KR102122166B1 - Flux for solder paste, solder paste, method of forming solder bumps using solder paste, and method of manufacturing joined body - Google Patents

Abstract

The flux for a solder paste of the present invention is a flux for a solder paste containing a viscous agent, a solvent, and a thixotropic agent, having an acid value of 100 mgKOH/g or less, and a reduction rate at 300°C in a thermogravimetric measurement of 80 mass%. Or more, the viscosity is 0.5 Pa·s or more, and the tacking force is 1.0 N or more.

Description

Flux for solder paste, solder paste, method of forming solder bumps using solder paste, and method of manufacturing joined body

The present invention relates to a flux for solder paste, a solder paste, a method for forming a solder bump using a solder paste, and a method for manufacturing a joined body, which can obtain solder used for bonding electronic components to a substrate.

The present application claims priority to Japanese Patent Application No. 2017-147084 filed in Japan on July 28, 2017 and Japanese Patent Application No. 2018-133872 filed in Japan on July 17, 2018, and the contents thereof. Use it here.

Conventionally, in soldering, a solder paste composed of a flux containing a rosin, a solvent, a thixotropic agent, and an active agent and a solder powder is used. When a solder bump is formed using such a solder paste, when the solder paste is applied onto the substrate and reflowed, residues based on rosin or the like remain on the upper surface of the solder, and the residue is cleaned with a chemical or the like. There is a need, it is complicated.

In order to reduce the trouble of cleaning such a residue, a flux in which no residue is generated after soldering and a solder paste containing the flux are known (see Patent Document 1).

Since the flux described in Patent Document 1 contains ammonium formate and a liquid at room temperature and contains an aliphatic polyalcohol having a boiling point of 150° C. or higher at atmospheric pressure, it has reducing properties and efficiently reduces the oxide film, thereby forming a substrate, etc. The generated oxide film is being removed. In the configuration of Patent Document 1, the residue of the flux after soldering electronic components or the like to the substrate is suppressed.

However, since the flux described in Patent Document 1 and the solder paste containing the flux decompose at a low temperature, the solder surface is exposed without being covered by the flux. For this reason, there is a fear that the surface of the solder is re-oxidized.

On the other hand, a method of forming a solder bump capable of suppressing reoxidation of the surface of the solder has been proposed (see Patent Document 2).

In the method of forming the solder bump described in this patent document 2, a mask having an opening is disposed on a substrate, the solder paste is printed so as to fill the opening with a solder paste containing flux and solder powder, and the mask is peeled off. , As a method of forming a solder bump by reflowing a bump precursor on a substrate, the flux contains a rosin, a solvent and a thixotropic agent, the acid value of the flux is 100 mgKOH/g or less, and the halogen content of the flux is 0.03 It is a mass% or less, and has a structure in which the reflow treatment is performed under a formic acid gas atmosphere and/or an atmosphere of a gas in which formic acid is decomposed by heat.

In the method of forming the solder bumps, the reflow treatment is performed under a formic acid gas atmosphere and/or an atmosphere of a gas in which formic acid is decomposed by heat to reduce oxide films such as solder powder to smooth solder melting.

Japanese Patent Application Publication No. 2011-83809 (A) Japanese Patent Application Publication No. 2016-78095 (A)

By the way, in the method of forming the solder bumps described in Patent Document 2, since a flux containing rosin as a main component is used, when the solder paste containing the flux used in this formation method reflows, rosin-based residues are generated. In that respect, it is necessary to clean the solder. Moreover, even if the solder is cleaned, the residue may not be completely removed, and in this case, there is a fear that the bonding property between the electronic component and the substrate is deteriorated.

The present invention has been made in consideration of such circumstances, and provides a flux for solder paste, a solder paste, a method for forming a solder bump using a solder paste, and a method for manufacturing a joined body, which can obtain solder capable of suppressing generation of residues. It aims to do.

The flux for a solder paste of one embodiment of the present invention (hereinafter referred to as "the flux for a solder paste of the present invention") is a flux for a solder paste containing a viscous agent, a solvent, and a thixotropic agent, with an acid value of 100 mgKOH/ g or less, the reduction rate at 300°C in the thermogravimetric measurement is 80 mass% or more, the viscosity is 0.5 Pa·s or more, and the tacking force is 1.0 N or more.

In addition, tacking force means the adhesive strength with respect to a board|substrate when the flux for solder is apply|coated to a board|substrate, etc., and is measured based on JISZ3284.

