Classifications

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Definitions

• the present invention relates to the formation of solder bumps that are used when FC (flip chip) or BGA (ball grid array) are manufactured by forming hemispherical solder bumps on a semiconductor substrate or interposer substrate.
• FC flip chip
• BGA ball grid array
• FC and BGA with hemispherical solder bumps are used as semiconductor devices to achieve this high-density mounting!
• solder method As a method for forming solder bumps on the nod electrode, a method in which the pad electrode is brought into contact with the molten solder (molten solder method), and a method in which a solder paste is screen printed on the pad electrode and reflowed (screen printing method)
• molten solder method a method in which the pad electrode is brought into contact with the molten solder
• screen printing method a method in which a solder paste is screen printed on the pad electrode and reflowed
• solder ball method a method of placing a solder ball on the solder electrode and reflowing
• meh method a method of soldering the solder electrode
• a solder bump forming method described in Patent Document 1 is known.
• FIG. 10 is a schematic cross-sectional view showing the solder forming method described in Patent Document 1. Hereinafter, description will be given based on this drawing.
• a wafer 82 having a copper electrode 81 on the surface thereof is immersed in an inert solvent 80 heated to a melting point or higher of the solder so that the surface is on the bottom.
• solder particles 84 made of molten solder 83 are sprayed upward in an inert solvent 80 to bring the solder particles 84 into contact with the wafer 82 and solder bumps (not shown) are formed on the copper electrodes 81. Form. This will be described in more detail.
• the temperature of the molten solder 83 and the inert solvent 80 in the heating tank 85 is controlled to a temperature slightly higher than the melting point of the solder, for example, 200 ° C.
• the molten solder 83 in the heating tank 85 is sucked into the solder fine particle device 87 from the solder introduction tube 86.
• the solder fine particle device 87 sucks the inert solvent 80 having the same temperature as the molten solder 83 from the inert solvent introduction pipe 88, and These two liquids are mixed and stirred to crush the molten solder 83 into particles.
• the inert solvent 80 containing the solder particles 84 is fed from the mixed solution outlet pipe 89 to the ejection device 90 and is ejected upward from the nozzle 91.
• solder particles 84 in the inert solvent 80 are covered with the inert solvent 80, they do not come into contact with the outside air. For this reason, the surface of the solder particle 84 keeps the metal surface and is in an active state. Then, when the solder particles 84 in the inert solvent 80 come into contact with the copper electrode 81 of the wafer 82 immersed in the inert solvent 80, a solder alloy layer is formed with the copper electrode 81 and adheres to the surface of the copper electrode 81. By doing so, the surface of the copper electrode 81 is covered with a molten solder film (not shown). Subsequently, since the solder particles 84 are likely to be adsorbed to the solder film, the solder particles 84 in this portion adhere to the solder film one after another.
• solder particles 84 that have not adhered to the copper electrode 81 gradually fall due to the difference in specific gravity, and accumulate on the bottom of the heating tank 85.
• solder bumps (not shown) can be selectively applied only to the surface of the copper electrode 81. ) Can be formed.
• Patent Document 1 Japanese Patent Publication No. 7-114205 (Fig. 1 etc.)
• the molten solder method has a feature that it is suitable for fine pitch of the nod electrode, it has a drawback that the solder amount of the solder bump is small and its variation is large.
• the screen printing method has the feature that solder bumps can be easily formed in one batch, clogging and uneven solder amount are likely to occur when a fine pitch mask is used.
• the solder ball method has a drawback in that the number of solder balls used in one semiconductor device is extremely large as a recent trend, and the manufacturing cost is high because the force and the size of the solder balls are extremely small.
• the plating method has the disadvantage that there is no suitable plating solution for lead-free solder, which has become widespread in recent years.
• solder fine particles are difficult to adhere to a copper electrode! / That is, solder wettability is poor, and thus it has been difficult to put it to practical use.
• the present inventor has developed the following technique. First, solder fine particles, a liquid having flux action, and a substrate having electrodes on the surface are prepared. Then, the liquid is heated above the melting point of the solder, the substrate is positioned in the liquid with the surface facing up, and solder fine particles are sprayed into the liquid and dropped toward the electrodes on the substrate. As a result, solder bumps are formed on the pad electrodes. As a result, the conventional problems could be solved, and finer pitch solder bumps were achieved.
• solder fine particles are large, solder bridges are likely to occur between the electrodes.
• solder fine particles the lower the falling speed of the solder fine particles in the liquid, and the longer it takes to form the solder bumps.
• the reason will be described below.
• the solder fine particles shall fall in the liquid while receiving a viscous resistance proportional to the velocity.
• the mass of the solder fine particles is m
• the gravitational acceleration is g
• the viscosity coefficient is k
• the z-axis is taken vertically upward
• an object of the present invention is to provide a solder bump forming method capable of obtaining a fine pitch of the nod electrode, obtaining a solder bump with a large amount of solder and little variation, and capable of forming the solder bump in a short time. And providing an apparatus.
• a method for forming a solder bump according to the present invention includes a substrate having a pad electrode on a surface thereof.
• the solder bumps are placed on the pad electrode by spraying (sending out) solder fine particles, which are positioned in an inert gas so that the surface is on top, and have a molten solder force, into the inert gas and dropping the solder fine particles onto the substrate. Is formed.
• a solder bump is formed on a node electrode by placing the substrate in a dispersion system (aerosol) composed of a dispersion medium of an inert gas and a dispersion phase of liquid solder fine particles. This technology is also included.
• the “substrate” here includes a semiconductor wafer, a wiring board, and the like.
• the “solder bump” is not limited to a hemispherical shape or a protrusion shape, but includes a film shape.
