JP6017726B2 - Reduced electroless gold plating solution and electroless gold plating method using the plating solution - Google Patents

Description

  The invention according to the present application relates to an electroless gold plating solution, an electroless gold plating method using the electroless gold plating solution, and a plated product plated by the electroless gold plating method. More specifically, the present invention relates to a reduction-type electroless gold plating technique that enables direct plating on the surface of an object to be plated.

  In recent years, demands for higher functionality and multi-functionality of electronic devices are increasing, and printed wiring boards used in these electronic devices are required to be lighter and thinner. In order to cope with this miniaturization and miniaturization, circuit patterns have been miniaturized, and advanced packaging technology is required with the miniaturization of the circuit patterns. In general, in the field of printed wiring boards, a technique using solder or wire bonding has been established as a technique for joining mounting parts and terminal parts.

  For the purpose of ensuring the connection reliability of bonding using solder or wire bonding, a plating process is performed as a surface treatment of the circuit pads on the printed wiring board and the wiring pads that are the terminal portions. As the plating process, there is a technique of sequentially performing nickel plating, palladium plating, and gold plating performed on a circuit pattern formed of a metal such as copper having low electrical resistance. The nickel plating film prevents erosion of the copper circuit by solder, and the palladium plating film prevents nickel constituting the nickel plating film from diffusing into the gold plating film. The gold plating film is formed in order to obtain good solder wettability while realizing low electrical resistance.

  As conventional techniques of the plating technique described above, for example, there are Patent Documents 1 to 3 shown below. The electroless gold plating method described in Patent Document 1 is a method in which a gold plating film is formed on an nickel by using an electroless gold plating solution containing a reducing agent. A plating film is formed.

  Further, in the electroless gold plating method described in Patent Document 2, an electroless nickel plating film is formed on a surface to be plated of an electronic component via a catalyst, and the electroless palladium plating film is formed on the electroless nickel plating film. Is formed, and further, an electroless gold plating film is formed on the electroless palladium plating film, the electroless gold plating film comprising a water-soluble gold compound, a complexing agent, The electroless gold plating film is formed by first electroless gold plating using an electroless gold plating bath containing formaldehyde and / or formaldehyde bisulfite adduct and a specific amine compound.

  Furthermore, the reduced deposition type electroless gold plating solution for palladium film described in Patent Document 3 is an electroless gold plating solution that can form a gold plating film directly on the palladium film, and includes a water-soluble gold compound and a reducing agent. And at least one compound selected from the group consisting of formaldehyde bisulfite, longalite and hydrazine as a reducing agent.

JP 05-222541 A JP 2008-266668 A JP 2008-174774 A

  However, in the electroless gold plating method of Patent Document 1, the displacement gold plating film is formed by depositing gold using a difference in oxidation-reduction potential between nickel as a base and gold ions in the plating bath. Therefore, there is a problem that nickel is diffused into the gold plating film because gold dissolves the base nickel and corrodes the base nickel. When nickel diffuses into the gold plating film, there is a problem that the gold-gold bonding strength of wire bonding is lowered. In order to prevent the inconvenience, in Patent Document 1, an electroless gold plating film is formed on a replacement gold plating film, and the gold film thickness is increased, thereby suppressing a decrease in wire bonding properties. However, since the technique requires the formation of a displacement gold plating film, there is a problem that the cost increases and productivity is poor.

  Moreover, when the electroless gold plating method described in Patent Document 2 described above or the reduced deposition type electroless gold plating solution for palladium film described in Patent Document 3 is used, corrosion of nickel as a base metal is suppressed. However, since the electroless gold plating bath contains highly toxic formaldehyde or formaldehyde bisulfite adduct, it is difficult to ensure safety in the plating process.

  Therefore, in the market, there is an increasing demand for an electroless gold plating solution that can suppress corrosion of the base metal and achieve good wire bonding properties and does not contain harmful substances.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research, and as a result, have come to provide the following electroless gold plating solution, electroless gold plating method and plated product.

  The reduced electroless gold plating solution according to the present invention is used for forming an electroless gold plating film on the surface of an object to be plated on which copper, palladium, gold, or nickel is present, and is water-soluble. Including a gold compound, citric acid or citrate, ethylenediaminetetraacetic acid or ethylenediaminetetraacetate, hexamethylenetetramine, and a chain polyamine containing an alkyl group having 3 or more carbon atoms and 3 or more amino groups It is characterized by that.

  The reducing electroless gold plating solution according to the present invention preferably has a pH of 7.0 to pH 9.0.

  In the reduced electroless gold plating solution according to the present invention, the chain polyamine is 3,3′-diamino-N-methyldipropylamine or N, N′-bis (3-aminopropyl) ethylenediamine. It is preferable.

  The reduced electroless gold plating solution according to the present invention preferably further contains a thallium compound as a precipitation accelerator.

  The electroless gold plating method according to the present invention uses an electroless gold plating film on the surface of an object to be plated on which copper, palladium, gold, or nickel is present, using the above-described reduced electroless gold plating solution. It is characterized by forming.

  Moreover, in the electroless gold plating method according to the present invention, the surface of the object to be plated preferably includes an electroless palladium plating film formed on the surface of the electroless nickel plating film.

