive silane, a reactive amine group, vinyl group, epoxy group So-called silane coupling agents having groups, halogen groups, etc. are not included. This is because the use of the silane coupling agent causes a complicated reaction in the flux and rather reduces the stability.

The surface treatment compound of the present invention is characterized in that the surface of the solder raw material powder is coated by a reaction or the like by the method described later. The surface of the solder raw material powder is generally oxidized by oxygen in the air, and most of it is SnO or PbO.
It is said that some OH groups are present, though the surface is covered with. The above-mentioned surface treatment compound generates Si-OH groups under appropriate hydrolysis conditions and reacts with oxides or OH groups on the metal surface to form a strong Si-OM bond or hydrogen bond with the metal surface. Will have a strong bond. However, in a strict sense, it is difficult to identify in what state they are bound, so the description of the claims of the present invention is defined as a product-by-process claim.

As a method for coating the solder raw material powder with the silane compound, a dry method, a wet method, a spray method or the like is used. In the dry method, water or alcohol aqueous solution of a silane compound is added by spraying or drip while stirring the solder raw material powder with a stirrer such as a V-type blender.
As the alcohol used, alcohols having a relatively low boiling point such as methyl alcohol, ethyl alcohol, isopropyl alcohol and the like are preferably used. If the boiling point is too high, it becomes difficult to remove the residual alcohol.
In the wet method, the solder raw material powder is dispersed in alcohol water, the silane compound is added, and then the reaction is performed with stirring, and the alcohol water component is removed by drying. In the spraying method, an alcohol aqueous solution of the silane compound is sprayed onto a relatively high temperature solder raw material powder. In particular, it is effective to prevent oxidative deterioration and to coat by directly spraying the solder raw material powder or by spraying with an inert gas for atomizing at the same time, and to omit the drying step. . In this case, an aqueous alcohol solution or an aqueous solution of a silane compound is preferably used.

The concentration of the silane compound to be coated with the solder raw material powder is preferably less than 4% and more than 0.0007% with respect to the weight of the solder raw material powder. If it exceeds 4%, the unreacted silane compound occupies the majority and causes an inconvenient side reaction, and at the same time, the viscosity of the entire system is lowered, so that the required printing characteristics cannot be maintained. In addition, the solder ball test is adversely affected. If it is less than 0.0007%, the effect of the coat is lost. More preferably, the weight ratio is 0.0
The concentration is from 0 to 1%.

When a solder paste is produced using the above-mentioned solder powder coated with the silane compound, it is kneaded with a known rosin, activator, thixotropic agent, solvent and additive. As the rosin, water white rosin, polymerized rosin, disproportionated rosin, hydrogenated rosin and the like are used, but synthetic resin-based ones may also be used.

As the activator, aniline hydrobromide,
Amine halogen salts such as isopropylamine hydrochloride, monoethylamine hydrobromide, diphenylguanidine hydrobromide, organic salts of amines, organic acids such as formic acid, acetic acid, myristic acid, palmitic acid, stearic acid, benzoic acid, etc. Organic dicarboxylic acids such as monocarboxylic acid, oxalic acid, malonic acid, succinic acid, adipic acid, fumaric acid, maleic acid and the like, and halogenated hydrocarbons such as 2,3-
One or a mixture of halogenated alcohols such as dibromo-2-butene-1,4-diol and 1,3-dibromo-2-propanol is used.

As the solvent, alcohols, ketones, esters and aromatic solvents can be used. For example, benzyl alcohol, ethanol, isopropyl alcohol, butanol, ethyl cellosolve, butyl cellosolve, butyl carbitol, terpineol, toluene, xylene, tetralin, propylene. Glycol monophenyl ether,
Diethylene glycol monohexyl ether or the like is used alone or in combination.

As the thixotropic agent added to improve the printability, fine silica particles, inorganic compounds such as kaolin particles, hydrogenated castor oil, hydrogenated castor oil and the like are used. In addition, additives such as an antioxidant and a copper damage inhibitor may be added. The solder paste of the present invention is a surface-treated solder powder 83-94 wt.
%, Rosin or resin component 4.5 to 7.5 wt%, solvent 2.5 to 5.5 wt%, activator 0.02 to 2 wt%, and thixotropic agent 0.02 to 2 wt%. Mixing is performed using a known device such as a planetary mixer.

