Comparison of Liquid Photoresist and Dry Film in Inner Layer PCB Manufacturing

Introduction

In PCB (Printed Circuit Board) manufacturing, both liquid photoresist (LPR) and dry film photoresist (DFR) are widely used for inner layer patterning. These materials serve as photo-sensitive coatings that define the circuit layout by blocking or exposing areas for etching. Choosing between liquid photoresist and dry film depends on factors such as resolution requirements, process efficiency, cost, and environmental impact.

This article compares liquid photoresist and dry film in terms of properties, application methods, cost, advantages, limitations, and best use cases to help manufacturers select the best solution for their PCB production needs.

Liquid Photoresist and Dry Film

Key Properties of Liquid Photoresist and Dry Film

Cost Comparison

• Liquid Photoresist (LPR) typically costs 20-30% less than Dry Film (DFR).
• The lower material cost makes LPR a cost-effective option for large-scale production.
• However, LPR requires additional processing equipment (coating systems, drying units), which may increase initial investment.
• DFR is more expensive per square meter but provides efficiency benefits in batch processing and high-precision applications.

Application Process Comparison

1. Application Method

• Liquid Photoresist (LPR):
  • Applied using spray coating or curtain coating.
  • Provides uniform coverage on complex or uneven surfaces.
  • Requires a controlled environment to prevent defects such as bubbles or uneven thickness.
• Dry Film Photoresist (DFR):
  • Applied by hot-roll lamination.
  • Ensures predefined thickness, making it ideal for standardized production.
  • Limited adaptability for non-flat or highly textured PCB surfaces.

2. Exposure Process

• Both LPR and DFR use UV light exposure through a photomask to define the circuit pattern.
• DFR typically has higher resolution, making it suitable for fine-pitch applications.
• LPR provides better coverage for high-density or multilayer PCBs with complex features.

3. Development & Etching

• LPR is developed using a liquid chemical process, removing unexposed areas.
• DFR is developed by immersing or spraying a developer solution, dissolving unwanted portions.
• After development, the PCB undergoes etching to remove unwanted copper.

4. Stripping Process

• LPR removal requires solvents, which need proper waste disposal.
• DFR can be removed by alkaline solutions, making it more environmentally friendly.

Advantages and Limitations

Liquid Photoresist (LPR)

✅ Advantages:

1. Better coverage for high-density circuits – Ideal for multilayer PCBs and complex inner layers.
2. Excellent adhesion to rough or textured surfaces – Reduces risk of peeling or lifting.
3. Easier thickness control – Can be adjusted based on spray or curtain coating parameters.
4. Lower material cost – More cost-effective for large-scale production.

❌ Limitations:

1. More complex application process – Requires specialized equipment for spray or curtain coating.
2. Higher chemical waste – Generates solvent-based waste, requiring proper disposal.
3. Limited resolution – Not as fine as dry film for high-precision PCBs.

Dry Film Photoresist (DFR)

✅ Advantages:

1. Higher resolution and precision – Ideal for fine-pitch circuits and HDI PCBs.
2. Simpler and cleaner process – Laminated film eliminates the need for liquid handling.
3. Less chemical waste – Environmentally friendly compared to solvent-based liquid resist.
4. Consistent thickness control – Ensures uniformity for standardized production.

❌ Limitations:

1. Less flexibility for uneven surfaces – Works best on flat PCB layers.
2. Higher material cost – Pre-made film sheets are more expensive than liquid resist chemicals.
3. More complex for multilayer PCBs – Requires additional handling steps for thicker stack-ups.

Best Use Cases: When to Choose LPR or DFR

Conclusion

Both liquid photoresist (LPR) and dry film photoresist (DFR) are essential materials in inner layer PCB manufacturing, each offering distinct advantages based on process requirements, design complexity, and cost considerations.

• Choose LPR for multilayer PCBs, high-density circuits, and flexible PCB applications where better surface coverage and lower material costs are needed.
• Choose DFR for fine-pitch, high-precision circuits, and standardized production where high resolution and cleaner processing are essential.

By understanding the differences between liquid and dry film photoresists, manufacturers can optimize their PCB fabrication processes to achieve higher efficiency, lower costs, and better performance for modern electronic applications.

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