JP2008272779A - Surface treated solder ball and surface treatment method of solder ball - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface treated solder ball that causes no blackening phenomenon and that excels in storage stability as well as wettability, and also to provide a manufacturing method of the same. <P>SOLUTION: This is a solder ball the surface of which is covered with two or more kinds of organic acid having 10-25 carbon number. In the surface treated solder ball, the carboxyl group of the organic acid is coordinated in chelate with the solder ball surface, or infrared absorption peak caused by the carboxyl group of the organic acid is 1,650-1,700 cm<SP>-1</SP>. The surface treatment method of the ball includes: a process in which two or more kinds of organic acid having 10-25 carbon number is dissolved in an organic solvent; a process in which the solder balls are dispersed in the solution; a process in which the organic solvent is removed from the solder ball; and a process in which the solder ball with the organic solvent removed is thermally treated at 90-180°C and in which the carboxyl group of the organic acid is coordinated in chelate with the solder ball surface. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a solder ball used for connecting an electronic component in surface mounting of an electronic device substrate, and more particularly to a solder ball and a solder ball surface treatment method used for forming a bump of the electronic component.

  In recent years, electronic devices are becoming lighter, thinner, and smaller, and electronic components used in electronic devices are required to be smaller and thinner. In order to cope with this, a bump forming technique using a solder ball has been used for an electronic component on which a semiconductor or the like is mounted on a substrate. There are high-function packages called BGA (Ball Grid Array) and CSP (Chip Size Package). The solder balls used in these are required to have a small ball diameter and high dimensional accuracy and stable bondability. Regarding stable bondability, the smaller the diameter of the solder ball, the greater the influence of the surface state of the solder ball, and the management of the surface state such as surface oxidation becomes important.

  On the other hand, Pb-free solder, in which solder balls do not contain lead (Pb), has been developed while environmental issues are increasingly regarded as important. For example, Sn-Ag system, Sn-Ag-Cu system, Sn-Bi system, Sn-Zn system, and the like. However, as represented by Sn—Zn, when solder balls are used, the surface is more likely to oxidize than conventional solder balls, and there is a problem that the wettability at the time of melting the solder balls is not sufficient. Therefore, it is desired to develop an excellent surface treatment method that can be applied to Pb-free solder balls.

  As a surface treatment of the solder ball, for example, Patent Document 1 discloses that the surface of the solder ball is uniformly coated with a lubricant in order to prevent the solder ball from being blackened. The solder balls have a phenomenon that the balls collide with each other due to vibration during transportation or the balls collide with the container wall, resulting in blackening of the solder balls. The blackening phenomenon of the solder ball is because the surface of the solder ball is oxidized by collision or friction, and this causes a decrease in wettability when the solder ball is melted. Further, in the semiconductor mounting process, although the quality of the solder balls is detected with light, the blackened solder balls have a problem that the light reflectance is poor and a detection error occurs. In Patent Document 1, a lubricant such as fatty acid amide-based stearic acid amide (stearic acid amide) is coated for the purpose of improving the lubricity of the surface of the solder ball in order to solve the above-mentioned problem. If the lubricity of the solder surface is increased by coating with a lubricant, it is presumed that local heat generation due to collision and friction can be reduced, and oxidation of tin can be prevented, that is, the blackening phenomenon can be suppressed.

  Patent Document 2 discloses that a metal soap molecular film such as calcium stearate, magnesium stearate, and barium stearate is adsorbed on the surface of a solder ball to prevent fine adhesion and improve wettability. When the diameter of the solder balls becomes 400 μm or less, weak adhesion (fine adhesion) between the solder balls becomes a problem. Although the blackening can be reduced by the process of Patent Document 1, there is no effect on the fine adhesion, but it may be promoted. Inventors of Patent Document 2 show that a non-polar organic acid is present on the surface of a solder ball because a metal group such as calcium stearate, magnesium stearate, and barium stearate has a weak polar group compared to a salt such as Na. In order to repel moisture having a strong polarity, it is explained that fine adhesion caused by moisture adsorption is less likely to occur.

