Demonstrating Plasma As A Viable Alternative To KOH For LCP Metallization Applications

This blog examines the use of plasma technology as an alternative surface treatment method for liquid crystal polymer (LCP) materials. The study demonstrates how optimized plasma processing can achieve effective surface roughening and activation, providing a viable alternative to conventional KOH treatment while delivering the coverage and adhesion required for subsequent electroless copper plating.

The challenge

LCP is a high-performance engineering plastic widely used in the electronics, automotive, medical, and communications industries because of its excellent mechanical properties, thermal stability, and electrical insulation characteristics. However, untreated LCP surfaces are extremely smooth, exhibit low surface energy, and have poor wettability. As a result, direct electroless copper plating typically cannot achieve the adhesion and coverage required for manufacturing processes.

Traditionally, KOH treatment has been the only widely accepted industrial solution for processing LCP materials. However, KOH is a strong alkaline chemical that requires special safety precautions and dedicated process infrastructure. Many PCB manufacturers do not have KOH desmear capability and are reluctant to add a chemical process to their production facilities.

The objective of this project was to determine whether plasma processing could provide a practical alternative to KOH by addressing several key challenges:

• Demonstrate surface roughening performance comparable to KOH treatment.
• Achieve both surface roughening and activation of the LCP material.
• Effectively process thicker LCP boards, which are more difficult to treat than conventional PCB materials.

Application development process

Nordson’s applications team evaluated plasma processing using the Nordson MARCH MaxVIA system, a high-performance platform engineered for high-volume PCB plasma treatment. Featuring an advanced power-power electrode configuration, the system delivers outstanding etchback and desmear uniformity while ensuring excellent process consistency. Together with sophisticated vacuum and gas-flow control and enhanced temperature management, the MaxVIA system enables reliable, repeatable plasma processing for demanding manufacturing applications.

Initial process development

The team used a three-step plasma process:

1. Material Warm-Up.
2. Hole Wall Roughening.
3. Surface Activation.

Initial evaluation confirmed that both etch rate and process uniformity met specification requirements while leaving no detectable LCP residue on copper surfaces.

Cross-sectional analysis and SEM inspection verified successful roughening throughout the treated structures, as shown in Figures 1 and 2.

Surface activation evaluation

Experiments compared process results with and without the H₂/N₂ activation step, as shown in Figures 3 and 4. The results demonstrated that the activation step was necessary to achieve good plating coverage, indicating that roughening alone was insufficient for optimal performance.

Process optimization

Additional experiments evaluated the effect of treatment duration on process efficiency. Comparative testing at 20, 30, and 60 minutes demonstrated that the treatment time could be reduced to 30 minutes while maintaining acceptable results, as shown in Figures 5-7.

The optimized process enabled effective treatment of LCP material while reducing overall processing time and maintaining the required surface characteristics for subsequent metallization.

The conclusion

The optimized plasma process successfully demonstrated that plasma treatment can serve as a practical alternative to KOH processing for LCP materials. The plasma treatment effectively roughened and activated the material surface, producing the surface characteristics required for reliable metallization, as shown in Figures 8–12.

Surface analysis showed significant texturing after plasma treatment compared with untreated LCP. Results following activation demonstrated good plating coverage and adhesion. Solder float testing further confirmed process effectiveness on both four-core and eight-core structures.

Key results

• Plasma proved to be a suitable alternative to KOH treatment for LCP materials.
• Plasma treatment successfully roughened and activated the LCP surface.
• Activated samples demonstrated good copper coverage and adhesion performance.
• Process optimization reduced treatment time to 30 minutes while maintaining successful results

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