JP5066691B2 - Method to stabilize electroless gold plating bath - Google Patents

Description

  The present invention relates to an electroless gold plating bath and an electroless gold plating method.

  One of the final steps in the production of printed wiring boards, semiconductor packages, electronic components, etc. is a process in which electroless nickel plating is applied to conductor circuits, terminal portions, etc., followed by electroless gold plating. This is to prevent oxidation of the copper circuit surface of the printed wiring board, to exhibit good solder connection performance, and to wire bond the semiconductor package and the electronic component mounted thereon, the semiconductor package, The object is to bond the metal of the terminal portion of the electronic component or the like and the wire of gold or aluminum in a good state.

  As a method of forming such a plating film, an electroless nickel plating film is deposited on a copper film of a printed wiring board or a metal paste of a semiconductor package or an electronic component in an autocatalytic manner, and then the electroless nickel film A general method is a method in which a gold plating film is deposited on the top of the film, and a thick electroless gold plating film is formed in an autocatalytic manner.

  However, when the conventional autocatalytic electroless gold plating is used in the manufacturing process described above, a phenomenon in which the gold plating film is deposited not only on the target substitutional gold plating film but also in an unnecessary portion, so-called Out-of-pattern precipitation is likely to occur. Such a phenomenon causes a defective product and causes a decrease in reliability.

  In particular, when an article in which a metal part is formed on a ceramic material typified by a ceramic IC package is used as an object to be plated, this tendency is remarkable, and plating spread such as out-of-pattern precipitation is a big problem.

As additives for preventing such out-of-pattern precipitation, metal cyanide, acetylacetone, ethyl oxalic acid, and the like are known (see Non-Patent Document 1 below). However, among these additives, metal cyanide has a drawback that it is highly toxic, and acetylacetone, ethyl oxalic acid, etc. have a small effect of addition, and in order to obtain a sufficient effect, they should be added in a large amount. Is required.
FUJITA Tetsuya, "NP Series Precious Metal Plating", published on June 10, 1992 by Sakai Shoten, P36

  The present invention has been made in view of the current state of the prior art described above, and its main purpose is to deposit with high selectivity on a metal part or the like formed on a ceramic material and to prevent out-of-pattern precipitation from occurring. The object is to provide a novel electroless gold plating bath with excellent stability, which does not easily cause decomposition or precipitation of the plating bath.

  The present inventor has intensively studied to achieve the above-described object. As a result, an autocatalytic electroless gold plating bath containing a water-soluble gold compound, a complexing agent and a reducing agent, and further, as a stabilizer, at least one component selected from the group consisting of isothiourea and derivatives thereof. As a result of the addition, it has been found that an electroless gold plating bath having improved stability of the plating solution, less likely to cause out-of-pattern precipitation, and excellent in bath stability can be obtained, and the present invention has been completed here. It was.

That is, the present invention provides the following autocatalytic electroless gold plating bath.
1.
(I) a water-soluble gold compound,
(Ii) complexing agents,
(Iii) a reducing agent, and (iv) a stabilizer comprising at least one component selected from the group consisting of isothiourea and derivatives thereof,
An electroless gold plating bath comprising an aqueous solution containing
2. Stabilizers have the general formula:

(Wherein R ¹ and R ² are the same or different and are a hydrogen atom, a lower alkyl group, a benzyl group, a phenyl group, a halogen atom, a group: —N (R ⁴ ) ₂ (where R ⁴ is a hydrogen atom or A lower alkyl group), a hydroxyl group, a group: —SO ₃ M ¹ (wherein M ¹ is a hydrogen atom or an alkali metal), a cyano group, a nitro group or a phosphone group, R ³ is a halogen atom, Group: —N (R ⁵ ) ₂ (where R ⁵ is a hydrogen atom or a lower alkyl group), hydroxyl group, group: —SO ₃ M ² (where M ² is a hydrogen atom or an alkali metal), A lower alkyl group or a hydrogen atom which may have at least one substituent selected from the group consisting of a cyano group, a nitro group, a phosphone group and a phenyl group) and a salt thereof. Less Electroless gold plating bath of claim 1 is a kind of compound.
3. 3. An electroless gold plating method comprising immersing an object to be processed in the electroless gold plating bath according to item 1 or 2.

