High-Quality PI Film Lamination Services for Rigid PCBs

At Highleap Electronic, we are a leading, full-service PCB manufacturing and assembly company, equipped to handle all types of PCB production. With our expertise in producing a wide range of PCBs, from simple to highly complex designs—including those with small-pitch and intricate layouts—we ensure that every product meets the highest standards of quality and precision.
Our Rigid PCB Polyimide (PI) Film Application Guidelines provide detailed, professional insights into the application of PI films, which are essential for many high-performance PCBs. These guidelines cover all aspects of PI film application, from material selection to the precise design and manufacturing processes, helping ensure that each project meets both functional and aesthetic requirements.
Whether you need standard rigid PCBs or advanced, complex solutions with PI film applications, we offer the expertise and capabilities to deliver. Our comprehensive approach ensures that every PCB, regardless of complexity, is produced with the utmost care and attention to detail, making us your trusted partner for all PCB manufacturing needs.
This document details the definitions, specifications, and design considerations required for the application of PI film, including step-by-step instructions for successful integration. Whether you are developing complex multi-layer PCBs or require specific film thickness and adhesive configurations, our guidelines provide clear, practical information to support the manufacturing process.
1. Introduction to Polyimide (PI) Film
Polyimide (PI) film is a high-performance thermosetting polymer known for its excellent mechanical, electrical, and thermal properties. It is widely used in the electronics industry, particularly in printed circuit board (PCB) manufacturing. PI films are primarily employed as insulating materials for flexible circuit boards (flex-PCBs) and as protective coatings for external wiring, offering exceptional dielectric strength, heat resistance, and electrical insulation.
- Structure: PI films typically have a two-layer structure—one layer of polyimide and one layer of epoxy resin adhesive, which bonds the film to the PCB. This configuration, referred to as a cover film (or CVL), allows for efficient and secure attachment of the PI film to the board’s surface.
2. Types of PI Films Suitable for Rigid PCBs
The application of PI film depends on the type of PCB and its specifications. Below are the conditions for applying PI films to rigid PCBs:
- Bare Board with PI Film: The copper thickness on the surface should not exceed 2 oz. when PI film is applied directly to the PCB.
- After Solder Mask Application: If the solder mask is already applied, the copper thickness should be ≤ 4 oz. to ensure proper adhesion of the PI film.
- Board Size: The maximum length of the board for PI film application should not exceed 24 inches (610 mm) on the longer side.
3. Product Design and Engineering Considerations
The design and preparation stages are critical to ensure the PI film is applied correctly and to prevent future issues during the manufacturing process. The following considerations must be taken into account:
- Through-Hole and PI Film Windowing: For designs involving through-holes, it is essential to manage the windowing of PI film correctly. If PI film is applied to cover holes, it can trap liquid flux or other chemicals inside the holes, leading to issues with subsequent surface finishing processes (such as gold or silver plating). It is crucial to discuss windowing requirements with the customer at the design stage to avoid potential issues with plating.
- Surface Treatment Considerations: If the surface finishes are applied before PI film (e.g., tinning, soldering, immersion silver), there is a risk of aesthetic issues such as oxidation, discoloration, or poor solderability. In such cases, applying PI film after surface treatment may lead to these risks. We need customer confirmation on whether these issues are acceptable or if modifications (e.g., using gold plating instead of other finishes) are necessary.
- Metalized Holes and Opening Design: When applying PI film over metalized holes, it is essential to design window openings with a minimum distance of 10 mils (0.25 mm) between adjacent hole edges. This safety margin ensures the film is applied properly without compromising the integrity of the circuit. If hole spacing is insufficient, window adjustments must be discussed with the customer.
- Manual Handling and Placement: As PI film application is generally a manual process, clear alignment and positioning are crucial to avoid errors. There are three methods for ensuring correct placement:
- Option 1: Etched alignment marks on the external layer (e.g., copper traces) to guide placement. This method provides high precision.
- Option 2: Using silkscreen character lines for alignment, which provides moderate precision.
- Option 3: Aligning via pads and holes if the previous two options are not feasible, though this method has lower accuracy and efficiency.
