JPWO2020116403A1 - Flux sheet and solder joining method using flux sheet - Google Patents

Abstract

An object of the present invention is to provide a flux sheet which has strong adhesiveness to a substrate and does not cause displacement of solder balls during reflow. In order to solve the above problems, the flux sheet containing the resin (A) has a glass transition point of 40 ° C. or less and a melt viscosity of 150 ° C. of 500 Pa · s (shear velocity 10 mm /). Provided is a flux sheet characterized by containing the following resin (a1) (measured in minutes). As a result, when the substrate and the solder are joined, the adhesiveness with the substrate is strong, and it is possible to obtain the effect that the solder balls do not shift during the reflow. [Selection diagram] None

Description

The present invention relates to a flux sheet used for solder bonding of electronic components, wiring boards, substrates, semiconductor chips, wafers, panels, etc., and a solder bonding method using the flux sheet. More specifically, the present invention relates to a flux sheet having excellent adhesiveness to a substrate.

Known methods for mounting electronic components on a board or the like include, for example, a surface mounting method in which the surface of a board is soldered, and a through-hole mounting method in which an electrode lead terminal is inserted into a hole in the board and soldered. There is. As a surface mounting method, for example, there is a method of forming solder bumps on the electrodes of the substrate in advance and electrically joining the electronic component and the substrate through the solder. As a method of forming a solder bump, a method of mounting a solder ball or the like on a circuit electrode of a substrate or the like is known.

On the other hand, the surface of solder used for solder balls and the like is easily oxidized, and it is necessary to remove the metal oxide covering the solder surface in order to form a normal solder bond. As a method for removing metal oxides, for example, a method of applying a liquid or paste-like flux (flux) to solder in advance is known.

Liquid or paste-like flux is difficult to adjust the coating amount and is inferior in workability, and bumps with a small flux coating amount have a weak oxide removing action, which causes a problem of poor solder bonding. .. Therefore, for example, in Patent Document 1, in order to solve the above problem, a resin (A1) having a structure derived from polyvinyl alcohol, or a resin (A2) having a structure derived from polyvinylpyrrolidone and a flux agent (B) are used. A flip-chip bonding method using a flux film including the above is disclosed.

Japanese Unexamined Patent Publication No. 2014-168791

However, since the flux film disclosed in the prior art document has a weak adhesiveness to the substrate, the film and the substrate are displaced during work or during solder reflow, and as a result, the solder balls and the electrodes on the substrate are displaced. Therefore, there is a problem that it is necessary to separately fix it with a polyimide tape or the like.
Therefore, an object of the present invention is to provide a flux sheet that has strong adhesiveness to a substrate and does not cause displacement of solder balls during reflow.

As a result of diligent studies on the above problems, the inventor contains a resin (a1) having a glass transition point of 40 ° C. or lower and a melt viscosity of 150 ° C. of 500 Pa · s (measured at a shear rate of 10 mm / min) or less. By doing so, it was found that a flux sheet having good adhesion to the substrate and no displacement of the solder balls during reflow can be obtained, and the present invention has been completed.
That is, the present invention is the following flux sheet and solder bonding method.

The flux sheet of the present invention for solving the above problems is a flux sheet containing a resin (A), wherein the resin (A) has a glass transition point of 40 ° C. or lower and 150 ° C. It is characterized by containing a resin (a1) having a melt viscosity of 500 Pa · s (measured at a shear rate of 10 mm / min) or less.
According to this feature, the adhesiveness to the substrate and the holding power of the solder balls are strong, and the flatness of the sheet is good. Therefore, the solder balls can sink directly under the sheet after softening, and the solder balls do not shift. It can exert the effect. Further, the flux sheet of the present invention can be laminated even at a low temperature, and even if it is not laminated, it has an effect that the adhesiveness to the substrate is good.

Further, as one embodiment of the flux sheet of the present invention, the resin (A) has a glass transition point of 40 ° C. or lower and a melt viscosity of 150 ° C. of 500 Pa · s (measured at a shear rate of 10 mm / min) or less. It is characterized by containing 35 to 99% by mass of a certain resin (a1) and 1 to 65% by mass of a resin (a2) having a glass transition point larger than that of the resin (a1).
According to this feature, the adhesiveness to the substrate is good, the effect that the solder balls do not shift during reflow can be exhibited, and the adhesiveness and tackiness of the flux sheet can be controlled, which is an excellent rework. Can demonstrate sex.

Moreover, one embodiment of the flux sheet of the present invention is characterized in that the flux sheet contains a flux agent (B).
According to this feature, the wettability of the solder ball can be improved, and the effect (self-alignment effect) that the positional deviation between the solder ball and the electrode can be corrected at the time of solder reflow can be exhibited.

Moreover, one embodiment of the flux sheet of the present invention is characterized in that the flux sheet does not substantially contain a small molecule compound other than (B).
According to this feature, it is possible to exert the effect of suppressing substrate contamination due to vaporization of small molecule compounds during solder reflow and displacement due to solder rolling.

Moreover, one embodiment of the flux sheet of the present invention is characterized in that the resin (a1) is water-soluble.
According to this feature, an aqueous solvent can be used at the time of producing or mounting the flux sheet, after solder reflow, and when cleaning the flux sheet. As a result, the flux sheet can be washed without using a highly volatile organic solvent, so that the effect of reducing the environmental load due to the volatility of the organic solvent can be exhibited.

Further, as one embodiment of the flux sheet of the present invention, the resin (a1) has a partial structure in which a part of hydroxy groups (-OH) of polyvinyl alcohol are linked by one or more alkylene oxide chains- (CH (CH (CH). R ¹ ) CH (R ² ) O) _n— R ³ (n represents the number of repetitions (average value) of the alkylene oxide chain and is 1.0 or more. R ¹ , R ² and R ³ are independent of each other. It indicates a hydrogen atom or an organic group. When ^{there are a plurality of R 1} , R ² and R ³ , they may be the same or different from each other.) It is selected from modified polyvinyl alcohol, polyamide and polyester. It is characterized by containing one or more kinds.
According to this feature, the adhesiveness to the substrate is good, and the effect that the solder balls do not shift during the reflow can be further exhibited.

Moreover, one embodiment of the flux sheet of the present invention is characterized by containing polyvinyl alcohol as (a2).
According to this feature, it is possible to control the adhesiveness and tackiness to improve the handleability during work, to have excellent reworkability, and to improve the apparent water solubility.

Further, one embodiment of the flux sheet of the present invention is characterized in that the content of the resin (A) in the flux sheet is 50% by mass or more.
According to this feature, it is possible to achieve both a solder ball holding force and good handleability.

Further, one embodiment of the flux sheet of the present invention is characterized in that ^{the area of the flux sheet is 30,000 mm 2 or more.}
According to this feature, it is possible to exert an effect that the positional deviation can be further suppressed for a large-area wafer or substrate in which the positional deviation between the solder ball and the electrode is larger.

The solder joining method of the present invention for solving the above problems is a solder joining method using the flux sheet, and is characterized by having the following steps (1) to (4).
(1) Step of arranging the flux sheet on the surface of the substrate having an electrode having an electrode (2) Step of arranging a solder ball on the flux sheet (3) Heating to a temperature at which the flux sheet melts or softens Steps (4) Simultaneously with (3) or after that, heating to a temperature higher than the melting point of the solder According to this feature, a flux sheet that has strong adhesion to the substrate and does not cause displacement of the solder balls during reflow. Since it is used, it is possible to exert the effect that defects such as solder joints do not occur.

According to the present invention, it is possible to provide a flux sheet that has strong adhesiveness to a substrate and does not cause displacement of solder balls during reflow.