  The reduced electroless gold plating solution of the present invention comprises a water-soluble gold compound, citric acid or citrate, ethylenediaminetetraacetic acid or ethylenediaminetetraacetate, hexamethylenetetramine, an alkyl group having 3 or more carbon atoms and 3 By including a chain polyamine containing one or more amino groups, it becomes easy to thicken the gold plating film on the surface of the object to be plated.

  Further, even when a nickel plating film / palladium plating film / gold plating film provided at an electrical connection site is formed using the reduced electroless gold plating solution of the present invention, the film thickness of the palladium plating film is reduced. The gold plating film can be rapidly formed on the surface of the palladium plating film without being affected. Furthermore, according to the reduced electroless gold plating solution of the present invention, even if the electroless gold plating film is formed on the surface of the electroless palladium plating film formed on the surface of the electroless nickel plating film, the replacement is performed. Compared with the case of forming a gold plating film, the elution of nickel can be remarkably suppressed, and the diffusion of nickel into the gold plating film can be prevented. Therefore, according to the reduced electroless gold plating solution of the present invention, it is possible to provide a gold plating film capable of realizing high bonding reliability of wire bonding.

  Furthermore, the reduced electroless gold plating solution of the present invention has a higher solution stability than conventional electroless gold plating solutions and does not contain toxic formaldehyde or formaldehyde bisulfite adducts. It is easy to ensure safety in work.

  In addition, in the reduced electroless gold plating solution of the present invention, the gold precipitation reaction occurs only on the surface of gold, palladium, nickel, copper, etc., which can be a catalyst nucleus, and does not occur in a portion without the catalyst nucleus. Good selective precipitation. Therefore, it is advantageous in that the formation of a gold plating film on a portion where no gold deposition is necessary can be avoided and the raw material can be saved.

It is a graph which shows the relationship between the plating time of the reduction | restoration type electroless gold plating film of the implementation sample group 1A, and a plating film thickness. It is a graph which shows the relationship between the plating time of the reduction type electroless gold plating film of Example 2, and a plating film thickness. It is a figure which shows the relationship between the film thickness of the foundation | substrate palladium plating film at the time of using the electroless gold plating solution of Example 1 and Comparative Example 1, and the deposition rate of a gold plating film. It is an electron micrograph (x10000 and x30000) of the reduction type electroless gold plating film of execution sample 1A-2. It is an electron micrograph (x30000) of the reduced electroless gold plating film of Example 2-2 and Comparative Example 2. It is an electron micrograph (x5000) of the nickel plating film surface after peeling a reduction type electroless gold plating film and an electroless palladium plating film from a plating film of execution sample 1A-2. It is an electron micrograph (x3000) of the nickel plating film surface after peeling a reduction type electroless gold plating film from a plating film of example sample 2-2 and comparative example 2. It is a cross-sectional observation photograph (x30000) of the reduction type electroless gold plating film of execution sample 1A-6. It is an electron micrograph (x500) of the edge part and center part of the plating product which formed the plating film on the conditions similar to execution sample 1A-6. It is a figure which shows the relationship of the nickel elution amount in the gold plating solution at the time of using the electroless gold plating solution of Example 1 and Comparative Example 1. FIG. It is a figure which shows the variation in the film thickness of the electroless gold plating film of Example 2 and Comparative Example 2. It is a figure which shows the wire bonding characteristic of the electroless gold plating film of Example 2 and Comparative Example 2.

  Hereinafter, embodiments of the reduced electroless gold plating solution according to the present invention, the electroless gold plating method using the plating solution, and the plated product treated by the method will be described.

1. Reduced electroless gold plating solution according to the present invention The reduced electroless gold plating solution according to the present invention is used for forming an electroless gold plating film on the surface of an object to be plated. And "citric acid or citrate", "ethylenediaminetetraacetic acid or ethylenediaminetetraacetate", "hexamethylenetetramine", and a chain containing an alkyl group having 3 or more carbon atoms and 3 or more amino groups Polyamine ". Hereinafter, each component will be described.

(1) Water-soluble gold compound If the water-soluble gold compound used in the reduced electroless gold plating solution according to the present invention is soluble in the plating solution and can obtain a predetermined concentration, a cyanic gold salt Any water-soluble gold compound of non-cyanide gold salts can be used. Specific examples of water-soluble gold compounds of cyanide gold salts include potassium gold cyanide, sodium gold cyanide, ammonium gold cyanide and the like. Specific examples of water-soluble gold compounds of non-cyanide gold salts include chloroaurate, gold sulfite, and gold thiosulfate. Among these, potassium gold cyanide is particularly preferable. Moreover, you may use a water-soluble gold compound individually by 1 type or in combination of 2 or more types. In addition, a water-soluble gold compound is not limited to the gold compound illustrated here.

  The concentration of the water-soluble gold compound in the reduced electroless gold plating solution according to the present invention is preferably 0.0025 mol / L to 0.0075 mol / L. This is because when the concentration of the water-soluble gold compound is less than 0.0025 mol / L, the deposition rate of the gold plating film is slow and it is difficult to obtain a gold plating film having a desired film thickness. This is because if the concentration of the water-soluble gold compound exceeds 0.0075 mol / L, the stability of the plating solution may be lowered, and it is economically disadvantageous.

