JP2013110403A - Reflow film, method for forming solder bump, method for forming solder join, and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide, by unevenly distributing a solder constituent on an electrode of a substrate by means of self-structuring thereof, a reflow film which is excellent in self stability, transportability, and handleability in use, and which allows selective formation of a solder bump or solder join on the electrode, and to provide a simple and convenient method for forming a solder bump or solder join by use of the reflow film, a solder bump having less voids and smaller variation thereby formed, and a substrate with such solder bumps.SOLUTION: The reflow film 21 comprises: a polyvinyl alcohol; a compound which has a molecular weight of 500 or less and which is dissolved or dispersed in water; and solder particles dispersed therein. In the film, the compound with a molecular weight of 500 or less accounts for 20-300 pts.mass to 100 pts.mass of the polyvinyl alcohol. The method for forming a solder bump comprises the steps of: putting the reflow film on a face of a substrate 10 where an electrode 12 is located; further putting a plat plate 12 thereon; heating them; and removing and melting the reflow film.

Description

  The present invention relates to a reflow film used for bump formation of an electronic component, a wiring board, a substrate, a semiconductor chip and the like, a solder bump forming method, a solder bonding forming method, and a semiconductor device formed by them.

  As a method for mounting an electronic component on a circuit board or the like, for example, a method using solder bumps formed on electrodes of the substrate is known. In the semiconductor package, the number of I / O electrodes (terminals) is increased and the distance between the electrodes (terminals) is shortened (narrow pitch) due to the demand for downsizing, thinning, and high performance of the electronic devices. 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. In this connection method, solder bumps are formed in advance on the electrodes of the circuit board, and the solder bumps are joined to circuit electrodes such as the board. Solder bumps can be formed by mounting solder balls on circuit electrodes such as electronic components, liquid solder or solder paste containing solder particles, or solder paste through a metal mask through hole. A method of printing on an electrode of a circuit board is known.

In the solder ball mounting method, since the solder balls prepared in advance are mounted, the required bump height can be reduced by narrowing the size and particle size distribution of the prepared solder balls, and the bump height variation can be kept low. it can. However, production of solder balls that meet the standards is expensive. Moreover, the process of mounting the solder balls on the electrodes is complicated, and the introduction of the solder ball mounting apparatus requires a large capital investment. On the other hand, in the solder paste (cream solder) printing method, voids are easily formed in the bumps by entraining air during the printing operation, and there is also a possibility that the bump heights vary and the opposing electrodes cannot be joined. .

  Recently, as a new method for forming solder bumps and a new method for joining between counter electrodes, a simple process using self-organization of solder components on electrodes or between counter electrodes has been proposed. For example, according to Patent Document 1, solder bumps are formed on electrodes using a paste containing solder powder, a convection additive and an epoxy resin. After supplying the paste to the electrode surface side of the substrate provided with electrodes, when a plate is placed on the paste and heated above the melting point of the solder powder and above the boiling point of the convective additive, the bubbles of the convective additive are convected. The melted solder powder is agitated, the solder powders are combined, and the solder powder grows to a uniform size and is accumulated on the electrode. As a result, a highly uniform bump is formed. According to Patent Document 2, the counter electrodes can be similarly joined by solder. Moreover, after joining between counter electrodes with solder, the epoxy resin unevenly distributed in areas other than between counter electrodes can be hardened, and an underfill can be formed.

  The paste as described in Patent Document 1 is a simple process as compared with the solder paste printing method or the solder ball mounting method, but it uses a liquid or paste-like composition, so that the storage stability, There is a problem that it is inferior in transportability and handling property during use. Moreover, although the height variation of a solder bump can be suppressed, since bubbles are generated by a convective additive, there is a defect that bubbles are likely to be mixed into the bumps and voids are easily formed. In addition, when the thermosetting resin proceeds before the solder component accumulates on the electrode, the self-organization of the solder component on the electrode is difficult to complete. Furthermore, in the step of washing the resin after heating, the resin may not be dissolved due to the curing of the thermosetting resin, or may not be completely removed by washing.

  In addition, when soldering is performed between the counter electrodes as in Patent Document 2, a small amount of solder residue is left in the epoxy resin that is unevenly distributed in a region other than between the counter electrodes. This solder residue can cause a short circuit due to a decrease in electrical resistance between adjacent electrodes.

Japanese Patent No. 3964911 JP 2006-114865 A

  The present invention is a reflow film having excellent storage stability, transportability, and handling during use, and a simple solder bump forming method for selectively forming solder bumps only on electrodes using the film. It is an object of the present invention to provide a solder bump with a small number of voids and a small height variation, a substrate with a solder bump in which the solder bump is formed on an electrode of the substrate, and a semiconductor device obtained therefrom. In addition, a simple solder joint forming method that selectively forms solder joints only between the opposing electrodes using the reflow film without the step of forming solder bumps, and solder joints with fewer voids formed thereby. An object of the present invention is to provide a semiconductor device joined by the solder joint part.

  As a result of diligent research by the present inventors, after reflow film and flat plate are sequentially stacked and fixed on the electrode surface side of the substrate provided with electrodes by a reflow film containing polyvinyl alcohol and a compound having a molecular weight of 500 or less, solder particles The solder component was unevenly distributed on the electrode of the substrate by self-organization by heating to a temperature not lower than the melting temperature and higher than the temperature at which the polyvinyl alcohol and the compound having a molecular weight of 500 or less dissolved or dispersed in water were liquefied. After that, it was found that the reflow film containing the solder residue existing between the substrate other than on the electrode and the flat plate can be dissolved and removed with a solvent to form a solder bump, and this is also applied to the solder joint between the counter electrodes. Thus, the present invention has been completed. That is, the present invention is as follows.

(1) A film containing polyvinyl alcohol, a compound having a molecular weight of 500 or less dissolved or dispersed in water, and solder particles, wherein the compound having a molecular weight of 500 or less is 20 to 300 parts by mass with respect to 100 parts by mass of polyvinyl alcohol. The reflow film is characterized in that the solder particles are dispersed in the film.

(2) The reflow film as described in (1) above, wherein the compound having a molecular weight of 500 or less is a low molecular weight alcohol having a boiling point of 100 ° C. or higher.

(3) The reflow film according to any one of (1) to (2), wherein the compound having a molecular weight of 500 or less is glycerin.

(4) The reflow film as described in any one of (1) to (3) above, further comprising a component for removing the metal oxide.

(5) From the fine particle side of the cumulative particle size distribution of the solder particles, a cumulative particle size of 10% and a cumulative particle size of 90% are both in the range of 1 to 50 μm. The reflow film according to any one of the above.

(6) The reflow film according to any one of (1) to (5), wherein the solder particles are lead-free solder. The solder particles are an alloy of tin, silver, and copper. The reflow film according to any one of (1) to (6) above, wherein

(8) The reflow film according to any one of (1) to (7), wherein the solder particles are included in an amount of 30 to 500 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol.

(9) A solder bump forming method using the reflow film according to any one of (1) to (8),
(A) a step of placing the reflow film on the electrode surface side of a substrate provided with electrodes;
(A) a step of placing and fixing a flat plate on the reflow film;
(C) a step of heating above the melting temperature of the solder particles in the reflow film and above the temperature at which the polyvinyl alcohol and the compound having a molecular weight of 500 or less dissolved or dispersed in water are liquefied; A solder bump forming method comprising a step of dissolving and removing the reflow film after completion of the step (c).

(10) The method for forming a solder bump according to (9), wherein the step (c) is performed in an inert gas atmosphere.

(11) The solder bump forming method according to any one of (9) to (10), wherein the step (c) is performed in a state of being pressed from a flat plate toward the substrate.

(12) In the step (d), the reflow film containing a residue of solder particles other than the surface of the electrode is removed with water, alcohol, or a mixed solvent thereof (9) to (9) The solder bump forming method according to any one of 11).

(13) The solder bump forming method according to any one of (9) to (12), wherein ultrasonic waves are irradiated in the step (d).

(14) A method for forming a solder joint using the reflow film according to any one of (1) to (8),
(A) a step of placing the reflow film on the electrode surface side of a substrate including an electrode;
(B) on the reflow film, loading the electrode surface side of another substrate having electrodes, and fixing the electrodes of the upper and lower substrates at positions facing each other via the reflow film;
(C) In the state of (b), heated above the melting temperature of the solder particles in the reflow film and above the temperature at which the polyvinyl alcohol and the compound having a molecular weight of 500 or less dissolved or dispersed in water are liquefied. And (d) a step of dissolving and removing the reflow film after completion of the step (c).

(15) The method for forming a solder joint according to (14), wherein the step (c) is performed in an inert gas atmosphere.

(16) The method for forming a solder joint according to any one of (14) to (15), wherein the step (c) is performed in a state where the loaded substrate is pressed.

(17) In the step (d), the reflow film containing a residue of solder particles other than between the opposing electrodes is removed with water, alcohol, or a mixed solvent thereof (14) ) To (16) The method for forming a solder joint according to any one of (16).

(18) The method for forming a solder joint according to any one of (14) to (17), wherein in the step (d), an ultrasonic wave is irradiated.

(19) A solder bump formed by the solder bump forming method according to any one of (9) to (13).

(20) A substrate with solder bumps, wherein bumps are formed on electrodes of the substrate by the solder bump forming method according to any one of (9) to (13).

(21) The solder bump according to (19), wherein the substrate is a semiconductor chip or an interposer.

(22) The substrate with solder bumps according to (20), wherein the substrate is a semiconductor chip or an interposer.