4. Selection of PI Film Specifications
The selection of PI film thickness and adhesive layer thickness is essential for ensuring proper adhesion and performance. The following PI films and adhesive options are available:
-
PI Film with Adhesive Layer (CVL):
- 515: 0.5 mil PI film + 15 µm adhesive
- 1025: 1 mil PI film + 25 µm adhesive
- 2030: 2 mil PI film + 30 µm adhesive
-
Pure Adhesive Types:
- BH-10: 10 µm adhesive
- BT-25: 25 µm adhesive
- BT-40: 40 µm adhesive
Adhesive Thickness and Copper Thickness Ratio:
- The adhesive thickness should be proportionate to the copper thickness on the board. The optimal ratio is between 0.7 and 1.2 times the copper thickness, with 1:1 being the preferred ratio.
- Example: For a finished copper thickness of 70 µm, the adhesive thickness should also be approximately 70 µm. If the adhesive thickness provided by the PI film is insufficient (e.g., 15 µm), additional adhesive (e.g., BT-40 with 40 µm thickness) should be used to ensure proper bonding.
PI Film Thickness:
- The PI film thicknesses available for use are 0.5 mil, 1 mil, and 2 mil. The standard choice for most applications is 1 mil, but this should be confirmed with the customer based on the board’s design and thickness requirements.
5. Process Flow for PI Film Application
The process flow for applying PI film on rigid PCBs follows these steps:
Covering Holes with PI Film
Normal Process Flow: PI film application should occur after surface treatments (e.g., solder mask) and before the final inspection. The typical flow is: Normal Pre-Processing → PI Film Application → Lamination → Final Inspection.
Windowing of PI Film
For designs requiring windowing to expose copper pads or traces, PI film application can occur before surface treatment. The process flow is: Normal Pre-Processing → PI Film Application → Lamination → Surface Treatment → Post-Processing.
6. Engineering Design and CAM Requirements
To ensure smooth production, proper design files are essential. CAM (Computer-Aided Manufacturing) files should include detailed instructions for PI film application:
- PI Film Positioning: CAM files should specify the exact position of PI film on each layer. Clear markings must be made, using etched copper lines or silkscreen symbols to guide the application process.
- Windowing for Metalized Holes: When applying PI film over metalized holes, the window dimensions must be accurate to avoid overflow of adhesive that could interfere with component mounting. The recommended window size for pads and drilled holes should follow specific guidelines depending on the adhesive thickness.
- PI Film Panelization: When creating the panel for PI film, all shapes (e.g., rectangular, circular, and irregular) should be consolidated into a single panel file (in DXF format). The file should include precise measurements, with a 1 mm gap between units unless all units are rectangular or square. Panel length must not exceed 24 inches (610 mm).
7. ERP System Integration and Processing Instructions for PI Film Application
To ensure smooth production and maintain consistency in the application of Polyimide (PI) film, the ERP system should integrate detailed instructions that guide CAM engineers through the entire process. These instructions should specify material handling, processing methods, and quality checks to ensure precision and efficiency throughout the manufacturing stages.
1. Material Specifications and Handling
CAM engineers should be provided with specific details regarding the type and thickness of the PI film in the ERP system. For example, the system should indicate whether the film is 1025 with 25 µm adhesive or another variant (e.g., 515 or 2030). These specifications are crucial for ensuring the correct material is used for the PCB’s required performance. Additionally, engineers must have access to the material batch numbers for tracking purposes, allowing for full traceability during production. They should also be aware of the adhesive thickness, which should be selected based on the copper thickness of the PCB to maintain the correct ratio (e.g., adhesive thickness between 0.7 and 1.2 times the copper thickness).
2. Processing Method for Non-Circular Shapes
When dealing with non-circular shapes for PI film, such as custom cutouts or irregular designs, the ERP system must provide clear instructions for cutting methods. The CAM engineer should be directed to use appropriate cutting tools (e.g., laser cutting or die cutting) based on the design requirements. The ERP system should also define dimensions for each shape and provide the engineer with a cutting path to follow. These details ensure that the PI film is processed with accuracy, preventing material waste or defects due to incorrect cuts.