(2) Citric acid or citrate The reduced electroless gold plating solution according to the present invention contains citric acid or citrate. These citric acids or citrates are used as complexing agents capable of complexing with gold ions. The concentration of citric acid or citrate in the reduced electroless gold plating solution according to the present invention is preferably 0.05 mol / L to 0.15 mol / L. If the concentration of the citric acid or citrate used as a complexing agent is less than 0.05 mol / L, gold is deposited in the plating solution, resulting in poor solution stability, exceeding 0.15 mol / L. In this case, complex formation proceeds excessively, the gold deposition rate decreases, and a gold plating film having a desired film thickness is difficult to obtain.

(3) Ethylenediaminetetraacetic acid (EDTA) or ethylenediaminetetraacetate The reduced electroless gold plating solution according to the present invention contains ethylenediaminetetraacetic acid (EDTA) or ethylenediaminetetraacetate. This ethylenediaminetetraacetic acid or ethylenediaminetetraacetate is a complexing agent used in combination with the citric acid or citrate described above. The concentration of ethylenediaminetetraacetic acid or ethylenediaminetetraacetate in the reduced electroless gold plating solution according to the present invention is preferably 0.03 mol / L to 0.1 mol / L. This is because if the concentration of ethylenediaminetetraacetic acid or ethylenediaminetetraacetate used as a complexing agent is less than 0.03 mol / L, gold is deposited in the plating solution, resulting in poor solution stability. In the case of exceeding, complex formation proceeds excessively, the gold deposition rate decreases, and it is difficult to obtain a gold plating film having a desired film thickness.

(4) Hexamethylenetetramine The reduced electroless gold plating solution according to the present invention contains hexamethylenetetramine. The hexamethylenetetramine is used as a reducing agent that reduces gold ions in the plating solution and deposits gold on the surface of the object to be plated.

  The concentration of hexamethylenetetramine in the reduced electroless gold plating solution according to the present invention is preferably 0.003 mol / L to 0.009 mol / L. When the concentration of hexamethylenetetramine is less than 0.003 mol / L, the deposition rate of the gold plating film is slow, and it is difficult to obtain a gold plating film with a desired film thickness. When the concentration exceeds 0.009 mol / L, the reduction reaction rapidly occurs. This is because the gold salt in the plating solution may precipitate abnormally, resulting in poor solution stability and economical disadvantage.

(5) Chain polyamine The reducing electroless gold plating solution according to the present invention contains a chain polyamine containing an alkyl group having 3 or more carbon atoms and three or more amino groups. The chain polyamine is an amine compound that acts as a reduction auxiliary agent that assists the reduction of gold ions in the plating solution. Specifically, 3,3′-diamino-N-methyldipropylamine, N, N′-bis (3-aminopropyl) ethylenediamine or the like can be used as the chain polyamine. This is because the obtained plating film performance and economic efficiency are particularly preferable.

  The concentration of the chain polyamine in the reduced electroless gold plating solution according to the present invention is preferably 0.02 mol / L to 0.06 mol / L. By setting the concentration of the chain polyamine in the range of 0.02 mol / L to 0.06 mol / L, it is possible to maintain a high deposition rate without affecting the film thickness of the underlying metal film. Further, the throwing power of the gold plating film can be improved, and the gold plating film can be thickened by 0.2 μm or more. Furthermore, the solution stability can be remarkably increased.

(6) Other components The reduced electroless gold plating solution according to the present invention includes the above-described water-soluble gold compound, citric acid or citrate, ethylenediaminetetraacetic acid or ethylenediaminetetraacetate, hexamethylenetetramine, In addition to a chain polyamine containing an alkyl group having 3 or more carbon atoms and three or more amino groups, a precipitation accelerator may be contained. Examples of the precipitation accelerator used here include thallium compounds and lead compounds. It is preferable to use a thallium compound from the viewpoint of increasing the thickness of the resulting gold plating film.

  The concentration of the thallium compound as a deposition accelerator in the reduced electroless gold plating solution according to the present invention is preferably 1 mg / L to 10 mg / L. If the concentration of the thallium compound as the precipitation accelerator is less than 1 mg / L, it is difficult to increase the thickness of the gold plating film. On the other hand, if the concentration of the thallium compound as the precipitation accelerator exceeds 10 mg / L, it is not economical because a thicker film cannot be formed.

  The reduced electroless gold plating solution according to the present invention can contain additives such as a pH adjuster, an antioxidant, a surfactant, and a brightener in addition to the essential components described above.

  Although there is no restriction | limiting in particular as a pH adjuster, Potassium hydroxide, sodium hydroxide, ammonia aqueous solution, a sulfuric acid, phosphoric acid etc. are mentioned. The reduced electroless gold plating solution according to the present invention is preferably maintained at pH 7.0 to pH 9.0 by using a pH adjuster. When the pH of the reduced electroless gold plating solution is below 7.0, the plating solution is easily decomposed. When the pH is above 9.0, the plating solution is too stable, and the deposition rate of plating is slowed down. This is because it takes a lot of time to increase the thickness of the gold plating film. Furthermore, by adjusting the pH condition to 7.0 to 9.0, it is possible to perform a plating treatment of an object to be plated made of a material weak to alkali. Moreover, well-known things can be used as additives, such as antioxidant, surfactant, and a brightener.

