JP6167966B2 - Solder ball manufacturing method and manufacturing apparatus - Google Patents

Description

  The present invention relates to a solder ball manufacturing method and a manufacturing apparatus, and in particular, a solder ball capable of manufacturing a solder ball mainly used for joining and sealing of electronic components in a high yield while suppressing variation in particle size. The present invention relates to a ball manufacturing method and a manufacturing apparatus.

  Conventionally, various manufacturing methods such as an atomizing method, a drip method in oil, a drip method in water, and a mechanical processing method are known as solder ball manufacturing methods. Among them, solder balls and zinc grains used in the electronics industry are known. In the production, a dripping method in water and a dripping method in oil are frequently used. For example, Patent Document 1 discloses a method of obtaining granular metal by dropping molten metal into cooling water from a nozzle or the like and cooling and solidifying as a submerged dripping method. It is described that metal grains having a desired shape and size can be formed by selecting conditions such as the diameter, the distance between the tip of the nozzle and the cooling water surface, and the cold water temperature.

  Patent Document 2 discloses an in-oil dropping method in which molten metal is discharged into oil having excellent oxidation resistance that is heated to near the melting point of the molten metal in order to produce a solder ball having a good shape. . The apparatus used in this in-oil dropping method is basically composed of a molten solder supply section provided with a high-frequency coil and a column filled with oil located below. The tip of the nozzle provided in the molten solder supply section is located below the oil level, and the molten solder that is pressurized with gas is continuously discharged from this nozzle. And is spherical with its own surface tension and solidifies while falling in the column.

Japanese Patent Laid-Open No. 1993-214412 JP 1999-229004 A

  However, the underwater dropping method shown in Patent Document 1 has a problem that it is difficult to suppress the oxidation of the molten metal because the tip of the nozzle is spaced apart from the water surface. Also, when molten metal enters the water, it needs to enter the water while colliding with the water surface and breaking the water surface tension, and since it is cold water, it solidifies in an instant, so many flat particles are generated, As a result, there is a problem that the yield is low.

  On the other hand, the in-oil dropping method of Patent Document 2 can produce solder balls with higher roundness than the underwater dropping method, but the oil is locally heated in the column, so the temperature distribution of the oil is It becomes non-uniform, and the division of the molten metal discharged from the nozzle is unstable due to the influence of the convection generated thereby, the particle size distribution of the solder balls is widened, and the yield of solder balls having a desired particle size is low. Had the problem of becoming.

  The present invention has been made in view of the problems of the conventional oil-in-oil dropping method described above, and suppresses the generation of unstable solder balls due to convection of heated oil, thereby reducing solder particle diameter variation. An object of the present invention is to provide a solder ball manufacturing method and a manufacturing apparatus that can be stably manufactured.

  In order to achieve the above object, a method for producing a solder ball according to the present invention is a method for producing a solder ball by dripping a molten solder material pressurized with an inert gas in oil. It is characterized in that the solder raw material is discharged at a position in the oil within a range from the liquid surface to a depth of 40 mm where convection due to heat does not substantially occur.

  The oil dropping apparatus according to the present invention includes a nozzle that discharges a molten solder material pressurized with an inert gas and a column in which the discharged solder material is dropped in oil. It is an apparatus, and the tip of the nozzle is arranged in the oil up to a depth of 40 mm from the oil level in the column, and is reduced in diameter downward and partially immersed in the oil. It is characterized by being surrounded by a convection suppressing member comprising a truncated cone portion and a cylindrical portion extending downward from the lower end portion thereof.

  According to the present invention, it is possible to produce solder balls with a very high yield with less variation in particle size as compared with conventional oil-in-drop methods.

It is a longitudinal cross-sectional view which shows one specific example of the in-oil dripping apparatus which concerns on this invention.

  Hereinafter, a specific example of the in-oil dropping device of the present invention will be described with reference to FIG. The in-oil dropping device according to one specific example of the present invention includes a nozzle 10 preferably made of quartz that discharges a molten solder material pressurized with an inert gas such as nitrogen gas downward. This is mainly composed of a column 20 for forming solder balls by dropping the solder raw material discharged from the nozzle 10 in oil.

  More specifically, the nozzle 10 has a high-frequency coil 11 wound around it, and is heated so that the solder material discharged from the nozzle 10 is in a molten state. A gas supply pipe 13 having a pressure adjusting means 12 is connected to the upper portion of the nozzle 10, and an inert gas such as nitrogen gas is supplied at a predetermined pressure from a gas supply source (not shown) through the gas supply pipe 13. The Thereby, the molten solder raw material can be discharged from the hole of the nozzle 10 at a constant discharge pressure.

