JP2007083253A - Solder paste composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solder paste composition capable of uniformly sticking solder to the surface of an electrode. <P>SOLUTION: The solder paste composition is used in a solder precoat process where the surface of an electronic circuit board is painted with a solder paste composition all over, the solder paste composition painted all over is heated, and the solder is stuck to the surface of an electrode in the electronic circuit board. The solder paste composition comprises flux, and the flux includes a solvent having a specific gravity higher than 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a solder paste composition suitable for pre-coating solder by solid coating on an electronic component board before the electronic component is mounted on the board.

  Conventionally, various solder paste compositions have been used in pre-coating solder on electrodes. For example, Patent Literature 1 and Patent Literature 2 describe cream solder (solder paste composition) containing cellulose in a predetermined ratio. According to these documents, the cellulose is described as functioning as a binding inhibitor that prevents the solder powders contained in the solder paste composition from being bonded to each other. And after soldering this solder paste composition on the electrode arrangement | sequence part of 0.3 mm (300 micrometer) pitch, it heats and the solder is deposited on each electrode surface.

  Recently, as electronic devices have become smaller and lighter, the number of mounted electronic components has also become narrower, and the pitch on the electronic circuit board is also reduced to a fine pitch with many electrodes formed in a narrow range. (For example, about 60 μm) is in progress.

  However, when the solder paste composition described in Patent Document 1 and Patent Document 2 is used for an electronic circuit board having electrodes with fine pitches, the cellulose adheres uniformly to the electrode surface. The problem of inhibiting occurred. For this reason, a solder paste composition from which cellulose is removed is used for an electronic circuit board having such an electrode.

  However, even if a solder paste composition from which cellulose is removed is used, a uniform solder is not always obtained. Specifically, at the time of reflow, the solder cannot uniformly adhere to the electrode surface, and as a result, the height of the obtained solder varies, the solder is cut in the middle of the electrode surface, so-called solder loss, There is a problem in that the yield decreases due to the generation of a bridge where the solder is connected between the electrodes.

Japanese Patent Laid-Open No. 5-391 JP-A-5-96396

  The subject of this invention is providing the solder paste composition which can adhere a solder uniformly to the electrode surface.

  As a result of intensive studies to solve the above problems, the present inventors have obtained the following knowledge. That is, the reason why the solder cannot uniformly adhere to the electrode surface is due to the movement, that is, convection, of the solder powder contained in the solder paste composition during reflow. Furthermore, examples of the flux solvent contained in the normal solder paste composition include hexyl carbitol, butyl carbitol, octyl carbitol, mineral spirit, and the like. The specific gravity of these solvents is all 1 or less. .

  Therefore, the present inventors can reduce the convection of the solder powder by adding a solvent having a specific gravity higher than 1 as the solvent contained in the flux, and as a result, the solder can be uniformly attached to the electrode surface. As a result of further intensive studies, the present invention was completed.

That is, the solder paste composition of the present invention has the following configuration.
(1) A solder paste composition used in a solder pre-coating method in which a solder paste composition is solid-coated on an electronic circuit board, the solid-soldered solder paste composition is heated, and solder is adhered to the electrode surface of the electronic circuit board. A solder paste composition, wherein the solder paste composition contains a flux, and the flux contains a solvent having a specific gravity higher than 1.
(2) The solder paste composition according to (1), wherein the solvent is one or more selected from glycols, carbitols, phthalates, and 2-pyrrolidones.
(3) The glycols are phenyl glycol, the carbitols are phenyl carbitol and benzyl carbitol, the phthalates are dibutyl phthalate, and the 2-pyrrolidones are N-methyl-2 -Solder paste composition as described in said (2) which is pyrrolidone.
(4) The solder paste composition according to any one of (1) to (3), which is a precipitation-type solder composition.

  According to the present invention, in the solder paste composition used in the solder pre-coating method in which the solder paste composition is solid-coated on the electronic circuit board and heated to adhere the solder to the electrode surface of the electronic circuit board, the solder paste composition Since the specific gravity of the solvent of the flux contained in the composition is higher than 1, the solder can be uniformly attached to the electrode surface. As a result, the height of the attached solder becomes uniform and the solder loss is suppressed. This has the effect of improving yield. Furthermore, it is possible to accurately deposit solder on the electrode even with a fine pitch, and to suppress the generation of voids.