(7) Plating conditions Although the gold plating conditions using the reduced electroless gold plating solution according to the present invention are not particularly limited, the liquid temperature is preferably 40 ° C to 90 ° C, and particularly preferably 75 ° C to 85 ° C. . The plating time is not particularly limited, but 1 minute to 2 hours is preferable, and 2 minutes to 1 hour is particularly preferable.

  As described above, the reduced electroless gold plating solution according to the present invention comprises a water-soluble gold compound, citric acid or citrate, ethylenediaminetetraacetic acid or ethylenediaminetetraacetate, hexamethylenetetramine, and 3 carbon atoms. By using the above-mentioned alkyl group and a chain polyamine containing three or more amino groups as essential components, it becomes easy to thicken the gold plating film on the surface of the object to be plated by the electroless plating method.

  In addition, even when a nickel plating film / palladium plating film / gold plating film provided at an electrical connection site is formed, the film thickness of the palladium plating film can be obtained by using the reduced electroless gold plating solution according to the present invention. The gold plating film can be rapidly formed on the surface of the palladium plating film without being affected by the above. Furthermore, even when the electroless gold plating film is formed on the surface of the electroless palladium plating film formed on the surface of the electroless nickel plating film, by using the reduced electroless gold plating solution of the present invention, Compared with the case of forming a displacement gold plating film, the elution of nickel can be remarkably suppressed, and the diffusion of nickel into the gold plating film can be prevented. Therefore, according to the reduced electroless gold plating solution of the present invention, it is possible to provide a gold plating film capable of realizing high bonding reliability of wire bonding.

  Furthermore, the reduced electroless gold plating solution of the present invention has higher solution stability than conventional electroless gold plating solutions. For example, when continuous plating is performed while replenishing the plating solution, metal turnover is used as an indicator of aging of the plating solution (MTO. One turn is when all of the gold in the plating solution during the bathing is deposited). Is used. In the case of the conventional reduced electroless gold plating solution, the MTO is 2.0 to 3.0 turns, whereas the reduced electroless gold plating solution of the present invention realizes an MTO of 5.0 turns or more. It becomes possible.

  In addition, the reduced electroless gold plating solution of the present invention does not contain the highly toxic formaldehyde or formaldehyde bisulfite adducts contained in the conventional reduced electroless gold plating solution. Is easily secured.

  In addition, in the reduced electroless gold plating solution of the present invention, the gold precipitation reaction occurs only on the surface of gold, palladium, nickel, copper, etc., which can be a catalyst nucleus, and does not occur in a portion without the catalyst nucleus. Good selective precipitation. Therefore, it is advantageous in that the formation of a gold plating film on a portion where no gold deposition is necessary can be avoided and the raw material can be saved.

2. Next, the electroless gold plating method according to the present invention will be described. In the electroless gold plating method according to the present invention, a gold plating film is formed by performing an electroless gold plating process on the surface of an object to be plated using any one of the above-described reduced electroless gold plating solutions. In the electroless gold plating method, the plating process is performed by a method of immersing an object to be plated in an electroless gold plating solution in the same manner as in a normal reduction type electroless plating process.

  In the electroless gold plating method according to the present invention, it is preferable that the surface of an object to be processed is one of copper, palladium, gold, and nickel. As long as any of copper, palladium, gold, and nickel is present on the surface of the object to be plated, the presence form may be any case. In particular, the object to be plated itself is made of copper, or the surface of the object to be plated has any of copper, palladium, gold, nickel, or a film made of an alloy containing these metals. More preferred. For example, gold cobalt can be mentioned as an alloy containing these metals. Gold, palladium, nickel, copper, or an alloy containing these metals serves as a base metal for the electroless gold plating in the present invention, and these metals or alloys are included in the reduced electroless gold plating solution described above. It exhibits catalytic activity against hexamethylenetetramine as a reducing agent. As the film formed on the surface of the object to be plated, it is particularly preferable to use an electroless palladium plating film, a displacement gold plating film or a copper plating film. For example, when electroless nickel plating is applied to the surface of the printed circuit board mounting part or terminal part, an electroless palladium plating film is formed on the surface of the electroless nickel plating film. Preferably there is. This is because if a palladium plating film is formed on the surface of the nickel plating film, it is particularly effective in that the diffusion of the nickel plating film into the gold plating film can be prevented.

3. Next, the plated product according to the present invention will be described. The plated product according to the present invention is obtained by subjecting the surface of the object to be plated to electroless gold plating by the above-described electroless gold plating method using any of the above-described electroless gold plating solutions. Features. Among these, it is preferable that the surface of the object to be plated is subjected to electroless gold plating using a reduced electroless gold plating solution having a pH of 7.0 to 9.0. Further, as long as any one of copper, palladium, gold, and nickel exists on the surface of the object to be plated, the presence form may be any case. In particular, the object to be plated itself is composed of copper, or the surface of the object to be plated has one of copper, palladium, gold, nickel, or a film made of an alloy containing these metals. Is more preferable. Especially, as a film | membrane formed on the to-be-plated object surface, it is preferable that they are an electroless palladium plating film | membrane, a substituted gold plating film | membrane, or a copper plating film | membrane. In particular, it is preferable that an object to be plated having an electroless palladium plating film on the surface is an electroless nickel plating film formed as a lower layer of the electroless palladium plating film. This is because the above-described plating treatment using the reduced electroless gold plating solution can be particularly suitably used for forming a plating film at an electrical connection site.