  The column 20 located on the lower side of the nozzle 10 has a height of 1300 to 1800 mm, for example, so that the solder raw material discharged from the nozzle 10 is solidified in oil and is solidified to form solder balls. And has a vertically long cylindrical shape with an inner diameter of about 100 to 300 mm. In order to heat the oil in the column 20 to near the melting point of the solder raw material, a heater 21 is wound around the top of the column 20. The heater 21 is not wound around the lower part of the column 20 and is a low temperature part. The upper portion of the portion around which the heater 21 is wound is provided with a large-diameter portion 20b having a height of 150 to 200 mm and an inner diameter of about 300 to 400 mm, for example, through the enlarged-diameter portion 20a so that the nozzle 10 can be accommodated. .

  The oil is filled up to about 1/3 of the height of the large-diameter portion 20b in the column 10, and the tip of the nozzle 10 is immersed in the oil. The nozzle 10 is attached to a height adjusting means 14 that is movable in the vertical direction. The nozzle 10 can be set to a desired height by adjusting the position of the tip of the nozzle 10 in the vertical direction. Is adjusted so as to be positioned in the oil up to a depth of 40 mm from the oil level in the column 10. The specific mechanism of the height adjusting means 14 is not particularly limited. For example, a gripping member is screwed into a threaded portion that is pivotally set perpendicular to the axial direction, and the nozzle 10 is attached to the gripping member. A mechanism for gripping can be mentioned.

  The entire tip of the nozzle 10 is surrounded by a convection suppressing member 22 that suppresses convection of oil caused by heat in the oil. The convection suppressing member 22 includes a truncated conical portion 22a that is reduced in diameter downward and partially immersed in oil, and a cylindrical portion 22b that extends downward in the oil from its lower end. The upper end portion of the truncated cone portion 22a is attached to the inner diameter of the large diameter portion 20b about 50 mm above the oil level in the column 10, and from here it is preferably 20 to 60 ° with respect to the vertical direction. Is inclined at an angle of The inner diameter of the cylindrical portion 22b connected to the lower end portion of the truncated cone portion 22a is preferably 10 to 50 mm.

  By surrounding the tip portion of the nozzle 10 with such a funnel-shaped convection suppressing member 22, the position of the tip portion of the nozzle 10 is arranged in oil up to a depth of 40 mm from the liquid level where convection due to heat does not substantially occur. When the molten metal is discharged from the nozzle 10 due to a synergistic effect with the operation, adverse effects such as vibration due to oil convection can be minimized, and the molten metal discharged from the nozzle 10 in a string is divided. Stability can be improved. Thereby, the dispersion | variation in the particle size of the solder ball B which settles in the column 20 can be suppressed, and the yield of the solder ball of a desired particle size improves markedly. Furthermore, the appearance / shape defect rate is reduced.

  Next, a method for producing solder balls by the in-oil dropping method using the above-described in-oil dropping apparatus will be described. First, the production of an alloy ingot to be charged into the oil dropping device will be described. First, each raw material metal is weighed so as to have a predetermined solder raw material composition. At this time, it is confirmed that the size of the raw material metal is non-uniform and there is no large lump, and it is put into a graphite crucible. This is because when the size of the raw metal is uneven and there are large lumps, the metal having a high melting point is difficult to melt, and there is a possibility that unmelted metal may be generated. It is more preferable to use a solder raw material mainly composed of an Au solid solution and a Ge solid solution, or an Au solid solution and an Sn solid solution, which are difficult to oxidize. Thereby, it is possible to produce a solder ball with higher yield and higher quality than conventional.

  A crucible containing raw metal is set in a high frequency furnace, and an inert gas is flowed from above to prevent oxidation of the molten metal. Next, in consideration of the amount of alloy input and the melting point of each metal, the coil is heated by passing an electric current so that the temperature is about 200 ° C. higher than the melting point. At this time, the molten state of the metal is confirmed while stirring the molten metal appropriately with a glass rod. When the molten metal is uniformly melted, the power of the high frequency is turned off, and it is quickly taken out from the graphite crucible and poured into a mold that matches the shape of the nozzle. After cooling sufficiently, confirm that the metal has hardened and remove it from the mold. Thereby, an alloy ingot for an in-oil dropping device is obtained.