(23) A solder joint portion formed between the opposing electrodes of two substrates having electrodes by the solder joint forming method according to any one of (14) to (18).

(24) The combination of the substrate having the solder joint portion according to (23) and including the electrode is any one of a semiconductor chip and an interposer, a semiconductor chip and a semiconductor chip, an interposer and an interposer. A semiconductor device.

  The present invention is a reflow film having excellent storage stability, transportability, and handling property at the time of use by adding a compound having a predetermined molecular weight of 500 or less to polyvinyl alcohol, and selectively using this to solder bumps only on electrodes. A simple solder bump forming method can be provided. The bump formed thereby has few voids, low electrical resistance (high electrical conductivity), and little height variation. Moreover, according to this invention, the board | substrate with a solder bump in which the said bump is formed on the electrode of a board | substrate, and the semiconductor device obtained by these can be provided. Further, it is possible to provide a simple solder joint forming method that selectively forms a solder joint only between the counter electrodes using the reflow film without a step of forming a solder bump.

It is a schematic plan view of a board | substrate (interposer) provided with the electrode used by the Example and comparative example of this invention. It is an example which shows the formation method of a solder bump, (a) is a sectional view of a substrate which mounted a reflow film and a flat plate, (b) is a sectional view showing the state where solder accumulated on an electrode after a heating process, (C) is sectional drawing which shows the state which the solder bump exposed after melt | dissolution removal by solvent washing | cleaning. It is a schematic plan view of the semiconductor chip used in the Example and the comparative example. It is an example of the formation method of the solder joint between counter electrodes at the time of laminating interposer / reflow film / semiconductor chip, (a) is mounting a reflow film, and also loading the electrode (copper pillar) side of a semiconductor chip (B) is a cross-sectional view showing a state in which the counter electrodes after the heating step are solder-bonded, and (c) is a cross-section showing a state in which the solder joint between the counter electrodes is exposed after dissolution by solvent. FIG. It is an example of the formation method of the solder joint between counter electrodes at the time of laminating | stacking a semiconductor chip / reflow film / semiconductor chip, (a) is sectional drawing which shows the state in which the counter electrodes after the heating process were solder-joined, b) is a cross-sectional view showing a state in which the solder joint between the counter electrodes is exposed after dissolution removal by solvent cleaning. It is an example of the formation method of the solder joint between opposing electrodes at the time of laminating | stacking an interposer / reflow film / interposer, (a) is sectional drawing which shows the state which the soldering joined between the opposing electrodes after a heating process, (b) FIG. 3 is a cross-sectional view showing a state in which a solder joint between counter electrodes is exposed after dissolution removal by solvent cleaning.

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

(Reflow film)
The “reflow film” in the present invention is a resin composition containing polyvinyl alcohol and a compound having a molecular weight of 500 or less dissolved or dispersed in water (hereinafter sometimes referred to simply as “resin”). A film formed by In addition, an additive component such as a fluxing agent may be included. In addition, dispersion | distribution of the solder particle may partially settle in the thickness direction of the film which is the up-down direction during film manufacture.

  The reflow film is a film-like solid at room temperature (25 ° C.). This reflow film is placed and fixed on a circuit board or the like having electrodes, and when heated above the melting temperature of the solder particles and above the temperature at which the resin liquefies, the solder component is self-adjusted on the electrode surface. Collect systematically and segregate. Moreover, when the electrode surfaces of the two substrates are fixed at positions where the electrodes face each other via the reflow film and heated in the same manner, the opposing electrodes are joined by solder.

  This is because heating to this temperature results in a liquid / liquid phase separation consisting of solder and resin, so that the molten solder particles can move within the liquid resin, and the solder components are self-organized on the electrodes. As a result, the resin component is unevenly distributed in a region other than on the electrode. Even when there are a plurality of electrodes, the solder component is segregated on the surface of each electrode, while the solder component does not segregate in a region other than the electrode. Here, when the accumulation of solder proceeds between the counter electrodes, the electrodes are joined by solder. And when it cools in that state, it solidifies in the state which the solder particle aggregated on the electrode surface, ie, the state which the solder became the lump shape, or the state which soldered between electrodes. That is, solder bumps or solder joints are selectively formed only between a plurality of electrode surfaces or counter electrodes.

  When a thermosetting resin is used instead of a thermoplastic resin such as polyvinyl alcohol as the resin used for the reflow film, a network of the resin is formed when heated, so that the solder particles cannot flow on the electrode or Accumulation between the electrodes hardly occurs. Further, even if accumulation on the electrode occurs, it cannot be used in the present invention because it does not dissolve in the solvent in the subsequent resin dissolution and removal step (details will be described later). In particular, since the lead-free solder has a high melting temperature of 200 ° C. or higher, the thermosetting resin is quickly cured and cannot be applied to the resin in the present invention.

  Further, when a thermosetting resin is used, an underfill can be formed simultaneously with the solder bonding by curing the thermosetting resin after the solder bonding is formed, and the mounting process can be shortened. However, in the thermosetting resin in a region other than between the electrodes, there is a small amount of solder residue left without being able to move between the electrodes, and this residual solder reduces the electrical resistance between adjacent electrodes. Can cause a short circuit.

(Description of self-organization of solder components)
The reason why the solder particles segregate on the electrode surface in the liquid / liquid phase separation state is estimated as follows. This is because the solder has a high wettability with respect to the metal of the electrode, while the wettability with respect to a component in a region other than the electrode on the substrate surface, such as a solder resist, is low. That is, the surface of the electrode with high wettability is stable because the contact angle is small and the center of gravity of the solder droplet is low, and the interaction attracting the solder and the electrode works and is held on the electrode. On the other hand, in areas other than electrodes with low wettability, the contact angle is large, the center of gravity of the solder droplet is high and unstable, and the repulsive interaction between the solder and the electrode works and moves around (in some cases Repelled). As a result, the solder component collects and accumulates on the electrode.

  The reason why the solder component accumulates on the electrode can also be explained by a Laplace equation representing the pressure difference inside the solder droplet. In the process in which droplets of different sizes come into contact with each other to form one large droplet, it is known that a droplet with a small radius is sucked into a droplet with a large radius. This phenomenon is explained by the fact that a droplet having a small radius has a higher internal pressure than a droplet having a large radius, and a droplet having a smaller radius is sucked into a large droplet by this pressure difference. This idea can be applied to solder droplets to explain the accumulation of solder components on the electrodes. For example, when a solder droplet exists across an electrode and a region other than the electrode, the radius of curvature is large because the contact angle is low in the electrode, and the radius of curvature is small because the contact angle is high in the region other than the electrode. Therefore, the solder in the region other than the electrode having a small radius of curvature has a higher pressure than the solder on the electrode having a large radius of curvature, so that the solder in the region other than the electrode moves to the electrode side due to the pressure difference (12th Symposium on Microjoining and Assembly Technology in Electronics, February 2-3, 2006, Yokohama, p381-386). As a result of this movement, the solder particles are accumulated on the electrode, and when the solder particles in the region other than the electrode approach and come into contact with the agglomerated solder mass, the solder particles on the region other than the electrode having a small radius of curvature are placed on the electrode. Sucked into the solder lump. By repeating the above, it is presumed that the solder component collects and accumulates on the electrode in a self-organized manner.

(Features of reflow film)
Since the reflow film according to the present invention is a film-like solid, components that can cause a reaction like a liquid are difficult to diffuse, so it has excellent storage stability, and there is no worry about liquid leakage, etc. In addition, there is little stickiness and excellent handling during use.

  Moreover, since the reflow film according to the present invention is a film-like solid in which solder particles are dispersed, there is no need for printing using a complicated metal mask or mounting of solder balls during use, and on the circuit board. Solder bumps or solder joints can be formed by a simple process of mounting and fixing at a desired position and then heating, and then washing away the remaining solder with a solvent.

(Washing solvent)
The washing solvent for dissolving and removing the reflow film is not particularly limited, but water is most preferable because it has a low environmental burden and is easily available. When the resin component is hardly soluble in water, a mixed solvent of water and alcohol or an alcohol solvent alone is preferable. There is no particular limitation on the mixing ratio of water and alcohol. Distilled water, ion exchange water, tap water and the like can be used as water, and distilled water and ion exchange water with few impurities are preferable. Examples of alcohols include methanol, ethanol, n-propanol and the like, and methanol and ethanol are particularly preferable because of their high polarity. Another reason for using highly polar water or alcohol as a solvent for resin cleaning is that a highly polar solvent has a high surface tension, so it easily enters a narrow space due to capillarity. This is because it is suitable for cleaning narrow gaps between substrates, between adjacent bumps, between adjacent solder joints, and the like.

(Film material)
Since the reflow film according to the present invention must be able to be dissolved and removed with the above-mentioned solvent in a state including a solder residue that is unevenly distributed other than on the electrodes or between the counter electrodes after the heating step, the film material used for the reflow film is polyvinyl Alcohol is used from the viewpoint of water solubility and film-forming ability. Furthermore, since polyvinyl alcohol is a polyhydric alcohol, it is extremely preferable because it has an effect of removing the oxide film of the solder particles on the resin itself.

(Molecular weight of polyvinyl alcohol)
In the heating process that makes the temperature higher than the melting temperature of the solder particles and the temperature at which the resin liquefies, in order for the solder particles to accumulate on the electrodes and between the counter electrodes, the viscosity of the resin must be so low that the solder particles can flow. preferable. The lower the viscosity of the resin, the more actively the solder particles move, and the solder particles are accumulated in contact with the electrode or the solder mass accumulated on the electrode. Therefore, the lower the viscosity of the resin, the better. For this purpose, it is preferable that the softening point, which is the temperature at which the resin softens, is low, but just having a low softening point does not necessarily result in a viscosity that is so low that the solder particles flow. That is, when the temperature is higher than the softening point, the resin becomes soft, but when the molecular weight of the resin is too high, the molecular chains are not easily entangled, so that the viscosity is not lowered so that the solder particles can flow.