  The embodiment according to the present invention described above is one aspect of the present invention, and it is needless to say that the embodiment can be appropriately changed without departing from the gist of the present invention.

  Below, Example 1 and Example 2 of the gold plating film produced using the reduced electroless gold plating solution of the present invention and Comparative Example 1 of the gold plating film produced using the substitutional electroless gold plating solution The present invention will be described more specifically with reference to Comparative Example 2 of a gold plating film produced using a conventional reduction type electroless plating solution. However, it should be noted that the present invention is not limited to the examples described below.

  In Example 1, using a reduced electroless gold plating solution to which the present invention is applied, a copper plate is used as a substrate, and an electroless nickel plating film / electroless palladium plating film / electroless gold plating film is formed on the substrate. A plating film was formed.

Adjustment of reduced electroless gold plating solution: The composition of the reduced electroless gold plating solution used in this example is shown below. The plating conditions (pH, liquid temperature) are shown together with the composition.
Potassium cyanide potassium 5mmol / L
Ethylenediaminetetraacetic acid dipotassium 0.03 mol / L
Citric acid 0.15 mol / L
Hexamethylenetetramine 3 millimol / L
3,3′-Diamino-N-methyldipropylamine 0.02 mol / L
Thallium acetate 5mg / L
pH 8.5
Liquid temperature 80 ℃

Preparation of plating film: The sample with the plating film as Example 1 is composed of an implementation sample group 1A to an implementation sample group 1D. The implementation sample group 1A to the implementation sample group 1D are classified according to the difference in film thickness of the electroless palladium plating film.

  The implementation sample group 1A is composed of implementation samples 1A-1 to 1A-6, and each implementation sample is formed with an electroless nickel plating film having a thickness of 5 μm on the surface of the copper plate, and then the electroless nickel plating film. An electroless palladium plating film having a thickness of 0.1 μm was formed on the surface of the film. Thereafter, a reducing electroless gold plating film was formed on the surface of the electroless palladium plating film using the above-described reducing electroless gold plating solution according to the conditions of each plating time. Specifically, the working sample 1A-1 to the working sample 1A-6 have a plating time condition of 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes when forming the reduced electroless gold plating film. As a result, a sample with a gold plating film was obtained.

  The implementation sample group 1B was composed of the implementation sample 1B-1 to the implementation sample 1B-6, and was produced in the same manner as the implementation sample group 1A, except that the film thickness of the electroless palladium plating film was 0.2 μm. In addition, each execution sample 1B-1-execution sample 1B-6 differ in the conditions of the plating time at the time of formation of a reduction type electroless gold plating film similarly to execution sample 1A-1-execution sample 1A-6. .

  The implementation sample group 1C was composed of the implementation sample 1C-1 to the implementation sample 1C-6, and was produced in the same manner as the implementation sample group 1A except that the film thickness of the electroless palladium plating film was 0.4 μm. In addition, each implementation sample 1C-1 to implementation sample 1C-6 is different from the implementation sample 1A-1 to implementation sample 1A-6 in the conditions of the plating time when forming the reduced electroless gold plating film. .

  The implementation sample group 1D was composed of the implementation sample 1D-1 to the implementation sample 1D-6, and was produced in the same manner as the implementation sample group 1A except that the film thickness of the electroless palladium plating film was 0.6 μm. In addition, each execution sample 1D-1-execution sample 1D-6 differ in the conditions of the plating time at the time of formation of a reduction type electroless gold plating film similarly to execution sample 1A-1-execution sample 1A-6. .

  In Example 2, a reduced electroless gold plating solution similar to that used in Example 1 was used, and a copper plate was used as a substrate, and an electroless nickel plating film / replaceable electroless gold plating film / reduced electroless film on the substrate. A plating film made of a gold plating film was formed. The sample with a plating film as Example 2 is composed of Example Sample 2-1 to Example Sample 2-6. In each of the implementation samples 2-1 to 2-6, an electroless nickel plating film having a thickness of 5 μm was formed on the surface of the copper plate, and then the thickness of 0.07 μm was replaced on the surface of the electroless nickel plating film. A mold electroless gold plating film was formed. Thereafter, using the above-described reduced electroless gold plating solution, a reduced electroless gold plating film was formed on the surface of the substitutional electroless gold plating film according to the conditions of each plating time. In addition, each implementation sample 2-1 to implementation sample 2-6 is different from the implementation sample 1A-1 to implementation sample 1A-6 in the conditions of the plating time when forming the reduced electroless gold plating film. .

Comparative example

[Comparative Example 1]
In Comparative Example 1, a substitutional electroless gold plating solution was used, as in Example 1, using a copper plate as a substrate, and an electroless nickel plating film / electroless palladium plating film / electroless gold plating film on the substrate. The plating film which consists of was produced.

Adjustment of substitutional electroless gold plating solution: The composition of the substitutional electroless gold plating solution used in Comparative Example 1 is shown below. The plating conditions (pH, liquid temperature) are shown together with the composition.
Potassium cyanide potassium 10mole / L
Ethylenediaminetetraacetic acid 0.03 mol / L
Citric acid 0.15 mol / L
Thallium acetate 50mg / L
pH 4.5
Liquid temperature 80 ℃

Preparation of plating film: The sample with the plating film as Comparative Example 1 is composed of Comparative Sample Group 1A to Comparative Sample Group 1D. The comparative sample group 1A to the comparative sample group 1D are classified according to the film thickness difference of the electroless palladium plating film.

