CN114959664A

CN114959664A - Activating solution and method for electroless plating treatment of non-conductive areas

Info

Publication number: CN114959664A
Application number: CN202110871558.7A
Authority: CN
Inventors: 张家诚
Original assignee: Chaote International Co ltd
Current assignee: Chaote International Co ltd
Priority date: 2021-02-24
Filing date: 2021-07-30
Publication date: 2022-08-30
Also published as: US20220267906A1

Abstract

The invention relates to an activation solution and a method for electroless plating of non-conductive areas. The invention discloses a novel activator system for electroless plating, in particular the activator may be free of tin and surfactants. The activators of the present invention are preferably used for electroless copper plating.

Description

Activating solution and method for electroless plating treatment of non-conductive areas

Technical Field

The present invention relates generally to the field of activators for metallization, and in particular to a novel activator system for electroless metallization. The activator system of the present invention is preferably used for electroless copper plating.

Background

Generally, a Printed Circuit Board (PCB) is an assembly into which electrical leads are integrated so that various devices can be mounted therein or electrically connected to each other. Due to the progress of technology, PCBs having various forms and functions are being introduced. As industries using PCBs grow, demands for PCBs have been increased, such as home appliances, communication devices, semiconductor devices, industrial machinery, vehicle electronic control, and related industries.

Electroless metal coatings have a wide range of applications, including use in printed circuit board and non-conductor manufacturing processes (e.g., decorating and processing plastic substrates). Printed circuit boards comprise a laminated non-conductive dielectric substrate (substrate) that must be drilled and plated through-holes (vias) to allow access between the sides or interior layers of the boardA connection is formed. As is well known, electroless plating has been used to produce a metal coating on a surface, and prior to plating the metal, an activator must be pre-deposited on the dielectric surface. One common method of catalyzing or activating a non-conductive dielectric substrate is to treat the substrate with an aqueous tin/palladium colloid prior to electroless plating. The colloid comprising a core of palladium metal surrounded by a stabilizing layer of a complex of tin (II) ions, e.g. SnCl ^3- As surface stabilizing groups to avoid aggregation of the colloid in suspension.

During activation, the palladium colloid is adsorbed onto an insulating substrate, such as epoxy or polyimide, to catalyze subsequent electroless copper plating. In theory, the activator particles function as supports in the path of electrons from the reducing agent to the metal ions in the electroplating bath. Although the performance of electroless plating is also affected by other factors such as bath solution composition and ligand (ligand) selection, the activation step is still a key factor in controlling the rate and mechanism of electroless plating. Tin/palladium colloids have been used commercially for decades as activators for electroless metallization, however, there is room for improvement in the sensitivity of palladium to air and the high cost thereof. In addition, the residual palladium adsorbed on the surface of the resin must be removed again to prevent a possible short circuit between two copper wires, which also increases the cost of the entire manufacturing process.

The search for new and better activators continues. For example, because of the high cost of palladium, much effort has been focused on the development of non-noble metal activators, particularly colloidal copper activators. However, such activators have not exhibited sufficient activity or reliability for via plating. In addition, these activators also generally become progressively inactive during storage, making such activators less reliable and impractical for commercial use.

Disclosure of Invention

Accordingly, one aspect of the present invention relates to a composition for depositing an electroless plating activator on a substrate, the composition comprising one or more metal ions and one or more organic acids; wherein the organic acid has at least one carboxylic acid group (carboxylic group) and at least one hydroxyl group (hydroxyl group).

In some embodiments, the organic acid is dicarboxylic acid terminated and has a formula as in formula (I):

wherein R is ₁ Selected from straight-chain or branched, substituted or unsubstituted C ₁ -C ₆ Alcohols.

In some embodiments, the organic acid is selected from tartaric acid (tartaratic), citric acid (citricacid), malic acid (malicacid), and 2, 2-bis (hydroxymethyl) malonic acid (2, 2-bis (hydroxymethyl) malonic acid).

