CN111164236A

CN111164236A - Electroless palladium plating solution and electroless palladium plating film

Info

Publication number: CN111164236A
Application number: CN201880064756.9A
Authority: CN
Inventors: 前田刚志; 田边克久; 和田真辅
Original assignee: C Uyemura and Co Ltd
Current assignee: C Uyemura and Co Ltd
Priority date: 2017-10-06
Filing date: 2018-10-03
Publication date: 2020-05-15
Also published as: JP2019070172A; WO2019069964A1; EP3693495A1; EP3693495A4; TW201925531A; JP7149061B2; KR20200062265A; US20200248312A1; TWI829653B

Abstract

The object of the present invention is to provide an electroless palladium plating solution which can obtain a Pd plating film that constitutes a plating film having excellent wire bondability even after a thermal process, and which is characterized by containing a palladium compound, at least one selected from hypophosphorous acid compounds and phosphorous acid compounds, at least one selected from amine borane compounds and borohydride compounds, and a complexing agent.

Description

Electroless palladium plating solution and electroless palladium plating film

Technical Field

The invention relates to a chemical palladium plating solution and a chemical palladium plating film.

Background

In the field of electronics industry, as a surface treatment method for a circuit of a printed circuit board, a mounting portion of an IC package, a terminal portion, or the like, a plating film (hereinafter, also referred to as "Electroless Ni/Pd/Au plating film") in which Electroless Nickel plating, Electroless Palladium plating, and Gold substitution (Electroless Nickel plating, Electroless Palladium plating, and Electroless Gold plating, respectively, are sequentially performed by an ENEPIG process, and which is capable of providing an excellent effect on plating film characteristics such as solder bondability and wire bondability (ENEPIG), is widely used.

In recent years, in order to meet the characteristics of plating films required for miniaturization and densification of electronic parts, there has been proposed a technique for improving the characteristics of plating films by improving electroless palladium plating solutions (hereinafter also referred to as "electroless Pd plating solutions"), for example.

For example, patent document 1 proposes an electroless Pd plating solution in which bismuth or a bismuth compound is used as a stabilizer instead of a sulfur compound, thereby obtaining a film having high bath stability, excellent corrosion resistance, solder bondability, and wire bondability to the same extent as in the case of using a sulfur compound.

Documents of the prior art

Patent document

Patent document 1: patent No. 4596553

Disclosure of Invention

The widely used electroless Ni/Pd/Au plating film has a problem that it exhibits excellent wire bondability before being exposed to a high-temperature thermal process such as reflow treatment, but the wire bondability is significantly reduced after the high-temperature thermal process.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an electroless Pd plating solution capable of obtaining a Pd plating film that constitutes a plating film having excellent wire bondability even after a high-temperature thermal process, and a Pd plating film.

The electroless palladium plating solution of the present invention, which solves the above problems, is characterized by containing a palladium compound, at least one selected from hypophosphorous acid compounds and phosphorous acid compounds, at least one selected from amine borane compounds and boron hydride compounds, and a complexing agent.

A preferred embodiment of the electroless palladium plating solution of the present invention further includes a configuration in which the following elements are arbitrarily combined.

(i) The amine borane compound is at least one selected from dimethylamine borane and trimethylamine borane;

(ii) the borohydride is borohydride;

(iii) the complexing agent is at least one selected from ammonia and amine compounds.

In addition, the invention also comprises an electroless palladium plating film which is characterized by containing phosphorus and boron. A structure in which an electroless gold plating film is further provided on the surface of the electroless palladium plating film is also a preferred embodiment of the electroless palladium plating film.

The invention also includes an electronic device constituent member having the electroless palladium plating film.

The electroless Pd plating solution of the present invention can provide a Pd plating film having excellent wire bondability even after a high-temperature thermal process such as reflow treatment.

Detailed Description

The present inventors have conducted intensive studies on the cause of a significant decrease in the connection output of the wire bonding after the laminated plating film "hereinafter also referred to as a Pd/Au laminated plating film" in which an Au plating film is formed on a Pd plating film is exposed to a high-temperature thermal process such as reflow. As a result, when the Au plating film is exposed to a high-temperature thermal process, Pd diffuses to the surface of the Au plating film, and a Pd — Au solid solution formed on the surface of the Au plating film lowers the connection power of the wire bonding. As one of the measures to solve such a problem, it is conceivable to form the Au plating film thick, but the cost is greatly increased.

