KR20210097105A - Solder bonding method using flux sheet and flux sheet - Google Patents

Abstract

An object of the present invention is to provide a flux sheet that has strong adhesion to a substrate and does not cause misalignment of solder balls during reflow. In order to solve the above problems, as a flux sheet containing the resin (A), 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 rate of 10 mm/min). to provide a flux sheet characterized by containing the following resin (a1). Thereby, when bonding a board|substrate with a solder, the adhesiveness with a board|substrate is strong, and it can acquire the effect that the misalignment of a solder ball does not generate|occur|produce during reflow.

Description

Solder bonding method using flux sheet and flux sheet

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

As a method for mounting an electronic component on a substrate or the like, for example, a surface mounting method in which soldering is performed on the surface of a substrate, a through-hole mounting method in which an electrode lead terminal is inserted into a hole in the substrate and soldering is known. As a surface mounting method, there exists a method, such as forming a solder bump in advance on the electrode of a board|substrate, and electrically bonding an electronic component and a board|substrate through this solder, for example. As a method of forming a solder bump, the method of mounting a solder ball etc. on circuit electrodes, such as a board|substrate, etc. are known.

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

For liquid or paste fluxes, it is difficult to adjust the application amount, and workability is poor, and since the oxide removal action is weak on bumps with a small amount of flux applied, it is a problem that solder joint failure occurs. Then, in patent document 1, for example, in order to solve the said problem, resin (A1) which has a structure derived from polyvinyl alcohol, or resin (A2) which has a structure derived from polyvinylpyrrolidone, and a flux A flip-chip bonding method using a flux film including the agent (B) is disclosed.

Japanese Laid-Open Patent Publication No. 2014-168791

However, since the flux film disclosed in the prior art document has weak adhesion to the substrate, the film and the substrate are misaligned during operation or during solder reflow, and as a result, the solder ball and the electrode on the substrate are misaligned. For this reason, the problem that the operation|work of fixing separately with a polyimide tape etc. is needed is generate|occur|produced.

Therefore, an object of the present invention is to provide a flux sheet that has strong adhesion to a substrate and does not cause misalignment of solder balls during reflow.

As a result of earnest examination of the above subject, the inventor 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. By containing the resin (a1), the substrate and The present invention was completed by discovering that a flux sheet having good adhesion and no misalignment of the solder balls during reflow was obtained.

That is, the present invention is the following flux sheet and solder bonding method.

A flux sheet of the present invention for solving the above problems is a flux sheet comprising a resin (A), wherein the resin (A) has a glass transition point of 40°C or less and a melt viscosity of 500°C at 150°C. It is characterized by containing the resin (a1) of Pa·s (measured at a shear rate of 10 mm/min) or less.

According to this feature, since the adhesion to the substrate and the holding force of the solder balls are strong, and the flatness of the sheet is good, the solder balls can sink immediately after the sheet is softened, and the effect that the solder balls do not misalign is obtained. can perform Further, the flux sheet of the present invention can be laminated even at a low temperature, and even without lamination, an effect of good adhesion to the substrate is produced.

Further, in one embodiment of the flux sheet of the present invention, 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. 35-99 mass % of resin (a1) and 1-65 mass % of resin (a2) whose glass transition point is larger than the said resin (a1) are contained, It is characterized by the above-mentioned.

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. Workability can be exhibited.

Further, 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 balls can be improved, and the effect (self-alignment effect) can be exhibited in that the positional misalignment between the solder balls and the electrodes can be corrected during solder reflow.

Further, one embodiment of the flux sheet of the present invention is characterized in that the flux sheet contains substantially no low molecular weight compounds other than (B).

According to this feature, it is possible to exhibit the effect that substrate contamination due to vaporization of low molecular weight compounds or the like during solder reflow and displacement due to solder clouding can be suppressed.

Further, in one embodiment of the flux sheet of the present invention, the resin (a1) is water-soluble.

According to this feature, an aqueous solvent can be used when the flux sheet is manufactured, mounted, or washed after solder reflow. Thereby, since it becomes possible to wash|clean a flux sheet without using a highly volatile organic solvent, the effect that the environmental load by volatilization of an organic solvent can be reduced can be exhibited.

Further, in one embodiment of the flux sheet of the present invention, the resin (a1) has a partial structure in which one or more alkylene oxide chains are linked to one or more hydroxyl groups (-OH) of polyvinyl alcohol - (CH (R ¹ )CH(R ² )O) _n -R ³ (n represents the repeating number (average value) of the alkylene oxide chain, and is 1.0 or more. R ¹ , R ² and R ³ are each independently a hydrogen atom or an organic group. When ^{there are a plurality of R 1} , R ² and R ³ , each of which may be the same or different.) containing at least one selected from modified polyvinyl alcohol, polyamide and polyester substituted with characterized.

According to this feature, the adhesiveness to the substrate is good, and the effect that the solder balls do not shift during reflow can be more exhibited.

Further, one embodiment of the flux sheet of the present invention is characterized in that it contains polyvinyl alcohol as (a2).

According to this feature, it is possible to control adhesiveness and tackiness to improve handleability at the time of work, to improve reworkability, and to improve the water solubility of appearance.

Further, in one embodiment of the flux sheet of the present invention, the content of the resin (A) in the flux sheet is 50 mass% or more.

According to this feature, it is possible to achieve both solder ball holding force and good handleability.

Further, an embodiment of the flux sheet of the present invention is characterized in that the flux sheet has an area of 30000 mm 2 or more.

According to this feature, it is possible to exhibit the effect that the position shift can be further suppressed with respect to a large-area wafer or substrate in which the position shift between the solder ball and the electrode is larger.

The solder bonding method of this invention for solving the said subject is a solder bonding method using the said flux sheet, It has the following steps (1) - (4), It is characterized by the above-mentioned.

(1) disposing the flux sheet on the electrode-bearing surface of the electrode-bearing substrate

(2) a step of disposing a solder ball on the flux sheet

(3) heating to a temperature at which the flux sheet is melted or softened

(4) a step of heating to a temperature equal to or higher than the melting point of the solder simultaneously with or after (3)

According to this feature, since a flux sheet which has strong adhesion to the substrate and does not cause misalignment of the solder balls during reflow is used, it is possible to exhibit the effect that defects in solder bonding or the like do not occur.

ADVANTAGE OF THE INVENTION According to this invention, the adhesiveness with a board|substrate is strong and it can provide the flux sheet|seat which does not generate|occur|produce the misalignment of a solder ball during reflow.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic for demonstrating the solder bonding method of this invention, and is a schematic plan view of the board|substrate provided with an electrode.
It is a schematic for demonstrating the solder bonding method of this invention, and is a schematic sectional drawing of the board|substrate provided with an electrode.
Fig. 3 is a schematic diagram for explaining the solder bonding method of the present invention, and is a schematic cross-sectional view showing an example of a method for arranging the flux sheet of the present invention on the electrode face side of the substrate provided with the electrode in the step (1). am.
Fig. 4 is a schematic diagram for explaining the solder bonding method of the present invention. An example of a method of arranging solder balls in the step (2) so as to be positioned on the electrodes of the substrate through the flux sheet of the present invention. It is a schematic cross-sectional view shown.
5 is a schematic diagram for explaining the solder bonding method of the present invention, and is a schematic cross-sectional view showing an example of a solder bonded substrate in which a solder ball is bonded to an electrode of the substrate in step (3).
6 is a schematic diagram for explaining the solder bonding method of the present invention, and is a schematic cross-sectional view showing an example of a solder bonded substrate from which the flux sheet is removed after the step (4) is finished.