  The comparative sample group 1A is composed of comparative samples 1A-1 to 1A-6, and each comparative sample is formed with an electroless nickel plating film having a thickness of 5 μm on the surface of the copper plate, and then the electroless nickel plating film. An electroless palladium plating film having a thickness of 0.1 μm was formed on the surface of the film. Thereafter, a substitutional electroless gold plating film was formed on the surface of the electroless palladium plating film using the substitutional electroless gold plating solution described above according to the conditions of each plating time. Specifically, Comparative Sample 1A-1 to Comparative Sample 1A-6 have plating time conditions of 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, and 60 minutes when forming a substitutional electroless gold plating film. As a result, a sample with a gold plating film was obtained.

  Comparative sample group 1B consists of comparative sample 1B-1 to comparative sample 1B-6, and was produced in the same manner as comparative sample group 1A, except that the film thickness of the electroless palladium plating film was 0.2 μm. Each of the comparative samples 1B-1 to 1B-6 is different from the comparative sample 1A-1 to the comparative sample 1A-6 in terms of the plating time conditions when forming the substitutional electroless gold plating film. .

  Comparative sample group 1C was composed of comparative sample 1C-1 to comparative sample 1C-6, and was prepared in the same manner as comparative sample group 1A, except that the film thickness of the electroless palladium plating film was 0.4 μm. Each of the comparative samples 1C-1 to 1C-6 is different from the comparative sample 1A-1 to the comparative sample 1A-6 in terms of the plating time conditions when forming the substitutional electroless gold plating film. .

  Comparative sample group 1D consists of comparative sample 1D-1 to comparative sample 1D-6, and was prepared in the same manner as comparative sample group 1A, except that the film thickness of the electroless palladium plating film was 0.6 μm. In addition, each comparative sample 1D-1 to comparative sample 1D-6 is different from the comparative sample 1A-1 to comparative sample 1A-6 in the conditions of the plating time when forming the substitutional electroless gold plating film. .

[Comparative Example 2]
In Comparative Example 2, a conventional reduced electroless gold plating solution was used, as in Example 2, using a copper plate as a substrate and an electroless nickel plating film / substitutional electroless gold plating film / conventional on the substrate. A plating film composed of a reduced electroless gold plating film was formed.

Preparation of conventional reduced electroless gold plating solution: The composition of the reduced electroless gold plating solution used in Comparative Example 2 is shown below. The plating conditions (pH, liquid temperature) are shown together with the composition.
Potassium cyanide potassium 0.015 mol / L
Potassium cyanide 0.03 mol / L
Sodium hydroxide 0.8mol / L
Dimethylamine borane 0.2mol / L
Lead compound 5mg / L (as lead)
pH 13
Liquid temperature 70 ℃

Preparation of plating film: In Comparative Example 2, after forming an electroless nickel plating film with a thickness of 5 μm on the surface of a copper plate, substitutional electroless gold with a film thickness of 0.05 μm on the surface of the electroless nickel plating film A plating film was formed. Thereafter, a reduced electroless gold plating film having a thickness of 0.20 μm was formed on the surface of the substitutional electroless gold plating film using the above-described reduced electroless gold plating solution.

[Evaluation]
Next, the deposition rate, the surface form, and the like were evaluated for Example 1 and Example 2 of the gold plating film produced using the reduced electroless gold plating solution of the present invention. Below, it produced using Example 1 and Example 2 and the comparative example 1 of the gold plating film produced using substitution type electroless gold plating liquid, and the conventional reduction type electroless plating liquid as needed. This will be specifically described in comparison with Comparative Example 2 of the gold plating film.

Deposition rate: Plating time and plating film of gold plating film of Example Sample Group 1A (Example Sample 1A-1 to Example Sample 1A-6) in Example 1 using the reduced electroless gold plating solution according to the present invention The relationship with the thickness is shown in FIG. Similarly, the relationship between the plating time and the plating film thickness of the gold plating film of Example 2 (Example 2-1 to Example 2-6) using the reduced electroless gold plating solution according to the present invention is shown in FIG. Shown in FIG. 2 shows an electron micrograph (× 10,000) of the gold plating film of Example 2-2 obtained with a plating treatment time of 20 minutes.

  The gold plating film formed on the surface of the electroless palladium plating film using the reduced electroless gold plating solution described above from FIG. 1 is stable without being affected by the thickness of the gold plating film to be formed. It was confirmed that a gold plating film was formed at a rate of 0.15 μm / 30 minutes.

  The reduced electroless gold plating film formed on the surface of the substitutional electroless gold plating film using the reduced electroless gold plating solution described above from FIG. 2 is affected by the thickness of the formed gold plating film. It was confirmed that the gold plating film was stably formed at a rate of 0.17 μm / 30 minutes.