  Similarly, Patent Document 3 discloses that an organic acid salt of a fatty acid such as lauric acid, myristic acid, or palmitic acid is attached to the surface of the solder ball. Patent Document 3 also discloses that an organic acid salt of a fatty acid such as lauric acid, myristic acid, and palmitic acid is provided on the surface of the solder ball as an organic film. By applying the organic acid salt to the surface of the solder balls, blackening can be suppressed and aggregation of the solder balls can be suppressed. Among the organic acid salts, it is described that organic acid copper salts such as copper phthalate, copper citrate, copper laurate, copper myristic acid, copper valmitate, copper threaric acid are suitable.

Further, Patent Document 4 discloses that an organic acid salt is attached to the surface of the solder powder even in the solder powder constituting the solder paste together with the flux. In particular, Sn—Zn-based solder has insufficient wettability, so that wettability is secured by attaching the organic acid salt. Examples of the organic acid salt include salts such as laurate, myristate, parimitinate and stearate.
Japanese Patent Laid-Open No. 2000-287771 JP 2006-9112 A JP 2005-254246 A JP 2000-317682 A

  As described above, by covering the surface of the solder ball with an organic acid salt, the blackening phenomenon and the decrease in wettability can be suppressed. However, if an amine salt or a metal salt is used as the organic acid salt, the following problems occur: Will occur.

  With amine salts such as stearic acid amide, corrosive ammonia gas is generated when the stearic acid amide coated on the surface decomposes at the temperature at which the solder ball melts, causing damage to the mounted components. Become. Further, as pointed out in Patent Document 2, stearic acid amide also has a problem that solder balls tend to adhere to each other and aggregate.

  On the other hand, when the organic acid salt is a metal salt, the organic acid portion is decomposed when the solder ball is melted, but the metal ions remain on the surface of the solder ball as foreign metal impurities, resulting in a decrease in wettability. Even with the same salt as copper and the like as the additive component of the solder ball alloy, the component concentration on the ball surface differs from the original solder ball composition, which causes a problem in wettability during melting.

  In order to solve the above-described problems, an object of the present invention is to provide a surface-treated solder ball having excellent storage stability that does not cause a blackening phenomenon and good wettability, and a method for producing the same.

  The inventors have coated the surface of a solder ball with an organic acid that does not contain a metal ion or does not use an amine as a counter cation, and chelates the surface of the solder ball with the organic acid to oxidize the surface. It has been found that a property that suppresses and has excellent storage stability can be obtained. That is, this is not achieved by simply applying an organic acid to the solder ball surface, but can be achieved by chelate coordination of the carboxyl group of the organic acid. Furthermore, it has been found that by combining a plurality of organic acids with the chelate, it exhibits good wettability when the solder balls are melted together with the above effects, and the present invention has been completed.

That is, the gist of the present invention is as follows.
(1) A solder ball whose surface is coated with at least two kinds of organic acids having 10 to 25 carbon atoms and having a carboxyl group, wherein the carboxyl group of the organic acid is chelate coordinated with the surface of the solder ball A surface-treated solder ball characterized by
(2) the feature that (1) surface treatment of solder balls according to that infrared absorption peak attributable to a carboxyl group of the organic acid is ^{1650cm -1 ~1700cm} -1.
(3) The surface-treated solder ball according to (1) or (2), wherein the organic acid contains at least two kinds of organic acids having a difference in melting point between 5 ° C. and 45 ° C.
(4) The surface-treated solder ball according to (1) or (2), wherein the organic acid includes at least stearic acid and palmitic acid.
(5) The surface-treated solder ball according to (1) or (2), wherein the solder ball is a lead-free solder ball.
(6) The lead-free solder ball is at least one selected from a tin simple solder ball, or copper, silver, bismuth, zinc, antimony, indium, aluminum, magnesium, phosphorus, arsenic, bismuth, or germanium. The surface-treated solder ball according to (5), which is a tin alloy solder ball containing metal.
(7) a step of dissolving at least two kinds of organic acids having 10 to 25 carbon atoms and having a carboxyl group in an organic solvent;
Dispersing solder balls in the solution;
Removing the organic solvent from the solder balls;
Removing the organic solvent, heat treating the solder ball at 60 ° C. to 180 ° C., and chelating the carboxyl group of the organic acid to the surface of the solder ball;
A method for surface treatment of a solder ball, comprising:

  Since the surface-treated solder ball of the present invention has two or more kinds of organic acids chelated to the surface of the solder ball, the surface property changes with time such as vibration during transportation and blackening phenomenon under mechanical wear conditions. It has a very excellent storage stability, and also exhibits very high wettability when the solder ball is melted. As a result, according to the surface solder ball of the present invention, connection failure in semiconductor mounting can be reduced, and high yield can be achieved.

  As shown in FIG. 1, the organic acid is in a state in which two carboxyl groups are associated. Even if the surface of the solder ball is coated in an associated state, the polarization is neutralized by the association, so that it has an interaction with the surface only with a weak hydrogen bond. Therefore, in the said state, a C10-C25 carboxyl group-containing organic acid has stickiness on the surface of a solder ball, and cannot be used as it is. This is due to the fact that most of the C10-25 carboxyl group-containing organic acids have a low melting point of 100 ° C. or lower. Therefore, in patent documents 1-4, it does not use an organic acid, but uses it in the form of a salt with an amine and metal ion whose melting point becomes high.

  However, the inventors of the present invention can cover the surface of the solder ball without stickiness by releasing the association of the organic acid and chelating with the surface of the solder ball as shown in FIG. I found what I could do. The apparently high melting point of the chelate-coordinated organic acid is considered to be the cause of no stickiness. In addition, chelated organic acid blocks the supply of oxidants such as oxygen and moisture to the surface of the solder ball, so that surface oxidation can be suppressed, blackening phenomenon does not occur, and excellent storage stability is exhibited. .

  The chelated organic acid undergoes a series of processes of melting, evaporation, and decomposition from a solid when the solder ball is melted. At that time, the organic acid acts as a melt and vapor on the surface of the solder ball to block oxygen and suppress the oxidation of the surface of the solder ball. The organic acid also has an action of reducing oxides on the surface of the solder balls. The two actions improve the wettability of the solder ball.

  However, when there is only one kind of organic acid, the melting point, boiling point, decomposition temperature, etc. are each one point, so the temperature range of the action is small, and the substantial wettability is not improved. Therefore, if two or more types exist on the surface of the solder ball, the melting point, boiling point, and decomposition temperature of each differ, so that the oxygen blocking action and reducing action by the organic acid occur in a wide temperature range during the melting process of the solder ball, and wetting Will significantly improve the performance.

  The organic acid that exhibits the above effect has 10 to 25 carbon atoms including carbon of the carboxyl group. If the number of carbon atoms is less than 10, even if chelate coordination is performed on the surface of the solder ball, the apparent melting point is too low or the organic group is too small, so that the entry of oxygen, moisture, etc. cannot be sufficiently blocked, and the surface Insufficient suppression of oxidation. When the number of carbons exceeds 25, the boiling point becomes too high and remains as a liquid even when the solder is melted, or it takes a long time to decompose, eventually impairing the wettability.

