Patent Application
20080053571
A preferred embodiment of the present invention is described below in detail.
A soldering flux of the present invention (hereinafter, in some cases, referred to simply as a “flux”) contains a base resin and an activating agent. The activating agent functions to remove an oxide film on a metal surface during the time of soldering, thereby realizing excellent solder wettability. The base resin functions as a binder for uniformly applying the activating agent to the metal.
No special limitations are imposed on the base resin used in the flux of the present invention. It is possible to use rosin and its derivative, or synthetic resins conventionally and normally used in fluxes. Examples of the rosin include usual gum rosin, tall oil rosin, and wood rosin. As their derivatives, there are polymerized rosin, acrylated rosin, hydrogenated rosin, disproportionated rosin, formylated rosin, rosin ester, rosin modified maleic acid resin, rosin modified phenol resin, and rosin modified alkyd resin. Examples of the synthetic resin include acrylic resin, styrene-maleic acid resin, epoxy resin, urethane resin, polyester resin, phenoxy resin, and terpene resin.
The content of the base resin is, without limitation, preferably 0.5 to 80% by weight, more preferably 2 to 60% by weight, to the total amount of the flux.
The flux of the present invention contains, as an activating agent, an oxygen-containing heterocyclic compound having at least one carboxyl group in a molecule (hereinafter referred to, in some cases, as an “oxygen-containing heterocyclic compound containing a carboxyl group”). This enables excellent wettability to lead-free metals and plating, irrespective of the type of the metals. In the present invention, the oxygen-containing heterocyclic compound means compounds having an oxygen atom in a heterocyclic ring structure. That is, the oxygen-containing heterocyclic compound containing a carboxyl group in the present invention is a compound having at least one carboxyl group and having a heterocyclic ring structure containing an oxygen atom, in a molecule. The number of carboxyl groups in the oxygen-containing heterocyclic compound containing a carboxyl group is preferably 1 to 5, more preferably 1 to 3, furthermore preferably 1 to 2, and most preferably 1.
Examples of the oxygen-containing heterocyclic compound containing a carboxyl group are 1,3-dioxolane-4-methyl-2-propionic acid (2,5-dioxo-4-methyl-3-pyrroline-3-propionic acid), 2-cumarone carboxylic acid, 2-pyrone-6-carboxylic acid, 5-hydroxy-4-pyrone-2-carboxylic acid, and 4-pyrone-2,6-dicarboxylic acid. In addition to these, there are ones having a five-membered ring structure selected from the group consisting of furan, hydrofuran and oxazol. Examples thereof include 2-furan carboxylic acid, 5-methyl-2-furan carboxylic acid, 3-(2-furil) acrylic acid, 2,5-dimethyl-3-furan carboxylic acid, 2,5-furan dicarboxylic acid, 4-butanolid-3-carboxylic acid, tetrahydrofuran-2-carboxylic acid, and 4-oxazol carboxylic acid. Especially preferred is one having the five-membered ring structure selected from the group consisting of furan, hydrofuran and oxazol, because of high reactivity to metals. Only one or at least two types of oxygen-containing heterocyclic compounds containing a carboxyl group may be used.
The content of the oxygen-containing heterocyclic compound containing a carboxyl group is preferably 0.1 to 50% by weight, more preferably 0.5 to 20% by weight, to the total amount of the flux. Below 0.1% by weight, the effect of improving wettability may be insufficient. Above 50% by weight, the film-forming property of the flux may be lowered and hydrophilic property may be increased, so that insulating property tend to fall, resulting in poor reliability. In a combination of at least two oxygen-containing heterocyclic compounds containing a carboxyl group, the total amount thereof may be within the abovementioned range.
Alternatively, in addition to the oxygen-containing heterocyclic compound containing a carboxyl group, it is possible to use, as an activating agent, a heterocyclic compound having at least one carboxyl group in a molecule, where a heteroatom in the heterocyclic ring is nitrogen or sulfur, instead of oxygen. The combined use of a nitrogen-containing or sulfur-containing heterocyclic compound containing a carboxyl group can further improve wettability to some metal plating such as palladium plating and nickel plating.
As a nitrogen-containing or sulfur-containing heterocyclic compound containing a carboxyl group, there are, for example, 2-thiophene carboxylic acid, 2-pyrrol carboxylic acid, 2,3-dimethylpyrrol-4-propyonic acid, 2,5-dioxyo-4-methyl-3-pyrrolin-3-propyonic acid, 1-methylpyrrolidine-2-carboxylic acid, 5-carboxy-1-methylpyrrolidine-2-acetic acid, 3-indoleacetic acid, nicotinic acid, picolinic acid, pyridine dicarboxylic acid, 2-quinoline carboxylic acid, 2-amino-3-(4-imidazolyl)propionic acid, and prolin. When containing these nitrogen-containing or the sulfur-containing heterocyclic compound containing a carboxyl group, the content thereof is preferably 0.1 to 20% by weight to the total amount of the flux.