In some preferred embodiments, the organic acid is tartaric acid or malic acid.

In some embodiments, the organic acid has a formula as in formula (II):

R ₂ -COOH (II)，

wherein R is ₂ Selected from straight-chain or branched, substituted or unsubstituted C ₁ -C ₆ Alcohols.

In some embodiments, the organic acid is selected from glyceric acid (glyceric acid), glycolic acid (glycolic acid), and lactic acid (lactic acid).

In some preferred embodiments, the organic acid is glyceric acid.

In some embodiments, the metal ion is selected from palladium, copper, silver, gold, platinum, iridium, aluminum, cobalt, and nickel ions.

In some preferred embodiments, the metal ions are copper ions.

In some embodiments, the pH of the composition is greater than 9.

Another aspect of the invention relates to a method of depositing an electroless plating activator on a substrate, comprising: (a) applying the composition to a substrate; (b) a reducing agent is applied to the substrate.

In some preferred embodiments, the reducing agent is dimethylamine borane (Dimethylamin)eBorane, DMAB) or NaBH ₄ 。

Yet another aspect of the invention relates to a method of forming an electroless copper plating film on a substrate, comprising: (a) depositing said electroless plating activator on a substrate; (b) electroless copper plating on the substrate.

In some embodiments, the plating bath used in the electroless plating step comprises: tartrate (tartrate), copper ions, Formaldehyde (formaldehydes), and 2,2-bipyridine (2, 2-bipyridine).

Drawings

FIG. 1 depicts a proposed chelation model of a chelator having one-COOH and one-OH with a metal ion, where R represents a linker.

FIG. 2 depicts a proposed chelation model for chelating agents with two-COOH and one-OH groups with metal ions, where R represents a linker group.

Figure 3 shows the proposed binding pattern of tartaric acid to metal ions.

FIG. 4 shows the via plating coverage of (A) example 1 and (B) comparative example 1 tested with a backlight.

FIG. 5 shows the through-hole plating coverage of (A) example 2 and (B) comparative example 2 tested with a backlight.

FIG. 6 shows the via plating coverage of (A) example 3 and (B) comparative example 3 tested with a backlight.

Fig. 7 shows the via plating coverage of example 4 tested in a backlight.

Detailed Description

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present specification will control.

The terms "electroplating" and "deposition" are used interchangeably in this specification. All amounts are weight percentages unless otherwise indicated. All numerical ranges are inclusive and combinable in any order unless the numerical ranges are limited to add up to 100% logical.

The technical content, characteristics and effects of the present invention will be described below by using specific embodiments and implemented accordingly, but not limiting the scope of the present invention. Generally, when the substrate to be metallized is a dielectric material on the surface of a printed circuit board or on the walls of a via, the substrate is degreased (degreasing) and then desmearing (desmearing) is performed on the walls of the via. Preferably, the substrate to be plated is a metal-clad substrate having a dielectric material and a plurality of through holes. Firstly, cleaning and degreasing the base material, and then removing glue residue on the through hole wall. Typical via desmear or dielectric preparation and softening or desmear utilizes a fluffer (sweller solvent).

Conditioning may be performed after desmearing, and examples of conditioning agents in the present disclosure include monoethanolamine (monoethanolamine), one or more quaternary amines (quaternaryamine), one or more nonionic surfactants, one or more conditioning polymers, and a pH adjuster. In some embodiments, such conditioning agents comprise 5-20g/L monoethanolamine, 0.1-15g/L triethanolamine (triethanolamine), 0.1-10g/L triton X-100(Dow Inc.), 1-5g/L basotronic PVI BASF, and sodium hydroxide for pH adjustment. The substrate and the via can then be rinsed with water.

The whole hole may be followed by microetching (microetching). The purpose of microetching is to impart microscopic roughness to the copper surfaces (e.g., the inner copper and surface copper surfaces) to enhance adhesion of subsequent electroless and electroplated layers. The microetching cleaning solution contains 50-150g/L of sodium persulfate and 10-30ml/L of sulfuric acid (98 wt%). The microetched substrate was rinsed with water to perform the following procedure.

