JP2011177774A - Flux for soldering and solder paste composition using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide flux for soldering which can suppress the generation of voids in a solder metal, and also can suppress the scattering of flux and the solder metal, and a solder paste composition using the same. <P>SOLUTION: The flux for soldering comprises acid-modified polyolefin. Further, the flux comprises a base resin and an activator, the base resin is made of rosin or a synthetic resin, and the flux further comprises acid-modified polyolefin. The paste composition comprises the above flux for soldering and the solder alloy powder. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a soldering flux used when a circuit component or the like is solder-connected to a circuit board such as a printed board of an electronic device, and a solder paste composition using the same.

  Conventionally, various solder paste compositions (hereinafter referred to as “paste compositions”) comprising solder metal and soldering flux (hereinafter sometimes referred to as “flux”) for soldering electronic circuit components and the like. Is sometimes used.) Is used. In conventional solder joints, voids (bubbles) are generated in the solder metal, and flux and solder metal are scattered outside the soldered part due to bumping of the flux when the paste composition is heated.

  In recent years, with the miniaturization and high functionality of electronic devices, the above phenomenon has been regarded as a problem as the solder joints are miniaturized and the mounting density is increased. That is, when a void is generated in the solder metal, it affects the bonding reliability due to generation of a crack or the like in a cooling / heating cycle test starting from the void. When the solder joint portion is relatively large as in the prior art, it is difficult to be affected by this. However, when the solder joint portion is miniaturized, the effect becomes large, causing a problem in joint reliability. That is, even if the void volume is the same, since the ratio of the void volume to the solder at the joint portion is increased, the joint reliability is lowered.

  Moreover, the scattering of the flux causes a failure in adhesion of an insulator to a portion such as a connector pattern where conduction must be ensured, and the scattering of the solder metal causes a short-circuit failure due to adhesion between component electrodes. Conventionally, these problems have been dealt with by devising the design such as disposing the part where adhesion of flux or solder metal is a problem away from the soldering part.

  However, as the mounting density is increased, the degree of freedom for such an arrangement is reduced, and it is difficult to avoid problems due to scattering of flux and solder metal only by design ingenuity. There is also a measure to stick heat-resistant tape or the like on the part where flux or solder metal should not adhere, and remove it after soldering, but this measure increases the manufacturing cost.

  On the other hand, Patent Document 1 describes a flux containing high-density oxidized polyethylene as a flux capable of preventing scattering of flux and the like. Patent Document 2 describes a flux containing, as a base resin, a polyhydric alcohol ester of a resin acid from which a low molecular weight substance has been removed as a flux that can reduce the generation of voids.

  However, the fluxes described in Patent Documents 1 and 2 are not necessarily sufficient in the effect of preventing scattering of the flux and the like and the effect of reducing the generation of voids. Further, Patent Document 1 does not describe the problem of voids generated in the solder metal, and Patent Document 2 does not describe the problem of scattering of flux or the like.

JP 2004-283905 A International Publication No. 06/077077 Pamphlet

  An object of the present invention is to provide a soldering flux capable of suppressing the generation of voids in the solder metal and suppressing the scattering of the flux and the solder metal, and a solder paste composition using the same Is to provide.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found a solution means having the following constitution and have completed the present invention.
(1) A soldering flux comprising an acid-modified polyolefin.
(2) A soldering flux containing a base resin and an activator, wherein the base resin is rosin or a synthetic resin and further contains an acid-modified polyolefin.
(3) The soldering flux according to (1) or (2), wherein the acid-modified polyolefin is at least one selected from polypropylene modified with a carboxylic anhydride group and polyethylene modified with a carboxylic anhydride group.
(4) The soldering flux according to any one of (1) to (3), wherein the acid-modified polyolefin has a density of 0.93 g / cm ³ or more.
(5) The soldering flux according to any one of (1) to (4), wherein the acid value specified in JIS K 0070 of the acid-modified polyolefin is 20 mgKOH / g or more.
(6) The soldering flux according to any one of (1) to (5), wherein the acid-modified polyolefin has a weight average molecular weight of 10,000 to 50,000.
(7) The soldering flux according to any one of (1) to (6), wherein the content of the acid-modified polyolefin is 0.1 to 10% by weight based on the total amount of the flux.
(8) The soldering flux according to any one of (1) to (7), further containing an organic solvent, wherein the organic solvent contains a high boiling point solvent.
(9) 20 to 74.9% by weight of the base resin, 3 to 20% by weight of the activator, 1 to 10% by weight of the wax, 20 to 50% by weight of the organic solvent, and 1 to 3% of the additive with respect to the total flux. The soldering flux according to any one of (1) to (8), which is contained in a proportion of 10% by weight.
(10) A solder paste composition comprising the soldering flux according to any one of (1) to (9) and a solder alloy powder.