  Therefore, in order to reduce the viscosity of the resin, it is possible to reduce the entanglement by lowering the molecular weight of the resin. Even in the step of dissolving and removing the reflow film after the heating step, generally, the lower the molecular weight of the resin, the faster it is dissolved. From this viewpoint, a resin having a lower molecular weight is better. On the other hand, if the molecular weight of the resin is lowered, the film-forming ability at room temperature is deteriorated. Therefore, a resin having a low molecular weight is preferred within the range of the molecular weight that can form a film.

  Among the resins, the preferred molecular weight of polyvinyl alcohol varies depending on the saponification degree. For example, in the case of polyvinyl alcohol having a saponification degree of 88%, the weight average molecular weight is preferably 3,000 to 60,000, and 4,000 to 40,000. More preferred is 5,000 to 30,000. If it is within this range, it has a sufficient film forming ability than when it is lower than this range, and solder is accumulated on the electrode due to the fluidity of the solder particles in the heating process than when it is higher than this range. It tends to be easy. Furthermore, if it is in this range, in the step of dissolving and removing the reflow film, it can be completely dissolved and removed without requiring a long time for dissolution.

(Bump forming ability and film forming ability compatible)
A reflow film in which solder particles are dispersed in polyvinyl alcohol, which is thermoplastic, can form solder bumps and solder joints by a simple process and has excellent handling properties. Here, the bump forming ability and the film forming ability are in a trade-off relationship. That is, in the bump forming process by solder self-organization, in order for the solder particles to accumulate on the electrode, it is necessary that the film has a low viscosity at the reflow temperature, and polyvinyl alcohol having a low molecular weight is preferable. On the other hand, polyvinyl alcohol having a high molecular weight is preferable for forming a film in order to improve handling properties. Since the commercially available polyvinyl alcohol has a higher molecular weight as the film forming ability is better, in the present invention, a compound having a molecular weight of 500 or less dissolved or dispersed in water is added thereto to improve the bump forming ability. That is, in order to achieve both the bump forming ability and the film forming ability, a compound that dissolves in water having a molecular weight of 500 or less or is dispersed like an emulsion is added to the reflow film. Since this compound acts as a plasticizer, it has the effect of weakening the interaction between molecules, so that the viscosity can be lowered at the reflow temperature. In addition, the low viscosity of the compound itself is considered to be a factor that lowers the viscosity at the reflow temperature.

(Compound with a molecular weight of 500 or less added to the reflow film)
As a compound having a molecular weight of 500 or less (hereinafter also referred to as a low molecular weight component) that is dissolved or dispersed in water, the boiling point of the film is a liquid or solid at room temperature so that it does not volatilize from the film system in the drying step in film formation. It is preferable that the drying temperature is higher. Also, in the solder self-assembly process, if it volatilizes from within the film system, the effect of reducing the viscosity cannot be expected. Therefore, it is preferable not to volatilize from the film system even at the reflow temperature. Although the preferred boiling point of the low molecular weight component varies depending on the reflow temperature, the boiling point of the low molecular weight component is preferably 100 ° C or higher, more preferably 130 ° C or higher, further preferably 150 ° C or higher, and 200 ° C or higher. Particularly preferred is 270 ° C. or higher. Moreover, since it mixes with polyvinyl alcohol uniformly, it is preferable that it is a low molecular weight alcohol with a molecular weight of 500 or less. Examples of the low molecular weight alcohol include glycerin (boiling point 290 ° C., molecular weight 92), ethylene glycol (boiling point 197 ° C., molecular weight 62), vinyl alcohol oligomer (average molecular weight 440) and the like. It is extremely preferable because it is higher than the SnAgCu reflow temperature. The molecular weight of the low molecular weight component is 500 or less, preferably 300 or less, more preferably 200 or less, and even more preferably 100 or less. Generally, the lower the molecular weight, the higher the effect of reducing the viscosity. Therefore, the lower the molecular weight of the low molecular weight component of the present invention, the better. The lower limit of the molecular weight of the low molecular weight component is not particularly limited, but is preferably 50 or more and more preferably 60 or more from the viewpoint of difficulty in volatilization.

(Content of low molecular weight components)
In this invention, content of a low molecular weight component is 20-300 mass parts with respect to 100 mass parts of polyvinyl alcohol. Although content of a low molecular weight component changes with kinds of low molecular weight component, it is generally more preferable that it is 20-200 mass parts, it is further more preferable that it is 30-100 mass parts, and 30-50 mass parts. Is very preferred. If the content of the low molecular weight component is not less than the above lower limit, the effect of reducing the viscosity is sufficient and the bump forming ability tends to be good. Moreover, if it is below the said upper limit, a tack | tuck is weak, it is easy to handle and it exists in the tendency which can be fully formed as a film.

(Removal of metal oxide)
It is preferable that the reflow film which concerns on this invention contains the component which removes a metal oxide. This is because the surface of the solder particles is covered with a metal oxide having a high melting point, and it is difficult to melt the solder unless it is removed. In general, acidic substances, basic substances, alcohols, and the like are effective for removing metal oxides on the surface of solder particles, and are called fluxing agents. Specific examples of the fluxing agent include salicylic acid, benzoic acid, m-dihydroxybenzoic acid, sebacic acid, and rosin. Moreover, the commercially available flux agent with which the viscosity was adjusted can also be used. However, depending on the combination of the resin and the fluxing agent, the solder particles may not flow, so the fluxing agent is appropriately selected and used. The reason for this is not necessarily clear, but it is presumed that the network was formed by a condensation reaction or the like. When a network is formed, it becomes difficult to dissolve in a solvent such as water, which affects the resin dissolution and removal process.

  In addition to the combination of resin and fluxing agent, the formation of this network is greatly influenced by the atmosphere. Compared to the atmosphere, network formation is relatively less likely to occur under an inert gas atmosphere such as nitrogen. Therefore, it is preferable to perform at least the resin heating step in an inert gas atmosphere.

  In addition, if the electrode surface is coated with a metal oxide, the wettability with the solder is reduced, but the flux agent described above also has the effect of removing this, so the solder and the electrode In order to improve the wettability, it is preferable to contain the above-mentioned flux agent.

  As a fluxing agent for polyvinyl alcohol, salicylic acid, benzoic acid, m-dihydroxybenzoic acid are used from the viewpoint of the removal property of the oxide film of the solder particles, the fluidity of the solder particles, and the dissolution and removal property of the resin after self-organization of the solder components. Sebacic acid is preferred, and salicylic acid is more preferred.

(Flux agent content)
The content of the fluxing agent varies depending on the content of the solder particles, the surface area of the solder particles, the thickness of the oxide film on the surface of the solder particles, but generally 1 to 40 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol. 2 to 30 parts by mass is more preferable, 3 to 20 parts by mass is particularly preferable, 3 to 15 parts by mass is extremely preferable, and 4 to 12 parts by mass is most preferable. If it is above this lower limit, the oxide film can be sufficiently removed, and if it is below the upper limit, a network is formed in the resin and solder particles do not easily flow. Furthermore, if the fluxing agent is used excessively, the fluxing agent may remain after the resin cleaning step, which may corrode the solder bumps.

(Solder particle size)
The solder particles used for the reflow film according to the present invention are preferably solder particles smaller than the shortest distance between adjacent electrodes (the shortest distance connecting the outer edges of the electrodes). When many solder particles having a particle diameter larger than the shortest distance between adjacent electrodes are included, there is a high possibility that the solder bridges and connects the adjacent electrodes, and a short circuit is likely to occur. On the other hand, since solder particles with a small particle size of 5 μm or less are generally easy to aggregate in the atmosphere and difficult to handle, in this case, the reflow film manufacturing, storage, and use processes are all inert, such as nitrogen gas. It is preferable to carry out in a gas atmosphere. As for the particle size of the solder particles used in the reflow film according to the present invention, the cumulative particle size distribution of the solder particles from the fine particle side is 10% of the cumulative particle size (d10) and 90% of the cumulative particle size (d90). It is preferable to be within the range. Since the preferable particle size range varies depending on the application such as the size of the electrode and the pitch between the electrodes, it is preferable to use solder particles having an appropriate particle size. Generally, the particle size range from the solder particles d10 to d90 is from 1 to 2 to 45 μm is preferable to 50 μm, 5 to 40 μm is more preferable, 8 to 30 μm is further preferable, 10 to 25 μm is particularly preferable, 10 to 20 μm is extremely preferable, and 10 to 15 μm is most preferable. If the number of solder particles having a large particle size is not too large, inter-electrode bridges may be formed in the solder self-assembly process, or precipitation may easily occur in the varnish described later for producing a reflow film. can avoid. If there are no particles having a particle size that is too small, the agglomeration between the solder particles hardly occurs even when the varnish is produced, and can be handled even in a nitrogen atmosphere.

