Was ist ein Starre Leiterplatte 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:
- Hohe mechanische Festigkeit: 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:
| Merkmal | Starre Leiterplatte | Flexible Leiterplatte |
|---|
| Substrate Type | FR-4, CEM-3, etc. | Polyimide (PI), PET |
| Flexibilität | Keine | Bendable and foldable |
| Gewicht | Heavier | Light (90% lighter than rigid) |
| Kosten | Low (advantage in mass production) | Höher |
| Anwendungen | Motherboards, power modules | Wearables, foldable screens |
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.
- AOI-Inspektion: Automated optical inspection checks parameters like line width and spacing.
- 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
- Übertragung von Mustern: Laser Direct Imaging (LDI) technology creates outer-layer circuits.
- Solder Mask and Silkscreen: Solder resist ink is applied, and component markings are printed.
- Oberfläche: Processes like HASL, ENIG, or OSP are chosen based on application needs.
- Elektrische Prüfung: Continuity tested via flying probe or bed-of-nails test.
- Validierung der Verlässlichkeit: 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:
- 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).
- Erdung Design: Use multi-point grounding for high-frequency circuits, single-point for low-frequency.
- Thermisches Management: Add thermal vias, use thick copper foil (≥2 oz).
- Signalintegrität: Control impedance deviation within ±10%, line width tolerance ±0.05mm.
- Lamination Prozess: Vacuum pressing reduces interlayer bubbles.
- Drilling Accuracy: Hole position error ≤50μm, aspect ratio ≤8:1.
- Lötprozess: Use SAC305 lead-free solder, reflow peak temperature 245°C±5°C.
- Follow industry standards like IPC-6012 und 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?
| Betrachtung | Suitable for Rigid PCBs | Suitable for Flexible PCBs |
|---|
| Mechanical Environment | Fixed installation, high vibration | Bendable, dynamic folding |
| Kosten-Empfindlichkeit | Mass production, cost-controlled | Low volume, high-value products |
| Space Constraints | Sufficient space | Confined or irregular spaces |
| Heat Dissipation | High-power components, active cooling | Low power, passive cooling |
| Signal Frequency | High-frequency/speed (>10GHz) with special materials | General frequency (<5GHz) |
5. Application Scenarios and Selection Recommendations
- Unterhaltungselektronik (motherboards, appliances): FR-4 preferred for low cost and mature process.
- Industrielle Steuerung (PLCs, sensors): High reliability needed; high-Tg FR-4 or multi-layer boards recommended.
- Kfz-Elektronik (ECUs, radar): Requires high-temperature resistance and vibration resistance; a metal substrate or a ceramic substrate is optional.
- Kommunikationsausrüstung (5G base stations, RF modules): High-frequency applications need PTFE or Rogers materials.