JP7262343B2 - Flux and molded solder - Google Patents

Description

TECHNICAL FIELD The present invention relates to flux and molded solder used for joining electronic components to electronic circuits formed on substrates.

2. Description of the Related Art In recent years, from the viewpoint of energy and environmental problems, power semiconductor devices for controlling and supplying electric power, so-called power semiconductors, have attracted attention. Among them, semiconductor elements using SiC (abbreviated as SiC elements) are used for various purposes because they have little power loss and can handle large currents. Since SiC elements can operate at high temperatures of 300 ° C. or higher, it can be used as a bonding material when bonding SiC elements to a circuit board, for example, a DCB substrate (Direct Copper Bond substrate) in which a copper circuit board is directly bonded to a ceramic substrate. is required to have a solidus temperature of 300° C. or higher so as not to melt during device operation.

Conventionally, as a bonding material used for bonding highly heat-resistant power semiconductors such as SiC elements, for example, metal powder containing Ag is placed on a DCB substrate, and this is heated while being pressed in one direction or both directions. and densifying (sintering) the metal powder. In this prior art, in order to sinter a metal powder containing Ag with a high liquidus temperature, for example, it is necessary to heat and pressurize for a long time under high temperature conditions of 200 to 300 ° C., and the production of power semiconductors. There was a problem of sexual interfering.

Therefore, as a technique for efficiently joining a SiC element onto a DCB substrate, a molded solder having a high solidus temperature and a high liquidus temperature has been proposed (see Patent Document 1). Molded solder, also called preformed solder, is molded into predetermined shapes such as washer, ring, pellet, disk, ribbon, and wire shapes. The formed solder is sandwiched between the DCB substrate and the SiC element, and this is heated to mount the SiC element on the DCB substrate.

As one of the molded solders, there is known one in which the surface of the molded solder is uniformly dried and coated with flux. This type of molded solder does not require a flux application process, and is suitable for simplification and automation of soldering work. Known fluxes used in this type of molded solder include dimer acid, which is a reaction product of oleic acid and linoleic acid, and trimer acid, which is a reaction product of oleic acid and linoleic acid (Patent Document 2).

Japanese Patent No. 6529632 Japanese Patent No. 6501003

The flux disclosed in Patent Document 2 uses dimer acid, trimer acid, etc., which are substances having a melting point higher than that of solder. Therefore, there is a problem that the substance in the flux remains as a solid when the solder melts, hindering the contact between the solder and the object to be joined, and leaving residue on the surface of the solidified solder and the electronic component. Moreover, when the flux is expected to have an effect as an activator, the activity cannot be exhibited if the substance in the flux remains solid. Therefore, in order to liquefy the flux containing dimer acid or trimer acid with a high melting point, it is necessary to apply a temperature higher than the melting temperature of the solder, which causes a problem of increasing the heating time.

The present invention has been proposed to solve the above problems. An object of the present invention is to provide a molded solder flux that does not interfere with the bonding between an electronic component and a substrate when solder is melted by substances in the flux, and that enables the solder to be melted without applying excessive heat. To provide a molded solder coated with an excellent flux.

The flux of the present invention is
A molded solder flux obtained by pressure-molding a plurality of types of metal powder,
The metal powder contains a solder alloy powder and one or more powders of Cu, Au, Ag, and Al having a higher liquidus temperature (T) than the solder alloy powder,
The flux contains an organic acid,
The melting point of the organic acid having the highest melting point among the organic acids is equal to or lower than the liquidus temperature (T) of the solder alloy powder,
The boiling point or decomposition temperature of the organic acid having the lowest boiling point or decomposition temperature among the organic acids exceeds the liquidus temperature (T) of the solder alloy powder,
The boiling point or decomposition temperature of the organic acid having the highest boiling point or decomposition temperature among the organic acids is lower than the main reflow heating temperature of the molding solder.

The present invention can be configured as follows.
(1) The organic acid is one or a combination of stearic acid, glutaric acid and azelaic acid.
(2) The flux contains one or more of base resin, solvent, activator and thixotropic agent.
(3) The boiling point or decomposition temperature of the organic acid is lower than the main reflow heating temperature of the molding solder.
(4) The metal powder contains solder alloy powder and powder of one or more of Cu, Au, Ag and Al.
(5) The solder alloy powder has a liquidus temperature (T) in the range of 130°C to 220°C.
(6) Molded solder having at least part of its surface coated with the flux for molded solder is also an aspect of the present invention.

