WO2001058639A1

WO2001058639A1 - Solder paste, soldering method using said solder paste and jointed product prepared by said soldering method

Info

Publication number: WO2001058639A1
Application number: PCT/JP2001/000877
Authority: WO
Inventors: Hitoshi Amita; Noriko Murase; Takashi Shoji
Original assignee: Showa Denko K.K.
Priority date: 2000-02-08
Filing date: 2001-02-08
Publication date: 2001-08-16
Also published as: AU3224201A; WO2001058639A9; CN1211183C; TW503147B; JP2002086292A; CN1358123A

Abstract

A solder paste which comprises a halogen compound as an activator in such an amount as to give a halogen ion concentration per 1 g of the flux used in the paste of 3,000 ppm or less in terms of a chlorine ion; a method for soldering using the solder paste; and a jointed product prepared by using the soldering method. The solder paste exhibits excellent storage stability.

Description

Description Solder paste, soldering method using the solder paste

And a joint manufactured by the soldering method

The present invention relates to a solder paste used for surface mounting of electronic components, and more particularly, to a solder paste having excellent storage stability, a soldering method using the solder paste, and a joined article. Background art

Solder paste is used in the electronics industry to surface mount electronic components. Solder paste is suitable for automation due to its printability and adhesiveness, and its use has been increasing in recent years.

In the electronics industry, solder paste is applied on a printed circuit board by screen printing or dispenser, electronic components are placed, and then reflowed to fix the electronic components. In the present specification, the term "rifle opening" means that a solder paste is applied to a predetermined position on a substrate, an electronic component to be joined is placed thereon, and then the substrate is heated to a temperature equal to or higher than the melting temperature of the solder paste. Means a series of operations for joining parts.

On the other hand, in recent years, fine pitch bonding has been required to reduce the size of electronic products, and the use of fine pitch components, for example, the use of a 0.3 mm pitch QFP (Quad Flat Package) type LSI, and the use of CSP ( Ch i Size Pacage) is often used. For this reason, solder paste is required to have a printing performance compatible with fine pitch. In order to respond to the demands of the industry, the average particle size of the solder particles has been reduced.However, the specific surface area of the entire solder particles has been increased, so that the reaction between the solder particles and the flux has been promoted. However, there is a problem that the storage stability of the solder paste deteriorates. The biggest cause of the decrease in the storage stability of the solder paste is that the solder powder reacts preferentially with the flux during storage, the oxidation of the solder powder progresses, the activator in the flux is consumed, and the activity of the flux decreases. At the same time, the viscosity of the solder paste increases due to the reaction products. For this reason, when using the solder paste, there is a problem that proper printing characteristics cannot be maintained and the solder paste does not dissolve during reflow.

Conventionally, efforts have been made to protect the surface of the solder particles and reduce the reactivity of the metal particles in order to improve the storage stability of the solder paste.

For example, a method of coating a solder powder with glycerin (Japanese Patent Publication No. 5-265898) and a method of coating a solder powder with a coating agent that is insoluble or hardly soluble in a solder paste solvent (Japanese Patent Laid-Open No. — 1 1 3 1 9 7) is disclosed. Preferable examples of the latter coating agent include silicone oil, silicone base high molecular weight compound, fluorinated silicone oil, fluorosilicone resin, and fluorinated hydrocarbon-based polymer compound.

Also, a method of coating a solder powder with a resin mainly composed of rosin, which is incompatible with the flux at room temperature but is compatible with the soldering temperature (Japanese Patent Application Laid-Open No. HEI 3-184696, Japanese Patent Application Laid-open No. No. 4-251691) has been proposed.

In the above-mentioned method of coating with a coating agent, coating with a relatively large amount of the coating agent is effective in suppressing the oxidation of the solder powder.However, a large amount of the coating material is required for reflow of the solder paste. This is rather inconvenient, and solder balls may be generated frequently. In addition, these coatings are only performed physically, and the adhesion is considered to be very weak, and there is a strong possibility that they will be peeled off during kneading when manufacturing the solder paste, transport during use, printing, etc. . In addition, it is difficult to say that the above-mentioned resin coating agent mainly composed of rosin contains a large amount of reactive organic acid itself and protects the powder.