In the present invention, since the flux for the solder paste has a reduction rate at 300° C. of 80% by mass or more in thermogravimetric measurement, when the solder paste containing the flux for the solder paste is reflowed, there are many volatile components as the flux. Even when the solder paste containing the flux for solder paste is reflowed to form solder bumps, generation of residues can be suppressed.

Moreover, when the viscosity of the flux for solder paste is less than 0.5 Pa·s, the viscosity of this flux is too small, so that a solder paste cannot be formed, and there is a fear that it cannot be applied to a substrate or the like. In addition, when the tacking force of the flux for solder paste is less than 1.0 N, the adhesive strength is low. Therefore, when the solder paste containing this flux is applied to a substrate or the like, there is a fear that the applied solder paste flows off the substrate or the like. . On the other hand, in the present invention, since the viscosity of the flux is 0.5 Pa·s or more, and the tacking force is 1.0 N or more, shape retention of the solder paste made of the flux for solder paste and the solder powder can be secured.

In addition, by setting the acid value of the flux for the solder paste to 100 mgKOH/g or less, the reaction of the remaining flux residue and surrounding metal parts, such as copper in the wiring, is suppressed and corrosion is suppressed. This can ensure long-term reliability of the joined body. In addition, since the reaction between the solder powder and the flux when using a solder paste is suppressed, and the viscosity change as a solder paste is reduced, a solder paste requiring refrigeration is usually stored at room temperature for a long period of time (for example, 6 months or more). ) Can be preserved, and long-term storage can be improved.

Moreover, when this acid value exceeds 100 mgKOH/g, the generation of the reduced water generated in the reduction reaction of the flux for the solder paste and the oxide of the solder powder increases, and the voids in the solder bumps increase. It is set at 100 mgKOH/g or less.

In addition, the flux for solder paste of the present invention preferably does not contain rosin or an active agent contained in a conventional flux, but may be contained in a minor amount as long as it satisfies the requirements of the thermogravimetric measurement and acid value.

As a preferable aspect of the flux for solder pastes of the present invention, the rosin content may be 10 mass% or less.

Even if rosin is contained in the flux for solder paste, if the amount is 10 mass% or less, the acid value of the flux for solder paste can be 100 mgKOH/g or less. In other words, the flux for the solder paste is not prevented from being contained as long as the rosin is in the range of 10% by mass or less.

The solder paste of another aspect of the present invention (hereinafter referred to as "the solder paste of the present invention") is made by mixing the above-mentioned solder paste flux and solder powder.

Since the solder paste of the present invention contains the flux for the solder paste, even when the solder paste is reflowed, generation of residues can be suppressed, and deterioration of bondability caused by residues can be suppressed. .

As a preferable aspect of the solder paste of this invention, the content rate of the said solder paste flux should just be 30 volume% or more and 90 volume% or less.

When the content of the flux for the solder paste is less than 30% by volume, there is a concern that the paste cannot be formed or becomes a dried paste, and the solder paste cannot be applied to a substrate or the like. On the other hand, if the content of the flux for the solder paste exceeds 90% by volume, the viscosity of the solder paste may be excessively lowered to deteriorate the coating performance, or the flux and the solder powder may be easily separated.

On the other hand, in the above aspect, since the solder paste flux content is 30% by volume or more and 90% by volume or less, a solder paste having an appropriate viscosity can be formed, and deterioration of coating performance and separation of flux and solder powder are suppressed. can do.

In a preferred embodiment of the solder paste of the present invention, the solder powder is Sn-Ag-Cu solder powder, Sn-Cu solder powder, Sn-Ag solder powder, Pb-Sn solder powder, Au-Sn solder powder, Au- It may be either Ge solder powder or Au-Si solder powder.

According to the above aspect, any of the above various powders can be used as the solder powder. In particular, when the solder powder is Au-Sn solder powder, since the solder paste containing the Au-Sn solder powder is a solder paste having a high melting point, it is easy to bounce the residue upon reflow, but the flux for the solder paste Since the generation of residues is suppressed by using, it is possible to prevent splashing of residues during reflow.

A method of forming a solder bump using a solder paste of another aspect of the present invention (hereinafter referred to as "the method of forming a solder bump using the solder paste of the present invention") is provided with a mask having an opening on a substrate, and within the opening The solder paste is printed to fill the solder paste, and after peeling off the mask, the bump precursor on the substrate is reflowed under a formic acid gas atmosphere to form a solder bump.

According to this configuration, by suppressing the generation of the residue, the cleaning process of the solder bumps can be omitted, and the reflow treatment is performed under a formic acid gas atmosphere, and thus contains rosin, which reduces and removes oxides. Even if it is not made, it is possible to smooth the solder melt by reducing the oxide film on the substrate and the oxide film on the surface of the solder.

