GOLD POWDER, PRODUCTION METHOD FOR GOLD POWDER, AND GOLD PASTE

Abstract

A gold powder comprising gold having a purity of 99.9% by mass or more and having an average particle size of 0.01 μm or more and 1.0 μm or less, a content of a chloride ion is 100 ppm or less, and a content of a cyanide ion is 10 ppm or more and 1000 ppm or less. A total of the content of a chloride ion and the content of a cyanide ion is preferably 110 ppm or more and 1000 ppm or less. The gold powder has improved adaptability to various processes including bonding or the like with a content of a chloride ion, that is, an impurity, optimized. A gold paste using this gold powder is suitably used in various uses for bonding such as die bonding of a semiconductor chip, sealing a semiconductor package, and forming an electrode/wire.

Claims

1. A gold powder comprising gold having a purity of 99.9% by mass or more and having an average particle size of 0.01 μm or more and 1.0 μm or less, wherein a content of a chloride ion is 100 ppm or less, and a content of a cyanide ion is 10 ppm or more and 1000 ppm or less.

2. The gold powder according to claim 1, wherein a total of the content of a chloride ion and the content of a cyanide ion is 110 ppm or more and 1000 ppm or less.

3. The gold powder according to claim 1, wherein the content of a cyanide ion is 100 ppm or more and 1000 ppm or less.

4. A production method for the gold powder defined in claim 1, comprising: a step of producing, by a wet reduction method, a gold powder comprising gold having a purity of 99.9% by mass or more and having an average particle size of 0.01 μm or more and 1.0 μm or less; and a step of reducing the content of a chloride ion by contacting the gold powder with a cyanide solution.

5. The production method for the gold powder according to claim 4, wherein a cyanide ion concentration in the cyanide solution is 0.01% by mass or more and 5% by mass or less.

6. A gold paste, comprising the gold powder defined in claim 1, and an organic solvent.

7. A method for bonding a pair of bonding members to each other, comprising: (a) a step of applying, to one bonding member, a gold paste comprising the gold powder defined in claim 1 and an organic solvent; and (b) a step of overlapping the one bonding member and the other bonding member on each other via the applied gold paste, and heating at least the gold paste at a temperature of 80° C. or more and 300° C. or less for bonding the pair of bonding members to each other.

8. The bonding method according to claim 7, comprising overlapping the one bonding member and the other bonding member on each other, and subsequently applying a pressure for bonding to the pair of bonding members in one direction or both directions under heating.

9. A method for bonding a pair of bonding members to each other, comprising: (a) a step of applying, to one bonding member, a gold paste comprising the gold powder defined in claim 1, and an organic solvent; (b) a step of sintering the gold paste at a temperature of 80 to 300° C. to obtain a metal powder sintered body; and (c) a step of overlapping the one bonding member on the other bonding member via the formed metal powder sintered body, and heating at least the metal powder sintered body and applying a pressure in one direction or both directions for bonding.

10. A method for bonding a base material holding a content thereon to a lid body for the base material, comprising: (a) a step of applying, to the base material or the lid body, a gold paste comprising the gold powder defined in claim 1 and an organic solvent; (b) a step of sintering the gold paste at a temperature of 80 to 300° C. to obtain a metal powder sintered body; and (c) a step of overlapping the base material on the lid body via the metal powder sintered body, and bonding the base material and the lid body to each other by applying a pressure in one direction or both directions under heating at least the metal powder sintered body.

11. An electrode or wire forming method for forming an electrode or a wire on a substrate, comprising: (a) a step of applying, to the substrate, a gold paste comprising the gold powder according to the claim 1, and an organic solvent; and (b) a step of sintering the gold paste at a temperature of 80 to 300° C. to form an electrode or a wire containing a metal powder sintered body.

12. The gold powder according to claim 2, wherein the content of a cyanide ion is 100 ppm or more and 1000 ppm or less.

13. A production method for the gold powder defined in claim 2, comprising: a step of producing, by a wet reduction method, a gold powder comprising gold having a purity of 99.9% by mass or more and having an average particle size of 0.01 μm or more and 1.0 μm or less; and a step of reducing the content of a chloride ion by contacting the gold powder with a cyanide solution.