ADVANTAGE OF THE INVENTION According to the present invention, it is possible to obtain flux and solder for molded solder that enable reliable soldering of an electronic component to a substrate and shorten the heating time during soldering.

A temperature profile showing the temperature conditions during reflow of molded solder using Sn-50In solder alloy powder and Cu metal powder. A temperature profile showing temperature conditions during reflow of molded solder using Sn-3.0Ag-0.5Cu solder alloy powder and Cu metal powder.

An embodiment of the molded solder with flux of the present invention will be described in detail below.

<Multiple types of metal powder>
The molded solder of the present invention is composed of a solder alloy powder and another metal powder having a higher liquidus temperature than the solder alloy powder. Examples of alloying elements constituting solder alloys include Sn, Ag, Cu, Bi, Zn, In, Ga, Sb, Au, Pd, Ge, Ni, Cr, Al, P and In. Solder alloys with multiple combinations of elements may be used. Among them, alloys containing Sn, particularly alloys containing 30% by mass or more of Sn are preferably used. More preferably, the Sn content is 42% by mass or more and 97% by mass or less.
A solder alloy having a solidus temperature of 250° C. or less is preferably used. Specifically, Sn-50In, Sn58Bi, Sn57Bi1Ag, and SAC305 solder alloys, which have a liquidus temperature in the range of 130°C to 220°C, depend on the boiling point, sublimation temperature, and decomposition temperature of the organic acid. preferable.

The molded solder of this embodiment is molded by pressure as described later. That is, since no heating is involved during molding, the solder alloy powder and the metal powder with a higher liquidus temperature have not yet melted and diffused in the molded solder before soldering, and the melting temperature has not changed. . When performing solder bonding using the shaped solder of the present embodiment, the solder alloy powder can be sufficiently melted even at the heating temperature for bonding using general lead-free solder, which has a peak temperature of about 250° C., for example. The molded solder of this embodiment can bond a power semiconductor such as a SiC element onto a DCB substrate even when heated at about 250.degree.

The average particle size of the solder alloy powder is preferably 1 μm or more and 30 μm or less. The average particle size is more preferably 2 µm or more and 25 µm or less, and particularly preferably 2 µm or more and 8 µm or less.

The metal powder having a higher liquidus temperature than the solder alloy powder preferably has a liquidus temperature difference of 50° C. or more. As such a metal powder, one or a plurality of powders of Cu, Au, Ag, and Al, which are excellent in conductivity and have a high liquidus temperature, can be used. Among them, Cu powder having a melting temperature as high as 1085° C. is preferable.

In the present embodiment, the Cu powder content is preferably 40% by mass or more and 80% by mass or less. The content ratio is more preferably 40% by mass or more and 60% by mass or less, and particularly preferably 40% by mass or more and 50% by mass or less. By setting the content of the Cu powder within this range, it is possible to further suppress remelting of the formed solder after soldering, and it is possible to perform good bonding between the DCB substrate and the power semiconductor. rate can be improved.

In the case of molded solder using Sn-50In solder alloy powder and Cu powder, the content ratio of Sn-50In solder alloy powder and Cu powder is Sn-50In solder alloy powder:Cu powder=30:70 to 60:40. is preferred. The Cu powder preferably has an average particle size of 1 μm or more and 30 μm or less. The average particle size is more preferably 1 μm or more and 10 μm or less, and particularly preferably 1 μm or more and 5 μm or less.

<Molding of molded solder>
The molded solder of the present embodiment is produced by mixing and dispersing a plurality of types of metal powders to prepare a mixture of a plurality of types of metal powders. It can be produced by pressing a compacting container.

As a method of mixing and dispersing a plurality of types of metal powders to prepare a mixture of the plurality of types of metal powders, for example, a method of mixing and dispersing a plurality of types of metal powders using a mixer, a stirrer, a sieve, or the like. is mentioned. Any method may be used as long as a plurality of types of metal powders can be mixed and dispersed. Before preparing a mixture of a plurality of types of metal powders, it is desirable to pass the plurality of types of metal powders through a sieve or the like to remove agglomerates and the like.
As the pressure molding container for containing the mixture of metal powders, any container that can be used for pressure molding of powders can be used. For example, a powder retaining ring made of aluminum or the like is preferably used.

