JP7194141B2 - SOLDER COMPOSITION FOR LASER SOLDERING AND METHOD FOR PRODUCING ELECTRONIC SUBSTRATE - Google Patents

Description

TECHNICAL FIELD The present invention relates to a solder composition for laser soldering, an electronic substrate, and a method for manufacturing an electronic substrate.

Generally, electronic components are mounted by thread solder using a soldering iron. In recent years, however, electronic products have become lighter, thinner, shorter and smaller, and printed circuit boards have become finer.
A non-contact soldering method using a laser beam is used for soldering to such minute parts that are difficult to solder with a soldering iron.
With this technology, a laser beam is emitted from the soldering head of a soldering machine toward the printed wiring board, and the light energy of the irradiated laser beam is absorbed by the solder, causing heat to melt and melt the solder. This method has the advantage that electronic components can be mounted in a minute portion of a printed wiring board in a short time.
In addition, since it is possible to selectively irradiate the laser beam to the part to be soldered, it is possible to mount electronic components without applying heat to the entire component compared to the flow method or reflow method. can be applied to heat-sensitive parts.

Thus, the method using laser light as a heat source enables non-contact soldering to minute portions. However, since rapid heating is performed, the occurrence of solder balls, the scattering of flux, the spread of flux residue, and the like, has remarkably occurred.
Therefore, as a solder composition that can solve these problems, for example, (A) a rosin resin, (B) an organic acid, (C) a solvent, and (D) a flux containing an organic halogen compound that is solid at 25 ° C. , (E) solder powder, the (A) component contains (A1) a high softening point rosin resin having a softening point of 130 ° C. or higher, and the amount of the (A1) component is A) A solder composition has been proposed in which the total amount of component A is 70% by mass or more with respect to 100% by mass (see Patent Document 1).

JP 2015-142936 A

According to the solder composition as described in Patent Document 1, the occurrence of solder balls, the scattering of flux, and the spread of flux residue can be suppressed to some extent in laser soldering. However, the suppression of the occurrence of solder balls is still not necessarily sufficient, and further improvement has been desired. In particular, when soldering an electronic component to be inserted into a through-hole, a large amount of solder is required, so solder balls are likely to occur.
The occurrence of solder balls tends to be suppressed by increasing the amount of the activator in the solder composition. However, if the amount of the activator is too large, the insulation reliability may deteriorate, so the activator cannot be excessively blended.

An object of the present invention is to provide a solder composition for laser soldering that can sufficiently suppress the occurrence of solder balls when performing laser soldering, an electronic substrate using the same, and a method for manufacturing the same.

A solder composition for laser soldering according to an aspect of the present invention comprises (A) a rosin resin, (B) an activator, (C) a solvent and (D) a flux composition containing a thixotropic agent; The (A) component contains (A1) a polymerized rosin having a softening point of 130° C. or higher and an acid value of 200 mgKOH/g or less, and the (C) component ( C1) It is characterized by containing a dialkyl sebacate.

In the solder composition for laser soldering according to one aspect of the present invention, the component (D) preferably contains (D1) ethylenebisstearic acid amide.

An electronic substrate according to an aspect of the present invention is characterized by comprising a soldered portion using the solder composition for laser soldering according to the above-described aspect of the present invention.

A method for manufacturing an electronic substrate according to one aspect of the present invention is a method for manufacturing an electronic substrate using the solder composition for laser soldering according to one aspect of the present invention, wherein a dispenser is placed on an electrode of a wiring substrate. Using a coating step of applying the solder composition, a mounting step of mounting an electronic component on the solder composition, and using a laser beam to heat the solder composition, the electrode and the electron and a soldering step of soldering the components together.