In addition, a method of adding a phenol-based, phosphite-based, or sulfur-based antioxidant as an activator for soldering flux (Japanese Patent Publication No. 59-226-32) JP-A-3-124092), one or more antioxidants containing one or more phenol skeletons having a tertiary butyl group in the molecule. Method of adding 30% by weight (Japanese Patent Application Laid-Open No. 5-185283), use of a specific surfactant (Japanese Patent Application Laid-Open No. 2-147147), etc. Has been proposed.

Recently, lead-free Pb-free solder paste has been recommended due to environmental issues, and development is under way to address this. Above all, Sn-Zn solder paste is advantageous in terms of resources and cost, and since the reflow temperature can be reduced to the same level as Sn-Pb solder, the length of mounted components can be reduced. It is drawing attention as a particularly promising product because it has a long life and can respond to the diversification of parts. However, the Sn-Zn solder paste has poorer storage stability than ordinary Pb-based solder paste, and the progress of oxidation of Zn in the solder powder and the relationship between Zn and flux. The reaction causes the viscosity to increase over time. In particular, Zn reacts with halogen compounds in the flux at room temperature, deteriorating the storage stability of the solder paste. In addition, the halogen compound in the flux reacts with Zn in the solder powder to generate a small amount of hydrogen gas, and the generated hydrogen gas is built into the solder fillet even after the parts are joined, so reliability is critical. Has a significant impact.

The present invention has been made in view of the above-described problems, and has an excellent storage stability, and in particular, a solder paste having excellent storage stability even when the solder particle diameter is reduced by fine pitching, and further using this solder paste. An object of the present invention is to provide a reliable soldering method and a joint. Disclosure of the invention

The present invention is a solder paste comprising, in a solder paste containing a halogen compound, a halogen ion concentration per gram of the flux of not more than 300 ppm in terms of chlorine. The halogen ions include bromine ions. In addition, the above-mentioned solder paste contains Zn as solder powder. including.

Further, the present invention provides a method of soldering a circuit board, comprising: a step of applying the solder paste on a circuit board; and a step of reflowing the solder paste, and a joined body manufactured by the method of soldering a circuit board. including.

As described above, long-term storage stability can be maintained by setting the concentration of halogen ions per gram of flux of the solder paste to 300 ppm or less in terms of chlorine. BEST MODE FOR CARRYING OUT THE INVENTION

The flux contained in the solder paste is a mixture of a rosin or synthetic resin-based resin component, a halogen compound and / or an organic acid component as an activator, a solvent, a thixotropic agent, and the like. Among these components, the effective components for removing the surface oxide of the solder metal at the mouth of the riff and obtaining good bonding are halogen compounds and / or organic acid components used as activators. is there. These activators can enhance the ability to remove surface oxides, but react with the solder powder during soldering and during storage to degrade the solder paste. In particular, halogen compounds have a high effect as an activator, but have a strong effect of deteriorating solder paste.

The present inventors have studied the reaction between the solder powder and the activator in the solder paste. As a result, the halogen ion concentration per gram of the flux of the solder paste was 300 ppm or less in terms of chlorine, preferably 100 ppm or less. 100 ppm or less, more preferably 50 O ppm or less, and most preferably 30 O ppm or less, the reaction between the solder powder and the activator is suppressed, the solder paste is prevented from deteriorating, and the storage is stable. It has been found that it is possible to enhance the character.

However, the activator is attached in order to remove the metal surface oxide and obtain a good bond. To obtain the above-mentioned effect, the halogen compound should be at least 1 in terms of the chlorine concentration of the halogen ion concentration. It is necessary to add 0 ppm or more, preferably 100 ppm or more. It is not clear why halogen ions have an adverse effect on the storage stability of the solder paste, but in the presence of halogen ions, the oxidizing power of the halogen compound added to the flux is enhanced, and the reaction with the solder metal is accelerated. It is thought that it will be done.