EMBODIMENT OF THE INVENTION Hereinafter, preferred embodiment of this invention is described in detail. However, this invention is not limited to the following embodiment.

[Flux Sheet]

The flux sheet of the present invention is a flux sheet comprising a 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 (shear rate of 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 to remove the oxide film on the solder surface. Specifically, a sheet having a flux effect can be obtained by satisfying at least one of the resin (A) containing a resin having a flux action or the flux sheet containing the flux agent (B). there is.

<Resin (A)>

Resin (A) of this invention contains resin (a1) whose glass transition point is 40 degrees C or less and 150 degreeC melt viscosity is 500 Pa*s or less, It is characterized by the above-mentioned.

The glass transition point is the temperature at which the glass transition of a material occurs (the temperature at which micro-Brownian motion occurs), and in a temperature region below the glass transition point, it is hard and exhibits glassy properties, and in a temperature region higher than the glass transition point, It is soft and shows the properties of rubber or liquid.

When the relationship between the glass transition point and adhesiveness of the resin (a1) is described, in the polymer sheet having an amorphous structure, a glass state that is hard at a lower temperature than the glass transition temperature and a soft rubber state at a high temperature are obtained. Therefore, the sheet containing the resin having a low glass transition temperature (near room temperature, furthermore, below room temperature) is soft in the temperature range 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 force of the sheet becomes stronger. In addition, it can be said that 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 the possibility of adverse effects such as warpage or thermal decomposition of the substrate is low. can As a result, by setting the glass transition point to 40°C or less, a flux sheet having good adhesion to the substrate and 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 less, and the upper limit is preferably 30°C or less, more preferably 20°C or less, still more preferably 10°C or less, especially Preferably it is 0 degreeC or less, Most preferably, it is -20 degrees C or less. By setting the glass transition point of the resin (a1) to 40°C or less, the resin (A) containing the resin (a1) becomes soft, and the adhesion between the substrate and the flux sheet is improved. Moreover, the solder ball can sink under its own weight, and the positional shift of the solder ball can be suppressed.

In this invention, a glass transition point can be measured using a differential scanning calorimetry apparatus (X-DSC7000 Seiko Instruments Co., Ltd. product).

Moreover, in this invention, the melt viscosity of 150 degreeC of resin (a1) is 500 Pa*s or less, It is characterized by the above-mentioned. As an upper limit, Preferably it is 400 Pa.s or less, More preferably, it is 350 Pa.s or less, More preferably, it is 200 Pa.s or less. By setting the melt viscosity at 150°C of the resin (a1) to 500 Pa·s or less, during solder reflow, the solder ball sinks by its own weight and can be in contact with the electrode of the substrate (that penetrates the sheet), and the solder When the temperature is raised above the melting point of

In this invention, a 150 degreeC melt viscosity can be measured with the conditions of a shear rate of 10 mm/min with a capillary rheometer (made by Capyrograph ID Toyo Seiki Seisakusho).

Although it does not specifically limit as resin (a1) whose glass transition point is 40 degrees C or less and 150 degreeC melt viscosity is 500 Pa.s or less, It is preferable that it is a thermoplastic resin, For example, polyethylene, polypropylene, polybutylene, poly Polyvinyl alcohol-based resins such as vinyl chloride, ethylene-cyclic olefin copolymer, polystyrene-based resin, poly(meth)acrylic acid-based resin, polyvinyl alcohol, and modified polyvinyl alcohol, polyvinyl acetate, poly(meth)acrylamide-based resin Resin, polybutadiene, polyisoprene, styrene maleic acid resin, carboxyl-terminated butadienenitrile copolymer (CTBN), etc. addition-based resin, polyester, polyamide, polyimide, polyurethane, polycarbonate resin, polyether ketone, poly Condensed resins such as ethersulfone, polyether resins such as polyethylene glycol and polypropylene glycol, polyalkyleneimine resins such as polyethyleneimine, and ring-opening polymerization resins such as polycycloolefin. These may be used individually by 1 type, and may be used in mixture of 2 or more types. Among these, it is preferable to contain 1 or more types chosen from modified polyvinyl alcohol, polyamide, and polyester.

Moreover, it is preferable from a water solubility viewpoint that polyvinyl alcohol is 75-90 mol%, and, as for polyvinyl alcohol, it is more preferable that it is 85-90 mol%. By setting the degree of saponification of polyvinyl alcohol within the above range, it is possible to suppress crystallization and difficulty soluble in water, or decrease in hydrophilic group and insoluble 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 modified polyvinyl alcohol described later, solubility can be improved by grafting a hydrophilic group other than a hydroxyl group or blocking in the main chain, so the degree of saponification is preferably 30 to 60 mol%, and 40 to 50 It is more preferable that it is mol%. As a hydrophilic group used for hydrophilic group modification, alkylene oxide compounds, such as ethylene glycol, etc. are preferable, for example.

In these resins, a resin containing a hydroxyl group, a carboxyl group, or an amino group can be used as a flux sheet without adding a fluxing agent because the resin itself has a fluxing action. Specifically, resins such as poly(meth)acrylic acid-based resins, polyvinyl alcohol-based resins, polyamides, polyesters, carboxyl-terminated butadienenitrile copolymer (CTBN), polyurethane, etc. can exhibit flux activity in a molten state. .

In the present invention, the weight average molecular weight of the resin (a1) is preferably 1×10 ³ to 2.0×10 ⁵ . As a lower limit, Preferably it is 3.0 x 10 ³ or more, More preferably, it is 8.0 x 10 ³ or more. As an upper limit, Preferably it is 1.5 x 10 ⁵ or less, More preferably, it is 1.0 x 10 ⁵ or less. More preferably, it is 5.0 x 10 ⁴ or less. When the weight average molecular weight of the resin (a1) falls within the above range, the moldability of the sheet becomes good, and the dissolution removal of the sheet after soldering and the sheet penetrability of the ball become good.

The molecular weight distribution (Mw/Mn) of the resin (a1) is preferably 1 to 30. As a lower limit, Preferably it is 1.5 or more, More preferably, it is 1.8 or more. As an upper limit, Preferably it is 15 or less, More preferably, it is 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 conversion value.

The resin (a1) of the present invention is preferably water-soluble. Water solubility means that 5 mass parts or more of resin (a1) is melt|dissolved with respect to 100 mass parts of water under the conditions of 25 degreeC and 1 atm. As a lower limit, Preferably it melt|dissolves 10 mass parts or more, More preferably, it is 20 mass parts or more, More preferably, it is 30 mass parts or more.

