2-Layer Ultra-Thin Flexible Polyimide, Adhesiveless PCB SF202 ENEPIG Green Solder Mask

2-Layer Ultra-Thin Flexible Polyimide, Adhesiveless PCBSF202 ENEPIG Green Solder Mask

1. Product Overview

This 2-Layer Ultra-Thin Flexible Printed Circuit Board (FPC) is a high-performance, miniaturized, and bendable interconnect solution engineered for compact, weight-sensitive, and dynamically flexing electronic assemblies. Built on ultra-thin polyimide base material with a double-sided conductor layout, advanced ENEPIG surface finish, and green liquid solder mask, this FPC PCB delivers exceptional mechanical flexibility, electrical reliability, thermal stability, and chemical resistance. It is purpose-designed for portable electronics, wearable devices, automotive sensors, medical diagnostic tools, camera modules, display interfaces, and compact industrial controls where thin form factor, consistent flex performance, and long-term durability are non-negotiable.

Compared with rigid PCBs, this flexible circuit board supports 3D assembly, dynamic bending, twisting, and repeated folding without electrical or mechanical failure. Compared with standard-thickness FPCs, this ultra-thin version reduces overall device volume, lowers weight, improves heat dissipation, and enables tighter packaging in slim consumer and industrial products. Every board undergoes 100% electrical testing before shipment to guarantee zero electrical defects, stable impedance, reliable conduction, and full compliance with customer functional specifications and industry quality standards.

2. PCB Construction Details

This section summarizes the complete structural composition, material selection, and processing characteristics of the 2-layer ultra-thin FPC PCB, covering base material, layer structure, dimensions, copper type, surface treatment, solder mask, and quality verification.

3. PCB Stackup

This stackup describes the layer sequence, material type, and thickness distribution from top to bottom, ensuring clarity of structural design and mechanical stability.

4. Key Material & Process Introduction

4.1 Copper Foil: ED Copper vs. RA Copper

Copper foil is the core conductive material in flexible circuits. Two dominant types are used in FPC manufacturing: Electrodeposited (ED) Copper and Rolled Annealed (RA) Copper.

• ED Copper (Electrodeposited Copper)

ED copper foil is produced through electrolytic deposition, the same process used for rigid PCB copper foils. One side of the foil is chemically treated to create a micro-rough surface, which improves bonding strength with dielectric substrates. Due to its vertical grain structure formed during electrolysis, ED copper has relatively low ductility and flex endurance. It is suitable for static-flex applications or fixed-installation FPCs that do not require repeated bending.

Typical thicknesses: 17.5 µm (0.5 oz), 35 µm (1 oz), 70 µm (2 oz), 105 µm (3 oz), 175 µm (5 oz).

• RA Copper (Rolled Annealed Copper)

RA copper starts from electrolytic cathode copper that is melted, cast, hot-rolled, surface-milled, cold-rolled, and annealed repeatedly to reach target thickness. It features a horizontal grain structure, delivering far superior flexibility, flex life, and bending fatigue resistance compared with ED copper. RA copper is the preferred choice for dynamic-flex applications such as foldable screens, camera modules, wearable devices, and dynamic interconnects.

Although the bonding surface of RA copper is smoother and offers lower initial adhesion, special electrolytic flash treatment can strengthen bonding without reducing flex performance. Typical thicknesses match ED copper: 17.5, 35, 70, 105, 175 µm (0.5–5 oz).

This FPC uses RA copper to ensure excellent dynamic flex performance and long-term bending reliability.

4.2 Solder Mask: Film Coverlay vs. Liquid Solder Mask Ink

Flexible PCBs use two main protective insulation materials: coverlay film and liquid solder mask ink.

Film Coverlay

Usually a polyimide film coated with adhesive, laminated onto the FPC surface. It offers stable dielectric performance, good mechanical protection, and high chemical resistance. However, it is less suitable for ultra-fine circuits and high-precision openings.

Liquid Solder Mask Ink

A photosensitive liquid ink coated, exposed, and developed on the FPC surface. It enables finer feature definition, thinner coating, smoother surface, and better compatibility with high-density assembly. This product uses green liquid solder mask ink on both sides, providing ideal insulation, solderability, and appearance for thin, high-precision FPCs.

