JP5756067B2 - Solder composition and printed wiring board using the same - Google Patents

Description

  The present invention relates to a solder composition (so-called solder paste) for mounting a component on a printed wiring board of an electronic device, and a printed wiring board on which an electronic component is mounted using the solder composition.

  In recent years, in solder paste, lead compounds are highly toxic and are regarded as a serious problem because they impair biological functions. Therefore, lead-free solder materials have been developed, such as Sn-Ag-Cu alloys, Sn-Ag alloys, Sn-Cu alloys, and alloys obtained by adding one or more metal elements to these alloys. The so-called lead-free solder alloy powder (lead-free solder alloy powder) has been used. In addition, as the Pb-free solder used for plating, Sn or an alloy containing Sn and Cu is mainly used.

The solder paste prepared using the above solder powder is a mixture obtained by dissolving solids such as rosin resin, thixotropic agent and activator with a solvent to form a paste. The rosin resin contained in the solder paste has an active action and an action of covering the molten solder surface and preventing oxidation. However, by changing the main component of the solder powder from Pb to Sn, the wettability decreased and the melting point increased, so the solder paste mounting temperature increased from the conventional mounting temperature of 230 ° C. to about 260 ° C. To ensure wettability.
However, there is a problem that it is difficult to obtain sufficient solderability to give reliability to a light and thin mounting board using lead-free solder only with the active action of the conventionally used activator and rosin resin. Has occurred. This problem cannot be obtained due to a sufficient activation effect. If solder paste is applied to the mounting board and electronic components are mounted on the mounting board, and then the solder paste is dissolved in a reflow furnace, the reliability of the mounting board is impaired. This is due to the generation of solder balls as a factor.
Furthermore, due to the recent soaring metal prices, Sn-Ag-Cu solder alloys have been used with reduced silver content and shifted from eutectic composition. It is getting worse.
In order to solve the above problems, a wide variety of active agents have been studied, and for example, a solder paste containing a specific active agent has been proposed (Patent Document 1).

JP 2006-110580 A

  However, in the solder paste as described in Patent Document 1, when using a solder alloy having poor wettability / solder meltability, such as a Sn-Ag-Cu solder alloy having a low silver content, The solder balls that occur during reflow cannot be sufficiently suppressed.

  Therefore, the present invention provides a solder composition that can sufficiently suppress solder balls during reflow even when a solder alloy having poor wettability and solder melting property is used, and a printed wiring board using this solder composition. The purpose is to provide.

In order to solve the above problems, the present invention provides the following solder composition and printed wiring board.
That is, the solder composition of the present invention has an Sn-Ag-Cu solder alloy having a melting point of 240 ° C. or less, an Ag content of 3% by mass or less, and a Cu content of 4% by mass or less. And a flux containing a rosin resin, an activator and a thixotropic agent, and the activator contains a polyvalent carboxylic acid represented by the following general formula (1): It is a feature. In the following general formula (1), X represents O, S, NH, N or P, m represents an integer of 1 to 3, and n represents 2 or 3.

In the solder composition of the present invention, the content of the polyvalent carboxylic acid represented by the general formula (1) is preferably 1% by mass or more and 10% by mass or less with respect to 100% by mass of the flux. .
In the solder composition of the present invention, the alloy composition (mass ratio) in the lead-free solder powder is 96.5Sn / 3.0Ag / 0.5Cu, 98.3Sn / 1.0Ag / 0.7Cu, and 99. It is preferably any one of 0.0Sn / 0.3Ag / 0.7Cu.
In the solder composition of the present invention, the activator preferably further contains an organic acid other than the polyvalent carboxylic acid represented by the general formula (1).
The printed wiring board of the present invention is characterized in that an electronic component is mounted on a printed wiring board using the solder composition.

  According to the present invention, even when a solder alloy having poor wettability / solder meltability is used, a solder composition capable of sufficiently suppressing solder balls during reflow, and a printed wiring board using the solder composition are provided. It becomes possible to provide.