Hereinafter, the electroless gold plating bath of the present invention will be described.
(I) Water-soluble gold compound:
In the autocatalytic electroless gold plating bath of the present invention, as the water-soluble gold compound, various compounds used as a gold supply source in a known gold plating solution can be used. Specific examples include sodium gold sulfite, sodium gold cyanide, potassium gold cyanide, sodium chloroaurate, and potassium chloroaurate, but are not limited to these gold compounds.

  The concentration of the water-soluble gold compound is not particularly limited. However, if the gold concentration is too low, the deposition rate of gold plating is slow, and a long time is required to form a predetermined gold plating film. On the other hand, if the gold concentration is too high, the amount of the gold compound taken out from the plating solution is increased and the cost is increased. From such a point, it is preferable to set it as about 0.001-0.1 mol / L as gold ion, and it is more preferable to set it as about 0.002-0.05 mol / L.

(Ii) Complexing agent:
The complexing agent is not particularly limited, and a complexing agent used in a known electroless gold plating solution can be used. For example, sulfites such as sodium sulfite, potassium sulfite, and ammonium sulfite; cyanides such as sodium cyanide and potassium cyanide; thiosulfates such as sodium thiosulfate, potassium thiosulfate, and ammonium thiosulfate; inorganic acids such as phosphoric acid and boric acid Salts thereof (sodium salt, potassium salt, ammonium salt, etc.); hydroxycarboxylic acids such as citric acid, gluconic acid, tartaric acid, lactic acid, malic acid, salts thereof (sodium salt, potassium salt, ammonium salt, etc.); Amine compounds such as ethanolamine; aminocarboxylic acids such as glycine, alanine, ethylenediaminetetraacetic acid, nitrilotritriacetic acid, salts thereof (sodium salt, potassium salt, ammonium salt, etc.); aminotrimethylenephosphonic acid, 1-hydroxyethylidene-1 , 1 Diphosphonic acid, ethylenediamine tetramethylene phosphonic acid, phosphonic acids such as diethylene triamine penta (methylene phosphonic acid), its salts (sodium salt, potassium salt, ammonium salt, etc.) and the like can be used.

  The concentration of the complexing agent is not particularly limited, but is usually about 0.01 mol / L or more. When the concentration of the complexing agent is too low, the effect as the complexing agent is insufficient. If the concentration is too high, the effect does not increase so much and it is uneconomical. In particular, the concentration of the complexing agent is preferably about 0.05 to 0.5 mol / L.

(Iii) Reducing agent:
The reducing agent is not particularly limited, and the same reducing agent as that used in known autocatalytic electroless gold plating solutions can be used. For example, hydrazine hydrate, hydrazine sulfate, neutral hydrazine sulfate, hydrazine maleate, and salts thereof; hydroxylamines and salts thereof; hydrazine derivatives such as adipic acid dihydrazide, isophthalic acid dihydrazide, isopropyl hydrazine sulfate, etc. Ascorbic acid, salts thereof (sodium, potassium, ammonium salts, etc.); borohydride compounds such as trimethylamine borane (TMAB), dimethylamine borane (DMAB); thiourea; hypophosphorous acid, salts thereof (sodium, potassium, Ammonium salt etc.) can be used.

  By the action of these reducing agents, gold ions in the plating solution are reduced, and gold is deposited on the object to be plated. The blending amount of the reducing agent is not particularly limited, but is usually about 1 to 100 g / L, preferably about 5 to 70 g / L. In this case, the plating rate increases almost in proportion to the concentration of these reducing agents. However, even if an amount exceeding 100 g / L is added, the plating rate does not increase so much, but rather the bath stability may deteriorate. It is not preferable. On the other hand, if the concentration of the reducing agent is less than 1 g / L, the plating rate becomes very slow, which is not preferable.