  The solder paste composition of the present invention is used in a solder precoat method in which the composition is solid-coated on an electronic circuit board and heated to adhere the solder to the electrode surface. Specifically, the screen mask used in the printing of the solder paste composition by screen printing or the like is not opened for each electrode on the electronic circuit board, but is opened in a wide range including a plurality of electrodes. use.

  For example, in the case of a quad flat package (QFP), a screen mask having an opening in the shape of each side of the QFP in which a plurality of electrodes are arranged in parallel at a small pitch or the shape of the entire QFP including those sides is used. The solder paste composition is printed roughly over a wide range including a large number of electrodes arranged at a small pitch, ignoring the positions and shapes of the individual electrodes.

  Next, when the substrate coated with the solder paste composition as described above is passed through a reflow furnace and the solder paste composition is heated, the molten solder adheres to the electrode portion of the substrate and is precoated. .

  In the present invention, the solder paste composition contains a flux, and the flux contains a solvent having a specific gravity higher than 1. Thereby, a solder can be made to adhere uniformly to the electrode surface after reflow. On the other hand, with a flux containing a solvent having a specific gravity of 1 or less, the solder does not adhere uniformly.

  As described above, the reason why the solder paste composition containing the flux containing the solvent having a specific gravity higher than 1 can uniformly adhere the solder is not necessarily clear, but during reflow, the solder paste composition It is observed that the convection of the solder powder described later contained in the product is less than that in the case of containing a solvent having a specific gravity of 1 or less, and that the solder particles are uniformly dispersed on the electrode. The reason that the solder can uniformly adhere is presumed that the convection of the solder is reduced and the solder particles are uniformly dispersed.

  Examples of the solvent having a specific gravity higher than 1 include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, phenyl glycol, benzyl glycol, phenylpropylene glycol, and 1,3-butylene glycol; methyl carbitol and phenyl carbitol. Carbitols such as benzyl carbitol; other glycol ethers such as pentaethylene glycol monobutyl ether, ethylene glycol monophenyl ether (phenyl cellosolve), triethylene glycol monomethyl ether, propylene glycol phenyl ether; dimethyl phthalate, phthalic acid Phthalic acid esters such as diethyl and dibutyl phthalate; maleic acid such as dimethyl maleate and diethyl maleate Ester compounds; may be used alone or two or more, such as 2-pyrrolidone such as N- methyl 2-pyrrolidone.

In the present invention, diethylene glycol, triethylene glycol, propylene glycol, phenyl glycol, benzyl glycol, methyl carbitol, phenyl, among those exemplified above from the viewpoint of environmental problems such as PRTR method (chemical substance emission grasp management promotion method) Carbitol, benzyl carbitol, pentaethylene glycol monobutyl ether, phenylpropylene glycol, dimethyl maleate, diethyl maleate, 1,3-butylene glycol, and N-methyl-2-pyrrolidone are preferred.
Among these, diethylene glycol, triethylene glycol, phenyl glycol, benzyl glycol, phenyl carbitol, benzyl carbitol, and N-methyl-2-pyrrolidone are particularly preferable.

  The boiling point of the solvent is not particularly limited and is, for example, about 180 to 350 ° C, preferably about 220 to 320 ° C. The content of the solvent is preferably 5 to 50% by weight, preferably 10 to 30% by weight, based on the total amount of flux.

  The flux according to the present invention contains a base resin, a thixotropic agent and the like in addition to the above-described predetermined solvent. As the base resin, for example, rosin or acrylic resin can be used. As the rosin, rosin and its derivatives that have been conventionally used for flux can be used. Examples of rosin and derivatives thereof include ordinary gum, toll, and wood rosin, and heat-treated resin, polymerized rosin, hydrogenated rosin, formylated rosin, rosin ester, rosin-modified maleic resin, and rosin-modified phenol resin. And rosin-modified alkyd resin. In addition, the grade of rosin is not specifically limited, For example, WW grade etc. are mentioned.

