JP2014168791A - Flux film, flip-chip connection method, and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flux film being a flux that exhibits a stable flux action, is excellent in formability of a solder joint, is excellent in workability and storage stability, and has a reduced load on the environment, a flip-chip connection method using the flux film, and a semiconductor device in which a chip and a substrate are connected by the connection method.SOLUTION: A flux film contains a resin (A1) having a structure derived from polyvinyl alcohol or a resin (A2) having a structure derived from polyvinyl pyrrolidone, and a flux agent (B).

Description

  The present invention relates to a flux film used for soldering or the like of electronic components, wiring boards, substrates, semiconductor chips, etc., a flip chip connecting method using the flux film, and a chip and a substrate connected by the connecting method. The present invention relates to a semiconductor device.

  Due to the recent demand for smaller and thinner electronic devices and higher performance with multiple functions, the number of I / O electrodes (terminals) in semiconductor packages has increased, and the distance between electrodes (terminals) has become shorter (narrow pitch). ). Therefore, the form of the semiconductor package is a method in which bumps such as BGA (Ball Grid Array) and CSP (Chip Scale Package) are arranged and connected to the lower part of the chip, instead of connection by lead such as QFP (Quad Flat Package). It has changed to a flip chip connection. The flip-chip connection method is a connection method in which a chip on which solder bumps are formed in advance is placed on the electrodes of the circuit board, and the solder bumps and the electrodes of the circuit board are joined (see Patent Document 1).

In order for a solder joint to be formed, the solder component and the electrode component must diffuse together at the solder / electrode interface. For that purpose, it is necessary that the solder bump and the electrode are in direct contact.
However, since the solder which is a bump material is easily oxidized, the surface of the solder bump is covered with a metal oxide, and the solder component and the electrode component are not in direct contact with each other. The metal oxide formed on the surface of the solder bump has a high melting point even when heated to the reflow temperature for mounting lead-free solder (in the case of normal lead-free solder, the maximum temperature in the heating process is about 260 ° C.) Therefore, it does not melt at that temperature. As a result, only the solder is melted, and the melted solder is confined in the metal oxide film.
Therefore, when the solder is not in direct contact with the electrode, the solder component and the electrode component are not diffused to each other at the solder / electrode interface, resulting in poor solder joint formability.

  In order to solve such problems, for example, as described in Non-Patent Documents 1 and 2 and Patent Document 2, a liquid or paste-like flux is applied to the solder bumps in advance, and is formed on the surface of the solder bumps. Removal of metal oxides is being carried out.

Dai Iwasa, Electronic Materials, Vol. 47, No. 1, p85-87, January 2008 Yasumiti Orii, Kazushige Toriyama, Hirokazu Noma, Yukifumi Oyama, Hidetoshi Nishiwaki, Misty Ishida, Toshihiko.

JP-A-9-97791 Japanese Patent No. 4687421

  However, liquid or paste-like fluxes are difficult to adjust the coating amount, are inferior in workability, and bumps with a small amount of flux coating often have poor solder joints and often cause poor solder joints. Furthermore, since the liquid or paste-like flux has fluidity, a flux agent having poor dispersibility is aggregated in the storage container, which causes a problem in terms of storage stability.

  The present invention uses a flux film that expresses a stable flux action, is excellent in solder bondability, has good workability and storage stability, and has a low environmental load, and the flux film. It is an object of the present invention to provide a flip chip connection method and a semiconductor device in which a chip and a substrate are connected by the connection method.

As a result of intensive studies, the present inventors have found that a flux film containing a specific thermoplastic resin solves the above problems, and have completed the present invention.
That is, the present invention relates to the following (1) to (9).
(1) A flux film comprising 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).
(2) The flux film according to (1) above, which contains the resin (A1) and the fluxing agent (B).
(3) The flux film according to (1) or (2), wherein the content of the flux agent (B) is 1 to 50 parts by mass with respect to 100 parts by mass of the resin (A1) or the resin (A2). .
(4) A flip chip connection method using the flux film according to any one of (1) to (3) above, comprising the following steps (1) to (4).
Step (1): Step of placing the flux film on the electrode surface side of the substrate provided with electrodes (2): Step of mounting a chip provided with solder bumps on the substrate, the solder bumps being the flux Step (3) of placing and fixing so as to be positioned on the electrode of the substrate through a film: The melting point of the solder bump provided on the chip is higher than the melting point, and the resin component (A) is liquefied Step (4) of heat-treating at a temperature higher than or equal to the temperature at which the flux film is dissolved and removed with a solvent after completion of Step (3) (5) In Step (3), the heat-treatment is performed under an inert gas atmosphere. The flip chip connecting method according to (4), wherein the flip chip connecting method is performed.
(6) The flip-chip connection method according to (4) or (5) above, wherein in the step (3), the heat treatment is performed in a state of being pressed from the chip toward the substrate.
(7) The flip-chip connection method according to any one of (4) to (6), wherein the solvent used in the step (4) is any one of water, alcohol, and a mixed solvent of water and alcohol. .
(8) The flip-chip connection method according to any one of (4) to (7), wherein in step (4), the flux film is dissolved and removed with a solvent while irradiating ultrasonic waves.
(9) A semiconductor device in which a chip including solder bumps and a substrate including electrodes are connected by the flip chip connecting method according to any one of (4) to (8).

  The flux film of the present invention exhibits a stable flux action, is excellent in solder joint formability, has good workability and storage stability, and can be a flux with a low environmental load.

It is a schematic plan view of a board | substrate provided with the electrode used by the Example and comparative example of this invention. It is a schematic plan view of the semiconductor chip used in the Example and the comparative example. It is a schematic sectional drawing of a semiconductor chip provided with the solder bump used in the Example and the comparative example. It is a schematic sectional drawing of a semiconductor chip provided with the bump by which the solder cap was attached on the copper pillar used in the Example and the comparative example. It is a schematic sectional drawing of a semiconductor chip and a board | substrate which shows an example of the method of carrying out the flip chip connection of the semiconductor chip provided with a solder bump on the electrode of a board | substrate. It is a schematic sectional drawing of a semiconductor chip and a board | substrate which shows an example of the method of carrying out the flip chip connection of the semiconductor chip provided with the bump by which the solder cap is attached on the copper pillar on the electrode of a board | substrate. It is the figure which showed an example of the method of mounting the flux film of this invention in the electrode surface side of a board | substrate provided with an electrode in a process (1). It is the figure which showed an example of the method to mount so that a solder bump may be located on the electrode of a board | substrate through the flux film of this invention in a process (2).

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

[Flux film]
The flux film of the present invention is a film containing 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).
In the present invention, the “flux film” is a film used for forming a solder joint, and is a film-like solid in which a flux component is dispersed in a thermoplastic resin (hereinafter also simply referred to as “resin”). Say.
In addition, the “flux component” here refers to a flux agent exhibiting a flux action or a functional group exhibiting a flux action contained in a thermoplastic resin.

Examples of the resin having a flux action on the resin itself include polyvinyl alcohol, which is a polyhydric alcohol, polyacrylic acid, which is a polycarboxylic acid, styrene maleic acid resin, polyethylenimine which is a polyvalent amine, and the like.
In the flux film of the present invention, when the resin (A1) having a structure derived from polyvinyl alcohol is included, the resin (A1) itself has a flux action, so that the solder bondability can be formed without blending a flux agent. Excellent. However, the flux film containing resin (A1) and a flux agent (B) is preferable from a viewpoint of improving a flux effect | action more.
On the other hand, when the resin (A2) having a structure derived from polyvinyl pyrrolidone is used, the resin (A2) itself does not have a flux action, and therefore it is necessary to use the resin (A2) and the flux agent (B) in combination.
Moreover, since resin (A1) and resin (A2) are water-soluble, when dissolving and removing the flux film after use, water can be used as a solvent, and the burden on the environment is low.
Hereinafter, the resin component (A) contained in the flux film of the present invention will be described. In the present invention, the resin component (A) contains at least the resin (A1) or the resin (A2).