4.3 Surface Finish: ENEPIG

ENEPIG (Electroless Nickel / Immersion Palladium / Immersion Gold) is a high-reliability surface treatment for high-end FPCs.

• Nickel layer provides excellent solderability and wire-bonding support.
• Palladium layer blocks nickel diffusion and prevents gold embrittlement.
• Thin gold layer offers outstanding corrosion resistance, oxidation resistance, and long shelf life.
• ENEPIG supports fine-pitch bonding, gold wire bonding, and repeated soldering, making it ideal for high-precision, long-life electronic products.

5. Product Performance & Application Advantages

5.1 Ultra-Thin & Lightweight

Finished thickness only 0.118 mm, significantly reducing device size and weight for slim and portable designs.

5.2 Excellent Flexibility

RA copper foil and polyimide substrate support repeated bending, folding, and twisting without cracking or open circuits.

5.3 High Reliability

ENEPIG surface finish ensures stable contact, strong oxidation resistance, and long-term performance under harsh conditions.

5.4 Stable Electrical Performance

Low line resistance, stable dielectric properties, and 100% electrical test guarantee consistent signal integrity.

5.5 Good Thermal & Chemical Resistance

Polyimide base material withstands high reflow temperatures and resists common chemicals used in electronics manufacturing.

5.6 High Precision Machining

Minimum drill hole 0.1 mm supports high-density interconnection and miniaturized assembly.

This FPC is widely used in: smart phones, tablet PCs, wearable devices, medical instruments, automotive electronics, camera modules, display components, slim sensors, and industrial control equipment.

SF202 Adhesiveless Double-Sided FCCL (Base Material for This FPC)

1. Product Introduction

SF202 is a double-sided, adhesiveless flexible copper clad laminate (FCCL) developed by Shengyi Technology for high-end flexible circuits. It uses a polyimide film directly bonded with copper foil without adhesive layers, delivering superior heat resistance, dimensional stability, chemical resistance, and electrical performance compared with adhesive-based FCCL. It is halogen-free, flame-retardant to UL94 VTM-0, fully RoHS compliant, and ideal for high-reliability, ultra-thin, dynamic-flex FPCs.

2. Core Features

• Ultra-high heat resistance, dimensional stability, and chemical resistance
• Excellent mechanical and electrical properties
• Halogen-free, UL94 VTM-0 flame rating
• Fully compliant with RoHS: free of Pb, Hg, Cd, Cr⁶⁺, PBB, PBDE
• Suitable for ultra-thin FPC, high-density circuit, dynamic flex, and fine-line applications

3. Typical Performance Properties (Complete Data Sheet Table)

4. Standard Specifications

SF202 supports various PI thicknesses and copper foil types (RTF / RA / ED):

PI film thickness: 12.5, 20, 25, 50, 75, 100, 125 µm

Copper foil thickness: 3, 6, 9, 12, 18, 35, 45, 50, 70, 105 µm

Copper types: RTF (Reverse Treated Foil), RA (Rolled Annealed), ED (Electrodeposited)

Typical applications: camera modules, LCM, touch panels, battery boards, industrial control, medical devices, wireless charging, fine-line high-density FPC.

5. Packaging & Storage

Standard width: 250±2 mm or 500±2 mm

Standard length: 50±1 m or 100±2 m per roll

Custom sizes available upon request

Storage: dry, non-corrosive environment; 5–35℃, humidity≤75%; shelf life: 12 months in original packaging

6. Material Image Description

SF202 FCCL Appearance: Smooth, uniform polyimide dielectric layer with tightly bonded double-sided copper foil, flat surface, no wrinkles or bubbles.

RA Copper Foil Cross-Section Image: Shows uniform horizontal grain structure, high ductility, excellent flex life.

ED Copper Foil Cross-Section Image: Shows vertical grain structure, suitable for static flex applications.

Conclusion

By combining the engineering wisdom of RA copper for flexibility, liquid solder mask for ultra-thin profile protection, ENEPIG for universal solderability, and the SF202 adhesiveless polyimide for thermal and dimensional stability, we present an FPC that does not compromise. It is ready for the most demanding applications of today and tomorrow.