(Composition of solder particles)
Examples of the composition of the solder particles used in the reflow film according to the present invention include SnPb-based, lead-free SnAgCu-based, SnAg-based, SnCu-based, SnZnBi-based, and SnAgBiIn-based. Moreover, SnBi type (melting point of 42Sn-58Bi is 138 ° C.) and InSn type (melting point of 52In-48Sn is 118 ° C.), which are lead-free and low melting point solder, can also be mentioned. The SnPb system was preferred from the viewpoints of mechanical properties and reliability, but the RoHS directive prohibiting the use of harmful substances such as lead for the environmental protection came into effect in the EU, so the present invention uses lead-free solder particles. Is preferred. Among lead-free solders, although it has a slightly high melting point, it is a tin, silver, and copper alloy that is generally used for joining semiconductors because of its good mechanical properties and reliability, that is, SnAgCu solder particles Is more preferable. Since the melting temperature of SnAgCu-based solder particles exceeds 200 ° C. (Sn-3Ag-0.5Cu has a melting point of about 217 ° C.), when a thermosetting resin such as an epoxy resin is used, the curing of the resin proceeds. Therefore, there is a high possibility that the solder particles cannot flow. Since the resin of the reflow film according to the present invention uses a thermoplastic resin, the solder particles can flow even at a high temperature exceeding 200 ° C., so that the solder particles accumulate on the electrodes to form solder bumps and solder joints. be able to. In addition, SnBi-based or InSn-based solder particles that are lead-free and low melting point solder can be used for materials such as liquid crystals that deteriorate in high-temperature processes exceeding 200 ° C.

(Solder particle content)
The content of the solder particles varies depending on the size of the electrode, the pitch between the electrodes, the required bump height, the distance between the counter electrodes, and the like, but it is 30 to 500 mass with respect to 100 mass parts of polyvinyl alcohol. Part, preferably 50 to 400 parts by weight, more preferably 80 to 300 parts by weight, and particularly preferably 100 to 200 parts by weight.

(Production method of reflow film)
A general method for producing a reflow film is, for example, as follows. First, a solution of a resin composition is prepared by dissolving polyvinyl alcohol and a low molecular weight component in a solvent for varnish that is water, alcohol or a mixture thereof. A predetermined amount of this resin composition solution and solder particles are mixed and stirred to prepare a varnish. Next, a varnish is applied on one main surface of the support film using an applicator having a certain gap to form a coating film, and then heated in an oven to remove the solvent for the varnish. Can be obtained.

(How to add flux agent)
It is preferable to add a flux agent to the varnish, and it is particularly preferable when the resin itself has a low flux action. The fluxing agent may be added after mixing the resin, solder particles and solvent for the varnish, but considering the effect of removing the oxide film of the solder particles, it is added directly to the solder particles before adding the solder particles to the resin solution. It is preferable to remove the oxide film. In this case, it may be used as it is when the fluxing agent is liquid, but when the fluxing agent is solid, it is preferably used after being dissolved in a solvent.

(Viscosity of varnish and points to keep in mind)
Since the solder particles may settle in the varnish, it is important to adjust the viscosity of the varnish. When the viscosity is increased, the solder particles are less likely to settle, but since the smoothness of the coating film surface is deteriorated, for example, streaks are formed during the formation of the coating film, the viscosity is adjusted to an appropriate viscosity with the amount of the varnish solvent. Moreover, after preparing a varnish, it is preferable to apply | coat using the varnish, after storing for a long period of time and before solder particles have settled.

(Drying the coating film)
The drying temperature and drying time of the coating film for obtaining the reflow film can be determined at an appropriate temperature and time depending on the solvent for varnish, the film thickness, etc. within a temperature range below the melting point of the solder particles.

(Reflow film shape)
Although the reflow film which concerns on this invention sets suitably as needed as thickness, it can be 0.01-0.5 mm, for example. However, in order to avoid the solder particles from protruding from the reflow film that is thinner than the particle size of the solder particles, the thickness of the reflow film should be set appropriately considering the particle size of the solder particles and the application of the reflow film. Is preferred.

  Moreover, as a magnitude | size (area) of a reflow film, the magnitude | size can be set in consideration of the magnitude | size of the board | 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.

  In the first embodiment of the present invention, solder bumps can be formed on the electrodes of the substrate using the reflow film according to the present invention described above. In the second embodiment of the present invention, a solder joint can be formed between the counter electrodes using the reflow film. With respect to the substrate used in the above forming method, each step of the forming step will be described below with reference to the drawings.

(substrate)
The substrate used in the solder bump forming method according to the first embodiment of the present invention and the solder joint forming method according to the second embodiment may be provided with one or more electrodes, for example, a semiconductor chip, an interposer, a motherboard. The printed wiring board etc. which mount various electronic components like are mentioned. In order to improve the wettability with the solder particles, it is preferable that an UBM (Under Bump Metallization) layer is formed on the electrode surface. Although copper is generally used for the circuit, 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 kept low.

  In addition, when dirt such as oil or fat is attached to the electrode surface of the substrate, the wettability with the solder is reduced and adversely affects self-organization. Therefore, degreasing with an organic solvent, acidic aqueous solution, basic aqueous solution, etc. in advance Is preferred. When degreasing, it is more preferable to apply ultrasonic waves since 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 after the removal of the oxide. For example, an acidic aqueous solution or a basic aqueous solution has a degreasing effect. In addition, since there is an effect of removing oxides, it is preferable to use this for cleaning from the viewpoint of removing oxides of electrodes. In addition, when the reflow film contains a flux agent, the oxide existing on the electrode surface can be removed in addition to the solder particle surface in the heating step.

  As described above, when the shortest distance between adjacent electrodes (shortest distance connecting the outer edges of the electrodes) is equal to or smaller than the particle size of the solder particles, a solder bridge is formed between the adjacent electrodes. Therefore, the particle size of the solder particles used for the reflow film is appropriately selected according to the shortest distance between adjacent electrodes. For example, if the cumulative particle size distribution from the fine particle side has a cumulative particle size of 10% and a cumulative particle size of 90% are both in the range of 1 to 50 μm, the substrate having the shortest distance between adjacent electrodes of 1 μm or more is used. preferable.

  FIG. 1 shows an example of a schematic plan view of a substrate provided with electrodes used in the present invention. The substrate 10 shown in FIG. 1 has a solder resist in a region 11 other than the electrode 12 on the upper surface, and the electrode 12 is composed of an electrode (group) 12a in the peripheral portion of the substrate and an electrode (group) 12b in the central portion of the substrate.

(Method of forming solder bumps)
In the method for forming solder bumps according to the first embodiment of the present invention, (a) a step of placing the reflow film on the electrode surface side of a substrate including electrodes, and (a) placing a flat plate on the reflow film. (C) heating above the melting temperature of the solder particles in the reflow film and above the temperature at which the polyvinyl alcohol and the compound having a molecular weight of 500 or less dissolved or dispersed in water are liquefied. And (d) a step of dissolving and removing the reflow film after completion of the step (c).

  FIGS. 2A to 2C show an example of a cross-sectional view of a substrate illustrating a method for forming solder bumps according to the first embodiment. (A) is the state of the process (A) which mounted the reflow film 21 in the electrode 12 surface side of the board | substrate 10, and also mounted the flat plate 22. FIG. (B) is sectional drawing which shows the state which the solder bump 23 accumulated on the electrode 12 after a heating process (c). (C) is sectional drawing which shows the state which the flat plate 22 peeled after the process (d), the reflow film 24 containing a solder residue was removed, and the solder bump 23 was exposed.

(Step (a) for placing the reflow film)
The said reflow film is mounted in the electrode surface side of a board | substrate provided with an electrode. The mounting method is not particularly limited. As described above, the substrate is preferably degreased in advance. The substrate is preferably heat-dried at 120 ° C. for about 4 hours so that water adsorbed in the substrate does not foam during heating.

(Process of (i) placing a flat plate)
The flat plate used in the step (a) needs to have heat resistance that can withstand the heating step in addition to the smooth surface shape. Furthermore, it is preferable that the flat plate is peeled off from the reflow film during the subsequent step (d), because the upper surface of the reflow film can all come into contact with the solvent and the resin dissolves quickly. Examples of the flat plate satisfying the above condition include a glass plate of eagle glass having heat resistance and low thermal expansion.

  Further, in the step (a), the flat plate may move due to evaporation of a small amount of low boiling point components in the next heating step. Therefore, it is preferable to fix the flat plate with a jig such as a clamp after placing the flat plate. . Further, in order to obtain a desired solder bump height, it is preferable to sandwich a spacer corresponding to the solder bump height between the substrate and the flat plate as necessary. In order to reduce the variation in the height of the solder bumps, it is preferable to place a flat plate parallel to the substrate and maintain this in the step (c).

(Step of heating (c))
The heating temperature and heating time (holding time) in the step (c) are the temperature above the melting temperature of the solder particles to be used, the temperature above the temperature at which polyvinyl alcohol and low molecular components are liquefied, the content of solder particles, and the heating step. The viscosity of the resin, the boiling point of the fluxing agent, the size of the electrodes of the substrate, the pitch between the electrodes of the substrate, and the like can be determined appropriately. For example, in the case of Sn-3Ag-0.5Cu having a solder melting point of about 217 ° C., the heating time can be set to about 1 minute at 260 ° C.

  Moreover, you may heat in the state which pressed and applied the pressure toward the board | substrate from the flat plate as needed. When pressure is applied, the flow of solder particles is activated, which is preferable because of the effect of promoting self-organization of the solder particles to the electrode. If too much pressure is applied, a large amount of resin and solder particles tend to be washed away from the outside of the flat plate. Therefore, the pressure is appropriately selected so that excessive outflow is suppressed and the desired solder bump height is maintained. To do.

  Moreover, in order to prevent a network from being formed by a condensation reaction or the like as described above, this step is preferably performed in an inert gas atmosphere.

