Cost Reduction Without Compromising Quality: How Chinese Display Manufacturers Navigate TFT Mask Reduction and CF OC Layer Elimination Challenges

In the fiercely competitive global display market, Chinese manufacturers continue to drive technological innovation and cost optimization. To meet customized customer demands, LCD module manufacturers often adopt two key process simplification strategies: reducing the number of photomasks for TFT glass from 5 to 4, and eliminating the OC (Over Coat) filling layer on CF (Color Filter) glass. These measures significantly reduce mask costs and improve production efficiency, but they also impose rigorous demands on production line process capabilities—particularly for aging lines, where minor oversights can trigger batch quality issues.

The Double-Edged Sword of Process Simplification: Technical Analysis and Risk Management

I. Risks and Countermeasures of Eliminating the OC Layer on CF Glass

The precise structure of CF glass (substrate → BM layer → RGB layer → OC layer → ITO layer) relies on the OC layer for critical functions:

• Planarization: Fills height differences between RGB color pixels
• Protection: Prevents damage to the RGB layer and maintains surface flatness

Eliminating the OC layer directly causes:

• Uneven ITO electrode surface → Disordered anchoring directions of liquid crystal molecules
• Frequent display defects: "Starry sky" bright spots, ghosting, image sticking (local liquid crystal response lag)

Counterstrategies by Chinese display manufacturers:

• Expand BM light-shielding area to compensate for light leakage caused by height differences
• Tightly control RGB step height processes, reducing pixel height fluctuations to the nanometer level
• Optimize driving schemes using dot inversion to reduce crosstalk (requires balancing higher power consumption)

II. Challenges and Breakthroughs of the 4-Mask TFT Glass Process

The traditional 5-mask TFT process includes: gate layer → gate insulation layer → S/D channel layer → via layer → ITO layer. The core of reducing to 4 masks lies in merging the gate insulation layer and S/D layer photolithography, controlling multi-zone exposure with a single mask.

Cascading effects of process reduction (based on research by CECEP Panda’s Ye Ning):

• Increased step height: New a-Si/n+a-Si film layers under the S/D layer create a 0.26μm step → Squeezes liquid crystal cell space
• 0.03μm increase in cell gap: S/D film taper angle increases by 8.99° → Relative liquid crystal height rises
• Gravitational Mura risk: High-temperature boundary LC margin shrinks by 1%, prone to display non-uniformity

Key process control points for Chinese manufacturers:

• Precise etching management: Eliminate residues to prevent GOA circuit short circuits (irreversible risks)
• Dynamic cell gap correction: Adjust CF PS (photo spacer) height based on Array film thickness variations
• Enhanced insulation protection: Prevent external pressure or long-term operation from damaging insulation between GOA circuits and Au balls

Chinese Wisdom: The Art of Balancing Cost and Quality

Leading Chinese display manufacturers have developed systematic solutions:
▶ Digital simulation first: Use modeling to predict step height impacts on cell electric fields and optimize designs
▶ Enhanced online monitoring: Deploy AI visual inspection for Mura and micro-shorts to intercept early anomalies
▶ Collaborative driver IC tuning: Customize dot inversion waveforms to compensate for response delays

Conclusion: Building Manufacturing Moats Through Technical Depth

The TFT mask reduction and CF OC layer elimination processes are akin to precision surgeries, testing the underlying technical expertise of Chinese LCD manufacturers. From material property control to nanometer-level step height elimination, from etching parameter optimization to driving algorithm innovation, every step embodies the commitment to "cost reduction without quality compromise." As the precision of domestic high-generation production lines continues to improve, China’s smart manufacturing is transforming the "impossible trinity" of cost, efficiency, and quality into a core competitive advantage, injecting new momentum into the global display industry.

About CNK

Founded in Shenzhen in 2010, CNK Electronics (CNK in brief) expanded the world leading factory in Longyan, Fujian in 2019. It is a specialized and innovative enterprise specializing in the design, development, production and sales of display products. CNK provides customers with a full range of cost-effective small and medium-sized display modules, solutions, and services with excellent quality worldwide. Oriented in technology and high quality, CNK keeps sustainable development, works to offer customers  better and stable services.