The chlorine equivalent value of the halogen ion concentration is determined by measuring the solder paste, quantifying the halogen ion concentration contained in the aqueous layer when extracted with an organic solvent-water system by ion chromatography, converting it to chlorine, and converting it to chlorine. It is calculated from the value converted per gram. The chlorine conversion value is a value when the contained halogen ion is converted into chloride ion. For example, when a bromine compound is used as the activator, the amount of bromine ion in the solder paste (zg / g) , 35.4 5 3/7 9.904 (atomic weight of chlorine Z atomic weight of bromine). When an iodine compound is used as the activator, the quantitative value (g / g) of the ion is calculated as 35.545 3 / 126.045 (atomic weight of chlorine / atomic weight of iodine). ). Here, the organic solvent used for the extraction may be any solvent which does not react with the flux, is insoluble in conventionally known water used in organic synthesis, and does not contain halogen ions. Examples include methylene, toluene, xylene, benzene, getyl ether, petroleum ether and the like. Form, toluene, xylene, getyl ether, and petroleum ether are preferably used from the viewpoint of the solubility of the flux and the ease of the extraction operation. The water used for the extraction need not contain halogen ions, and for example, ultrapure water is most preferably used. The measurement of the halogen ion concentration by extraction with an organic solvent-water can be carried out on a solder paste using either a water-soluble flux or a non-water-soluble flux. In the present invention, the solder paste is used in a solder paste flux. The concentration of halogen ions in is adjusted to be less than 300 ppm in terms of chlorine. For example, halogens such as isopropylamine hydrobromide, butylamine hydrochloride, and cyclohexylamine hydrobromide, which are preferably used as an activator, are organic base hydrohalides. Ammonium hydride, 1,3-diphenyl In the case of anidine hydrobromide or the like, all of the halogen contained in these compounds is a halogen ion. Therefore, when no other halogen compound is used in combination, the addition amount may be calculated and added so that the chlorine-equivalent value of the halogen ion is 3000 ppm or less.

As the halogen compound, a halogen compound used as a normal solder flux may be used.However, in order to further improve the solderability and wettability of the solder paste, it is stable as a halogen compound during storage of the solder paste. It is preferable to use a halogen compound, particularly an organic bromine compound, which decomposes and exhibits an activity at the reflow temperature so that the chlorine equivalent of the halogen ion becomes 3000 ppm or less.

Examples of the organic bromine compound having the above-mentioned properties include a benzyl bromide compound having an alkyl substituent having 10 or more carbon atoms or a fatty acid or alicyclic compound having 10 or more carbon atoms in one molecule. Examples thereof include a polybromine compound containing four or more bromines, and these may be used as a mixture.

Benzyl bromide compounds having an alkyl chain having at least 10 carbon atoms are, for example, 4-stearoyloxybenzylbutamide, 4-stearyloxybenzyl bromide, 4-stearylbenzylbenzyl bromide, 4 Examples include compounds such as —bromomethylbenzyl stearate, 4-stearoylaminobenzyl bromide, and 2,4-bisbromomethylbenzyl stearate. Other than these, 4-palmitoyloxybenzyl bromide, 4-myristoyloxybenzyl bromide, 4-lauroyloxybenzyl bromide, 4_ndecanyloxybenzyl bromide, etc. Is mentioned.

The polybromine compound may have, for example, a carboxyl group, an ester group, an alcohol group, an ether group, a ketone group, or the like, and is a compound in which four or more bromine atoms are bonded.