The manufacturing method of the joined body using the solder paste of another aspect of the present invention (hereinafter referred to as "the manufacturing method of the joined body using the solder paste of the present invention") is a manufacturing method of a joined body using a solder paste, and a joined object to be joined The solder paste is disposed therebetween, and the joint is joined to the joint to be solder by heating under a formic acid gas atmosphere.

According to such a structure, by suppressing the generation of the residue, the cleaning process of the junction can be omitted, and reflow treatment is performed under a formic acid gas atmosphere, and thus, rosin to reduce and remove oxides is contained. Even if it is not present, it is possible to smoothly melt the solder by reducing the oxide film on the joined material and the surface of the solder and the oxide film on the surface of the solder, so that the joint and the joined material can be joined more firmly.

In addition, the method of disposing the solder paste is not particularly limited, and for example, it can be disposed by a printing method, coating by a dispenser, pin transfer, or the like. Moreover, as a joined object, it is a board|substrate etc., for example, As a to-be-joined object, it is a semiconductor element, such as an LED element, etc., for example.

In the method for forming the flux for solder paste, solder paste, and solder bumps using the solder paste of the present invention and a method for manufacturing a bonded body, generation of residues and reoxidation of the surface of the solder can be suppressed.

Hereinafter, a method for forming a flux for a solder paste, a solder paste, and a solder bump using the solder paste according to the present invention will be described.

The flux for solder paste of the present embodiment (hereinafter sometimes simply referred to as flux) is a flux containing a viscous agent, a solvent, and a thixotropic agent, having an acid value of 100 mgKOH/g or less, and in thermogravimetric measurement. The reduction rate at 300°C is 80 mass% or more, the viscosity is 0.5 Pa·s or more, and the tacking force is 1.0 N or more.

Hereinafter, the reason for defining the structure of the flux, the acid value, and the reduction rate at 300°C, viscosity, and tacking force in thermogravimetric measurement as described above will be described.

[The composition of flux]

The flux is composed of a viscous agent, a solvent, and a thixotropic agent. In addition, in this embodiment, a flux is comprised only of a viscous agent, a solvent, and a thixotropic agent.

The acid value of the flux is 100 mgKOH/g or less. This is because by setting the acid value to 100 mgKOH/g or less, the reaction between the solder powder and the flux when using a solder paste is suppressed and the viscosity change as a solder paste is reduced. This is because when the acid value exceeds the above value, the generation of reduced water generated in the reduction reaction of the flux and the oxide of the solder powder increases, and the voids in the formed solder bumps increase. Further, the acid value of the flux is preferably 50 mgKOH/g or less, and more preferably 10 mgKOH/g or less. The lower limit of the acid value is not particularly limited, and may be less than or equal to the lower limit of detection of the measurement, but is, for example, 0.01 mgKOH/g.

In addition, the flux has a reduction rate at 300°C of 80% by mass or more in thermogravimetric measurement. This is because when the reduction rate at 300°C in the thermogravimetric measurement is less than 80% by mass, the amount of residue increases when the solder paste containing the flux is reflowed. Moreover, it is preferable that the reduction rate at 300 degreeC is 85 mass% or more in thermogravimetric measurement, and it is more preferable that it is 90 mass% or more. Although there is no restriction|limiting in particular in the upper limit of a reduction amount, it is 99.5 mass %, for example as a numerical value in the case of using the generally available viscous agent.

As the solvent contained in the flux, solvents such as alcohols, ketones, esters, ethers, aromatics, hydrocarbons, terpenes and terpenoids are used. Specifically, benzyl alcohol, ethanol, ethyl alcohol, isopropyl alcohol, butanol, diethylene glycol, ethylene glycol, ethyl cellosolve, butyl cellosolve, butyl carbitol, isopropyl alcohol, ethyl acetate, butyl acetate, benzoic acid Butyl, diethyl adipate, dodecane, tetradecene, α-terpineol, 2-methyl-2,4-pentanediol, 2-ethyl-1,3-hexanediol, toluene, xylene, propylene glycol monophenyl Ether, diethylene glycol monohexyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, diisobutyl adipate, hexylene glycol, cyclohexanedimethanol, 2-terfinyloxyethanol, 2-dihydroterpinyl Oxyethanol, citral, linalool, limonene, carbacrol, pinene, farnesene and the like are used alone or in combination.