The solder composition of the present invention contains a lead-free solder powder described below and a flux described below.
The content of the lead-free solder powder is preferably 85% by mass or more and 92% by mass or less with respect to 100% by mass of the solder composition. When the content of the lead-free solder powder is less than 85% by mass (when the content of the flux exceeds 15% by mass), it becomes difficult to form a sufficient solder joint when the obtained solder composition is used. On the other hand, if the content of the lead-free solder powder exceeds 92% by mass (if the content of the flux is less than 8% by mass), the flux as the binder is insufficient, so flux and lead-free solder It tends to be difficult to mix with powder.

The lead-free solder powder used in the present invention has a melting point of 240 ° C. or lower. When the lead-free solder powder having a melting point exceeding 240 ° C. is used, the lead-free solder powder cannot be melted at a normal thermocompression bonding temperature in the anisotropic conductive paste. Further, from the viewpoint of lowering the reflow temperature in the solder composition, the melting point of the lead-free solder powder is preferably 220 ° C. or less, and more preferably 150 ° C. or less.
Here, the lead-free solder powder refers to a solder metal or alloy powder to which lead is not added. However, it is allowed that lead is present as an inevitable impurity in the lead-free solder powder, but in this case, the amount of lead is preferably 100 mass ppm or less.

The lead-free solder powder is at least one selected from the group consisting of tin (Sn), copper (Cu), silver (Ag), bismuth (Bi), antimony (Sb), indium (In), and zinc (Zn). It is preferred to include a seed metal.
Moreover, as a specific solder composition (mass ratio) in the said lead-free solder powder, the following can be illustrated.
As binary alloys, for example, Ag-Bi type such as 95.3Ag / 4.7Bi, Ag-Li type such as 66Ag / 34Li, Ag-In type such as 3Ag / 97In, Ag-type such as 67Ag / 33Te, etc. Te, Ag-Tl such as 97.2Ag / 2.8Tl, Ag-Zn such as 45.6Ag / 54.4Zn, Au-Sn such as 80Au / 20Sn, 52.7Bi / 47.3In, etc. Bi-In series, 35In / 65Sn, 51In / 49Sn, In-Sn series such as 52In / 48Sn, Bi-Zn series such as 8.1Bi / 91.9Zn, Sn-Bi series such as 43Sn / 57Bi, 42Sn / 58Bi , 98Sn / 2Ag, 96.5Sn / 3.5Ag, 96Sn / 4Ag, Sn-Ag series such as 95Sn / 5Ag, 91Sn / 9Zn, 30Sn / 7 Sn-Zn-based, such as Zn, Sn-Cu system, such 99.3Sn / 0.7Cu, include Sn-Sb system, such as 95Sn / 5Sb.
Examples of ternary alloys include Sn—Ag—In such as 95.5Sn / 3.5Ag / 1In, Sn—Zn—In such as 86Sn / 9Zn / 5In, 81Sn / 9Zn / 10In, and 95.5Sn. Sn-Ag-Cu systems such as /0.5Ag/4Cu, 96.5Sn / 3.0Ag / 0.5Cu, 98.3Sn / 1.0Ag / 0.7Cu, 99.0Sn / 0.3Ag / 0.7Cu 90.5Sn / 7.5Bi / 2Ag, Sn-Bi-Ag system such as 41.0Sn / 58Bi / 1,0Ag, and Sn-Zn-Bi system such as 89.0Sn / 8.0Zn / 3.0Bi. It is done.
Examples of other alloys include Sn / Ag / Cu / Bi system.
Among these alloys, an alloy containing Sn and Ag and an alloy containing Sn and Cu are preferable.

  The average particle size of the lead-free solder powder is preferably 1 μm or more and 40 μm or less, and more preferably 20 μm or more and 36 μm or less. If the average particle diameter is within the above range, it is preferable for reflow soldering for the recent printed circuit board and solder bump formation in which the pitch of the soldering lands is becoming narrower. The average particle size can be measured with a dynamic light scattering type particle size measuring device.

The flux used in the present invention contains a rosin resin, an activator and a thixotropic agent.
Examples of the rosin resin used in the present invention include rosin and rosin derivatives. Examples of the rosin derivative include modified rosin, polymerized rosin, and hydrogenated rosin. Among these rosin-based resins, hydrogenated rosin is preferable from the viewpoint of activity. These rosin resins may be used alone or in combination of two or more.

