JP4955315B2 - Electroless gold plating solution for forming gold plating film for wire bonding - Google Patents

Description

  The present invention relates to an electroless gold plating solution. More specifically, the present invention relates to an electroless gold plating solution suitably used for forming a gold plating film for wire bonding bonding on the surface of a fine wiring of a fine wiring substrate.

  In a wiring board such as a printed board, the surface of a fine copper wiring formed on a normal board is usually nickel-plated, and further gold-plated. In recent years, with the miniaturization of electronic components, wiring is miniaturized, and wiring boards in which a large number of electrically independent wirings are formed on the board have become mainstream. When the electrically independent wiring is subjected to thick gold plating, a film forming method using an electroless gold plating solution is employed (for example, see Patent Document 1).

  In general, when thick gold plating is applied, first, a base gold plating film having a thickness of about 0.1 μm is formed on the electroless nickel plating film formed on the surface of the copper wiring by substitutional electroless gold plating. The Next, as necessary, a thick gold plating film is formed by reducing electroless gold plating (self-catalytic electroless gold plating: see, for example, Patent Document 2).

  Copper wiring boards that have been subjected to electroless nickel plating and electroless gold plating are evaluated for properties such as wire bonding strength, solderability, and solder ball shear strength in order to evaluate the properties of the resulting gold plating film. . However, in the conventional gold plating process using a displacement gold plating solution containing cyan (see, for example, Patent Document 3), the electroless nickel coating is corroded during the displacement gold plating process.

  On the other hand, in gold plating using a substitution reduction type electroless gold plating solution (substitution gold plating solution containing a reducing agent), gold is deposited by the reducing action of the reducing agent. Not corroded. However, if the surface of the electroless nickel film is coated with a gold plating film, gold does not precipitate further and the gold plating film does not continue to grow. Therefore, the thick gold plating film is not formed unlike the case where the plating film is formed by a general reduction gold plating method.

  The surface of the gold plating film is usually further subjected to a reduction gold plating process, and a top coat gold plating film having a large film thickness is formed. However, the gold plating film formed by the above-described substitution-reduction type electroless gold plating has weak adhesion to the underlying nickel film. For this reason, when the wire bonding process by which the said top coat metal plating film and gold wiring are joined is performed, there exists a problem in which the joined wire tends to peel from a base nickel film. Furthermore, there is a problem that analysis and replenishment of the reducing agent in the plating solution must always be performed during the plating operation.

  A replacement gold plating solution containing a surface oxidation inhibitor that acts as a base metal elution inhibitor has been proposed for the replacement gold plating solution containing the reducing agent. This displacement plating solution does not contain a reducing agent (see, for example, Patent Document 4). According to the gold plating process described in Patent Document 4, analysis and replenishment of the reducing agent during the plating operation is unnecessary, and the solder joint strength is improved by suppressing the dissolution of the base metal. Has been.

However, when wire bonding is performed on the gold plating film formed by this gold plating treatment, the bonded wires are easily peeled off, and this problem has not been solved.
Japanese Patent No. 3146757 (paragraph numbers [0002] to [0003]) JP 2000-87251 A (claims, paragraph numbers [0007] to [0022]) Japanese Patent Laid-Open No. 5-287541 (Claims, paragraph numbers [0004] to [0012]) Japanese Patent Publication No. 2004-38063 (Claims, Summary of the Invention)

  While various studies have been made by the present inventor to solve the above problems, a substituted electroless gold containing a gold cyanide compound, oxalic acid and / or a salt thereof, and no base metal elution inhibitor. It has been found that the gold plating film formed using the plating solution has high adhesion to the base metal.

  For this reason, the present inventor considered as follows. That is, in general, a substitutional electroless gold plating solution is mixed with a base metal elution inhibitor for the purpose of suppressing corrosion of a nickel film serving as a base of the gold plating film. By this base metal elution inhibitor, oxidation of the nickel coating surface is suppressed during plating, and the nickel coating surface is kept smooth. The gold plating film formed on the smooth nickel film surface is inferior in adhesion with the nickel film because the nickel surface is smooth. As a result, after the electroless top plating process, when the wire is bonded to the top coat, the bonded wire is easily peeled off.