  The acrylic resin has a molecular weight of 10,000 or less, preferably 3,000 to 8,000. If the molecular weight exceeds 10,000, crack resistance and peel resistance may be reduced. Moreover, in order to promote an active effect | action, it is preferable to use an acid value 30 or more, and since it needs to be softened at the time of soldering, it is preferable that a softening point is 230 degrees C or less. Therefore, monomers having a polymerizable unsaturated group, such as (meth) acrylic acid, various esters thereof, crotonic acid, itaconic acid, (anhydrous) maleic acid and esters thereof, (meth) acrylonitrile, (meth) acrylamide, vinyl chloride, It is preferable to use a polymer obtained by radical polymerization such as bulk polymerization, liquid polymerization, suspension polymerization or emulsion polymerization using vinyl acetate or the like and a catalyst such as peroxide.

  These base resins described above can be used in combination. For example, the rosin and the acrylic resin can be mixed and used. The content of the base resin is 0.5 to 80% by weight, preferably 20 to 80% by weight, based on the total flux.

  Examples of the thixotropic agent include hardened castor oil, hydrogenated castor oil, beeswax, carnauba wax and the like. The thixotropic agent content is preferably 1 to 50% by weight with respect to the total flux.

  Furthermore, the flux concerning this invention may contain an activator as needed. Examples of the activator include hydrohalates such as ethylamine, propylamine, diethylamine, triethylamine, ethylenediamine, and aniline, and organic carboxylic acids such as lactic acid, citric acid, stearic acid, adipic acid, diphenylacetic acid, and benzoic acid. Can be mentioned. The content of the activator is preferably 0.1 to 30% by weight with respect to the total flux.

  In addition, the flux of the present invention may be used in combination with conventionally known synthetic resins such as polyester resin, phenoxy resin, and terbene resin as a base resin of the flux, and additives such as antioxidants, antifungal agents, and matting agents. Can also be added. When the solder paste composition is a precipitation type solder composition described later, a metal salt or complex described later may be contained in the flux.

  The solder paste composition according to the present invention contains solder powder in addition to the above-described flux. As the composition of the solder powder, various known solder powders can be used. For example, tin (Sn) -lead (Pb) -based, Sn-Ag (silver) -based, Sn-Cu (copper) -based solder, etc. In addition to alloy powder, lead-free alloy powders such as Sn—Ag—In (indium), Sn—Ag—Bi (bismuth), and Sn—Ag—Cu can be used. These solder powders can be used alone or in combination of two or more. For example, Sn—Ag—In and Sn—Ag—Bi are blended, and Sn—Ag— An In-Bi system or the like may be used.

  In the Sn—Ag solder alloy powder, the Ag content is preferably 0.5 to 5.0% by weight and the balance is Sn. The content of components (In, Bi, Cu, etc.) other than Sn and Ag is preferably 0.1 to 15% by weight.

  The average particle size of the solder powder is 0.5 to 30 μm, preferably 1 to 10 μm. The average particle diameter is a value obtained by measurement with a particle size distribution measuring device. The weight ratio of the flux to the solder powder (flux: solder powder) in the solder paste composition of the present invention is preferably about 30:70 to 80:20.

  Here, the solder paste composition of the present invention is a precipitation type solder composition in which solder can be accurately formed on an electrode even at a fine pitch and generation of voids can be suppressed. Is more preferable.

  The precipitation-type solder composition includes, for example, tin powder as a solder powder and a lead salt of an organic acid, and when the composition is heated, the lead atom of the organic acid lead salt is replaced with a tin atom. It is liberated and diffuses into excess tin metal powder to form a Sn-Pb alloy.