  The content of the rosin resin is preferably 30% by mass or more and 70% by mass or less with respect to 100% by mass of the flux. If the content is less than the lower limit, oxidation of the copper foil surface of the soldering land is prevented and the molten solder is easily wetted on the surface. If the upper limit is exceeded, the amount of residual flux tends to increase.

  The activator used in the present invention needs to contain a polyvalent carboxylic acid represented by the following general formula (1).

  In the general formula (1), X represents O, S, NH, N or P. M represents an integer of 1 to 3, and n represents 2 or 3. When n is 2, X represents O, S or NH, and when n is 3, X represents N or P.

  Examples of the polyvalent carboxylic acid represented by the general formula (1) include diglycolic acid, diglycolamide acid, tris (carboxymethyl) amine, tris (2-carboxyethyl) phosphine, and dicarboxydimethylsulfide. It is done. Among these, diglycolic acid represented by the following structural formula (2) is preferable.

  The content of the polyvalent carboxylic acid represented by the general formula (1) is preferably 1% by mass to 10% by mass, and preferably 2% by mass to 7% by mass with respect to 100% by mass of the flux. It is more preferable that If the content is less than the lower limit, solder balls tend to be easily formed. On the other hand, if the content exceeds the upper limit, the insulating properties of the flux tend to decrease.

As the activator, it is preferable to use a polyvalent carboxylic acid represented by the general formula (1) in combination with an organic acid other than this.
Examples of such organic acids include monocarboxylic acids, dicarboxylic acids, and derivatives or amine salts thereof. These organic acids may be used alone or in combination of two or more.
Monocarboxylic acids include formic acid, acetic acid, propionic acid, petric acid, valeric acid, caproic acid, enanthic acid, capric acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, tuberculostearic acid Arachidic acid, behenic acid, lignoceric acid, glycolic acid and the like.
Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, tartaric acid, and other organic acids such as levulinic acid, Examples include lactic acid, acrylic acid, benzoic acid, salicylic acid, anisic acid, citric acid, and picolinic acid.

  The content of the activator is preferably 2% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 15% by mass or less with respect to 100% by mass of the flux. If the content is less than the lower limit, solder balls tend to be easily formed. On the other hand, if the content exceeds the upper limit, the insulating properties of the flux tend to decrease.

Examples of the thixotropic agent used in the present invention include olefin waxes, fatty acid amides, substituted urea waxes, polymer compounds, and inorganic particles.
Examples of the olefin wax include castor wax (hardened castor oil = hydrogenated castor oil), beeswax, and carnauba wax.
Examples of fatty acid amides include stearic acid amide, hydroxystearic acid bisamide, m-xylylene bisstearic acid amide, N, N′-distearylisophthalic acid amide, N, N′-distearyl sebacic acid amide, N, N′— Distearyl adipic acid amide, butylene bishydroxystearic acid amide, hexamethylene bishydroxystearic acid amide, hexamethylene bisbehenic acid amide, hexamethylene bisstearic acid amide, ethylene bisbehenic acid amide, ethylene bishydroxystearic acid amide, ethylene bis Stearic acid amide, ethylene bislauric acid amide, ethylene biscapric acid amide, ethylene biscaprylic acid amide, methylene bishydroxystearic acid amide, methylene bislauric acid amide, methylene Such Susutearin acid amide.
Examples of substituted urea waxes include N-butyl-N′-stearyl urea, N-phenyl-N′-stearyl urea, N-stearyl-N′-stearyl urea, xylylene bisstearyl urea, toluylene bisstearyl urea, hexamethylene Examples thereof include bisstearyl urea, diphenylmethane bisstearyl urea, and diphenylmethane bislauryl urea.
Examples of the polymer compound include polyethylene glycol, polyethylene oxide, methyl cellulose, ethyl cellulose, and hydroxyethyl cellulose.
Examples of the inorganic particles include silica particles and kaolin particles.
These thixotropic agents may be used alone or in combination of two or more.

  The thixotropic agent content is preferably 5% by mass or more and 15% by mass or less with respect to 100% by mass of the flux. If the content is less than the lower limit, thixotropy cannot be obtained and the sagging tends to occur. On the other hand, if the content exceeds the upper limit, the thixotropy tends to be too high and the coating tends to be poor.