  On the other hand, when gold plating is applied to a nickel film using a substitution electroless gold plating solution that does not contain an under metal dissolution inhibitor, the nickel film surface is appropriately oxidized during the plating process to produce irregularities on the surface. Has increased. Therefore, the gold plating film produced by plating on the surface of the nickel film increases the contact area with the nickel film. As a result, the adhesion between the nickel film and the gold plating film is increased. That is, it has been found that a moderately corroded nickel film has a so-called moderate anchor effect.

  By this anchor effect, it is learned that a plating solution that does not contain a base metal elution inhibitor is excellent as a base gold plating solution for a substitution electroless gold plating solution for wire bonding bonding, and the present invention is completed. It was.

  Accordingly, an object of the present invention is to provide an electroless gold plating solution that solves the above-mentioned problems.

  The present invention for achieving the above object is described below.

  [1] An electroless gold plating solution for forming a gold plating film for wire bonding, which contains a gold cyanide compound, oxalic acid and / or a salt thereof, and does not contain a base metal elution inhibitor.

  [2] Gold plating film formation for wire bonding joining according to [1] containing gold cyanide compound in gold ion concentration of 0.5 to 10 g / L and oxalic acid and / or a salt thereof in an amount of 5 to 50 g / L Electroless gold plating solution.

  [3] The electroless gold plating solution for forming a gold plating film for wire bonding bonding according to [1], which contains a concealing agent for a base eluting metal.

  [4] The electroless gold plating solution for forming a gold plating film for wire bonding bonding according to [3], wherein the base elution metal concealing agent is ethylenediaminetetraacetic acid and / or a salt thereof.

  [5] It contains at least one crystal modifier, and the crystal modifier is at least one selected from the group consisting of an arsenic compound, a thallium compound, and a lead compound. Electroless gold plating solution.

  The electroless gold plating solution of the present invention contains a gold cyanide compound and oxalic acid or a salt thereof, and does not contain a base metal elution inhibitor. Therefore, when plating is performed using this plating solution, Moderate corrosion occurs and surface area increases. As a result, an appropriate anchor effect is produced between the nickel coating surface and the gold plating coating, and the adhesion between the two is enhanced. A wire that is wire-bonded to the gold plating film exhibits good bonding strength.

  Hereinafter, the substitution electroless gold plating solution for forming a gold plating film for wire bonding bonding according to the present invention will be described in detail.

  The electroless gold plating solution of the present invention contains a gold cyanide compound and oxalic acid and / or a salt thereof as essential components.

  As the gold cyanide compound, sodium gold cyanide, potassium gold cyanide and the like are preferable. The gold ion concentration in the electroless gold plating solution is preferably 0.5 to 10 g / L, more preferably 1 to 5 g / L. When the gold ion concentration is less than 0.5 g / L, the deposition rate of the gold plating film is small. If it exceeds 10 g / L, there is no problem with the deposition of the gold plating film, but even if the gold ion concentration is increased, there is no advantage commensurate with it, which is not preferable from an economical viewpoint.

  The concentration of oxalic acid and / or a salt thereof is preferably 5 to 50 g / L, more preferably 10 to 30 g / L. If the concentration of oxalic acid and / or its salt is less than 5 g / L or exceeds 50 g / L, the electroless nickel film as the base metal tends to be corroded excessively. The salt is preferably a sodium salt or a potassium salt.

  The electroless gold plating solution of the present invention does not contain a base metal elution inhibitor. As the base metal elution inhibitor, an organic compound containing a plurality of nitrogen atoms in the main chain or ring and one or more of these nitrogen atoms having an —NH— structure is known. Specific examples include benzotriazole, benzimidazole and mercaptoimidazole. When these base metal elution inhibitors are contained in the electroless gold plating solution, the deposition rate of the gold plating film is reduced, and the adhesion between the nickel film surface and the gold plating film is deteriorated.

  As described above, some substitution-type electroless gold plating solutions contain a base metal elution inhibitor for the purpose of suppressing corrosion of the nickel film. When gold plating is performed on the surface of the nickel film using the substitutional electroless gold plating solution containing the base metal elution inhibitor, the surface of the nickel film is kept smooth. As a result, after the electroless gold plating overcoating process performed as a post-treatment, when wire bonding is performed on the overcoating gold plating film, the bonding strength between the bonded wire and the gold plating film becomes insufficient.