  When the step (c) is completed, the solder component is unevenly distributed on the electrode of the substrate due to self-organization, and the resin component of the film is unevenly distributed between the flat plate other than the electrode and the substrate. .

(Process of dissolving and removing resin (D))
The reflow film containing the solder residue existing between the flat plate and the substrate other than on the electrode can be washed with various solvents, but as described above, it is washed with water, alcohol, or a mixed solvent thereof. It is preferable to dissolve and remove. The temperature of the washing solvent is preferably room temperature if the reflow film can be removed even at room temperature. However, when it is difficult to dissolve or it takes time to dissolve, the washing solvent is heated and washed. You can also. As the temperature at this time, the higher the temperature, the easier the resin dissolves, but the washing is performed at a temperature below the boiling point. In addition, when the resin is difficult to dissolve, irradiation may be performed to the extent that the solder bumps integrated with ultrasonic waves are not decomposed before or after washing.

  When the step (d) is completed, the reflow film containing the solder residue existing between the substrate other than the electrode and the flat plate is removed, and the flat plate is also peeled off from the solder bump, and the solder bump on the electrode. Is formed.

(Method of forming solder joint)
The method for forming a solder joint according to the second embodiment of the present invention includes:
(A) a step of placing the reflow film on the electrode surface side of a substrate including an electrode;
(B) on the reflow film, loading the electrode surface side of another substrate having electrodes, and fixing the electrodes of the upper and lower substrates at positions facing each other via the reflow film;
(C) In the state of (b) above the melting temperature of the solder particles in the reflow film and above the temperature at which the polyvinyl alcohol and the compound having a molecular weight of 500 or less dissolved or dispersed in water are liquefied. A step of heating, and (d) a step of dissolving and removing the reflow film after completion of the step (c).

  At the end of step (c), the solder component is unevenly distributed between the opposing electrodes of the substrate by self-organization, the opposing electrodes are connected by solder, and the substrate and the substrate other than the region between the opposing electrodes In between, the resin component of the film is unevenly distributed. Further, at the end of the step (d), the reflow film including the solder residue existing in the region between the substrates other than the electrodes facing each other is removed, and the solder joining the electrodes facing each other is exposed. ing.

  The method for forming a solder joint according to the present invention does not require a step of attaching a solder ball to a substrate electrode, and the solder joint is removed by a simple process of removing a reflow film containing residual solder that may cause a short circuit with a solvent. Can be formed.

  FIG. 4 is a cross-sectional view illustrating an example of a method for forming a solder joint between opposing electrodes. 4A shows a state in which the reflow film 21 is placed on the electrode 12b side of the substrate 10 and the electrode 32 (copper pillar) side of the semiconductor chip 30 is further loaded. (B) shows a state in which the counter electrodes 32 and 12b after the heating step are solder-bonded by the solder joint portion 43. (C) shows the state where the solder joint portion 43 between the counter electrodes 32 and 12b is exposed after the reflow film 24 containing the solder residue is removed.

(Step (a) for placing the reflow film)
In the method for forming a solder joint according to the present invention, the step (a) is performed on the electrode surface side having the electrodes of the substrate in the same manner as the step (a).

(Step (b) of making another substrate and electrode face each other)
Another substrate provided with electrodes may be the same as or different from the above substrate, and the combination thereof is any one of a semiconductor chip and an interposer, a semiconductor chip and a semiconductor chip, an interposer and an interposer. Is preferred.

  In order to obtain a desired inter-electrode distance, it is preferable to sandwich a spacer corresponding to the inter-electrode distance between the upper and lower substrates as necessary. In order to reduce the variation, it is preferable that the upper and lower substrates be placed in parallel and maintained in the next heating step.

  Since the substrate mounted thereon may move due to evaporation of a small amount of low boiling point components in the next heating step, it is preferable to fix the substrate with a jig such as a clamp after loading the substrate.

(Step of heating (c))
In the heating step in the method for forming a solder joint of the present invention, the heating temperature and the heating time (holding time) are set to a temperature equal to or higher than the melting temperature of the solder particles used, a temperature equal to or higher than the temperature at which polyvinyl alcohol and low molecular components liquefy, It can be appropriately determined depending on conditions such as the content of the particles, the viscosity of the resin in the heating process, the boiling point of the flux agent, the size of the electrodes on the substrate, the pitch between the electrodes, and the distance between the counter electrodes.

  Moreover, it is preferable to carry out in inert gas atmosphere like the process of said (c), and you may heat in the state pressed applying the pressure as needed.

(Step (d) of dissolving and removing resin)
The reflow film containing the solder residue existing between the substrates other than between the counter electrodes can be dissolved and removed in the same manner as in the step (d). Further, when the resin is difficult to dissolve, ultrasonic waves may be similarly applied.

(Solder joint area)
By the method for forming solder joints described above, a solder joint portion is formed between the opposing electrodes of two substrates having electrodes. Since the reflow film does not contain a convection additive, it is difficult to foam in the reflow process, and voids are rarely caught in the solder joint portion. Further, since the thermosetting resin component is not included in the solder joint portion, even if a void is generated in the solder joint portion, the void can escape out of the solder joint portion. Therefore, the amount of voids in the solder joint site can be reduced.

  Moreover, since the said solder joining site | part does not contain a resin component as mentioned above, it shows low electrical resistance, and it is preferable from a viewpoint of electrical resistance as a joining material. Moreover, since there are few voids in the said solder joint location, the crack generation by a heat shock does not occur easily and it is preferable from a viewpoint of connection reliability as a joining material.

(Semiconductor device)
In the semiconductor device having a solder joint portion according to the present invention, the combination of the substrates having electrodes connected by the solder joint portion is any one of a semiconductor chip and an interposer, a semiconductor chip and a semiconductor chip, an interposer and an interposer. In some cases, the semiconductor device of the present invention has low electrical resistance and high connection reliability. Moreover, since this semiconductor device is formed by a simple process using the reflow film according to the present invention, there is an advantage that it can be easily manufactured. Further, similarly, an electronic component device other than the semiconductor device can be manufactured.

  FIG. 5 is an example of a method for forming a solder joint of a substrate on which semiconductor chip 30 / reflow film / semiconductor chip 30 are laminated. FIG. Sectional drawing which shows the joined state, (b) is sectional drawing which shows the state which the soldering joint part 43 between the counter electrodes 32 and 51 exposed after removing the reflow film 24 containing a solder residue.

  FIG. 6 shows an example of a method for forming a solder joint on a substrate on which the interposer 10 / reflow film / interposer 10 are laminated. FIG. 6 (a) shows a state in which the counter electrode 12b after the heating process is soldered by the solder joint portion 43. FIG. 6B is a cross-sectional view showing a state where the solder joint portion 43 between the counter electrodes 12b is exposed after the reflow film 24 containing the solder residue is removed.

(Solder bump)
The solder bump according to the present invention formed by the above-described solder bump forming method is formed by self-organizing only the solder component on the electrode. The conventional solder paste containing a convection additive and a resin component has a risk that the viscosity of the resin component increases with heating and the void cannot be removed. Compared to a solder bump obtained from such a solder paste, the solder bump according to the present invention can reduce the amount of voids in the bump due to the generation or entrainment of bubbles.

  Moreover, since the reflow film is restrained in the space sandwiched between the substrate and the flat plate, the height (thickness) of the formed solder bump is defined. That is, the solder bump formed on the electrode cannot grow higher than the surface where the flat plate and the reflow film are in contact. Therefore, the solder bump can be set to a desired height, and the height variation of the solder bump is small.

(Substrate with solder bumps)
The board | substrate with a solder bump based on this invention formed by the above-mentioned solder bump formation method is preferable from a viewpoint of electrical resistance as a joining material. This is because the bonding using the substrate with solder bumps shows a low electric resistance because the solder bumps do not contain a resin component. Moreover, the board | substrate with a solder bump which concerns on this invention is preferable from a viewpoint of connection reliability as a joining material. This is because, as described above, since there are few voids in the solder bumps, it is difficult for cracks to occur due to heat shock. Furthermore, the board | substrate with a solder bump also has the advantage which can be formed by the simple process using the reflow film which concerns on this invention.

  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.

Example 1
<Production of varnish>
As a polyvinyl alcohol (PVA), trade name “GOHSENOL (registered trademark) GL-03” (degree of saponification 86.5-89.0 mol%, viscosity 3.0-3.7 mPa · s) manufactured by Nippon Synthetic Chemical Industry Co., Ltd. Dissolved in distilled water to make an aqueous solution, and solder particles (Mitsui Metal Mining Co., Ltd. "Solder Powder Sn96.5Ag3Cu0.5" composition: Sn96.5 mol%, Ag3 mol%, Cu0.5 mol%; particle size: 20-38 μm, where 10% cumulative particle size and 90% cumulative particle size are shown from the fine particle side of the cumulative particle size distribution of the entire particle, the number of particles smaller than 20 μm is 10%, and the particle size exceeding 38 μm. The number of particles means 10%, the number of particles having a particle size of 20 to 38 μm means 80%. The same applies hereinafter.) And glycerin are mixed and stirred, and 100 parts by mass of polyvinyl alcohol and solder particles 1 0 parts by weight to prepare a glycerin 40 parts by weight of the varnish.

<Production of film>
The varnish was applied onto a polyethylene terephthalate film (support) having a release treatment on the surface to obtain a coating film. The coating film was heated and dried at 90 ° C. for 1 hour to obtain a reflow film of Example 1 having a thickness of 100 μm on the support. Table 1 shows the compositions of the reflow films of each example and comparative example. “Phr” represents a blending amount per 100 parts by mass of polyvinyl alcohol.