It is a schematic diagram for demonstrating the solder joining method of this invention, and is the schematic plan view of the substrate provided with an electrode. It is a schematic diagram for demonstrating the solder joining method of this invention, and is the schematic sectional view of the substrate provided with an electrode. It is a schematic diagram for demonstrating the solder bonding method of this invention, and is the schematic cross-sectional view which showed an example of the method of arranging the flux sheet of this invention on the electrode surface side of the substrate provided with an electrode in step (1). be. It is a schematic diagram for demonstrating the solder bonding method of this invention, and shows an example of the method of arranging a solder ball in a process (2) so that it may be located on the electrode of a substrate via the flux sheet of this invention. It is a schematic cross-sectional view. It is a schematic diagram for demonstrating the solder bonding method of this invention, and is the schematic sectional view which showed an example of the solder bonding substrate which bonded the solder ball with the electrode of the substrate in step (3). It is a schematic diagram for demonstrating the solder bonding method of this invention, and is the schematic cross-sectional view which showed an example of the solder bonding substrate which removed the flux sheet after the completion of step (4).

Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

[Flux sheet]
The flux sheet of the present invention is a flux sheet containing a resin (A), wherein the resin (A) has a glass transition point of 40 ° C. or lower and a melt viscosity of 150 ° C. of 500 Pa · s (shear velocity 10 mm / min). It is characterized by containing the following resin (a1). In the present invention, the "flux sheet" is a sheet used for forming a solder joint and is used for removing an oxide film on a solder surface. Specifically, a sheet having a flux effect (flux sheet) by satisfying at least one of the resin (A) containing a resin having a flux action or the flux sheet containing a flux agent (B). Can be.

<Resin (A)>
The resin (A) of the present invention is characterized by containing a resin (a1) having a glass transition point of 40 ° C. or lower and a melt viscosity of 150 ° C. of 500 Pa · s or less.
The glass transition point is the temperature at which the glass transition of a substance occurs (the temperature at which the microbrown motion occurs). Generally, in the temperature range below the glass transition point, it exhibits hard and glassy properties and is higher than the glass transition point. Then, it exhibits soft, rubber-like and liquid-like properties.
Explaining the relationship between the glass transition point of the resin (a1) and the adhesiveness, the polymer sheet having an amorphous structure is in a hard glass state at a temperature lower than the glass transition temperature and in a soft rubber state at a high temperature. Therefore, a sheet containing a resin having a low glass transition temperature (near room temperature, further below room temperature) is soft in the temperature range to be handled, and when the sheet is placed on the substrate, the adhesion at the interface with the substrate is improved. It can be said that the adhesive strength of the glass becomes stronger. In addition, a sheet containing a resin having a low glass transition temperature can be laminated without biting voids even in a relatively low temperature (about 60 to 80 ° C.) region where there is little possibility of adverse effects such as warpage of the substrate and thermal decomposition. It can be said that. As a result, by setting the glass transition point to 40 ° C. or lower, a flux sheet having good adhesiveness to the substrate / solder balls can be obtained without adding a tackifier or the like.

In the present invention, the glass transition point of the resin (a1) is 40 ° C. or lower, and the upper limit value is preferably 30 ° C. or lower, more preferably 20 ° C. or lower, still more preferably 10 ° C. or lower. It is particularly preferably 0 ° C. or lower, and most preferably −20 ° C. or lower. By setting the glass transition point of the resin (a1) to 40 ° C. or lower, the resin (A) containing the resin (a1) becomes soft and the adhesiveness between the substrate and the flux sheet is improved. In addition, the solder balls can sink under their own weight, and the displacement of the solder balls can be suppressed.
In the present invention, the glass transition point can be measured using a differential scanning calorimetry device (manufactured by X-DSC7000 Seiko Instruments Inc.).

Further, in the present invention, the resin (a1) is characterized in that the melt viscosity at 150 ° C. is 500 Pa · s or less. The upper limit value is preferably 400 Pa · s or less, more preferably 350 Pa · s or less, and further preferably 200 Pa · s or less. By setting the melt viscosity of the resin (a1) at 150 ° C. to 500 Pa · s or less, the solder balls can sink under their own weight during solder reflow and can come into contact with the electrodes of the substrate (penetrate the sheet). When the temperature rises above the melting point, the balls and the electrodes get wet and a solder joint can be formed, and the displacement of the solder balls can be suppressed.
In the present invention, the melt viscosity at 150 ° C. can be measured by a capillary rheometer (Capillary Graph ID Co., Ltd., manufactured by Toyo Seiki Seisakusho Co., Ltd.) under the condition of a shear rate of 10 mm / min.

The resin (a1) having a glass transition point of 40 ° C. or lower and a melt viscosity of 150 ° C. of 500 Pa · s or less is not particularly limited, but is preferably a thermoplastic resin, for example, polyethylene, polypropylene, polybutylene, or poly. Vinyl chloride, ethylene-cyclic olefin copolymer, polystyrene resin, poly (meth) acrylic acid resin, polyvinyl alcohol, polyvinyl alcohol resin such as modified polyvinyl alcohol, polyvinyl acetate, poly (meth) acrylamide resin, polybutadiene , Polyisoprene, styrene maleic acid resin, addition resin such as carboxyl group terminal butadiene nitrile copolymer (CTBN), condensation resin such as polyester, polyamide, polyimide, polyurethane, polycarbonate resin, polyether ketone, polyether sulfone, etc. , Polyether-based resins such as polyethylene glycol and polypropylene glycol, polyalkyleneimine-based resins such as polyethyleneimine, and ring-opening polymerization-based resins such as polycycloolefin. One of these may be used alone, or two or more thereof may be mixed and used. Among these, it is preferable to contain at least one selected from modified polyvinyl alcohol, polyamide and polyester.

Further, from the viewpoint of water solubility, polyvinyl alcohol preferably has a saponification degree of 75 to 90 mol%, more preferably 85 to 90 mol%. By setting the degree of saponification of polyvinyl alcohol within the above range, it is possible to prevent crystallization from becoming difficult to dissolve in water and suppressing hydrophilic groups from becoming difficult to dissolve in water. On the other hand, in the case of polyvinyl alcohol modified with a hydrophilic group, it is soluble in water even at a lower degree of saponification. In the case of the modified polyvinyl alcohol described later, the solubility can be improved by grafting a hydrophilic group other than the hydroxy group or blocking it in the main chain, so the degree of saponification is preferably 30 to 60 mol%. , 40 to 50 mol% is more preferable. As the hydrophilic group used for the hydrophilic group modification, for example, an alkylene oxide compound such as ethylene glycol is preferable.

Among these resins, the resin containing a hydroxy group, a carboxyl group, or an amino group can be used as a flux sheet without adding a flux agent because the resin itself has a flux action. Specifically, resins such as poly (meth) acrylic acid-based resin, polyvinyl alcohol-based resin, polyamide, polyester, carboxyl group-terminated butadiene nitrile copolymer (CTBN), and polyurethane may exhibit flux activity in a molten state. can.

In the present invention, the weight average molecular weight of the resin (a1) is preferably ^{1 × 10 3 ~2.0 × 10 5} . The lower limit is preferably at 3.0 × 10 ³ or more, more preferably 8.0 × 10 ³ or more. The upper limit is preferably not 1.5 × 10 ⁵ or less, more preferably 1.0 × 10 ⁵ or less. Still more preferably 5.0 × 10 ⁴ or less. By setting the weight average molecular weight of the resin (a1) within the above range, the moldability of the sheet is improved, the dissolution and removal of the sheet after solder joining, and the sheet penetration of the ball are improved.