The microetched substrate and vias may be pre-dipped to help stabilize the pH of the activation bath and clean the metal surface. The advantage of using a prepreg, which helps to improve interconnect defects and increase reliability, is that conventional aqueous prepreg solutions are inorganic or organic acids with a pH range of 3-5.

However, in some embodiments of the invention, the activation is performed under alkaline conditions, and thus the pH of the pre-dip may also be greater than 7. The pre-dip solution can be sodium hydroxide, sulfuric acid, boric acid or

Which are combined to adjust to the desired pH. In some embodiments of the invention, the activation may be followed by a composition comprising a chelating agent and a metal salt under alkaline conditions.

Activator compositions comprising metal ions, organic acids having one or more carboxyl groups and one or more hydroxyl groups form stable aqueous solutions of complexes that are useful in catalyzing the deposition of electroless metal coatings. The activator composition of the invention is preferably alkaline, maintaining a substantially alkaline pH promotes complex formation of the composition ingredients, which also enhances the performance of the composition.

The organic acid having a carboxyl group and a hydroxyl group as a chelating agent provides sufficient chelating ability for metal ions, particularly copper ions. Proposed chelation patterns of such chelators with metal ions are shown in FIGS. 1 (1-COOH, 1-OH) and 2 (2-COOH, 1-OH), where R represents a linking group. The tartaric acid of the present invention illustrates the binding pattern of an acid having 2 carboxyl groups and 2 hydroxyl groups (as shown in FIG. 3).

The metal ions may be provided by conventional metal salts, which will typically be included in the activator solution to provide 20ppm to 5000ppm, preferably 200ppm to 1500ppm, of metal ions. Metal ions include, but are not limited to: silver, gold, platinum, palladium, copper, cobalt and nickel ions. Preferably, the metal ions are selected from copper and palladium ions. The source of the metal ions can be provided using conventional water-soluble metal salts known in the art and found in the literature.

If the activator is an ionic activator in which the metal ion has not been reduced to the metallic state, then applying a reducing agent to the substrate reduces the metal ion of the activator to the metal. The reducing solution may be applied by dipping the substrate in the reducing solution or spraying the reducing solution on the substrate. A preferred reducing solution is one containing 1-25g/L dimethylamine borane (DMAB). In some embodiments of the invention, however, the use of NaBH-containing compositions is also used ₄ The reducing solution of (1). Followed by activation of the substrate and the vias

The holes are optionally rinsed with water. It is noted that in some embodiments of the present disclosure, no flushing is required at this step.

The substrate and the walls of the vias are then plated with a metal, such as copper, a copper alloy, nickel or a nickel alloy, using an electroless plating bath. Preferably, the metal is plated on the via walls using copper. The plating time and temperature may be conventional, or alternatively the substrate may be immersed in an electroless plating bath or the electroless plating bath may be sprayed onto the substrate. Typically, the plating may be performed for 5 seconds to 30 minutes, however the plating time may vary depending on the thickness of the metal on the substrate.

The performance of activator systems for catalytic electroless plating can be evaluated by examining the plating coverage of the via walls. Each substrate through-hole was cut transversely to expose the copper-plated wall of the through-hole, and the plating coverage was determined by the light passing through the hole wall as observed under a microscope. If no light transmission was observed, the part was completely black, and rated 5 on the backlight test, indicating complete copper coverage of the via walls. If the light passes through the entire wall of the hole without any dark areas, this represents almost no metal coating on the wall, which is rated 0. If the walls of the wells have some dark and light areas, they are rated between 0 and 5.

When electroless plating is performed on a non-conductive substrate using the aqueous activator solution of the present invention, the following method can be used. The following is an example of electroless copper plating, and all examples are not intended to limit the scope of the present invention, but are intended to further illustrate the present invention.