(Example 2)
<Production of varnish>
Solder particles ("Solder Powder Sn96.5Ag3Cu0.5", supra, manufactured by Mitsui Mining & Smelting Co., Ltd.) were added to a methanolic solution of salicylic acid to dissolve the oxide film of the solder particles for 10 minutes. Thereafter, a methanol solution of salicylic acid in which the solder was immersed was added to polyvinyl alcohol (PVA) (trade name “GOHSENOL (registered trademark) GL-05” manufactured by Nippon Synthetic Chemical Industry Co., Ltd.); degree of saponification of 86.5 to 89.0 mol%, In addition to an aqueous solution containing a viscosity of 4.8 to 5.8 mPa · s) and distilled water, glycerin is further added and mixed and stirred, 100 parts by mass of polyvinyl alcohol, 150 parts by mass of solder particles, 40 parts by mass of glycerin, salicylic acid 5 parts by mass of varnish was prepared.

<Production of film>
A film was prepared according to the method of Example 1.

(Example 3)
<Production of varnish>
A varnish was prepared according to the method of Example 2 except that the amount of salicylic acid used in the preparation of the varnish of Example 2 was increased to 10 parts by mass.

<Production of film>
A film was prepared according to the method of Example 1.

Example 4
<Production of varnish>
A varnish was produced according to the method of Example 3, except that the amount of glycerin used in the production of the varnish of Example 3 was increased to 100 parts by mass.

<Production of film>
A film was prepared according to the method of Example 1.

(Example 5)
<Production of varnish>
In place of “GL-05”, the varieties of polyvinyl alcohol (PVA) used in the production of the varnish of Example 3 were trade names “GOHSEFIMAR (registered trademark) L-7514” (manufactured by Nippon Gosei Co., Ltd.). Except for using a mixed solvent of methanol / distilled water = 1/1 (mass ratio) as a solvent for dissolving polyvinyl alcohol, instead of distilled water, using a saponification degree of 34.0 to 41.0 mol%) A varnish was prepared according to the method of No. 3.

<Production of film>
A film was prepared according to the method of Example 1.

(Example 6)
<Production of varnish>
Instead of “solder powder Sn96.5Ag3Cu0.5” (supra), the product name “solder powder ST-5” (composition: Sn96) manufactured by Mitsui Mining & Smelting Co., Ltd. was used instead of “solder powder Sn96.5Ag3Cu0.5” (above). 0.5 mol%, Ag 3 mol%, Cu 0.5 mol%; particle size: 2.7-7.8 μm), except that the work was performed in a glove box in a nitrogen atmosphere. A varnish was prepared according to

<Production of film>
A film was produced according to the method of Example 1 in a glove box in a nitrogen atmosphere.

(Example 7)
<Production of varnish>
Instead of “solder powder Sn96.5Ag3Cu0.5” (supra), the product name “solder powder Sn42Bi58” (composition: Sn42 mol%) manufactured by Mitsui Mining & Smelting Co., Ltd. was used instead of “solder powder Sn96.5Ag3Cu0.5” (above). , Bi58 mol%; particle size: 20-38 μm) was used to prepare a varnish according to the method of Example 3.

<Production of film>
A film was prepared according to the method of Example 1.

(Example 8)
<Production of varnish>
A varnish was produced according to the method of Example 3 except that the amount of solder particles used in the production of the varnish of Example 3 was increased from 150 parts by mass to 300 parts by mass.

<Production of film>
A film was prepared according to the method of Example 1.

(Comparative Example 1)
<Preparation of paste>
As an epoxy resin, 100 parts by mass of bisphenol F diglycidyl ether (manufactured by DIC Corporation, trade name “Epiclon (registered trademark) EXA-830”, epoxy equivalent 175 g / eq), and as a curing accelerator, 2-phenyl-4-methyl 0.5 part by mass of imidazole (manufactured by Shikoku Kasei Kogyo Co., Ltd., trade name “CURAZOLE (registered trademark) 2P4MZ”), as the solder particles, “solder powder Sn96.5Ag3Cu0.5” (particle diameter: 20-38 μm) A paste solder paste was prepared by blending 100 parts by mass, 5 parts by mass of sebacic acid as a fluxing agent, and 10 parts by mass of isopropyl alcohol as a convection additive.

(Comparative Example 2)
<Production of varnish>
Instead of “GL-05”, the high-molecular-weight “GH-17” (saponification degree: 86.5 to 89.0 mol%, viscosity: 27) was used instead of “GL-05”. A varnish was prepared according to the method of Example 3 except that glycerin was not added using ~ 33 mPa · s).

<Production of film>
A film was prepared according to the method of Example 1.

(Comparative Example 3)
<Production of varnish>
In the production of the varnish of Example 3, a varnish was produced according to the method of Example 3 except that the amount of glycerin used was increased from 40 parts by mass to 900 parts by mass.

<Production of film>
A film was prepared according to the method of Example 1.

(Comparative Example 4)
<Production of varnish>
In the production of the varnish of Example 3, a varnish was produced according to the method of Example 3 except that the amount of glycerin used was increased from 40 parts by mass to 400 parts by mass.

<Production of film>
A film was prepared according to the method of Example 1.

[Formation of solder bumps]
<Film or paste loading and heating process>
Solder bumps were formed using the reflow films obtained in Examples 1 to 8 and the comparative samples of Comparative Examples 1 to 4. In Examples 1 to 8, and Comparative Examples 2 and 4 which are film-like samples, the film was cut to an appropriate size. The film-like sample was formed with solder bumps in the following steps: (1) The film was placed on the electrode surface side of a substrate provided with electrodes to be described later, (2) High heat resistant low thermal expansion eagle glass on the film A glass plate was placed, a polyimide film having a thickness of 50 μm was sandwiched between the glass plate as a spacer at both ends of the glass plate, and fixed by applying pressure with an eyeball clip from above (3) The film was made of solder particles. It was heated in a nitrogen atmosphere at 260 ° C. for 1 minute, which is equal to or higher than the melting temperature and higher than the temperature at which the polyvinyl alcohol and low molecular weight components of the reflow film are liquefied. However, about Example 7 using SnBi solder particles, only heating temperature was changed and it heated at 200 degreeC.

  Moreover, the comparative example 1 which is a paste-form sample dripped the appropriate quantity to the electrode surface side of a board | substrate, mounted glass, and applied and spread it. Other steps were performed in the same manner as the film-like sample described above. In Comparative Example 3, an attempt was made to form a film, but since it became a paste, it was applied in the same manner as in Comparative Example 1.

<substrate>
FIG. 1 shows a schematic plan view of a substrate (interposer) used for forming solder bumps or solder joints in an embodiment of the present invention. The interposer used was an FR-4 substrate (glass epoxy substrate), the electrode 12 was 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 was 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 pitch between the electrodes is 200 μm. Further, the electrode 12a in the peripheral portion of the substrate has an electrode diameter of 1.5 mm and a pitch between the electrodes of 3 mm. The region 11 other than the electrode on the upper surface of the substrate is a solder resist.

  Examples 1 to 8 and Comparative Examples 2 and 4 which are film-like samples are electrodes on the substrate (diameter: 100 μm, pitch between electrodes: 200 μm) on the substrate central portion or electrodes on the substrate peripheral portion (diameter: 1.5 mm, The pitch between the electrodes was 3 mm). Similarly, Comparative Example 1 and Comparative Example 3 which are pasty samples are also electrodes on a group of electrodes (diameter: 100 μm, pitch between electrodes: 200 μm) at the center of the substrate or at the periphery of the substrate (1.5 mm in diameter, between the electrodes). The pitch was 3 mm).

<Washing>
After the solder was self-organized by heating in a nitrogen atmosphere, it was immersed in distilled water heated to 80 ° C., and washed for 10 minutes at 45 kHz using an ultrasonic cleaner VS-100 SUNPAR manufactured by Iuchi. However, in Example 5, a mixed solvent of methanol / water = 1/1 (mass ratio) was used instead of distilled water. The flat plate was peeled off after washing.

[Evaluation method]
<Workability>
Table 2 shows the evaluation of workability. The variation of the loading amount or the coating amount when the film-like or paste-like sample was placed or applied to the substrate 10 times was calculated from the following formula (1). When the variation was less than 20%, it was A, when it was more than 20% and less than 35%, B, and when it was 35% or more, C. The larger the variation in mass when placed or applied, the more frequently the placement amount and the application amount need to be adjusted, resulting in poor workability.

Placement amount (application amount) variation = {(Wmax−Wmin) / Wav} × 100 Formula (1)
Here, Wmax is the maximum placement amount or maximum application amount, Wmin is the minimum placement amount or minimum application amount, and Wav is the average value of the placement amount or application amount.

<Self-organization of solder>
In order to confirm the presence / absence of solder bump formation on the electrode, observation was performed visually and with a digital microscope VHX-200 manufactured by Keyence Corporation. The results are shown in Table 2. A is shown when solder is integrated on all electrodes, C is shown when there are one or more electrodes not integrated at all, and B is shown when there are one or more bridges between adjacent electrodes. However, the number of electrodes was 22 × 22 = 484, which is one block in the case of the center of the substrate, and 21 that is one side of the outer periphery in the case of the periphery of the substrate. The following observations are the same unless otherwise noted.