Effect of electroless palladium plating film thickness on deposition rate of gold plating film: Next, in contrast to Example 1 and Comparative Example 1, the effect of electroless palladium plating film on the deposition rate of gold plating film Describe the effect on thickness. FIG. 3 shows an implementation sample group 1A (implementation sample 1A-1 to implementation sample 1A-6) to implementation sample group in which a gold plating film is formed on the surface of the electroless palladium plating film using a reduced electroless gold plating solution. The relationship between the film thickness of the electroless palladium plating film of 1D (Execution Sample 1D-1 to Implementation Sample 1D-6) and the deposition rate of the gold plating film is shown. In addition, FIG. 3 shows comparative sample group 1A (comparative sample 1A-1 to comparative sample 1A-6) in which a gold plating film is formed on the surface of an electroless palladium plating film using a substitutional electroless gold plating solution. Sample Group 1D (Comparative Sample 1D-1 to Comparative Sample 1D-6) shows the relationship between the film thickness of the electroless palladium plating film and the deposition rate of the gold plating film.

  From FIG. 3, the gold plating film formed using the substitutional electroless gold plating solution of Comparative Sample Group 1A to Comparative Sample Group 1D decreases as the palladium plating film as the base metal becomes thicker. You can see that On the other hand, the gold plating film formed using the reduced electroless gold plating solution of the working sample group 1A to the working sample group 1D is gold at a stable rate regardless of the thickness of the palladium plating film that is the base metal. It was confirmed that a plating film was formed.

Surface morphology of gold plating film: Next, the surface morphology of the gold plating film formed on the surface of the electroless palladium plating film using the reduced electroless gold plating solution of the present invention was observed. FIG. 4 shows electron micrographs (× 10000 and × 30000) of the surface of the gold plating film of Example 1A-2 in which a reduced electroless gold plating film of Example 1 was formed with a film thickness of 0.1 μm. Moreover, the surface form of the reduced electroless gold plating film formed on the surface of the substitutional electroless gold plating film using the reduced electroless gold plating solution of the present invention was observed. FIG. 5 shows an electron micrograph (× 30000) of the surface of the gold plating film of Example 2-2 in which the reduced electroless gold plating film of Example 2 was formed with a film thickness of 0.13 μm. As a comparison, the surface morphology of the reduced electroless gold plating film formed on the surface of the substitutional electroless gold plating film using a conventional reduced electroless gold plating solution was observed. FIG. 5 shows an electron micrograph (× 30000) of the surface of the gold plating film of Comparative Example 2 in which a reduced electroless gold plating film is formed with a film thickness of 0.13 μm.

  4 and 5, it can be confirmed that the electroless gold plating film is formed densely using not only the reduced electroless gold plating solution of the present invention but also the conventional reduced electroless gold plating solution. It was.

Surface form after electroless gold plating film peeling: Nickel after peeling electroless gold plating film or electroless gold plating film and electroless palladium plating film from each plating film shown in FIGS. The surface morphology of the plating film was observed. FIG. 6 shows an electron micrograph (× 5000) of the surface of the nickel plating film after peeling the electroless gold plating film and the electroless palladium plating film from the state of FIG. FIG. 7 shows an electron micrograph (× 3000) of the surface of the nickel plating film after the electroless gold plating film is peeled from the state of FIG.

  As is clear from FIGS. 6 and 7, no local corrosion of the nickel plating film was confirmed in any of the examples and comparative examples formed using the reduced electroless gold plating solution.

Cross-sectional form of plating film: Next, electroless nickel plating film / electroless palladium plating of Example 1 in which a gold plating film was formed on the surface of the electroless palladium plating film using the reduced electroless gold plating solution of the present invention The cross section of the plating film having a layer structure of film / electroless gold plating film was observed. FIG. 8 shows a cross-sectional observation photograph (× 30000) of the plating film of Example Sample 1A-6 in which a reduced electroless gold plating film is formed with a film thickness of 0.3 μm. From FIG. 8, it was confirmed that the electroless gold plating film formed using the above-described reduced electroless gold plating solution was uniformly formed on the surface of the palladium plating film.

Selective precipitation of gold plating film: Next, in the same manner as in Example 1A-6 in Example 1 in which a gold plating film was formed on the surface of the electroless palladium plating film using the reduced electroless gold plating solution of the present invention. FIG. 9 shows electron micrographs (× 500) of the end portion and the center portion of the plated product on which the plating film is formed under the conditions described above. From FIG. 9, it can be confirmed that the electroless gold plating film is formed uniformly and uniformly at the end portion and the central portion of the plated product. Therefore, also from the photograph of FIG. 9, it can be said that the reduced electroless gold plating solution of the present invention has a good selective deposition property of the electroless gold plating film.

Effect of elution of nickel in gold plating solution: Next, with respect to Example 1 in which a gold plating film was formed on the surface of an electroless palladium plating film using the reduced electroless gold plating liquid of the present invention, reduced electroless gold The effect of electroless nickel elution on the plating solution was investigated. Specifically, the elution amount of the base nickel into the electroless gold plating solution when 1 g of gold was deposited on the surface of the electroless palladium plating film was measured using ICP. As a comparison, Comparative Example 1 using a substitutional electroless gold plating solution was also measured in the same manner as in Example 1. FIG. 10 shows the elution amount of electroless nickel of Example 1 using a reduced electroless gold plating solution and the elution amount of base nickel of Comparative Example 1 using a substitutional electroless gold plating solution. FIG. 10 shows values when the elution amount of Ni into the gold plating solution when 1 g of gold is deposited is measured using ICP.