The reason why the solder composition for laser soldering of the present invention can sufficiently suppress the occurrence of solder balls during laser soldering is not necessarily clear, but the present inventors speculate as follows.
That is, the present inventors presume that the reason why solder balls are generated in laser soldering or the like in which rapid heating is performed is as follows. In other words, due to rapid heating by laser irradiation, the flux whose fluidity has suddenly increased flows out of the pad before the solder powder melts, and at that time, the unmelted solder powder flows out of the pad at the same time. The inventors speculate that there is. In contrast, the solder composition for laser soldering of the present invention contains (A1) a polymerized rosin having a softening point of 130° C. or higher and an acid value of 200 mgKOH/g or lower. In the present invention, during soldering involving rapid heating, the component (A1) tends to be distributed so as to cover the surface of the solder composition, temporarily forming a film. Such a film has relatively low fluidity because it consists of the high-melting-point component (A1) dispersed with other components. Therefore, the film can prevent the (B) active agent and (C) solvent from scattering and flowing out of the pad.
In addition, the present inventors have surprisingly found that, among high-melting rosin-based resins, when polymerized rosin is used, the occurrence of solder balls can be dramatically suppressed. Furthermore, it has been found that the use of (C1) dialkyl sebacate together with component (A1) can also dramatically suppress the occurrence of solder balls. The present inventors presume that the effects of the present invention are achieved by the action of these components (A1) and (C1).

ADVANTAGE OF THE INVENTION According to this invention, the solder composition for laser soldering which can fully suppress the generation|occurence|production of a solder ball, an electronic substrate using the same, and its manufacturing method can be provided when performing laser soldering.

The solder composition for laser soldering of the present embodiment contains a flux composition described below and (E) solder powder described below.

[Flux composition]
First, the flux composition used in this embodiment will be described. The flux composition used in this embodiment is a component other than the solder powder in the solder composition, and contains (A) a rosin resin, (B) an activator, (C) a solvent and (D) a thixotropic agent. be.

The amount of the flux composition is preferably 8% by mass or more and 20% by mass or less, more preferably 10% by mass or more and 15% by mass or less, based on 100% by mass of the solder composition. When the amount of flux is less than 8% by mass (when the amount of solder powder is more than 92% by mass), the coatability tends to be insufficient. When it exceeds (when the amount of solder powder is less than 80% by mass), it tends to be difficult to form a sufficient solder joint when the resulting solder composition is used.

[(A) Component]
The (A) rosin-based resin used in this embodiment must contain (A1) a polymerized rosin having a softening point of 130° C. or higher and an acid value of 200 mgKOH/g or lower. Such a component (A1) can suppress the occurrence of solder balls during laser soldering.
If the softening point of the component (A1) is less than 130° C., the flux scattering cannot be suppressed and the occurrence of solder balls cannot be sufficiently suppressed. From the viewpoint of suppressing the occurrence of solder balls, the softening point of the component (A1) is preferably 135° C. or higher, more preferably 140° C. or higher. The upper limit of the softening point of component (A1) is not particularly limited. For example, the softening point of component (A1) may be 200°C or lower.
If the acid value of component (A1) exceeds 200 mgKOH/g, insulation reliability will be insufficient. In addition, from the viewpoint of activation action and insulation reliability, the acid value of component (A1) is preferably 20 mgKOH/g or more and 180 mgKOH/g or less, more preferably 100 mgKOH/g or more and 150 mgKOH/g or less.
The acid value (average acid value) can be measured by obtaining potassium hydroxide required to neutralize the free fatty acids contained in 1 g of the sample. Also, the softening point can be measured by the ring and ball method.

A polymerized rosin is obtained by polymerizing rosins by a known method. Rosins include gum rosin, wood rosin and tall oil rosin. Although these rosins may be used unpurified, it is preferable to use rosins after purification from the viewpoint of obtaining a polymerized rosin with good color tone (low Gardner color number).
The Gardner color number of the polymerized rosin is preferably 8 or less from the viewpoint of the effect of suppressing solder balls.
The polymerized rosin is generally obtained by reacting rosins in the presence of a sulfuric acid catalyst in an organic solvent at a temperature of, for example, 40° C. or higher and 160° C. or lower for 1 hour or longer and 10 hours or shorter. Sulfuric acid-based catalysts include sulfuric acid, p-toluenesulfonic acid, methanesulfonic acid, and sulfonated copolymers such as styrene-divinylbenzene. In addition to sulfuric acid-based catalysts, formic acid, hydrogen fluoride, zinc chloride, aluminum chloride, titanium tetrachloride, and the like can also be used in combination. Organic solvents include toluene, xylene, and halogenated hydrocarbons. In order to remove the catalyst after completion of the reaction, various known methods such as washing with water and filtration can be generally employed. Also, unreacted rosin and decomposition products can be removed by vacuum distillation.