• the inert gas is mainly composed of nitrogen or argon, it may be a gas containing a certain amount of oxygen so long as it is substantially inert without adversely affecting the soldering.
• the substrate In the inert gas, the substrate is held with the nod electrode side facing up. At this time, when the solder fine particles are sprayed into the inert gas on the substrate, the solder fine particles spontaneously drop due to gravity and reach the substrate. The solder fine particles that have reached the pad electrode of the substrate stay there due to gravity, and after a certain period of time, spreads on the surface of the pad electrode to form a solder film. Subsequently, the solder fine particles that have reached the solder film stay there due to gravity, and in the same way, after a certain amount of time has passed, it spreads and thickens the solder film. This is repeated, and the solder film grows to become solder bumps.
• solder wetting time In order for the solder to get wet, the aforementioned “certain time” (hereinafter referred to as “solder wetting time”) is necessary.
• solder wetting time since the solder fine particles are sprayed and brought into contact with the downward-facing pad electrode in the inert liquid, it takes only a moment for the solder fine particles to contact the pad electrode. The wettability is considered bad.
• solder fine particles even if the solder fine particles come into contact with each other during the fall in the inert gas, the present inventor cannot easily prepare the condition that these fine particles are united into large solder fine particles. It has been found that there is no problem in sending out toward the substrate through the inert gas. Therefore, in the present invention, a solder bridge or the like does not occur even for a fine pitch pad electrode. Furthermore, the solder amount of the solder bump can be easily adjusted by changing the supply amount of the solder fine particles. Since the solder fine particles are extremely small compared to the node electrode, a large amount of solder fine particles are supplied, so that the solder fine particles are uniformly dispersed in the inert gas.
• solder fine particles are foggy. Since it is extremely fine, it is suitable for making fine pitches of pad electrodes.
• the soldering force the falling speed of the solder fine particles is large because the solder fine particles fall in the gas, not in the liquid, and the viscosity coefficient k in the above-mentioned formula ⁇ 3 >> becomes extremely small. That is, even if the solder fine particles are small, they fall quickly, so the time required for forming the solder bumps is short.
• solder bumps are formed on the pad electrodes.
• solder fine particles are sprayed toward the pad electrode, the surface of the substrate does not necessarily have to be in the inert gas, and may be laterally, downwardly or diagonally! / ⁇ . Solder particles move erratically due to Brownian motion due to their mist, ie, very fine. Therefore, when the solder fine particles are sprayed toward the pad electrode, the solder fine particles float around the pad electrode, so that the solder fine particles can remain on the pad electrode for the solder wet time or longer. In this case, solder fine particles are sprayed at the initial velocity V in the + z direction.
• the solder bump forming method according to the present invention is such that when the substrate is positioned in an inert gas, the surface of the substrate is positioned downward. In this case, unnecessary solder fine particles that have the same force as the solder bumps can easily drop on the substrate, facilitating cleaning in subsequent processes.
• the solder bump forming method according to the present invention is such that when the solder fine particles are sprayed, the flux is also sprayed.
• the spraying of solder fine particles is, for example, before spraying the solder fine particles, at the same time as spraying, or immediately after spraying.
• the solder wettability in an inert gas is further improved by the action of the flux.
• flux includes rosin, surfactant, and other substances that have the effect of removing the acid film on the solder surface.
• the solder bump forming method according to the present invention is such that hydrogen gas is mixed in an inert gas. Since hydrogen gas reduces and removes the oxide film on the surface of the pad electrode and the surface of the solder fine particles, the solder wettability in an inert gas is further improved.
• the solder bump forming method according to the present invention is such that the diameter of the solder fine particles is smaller than the shortest distance between the peripheral ends of adjacent pad electrodes. In this case, the solder fine particles that have reached each of the two adjacent pad electrodes do not come into contact with each other, so that they do not combine to form a solder bridge.
• the solder bump forming method according to the present invention is such that the inert gas is heated to a temperature higher than the melting point of the solder.
• the solder fine particles are in an inert gas having a melting point higher than the melting point of the solder, the solder fine particles are surely kept in a liquid state. In other words, the solder fine particles do not solidify by any chance, so the solder wettability is good.
• solder bump forming method according to the present invention is such that the solder fine particle force is sprayed as a solid and melted in an inert gas. Solid solder fine particles will not be combined in that state! So, handle! /, Easy.
• the solder bump forming apparatus includes a gas tank and a solder sprayer.
• the gas tank contains an inert gas and a substrate that has a pad electrode on its surface and is positioned in the inert gas so that the surface is on top.
• the solder sprayer sprays solder fine particles, such as molten solder particles, into an inert gas and drops the solder fine particles onto the substrate.
• the substrate In an inert gas in the gas tank, the substrate is held with the pad electrode side facing up. At this time, when the solder fine particles are sprayed into the inert gas on the substrate such as the solder sprayer, the solder fine particles naturally fall by gravity and reach the substrate. Hereinafter, the same effect as the above forming method is exhibited.
• a solder bump forming apparatus includes a gas tank and a solder sprayer.
• the gas tank accommodates an inert gas heated to a temperature equal to or higher than the melting point of the solder and a substrate that has a nod electrode on its surface and is positioned in the inert gas.
• the solder sprayer sprays solder fine particles with molten solder force toward the pad electrode in an inert gas. The same effect as the above forming method is achieved.
• the solder bump forming apparatus according to the present invention is such that the substrate is positioned in an inert gas so that the surface of the substrate faces down. It has the same effect as the above forming method.
• the solder bump forming apparatus according to the present invention is such that when the solder sprayer sprays solder fine particles toward the pad electrode, the flux is also sprayed. It has the same effect as the above forming method.
• hydrogen gas is mixed in an inert gas.