Specific examples of these compounds include 9,10,12,13,15,16-hexabutamostate and 9,10,12,13,15,16-hexabuta Mostearic acid methyl ester, same ethyl ester, 9, 10, 12, 13-tetra Labromostearic acid, the same ethyl ester, the same ethyl ester, 9,10,12,13,15,16-hexabutamostearyl alcohol, 9,10,12,13-tetrabromostearyl alcohol, 1, 2,5,6,9,10-hexasub mouth mocyclo dodecane. Particularly preferred are mosabetic mostearic acid and hexabolic mocyclododecane.

In addition to the above, examples of organic bromine compounds include 1-bromo-2-butanol, 1-bromo-2-propanol, 3-bromo-11-propanol, and 3-bromo-1,2-propanediol. 1,4-dibromo-1-2-butanol, 1,3-dibromo-l-propanol, 2,3-dibromo-l-propanol, 1,4-dibromol-mo, 2,3-butanediol, 2,3-Dibromo-2-butene-1,4-diol, 1-bromo-3-methyl-1-butene, 1,4-dibromobutene, 1-bromo-1-propene, 2,3-dibromopropene, bromo Ethyl acetate, ethyl ethyl bromocaprylate, ethyl ethyl bromopropionate, ethyl ethyl bromopropionate, ethyl ethyl bromoacetate, 2,3-dibromosuccinic acid, 2-bromosuccinic acid, 2, 2-bromoazivic acid, 2, Examples include bromides such as 4-dibromoacetophenone, 1,1-dibromotetrachloroethane, 1,2-dibutene 1,1-phenylene, and 1,2-dibutene mostyrene. It is not limited. An organic halogen compound containing chlorine or iodine may be used instead of bromine.

The addition amount of these halogen compounds is set so that the halogen ions in the solder paste fall below 3000 ppm in terms of chlorine per gram of flux. One or more halogen compounds may be added, or an organic halogen compound and an organic base hydrochloride may be used in combination.

Examples of the organic acid component in the present invention include conventionally known succinic acid, fumaric acid, stearic acid, sebacic acid and the like, and an organic acid derivative which is a compound that generates an organic acid when the reflow temperature is reached is preferable. Used for Examples thereof include various aliphatic carboxylic esters, aromatic carboxylic esters, aliphatic sulfonic esters, and aromatic sulfonic esters. Alcohol residues of these esters are preferably alkyl, aryl, particularly t-butyl, isopropyl and isobutyl, which have high ester decomposability, and these compounds may contain a halogen atom.

Specific examples include n-provyl paratoluenesulfonate, isopropyl p-toluenesulfonate, isobutyl p-toluenesulfonate, n-butyl p-toluenesulfonate, n-provyl benzenesulfonate, and iso-propyl benzenesulfonate. Bil, isoptyl benzenesulfonate, salicylic acid-n-butyl mouth pill, isopropyl salicylate, isoptyl salicylate, n-butyl salicylate, isopropylate 4-nitrobenzoate, t-butyl 4-nitrobenzoate, methacrylic acid- Examples include t-butyl, t-butyl acrylate, t-butyl malonate, and t-butyl bromoacetate. Of these, para-toluenesulfonate-n-propyl, isoptyl salicylate, and t-butyl bromoacetate are particularly preferred. The addition amount is in the range of 0.01 to 20% by mass, and preferably 0.05 to 5% by mass, based on the total amount of the flux.

Since the above decomposable organic acid ester alone has low decomposability even at a reflow temperature, it is effective to add a small amount of an ester decomposing catalyst to accelerate the decomposition. As the ester decomposition catalyst, any catalyst can be used as long as the decomposable organic acid ester has a function of decomposing at the reflow temperature to promote the generation of acid. Among them, a hydrohalide of an organic base is particularly effective. is there.

As the resin component blended in the solder paste of the present invention, a well-known resin blended in a conventional flux can be used. For example, natural rosin, disproportionated rosin, polymerized rosin, modified rosin, etc. Polyester, polyurethane, acrylic resin and others are used.