  The wire bonding characteristics will be specifically described with reference to the drawings. FIG. 1 shows the thickness of an electroless nickel coating formed on a copper wiring substrate by forming a base gold plating coating using the electroless gold plating solution of the present invention, and further forming an overcoat gold plating coating by a conventional method. It is a schematic explanatory drawing which shows an example in the case of wire-bonding joining to the gold plating film which increased the number.

  In FIG. 1, reference numeral 2 denotes a copper base portion of a copper wiring formed on a not-illustrated printed circuit board. A nickel film 4 formed by electroless plating is laminated on the surface of the copper base portion 2. An electroless gold plating film 6 is formed on the surface of the nickel film 4. A gold wire 8 is bonded to the gold plating film 6 by wire bonding. Wire bonding is usually performed by applying ultrasonic waves and a load.

  When an ultrasonic wave and a load are applied, frictional heat is generated at the interface 10 between the wire 8 and the gold plating film 6. Due to this frictional heat, the mutual contact surface between the gold plating film 6 and the gold wire 8 is fused, and the gold plating film 6 and the gold lead wire 8 are bonded to each other at the bonding surface.

  The electroless gold plating solution of the present invention contains a gold cyanide compound, oxalic acid and / or a salt thereof, and does not contain a base metal elution inhibitor, so that the surface of the nickel film 4 is appropriately corroded during plating. Is done. As a result, as shown in FIG. 1, fine irregularities are formed at the interface 10 between the nickel coating 4 and the gold plating coating 6. Fine irregularities formed at the interface 10 between the nickel film 4 and the gold plating film 6 increase the contact area at the interface between the two. As a result, the adhesive strength between the two is improved.

  In contrast, when gold plating is performed with a conventional substitutional electroless gold plating solution containing a base metal elution inhibitor, the nickel film surface is kept smooth by the reducing action of the base metal elution inhibitor. As a result, the contact area between the gold plating film and the nickel film 4 is kept relatively small. Therefore, the wire bonded to the gold plating film is easily peeled between the gold plating film 6 and the nickel film 4.

  FIG. 2 shows a case where solder ball bonding is performed on the gold plating film 26. FIG. 2A shows a state before the solder balls are joined. In FIG. 2, 22 is a copper base portion, 24 is a nickel coating formed by electroless plating, and 26 is an electroless gold plating coating formed on the surface of the nickel coating 24.

  FIG. 2B shows a state after the solder balls 32 are joined to the gold plating film 26. In this case, the portion of the gold plating film 26 where the solder ball 32 is bonded is absorbed into the solder ball 32 and alloyed during bonding. As a result, the solder ball is directly bonded to the nickel film 24. The nickel film 24 has higher adhesion to the solder balls 32 on the non-oxidized surface than on the oxidized surface. Therefore, when solder ball bonding is performed, it is preferable to add a base metal elution inhibitor to the electroless gold plating solution to prevent oxidation of the nickel film 24. Reference numeral 34 denotes a solder resist.

  The electroless gold plating solution of the present invention includes, as other optional components, a base elution metal concealing agent (chelating agent), a pH buffering agent, a crystal adjusting agent, and various additives usually added to the gold plating solution. Can be added. These addition amounts follow a conventional method.

  As the masking agent for the base eluting metal, various chelating agents having an iminodiacetic acid structure such as ethylenediaminetetraacetic acid, hydroxyethyliminodiacetic acid, nitrotriacetic acid in the molecule, and / or salts thereof are preferable. Of these, ethylenediaminetetraacetic acid is particularly preferred. The density | concentration of the masking agent of the base elution metal in an electroless gold plating solution becomes like this. Preferably it is 1-30 g / L, More preferably, it is 3-10 g / L. If the concentration of the masking agent for the base eluted metal is less than 1 g / L, the masking effect of the eluted metal is weak, and if it exceeds 30 g / L, corrosion of the electroless nickel film tends to occur. The salt is preferably a sodium salt or a potassium salt.