14. A production method for the gold powder defined in claim 3, comprising: a step of producing, by a wet reduction method, a gold powder comprising gold having a purity of 99.9% by mass or more and having an average particle size of 0.01 μm or more and 1.0 μm or less; and a step of reducing the content of a chloride ion by contacting the gold powder with a cyanide solution.

15. A gold paste, comprising the gold powder defined in claim 2, and an organic solvent.

16. A gold paste, comprising the gold powder defined in claim 3, and an organic solvent.

17. A method for bonding a pair of bonding members to each other, comprising: (a) a step of applying, to one bonding member, a gold paste comprising the gold powder defined in claim 2 and an organic solvent; and (b) a step of overlapping the one bonding member and the other bonding member on each other via the applied gold paste, and heating at least the gold paste at a temperature of 80° C. or more and 300° C. or less for bonding the pair of bonding members to each other.

18. A method for bonding a pair of bonding members to each other, comprising: (a) a step of applying, to one bonding member, a gold paste comprising the gold powder defined in claim 3 and an organic solvent; and (b) a step of overlapping the one bonding member and the other bonding member on each other via the applied gold paste, and heating at least the gold paste at a temperature of 80° C. or more and 300° C. or less for bonding the pair of bonding members to each other.

19. A method for bonding a pair of bonding members to each other, comprising: (a) a step of applying, to one bonding member, a gold paste comprising the gold powder defined in claim 2, and an organic solvent; (b) a step of sintering the gold paste at a temperature of 80 to 300° C. to obtain a metal powder sintered body; and (c) a step of overlapping the one bonding member on the other bonding member via the formed metal powder sintered body, and heating at least the metal powder sintered body and applying a pressure in one direction or both directions for bonding.

20. A method for bonding a pair of bonding members to each other, comprising: (a) a step of applying, to one bonding member, a gold paste comprising the gold powder defined in claim 3, and an organic solvent; (b) a step of sintering the gold paste at a temperature of 80 to 300° C. to obtain a metal powder sintered body; and (c) a step of overlapping the one bonding member on the other bonding member via the formed metal powder sintered body, and heating at least the metal powder sintered body and applying a pressure in one direction or both directions for bonding.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0099] First Embodiment: An embodiment of the present invention will now be described. In the present embodiment, a gold powder in which contents of a chloride ion and a cyanide ion were respectively adjusted was produced. Then, an agglomerating property of each gold powder was studied to examine suitable contents of the impurities. For producing a gold powder of the present embodiment, a gold powder was produced by a wet reduction method, and the resultant gold powder was treated with a cyanide solution.

[0100] [Production of Gold Powder]

[0101] A beaker was charged with 1 L of pure water, and was heated on a hot plate up to 81° C. When the pure water was heated to 81° C., 3 g of alkylamine acetic acid was added thereto, and the resultant was stirred with the temperature kept until the solution became clear. After the stirring, 0.2 g of hydroxylammonium chloride was added to the resultant solution, followed by stirring for 1 minute. Then, a chloroauric acid solution (corresponding to 0.04 g of gold) was added thereto, the resultant was stirred for 1 hour with the solution temperature kept at 80±2° C., and thus, a violet transparent gold colloidal solution was obtained. A gold nuclear fine particle thus obtained was observed with a transmission electron microscope, resulting in finding that an average particle size was within a range of 10 nm to 50 nm.

[0102] To the gold colloidal solution, 2 L of a chloroauric acid solution was added for adjusting the particle size. This chloroauric acid solution was obtained by dissolving, in aqua regia, 200 g of gold bullion having a purity of 99.99% by mass or more. After adding the chloroauric acid solution, 200 g of hydroxylammonium chloride used as a reducing agent was added thereto, the resultant was stirred for 0.5 hours with the solution temperature kept at 80±2° C., and thus, 200 g of a gold powder was produced. The gold powder was filtered out, immersed in 1 L of isopropyl alcohol (IPA), and washed by stirring for 30 minutes.