As the solvent, alcohols, ethers, esters, or aromatic solvents can be used as in the case of conventional fluxes and solder pastes.For example, benzyl alcohol, butanol, ethyl solvent, butyl solvent, butyl carbitol , Diethylene glycol hexyl ether, propylene glycol monophenyl ether, dioctyl phthalate, xylene, etc. Used.

As the thixotropic agent added to improve printability, inorganic agents such as fine silica particles and kaolin particles, or organic agents such as hydrogenated castor oil and amide compounds are used. You.

In the solder paste of the present invention, storage stability can be further improved by using a reducing agent as a stabilizer in combination.

The reducing agent is usually used as an antioxidant for resins and the like, and is soluble in solvents such as phenolic compounds, phosphorus compounds, sulfur compounds, tocopherol and derivatives thereof, and L-ascorbic acid and derivatives thereof. And the like. Specifically, phenolic compounds include hydroquinone, catechol, 2,6-di-t-butyl-p-cresol, butylhydroxyanisole, 2,2,1-methylenebis (4-methyl-6-t-butylphenol ).

Examples of the phosphorus-based compound include triphenylphosphite, trioctyl phosphite, tridecyl phosphite and the like.

Examples of the sulfur compound include dilauryl-1,3,3,1-thiodipropionate, distearyl-1,3,3′-thiodipropionate, and dimyristyl-1,3,3,1-thiodipropionate.

As tocopherol and its derivatives, and L-ascorbic acid and its derivatives, any compounds which have reducing properties and are soluble in a solvent, for example, esters thereof, can be used. Particularly good results are obtained when two kinds of tocopherol or a derivative thereof and L-ascorbic acid or a derivative thereof are used in combination. The mixing ratio is preferably 0.5: 1 to 1: 0.5 by weight, particularly preferably about 1: 1.

Specific examples of L-ascorbic acid derivatives include ascorbic acid-2-phosphate, ascorbic acid-12-sulfate, ascorbic acid-2-glucoside, ascorbic acid-12,6-dibutylate, ascorbic acid-12, 6-distearate, ascorbic acid 1, 2, 6-dimyristate, ascorbic acid 6-palmitate, ascorbic acid 6-stearate, ascorbic acid 6-myristylate, Ascorbic acid 1,2,3,5,6-tetrapalmitate, ascorbic acid—2,3,5,6—tetramyristylate, ascorbic acid 1,2,3,5,6-tetrastearate, ascorbic acid 12—glucoside 6 — palmitate, ascorbic acid 1 2 — glucoside 1 6 — myristylate, ascorbic acid 1 2 — glucoside 6—stearate, ascorbic acid 1,5,6—benzylidene, ascorbic acid 1,5,6 —propylidene, Ascorbic acid 1-2-phosphate 5,6-benzylidene, ascorbic acid 12-5-phosphate 6,5-propylidene, etc., and specific examples of tocopherol derivatives include tocoyl, tocopherol acetate, and phosphoric acid. Examples include tocopherol, tocopherol sorbate, and tocopherol nicotinate.

These reducing agents may be used alone or in combination. The amount of the reducing agent added may be an amount sufficient to sufficiently secure the storage stability of the solder paste, but is generally from 0.005% by mass to 20% by mass with respect to the total amount of the flux. And more preferably 0.01% by mass or more and 10% by mass or less. If the addition amount is too small, there is no stabilizing effect, and even if it is added in an amount of 20% by mass or more, no improvement in the effect corresponding to high concentration addition is observed, which is not preferable.

The flux used in the solder paste of the present invention is, for example, 20 to 60% by mass of a resin component, 0.04 to 20% by mass of a thixotropic agent, and 0.01% by mass based on the total amount of the flux. To 20% by mass of an organic acid component, a halogen compound satisfying the above-mentioned range of halogen ions, 0.05 to 20% by mass of a reducing agent, and a solvent or the like as a balance. This flux is kneaded with, for example, 14 to 8% by mass and solder powder of 86 to 92% by mass based on the total amount of the solder paste to obtain a solder paste of the present invention. In this case, the amount of the halide to be added must be such that the halogen ion concentration in the flux after kneading the solder paste is not more than 300 ppm in terms of chlorine.