  According to the present invention, it is possible to suppress the generation of voids in the solder metal and the scattering of the flux and the solder metal, and therefore, with high joint reliability even in soldering to fine joints and high-density mounting. In addition, there is an effect that it is possible to realize a good solder connection without causing an insulator adhesion failure or a short circuit failure.

  The soldering flux of the present invention contains an acid-modified polyolefin. The flux usually contains rosin or synthetic resin as described later as a base resin. The acid-modified polyolefin is obtained by imparting polarity to a non-polar polyolefin by acid modification, and therefore exhibits excellent compatibility with the base resin. Therefore, when the acid-modified polyolefin is contained in the flux, the flux melt viscosity during reflow can be increased. As a result, solder melting becomes slow and air bubbles easily move to the surface of the paste composition, so that generation of voids in the solder metal can be suppressed. Moreover, since the viscosity of the flux is increased, it is possible to prevent the flux from bumping when the paste composition is heated, and the flux and the solder metal are hardly scattered. The problem of voids generated in solder metal and the problem of scattering of flux and the like are remarkable in lead-free solder having a high melting point. Therefore, the soldering flux of the present invention can be suitably used as a lead-free soldering flux.

  The acid-modified polyolefin is a polyolefin having an acid group introduced by acid modification. Examples of the acid group include a carboxylic anhydride group (—CO—O—OC—) and a carboxylic acid group (—COOH). Examples of the compound capable of introducing the acid group into the polyolefin include maleic anhydride, itaconic anhydride, succinic anhydride, glutaric anhydride, adipic anhydride, maleic acid, itaconic acid, fumaric acid, acrylic acid, and methacrylic acid. Can be mentioned. Examples of the polyolefin include polypropylene, polyethylene, and ethylene-propylene copolymer resin. The acid-modified polyolefin is preferably at least one selected from polypropylene modified with a carboxylic anhydride group and polyethylene modified with a carboxylic anhydride group.

The acid-modified polyolefin is preferably a high-density acid-modified polyolefin having a high density. Specifically, the acid-modified polyolefin preferably has a density of 0.93 g / cm ³ or more. If the density is too small, the flux viscosity does not increase so much during reflow, which is not preferable. The upper limit of the density is suitably about 1.0 g / cm ³ .

  The acid value of the acid-modified polyolefin is preferably 20 mgKOH / g or more. If the acid value is too small, the compatibility with the base resin tends to decrease, such being undesirable. The upper limit of the acid value is suitably about 70 mgKOH / g. The acid value is a value that can be measured according to JIS K 0070.

  The acid-modified polyolefin preferably has a weight average molecular weight of 10,000 to 50,000. If the weight average molecular weight is too small, the effect of the acid-modified polyolefin tends to be difficult to obtain. On the other hand, if the weight average molecular weight is too large, the compatibility with the base resin tends to decrease, such being undesirable. The weight average molecular weight is a value obtained by measuring acid-modified polyolefin by gel permeation chromatography (GPC).

  The content of the acid-modified polyolefin is preferably 0.1 to 10% by weight, and more preferably 1 to 5% by weight, based on the total amount of the flux. Thereby, the effect by acid-modified polyolefin can be acquired.

  Commercially available acid-modified polyolefins can be used, and specific examples include Umex 1001, Umex 1010, Umex 2000 and the like manufactured by Sanyo Kasei.

  On the other hand, the flux usually contains a base resin as described above. The base resin is not particularly limited, and those conventionally used for fluxes can be used. Specific examples include rosin, derivatives thereof, and synthetic resins.

  Examples of the rosin include ordinary gum rosin, tall rosin, wood rosin and the like. Derivatives thereof include, for example, polymerized rosin, acrylated rosin, hydrogenated rosin, disproportionated rosin, formylated rosin, rosin ester, and rosin modified. A maleic acid resin, a rosin modified phenol resin, a rosin modified alkyd resin, etc. are mentioned, These may be used alone or in combination of two or more. Examples of the synthetic resin include acrylic resin, styrene-maleic acid resin, epoxy resin, urethane resin, polyester resin, phenoxy resin, terpene resin, polyalkylene carbonate such as polypropylene carbonate and polybutylene carbonate, and the like. You may use a seed | species or 2 or more types in mixture. The content of the base resin is not particularly limited, but is preferably 20 to 80% by weight, and more preferably 30 to 60% by weight with respect to the total amount of flux.

