WO2023246676A1 - Low-copper-salt weakly-alkaline electronic copper electroplating liquid for compact copper filling of pcb blind hole, and electroplating method therefor - Google Patents

Abstract

Disclosed in the present invention are a low-copper-salt weakly-alkaline electronic copper electroplating liquid and a use thereof. The low-copper-salt weakly-alkaline electronic copper electroplating liquid is composed of deionized water, an inorganic bivalent copper salt, a coordination agent, a pH buffering agent, and a leveling agent. According to the present invention, an organic matter containing hydroxyl and/or carboxyl serves as a bivalent copper ion coordination agent, and the pH buffering agent and the leveling agent which have specific compositions and content are used, such that compact filling of a PCB blind hole is achieved; and the present invention has the characteristics of being simple in composition, low in copper salt concentration, weakly-alkaline, low in corrosivity, and easy to regulate and control.

Description

A low-copper salt weakly alkaline electronic electroplating copper solution for densely filling PCB blind holes with copper and its electroplating method

This application is required to be filed with the State Intellectual Property Office of China on June 24, 2022. The application number is: 202210732337.6. The name of the invention is: “A low copper salt weakly alkaline electronic electroplating copper liquid for dense filling of PCB blind hole copper and its Application" is based on the Chinese patent application and claims its priority. The disclosure content of the Chinese patent application is hereby incorporated into the text of this application as a whole.

Technical field

The invention belongs to the technical field of electronic electroplating, and specifically relates to a low copper salt weakly alkaline electronic electroplating copper liquid used for dense filling of copper in blind holes of PCB and an electroplating method.

Background technique

The printed circuit board (PCB) industry occupies an important position in the global electronic product manufacturing supply chain. PCB is one of the core components of all electronic systems. It can be used as a carrier for many devices (such as integrated circuits, resistors, capacitors and inductors, etc.) and is known as the "mother of electronic products". As one of the most basic hole structures in PCB, blind holes need to be densely filled with metal without pores to achieve high-quality interconnection of internal and external circuits. Metal copper has high electromigration resistance, excellent thermal conductivity (401W·m ^-1 K ^-1 ) and electrical conductivity (1.67μΩ·cm), so it is used as a filler metal. Acid sulfate electroplating of copper is the most common process for achieving void-free filling of blind vias.

It is known in the art that due to the special geometric structure of PCB blind holes, current is unevenly distributed in the holes and on the hole surface. The deposition rate of copper on the surface of the hole is higher than the deposition rate at the bottom of the hole, resulting in the rapid closure of the hole or the formation of voids in the hole. In order to achieve dense filling without pores, the acidic copper plating solution with high copper salt concentration (copper sulfate pentahydrate 180g/L or more) is commonly used in the existing technology, in which various low-concentration additives need to be added (less than 100mg/L, such as inhibitors, accelerators and levelers). However, due to the different consumption rates of each additive and the complex synergistic effects, it is difficult to precisely control the additives and their concentration changes, and the accompanying high-concentration sulfuric acid is extremely easy to corrode equipment. Therefore, it is necessary to invent an electronic electroplating copper solution that is different from the acidic sulfate electronic electroplating copper solution, is suitable for dense filling of blind holes, and has the characteristics of simple plating solution composition, low copper salt concentration, weak alkalinity, low corrosiveness, and easy control. liquid, which has important industrial application value.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the prior art and provide a low-copper salt weakly alkaline electronic electroplating copper solution for dense copper filling of blind holes in PCBs.

Another object of the present invention is to provide an electroplating method based on the above-mentioned low copper salt weakly alkaline electronic electroplating copper liquid.

The technical solution of the present invention is as follows:

A low-copper salt weakly alkaline electronic electroplating copper solution for densely filling PCB blind hole copper, consisting of deionized water, inorganic divalent copper salt, complexing agent, pH buffering agent and leveling agent, wherein,

The inorganic divalent copper salt is copper sulfate pentahydrate, copper nitrate trihydrate or anhydrous copper acetate. Its concentration in the low copper salt weakly alkaline electronic electroplating copper solution is 20-50g/L, and the divalent copper salt The concentration of ions is 5.1-17.6g/L,

The complexing agent is at least one of gluconate, tartrate, citrate or ethylenediaminetetraacetate, and its molar ratio to the divalent copper ion is 2-6:1,

The pH buffer is composed of sodium tetraborate and sodium bicarbonate, and the concentration of the sum of sodium tetraborate and sodium bicarbonate in the low copper salt weakly alkaline electronic electroplating copper solution is 24-60g/L,

The leveling agent is composed of a nitrogen-containing heterocyclic compound and an acetylenic alcohol compound in a mass ratio of 10:1-4, and the nitrogen-containing heterocyclic compound and the acetylenic alcohol compound are added to the low copper salt weakly alkaline electronic electroplating copper liquid. The concentrations in are 4-20g/L and 0.4-8g/L respectively.