In the preparation and kneading of the mixture, the moisture such as the flux and the humidity of the atmosphere are adjusted, and the moisture content in the solder paste is controlled to 0.5% by mass or less, more preferably 0.3% by mass or less. Is preferred. More than 0.5% by weight of water in the paste If mixed in, the dissociation of the halide is promoted, and the dissociated halogen reacts with the solder alloy powder, which is not preferable. Further, the pH value of the solder paste is preferably in the range of 4 to 9, more preferably 6 to 8, from the viewpoint of suppressing the reaction between the solder powder and the flux. In this case, it is preferable to use an amine compound such as an alkanolamine, an aliphatic primary to tertiary amine, an aliphatic unsaturated amine, an alicyclic amine or an aromatic amine as the pH adjuster. .

Specific examples of these amine compounds include ethanolamine, butylamine, aminopropanol, polyoxyethyleneoleylamine, polyoxyethylenelaurelamine, polyoxyethylenestearylamine, getylamine, triethylamine, and methylamine. Toxipropylamine, dimethylaminopropylamine, dibutylaminopropylamine, ethylhexylamine, ethoxypropylamine, ethylhexyloxypropylamine, bisproviramine, isopropylamine, diiso Propylamine and the like can be mentioned.

The amount of the amine compound used is preferably 0.05 to 20% by mass based on the total amount of the solder paste flux. If the content is less than 0.05% by mass, the effect as a pH adjuster is not sufficient. If the content is more than 20% by mass, the pH generally exceeds 9, shifting to the alkaline side, and the solder paste tends to absorb moisture.

Further, azoles, for example, benzotriazole, benzimidazole, tolyltriazole, etc. may be added to the flux to prevent copper in the circuit. The addition amount of the antibacterial agent is preferably 0.5 to 20% by mass based on the total amount of the flux. The solder powder used in the solder paste of the present invention may have a conventionally known metal composition, but a solder powder containing Zn which is easily oxidized is preferably used. For example, Sn-Zn, Sn_Ag-Zn, Sn-Bi-Sb-Zn, Sn-Bi-Cu-Zn, Sn-Ag-Sb-Zn, Sn-Ag-Cu- Zn-based and Sn-ZnBi-based are mentioned.

As an example of the above, 95.5Sn / 3.5Ag / Ng is mainly composed of eutectic solder having 91% by mass of Sn and 9% by mass of Zn (hereinafter referred to as 91Sn / 9Zn). 1 Zn, 5 1 Sn / 45B i / 3 Sb / 1 Zn, 84 S n / 10 Bi / 5 Sb / 1 Zn, 88.2 S n / 10 B i / 0.8 Cu / l Zn, 88 S n / 4 A g / 7 Sb / l Zn, 97 S n / 1 Ag / 1 S b / 1 Z n, 91. 2 S n / 2 Ag / 0.8 Cu / 6 Zn, 89 S n / 8 Z n / 3 B i, 86 S n / 8 Z n / 6 B i, 89.1 S n / 2 Ag / 0. 9 Cu / 8Zn. The solder powder of the present invention may be a mixture of two or more types of solder powders having different compositions.

By adjusting the content of halogen ions to 3000 ppm or less in terms of chlorine per gram of flux as described above, the prepared solder paste can maintain the wettability of the solder on the substrate even after storage for 10 days. Is maintained well, and a reliable joint can be obtained.

The solder paste of the present invention is suitably used when a board, for example, a printed wiring board and an electronic component are joined together to produce a joint. In the method of using a solder paste and the method of manufacturing an electronic component joint according to the present invention, for example, a solder paste is applied to a portion where soldering is desired by a printing method or the like, and the electronic component is placed. The electronic components can be joined to the substrate by heating and melting and solidifying the solder particles.

