I. What is dry film photoresist?
Dry film photoresist (photosensitive dry film) is an indispensable photosensitive material in PCB-Herstellung, consisting of a three-layer structure: polyester film (PET) carrier layer, photopolymer photosensitive layer, and polyethylene (PE) protective layer. Through photochemical reactions, it accurately transfers circuit designs onto copper-clad laminates, enabling the production of micron-level circuit patterns.
II. Comparative Analysis: Dry Film vs. Liquid Photoresist
| Charakteristisch | Dry Film Photoresist | Liquid Photoresist |
|---|
| Uniformity | High, thickness deviation < ±5% | Lower, depending on the coating process |
| Auflösung | Up to 10μm line width | Up to 5μm line width |
| Ease of Operation | Low simplifies process flow | High, requires precise control of coating parameters |
| Environmental Impact | Less wastewater generated | High usage of organic solvents |
| Applicable Board Types | HDI, multilayer boards, flexible boards | Ultra-high precision boards, semiconductor packaging |
III. Detailed Workflow of Dry Film Photoresist
3.1 Surface Preparation Stage
PCB substrates require mechanical or chemical cleaning to remove surface oxides and contaminants, ensuring dry film adhesion. Typical cleaning processes include:
- Alkaline degreasing (5-10% NaOH solution, 50-60°C)
- Micro-etching (Na₂S₂O₈/H₂SO₄ system)
- Acid washing and neutralization (5% H₂SO₄ solution)
- Drying (80-100°C, 10-15 minutes)
3.2 Lamination Process Parameter Optimization
Lamination is a critical step in ensuring dry film quality. Recommended parameters are as follows:
| Parameter | Range | Auswirkungen |
|---|
| Temperature | 105-125°C | Too high causes excessive flow; too low affects adhesion |
| Pressure | 0.4-0.6MPa | Ensures even adhesion and avoids bubble formation |
| Geschwindigkeit | 1.0-2.5m/min | Affects production efficiency and quality stability |
| Roller Hardness | 80-90 Shore A | Excessive hardness may cause film damage |
3.3 Exposure Technology Selection
Choose exposure methods based on PCB precision requirements:
- Contact Exposure: Suitable for ≥50μm line width
- Proximity Exposure: Suitable for 25-50μm line width
- LDI Direct Imaging: Suitable for <25μm ultra-high precision circuits
IV. Impact of Thickness on PCB Performance
4.1 Standard Thickness Specifications and Application Scenarios
| Thickness (mil/μm) | Applicable PCB Types | Line Width/Spacing Capability | Typische Anwendungsszenarien |
|---|
| 0.8/20μm | FPC Flexible Boards | 10/10μm | Smartphones, wearable devices |
| 1.2/30μm | Inner Layer Boards | 20/41μm | Conventional multilayer board inner layers |
| 1.5/38μm | Outer Layer Boards | 30/60μm | Power boards, automotive electronics |
| 2.0/50μm | Special Boards | 60/60μm | High-current boards, thick copper boards |
4.2 Impact of Thickness on Process Quality
- Pattern Transfer Accuracy: A 10% increase in thickness leads to a 3-5% increase in line width deviation
- Etching Effect: Excessive thickness increases undercut; insufficient thickness reduces etch resistance
- Plating Performance: Affects copper thickness uniformity in holes
- Kosten-Faktoren: A 20% increase in thickness raises material costs by 15-18%
V. Dry Film Photoresist Selection Guide
5.1 Key Performance Parameter Evaluation
Selecting dry film photoresist requires comprehensive consideration of the following parameters:
RLS Triangle Balance:
- Auflösung: Minimum achievable feature size
- Line Width Roughness: Edge smoothness indicator
- Sensitivity: Minimum required exposure dose
Other Key Parameters:
- Contrast: ≥3.0 (ideal value)
- Development Latitude: ≥30%
- Thermal Stability: ≥150°C
- Elongation: ≥50%
5.2 Application Scenario Matching Guide
| Application Field | Recommended Type | Besondere Anforderungen |
|---|
| HDI-Tafeln | High-Resolution Type | Resolution ≤15μm, high chemical resistance |
| Flexible Boards | High-Elasticity Type | Elongation ≥80%, low stress |
| Hochfrequenz-Platten | Low-Dielectric Type | Dk ≤3.0, Df ≤0.005 |
| Kfz-Elektronik | High-Temperature Type | Heat resistance ≥160°C |
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VI. Development Time Control Methods
6.1 Factors Influencing Development Time
| Faktor | Ebene der Auswirkungen | Control Method |
|---|
| Developer Concentration | Hoch | Maintain within 0.8-1.2% range |
| Temperature Fluctuation | Hoch | Optimal range: 23±1°C |
| Spray Pressure | Mittel | Adjustable range: 1.5-2.5bar |
| Conveyor Speed | Hoch | Adjust based on thickness (1-3m/min) |
6.2 Development Time Optimization Plan
Positive Photoresist: 30-90 seconds (recommended: 60 seconds)
Negative Photoresist: 2-5 minutes (recommended: 180 seconds)
Control development point position at 40-60% of the development section
Regularly monitor developer pH (maintain 10.5-11.5)
VII. Application Scenarios and Case Studies
7.1 High-Density Interconnect (HDI) Board Manufacturing
Dry film photoresist enables the production of fine lines ≤30μm in HDI boards, supporting 3+ stage HDI structures. A smartphone motherboard case study showed that using 1.2mil dry film achieved stable production of 25/25μm line width/spacing with a yield rate of 98.5%.
7.2 Flexible PCB Applications
In the flexible board sector, dry film photoresist provides the necessary flexibility and adhesion. A renowned wearable device manufacturer used 0.8mil special flexible dry film to achieve 10μm line width and pass 1 million bend tests.
View Flexible PCB Manufacturing Case →
VIII. Technology Trends and Innovations
8.1 Next-Generation Photoresist Technologies
- Chemically Amplified Photoresists (CAR): 3-5x improved sensitivity
- Nanoimprint Lithography Photoresists: Support <10nm feature sizes
- Eco-Friendly Water-Developable Photoresists: 90% reduction in VOC emissions
8.2 Market Outlook
According to industry reports, the semiconductor PCB output value in mainland China is projected to reach $54.6 billion by 2026, driving an average annual growth rate of 8.5% in dry film photoresist demand. High-end products such as LDI-specific dry films are expected to grow at over 15%.
Schlussfolgerung
As a core material in PCB manufacturing, the selection and application of dry film photoresist directly impact the performance and quality of final products. By optimizing thickness selection, strictly controlling development processes, and choosing appropriate types based on specific application needs, manufacturers can significantly improve production efficiency and product yield. As electronic devices trend toward miniaturization and higher density, dry film photoresist technology will continue to innovate to meet increasingly stringent process requirements.