• the solder bump forming apparatus according to the present invention is such that the diameter of the solder fine particles is smaller than the shortest distance between the peripheral edges of adjacent pad electrodes. The same effect as the above forming method is achieved.
• the solder bump forming apparatus according to the present invention is such that the inert gas is heated above the melting point of the solder. The same effect as the above forming method is achieved.
• the solder bump forming apparatus according to the present invention is such that the solder fine particle force is sprayed as a solid and melts in an inert gas. The same effect as the above forming method is achieved.
• the method for forming a solder bump according to the present invention uses solder fine particles having a solid solder force instead of solder fine particles having a molten solder force, and coats the solder fine particles with a liquid having a flux action. It sprays fine particles.
• the method for forming a solder bump according to the present invention uses a solder fine particle having a solid solder force instead of a solder fine particle having a melted solder force, and coats the solder fine particle with an organic film, and further a liquid having a flux action. In this state, solder fine particles are coated and solder fine particles are sprayed.
• the solder bump forming method according to the present invention heats the solder fine particles dropped on the substrate to the melting point or higher and evaporates the liquid by this heating. As the liquid evaporates, the solder particles gradually approach and unite to form solder bumps. For this reason, unnecessary coalescence of solder fine particles is unlikely to occur, and the occurrence of solder bridges is suppressed.
• the solder bump forming method according to the present invention is inactive when the solder fine particles are sprayed.
• the gas is depressurized below atmospheric pressure.
• the viscosity coefficient k decreases, so that the falling speed of the solder fine particles further increases. For this reason, the time required for forming the solder bumps is further reduced.
• the sprayer is coated with a liquid having a flux action and the solder fine particles having a solid solder force. To spray, t.
• the sprayer is coated with a liquid having a flux action and is coated with an organic film, instead of the solder fine particles made of molten solder powder. It sprays solder fine particles that also have soldering power.
• the solder bump forming apparatus further includes heating means for heating the solder fine particles dropped on the substrate to the melting point or higher and evaporating the liquid by this heating. The same effect as the above forming method is achieved.
• the solder bump forming apparatus further includes a depressurizing means for depressurizing the inert gas to atmospheric pressure or lower when spraying the solder fine particles. Has the same effect as the above formation method.
• the solder fine particles are sprayed in an inert gas, and the solder fine particles are dropped on the substrate to form the solder bumps on the pad electrodes.
• the solder wettability can be improved because the solder fine particles can be kept there by the gravitational force over the solder wetting time.
• solder fine particles come into contact with each other in an inert gas, there are few things that coalesce into large solder fine particles, and the solder fine particles are mist-like, that is, extremely fine. Solder bridges etc. at pad electrodes can be prevented.
• the amount of solder bumps can be easily adjusted by changing the amount of solder fine particles supplied. Since the solder fine particles are extremely small as compared with the pad electrode, they are supplied in a large amount and uniformly dispersed in the inert gas, so that the solder amount of the solder bumps can be made uniform. Accordingly, it is possible to obtain a solder bump with a small amount of solder and a small amount of variation while achieving a fine pitch of the electrode / electrode. [0048] Moreover, the time required for the solder fine particles to reach the pad electrode is extremely short compared to that in the liquid! As a matter of fact, even if the solder fine particles are small, they reach the pad electrode immediately, which is necessary for forming the solder bumps. You can save time. This effect can greatly contribute to the reduction of solder fine particles accompanying further fine pitch.
• the substrate can be placed in any direction in the inert gas by spraying the solder fine particles toward the pad electrode. Therefore, the degree of freedom of work can be improved.
• solder fine particles that have the same strength as solder bumps are sprayed from the lower side with the pad electrode side of the substrate facing down. Since it is difficult to adhere to the substrate, it is possible to facilitate cleaning in a later process.
• solder bump forming method and apparatus of the present invention since the flats are also sprayed in the inert gas, the solder wettability in the inert gas can be further improved.
• solder bump forming method and apparatus of the present invention since hydrogen gas is included in the inert gas, the solder wettability in the inert gas can be further improved.
• the diameter of the solder fine particles is made smaller than the shortest distance between the peripheral ends of adjacent pad electrodes, so that Therefore, it is possible to prevent the solder bridges from being generated more reliably.
• the inert gas is heated to the melting point of the solder or higher, so that the solder fine particles are reliably kept in a liquid state in the inert gas. Therefore, solderability can be improved reliably.
• the solder fine particles are sprayed in a solid state and melted in an inert gas, so that it can be stored in the state of solid solder fine particles. Therefore, the handleability can be improved.
• solder bumps According to the method and apparatus for forming solder bumps according to the present invention, by spraying solid solder fine particles coated with a liquid having a flux action, the same degree as solder bump formation in the liquid. Despite the quality of Since the time to reach the pole is much shorter than in liquid, the time required to form solder bumps can be greatly reduced.
• the organic film and the liquid are used by spraying solid solder fine particles coated with the organic film and a liquid having a flux action.
• the time required for solder bump formation can be greatly reduced because the time for solder fine particles to reach the pad electrode is much shorter than in liquid.
• solder fine particles dropped on the substrate are heated to the melting point or higher, and the liquid is evaporated by this heating. As the solder fine particles gradually approach and unite with each other, the occurrence of solder bridges can be suppressed.
• the falling velocity of the solder fine particles can be further increased by reducing the inert gas to atmospheric pressure or lower. Therefore, the time required for forming the solder bumps can be further shortened.
• FIG. 1 is a schematic configuration diagram showing a first embodiment of a solder bump forming method and apparatus according to the present invention, and the process proceeds in the order of FIG. 1 [1] to FIG. 1 [3].