In a preferred embodiment of the present invention, the concentration of the complexing agent in the low copper salt weakly alkaline electronic electroplating copper liquid is 29.5-554.4g/L.

In a preferred embodiment of the present invention, the mass ratio of the sodium tetraborate and the sodium bicarbonate is 1-5:1.

In a preferred embodiment of the present invention, the nitrogen-containing heterocyclic compound is benzimidazole, thymine, succinimide, hydantoin, dimethylhydantoin, nicotinic acid, nicotinamide, At least one of histidine and proline.

Further preferably, the nitrogen-containing heterocyclic compound is succinimide, dimethylhydantoin or proline.

In a preferred embodiment of the present invention, the acetylenic alcohol compound is at least one of butynediol, dipropoxybutynediol, propargyl alcohol and diethylaminopentynediol.

Further preferably, the acetylenic alcohol compound is butynediol or propargyl alcohol.

An electroplating method for dense copper filling of blind holes in PCB, applying the above-mentioned low copper salt weak alkaline electronic copper electroplating liquid.

In a preferred embodiment of the present invention, the method includes: adjusting the pH of the low copper salt weakly alkaline electronic electroplating copper solution to 8.0-10.5, setting the temperature to 25-65°C, and stirring, blowing air or The cathode movement is:, and different currents are set for three time periods in sequence for electroplating. .

Further preferably, the plating time and current in the three time periods are:

a. 0.2-0.5A/dm ² , 5-20min; b. 0.8-1.2A/dm ² , 20-40min; c. 1.8-2.2A/dm ² , 30-50min.

In acidic systems, commonly used additives are inhibitors, accelerators and leveling agents. The three additives have complex functions. Acidic systems require inhibitors and accelerators to achieve high-quality copper filling. The complexing agent used in the present invention can greatly improve the dispersion ability of the plating solution, and it is restored to charge transfer control and is not affected by diffusion. Levelers significantly affect the copper deposition process. The regulation of convection diffusion of the leveling agent is based on the different adsorption amounts at the pore opening and the bottom of the pores, and the different degrees of inhibition of copper reduction.

The leveling agent in the present invention is a nitrogen-containing heterocyclic compound and an acetylenic alcohol compound. The combination of the two produces a synergistic effect and enhances the influence of mass transfer and diffusion. The principle of synergy is: nitrogen-containing heterocyclic compounds and acetylenic alcohol compounds form a complex, which is strongly adsorbed at the pore opening and weakly adsorbed at the bottom of the pore opening, balancing the speed of copper reduction in the blind hole. Thus, the present invention achieves the following beneficial effects:

1. The present invention uses organic matter containing hydroxyl and/or carboxyl groups as divalent copper ion complexing agents, combined with pH buffers and leveling agents of specific composition and content, to achieve dense filling of PCB blind holes, with simple composition and low copper salt. Concentration, weak alkalinity, low corrosiveness, easy control and other characteristics.

2. The specific complexing agent in the present invention coordinates with divalent copper ions to increase the cathode reduction overpotential of copper ions and improve the dispersion and covering capabilities of the plating solution. When the mass concentration of the complexing agent is lower than 29.5g/L, the coordination agent The colocating agent cannot completely coordinate copper ions, and copper hydroxide precipitation is prone to occur; when the mass concentration of the coordinating agent is higher than 554.4g/L, the viscosity of the electronic plating solution increases and the dispersing ability decreases. In addition, the divalent copper ions in the present invention The copper coordination ions formed by coordination with the complexing agent are controlled by the charge transfer process during the electroreduction; if the copper coordination ions are controlled by diffusion during the reduction process, the leveler in the present invention will not be able to fully exert its effect.

3. The pH buffer in the present invention can stabilize the pH value at 8.0-10.5 during the electronic copper plating process. If the pH value is too high, the electroplating equipment will be corroded; if the pH value is too low, there will be a variety of copper with different structures in the electronic electroplating solution. Coordination distance The components are complex and are not conducive to the bottom-up dense filling of blind holes.