<Resolution removal of resin>
In order to confirm the presence or absence of solder residue or resin remaining in a region other than the electrodes, observation was performed visually and with the above-described digital microscope VHX-200. The results are shown in Table 2. A when no solder residue or resin residue is observed, B when the residue having a size that fits in a circle having a diameter of 10 μm is observed at 1 to 3 locations, and 4 or more when the residue having the size is observed. Or when the said residue larger than the said magnitude | size is observed one or more places, it shows by C.

<Bump height variation>
The height of the solder bump was measured using a laser microscope (model number 1LM21H) manufactured by Lasertec Corporation or a non-contact shape measuring machine (model number YP10-T12) manufactured by Sony Precision Technology Corporation. The height of arbitrary 10 bumps (all bumps when the number of bumps is 10 or less) was measured, and the height variation was calculated from the following equation (2). Table 2 shows A when the height variation is 15% or less, B when it exceeds 15% and 35% or less, and C when it exceeds 35%.

Height variation = {(Tmax−Tmin) / Tav} × 100 Formula (2)
Here, Tmax is the maximum bump height, Tmin is the minimum bump height, and Tav is the average bump height.

  When both the self-organization of the solder and the resin removability are B or C, it is determined that the bump is not formed, and evaluation is not performed, and − is shown in Table 2.

<Void in the bump>
The voids in the solder bumps were observed using a microfocus X-ray inspection apparatus MF160C manufactured by Hitachi Construction Machinery Finetech Co., Ltd. In X-ray transmission observation, a contrast image is generally obtained in which heavy elements are dark and light elements are brightly displayed. From this, it can be seen that the solder bumps are dark (black) and the voids are bright (white). After bumps were formed on the substrate, arbitrary 10 bumps (all bumps when the number of bumps was 10 or less) were observed by X-ray transmission. Table 2 shows A when no void is observed in the bump, B when the number of bumps where the void is observed is 1-2, and C when the number of bumps where the void is observed is 3 or more. .

When both the self-organization of the solder and the resin removability are B or C, it is determined that the bump is not formed, and evaluation is not performed, and − is shown in Table 2.

  Example 1 consists of polyvinyl alcohol which is a water-soluble resin used in the present invention, glycerin as a low molecular weight component used in the present invention, and Sn96.5Ag3Cu0.5 which is a lead-free solder particle used in the present invention. Reflow film is used. The filling amount of glycerin, which is a low molecular weight component used in Example 1, is 40 parts by mass with respect to 100 parts by mass of polyvinyl alcohol, and is within the conditions of the present invention. The reflow film of Examples 2-8 contains the flux agent used for this invention other than the said composition. In Example 1, a reflow film is made using polyvinyl alcohol having a flux effect on the resin itself. In Examples 2 to 3, the reflow film of Example 1 was added by changing the amount of the fluxing agent. In Example 4, the amount of glycerin, which is a low molecular component of the reflow film of Example 3, was increased to 100 parts by mass. In Example 5, the type of polyvinyl alcohol in Example 3 was replaced with polyvinyl alcohol having a low saponification degree soluble in a mixed solvent composed of 1 part by mass of water and 1 part by mass of methanol. In Example 6, the particle size of Sn96.5Ag3Cu0.5, which is the solder particles of the reflow film of Example 3, was changed to a smaller one. In Example 7, Sn96.5Ag3Cu0.5, which is the solder particles of the reflow film of Example 3, was replaced with Sn42Bi58 having a low melting temperature. In Example 8, the amount of solder particles filled in the reflow film of Example 3 was increased. In each of Examples 1 to 8, good evaluation was obtained in all of the workability, the self-organization of the solder, the dissolution and removal of the resin, the height variation of the bump, and the void in the bump.

  On the other hand, Comparative Example 1 is in a paste form and thus has poor workability. Since an epoxy resin that is a thermosetting resin is used, the resin is poorly dissolved and removed, and a convection additive is added to the bump. Voids were observed. In Comparative Example 2, high molecular weight polyvinyl alcohol is used and glycerin which is a low molecular weight component is not added. Although workability was good, solder self-organization did not occur. In addition, the resin removability was poor. In Comparative Example 3, the content of glycerin was significantly increased, and the paste was tacky without being a film. Therefore, workability was poor and there was variation in bump height. In Comparative Example 4, the amount of glycerin was added in an amount exceeding the conditions of the present invention, and although it was a film and the workability was good, the degree of self-organization of the solder was poor and the bump height varied.

  When solder bumps were formed using the reflow films of Examples 1 to 8 as described above, a paste containing no polyvinyl alcohol of Comparative Example 1 and a polyvinyl alcohol film containing no low molecular weight component of Comparative Example 2 In comparison with the polyvinyl alcohol paste and film in which the content of the low molecular weight component in Comparative Examples 3 to 4 and the conditions of the present invention is deviated, the workability, the self-organization of the solder, and the dissolution and removal of the resin are improved. It is possible to produce a solder bump and a substrate with a solder bump that are excellent, have a small bump height variation, and have a small number of voids in the bump.

[Manufacture of semiconductor devices by forming solder joints between opposing electrodes]
<Film or paste loading and heating process>
Solder joints were formed between the counter electrodes between the substrates using the reflow films obtained in Examples 1 to 8 and the comparative samples (film and paste) of Comparative Examples 1 to 4. The combinations of substrates used were three types: an interposer below the reflow film, a combination of semiconductor chips on the top, a combination of semiconductor chips on both the top and bottom of the reflow film, or a combination of interposers on both the top and bottom of the reflow film.

  In Examples 1 to 8, and Comparative Examples 2 and 4 which are film-like samples, the film was cut to an appropriate size. The film-like sample formed a solder joint between the counter electrodes in the following steps: (1) The film was placed on the electrode surface side of a substrate provided with an electrode to be described later and fixed with a polyimide tape, (2) Using a flip chip bonder FCB3 manufactured by Panasonic Corporation, using a substrate to be described later, the upper and lower electrodes were temporarily fixed in accordance with the facing positions. At this time, a polyimide film having a thickness of 50 μm was sandwiched as a spacer. After temporarily fixing, it was fixed by applying pressure with an eyeball clip. (3) The substrate fixed with the eyeball clip is at the melting temperature of the solder particles and at a temperature higher than the temperature at which the polyvinyl alcohol and low molecular weight components of the reflow film are liquefied at 260 ° C. for 1 minute in a nitrogen atmosphere. Heating was performed. However, about Example 7 using SnBi solder particles, only heating temperature was changed and it heated at 200 degreeC.

  Moreover, the comparative example 1 which is a paste-form sample dripped the appropriate quantity to the electrode surface side of a board | substrate, mounted the board | substrate to connect, and applied and spread the load. Other steps were performed in the same manner as the film samples of Examples 1-8. In Comparative Example 3, an attempt was made to form a film, but since it became a paste, it was applied in the same manner as in Comparative Example 1.

<Substrate (interposer)>
The interposer used for forming the solder joint is the above-described one shown in FIG. Examples 1 to 8, which are film samples, Comparative Example 2 and Comparative Example 4 were loaded on a group of four blocks (diameter: 100 μm, pitch between electrodes: 200 μm) in the center of the substrate. Moreover, the comparative example 1 and the comparative example 3 which are paste-like samples were similarly apply | coated on the electrode group which has four blocks of the board | substrate center part.

<Semiconductor chip>
A schematic plan view of the used semiconductor chip is shown in FIG. The semiconductor chip 30 is formed so as to be opposed to the electrodes 12b in the four blocks at the center of the interposer. The chip is made of silicon, the chip size is 10 mm × 10 mm × 0.7 mm, and the electrodes 32 are arranged in 4 blocks in an area array. The electrode of each block is a copper post having a diameter of 96 μm and a height of 40 μm, and the pitch between the electrodes is 200 μm. The number of electrodes in one block is 22 × 22 = 484. In one chip, that is, four blocks, 484 × 4 = 1936 electrodes are provided. The region 31 other than the electrode (copper pillar) on the upper surface of the semiconductor chip is polyimide which is a circuit protection layer of the silicon chip. Further, when semiconductor chips were stacked on the upper and lower sides of the reflow film, the semiconductor chip of the gold electrode 51 was used as the electrode of the semiconductor chip located below, not a copper post, as shown in FIG.

<Washing>
After the solder was self-organized by heating in a nitrogen atmosphere, it was immersed in distilled water heated to 80 ° C., and washed for 10 minutes at 45 kHz using an ultrasonic cleaner VS-100 SUNPAR manufactured by Iuchi. However, in Example 5, a mixed solvent of methanol / distilled water = 1/1 (mass ratio) was used instead of distilled water.

  Table 3 shows the evaluation of workability, solder self-organization, resin dissolution and removal, voids at the solder joints between the counter electrodes, and electrical conductivity of the semiconductor device. The evaluation methods and evaluation criteria that are not specified are the same as those in Table 2.

<Workability>
As the workability evaluation, the variation in the amount of placement or the amount of application when a film-like or paste-like sample was placed on or applied to the substrate 10 times was calculated from the above formula (1). When the variation was less than 20%, it was A, when it was more than 20% and less than 35%, B, and when it was 35% or more, C. The larger the variation in mass when placed or applied, the more frequently the placement amount and the application amount need to be adjusted, resulting in poor workability.

[Evaluation method]
<Self-organization of solder>
After the heating step (reflow) in a nitrogen atmosphere, X-ray transmission observation was performed using the above-described microfocus X-ray inspection apparatus MF160C in order to confirm the self-organization of the solder on the electrode. Since an electrode on which solder is not accumulated is also observed dark, the accumulation of solder can be determined by the fact that it is darker than that.

