JP6012946B2 - Flux and solder paste composition - Google Patents

Description

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

  Conventionally, various solder paste compositions composed of solder powder and flux are used for soldering electronic circuit components and the like.

  By the way, the solder paste application method can be roughly classified into a printing method and a discharge method. The printing method is a method in which a metal mask or a silk screen provided with a hole in a soldering portion is placed on a printed circuit board, and a solder paste is applied thereon. On the other hand, the discharge method is a method in which a solder paste is applied to the soldering portion one by one using a dispenser or the like. The fine pitch pattern has a drawback that it cannot be applied by a discharge method. For example, when an electronic circuit component or the like is solder-connected to a fine pitch circuit board, a printing method is used.

  The packaging technology has been increased due to the downsizing of electronic devices, and fine pitches are increasingly being developed. For this reason, the solder paste is required to have excellent printability (transferability) in addition to conventionally required characteristics (stability, reliability, etc.). For example, when a metal mask is used, the printability is to efficiently transfer the solder paste attached to the wall surface of the metal mask opening to the substrate. So far, in order to realize improvement in printability, means such as refinement of the metal particle size and increase in the amount of wax have been proposed. However, when the metal particle size is made finer, printability is improved, but “storage stability”, “decrease in wettability” and the like are observed. On the other hand, when the amount of wax increases, it is difficult to adjust the viscosity, and the wettability tends to decrease.

  In order to solve such a problem, solder pastes described in Patent Documents 1 and 2 are disclosed. Patent Document 1 describes that by adding a predetermined amount of liquid paraffin to the solder paste, the fluidity is improved and a fine pattern can be printed. In Patent Document 2, when liquid paraffin or paraffin wax is added to the flux used in the solder paste, even if the soldered Cu land printed circuit board is exposed to an environment of high temperature and high humidity, the bonding strength is not reduced. It is described.

  In recent years, in addition to the above properties, the crack resistance of the residue has been demanded. In order to prevent cracking of the residue, a resin having a low glass transition temperature (Tg) is used as a base resin for the flux (Patent Document 3). However, although a resin having a low Tg is useful for preventing cracking of the residue, there is a problem that the residue becomes sticky after reflow. Also, Patent Documents 1 and 2 do not mention improving the stickiness of the residue after reflow.

JP 7-132395 A Japanese Patent Laid-Open No. 2005-21958 JP 2010-75960 A

  An object of the present invention is to provide a soldering flux capable of preventing residual cracking and improving the stickiness of the residue after reflow without impairing printability, wettability, and electrical reliability (insulation resistance). It is to be.

As a result of intensive studies to solve the above problems, the present inventors have found a solution means having the following configuration, and have completed the present invention.
(1) A soldering flux comprising a synthetic resin, an activator, an organic solvent, and paraffin wax having a melting point of 60 ° C. or higher.
(2) The soldering flux according to (1), wherein the paraffin wax contains only carbon and hydrogen as constituent elements.
(3) The soldering flux according to (1) or (2), wherein the paraffin wax is contained in a proportion of 3 to 8% by mass with respect to the total amount of the flux.
(4) The synthetic resin is at least one selected from the group consisting of acrylic resin, styrene-maleic acid resin, epoxy resin, urethane resin, polyester resin, phenoxy resin, terpene resin and polyalkylene carbonate. The soldering flux according to any one of (1) to (3).
(5) The soldering flux according to any one of claims (1) to (4), wherein the synthetic resin has a glass transition temperature of -30 to -100 ° C.
(6) A solder paste composition containing the soldering flux according to any one of (1) to (5) above and a solder alloy powder. (7) The soldering flux and the solder alloy powder. Is contained in a mass ratio of 8:92 to 15:85. The solder paste composition according to (6).

  According to the present invention, in the soldering flux, it is possible to prevent residue cracking and improve the stickiness of the residue after reflow without impairing printability, wettability, and electrical reliability (insulation resistance). The effect is obtained.

(Soldering flux)
The soldering flux of the present invention (hereinafter sometimes simply referred to as “flux”) contains a synthetic resin, an activator, an organic solvent, and a paraffin wax having a melting point of 60 ° C. or higher.

  The flux of the present invention contains a synthetic resin as a base resin. If it is a synthetic resin, it will not specifically limit, For example, an acrylic resin, a styrene-maleic acid resin, an epoxy resin, a urethane resin, a polyester resin, a phenoxy resin, a polyalkylene carbonate, etc. are mentioned.