  Next, the in-oil dropping method will be described. The alloy ingot prepared above is inserted into a quartz nozzle, the nozzle is attached to the center of the high frequency coil, and a jig for supplying compressed gas is attached to the upper part of the nozzle. Turn on the power of the heater that heats the oil, heat the oil at a rate of temperature increase of 20-100 ° C./min, stop the temperature increase when the temperature near the melting point of the solder raw material, Maintain until finished. Thereafter, the tip of the nozzle is submerged to a depth of 40 mm from the heated oil level. In particular, in order to avoid vigorous convection caused by a difference in temperature distribution of oil in the column, the depth in the oil at the tip of the nozzle is more preferably in the range of 2 to 25 mm from the liquid level. If the position of the tip of the nozzle exceeds 40 mm from the liquid level, the distance between the high-frequency coil and the ingot is increased, and a solid phase is formed, which is not preferable.

  Next, the power of the high-frequency coil is turned on and heated at a heating rate of 150 to 300 ° C./min to melt the alloy ingot. When reaching a temperature higher than the melting point of the alloy by 100 to 300 ° C., more preferably 200 to 300 ° C. higher than the melting point of the alloy, the inert gas valve is opened and pressurized to 0.01 MPaG or more and 0.50 MPaG or less, Discharge the molten metal. The discharge pressure is preferably adjusted according to the density of the metal. For example, when Au is the main component, 0.08 MPaG or more and 0.25 MPaG or less is preferable. In the nozzle, it is preferable that the nozzle is heated and held in a molten state at a temperature higher by 100 ° C. than the melting point of the alloy for a time of 0 seconds to 1800 seconds. As a result, the composition can be made more uniform, and discharge can be performed while minimizing the occurrence of undissolved material and segregation. In the case of a solder alloy mainly composed of Au, the heating and holding time is more preferably about 100 seconds.

  When discharging molten metal, in the conventional drop-in-oil method, the division of the discharged molten metal is affected by the vibration caused by the convection of the oil, so that the molten metal cannot always be divided into pieces of the same volume and becomes unstable. As a result, the particle size distribution of the solder balls becomes broad, and the yield of solder balls having a desired particle size has deteriorated. On the other hand, by dripping in oil by the method described above, variation in the particle size of the solder balls is suppressed, and the yield is remarkably improved. In particular, by controlling the discharge pressure and optimizing the holding time during heating with high frequency, the pressure in the nozzle system is stabilized, so that the shape and particle size distribution of the solder balls are stable and overpressurized. As a result, almost no solder balls having poor shape and appearance such as two balls, deformed balls, and knurled balls, which are likely to be generated due to the above, are formed, and an extremely high yield is possible. This effect is particularly remarkable when the solder alloy is Au-based solder.

  After the molten metal serving as the solder ball raw material is completely discharged, the molten metal is sufficiently cooled at the low temperature portion at the bottom of the column, and then the valve at the bottom of the column is opened to collect the solder ball. The collected solder balls are preferably washed with an organic solvent since oil is adhered. At this time, a material that is highly volatile and does not oxidize the solder balls is preferable. For example, ethanol is preferable because it has high volatility and can shorten the washing time.

  An AuGe solder ball having a Ge content of 12% by mass and an Au content of 88% by mass having a eutectic composition around 356 ° C. was prepared using an in-oil dropping apparatus as shown in FIG. Specifically, first, Au and Ge having a purity of 99.9% by mass or more were prepared as raw materials. Each raw material was weighed with an electronic balance so as to have the above-described composition, and placed in a graphite crucible for a high-frequency melting furnace.

  The crucible containing this raw material was placed in a high-frequency melting furnace, and the melting furnace was turned on to heat and melt the raw material. When heating, nitrogen gas was flowed at a flow rate of 0.6 liter / min or more per 1 kg of the raw material in order to suppress oxidation. When the metal began to melt, it was mixed uniformly with a glass rod so that segregation did not occur. After confirming that it was sufficiently melted, the crucible was quickly taken out, and the molten metal in the crucible was poured into a mold matching the shape of the nozzle. In this way, a total of 28 ingots were produced.

  Solder balls of Samples 1 to 28 were produced from the 28 ingots produced as described above. In the production of the solder balls for each sample, an oil-in-water dropping device as shown in FIG. 1 was used. At that time, as shown in Table 1 below, the depth from the liquid surface of the nozzle tip (mm), the discharge pressure from the nozzle (MPaG), and the holding time at a temperature 200 to 300 ° C. higher than the melting point (seconds) And the four parameters of the presence or absence of the convection suppressing member were changed variously. That is, each ingot is put into a quartz nozzle, the tip of the nozzle is submerged to a depth of 0.1 to 70 mm from the oil level, and the metal ingot is heated to 800 ° C. with a high frequency coil. After confirming that it was completely dissolved by visual observation, the temperature of the high frequency was lowered, held at 556 ° C. for any time from 0 to 1800 seconds, and then the molten metal was added with nitrogen gas to 0.05 to 0.9 MPaG. The AuGe ball was manufactured by pressurizing and discharging. The hole diameter at the tip of the nozzle was adjusted in advance so that the set value of the ball diameter was 0.025 mm. Moreover, the oil in the column of the dripping apparatus in oil used the oil with the big oxidation inhibitory effect of a solder ball.