  The flux usually contains an activator. As the activator, those conventionally used in fluxes can be used. Specific examples include amines (diphenylguanidine, naphthylamine, diphenylamine, triethanolamine, monoethanolamine, etc.), amine salts (polyamines such as ethylenediamine, organic acid salts and inorganic acids of amines such as cyclohexylamine, ethylamine, and diethylamine). (Mineral acids such as hydrochloric acid and sulfuric acid) salts), organic acids (succinic acid, adipic acid, glutaric acid, sebacic acid, maleic acid and other dicarboxylic acids; myristic acid, palmitic acid, stearic acid, oleic acid and other fatty acids; Hydroxycarboxylic acids such as lactic acid, dimethylolpropionic acid, malic acid; benzoic acid, phthalic acid, trimellitic acid, etc.), amino acids (glycine, alanine, aspartic acid, glutamic acid, valine, etc.), etc. Use a seed or a mixture of two or more Good. Specific examples of the amine salts include diphenylguanidine hydrobromide.

  In particular, when a polyalkylene carbonate is adopted as the base resin, it is preferable to add an organic carboxylic acid as the activator to the flux. As a result, the wettability of the solder can be improved, and melting at a low temperature is possible with almost no decomposition residue. Examples of the organic carboxylic acid include sebacic acid and the like.

  When a carboxyl group-containing resin such as rosin or acrylic resin is adopted as the base resin, it is preferable to add methyl succinic acid to the flux as the activator. This allows the oxide to be removed from the metal surface even at the high temperatures required for lead-free solder alloys, and also from the oxidation that takes place during the long soldering periods required for lead-free soldering. Can be protected. Moreover, corrosion of the solder metal before, during, or after soldering can be suppressed, and a small solder adhesion layer can be protected during the reflow operation.

  The content of the activator is not particularly limited, but is preferably 3 to 20% by weight with respect to the total flux. If the content of the activator is too small, there is a risk that the activator's activity will be insufficient and solderability will be reduced. Moreover, when there is too much content of an activator, since the film property of a flux will fall and hydrophilicity will become high, there exists a possibility that corrosivity and insulation may fall.

  The flux may contain a wax if necessary. Examples of the wax include hydrogenated castor oil, beeswax, carnauba wax, stearic acid amide, hydroxystearic acid ethylene bisamide and the like, and these may be used alone or in combination. The content of the wax is not particularly limited, but is preferably 1 to 10% by weight with respect to the total flux.

  When the flux is used in a liquid state, an appropriate organic solvent can be contained in the flux. Examples of the organic solvent include alcohol solvents such as ethyl cellosolve, butyl carbitol, and hexyl carbitol; ester solvents such as butyl acetate; hydrocarbon solvents such as turpentine oil, and the like. You may mix and use a seed | species or more.

  The organic solvent preferably contains a high boiling point solvent. That is, it is preferable to use the organic solvent exemplified above and the high boiling point solvent in combination. The high boiling point solvent means an organic solvent having a boiling point higher than the soldering temperature. If the flux contains a high-boiling solvent, the flux melt viscosity during reflow can be increased, so that the effect of suppressing the generation of voids in the solder metal and the effect of suppressing the scattering of flux and the like can be improved. it can. Examples of the high boiling point solvent include polyhydric alcohol solvents such as polyethylene glycol, polypropylene glycol, and polyglycerin, ether compounds or ester compounds thereof, ester solvents such as trimellitic acid ester and phthalic acid ester, and sorbitol ether. And ether solvents such as these may be used, and these may be used alone or in combination. The boiling point of the high boiling point solvent is usually 280 ° C. or higher.

  The content of the organic solvent is not particularly limited, but is preferably 20 to 50% by weight with respect to the total flux, and more preferably 1 to 10% by weight is a high boiling point solvent. When the content of the organic solvent is too small, the viscosity of the flux increases, and the applicability of the flux and the printability of the solder paste composition may be deteriorated. Moreover, when there is too much content of an organic solvent, since the ratio of the active ingredient as a flux, ie, a base resin, will become relatively small, there exists a possibility that solderability may fall.