[0103] The high purity gold powder (having a purity of 99.99% by mass) produced by the above-described wet reduction method was treated with a cyanide solution. 200 g of the washed gold powder was transferred to a cyanide solution obtained by dissolving 0.5 to 5 g of potassium cyanide in 1 L of pure water, the resultant was stirred at room temperature for 1 minute to 30 minutes, and thereafter, the gold powder was caused to settle, and a supernatant was collected. Thus, a chloride ion was removed from the gold powder, and a cyanide ion was imparted thereto.

[0104] After the treatment with the cyanide solution, the resultant gold powder was washed by repeating immersion in 1 L of IPA and stirring several times, and thus, the gold powder of the present embodiment was produced. The gold powder thus produced was observed with a scanning electron microscope (SEM) (5000×) to measure an average particle size. The average particle size of the gold powder of the present embodiment was 0.3 μm.

[0105] In the present embodiment, in the treatment with the cyanide solution, a cyanide concentration in the solution and a stirring time were adjusted to produce a plurality of types of gold powders different in a chloride ion concentration and the content of a cyanide ion. Besides, some of the gold powders thus produced were used for producing gold powders in which the content of a cyanide ion was adjusted by increasing the number of times of performing the washing after the treatment with the cyanide solution.

[0106] [Measurement of Chloride Ion Content]

[0107] Each of the gold powders of the present embodiment thus produced was measured for a chloride ion content. The measurement of the chloride ion content was performed by a heat desorption method. The gold powder was collected and weighed to be heated to 900° C. in a combustion tube, and a gas thus generated was caused to be absorbed by an adsorbing liquid (a mixture of 25 mL of a hydrogen peroxide solution and 15 mL of ultrapure water). The resultant absorption liquid was analyzed with an ion chromatograph to measure a chlorine amount (4), and a chorine amount (μg/g (ppm)) per unit mass of the collected gold powder (g) was defined as a chloride ion content in the gold powder. A minimum limit of determination is 10 μg/g. The measurement of the chloride ion content was performed on a gold powder prior to the treatment with the cyanide solution in the production process (washed gold powder obtained immediately after wet reduction), and on a gold powder obtained after the production (gold powder obtained after the final washing). Besides, the measurement was also performed on a gold powder not subjected to the treatment with the cyanide solution.

[0108] [Measurement of Cyanide Ion Content]

[0109] Each of the gold powders obtained after the treatment with the cyanide solution produced as described above was measured for a cyanide ion content. The measurement of the cyanide ion content was also performed by the heat desorption method. The operation was substantially the same as that described above, but for a cyanide ion, heating was performed at a temperature of 300° C. for 4 hours to generate a gas. Besides, quantitative determination of a cyanide ion in an absorption liquid was measured by ion chromatography-post column absorptiometry. Then, based on a cyanide amount (μg) in the absorption liquid, a cyanide amount (μg/g (ppm)) per unit mass of the collected gold powder (g) was defined as a cyanide ion content in the gold powder. A minimum limit of determination is 5 μg/g.

[0110] Particle sizes, the chloride ion contents, and the cyanide ion contents of the various gold powders produced in the present embodiment were as follows:

TABLE-US-00001 TABLE 1 Treatment with Chloride Ion Cyanide Ion No. Cyanide Compound (ppm) (ppm) 1 not performed 200 0 2 100 0 3 performed 98 6 4 90 20 5 55 105 6 20 500 7 10 800 8 18 200 9 12 100 * Gold Powder No. 1 is a gold powder produced by performing the washing only once after the wet reduction. * Gold Powder No. 2 is a gold powder obtained by washing Gold Powder No. 1 further twice to reduce the chloride ion content. * Gold Powders Nos. 3 to 7 are gold powders in which the chloride ion and cyanide ion contents were adjusted by adjusting a concentration of the cyanide solution and the stirring time. * Gold Powders Nos. 8 and 9 are gold powders obtained by washing Gold Powder No. 6 further twice or three times to adjust mainly the cyanide ion content.