<Resin component (A)>
The flux film of the present invention contains, as the resin component (A), at least a resin (A1) having a structure derived from polyvinyl alcohol or a resin (A2) having a structure derived from polyvinyl pyrrolidone. By using the resin (A1) or the resin (A2), it is excellent in forming a film, so that workability and storage stability are good, and since it is water-soluble, a flux film having a low environmental load is obtained. Can do.
In addition, since the flux film is melted by its own weight or load and the solder bump is pushed into the flux film, the resin (A1) or the resin (A2) is difficult to form a network between the resins. It becomes easy for the bump to directly contact the electrode. Therefore, the flux film of the present invention is also excellent in the formability of solder joints.
Furthermore, the polyvinyl alcohol derived from the structure of the resin (A1) has an effect of removing the oxide film of the solder particles on the resin itself, and is a biodegradable resin and can easily treat the waste liquid, so that the resin component (A) As for it, it is preferable to contain resin (A1).

  The total content of the resin (A1) and the resin (A2) in the resin component (A) is preferably 70 to 100% by mass, more preferably 80 to 100% by mass, based on the total amount of the resin component (A). More preferably, it is 90-100 mass%, More preferably, it is 95-100 mass%, More preferably, it is 99-100 mass%.

  In addition, although the said resin (A1) and resin (A2) may be used together as a resin component (A), from a compatible viewpoint and a viewpoint of an improvement of a flux effect | action, resin (A1) or resin (A2) Are preferably used alone.

Moreover, you may contain other resin other than resin (A1) and resin (A2) as a resin component (A).
As the other resin, it is preferable to use a thermoplastic resin other than the resin (A1) and the resin (A2). From the viewpoint that water can be used as a solvent when the flux film is dissolved and removed, it is water-soluble. A thermoplastic resin is more preferable.
Examples of such water-soluble thermoplastic resins include polyethylene glycol, polypropylene glycol, polyacrylic acid, styrene maleic acid resin, polyethyleneimine, polyacrylamide, starch, and modified cellulose. These thermoplastic resins may be used alone or in admixture of two or more.

  The content of other resins other than the resin (A1) and the resin (A2) is preferably 30% by mass or less, more preferably 20% by mass or less, more preferably 10% by mass with respect to the total amount of the resin component (A). % Or less, more preferably 5% by mass or less, and still more preferably 1% by mass or less.

In addition, in this invention, it is preferable not to contain a thermosetting resin as a resin component (A). When a thermosetting resin is used instead of the thermoplastic resin, the thermosetting resin forms a resin network when heated, and may not be dissolved in a solvent in the step of dissolving and removing the resin after soldering. Moreover, when heated, the fluidity of the film is suppressed by the thermosetting resin network, and the flux agent cannot be sufficiently diffused into the solder bumps, which causes poor solder joints. Furthermore, if a network is formed in the course of the solder bump being pushed inside the film melted by its own weight or load, the bump becomes difficult to directly contact the electrode, and a solder joint failure is likely to occur.
Even if the thermosetting resin is contained in the flux film of the present invention, the content of the thermosetting resin is preferably 5% by mass or less based on the total amount of the resin component (A). More preferably, it is 1 mass% or less, More preferably, it is 0.1 mass% or less, More preferably, it is 0.01 mass% or less.

  As content of the resin component (A) with respect to the total mass of the flux film of this invention, Preferably it is 50-100 mass%, More preferably, it is 65-100 mass%, More preferably, it is 70-99 mass%.

The viscosity of the resin component (A) is preferably low enough to allow the flux component in the film to diffuse in the heating step to a temperature higher than the melting temperature of the solder bumps and higher than the temperature at which the resin liquefies. The lower the viscosity of the resin, the more actively the flux component moves around in the film, and the soldering site can be supplemented with the fluxing agent.
From the above viewpoint, the viscosity of the resin component (A) at 25 ° C. is preferably 0.1 to 100 mPa · s, more preferably 1.0 to 50 mPa · s, still more preferably 1.5 to 30 mPa · s, and more. More preferably, it is 1.8-10 mPa * s.
If the viscosity is 0.1 mPa · s or more, the film formability is good. On the other hand, if the said viscosity is 100 mPa * s or less, the diffusibility of the flux agent (B) in the flux film at the time of reflow will be favorable, and the contact property of a bump and an electrode will also become favorable.
The viscosity of the resin component (A) at 25 ° C. means a value measured according to JIS K 6726.

The softening point of the resin component (A) is preferably low, but just having a low softening point does not necessarily result in a viscosity that is low enough that the fluxing agent flows. In other words, the resin becomes soft when the temperature is higher than the softening point, but if the degree of polymerization (molecular weight) of the resin is too high, the molecular chains are not easily entangled, so that the viscosity does not decrease so much that the flux agent can flow. .
Therefore, in order to reduce the viscosity of the resin component (A), it is preferable to reduce the degree of polymerization (molecular weight) of the resin component (A) to reduce entanglement. Even in the step of dissolving and removing the resin after the heating step, the lower the degree of polymerization (molecular weight) of the resin, the faster it dissolves, so a resin with a low degree of polymerization is preferable from the viewpoint of dissolution and removal, but film formation at room temperature From the viewpoint of obtaining good performance, a resin having a polymerization degree of a predetermined value or more is preferable.

From the above viewpoint, the average degree of polymerization of the resin component (A) is preferably 100 to 1000, more preferably 150 to 800, still more preferably 200 to 700, and still more preferably 250 to 600.
In addition, in this invention, the average degree of polymerization of resin means the value measured based on the method prescribed | regulated by JISK6726.

(Resin (A1))
The resin (A1) is a resin including a structure derived from polyvinyl alcohol.
The resin (A1) may be a copolymer including a structure derived from a monomer other than polyvinyl alcohol.
Examples of such monomers include addition polymerization reactive monomers such as acrylic acid, maleic acid, N-vinyl-2-pyrrolidone, and acrylamide. In addition to these addition polymerization reactive monomers, it can also be used as a monomer component such as ethylene glycol, propylene glycol, glucose, cellulose, etc., which is a monomer for condensation polymerization reaction. Therefore, the monomer cannot be introduced in one reaction. Therefore, after the addition polymerization reaction is completed, a condensation polymer of these monomers is introduced as a block component by a condensation polymerization reaction.

The content ratio of the structure derived from the polyvinyl alcohol in the resin (A1) is preferably 50 to the total structural unit in the resin (A1) from the viewpoint of water solubility, environmental aspects, and solder bondability. It is 100 mass%, More preferably, it is 70-100 mass%, More preferably, it is 85-100 mass%, More preferably, it is 95-100 mass%, More preferably, it is 99-100 mass%.
The resin (A1) is preferably a homopolymer consisting only of a structure derived from polyvinyl alcohol from the above viewpoint.

The saponification degree of the resin (A1) is preferably 27 to 99 mol%, more preferably 28 to 99 mol%, still more preferably 28 to 98 mol%.
In addition, the saponification degree of resin (A1) means the value measured based on JISK6726.

  Further, the average polymerization degree of the resin (A1) having a saponification degree of 85 to 90 mol% is a film forming ability, an improvement in solder bondability due to fluidity of flux components and indentation of bumps, and a viewpoint of solubility. Therefore, it is preferably 100 to 1000, more preferably 150 to 800, still more preferably 200 to 700, and still more preferably 250 to 500.