As a method for pressurizing the mixture of the plurality of types of metal powders and the pressure-molded container, any method may be used as long as the powder can be pressure-molded (solidified), for example, using a briquette machine. be able to. Note that the pressurization is preferably performed at room temperature. The pressurization conditions may be any conditions as long as the mixture of the plurality of types of metal powders can be molded (solidified), and can be appropriately adjusted depending on the metals constituting the plurality of types of metal powders. For example, pressurization conditions of 200 kN or more can be done at

The thickness of the molded solder of the present embodiment can be appropriately adjusted depending on the DCB substrate to be used, the type of element to be mounted, and the types of the plurality of types of metal powder used for molding the molded solder. Preferably.

<Flux>
The flux of this embodiment includes, for example, a flux containing a base resin, a solvent, an activator, and a thixotropic agent. The types and blending amounts of these components can be appropriately adjusted.

Examples of base resins include starting rosins such as gum rosin, wood rosin and tall oil rosin, and derivatives obtained from the starting rosins. Examples of the derivatives include purified rosin, hydrogenated rosin, disproportionated rosin, polymerized rosin, acid-modified rosin, phenol-modified rosin and α,β unsaturated carboxylic acid-modified products (acrylated rosin, maleated rosin, fumarized rosin). rosin, etc.), and purified products, hydrides and disproportionated products of the polymerized rosin, and purified products, hydrides and disproportionated products of the α,β unsaturated carboxylic acid-modified product, and the like, one or Two or more types can be used. The base resin can be added in the range of 0% by mass to less than 30% by mass with respect to 100% by mass of the flux composition.

The active agent contains one or more organic acids. The organic acid includes organic compounds having a carboxyl group, including monocarboxylic acids and dicarboxylic acids, and it is necessary to prevent the organic acid from remaining as a solid when the solder melts and hindering bonding with the solder. The melting point of the organic acid is preferably lower than the liquidus temperature (T) of the metal powder having the lowest liquidus temperature among the plurality of metal powders. More preferably, if it is a substance that volatilizes in the reflow temperature range, it is possible to reduce flux residue. The boiling point or decomposition temperature of the organic acid is preferably higher than the liquidus temperature (T). Specific examples include organic acids such as stearic acid, glutaric acid, azelaic acid, pimelic acid, and sebacic acid. The organic acid can be added in a range of 0.5% by mass to 100% by mass with respect to 100% by mass of the flux composition.

Here, the flux composition is composed of a solvent, an organic acid, and other additives. In the case of organic acids that are solid at room temperature, the proportion of the solvent in the flux composition is large for the convenience of coating operations. Therefore, it may be desirable to add about 0.5% by mass of the organic acid, and if the organic acid is liquid or can be powdered or sprayed even if it is solid, the organic acid should be 100% by mass. It may be added amount.

In addition, as the activator, a non-dissociative activator composed of a non-dissociable halogenated compound, an amine-based activator (halogen-free), and the like may be contained. In this case, the content of the activator is desirably in the range of 20 mass % or less with respect to the amount of the organic acid added. If the amount of the activator added exceeds 20% by mass, the flux function of the organic acid is impaired.

The non-dissociation type activator includes non-salt organic compounds to 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, fluorine and iodine such as chloride, bromide, fluoride and iodide. may have two or all of the respective covalent bonds. 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 compound, 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, 1,4-dibromo-2-butanol, and brominated alcohols such as tribromoneopentyl alcohol, chlorinated alcohols such as 1,3-dichloro-2-propanol and 1,4-dichloro-2-butanol, fluorinated alcohols such as 3-fluorocatechol, and In addition, compounds similar to these may be mentioned. Halogenated carboxyl compounds include iodinated carboxyl compounds such as 2-iodobenzoic acid, 3-iodobenzoic acid, 2-iodopropionic acid, 5-iodosalicylic acid, and 5-iodoanthranilic acid, 2-chlorobenzoic acid, and Chlorinated carboxyl compounds such as 3-chloropropionic acid, brominated carboxyl compounds such as 2,3-dibromopropionic acid, 2,3-dibromosuccinic acid, and 2-bromobenzoic acid, and other like compounds. .

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

As the solvent, water, an ester solvent, an alcohol solvent, a glycol ether solvent, a flux solvent such as terpineols can be used. Examples include ethanol and isopropyl alcohol. The flux of the present invention is mainly composed of an organic acid having a melting point lower than the liquidus temperature (T) of the metal powder having the lowest liquidus temperature among a plurality of metal powders, so that the viscosity of the organic acid itself is is relatively low, and there are many organic acids that can be applied to the surface of molded solder by themselves. In this case, the solvent is not always necessary, and the amount of solvent used is such that the coating work can be carried out smoothly in consideration of the properties and amount of addition of the base resin and the organic acid.
In the case of an organic acid that is solid at room temperature, it is preferable to contain the solvent in an amount of 50% by mass or more and 99.5% by mass or less with respect to 100% by mass of the flux composition in order to facilitate uniform coating on the preform. . Isopropyl alcohol is particularly preferred in terms of compatibility with organic acids.