Moreover, as the thixotropic agent contained in the flux, cured castor oil, hydrogenated castor oil, carnauba wax, amides, hydroxy fatty acids, dibenzylidene sorbitol, bis(p-methylbenzylidene) sorbitol, beeswax, stear Acid amide and ethylene bisamide hydroxystearate are used alone or in combination. In addition, if necessary, fatty acids such as caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, hydroxy fatty acids such as 1,2-hydroxystearic acid, antioxidants, and surfactants , Amines, etc. are used.

The viscosity of the flux is 0.5 Pa·s or more. If the viscosity of the flux is less than 0.5 Pa·s, the viscosity of this flux is too small, so that a solder paste cannot be formed, and there is a fear that it cannot be applied to a substrate or the like. Moreover, it is preferable that the viscosity of a flux is 1.0 Pa*s or more. In addition, viscosity is the viscosity at room temperature (25 degreeC). Although there is no restriction|limiting in particular in the upper limit of a viscosity, It is 100 Pa*s, for example from a viewpoint of coatability, etc.

Moreover, the tacking force of the flux is 1.0 N or more. When the tacking force of the flux is less than 1.0 N, the adhesive strength is low, and therefore, when the solder paste containing this flux is applied to a substrate or the like, there is a fear that the applied solder paste flows off the substrate or the like and may fall off. Moreover, it is preferable that the tacking force of a flux is 1.2 N or more. In addition, the tacking force is a value at room temperature (25 degreeC). Although there is no restriction|limiting in particular in the upper limit of a tacking force, It is 100N, for example from a viewpoint of board peeling property from a mask.

[Constituent composition]

It is preferable that the viscous agent is a solid at room temperature (25°C) or a liquid having a viscosity of 1 Pa·s or more. This is because if the viscous agent is a liquid having a viscosity of less than 1 Pa·s at room temperature, the viscosity of the flux is too small to form a solder paste, and may not be applied to a substrate or the like. As described above, since the viscous agent has a viscosity of 1 Pa·s or more at room temperature or is solid at room temperature, the solder paste comprising the flux and the solder powder containing the viscous agent has shape retention properties. Although there is no particular limitation on the upper limit of the viscosity, it is, for example, 400 Pa·s from the viewpoint of coatability and the like.

In addition, in the thermogravimetric measurement, the viscous agent has a reduction amount at 300°C of 90% by mass or more. This is because, since most of the flux components are viscous agents, if the reduction rate at 300°C in thermogravimetric measurement is less than 90% by mass, the reduction rate at 300°C in thermogravimetric measurement of the flux cannot be 80% or more. . There is no particular limitation on the upper limit of the reduction rate, and it is also possible to use a viscous agent which decreases by 100 mass%.

The tacking force of this viscous agent is set to 1.1 N or more. This is because, as described above, since most of the flux components are viscous agents, if the tacking force of the viscous agent is less than 1.1 N, the tacking force of the flux cannot be 1.0 N or more. Although there is no restriction|limiting in particular in the upper limit of a tacking force, It is 200N, for example from a viewpoint of board|substrate peelability from a mask.

As the viscous agent contained in the flux, it is preferable that the decomposition temperature is low and has viscous properties. For example, in addition to isobornylcyclohexanol, isobornylphenol and derivatives thereof, polybutenes having a number average molecular weight of 700 or more and 1500 or less are used as the viscous agent. Moreover, the number average molecular weight of polybutene is 700 or more and 1500 or less because the number average molecular weight is less than 700 because the viscosity becomes less than 1 Pa·s, the viscosity effect is low, and the printability of the solder paste decreases. This is because when the average molecular weight exceeds 1500, heat resistance becomes high and it is easy to remain as a residue.

Thus, in this embodiment, since the viscous agent is not composed of rosin, dimer acid, and polybutene having a number average molecular weight exceeding 1500, the reduction rate at 300°C in thermogravimetric measurement is 90 mass% or more. This ensures viscous property while suppressing residual residues on the solder bumps.

In addition, since the flux of the present embodiment does not contain rosin or the like as the main component as described above, it is insufficient to reduce and remove oxides, soak them in the base, and coat the solder bumps to prevent reoxidation. The function of such rosin is supplemented by formic acid gas, which will be described later.

The compounding composition of such a flux is, for example, 19% by mass to 60% by mass of the solvent, 30% by mass to 80% by mass of the viscous agent, and 1.0% by mass to 10% by mass of the thixotropic agent. When the solvent is less than 19% by mass, the solder paste is difficult to form a paste, and when the solvent exceeds 60% by mass, the shape-retaining property of the solder paste (hereinafter, sometimes referred to as a bump precursor) in a printed state on the substrate. It becomes bad. When the thixotropic agent is less than 1.0 mass%, the shape retention property of the solder paste becomes poor, and when it exceeds 10 mass%, the solder paste becomes too hard. Moreover, when the viscous agent is less than 30% by mass, there is a concern that the paste cannot be formed or becomes a dried paste, and the solder paste cannot be applied to a substrate or the like.