(Iv) Stabilizer The self-catalyzed electroless gold plating solution of the present invention contains at least one component selected from the group consisting of isothiourea and derivatives thereof as a stabilizer. By containing such a specific compound as a stabilizer, the electroless gold plating solution of the present invention improves the stability of the plating bath, prevents precipitation outside the pattern, and prevents gold from being deposited only on the target portion. A plating film can be formed. Furthermore, the plating solution can be used for a long time without causing decomposition or precipitation of the plating bath.

  In particular, stabilizers include the following general formula:

It is preferable to use at least one component selected from the group consisting of a compound represented by formula (I) and a salt thereof. In the above general formula, R ¹ and R ² are the same or different and are a hydrogen atom, a lower alkyl group, a benzyl group, a phenyl group, a halogen atom, or a group: —N (R ⁴ ) ₂ (where R ⁴ is a hydrogen atom) Or a lower alkyl group), a hydroxyl group, a group: —SO ₃ M ¹ (where M ¹ is a hydrogen atom or an alkali metal (Na, K, etc.)), a cyano group, a nitro group, or a phosphone group, R ³ is a lower alkyl group or a hydrogen atom, and the lower alkyl group is a halogen atom, a group: —N (R ⁵ ) ₂ (where R ⁵ is a hydrogen atom or a lower alkyl group), a hydroxyl group, Group: —SO ₃ M ² (where M ² is a hydrogen atom or an alkali metal (Na, K, etc.)), at least one substitution selected from the group consisting of a cyano group, a nitro group, a phosphone group, and a phenyl group Have group It may be.

  In the above general formula, the lower alkyl group is preferably a linear or branched alkyl group having about 1 to 5 carbon atoms, and specific examples thereof include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, Examples thereof include tert-butyl and pentyl. Examples of the halogen atom include chlorine, bromine and iodine.

  Examples of the salt of the compound represented by the general formula include ammonium salt, hydrochloride, hydrobromide, sulfate, iodate and the like.

Isothiourea and its derivatives can be used singly or in combination of two or more.
Specific examples of the isothiourea derivative include the following compounds.
S-methylisothiourea:

S-ethylisothiourea:

S-isopropylisothiourea:

S-2-aminoethylisothiourea:

N-cyano-N ', S-dimethylisothiourea:

・ Benzylisothiourea:

N-cyano-S-methyl-N'phenylisothiourea:

S- (2-dimethylaminoethyl) isothiourea:

Isothiourea and its derivatives can be used singly or in combination of two or more.
be able to.

  The concentration of at least one component selected from the group consisting of isothiourea and derivatives thereof is not particularly limited, but is usually about 0.001 to 100 mg / L, and about 0.003 to 50 mg / L. It is preferable that If the concentration of these components is low, the plating solution becomes unstable, decomposition of the plating solution or out-of-pattern precipitation may occur, and if too large, plating appearance defects may occur.

  The electroless gold plating bath of the present invention consists of an aqueous solution containing the above-mentioned water-soluble gold compound, complexing agent, reducing agent and stabilizer as essential components, so long as it does not adversely affect the properties of the plating solution. In addition to the above components, other metal salts, organic compounds, and the like may be included.

Electroless gold plating method The plating method using the electroless gold plating bath of the present invention may be the same as the processing method of a normal autocatalytic electroless plating. Usually, the plating treatment can be performed by a method of immersing an object to be plated in an electroless gold plating bath.

  The object to be treated is not particularly limited, but the typical object to be treated is a replacement type after forming an electroless nickel plating film on a printed circuit board, a ceramic IC package, a conductor circuit such as an electronic component, and a terminal part. This is an article on which a gold plating film is formed. In this case, it is possible to perform the plating treatment directly on the substitutional gold plating film using the electroless gold plating solution of the present invention.

  In addition, for an object to be plated that has no catalytic activity with respect to the autocatalytic electroless gold plating bath, after applying an electroless plating catalyst to the object to be plated according to a known method, the electroless gold plating of the present invention Plating may be performed using a bath.