Since the resin (a1) is water-soluble, it can be prepared using an aqueous solvent when manufacturing the flux sheet. Moreover, when washing|cleaning a flux sheet, an aqueous solvent can be used and the effect that the environmental load by volatilization of an organic solvent can be reduced can be exhibited.

The resin (a1) is, for example, a partial structure in which one or more alkylene oxide chains are linked to a hydroxyl group (-OH) of a part of polyvinyl alcohol -(CH(R ¹ )CH(R ² ) O) modified polyvinyl alcohol substituted with _n -R ^{3 ) is mentioned.}

n represents the repeating number (average value) of an alkylene oxide chain, Preferably it is 1.0 or more. As a lower limit of n, Preferably it is 1.0 or more, More preferably, it is 2.0 or more, More preferably, it is 5.0 or more, Especially preferably, it is 6.0 or more. As an upper limit, Preferably it is 300.0 or less, More preferably, it is 200.0 or less, More preferably, it is 65.0 or less.

When n falls within the above range, a flux sheet excellent in adhesiveness can be obtained.

A hydrogen atom or an organic group is preferable as R<^1> , R<^2> , respectively, and a C1-C10 alkyl group is preferable as an organic group. As a C1-C10 alkyl group, a methyl group, an ethyl group, n-propyl group, i-propyl group, a butyl group, a pentyl group, a hexyl group etc. are mentioned, for example.

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 alkylester group having 1 to 10 carbon atoms, or an alkylester group having 1 to 10 carbon atoms. of alkylamide group and sulfonate group are preferable.

As a C1-C10 alkyl group, a methyl group, an ethyl group, n-propyl group, i-propyl group, a butyl group, a pentyl group, a hexyl group etc. are mentioned, for example.

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 carbonyl group.

Examples of the alkylester group having 1 to 10 carbon atoms include a methyloxycarbonylmethylene group, a methylcarbonyloxymethylene group, an ethyloxycarbonylethylene group, and an ethylcarbonyloxyethylene group.

Examples of the alkylamide group having 1 to 10 carbon atoms include a N,N′-dimethylamidealkylene group and a N,N′-diethylamidealkylene group.

As said modified polyvinyl alcohol, specifically, the brand name "Gosenex (trademark) LW-100 (made by Nippon Synthetic Chemical Industry Co., Ltd.; melt viscosity of glass transition point -0.5 degreeC, 150 degreeC: 63 Pa.s (shear rate 10) mm/min) and a saponification degree of 43.1 mol%").

As said polyester, specifically, a brand name "Fesresin A-680 (manufactured by Takamatsu Oil Corporation; glass transition point 30°C, melt viscosity at 150°C: 29 Pa·s (shear rate 10 mm/min))), said Specific examples of the polyamide include a brand name "AQ nylon T-70 (manufactured by Toray Corporation; glass transition point -46°C, melt viscosity at 150°C: 17 Pa·s (shear rate 10 mm/min))). .

It is preferable that resin (A) of this invention contains the said resin (a1) 35 mass % or more. Moreover, in addition to the said resin (a1), resin (A) of this invention can also contain other resin. As other resin, it is preferable to contain resin (a2) whose glass transition point is higher than the said resin (a1).

The resin (a2) is not limited as long as it is a resin having a higher glass transition point than that of the resin (a1), and for example, a thermoplastic resin exemplified in the resin (a1) can be used. Moreover, in addition to the said thermoplastic resin, although a thermosetting resin etc. can be contained, it is preferable from a viewpoint of a washability that a thermosetting resin is 45 mass % or less. When content of a thermosetting resin shall be 60 mass % or less, since a thermosetting resin can form an island phase in a composition and favorable washability can be acquired, it is preferable.

As a glass transition point of resin (a2), it is preferable that it is higher than 40 degreeC. Moreover, as a lower limit, More preferably, it is 50 degreeC or more, More preferably, it is 60 degreeC or more.

Examples of the resin (a2) having a glass transition point higher than the resin (a1) include polyethylene, polypropylene, polybutylene, polyvinyl chloride, ethylene-cyclic olefin copolymer, polystyrene-based resin, poly(meth)acryl Acid-based resins, polyvinyl alcohol-based resins, polyvinyl acetate, poly(meth)acrylamide-based resins, polybutadiene, polyisoprene styrene maleic acid resins, and other addition-based resins, polyester, polyamide, polyimide, polyurethane, poly Condensed resins such as carbonate-based resins, polyetherketones and polyethersulfones, polyether-based resins such as polyethylene glycol and polypropylene glycol, polyalkyleneimine-based resins such as polyethyleneimine, and ring-opening polymerization resins such as polycycloolefins can be heard These may be used individually by 1 type, and may be used in mixture of 2 or more types.

When resin (A) of this invention contains resin (a2), Preferably it contains 35-99 mass % of resin (a1), and 1-65 mass % of resin (a2).

As a lower limit, content of resin (a1) becomes like this. Preferably it is 60 mass % or more, More preferably, it is 65 mass % or more, More preferably, it is 70 mass % or more. As an upper limit, it is 95 mass % or less, More preferably, it is 90 mass % or less.

As a lower limit, content of resin (a2) becomes like this. Preferably it is 5 mass % or more, More preferably, it is 10 mass % or more. As an upper limit, it is 40 mass % or less, More preferably, it is 35 mass % or less, More preferably, it is 30 mass % or less.

In addition to resin (a1), resin (A) of invention can control the adhesive force to a board|substrate etc. by adding resin (a2). In addition, the position of the arranged solder balls can be easily corrected, and the reworkability is improved. Moreover, it is excellent in the flexibility and handling property of the sheet|seat itself. Moreover, by making content of resin (a2) into the said range, it becomes possible to wash|clean with an aqueous solvent.

When the compatibility of the resin (a1) and the resin (a2) is poor, compatibility can be improved by using a compatibilizer, a modifier, and a dispersing agent. As compatibilizers, modifiers, and dispersants, a block (co) polymer or graft (co) polymer in which a segment with high affinity to the resin (a1) and resin (a2) is chemically bonded at one point or multiple points, respectively. do.

Since the modified polyvinyl alcohol has a polyvinyl alcohol chain and a (poly)alkylene oxide chain in the molecule, it exhibits functions as a compatibilizer, modifier, and dispersant with polyvinyl alcohol and polyalkylene oxide, respectively. In addition, in the mixing of the modified polyvinyl alcohol and polyvinyl alcohol, as a compatibilizer/modifier/dispersant, preferably polyalkylene oxide, carboxymethyl cellulose, sodium salt of carboxymethyl cellulose, potassium of carboxymethyl cellulose salts and the like can be used.

The blending amount of the compatibilizer, modifier, and dispersant is not particularly limited, but in consideration of the effect of compatibilization and reduction of low molecular weight components, the lower limit is preferably based on 100 parts by mass of the total of the resin (a1) and the resin (a2). is 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and still more preferably 0.5 parts by mass or more. As an upper limit, Preferably it is 15 mass parts or less, More preferably, it is 10 mass parts or less, More preferably, it is 5 mass parts 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 expressed or improved, the formability of a solder joint can be improved, and electrical conductivity can be improved. Moreover, the wettability of the solder can be improved, and the effect (self-alignment effect) of being able to correct the position shift of a solder ball and an electrode at the time of solder reflow can be exhibited.