On the other hand, if the viscosity of the viscous agent exceeds 80% by mass, the viscosity of the solder paste may be too high, or the adhesive strength may be too high, resulting in deterioration in scratchability during printing, or deterioration in shape during application by a dispenser or during pin transfer. There is. The preferred composition of the flux composition is a viscous agent of 35 mass% or more and 80 mass% or less, a thixotropic agent of 2 mass% or more and 6 mass% or less, and the remainder being a solvent. Moreover, as for the more preferable flux compounding composition, a viscous agent is 35 mass% or more and 70 mass% or less, a thixotropic agent is 2.5 mass% or more and 5.5 mass% or less, and the balance is a solvent.

In addition, when a large amount of the active agent is contained in the flux for the solder paste, the solder powder and the flux in the case of the solder paste react and the viscosity change becomes large, so even if refrigerated, it can be stored only for several months. For this reason, in this embodiment, it is assumed that the flux for solder paste does not contain an activator.

[Composition of solder paste]

The solder paste is a mixture obtained by mixing the above-described flux and solder powder, and the content of the flux is set to 30% by volume or more and 90% by volume or less. When the content of the flux for the solder paste is less than 30% by volume, there is a concern that the paste cannot be formed or becomes a dried paste, and the solder paste cannot be printed and applied to a substrate or the like. On the other hand, when the content of the flux for the solder paste exceeds 90% by volume, the viscosity of the solder paste becomes too high, or the adhesive strength becomes too high, the scratchability during printing deteriorates, or when applying by a dispenser or during pin transfer. There is a fear that the shape may deteriorate. For this reason, in this embodiment, the content rate of the flux is set to 30 volume% or more and 90 volume% or less. Moreover, it is preferable that the content rate of a flux is 40 volume% or more and 90 volume% or less.

Thereby, the viscosity of the solder paste becomes 0.4 Pa·s or more, and the tacking force of the solder paste becomes 0.8 N or more.

Moreover, as a solder powder, Sn-Ag-Cu solder powder, Sn-Cu solder powder, Sn-Ag solder powder, Pb-Sn solder powder, Au-Sn solder powder, Au-Ge solder powder can be illustrated. Moreover, the average particle diameter of the solder powder is, for example, in the range of 0.1 to 30.0 µm, whereby the filling property of the mask opening and the shape retention property of the bump precursor can be improved.

Moreover, in order to make bump formation a narrow pitch, it is preferable that the average particle diameter of the solder powder is in the range of 0.1 to 10.0 µm.

[How to form a solder bump]

Next, a method of forming a solder bump using a solder paste will be described.

This forming method includes a printing process for printing the solder paste and a reflow process for heating the solder paste under a formic acid gas atmosphere. Hereinafter, details will be described in the order of the printing process and the reflow process.

(Printing process)

In the printing process, a mask having an opening is disposed on a substrate such as a silicon wafer or a glass epoxy resin substrate, and the solder paste is printed and applied to fill the solder paste in the opening. After this printing application, the mask is peeled off the substrate to form a bump precursor on the substrate. In addition, although the solder paste is supposed to be applied by printing, discharge supply by a dispenser or the like may be used, or pin transfer by a pin transfer device or the like may be used.

In this case, since the viscous agent is a solid at room temperature or a liquid having a viscosity of 1 Pa·s or more, it is possible to secure shape retention of the solder paste comprising a flux and a solder powder for a solder paste containing the viscous agent. Further, since the content of the flux for the solder paste is 30% by volume or more and 90% by volume or less, a solder paste having an appropriate viscosity and adhesive strength can be formed, and deterioration of the scratchability during printing can be suppressed.

(Reflow process)

In the reflow process, first, as a preliminary heating, in a formic acid gas atmosphere, the bump precursor formed on the substrate is heated at a temperature lower than the melting point of the solder powder for 30 seconds to 2 minutes (preheat process), and the solvent that is a void source in the flux is volatilized. Order. Each heat process under this formic acid gas atmosphere generates a gas in which formic acid is dissolved in N ₂ gas by bubbling N ₂ into formic acid having a purity of 99% at room temperature, and the N ₂ gas in which formic acid is introduced is supplied into the furnace. Is executed. The concentration of formic acid in the N ₂ gas (formic acid gas) in which this formic acid is dissolved is, for example, set to approximately 3% by volume. Further, formic acid gas atmosphere may be generated by placing formic acid in the furnace.