• description will be made based on this drawing. Since there is no appropriate symbol for indicating gas, in Fig. 1 and Fig. 2, the symbol of liquid is used to indicate inert gas.
• the forming apparatus 10 includes a gas tank 11 and a solder sprayer 12.
• the gas tank 11 accommodates an inert gas 13 heated to the melting point of the solder or higher and a substrate 20 positioned in the inert gas 13 so that the surface 21 faces upward.
• the solder sprayer 12 is provided with a blow pipe 16 for spraying the solder fine particles 14 having a molten solder force into the inert gas 13 and evenly dropping the solder fine particles 14 onto the substrate 20.
• Solder is, for example, Sn-Pb (melting point 183 ° C), Sn-Ag-Cu (melting point 218 ° C), Sn-Ag (melting point 221 ° C), Sn-Cu (melting point 227 ° C) Etc.
• the inert gas 13 can be anything as long as it does not react with the solder, for example, nitrogen gas. Good. Further, the inert gas 13 may be mixed with hydrogen gas.
• the temperature of the inert gas 13 is not necessarily higher than the melting point of the solder as long as the solder fine particles 14 can be kept in a liquid state.
• the inert gas 13 need not be 100%, but may contain a small amount of oxygen without adversely affecting the soldering.
• the gas tank 11 is a container made of, for example, stainless steel or heat-resistant resin, and an electric heater (not shown) or a cooling device for keeping the inert gas 13 at or above the melting point of the solder (for example, a melting point + 50 ° C). Water rejection piping etc. are installed.
• a mounting table 17 for positioning the substrate 20 in the inert gas 13 is provided in the gas tank 11.
• the gas tank 11 is provided with an introduction pipe 111 for introducing the inert gas 13 into the gas tank 11 and a discharge pipe 112 for discharging the inert gas 13 from the gas tank 11.
• the mounting table 17 is maintained at a temperature equal to or higher than the melting point of the solder, like the inert gas 13.
• the solder sprayer 12 forms solder fine particles 14 by atomizing molten solder in an inert gas 13 using, for example, a spraying principle or an ultrasonic vibrator.
• a pipe for introducing the solder fine particles 14 (molten solder) sinking to the bottom of the gas tank 11 and the inert gas 13 in the gas tank 11 may be provided between the gas tank 11.
• the solder sprayer 12 may be configured to spray the flux, or a separate flux sprayer may be provided.
• the blow-out pipe 16 has a large number of blow-out openings (not shown) up to the tip, and the solder fine particles 14 are evenly dropped into the inert gas 13 from the blow-out openings. Thereby, the solder fine particles 14 are sent out from the solder sprayer 12 and fall into the inert gas 13 in the gas tank 11 from the blowing pipe 16.
• the solder fine particles 14 may be mixed with an inert gas and sent out from the blowing pipe 16.
• FIG. 2 is a partially enlarged cross-sectional view of FIG. 1, and FIGS. 2 [1] to 2 [3] correspond to FIGS. 1 [1] to 1 [3], respectively.
• FIG. 2 is a partially enlarged cross-sectional view of FIG. 1, and FIGS. 2 [1] to 2 [3] correspond to FIGS. 1 [1] to 1 [3], respectively.
• description will be given based on these drawings. However, the same parts as those in FIG. In FIG. 2, the up-down direction is shown larger than the left-right direction.
• the substrate 20 used in the present embodiment will be described.
• the substrate 20 is a silicon wafer.
• a pad electrode 22 is formed on the surface 21 of the substrate 20.
• Solder bumps 23 are formed on the pad electrodes 22 by the forming method of the present embodiment.
• Board 20 is solder The bumps 23 are electrically and mechanically connected to other semiconductor chips and wiring boards.
• the pad electrode 22 has a circular shape, for example, and a diameter c of, for example, 40 m.
• the distance d between the centers of the adjacent pad electrodes 22 is, for example, 80 m.
• the diameter b of the solder fine particles 14 is, for example, 1 to 15 ⁇ m.
• the pad electrode 22 includes an aluminum electrode 24 formed on the substrate 20, a nickel layer 25 formed on the aluminum electrode 24, and a gold layer 26 formed on the nickel layer 25.
• -The Keckenore layer 25 and the gold layer 26 are UBM (under barrier metal or under bump metallurgy) layers. Portions other than the pad electrode 22 on the substrate 20 are covered with a protective film 27.
• the aluminum electrode 24 is formed on the substrate 20, and the protective film 27 is formed on the portion other than the aluminum electrode 24 by polyimide resin. These are formed using, for example, a photolithography technique and an etching technique. Subsequently, after the surface of the aluminum electrode 24 is subjected to a zincate treatment, a nickel layer 25 and a gold layer 26 are formed on the aluminum electrode 24 using an electroless plating method. The reason for providing this UBM layer is to provide solder wettability to the aluminum electrode 24.
• the substrate 20 is positioned in the inert gas 13 in the gas tank 11 so that the surface 21 faces upward.
• a pad electrode 22 is formed on the surface 21 of the substrate 20.
• the inert gas 13 is heated above the melting point of the solder. At this time, apply flux to the surface of the pad electrode 22!
• the inert gas 13 containing the solder fine particles 14 is sent from the solder sprayer 12 to the blowing pipe 16, and the solder fine particles 14 are also fed into the blowing pipe 16 by force. Drop onto substrate 20 in inert gas 13.
• the flux is sprayed together with the solder fine particles 14, before spraying the solder fine particles 14, or immediately after the solder fine particles 14 are sprayed.
• hydrogen gas may be mixed in the inert gas 13.
• the solder fine particles 14 fall in the gas instead of in the liquid, so that the viscosity coefficient k in the above-mentioned equation ⁇ 3 >> becomes extremely small.
