Titanium anodes for electroplating of PCB printed circuit boards

Titanium Anodes for PCB Electroplating — MMO Electroplating Electrode Technical Specifications and Applications

Titanium anodes are dimensionally stable electrodes used in printed circuit board (PCB) electroplating processes to provide a stable anode current. The substrate material is pure titanium (TA1/TA2, conforming to GB/T 3621 or ASTM B265), and the surface thermally decomposes into a mixed metal oxide (MMO) active layer, primarily composed of a composite of ruthenium oxide (RuO2), iridium oxide (IrO2), and titanium oxide (Ta2O₅).

In the PCB electroplating bath, titanium anodes eliminate the need for traditional phosphorus copper anodes, serving as an insoluble anode in conjunction with a soluble copper ion replenishment system. An oxidation reaction occurs on the anode surface, providing a stable current to the electroplating solution and driving the uniform deposition of copper ions on the cathode (PCB board) surface. The introduction of titanium anodes eliminates problems such as uneven dissolution of phosphorus copper anodes, copper ion contamination of the anode, and film management, making the PCB copper deposition process easier to automate.

Working Principle

The titanium anode used in PCB electroplating functions as an insoluble anode in a sulfuric acid/copper sulfate plating solution. Upon energization, a series oxidation reaction of water occurs on the anode surface, releasing oxygen:

2H₂O → O₂ + 4H⁺ + 4e⁻

Copper ions lost in the circuit are continuously replenished by an external copper ball dissolution system (copper ball basket) or an automatic copper replenishment device, maintaining the copper concentration in the plating solution within the process range. The titanium anode itself does not participate in dissolution; it acts as an electron medium, thus avoiding copper ion irradiation and significantly extending the plating solution maintenance cycle.

Coating System

Based on the current density range and plating solution system of the PCB electroplating process, titanium anode coatings are classified into the following types:

RuO₂-IrO₂-TiO₂ Ternary Composite Coating (Standard Type)
Suitable for acidic copper sulfate electroplating systems, with low oxygen release overpotential, strong coating adhesion, and suitable for high-speed pattern plating lines and processes.

IrO2-Ta2O₅ Binary Coating (High Stability): Suitable for precision electroplating solutions containing organic additives, offering enhanced resistance to oxidation and degradation. Used in high-density interconnect (HDI) boards and flexible board plating lines.

Multi-layer Gradient Coating (Customized): Customized for high current densities (>500 A/m²) or special plating solution systems, providing longer coating life and consistency.

Technical parameters

Parameter Items	Specifications
Base Material	TA1 / TA2 (GB/T 3621); Grade 1 / Grade 2 (ASTM B265)
Coating Typ	≥RuO₂-IrO₂-TiO₂ / IrO₂-Ta₂O₅ / Custom Gradient Coating
Coating Thickness	8–20 µm
Recommended Current Density	100–600 A/m²
Operating temperature range	15–55 °C
Available Forms	SPlates, Mesh (diamond mesh/perforated mesh), Tubes, Rods, Shaped Parts

Product Advantages

Improved Coating Uniformity

Titanium anodes are insoluble anodes, resulting in uniform current density distribution, which is beneficial for controlling the copper layer thickness on the PCB surface, especially for high aspect ratio vias and blind vias.

Eliminating Copper Ion Irradiation

During the dissolution process, phosphorus bronze anodes generate copper powder, copper particles, and black phosphating film waste. These particles contaminate the plating solution and coat the board surface, becoming a major source of short circuits and appearance defects in PCB plating. Titanium anodes do not participate in dissolution, eliminating particle contamination from phosphorus, reducing the burden on plating solution filtration, and decreasing the scrap rate of boards due to particle defects.

AI-Powered Pulse and Reversed Plating

Pulse plating (PP) and periodically reversed plating (PR/PPR) are important processes for improving the copper layer filling rate and uniformity of PCB vias. The low electroplating characteristics and stable active surface activation of titanium anodes are more suitable for responding to pulsed current waveforms, while phosphorus bronze anodes exhibit the highest peak-to-peak value in pulse mode, affecting plating accuracy.