(Resin (A2))
The resin (A2) is a resin including a structure derived from polyvinyl pyrrolidone.
The resin (A2) may be a copolymer including a structure derived from a monomer other than polyvinyl alcohol. Examples of such a monomer include those exemplified for the resin (A1).

The content ratio of the structure derived from polyvinylpyrrolidone in the resin (A2) is preferably 50 to all structural units in the resin (A2) from the viewpoints of water solubility, environmental aspects, and solder bondability. 100 mass%, More preferably, it is 70-100 mass%, More preferably, it is 85-100 mass%, More preferably, it is 95-100 mass%, More preferably, it is substantially 100 mass%.
In addition, the resin (A2) is preferably a homopolymer including only a structure derived from polyvinyl pyrrolidone from the above viewpoint.

<Flux agent (B)>
When the resin (A1) is used as the resin component (A) in the flux film of the present invention, the resin (A1) itself has a fluxing action, so it is not always necessary to add a fluxing agent. The resin (A1) and the fluxing agent are preferably contained from the viewpoint of improving the solder bondability and improving the electrical conductivity.
On the other hand, when the resin (A2) having a structure derived from polyvinyl pyrrolidone is used, the resin (A2) itself does not have a flux action, and therefore it is necessary to use the resin (A2) and the flux agent (B) in combination.

  A flux agent (B) is a component mix | blended in order to remove the high melting metal oxide in the solder surface, and to let the molten solder contact an electrode directly. In general, the solder is mainly composed of an amphoteric element such as tin (Sn) that is soluble in both an acid and a base. Therefore, acidic substances and basic substances are effective in removing the metal oxide on the solder surface. In addition to these, alcohols and the like can also be used as a flux agent because they have a flux action at high temperatures.

Specific examples of the fluxing agent include salicylic acid, benzoic acid, m-dihydroxybenzoic acid, sebacic acid, rosin resin, and the like.
Note that, depending on the combination of the resin and the flux agent, the flux film may not flow, so it is preferable to select and use the flux agent as appropriate.
As the flux agent (B) contained in the flux film of the present invention, from the viewpoints of removal of the oxide film of the solder particles, fluidity of the film, dissolution and removal of the resin after solder bonding, and improvement of wettability with the solder. , Salicylic acid, benzoic acid, m-dihydroxybenzoic acid and sebacic acid are preferred, and salicylic acid is more preferred.

The content of the flux agent (B) can be appropriately set depending on the number and size of solder bumps, the thickness of the oxide film on the surface, the thickness of the flux film, etc. From the viewpoint of improving the electrical conductivity, the resin (A1) or the resin (A2) is 100 parts by mass with respect to 100 parts by mass of the resin (A1) and the resin (A2). (Based on a total of 100 parts by mass of (A1) and resin (A2)), preferably 1 to 50 parts by mass, more preferably 2 to 30 parts by mass, more preferably 3 to 20 parts by mass, and even more preferably 3 to 15 parts. It is 4-12 mass parts, More preferably, it is 4-12 mass parts.
If it is within the above range, the oxide film can be sufficiently removed, and a network is formed in the resin, and the flux agent tends to be less likely to flow. Moreover, the phenomenon that the solder bumps corrode due to the flux agent remaining after the resin cleaning step can be suppressed.

  In addition, as content of the resin component (A) with respect to the total mass of the flux film of this invention, Preferably it is 0.5-35 mass%, More preferably, it is 1.0-25 mass%, More preferably, 1.5- It is 20 mass%, More preferably, it is 2.0-15 mass%, More preferably, it is 2.5-12 mass%.

<Other additives>
The flux film of the present invention may contain additives contained in general flux in addition to the resin component (A) and the flux agent (B) as long as the effects of the present invention are not impaired. .
Examples of such additives include hydrohalates of amines such as diethylamine hydrobromide and cyclohexylamine hydrobromide; organic acids such as adipic acid and stearic acid; and organic amines such as tributylamine. Activators such as organic halides such as trans-2,3-dibromo-2-butene-1,4-diol.

<Flux film production method>
The method for producing the flux film is not particularly limited. For example, the resin component (A) is dissolved in a solvent, and if necessary, a flux agent (B) is added to prepare a resin solution. This resin solution Is applied to a support having a release treatment on the surface by a known method to form a coating film, and the solvent is removed by drying the coating film.

Examples of the solvent for dissolving the resin component (A) include water, alcohol, a mixed solvent of water and alcohol, and water is preferable from the viewpoint of reducing environmental burden.
When the resin component (A) is dissolved using water, water heated to 40 to 95 ° C. may be used from the viewpoint of increasing the dissolution rate. When setting it as the form of the aqueous solution which dissolved the resin component (A) in water, the density | concentration of the resin component (A) in the said aqueous solution becomes like this. Preferably it is 0.1-40 mass%.
When the flux agent (B) is liquid, the flux agent (B) may be added as it is. However, when the flux agent (B) is solid, water, alcohol, a mixed solvent of water and alcohol, etc. It is preferable to dissolve in a solvent to form a solution and add the solution. By doing in this way, a resin solution having an appropriate viscosity can be obtained, and when the viscosity is too high, streaks are generated and the smoothness of the coating film surface is deteriorated, or the viscosity is too low. The occurrence of pin fall can be suppressed.

  The drying temperature and drying time of the coating can be appropriately set depending on the solvent for the resin solution, the film thickness, etc. For example, the change in physical properties of the obtained flux film such as a decrease in the fluidity of the film during reflow From the viewpoint of suppression, it is preferable to perform the drying treatment at a drying temperature of 25 to 180 ° C. (more preferably 40 to 100 ° C.) and a drying time of 5 to 60 minutes (more preferably 10 to 50 minutes).

<Flux film thickness and size (area)>
The thickness of the flux film of the present invention can be appropriately set in consideration of the distance between chip / substrate, flux activity, temporary fixing force, detergency, etc., preferably 1 to 500 μm, more preferably 2 to 350 μm. More preferably, it is 3 to 200 μm.
Note that when a flux film thicker than the chip / substrate distance is used, the chip / substrate is filled with the flux film without any gaps, so the amount of flux is so large that bonding failure is unlikely to occur, and the entire chip surface and substrate surface Since the flux film is affixed to the film, the temporary fixing force tends to increase.
In addition, when a flux film thinner than the chip / substrate distance is used, the flux film is adhered to either the chip or the substrate, but on the back surface of the surface to which the flux film is adhered, A space is formed because it is not in contact. Therefore, the water permeability is good and the cleaning property is improved.

  In addition, the size (area) of the flux film can be appropriately set in consideration of the size of the substrate to be used. Specifically, it is preferable to set the area slightly larger than the area where the electrode (group) is located. Alternatively, it may be formed larger than the size that is planned to be used in advance, and cut into a desired size when used.

<Features of flux film>
Since the flux film of the present invention contains the resin (A1) or resin (A2), the flux agent has good diffusibility, and the flux film is melted by its own weight or load, and the solder is placed inside the flux film. In the process in which the bumps are pushed in, the resin (A1) or the resin (A2) is difficult to form a network between the resins, so that the bumps easily come into direct contact with the electrodes. Therefore, by using the flux film of the present invention, it is possible to suppress solder joint defects.
Further, in the flux film containing the resin (A1), even if the flux film is thin and the flux component amount capable of reacting with the metal oxide is insufficient, the film liquefies when heated to the reflow temperature. Since the flux component diffuses throughout the film, it is possible to compensate for a sufficient amount of the flux component for solder joining. For this reason, it is difficult to cause a solder joint failure due to a lack of flux components, and a stable solder action can be exhibited and a good solder joint can be formed.