  Examples of the acrylic resin include a homopolymer of an alkyl (meth) acrylate having an alkyl portion of 1 to 23 carbon atoms, and a copolymer having the alkyl (meth) acrylate as a main component. Specifically, polymethyl (meth) acrylate, polyethyl (meth) acrylate, polybutyl (meth) acrylate, poly-2-ethylhexyl (meth) acrylate, methyl (meth) acrylate- (meth) acrylic acid copolymer, ethyl (meth ) Acrylate- (meth) acrylic acid copolymer, butyl (meth) acrylate- (meth) acrylic acid copolymer, methyl (meth) acrylate-styrene copolymer, ethyl (meth) acrylate-styrene copolymer, butyl (Meth) acrylate-styrene copolymer, methyl (meth) acrylate-ethyl (meth) acrylate copolymer, methyl (meth) acrylate-butyl (meth) acrylate copolymer, ethyl (meth) acrylate-butyl (meth) An acrylate copolymer etc. are mentioned. In the present specification, “(meth) acrylate” means acrylate or methacrylate, and “(meth) acrylic acid” means acrylic acid or methacrylic acid.

  Epoxy resins include bisphenol A type, bisphenol F type, brominated bisphenol A type, hydrogenated bisphenol A type, bisphenol S type, bisphenol AF type, biphenyl type, naphthalene type, fluorene type, and various glycidyl ether type epoxies. Examples thereof include resins, glycidyl ester type epoxy resins, glycidyl amine type epoxy resins, and alicyclic epoxy resins.

  Examples of the urethane resin include diphenylmethane diisocyanate and a condensate of tolylene diisocyanate and a polyol (such as ethylene glycol and propylene glycol).

  Examples of the polyester resin include polyethylene terephthalate and polybutylene terephthalate.

  Examples of the phenoxy resin include bisphenol A type phenoxy resin and bisphenol F type phenoxy resin.

  Examples of the polyalkylene carbonate include polypropylene carbonate and polybutylene carbonate.

  These synthetic resins preferably have a low glass transition temperature (Tg), and for example, synthetic resins having a Tg of −30 to −100 ° C. are preferable. When a resin having a high Tg is used, it becomes difficult to stick, but cracks are likely to occur in the residue. Moreover, although the acid value of resin is not specifically limited, It is preferable that it is about 0-100 mgKOH / g.

  The flux of the present invention may further contain rosin. Examples of rosins include gum rosin, tall rosin, wood rosin, and derivatives thereof. Examples of these derivatives include polymerized rosin, acrylated rosin, hydrogenated rosin, disproportionated rosin, formylated rosin, rosin ester, rosin modified maleic resin, rosin modified phenolic resin, rosin modified alkyd resin and the like.

  The paraffin wax used in the present invention is a paraffin wax having a melting point of 60 ° C. or higher (hereinafter sometimes referred to as “specific paraffin wax”). When a paraffin wax having a melting point of less than 60 ° C. (that is, a paraffin wax that is liquid at a temperature of less than 60 ° C.) is used, the effect of improving stickiness cannot be obtained.

  Among the specific paraffin waxes, paraffin wax having a melting point of 70 to 80 ° C. is preferable. Paraffin wax having a melting point of 100 ° C. or higher may be used, but the upper limit is preferably about 100 ° C. in consideration of the balance between cost and effect.

  The specific paraffin wax may be a simple hydrocarbon-based one (that is, one containing only carbon and hydrogen as constituent elements), or may be one modified with acid or alcohol. However, a simple hydrocarbon-based one is preferable in that the stickiness can be further improved.

  The paraffin wax is classified into a normal form (linear form), an iso form (branched form), and a cyclo form (cyclic form) depending on the shape of the paraffin (hydrocarbon) constituting the paraffin wax. Moreover, the mixture of a normal body, an iso body, and a cyclo body may be sufficient.

  The activator used in the present invention is not particularly limited as long as it is a conventionally used activator. Examples of the activator include amines (diphenylguanidine, naphthylamine, diphenylamine, triethanolamine, monoethanolamine, etc.), amine salts (polyamines such as ethylenediamine, and organic acid salts of amines such as cyclohexylamine, ethylamine, and diethylamine) Inorganic acids (mineral acids such as hydrochloric acid and sulfuric acid) salts, organic acids (dicarboxylic acids such as succinic acid, adipic acid, glutaric acid, sebacic acid, maleic acid; myristic acid, palmitic acid, stearic acid, oleic acid, etc. 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.), hydrogen halides of aniline acid (Such as aniline hydrobromide) and the like.

  The organic solvent used in the present invention is not particularly limited, and examples thereof include alcohol solvents (ethyl alcohol, isopropyl alcohol, ethyl cellosolve, butyl carbitol, etc.), ester solvents (ethyl acetate, butyl acetate, etc.), hydrocarbon solvents. (Toluene, turpentine oil, etc.). Among these, isopropyl alcohol, butyl carbitol and the like are preferable. Isopropyl alcohol is excellent in volatility and solubility of the active agent, and is preferably used for, for example, a liquid flux. On the other hand, when the flux is mixed with the solder alloy powder and used as a solder paste composition, an ether of a polyhydric alcohol having a high boiling point such as butyl carbitol is preferably used.