  About the liquid temperature of the gold plating bath at the time of electroless gold plating, if it is too low, the precipitation reaction becomes slow and the gold plating film is not easily precipitated and the appearance is liable to occur. Good. On the other hand, if the solution temperature is too high, the plating solution is likely to be decomposed, and the evaporation of water is too intense, making it difficult to maintain the concentration of the components contained in the plating solution. For this reason, it is preferable that the liquid temperature of a plating solution shall be about 30-90 degreeC, and it is more preferable to set it as about 50-80 degreeC.

  When the pH of the electroless gold plating solution is too low, the plating reaction hardly proceeds, and when the pH is too high, the stability is lowered and self-decomposition tends to occur. For this reason, it is preferable to make pH into about 4-13, and it is more preferable to set it as about 5-10.

  The electroless gold plating bath of the present invention has excellent stability, for example, when performing electroless gold plating treatment autocatalytically on metal parts such as gold formed on various materials, The gold plating film can be selectively formed only on the target metal portion without almost depositing the gold plating film on the unnecessary portion, and the spreading of the plating can be prevented. Moreover, since the bath stability is good, the plating bath can be used stably for a long period of time without causing bath decomposition or precipitation.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1
A 3 x 5 cm heat-resistant glass-based epoxy resin laminate (heat-resistant grade FR-4) having a wiring pattern with a line width of 50 µm and a space width of 50 µm is used as an object to be processed, and an electroless Ni-P plating film is formed on the wiring pattern. 4 μm was formed, and a displacement gold plating film was further formed 0.1 μm thereon.

  Subsequently, the to-be-processed object was immersed in the electroless gold plating bath of each composition shown in following Table 1, and the electroless gold plating film was formed on the following conditions.

Plating bath condition pH 9
Liquid temperature 70 ℃
1L of liquid
Liquid stirring Air stirring About each to-be-processed object, the surface state was observed using the optical microscope of 80-times multiplication factor, and the presence or absence of plating spreading was evaluated. Table 1 below shows the results of evaluation of plating spread, where ◯ indicates that the gold plating film is formed only on the wiring pattern, and x indicates that the gold plating film is formed on the resin.

  Moreover, after completion | finish of the said plating process, each electroless gold plating bath was left to stand at 80 degreeC for 3 hours, the presence or absence of gold precipitation was confirmed, and the stability of the plating bath was evaluated. The results of evaluating the stability of the plating bath are shown in Table 1 below, where ◯ indicates that no precipitation has occurred, and x indicates that precipitation has occurred.

Claims (2)

A stabilizer for an electroless gold plating bath comprising an aqueous solution containing a water-soluble gold compound, a complexing agent, and a reducing agent , comprising as an active ingredient at least one component selected from the group consisting of isothiourea and derivatives thereof, A method for stabilizing an electroless gold plating bath, comprising adding the electroless gold plating bath to a concentration of 0.003 to 50 mg / L. The stabilizer has the general formula:

(Wherein R ¹ and R ² are the same or different and are a hydrogen atom, a lower alkyl group, a benzyl group, a phenyl group, a halogen atom, a group: —N (R ⁴ ) ₂ (where R ⁴ is a hydrogen atom or A lower alkyl group), a hydroxyl group, a group: —SO ₃ M ¹ (wherein M ¹ is a hydrogen atom or an alkali metal), a cyano group, a nitro group or a phosphone group, R ³ is a halogen atom, Group: —N (R ⁵ ) ₂ (where R ⁵ is a hydrogen atom or a lower alkyl group), hydroxyl group, group: —SO ₃ M ² (where M ² is a hydrogen atom or an alkali metal), A lower alkyl group or a hydrogen atom which may have at least one substituent selected from the group consisting of a cyano group, a nitro group, a phosphone group and a phenyl group) and a salt thereof. Less Method of stabilizing the electroless gold plating bath of claim 1 is a kind of compound.