3. Drilling and Windowing for Metalized Holes
For applications where PI film is to be applied over metalized holes, the ERP system should outline the process for windowing—removing portions of the film to expose metalized areas or pads. The system must specify the window size, ensuring it fits the hole and leaves enough space for proper adhesion. CAM engineers should receive instructions on the drilling or laser cutting required to achieve the window shape, with specifications for hole diameter and tolerance. Detailed instructions for aligning the window with the hole on the PCB must also be included to avoid misalignment during lamination.
4. Lamination and Pressing Specifications
The ERP system should include lamination process details, including the necessary temperature, pressure, and time required for curing the adhesive and bonding the PI film to the PCB. CAM engineers need to verify these parameters during the setup of the lamination machine. The system should also outline the sequence of lamination, specifying whether the PI film should be applied before or after other surface treatments such as solder mask or tin plating. Clear instructions on how to handle adhesive overflow or adhesive cure times are also essential to avoid defects in the final product.
5. Quality Control and Process Validation
To ensure the PI film is applied with precision, the ERP system must integrate quality control checkpoints at critical stages of the production process. CAM engineers should perform checks for adhesive coverage, film alignment, and film bonding strength at predefined intervals. The ERP system should include automated visual inspection protocols to flag any issues, such as misalignment, wrinkles, or air bubbles in the film. Additionally, engineers must validate the film thickness at various points during production to ensure it meets the specified tolerances. The system should also track material consumption and allow for easy inventory management, ensuring the correct amount of PI film is used and reordered when necessary.
8. Final Considerations and Benefits of PI Film for Rigid PCB Lamination
The application of Polyimide (PI) film to rigid PCBs is a critical step in ensuring the high performance, durability, and reliability of the final product, especially in advanced and high-demand electronic applications. The integration of PI film into rigid PCBs provides a superior insulating layer, excellent thermal resistance, and enhanced protection against environmental factors such as moisture and heat.
By selecting the correct PI film thickness and adhesive type, and ensuring the precise lamination process, manufacturers can achieve optimal electrical insulation and mechanical strength for the PCB. These properties are essential for PCBs used in industries such as telecommunications, aerospace, and automotive, where high-performance and long-term reliability are paramount.
One of the key advantages of PI film lamination in rigid PCBs is the protection it provides to the underlying circuitry. PI film acts as a robust protective layer for sensitive components, preventing issues like oxidation, wear, or damage during assembly and operation. This is particularly crucial in environments where PCBs are exposed to high temperatures or harsh conditions.
Additionally, the lamination of PI film on rigid PCBs improves thermal management, allowing for better heat dissipation and stability of the board. This is especially important for applications where components generate significant amounts of heat, ensuring that the PCB can operate efficiently without overheating or experiencing performance degradation.
In conclusion, the proper application of PI film to rigid PCBs not only enhances the electrical, mechanical, and thermal properties of the board but also ensures long-term reliability and functional performance under demanding conditions. By carefully following best practices in the lamination process and selecting the appropriate materials, manufacturers can achieve high-quality, durable, and high-performance PCBs that meet the rigorous standards required in modern electronics.
Partner with Highleap Electronic for Advanced PI Film Lamination Solutions for Rigid PCBs
At Highleap Electronic, we are a leading, full-service PCB manufacturer, offering a wide range of PCB solutions for various industries. From simple to complex designs, including small-pitch and advanced multi-layer PCBs, our team has the expertise to meet your diverse needs.
Whether you need rigid PCBs with PI film lamination or require customized PCB designs for specific applications, we provide end-to-end services, including material selection, design, precision lamination, and final assembly. Our advanced manufacturing capabilities allow us to deliver reliable, high-performance PCBs tailored to your exact specifications.
If you’re looking for a trusted PCB manufacturer with extensive experience in handling all types of designs, from the simplest to the most intricate, contact us today. At Highleap Electronic, we are committed to delivering premium, high-quality solutions that meet the highest standards of performance and reliability for all your PCB projects.
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