As a bonding method (mounting method) between a substrate and an electronic component, for example, surface mounting technology (SMT) can be cited. In this mounting method, first, a solder paste is applied to a desired portion on a substrate, for example, a wiring board by a printing method. Next, electronic components such as chip components and QFPs are placed on the solder paste, and soldered collectively by a reflow heat source. As the reflow heat source, a hot blast stove, an infrared stove, a steam condensing soldering device, a light beam soldering device, or the like can be used.

Although the reflow process of the present invention differs depending on the solder alloy composition, in the case of a Sn--Zn system such as 91Sn / 9Zn, 89Sn / 8Zn / 3Bi, 86Sn / 8Zn / 6Bi, preheating is performed. And the reflow are preferably performed in two steps.The preheating temperature is 130-180 ° C, preferably 130-150 ° C, and the preheating time is 60-120 seconds, preferably 60-90. Second, reflow temperature is 210-230 °, preferably 210-220 °, riff opening hour 30 660 seconds, preferably 30 to 40 seconds. The reflow temperature in other alloy systems is +20 to 150 ° C with respect to the melting point of the alloy used (preferably +20 to 130 ° C with respect to the melting point of the alloy; The temperature, the preheating time, and the one hour of the riff opening may be in the same ranges as described above.

With the solder paste of the present invention, the above reflow process can be carried out both in nitrogen and in air. In the case of nitrogen reflow, by setting the oxygen concentration to 5 V o 1% or less, preferably 0.5 vo 1% or less, the wettability of solder to a substrate such as a wiring board is improved as compared with the case of air reflow, The generation of solder balls is reduced and stable processing can be performed.

After that, the board is cooled and the surface mounting is completed. In the method of manufacturing a bonded electronic component by this mounting method, bonding may be performed on both surfaces of a substrate (plate to be bonded) such as a printed wiring board. The electronic parts on which the solder paste of the present invention can be used include, for example, an LSI, a resistor, a capacitor, a transformer, an inductance, a filter, an oscillator and a vibrator, but are not limited thereto. It is not done.

Further, the present invention provides a method of forming an adhesive film only on a predetermined surface of a substrate, for example, a predetermined surface of a circuit metal of a printed circuit board by a chemical reaction, as disclosed in Japanese Patent Publication No. 7-7244, After applying solder powder to this, apply flux, heat to the melting temperature of the solder and reflow, and mount it on the circuit board on which solder bumps have been formed using SMT (Surface Mount Technology) using the solder paste of the present invention. In this case, more excellent solderability can be obtained.

INDUSTRIAL APPLICABILITY The present invention can be applied to solder paste for fine pitch joining of microelectronic components made of a solder alloy that does not contain Pb and has low environmental pollution, and a reliable joint can be obtained even if a solder paste prepared in advance is used. As a result, for example, it is possible to cope with fine pitch bonding of a mounting wiring board, and as a result, it is possible to provide a wiring board having an excellent component life.

Hereinafter, the content of the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Claims

Example

[Test method]

①Halogen ion concentration measurement

To 1 g of the solder paste was added 5 ml of black form and stirred to dissolve the flux, and then 10 ml of ultrapure water was added to extract the halogen ions into water. The aqueous layer was measured by ion chromatography.

Equipment used: YOKOGAWA I C— 100

Separation column: S AM3— 125

Filler: hydrophilic low exchange capacity strong ion exchange resin

Particle size: 10 m

Exchange capacity: 60 eq / ml

Eluent and flow rate: 4 mM Na 2 CO 3/4 mM NaHC03, 2 ml / min Eluent and flow rate: 0.05 M n-dodecylbenzenesulfonic acid, 2 ml / min Temperature: 40 ° C

Sample volume: 100 1

②Viscosity measurement

The viscosity of the solder paste at 10 rpm was measured using a Malco PCU-205 spiral viscometer.