• the falling speed of the solder fine particles 14 is large. That is, even if the solder fine particles 14 are small, they quickly fall and reach the substrate 20, so that the time required for forming the solder bumps 23 is short.
• the substrate 20 is held with the pad electrode 22 side facing up.
• solder fine particles 14 when the solder fine particles 14 are sprayed into the inert gas 13 on the substrate 20, the solder fine particles 14 spontaneously drop by gravity and reach the substrate 20.
• the plurality of solder fine particles 14 that have reached the pad electrode 22 of the substrate 20 stay there due to gravity, and the surface oxide film is removed by the action of the flux.
• a solder film 23 ′ is formed on the surface of the nod electrode 22.
• solder film 23 'grows into solder bumps 23 (Fig. 1 [3] and Fig. 2 [3]). Thereafter, unnecessary solder fine particles 14 (FIG. 2 [3]) having a sufficient force on the solder bump 23 are also removed by cleaning or the like.
• the solder wetting time is a time for which the solder fine particles 14 are in contact with the pad electrode 22 or the solder film 23 'and is a time necessary for the solder to get wet (for example, several seconds to several tens of seconds).
• the solder fine particles 14 fall and reach the pad electrode 22 or the solder coating 23 ', the solder fine particles 14 remain there due to the action of gravity. Therefore, the solder fine particles 14 and the pad electrode 22 or the solder film 23 ′ are in contact with each other until the solder wetting time elapses. Therefore, the solder wettability is good.
• the present inventor has also found that even when the solder fine particles 14 come into contact with each other during the fall in the inert gas 13, there are few that combine to become large solder fine particles. Therefore, no solder bridge or the like is generated on the fine pitch pad electrode 22.
• the diameter b of the solder fine particles 14 is preferably smaller than the shortest distance a between the peripheral ends of the adjacent pad electrodes 22. In this case, the solder fine particles 14 that have reached the two adjacent pad electrodes 22 do not come into contact with each other, so that they do not merge to form a solder bridge.
• solder amount of the solder bump 23 is determined by the solder sprayer 12 using the solder fine particles 14. It can be easily adjusted by changing the supply amount. Since the solder fine particles 14 are supplied in a large amount because they are extremely small compared to the pad electrode 22, they are uniformly dispersed in the inert gas 13. Therefore, the solder bump 23 has little variation in the amount of solder.
• the present invention is not limited to the above embodiment.
• the surface of the substrate does not necessarily have to be up in an inert gas, and may be horizontal, down, or diagonal.
• a wiring board (BGA) may be used instead of the silicon wafer (FC).
• the solder fine particles may be sprayed in a solid state, and the solder fine particles may be melted in an inert gas.
• 3 to 6 show a second embodiment of a solder bump forming method and apparatus according to the present invention.
• description will be given based on these drawings.
• the same part as 1st embodiment attaches
• FIG. 3 is an enlarged cross-sectional view showing a first example of solder fine particles used in the present embodiment.
• the solder fine particles 14 sprayed in the present embodiment are made of solid solder powder and the surface thereof is coated with a liquid 31 having a flux action.
• the liquid 31 having a flux action means that the liquid 31 contains a component having a flux action.
• the main component of the liquid 31 is preferably a volatile liquid such as hydrocarbons, esters, alcohols, glycols and the like.
• an acid or an organic acid metal salt is used as the component having a flux action.
• the acid promotes coalescence of the solder particles.
• the acid include organic acids such as carboxylic acid, inorganic acids such as hydrochloric acid, and rosin.
• Examples of the carboxylic acid include formic acid, oleic acid, stearic acid, and succinic acid.
• Examples of the rosin include rosin derivatives such as L-abietic acid, rosin, and hydrogenated rosin.
• the organic acid metal salt is composed of, for example, an acid and at least one metal element constituting the solder fine particles 14. The organic acid metal salt promotes the flux action, reacts with the molten metal salt, precipitates into an organic film, and suppresses the coalescence of solder fine particles. In the present embodiment, it is assumed that the main component of the liquid 31 is isopropyl alcohol, and the component having a flux action is an organic acid.
• FIG. 4 and 6 show a solder bump forming process in the second embodiment
• FIG. 4 and FIG. 5 are schematic configuration diagrams
• FIG. 6 is a partially enlarged sectional view. The process proceeds in the order of Fig. 4 [1] to Fig. 6 [3].
• action and effect are demonstrated about the formation method and apparatus of the solder bump of this embodiment.
• the solder bump forming apparatus 30 of this embodiment includes a heater 32 as a heating means.
• the heater 32 heats the substrate 20 from the bottom surface of the gas tank 11.
• the solder sprayer may be the same as that of the first embodiment.
• the mounting table for the substrate 20 is not shown.
• the substrate 20 is positioned in the inert gas 13 in the gas tank 11 with the pad electrode 22 facing up. Then, a solder composition in which the liquid 31 and the solid solder fine particles 14 are mixed is sprayed into the inert gas 13 from the blowing pipe 16 (FIG. 4 [1]).
• the solder fine particles 14 are coated with the liquid 31 shown in FIG. 3 [1] and drop onto the substrate 20 in the inert gas 13.
• the solder fine particles 14 naturally fall by gravity and reach the substrate 20 (FIG. 4 [2]).
• the falling speed of the solder fine particles 14 is falling in the gas, it is much higher than the falling speed in the liquid. Therefore, even if the solder fine particles 14 are small, they quickly fall and reach the substrate 20, so that the time required for forming the solder bumps 23 is short.
• solder fine particles 14 are melted to the melting point or higher, and the liquid 31 starts to evaporate.