As a result of further extensive studies, the inventors of the present invention have found that when a Pd plating film containing both P and B (hereinafter also referred to as "P-B-Pd ternary alloy plating film") is formed as an underlayer of an Au plating film, the wire bondability after a high-temperature thermal process can be improved. That is, when both P and B are contained in the Pd plating film, the formation of a Pd — Au solid solution on the surface of the Au plating film can be suppressed even by a high-temperature thermal process, and as a result, excellent wire bondability can be obtained as compared with the conventional ones even when the thickness is the same as or less than that of the conventional Au plating film.

The P-B-Pd ternary alloy plating film having such effects can be easily formed by using the electroless Pd plating solution of the present invention. Specifically, the electroless Pd plating solution of the present invention is an electroless Pd plating solution containing a palladium compound, at least one selected from hypophosphorous acid compounds and phosphorous acid compounds, at least one selected from amine borane compounds and boron hydride compounds, and a complexing agent.

In addition, various reducing agents for electroless Pd plating baths are known, and hypophosphorous acid compounds, phosphorous acid compounds, amine borane compounds and borohydride used in the plating bath of the present invention are also part thereof. However, conventionally, when a plurality of reducing agents having different reducing abilities are used in combination, the stability of the plating solution is deteriorated, and the plating film characteristics such as abnormal deposition are deteriorated, so that the reducing agent is not used. In particular, since the hypophosphorous acid compound or the phosphorous acid compound has sufficient reducing ability when used alone, it is not necessary to use the hypophosphorous acid compound or the phosphorous acid compound in combination with another reducing agent. However, the solid solution inhibiting effect of Pd on the Au plating film by the addition of the reducing agent alone and the use of the reducing agents other than the above cannot be obtained, and the Pd plating film can be formed at a practical level without causing the above-mentioned problems only in the above specific combination of the present invention, and this solid solution inhibiting effect is a specific effect obtained only by the above combination.

Palladium compound

The palladium compound is a source of palladium ions for obtaining the palladium plating layer. As the palladium compound, water-soluble compounds, for example, can be used: inorganic water-soluble palladium salts such as palladium chloride, palladium sulfate and palladium acetate; organic water-soluble palladium salts such as tetraamine palladium hydrochloride, tetraamine palladium sulfate, tetraamine palladium acetate, tetraamine palladium nitrate, and dichlorodiethylenediamine palladium. These palladium compounds may be used alone or in combination of two or more. The concentration of Pd ions in the electroless Pd plating solution is not limited, but if the concentration of Pd ions is too low, the deposition rate of the plating film is significantly reduced. On the other hand, if the Pd ion concentration is too high, the physical properties of the plating film may be deteriorated due to abnormal deposition or the like. Therefore, the content of the palladium compound in the plating solution is preferably 0.01g/L or more, more preferably 0.1g/L or more, further preferably 0.3g/L or more, further preferably 0.5g/L or more, preferably 10g/L or less, more preferably 5g/L or less, further preferably 3g/L or less in terms of the Pd ion concentration. The Pd ion is measured by Atomic Absorption Spectrometry (AAS) using an Atomic Absorption spectrophotometer.

In the electroless Pd plating solution of the present invention, in order to exhibit the solid solution inhibition effect of Pd, (1) at least one selected from the group consisting of a hypophosphorous acid compound and a phosphorous acid compound (hereinafter also referred to as "phosphoric acid compound") and (2) at least one selected from the group consisting of an amine borane compound and a borohydride compound (hereinafter also referred to as "boron compound") must be used in combination.

(1) At least one selected from the group consisting of a hypophosphorous acid compound and a phosphorous acid compound

These are a P supply source for supplying P to the Pd plating film, and function as a reducing agent for precipitating Pd in the electroless Pd plating solution. Examples of the hypophosphorous acid compound include hypophosphorous acid, sodium hypophosphite, and other hypophosphorous acid salts, and examples of the phosphorous acid compound include phosphorous acid, sodium phosphite, and other phosphorous acid salts. The hypophosphorous acid compound and the phosphorous acid compound may be used alone or in combination. If the content of the hypophosphorous acid compound and/or phosphorous acid compound in the electroless Pd plating solution is too small, the precipitation rate during plating treatment is lowered, and the effect of suppressing the solid solution of Pd into the Au plating film due to a high-temperature thermal process cannot be sufficiently obtained, resulting in deterioration of wire bondability. The greater the contents of the hypophosphorous acid compound and the phosphorous acid compound in the electroless Pd plating solution, the better the above-described solid solution inhibition effect, but the stability of the electroless Pd plating solution may be lowered. The contents of the hypophosphorous acid compound and the phosphorous acid compound in the electroless Pd plating solution (which may be contained individually in an amount of 2 or more, and in total) are preferably 0.1g/L or more, more preferably 0.5g/L or more, still more preferably 1g/L or more, yet more preferably 2g/L or more, preferably 100g/L or less, yet more preferably 50g/L or less, yet more preferably 20g/L or less, and still more preferably 15g/L or less.