  In the flux film of the present invention, since the resin (A1) or the resin (A2) is uniformly dispersed in the film-like solid, aggregation of the flux agent due to long-term storage that frequently occurs in liquid and paste-like flux occurs. Difficult and excellent in storage stability. The flux film is a solid film and has no fluidity at room temperature. Therefore, aggregation of the flux agent due to long-term storage hardly occurs, and uniform dispersibility can be maintained.

  The liquid and paste-like fluxes are applied only to the electrodes or solder bumps that are the parts to be joined, and are temporarily fixed only at the portions that are in contact with these, so that the temporary fixing force is weak. On the other hand, since the flux film of the present invention can be laminated with the chip / substrate between the entire surface of the film by laminating, the temporary fixing force is strong.

  When applying a liquid or paste-like flux by printing or the like, since the variation in the coating amount is large, it is necessary to appropriately adjust the coating amount and the workability is poor. On the other hand, the flux film of the present invention only has to mount a predetermined amount of film between the bump on the chip and the electrode on the substrate, and is excellent in workability. Further, even if the place for placing is wrong, it is possible to peel off the film and place it again at a predetermined place, so that the repairability is excellent.

  Since the resin (A1) and the resin (A2) used in the flux film of the present invention are water-soluble resins, water can be used when the flux film is manufactured or mounted, and an organic solvent that volatilizes and is released into the atmosphere is used. Since it is not necessary, the load on the environment is low. Moreover, since the waste liquid which wash | cleaned and collect | recovered after using the flux film using resin (A1) can be decomposed | disassembled (active sludge method) by microorganisms, the load to an environment is remarkably low.

[Flip chip connection method]
According to the flip-chip connection method of the present invention, a solder joint can be formed by flip-chip connection using the above-described flux film of the present invention.
The flip chip connecting method of the present invention includes the following steps (1) to (4).
Step (1): Step of placing the flux film on the electrode surface side of the substrate provided with electrodes (2): Step of mounting a chip provided with solder bumps on the substrate, the solder bumps being the flux Step (3) of placing and fixing so as to be positioned on the electrode of the substrate through a film: The melting point of the solder bump provided on the chip is higher than the melting point, and the resin component (A) is liquefied Step (4) of heat-treating at a temperature equal to or higher than the temperature at which the flux film is dissolved and removed with a solvent after completion of Step (3).

The flip chip connection method according to the present invention does not require a complicated coating process such as printing, and only has to place a flux film between the bumps of the chip and the electrodes of the substrate, and is excellent in workability. In addition, when pasted with a laminate, the temporary fixing force is strong, so that deviation after alignment of the bumps / electrodes facing each other hardly occurs. Moreover, since the flux film in which the flux agent is uniformly dispersed is used, a stable flux action is expressed and a good solder joint is formed. Further, when the resin (A1) is used as the resin for the flux film, there is little organic solvent released into the atmosphere, and the waste liquid can be treated by an activated sludge method that is decomposed by microorganisms, so the burden on the environment is low. It can be a flip chip connection method.
Hereinafter, after explaining the substrate and chip used in the connection method, the details of each process will be described with reference to the drawings.

(substrate)
The substrate used in the flip-chip connection method of the present invention is a substrate provided with electrodes, and may be provided with one or more electrodes. For example, the substrate shown in FIG.
A substrate 10 shown in FIG. 1 has a plurality of electrodes 12, and the electrode 12 includes an electrode (group) 12 a at the periphery of the substrate and an electrode (group) 12 b at the center of the substrate. A solder resist is formed in the region 11 other than the electrodes on the upper surface of the substrate.

As a board | substrate provided with such an electrode, the printed wiring board etc. which mount various electronic components like a semiconductor chip, an interposer, and a motherboard are mentioned, for example.
It is preferable that an UBM (Under Bump Metallization) layer is formed on the electrode surface in order to improve the wettability with the solder bump.
Copper is generally used for the circuit, and examples of the UBM layer applied to the copper circuit surface include Cu / Ni / Au and Cu / Ni-P / Au. Au on the outermost surface of the electrode improves the wettability with the solder, and the Ni layer thereunder suppresses the diffusion of copper, thereby affecting the reliability of the solder joint. The formation of is suppressed.

In addition, when dirt such as oil or fat is adhered to the electrode surface of the substrate, the wettability with the solder bumps is reduced and the bonding property is adversely affected. Therefore, degreasing with an organic solvent, an acidic aqueous solution, a basic aqueous solution, etc. in advance. Is preferred. In degreasing, it is more preferable to apply ultrasonic waves because the cleaning effect is further enhanced.
When there is no UBM layer on the electrode surface, an oxide film is likely to be formed on the electrode surface and tends to be gradually oxidized even after the oxide is removed. From the viewpoint of removing the oxide formed on the electrode surface. The substrate is preferably washed with an acidic aqueous solution or a basic aqueous solution.

(Chip)
The chip used in the flip-chip connection method of the present invention is a chip having solder bumps, in which bumps are arranged at positions facing the electrodes on the substrate to be mounted. For example, the chip shown in FIG. Is mentioned.
The chip 20 shown in FIG. 2 has a plurality of bumps 22. Note that the surface of the silicon 21 on the chip surface in a region other than the bumps 22 may be covered with a buffer coat as a normal protective layer.

Usually, flip-chip connection means C4 (Controlled Collapse Chip Connection) developed by IBM (International Business Machines Corporation).
C4 is a method of forming a solder joint with a substrate using a chip on which spherical solder bumps are mounted. In C4, for example, a chip 20a having an electrode 31 on a silicon substrate and a spherical solder bump 32 mounted on the electrode 31 as shown in FIG. 3 is used.
However, in C4, bumps swell laterally due to the weight of the chip at the time of reflow, so that a short circuit (bump short) occurs between adjacent bumps at a narrow pitch of less than 150 μm, so it is difficult to use for narrow pitch connection.
Therefore, C2 (Chip Connection), which uses a chip with a hemispherical solder-capped bump mounted on the tip of a metal pillar, was developed at IBM Japan as a method for flip chip connection even at narrow pitches of less than 150 μm. (See Patent Document 1 and Non-Patent Document 2). In C2, for example, a chip 20b having a metal pillar 41 such as copper on a silicon substrate and a hemispherical solder bump 42 with the tip of the metal pillar 41 capped is used as shown in FIG. Is done.

The chip used in the flip chip connecting method of the present invention may be a chip mounted with spherical solder bumps used for C4, or a chip mounted with hemispherical solder-capped bumps on the metal pillar tip used for C2. It is possible to appropriately select from both chips according to the inter-pitch. In addition, a chip having a gold stud bump may be used to mount on a substrate having a solder precoated electrode.
Note that the type of bump is not particularly limited as long as it uses solder to connect the chip and the substrate.

(Composition of solder bump)
Examples of the composition of the solder bump used in the Philip chip connecting method of the present invention include SnPb-based, lead-free SnAgCu-based, SnAg-based, SnCu-based, SnZnBi-based, and SnAgBiIn-based. Also, SnBi-based (Sn58Bi melting temperature is 138 ° C.) or InSn-based (In48Sn melting temperature is 118 ° C.) solder-free lead-free and low melting point solder can be used.
SnPb is preferable from the viewpoint of mechanical properties and reliability, but in the present invention, the RoHS directive prohibiting the use of hazardous substances such as lead for environmental protection has been issued in the EU. It is preferable to use a solder hump.
Among the lead-free solder humps, SnAgCu solder humps are preferable from the viewpoints of mechanical properties and reliability.