Thixotropic agents include hydrogenated castor oil, polyamides, amides, kaolin, colloidal silica, organic bentonites, and glass frits. These thixotropic agents may be used singly or in combination of two or more. The content of the thixotropic agent is preferably 0% by mass or more and 20% by mass or less with respect to 100% by mass of the flux composition. Addition of a thixotropic agent makes it possible to improve the coatability and adhesion of the flux to the molded solder surface.

The effect of the molded solder with flux of the present invention will be described below with reference to examples and comparative examples. It should be noted that the present invention is in no way limited by the following examples.

A copper plate bondability test was conducted using the following members.
<Material>
Molded solder 5 mm × 5 mm × 0.1 mmt
Copper plate 30mm x 30mm x 0.3mmt
Copper chip 5mm x 5mm x 1.3mmt

<Evaluation method>
A flux was prepared by appropriately dissolving each organic acid in isopropyl alcohol at a concentration of 0.5% by mass to 50% by mass. Subsequently, the above-mentioned flux was applied to the prepared molded solder and air-dried to obtain a flux-coated preform sample. At this time, the film thickness of the flux coat was adjusted to 3 to 5 μm. The film thickness was confirmed using a laser microscope VK-X1050 manufactured by KEYENCE CORPORATION. This flux-coated molded solder is placed on a copper plate, a copper chip corresponding to an electronic component is mounted on it, a pressure of 0.6 Mpa is applied from above the copper chip, and under any of the following conditions Reflow heating was performed.
<Reflow condition 1>
Using a high-temperature observation device (SMT Scope SK-5000, manufactured by Sanyo Seiko Co., Ltd.), under the condition of an oxygen concentration of 100 ppm, preheating shown in FIG. Heated with a temperature profile of 1 min.
<Reflow condition 2>
Using a high-temperature observation device (SMT Scope SK-5000, manufactured by Sanyo Seiko Co., Ltd.), the sample was heated at an oxygen concentration of 100 ppm with the temperature profile shown in FIG. 2 for main heating at 240° C. for 5 minutes.
<Evaluation Criteria>
After that, the copper chip was sheared with a shearing device (Dage 4000 bond tester, manufactured by Nordson), and the bonding area was measured from the fracture surface to evaluate bondability according to the following criteria.
A: bonding area 95% or more B: bonding area 90% or more and less than 95% C: bonding area less than 90% Evaluations A and B are practical when mounting electronic components, and evaluation C is evaluated as poor bonding. should be.

<Example 1>
The molded solder was molded using a Sn-50In solder alloy powder (a) with a liquidus temperature of 120°C and a Cu metal powder (e) with a melting temperature of 1085°C. The content of the metal powder is metal powder (a):metal powder (e)=60:40.
Stearic acid having a liquidus temperature of 70°C and a boiling point or decomposition temperature of 383°C was used as the organic acid.
The reflow temperature profile was the temperature profile shown in FIG. 1 (reflow condition 1).

<Example 2>
The molding solder and reflow conditions were the same as in Example 1, and azelaic acid having a liquidus temperature of 106°C and a boiling point or decomposition temperature of 286°C was used as the organic acid.

<Example 3>
The melting point deforming solder and reflow conditions were the same as in Example 1, and glutaric acid with a liquidus temperature of 98°C and a boiling point or decomposition temperature of 200°C was used as the organic acid.

<Comparative Example 1>
The molding solder and reflow conditions were the same as in Example 1, and the organic acid used was adipic acid with a liquidus temperature of 153°C and a boiling point or decomposition temperature of 338°C.

A summary of the results of Examples 1 to 3 and Comparative Example 1 is shown in Table 1 below. In this specification, among the numerical values shown in the tables, the unit for the content of each metal powder is % by mass unless otherwise specified.