The precipitation type solder composition according to the present invention contains the above-described flux according to the present invention, and (a) a precipitation type solder composition containing tin powder and a metal salt such as lead, copper, silver, or the like. (B) Precipitated solder compositions containing a tin powder and a complex of at least one selected from silver ions and copper ions and at least one selected from arylphosphines, alkylphosphines and azoles. . The metal salt of (a) and the complex of (b) can be mixed and used. In the present invention, it is particularly preferable to use a lead-free precipitation-type solder composition containing no lead.
In the present invention, the term “tin powder” includes, in addition to metal tin powder, for example, tin-silver tin alloy powder containing silver, tin-copper tin alloy powder containing copper, and the like.

  Examples of the metal salt include organic carboxylates and organic sulfonates. As the organic carboxylic acid, a mono- or dicarboxylic acid having 1 to 40 carbon atoms can be used. Illustrative examples include lower fatty acids such as formic acid, acetic acid, propionic acid, caproic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid and other fatty acids obtained from animal and vegetable oils and fats, 2, Various synthetic acids obtained from organic synthesis reactions such as 2-dimethylpentanoic acid, 2-ethylhexanoic acid, isononanoic acid, 2,2-dimethyloctanoic acid, n-undecanoic acid, pimaric acid, abietic acid, dehydroabietic acid, dihydro Resin acids such as abietic acid, monocarboxylic acids such as naphthenic acid obtained from petroleum and dimer acid obtained by synthesis from tall oil fatty acid or soybean fatty acid, dicarboxylic acids such as polymerized rosin obtained by dimerizing rosin, etc. Two or more of these may be included.

  Examples of the organic sulfonic acid include methanesulfonic acid, 2-hydroxyethanesulfonic acid, 2-hydroxypropane-1-sulfonic acid, trichloromethanesulfonic acid, trifluoromethanesulfonic acid, benzenesulfonic acid, toluenesulfonic acid, and phenolsulfone. Examples thereof include acids, cresol sulfonic acids, anisole sulfonic acids, naphthalene sulfonic acids, and the like, which may include two or more of these.

  Examples of the silver or copper complex include a complex of silver ion and / or copper ion and at least one selected from arylphosphines, alkylphosphines and azoles.

  Examples of the phosphines include 5-mercapto-1-phenyltetrazole, 3-mercapto-1,2,4-triazole, benzotriazole, tolyltriazole, carboxybenzotriazole, imidazole, benzimidazole, 2-octylbenzimidazole, 2 -Mercaptobenzimidazole, benzothiazole, 2-mercaptobenzothiazole, benzoxazole, 2-mercaptobenzoxazole and the like are preferably used.

  Since complexes with aryl phosphines or alkyl phosphines are cationic, a counter anion is required. As the counter anion, organic sulfonate ions, organic carboxylate ions, halogen ions, nitrate ions or sulfate ions are suitable. These can be used alone or in combination of two or more.

  As the organic sulfonic acid used as the counter anion, for example, methanesulfonic acid, toluenesulfonic acid, phenolsulfonic acid and the like are suitable. As the organic carboxylic acid used as the counter anion, for example, formic acid, acetic acid, oxalic acid, lactic acid, trichloroacetic acid, trifluoroacetic acid, or perfluoropropionic acid is preferable, and acetic acid, lactic acid, trifluoroacetic acid, and the like are preferable. Used for.

  Examples of the azoles include tetrazole, triazole, benzotriazole, imidazole, benzimidazole, pyrazole, indazole, thiazole, benzothiazole, oxazole, benzoxazole, pyrrole, indole, or a mixture of two or more of these derivatives. can do. Among these, 5-mercapto-1-phenyltetrazole, 3-mercapto-1,2,4-triazole, benzotriazole, tolyltriazole, carboxybenzotriazole, imidazole, benzimidazole, 2-octylbenzimidazole, 2-mercaptobenz Imidazole, benzothiazole, 2-mercaptobenzothiazole, benzoxazole, 2-mercaptobenzoxazole and the like are preferably used.

  The ratio of the tin powder to the metal salt or complex in the composition (weight of tin powder: weight of metal salt or complex) is about 99: 1 to 50:50, preferably 97: 3 to 60. : It should be about 40.