[0111] Next, each of the gold powders thus produced was evaluated for the agglomerating property. In this examination, 10 g of the gold powder was put in 100 mL of IPA, and ultrasonic vibration was applied with an ultrasonic cleaner to a beaker holding the resultant solution to obtain a homogeneous suspension. Here, after confirming that a reddish brown suspension was obtained, and that the suspension was homogeneous, the ultrasonic cleaner was stopped. Thus, the gold powder settled, and the color was faded from an upper layer of the suspension. In the present embodiment, a time until a settled deposit was piled up to a 25 mL marked line of the beaker (which time is designated as the settle time) was measured. A gold powder having a high agglomerating property has a large apparent particle size because of agglomeration, and hence settles faster, and the settle time is shorter. Therefore, the settle time was used as an index of the agglomerating property. Measurement results of the settle time are shown in Table 2.

TABLE-US-00002 TABLE 2 Chloride Ion Cyanide Ion Settling Time No. (ppm) (ppm) (min) 1 200 0 80 2 100 0 40 3 98 6 45 4 90 20 75 5 55 105 105 6 20 500 115 7 10 800 120 or more 8 18 200 110 9 12 100 90

[0112] In the gold powder (No. 1) washed once after the production by the wet reduction method, the chloride ion content was 200 ppm. This gold powder was a gold powder in which the settle time was long and the agglomerating property was low owing to the high chloride ion content. It was confirmed, in the gold powder (No. 2) obtained by washing the former gold powder to reduce the chloride ion content to 100 ppm or less, that the settling speed was largely shorter, and that the agglomerating property was increased. In all the gold powders No. 3 to No. 9 in which a cyanide ion was added with the chloride ion content reduced, the settling speed was longer than that of the gold powder No. 2, and thus, the effect of inhibiting the agglomerating property derived from a cyanide ion was found. In the gold powder (No. 3) in which the cyanide ion content was less than 10 ppm, however, the settling speed was not largely different from that of the gold powder No. 2, and it is presumed that a cyanide ion should be added in an amount of about 10 ppm. Besides, it is presumed that the gold powders in each of which a total of the chloride ion content and the cyanide ion content is 110 ppm or more (No. 4 to No. 9) are particularly effective gold powders.

[0113] Second Embodiment (Bonding Method): In this embodiment, the gold powders produced in the first embodiment were used to produce a gold paste. Then, a demonstration test of bonding process for an electronic member using the gold paste thus produced was performed.

[0114] For obtaining the gold pastes, three gold powders (purity: 99.99% by weight, average particle size: 0.3 μm) of the gold powders Nos. 1, 4 and 6 of the first embodiment were used. Each of these gold powders was mixed with an organic solvent, an ester alcohol (2,2,4-trimethyl-3-hydroxypentaisobutyrate (C.sub.12H.sub.24O.sub.3)) to prepare a gold paste. A blending ratio of the organic solvent was 5% by weight.

[0115] In the present embodiment, a Ni plate was bonded to a semiconductor (Si) chip as an electronic member. On the semiconductor chip, a film of Au (0.3 μm)/Pt (0.1 μm)/Ti (0.05 μm) was formed by a deposition method. Besides, a film of Au (1 μm)/Pd (1 μm) was formed on the Ni substrate by a plating method.

[0116] First, the gold paste was applied to the semiconductor chip (application area: 4 mm.sup.2). After the application, the Ni plate was placed on the semiconductor chip, and then, bonding was performed by heating the resultant to 200° C. and keeping the resultant for 20 minutes with no pressure applied.

[0117] The above-described bonding step was performed using each of the various gold powders (gold pastes), and soundness of a bonding portion of each semiconductor chip was evaluated. In this evaluation test, the semiconductor chip was heated in vacuum to 200° C., and air released from a heating furnace was contacted with an absorption liquid to check whether or not chlorine or cyanogen was detected. Detection of chlorine or cyanogen means that an impurity gas was released from the bonding portion.

[0118] As a result of this test, it was confirmed that an impurity gas was not released from the bonding portions formed from the gold powder No. 4 (chloride ion content: 90 ppm, cyanide ion content: 20 ppm) and the gold powder No. 6 (chloride ion content: 20 ppm, cyanide ion content: 500 ppm). On the other hand, it was confirmed that a very small amount of chlorine was detected in using the gold powder No. 1 (chloride ion content: 200 ppm, cyanide ion content: 0 ppm). A bonding temperature employed in the bonding test of the present embodiment was set to a relatively low temperature of 200° C. In using the gold powder No. 1, it is presumed that a chloride ion remained in the bonding portion in employing this bonding temperature. On the other hand, in using the gold powders No. 4 and No. 6, the chloride ion content was reduced, and hence a chloride ion was unlikely to remain. In using the gold powder No. 6, although the cyanide ion content is high, it is presumed that many cyanide ions had been released during drying and sintering process performed after the application of the gold paste, and hence a cyanide ion little affected the bonding step.