The solder paste using the surface-treated solder powder is stable in viscosity because the metal surface is inactive to the activator, so that the activator is prevented from eroding the metal surface and unnecessary side reaction components cannot be formed. It has good stability, and therefore has very good storage stability and stability during use. Also, since the coating film blocks the effect of oxygen in the air, it is difficult for oxygen-mediated reactions to occur, and when solder paste is applied to printing,
That is, stability during use is improved. During reflow, the coating film separates due to the high temperature, and the solder metal particles are melted and soldering is performed. Since the coating prevents oxidative deterioration, the solder ball test is better than when uncoated solder powder is used, and the coating film does not harm the fusion of solder powder at all. Further, the coated solder powder has good storage stability as a powder, is resistant to oxidative deterioration, and can withstand long-term storage.

[0017]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited thereto. Example 1 0.5 g of octadecyltrimethoxysilane, 45 g of ethanol and 0.05 g of water were taken and stirred at room temperature for 30 minutes to hydrolyze the silane compound. After that, 22 μm to 50
100 g of eutectic spherical solder raw material powder of μm 63Sn-37Pb was added and reacted at 45 ° C. for 3 hours, and after the reaction was completed, the pressure was reduced to remove ethanol and water. This particle is X
When the surface was measured by a line photoelectron spectroscopy (X-Probe manufactured by SSI), Si was detected and it was confirmed that the surface was covered with a silane compound. Examples 2 to 8 and Comparative Examples 1 to 3 In the same manner as in Example 1, the solder raw material powder was treated with the compounds shown in Table 1.

[0018]

[Table 1] The weight ratio in Table 1 is the weight ratio (%) to the solder raw material powder.

Application Example Using the solder powders of Examples 1 to 8 and Comparative Examples 1 to 3, 10 parts by weight of flux having the composition shown in the following table and solder powder 9 were used.
0 parts by weight was kneaded to prepare a solder paste.

[0020]

[Table 2]

The solder paste is usually stored at a low temperature of about 5 ° C., but for the long-term storability test, it was heated to 40 ° C. and an accelerated deterioration test was conducted. Viscosity immediately after preparing solder paste and accelerated deterioration at 40 ° C 16 hours later,
The viscosity ratio after 32 hours was used as an index of storage stability. The viscosity was measured at 25 ° C. using an E-type viscometer manufactured by Toki Sangyo using a cone having a diameter of 14 mm and an angle of 3 ° at a shear rate of 0.2 s ⁻¹ . In addition, in order to test the wettability of the solder paste and the occurrence of solder balls, JIS
A solder ball test was conducted according to Z3284-1994. The results are as shown in Table 3. The evaluation display of the solder ball test is performed in four stages, "1" is excellent and "4" is poor.

[0022]

[Table 3]

As shown in Table 3, in comparison with Comparative Example 1 in which untreated solder powder was used, all of the Examples showed good viscosity stability, showing that the storage stability was improved. The effect is somewhat inferior when a small amount of silane compound is used. On the contrary, in Example 4 in which a large amount was used, the viscosity stability was obtained, but the solder ball test was somewhat inferior. Further, the silane compounds having a reactive functional group shown in Comparative Examples 2 and 3, that is, the silane coupling agent, results in a decrease in viscosity stability. As described above, it is understood that by treating the solder raw material powder with the silane compound of the present invention, a solder paste having good storage stability and use stability can be produced.

[0024]

INDUSTRIAL APPLICABILITY The solder powder of the present invention is a solder powder for a solder paste which is particularly stable against oxidation, has excellent storage stability, has an inert surface, and has excellent reflow characteristics and printing characteristics.

Front page continuation (72) Inventor Tetsuro Sakurai 1-1-1 Onodai, Midori-ku, Chiba-shi, Chiba Showa Denko K.K.

Claims (2)

[Claims] [Claim 1] The surface of the solder powder is treated with at least one of the above. (However, in the formula, R _{1 to} R ₄ are an alkyl group, an aryl group, or an aralkyl group.) 2. The solder powder according to claim ₁ , wherein the hydrogen atom of R ₁ is substituted with one or more fluorine atoms.