Since the melting temperature of SnAgCu-based solder particles exceeds 200 ° C. (for example, the melting temperature of Sn3Ag0.5Cu is about 217 ° C.), when a flux containing a thermosetting resin such as an epoxy resin is used, the resin is cured. It is highly possible that the flux agent cannot be diffused.
Since the flux film of the present invention contains the resin (A1) or the resin (A2) which is a thermoplastic resin, the flux agent diffuses even at a high temperature exceeding 200 ° C. Therefore, the solder agent can be filled with the flux agent, and the solder The bond formability can be improved.
Note that a lead-free, low-melting solder hump may be used for a material that deteriorates itself such as liquid crystal in a high-temperature process exceeding 200 ° C. Examples of lead-free and low melting point solder humps include SnBi-based and InSn-based solder bumps.

  Hereinafter, each step of the flip chip connecting method of the present invention will be described with reference to FIGS. 5 and 6 are schematic cross-sectional views showing an example of a flip chip connecting method using the flux film of the present invention. FIG. 5 shows a connecting method by C4 using spherical solder bumps, and FIG. The connection method by C2 using the bump capped with the hemispherical solder at the pillar tip is shown.

<Step (1)>
This step is a step of placing the flux film of the present invention on the electrode surface side of the substrate provided with electrodes.
As shown in FIGS. 5A and 6A, the flux film 51 of the present invention is placed on the electrode surface side of the substrate 10 including the electrodes 12b.
Before placing the flux film 51, it is preferable to degrease the substrate in advance based on the method described above.
The method of placing the flux film 51 on the substrate 10 is not particularly limited and may be placed as it is as shown in FIGS. 5 (1) and 6 (1). It is preferable to use and temporarily fix (refer FIG. 7).
The laminating temperature is preferably a temperature equal to or higher than the softening point of the resin component (A).

<Step (2)>
This step is a step of mounting a chip having solder bumps on the substrate, and is a step of mounting and fixing the solder bumps so as to be positioned on the electrodes of the substrate via a flux film.
As shown in FIG. 5 (2), the chip to be used may be a chip 20a having a spherical solder bump 32 on the electrode 31 used in C4, and is used in C2 as described in FIG. 6 (2). Alternatively, the chip 20b including the hemispherical solder bump 42 with the tip of the metal pillar 41 capped may be used.

As a method of aligning the bumps of the chip at positions facing the electrodes on the substrate, it is preferable to use a flip chip bonder from the viewpoint of improving alignment accuracy.
In order to temporarily fix the chip and the substrate via the flux film, it is preferable to heat the chip at a temperature equal to or higher than the softening point of the resin component (A) in the flux film.

In addition, when the chip | tip 20a provided with the spherical solder bump 32 for C4 is used, after mounting the chip | tip 20a on the electrode 12b of the board | substrate 10 via the flux film 51, it is preferable to laminate. As shown in FIG. 8, by laminating, the unevenness of the electrodes 12b and the bumps 32 is buried in the flux film 51, so that the adhesion between the chip 20a, the flux film 51, and the substrate 10 is improved.
In addition, it is preferable to perform lamination, pressing with a roll at the temperature more than the softening point of a resin component (A).

<Step (3)>
This step is a step of performing heat treatment at a temperature equal to or higher than the melting temperature of the solder bumps provided in the chip and higher than the temperature at which the resin component (A) is liquefied.
By performing the heat treatment at the above temperature, the metal oxide formed on the surface of the solder bump can be removed by the flux action of the flux film. Further, not only the surface of the solder hump but also the oxide present on the surface of the electrode can be removed together.
In the present invention, since the flux film containing the resin (A1) or the resin (A2) is used, it is difficult to form a network between the resins in this step (3). It is easy to contact and the formability of solder joints is good.

The heating temperature (maximum temperature reached) and the heating time at that temperature (holding time) are the melting temperature of the solder bump used, the temperature at which the resin component (A) liquefies, the viscosity of the resin component (A), the flux agent It can be set as appropriate depending on conditions such as boiling point, substrate electrode size, and electrode pitch.
The heating temperature (maximum temperature reached) is preferably T + 10 ° C. or higher and T + 80 ° C. or lower, where T (° C.) is the higher temperature of the solder bump melting temperature or the temperature at which the resin component (A) liquefies. More preferably, it is T + 20 ° C. or more and T + 70 ° C. or less, and further preferably T + 30 ° C. or more and T + 45 ° C. or less.
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 preferably 20 seconds to 10 minutes. More preferably, it is 30 seconds to 5 minutes, and still more preferably 40 seconds to 3 minutes.

Moreover, it is preferable to perform this process in inert gas atmosphere, such as nitrogen.
By performing the heat treatment in an inert gas atmosphere such as nitrogen as compared with the atmosphere, the resin component (A) and the fluxing agent (B) are prevented from condensation reaction and a network is formed. The phenomenon can be suppressed. By suppressing the formation of the network, the water solubility of the flux film is maintained by the steps described later, and the flux film can be easily dissolved and removed using water as a solvent.

In addition, from the viewpoint of suppressing the occurrence of misalignment between the solder bump and the electrode due to evaporation of a small amount of low boiling point components by heat treatment, and from the viewpoint of sufficient contact between the solder bump and the electrode, in this step, from the chip to the substrate. The heat treatment is preferably performed in a state where the pressure is applied and pressed.
In this case, it is preferable to use a flip chip bonder that can move to the heating step continuously after alignment between the bumps / electrodes facing each other. When heat treatment is performed without using a flip chip bonder, the substrate mounted on the substrate may move due to evaporation of a small amount of low-boiling components. After mounting the substrate, fix it with a jig such as a clamp. It is preferable to do.
Further, when the resin component flows by performing the heat treatment, the flux film sandwiched between the bumps / electrodes may leak to the outside due to the weight of the chip itself, and the solder bumps and the electrodes may be in direct contact with each other. Here, from the viewpoint of ensuring the contact between the bumps / electrodes, it is preferable to press with a jig such as a clamp.

  After the completion of this step, as shown in FIGS. 5 (3) and 6 (3), the electrodes 31 and 12 b facing each other are in a solder-joined state by the solder joint portions 61 and 62.

<Process (4)>
This step is a step of dissolving and removing the flux film of the present invention with a solvent after the end of the step (3).
At the end of the step (3), as shown in FIGS. 5 (3) and 6 (3), solder bonding is performed between the bumps of the chip and the electrodes of the substrate by the solder bonding portions 61 and 62. Is formed. By this step, the flux film 51 existing in the region other than the solder-bonded region is dissolved and removed by the solvent, and as shown in FIGS. 5 (4) and 6 (4), the solder-bonded portions 61 and 62 are exposed. It will be in the state.

  As shown in FIG. 6 (3), in C2, since there is a gap between the surface of the flux film 51 and the surface of the silicon substrate of the chip, the solvent enters the gap. The processing time tends to be shorter than C4.

The solvent for washing and removing the flux film is not particularly limited, and examples include water, alcohol, a mixed solvent of water and alcohol, and an organic solvent. Water is preferred.
In addition, when the resin component (A) is hardly soluble in water, it is preferable to use alcohol or a mixed solvent of water and alcohol. In the mixed solvent of water and alcohol, the mixing ratio is not particularly limited, but the alcohol ratio is preferably low from the viewpoint of reducing the environmental load.
Distilled water, ion exchange water, tap water or the like can be used as the water, and distilled water or ion exchange water with few impurities is preferable.
Examples of alcohols include methanol, ethanol, n-propanol and the like, and methanol and ethanol are preferred from the viewpoint of being a highly polar solvent.
By using highly polar water or alcohol as the cleaning solvent, the highly polar solvent has high surface tension, so it can easily enter narrow spaces due to capillary action, such as between the chip and the substrate, between adjacent solder joints, etc. Suitable for cleaning narrow gaps.