Thereafter, heating is performed at a temperature higher than the melting point of the solder powder, for example, at a temperature of +30°C of the solder powder for 10 seconds to 1 minute (this heat process), and the solder powder is melted. At this time, formic acid is reacted with a metal oxide such as Sn contained in the solder powder to produce formate, and then is subjected to high temperature, whereby formate is reduced by formic acid. As described above, when each heat step is performed under a formic acid gas atmosphere, an oxide film such as solder powder is reduced by the reducing power of formic acid. Then, when the molten solder is cooled, an approximately hemispherical solder bump is formed by surface tension.

In this case, in the present embodiment, the flux for solder paste has a reduction rate at 300°C of 80% by mass or more in thermogravimetric measurement, and a viscous agent has a reduction amount of 300% or more at 300°C in thermogravimetric measurement among them. Therefore, when the solder paste containing the flux for the solder paste is reflowed, since the flux is also largely volatile, even when the bump precursor is reflowed and the solder bump is formed, the generation of residues can be suppressed, and the solder bump can be suppressed. The washing process of can be omitted.

In addition, since the reflow treatment is performed under an atmosphere of formic acid gas, even if no rosin to reduce and remove oxides is contained in the flux constituting the solder paste, the solder powder or the oxide film on the substrate is reduced and soldered by the reducing power of formic acid gas. Melting can be smoothed.

In addition, since the generation of residues is suppressed by using the flux for solder paste of the present embodiment, even if the solder powder is a Au-Sn solder powder having a high melting point, the rebound of the residue during reflow can be prevented.

In addition, since the acid value of the flux for the solder paste is set at 100 mgKOH/g or less, the generation of voids in the solder bumps can be suppressed, and the solder paste can be used for a long time (for example, 6 months or more). ) Can be preserved, and long-term storage can be improved.

In addition, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention.

In the above embodiment, the flux is composed of only a viscous agent, a solvent, and a thixotropic agent, but is not limited to this, the acid value is 100 mgKOH/g or less, and the rate of decrease at 300°C in thermogravimetric measurement is 80. If it is in the range of mass% or more, the viscosity is 0.5 Pa·s or more, and the tacking force is 1.0 N or more, the flux may contain a trace amount of rosin and an active agent. For example, in the case of rosin, if it is in the range of 10% by mass or less, and in the case of the active agent, 0.1% by mass or less, the flux may contain these.

Moreover, in the said embodiment, although the preheating process and this heat process were performed in a reflow process, it was supposed to raise the heating temperature stepwise in two steps, but is not limited to this, You may perform only this heat process. Further, the heating temperature may be increased stepwise in three or more steps.

In addition, although the manufacturing method of the solder bump using a solder paste was demonstrated in the said embodiment, it is not limited to this, The solder paste of this invention is arrange|positioned between a joined object and a to-be-joined object, and heated under a formic acid gas atmosphere By doing so, it may be used for a method of manufacturing a joined body in which solder joints are joined to a joined object.

Example

While changing various conditions, a solder paste was prepared, and experiments were conducted on the amount of residue after reflow of the solder bumps obtained from the solder paste, long-term storage properties of the solder paste, and shape retention. The samples of Examples 1 to 9 and Comparative Examples 1 to 6 obtained will be described with reference to Tables 1 and 2.

In addition, in Table 1, the reduction rate at 300°C in the thermogravimetric measurement of each of the flux and the viscous agent (hereinafter referred to as 300°C TG reduction in Table 1) was measured using a general thermogravimetric device. Did. For example, in the thermogravimetric measurement of the flux, the rate of decrease is measured by measuring the change in weight when the temperature of the 10 mg flux is increased from 10° C./min at room temperature (25° C.) to 300° C. under an N ₂ atmosphere. Was obtained. The same is true of the viscous system.

Moreover, the viscosity of the flux and the viscous agent was measured according to JIS Z 8803. Moreover, in Table 1, the viscosity measured according to the above-mentioned JIS Z 8803 is indicated for a liquid at room temperature (25°C), and a solid at room temperature is shown as a solid in Table 1.

In addition, the acid value of the flux was measured according to JIS Z 3197. In addition, about the acid value which was too small and exceeded a detection limit, it displayed below the detection limit.

Solder pastes were prepared by mixing the solder powders and fluxes shown in Table 1 in the proportions shown in Table 1. In addition, the flux was prepared by mixing a viscous agent, a thixotropic agent, a solvent, and an active agent, and the viscous agent, a thixotropic agent, a solvent, and an active agent were as shown in Table 1, and the thixotropic agent was 5 mass%, and the remainder was used as a solvent.