  The flux may contain an additive as necessary. Examples of the additive include an antioxidant, a chelating agent, and a rust inhibitor.

  In particular, it is preferable to add a bismuth organic acid salt and a carboxyl compound latentized by a vinyl ether compound to the flux as the additive. Thereby, the wettability of the solder can be improved, the generation of voids in the solder joints and the size of the voids can be suppressed, and this state can be maintained for a long time.

  The organic acid bismuth salt means a compound in which an acyloxy group is bonded to bismuth. Specific examples include bismuth acetate, bismuth octylate, bismuth neodecanoate, bismuth stearate, bismuth rosinate, bismuth naphthenate, bismuth oleate, and bismuth oxalate.

  The carboxyl compound means a compound having at least one carboxyl group in the molecule. Specific examples include rosin derivatives such as natural rosin, polymerized rosin, disproportionated rosin and unsaturated dibasic acid-modified rosin; aliphatic carboxylic acids such as oleic acid and adipic acid; aromatics such as benzoic acid and trimellitic acid Examples thereof include carboxylic acids; hydroxycarboxylic acids such as hydroxypivalic acid, malic acid, and lactic acid; and carboxylic acids obtained from the reaction of acid anhydrides with alcohols.

  The carboxyl compound made latent by the vinyl ether compound means a carboxyl compound that is protected by the vinyl ether compound and dissociates by heating to generate a carboxyl group. The compound containing one or more latent carboxyl groups is usually a non-catalytic or acid-catalyzed ester compound such as an acid phosphate compound, and the carboxyl compound and vinyl ether, or an anhydride of the carboxyl compound and hydroxy vinyl ether. It can be obtained by reacting at room temperature to 100 ° C. in the presence.

  In the flux, a carboxylic acid derivative obtained by subjecting a compound having two or more hydroxyl groups in one molecule to a ring-opening half esterification reaction with a cyclic acid anhydride having a carbon 6-membered ring structure on the hydroxyl group is used as the additive. It is preferable to add. Thereby, the wettability of the solder can be improved, and the generation of voids and the size of the voids in the solder joint can be suppressed.

  Examples of the compound having two or more hydroxyl groups in one molecule include ethylene glycol, diethylene glycol, and trimethylolpropane. Examples of the cyclic acid anhydride include hexahydrophthalic anhydride, hydrogenated trimellitic anhydride, and the like.

  It is preferable to add a porous adsorbent, spherical polymer fine particles or the like as the additive to the flux. Thereby, generation | occurrence | production of a void can be suppressed. Examples of the porous adsorbent include activated carbon, silica gel, activated alumina and the like. Examples of the spherical polymer fine particles include polyimide fine particles, polyurea fine particles, benzoguanamine fine particles, acrylic crosslinked fine particles, and styrene crosslinked fine particles. The spherical polymer fine particles preferably have a particle size of 5 μm or less.

  The content of the additive is not particularly limited, but is preferably 1 to 10% by weight based on the total amount of flux.

  The solder paste composition of the present invention contains the flux and solder alloy powder. There is no restriction | limiting in particular as this solder alloy powder, The tin-lead alloy etc. which silver, bismuth, indium, etc. added further generally used can be used. In addition, a lead-free alloy such as tin-silver, tin-copper, tin-silver-copper may be used. The particle size of the solder alloy powder is preferably about 10 to 40 μm.

  The weight ratio of the flux to the solder alloy powder (flux: solder alloy powder) in the solder paste composition may be appropriately set according to the desired use and function of the solder paste, and is not particularly limited. : It is good that it is about 90-15: 85.

  The solder paste composition is applied onto a substrate by a dispenser, screen printing, or the like when soldering an electronic device component or the like. And after application | coating, it preheats, for example at about 150-200 degreeC, and performs reflow at the maximum temperature of about 170-250 degreeC. The application and reflow on the substrate may be performed in the air or in an inert gas atmosphere such as nitrogen, argon, or helium.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited only to a following example. In the following examples and comparative examples, the acid-modified polyolefins (A) to (C), oxidized polyethylene and solder alloy powder used for the preparation of the solder paste composition are as follows.