(2) At least one selected from amine borane compounds and boron hydride compounds

These are boron supply sources for supplying boron to the Pd plating film, and function as reducing agents for precipitating palladium in the electroless Pd plating solution. Examples of the amine borane compound include dimethylamine borane (DMAB) and trimethylamine borane (TMAB), and examples of the boron hydride compound include alkali metal borohydride salts such as Sodium Borohydride (SBH) and potassium borohydride (KBH). In the present invention, at least one selected from the group consisting of dimethylamine borane, trimethylamine borane, sodium borohydride and potassium borohydride is preferably used. If the boron compound content in the electroless palladium plating solution is too low, the precipitation rate during plating treatment is reduced, and the effect of suppressing the solid solution of Pd in the Au plating film due to the high-temperature thermal process is not sufficiently obtained, resulting in deterioration of wire bondability. The solid solution inhibiting effect is more improved as the content of the boron compound in the electroless Pd plating solution is higher, but the stability of the electroless Pd plating solution may be lowered. The boron compound content (which may be an amount of 2 or more by itself, or a total amount in the case of 2 or more by itself) in the electroless Pd plating solution is preferably 0.01g/L or more, more preferably 0.1g/L or more, still more preferably 0.5g/L or more, yet more preferably 1g/L or more, preferably 100g/L or less, still more preferably 50g/L or less, still more preferably 30g/L or less, and still more preferably 20g/L or less.

Complexing agents

The complexing agent mainly has the function of stabilizing the solubility of Pd in the electroless Pd plating solution. The complexing agent may be any known complexing agent, preferably at least one selected from ammonia and amine compounds, and more preferably an amine compound. Examples of the amine compound include: methylamine, dimethylamine, trimethylamine, benzylamine, methylenediamine, ethylenediamine derivatives, tetramethylenediamine, diethylenetriamine, ethylenediaminetetraacetic Acid (EDTA) or alkali metal salts thereof, EDTA derivatives, glycine. The complexing agents may be used alone or in combination of two or more. The content of the complexing agent in the electroless Pd plating solution (which may be an amount of 2 or more by itself, or a total amount thereof) may be appropriately adjusted so as to obtain the above-described effects, and is preferably 0.5g/L or more, more preferably 1g/L or more, still more preferably 3g/L or more, still more preferably 5g/L or more, preferably 50g/L or less, and still more preferably 30g/L or less.

The electroless Pd plating solution of the present invention can achieve the above-described effects by having the above-described composition of components, and therefore can be composed of only the above-described composition of components, but can contain various additives such as a pH adjuster and a stabilizer as needed.

pH regulator

In the Pd plating solution of the present invention, if the pH is too low, the precipitation rate of Pd tends to decrease, and on the other hand, if the pH is too high, the stability of the electroless palladium plating solution may decrease. Preferably at a pH of 4-10, more preferably at a pH of 6-8. The pH of the electroless palladium plating solution can be adjusted by adding a known pH adjuster. Examples of the pH adjuster include: hydrochloric acid, sulfuric acid, nitric acid, citric acid, malonic acid, malic acid, tartaric acid, phosphoric acid, and other acids, and sodium hydroxide, potassium hydroxide, ammonia water, and other bases. These may be used singly or in combination of two or more.

Stabilizer

The stabilizer is added as necessary for the purpose of improving plating stability, appearance after plating, adjusting plating film formation speed, and the like. The electroless Pd plating solution of the present invention may further contain a known sulfur-containing compound. The sulfur-containing compound is preferably one or more compounds selected from the group consisting of a thioether compound, a thiocyanate compound, a thiocarbonyl compound, a thiol compound, thiosulfuric acid, and a thiosulfate. Specifically, there may be mentioned: thioether compounds such as methionine, dimethyl sulfoxide, thiodiglycolic acid, and benzothiazole; thiocyanate compounds such as thiocyanic acid, potassium thiocyanate, sodium thiocyanate, and ammonium thiocyanate; thiocarbonyl compounds such as thiourea and derivatives thereof; thiol compounds such as cysteine, thiolactic acid, thioglycolic acid, mercaptoethanol, and butanethiol; sodium thiosulfate and the like. These sulfur-containing compounds may be used alone or in combination of two or more. The content of the stabilizer in the electroless Pd plating solution (which may be an individual amount, or a total amount when 2 or more are contained) may be appropriately adjusted so as to obtain the effect such as plating stability, and is preferably 0.1mg/L or more, more preferably 0.5mg/L or more, preferably 500mg/L or less, and more preferably 100mg/L or less.