Examples of organic acids include capric acid (decanoic acid, CH ₃ (CH ₂ ) ₈ -COOH), lauric acid (dodecanoic acid, CH ₃ (CH ₂ ) ₁₀ -COOH), myristic acid (tetradecanoic acid, CH ₃ (CH _{2) 12} -COOH), pentadecyl acid (pentadecanoic _{acid, CH 3 (CH 2) 13} -COOH), palmitic acid (hexadecanoic _{acid, CH 3 (CH 2) 14} -COOH), palmitoyl acid (9-hexadecenoic acid, CH ₃ (CH ₂ ) ₅ CH = CH (CH ₂ ) ₇ -COOH), margaric acid (heptadecanoic acid, CH ₃ (CH ₂ ) ₁₅ -COOH), stearic acid (octadecanoic acid, CH ₃ (CH ₂ ) ₁₆ -COOH ), Oleic acid (cis-9-octadecenoic acid, CH ₃ (CH ₂ ) ₇ CH═CH (CH ₂ ) ₇ —COOH), vaccenic acid (11-octadecenoic acid, CH ₃ (CH ₂ ) ₅ CH═CH ( CH ₂ ) ₉ -COOH), linoleic acid (cis, cis-9,12-octadecadienoic acid, CH ₃ (CH ₂ ) ₃ (CH ₂ CH═CH) ₂ (CH ₂ ) ₇ -COOH), (9 , 12,15) -Linolenic acid (9,12,15-octadecanetrienoic acid, CH ₃ (CH ₂ CH═CH) ₃ (CH ₂ ) ₇ -CO OH) tuberculostearic acid (nonadecanoic acid, CH ₃ (CH ₂ ) ₁₇ -COOH), arachidic acid (eicosanoic acid, CH ₃ (CH ₂ ) ₁₈ -COOH), arachidonic acid (5,8,11-icosatetraenoic acid, CH ₃ (CH ₂ ) ₃ (CH ₂ CH = CH) ₄ (CH ₂ ) ₃ -COOH), behenic acid (docosanoic acid, CH ₃ (CH ₂ ) ₂₀ -COOH), lignoceric acid (tetracosanoic acid, CH ₃ ( CH _{2) 22} -COOH), nervonic acid (cis-15-tetracosanoic _{acid, CH 3 (CH 2) 6} CH 2 CH = CH (CH 2) 13 -COOH), pentacosanoic acid _{(CH 3 (CH 2) 23} - COOH).

The above are saturated aliphatic and unsaturated aliphatic monocarboxylic acids, but may be organic acids having a plurality of carboxyl groups such as dicarboxylic acids and tricarboxylic acids. Examples thereof include decanedioic acid (1,8-octanedicarboxylic acid, HOOC (CH ₂ ) ₈ COOH), dodecanedioic acid (1,10-decanedicarboxylic acid, HOOC (CH ₂ ) ₁₀ COOH), and the like. Moreover, not only aliphatic carboxylic acid but aromatic carboxylic acid etc. may be sufficient. Examples of the aromatic carboxylic acid include hydroxydiphenylacetic acid ((CH ₅ ) ₂ C (OH) CO ₂ H), 3- (3-hydroxy-4-methoxyphenyl) propanoic acid (3,4-HO (CH ₃ O) C ₆ H ₃ CH ₂ CH ₂ CO ₂ H)) and the like.

  As described above, two or more kinds of organic acids are contained, but it is preferable that at least two kinds of organic acids having a difference in melting point of the organic acids of 5 ° C. to 45 ° C. are contained. If the difference between the melting points of the organic acids is less than 5 ° C., the wettability during solder melting may be insufficient. On the other hand, if the difference between the melting points of the organic acids exceeds 45 ° C., there may be a decrease in wettability due to the presence of the organic acid remaining at the time of melting the solder, or it will evaporate at a low temperature and exhibit the effect of improving wettability. There may be no. In order to maintain the continuity of the effective temperature of the effect at the time of melting the solder, the difference in melting point of the organic acid is more preferably 5 ° C to 30 ° C.

  As described above, the number of organic acids may be two or more, but if it exceeds ten, it may not be economical. It is more preferable that at least two kinds of the organic acids are included in a molar ratio of 1: 4 to 4: 1.