The amount of component (A1) is preferably 10% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 50% by mass or less, and 25% by mass, based on 100% by mass of the flux composition. % or more and 40 mass % or less is particularly preferable. When the blending amount of the component (A1) is at least the above lower limit, solder balls can be suppressed more reliably during laser soldering. Moreover, if the compounding quantity of (A1) component is below the said upper limit, the amount of flux residue can fully be suppressed.

In this embodiment, the (A) component may contain a rosin-based resin ((A2) component) other than the (A1) component.
The (A2) rosin-based resin used in the present embodiment includes rosins and rosin-based modified resins. Rosins include gum rosin, wood rosin and tall oil rosin. Examples of rosin-based modified resins include disproportionated rosin, hydrogenated rosin and derivatives thereof. Hydrogenated rosins include fully hydrogenated rosins, partially hydrogenated rosins, unsaturated organic acids (aliphatic unsaturated monobasic acids such as (meth)acrylic acid, α,β- Hydrogenated unsaturated organic acid-modified rosin ("hydrogenated acid-modified (also referred to as "rosin"). These rosin-based resins may be used singly or in combination of two or more.

The softening point of component (A2) is preferably 120° C. or higher, more preferably 130° C. or higher, and particularly preferably 140° C. or higher, from the viewpoint of suppressing flux scattering and solder balls.
The acid value of component (A2) is not particularly limited. For example, the acid value of component (A2) may be 220 mgKOH/g or more and 500 mgKOH/g or less.

As means for adjusting the softening point of component (A), (i) the degree of polymerization of rosin is adjusted (the higher the degree of polymerization, the higher the softening point tends to be), and (ii) the modification of rosin. (For example, modifying with acrylic acid or maleic acid tends to increase the softening point), (iii) adjusting the molecular weight of rosin (the higher the molecular weight, the higher the softening point. (iv) subjecting rosin to hydrogenation reaction, or (v) subjecting rosin to esterification reaction or transesterification reaction.
In addition, as a means for adjusting the acid value of component (A), changing the method of modifying rosin (for example, modifying with acrylic acid or maleic acid tends to increase the acid value, and esterification As a result, the acid value tends to be low).

The amount of component (A) is preferably 25% by mass or more and 65% by mass or less, more preferably 27% by mass or more and 60% by mass or less, and 30% by mass, based on 100% by mass of the flux composition. % or more and 58 mass % or less is particularly preferable. If the blending amount of component (A) is at least the above lower limit, it is possible to prevent oxidation of the copper foil surface of the soldering land and make it easier for molten solder to wet the surface, so-called solderability can be improved, and solder balls can be sufficiently formed. can be suppressed to Moreover, if the compounding quantity of (A) component is below the said upper limit, the flux residue amount can fully be suppressed.

[(B) Component]
Examples of the (B) activator used in this embodiment include organic acids, non-dissociative activators comprising non-dissociable halogenated compounds, and amine-based activators. These activators may be used singly or in combination of two or more.
Examples of organic acids include monocarboxylic acids, dicarboxylic acids, and other organic acids.
Monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, capric acid, lauric acid, myristic acid, pentadecyl acid, palmitic acid, margaric acid, stearic acid, and tuberculostearic acid. , arachidic acid, behenic acid, lignoceric acid, and glycolic acid.
Dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, eicosanedioic acid, fumaric acid, maleic acid, tartaric acid, and diglycolic acid. mentioned.
Other organic acids include dimer acid, levulinic acid, lactic acid, acrylic acid, benzoic acid, salicylic acid, anisic acid, citric acid, and picolinic acid.