  From FIG. 10, in Comparative Example 1 in which a gold plating film was deposited per gram using a substitutional electroless gold plating solution, 162 ppm of Ni used as a base metal was eluted in the substitutional electroless gold plating solution. On the other hand, in Example 1 in which a gold plating film was deposited per gram using the reduced electroless gold plating solution of the present application, Ni used as a base metal in the reduced electroless gold plating solution was only 0.2 ppm. It did not elute.

  From the results of the evaluation test, the reduced electroless gold plating solution according to the present application can remarkably suppress the elution of the base nickel through the palladium plating film as compared with the case of forming the displacement gold plating film. It can be said that nickel can be prevented from diffusing.

Next, the variation in the film thickness of the gold plating film formed on the surface of the substitutional electroless gold plating film using the reduced electroless gold plating solution will be examined. Here, as an example using the reduced electroless gold plating solution according to the present invention, the film thickness of the reduced electroless gold plating film was measured for Example 2-2 of Example 2. As a comparison, the film thickness of the reduced electroless gold plating film was measured for Comparative Example 2 using a conventional reduced electroless gold plating solution. Table 1 summarizes the results of measurement of film thickness at 20 locations for each. Further, FIG. 11 shows a diagram showing a variation state.

  The average thickness of the electroless gold plating film of Example 2-2 using the reduced electroless gold plating solution according to the present invention is 0.199 μm, and the difference between the maximum value and the minimum value is 0.01 μm, The standard deviation was extremely small as 0.004. In contrast, the average thickness of the electroless gold plating film of Comparative Example 2 using a conventional reduced electroless gold plating solution is 0.206 μm, and the difference between the maximum value and the minimum value is 0.036 μm, The standard deviation was 0.013. Therefore, by using the reduced electroless gold plating solution according to the present invention, the film thickness of the obtained electroless gold plating film is considerably larger than the case where the conventional reduced electroless gold plating solution is used. It can be seen that the variation is small and uniform at high levels. From the result, by using the reduced electroless gold plating solution according to the present invention, the entire surface to be plated can be more uniformly plated, and the quality can be improved. In addition, since the electroless gold plating film can be uniformly formed with the required film thickness, the formation of the electroless gold plating film exceeding the required film thickness is suppressed, and the excessive carry-out of gold can be greatly reduced. It becomes possible.

Next, the wire bonding characteristics of the gold plating film formed using the reduced electroless gold plating solution according to the present invention will be examined. Here, as an example using the reduced electroless gold plating solution according to the present invention, the strength of wire bonding of the reduced electroless gold plating film was measured for Example 2-2 of Example 2. For comparison, the strength of wire bonding of the reduced electroless gold plating film was measured for Comparative Example 2 using a conventional reduced electroless gold plating solution. Specifically, a gold wire having a wire diameter of 25 μm is bonded to the reduced electroless plating film of Example 2-2 and Comparative Example 2 with a wire bonding apparatus, and the wire is pulled with a pull tester. The strength was measured. Twenty points were measured, and the maximum value, minimum value, and average value of the wire bonding strength were obtained. The measurement results are shown in FIG.

  The maximum value of the wire bonding strength of the electroless gold plating film of Example 2 (Example 2-2) using the reduced electroless plating solution according to the present invention is 6.0 gf, and the minimum value is 4.8 gf. The average value was 5.3 gf. The maximum value of the wire bonding strength of the electroless gold plating film of Comparative Example 2 using the conventional reduced electroless plating solution is 6.0 gf, the minimum value is 4.8 gf, and the average value is 5.3 gf. Met. From these results, the electroless gold plating film obtained by using the reduced electroless plating solution according to the present invention is almost the same as the case of using the conventional reduced electroless plating solution, and good wire bonding. It was found that strength was obtained. Therefore, it can be said that according to the reduced electroless gold plating solution of the present invention, it is possible to provide a gold plating film capable of realizing high bonding reliability of wire bonding.

  The reduced electroless gold plating solution of the present invention remarkably suppresses elution of the base metal such as nickel and palladium, and can thicken the gold plating film on the surface of the base metal at a high deposition rate. Therefore, according to the present invention, it is possible to provide a gold plating film with high bonding reliability of wire bonding.

Claims (6)

A reduced electroless gold plating solution used to form an electroless gold plating film on the surface of an object to be plated on which copper, palladium, gold, or nickel exists,
A water-soluble gold compound, citric acid or citrate, ethylenediaminetetraacetic acid or ethylenediaminetetraacetate, hexamethylenetetramine, a chain polyamine containing an alkyl group having 3 or more carbon atoms and 3 or more amino groups; And a reduced electroless gold plating solution.   The reduced electroless gold plating solution according to claim 1, which has a pH of 7.0 to pH 9.0.   The reduced electroless device according to claim 1 or 2, wherein the chain polyamine is 3,3'-diamino-N-methyldipropylamine or N, N'-bis (3-aminopropyl) ethylenediamine. Gold plating solution.   The reduced electroless gold plating solution according to any one of claims 1 to 3, comprising a thallium compound as a deposition accelerator.   Using the reduced electroless gold plating solution according to any one of claims 1 to 4, an electroless gold plating film is formed on a surface of an object to be plated on which copper, palladium, gold, or nickel is present. Forming an electroless gold plating method.   The electroless gold plating method according to claim 5, wherein the surface of the object to be plated includes an electroless palladium plating film formed on a surface of an electroless nickel plating film.

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