The molecular weight distribution (Mw / Mn) of the resin (a1) is preferably 1 to 30. The lower limit is preferably 1.5 or more, and more preferably 1.8 or more. The upper limit is preferably 15 or less, and more preferably 8 or less. The molecular weight of the resin (a1) is measured by a gel permeation chromatography method (GPC method) using tetrahydrofuran (THF) as an eluent, and the molecular weight of the resin (a1) is a polystyrene-equivalent value.

The resin (a1) of the present invention is preferably water-soluble. Water-soluble means that the resin (a1) dissolves in an amount of 5 parts by mass or more with respect to 100 parts by mass of water under the conditions of 25 ° C. and 1 atm. The lower limit is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and further preferably 30 parts by mass or more.
Since the resin (a1) is water-soluble, it can be produced by using an aqueous solvent when producing the flux sheet. Further, when cleaning the flux sheet, an aqueous solvent can be used, and the effect of reducing the environmental load due to the volatilization of the organic solvent can be exhibited.

The resin (a1) includes, for example, a partial structure in which one or more hydroxy groups (-OH) of polyvinyl alcohol are linked by one or a plurality of alkylene oxide chains- (CH (R ¹ ) CH (R ² ) O). Examples thereof include modified polyvinyl alcohol substituted with _n ^{−R 3).}

n represents the number of repetitions (average value) of the alkylene oxide chain, and is preferably 1.0 or more. The lower limit of n is preferably 1.0 or more, more preferably 2.0 or more, still more preferably 5.0 or more, and particularly preferably 6.0 or more. The upper limit is preferably 300.0 or less, more preferably 200.0 or less, and further preferably 65.0 or less.
By setting n within the above range, a flux sheet having excellent adhesiveness can be obtained.

As R ¹ and R ² , hydrogen atoms or organic groups are preferable, respectively, and as the organic group, an alkyl group having 1 to 10 carbon atoms is preferable. Examples of the alkyl group having 1 to 10 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, a butyl group, a pentyl group, a hexyl group and the like.

The R ³ is preferably a hydrogen atom or an organic group, and the organic group is an alkyl group having 1 to 10 carbon atoms, an acyl group having 1 to 10 carbon atoms, an alkyl ester group having 1 to 10 carbon atoms, and 1 carbon atom. 10 to 10 alkylamide groups and sulfonic acid bases are preferable.
Examples of the alkyl group having 1 to 10 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, a butyl group, a pentyl group, a hexyl group and the like.
Examples of the acyl group having 1 to 10 carbon atoms include a methylcarbonyl group, an ethylcarbonyl group, an n-propylcarbonyl group, an i-propylcarbonyl group, a butylcarbonyl group, a pentylcarbonyl group, and a hexyl group carbonyl.
Examples of the alkyl ester group having 1 to 10 carbon atoms include a methyloxycarbonylmethylene group, a methylcarbonyloxymethylene group, an ethyloxycarbonylethylene group, an ethylcarbonyloxyethylene group and the like.
Examples of the alkylamide group having 1 to 10 carbon atoms include an N, N'-dimethylamide alkylene group and an N, N'-diethylamide alkylene group.

Specifically, the modified polyvinyl alcohol has a trade name of "Gosenex (registered trademark) LW-100 (manufactured by Nippon Synthetic Chemical Industry Co., Ltd .; glass transition point -0.5 ° C., melt viscosity at 150 ° C.): 63 Pa · s (shear). The speed is 10 mm / min) and the degree of saponification is 43.1 mol% ”).
Specifically, as the polyester, the trade name "Pesresin A-680 (manufactured by Takamatsu Oil & Fat Co., Ltd .; melt viscosity at glass transition point 30 ° C. and 150 ° C.: 29 Pa · s (shear rate 10 mm / min)), as the polyamide. Specifically, the trade name "AQ Nylon T-70 (manufactured by Toray Co., Ltd .; glass transition point -46 ° C., melt viscosity at 150 ° C.: 17 Pa · s (shear rate 10 mm / min)) can be mentioned.

The resin (A) of the present invention preferably contains the above resin (a1) in an amount of 35% by mass or more. Further, the resin (A) of the present invention may contain other resins in addition to the above resin (a1). As the other resin, it is preferable to contain a resin (a2) having a glass transition point higher than that of the resin (a1).
The resin (a2) is not limited as long as it has a glass transition point higher than that of the resin (a1), but for example, the thermoplastic resin exemplified in the resin (a1) can be used. Further, in addition to the above-mentioned thermoplastic resin, a thermosetting resin or the like can be contained, but from the viewpoint of detergency, the thermosetting resin is preferably 45% by mass or less. When the content of the thermosetting resin is 60% by mass or less, the thermosetting resin can form an island phase in the composition, and good detergency can be obtained, which is preferable.
The glass transition point of the resin (a2) is preferably higher than 40 ° C. The lower limit is more preferably 50 ° C. or higher, and even more preferably 60 ° C. or higher.

Examples of the resin (a2) having a glass transition point higher than that of the resin (a1) include polyethylene, polypropylene, polybutylene, polyvinyl chloride, ethylene-cyclic olefin copolymer, polystyrene-based resin, and poly (meth) acrylic acid-based resin. , Polypoly alcohol resin, polyvinyl acetate, poly (meth) acrylamide resin, polybutadiene, polyisoprenestyrene maleic acid resin and other additive resins, polyester, polyamide, polyimide, polyurethane, polycarbonate resin, polyether ketone, polyether Examples thereof include condensation resin such as sulfone, polyether resin such as polyethylene glycol and polypropylene glycol, polyalkyleneimine resin such as polyethyleneimine, and ring-opening polymerization resin such as polycycloolefin. One of these may be used alone, or two or more thereof may be mixed and used.

When the resin (A) of the present invention contains the resin (a2), it preferably contains 35 to 99% by mass of the resin (a1) and 1 to 65% by mass of the resin (a2).
The lower limit of the content of the resin (a1) is preferably 60% by mass or more, more preferably 65% by mass or more, and further preferably 70% by mass or more. The upper limit value is 95% by mass or less, more preferably 90% by mass or less.

The content of the resin (a2) is preferably 5% by mass or more, and more preferably 10% by mass or more as the lower limit value. The upper limit value is 40% by mass or less, more preferably 35% by mass or less, and further preferably 30% by mass or less.
The resin (A) of the present invention can control the adhesive force to a substrate or the like by adding the resin (a2) in addition to the resin (a1). In addition, the position of the arranged solder balls can be easily corrected, and the reworkability is improved. Further, the sheet itself is excellent in flexibility and handleability. Further, by setting the content of the resin (a2) within the above range, it becomes possible to wash with an aqueous solvent.

When the compatibility between the resin (a1) and the resin (a2) is poor, the compatibility can be improved by using a compatibility agent, a modifier, and a dispersant. As the compatibilizer / modifier / dispersant, a block (co) polymer or graft (co) polymer or graft in which the resin (a1) and the segment having a high affinity with the resin (a2) are chemically bonded at one place or a plurality of places, respectively. Co) A polymer or the like may be used.

Since the modified polyvinyl alcohol has a polyvinyl alcohol chain and a (poly) alkylene oxide chain in the molecule, it functions as a compatibilizer, a modifier, and a dispersant with polyvinyl alcohol, polyalkylene oxide, and the like, respectively. Express. Further, in the mixing of the modified polyvinyl alcohol and polyvinyl alcohol, polyalkylene oxide, carboxylmethyl cellulose, sodium salt of carboxylmethyl cellulose, potassium salt of carboxylmethyl cellulose and the like are preferably used as compatibilizers, modifiers and dispersants. Can be used.