• the solder bumps 23 are formed as the molten solder particles 14 gradually approach and unite (Figs. 5 [2] and 6 [1]-[3] ). Therefore, unnecessary coalescence of the solder fine particles 14 hardly occurs! /, So that the occurrence of solder bridges is suppressed.
• the following state is caused by the action of the organic acid contained in the liquid 31. First, the coalescence between the solder fine particles 14 is suppressed. However, although not shown in FIG. 6 [2], some of the solder fine particles 14 become larger together.
• solder fine particles 14 there is no problem even if the solder fine particles 14 are united with each other as long as they are below a certain size.
• the solder fine particles 14 spread on the pad electrode 22 and form an alloy layer at the interface.
• a solder film 23 ′ is formed on the pad electrode 22, and solder fine particles 14 are further combined with the solder film 23 ′. That is, the solder film 23 'grows to become a solder bump 23 as shown in FIG. 6 [3].
• the solder fine particles 14 that have not been used for forming the solder bumps 23 are washed away in the subsequent process together with the liquid 31 residue.
• the solder fine particles 14 have only a natural oxide film on the surface.
• the flux action of the liquid 31 promotes the soldering between the solder fine particles 14 and the pad electrode 22 while suppressing the coalescence of the solder fine particles 14 while being heated to the melting point of the solder fine particles 14 or more, and the It promotes coalescence of the solder coating 23 ′ formed on the electrode 22 and the solder fine particles 14.
• Such a component of flux action has been discovered by the present inventors through repeated experiments and considerations.
• Acids can be broadly classified into inorganic acids (for example, hydrochloric acid) and organic acids (for example, fatty acids).
• organic acids for example, fatty acids.
• the organic acid has a small effect of bringing the solder fine particles 14 together, but has a great effect of causing the solder to wet the pad electrode 22”.
• the following (1) and (2) can be considered as the reason why such an action occurs.
• the organic acid has a weak effect of removing the acid film of the solder fine particles 14. For this reason, the coalescence of the solder fine particles 14 can be suppressed by the natural oxide film of the solder fine particles 14 without intentionally forming an oxide film on the solder fine particles 14.
• the organic acid spreads the solder fine particles 14 to the pad electrode 22 to alloy the interface, and combines the solder fine particles 14 with the solder film 23 'formed on the nod electrode 22. There is an action to make it. Despite the fact that the solder fine particles 14 hardly merge with each other, the mechanism of solder wetting on the pad electrode 22 is not clear. As a presumption, there is something that breaks a little oxide film between the solder fine particles 14 and the pad electrode 22. It is thought that this reaction is occurring. For example, in the case of the gold-plated pad electrode 22, the solder wets due to the diffusion effect of gold into the solder even if the solder fine particles 14 have a thin oxide film.
• the pad electrode 22 that also has copper power
• copper reacts with an organic acid to form an organic acid copper salt
• the organic acid copper salt is reduced by the difference in ionization tendency by contacting with the solder, and the metallic copper is contained in the solder. Diffusion and solder wetting progress.
• the reason why the solder fine particles 14 are united with the solder film 23 ′ formed on the pad electrode 22 is, for example, surface tension.
• solder fine particles 14 are coated with the organic film 33, and the solder fine particles 14 are further coated with the liquid 31 having a flux action, and the solder fine particles 14 are sprayed in this state.
• the solder fine particles 14 As a method of coating the solder fine particles 14 with the organic film 33, the solder is melted in a dispersion medium of a heated oily liquid, and this is stirred to form droplet fine particles, which are cooled and solidified to form a spherical shape.
• An oil-in-atomization method that obtains solder particles of the above may be mentioned. An example is described.
• Tin-silver-copper solder is a lead-free solder with a composition of Sn 3.0 mass% Ag 0.5 mass% Cu and a melting point of 220 ° C.
• the refined castor oil is heated to 230 ° C and the stirrer is rotated at 10,000 rpm to break the solder alloy in the refined castor oil.
• a solder powder having the surface of the solder fine particles 14 with the organic coating 33 of maleic acid-modified rosin is obtained.
• the inside of the container is replaced with a nitrogen atmosphere. Solder powder is washed with ethyl acetate after removing the supernatant of the container and dried in vacuum.
• solder fine particles 14 coated with the organic film 33 are heated in the same state as in FIGS. 6 [1] to [3].
• Each solder fine particle 14 is substantially spherical and has a uniform diameter.
• n pieces of the fine particles 14 are united, and the volume and the amount of the organic film are n times and the surface area is n / 3 times.
• the new solder fine particles 14 in which n solder fine particles 14 are united have an organic film amount per unit surface area n 1/3 times. That is, as the coalescence of the solder fine particles 14 progresses, the amount of the organic film per unit surface area increases.
• solder fine particles 14 For example, eight solder fine particles 14 As a result, the volume and the amount of organic film are 8 times, the surface area is 4 times, and the amount of organic film per unit surface area is doubled. Also, as the amount of organic film per unit surface area increases, it becomes more difficult for the solder particles 14 under the organic film 33 to contact each other, so coalescence of solder particles is suppressed.
• the solder film 23 ′ on the nod electrode 22 grows when the solder fine particles 14 merge with the solder film 31. Therefore, as the coalescence of the solder fine particles 14 progresses on the pad electrode 22, the growth of the solder film 23 ′ stops when the amount of the organic film per unit surface area of the solder film 23 ′ reaches a constant value. That is, the final solder amount of the solder film 23 ′ is determined by the size of the first solder fine particles 14 and the amount of the organic film in addition to the size of the nod electrode 22. It should be noted that the solder fine particles 14 whose amount of organic film per unit surface area has reached a constant value do not merge with the solder film 23 '.