  As the pH buffering agent, phosphate, borate, phthalate and the like can be used. As the phosphate, for example, potassium hydrogen phosphate, potassium dihydrogen phosphate, and dipotassium hydrogen phosphate can be used. The concentration of the pH buffer in the electroless gold plating solution is preferably 1 to 50 g / L, more preferably 3 to 30 g / L. When the buffer concentration is less than 3 g / L, the fluctuation of pH is large, and when it exceeds 50 g / L, there is no particular problem, but it is not economical.

  Examples of the crystal modifier include at least one selected from the group consisting of arsenic compounds, thallium compounds, and lead compounds. As the arsenic compound, thallium compound and lead compound, for example, arsenous acid, arsenic acid, thallium acetate, thallium sulfate, thallium nitrate, thallium formate, thallium malonate, lead acetate, lead nitrate and lead chloride can be used.

  In the electroless gold plating solution of the present invention, the total content of at least one selected from the group consisting of arsenic compounds, thallium compounds and lead compounds is preferably 1 to 100 mg / L, more preferably 2 to 50 mg / L. is there. When the content of these crystal modifiers is less than 1 mg / L, there is no effect of promoting smooth crystal growth, and when it exceeds 100 mg / L, the plating appearance tends to deteriorate.

  The pH of the electroless gold plating solution of the present invention is preferably 4.5 to 7.0, more preferably 5.0 to 6.5, and particularly preferably 5.0 to 6.0. When the pH is less than 4.5, the stability of the plating solution is deteriorated. When the pH exceeds 7.0, the underlying metal tends to be corroded. The pH is preferably adjusted by adding potassium hydroxide, sodium hydroxide, ammonium hydroxide or the like.

  The electroless gold plating solution of the present invention can be used at a solution temperature of 60 to 95 ° C, but more preferably 70 to 90 ° C. When the temperature of the plating solution is less than 60 ° C., the progress of the plating is slow, and when it exceeds 95 ° C., the plating solution is easily decomposed.

  Although the plating time is related to the plating temperature, it is usually preferably 1 to 20 minutes, more preferably 3 to 10 minutes, and about 5 minutes is a normal plating time.

  The present invention will be described in more detail with reference to examples.

[Example 1]
A resin test substrate (a line width of 50 to 100 μm, a bonding pad, and a land diameter of 0.6 mm for shear strength) having a copper substrate fine circuit with a size of 50 × 50 mm formed using a solder resist was prepared. An electroless nickel plating film having a thickness of 5 μm was formed on the test substrate using a commercially available electroless nickel plating solution (SN-150 manufactured by Nippon Kanisen). Hereinafter, this electroless nickel-plated substrate is referred to as a nickel-plated sample.

  2 g / L of potassium gold cyanide as Au, 20 g / L of potassium oxalate monohydrate, 5 g / L of ethylenediaminetetraacetic acid, 5 g / L of potassium dihydrogen phosphate dissolved in pure water A replacement electroless gold plating solution was prepared.

  The base gold plating solution was adjusted to pH 5.0, the solution temperature was set to 85 ° C., and the nickel plating sample was immersed in this for 5 minutes to perform the base gold plating treatment. Hereinafter, the substrate subjected to the base gold plating process is referred to as a base gold plating sample. The base gold plating sample was taken out from the plating solution, and the deposited film thickness was measured with a film fluorescent X-ray thickness meter. The gold film thickness of the base gold plating sample was 0.05 μm.

[Example 2]
The plating solution prepared in Example 1 was adjusted to pH 7.0 with potassium hydroxide, the solution temperature was 85 ° C., and the nickel plating sample was immersed in this for 5 minutes. After 5 minutes, the base gold plating sample was taken out, and the deposited film thickness was measured with a film fluorescent X-ray thickness meter. The gold film thickness of the base gold plating sample was 0.05 μm.

[Comparative Example 1]
2 g / L of potassium gold cyanide in pure water, 20 g / L of potassium oxalate monohydrate, 5 g / L of ethylenediaminetetraacetic acid, 5 g / L of potassium dihydrogen phosphate, 5 g / L of benzotriazole Dissolved electroless gold plating solution was prepared by dissolution.