The presence or absence of the residue after reflow, evaluation of long-term storage properties and shape retention of the solder paste were performed by the following method.

(Presence or absence of residue after reflow)

A stencil mask for printing with a thickness of 200 µm was used on the surface of the copper plate, and each of the solder pastes of Examples 1 to 9 and Comparative Examples 1 to 6 was printed and applied in a circular shape having a diameter of 6.5 mm, and a stencil mask for printing was printed from the copper plate. Removed. In this way, for each sample, a circular bump precursor was formed on a copper plate, and used as a substrate for evaluation.

Next, the bump precursor was reflowed by heating this evaluation substrate under a formic acid gas atmosphere. At this time, the peak temperature was set to +30°C of the melting point of each solder powder, and the heating time was 1 minute. Heating under a gas atmosphere, formic acid, by bubbling N ₂ at room temperature to generate a gas that penetration of formic acid in the N ₂ gas was performed by supplying the N ₂ gas is formic acid the penetration in the furnace. The concentration of formic acid in the N ₂ gas (formic acid gas) in which this formic acid was dissolved was set to approximately 3% by volume.

Then, using an electron microscope (SEM), the bump precursor (solder bump) subjected to the reflow treatment was observed, and it was judged as good when the area of the residue was less than 30% of the application area of the solder paste, and the residue was soldered. A case where more than 30% of the application area of the paste was covered was judged as defective.

(Long-term storage of solder paste)

After storing the paste at room temperature for 6 months, this paste was used to prepare the same evaluation substrate, and subjected to the reflow treatment to form a solder bump.

Thereafter, it was observed with an optical microscope, and the case where the amount of non-melting powder generated in the solder powder was the same as immediately after production of the solder paste was judged as good, and the case where the amount of non-melting powder generated in the solder powder increased immediately after production of the solder paste was defective It was judged as.

(Shape retention)

On the evaluation substrate, solder paste was applied on a mask having a pitch of 200 μm, an aperture diameter of 120 μm, and a thickness of 25 μm to form 100 bump precursors. The evaluation substrate on which 100 bump precursors were formed was observed with a naked eye or an optical microscope, and among the 100 solder bump precursors, there were 5 or less missing points, 5 or less bridges due to printing sagging, and 5 defects of the bump precursors. A case in which the number of points was less than or equal to one point was judged as good, and a case in which any of the sewing machine, bridge, and defect occurred more than five points was judged as defective.

As can be seen from Tables 1 and 2, Comparative Examples 1, 3, and 6 show that the residual amount after reflow is low because the amount of reduction at 300°C in the thermogravimetric measurement of the flux is as low as 60% by mass or less. The generated area exceeded 30% of the application area of the solder paste, and there were many residues after reflow. On the other hand, in Examples 1-9, since the reduction rate at 300 degreeC in the thermogravimetric measurement of a flux was 80 mass% or more, there were few residues after reflow. Moreover, since the reduction rate at 300 degreeC in the thermogravimetric measurement of the comparative examples 2, 4 and 5 degree flux was 80 mass% or more, there were few residues after reflow. For this reason, it was found that in the thermogravimetric measurement of the flux, the reduction amount at 300°C was 80% by mass or more.

Moreover, in Comparative Examples 1, 2 and 5, since the acid value of the flux was high at 200 to 1500 mgKOH/g, long-term storage was poor. On the other hand, in Examples 1 to 9, since the acid value of the flux was 100 mgKOH/g or less, the long-term storage property of the solder paste was excellent. Moreover, since the acid values of the comparative examples 3, 4 and 6 degrees flux were below the detection limit, the long-term storage property of the solder paste was excellent. For this reason, it was found that an effective range is that the acid value of the flux is 100 mgKOH/g or less.

Further, in Example 2, the flux contained 0.1% by mass of the active agent, but the acid value of the flux was 100 mgKOH/g or less, and thus excellent in long-term storage. On the other hand, in Comparative Example 2, since the flux contained 0.2% by mass of the active agent, the acid value of the flux increased to 200 mgKOH/g, resulting in poor long-term storage. For this reason, it was found that if the acid value of the flux is within the above range, it may contain 0.1% by mass or less of the active agent.

In Comparative Example 5, since the flux contained 40% by mass of polymerization rosin, the acid value of the flux increased to 800 mgKOH/g, resulting in poor long-term storage. On the other hand, in Example 8, the flux contained 5% by mass of the polymerization rosin, but was excellent in long-term storage.