Non-dissociative activators comprising non-dissociable halogenated compounds include non-salt organic compounds in which halogen atoms are covalently bonded. The halogenated compound may be a compound formed by a covalent bond of each single element of chlorine, bromine and fluorine, such as chloride, bromide and fluoride, but any two or all of chlorine, bromine and fluorine may be may be a compound having a covalent bond of These compounds preferably have a polar group such as a hydroxyl group or a carboxyl group, such as a halogenated alcohol or a halogenated carboxyl group, in order to improve the solubility in an aqueous solvent. Examples of halogenated alcohols include 2,3-dibromopropanol, 2,3-dibromobutanediol, trans-2,3-dibromo-2-butene-1,4-diol (TDBD), 1,4-dibromo-2 -butanol, brominated alcohols such as tribromoneopentyl alcohol, chlorinated alcohols such as 1,3-dichloro-2-propanol, 1,4-dichloro-2-butanol, fluorinated alcohols such as 3-fluorocatechol, etc. Compounds similar to these can be mentioned. Carboxyl halides include carboxyl iodides such as 2-iodobenzoic acid, 3-iodobenzoic acid, 2-iodopropionic acid, 5-iodosalicylic acid, 5-iodoanthranilic acid, 2-chlorobenzoic acid, and 3-chloropropione. carboxyl chlorides such as acids, bromides such as 2,3-dibromopropionic acid, 2,3-dibromosuccinic acid, 2-bromobenzoic acid, and other similar compounds.

Amine surfactants include amines (polyamines such as ethylenediamine, etc.), amine salts (trimethylolamine, cyclohexylamine, diethylamine, etc.), organic acid salts such as aminoalcohols, and inorganic acid salts (hydrochloric acid, sulfuric acid, brominated hydrogen acid, etc.), amino acids (glycine, alanine, aspartic acid, glutamic acid, valine, etc.), amide compounds, and the like. Specifically, diphenylguanidine hydrobromide, cyclohexylamine hydrobromide, diethylamine salts (hydrochloride, succinate, adipate, sebacate, etc.), triethanolamine, monoethanolamine, and , hydrobromides of these amines, and the like.

The blending amount of component (B) is preferably 0.1% by mass or more and 10% by mass or less, and preferably 0.5% by mass or more and 6% by mass or less, based on 100% by mass of the flux composition. More preferably, it is particularly preferably 1% by mass or more and 3% by mass or less. If the blending amount of component (B) is at least the above lower limit, solder balls can be suppressed more reliably. Moreover, if the compounding quantity of (B) component is below the said upper limit, the insulation reliability of a flux composition can be improved.
In the present embodiment, solder balls can be sufficiently suppressed during laser soldering even if the blending amount of component (B) is equal to or less than the upper limit.

[(C) component]
The (C) solvent used in this embodiment must contain (C1) dialkyl sebacate. Such a (C1) component can suppress the occurrence of solder balls when performing laser soldering.
Alkyl in component (C1) is preferably linear alkyl having 1 to 10 carbon atoms or branched alkyl having 3 to 10 carbon atoms. Further, from the viewpoint of the effect of suppressing solder balls, the alkyl in the component (C1) is more preferably straight-chain alkyl having 2 to 9 carbon atoms or branched-chain alkyl having 3 to 9 carbon atoms. Straight-chain alkyl of 8 or branched-chain alkyl of 3 to 8 carbon atoms are particularly preferred.
Two alkyl groups in the component (C1) may be the same or different, but are preferably the same.

Component (C1) includes dimethyl sebacate, diethyl sebacate, dipropyl sebacate (diisopropyl sebacate, etc.), dibutyl sebacate, dipentyl sebacate, dihexyl sebacate, diheptyl sebacate, and dioctyl sebacate (di(di(sebacate 2-ethylhexyl), etc.). These may be used individually by 1 type, and may be used in mixture of 2 or more types.

Component (C) may contain a solvent (component (C2)) other than component (C1) as long as it does not affect the object of the present invention. However, when component (C2) is used, the amount of component (C1) is preferably 25% by mass or more, more preferably 50% by mass or more, relative to 100% by mass of component (C). , more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

Component (C2) includes diethylene glycol, dipropylene glycol, triethylene glycol, hexylene glycol, 1,5-pentanediol, methyl carbitol, butyl carbitol, octanediol, phenyl glycol, diethylene glycol monohexyl ether (DEH), Diethylene glycol mono-2-ethylhexyl ether (EHDG), tetraethylene glycol dimethyl ether, dibutyl maleic acid, and the like. These may be used individually by 1 type, and may be used in mixture of 2 or more types.