4. The leveling agent in the present invention can inhibit the reduction of divalent copper coordination ions, promote the reduction of monovalent copper intermediate products, and its consumption in the electronic plating process is controlled by diffusion.

Description of the drawings

Figure 1 is a metallographic microscope picture of PCB blind holes electroplated with copper filling in Comparative Example 1 of the present invention, with no leveling agent added and pores present.

Figure 2 is a metallographic microscope diagram of copper-filled electroplated blind holes in PCB in Example 1 of the present invention.

Figure 3 is a metallographic microscope picture of copper-filled electroplated blind holes in PCB in Example 2 of the present invention.

Figure 4 is a metallographic microscope diagram of copper-filled electroplated blind holes in PCB in Example 3 of the present invention.

Detailed ways

The technical solution of the present invention will be further illustrated and described below through specific embodiments and in conjunction with the accompanying drawings. Examples 1 to 3 and Comparative Example 1

The specific preparation process of the low copper salt weakly alkaline electronic electroplating copper liquid used for dense filling of PCB blind hole copper is as follows (taking the preparation of 1000mL as an example):

①According to the material concentration requirements of 20~50g/L inorganic copper salt and 29.5~554.4g/L complexing agent, accurately weigh the corresponding weight of inorganic copper salt and complexing agent respectively, and dissolve them in 500mL deionized water in advance to obtain a solution A;

②According to the substance concentration requirement of 24 to 60g/L, accurately weigh the corresponding weight of pH buffer and dissolve it in 200mL of deionized water in advance to obtain solution B;

③According to the material concentration requirements of 4-20g/L nitrogen-containing heterocyclic compounds and 0.4-8g/L acetylenic alcohol compounds, accurately weigh the corresponding weight of nitrogen-containing heterocyclic compounds and acetylenic alcohol compounds in advance, and dissolve them in 200 mL of deionized In water, solution C is obtained;

④Slowly add the above solution B and solution C to solution A respectively, and adjust the pH value of the mixed solution with a 10% mass concentration of sulfuric acid or nitric acid or acetic acid aqueous solution and a mass concentration of 10% potassium hydroxide aqueous solution to stabilize the pH value. In the range of 8.0 to 10.5; then use deionized water to adjust the volume of the above mixed solution to 1000 mL to obtain the low copper salt weakly alkaline electronic electroplating copper solution.

Furthermore, the electroplating process flow for dense copper filling of PCB blind holes is as follows (taking a blind hole plating workpiece with a hole diameter of 100 μm and a hole depth of 50 μm as an example):

Degreasing (50~70℃, 5min) → deionized water washing → 5% dilute sulfuric acid activation, ultrasonic (30s) → deionized water washing → pre-soaking in plating solution (3min) → electronic copper plating (120min) → passivation treatment ( 1min).

Degreasing is to remove grease from the surface of electroplated workpieces to prevent contaminants from affecting electroplating. Specifically, the oil removal step is to use Na ₂ CO ₃ with a concentration of 20 g/L and Na ₃ PO ₄ at a concentration of 50 g/L at a temperature of 50-70°C and soak the oil for 5 minutes. After degreasing, wash the electroplated workpiece several times with deionized water to rinse away the deposited dirt on the surface of the workpiece to be electroplated. After washing with water, soak and activate it with dilute sulfuric acid with a mass concentration of 5%, ultrasonic for 30 seconds, use the surface of the workpiece to increase activity, and then wash with deionized water to remove the acid to reduce the impact on the pH value of the plating solution.

Specifically, take an electroplating workpiece with 1000mL of electronic plating solution, a blind hole diameter of 100 μm, and a hole depth of 50 μm as an example; using the above-mentioned low copper salt weakly alkaline electronic electroplating copper solution and its electroplating method, pure copper plates, phosphorus-containing copper plates, and insoluble The iridium-coated titanium mesh is used as the anode, and the PCB board with electroless copper conductive treatment is used as the cathode. Electroplating is performed using mass transfer methods such as stirring, air blowing or cathode movement, which can achieve dense filling of blind holes with copper. The specific electronic plating solution composition, implementation conditions and filling effect are shown in Table 1 and Figures 1 to 4 below: When no leveling agent is added to the electronic plating solution, the copper deposition rate at the hole mouth is higher than the copper deposition rate at the bottom of the hole. As a result, blind holes are filled and sealed, leaving holes. When a leveling agent is added to the electronic plating solution, the copper deposition rate at the hole mouth is lower than the copper deposition rate at the bottom of the hole, allowing dense filling of blind holes.

