In printed circuit board manufacturing, acidic copper electrolytes are used in electrolytic (galvanic) processes for plating in order to make non-conductive drill hole walls conductive and to build up the required copper layer thickness for conductive traces.

There are a variety of process types available for creating the desired conductive structures on printed circuit boards. These include standard processes such as panel plating (full copper plating), pattern plating (selective copper plating), and hybrid forms (semi-pattern plating). For particularly demanding printed circuit boards with fine conductor traces (High-Density Interconnection, HDI) or multilayer boards, there are also a number of important copper plating processes, such as plating through holes (PTH), blind via filling, through-hole filling, and conformal via plating.

The more complex the printed circuit board, the more extreme the physical and geometric requirements for electrolytic copper deposition. Inadequate plating immediately leads to signal loss, overheating, or total system failure. This applies above all to PCB types such as high-layer-count multilayer (HLC), any-layer HDI PCBs, IC substrates (package substrates), and rigid-flex PCBs.

In the electroplating processes used to manufacture these PCBs, the deposition behavior is specifically controlled via the electrolyte composition (organic additives) and the current waveform. These organic additives play a crucial role: they control the deposition behavior of the copper at the atomic level. Without them, the copper would preferentially deposit on corners and edges (where the current density is highest), leaving holes or vias incompletely coated.

For modern processes such as via filling or HDI manufacturing, three organic additives essentially interact within the electrolyte, regulating one another:

• Suppressor (inhibitor / wetting agent)
• Brightener (accelerator / gloss enhancer)
• Leveler (equalizer)

During copper plating in the electroplating bath, the electrochemical oxidation and reduction of these additives—particularly during pulse plating—result in the formation of a variety of organic substances, some of which cause significant side effects. These side effects lead to a decline in the performance of the copper electrolyte and an increase in coating defects.

As the most effective method for removing organic contaminants resulting from the decomposition of additive systems, enviolet offers its UV oxidation systems, which have been proven in this field for decades.

The enviolet process breaks down the organic compounds in the electroplating electrolyte and largely mineralizes them. After UV treatment and the corresponding rejuvenation, an electrolyte with the properties of a fresh batch is once again available. This allows acidic copper electrolytes to be maintained continuously at a high level of production and quality.

UV-AOP technology is fundamentally applicable to all acidic copper electrolytes in printed circuit board manufacturing, as it is based on the universal mechanism of UV oxidation.

Conventionally, the accumulation of organic degradation products is compensated for by increased rinsing, regular activated carbon treatment, and ultimately by draining the bath and preparing a fresh batch. This results in higher volumes of wastewater, costs for disposing of spent activated carbon, and significant costs for preparing a fresh batch of electrolyte. Compared to conventional electrolyte maintenance with activated carbon, UV oxidation offers, in particular, high reproducibility of the treatment, sustainable removal of organic contaminants, and the possibility of continuous bath maintenance. Furthermore, UV oxidation can be largely automated and significantly reduces the workload on operating personnel, especially when compared to activated carbon treatment.

With UV oxidation, however, the electrolyte can be returned to the production bath once the relevant organic parameters have been adjusted.

This continuous renewal of the electrolyte contributes to consistently high bath quality and reproducible plating results, and enables a theoretically unlimited service life of the electrolyte (see also “A Method toward Infinite Bath Life for Acid Copper Electrolytes by Atotech”), which in practice is limited only by electrolyte drag-out.

Multek Böblingen was one of the first companies to adopt and pioneer the industrial use of UV oxidation for the maintenance of acidic copper electrolytes. As early as 2003, the process was successfully introduced and implemented in production operations.

Even electrolytes that had been treated multiple times were able to achieve a microdistribution comparable to that of a fresh batch. By introducing UV oxidation, Multek laid the groundwork early on for consistent, high-quality, and environmentally sustainable production.

In addition to ensuring process and product quality, this approach also reduced operating costs and supported the requirements for modern production technologies and sustainability.

A detailed case study on this project can be found here.