  Among organic acids, aliphatic carboxylic acids can be used more suitably. Aliphatic carboxylic acids having 15 to 20 carbon atoms are particularly preferred from the viewpoints of storage stability by blocking moisture and oxygen, and oxygen blocking action and reducing action near the solder ball surface during reflow. More preferably, it contains stearic acid having 18 carbon atoms (melting point: 70 ° C.) and palmitic acid having 16 carbon atoms (melting point: 62 ° C.). When the number of carbon atoms is above, the organic acid can be highly chelate-coordinated on the surface of the solder ball without bending the linear alkyl group portion and interfering with the chelate coordination of the adjacent organic acid. If the number of carbon atoms is less than the above, the density of the organic acid chelate-coordinated to the surface of the solder ball is high, but the ability to suppress surface oxidation may be low.

  In particular, wettability is further improved by mainly containing the two stearic acids and palmitic acid. That is, since the melting points of the two organic acids are 60 ° C. to 70 ° C., they volatilize and decompose more effectively when the solder ball is melted by reflow, and the oxygen blocking action and the reducing action near the ball surface by the organic acid are increased. Excellent wettability. Further, the melting point temperature difference between the two organic acids can continuously widen the temperature range with the wettability effect centered on the ball melting temperature by reflow.

  The molar ratio of stearic acid: palmitic acid is preferably in the range of 1: 4 to 4: 1. When the above range is exceeded, the effect of either one of the organic acids in the oxygen blocking action or reduction action near the ball surface due to the volatilization and decomposition of the organic acid is increased, and the temperature range at which the action can be exerted is substantially narrowed. There is a case. The molar ratio is more preferably in the range of 3: 4 to 4: 3.

  In the present invention, as described above, it is necessary that the carboxyl group of the organic acid is chelated with the surface of the solder ball. That is, in the chelate coordination of the present invention, as shown in FIG. 2, two positions of the carboxyl group are coordinated with the metal on the surface of the solder ball, or with the metal surface oxygen or the metal surface hydroxyl group. Although the organic acid is associated as shown in FIG. 1, the effect of the present invention cannot be obtained in the associated state as described above.

The chelate coordination of the carboxyl group can be confirmed by vibrational spectral methods such as infrared spectroscopy and Raman spectroscopy, nuclear magnetic resonance, ultraviolet photoelectron spectroscopy, or X-ray photoelectron spectroscopy. For example, in infrared spectroscopy or Raman spectroscopy, the chelate coordination of the carboxyl group can be confirmed from the change in the absorption peak based on the C═O stretching vibration of the carboxylic acid. Specifically, an associated carboxylic acid, that is, a carboxyl group that is not chelate-coordinated has an absorption peak at 1710 cm ⁻¹ or more, but when chelate is coordinated, it shifts to the low wavenumber side as described later. In the nuclear magnetic resonance method, the chelate coordination of the carboxyl group can be confirmed from the change in the chemical shift of C of the carboxyl group. In ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy, chelate coordination can be confirmed from changes in the C and O binding energy of the carboxyl group.

Infrared absorption peak attributable to a carboxyl group of an organic acid coated on the solder ball surface of the present invention is ^preferably in the range of 1650cm ^-1 ~1700cm -1. The associated carboxylic acid has an infrared absorption peak due to the carboxyl group at 1714 cm ⁻¹ , and when the association is released, the bond strength of the C—O bond increases, so that the high wave number side (high energy side) is 1760 cm. ^The peak shifts to ^-1 . On the other hand, in the case of a metal salt or amine salt, the counter cation strongly attracts electrons from the C—O bond, and as a result, the bond strength of the C—O bond decreases, so the low wavenumber side (low energy) is reduced to around 1600 cm ^−1. Shift to the side).

  Simply, it can be understood from the following. The stretching frequency ν of a diatomic molecule composed of atoms having mass numbers m and m ′ can be expressed by equation (1). C is the speed of light, and f is a force constant (coupling strength corresponding to the spring Hooke constant). The position of the infrared absorption band is related to the bond strength and the mass of the bonded atom. Focusing on the coupling strength, the stronger the coupling strength, the higher the absorption wave number of the vibration (infrared absorption peak), and the lower the coupling strength, the lower the wave number side.