Table 1 1000mL electroplating solution formula and corresponding effects in Examples 1 to 3 and Comparative Example 1

The above are only preferred embodiments of the present invention, and therefore cannot be used to limit the scope of the present invention. That is, equivalent changes and modifications made based on the patent scope of the present invention and the content of the specification should still be covered by the present invention. In the range.

Industrial applicability

The invention discloses a low-copper salt weakly alkaline electronic electroplating copper liquid and its application, which is composed of deionized water, inorganic divalent copper salt, complexing agent, pH buffering agent and leveling agent. The invention uses organic matter containing hydroxyl and/or carboxyl groups as divalent copper ion complexing agents, combined with pH buffers and leveling agents of specific composition and content, to achieve dense filling of PCB blind holes, with simple composition, low copper salt concentration, and weak It has the characteristics of alkalinity, low corrosion, easy control and high-precision photolithography process, and has industrial practicality.

Claims (9)

1. A low-copper salt weakly alkaline electronic electroplating copper solution for densely filling PCB blind hole copper, which is characterized in that: it is composed of deionized water, inorganic divalent copper salt, complexing agent, pH buffering agent and leveling agent. in:

   The inorganic divalent copper salt is copper sulfate pentahydrate, copper nitrate trihydrate or anhydrous copper acetate. Its concentration in the low copper salt weakly alkaline electronic electroplating copper solution is 20-50g/L, and the divalent copper salt is 20-50g/L. The concentration of copper ions is 5.1-17.6g/L;

   The complexing agent is at least one of gluconate, tartrate, citrate or ethylenediaminetetraacetate, and the molar ratio of the divalent copper ions is 2-6:1;

   The pH buffer is composed of sodium tetraborate and sodium bicarbonate, and the concentration of the sum of the sodium tetraborate and the sodium bicarbonate in the low copper salt weakly alkaline electronic electroplating copper solution is 24-60g/L ;

   The leveling agent is composed of a nitrogen-containing heterocyclic compound and an acetylenic alcohol compound in a mass ratio of 10:1-4, and the nitrogen-containing heterocyclic compound and the acetylenic alcohol compound are weakly alkaline in the low copper salt. The concentrations in the electronic electroplating copper solution are 4-20g/L and 0.4-8g/L respectively.
2. The low copper salt weakly alkaline electronic electroplating copper liquid according to claim 1, characterized in that: the concentration of the complexing agent in the low copper salt weakly alkaline electronic electroplating copper liquid is 29.5-554.4g/L. .
3. The low copper salt weakly alkaline electronic electroplating copper liquid according to claim 1, characterized in that: the mass ratio of the sodium tetraborate and the sodium bicarbonate is 1-5:1.
4. The low copper salt weakly alkaline electronic electroplating copper solution as claimed in claim 1, characterized in that: the nitrogen-containing heterocyclic compound is benzimidazole, thymine, succinimide, hydantoin, dimethyl at least one of hydantoin, nicotinic acid, nicotinamide, histidine and proline.
5. The low copper salt weakly alkaline electronic electroplating copper liquid according to claim 4, wherein the nitrogen-containing heterocyclic compound is succinimide, dimethylhydantoin or proline.
6. The low copper salt weakly alkaline electronic electroplating copper solution as claimed in claim 1, characterized in that: the acetylenic alcohol compounds are butynediol, dipropoxybutynediol, propargyl alcohol and diethylaminopentane At least one acetylenic diol.
7. A low copper salt weakly alkaline electronic electroplating copper solution as claimed in claim 6, characterized in that: the acetylenic alcohol compound is butynediol or propargyl alcohol.
8. An electroplating method for dense copper filling of PCB blind holes, characterized in that: applying the low copper salt weakly alkaline electronic electroplating copper liquid according to any one of claims 1 to 7, and adding the low copper salt The pH of the weakly alkaline electronic electroplating copper solution is adjusted to 8.0-10.5, the set temperature is 25-65°C, and the mass transfer method is: stirring, air blowing or cathode Move, and set different currents for electroplating according to these three time periods.
9. The electroplating method according to claim 8, characterized in that: the current and duration of electroplating control in the three time periods are: a, 0.2-0.5A/dm ² , 5-20min; b, 0.8-1.2A /dm ² , 20-40min; c, 1.8-2.2A/dm ² , 30-50min.