The flux agent (B) is not particularly limited as long as it is a component capable of removing the high-melting-point metal oxide present on the solder surface, and an acidic substance, a basic substance, or an alcohol is preferably used. In addition, those that are active at room temperature and those that are activated by heating can be used.

Specific examples of the flux agent (B) include carboxylic acids such as adipic acid, malonic acid, succinic acid, maleic acid, pentanoic acid, salicylic acid, benzoic acid, m-dihydroxybenzoic acid, and sebacic acid; Amines, such as dodecylamine, the hydrohalic acid salt of an amine, rosin resin, etc. are mentioned. Moreover, a flux agent may be used independently and may use 2 or more types together. As the flux agent (B) contained in the flux sheet of the present invention, 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 of solder balls, the size (surface area), the thickness of the oxide film on the surface, the thickness of the flux sheet, etc., but 10 parts by mass per 100 parts by mass of the resin (A) It is preferable that it is less than part. Moreover, as an upper limit, More preferably, it is 8 mass parts or less, More preferably, it is 7 mass parts or less, Especially preferably, it is 6 mass parts or less. On the other hand, as a lower limit, Preferably it is 1 mass part or more, More preferably, it is 3 mass parts or more.

When the content of the flux agent (B) is 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. Moreover, by suppressing that a flux agent remains in a board|substrate, the fall suppression of insulation resistance in high temperature, high humidity, and corrosion and migration of a metal can be prevented.

<Other additives>

The flux sheet of the present invention may contain, in addition to the resin (A) and the flux agent (B), an additive contained in a general flux, for example, within a range that does not impair the effects of the present invention. Examples of the additive include a thixotropic imparting agent, a flux activation aid, an antifoaming agent, and the like.

Examples of the thixotropic imparting agent include fatty acid amides such as m-xylylenebisstearic acid amide, polyolefin waxes such as castor wax (hydrogenated castor oil), substituted urea waxes such as N-butyl-N'-stearylurea, polyethylene and high molecular compounds such as glycol, methyl cellulose, ethyl cellulose and hydroxyethyl cellulose, and inorganic particles such as silica particles and kaolin particles.

A thixotropy imparting agent may be used individually by 1 type, and may use 2 or more types together.

When a thixotropy imparting agent is used in the flux of the present invention, the content thereof is preferably 0.1 to 20 parts by mass based on 100 parts by mass of the polymer (A). As a lower limit, Preferably it is 0.2 mass part or more, More preferably, it is 0.5 mass part or more. As an upper limit, Preferably it is 15 mass parts or less, More preferably, it is 10 mass parts or less. When the content of the thixotropy imparting agent is within the above range, the adhesive force with the solder ball or the substrate can be adjusted.

Examples of the flux activity auxiliary agent include amine hydrohalides such as diethylamine hydrobromide and cyclohexylamine hydrobromide, organic acids such as stearic acid, organic amines such as tributylamine, trans-2, Activators, such as organic halides, such as 3-dibromo-2-butene-1, 4- diol, etc. are mentioned.

Examples of the defoaming agent include alcohols such as lauryl alcohol, cetyl alcohol, stearyl alcohol, eicosanol and docosanol, polyethylene wax, paraffin wax, and hydrocarbon compounds such as white oil, carboxylic acid (eg For example, palmitic acid, oleic acid, stearic acid, etc.) and alcohol (e.g., methanol, ethanol, octanol, etc.) fatty acid esters obtained by condensation, natural fats and oils such as tallow, soybean oil, linseed oil, polydimethyl Siloxanes, such as siloxane and polymethylphenyl siloxane, etc. are mentioned. Moreover, surfactant with high lipophilicity, such as a cationic surfactant, an anionic surfactant, and a nonionic surfactant, can also be used.

Further, it is preferable that the flux sheet of the present invention contains substantially no low molecular weight compounds other than (B). As a low molecular weight compound other than (B), molecular weight is 1000 or less, for example, Plasticizers, such as glycerol, phthalic acid ester, adipic acid ester, trimellitic acid ester, are mentioned as a typical example.

By substantially not containing low molecular weight compounds other than (B), substrate contamination caused by vaporization of low molecular weight compounds during solder reflow, and shifting due to solder rolling caused by sudden vaporization can be suppressed. can perform

Substantially free means not intentionally adding a low molecular weight compound other than (B) as a component of the flux sheet. In the flux sheet, there are cases where a solvent necessary in the sheet preparation step, a low molecular weight compound derived from the raw material monomer of the resin (A), etc. remain, but in that case, the content is, for example, less than 10 mass%, and the upper limit is , Preferably it is less than 5 mass %, More preferably, it is less than 3 mass %, More preferably, it is less than 2 mass %, Especially preferably, it is less than 1 mass %.

<Features of flux sheet>

In the flux sheet of the present invention, the resin (A) contains a resin (a1) having 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. Because of this feature, the adhesiveness to the substrate is strong, and there is an effect that the solder balls do not shift during reflow. In addition, since it contains the resin (a1) whose melt viscosity at 150°C is 500 Pa·s or less, the solder balls can sink by their own weight during solder reflow, so that the position shift of the solder balls can be suppressed. Therefore, the effect excellent in solder bonding property can be exhibited.

Since the flux sheet of the present invention does not have the same fluidity at room temperature as liquid and paste fluxes, aggregation, separation, sedimentation, etc. of the flux do not easily occur even when a flux agent is contained, and the storage stability is excellent.

In addition, when liquid and paste-like fluxes are applied by printing, etc., since there is a large variation in the application amount, it is necessary to appropriately adjust the application amount, etc., so that workability is poor. It only needs to be mounted on a board|substrate and lamination, and it is excellent in workability|operativity.

If the solvent remains, it may evaporate at the time of bonding to form voids. Therefore, in the flux sheet of the present invention, the content of the remaining solvent is preferably less than 10% by mass. This content rate can be measured, for example by the Karl Fischer method or the weight reduction by heating.

When the flux sheet of the present invention contains the water-soluble resin (a1), water can be used for manufacturing or mounting the flux sheet, or for cleaning the flux sheet. Therefore, since it is not necessary to use the organic solvent which volatilizes and is discharged|emitted into the atmosphere, it is possible to reduce the environmental load.

The thickness of the flux sheet of the present invention can be appropriately set in consideration of flux activity, cleaning properties, etc., but is preferably 1 to 500 µm. As a lower limit, Preferably it is 3 micrometers or more, More preferably, it is 5 micrometers or more. As an upper limit, Preferably it is 100 micrometers or less, More preferably, it is 50 micrometers or less.

The size (area) of the flux sheet can be appropriately set in consideration of the size of the substrate, chip, wafer or the like to be used. Specifically, it is preferable to set the area to be slightly larger than the area where the electrode (group) on the substrate is located. Alternatively, it may be formed to be larger than the size planned to be used in advance, and used after being cut to a desired size during use. Alternatively, the sheet may be transferred and laminated by directly pressing the target substrate against the sheet without cutting the sheet.