In addition to the rosin resin, the activator, and the thixotropic agent, it is preferable to use a solvent and an antioxidant together with the flux used in the present invention.
As the solvent, a known solvent can be appropriately used. As the solvent, a water-soluble solvent having a boiling point of 170 ° C. or higher is preferably used. Examples of the solvent include diethylene glycol, dipropylene glycol, triethylene glycol, hexylene glycol, hexyl diglycol, 1,5-pentanediol, methyl carbitol, butyl carbitol, 2-ethylhexyl diglycol, octanediol, and phenyl. Glycol.
When using the said solvent, it is preferable that content of the said solvent is 10 to 40 mass% with respect to 100 mass% of said fluxes. If content of the said solvent is in the said range, the viscosity of the solder composition obtained can be suitably adjusted to an appropriate range.

As the antioxidant, a known antioxidant can be appropriately used. Examples of the antioxidant include a sulfur compound, a hindered phenol compound, and a phosphite compound.
As sulfur compounds, dilauryl-3,3′-thiodipropionate, dimyristyl-3,3′-thiodipropionate, distearyl-3,3′-thiodipropionate, dilauryl sulfide, 2-mercaptobenz Imidazole, 2-mercaptomethylbenzimidazole, 2-mercaptobenzothiazole, dibenzothiazyl disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetrakis (2-ethylhexyl) thiuram disulfide, N, N′-diphenylthiourea, dithiocarbamine Zinc acid salt, Nt-butyl-2-benzothiazolylsulfenamide, zinc butylxanthate and the like can be mentioned.
Examples of the hindered phenol compound include triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3,5- Di-t-butyl-5-methyl-4-hydroxyphenyl) propionate], pentaerythrityltetrakis [3- (3,5-di-t-butyl-5-methyl-4-hydroxyphenyl) propionate], pentaerythris Lityltetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-t-butyl-5-methyl-4-hydroxyphenyl) propionate, 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) ben Such as emissions, and the like.
Examples of the phosphite compound include triphenyl phosphite, trisnonylphenyl phosphite, tris (2,4-di-t-butylphenyl) phosphite, distearyl pentaerythritol diphosphite, diphenylisodecyl phosphite and the like. .
In the case of using the antioxidant, the content of the antioxidant is preferably 1% by mass or more and 5% by mass or less with respect to 100% by mass of the flux.

  The flux used in the present invention contains additives such as a thixotropic agent, an antifoaming agent, an antioxidant, a rust inhibitor, a surfactant, and a thermosetting agent in addition to the above components as necessary. Also good. The content of these additives is preferably 20% by mass or less with respect to 100% by mass of the flux.

  Next, the printed wiring board of the present invention will be described. The printed wiring board of the present invention is characterized in that an electronic component is mounted on a printed wiring board using the solder composition described above. Therefore, even in the printed wiring board of the present invention, it is possible to sufficiently suppress solder balls during reflow.

EXAMPLES Next, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited at all by these examples. In addition, the material used in the Example and the comparative example is shown below.
Rosin resin A: trade name “KE-604”, Arakawa Kogyo rosin resin B: trade name “RHR-301”, Maruzen Oil Chemicals Co., Ltd. activator A: diglycolic acid activator B: polymerized fatty acid, Trade name “UNIDYME14”, ARINO CHEMICAL COMPANY activator C: picolinic acid activator D: malonic acid activator E: 1,2,3-propanetricarboxylic acid activator F: glutaric acid thixotropic agent: fatty acid amide, trade name “ "Sripacs H", Nippon Kasei Co., Ltd. solvent: hexyl diglycol (DEH), Nippon Emulsifier Co., Ltd. antioxidant: Trade name "Irganox 245", Ciba Japan Co., Ltd. defoaming agent: Trade name "AC-303" Kyoeisha Chemical Co., Ltd. additive: trade name “BI-2000”, Nippon Soda Co., Ltd. lead-free solder powder A: average particle size is 28 μm, solder melting point is 21 7-227 ° C., solder composition is 99.0 Sn / 0.3 Ag / 0.7 Cu
Lead-free solder powder B: The average particle size is 28 μm, the melting point of the solder is 217 to 224 ° C., and the composition of the solder is 98.3 Sn / 1.0 Ag / 0.7 Cu
Lead-free solder powder C: average particle size 28 μm, solder melting point 217-220 ° C., solder composition 96.5Sn / 3.0Ag / 0.5Cu