The blending amount of the compatibilizer, modifier, and dispersant is not particularly limited, but the total of the resin (a1) and the resin (a2) is taken into consideration in consideration of the effect of compatibilization and the reduction of low molecular weight components. The lower limit is preferably 0.1 part by mass or more, more preferably 0.2 part by mass or more, and further preferably 0.5 part by mass or more with respect to 100 parts by mass. The upper limit is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and further preferably 5 parts by mass or less.

<Flux agent (B)>
The flux sheet of the present invention may contain, for example, a flux agent (B) in addition to the resin (A). By containing a flux agent, a stronger flux action can be exhibited or improved, the formability of the solder joint can be improved, and the electrical conductivity can be improved. In addition, the wettability of the solder can be improved, and the effect (self-alignment effect) of being able to correct the positional deviation between the solder balls and the electrodes during solder reflow can be further exhibited.
The flux agent (B) is not particularly limited as long as it is a component capable of removing a metal oxide having a high melting point on the surface of the solder, and an acidic substance, a basic substance, an alcohol or the like is preferably used. Further, those which are active at room temperature and those which are activated by heating can be used.

Specific examples of the flux agent (B) include adipic acid, malonic acid, succinic acid, maleic acid, pentanoic acid, salicylic acid, benzoic acid, m-dihydroxybenzoic acid, carboxylic acids such as sebacic acid, dodecylamine and the like. Examples of amines, hydrogen halides of amines, rosin resins and the like. Further, the flux agent may be used alone or in combination of two or more. The flux agent (B) contained in the flux sheet of the present invention is used from the viewpoints of removing the oxide film of the solder particles, the fluidity of the sheet, the dissolution and removal property of the resin after solder bonding, and the improvement of the wettability with the solder. , Adipic acid, salicylic acid, dodecylamine, benzoic acid, m-dihydroxybenzoic acid and sebacic acid are preferable, and adipic acid, salicylic acid and dodecylamine are more preferable.

The content of the flux agent (B) can be appropriately set depending on the number and size (surface area) of the solder balls, the thickness of the oxide film on the surface, the thickness of the flux sheet, and the like, but the resin (A) 100 It is preferably 10 parts by mass or less with respect to the mass part. The upper limit is more preferably 8 parts by mass or less, further preferably 7 parts by mass or less, and particularly preferably 6 parts by mass or less. On the other hand, the lower limit value is preferably 1 part by mass or more, and more preferably 3 parts by mass or more.
By setting the content of the flux agent (B) within the above range, the oxide film on the solder surface can be sufficiently removed without suppressing the adhesiveness between the flux agent and the substrate. Further, by suppressing the residual flux agent in the substrate, it is possible to suppress a decrease in insulation resistance at high temperature and high humidity, and to prevent metal corrosion and migration.

<Other additives>
In addition to the resin (A) and the flux agent (B), the flux sheet of the present invention may contain, for example, an additive contained in a general flux as long as the effect of the present invention is not impaired. Examples of the additive include a thixotropy-imparting agent, a flux activation aid, and an antifoaming agent.
Examples of the thixotropic property-imparting agent include fatty acid amides such as m-xylylene bisstearic acid amide, polyolefin waxes such as caster wax (hardened castor oil), substituted urea waxes such as N-butyl-N'-stearyl urea, and polyethylene glycol. Examples thereof include high molecular compounds such as methyl cellulose, ethyl cellulose and hydroxyethyl cellulose, and inorganic particles such as silica particles and kaolin particles.
The thixotropy-imparting agent may be used alone or in combination of two or more.

When a thixotropy-imparting agent is used in the flux of the present invention, its content is preferably 0.1 to 20 parts by mass with respect to 100 parts by mass of the polymer (A). The lower limit is preferably 0.2 parts by mass or more, and more preferably 0.5 parts by mass or more. The upper limit is preferably 15 parts by mass or less, and more preferably 10 parts by mass or less. By setting the content of the thixotropy-imparting agent within the above range, the adhesive force with the solder ball or the substrate can be adjusted.

Examples of the flux activation aid include hydrogen halides of amines such as diethylamine hydrobromide and cyclohexylamine hydrobromide, organic acids such as stearic acid, organic amines such as tributylamine, and trans-. Examples thereof include activators such as organic halides such as 2,3-dibromo-2-butene-1,4-diol.
Examples of the defoaming agent include alcohols such as lauryl alcohol, cetyl alcohol, stearic alcohol, eikosanol and docosanol, hydrocarbon compounds such as polyethylene wax, paraffin wax and white oil, and carboxylic acids (for example, palmitic acid and oleic acid). Fatty acid esters obtained by condensing with alcohol (eg, methanol, ethanol, octanol, etc.), natural fats and oils such as beef fat, soybean oil, flaxseed oil, and siloxanes such as polydimethylsiloxane and polymethylphenylsiloxane. Kind and so on. Further, a highly lipophilic surfactant such as a cationic surfactant, an anionic surfactant, or a nonionic surfactant can also be used.

Further, it is preferable that the flux sheet of the present invention does not substantially contain a small molecule compound other than (B). Examples of the low molecular weight compound other than (B) include those having a molecular weight of 1000 or less, and typical examples thereof include plasticizers such as glycerin, phthalate ester, adipate ester, and trimellitic acid ester. ..
By substantially not containing a small molecule compound other than (B), it is possible to suppress substrate contamination due to vaporization of the small molecule compound during solder reflow and displacement due to rolling of the solder due to sudden vaporization. Can be demonstrated.
Substantially not contained means that a small molecule compound other than (B) is not intentionally added as a constituent component of the flux sheet. In the flux sheet, a solvent required for the sheet preparation process and a small molecule compound derived from the raw material monomer of the resin (A) may remain. In that case, for example, the content is less than 10% by mass, which is the upper limit. The value is preferably less than 5% by mass, more preferably less than 3% by mass, still more preferably less than 2% by mass, and particularly preferably less than 1% by mass.

<Characteristics of flux sheet>
The flux sheet of the present invention contains the resin (A) in which the resin (A) has a glass transition point of 40 ° C. or lower and a melt viscosity of 150 ° C. of 500 Pa · s (measured at a shear rate of 10 mm / min) or less. Therefore, it has a strong adhesiveness to the substrate and has an effect that the solder balls do not shift during reflow. Further, since the resin (a1) having a melt viscosity at 150 ° C. of 500 Pa · s or less is contained, the solder balls can sink under their own weight during solder reflow, and the displacement of the solder balls can be suppressed. .. Therefore, it is possible to exert an effect of excellent solder bondability.

Since the flux sheet of the present invention does not have fluidity at room temperature like liquid and paste-like fluxes, even if a flux agent is contained, flux aggregation, separation, sedimentation, etc. are unlikely to occur, and storage stability is stable. Excellent in sex.
Further, when liquid or paste-like flux is applied by printing or the like, the amount of application varies widely, so it is necessary to adjust the amount of application as appropriate, and the workability is inferior. However, the flux sheet of the present invention has a predetermined amount. It is only necessary to place and laminate the sheet of No. 1 on the substrate, and it is excellent in workability.
If the solvent remains, it may evaporate to form voids at the time of bonding. Therefore, the flux sheet of the present invention preferably has a residual solvent content of less than 10% by mass. This content can be measured, for example, by the curl fisher method or weight reduction by heating.

When the flux sheet of the present invention contains a water-soluble resin (a1), water can be used when producing or mounting the flux sheet, or when cleaning the flux sheet. Therefore, it is not necessary to use an organic solvent that volatilizes and is released into the atmosphere, so that the environmental load can be reduced.

The thickness of the flux sheet of the present invention can be appropriately set in consideration of flux activity, detergency, etc., but is preferably 1 to 500 μm. The lower limit is preferably 3 μm or more, and more preferably 5 μm or more. The upper limit is preferably 100 μm or less, and more preferably 50 μm or less.