The amount of component (C) is preferably 10% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 50% by mass or less, and 25% by mass, based on 100% by mass of the flux composition. % or more and 40 mass % or less is particularly preferable. If the blending amount of the solvent is within the above range, the viscosity of the resulting solder composition can be appropriately adjusted to an appropriate range.

[(D) Component]
The (D) thixotropic agent used in the present embodiment preferably contains (D1) ethylenebisstearic acid amide. By combining the (D1) component and the (A1) component, the fluidity of the coating containing the (A1) component as the main component can be made lower during laser soldering, and the effect of suppressing flux scattering and solder balls can be enhanced. can be done.

From the viewpoint of suppressing solder balls, the amount of component (D1) is preferably 1% by mass or more and 10% by mass or less, and 1% by mass or more and 5% by mass or less, based on 100% by mass of the flux composition. more preferably, and particularly preferably 1.5% by mass or more and 3% by mass or less.

Component (D) may contain a thixotropic agent (component (D2)) other than component (D1) as long as it does not affect the object of the present invention.
Component (D2) includes amides other than component (D1), hydrogenated castor oil, kaolin, colloidal silica, organic bentonite, and glass frit. These may be used individually by 1 type, and may be used in mixture of 2 or more types.

The amount of component (D) is preferably 1% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 15% by mass or less, and 5% by mass, based on 100% by mass of the flux composition. % or more and 12 mass % or less is particularly preferable. When the blending amount is at least the above lower limit, sufficient thixotropic properties can be obtained, and sagging can be sufficiently suppressed. Further, if the blending amount is equal to or less than the above upper limit, the thixotropy is too high, and printing defects do not occur.

[Other ingredients]
In addition to components (A), (B), (C) and (D), other additives may be added to the flux composition used in this embodiment, if necessary. Other additives include antioxidants, defoamers, modifiers, flatting agents, foaming agents, and the like.

[(E) Component]
The (E) solder powder used in this embodiment is preferably composed of only lead-free solder powder, but may be lead-containing solder powder. As the solder alloy in this solder powder, an alloy containing tin (Sn) as a main component is preferable. In addition, the second elements of this alloy include silver (Ag), copper (Cu), zinc (Zn), bismuth (Bi), indium (In) and antimony (Sb). Furthermore, other elements (third and subsequent elements) may be added to this alloy, if necessary. Other elements include copper, silver, bismuth, indium, antimony, and aluminum (Al).
Here, the lead-free solder powder means powder of solder metal or alloy to which lead is not added. However, the presence of lead as an unavoidable impurity in lead-free solder powder is allowed, but in this case, the amount of lead is preferably 300 ppm by mass or less.

Specifically, the solder alloy in the lead-free solder powder includes Sn--Ag, Sn--Ag--Cu, Sn--Cu, Sn--Ag--Bi, Sn--Bi, Sn--Ag--Cu--Bi, Sn--Sb , Sn--Zn--Bi, Sn--Zn, Sn--Zn--Al, Sn--Ag--Bi--In, Sn--Ag--Cu--Bi--In--Sb and In--Ag. Among these, Sn--Ag--Cu based solder alloys are preferably used from the viewpoint of solder joint strength. The melting point of the Sn--Ag--Cu solder is usually 200.degree. C. or higher and 250.degree. C. or lower. Among Sn--Ag--Cu based solders, the melting point of solder with a low silver content is 210.degree. C. to 250.degree. C. (more preferably, 220.degree. C. to 240.degree.

The average particle size of the component (E) is usually 1 μm or more and 40 μm or less, but from the viewpoint of compatibility with electronic substrates having narrow soldering pad pitches, it is more preferably 1 μm or more and 35 μm or less, and 2 μm or more and 30 μm. It is even more preferred that: The average particle size can be measured with a dynamic light scattering particle size measuring device.