The above-described solder paste composition of the present invention is applied by solid coating on a substrate by screen printing or the like. And after application | coating, preheating is performed at about 150-200 degreeC, for example, and reflow is performed at the maximum temperature of about 170-280 degreeC. Application and reflow on the substrate may be performed in the air or in an inert atmosphere such as N ₂ , Ar, or He.

  The solder formed using the solder paste composition of the present invention usually has a height of about 10 to 20 μm, and there is little variation in the height. Moreover, if the solder paste composition of the present invention is used, this solder can be arranged at a narrow pitch, and can correspond to a pitch of about 40 to 60 μm.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to a following example.
[Examples 1 to 5 and Comparative Examples 1 and 2]
(Flux preparation)
WW class tall rosin, a solvent having a specific gravity shown in Table 1 and hydrogenated castor oil were mixed in the following proportions, heated and melted at 120 ° C., and cooled to room temperature to prepare viscous fluxes.
WW class tall rosin 70% by weight
20% by weight of solvent
Hydrogenated castor oil (thixotropic agent) 10% by weight

(Preparation of solder paste composition)
The Sn-3.5Ag alloy powder and each of the above-prepared fluxes were kneaded at a ratio shown below using a conditioning mixer [“Awatori Netaro” manufactured by Shinkey Co., Ltd.], and each solder paste composition was kneaded. Obtained.
Sn-3.5Ag alloy powder 35% by weight
Flux 65 wt%

(Evaluation of solder paste composition)
Using each solder paste composition obtained above, the uniformity of solder, the height of solder, its variation, the lack of solder and the bridge were evaluated. Each evaluation method is shown below, and the results are also shown in Table 2.

(Solder uniformity)
Each solder paste composition obtained above is printed in a solid form with a thickness of 100 μm on a semiconductor package substrate on which electrodes are formed at a pitch of 60 μm, and heated in a high-temperature observation furnace having a maximum temperature of 260 ° C. The molten state was observed with a camera (magnification: 100 times) installed on the upper surface in the observation furnace. The evaluation criteria were set as follows.
○: Solder particles are uniformly dispersed on the electrode ×: Solder particles are not uniformly dispersed on the electrode

(Solder height and variation)
Each solder paste composition obtained above is printed in a solid form with a thickness of 100 μm on a semiconductor package substrate on which electrodes are formed at a pitch of 60 μm, and the maximum temperature is 260 ° C. using a reflow oven in a nitrogen atmosphere. Heated. Next, the substrate was immersed in an ultrasonic cleaner containing a butyl carbitol solution at 60 ° C. to remove the flux. Thereafter, the solder height on the electrode was measured at 20 points with a depth of focus meter (manufactured by Keyence Co., Ltd.), the average height was calculated, and the height variation (standard deviation) was calculated.

(Solder missing and bridge)
With respect to the solder obtained in the height and variation of the solder, the lack of solder and the presence or absence of bridges were observed with a microscope. The evaluation criteria were set as follows.
○: Solder is not cut in the middle of the electrode surface and is not bridged ×: Solder is cut or bridged in the middle of the electrode surface

  As is apparent from Table 2, the solder formed using the solder paste compositions of Examples 1 to 5 is uniformly attached to the electrode surface, has a small height variation, and lack of solder and bridges. It turns out that it is excellent in evaluation. On the other hand, the solder formed using the solder paste composition of Comparative Examples 1 and 2 showed the result that the uniformity, the variation in height, and the lack of solder were inferior.

Claims (4)

A solder paste composition used in a solder pre-coating method in which a solder paste composition is solid-coated on an electronic circuit board, the solid solder paste composition is heated, and solder is attached to the electrode surface of the electronic circuit board. And
The solder paste composition contains a flux, and the flux contains a solvent having a specific gravity higher than 1.   The solder paste composition according to claim 1, wherein the solvent is one or more selected from glycols, carbitols, phthalates, and 2-pyrrolidones.   The glycols are phenyl glycol, the carbitols are phenyl carbitol and benzyl carbitol, the phthalates are dibutyl phthalate, and the 2-pyrrolidones are N-methyl-2-pyrrolidone. The solder paste composition according to claim 2. The solder paste composition according to claim 1, which is a precipitation type solder composition.