Further, the size (area) of the flux sheet can be appropriately set in consideration of the size of the substrate, chip, wafer, etc. to be used. Specifically, it is preferable to set the area slightly wider than the area where the electrodes (groups) on the substrate are located. Alternatively, it may be formed to be larger than the size planned to be used in advance, and may be cut into a desired size at the time of use. It is also possible to transfer and laminate the sheet by directly pressing the target substrate against the sheet without cutting it.

In the present invention, the area of the flux sheet is preferably 30,000 mm ² or more.
By setting the area of the flux sheet to 30,000 mm ² or more, it is possible to attach the flux sheet to the entire surface of the substrate at once even on an electronic member substrate such as a panel or a wafer having a large area.
The large-area electronic member substrate includes a wafer having a diameter of 200 mm (8 inches) or more and a panel having a diameter of 300 mm square or more.

The wafer includes a silicon wafer, a sapphire wafer, a compound semiconductor wafer, a glass substrate, a resin substrate (glass epoxy substrate (FR-4), a bismaleimide triazine substrate, a polyimide resin substrate, a fluororesin, etc.), a printed wiring substrate, and the like. Is done.
The wafer size includes a wafer having a diameter of 200 mm (8 inches), a wafer having a diameter of 300 mm (12 inches), and the like.

The panel includes a glass substrate, a silicon substrate, a resin substrate (glass epoxy substrate (FR-4), bismaleimide triazine substrate, polyimide resin substrate, fluororesin, etc.), a compound semiconductor substrate, a printed wiring board, and the like. The size is, for example, 250 mm square or more, 250 mm × 350 mm, 300 mm square or more, and there are panels of 320 mm × 320 mm, 370 × 470 mm, and the like. Further, a panel of 400 mm square or larger, a panel of 410 mm × 515 mm, a panel of 508 mm × 610 mm, a panel of 500 mm × 510 mm, a panel of 610 mm × 457 mm and the like are included.

[How to make a flux sheet]
The method for producing the flux sheet is not particularly limited, but for example, the resin component (A) is dissolved in a solvent to prepare a resin solution, and a roll coater, a comma coater, etc. Examples thereof include a method in which a coating film is formed by coating by a known method such as a gravure coater, and the coating film is dried to remove a solvent. Further, a flux agent (B) or the like may be added as needed. It should be noted that (A), (B) and the like may be kneaded and melted without a solvent to form a sheet without making a solution using a solvent.

Examples of the solvent for dissolving the resin component (A) include water, an organic solvent, a mixed solvent of water and an organic solvent, and the like, but water is preferable from the viewpoint of reducing the environmental load. Examples of the organic solvent include alcohols and ketones, but alcohols are preferable. Distilled water, ion-exchanged water, tap water and the like can be used as the water, and distilled water having less impurities, ion-exchanged water, ultra-pure water and the like are preferable. Examples of alcohols include methanol, ethanol, n-propanol, n-butanol and the like, and ketones include acetone, methyl ethyl ketone and the like. When an organic solvent is used, it may be used alone or in combination of two or more.

When the resin component (A) is dissolved in water, it is preferable to use warm water heated to 40 to 95 ° C. from the viewpoint of increasing the dissolution rate. The solid content concentration of the resin component (A) is preferably 0.1 to 60% by mass. When the flux agent (B) is added, it is preferable to dissolve the resin component (A) in the same solvent as that used to dissolve the resin component (A), and when the flux agent (B) is a liquid, it is directly added. May be good. If it is easy to separate by adding and mixing, it is preferable to emulsify with a surfactant or the like before adding. By using the solvent to prepare a resin solution having an appropriate melt viscosity, it is possible to suppress a phenomenon in which the smoothness of the coating film surface deteriorates and the occurrence of pinholes.

The drying temperature and drying time of the coating film can be appropriately set depending on the solvent for the resin solution, the film thickness, etc. From the viewpoint of suppressing changes in the physical properties of the obtained flux sheet such as a decrease in the fluidity of the sheet during reflow, it is preferable to dry at a drying temperature of 25 to 180 ° C., more preferably 40 to 100 ° C. Further, it is preferable to provide a plurality of drying furnaces and perform drying step by step. The drying time is preferably, for example, 1 to 90 minutes, more preferably 10 to 70 minutes.

[Soldering method]
The solder joining method of the present invention is characterized by using the flux sheet of the present invention and including the following steps.
(1) Step of arranging the flux sheet on the surface of the substrate having the electrode having the electrode (2) Step of arranging the solder balls on the flux sheet (3) The temperature of the flux sheet is equal to or higher than the melting point of the solder. And at the same time as or after the steps (4) and (3) of heating the resin sheet to a temperature at which the resin sheet is liquefied, a step of heating to a temperature equal to or higher than the melting point of the solder. According to this feature, the adhesiveness to the substrate is good. Therefore, since a flux sheet that does not cause the solder balls to shift during reflow is used, it is possible to exert the effect that defects such as solder joints do not occur.
The solder joining method according to the present invention does not require a complicated coating process such as printing, and only requires arranging a flux sheet between the solder balls and the electrodes of the substrate, and is excellent in workability.
Hereinafter, the substrate and the solder balls used in the above joining method will be described, and then the details of each step will be described with reference to the drawings.

Hereinafter, each step of the solder joining method of the present invention will be described with reference to FIGS. 1 to 5 as appropriate. It should be noted that FIGS. 1 to 5 are schematic views for explaining the solder joining method of the present invention, and the solder joining method of the present invention is not limited thereto.
<Step (1) A step of arranging the flux sheet on the surface of the substrate having the electrodes having the electrodes>
This step is a step of arranging the flux sheet on the surface of the substrate having electrodes. FIG. 1 is a schematic plan view of a substrate including electrodes. Further, FIG. 2 is a schematic view of a substrate having electrodes as viewed from the side surface. Next, as shown in FIG. 3A, the flux sheet of the present invention is arranged on the electrode surface side provided with the electrodes of the substrate. Further, as shown in FIG. 3B, the substrate electrodes may be laminated so as to be embedded in the flux sheet. It is preferable to degreas the substrate in advance before arranging the flux sheet. The method of arranging the flux sheet on the substrate is not particularly limited, and the flux sheet may be placed as it is, but it is preferable to temporarily fix the flux sheet under atmospheric pressure or under vacuum conditions using a laminating device. As the laminating device, a vacuum laminating device or a roll laminator device can be used. The temperature at the time of laminating is preferably a temperature equal to or higher than the glass transition temperature, more preferably 20 ° C or higher than the glass transition temperature or a softening point or higher (if there is no softening point, the rubber state is equal to or higher than the glass transition temperature). Is preferable. The temperature varies depending on the type of the resin component (A) and the like, but is, for example, 30 to 100 ° C.

(substrate)
The substrate used in the solder bonding method of the present invention is a substrate provided with electrodes, and may include one or more electrodes. For example, a substrate, a chip, or a substrate provided with a plurality of electrodes shown in FIG. Examples include wafers. Further, a solder resist is formed in a region other than the electrodes on the upper surface of a part of the substrate (note that the solder resist is not shown in FIGS. 2 to 5 for simplification). Examples of the substrate provided with such an electrode include the printed wiring board shown above. In order to improve the wettability with solder balls on the electrode surface, for example, the Cu electrode surface is made of UBM composed of Cu / Ni / Pd / Au, Cu / Ni / Au, Cu / Ni-P / Au, etc. It is preferable to form a (Under Copper Metallization) layer or a Surface Finish-treated layer.