Moreover, in the comparative example 6, since the flux contained 40 mass% of rosin ester, the reduction amount at 300 degreeC in thermogravimetry was lowered to 60 mass% or less, and there were many residues after reflow. On the other hand, in Example 9, the flux contained 10% by mass of the rosin ester, but had little residue after reflow.

From these points, it was found that if the amount of the acid value of the flux and the reduction at 300°C in the thermogravimetric measurement were within the above range, rosins of 10% by mass or less may be contained.

In addition, in Comparative Example 4, since the viscosity of the flux was low at 0.3 Pa·s and the tacking force was also as small as 0.8 N, printing sagging and the like occurred, resulting in poor shape retention. On the other hand, Examples 1 to 9 were excellent in shape retention since the viscosity of the flux was 1 Pa·s or more and the tacking force was 1.0 N or more. Further, Comparative Examples 1 to 3 and 5 had excellent shape retention since the viscosity of the flux was 0.5 Pa·s or more and the tacking force was 1.0 N or more. For this reason, it was found that the viscosity of the flux was 0.5 Pa·s or more, and the tacking force was 1.0 N or more.

Industrial availability

The reliability of bonding of electronic components to a substrate can be effectively improved.

Claims (14)

A flux for a solder paste containing a viscous agent, a solvent, and a thixotropic agent,
The flux for the solder paste has an acid value of 100 mgKOH/g or less, and a rate of weight loss when the temperature is raised from room temperature to 300 °C at an elevated temperature of 10 °C/min and 25 °C under an N ₂ atmosphere. A flux for solder paste, wherein the flux is 80 mass% or more, the viscosity is 0.5 Pa·s or more, and the tacking force is 1.0 N or more. According to claim 1,
A flux for solder paste, characterized in that the content of rosin is 10% by mass or less. A solder paste comprising the flux for a solder paste according to claim 1 and a solder powder. The method of claim 3,
Solder paste, characterized in that the content of the flux for the solder paste is 30% by volume or more and 90% by volume or less. The method of claim 3,
The solder powder, any of Sn-Ag-Cu solder powder, Sn-Cu solder powder, Sn-Ag solder powder, Pb-Sn solder powder, Au-Sn solder powder, Au-Ge solder powder, Au-Si solder powder Solder paste characterized by being one. A mask having an opening is disposed on the substrate, the solder paste is printed to fill the opening with the solder paste according to any one of claims 3 to 5, and the mask is peeled off, and then the bump precursor on the substrate is removed. Method of forming a solder bump using a solder paste, characterized in that to form a solder bump by reflow treatment in a formic acid gas atmosphere. As a manufacturing method of a joined body using a solder paste,
A solder characterized by arranging the solder paste according to any one of claims 3 to 5 between the joined object and the joined object, and soldering the joined object to the joined object by heating under a formic acid gas atmosphere. Method for manufacturing a joined body using a paste. A solder paste comprising the flux for a solder paste according to claim 2 and a solder powder. The method of claim 8,
Solder paste, characterized in that the content of the flux for the solder paste is 30% by volume or more and 90% by volume or less. The method of claim 4,
The solder powder, any of Sn-Ag-Cu solder powder, Sn-Cu solder powder, Sn-Ag solder powder, Pb-Sn solder powder, Au-Sn solder powder, Au-Ge solder powder, Au-Si solder powder Solder paste characterized by being one. The method of claim 8,
The solder powder, any of Sn-Ag-Cu solder powder, Sn-Cu solder powder, Sn-Ag solder powder, Pb-Sn solder powder, Au-Sn solder powder, Au-Ge solder powder, Au-Si solder powder Solder paste characterized by being one. The method of claim 9,
The solder powder, any of Sn-Ag-Cu solder powder, Sn-Cu solder powder, Sn-Ag solder powder, Pb-Sn solder powder, Au-Sn solder powder, Au-Ge solder powder, Au-Si solder powder Solder paste characterized by being one. A mask having an opening is disposed on a substrate, the solder paste is printed to fill the opening with the solder paste according to any one of claims 8 to 12, and the mask is peeled off, and then the bump precursor on the substrate is removed. Method of forming a solder bump using a solder paste, characterized in that to form a solder bump by reflow treatment in a formic acid gas atmosphere. As a manufacturing method of a joined body using a solder paste,
A solder characterized by arranging the solder paste according to any one of claims 8 to 12 between the joint and the joined object, and soldering the joint to the joined object by heating under a formic acid gas atmosphere. Method for manufacturing a joined body using a paste.