Introduction to Plasma Treatment for PCB Boards

March 29, 2026

With the advent of the digital information era, requirements for high-frequency communication, high-speed transmission, and high communication confidentiality are increasing. As an essential supporting product for the electronic information technology industry, PCBs require substrate materials that meet performance criteria such as low dielectric constant, low dielectric loss factor, and high-temperature resistance. To meet these requirements, special high-frequency substrate materials must be used, among which polytetrafluoroethylene (PTFE) is relatively common. However, during the PCB manufacturing process, due to the poor surface wettability of PTFE material, plasma treatment is required before hole metallization to improve its surface wettability, ensuring the smooth progress of the hole metallization process.

What is Plasma

Plasma is a state of matter primarily composed of free electrons and charged ions. It exists widely in the universe and is often regarded as the fourth state of matter, referred to as the plasma state, or "super gaseous state," also known as "electrified fluid." Plasma has high electrical conductivity and exhibits strong coupling effects with electromagnetic fields

Mechanism×

By applying energy (such as electrical energy) to gas molecules inside a vacuum chamber, accelerated electrons collide, exciting the outermost electrons of molecules and atoms, generating ions or highly reactive free radicals. These ions and free radicals are continuously collided and accelerated by electric field forces, causing them to collide with the material surface. This disrupts molecular bonds within a range of several micrometers, induces reduction to a certain thickness, creates an uneven surface, and simultaneously forms functional groups from gas components. These physical and chemical changes on the surface improve copper plating adhesion, desmear, and other effects.

Common gases used for the aforementioned plasma treatment include oxygen, nitrogen, and carbon tetrafluoride.

Applications of Plasma Treatment in the PCB Field

• Desmearing and etch-back of hole walls after drilling, removing drill smear

• Removing carbon residues after laser drilling of blind vias

• Removing dry film residues during fine line circuit fabrication

• Surface activation of hole walls in PTFE materials before electroless copper plating

• Surface activation of inner layers before lamination

• Cleaning before ENIG (Electroless Nickel Immersion Gold)

• Surface activation before applying dry film and solder mask

• Modifying inner layer surface morphology and wettability to improve interlayer adhesion

• Removing resist and solder mask residues

Comparison Images After Treatment

Explanation of Plasma Effects

(1) Activation Treatment of Polytetrafluoroethylene (PTFE) Materials:

Any engineer engaged in the hole metallization processing of PTFE materials understands that using the ordinary hole metallization methods applied to FR-4 multilayer printed circuit boards will not successfully achieve hole metallization for PTFE. Among these, the pre-treatment for PTFE activation before electroless copper plating is a significant challenge and a critical step. There are many methods available for the activation treatment of PTFE materials before electroless copper plating, but overall, the following two methods can ensure product quality and are suitable for mass production:

a) Chemical Processing Method: Metallic sodium and naphthalene react in a non-aqueous solvent solution such as tetrahydrofuran or ethylene glycol dimethyl ether to form a naphthalene-sodium complex. This sodium-naphthalene treatment solution can etch the surface atoms of polytetrafluoroethylene inside the hole, thereby achieving the purpose of wetting the hole wall. This is a typical method with good effect and stable quality, and it is widely used currently.
b) Plasma Treatment Method: This process is simple to operate, with stable and reliable treatment quality, suitable for mass production, using a dry plasma process. In contrast, the sodium-naphthalene treatment solution prepared by chemical methods is difficult to synthesize, highly toxic, has a short shelf life, needs to be prepared according to production conditions, and has high safety requirements. Therefore, currently, the plasma treatment method is mostly used for the activation treatment of PTFE surfaces due to its ease of operation and significant reduction in wastewater treatment.

(2) Removal of Hole Wall Etch-back / Resin Smear:

For the processing of FR-4 multilayer printed circuit boards, the removal of resin smear and other substances from the hole wall after CNC drilling typically involves treatment with concentrated sulfuric acid, chromic acid, alkaline potassium permanganate, and plasma treatment. However, in the treatment of removing drilling debris from flexible printed circuit boards and rigid-flex printed circuit boards, due to differences in material characteristics, the aforementioned chemical treatment methods are not ideal. Using plasma to remove drilling debris and perform etch-back can achieve better hole wall roughness, which is beneficial for hole metallization electroplating, and also provides the connection characteristics of "three-dimensional" etch-back.