Acid-modified polyolefin (A): Polypropylene modified with a carboxylic anhydride group, “Umex 1001” manufactured by Sanyo Chemical Co., Ltd. having an acid value of 26 mg KOH / g and a weight average molecular weight of 40,000 was used.
Acid-modified polyolefin (B): Polypropylene modified with a carboxylic anhydride group, “Umex 1010” manufactured by Sanyo Chemical Co., Ltd. having an acid value of 52 mg KOH / g and a weight average molecular weight of 30,000 was used.
Acid-modified polyolefin (C): Polyethylene modified with a carboxylic anhydride group, “Umex 2000” manufactured by Sanyo Kasei Co., Ltd. having an acid value of 27 mg KOH / g and a weight average molecular weight of 16,000 was used.
Oxidized polyethylene: “Sun Wax E-330” manufactured by Sanyo Chemical Co., Ltd. having an acid value of 17 mg KOH / g was used.
Solder alloy powder: A solder alloy powder made of a tin-silver-copper alloy having a particle size of 20 to 30 μm and a weight ratio of tin: silver: copper = 96.5: 3.0: 0.5 was used.

[Examples 1 to 3 and Comparative Examples 1 and 2]
<Preparation of solder paste composition>
First, each component shown in Table 1 was charged into a container with the composition shown in Table 1, dissolved after heating, and then cooled to obtain a flux. Next, each obtained flux and solder alloy powder were mixed at a weight ratio of flux: solder alloy powder = 11: 89 to obtain solder paste compositions, respectively.

<Evaluation>
About each obtained solder paste composition, the void area rate and the number of flux scattering were evaluated. Each evaluation method is shown below, and the results are shown in Table 1.

(Void area ratio)
First, the solder paste composition was printed on a substrate with a diameter of 0.4 mmφ and a thickness of 150 μm, and a CSP component with a pitch of 0.8 mm was mounted. Next, in the atmosphere, preheating was performed at 175 ± 5 ° C. for 80 ± 5 seconds, melting at a maximum temperature of 235 ± 5 ° C., and soldering was performed. The soldered board is observed with a soft X-ray fluoroscope (“NLX-3500F2” manufactured by Nagoya Electric Industry Co., Ltd.) and photographed, and the photographed image is image analysis software (“Azo-kun” manufactured by Asahi Engineering Co., Ltd.) The area ratio (%) of voids in the solder metal was calculated.

(Flux scattering number)
First, a solder paste composition was printed at a diameter of 6.0 mmφ and a thickness of 200 μm on the center of a copper plate having a length of 50 mm × width of 50 mm × thickness of 0.3 mm. Subsequently, the scattering of the flux when melted at the maximum temperature of 235 ± 5 ° C. was observed with a microscope (magnification: 20 times), and the number of flux scattering (pieces) was counted.

  As is clear from Table 1, Examples 1 to 3 containing acid-modified polyolefin showed a result that the void area ratio was small and the number of flux scattering was small. From this result, according to Examples 1 to 3, it is expected that the scattering of the solder metal can be suppressed. In contrast, Comparative Example 1 that does not contain acid-modified polyolefin and Comparative Example 2 that contains oxidized polyethylene instead of acid-modified polyolefin have a larger void area ratio than Examples 1 to 3, and the number of flux scattering Also showed significantly more results.

Claims (10)

  A soldering flux comprising acid-modified polyolefin. A soldering flux containing a base resin and an activator,
The base resin is rosin or synthetic resin;
A soldering flux further comprising an acid-modified polyolefin.   The soldering flux according to claim 1 or 2, wherein the acid-modified polyolefin is at least one selected from polypropylene modified with a carboxylic anhydride group and polyethylene modified with a carboxylic anhydride group. The soldering flux according to claim 1, wherein the acid-modified polyolefin has a density of 0.93 g / cm ³ or more.   The soldering flux according to any one of claims 1 to 4, wherein an acid value defined in JIS K 0070 of the acid-modified polyolefin is 20 mgKOH / g or more.   The soldering flux according to any one of claims 1 to 5, wherein the acid-modified polyolefin has a weight average molecular weight of 10,000 to 50,000.   The soldering flux according to any one of claims 1 to 6, wherein the content of the acid-modified polyolefin is 0.1 to 10% by weight based on the total amount of the flux.   The soldering flux according to any one of claims 1 to 7, further comprising an organic solvent, wherein the organic solvent contains a high boiling point solvent. For the total flux,
20-74.9% by weight of base resin,
3-20% by weight of active agent,
1-10% by weight of wax,
20-50% by weight of organic solvent,
The soldering flux according to any one of claims 1 to 8, which contains an additive in a proportion of 1 to 10% by weight.   A solder paste composition comprising the soldering flux according to claim 1 and a solder alloy powder.