Basic PCB Knowledge: Classification, Materials, Manufacturing Process & Core Advantages

Basic PCB Knowledge: Classification, Materials, Manufacturing Process & Core Advantages

 

1. What is PCB (printed circuit board)

PCB (printed circuit board) is the fundamental core component of all electronic devices, widely known as the "mother of electronic products". It serves as the structural carrier for electronic components and provides fixed electrical interconnection between all electronic parts. Named after the electronic printing manufacturing process, PCB is an indispensable basic substrate for consumer electronics, industrial control, automotive, communication and aerospace equipment.

2. PCB Classification by Layer Count

According to the number of conductive wiring layers, PCBs are mainly divided into three categories: single-sided boards, double-sided boards, and multilayer boards. Common industrial PCBs adopt 4-layer and 6-layer structures, while high-precision industrial and military equipment can support dozens of layers or even nearly 100-layer ultra-thick multilayer PCBs.

2.1 Single-Sided PCB

A single-sided PCB is the most basic circuit board structure. Electronic components are mounted on one side, and conductive copper traces are distributed exclusively on the opposite side. Due to the single-layer wiring limitation, traces cannot cross each other and require detour routing, resulting in strict design constraints. Single-sided PCBs are only suitable for simple early circuit designs and low-cost basic electronic products.

2.2 Double-Sided PCB

Double-sided PCBs feature conductive wiring on both top and bottom layers. Electrical connection between the two layers is realized through plated through vias — metal-filled or metal-coated tiny holes that conduct cross-layer signals. With double the wiring area compared with single-sided boards, double-sided PCBs completely solve single-layer trace crossing limitations and are suitable for moderately complex circuit systems.

2.3 Multilayer PCB

Multilayer PCBs are formed by alternately laminating multiple single-sided and double-sided conductive layers with insulating prepreg and core materials through precise positioning and pressing technology. Common structures include 4-layer, 6-layer, 8-layer PCBs, which integrate signal layers, power layers and ground layers. Most multilayer PCBs adopt even-layer design, and blank insulating layers can be added to adjust board thickness as required. High-density multilayer PCBs are widely used in motherboards, high-speed communication equipment and precision industrial instruments.

3. PCB Classification by Flexibility

Based on substrate flexibility, PCBs are classified into rigid PCB, flexible PCB (FPC), and rigid-flex combined PCB, adapting to different product assembly and usage scenarios.

3.1 Rigid PCB

Rigid PCBs feature fixed hardness and non-bendable substrate, with stable mechanical structure and strong anti-deformation performance. Common finished thicknesses include 0.2mm, 0.4mm, 0.6mm, 0.8mm, 1.0mm, 1.2mm, 1.6mm and 2.0mm. mainstream rigid PCB substrate materials include phenolic paper laminates, epoxy paper laminates, polyester glass mat laminates and epoxy glass cloth (FR4) laminates.

3.2 Flexible PCB (FPC)

Flexible PCBs are bendable, foldable and torsion-resistant circuit boards. The conventional base thickness is 0.2mm, and the welding area is locally thickened to 0.2mm–0.4mm to enhance soldering reliability. Common FPC materials include polyester film, polyimide (PI) film and fluorinated ethylene propylene film, widely used in wearable devices, folding screens and miniature electronic equipment.

3.3 Rigid-Flex PCB

Combining the advantages of rigid and flexible boards, rigid-flex PCBs integrate rigid fixed assembly areas and flexible bending areas, realizing integrated assembly of complex 3D circuit structures.

4. PCB Core Substrate Materials

4.1 Copper Clad Laminate (CCL)

Copper clad laminate is the base material for all PCB manufacturing. It provides stable mechanical support for electronic components and achieves electrical insulation and conductive circuit distribution between components, which is the foundational raw material for PCB etching, routing and lamination processes.

4.2 Aluminum Substrate PCB

Aluminum substrate PCB belongs to metal-based heat-dissipating PCBs, including aluminum, copper and iron substrates. It adopts high-plasticity Al-Mg-Si alloy base, featuring excellent thermal conductivity, electrical insulation and mechanical processing performance. As the mainstream heat-dissipating PCB, it is widely used in LED lighting, power supplies and high-heat industrial equipment.

5. Professional PCB Surface Finish Process

Solder mask green oil covers most PCB copper surfaces to prevent oxidation and short circuits. Only soldering terminals and contact points are exposed, requiring professional surface finish treatment to ensure long-term connection stability and soldering performance.

- Electroplated Hard Gold: Plated with nickel layer + high-stability hard gold on board golden fingers. With cobalt doping for excellent wear resistance and chemical stability, it ensures stable plug-in connection for a long time.

- Tin Spray (HASL): Cover the soldering terminals with tin-lead alloy and level through hot air, providing good solderability and surface oxidation resistance.

- Pre-Solder Anti-Oxidation: Coat a layer of organic anti-oxidation film on soldering pads to temporarily protect terminals, maintain flat pad surface and ensure reliable soldering.

- Carbon Ink Printing: Print conductive carbon ink on contact terminals to improve conductivity and anti-oxidation performance for stable signal contact.

6. PCB Molding & Finishing Process

After circuit production and surface treatment, PCBs are shaped by CNC routing or die stamping according to customer size requirements. Positioning holes are used for fixing during cutting. The golden finger area is chamfered to facilitate plug-in assembly. For panelized PCBs, V-Cut grooves are added between units for convenient customer splitting. Finally, professional cleaning is performed to remove surface dust and ionic contaminants.

7. Final Inspection & Vacuum Packaging

Before delivery, all finished PCBs undergo strict quality tests, including electrical conduction testing, impedance testing, solderability testing and thermal shock resistance testing. Baking treatment is conducted to remove process moisture and eliminate thermal stress. Finally, qualified products are vacuum-packaged to prevent oxidation and moisture damage during transportation and storage.

8. Core Advantages of PCB Products

The wide application of PCBs in the electronics industry stems from their unique comprehensive performance advantages, supporting high-end miniaturization and high-speed development of electronic equipment:

- High Density Integration: With the upgrading of integrated circuits and mounting technology, PCB wiring density continues to improve, realizing miniaturization and lightweight design of electronic equipment.

- Long-Term Reliability: Through strict aging tests, electrical performance tests and reliability inspections, PCBs can maintain stable operation for up to 20 years, ensuring long-term service life of electronic systems.

- Strong Designability: Support customized design of electrical, mechanical, physical and chemical properties. Standardized design specifications shorten R&D cycles and improve design efficiency.

- Mass Productivity: Adapt to standardized, automated and large-scale industrial production, ensuring consistent product quality and stable delivery capacity.

- Complete Testability: Mature testing standards and professional testing equipment support full inspection of PCB qualification, performance parameters and service life.

- High Assembly Efficiency: Standardized PCB structure supports automated SMT assembly and large-scale batch production, suitable for integrated assembly of complete machine systems.

- Convenient Maintainability: Standardized component layout and circuit design enable rapid fault location and component replacement, greatly improving system maintenance efficiency.

- High-Speed Signal Performance: Optimized stacking and wiring design supports high-speed signal transmission, meeting the performance requirements of communication and precision electronic equipment.

9. Conclusion

As the core carrier of electronic circuits, PCBs cover diversified types such as single/double/multilayer boards, rigid/flexible/rigid-flex boards. With diverse substrate materials, mature surface finishing and molding processes, and outstanding comprehensive advantages in integration, reliability and mass production, PCBs have become an indispensable basic component in the global electronic manufacturing industry.

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