Copper Foil Surface Cleaning – Flex PCB Manufacturing Process

In double-sided flexible printed circuit manufacturing, copper foil surface cleaning is a critical pretreatment step performed before photoresist coating. At Flex Plus, this process is based on long-term production experience in flexible and rigid-flex PCB manufacturing and is strictly controlled to support stable mass production of fine-line flexible PCB products.

Although surface cleaning may appear to be a simple operation, it requires special attention in flexible PCB fabrication due to the thin, flexible nature of the base material and the increasing demand for high-density circuit designs.

Why Copper Foil Surface Cleaning Is Necessary?

During material storage and early-stage processing, copper foil surfaces may be affected by:

Light oxidation, oil residues, dust and fine particles

If these contaminants are not effectively removed, the adhesion between the copper foil and the photoresist layer will be reduced. This directly increases the risk of resist lifting during processing and leads to unstable etching results.

For this reason, copper foil surface cleaning is treated as a foundational process within our double-sided flexible circuit board manufacturing workflow, especially for products requiring tight dimensional control and high reliability.

Surface Cleaning Methods Used in flexible PCB Fabrication

In Flex Plus flexible PCB production, copper foil surface cleaning typically involves a combination of:

• Chemical cleaning, used to remove oxidation layers and organic residues

• Mechanical brushing, used to create a uniform and stable copper surface condition

For fine-pitch and precision circuit designs, these two methods are often combined. This approach helps ensure consistent photoresist adhesion before exposure and etching.

Mechanical Brushing Process Control

Mechanical surface cleaning is carried out using rotary brushing rollers.Brush material selection and process parameters are carefully evaluated:

• Brushes that are too hard may damage the copper foil surface

• Brushes that are too soft may result in insufficient surface preparation

Nylon brushes are commonly used, and their length and hardness are optimized through process validation.

Brushing pressure is also strictly controlled. Excessive pressure can apply tensile force to the flexible substrate, causing elongation and dimensional variation. This is a known factor affecting dimensional stability in flexible printed circuit manufacturing and is monitored as part of our internal process control system.

Influence on Etching Quality and Yield

If copper foil surface cleaning is insufficient, poor photoresist adhesion may occur, leading to:

• Partial resist peeling or lifting

• Irregular circuit edges

• 3. Incomplete or uneven etching

• 4. Reduced etching yield

By maintaining stable and repeatable surface cleaning conditions, Flex Plus improves etching consistency and supports reliable circuit formation in volume production.

Application Scope in Flex PCB Manufacturing

With improvements in copper foil material quality, surface cleaning may be omitted in certain single-sided flexible PCB applications.However, for the following products, copper foil surface cleaning remains essential:

• Double-sided flexible PCBs

• Fine-line circuit designs

• Line widths below 100 μm

For high-density and precision flexible circuits, proper surface preparation is a basic requirement to achieve consistent quality and long-term reliability, particularly in industrial, automotive, and other demanding applications.

Summary

Copper foil surface cleaning is a key pretreatment process in double-sided flexible PCB manufacturing. Through controlled chemical cleaning and mechanical brushing, Flex Plus ensures stable photoresist adhesion, dimensional accuracy, and consistent etching performance. This process forms a reliable foundation for manufacturing fine-pitch flexible printed circuits that meet strict quality and reliability requirements.