  The temperature of the solvent to be used can be appropriately set depending on the resin component (A) contained in the flux film, but is preferably performed at room temperature from the viewpoint of workability. When it is difficult to dissolve the flux film or when it takes time to dissolve the flux film, a heated solvent may be used. The higher the temperature of the heated solvent, the easier it is to dissolve the flux film, but it is preferably a temperature below the boiling point of the solvent.

Further, from the viewpoint of improving the efficiency of flux film dissolution and removal, it is preferable to dissolve and remove the flux film with a solvent while irradiating with ultrasonic waves, and a cleaning process is performed by a direct path method using the solvent irradiated with ultrasonic waves. It is more preferable.
If the flux agent in the flux film remains after cleaning, the solder joint portion may be corroded, which causes a decrease in reliability for long-term use. The flux agent removal efficiency can be improved by dissolving and removing while irradiating with ultrasonic waves, and the flux agent removal efficiency can be improved by performing a direct-pass cleaning process using a solvent irradiated with ultrasonic waves. Can be further improved. In addition, it is preferable to adjust as the intensity | strength of an ultrasonic wave so that the formed solder joint may not be cut | disconnected.

(Waste liquid treatment method)
For example, when a resin (A1) having a structure derived from polyvinyl alcohol is used, the waste liquid recovered by cleaning the flux film can be easily treated by an activated sludge method that decomposes by microorganisms.

(Solder joint area)
As described above, as shown in FIGS. 5 (4) and 6 (4), exposed solder joint portions 61 and 62 are formed between the opposing electrodes 31 and 12b.
The solder joint portion formed by the flip chip connecting method of the present invention is preferable as a joint material between the chip and the substrate. In liquid or paste flux, the solvent evaporates during the reflow process, so there is a tendency for voids to occur in the solder joints. However, since the flux film does not contain solvent, the amount of voids in the solder joints is greatly reduced. it can. The solder joint portion with few voids is less likely to generate cracks due to heat shock, and is preferable as a joining material from the viewpoint of connection reliability. Moreover, since the said solder joint site | part can form favorable solder joint by the stable flux effect | action, it shows low electrical resistance, and it is preferable from a viewpoint of electrical resistance as a joining material.

[Semiconductor device]
5 (4) and 6 (4) show the semiconductor device of the present invention having a chip / substrate solder joint portion according to the present invention, which is manufactured by the flip chip connecting method using the Lux film of the present invention. It is shown.
The semiconductor device of the present invention has high connection reliability such as low electrical resistance and resistance to cracks. Further, since this semiconductor device is formed by a simple process using the flux film according to the present invention, there is an advantage that it can be easily manufactured.

  EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples. In addition, about the physical-property value of each component used in the following Examples, the value measured based on the following method was used.

(1) Average polymerization degree of resin (A1) Measured according to JIS K 6726.
(2) Viscosity Measured according to JIS K 6726.

Example 1
(1) Preparation of resin solution Polyvinyl alcohol (PVA) (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name “GOHSENOL (registered trademark) GL-03”; degree of saponification 86.5-89.0 mol%, viscosity 3.0 To 3.7 mPa · s, average polymerization degree 300; in Table 1, “PVA (GL03)”) was dissolved in distilled water to prepare a resin solution.
(2) Production of film The prepared resin solution was applied onto a polyethylene terephthalate film, which was a support and the surface was subjected to a release treatment, to form a coating film. And this coating film was heat-dried at 50 degreeC for 30 minute (s), and the flux film whose film thickness is 5 micrometers, 30 micrometers, and 100 micrometers was each produced on the support body.

(Example 2)
Polyvinyl alcohol (PVA) (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name “GOHSENOL (registered trademark) GL-03”; degree of saponification: 86.5-89.0 mol%, viscosity: 3.0-3.7 mPa · s, Average polymerization degree 300) To an aqueous solution in which 100 parts by mass (active ingredient) is dissolved in distilled water, an aqueous solution in which 5 parts by mass of benzoic acid (effective ingredient ratio) is dissolved in distilled water is added as a fluxing agent and stirred to obtain a resin solution Was made.
Then, using the prepared resin solution, flux films having film thicknesses of 5 μm, 30 μm, and 100 μm were respectively produced by the same method as in Example 1.

(Example 3)
A resin solution was prepared in the same manner as in Example 2 except that 10 parts by mass of salicylic acid (effective ingredient ratio) was used in place of benzoic acid as the fluxing agent. 5 μm, 30 μm, and 100 μm flux films were respectively produced.

Example 4
A resin solution was prepared in the same manner as in Example 2 except that 30 parts by mass of salicylic acid (effective ingredient ratio) was used in place of benzoic acid as the fluxing agent. 5 μm, 30 μm, and 100 μm flux films were respectively produced.

(Example 5)
Polyvinyl alcohol (PVA) (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name “Gosefimer (registered trademark) L-7514”; degree of saponification 34.0 to 41.0 mol%, viscosity 20.0 to 28.0 mPa · s, average polymerization degree 600; described in Table 1 as “PVA (L-7514)”) 100 parts by mass (active ingredient) was dissolved in a mixed solvent of methanol / distilled water = 1/1 (mass ratio). A solution obtained by dissolving 10 parts by mass (effective ingredient ratio) of sebacic acid in a mixed solvent of methanol / distilled water = 1/1 (mass ratio) as a fluxing agent was added to the solution and stirred to prepare a resin solution.
Then, using the prepared resin solution, flux films having film thicknesses of 5 μm, 30 μm, and 100 μm were respectively produced by the same method as in Example 1.

(Example 6)
Polyvinylpyrrolidone (PVP) (Nippon Shokubai Co., Ltd., trade name “K-30”; described as “PVP (K-30)” in Table 1) 100 parts by mass (active ingredient) dissolved in distilled water As a flux agent, an aqueous solution in which 10 parts by mass of salicylic acid (active ingredient ratio) was dissolved in distilled water was added and stirred to prepare a resin solution.
Then, using the prepared resin solution, flux films having film thicknesses of 5 μm, 30 μm, and 100 μm were respectively produced by the same method as in Example 1.

(Comparative Example 1)
Epoxy resin, bisphenol F diglycidyl ether (manufactured by DIC Corporation, trade name “Epiclon (registered trademark) EXA-830”, epoxy equivalent 175 g / eq) 100 parts by mass (active ingredient), salicylic acid 10 mass as a flux agent Parts (active ingredient ratio), as a curing accelerator, 2-phenyl-4-methylimidazole (2P4MZ) (manufactured by Shikoku Kasei Kogyo Co., Ltd., trade name “CUREZOL (registered trademark) 2P4MZ”; in Table 1, “2P4MZ” A paste-form flux was prepared by blending 0.5 parts by mass (the active ingredient ratio).

(Comparative Example 2)
Hydrogenated rosin (trade name “Pine Crystal (registered trademark) KR-85”, acid value 174 mg KOH / g, softening point 87 ° C.) 30 parts by mass (active ingredient), active, which is a rosin resin As agents, triethylamine hydrochloride (TMA hydrochloride) 0.1 parts by mass (active ingredient ratio), adipic acid 1.0 part by mass (active ingredient ratio), isopropyl alcohol (IPA) 68.9 parts by mass (active ingredient ratio) To prepare a viscous liquid flux.