  The content of the above four components (synthetic resin, activator, organic solvent and specific paraffin wax) is not particularly limited as long as it can constitute a flux. For example, the following ratio (ratio to the total flux): Contained. In addition, these content is a suitable range to the last, and as long as an effect is not affected, at least 1 component may be outside this range.

Synthetic resin: 20 to 80% by mass, preferably 30 to 60% by mass,
Specific paraffin wax: 3 to 8% by mass, preferably 5 to 8% by mass,
Activator: 5 to 25% by mass, preferably 10 to 20% by mass,
Organic solvent: 5 to 50% by mass, preferably 10 to 30% by mass.

  Generally, the thixotropic agent is contained in the flux, but the thixotropic agent may also be contained in the flux of the present invention. Examples of the thixotropic agent include hydrogenated castor oil, beeswax, carnauba wax, stearamide, hydroxystearic acid ethylenebisamide, and the like. The content of the thixotropic agent is usually about 2 to 10% by mass with respect to the total flux.

  Furthermore, the flux of the present invention may contain additives such as an antioxidant, a chelating agent, and a rust preventive agent as necessary, as long as the effects of the present invention are not impaired. In addition, you may add these additives, for example when mixing a flux and solder alloy powder.

(Solder paste composition)
The solder paste composition of the present invention contains the flux of the present invention and a solder alloy powder. The solder alloy powder is not particularly limited. For example, an Sn—Pb alloy, an alloy obtained by adding silver, bismuth, indium or the like to an Sn—Pb alloy, an Sn—Ag alloy, an Sn—Cu alloy, an Sn—Ag—Cu Based alloys. Considering the influence on the environment, lead-free alloys such as Sn—Ag alloys, Sn—Cu alloys, Sn—Ag—Cu alloys are preferable. Although the average particle diameter of solder alloy powder is not specifically limited, For example, about 10-40 micrometers is preferable.

  The mass ratio between the flux and the solder alloy powder (flux: solder alloy powder) is not particularly limited as long as it is appropriately set according to the use of the solder paste, but is preferably about 8:92 to 15:85.

  The solder paste composition of the present invention is applied onto a substrate by a dispenser, screen printing, or the like when soldering an electronic device component or the like. After application, preheating is performed at about 150 to 200 ° C., and reflow is performed at a maximum temperature of about 170 to 250 ° C. The application and reflow on the substrate may be performed in the air or in an inert atmosphere such as nitrogen, argon, helium.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated concretely, this invention is not limited to these Examples.

Example 1
<Preparation of flux>
The components listed in Table 1 were mixed at the ratios listed in Table 1 and heated until evenly dissolved, and after dissolution, cooled to obtain a flux. As the acrylic resin, a copolymer of 2-ethylhexyl acrylate, lauryl methacrylate, and methacrylic acid was used.
Acrylic resin (Tg = −60 ° C., acid value = 100 mgKOH / g): 30% by mass
Sebacic acid (active agent): 10% by mass
Aniline hydrobromide (activator): 0.3% by mass
Paraffin wax (melting point: 70 to 80 ° C., linear): 7% by mass
Butyl carbitol (organic solvent): 47.7% by mass
Hardened castor oil (thixotropic agent): 5% by mass

<Preparation of solder paste composition>
12 parts by mass of the obtained flux and 88 parts by mass of solder alloy powder (Sn-3.0 mass% Ag-0.5 mass% Cu, average particle size 25 to 38 μm) were mixed (flux: solder alloy powder = 12:88), a solder paste composition was obtained.

(Examples 2-6 and Comparative Examples 1-6)
A flux was obtained in the same manner as in Example 1 except that the components shown in Table 1 were used in the proportions shown in Table 1, and a solder paste composition was obtained in the same manner as in Example 1, respectively.

  Using the solder paste compositions obtained in each Example and each Comparative Example, (1) Stickiness of residue after reflow, (2) Printability of solder paste, (3) Electrical reliability, (4) Wetting (Solder ball test) and (5) Residual cracks were evaluated.

(1) Residual stickiness after reflow According to JIS Z 3284 appendix 12, the stickiness of the residue after reflow was evaluated. Printing was performed on a test piece (copper plate: 50 mm × 25 mm × 0.5 mm) using a metal mask having a thickness of 200 μm (openings of 6.5 mmφ were present at four locations). The test piece was left on a hot plate at 50 ± 2 ° C. from the liquidus temperature of the metal (solder alloy) used, and heating was continued for 5 seconds after the metal was melted. Subsequently, the test piece was kept horizontal and allowed to stand at room temperature for about 30 minutes. Powder talc was thoroughly sprinkled on the test piece and lightly wiped with a soft brush, and evaluated according to the following criteria. The results are shown in Table 2.
A: When the powder talc on the test piece is completely removed.
○: When the powder talc on the test piece is not perfect but almost removed.
Δ: The powder talc on the test piece remained slightly, but the ground was visible.
X: When the powder talc on a test piece remains and the foundation | substrate was not visually recognized.