As an activating agent, other normally used activating agent may be used together. Examples thereof include amines (diphenylguanidine, naphthylamine, diphenylamine, triethanol amine, monoethanol amine, etc); amine salts (organic acid salts or inorganic acid (mineral acid such as hydrochloric acid and sulfuric acid) salts of polyamines such as ethylenediamine, or of amines such as cyclohexyl amine, ethyl amine, diethyl amine); organic acids (dicarboxylic acids such as succinic acid, adipic acid, glutaric acid, sebacic acid and maleic acid; fatty acids such as myristic acid, palmitic acid, stearic acid and oleic acid; hydroxy carboxylic acids such as lactic acid, dimethylol propionic acid and malic acid; benzoic acid, phthalic acid and trimellitic acid); and amino acids (glycine, alanine, aspartic acid, glutamic acid and valine). When these other activating agents are contained, the content thereof is preferably not more than 30% by weight to the total amount of the flux.
The flux of the present invention can also contain a thixotropic agent as needed, in addition to the base resin and the activating agent as described above. Alternatively, the flux of the present invention may also contain a suitable organic solvent as needed.
Examples of the thixotropic agent include cured castor oil, bees wax, carnauba wax, stearic acid amide, and hydroxy stearic acid ethylene bisamide. The content of the thixotropic agent is preferably 1.0 to 25% by weight to the total amount of the flux.
Examples of the organic solvent include alcohol based solvents such as ethyl alcohol, isopropyl alcohol, ethyl cellosolve, butyl carbitol and hexyl carbitol; ester based solvents such as ethyl acetate and butyl acetate; and hydrocarbon based solvents such as toluene and turpentine oil. When the flux of the present invention is used as a liquid flux, isopropyl alcohol is particularly preferred in the points of volatility and the solubility of the activating agent. On the other hand, when the flux of the present invention is applied to a solder paste composition, ethers of polyhydric alcohol, such as butyl carbitol or hexyl carbitol having a high boiling point, are commonly employed and preferred. The content of the organic solvent is preferably 20 to 99% by weight to the total amount of the flux. Below 20% by weight, the viscosity of the flux might be increased, so that the coating property of the flux, and the printability when used as a solder paste composition tend to deteriorate. On the other hand, if the organic solvent exceeds 99% by weight, the effective component (a base resin or the like) as the flux might be relatively reduced, so that solderability might be lowered.
In addition to the abovementioned respective components, the flux of the present invention can also contain, in such a range as not to impair the effect of the present invention, oxidation inhibitor, rust inhibitor, chelating agent etc may be added as needed.
A solder paste composition of the present invention contains the abovementioned flux of the present invention and the solder alloy powder.
No special limitations are imposed on the solder alloy powder. For example, tin-lead alloy generally used, or tin-lead alloy further containing silver, bismuth, or indium may be used. However, taking into consideration that the present invention aims at improving the wettability to lead-free plating, it is desirable to use lead-free alloys such as the alloys based on tin-silver, tin-copper or tin-silver-copper. The particle size of the solder alloy powder is preferably about 5 to 50 μm.
The weight ratio of the flux and the solder alloy power in the solder paste composition of the present invention may be suitably set in accordance with the necessary use and function of a solder paste. That is, flux:solder alloy powder, is preferably about 5:95 to 20:80, without special limitations.
The solder paste composition of the present invention is applied onto a board by a dispenser, screen printing or the like, in the solder connection of electronic equipment parts and the like. After the application, preheating is carried out at, for example, about 150° C. to 200° C., followed by reflow at about a maximum temperature of 170° C. to 250° C. The application and the reflow with respect to the board may be performed in the atmosphere, or alternatively an inactive atmosphere of the gas such as nitrogen, argon, or helium.
The present invention will be described below in further detail with reference to Examples and Comparative Examples.
The respective compositions shown in Table 1-1 and Table 1-2 were mixed in the blending composition shown in Table 1-1 and Table 1-2. Sufficiently applying heat, the mixture was dissolved uniformly to obtain individual fluxes.
The obtained respective fluxes were evaluated in the following manners. The results are shown in Table 1-1 and Table 1-2.
