UGPCB In-Depth Analysis: 6-Layer Rigid + 4-Layer Flexible Yellow Soldermask Rigid-Flex Board – Ushering in a New Era of High-Density Interconnection

In today’s rapid evolution toward lightweight, thin, short, and compact electronic devices, cel PCB rigid-flex has become indispensable in high-precision fields such as telecommunications, medical instruments, și aerospațial. Its unique combination of rigid support and three-dimensional flexibility makes it a critical interconnect component.

As a professional Producător de PCB, UGPCB introduces its high-performance Yellow Soldermask Rigid-Flex PCB (R-FPCB) . This article explores this advanced board, built with FR-4 + PI materials și a 6-layer rigid plus 4-layer flexible structura. We will examine its design principles, manufacturing processes, and applications, showing how it enables more stable signal transmission and a more compact system layout.

1. Product Definition and Overview

UGPCBYellow Soldermask Rigid-Flex Board integrates a rigid PCB and a flexible circuit board into a single interconnect solution through a lamination process.

Key Specifications:

• Layer Stackup: 6 straturi (6L) in rigid sections / 4 straturi (4L) in flexible sections

• Material Combination: FR-4 (rigid areas) + Pi (Polyimide, flexible areas)

• Surface Color: Yellow soldermask (rigid) / White coverlay (flex)

• Grosime terminată: 0.4mm (rigid sections) / 0.2mm (flex sections)

This design retains the structural support and component-carrying capacity of rigid areas while utilizing the bendability of flexible sections. It achieves a true rigid-flex integration, eliminating the need for traditional connectors and ribbon cables.

2. Design Principles and Technology

O. Principiul de lucru

The core of rigid-flex technology lies in seamless interconnection. UGPCB laminates flexible PI layers with rigid FR-4 layers under high temperature and pressure. In flexible zones, FR-4 material is removed, leaving the PI base with a coverlay to allow bending. In rigid zones, FR-4 remains to support componente. This structure eliminates physical contact points from connectors, significantly enhancing signal integrity (SI) and vibration resistance.

B. Considerații de proiectare

• Controlul impedanței: For high-frequency communication PCBs, strict control of 3.5mil trace width and spacing ensures consistent differential impedance (De ex., 100Oh).

• Transition Zone Protection: The junction between rigid and flexible sections (the stub) is a stress point. UGPCB’s design uses rounded transitions and tapered trace widths to prevent cracking during bending.

• Stackup Matching: Uniform 1OZ copper thickness is maintained to prevent fatigue failure in the flexible sections during dynamic flexing.

3. Material and Performance Analysis

O. Core Materials

• FR-4 (Rigid Areas): A fiberglass-reinforced epoxy laminate. It offers high mechanical strength, rezistenta la caldura, and insulation, providing a stable platform for mounting heavy components like chips and connectors.

• Pi (Flexible Areas): Polyimide film. It provides excellent high-temperature resistance (operating >150°C), a low dielectric loss factor (Df), and a high flex life.

• Surface Finish: Aur de imersiune (De acord). This chemical process deposits a nickel-gold layer over copper.

  • Advantages: High surface flatness suitable for fine-pitch circuits (3.5mil spacing), strong oxidation resistance, and good solderability along with aluminum wire bonding capability.

B. Key Performance Specifications

4. Structural Classification and Features

O. Structural Classification

This product is an asymmetric structure (6-layer rigid + 4-layer flexible) within the category of multi-layer rigid-flex boards. În general, rigid-flex boards are classified as:

• Layered Type: Flexible layers extend out independently, as seen in this product.

• Non-layered Type: The entire board uses flexible material, with stiffeners added to specific areas.

B. Product Features

• Fiabilitate ridicată: The immersion gold finish combined with PI material ensures stable electrical performance even in harsh environments (high temperature and humidity).

• Precizie înaltă: Manufacturing capabilities for 3.5mil fine lines and 0.1mm micro vias solve high-density interconnect challenges.

• Space Optimization: Replaces connectors, reducing installation volume by over 60% and lowering overall product weight.

• Visual Differentiation: The yellow soldermask provides a unique appearance and offers clearer contrast during SMT assembly, facilitating optical inspection.

5. Manufacturing Process and Quality Control

To ensure the reliability of this complex 6L+4L structure, UGPCB follows a rigorous production flow:

1. Inner Layer Circuit (Flex Area): Fine 3.5mil circuits are formed on the PI base material using laser or photolithography.

2. Coverlay Lamination: A protective film is laminated onto the flexible circuit, leaving only the pad areas exposed.

3. Laminare: Rigid and flexible layers are aligned and laminated under vacuum. Key controls are the temperature profile and resin flow to prevent voids.

4. Foraj & Placare: 0.1mm micro vias are drilled. Electroless copper deposition creates interlayer connections.

5. Stratul exterior & Soldermask: Yellow soldermask is applied to rigid areas; white coverlay remains on flexible areas.

6. Surface Finish: Aur de imersiune (De acord) is applied with controlled thickness: 0.05-0.1μm Au / 3-5μm Ni.

7. Profiling & Electrical Test: Laser routing or die punching defines the final shape. 100% AOI and Sonda zburătoare testing verify electrical integrity.

6. Aplicații

This product is primarily targeted at thecommunication PCB sector. Key applications include:

• 5G Communication Base Stations: Used for flexing connections in RF modules, solving compact interconnect needs between antennas and mainboards.

• Smartphones & Wearables: The 0.2mm flexible section enables dynamic bending in foldable phone hinges.

• Electronică medicală: Used in devices like ultrasonic endoscope probes, leveraging PI’s biocompatibility and high-density routing.

• Electronică auto: ADAS camera modules that must withstand constant vibration and thermal shock.

7. De ce să alegeți UGPCB?

Engineers often face challenges with low yields and long lead times for complex rigid-flex designs. UGPCB is a reliable supply chain partner offering:

• Manufacturing Capability: Mass production capability for 3.5mil trace/space, overcoming high-density interconnect barriers.

• Aprovizionare cu materiale: Uses high-quality materials from suppliers like Shengyi/ITEQ for FR-4 and DuPont/Tayoho for PI, ensuring quality from the source.

• Engineering Support: Provides free DFM (Proiectare pentru producție) checks to help optimize designs, especially in the rigid-flex transition zone.

Are you designing a circuit board that must both carry complex ICs and flex within a tight space?

UGPCB now offers prototyping and mass production services for this6-layer rigid + 4-layer flexible yellow soldermask rigid-flex PCB.

👉 Get a Quick Quote Today

Send your Gerber files and technical requirements to [sales@ugpcb.com] or click the online chat. Our engineering team will provide a professional DFM report and a competitive quote within 24 ore.