[Method for producing solder composition for laser soldering]
The solder composition for laser soldering of the present invention can be produced by blending the flux composition described above and the solder powder (E) described above in the above-described predetermined ratio and stirring and mixing.

[Electronic substrate and its manufacturing method]
Next, the electronic board of this embodiment will be described.
The electronic board of the present embodiment is characterized by having a soldered portion using the solder composition for laser soldering described above. The electronic substrate of this embodiment can be manufactured, for example, by the method of manufacturing an electronic substrate of this embodiment described below.
The method for producing an electronic substrate according to the present embodiment is a method for producing an electronic substrate using the above-described solder composition for laser soldering, and is a method comprising a coating step, a mounting step, and a soldering step described below. be.

In the application step, the solder composition for laser soldering is applied onto the electrodes of the wiring board using a dispenser.
As a dispenser, an air type or a jet type is used.
The wiring board may be a rigid board or a flexible board. The base material of the wiring board is not particularly limited, and known base materials can be used as appropriate.
Metals for the wiring include copper, silver, and gold. Also, the wiring can be formed by a vapor deposition method, a plating method, or the like.
The solder composition for laser soldering of the present embodiment has excellent applicability with a dispenser, and can be applied satisfactorily with such a dispenser.

In the mounting step, an electronic component is mounted on the solder composition for laser soldering.
Electronic components include chips, package components, and the like.
As the mounting device, a known mounting device can be used as appropriate.

In the soldering step, a laser beam is used to heat a solder composition for laser soldering, thereby soldering the electrode and the electronic component.
In the present embodiment, as described above, when laser soldering is performed, a solder composition that can sufficiently suppress the occurrence of solder balls is used, so laser soldering can be performed appropriately.
The type of laser light source for the laser light used for soldering is not particularly limited, and can be appropriately employed according to the wavelength matched to the absorption band of the metal. Examples of laser light sources include solid lasers (ruby, glass, YAG, etc.), semiconductor lasers (GaAs, InGaAsP, organic substances, etc.), liquid lasers (dyes, etc.), and gas lasers (He—Ne, Ar, CO ₂ , excimer etc.).
Laser irradiation conditions are not particularly limited. For example, the spot diameter φ is preferably 0.1 mm or more and 2 mm or less. Also, the irradiation time is preferably 0.1 seconds or more and 5 seconds or less.
The output of laser light is not particularly limited.

In the present embodiment, the flux residue may remain coated on the wiring board on which electronic components are mounted without being washed.
The solder composition for laser soldering and the method for producing an electronic substrate of the present invention are not limited to the above-described embodiments, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention. It is something that can be done.

Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. Materials used in Examples and Comparative Examples are shown below.
((A1) component)
Polymerized rosin: Polymerized rosin (softening point: 140°C, acid value: 145 mgKOH/g, Gardner color number: 8), trade name "China polymerized rosin 140", manufactured by Arakawa Chemical Industries, Ltd. ((A2) component)
Rosin-based resin: Hydrogenated acid-modified rosin (softening point: 130°C, acid value: 245 mgKOH/g), trade name "KE-604", manufactured by Arakawa Chemical Industries, Ltd. (component (B))
Active agent A: glutaric acid Active agent B: picolinic acid (component (C1))
Solvent A: Diisopropyl sebacate, manufactured by Toyokuni Oil Co., Ltd. Solvent B: Dioctyl sebacate, manufactured by Toyokuni Oil Co., Ltd. (Component (C2))
Solvent C: Diethylene glycol monohexyl ether (DEH), Solvent D: Diethylene glycol mono-2-ethylhexyl ether (EHDG), manufactured by Nippon Emulsifier Co., Ltd. Solvent E: Diethylene glycol monoethyl ether acetate (EDGAC), manufactured by Daicel ((D1 )component)
Thixotropic agent A: ethylenebisstearic acid amide, trade name "Slipax E", manufactured by Nippon Kasei Co., Ltd. (component (D2))
Thixotropic agent B: trade name "Slipax ZHH", manufactured by Nippon Kasei Co., Ltd. (component (E))
Solder powder: particle size 15-25 μm, solder melting point 216-220° C., solder composition Sn/Ag/Cu
(other ingredients)
Antioxidant: trade name "Irganox 245", manufactured by BASF