(3) Removal of Carbides:

The plasma treatment method is not only effective in treating drilling contamination for various types of boards but also demonstrates its superiority in treating drilling contamination for composite resin materials and microvias. Furthermore, due to the increasing production demand for build-up multilayer printed circuit boards with high interconnection density, many blind vias are manufactured using laser technology. This is a by-product of laser blind via drilling – carbon – which needs to be removed before the hole metallization production process. At this point, plasma treatment technology readily undertakes the critical task of removing carbides.

(4) Inner Layer Pre-treatment:

Due to the growing production demand for various types of printed circuit boards, the requirements for corresponding processing technologies are also increasing. Performing inner layer pre-treatment for flexible printed circuit boards and rigid-flex printed circuit boards can increase surface roughness and activation level, enhance the bonding force between inner layers, and also significantly contribute to improving production yield.

Advantages and Disadvantages of Plasma Treatment

Plasma treatment is a relatively convenient, efficient, and high-quality method for desmearing and back etching printed circuit boards. Plasma treatment is particularly suitable for polytetrafluoroethylene (PTFE) materials because these materials have poor chemical activity, and plasma treatment can activate them. Using a high-frequency generator (typically 40 kHz), the energy of the electric field is utilized under vacuum conditions to dissociate process gases and establish plasma technology. These excited, unstable dissociated gaseous species modify and bombard the surface. Treatment processes such as UV fine cleaning, activation, consumption and crosslinking, as well as plasma polymerization, are the effects of plasma surface treatment. The plasma treatment process occurs after drilling and before electroless copper plating, primarily for treating the holes. The general plasma treatment process sequence is: Drilling — Plasma Treatment — Electroless Copper Plating. Plasma treatment can solve problems such as voids in holes, residual smear, poor electrical bonding with inner copper layers, and insufficient etch-back. Specifically, plasma treatment can effectively remove resin residues generated during the drilling process, also known as smear. This smear hinders the connection between the hole copper and the inner layer copper during the metallization process. To improve the bonding strength between the electroplated layer and the resin, glass fiber, and copper, this smear must be completely removed. Therefore, plasma desmearing and etch-back treatment ensure reliable electrical connections after electroless copper plating.

A plasma machine generally includes a processing chamber maintained in a vacuum state and situated between two electrode plates. The two electrode plates are connected to a radio frequency generator to form a large amount of plasma within the processing chamber. Within the processing chamber between the two electrode plates, multiple pairs of opposing card slots are equidistantly arranged to form multiple compartments (containment spaces) that can accommodate circuit boards for plasma treatment. In the existing plasma treatment process for PCB boards, when placing a PCB substrate into the plasma machine for treatment, one PCB substrate is typically placed between a pair of opposing card slots in the machine's processing chamber (i.e., within one compartment space for accommodating circuit boards). Plasma is then used to treat the holes on the PCB substrate to improve the surface wettability of the holes.

The processing chamber space of the plasma machine is relatively small. Therefore, typically, four pairs of opposing card slots are equidistantly arranged within the processing chamber between the two electrode plates, forming four compartments that can accommodate circuit boards for plasma treatment. Generally, the size of each compartment space is 900mm (length) * 600mm (height) * 10mm (width, accommodating the thickness of the circuit board). According to the existing plasma treatment process for PCB boards, the production capacity of circuit boards per plasma treatment cycle is approximately 2 square meters (900mm * 600mm * 4). The cycle time for each plasma treatment is 1.5 hours, resulting in a daily production capacity of about 35 square meters. It can be seen that using the existing plasma treatment process for PCB boards, the production capacity for plasma treatment is not high.

Conclusion

Plasma treatment is currently mainly used for high-frequency boards, HDI, rigid-flex boards, and is particularly suitable for boards made of polytetrafluoroethylene (PTFE) material. Its disadvantages include low production capacity and high cost. However, the advantages of plasma treatment are also significant. Compared to other surface treatment methods, its advantages in treating Teflon activation, improving its hydrophilicity, ensuring hole metallization, treating laser-drilled holes, removing residual dry film between fine-pitch circuits, roughening, pre-treatment for reinforcement, solder mask, and pre-treatment for silkscreen legend are irreplaceable. Additionally, it is characterized by being clean and environmentally friendly.