  This aqueous solution was adjusted to pH 5.0, and the nickel plating sample was immersed for 5 minutes at a liquid temperature of 85 ° C. After 5 minutes, the base gold plating sample was taken out from the plating solution, and the deposited film thickness was measured with a film fluorescent X-ray thickness meter. The gold film thickness of the base gold plating sample was 0.04 μm.

[Comparative Example 2]
The plating solution prepared in Comparative Example 1 was adjusted to pH 7.0 with potassium hydroxide, and the nickel plating sample was immersed for 5 minutes at a solution temperature of 85 ° C. After 5 minutes, the base gold plating sample was taken out from the plating solution, and the deposited film thickness was measured with a film fluorescent X-ray thickness meter. The gold film thickness of the base gold plating sample was 0.03 μm.

[Evaluation test]
The base gold-plated samples obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were further subjected to electroless gold plating overcoating using a reduced gold plating solution (Super Chemx # 850 manufactured by N.E. Chemcat). The gold film thickness was 0.5 μm. Hereinafter, the substrate on which the top coat gold plating is performed is referred to as a top coat gold plating sample. A wire bonding pull strength test was performed on the obtained top coat gold plating sample, and the test results shown in Table 1 were obtained.

  In Table 1, “unbondable wire” refers to the number of wires that are not bonded by 20 wire bondings.

[Example 3]
Except not adding EDTA, it operated similarly to Example 1 using the substitution electroless gold plating solution for base gold plating similar to Example 1. FIG.

  The deposited film thickness was measured with a film fluorescent X-ray thickness meter. The gold film thickness of the base gold plating sample was 0.05 μm. The properties of the gold plating film were the same as in Example 1. The same operation was repeated three more times, but no abnormality occurred and the properties of the gold plating film were good.

  As for the test result, Examples 1-2 were good in both the number of wire joining, and pull strength compared with Comparative Examples 1-2.

It is a schematic explanatory drawing which shows the example of wire bonding joining with respect to the electroless gold plating film formed using the electroless gold plating liquid of this invention. It is a schematic explanatory drawing which shows the example which carries out the plating ball joining with respect to the electroless gold plating film formed using the conventional electroless gold plating solution. FIG. 2A shows a state before the solder balls are joined. FIG. 2B shows a state after the solder balls 32 are joined to the gold plating film 26.

Explanation of symbols

2 Copper substrate portion of copper wiring board 4 Electroless nickel coating 6 Electroless gold plating coating 8 Gold lead wire 10 Interface between nickel coating and gold plating coating 22 Copper substrate 24 Nickel coating 26 Electroless gold plating coating 32 Solder ball 34 Solder resist

Claims (8)

A copper wiring composition characterized by containing a gold cyanide compound in a gold ion concentration of 0.5 to 10 g / L , oxalic acid and / or a salt thereof in an amount of 5 to 50 g / L, and containing no base metal elution inhibitor . A substitution electroless gold plating solution for forming a gold plating film , for wire bonding joining to the surface of a nickel film formed on the surface of a copper substrate . The substitutional electroless gold plating solution according to claim 1, which contains a masking agent for the base eluting metal. The substitutional electroless gold plating solution according to claim 2 , wherein the base eluting metal concealing agent is ethylenediaminetetraacetic acid and / or a salt thereof. The substitutional electroless gold plating solution according to claim 1, comprising a crystal modifier, wherein the crystal modifier is at least one selected from the group consisting of an arsenic compound, a thallium compound, and a lead compound. A substituted electroless gold plating solution containing 0.5 to 10 g / L of gold cyanide compound in gold ion concentration, 5 to 50 g / L of oxalic acid and / or a salt thereof , and containing no base metal elution inhibitor. , wherein the substituted electroless gold plating the formed nickel film surface on the surface of the copper matrix portion of the copper wiring Ru to form a gold plating film, substituted electroless gold plating method for wire bonding junction. Substituted electroless gold plating method according to claim 5 using a substituted electroless gold plating solution containing a base dissolved metal masking agent. The substitution electroless gold plating method according to claim 6 , wherein the base eluting metal concealing agent is ethylenediaminetetraacetic acid and / or a salt thereof. Containing crystal modifiers, the crystal modifier arsenic compounds, thallium compounds and substituted electroless gold plating according to claim 5 using a substituted electroless gold plating solution is at least one selected from the group consisting of lead compounds Way .

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