In Examples 1 and 2, good results of bonding area of 90% or more and less than 95% were obtained. In Example 3, an excellent result of a bonding area of 95% or more was obtained. In Example 3, heating to 200° C. or higher, which is the boiling point or decomposition temperature of the organic acid, ensures volatilization of the organic acid, and the organic acid remains as a solid to inhibit contact between the solder and the object to be joined. It is considered that the effect as an activator was sufficiently exhibited from the fact that there was no reaction and the fact that the organic acid was reliably melted. Since the organic acid volatilizes, residue-free bonding is also possible. On the other hand, Comparative Example 1 uses adipic acid (153° C.) whose melting point of the organic acid is higher than the liquidus temperature (120° C.) of the metal powder with the lowest liquidus temperature among the metal powders. , the bonding area was less than 90%.

As can be seen from these examples, even in Examples 1 and 2 in which the evaluation was B, the main heating temperature in the reflow profile was set to a temperature higher than the boiling point of the organic acid within the range of the heat resistant temperature of the electronic component. , it is possible to obtain better soldering properties as in Example 3.

<Example 4>
Next, the molded solder was molded using a Sn58Bi solder alloy powder (b) with a liquidus temperature of 139°C and a metal powder (e) made of Cu with a melting temperature of 1085°C. . The content of the metal powder is metal powder (b):metal powder (e)=60:40.
Stearic acid having a liquidus temperature of 70°C and a boiling point or decomposition temperature of 383°C was used as the organic acid.
The reflow temperature profile was the temperature profile shown in FIG. 1 (reflow condition 1).

<Example 5>
The molding solder and reflow conditions were the same as in Example 2, and azelaic acid having a liquidus temperature of 106°C and a boiling point or decomposition temperature of 286°C was used as the organic acid.

<Example 6>
The molding solder and reflow conditions were the same as in Example 2, and glutaric acid with a liquidus temperature of 98°C and a boiling point or decomposition temperature of 200°C was used as the organic acid.

<Comparative Example 2>
The molding solder and reflow conditions were the same as in Example 2, and succinic acid with a liquidus temperature of 182°C and a boiling point or decomposition temperature of 235°C was used as the organic acid.

A summary of the results of Examples 4 to 6 and Comparative Example 2 is shown in Table 2 below.

In Examples 4 and 5, good results of bonding area of 90% or more and less than 95% were obtained. In Example 6, an excellent result of a bonding area of 95% or more was obtained. Like Example 3, the excellent results of Example 6 are believed to be due to the fact that heating to 200° C. or higher, which is the boiling point or decomposition temperature of the organic acid, ensured volatilization of the organic acid. On the other hand, Comparative Example 2 uses succinic acid (182 ° C.) whose melting point of the organic acid is higher than the liquidus temperature (139 ° C.) of the metal powder with the lowest liquidus temperature among the metal powders. , the bonding area was less than 90%.

As can be seen from these examples, even in Examples 4 and 5 in which the evaluation was B, the main heating temperature in the reflow profile was set to a higher temperature than the boiling point of the organic acid within the range of the heat resistant temperature of the electronic component. , it is possible to obtain better soldering properties as in Example 6.

<Example 7>
The molded solder was molded using a Sn57Bi1Ag solder alloy powder (c) with a liquidus temperature of 139°C and a metal powder (e) of Cu with a melting temperature of 1085°C. The content of the metal powder is metal powder (c):metal powder (e)=60:40.
Stearic acid having a liquidus temperature of 70°C and a boiling point or decomposition temperature of 383°C was used as the organic acid.
The reflow temperature profile was the temperature profile shown in FIG. 1 (reflow condition 1).

<Example 8>
The molding solder and reflow conditions were the same as in Example 7, and azelaic acid having a liquidus temperature of 106°C and a boiling point or decomposition temperature of 286°C was used as the organic acid.

<Comparative Example 3>
The molding solder and reflow conditions were the same as in Example 7, and succinic acid with a liquidus temperature of 182°C and a boiling point or decomposition temperature of 235°C was used as the organic acid.

A summary of the results of Examples 7, 8 and Comparative Example 3 is shown in Table 3 below.

In Examples 7 and 8, good results of bonding areas of 90% or more and less than 95% were obtained. On the other hand, in Comparative Example 3, succinic acid (182° C.), which has a melting point of the organic acid that is higher than the liquidus temperature (139° C.) of the metal powder with the lowest liquidus temperature among the metal powders, was used. The bonding area was less than 90%. As can be seen from the above examples, even in Examples 7 and 8 in which the evaluation was B, the main heating temperature in the reflow profile was set to a higher temperature than the boiling point of the organic acid within the range of the heat resistant temperature of the electronic component. , it is possible to obtain better soldering properties.