In the present invention, since the solder ball surface and the carboxyl group as shown in FIG. 2 are chelate-coordinated, electrons are attracted from the C—O bond by the coordination bond, and the bond strength of the C—O bond is lowered. infrared absorption peak at ^{1650cm -1 ~1700cm} -1, such as described above is incoming. Therefore, it is preferable that it is in the above-mentioned wave number range from the viewpoint of storage stability and wettability of the solder ball. If it is less than 1650 cm ⁻¹ , the free salt as shown in FIG. 3 is formed, and since the chelate is not coordinated to the surface of the solder ball, the adhesion is weakened, so that good storage stability and wettability can be obtained. It will disappear. On the other hand, if it exceeds 1700 cm ⁻¹ , the carboxyl group remains in an associated state and is not chelate coordinated to the surface of the solder ball.

FIG. 4 shows an example of the typical absorption spectrum of the carboxyl group when stearic acid and palmitic acid are mixed at 1: 1. The absorption peak of a in FIG. 4 is due to the carboxyl group in an associated state that is not chelate coordinated as shown in FIG. 1, and is present in the vicinity of 1710 cm ⁻¹ . The b absorption peak in FIG. 4 is due to the chelate coordinated carboxyl group as shown in FIG. 2, and is present in the vicinity of 1660 cm ⁻¹ . The absorption peak of c in FIG. 4 is that in which the carboxyl group forms Sn and a metal salt, and exists in the vicinity of 1600 cm ⁻¹ .

  The solder balls used in the present invention are not particularly limited. For example, lead-based solder balls such as Sn—Pb, Sn—Pb—Ag, Sn—Ag, Sn—Ag—Cu, Sn—Bi Sn-Zn based lead-free solder balls and the like. In particular, for the lead-free solder balls, the coating of the present invention is more preferably used from the viewpoint of improving wettability. The lead-free solder balls are tin simple solder balls or tin containing one or more metals selected from copper, silver, bismuth, zinc, antimony, indium, aluminum, magnesium, phosphorus, arsenic, bismuth, or germanium. In the case of an alloy solder ball, the coating of the present invention can be more suitably applied.

  The size of the solder ball is not particularly limited, but the diameter is more preferably 10 μm to 1000 μm.

  In the present invention, the method for coating the surface of the solder ball by chelating the organic acid is not particularly limited. For example, the method of melting the organic acid and applying it to the solder ball, the organic acid under normal pressure or reduced pressure. Examples include a method of vaporizing and adhering to the solder ball surface, a method of dissolving an organic acid in an organic solvent, applying the solution onto the solder ball, and drying. Among these, a method of applying an organic solvent in which an organic acid is dissolved is more preferable.

  Specifically, two or more kinds of organic acids having 10 to 25 carbon atoms are dissolved in an organic solvent, and solder balls are dispersed in the solvent. The dispersion solvent is removed by filtration, evaporation, centrifugation, or the like, and the solder ball from which the solvent has been removed is heat-treated at 60 ° C. to 180 ° C. so that the carboxyl group of the organic acid is chelated to the surface of the solder ball. Perform solder ball surface treatment.

  When the heat treatment temperature is less than 60 ° C., the carboxyl group disassociates and does not chelate, so that stickiness remains. On the other hand, when the temperature exceeds 180 ° C., there is no such stickiness as mentioned above, but since the constituent metal ions such as tin liberated from the solder surface and the free salt shown in FIG. 3 are formed, the chelate coordination is not performed on the solder ball surface. Adhesive strength becomes weak, and good storage stability and wettability cannot be obtained. The heat treatment temperature is more preferably 90 ° C to 160 ° C, and further preferably 100 ° C to 150 ° C.

  The organic solvent used in the present invention is not particularly limited as long as it can dissolve the organic acid to be used. For example, alcohol such as methanol, ethanol, propanol, butanol, acetone, methyl ethyl ketone, ethyl acetate, toluene, xylene Etc. The organic solvent to be used may be the above-mentioned single solvent or a mixture of several solvents.