In the present invention, the area of the flux sheet is preferably 30000 mm 2 or more.

By setting the area of the flux sheet to 30000 mm 2 or more, it is possible to affix to the entire surface of the substrate at a time also for an electronic member substrate such as a large-area panel or wafer.

The large-area electronic member substrate includes a wafer having a diameter of 200 mm (8 inches) or more and a panel having a width of 300 mm or more.

The above-mentioned wafers include silicon wafers, sapphire wafers, compound semiconductor wafers, glass substrates, resin substrates (glass epoxy substrates (FR-4), bismaleimide triazine substrates, polyimide resin substrates, fluororesins, etc.), printed wiring boards, etc. This is included.

The size of the wafer 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 (a glass epoxy substrate (FR-4), a bismaleimide triazine substrate, a polyimide resin substrate, a fluororesin, etc.), a compound semiconductor substrate, a printed wiring board, etc. , The size is, for example, 250 mm or more in width and height, 250 mm × 350 mm, 300 mm or more in width, and there are panels such as 320 mm × 320 mm and 370 × 470 mm. Moreover, a panel of 400 mm or more in width and height, a panel of 410 mm x 515 mm, 508 mm x 610 mm, 500 mm x 510 mm, a panel of 610 mm x 457 mm, etc. are contained.

[Method for manufacturing flux sheet]

Although it does not specifically limit as a manufacturing method of a flux sheet, For example, the resin component (A) is melt|dissolved in a solvent, a resin solution is prepared, and the support body etc. whose surface was mold release-treated are roll coater, comma coater, gravure coater. A method of applying by a known method such as a coating film to form a coating film and drying the coating film to remove the solvent is mentioned. Moreover, you may add a flux agent (B) etc. as needed. Further, without using a solvent to form a solution, (A) (B) or the like may be kneaded and melted without a solvent to form a sheet.

As a solvent in which a resin component (A) is dissolved, although water, an organic solvent, the mixed solvent of water and an organic solvent, etc. are mentioned, for example, From a viewpoint of reduction of environmental load, water is preferable. Although alcohol, a ketone, etc. are mentioned as an organic solvent, Preferably it is alcohol. Distilled water, ion-exchanged water, tap water, etc. can be used as water, and distilled water, ion-exchanged water, and ultrapure water with few impurities are preferable. Examples of the alcohol include methanol, ethanol, n-propanol, and n-butanol, and examples of the ketone include acetone and methyl ethyl ketone. When using an organic solvent, you may use independently and may use 2 or more types together.

When dissolving a resin component (A) in water, it is preferable to use the hot water heated at 40-95 degreeC from a viewpoint of raising a dissolution rate. As solid content concentration of a resin component (A), Preferably it is 0.1-60 mass %. In addition, when adding the flux agent (B), it is preferable to dissolve it in the same solvent as the solvent in which the resin component (A) is dissolved and add it. When the flux agent (B) is a liquid, it may be added directly. Moreover, when it is easy to isolate|separate by addition mixing, it is preferable to emulsify with surfactant etc. and to add. By setting it as a resin solution which has an appropriate melt viscosity using the said solvent, the phenomenon in which the smoothness of the surface of a coating film worsens and generation|occurrence|production of a pinhole can be suppressed.

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, and the like. From a viewpoint of suppressing the change of the physical property of the flux sheet obtained, such as the fluidity|liquidity of a sheet|seat falling, it is preferable to dry at a drying temperature of 25-180 degreeC, More preferably, it is 40-100 degreeC. In addition, it is preferable to provide a plurality of drying furnaces and to dry in stages. The drying time is, for example, preferably from 1 to 90 minutes, more preferably from 10 to 70 minutes.

[Solder joint method]

The solder bonding method of the present invention is characterized in that it is a method including the following steps using the flux sheet of the present invention.

(1) disposing the flux sheet on the electrode-bearing surface of the electrode-bearing substrate

(2) a step of disposing a solder ball on the flux sheet

(3) heating the flux sheet to a temperature equal to or higher than the melting point of the solder and to a temperature at which the resin sheet is liquefied

(4) a step of heating to a temperature equal to or higher than the melting point of the solder simultaneously with or after (3)

According to this feature, since the flux sheet has good adhesion to the substrate and does not cause misalignment of the solder balls during reflow, it is possible to exhibit the effect that defects such as solder bonding do not occur.

In the solder bonding method according to the present invention, a complicated application process such as printing is unnecessary, and it is only necessary to arrange a flux sheet between the solder ball and the electrode of the substrate, and the workability is excellent.

Hereinafter, after the board|substrate and solder ball used for the said bonding method are demonstrated, the detail of each process is demonstrated, referring drawings.

Hereinafter, each process of the solder bonding method of this invention is demonstrated, referring FIGS. 1-5 suitably. 1 to 5 are schematic diagrams for explaining the solder bonding method of the present invention, and the solder bonding method of the present invention is not limited thereto.

<Step (1) Step of disposing the flux sheet on the electrode-bearing surface of the electrode-bearing substrate>

This step is a step of disposing the flux sheet on the electrode-bearing surface of the substrate. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic plan view of the board|substrate provided with an electrode. Moreover, FIG. 2 is the schematic which looked at the board|substrate which has an electrode from the side. Next, as shown in Fig. 3(A), the flux sheet of the present invention is disposed on the electrode surface side provided with the electrode of the substrate. Moreover, as shown in FIG.3(B), you may laminate so that a board|substrate electrode may be embedded in a flux sheet. Before disposing the flux sheet, it is preferable to degrease the substrate in advance. The method of disposing the flux sheet on the substrate is not particularly limited and may be left as it is, but it is preferable to temporarily fix the flux sheet under atmospheric pressure or under vacuum conditions using a laminating apparatus after placing it. As a lamination apparatus, a vacuum lamination or a roll laminator apparatus can be used. The temperature at the time of lamination is preferably at least the glass transition temperature, more preferably at least 20 ° C. higher than the glass transition temperature, or at least the softening point (if there is no softening point, it is in a rubber state above the glass transition temperature). Although it changes with the kind etc. of a resin component (A), it is 30-100 degreeC, for example.

(Board)

The substrate used in the solder bonding method of the present invention is a substrate provided with electrodes, and may be provided with one or more electrodes. can Moreover, the soldering resist is formed in the area|region other than the electrode of one part board|substrate upper surface (In addition, in FIGS. 2-5, a soldering resist is not shown for simplification). As a board|substrate provided with such an electrode, the printed wiring board etc. which were shown above are mentioned, for example. In order to improve the wettability with the solder ball on the electrode surface, for example, on the surface of the Cu electrode, UBM (Under) made of Cu/Ni/Pd/Au, Cu/Ni/Au, Cu/Ni-P/Au It is preferable to form a bump metallization) layer or a surface finish treatment layer.