In addition, if dirt such as oils and fats adheres to the electrode surface of the substrate, the wettability with the solder balls will decrease and the bondability will be adversely affected. Is preferable. At the time of degreasing, it is more preferable to apply ultrasonic waves because the cleaning effect is further enhanced. When there is no UBM layer or Surface Finish-treated layer on the electrode surface, an oxide film is likely to be formed on the electrode surface, so the substrate may be washed in advance with an acidic aqueous solution, a basic aqueous solution, or the like.

<Step (2) Step of arranging the solder balls on the flux sheet>
This step is a step of arranging and fixing the solder balls so as to be located on the electrodes of the substrate via the flux sheet as shown in FIG. Regarding the placement, various ball mounter devices may be used, a method of dropping the balls with a brush or the like using a metal mask opened on the electrodes, or a thin wire or pin having an adhesive applied to the tip. After carrying the ball to the electrode using the above method, a method of adhering the ball to the flux sheet and arranging the ball may be used. When arranging the solder for temporary fixing to the solder ball and the substrate via the flux sheet, the temperature is about the same as the temperature at which the flux sheet is laminated, that is, preferably above the glass transition point, more preferably above the glass transition point. It is preferable to heat at a temperature higher than 20 ° C. or a temperature of a softening point or higher (when there is no softening point, a rubber state of a glass transition point or higher). The temperature varies depending on the type of the resin component (A) and the like, but is, for example, 30 to 100 ° C. Further, when the solder balls are arranged on the electrodes of the substrate via the flux sheet, they may be pressed, but the sheet of the present invention contains a resin (a1) having a glass transition point of 40 ° C. or lower and is flexible. Since it has a simple structure, it is not necessary to press it positively. By using the flux sheet of the present invention, the solder balls are buried in the flux sheet by their own weight, so that the adhesion between the solder balls and the flux sheet and the substrate is improved.

(Solder ball)
The composition of the solder balls used in the solder bonding method of the present invention includes, for example, Sn-Pb system, Pb-Sn-Sb system, Sn-Sb system, Sn-Pb-Bi system, lead-free Sn-Ag system, and the like. Examples thereof include Sn-Ag-Cu system, Bi-Sn system, Sn-Cu system, Sn-Ag-Bi-In system, Sn-Zn-Bi system and the like. In addition, Sn-Bi-based (Sn58Bi: melting temperature: 138 ° C.) or In-Sn-based (In48Sn: melting temperature: 118 ° C.) solder, which is lead-free and has a low melting point, can also be used. In the present invention, it is preferable to use lead-free solder that does not contain lead. Among the lead-free solders, Sn—Ag—Cu-based solders are preferable from the viewpoint of mechanical properties and the like, and for example, Sn3Ag0.5Cu (melting temperature: about 217 ° C.) is more preferable. Further, for a material such as a liquid crystal display in which the material itself deteriorates in a high temperature process exceeding 200 ° C., it is preferable to use lead-free and low melting point solder.

The size of the solder balls used in the solder joining method of the present invention is, for example, 10 μm or more and 1000 μm or less. The lower limit value is preferably 30 μm or more, more preferably 40 μm or more, and further preferably 50 μm or more. The upper limit is preferably 760 μm or less, more preferably 610 μm or less, still more preferably 450 μm or less, and particularly preferably 300 μm or less.

<Step (3) Step of heating to a temperature at which the flux sheet melts or softens>
This step is a step of heat-treating at a temperature higher than the temperature at which the flux sheet melts or softens. By performing the heat treatment at the above temperature, when a flux component activated by heat is contained, the metal oxide formed on the surface of the solder ball can be removed by the flux action of the sheet. Further, not only the surface of the solder but also the oxide existing on the surface of the electrode can be removed at the same time. In the present invention, since the flux sheet containing the resin (a1) in the resin (A) is used, in this step (3), the electrode and the solder do not shift as shown in FIG. 5, and the solder is further formed. Can easily penetrate the substrate by its own weight, and the solder bondability is improved.

<Step (4): Simultaneously with or after (3), the step of heating to a temperature equal to or higher than the melting point of the solder>
This step is a step of temperature-treating the temperature above the melting point of the solder. By heat-treating at the above temperature, the solder balls can be melted and soldered. The step (4) may be performed at the same time as (3) or after (3).

The heating temperature (maximum reached temperature) and the heating time (holding time) at the temperature in steps (3) and (4) are the melting temperature of the solder ball, the temperature at which the resin component (A) softens, and the resin component ( It can be appropriately set depending on the conditions such as the melt viscosity of A), the boiling point of the flux agent, the size of the electrodes on the substrate, and the pitch between the electrodes.
(3) The heating temperature is preferably equal to or higher than the melting temperature or softening temperature of the resin sheet, for example, melting temperature (softening temperature) + 20 ° C. or higher and + 100 ° C. or lower. The heating time is preferably, for example, 5 seconds to 10 minutes. (4) The heating temperature (maximum temperature reached) is, for example, T + 10 ° C. or higher and T + 80 ° C. or lower when the melting temperature of the solder balls is T (° C.). The lower limit is preferably T + 20 ° C. or higher, and more preferably T + 30 ° C. or higher. The upper limit is preferably T + 70 ° C. or lower, and more preferably T + 45 ° C. or lower. The heating time can be appropriately set depending on the heating temperature (maximum temperature reached), but when the heating temperature (maximum temperature reached) is within the above range, the heating time (holding time) is, for example, 5 seconds to 10 minutes. Is. The lower limit is preferably 10 seconds or longer, more preferably 20 seconds or longer. The upper limit is 5 minutes or less, more preferably 3 minutes or less. Further, this step may be carried out under atmospheric pressure conditions or in an atmosphere of an inert gas such as nitrogen, but it is more preferable to carry out the step in an atmosphere of an inert gas such as nitrogen.

The temperature profile in the case of carrying out (4) after (3) is, for example, in the case of Sn37Pb, (3) 100 to 150 ° C., 60 to 120 seconds, (4) 183 ° C. or higher for 60 to 150 seconds, peak temperature 225. It may be ~ 240 ° C. (heating rate 3 ° C./sec or less). In the case of Sn3Ag0.5Cu, (3) 150 to 200 ° C., 60 to 180 seconds, (4) 217 ° C. or higher and 60 to 150 seconds, peak temperature 245 to 260 ° C. (heating rate 3 ° C./sec or less). It's okay. These steps may be performed multiple times, if desired. The temperature profile is preferably a recommended condition of the Semiconductor Technology Association (JEDEC) (based on IPC / JEDEC J-STD-020C).
Further, since the flux sheet of the present invention contains a resin (a1) having a glass transition point of 40 ° C. or lower and a melt viscosity of 150 ° C. of 500 Pa · s or less, it is in a state of being pressed from a solder ball toward a substrate. There is no need to perform heat treatment with. After the completion of this step, as shown in FIG. 5, the soldered state is obtained.

Further, after the completion of the above solder joining method, the flux sheet of the present invention may be dissolved and removed with a solvent. By dissolving and removing the flux sheet with a solvent, the flux sheet existing in the region other than the solder-bonded region is dissolved and removed by the solvent, and as shown in FIG. 6, the solder-bonded portion is exposed. The cleaning solvent for dissolving and removing the flux sheet is not particularly limited, and examples thereof include water, an organic solvent, and a mixed solvent of water and an organic solvent. However, from the viewpoint of low environmental load and easy availability, there is no particular limitation. Water is preferred. Examples of the organic solvent include alcohols and ketones, but alcohols are preferable. When an organic solvent is used, it may be used alone or in combination of two or more. When the resin component (A) is difficult to dissolve in water, it is preferable to use an organic solvent or a mixed solvent of water and an organic solvent. The mixing ratio of the mixed solvent of water and the organic solvent is not particularly limited, but it is preferable that the ratio of the organic solvent is low from the viewpoint of reducing the environmental load. Distilled water, ion-exchanged water, tap water and the like can be used as the water, and distilled water having less impurities, ion-exchanged water, ultra-pure water and the like are preferable. Examples of the alcohol include methanol, ethanol, n-propanol, n-butanol and the like, and examples of the ketone solvent include acetone, methyl ethyl ketone and the like. The temperature of the solvent to be used can be appropriately set depending on the resin component (A) contained in the flux sheet, but from the viewpoint of workability, it is preferably performed at room temperature.