In addition, the electroless Pd plating solution does not contain a surfactant. If a surfactant is added to the electroless Pd plating solution of the present invention, the surface of the obtained Pd plating film is in a state of adsorbing the surfactant, and the film forming property of the Au plating film is poor. As a result, the wire bondability also deteriorates. Surfactants are various well-known nonionic, cationic, anionic and amphoteric surfactants.

The invention comprises a Pd plating film containing P and B, which is prepared by using the chemical Pd plating solution. Since the solid solution inhibition effect of Pd can be obtained if both P and B are contained in the Pd plating film, each content is not limited, but if the content of P and B contained in the Pd plating film is increased, a more excellent solid solution inhibition effect of Pd can be obtained. The P content in the Pd-plated film is preferably 0.1 mass% or more, more preferably 0.3 mass% or more, preferably 10 mass% or less, and more preferably 5 mass% or less. The B content in the Pd plating film is preferably 0.1 mass% or more, more preferably 0.5 mass% or more, preferably 15 mass% or less, and more preferably 10 mass% or less. Further, by appropriately controlling the ratio of P and B, a more excellent solid solution suppressing effect of Pd can be obtained. The mass ratio (P: B) of the contents of P and B in the electroless Pb-plated film is preferably 10: 1-1: 10, more preferably 5: 1-1: 5. the Pd plating film of the present invention may contain P, B, and may contain components derived from the above-mentioned various additives. The balance being Pd and unavoidable impurities.

The electroless Pd plating solution of the present invention is preferably also suitable for use as a Pd/Au laminated plating film in which an Au plating film is laminated on a Pd plating film used for plating for bonding of electronic parts and the like. Therefore, the laminated plating film having the Pd plating film and the Au plating film of the present invention is also a preferable embodiment. The Pd plating film of the present invention can confirm the solid solution inhibiting effect of Pd at least in the Pd/Au laminated plating film in which Au plating films are laminated. Therefore, the base for forming the Pd plating film is not limited, and examples thereof include various known substrates such as Al, Al-based alloys, Cu, and Cu-based alloys, and plating films obtained by covering the substrates with a metal having catalytic activity, which is deposited by reduction of the Pd plating film using Fe, Co, Ni, Cu, Zn, Ag, Au, Pt, and alloys thereof. In addition, even if the metal is not catalytic, it can be used as the plating object by various methods.

In another preferred embodiment, the electroless palladium plating solution of the present invention can be applied to an ENEPIG process. In the ENEPIG process, an electroless Ni/Pd/Au plating film containing the Pd plating film of the present invention is obtained by forming a Ni plating film on Al or an Al-based alloy, Cu or a Cu-based alloy constituting an electrode, then forming a Pd plating film, and further forming an Au plating film thereon. In addition, the formation of each plating film may be performed by a method generally performed. The method for producing the electroless Ni/Pd/Au plating film having a Pd plating film of the present invention will be described below based on the ENEPIG process, but the conditions for forming the Pd plating film of the present invention are not limited thereto and may be appropriately changed according to the known techniques.

The plating conditions and plating apparatus for electroless Ni plating using the electroless Ni plating solution are not particularly limited, and various known methods can be appropriately selected. For example, the object to be plated is contacted with the chemical Ni plating solution at 50-95 ℃ for about 15-60 minutes. The thickness of the Ni plating film may be appropriately set according to the required characteristics, and is usually about 3 to 7 μm. In addition, various known compositions such as Ni-P alloy and Ni-B alloy can be used as the electroless Ni plating solution.

The plating conditions and plating apparatus for the electroless plating of Pb using the electroless Pd plating solution of the present invention are not particularly limited, and various known methods can be appropriately selected. For example, the Ni plating film is formed on the plating object and contacted with the chemical Pd plating solution at 50-95 ℃ for about 15-60 minutes. The thickness of the Pd plating film may be appropriately set according to the required characteristics, and is usually about 0.001 to 0.5. mu.m.

The plating conditions and plating apparatus for electroless gold plating using the electroless gold plating solution are not particularly limited, and various known methods can be appropriately selected. For example, the object to be plated with the Pd plating film is contacted with an electroless gold plating solution at a temperature of 40-90 ℃ for about 3-20 minutes. The thickness of the gold plating film may be appropriately set according to the required characteristics, and is usually about 0.01 to 2 μm.