In addition, if contamination such as oil and fat adheres to the electrode surface of the substrate, the wettability with the solder ball is lowered and the bondability is adversely affected. At the time of degreasing, the application of ultrasonic waves is more preferable because the cleaning effect is further enhanced. When there is no UBM layer or a surface finish-treated layer on the electrode surface, since an oxide film is easy to form on the electrode surface, you may wash|clean the board|substrate beforehand with an acidic aqueous solution, a basic aqueous solution, etc.

<Step (2) Step of disposing a solder ball on the flux sheet>

This step is a process of arrange|positioning and fixing a solder ball so that it may be located on the electrode of a board|substrate via a flux sheet|seat, like FIG. Regarding placement, various ball mounters may be used, a method of placing balls by dropping them with a brush or the like using a metal mask opened on the electrode, etc. Then, after moving the ball to the electrode, it may be adhered to the flux sheet and placed. In order to temporarily fix the solder ball and the substrate via the flux sheet, when the solder is placed, the temperature is the same as the temperature when the flux sheet is laminated, that is, preferably above the glass transition point, more preferably at the glass transition point. It is preferable to heat at a temperature higher than 20 DEG C or higher or at a temperature equal to or higher than the softening point (in the case where there is no softening point, the rubber is at the glass transition point or higher). Although it changes with the kind etc. of a resin component (A), it is 30-100 degreeC, for example. Further, when the solder ball is placed on the electrode of the substrate through the flux sheet, it may be pressed, but the sheet of the present invention contains the resin (a1) having a glass transition point of 40° C. or less and has a flexible structure. , there is no need to actively press By using the flux sheet of the present invention, since the solder balls are filled in the flux sheet by their own weight, the adhesion of the solder balls to the flux sheet and the substrate is improved.

(solder ball)

The composition of the solder ball used in the solder joining method of the present invention is, for example, Sn-Pb-based, Pb-Sn-Sb-based, Sn-Sb-based, Sn-Pb-Bi-based, or lead-free Sn-Ag. type, Sn-Ag-Cu type, Bi-Sn type, Sn-Cu type, Sn-Ag-Bi-In type, Sn-Zn-Bi type, and the like. Moreover, Sn-Bi type (Sn58Bi: melting temperature: 138 degreeC) or In-Sn type (In48Sn: melting temperature: 118 degreeC) solder which is lead-free and is a low-melting-point solder can also be used. In the present invention, it is preferable to use a lead-free solder containing no lead. Among the lead-free solders, from the viewpoint of mechanical properties and the like, a Sn-Ag-Cu type solder is preferable, and for example, Sn3Ag0.5Cu (melting temperature: about 217°C) is more preferable. Moreover, in a high-temperature process exceeding 200 degreeC, it is preferable to use lead-free and low-melting-point solder about the material in which material itself, such as a liquid crystal, deteriorates.

As a size of the solder ball used in the solder bonding method of this invention, it is 10 micrometers or more and 1000 micrometers or less, for example. As a lower limit, Preferably it is 30 micrometers or more, More preferably, it is 40 micrometers or more, More preferably, it is 50 micrometers or more. As an upper limit, Preferably it is 760 micrometers or less, More preferably, it is 610 micrometers or less, More preferably, it is 450 micrometers or less, Especially preferably, it is 300 micrometers or less.

<Step (3) Step of heating to a temperature at which the flux sheet is melted or softened>

This step is a process of heat-processing above the temperature at which the said flux sheet melts or softens. By heat-treating at the above temperature, when a flux component activated by heat is included, the metal oxide formed on the surface of the solder ball can be removed by the flux action of the sheet. In addition, not only the surface of the solder but also the oxide present on the surface of the electrode can be removed as well. Further, in the present invention, since the flux sheet containing the resin (a1) is used for the resin (A), in this step (3), there is no displacement between the electrode and the solder as shown in Fig. 5, and furthermore The solder can easily penetrate the substrate by its own weight, resulting in good solder bonding properties.

<Step (4): A step of heating to a temperature equal to or higher than the melting point of the solder simultaneously with or after (3)>

This step is a process of performing temperature treatment above the melting point of the solder. By heat-processing at the said temperature, a solder ball can be melt|dissolved and soldering can be carried out. The step of (4) may be performed simultaneously with (3) or after (3).

In step (3) (4), the heating temperature (maximum achieved temperature) and the heating time (holding time) at this temperature are the melting temperature of the solder ball, the temperature at which the resin component (A) softens, the resin component ( According to conditions, such as melt viscosity of A), the boiling point of a flux agent, the size of the electrode of a board|substrate, and an interelectrode pitch, it can set suitably.

(3) As heating temperature, it is more than the melting temperature or softening temperature of a resin sheet, for example, it is preferable that it is melting temperature (softening temperature) +20 degreeC or more and +100 degreeC or less. As heating time, 5 second - 10 minutes are preferable, for example. (4) The heating temperature (maximum achieved temperature) is, for example, T+10°C or higher and T+80°C or lower when the melting temperature of the solder ball is T (°C). As a lower limit, Preferably it is T+20 degreeC or more, More preferably, it is T+30 degreeC or more. As an upper limit, Preferably it is T+70 degreeC or less, More preferably, it is T+45 degreeC or less. The heating time can be appropriately set depending on the heating temperature (maximum achieved temperature), but when the heating temperature (maximum achieved temperature) is within the above range, the heating time (holding time) is, for example, from 5 seconds to It's 10 minutes. As a lower limit, Preferably it is 10 second or more, More preferably, it is 20 second or more. As an upper limit, it is 5 minutes or less, More preferably, it is 3 minutes or less. Moreover, although you may carry out this process in atmospheric pressure conditions or inert gas atmosphere, such as nitrogen, it is more preferable to carry out in inert gas atmosphere, such as nitrogen.

(3) The temperature profile in the case of performing (4) later, for example, in the case of Sn37Pb, (3) 100-150 degreeC, 60-120 second, (4) 183 degreeC or more 60-150 second, peak temperature 225-240 degreeC (temperature increase rate 3 degree-C/sec or less) may be sufficient. Moreover, in the case of Sn3Ag0.5Cu, (3) 150-200 degreeC, 60-180 second, (4) 217 degreeC or more 60-150 second, and peak temperature 245-260 degreeC (temperature increase rate 3 degree-C/sec or less) may be sufficient. You may implement these steps multiple times as needed. As a temperature profile, it is preferable that it is the conditions recommended by the Semiconductor Technology Association (JEDEC) (based on IPC/JEDEC J-STD-020C).

In addition, since the flux sheet of the present invention contains the resin (a1) having a glass transition point of 40° C. or less and a melt viscosity of 150° C. 500 Pa·s or less, heat treatment is performed in a pressed state from the solder ball toward the substrate. no need to carry out After the completion of this step, as shown in FIG. 5 , it is in a soldered state.