[Flip chip connection]
The base material (interposer) and semiconductor chip used for flip chip connection are as follows.

(Substrate (interposer))
A substrate 10 (interposer) having a configuration as shown in FIG. 1 was used.
The substrate 10 (interposer) used was an FR-4 substrate (glass epoxy substrate), the electrodes 12a and 12b were made of copper, the UBM layer on the electrode surface was Cu / Ni / Au (the thickness of the Ni layer was 5 μm, The thickness of the Au layer is 0.05 μm).
The electrode group includes an electrode (group) 12a at the peripheral portion of the substrate and an electrode (group) 12b at the central portion of the substrate. The electrode 12b at the center of the substrate has four blocks, the electrode diameter is 100 μm, and the electrode pitch is 200 μm. Moreover, the electrode 12a in the peripheral portion of the substrate has an electrode diameter of 1.5 mm and an electrode pitch of 3 mm. A solder resist is formed in the region 11 other than the electrodes on the upper surface of the substrate. The number of electrodes in one block is 22 × 22 = 1484, and the number of electrodes in the area where one chip is mounted is 484 × 4 = 1936.

(Semiconductor chip)
A chip 20 having a configuration as shown in FIG. 2 was used.
The chip 20 used is made to be mounted so as to face the electrodes 12b in the four blocks in the central portion of the substrate 10 (interposer). The chip 20 is made of silicon, the chip size is 10 mm × 10 mm × 0.7 mm, and the bumps 22 are arranged in 4 blocks in an area array.
As the bumps of the chip 20, two kinds of bumps capped with a spherical solder used for C4 and a hemispherical solder at the tip of the copper pillar used for C2 were used.
The semiconductor chip having spherical solder bumps used in C4 has the same structure as the chip 20a shown in FIG. 3, and has a structure having spherical solder bumps 32 having a diameter of 90 μm on the electrodes 31 of the chip 20a. ing.
A semiconductor chip having a bump capped with a hemispherical solder bump at the tip of a copper pillar used in C2 has the same structure as the chip 20b shown in FIG. 4, and is a metal made of copper having a diameter of 96 μm and a height of 40 μm. On the pillar 41, a hemispherical solder bump 42 having a diameter of 90 μm is provided.
The solder composition used was Sn3Ag0.5Cu (Sn96.5% by mass, Ag3% by mass, Cu0.5% by mass, melting temperature: about 217 ° C.) for C4, and Sn3.5Ag (Sn96.5% by mass, for C2). (Ag 3.5% by mass, melting temperature: 221 ° C.) was used.
In Example 3, for both C4 and C2, in addition to the above composition, solder having a composition of Sn58Bi (Sn42 mass%, Bi58 mass%, melting temperature: 138 ° C.) was also used.

  Using the flux films obtained in Examples 1 to 6 and the paste-like or liquid fluxes of Comparative Examples 1 and 2, solder joints were formed by flip chip connection, and semiconductor devices were manufactured. In Examples 1 to 6, which are film samples, the film was cut into an appropriate size and used.

[Flip chip connection when using flux films of Examples 1 to 6]
First, the flux film produced in Examples 1 to 6 cut to an appropriate size is placed on the electrode 12a (diameter: 100 μm, pitch between electrodes: 200 μm) surface side in the four blocks at the center of the substrate (interposer). , And fixed using a polyimide tape (step (1)).

  Next, the chip having solder bumps used in C4 or C2 is placed so as to be positioned on the electrode of the substrate via a flux film, and a flip chip bonder FCB3 (product name, manufactured by Panasonic Corporation). Was temporarily fixed (step (2)).

  And the board | substrate which mounted the chip | tip was heat-processed in nitrogen atmosphere for 1 minute at 260 degreeC which is more than the melting temperature of the solder bump to be used, and more than the temperature which this resin film liquefies ( Step (3)). However, in Example 3, when a chip having solder bumps with a solder composition of Sn58Bi was used, heat treatment was performed by changing only the heating temperature to 200 ° C. to form a solder joint.

After the heat treatment, the substrate on which the solder joints were formed was distilled water (H ₂₎ heated to 80 ° C. and oscillated at 45 Hz using an ultrasonic cleaner “VS-100 SUNPAR” (product name, manufactured by Inai Co., Ltd.). O) and a cleaning process for 10 minutes was performed by the direct pass method (step (4)). In Example 5, instead of distilled water, a mixed solvent of methanol (MeOH) / distilled water (H ₂ O) = 1/1 (mass ratio) was used.
Through the above steps, flip chip connection was performed when a flux film was used to obtain a semiconductor device.

[Flip chip connection using paste flux of Comparative Example 1]
The paste-like flux of Comparative Example 1 was printed on the surface of the electrode 12a (diameter: 100 μm, pitch between electrodes: 200 μm) in 4 blocks at the center of the substrate using a metal mask. Subsequent processes were carried out in the same manner as in Examples 1 to 6 to form solder joints, thereby obtaining semiconductor devices.

[Flip chip connection using the liquid flux of Comparative Example 2]
The liquid flux of Comparative Example 2 was applied by spraying onto the surface of the electrode 12a (diameter: 100 μm, pitch between electrodes: 200 μm) in the four blocks at the center of the substrate. Subsequent processes were carried out in the same manner as in Examples 1 to 6 to form solder joints, thereby obtaining semiconductor devices.

[Evaluation method]
The following items (1) to (7) were evaluated based on the following methods. The evaluation results are shown in Table 1.

(1) Workability A: The work of placing the flux on the substrate could be easily performed.
C: When carrying out the work of placing the flux on the substrate, it was necessary to adjust the amount applied to the substrate, and the workability was poor.

(2) Electrical conductivity after flip chip connection For a daisy chain circuit that passes through all the counter electrodes (484 locations) in one block of the electrode group of the semiconductor device soldered by flip chip connection, R6871E DIGITAL MULTITIMER (product name) , Manufactured by ADVANTEST) and an ammeter (product name “MODEL 5964”, manufactured by Mechatronics), the electric current was fixed at 1 mA, and the electric resistance was measured by a four-terminal method (Kelvin double bridge). Based on the measured value of electrical resistance, the following criteria were used for evaluation.
The daisy chain circuit is a circuit in which the upper and lower chips and the board are sewn with a thread. “→ → Lower board → Internal circuit → Board side electrode → Solder joint area → Opposite chip side electrode → Inside chip Circuit → Adjacent chip side electrode → Solder bonding site → Opposing substrate side electrode → Substrate internal circuit → Adjacent substrate side electrode → Solder bonding site → Opposing chip side electrode → Chip internal circuit → Adjacent chip side electrode → Solder bonding This is a circuit in which “part →→” is repeated. When the electrical resistance is low, it can be said that a good solder joint is formed between the solder bumps / electrodes and a stable flux activity is expressed.
A: The measured value of electrical resistance is less than 17Ω.
B: The measured value of electrical resistance is 17Ω or more and 19Ω or less.
C: The measured value of electric resistance exceeds 19Ω.

(3) Solder bridge Using “Microfocus X-ray inspection device MF160C” (product name, manufactured by Hitachi Construction Machinery Finetech Co., Ltd.), observe whether a solder bridge is formed between adjacent electrodes, and a short circuit is observed. did. Evaluation was made according to the following criteria depending on the number of short-circuited portions between the electrodes.
A: The location which is short-circuited between electrodes is not seen.
B: One to three short circuits are observed between the electrodes.
C: Four or more short circuits are observed between the electrodes.