[0119] Third Embodiment (Sealing Method): In this embodiment, a gold paste was produced from a gold powder produced by changing production conditions for the gold powder (No. 6) produced in the first embodiment. Then, the gold paste thus produced was used to hermetically seal a package for an electronic component.

[0120] Gold powders used here are three gold powders, that is, the gold powder No. 6 of the first embodiment, and two gold powders having different particle sizes produced by partly changing the production conditions employed in the first embodiment. The gold powder produced in the present embodiment was produced by changing, in the wet reduction method of the first embodiment, the amount of the chloroauric acid solution to be added to a gold colloidal solution of a nuclear ultrafine particle to 1/10 or 10 times. Then, the treatment with the cyanide solution was performed under the same conditions as those for the gold powder No. 6. These gold powders (No. 10 and No. 11) respectively had average particle sizes of 0.1 μm (No. 10) and 0.5 μm (No. 11). These gold powders were measured for the chloride ion content and the cyanide ion content in the same manner as in the first embodiment (and the results will be described later).

[0121] In the present embodiment, a gold paste was produced by employing the same solvent and conditions as those employed in the second embodiment to attempt hermetical sealing of a package. This package was a package used in a piezoelectric device package or the like, and included a base member of alumina ceramics (dimension: 2.5 mm×2.0 mm), and a cap member (cover member) of kovar. On both of these members, a Au (1 μm)/Pd (1 μm)/Ni (1 μm) plating film was formed.

[0122] In a sealing operation, the gold paste was applied, by a photoresist method, to a frame-shaped region with a width of 20 μm along the four sides of the cap member. After applying the gold paste, a resist was removed, the cap member was heated in an electric furnace at 230° C. for 30 minutes to sinter the gold paste, and thus, a metal powder sintered body to be used as a sealant was formed.

[0123] Next, the cap member having been subjected to the sintering step was placed on and bonded to the base member. The bonding of the cap member was performed by placing the package on a heat stage placed in a vacuum atmosphere (1×10.sup.−1 Pa) with the package kept at a set bonding temperature (200° C.) through heat transfer from the stage, and applying a load of 10 N (100 MPa) through the cap member. In this sealing step, a heating and pressure applying time was 10 minutes.

[0124] After the sealing step, the package was subjected to a helium leak test (bell jar method) to check soundness of a sealing portion. In this evaluation, a helium leak rate of 10.sup.−9 Pa.Math.m.sup.3/s or less was determined as acceptable. Results of the test are shown in Table 3.

TABLE-US-00003 TABLE 3 Gold Powder Particle Chloride Cyanide Sealing Test Result Size Ion Ion Leak Rate No. (μm) (ppm) (ppm) (Pa .Math. m.sup.3/s) Determination 6 0.3 20 500 10.sup.−11-10.sup.−12 Acceptable 10 0.1 15 400 10.sup.−11-10.sup.−12 Acceptable 11 0.5 30 550 10.sup.−11-10.sup.−12 Acceptable

[0125] It was confirmed, based on Table 3, that the gold powders used in the present embodiment are useful for package sealing. It was found that although the cyanide ion content is relatively high, the cyanide ion content does not affect the gold powders of the present embodiment. Even when the bonding temperature in sealing is 200° C., the gold powder of the present embodiment can form an effective sealing portion.

INDUSTRIAL APPLICABILITY

[0126] A gold powder of the present invention is inhibited from agglomerating when formed into a paste with a harmful influence derived from a chloride ion reduced. In the present invention, an action, like that of a protective agent, of an impurity contained in a gold powder is recognized, and a cyanide ion is specified as a suitable impurity, and a suitable content thereof is set. The gold powder of the present invention is applicable to low-temperature packaging, and is useful for uses for bonding, sealing, and forming an electrode/wire in various applications to electronic components, semiconductor devices, power devices, MEMSs and the like.