In addition, after completion|finish of said soldering method, you may dissolve and remove the flux sheet|seat of this invention with a solvent. By dissolving and removing the flux sheet with the solvent, the flux sheet existing in the region other than the solder joint is dissolved and removed by the solvent, and as shown in FIG. 6 , the solder joint portion is exposed. The solvent for washing by dissolving and removing the flux sheet is not particularly limited, and water, an organic solvent, a mixed solvent of water and an organic solvent, etc. are mentioned, but from the viewpoint of low environmental load and easy availability, water is desirable. Although alcohol, a ketone, etc. are mentioned as an organic solvent, Preferably it is alcohol. When using an organic solvent, you may use independently and may use 2 or more types together. In addition, when the resin component (A) is hardly soluble in water, it is preferable to use an organic solvent or a mixed solvent of water and an organic solvent. In the mixed solvent of water and an organic solvent, although there is no restriction|limiting in particular in a mixing ratio, From a viewpoint of reduction of environmental load, the one where the ratio of an organic solvent is low is preferable. Distilled water, ion-exchanged water, tap water, etc. can be used as water, and distilled water, ion-exchanged water, and ultrapure water with few impurities are preferable. Examples of the alcohol include methanol, ethanol, n-propanol, and n-butanol, and examples of the ketone solvent include acetone and methyl ethyl ketone. Although the temperature of the solvent to be used can be suitably set according to the resin component (A) contained in a flux sheet, it is preferable to carry out at room temperature from a viewpoint of workability|operativity.

Moreover, when it is difficult to dissolve a flux sheet, or when it takes time to melt|dissolve, you may use a heated solvent or the solvent containing surfactant. As the temperature of the heated solvent, the higher the temperature, 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 surfactant, surfactants, such as an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and a nonionic surfactant, can be used.

Moreover, from a viewpoint of improving the efficiency of dissolution removal of a flux sheet, it is preferable to carry out dissolution removal while irradiating an ultrasonic wave. When the flux agent (B) is used, if the flux agent remains, it may corrode the solder joint site and cause a decrease in reliability of long-term use. It is preferable to perform a washing process while doing it. In addition, it is preferable to adjust the intensity|strength of an ultrasonic wave to such an extent that the formed solder joint does not fracture|rupture. In addition, washing with a water flow generator such as a submerged jet or a direct pass is preferable in order to improve the removal effect of the flux agent.

Example

Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to the following Example. In addition, about the physical property value of each component used in the following example, the value measured based on the following method was used.

(Preparation of resin solution)

[Production 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 ( A shear rate of 10 mm/min) (measured with resin alone by volatilizing water) and a saponification degree of 39.0 to 46.0) were used as a resin solution (solid content: 40 mass% aqueous solution).

(Manufacture of flux sheet)

The prepared resin solution was apply|coated on the polyethylene terephthalate film (6502 by Lintec Corporation) (henceforth a release film) to which the release process was given to the surface which is a support body, and the coating film was formed. And this coating film was heat-dried at 80 degreeC for 60 minutes, and the flux sheet|seat with a film thickness of 30 micrometers was manufactured on the support body.

[Production Example 2]

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

[Production Example 3]

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

[Production Example 4]

Polyamide (PA) (manufactured by Toray Corporation, trade name "AQ Nylon T-70; glass transition point -46°C, melt viscosity at 150°C: 17 Pa·s (shear rate 10 mm/min)) (resin alone by volatilizing water) to 100 parts by mass (solid content of 51 mass%)) as a flux agent, 5 parts by mass of dodecylamine (relative to 100 parts by mass of resin solid content of T-70) was added and stirred to prepare a resin solution. And using this adjusted resin solution, the flux sheet with a film thickness of 30 micrometers was manufactured by the method similar to manufacture example 1.

[Production Example 5]

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

[Production Example 6]

Polyester (PEs) (manufactured by Takamatsu Oil Co., Ltd., trade name "Pesresin A-680; Glass transition point 30°C, melt viscosity at 150°C: 29 Pa·s (shear rate 10 mm/min)) (Water volatilized and resin To 100 parts by mass (measured alone)) (solid content: 20 mass%), an aqueous solution in which 5 parts by mass of adipic acid (relative to 100 parts by mass of resin solid content of pesresin A-680) was dissolved in distilled water as a flux agent was added, By stirring, a resin solution was prepared. And using this adjusted resin solution, the flux sheet with a film thickness of 30 micrometers was manufactured by the method similar to Example 1.

[Production Example 7]

A flux sheet having a film thickness of 30 µm was produced in the same manner 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.

[Production Example 8]

The solid content of LW-100 was 70 parts by mass, and 30 parts by mass of polyvinyl alcohol (PVA) (manufactured by Nippon Saku Bipoval Co., Ltd., trade name "Poval JP-03"; glass transition point 63°C) was used, and 5 mass parts of adipic acid A flux sheet having a film thickness of 30 µm was produced in the same manner as in Production Example 1, except that parts (with respect to a total of 100 parts by mass of the LW-100 and JP-03) were used.

[Production Example 9]

The blending amount of the solid content of LW-100 was 60 parts by mass, the blending amount of JP-03 was 40 parts by mass, and 5 parts by weight of carboxymethyl cellulose (CMC) (manufactured by Daicel Finechem Co., Ltd., trade name “CMC1220”) as a compatibilizer was used. A flux sheet having a film thickness of 30 µm was manufactured in the same manner as in Production Example 8 except for this.

[Production Example 10]

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

[Production Example 11]

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

[Comparative Preparation Example 1]

Polyvinyl butyral (PVB) (manufactured by Sekisui Chemical Industry Co., Ltd., trade name "S-Rec KW-1; glass transition point 65°C, melt viscosity at 150°C: 1444 Pa·s (shear rate 10 mm/min)) (water An aqueous solution obtained by dissolving 5 parts by mass of adipic acid (relative to 100 parts by mass of solid resin of KW-1) in distilled water as a flux agent in 100 parts by mass (solid content of 20 mass%) of adipic acid (measured with resin alone by volatilization)) was added and stirred to prepare a resin solution. And using this adjusted resin solution, the flux sheet with a film thickness of 30 micrometers was manufactured by the method similar to manufacture example 1.

[Comparative Preparation Example 2]

Polyvinyl alcohol (PVA) (manufactured by Nihonsaku Bipoval Co., Ltd., trade name "Poval JP-03; does not melt at a glass transition point of 63°C and 150°C) in 100 parts by mass of a solid content of adipic acid as a flux agent by 5 mass parts (relative to 100 parts by mass of the resin solid content of JP-03) were added and stirred to prepare a resin solution. And using this adjusted resin solution, the flux sheet with a film thickness of 30 micrometers was manufactured by the method similar to manufacture example 1.

[Comparative Production Example 3]

To 100 parts by mass of the solid content of the ethylene/vinyl acetate copolymer (EVA) (manufactured by Denka Corporation, trade name "Denka EVA Latex 55N"; glass transition point -10°C, does not melt at 150°C), adipic acid as a flux agent An aqueous solution in which 5 parts by mass (with respect to 100 parts by mass of resin solid content of Denka EVA Latex 55N) was dissolved in distilled water was added and stirred to prepare a resin solution. And using this adjusted resin solution, the flux sheet with a film thickness of 30 micrometers was manufactured by the method similar to manufacture example 1.

[Solder joint test using flux sheet]

The solder joint test WHEREIN: The board|substrate and solder ball used are as follows.