  Comparing the electrode and the non-electrode region relatively, it is assumed that A is self-organized when it is dark in all of the 484 electrodes and brightly observed in the region other than the electrode, and C, if not, However, when there is a bridge between the electrodes (the electrodes are connected in a dark color), it is indicated by B.

<Resolution removal of resin>
The presence or absence of solder residue or residual resin in the region other than the electrodes was confirmed by X-ray transmission observation and visual observation using the above-described microfocus X-ray inspection apparatus MF160C. The evaluation of the presence or absence of a solder residue is A. When the solder residue is not observed by X-ray transmission observation after the resin is dissolved and removed, the residue having a size that fits in a circle having a diameter of 10 μm is observed at 1 to 3 locations. B, when 4 or more of the residue of the size is observed or when 1 or more of the residue larger than the size is observed, C is shown in Table 3. The presence or absence of residual resin was evaluated by X-ray transmission observation and visual observation (or using a loupe or the like) before and after cleaning.

  In X-ray transmission observation, when one or more solder residues are confirmed before resin cleaning, and solder residues cannot be confirmed after cleaning, the solder residue is removed, so the resin is also removed. However, when one or more solder residues were confirmed, it was considered that the resin could not be removed. Even after cleaning, B is observed when solder residues having a size that fits in a circle having a diameter of 10 μm are observed at 1 to 3 locations, and when solder residues of the size are observed at 4 locations or more, or solder residues larger than the size are observed. When one or more places were observed, it was set as C. It is shown in Table 3 because it cannot be evaluated when no solder residue is confirmed before resin washing. In addition, as a result of observing between the substrates visually or using a magnifying glass, A is shown when the resin cannot be confirmed at all; Show.

<Void of solder joint part between counter electrodes>
The voids in the solder bumps were observed using the above-described microfocus X-ray inspection apparatus MF160C. When no voids are observed at all the solder joints in 484 locations, A when the number of bumps where voids are observed is 1-2, and when the number of bumps where voids are observed is 3 or more C shows in Table 3. When both the self-organization of the solder and the dissolution / removability of the resin are B or C, it is determined that no solder joint is formed, and the evaluation is shown as-in Table 3 without performing the evaluation.

<Electrical conductivity of semiconductor devices>
For a daisy chain circuit that passes through all the counter electrodes (484 locations) in one block of a group of electrodes of a semiconductor device soldered by flip-chip connection, using AD687TEST R6871 DIGITAL MULTITIMER and Mechatronics ammeter MODEL 5964, The electric resistance was measured with a constant current of 1 mA. When the measured value was less than 17Ω, it was A, when it was 17-19Ω, it was C when it exceeded 19Ω. A daisy chain circuit is a circuit in which the upper and lower boards are sewn with a thread. `` → Lower board internal circuit → Lower board side electrode → Solder joint site → Opposing upper board side electrode → Upper board internal circuit → Adjacent This is a circuit in which “upper substrate side electrode → solder joint site → opposing lower substrate side electrode → lower substrate internal circuit →” is repeated.

When both the self-organization of the solder and the dissolution / removability of the resin are B or C, it is determined that no solder joint is formed, and the evaluation is shown as-in Table 3 without performing the evaluation.

However, a represents a semiconductor chip, b represents an interposer, and * represents MeOH / H ₂ O = 1/1.

  Examples 1 to 8 all obtained favorable evaluations in terms of workability, solder self-assembly, resin dissolution and removal, solder joint voids, and electrical resistance.

  On the other hand, Comparative Example 1 is paste-like, so the workability is poor, and since an epoxy resin that is a thermosetting resin is used, the resin is poorly dissolved and removed, and a convection additive is added to the solder joint. Site voids were observed. Further, since the solder joint includes an epoxy resin, the electrical resistance is high. In Comparative Example 2, high molecular weight polyvinyl alcohol is used and glycerin which is a low molecular weight component is not added. Although workability was good, solder self-organization did not occur. In addition, the resin removability was poor. In Comparative Example 3, the content of glycerin was significantly increased, and the paste was tacky without being a film. Therefore, workability was bad. In Comparative Example 4, the amount of glycerin was added in an amount exceeding the conditions of the present invention, and although it became a film and the workability was good, the degree of self-organization of the solder was poor and the electrical conductivity was also bad.

  When solder joints were formed using the reflow films of Examples 1 to 8 as described above, the paste containing no polyvinyl alcohol of Comparative Example 1, the polyvinyl alcohol film containing no low molecular weight component of Comparative Example 2, and the comparison Compared with the polyvinyl alcohol paste and film in which the content of low molecular weight components in Examples 3 to 4 deviates from the conditions of the present invention, the workability, the self-organization of the solder, and the dissolution and removal of the resin are excellent. A solder bump and a substrate with a solder bump can be made with a small height variation and a small number of voids in the bump.

  Moreover, it is excellent in workability, solder self-organization, and resin dissolution / removability, so that it is possible to produce a solder joint portion and a semiconductor device with low voids in the solder joint portion and low electrical resistance.

10 Substrate (interposer)
11 Substrate upper surface area other than electrodes (solder resist)
12 Electrode 12a Electrode (group) around substrate
12b Substrate electrode (group)
21 Reflow film 22 Eagle glass plate (flat plate)
23 Solder bump 24 Reflow film 30 containing solder residue Semiconductor chip 31 Area (polyimide) other than electrodes (copper pillars) on the upper surface of the semiconductor chip
32 Semiconductor chip electrodes (copper pillars)
43 Solder joint part 51 formed between opposed electrodes Semiconductor chip electrode (gold)

Claims (24)

  A film comprising polyvinyl alcohol, a compound having a molecular weight of 500 or less dissolved or dispersed in water, and solder particles, wherein the compound having a molecular weight of 500 or less is 20 to 300 parts by mass with respect to 100 parts by mass of polyvinyl alcohol, The reflow film, wherein the solder particles are dispersed in the film.   The reflow film according to claim 1, wherein the compound having a molecular weight of 500 or less is a low molecular weight alcohol having a boiling point of 100 ° C. or more.   The reflow film according to claim 1, wherein the compound having a molecular weight of 500 or less is glycerin.   Furthermore, the component which removes a metal oxide is contained, The reflow film of any one of Claims 1-3 characterized by the above-mentioned.   The cumulative particle size distribution of the solder particles has a cumulative particle size of 10% and a cumulative particle size of 90% both within a range of 1 to 50 μm from the fine particle side. Reflow film as described in 2.   The reflow film according to claim 1, wherein the solder particles are lead-free solder.   The reflow film according to claim 1, wherein the solder particles are an alloy of tin, silver, and copper.   The reflow film according to any one of claims 1 to 7, comprising 30 to 500 parts by mass of the solder particles with respect to 100 parts by mass of the polyvinyl alcohol. A solder bump forming method using the reflow film according to any one of claims 1 to 8,
(A) a step of placing the reflow film on the electrode surface side of a substrate provided with electrodes;
(A) a step of placing and fixing a flat plate on the reflow film;
(C) a step of heating above the melting temperature of the solder particles in the reflow film and above the temperature at which the polyvinyl alcohol and the compound having a molecular weight of 500 or less dissolved or dispersed in water are liquefied; A solder bump forming method comprising a step of dissolving and removing the reflow film after completion of the step (c).   The method of forming a solder bump according to claim 9, wherein the step (c) is performed in an inert gas atmosphere.   The method of forming a solder bump according to any one of claims 9 to 10, wherein the step (c) is performed in a state where the flat plate is pressed toward the substrate.   The reflow film containing a residue of solder particles existing on the surface other than the electrode surface is removed with water, alcohol, or a mixed solvent thereof in the step (d). The method for forming a solder bump as described in the item.   The method of forming a solder bump according to claim 9, wherein an ultrasonic wave is irradiated in the step (d). A method for forming a solder joint using the reflow film according to any one of claims 1 to 8,
(A) a step of placing the reflow film on the electrode surface side of a substrate including an electrode;
(B) on the reflow film, loading the electrode surface side of another substrate having electrodes, and fixing the electrodes of the upper and lower substrates at positions facing each other via the reflow film;
(C) In the state of (b), heated above the melting temperature of the solder particles in the reflow film and above the temperature at which the polyvinyl alcohol and the compound having a molecular weight of 500 or less dissolved or dispersed in water are liquefied. And (d) a method for forming a solder joint, comprising: a step of dissolving and removing the reflow film after completion of the step (c).   The method of forming a solder joint according to claim 14, wherein the step (c) is performed in an inert gas atmosphere.   The method of forming a solder joint according to claim 14, wherein the step (c) is performed in a state where the loaded substrate is pressed.   In the step (d), the reflow film containing a residue of solder particles existing other than between the opposing electrodes is removed with water, alcohol, or a mixed solvent thereof. The method for forming a solder joint according to any one of the above items.   The method for forming a solder joint according to any one of claims 14 to 17, wherein in the step (d), ultrasonic waves are applied.   A solder bump formed by the solder bump forming method according to any one of claims 9 to 13.   A substrate with solder bumps, wherein the bumps are formed on the electrodes of the substrate by the method for forming solder bumps according to any one of claims 9 to 13.   The solder bump according to claim 19, wherein the substrate is a semiconductor chip or an interposer.   The substrate with solder bumps according to claim 20, wherein the substrate is a semiconductor chip or an interposer.   A solder joint portion formed between the opposing electrodes of two substrates having electrodes by the method for forming a solder joint according to any one of claims 14 to 18.   24. A semiconductor device having the solder joint portion according to claim 23, wherein the combination of the substrates including the electrodes is any one of a semiconductor chip and an interposer, a semiconductor chip and a semiconductor chip, an interposer and an interposer. .