Desmear/etch removal process

Supplied by super International Ltd

The base material is washed by alkaline expanding agent solution to remove grease, washed by water, micro-etched by alkaline permanganate solution, washed by water and finally immersed in reducing solution containing neutralizer and acid.

The flow after desmear/etch is further described as follows:

example 1

Supplied by super International Ltd

Supplied by basf

In this example, the microetched substrate is immersed in a pre-dip solution containing NaOH for subsequent alkaline activation. The activating composition comprises 1.44g/L tartaric acid (tartric) and 0.2g/L palladium ion, and the pH is adjusted to 12.1. Activated at 40 ℃ for 10 minutes and then rinsed with water.

The reducing solution contained 6g/LDMAB and the pH was adjusted to 9.5 using 1.0N NaOH. Reduction was carried out at 40 ℃ for 2 minutes, and the activated substrate was then rinsed with water.

The substrate was immersed in a 33 ℃ electrocesscumc (super international corporation) plating bath for 8 minutes. The backlight test results are shown in fig. 4A.

Comparative example 1

In this comparative example, the procedure was the same as in example 1 except for the following conditions. The pre-dip solution contains 1.0NH ₂ SO ₄ And the pH value is 2.3. The activating composition comprised 1.44g/L tartaric acid and 0.2g/L palladium ions, adjusted the pH to 1.3. The backlight test results are shown in fig. 4B.

According to example 1 and its comparative examples, activator compositions containing tartaric acid proved to be suitable for use at a pH between 12.1 and 1.3. However, backlight testing showed that the activator system performed better under alkaline conditions than under acidic conditions, with scores of 4.75 and 4.25, respectively. Deprotonation of carboxylic acids promotes chelation, thereby stabilizing metal ions, allowing these acids to mediate the activation process.

Example 2

In this example, the performance of the chelating agent malic acid (malicacid) in activation was tested. The microetched substrate was immersed in a prepreg solution containing 5.0g/L boric acid and having a pH of 9.0, and immersed at 25 ℃ for 5 minutes. The activating composition comprised 12.0g/L malic acid and 0.2g/L palladium ion, and the pH was adjusted to 12.6. Activated at 40 ℃ for 10 minutes and then rinsed with water.

The reducing solution contained 6g/LDMAB and the pH was adjusted to 9.5 using 1.0N NaOH. Reduction was carried out at 40 ℃ for 2 minutes, and the activated substrate was then rinsed with water. The substrate was immersed in a 33 ℃ electrolemsscumc (super international limited) plating bath for 8 minutes. The backlight test results are shown in fig. 5A.

Comparative example 2

In this comparative example, the procedure was the same as in example 2 except for the following conditions. The pre-dip solution contained boric acid 5.0g/L at pH 2.3. The activating composition contained 12g/L malic acid and 0.2g/L palladium ion, and the pH was adjusted to 1.3. The backlight test results are shown in fig. 5B.

Malic acid is another example of an organic acid having at least 1 carboxyl group and at least 1 hydroxyl group, and can also be used in the activation process at a pH between 12.6 and 1.3. The backlight test scores under alkaline and acidic conditions were 4.75 and 3.25, respectively.

Example 3

In this example, copper ions are used in place of the expensive palladium ions in the activator system. The microetched substrate was immersed in a prepreg solution containing NaOH at a pH of 9.0 and immersed at 25 ℃ for 5 minutes. The activating composition contained 5.0g/L tartaric acid and 1.5g/L copper ions, and the pH was adjusted to 12.0. Activated at 40 ℃ for 10 minutes and then rinsed with water.

The reduction was also carried out using DMAB, and it was selected whether or not the reduced substrate and the through-hole were rinsed with water. In some embodiments, however, electroless plating may be performed immediately after reduction without rinsing to avoid passivation of the as-deposited copper. The electroless plating bath contained 30g/L potassium sodium tartrate, 2.5g/L copper sulfate, 0.5g/L nickel sulfate, 10g/L NaOH, 4g/L formaldehyde and 60 mg/L2, 2' -bipyridine. The substrate was immersed in an electroless plating bath and reacted at 33 ℃ for 15 minutes. The backlight test results are shown in fig. 6A.