Substrate: FR-4 (a glass epoxy substrate, the electrode is made of copper, and the UBM layer on the electrode surface is made of Cu/Ni/Au (the thickness of the Ni layer is 3 μm, the thickness of the Au layer is 0.03 μm). )

Solder ball: Solder composition (diameter 760 µm, Sn-Ag-Cu; Sn: 96.5 mass%, Ag: 3.0 mass%, Cu: 0.5 mass% (melting temperature 217 to 219°C)))

[Examples 1 to 11, Comparative Examples 1 to 3]

Using the flux sheets produced in Production Examples 1 to 11 and Comparative Production Examples 1 to 3, the following items (1) to (6) were evaluated based on the following method. Table 1 shows the evaluation results.

(1) Adhesion between the flux sheet and the substrate

The above-prepared flux sheet with a release film attached thereto was heated to 80° C., pressurized to the substrate in vacuum, and laminated to the substrate. It returned to room temperature and the mode of the board|substrate at the time of peeling a release film was observed.

A: The flux sheet moved away from the release film and transferred to the substrate.

C: Peeling at the flux sheet/substrate interface, or/or breakage in the flux sheet occurred.

(2) Tackiness of the flux sheet

The flux sheet prepared above was touched and sensory evaluation was performed for tackiness at room temperature.

A : It has a suitable tag (there is stickiness).

C: No tack (no stickiness and impossible to adhere to other materials).

(3) Reworkability and handling properties of the flux sheet

For the flux sheet prepared above, after touching the sheet, the glue residue was checked by the presence or absence of adhesion when the finger pressed against the sheet was pressed against another finger, and reworkability and handleability at room temperature (body temperature) was sensory evaluated.

A: There is no glue residue for the fingers.

C: There is glue residue on the finger.

(4) Retaining force of the solder ball

Using a metal mask, 36 solder balls were placed on a substrate laminated with a flux sheet, and the temperature was once raised to 80° C. 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: When the solder ball is tilted 90 degrees after placement, the solder ball does not fall off.

C: When the solder ball was tilted 90 degrees after placement, the solder ball fell off.

(5) dissolution removal properties (visual and loupe observation)

The board on which the solder ball was mounted was heat-treated at 250 DEG C in the atmosphere to bond the solder to the board.

The board|substrate on which the solder joint was formed was immersed in the distilled water of 25 degreeC rocked|fluctuated at 42 kHz using the ultrasonic cleaner "Bransonic" (product name 5510, manufactured by BRANSON), and the washing process for 5 minutes was performed. In Example 6, a mixed solvent of methanol/distilled water = 1/1 (mass ratio) was used instead of distilled water. Through the above steps, a solder joint in the case of using a flux sheet was obtained.

The substrate after cleaning was observed for the presence or absence of a flux sheet remaining in the gap between the solder/substrate using the naked eye and a loupe, and evaluated according to the following criteria.

A: No flux sheet remains at all.

B: A flux sheet is slightly observed at the solder end.

C: The flux sheet remains throughout.

(6) Solder bonding strength

With a die share tester, a share test was performed on five solder balls joined, and the solder bonding strength was confirmed.

A: All are cohesive failures.

C: Some or all are interfacial fractures.

Since Examples 1 to 11 use a flux sheet containing a resin having a glass transition point of 40°C or less and a melt viscosity of 150°C of 500 Pa·s or less, adhesiveness, tackiness, reworkability, solder holding power, dissolution removal Good results were obtained in any evaluation of the properties and solder bonding strength. Further, comparing Examples 1 to 5, 7 to 11 and Example 6, the sheets of Examples 1 to 5 and 7 to 11, which have weaker hydrogen bonding with water, are more resistant to water than the sheets of Example 6. The result was more excellent in solubility. In Examples 8 to 11, the glass transition point contains a resin having a melt viscosity of 40° C. or less and a melt viscosity of 150° C. of 500 Pa·s or less, and contains a resin having a glass transition point higher than that of the resin, so reworkability and handleability are excellent. could be seen to improve.

In Comparative Examples 1 and 2, since the resin having a glass transition point of 40°C or less was not used, the adhesive force with the substrate was weak and the solder ball holding force was weak, resulting in poor solder bonding strength. Moreover, in Comparative Example 3, since the resin having a melt viscosity at 150°C of 500 Pa·s or less was not used, the adhesive force with the substrate was weak, and due to insufficient sinking of the solder balls, the solder bonding strength and the like were inferior.

Industrial Applicability

ADVANTAGE OF THE INVENTION According to this invention, the adhesiveness with a board|substrate is strong and it can provide the flux sheet|seat which does not generate|occur|produce the misalignment of a solder ball during reflow.

Further, according to the present invention, it is possible to provide a solder bonding method in which a large number of solder bumps can be formed with good uniformity, and the productivity is high and the environmental load is small.

1 electrode
2 Solder Resist
3 flux sheet
4 Solder Balls
100 boards

Claims (10)

A flux sheet comprising a 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 (a1) ), characterized in that it contains a flux sheet. The method of claim 1,
The resin (A) has a glass transition point of 40°C or less, and a viscosity of 150°C is 35 to 99% by mass of the resin (a1) having a viscosity of 500 Pa·s (measured at a shear rate of 10 mm/min) or less, the glass transition point is the above A flux sheet characterized by containing from 1 to 65 mass% of a resin (a2) higher than the resin (a1). 3. The method according to claim 1 or 2,
The flux sheet, characterized in that the flux sheet contains a flux agent (B). 4. The method according to any one of claims 1 to 3,
The flux sheet is characterized in that it contains substantially no low molecular weight compounds other than (B). 5. The method according to any one of claims 1 to 4,
The flux sheet, characterized in that the resin (a1) is water-soluble. 6. The method according to any one of claims 1 to 5,
The resin (a1) has a partial structure in which one or more alkylene oxide chains are linked to a hydroxyl group (-OH) of a part of polyvinyl alcohol -(CH(R ¹ )CH(R ² )O) _n -R ³ (n represents the repeating number (average value) of the alkylene oxide chain, and is 1.0 or more. R ¹ , R ² and R ³ each independently represent a hydrogen atom or an organic group. R ¹ , R ² and R ³ are A flux sheet comprising at least one selected from modified polyvinyl alcohol substituted with , polyamide, and polyester. 7. The method according to any one of claims 2 to 6,
A flux sheet comprising polyvinyl alcohol as the resin (a2). 8. The method according to any one of claims 1 to 7,
In the flux sheet, the content of the resin (A) is 50 mass% or more. 9. The method according to any one of claims 1 to 8,
The flux sheet, characterized in that the area of the flux sheet is 30000 mm2 or more. A solder bonding method using the flux sheet according to any one of claims 1 to 9, comprising the following steps (1) to (4).
(1) disposing the flux sheet on the electrode-bearing surface of the electrode-bearing substrate
(2) a step of disposing a solder ball on the flux sheet
(3) heating to a temperature at which the flux sheet is melted or softened
(4) a step of heating to a temperature equal to or higher than the melting point of the solder simultaneously with or after (3)

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