When the Pd plating film of the present invention is used, diffusion and solid solution of palladium from the Pd plating film to the Au plating film due to a thermal process in a mounting step after the formation of the plating film such as reflow treatment can be suppressed, and therefore, excellent wire bondability can be achieved even after the thermal process. The temperature of the thermal process is a temperature assumed in the mounting step, and is not particularly limited. When the Pd plating film of the present invention is used, excellent wire bondability can be achieved even after a thermal process at a high temperature of, for example, 50 ℃ or higher, more preferably 100 ℃ or higher.

Electronic device component

The invention also provides an electronic equipment component with the coating film. Examples of the electronic device component include: the chip component, the crystal oscillator, the bump, the connector, the lead frame, the hoop material, the semiconductor package, and the printed circuit board are formed. Particularly suitable for UBM (under Barrier Metal) formation technology for the purpose of solder bonding and wire bonding (W/B) bonding of Al electrodes or Cu electrodes on a wafer. By laminating an Au plating film on a Pd plating film using the electroless Pd plating solution of the present invention, excellent wire bondability can be achieved even after a thermal process.

The present application claims the benefit of priority from japanese patent application No. 2017-195651, filed on 6/10/2017. The entire contents of the specification of japanese patent application No. 2017-195651, filed on 6.10.2017, are incorporated herein by reference.

Examples

The present invention will be described more specifically below with reference to examples, but the present invention is not limited to the following examples, and can be carried out with modifications within a range that meets the aforementioned and later-described gist, and all of them are included in the technical scope of the present invention.

A BGA substrate (Ball Grid Array, 5 cm. times.5 cm, manufactured by Shanmura industries, Ltd.) was subjected to the pretreatment and plating treatment shown in Table 1 in this order, and test pieces 1 to 20 were prepared in which a Ni plating film, a Pd plating film, and an Au plating film were formed in this order from the substrate side. The obtained test piece was examined for wire bondability.

Wire bondability

Wire bonding was performed using a test apparatus (semiautomatic wire bonding machine HB16 manufactured by TPT), and 20 points were evaluated for each condition under the following measurement conditions using a Bondtester SERIES4000 manufactured by Dage. In addition, the measurement was performed before and after the heat treatment (holding at 175 ℃ C. for 16 hours). As the wire bondability evaluation, the case where the average wire bonding strength after the heat treatment was 9.0g or more was evaluated as "good", the case where the average wire bonding strength was 8.5g or more and less than 9.0g was evaluated as "good", the case where the average wire bonding strength was 7.5g or more and less than 8.5g was evaluated as "pass", and the case where the average wire bonding strength was less than 7.5g was evaluated as "poor".

[ measurement conditions ]

Capillary tube: b1014-51-18-12 (manufactured by PECO Co.)

Leading wires: 1mil-Au wire (SPM company)

Stage temperature: 150 ℃ C

Ultrasonic wave (mW): 250(1st), 250(2nd)

Bonding time (milliseconds): 200(1st), 50(2nd)

Tensile force (gf): 25(1st), 50(2nd)

Step size (length from first to second): 0.7mm

The measurement method comprises the following steps: lead testing

The device comprises the following steps: universal strength tester #4000 (manufactured by Nordson Advanced Technology K.K.)

Testing speed: 170 μm/sec

[ TABLE 1 ]

Preparation of Hao Chun Industrial society of Xian (color Green 1)

[ TABLE 2 ]

As shown in Table 2, the wire bonding properties after the heat treatment of the test pieces No.1 to 9 using the electroless Pd plating solutions containing the "complexing agent", "hypophosphorous acid compound and/or phosphorous acid compound" and "amine borane compound and/or boron hydride compound" defined in the present invention were evaluated to be "good".

On the other hand, test pieces No.10-18 using electroless Pd plating solutions that do not satisfy the requirements of the present invention were evaluated for "poor" wire bondability after heat treatment. Since nos. 19 and 20 contained the surfactant, both of the wire bondability after the heat treatment was evaluated as "poor".

Claims

1. An electroless palladium plating solution, characterized in that the electroless palladium plating solution contains a palladium compound, at least one selected from hypophosphorous acid compounds and phosphorous acid compounds, at least one selected from amine borane compounds and boron hydride compounds, and a complexing agent.

2. The electroless palladium plating solution according to claim 1, wherein the amine borane compound is at least one selected from dimethylamine borane and trimethylamine borane, and the boron hydride compound is a borohydride salt.

3. The electroless palladium plating solution according to claim 1 or 2, wherein the complexing agent is at least one selected from ammonia and amine compounds.

4. An electroless palladium plating film is characterized by containing phosphorus and boron.

5. The electroless palladium plating film according to claim 4, further comprising an electroless gold plating film on the surface of the electroless palladium plating film.

6. An electronic device constituent member having the electroless palladium plating film according to claim 4 or 5.