Comparative example 3

In this comparative example, the procedure was the same as in example 3 except for the following conditions. The reducing solution contained 12g/L DMAB, 20g/L boric acid and the pH was adjusted to 3.0 using 1.0N sulfuric acid. Backlight test results are shown in fig. 6B.

In example 3 and its comparative examples, it was demonstrated that copper ions are compatible with the activator system and that the subsequent reduction step is also one of the factors affecting the activation performance, the backlight fraction using alkaline or acidic condition reducing compositions being 4.75 and 3, respectively.

Example 4

The above table shows another example of using copper ions instead of palladium ions in the activator system. The activating composition contained 5.0g/L glyceric acid and 0.5g/L copper ions and the pH was adjusted to 12.0. Activation was carried out at 40 ℃ for 10 minutes. The reduction was carried out in a solution containing 2g/L of CaBH4pH12.6, and the reaction was carried out at 40 ℃ for 2 minutes.

The electroless plating bath contained 30g/L potassium sodium tartrate, 2.5g/L copper sulfate, 0.5g/L nickel sulfate, 10g/L NaOH, 4g/L formaldehyde and 60 mg/L2, 2' -bipyridine. The substrate was immersed in an electroless plating bath and reacted at 33 ℃ for 15 minutes. The backlight test score was 5 (as shown in fig. 7), indicating that glyceric acid and NaBH4 can be used for the activation and subsequent reduction steps, respectively.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not intended to limit the scope of the present invention. Any changes and modifications to the stereochemistry, concentration, temperature, pH, reaction time and spirit mentioned in the claims are to be included in the claims of this work.

Claims

1. A composition for depositing an electroless plating activator on a substrate, comprising at least one metal ion and at least one organic acid; wherein the organic acid has at least one carboxylic acid group and at least one hydroxyl group.

2. The composition of claim 1, wherein the organic acid is dicarboxylic acid terminated and has the following formula (I):

HOOC-R ₁ -COOH (I)，

wherein R1 is selected from straight or branched, substituted or unsubstituted C _1-6 An alcohol.

3. The composition of claim 2, wherein the organic acid is selected from the group consisting of tartaric acid, citric acid, malic acid, and 2, 2-bis (hydroxymethyl) malonic acid.

4. The composition of claim 3, wherein the organic acid is tartaric acid or malic acid.

5. The composition of claim 1, wherein the organic acid has the following formula (II):

R ₂ -COOH (II)，

wherein R is ₂ Selected from straight-chain or branched, substituted or unsubstituted C _1-6 An alcohol.

6. The composition of claim 5, wherein the organic acid is selected from the group consisting of glyceric acid, glycolic acid, and lactic acid.

7. The composition of claim 6, wherein the organic acid is glyceric acid.

8. The composition of claim 1, wherein the metal ion is selected from the group consisting of palladium, copper, silver, gold, platinum, iridium, aluminum, cobalt, and nickel ions.

9. The composition of claim 8, wherein the metal ions are copper ions.

10. The composition of claim 1 having a pH greater than 9.

11. A method of depositing an electroless plating activator on a substrate, comprising:

(a) applying the composition of claim 1 to a substrate;

(b) a reducing agent is applied to the substrate.

12. The method of claim 11, wherein the reducing agent comprises dimethylamine borane or NaBH ₄ 。

13. A method of forming an electroless copper plating film on a substrate, comprising:

(a) the method of claim 11 depositing an electroless plating activator on a substrate;

(b) electroless copper plating is performed on the substrate in a plating bath.

14. The method of claim 13, wherein the plating bath comprises: tartrate, copper ions, formaldehyde and 2,2' -bipyridine.