  Although the density | concentration of the organic acid in the organic solvent in this invention is not specifically limited, It is preferable to prepare by 0.002g / l (solvent)-20g / l (solvent). If it is less than 0.002 g / l, the amount of adhesion is small and sufficient effects may not be obtained. On the other hand, when the amount exceeds 20 g / l, the amount of adhesion increases, and a large amount of organic acid that is not chelate coordinated adheres to the surface of the solder ball, and stickiness may remain.

  The adhesion amount of the organic acid is not particularly limited. For example, if the solder ball is a fatty acid and has a diameter of 300 μm, it is preferably about 0.0001 g to 0.01 g for a 100 g ball. If it is less than 0.0001 g, the amount of adhesion is small and a sufficient effect may not be obtained. If the amount exceeds 0.01 g, the amount of adhesion increases, and a large amount of organic acid that is not chelate-coordinated to the surface of the solder ball may adhere and leave stickiness.

  The present invention will be described more specifically based on the following examples.

  Below, the Example and comparative example which performed the surface treatment of this invention, and the comparative example which does not surface-treat anything are shown.

  1 kg of solder balls having a diameter of 300 μm were prepared. In addition, Sn-3.0Ag-0.5Cu was used for the material of the ball.

  Next, 0.2 g each of stearic acid and palmitic acid was dissolved in 2 liters of acetone (in a molar ratio of 1.1: 1.0). The solder balls were put into the solution and stirred vigorously. Thereafter, the solvent was removed by filtration and dried at room temperature. Then, the dried product was taken out.

  Some samples were evaluated as they were as comparative examples in which the carboxyl group was not chelated (dry sample, Table 1). Some other samples were further heat-treated at 140 ° C. for 20 minutes to produce surface-treated solder balls in which carboxyl groups were chelated (Table 2).

  Furthermore, under the same conditions as described above, solder balls surface-treated using a salt of tin stearate and tin palmitate were prepared (Table 3).

The surfaces of the three types of surface-treated solder balls were analyzed by Raman spectroscopy, and the chelate coordination of the carboxyl group of the organic acid was confirmed. In the dried sample, the carboxyl group of the organic acid was not chelate coordinated and was the same as the carboxyl group associated with the raw materials stearic acid and palmitic acid. In the heat treatment at 140 ° C., it was confirmed that the carboxyl group of the organic acid was chelated. In the sample using a tin salt, it was confirmed that the organic acid formed a salt with Sn ⁴⁺ ions, and the carboxyl group was not chelated on the solder ball surface.

  Further, the surface-treated solder balls were mounted on a printed circuit board with 3025 copper electrodes having a diameter of 15 mm and a diameter of 130 μm without flux, and reflowed in the atmosphere at 250 ° C. for 40 seconds. And about the electrode board | substrate which mounted the said solder ball, the characteristic of the ball | bowl was evaluated by the number of drop | omission of a ball | bowl, ball height, and shear strength.

  The number of balls dropped out was the number of balls dropped after reflowing and washing. The shear strength was measured with a ball shear strength measuring instrument manufactured by Dage. The ball height and the shear strength were evaluated by an average value of 20 points. If the wettability between the electrode and the ball is good after reflow, the ball spreads further on the electrode, so the number of balls falling off is small and the height of the ball from the substrate is low (ideally 233 μm). When the test is performed, the better the wettability, the greater the shear strength.

  Ball dropout and shear tests were measured immediately after reflow. Further, the same evaluation was performed after 1 day, 7 days, and 1 month later.

  About blackening, it evaluated by whether the number g of balls was put into a small bottle and it blackened when shaken for 5 hours.

  Table 1, Table 2, Table 3, and Table 4 show the evaluation results of the three types of surface-treated solder balls and the untreated solder balls, respectively.