(2) Printability of solder paste Using a board for evaluation of printability (a glass epoxy board having a 10 mm x 10 pin 0.5 mm pitch BGA 0.25 mmφ opening pattern) and a corresponding thickness of 120 μm mask, 20 continuous prints Sex was evaluated according to the following criteria. The results are shown in Table 2.
A: When all of the substrates are missing from 0 (no chipping) to 10% of 10 × 10 pins.
A: When 10% to 50% of 10 × 10 pins are missing on all substrates.
Δ: When 50% to 80% of 10 × 10 pins are missing on all substrates.
X: When 80% or more of 10 × 10 pins are missing on all the substrates.

(3) Electrical reliability Insulation resistance was measured in accordance with JIS Z 3197 to evaluate electrical reliability. A solder paste composition was printed on a comb-type substrate (type II) defined in JIS Z 3197 using a metal mask having the same pattern and a thickness of 100 μm. Within 10 minutes after printing, preheating was performed at 175 ± 5 ° C. for 80 ± 5 seconds in the air, and reflow was performed at a maximum temperature of 235 ± 5 ° C. Next, the substrate after reflow was subjected to a cold cycle load under the same conditions as in the residual crack test. Thereafter, the substrate was left in a constant temperature and humidity chamber at a temperature of 85 ° C. and a humidity of 85%, and the resistance value (Ω) at the initial stage (0 hour), after 500 hours and after 1000 hours was measured. From the initial stage to 1000 hours, when the resistance value was 1 × 10 ⁸ Ω or more, it was evaluated that the electrical reliability was high (◯). The results are shown in Table 2.

(4) Wettability (solder ball test)
A solder paste composition was printed on a substrate having a 0.8 mm pitch QFP (Quad Flat Package) pattern using a metal mask having the same pattern and a thickness of 200 μm. Within 10 minutes after printing, preheating was performed at 175 ± 5 ° C. for 80 ± 5 seconds in the atmosphere, and reflow was performed at a maximum temperature of 235 ± 5 ° C. Then, by measuring the number of solder balls generated around the 80 pads (80 soldering portions) using a 20 × stereo microscope, the number of solder balls (pieces) generated as a solderability index is counted. evaluated. The results are shown in Table 2.

(5) Presence or absence of residual cracks The substrate after performing the above solder ball test was used as a test piece, and the test piece was cooled at 1000 cycles under the condition of −40 ° C. × 30 minutes → 125 ° C. × 30 minutes. A cycle load was applied. After 1000 cycles, the crack generation state in the soldered portion of the SOP pattern or QFP pattern on the substrate was visually observed and evaluated according to the following criteria. The results are shown in Table 2.
○: No cracks are observed.
Δ: Cracks are generated, but cracks that adversely affect reliability, that is, cracks that straddle two or more adjacent soldered portions (hereinafter referred to as “connected cracks”) are not recognized.
X: The connection crack has generate | occur | produced.

  As shown in Table 2, in Examples 1-6, it turned out that the stickiness of the residue after reflow is improved, without impairing all the printability of solder paste, electrical reliability, and wettability. It was also found that no residual cracks occurred. On the other hand, in Comparative Examples 1-6, the stickiness of the residue after reflow was not improved. Further, it was also found that the printability of the solder paste was impaired and a residual crack was generated.

Claims (5)

Containing a synthetic resin, an activator, an organic solvent and a paraffin wax having a melting point of 60 ° C. or higher, and the paraffin wax is contained in a ratio of 3 to 8% by mass with respect to the total amount of the flux;
Synthetic resin, an acrylic resin, a styrene - to maleic acid resins, epoxy resins, urethane resins, polyester resins, phenoxy resins, and at least Tanedea wherein Rukoto selected from the group consisting of terpene resins and polyalkylene carbonate, Soldering flux.   The soldering flux according to claim 1, wherein the paraffin wax contains only carbon and hydrogen as constituent elements. The soldering flux according to claim 1 or 2 , wherein the synthetic resin has a glass transition temperature of -30 to -100 ° C. A solder paste composition comprising the soldering flux according to any one of claims 1 to 3 and a solder alloy powder. The solder paste composition according to claim 4 , wherein the soldering flux and the solder alloy powder are contained in a mass ratio of 8:92 to 15:85.