[Example 1]
30% by weight of polymerized rosin, 27% by weight of rosin resin, 1.3% by weight of activator A, 0.5% by weight of activator B, 32% by weight of solvent A, 2% by weight of thixotropic agent A, 5.2% by weight of thixotropic agent B, and oxidation 2 mass % of the inhibitor was put into each container and mixed using a scouring machine to obtain a flux composition.
12.6% by mass of the resulting flux composition and 87.4% by mass of solder powder (100% by mass in total) were charged into a container and mixed with a kneader to obtain solder having the composition shown in Table 1 below. A composition was prepared.

[Examples 2 to 4]
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 below.
[Comparative Examples 1 to 3]
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 below.

<Evaluation of Solder Composition>
The solder composition was evaluated (viscosity, solder balls, wettability) by the following methods. Table 1 shows the results obtained.
(1) Viscosity The viscosity of the solder composition at a temperature of 25° C. was measured using a spiral viscometer (product name “PCU-02”, manufactured by Malcom).
(2) Solder balls Solder balls were evaluated under the following two test conditions.
(i) Test 1
A substrate having 100 copper pads of 0.3 mm diameter was printed with a solder composition on each copper pad using a 130 μm thick metal mask. After that, laser soldering was performed on each copper pad under the conditions of a laser wavelength of 808 nm, a spot diameter of 400 μm, and an irradiation time of 0.5 seconds to obtain a test substrate. Then, the test substrate was visually observed, and solder balls were evaluated according to the following criteria.
A: The number of solder balls is 0.
Good: The number of solder balls is 1 or more and less than 10.
x: The number of solder balls is 10 or more.
(ii) Test 2
A substrate having 100 copper pads of 1 mm diameter was printed with a solder composition on each copper pad using a 130 μm thick metal mask. After that, laser soldering was performed on each copper pad under the conditions of a laser wavelength of 808 nm, a spot diameter of 1.2 mm, and an irradiation time of 1.0 second to obtain a test substrate. Then, the test substrate was visually observed, and solder balls were evaluated according to the following criteria.
A: The number of solder balls is 30 or less.
Good: The number of solder balls is 30 or more and less than 50.
x: The number of solder balls is 50 or more.
(3) Wettability The pads (200 pads in total) of the two evaluation boards (Test 1 and Test 2) obtained in the above (2) solder ball test were visually observed. Then, wettability was evaluated according to the following criteria.
◯: There is no insufficiently wetted pad.
Δ: The number of insufficiently wetted pads is 1 or more and less than 5.
x: The number of insufficiently wetted pads is 5 or more.

As is clear from the results shown in Table 1, when the solder composition for laser soldering of the present invention was used (Examples 1 to 4), solder balls were sufficiently generated when laser soldering was performed. It was confirmed that the

INDUSTRIAL APPLICABILITY The solder composition for laser soldering of the present invention can be suitably used as a technology for mounting components on printed wiring boards of electronic devices using laser light.

Claims (3)

A flux composition containing (A) a rosin resin, (B) an activator, (C) a solvent and (D) a thixotropic agent, and (E) a solder powder,
The component (A) contains (A1) a polymerized rosin having a softening point of 130° C. or higher and an acid value of 200 mgKOH/g or lower,
The component (C) contains (C1) dialkyl sebacate,
The alkyl in the component (C1) is straight-chain alkyl having 1 to 10 carbon atoms or branched-chain alkyl having 3 to 10 carbon atoms,
A solder composition for laser soldering, wherein the compounding amount of the component (C1) is 50% by mass or more with respect to 100% by mass of the component (C). In the solder composition for laser soldering according to claim 1,
A solder composition for laser soldering, wherein the component (D) contains (D1) ethylenebisstearic acid amide. A method for manufacturing an electronic substrate using the solder composition for laser soldering according to claim 1 or 2,
A coating step of coating the solder composition on the electrodes of the wiring board using a dispenser;
A mounting step of mounting an electronic component on the solder composition;
and a soldering step of heating the solder composition using a laser beam to solder-bond the electrode and the electronic component.