<Example 9>
The molded solder was molded using a SAC305 solder alloy powder (d) with a liquidus temperature of 220°C and a metal powder (e) made of Cu with a melting temperature of 1085°C. The content of the metal powder is metal powder (d):metal powder (e)=60:40.
Stearic acid having a liquidus temperature of 70°C and a boiling point or decomposition temperature of 383°C was used as the organic acid.
The reflow temperature profile was the temperature profile shown in FIG. 2 (reflow condition 2).

<Example 10>
The molding solder and reflow conditions were the same as in Example 9, and azelaic acid having a liquidus temperature of 106°C and a boiling point or decomposition temperature of 286°C was used as the organic acid.

<Comparative Example 4>
The molding solder and reflow conditions were the same as in Example 9, and fumaric acid having a liquidus temperature of 286°C and a boiling point or decomposition temperature of less than 300°C was used as the organic acid.

<Comparative Example 5>
The molding solder and reflow conditions were the same as in Example 9, and malonic acid with a liquidus temperature of 135°C and a boiling point or decomposition temperature of 140°C was used as the organic acid.

<Comparative Example 6>
The molded solder was the same as in Example 9, and the organic acid used was succinic acid with a liquidus temperature of 98°C and a boiling point or decomposition temperature of 200°C.
The reflow temperature profile was the temperature profile shown in FIG. 1 (reflow condition 1).

A summary of the results of Examples 9, 10 and Comparative Examples 4 to 6 is shown in Table 4 below.

In Examples 9 and 10, good results of a bonding area of 90% or more and less than 95% were obtained. On the other hand, Comparative Example 4 used fumaric acid (286° C.) whose melting point of the organic acid was higher than the liquidus temperature (220° C.) of the metal powder with the lowest liquidus temperature among the metal powders. The bonding area was less than 90%. Comparative Example 5 uses malonic acid (140° C.) whose boiling point or decomposition temperature of the organic acid is lower than the liquidus temperature (220° C.) of the metal powder with the lowest liquidus temperature. %. In Comparative Example 6, since glutaric acid (200° C.) was used, the bonding area was less than 90%.
As can be seen from the above examples, even in Examples 9 and 10 in which the evaluation was B, the main heating temperature in the reflow profile was set to a higher temperature than the boiling point of the organic acid within the range of the heat resistant temperature of the electronic component. , it is possible to obtain better soldering properties.

In this way, the flux-coated molded solder according to Examples 1 to 10 protects the solder surface without the flux interfering with the bonding when the solder is melted, and the solder can be melted without applying excessive heat.

Claims (5)

A flux for molded solder that coats at least a part of the surface of molded solder obtained by pressure-molding a plurality of types of metal powder,
The metal powder contains a solder alloy powder and one or more powders of Cu, Au, Ag, and Al having a higher liquidus temperature (T) than the solder alloy powder,
The flux contains an organic acid,
The melting point of the organic acid having the highest melting point among the organic acids is equal to or lower than the liquidus temperature (T) of the solder alloy powder,
The boiling point or decomposition temperature of the organic acid having the lowest boiling point or decomposition temperature among the organic acids exceeds the liquidus temperature (T) of the solder alloy powder,
A flux for molding solder , wherein the boiling point or decomposition temperature of the organic acid having the highest boiling point or decomposition temperature among the organic acids is lower than the main reflow heating temperature of the molding solder. 2. The flux for molding solder according to claim 1, wherein said organic acid is one or more of stearic acid, glutaric acid and azelaic acid. 3. The flux for molding solder according to claim 1, which contains one or more of a base resin, a solvent and a thixotropic agent. The flux for forming solder according to any one of claims 1 to 3, wherein the solder alloy powder has a liquidus temperature (T) in the range of 130°C to 220°C. A molded solder obtained by pressure-molding a plurality of types of metal powder,
The metal powder contains a solder alloy powder and one or more powders of Cu, Au, Ag, and Al having a higher liquidus temperature (T) than the solder alloy powder,
The melting point of the organic acid having the highest melting point among the organic acids is equal to or lower than the liquidus temperature (T) of the solder alloy powder,
The boiling point or decomposition temperature of the organic acid having the lowest boiling point or decomposition temperature among the organic acids exceeds the liquidus temperature (T) of the solder alloy powder,
A molded solder having a coating of the flux for molded solder according to any one of claims 1 to 4 provided on at least part of the surface of the molded solder.

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