When the flux sheet is difficult to dissolve or when it takes a long time to dissolve, a heated solvent may be used, or a solvent containing a surfactant may be used. The higher the temperature of the heated solvent, the easier it is to dissolve the flux sheet, but it is preferable that the temperature is lower than the boiling point of the solvent.
As the surfactant, a surfactant such as an anionic surfactant, a cationic surfactant, an amphoteric ionic surfactant, or a nonionic surfactant can be used.

Further, from the viewpoint of improving the efficiency of dissolution and removal of the flux sheet, it is preferable to dissolve and remove the flux sheet while irradiating it with ultrasonic waves. When the flux agent (B) is used, if the flux agent remains, it may corrode the solder joint portion and cause a decrease in reliability of long-term use. Therefore, in order to improve the removal efficiency of the flux agent. , It is preferable to perform the cleaning treatment while irradiating ultrasonic waves. The intensity of the ultrasonic waves is preferably adjusted so that the formed solder joint does not break. Further, cleaning with a water flow generator such as a submerged jet or a direct path is preferable in order to improve the effect of removing the flux agent.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to the following Examples. As for the physical property values of each component used in the following examples, the values measured based on the following method were used.

(Preparation of resin solution)
[Manufacturing Example 1]
Modified polyvinyl alcohol (polyvinyl alcohol to which polyethylene glycol is added: manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosenex (registered trademark) LW-100; glass transition point -0.5 ° C, melt viscosity at 150 ° C: 63 Pa · s" (Shearing rate 10 mm / min) (measured by volatilizing water with the resin alone) and saponification degree 39.0 to 46.0) were used as the resin solution (solid content 40% by mass aqueous solution).

(Preparation of flux sheet)
A coating film is formed by applying the above-prepared resin solution on a polyethylene terephthalate film (6502 manufactured by Lintec Corporation) (hereinafter referred to as a release film) which is a support whose surface has been subjected to a mold release treatment. bottom. Then, this coating film was heated and dried at 80 ° C. for 60 minutes to prepare a flux sheet having a film thickness of 30 μm on the support.

[Manufacturing example 2]
A flux sheet having a film thickness of 30 μm was produced by the same method as in Production Example 1 except that 5 parts by mass of adipic acid (relative to 100 parts by mass of the resin solid content of LW-100) was used as the flux agent.

[Manufacturing example 3]
A flux sheet having a film thickness of 30 μm was produced by the same method as in Production Example 1 except that 5 parts by mass of salicylic acid (relative to 100 parts by mass of the resin solid content of LW-100) was used as the flux agent.

[Manufacturing example 4]
Polyamide (PA) (manufactured by Toray Co., Ltd., trade name "AQ nylon T-70; glass transition point -46 ° C, 150 ° C, melt viscosity: 17 Pa · s (shear rate 10 mm / min)) (resin alone by volatilizing water) )) To 100 parts by mass (51% by mass of solid content), 5 parts by mass of dodecylamine (relative to 100 parts by mass of resin solid content of T-70) was added as a flux agent and stirred to prepare a resin solution. Then, using this prepared resin solution, a flux sheet having a thickness of 30 μm was prepared by the same method as in Production Example 1.

[Manufacturing Example 5]
A flux sheet having a film thickness of 30 μm was produced by the same method as in Production Example 4 except that 5 parts by mass of adipic acid (based on 100 parts by mass of the resin solid content of T-70) was used as the flux agent.

[Manufacturing example 6]
Polyester (PEs) (manufactured by Takamatsu Oil & Fat Co., Ltd., trade name "Pesresin A-680; glass transition point 30 ° C., 150 ° C. melt viscosity: 29 Pa · s (shear rate 10 mm / min)) Measurement)) To 100 parts by mass (solid content 20% by mass), add an aqueous solution prepared by dissolving 5 parts by mass of adipic acid (relative to 100 parts by mass of resin solid content of pesresin A-680) in distilled water as a flux agent. A resin solution was prepared by stirring. Then, using this adjusted resin solution, a flux sheet having a thickness of 30 μm was prepared by the same method as in Example 1.

[Manufacturing example 7]
A flux sheet having a film thickness of 30 μm was produced by the same method as in Production Example 1 except that 43 parts by mass of salicylic acid (relative to 100 parts by mass of the resin solid content of LW-100) was used as the flux agent.

[Manufacturing Example 8]
The solid content of LW-100 is 70 parts by mass, and 30 parts by mass of polyvinyl alcohol (PVA) (manufactured by Japan Vam & Poval Co., Ltd., trade name "Poval JP-03"; glass transition point 63 ° C.) is used, and 5 parts by mass of adipic acid is used. A flux sheet having a thickness of 30 μm was produced by the same method as in Production Example 1 except that parts (relative to a total of 100 parts by mass of LW-100 and JP-03) were used.
[Manufacturing example 9]
The solid content of LW-100 is 60 parts by mass, the amount of JP-03 is 40 parts by mass, and carboxymethyl cellulose (CMC) as a compatibilizer (manufactured by Daicel FineChem Co., Ltd., trade name "CMC1220") 5 A flux sheet having a thickness of 30 μm was produced by the same method as in Production Example 8 except that the parts by weight were used.

[Manufacturing Example 10]
A flux sheet having a film thickness of 30 μm was produced by the same method as in Production Example 9 except that the solid content of LW-100 was 50 parts by mass and the amount of JP-03 was 50 parts by mass.

[Manufacturing Example 11]
A flux sheet having a film thickness of 30 μm was produced by the same method as in Production Example 10 except that the solid content of LW-100 was 40 parts by mass and the amount of JP-03 was 60 parts by mass.

[Comparative Manufacturing Example 1]
Polyvinyl butyral (PVB) (manufactured by Sekisui Chemical Co., Ltd., trade name "Eslek KW-1; glass transition point 65 ° C., 150 ° C. melt viscosity: 1444 Pa · s (shear rate 10 mm / min)) (resin by volatilizing water 5 parts by mass of adipic acid (relative to 100 parts by mass of resin solid content of KW-1) was dissolved in distilled water as a flux agent in 100 parts by mass of solid content (20% by mass of solid content) of))). An aqueous solution was added and stirred to prepare a resin solution. Then, using this prepared resin solution, a flux sheet having a thickness of 30 μm was prepared by the same method as in Production Example 1.

[Comparative Manufacturing Example 2]
Polyvinyl alcohol (PVA) (manufactured by Japan Vam & Poval Co., Ltd., trade name "Poval JP-03; does not melt at glass transition point 63 ° C. and 150 ° C.)" has a solid content of 100 parts by mass and 5 parts by mass of adipic acid as a flux agent. (With respect to 100 parts by mass of the resin solid content of JP-03) was added and stirred to prepare a resin solution. Then, using this adjusted resin solution, the film thickness was 30 μm by the same method as in Production Example 1. Flux sheet was prepared.