The obtained balls of each sample were classified into predetermined particle diameters by the following method, the standard deviation of the ball diameter, the defect rate, and the yield of non-defective products were examined and evaluated by the following evaluation methods. That is, the solidified balls were collected from the lower end of the column, washed with an ethanol solution, and dried at 85 ° C. using a dryer. 200 dried balls were extracted at random, the diameter of the balls was measured with a laser microscope, and the standard deviation of the ball diameter was calculated. Next, the shape / appearance defects and non-defective balls were selected using a plating machine, and the defect ratio of the balls was calculated. On the other hand, the remaining solder balls were classified in a range of diameter 0.025 ± 0.002 mm using a biaxial classifier, and the yield of the balls obtained by this classification was calculated by the following formula 1. . The evaluation results are shown in Table 2 below.
[Formula 1]
Ball yield (%) = mass of ball of diameter 0.025 ± 0.002 mm ÷ mass of charged ball of classification × 100

  As can be seen from Table 2 above, each AuGe ball of Samples 1 to 20 produced based on the method of the present invention has a small ball diameter standard deviation and a defective rate, and shows a high yield. Particularly, in the sample 14 equipped with a convection suppressing member having a nozzle and liquid surface depth of 20 mm, a discharge pressure of 0.1 MPaG, a retention time of 556 ° C. for 500 seconds, and an extremely high yield of 68.3%. In addition, it can be seen that the yield and quality of the other samples are dramatically improved as compared with the samples 21 to 28 as comparative examples. That is, the yield and quality of the product can be controlled by appropriately controlling the four parameters of the nozzle tip depth from the liquid surface, the discharge pressure, the holding time at a temperature 200 to 300 ° C. higher than the melting point, and the convection suppressing member. It can be seen that the effect of significantly improving the is obtained.

  On the other hand, the AuGe balls of Samples 21 to 28 produced by a method that did not satisfy any of the requirements of the present invention resulted in undesirable results. That is, the yield of the balls was 14% at the highest, which was lower than any of the samples 1 to 20, and the standard deviation of the ball diameter and the defect rate were clearly worse than all the samples of the present invention. In particular, when the discharge pressure is 0.6 MPaG or more, the molten metal is discharged from the nozzle vigorously, making it difficult to divide, and solidifying before being divided into balls. It increased to. Moreover, when the convection suppressing member was not attached, the yield of the balls was reduced by more than half. Furthermore, when the nozzle tip is submerged so that the depth from the oil surface exceeds 40 mm, the upper high-frequency coil and the ingot are displaced from each other, so that the ingot cannot be dissolved well and the nozzle tip is clogged. Occasionally, molten metal may not be discharged.

DESCRIPTION OF SYMBOLS 10 Nozzle 11 High frequency coil 12 Pressure adjustment means 13 Gas supply piping 14 Height adjustment means 20 Column 21 Heater 22 Convection suppression member B Solder ball

Claims (7)

  A method for producing a solder ball by dropping molten solder material pressurized with an inert gas in oil, the convection being within a range from the liquid level of the oil to a depth of 40 mm and by heat A method for producing a solder ball, wherein the solder raw material is discharged at a position in oil where substantially no occurrence of the solder occurs.   The method of manufacturing a solder ball according to claim 1, wherein the solder raw material is an alloy containing Au as a main component. The solder ball manufacturing method according to claim 1, wherein the pressure of the inert gas is 0.01 MPaG or more and 0.50 MPaG or less on a gauge pressure basis .   The solder ball manufacturing method according to claim 1, wherein the solder raw material is held in the molten state for more than 0 seconds and not more than 1800 seconds before being discharged. An in-oil dropping device comprising a nozzle for discharging a molten solder material pressurized with an inert gas, and a column in which the discharged solder material is dropped in oil,
The tip of the nozzle is disposed in the oil up to a depth of 40 mm from the oil level in the column, and has a truncated cone portion that is reduced in diameter downward and partially immersed in the oil. A dripping device in oil characterized by being surrounded by a convection suppressing member comprising a cylindrical portion extending downward from a lower end portion thereof.   The in-oil dripping device according to claim 5, wherein the nozzle is movable in the vertical direction.   The incline according to claim 5 or 6, wherein the frustoconical portion has an inclined surface of 20 to 60 ° with respect to a vertical direction, and an inner diameter of the cylindrical portion is 10 to 50 mm. Dripping device.

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