3) Observation of void (reliability of joint)

After printing a pattern of 6 mm diameter x 6 pieces on a 60 mm square copper plate using a 150 micron thick metal mask, reflow under the air atmosphere, then cut the copper plate together with the solder with a cutter, and then microscope the solder part To observe the occurrence of voids. The size of a board with a size of 10 m or more was measured for 6 patterns, and the case where the average number per pattern was 2 or more was rejected.

(Examples 1-9, Comparative Examples 1-3)

Polymerized rosin 17.5% by mass, disproportionated rosin 27.5% by mass as resin component, 7% by mass of hydrogenated castor oil as a thixotropic agent, dihydroguanidine hydrobromide, cyclohexylamine hydrobromide as an organic base hydrocyanic acid hydrochloride, and hexacyclohexyl moclocyclo as a halogen compound Table 1 shows dodecane, 2,3-dibromo-12-butene-11,4-diol, 4-stearoyloxybenzylbutamate, isobutyl salicylate and p-toluenesulfonic acid-n-propyl as organic acid components. In addition, 2% by mass of triethanolamine as a pH adjuster, 0.3% by mass of hydroquinone as a reducing agent, 1% by mass of benzimidazole as a protective agent, and diethylene glycol mono-monomer as a solvent were added. A flux was prepared by adding ethyl hexyl ether to 100% by mass.

table 1

89% by mass of Pb free solder powder of 89 Sn / 8Zn / 3Bi was added to 11% by mass of this flux and kneaded with a planetary mill to produce a 3 kg solder paste.

As comparative examples, hydrohalides, halogen compounds

Was added as shown in Table 1 so as to exceed 3000 ppm, and a solder paste was produced in the same manner as in the example. Manufacturing of electronic component joints>

SMT was used as the mounting method. Each of the solder pastes of Examples 1 to 9 and Comparative Examples 1 to 3 was printed on one circuit board, and the LSI, chip resistor, and chip capacitor were mounted on the solder paste and heated by a reflow heat source. And soldered. A hot blast stove was used as a heat source for the riff opening.

One condition of the riff opening was that the preheating was performed at a temperature of 130 ° (preheating time was set to 80 seconds, and the reflow was performed at a beak temperature of 220 ° C and a reflow time of 200 ° C or more was set to 50 seconds. The solder paste used in both the examples and comparative examples was the one immediately after production and the one stored for 7 days after production.

The characteristics of the produced printed wiring board and the used solder paste were measured by the measurement method described above. Table 2 shows the measurement results. Note that the halogen ion concentration in Table 2 indicates the value in terms of chlorine, the bonding state indicates the state when bonding was performed using solder paste stored for 7 days, and the symbol 〇 indicates that no more than 2 voids per pattern Indicates that the bonding is good, and the X mark indicates that the bonding is two or more, indicating a poor bonding. Table 2

As is evident from Table 2 above, when the solder paste according to the present invention was stored for 7 days, both the halogen ion concentration and the viscosity increased slightly as compared to the solder paste immediately after the production, but the bonding state was good in each case. . Further, similar experiments were performed using Pb-free solder powders of 9311/9211 and 86Sn / 8Zn / 6Bi, and the same result was obtained.

Also, a comparison of the solder alloy structure after the riff opening of Examples 1 to 9 with the conventional Sn—Pb based solder alloy structure shows that in the case of Sn—Pb based In contrast to the remarkable coarsening of the crystal, the Sn—Zn-based solder alloy of the present invention has a small tendency to coarsen, thereby improving the mechanical properties of the solder and mounting wiring using the solder alloy. Improvement of the life characteristics of the plate was confirmed. Industrial applicability

With the solder paste of the present invention, the reaction between the solder alloy and the flux was significantly suppressed, and extremely excellent storage stability was obtained. In particular, the present invention has significantly improved the storage stability of Sn—Zn-based solder paste, which has been conventionally regarded as having poor storage stability, and its effectiveness has been confirmed.

In addition, the development of the solder paste of the present invention has made it possible to provide a highly reliable circuit board soldering method and a soldered joint corresponding to the fine pitch of the mounting wiring board and diversification of components. Was.