[Example 1]
Rosin-based resin A 32.5% by mass, rosin-based resin B 17.5% by mass, activator A 3% by mass, activator B 3% by mass, activator C 1% by mass, activator D 2% by mass, thixotropic agent 10% by mass, solvent 26 Mass%, antioxidant 2 mass%, defoaming agent 1 mass%, and additive 2 mass% were put into a container and mixed using a rough machine to obtain a flux.
Thereafter, 12% by mass of the obtained flux and 88% by mass of lead-free solder powder were put into a container and mixed in a kneader for 2 hours to prepare a solder composition.

[Examples 2 to 6]
A solder composition was obtained in the same manner as in Example 1 except that each material was blended according to the composition shown in Table 1.
[Comparative Examples 1-5]
A solder composition was obtained in the same manner as in Example 1 except that each material was blended according to the composition shown in Table 1.

<Evaluation of solder composition>
The evaluation of the solder composition (solder ball, sagging property during heating) was evaluated by the following method. The obtained results are shown in Table 1.
(1) Solder balls Solder compositions obtained in Examples and Comparative Example 1 by screen printing on an electrode pattern provided on a circuit board (Test board manufactured by Tamura Corporation, FR-4, thickness: 1.6 mm) Was applied. Thereafter, this circuit board was put into a high-temperature observation apparatus (SMT scope), the preheating start temperature was raised from 150 ° C. to 190 ° C., and then heated to a peak temperature of 230 ° C. to melt the solder composition. The number of solder balls scattered around the electrode pattern (observation area: 4.5 cm ² ) was counted.
(2) Sagging property during heating A clean ceramic substrate (manufactured by Sanyu Industrial: 25 mm × 50 mm × 0.8 mm) is prepared. It has a pattern hole of 3.0 mm x 1.5 mm and has a pattern hole in which it is arranged in steps of 0.1 mm from 0.1 mm to 1.2 mm, with a thickness of 0.2 mm (error is within 0.001 mm) Using a metal mask, the solder composition is printed on this ceramic substrate to obtain a test plate. Then, the test plate is placed in a furnace heated to 170 ° C. and heated for 1 minute. The test plate after heating is observed, and the minimum interval at which the printed solder composition is not integrated is measured among the pattern holes.

As is clear from the results shown in Table 1, when the solder composition of the present invention was used (Examples 1 to 6), it was confirmed that the solder balls during reflow can be sufficiently suppressed.
On the other hand, when the activators E and F are used instead of the activator A (Comparative Examples 1 to 4), or when the activator A is not used (Comparative Example 5), the solder balls are not reflowed. Many were confirmed to occur.
In addition, it was surprisingly confirmed that the solder compositions (Examples 1 to 6) of the present invention were excellent in drooling during heating.

  The solder composition of the present invention can be suitably used as a technique for mounting a component on a printed wiring board of an electronic device.

Claims (5)

A lead-free solder powder comprising a Sn—Ag—Cu solder alloy having a melting point of 240 ° C. or lower, an Ag content of 3% by mass or less, and a Cu content of 4% by mass or less; Containing flux containing resin, activator and thixotropic agent,
The activator contains a polyvalent carboxylic acid represented by the following general formula (1).

(In the general formula (1), X represents O, S, NH, N or P, m represents an integer of 1 to 3, and n represents 2 or 3.) The solder composition according to claim 1,
The content of polycarboxylic acid represented by the said General formula (1) is 1 mass% or more and 10 mass% or less with respect to 100 mass% of said flux. The solder composition characterized by the above-mentioned. In the solder composition according to claim 1 or 2,
The alloy composition (mass ratio) in the lead-free solder powder is 96.5Sn / 3.0Ag / 0.5Cu, 98.3Sn / 1.0Ag / 0.7Cu, and 99.0Sn / 0.3Ag / 0. A solder composition characterized by being any one of 7Cu. In the solder composition according to any one of claims 1 to 3,
The activator further contains an organic acid other than the polyvalent carboxylic acid represented by the general formula (1).   An electronic component is mounted on a printed wiring board using the solder composition according to claim 1.