(4) Void in Solder Joint Part Using a microfocus X-ray inspection apparatus (manufactured by Hitachi Construction Machinery Finetech Co., Ltd., product name “MF160C”), the presence or absence of voids inside the solder joint part was observed. In general, in X-ray transmission observation, a contrast image in which a heavy element is dark and a light element is bright is obtained. As a result, the solder bumps are dark (black) and the voids are bright (white), so that the presence or absence of voids can be observed. After bumps were formed on the substrate, arbitrary 30 bumps were observed by X-ray transmission, and evaluated according to the following criteria based on the number of observed voids.
A: No void was observed in the bump.
B: 1 to 3 voids were observed.
C: Four or more voids were observed.

(5) Storage stability After leaving the fluxes prepared in Examples and Comparative Examples at room temperature (25 ° C.) for 3 months, the flip chip connection is performed in the same manner as described above, and the electricity after the flip chip connection described above is performed. According to the conductivity method, the electrical resistance was measured, compared with the measured value of the electrical resistance before storage, and evaluated according to the following criteria. When the electrical conductivity before storage was C, the storage stability was not evaluated.
A: The measured value of electrical resistance when using the flux after storage for 3 months was the same or improved as compared to the measured value before storage.
C: The measured value of electrical resistance when using the flux after storage for 3 months was lower than the measured value before storage.

(6) Dissolvability (visual observation and observation with a magnifying glass)
The presence or absence of flux (resin component) remaining in the gap between the chip and the substrate after washing with a solvent was observed visually and using a magnifying glass, and evaluated according to the following criteria.
A: The remaining flux (resin component) is not observed.
C: Remaining flux (resin component) is observed.
(X-ray observation)
Since only the outermost solder joint portion of the chip can be observed visually and with a magnifying glass, a microfocus X-ray inspection apparatus (manufactured by Hitachi Construction Machinery Finetech Co., Ltd., product name “MF160C”) is used for detailed observation. The presence or absence of a flux (resin component) remaining in the gap between the chip and the substrate after the cleaning was observed and evaluated according to the following criteria.
A: The remaining flux (resin component) is not observed.
B: One to three remaining fluxes (resin components) exceeding the area of the electrode are observed.
C: Residual flux (resin component) larger than the area of the electrode is observed at four or more locations.

(7) Environmental load (environmental load during flux production)
The environmental load at the time of flux preparation was evaluated according to the following criteria depending on whether or not a volatile organic solvent was used and whether or not a drying step was performed.
A: No volatile organic solvent was used when producing the flux.
B: Although the volatile organic solvent was used at the time of producing the flux, the volatile organic solvent was not discharged because the drying process was not performed.
C: A volatile organic solvent was used at the time of producing the flux, and the drying process was performed.
(Environmental impact during mounting)
Regarding the environmental load at the time of flip chip mounting, the mass after drying 1 g of the flux of Examples and Comparative Examples at 150 ° C. for 1 hour was measured and evaluated according to the following criteria.
A: Mass reduction is less than 10%.
B: Weight reduction is 10% or more and 20% or less.
C: Mass reduction exceeds 20%.
(Waste liquid treatment)
From the viewpoint of waste liquid treatment, the environmental load was evaluated according to the following criteria. In addition, the value computed from the compounding ratio of the component contained in a flux is used for the content rate of the said biodegradable organic compound. In addition, when the evaluation of dissolution / removability was C, it was determined that washing was impossible, and the evaluation of waste liquid treatment was not performed.
A: Water is used as the cleaning liquid, and the biodegradable organic compound is 70% by mass or more among the organic compounds contained in the waste liquid.
B: Water is used as the cleaning liquid, and the biodegradable organic compound is less than 70% by mass among the organic compounds contained in the waste liquid.
C: An organic solvent is used as the cleaning liquid.

In Examples 1 to 4 and 6, good results were obtained in any of the evaluations of workability, electrical conductivity, solder bridge, presence / absence of voids in the solder joint part, storage stability, dissolution and removability, and environmental load. It was.
In addition, since Example 2 etc. used the flux agent, the result that electrical conductivity was still more favorable compared with Example 1 was obtained.
Moreover, in Example 5, since methanol is used at the time of preparation of a flux film and in a washing process, a part of evaluation of environmental load is C, but other evaluations are good results. It was.

  On the other hand, in the comparative example 1, since the used flux was paste-like, adjustment of the coating amount was complicated and the workability was inferior. As for electrical conductivity, a flux agent is added. However, since flux fluidity is low, C4 is evaluated as B, C2 is evaluated as C, flux activity is poor, and good solder joints are not formed. . Moreover, since low molecular weight components, such as a volatile epoxy resin, are contained, the evaluation of the void in a solder joint site | part and the environmental load at the time of mounting was inferior compared with the Example. Moreover, since the thermosetting resin was used, it was evaluated that the resin dissolution and removal were poor. Furthermore, the storage stability was inferior.

  Moreover, in the comparative example 2, since the used flux was liquefied, the adjustment of the coating amount was complicated, resulting in poor workability. Moreover, since isopropyl alcohol, which is a volatile component, is used as a solvent, voids frequently occur in the solder joints, and the environmental load during mounting is poor. In addition, since it contains a rosin resin that cannot be biodegraded, an environmental load is imposed from the viewpoint of waste liquid treatment. Moreover, regarding storage stability, both C4 and C2 were inferior to the examples.

  The flux film of the present invention is suitable as a flux used for flip-chip connection, and has a workability, electrical conductivity, solder bridges, voids in solder joints, and resin dissolution / removability compared to paste or liquid flux. Excellent in terms of storage stability and reduction of environmental load. Further, since there are no solder bridges and no voids at the solder joints, it is possible to manufacture a highly reliable semiconductor device with good electrical conductivity.

10 Substrate 11 Region other than electrode on substrate upper surface 12 Electrode 12a Electrode (group) in substrate peripheral portion
12b Substrate electrode (group)
20, 20a, 20b Chip 21 Silicon 22 on chip surface Bump 31 Electrode 32 Spherical solder bump 41 Metal pillar 42 Hemispherical solder bump 51 Solder joint part 62 formed by flux film 61 C4 Solder joint part formed by C2

Claims (9)

  A flux film comprising 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).   The flux film of Claim 1 containing resin (A1) and a flux agent (B).   The flux film of Claim 1 or 2 whose content of the said flux agent (B) is 1-50 mass parts with respect to 100 mass parts of resin (A1) or resin (A2). It is a flip chip connection method using the flux film of any one of Claims 1-3, Comprising: The flip chip connection method which has the following process (1)-(4).
Step (1): Step of placing the flux film on the electrode surface side of the substrate provided with electrodes (2): Step of mounting a chip provided with solder bumps on the substrate, the solder bumps being the flux Step (3) of placing and fixing so as to be positioned on the electrode of the substrate through a film: The melting point of the solder bump provided on the chip is higher than the melting point, and the resin component (A) is liquefied Step (4) of heat-treating at a temperature equal to or higher than the temperature at which the flux film is dissolved and removed with a solvent after completion of Step (3).   The flip-chip connection method according to claim 4, wherein in the step (3), the heat treatment is performed in an inert gas atmosphere.   The flip-chip connection method according to claim 4 or 5, wherein in the step (3), the heat treatment is performed in a state of being pressed from the chip toward the substrate.   The flip-chip connection method according to any one of claims 4 to 6, wherein the solvent used in the step (4) is any one of water, alcohol, and a mixed solvent of water and alcohol.   The flip-chip connection method according to any one of claims 4 to 7, wherein in the step (4), the flux film is dissolved and removed with a solvent while irradiating ultrasonic waves.   The semiconductor device with which the chip | tip provided with a solder bump and the board | substrate provided with an electrode are connected by the flip-chip connection method of any one of Claims 4-8.

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