Supports high-density PCB manufacturing

The electroplating process for HDI boards, multilayer interconnect (ELIC) boards, and IC substrates, which require fine lines and small apertures, offers higher precision and stability. The stable current environment provided by titanium anodes, combined with an appropriate additive system, can meet advanced PCB electroplating specifications requiring line widths/spacings of less than 50 µm and apertures of less than 100 µm.

Application Areas

1. Through-Hole Plating (PTH)
Through-hole plating is a core process in PCB manufacturing that connects different layers of circuitry. After plating, the board undergoes chemical copper plating (PTH) to activate the hole walls before proceeding to full-board or pattern plating processes. Electrodeposited copper thickens the copper layer on the hole walls to the specified thickness.

In the through-hole plating bath, titanium anodes are mounted in a plate or mesh form at the bath's edge. Combined with a gas agitation and jetting system, this ensures sufficient exchange of the plating solution within the holes. The stable current distribution of the titanium anodes helps control the copper thickness ratio (TP value) between the board surface and the hole, meeting the IPC-6012 Class 2 / Class 3 requirements for hole copper thickness.

2. Carrier and Packaging Substrate Plating
IC carriers and advanced packaged chips (such as ABF carriers and BT carriers) are core materials for semiconductor packaging. Linewidth/spacing requirements have entered the 2/2 µm to 5/5 µm range. Copper plating on substrates demands significantly higher requirements for copper layer thickness uniformity, surface roughness, and additive cleanliness than ordinary PCBs.

Titanium anodes are widely used to replace soluble copper anodes in substrate manufacturing. Combined with high-purity copper sulfate plating solutions and ultra-fine filtration systems, they achieve a control target of particulate matter levels below 0.5 µm in the plating solution, meeting the stringent quality requirements of advanced packaging processes.

3: Continuous High-Speed ​​Plating Lines (VCP/HVM)
Vertical continuous plating lines (VCP) and horizontal plating lines are used for high-volume PCB manufacturing. Boards are continuously conveyed through the plating bath, resulting in high production speeds and high current densities (typically 150–500 A/dm² equivalent surface current). High-speed continuous plating places high demands on the response speed and long-term stability of the workpieces.

The titanium nodes in VCP lines typically adopt a diamond-shaped unfolded mesh configuration, installed on the end frame of the conveyor waterfall. Multi-channel regulators provide segmented power supply, enabling zoned current control of the boards along the conveying direction. The non-dissolving technology of titanium nodes on high-speed lines extends maintenance cycles from weekly replacements to quarterly inspections, improving production line efficiency.

4: Electroplated Copper Foil Production
Electrolytic copper foil (ED copper foil) is the core component of current collectors in PCBs and lithium batteries. Copper foil production uses large titanium foils (usually curved or electroplated) in conjunction with a rotating titanium drum cathode, continuously electrodepositing copper foil in a high current density (500–3000 A/m²) copper sulfate electroplating solution.

Titanium foil used in copper foil production has very high requirements for coating uniformity and lifespan. Localized coating losses can lead to abnormal current distribution, resulting in copper foil thickness deviations and surface defects. Thicker foil and high-iridium coating formulations are technical features specific to copper foil production.

Titanium Coating Recoating Service

When a titanium anode coating reaches the end of its lifespan, the tank terminal voltage typically rises beyond the process range under continuous current, leading to localized passivation of the anode surface or visible coating peeling. At this point, the titanium anode can be recoated to restore electrode performance and replace the entire anode structure.

Recoating Process Flow:

Incoming Inspection—Identifying substrate deformation, corrosion pits, weld cracks, and dimensional deviations.
Chemical Stripping—Removing the remaining surface coating with oxalic acid or a nitric acid/nitric acid mixture.
Substrate Reconstruction—Sandblasting roughening + oxalic acid etching to restore titanium surface activity.
MMO Re-design—Hotly splitting the substrate according to the original specifications and repeating the cycle multiple times.
Factory Inspection—Full inspection according to the original factory standards before shipment.

Titanium substrates can generally withstand repeated recoating treatments. Replacement of the substrate is only necessary when acid etching thins the substrate, resulting in insufficient substrate wall thickness.

Titanium Pioneer's applications in PCB electroplating cover the entire product line, from large-scale general-purpose boards to advanced substrates. The selection of coating formulation, mesh size, molding size and current density parameters depends on the specific PCB product type, electroplating process system and production line equipment configuration.