• the amount of the organic film of the first solder fine particle 14 allows the coalescence of the solder fine particle 14 to the solder film 23 ′ until the solder film 23 ′ reaches a certain amount of solder and is suppressed when the certain amount of solder is exceeded. Is set to do.
• the volume is VI and the amount of the organic film is F1.
• the shape of the solder fine particles 14 is spherical.
• the volume is V2
• the organic coating amount is F2
• the surface area is S2.
• the area of the pad electrode 22 is SO.
• A is a correction coefficient indicating the relationship between the surface area of the solder bump 23 and the area of the pad electrode 22. Let Fmax be the maximum amount of organic coating per unit surface area.
• the correction coefficient A varies depending on the volume of the solder bump 23, the shape of the pad electrode 22, the surface tension of the molten solder, and the like. For example, since the surface area of the solder bump 23 increases as the volume of the solder bump 23 increases, A also increases. Since the shape of the anode / node electrode 22 is less likely to be a square spherical force than a circle, the surface area is increased, and therefore A is a large value. The smaller the surface tension of the molten solder, the greater the surface area due to the difficulty of becoming a spherical surface, so A is also a large value. The actual correction factor A is obtained experimentally.
• FIG. 7 is a schematic configuration diagram showing a third embodiment of the method and apparatus for forming solder bumps according to the present invention, and the process proceeds in the order of FIG. 7 [1] to FIG. 7 [2].
• description will be made based on this drawing. However, the same parts as those in FIG. 1 and FIG.
• the solder bump forming apparatus 40 of the present embodiment is further provided with a depressurizing means for depressurizing the inert gas 13 to an atmospheric pressure or lower when the solder fine particles 14 are sprayed.
• This pressure reducing means is constituted by a part of the function of the controller 41, a vacuum pump 42, electromagnetic valves 43, 44, and the like.
• the controller 41 is, for example, a microcomputer, and controls on / off of the vacuum pump 42 and the solder sprayer 12 and also controls opening and closing of the electromagnetic valves 43 and 44 according to a program.
• Solenoid valve 43 is a pipe connecting vacuum pump 42 and gas tank 11
• the solenoid valve 44 is provided in a pipe 46 that connects the solder sprayer 12 and the blowing pipe 16.
• the controller 41 operates as follows, for example. First, the inert gas 13 in the gas tank 11 is decompressed by turning on the vacuum pump 42, opening the solenoid valve 43, turning off the solder sprayer 12, and closing the solenoid valve 44 (FIG. 7 [1]). When a certain time elapses or the pressure of the inert gas 13 falls below a certain level, the vacuum pump 42 is turned off, the solenoid valve 43 is closed, the solder sprayer 12 is turned on, and the solenoid valve 44 is opened. Fine particles 14 are sprayed into the gas tank 11 (Fig. 7 [2]).
• the flux based on the inert gas 13 in the gas tank 11 or the viscosity based on the hydrogen gas affects the solder fine particles 14 as the inert gas 13 is depressurized. Since the viscosity coefficient k during the dropping of the solder fine particles 14 becomes small, the falling velocity V of the solder fine particles 14 becomes further larger. Therefore, the time required for forming the solder bump can be further shortened.
• the surface of the solder fine particles 14 shown in Fig. 3 [2] is covered with the organic film 33, and the surface of the organic film 33 is covered with the liquid 31 containing the flux component. Yes.
• the liquid 31 may be the flack material itself. In the following embodiment, the case where a flux material is used as the liquid 31 will be described.
• solder bump forming apparatus used in the present embodiment is constructed as shown in FIG. 8, and the solder bump forming apparatus shown in FIG. 8 has substantially the same configuration as the solder bump forming apparatus shown in FIG. Built.
• the solder bump forming apparatus 50 used in the present embodiment includes a gas tank 11, an inert gas supply device 51, a solder supply device 52, a flux supply device 53, a redox agent supply device 54, It has a controller 55 that controls these!
• the gas tank 11 includes a mounting table 17.
• the substrate 20 is set on the mounting table 17 with the surface 21 on which the pad electrode is formed facing upward.
• the solder feeder 50 is used to evenly drop the solder fine particles having the structure shown in FIG. 3 [2] toward the substrate 20 on the mounting table 17.
• the blowout pipe 56 is arranged in the upper space in the gas tank 11.
• the blower pipe 56 of the solder feeder 50 has a number of blowout ports (not shown) arranged in a line up to the tip of the base force, so that the solder fine particles 14 can be evenly dropped into the inert gas 13 from the blowout ports. It has become.
• solder fine particles other than the structure shown in FIG.
• the solder dispenser 50 makes the molten solder into a fine particle state by using, for example, a spraying principle or an ultrasonic vibrator.
• the structure to be supplied to may be out of alignment.
• the gas tank 11 may be additionally provided with piping equipment for discharging the remaining excess solder in which solder bumps are formed on the pad electrodes of the substrate.
• the gas tank 11 is an electric heating (not shown) for keeping the inert gas 13 above the melting point of the solder (for example, a melting point + 50 ° C) in a container made of, for example, stainless steel or heat resistant resin.
• a heater and cooling water piping are provided.
• the mounting table 17 is maintained in the vicinity of the melting point of the solder in the same manner as the inert gas 13 by an electric heater (not shown).
• the inert gas supplier 51 supplies the inert gas 13 into the gas tank 11 under the control of the controller 55.
• An inert atmosphere is formed in the gas tank 11 by the inert gas 13 supplied from the inert gas supply device 51.
• the flux supplier 53 supplies the flux into the inert atmosphere (inert gas 13) in the gas tank 11 under the control of the controller 55.
• the solder fine particles 14 shown in FIG. 3 [2] have a flux, so there is no need to actively supply the flux into the gas tank 11 by the flux feeder 53. On the contrary, when the flux held by the solder fine particles 14 is insufficient, the insufficient flux is supplementarily supplied.