SOP (shrink outline-package) parts were prepared where a glass epoxy board provided with a SOP pattern of 0.8 mm pitch having 20 leads is subjected to various types of plating (tin plating, nickel plating, palladium plating, gold plating, silver plating, tin-copper alloy plating, and tin-bismuth alloy plating) by using thermosetting resin. The flux was applied after 10 pieces of these SOP parts were temporarily fixed to each type of plating (70 pieces in total). The board after applying the flux was then soldered by a wave soldering machine. With a stereoscopic microscope of 20 times, the SOP parts were then observed to judge whether de-wetting occurred at the electrode sections of the parts. If de-wetting occurred, the number thereof (the number of occurrences of defects) was counted. A value that expresses, by percentage, the ratio of the number of occurrences of the defects to the total number of the SOP patterns each of plating (200 leads) was obtained as a percentage of defects (%), and evaluated. In the above soldering, solder alloy powder composed of Sn—Ag—Cu alloy (Sn:Ag:Cu=96.5:3.0:0.5 (weight ratio) was used.
The flux was applied to a comb type board (II type) as defined in JIS-Z-3197. After applying the flux, soldering was performed by a wave soldering machine. The resulting board was left in a thermo-hygrostat having a temperature of 85° C. and a humidity of 85%. With time (at the beginning, after 500 hours, and after 1000 hours), the resistance value (Ω) was measured to evaluate an insulation resistance as electrical reliability. In the above soldering, solder alloy powder composed of Sn—Ag—Cu alloy (Sn:Ag:Cu=96.5:3.0:0.5 (weight ratio) was used.
In Table 1-1 and Table 1-2, for example, the resistance value at the beginning of Example 1, 5×1013Ω, is represented by “5E13.” Those of other examples are represented in this manner.
The respective compositions shown in Table 2-1 and Table 2-2 were mixed in the blending composition shown in Table 2-1 and Table 2-2. Sufficiently applying heat, the mixture was dissolved uniformly to obtain individual fluxes.
Subsequently, each of the obtained fluxes and solder alloy powder (38 to 25 μm in particle size) composed of Sn—Ag—Cu alloy (Sn:Ag:Cu=96.5:3.0:0.5 (weight ratio)) were mixed at the ratio of flux:solder alloy powder 11:89 (weight ratio), thereby obtaining individual solder paste compositions.
The obtained respective solder paste compositions were evaluated in the following manners. The results are shown in Table 2-1 and Table 2-2.
On a board provided with a QFP (quad flat package) pattern of 0.8 mm pitch having 100 leads, each solder paste composition was printed using a 200 μm thick metal mask having the same pattern. Separately, there were prepared QFP parts subjected to various types of plating (tin plating, nickel plating, palladium plating, gold plating, silver plating, tin-copper alloy plating, and tin-bismuth alloy plating). On the above printed paste, 10 pieces of these QFP parts were mounted for each plating (70 pieces in total). Within 10 minutes after the mounting, preheating was performed at 175±5° C. for 80±5 seconds in the atmosphere, followed by reflow at a maximum temperature of 235±5° C. With a stereoscopic microscope of 20 times, the resulting parts were observed to judge whether de-wetting occurred. If de-wetting occurred, the number thereof (the number of occurrences of defects) was counted. A value that expresses, by percentage, the ratio of the number of occurrences of the defects to the total number of the QFP patterns each of plating (1000 leads) was obtained as a percentage of defects (%), and evaluated.
The solder paste composition was printed on a comb type board (II type) as defined in JIS-Z-3197, by using a 100 μm thick metal mask having the same pattern. Within 10 minutes after the printing, preheating was performed at 175±5° C. for 80±5 seconds in the atmosphere, followed by reflow at a maximum temperature of 235±5° C. The resulting board was then left in a thermo-hygrostat having a temperature of 85° C. and a humidity of 85%. With time (at the beginning, after 500 hours, and after 1000 hours), the resistance value (Ω) was measured to evaluate an insulation resistance as electrical reliability. In Table 2-1 and Table 2-2, for example, the resistance value at the beginning of Example 7, 6×1013Ω, is represented by “6E13.” Those of other examples are represented in this manner.
It can be said from Tables 1-1, 1-2, 2-1 and 2-2 that the respective fluxes of Examples, containing 3-(2-furil) acrylic acid or 2-furan carboxylic acid as an oxygen-containing heterocyclic compound containing a carboxyl group, are extremely excellent. This is because they substantially similarly exhibit excellent wettability to the element electrodes subjected to the various plating, and also had excellent insulation resistance after elapsing of 1000 hours, with regard to the electrical reliability after connection.
While one preferred embodiment of the present invention has been described, the present invention is not limited to the above embodiment.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-240229 | Sep 2006 | JP | national |