[Comparative Manufacturing Example 3]
As a flux agent on 100 parts by mass of the solid content of ethylene-vinyl acetate copolymer (EVA) (manufactured by Denka Co., Ltd., trade name "Denka EVA Latex 55N"; does not melt at glass transition point -10 ° C and 150 ° C). An aqueous solution prepared by dissolving 5 parts by mass of adipic acid (relative to 100 parts by mass of the resin solid content of Denka EVA latex 55N) in distilled water was added and stirred to prepare a resin solution. Then, using this adjusted resin solution, a flux sheet having a film thickness of 30 μm was produced by the same method as in Production Example 1.

[Soldering joint test using flux sheet]
The substrates and solder balls used in the solder joint test are as follows.
Substrate: FR-4 (glass epoxy substrate, electrode made of copper, UBM layer on the electrode surface made of Cu / Ni / Au (Ni layer thickness is 3 μm, Au layer thickness is 0.03 μm) Is.)
Solder ball: Solder composition (diameter 760 μm, Sn-Ag-Cu; Sn: 96.5% by mass, Ag: 3.0% by mass, Cu: 0.5% by mass (melting temperature 217 to 219 ° C.))

[Examples 1 to 11, Comparative Examples 1 to 3]
The items (1) to (6) below were evaluated based on the following methods using the flux sheets prepared in Production Examples 1 to 11 and Comparative Production Examples 1 to 3. The evaluation results are shown in Table 1.
(1) Adhesion between Flux Sheet and Substrate The flux sheet with a release film produced above was heated to 80 ° C., pressed against the substrate in a vacuum, and laminated on the substrate. After returning to room temperature, the state of the substrate when the release film was peeled off was observed.
A: The flux sheet was separated from the release film and transferred to the substrate.
C: Peeling at the flux sheet / substrate interface or / and destruction in the flux sheet occurred.
(2) Tackiness of Flux Sheet The flux sheet prepared above was touched and sensory evaluated for its tackiness at room temperature.
A: Has moderate tack (sticky)
C: No tack (non-sticky and cannot be attached to other materials)
(3) Reworkability and handleability of the flux sheet For the flux sheet produced above, after touching the sheet, check the adhesive residue when the finger pressed against the sheet is pressed against another finger. , Reworkability and handleability at room temperature (body temperature) were sensory evaluated.
A: No adhesive residue on the finger C: No adhesive residue on the finger (4) Holding power of solder balls Using a metal mask, 36 solder balls are placed on a substrate laminated with a flux sheet, and once at 80 ° C. The temperature was raised to room temperature and returned to room temperature.
The substrate after the solder balls were placed was tilted at a specific angle, and the holding force of the solder balls by the flux sheet was measured.
A: The solder balls do not fall when tilted 90 degrees after the solder balls are placed.
C: When the solder ball was tilted 90 degrees after placement, the solder ball fell.

(5) Dissolving and removing property (visual observation and loupe observation)
The substrate on which the solder balls were mounted was heat-treated at 250 ° C. in the atmosphere to bond the solder and the substrate.
The solder-bonded substrate is immersed in distilled water at 25 ° C. rocked at 42 kHz using an ultrasonic cleaner "Plansonic" (product name 5510, manufactured by BRANSON) for 5 minutes. rice field. In Example 6, instead of distilled water, a mixed solvent of methanol / distilled water = 1/1 (mass ratio) was used. Through the above steps, a solder joint using a flux sheet was obtained.
The cleaned substrate was visually observed and the presence or absence of the flux sheet remaining in the gap between the solder / substrate was observed using a loupe, and the evaluation was made according to the following criteria.
A: No flux sheet remains.
B: A flux sheet is slightly observed at the end of the solder.
C: The flux sheet remains throughout.
(6) Solder bonding force A die share tester was used to perform a share test on five bonded solder balls to confirm the solder bonding force.
A: All are cohesive fractures.
C: Partial or all interfacial fracture.

Since Examples 1 to 11 use a flux sheet containing a resin having a glass transition point of 40 ° C. or lower and a melt viscosity of 150 ° C. of 500 Pa · s or less, adhesiveness, tackiness, reworkability, and solder holding power Good results were obtained in all of the evaluations of dissolution and removability and solder bonding strength. Comparing Examples 1 to 5 and 7 to 11 with Example 6, the sheets of Examples 1 to 5 and 7 to 11 having weaker hydrogen bonds with water are more water than the sheets of Example 6. The result was that it was more soluble in water. In Examples 8 to 11, a resin having a glass transition point of 40 ° C. or lower and a melt viscosity of 150 ° C. of 500 Pa · s or less is contained, and a resin having a glass transition point higher than that of the resin is contained. It was found that the handleability was improved.

In Comparative Examples 1 and 2, since a resin having a glass transition point of 40 ° C. or lower was not used, the adhesive force with the substrate was weak and the solder ball holding force was weak, resulting in inferior solder bonding force. Further, in Comparative Example 3, since a resin having a melt viscosity at 150 ° C. of 500 Pa · s or less is not used, the adhesive force with the substrate is weak, and the solder ball is insufficiently subducted, resulting in inferior solder bonding force and the like. It became.

According to the present invention, it is possible to provide a flux sheet that has strong adhesiveness to a substrate and does not cause displacement of solder balls during reflow.

Further, according to the present invention, it is possible to provide a solder joining method capable of forming a large number of solder bumps with good uniformity, high productivity, and low environmental load.

1 ... Electrode, 2 ... Solder resist, 3 ... Flux sheet, 4 ... Solder ball, 100 ... Substrate

Claims (10)

A flux sheet containing the resin (A), wherein the resin (A) has a glass transition point of 40 ° C. or less and a melt viscosity of 150 ° C. of 500 Pa · s (measured at a shear rate of 10 mm / min) or less. A flux sheet containing (a1). The resin (A) contains 35 to 99% by mass of the resin (a1) having a glass transition point of 40 ° C. or lower and a viscosity of 150 ° C. of 500 Pa · s (measured at a shear rate of 10 mm / min) or less, and a glass transition point. The flux sheet according to claim 1, wherein the flux sheet contains 1 to 65% by mass of the resin (a2), which is higher than the resin (a1). The flux sheet according to claim 1 or 2, wherein the flux sheet contains a flux agent (B). The flux sheet according to any one of claims 1 to 3, wherein the flux sheet does not substantially contain a small molecule compound other than (B). The flux sheet according to any one of claims 1 to 4, wherein the resin (a1) is water-soluble. The resin (a1) has a partial structure in which one or more hydroxy groups (-OH) of polyvinyl alcohol are linked by one or more alkylene oxide chains- (CH (R ¹ ) CH (R ² ) O) _n- R ³ (N represents the number of repetitions (average value) of the alkylene oxide chain and is 1.0 or more. R ¹ , R ² and R ³ represent hydrogen atoms or organic groups independently of each other. R ¹ , R ² and if there are a plurality of R ^3, characterized in that it comprises one or more selected respectively may be different may be the same.) substituted and modified polyvinyl alcohol, polyamide and polyester, according to claim 1 The flux sheet according to any one of 1 to 5. The flux sheet according to any one of claims 2 to 6, wherein the resin (a2) contains polyvinyl alcohol. The flux sheet according to any one of claims 1 to 7, wherein the content of the resin (A) in the flux sheet is 50% by mass or more. The flux sheet according to any one of claims 1 to 8, wherein the area of the flux sheet is 30,000 mm ^{2 or more.} A solder joining method using the flux sheet according to any one of claims 1 to 9, wherein the solder joining method includes the following steps (1) to (4).
(1) Step of arranging the flux sheet on the surface of the substrate having an electrode having an electrode (2) Step of arranging a solder ball on the flux sheet (3) Heating to a temperature at which the flux sheet melts or softens Steps (4) Simultaneously with (3) or after that, the step of heating to a temperature equal to or higher than the melting point of the solder.

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