• the acid reducing agent supplier 54 supplies, for example, an oxygen reducing agent such as hydrogen gas as fine particles to the inert atmosphere (inert gas 13) in the gas tank 11. It is like this.
• an oxygen reducing agent such as hydrogen gas
• the oxidation-reduction agent supplier 54 supplies the solder fine particles adhering to the natural oxide film into the gas tank. It is desirable to actively supply the acid reducing agent into the gas tank.
• the inert gas 13 is supplied from the inert gas supply 51 into the gas tank 11, and the inert gas 13 and the mounting table 17 in the gas tank 11 are attached with a solder melting point. Heat to near.
• the substrate 20 is temporarily set and preheated in a preliminary chamber (not shown) communicating with the gas tank 11 and shielded from the external atmosphere.
• the preliminary chamber communicates with the gas tank 11, the substrate 20 is set on the mounting table 17 in the gas tank 11, and the substrate 20 is positioned in the inert atmosphere of the inert gas 13. In this state, the pad electrode 22 of the substrate 20 is heated to near the solder melting point.
• solder fine particles 14 shown in FIG. Is fed into the inert atmosphere in the gas tank 11 through the blow pipe 56.
• the sent solder fine particles 14 form a layer and drop toward the pad electrode 22 of the substrate 20.
• solder fine particles those having a nano-order particle size may be used. For example, when such solder fine particles are allowed to settle in a liquid, they may not reach the substrate 20 smoothly due to the viscosity of the liquid, and the settling direction may be bent.
• the viscosity coefficient k in the above-described equation ⁇ 3> is extremely small, so that the solder fine particles 14 fall at a high speed. That is, even if the solder fine particles 14 are small, the solder fine particles 14 immediately fall and reach the substrate 20, so that the time required for forming the solder bumps 23 is short.
• the solder particles 14 fall in the inert gas 13
• the solder fine particles 14 easily take a form of falling in a layered form when supplied from the blowing pipe 56.
• the inert gas 13 is heated near the melting point of the solder when the solder fine particles 14 fall in the inert gas 13, the solder fine particles 14 receive the radiant heat from the inert gas 13, while the substrate 20 Drops toward the pad electrode 22
• solder film 23 ′ is formed on the surface of the pad electrode 22 using the solder fine particles 14 as the core of the film.
• the solder film Consider the process by which 23 'is formed. This consideration is based on the assumption of the present inventor, but based on this consideration, the principle that the solder bump 23 is formed on the pad electrode 22 can be reasonably explained.
• solder fine particles 14 shown in FIG. 3 [2] reach the cathode / node electrode 22 of the substrate 20, they receive the radiant heat of the heated substrate 20, and the flux 31, the organic film 33 and the solder fine particles 14 Is heated.
• the organic film 33 dissolves into the melting flux 31 as indicated by the arrows.
• solder 14a is the core of the solder bump 23.
• the solder bump 23 is formed on the pad electrode 22 by the eutectic phenomenon at the interface between the solder 14a and the pad electrode 22 and the action of the newly formed organic film 33a.
• the nucleus of the solder bump 23 is localized and grown in the range of the pad electrode 22 of the substrate 20, Even when the pad electrodes 22 are formed with a fine pitch interval, the occurrence of solder bridges between adjacent pad electrodes 22 can be suppressed.
• the present embodiment illustrated in FIG. 8 is not limited to the illustrated configuration.
• the surface of the substrate does not necessarily have to be up in the inert gas, and may be horizontal, down, or diagonal.
• a wiring board (BGA) may be used instead of the silicon wafer (FC).
• the solder fine particles may be sprayed as a solid, and the solder fine particles may be melted in an inert gas.
• the inert gas supply device 51, the solder supply device 52, the flux supply device 53, and the oxidation-reduction agent supply device 54 may be integrated in an integrated structure like the solder sprayer 12 shown in FIG.
• the solder bump forming apparatus shown in FIG. 8 may be equipped with a decompression means for decompressing the gas tank 11 as shown in FIG.
• the fine pitch of the nod electrode can be achieved, and a solder bump having a large amount of solder and little variation can be obtained, and a bump can be formed in a short time. .
• FIG. 1 is a schematic configuration diagram showing a first embodiment of a solder bump forming method and apparatus according to the present invention, and the steps proceed in the order of FIG. 1 [1] to FIG. 1 [3].
• FIG.2 Partially enlarged sectional view of Fig. 1.
• Fig.2 [1] to Fig.2 [3] correspond to Fig.1 [1] to Fig.1 [3], respectively.
• FIG. 3 [1] is a first example
• FIG. 3 [2] Is a second example.
• ⁇ 4 It is a schematic configuration diagram showing the second embodiment, and the process proceeds in the order of FIG. 4 [1] to FIG. 4 [2].
• ⁇ 5 It is a schematic configuration diagram showing the second embodiment, and the process proceeds in the order of FIG. 5 [1] to FIG. 5 [2].
• FIG. 7 is a schematic configuration diagram showing a third embodiment of the method and apparatus for forming solder bumps according to the present invention, in which the process proceeds in the order of FIGS. 7 [1] to 7 [2].
• FIG. 8 is a schematic configuration diagram showing another embodiment of the present invention.
• FIG. 10 is a schematic cross-sectional view showing a conventional solder bump forming method.

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• 2005
  • 2005-11-29 WO PCT/JP2005/021833 patent/WO2006057394A1/ja active Application Filing
  • 2005-11-29 JP JP2006547921A patent/JPWO2006057394A1/ja not_active Withdrawn
  • 2005-11-29 CN CNA2005800297040A patent/CN101124669A/zh active Pending

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