What is a rigid PCB, and how is a rigid PCB manufactured?

O que é um PCB rígido and How is it Manufactured?

Rigid Printed Circuit Board (PCB) is a printed circuit board based on a rigid substrate, featuring a stable mechanical structure and excellent electrical performance. It is widely used in computers, communication equipment, industrial control, and consumer electronics, providing reliable electrical connections and physical support for electronic components.

1. Characteristics and Advantages of Rigid PCBs

Rigid PCBs primarily use glass-reinforced epoxy laminate (such as FR-4, CEM-3) as the base material, manufactured through processes like lamination, pattern transfer, and etching. Their key features include:

• Elevada resistência mecânica: The rigid substrate offers high resistance to bending and vibration, suitable for fixed installations.
• Excellent Electrical Performance: Stable dielectric constant and low signal transmission loss, supporting high-frequency and high-speed applications.
• Good Thermal Stability: Heat-resistant with a glass transition temperature (Tg) typically above 140°C.
• High Wiring Density: Supports multi-layer designs (usually 4–12 layers), enabling complex circuit layouts.

Compared to Flexible PCBs (Flex PCBs), rigid PCBs are lower in cost and have more mature manufacturing processes, but they are less flexible and lightweight. The table below compares the main characteristics of the two types:

2. Manufacturing Process of Rigid PCBs

The manufacturing of rigid PCBs is a multi-step, high-precision process, primarily comprising the following stages:

• Inner Layer Circuit Production

• Cutting: Copper-clad laminate is cut to design dimensions with ±0.1mm accuracy.
• Film Lamination and Exposure: Photosensitive dry film is applied, and circuit patterns are transferred via UV exposure.
• Development and Etching: Unexposed dry film and copper are removed to form conductive circuits.
• Inspeção AOI: Automated optical inspection checks parameters like line width and spacing.

• Lamination and Pressing

• Brown Oxidation: Enhance adhesion between inner copper layers and prepreg.
• Layer Stacking and Pressing: Multiple layers are pressed together under high temperature (180–200°C) and pressure (300–400 psi).

• Drilling and Metallization

• Mechanical/Laser Drilling: Creates through-holes, blind vias, or buried vias.
• Copper Deposition and Plating: Chemically deposited and electroplated copper metallizes hole walls for interlayer connections.

• Outer Layer Circuit and Surface Finish

• Transferência de padrões: Laser Direct Imaging (LDI) technology creates outer-layer circuits.
• Solder Mask and Silkscreen: Solder resist ink is applied, and component markings are printed.
• Acabamento da superfície: Processes like HASL, ENIG, or OSP are chosen based on application needs.

• Testes e inspecções

• Ensaios eléctricos: Continuity tested via flying probe or bed-of-nails test.
• Validação da fiabilidade: Includes thermal cycling, high temperature/humidity testing, impedance testing, etc.

3. How to Improve the Reliability of Rigid PCBs?

To enhance the reliability of rigid PCBs in harsh environments, systematic optimization of materials, design, manufacturing, and testing processes is required:

• Seleção de materiais

• For high-frequency applications, use PTFE substrates (Dk≈3.0, Df<0.005).
• For high-temperature environments (e.g., automotive electronics), use high-Tg FR-4 (Tg≥170°C).
• For heat dissipation needs, use metal-core substrates (aluminum core thermal conductivity 1–3 W/m·K).

• Otimização da conceção

• Conceção da ligação à terra: Use multi-point grounding for high-frequency circuits, single-point for low-frequency.
• Gestão térmica: Add thermal vias, use thick copper foil (≥2 oz).
• Integridade do sinal: Control impedance deviation within ±10%, line width tolerance ±0.05mm.

• Controlo de processos

• Processo de laminação: Vacuum pressing reduces interlayer bubbles.
• Drilling Accuracy: Hole position error ≤50μm, aspect ratio ≤8:1.
• Processo de soldadura: Use SAC305 lead-free solder, reflow peak temperature 245°C±5°C.

• Testing Standards

• Follow industry standards like IPC-6012 e IPC-A-600.
• Implement Environmental Stress Screening (ESS), e.g., 1000 thermal cycles (-40°C to 125°C).

4. Rigid PCB vs. Flexible PCB: How to Choose?

5. Application Scenarios and Selection Recommendations

• Eletrónica de consumo (motherboards, appliances): FR-4 preferred for low cost and mature process.
• Controlo industrial (PLCs, sensors): High reliability needed; high-Tg FR-4 or multi-layer boards recommended.
• Eletrónica automóvel (ECUs, radar): Requires high-temperature resistance and vibration resistance; a metal substrate or a ceramic substrate is optional.
• Equipamento de comunicação (5G base stations, RF modules): High-frequency applications need PTFE or Rogers materials.