  Those in which the carboxyl group of the organic acid was coordinated with the chelate on the surface of the solder ball (Table 2) had no dropout for one month. There was no blackening. That is, it showed excellent wettability and storage stability. Similar results were obtained even when the alloy type of the solder balls was changed. The sample of Table 1 in which the carboxyl group of the organic acid was not chelate coordinated to the surface of the solder ball had stickiness in the applied organic acid, poor wettability, blackening was observed, and storage stability was low. The samples in Table 3 in which the metal ions of the solder balls and the organic acid were liberated by forming a salt were inferior in wettability, blackening was observed, and the storage stability was low. Furthermore, as shown in Table 4, all untreated solder balls dropped off on the seventh day. Blackening was also observed immediately after fabrication.

  The surface treatment of the solder balls was performed in the same manner as in Example 1 using organic acids having different carbon numbers and melting points. Conditions such as the heat treatment temperature shown in Table 5 are different from those in Example 1. The surface-treated solder balls were measured for infrared (IR) absorption peaks of carboxyl groups by the diffuse reflection method of infrared spectroscopy. The properties of the surface-treated solder balls were measured after 7 days in the same manner as in Example 1. The evaluation results are shown in Table 6.

Carbon atoms and two using organic acids 10-25, infrared absorption peak of a carboxyl ^group, a sample in a 1650cm ^-1 ~1700cm -1 showed good storage stability and wettability (No.2 -3 to 2-5, 2-8 to 2-13). Among them, Nos. 2-4, 2-9, and 2-10 showed better performance. Infrared absorption peak of a carboxyl ^group, the sample (No.2-1,2-2,2-6) that is outside the range of 1650cm ^-1 ~1700cm -1 is not sufficient storage stability and wettability is obtained It was. When one kind of organic acid was used (No. 2-7), sufficient wettability could not be obtained. Further, even when two kinds of organic acids having 10 to 25 oxygen numbers were not included (No. 2-14, 15), sufficient storage stability or sufficient wettability could not be obtained.

It is a schematic diagram which shows the structure (example of palmitic acid) with which the carboxylic group of organic acid is associating. It is a schematic diagram which shows the structure (example of palmitic acid) which the carboxyl group of the organic acid carried out the chelate coordination on the solder ball surface. It is a schematic diagram showing an organic acid salt liberated by forming a salt with a metal ion (for example, Sn ⁴⁺ ion) on the surface of a solder ball. It is an infrared absorption spectrum of a carboxyl group, and shows a: association state, b: coordination state, c: Sn salt formation state.

Claims (7)

A solder ball having a surface coated with at least two kinds of organic acids having 10 to 25 carbon atoms and having a carboxyl group, wherein the carboxyl group of the organic acid is chelate-coordinated with the surface of the solder ball A surface-treated solder ball characterized by that. 2. The surface-treated solder ball according to claim ¹ , wherein an infrared absorption peak due to a carboxyl group of the organic acid is 1650 cm ^{−1 to} 1700 cm ⁻¹ . The surface-treated solder ball according to claim 1, wherein the organic acid contains at least two kinds of organic acids having a difference in melting point between 5 ° C. and 45 ° C. The surface-treated solder ball according to claim 1, wherein the organic acid contains at least stearic acid and palmitic acid. The surface-treated solder ball according to claim 1, wherein the solder ball is a lead-free solder ball. The lead-free solder ball includes a tin simple solder ball or one or more metals selected from copper, silver, bismuth, zinc, antimony, indium, aluminum, magnesium, phosphorus, arsenic, bismuth, or germanium. 6. The surface-treated solder ball according to claim 5, wherein the surface-treated solder ball is a tin alloy solder ball. Dissolving at least two organic acids having 10 to 25 carbon atoms and having a carboxyl group in an organic solvent;
Dispersing solder balls in the solution;
Removing the organic solvent from the solder balls;
Removing the organic solvent, heat treating the solder ball at 60 ° C. to 180 ° C., and chelating the carboxyl group of the organic acid to the surface of the solder ball;
A method for treating a surface of a solder ball, comprising: