What is the Function of the Main PCB Board?

A main PCB board (Printed Circuit Board) is a critical component in almost every electronic device. It serves as the mechanical foundation for electronic components, ensuring they are securely attached, properly connected, and able to perform their intended functions. In this article, we’ll dive deep into the purpose, materials, manufacturing process, and assembly of the main PCB board to better understand its importance in electronics.

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The Function of the Main PCB Board

1. Mechanical Support
   The main PCB board provides a flat, sturdy platform for mounting electronic components such as transistors, resistors, capacitors, and connectors. These components are installed on the outer layer of the PCB to form the required electronic circuits.

2. Electrical Connections
   PCBs use conductive traces (usually made of copper) to create pathways for electrical signals. These traces connect the terminals of components, enabling them to communicate and function as part of a cohesive circuit.

3. Platform for Circuit Integration
   As the building block of electronic devices, the main PCB can be designed as single-sided, double-sided, or multi-layered, depending on the complexity of the circuit. Multi-layer boards allow for better signal integrity, higher component density, and more routing options.

Types of Main PCB Boards

Single-Layer PCB: A basic design with components and conductive traces on one side of the substrate.

Double-Layer PCB: Features conductive copper layers on both sides, providing more routing options and higher functionality.

Multi-Layer PCB: Composed of multiple layers of conductive copper, ideal for complex circuits like those used in computers and advanced electronics.

Materials Used in Main PCB Boards

1. Substrate

Rigid Substrate: Typically uses materials like FR4 (fiberglass-reinforced epoxy) for durability and rigidity.

Flexible Substrate: Uses high-temperature polyimide film for flexible applications.

1. Copper Layer
   A thin layer of copper foil is laminated on the substrate to create electrical connections. The thickness of the copper layer can vary depending on the board’s design requirements.

2. Solder Mask
   The solder mask acts as the PCB’s skin, protecting the copper traces from oxidation and preventing solder bridges between adjacent traces during assembly.

3. Silkscreen
   The silkscreen layer is used to print logos, component labels, and instructions onto the board, aiding assembly and troubleshooting.

Manufacturing Process of the Main PCB Board

1. PCB Boards Manufacturing: Cutting the Raw Material

The PCB manufacturing process begins with cutting the raw PCB material. The material, typically fiberglass-reinforced copper foil, is cut to the required size. The accuracy of cutting is critical, with a tolerance of +/-2mm. Common material sheet sizes include 36”*48”, 40”*48”, and 42”*48”. Material utilization is important for reducing waste, and in special cases, materials can be mixed for cutting to optimize production efficiency.

2. PCB Boards Manufacturing: Inner Layer Processing

This stage involves several sub-processes:

Pre-treatment: Cleaning and preparing the laminate to ensure a contaminant-free surface.

Coating: Applying a photosensitive coating on the laminate surface.

Exposure: Using a photomask to expose the coating to UV light, transferring the design pattern onto the laminate.

Development and Etching: Developing the exposed pattern and removing unwanted copper using a chemical etching solution.

Drilling: Drilling holes for vias and component leads.

AOI (Automated Optical Inspection): Conducting visual inspection to ensure quality.

At SQPCB, advanced techniques such as LDI (Laser Direct Imaging) exposure machines and fully automated coating and baking lines are used. The use of LDI technology minimizes film shrinkage issues, ensuring precise alignment and reducing registration errors. This innovation helps maintain controlled shrinkage within 0.1um, improving the overall quality of the inner layers.

3. Lamination and Pressing

The lamination process involves the bonding of multiple layers to create multi-layer PCBs. This step includes:

Brown-Out and Riveting: Pre-pressing the laminate to form a stable base.

Pre-Stacking: Aligning the stacked layers of copper, laminate, and prepregs.

Pressing: Applying heat and pressure to bond the layers together.

X-ray Drilling Targets: Drilling targets are aligned and inspected using X-ray systems.

Edge Trimming and Grinding: Trimming the edges and ensuring uniformity in thickness.

Pressing is one of the most critical steps in multi-layer PCB production. SQPCB has optimized this process by selecting structures that not only meet the required board thickness but also improve impedance control. Materials such as 7628 are selected over more expensive options like 2116, significantly reducing costs while ensuring high performance.

4. Drilling Process

Drilling is a crucial step for creating holes for vias and through-hole components. It involves:

Pre-Drilling: Initial drilling to prepare the material for deeper cuts.

Drill Bit Grinding: Ensuring the drill bits are sharpened to maintain precision.

Pinning and Drilling: Ensuring accurate hole placement and depth.

Drill Bit Retirement and Peak Polishing: Polishing drill bits after 3,000-5,000 holes to maintain their effectiveness.

SQPCB uses linear motor-driven drilling machines, ensuring high-speed and high-precision drilling. These machines guarantee hole accuracy and consistency, ensuring that all holes meet IPC standards with a tolerance of +/-2mil.

5. Electroplating Process

Electroplating is essential for copper deposition inside drilled holes and on the PCB surface. The process includes:

High-pressure Water Washing: Ensuring the board is clean before electroplating.

PTH (Plated Through-Hole): Plating copper inside the holes for electrical conductivity.

Copper Electroplating: Depositing a thin layer of copper onto the surface and inside the holes to ensure good electrical connections.

SQPCB uses renowned electroplating equipment, investing in high-quality systems that improve yield and reduce the failure rate. While equipment costs may be higher, the long-term benefits of reduced downtime and superior quality outweigh the initial investment.

6. Outer Layer Processing

After the inner layers are completed, the outer layer processing begins. It includes:

Pre-treatment: Cleaning the copper surface before applying the protective coatings.

Film Lamination: Applying a protective film for further processing.

Exposure and Development: Using LDI technology to transfer the design onto the outer layer.

Etching and Removal: Removing the unwanted copper, leaving behind the designed circuit pattern.

AOI and Impedance Testing: Ensuring the design meets the required impedance and quality standards.

At SQPCB, LDI exposure machines with linear motor and optical scale control help achieve shrinkage accuracy within 0.1um, ensuring excellent alignment and reducing defects caused by manual handling.

7. Solder Mask Application

A solder mask is applied to the PCB to protect copper traces and prevent solder bridges during the assembly process. The steps include:

Pre-treatment and Silk Printing: Printing the solder mask onto the PCB.

Pre-baking: Pre-curing the solder mask to harden it before exposure.

Exposure and Development: Using UV light to expose and harden the mask where needed.

SQPCB implements automated solder mask applications, significantly reducing manual errors such as solder mask shift or incorrect pad coverage. This system helps maintain uniformity and ensures a high-quality finish for all PCBs.

8. Text and Legend Printing

Text and legends are applied to the PCB to mark components, references, and other essential information. The process includes:

Silk Screen and Inkjet Printing: Printing labels and other markings.

Post-Baking: Curing the printed ink to ensure durability.

SQPCB uses linear motor-driven inkjet printing machines, achieving exceptional control over shrinkage and print accuracy. This technology reduces defects caused by misalignment and guarantees clear, legible text.

9. Surface Finishing

A surface finish is applied to exposed copper areas to protect against oxidation and improve solderability. This step includes:

Gold Immersion (ENIG), HASL, or OSP: The choice of surface finish is based on customer requirements for durability and solderability.

10. Final Inspection and Electrical Testing

Before assembly, PCBs undergo a series of tests to ensure their functionality:

Electrical Testing: Detects open circuits, short circuits, or misalignments.

Flying Probe Testing and AOI: Ensure the PCB meets design specifications.

Final inspection is essential to ensure that no defects are present and the PCBs meet industry standards before packaging.

If you’re seeking high-quality PCB manufacturing with strict process control and fast turnaround times, SQPCB offers advanced multilayer PCB production and material options tailored for high-frequency or industrial use.

Assembly of the Main PCB Board

The assembly process involves attaching components to the PCB to create a fully functional electronic device. Key steps include:

1. 1. Design File Preparation
      Begins with a Design for Manufacturability (DFM) check, reviewing the PCB design to ensure production readiness.

   2. Material Preparation
      Involves sourcing high-quality PCB substrates, components, solder paste, and flux. Material quality directly affects the performance of the final product.

   3. Solder Paste Printing
      A layer of solder paste is applied to the PCB using a stencil to prepare it for component placement.

   4. Component Placement
      Automated pick-and-place machines install components onto the PCB with high precision and speed.

   5. Reflow Soldering
      The PCB is heated in a reflow oven, melting the solder paste and securing components in place.

   6. Inspection and Testing
      Boards are inspected for defects using AOI, X-ray inspection, and functional testing.

   7. Through-Hole Component Insertion
      For boards requiring through-hole components, manual or wave soldering ensures solid mechanical connections.

   8. Cleaning
      Flux residue is cleaned from the PCB surface to enhance reliability and visual appearance.

   9. Final Testing
      Final inspection includes full electrical testing and visual checks to verify full functionality.

Importance of the Main PCB Board in Electronics

The main PCB board is often referred to as the “heart” of electronic devices because it enables components to work in harmony. Without it, modern electronics—from smartphones to aerospace systems—would be impossible. It’s the silent enabler behind today’s technological breakthroughs.

SQPCB has a strong track record of delivering precision-assembled main PCB boards with LDI exposure, in-house pressing, and advanced solder finish capabilities—all backed by ISO and UL certifications.

Conclusion

The main PCB board is an indispensable component in modern electronics. By providing mechanical support, electrical connectivity, and a platform for component integration, it enables the functionality of virtually all electronic devices. Understanding its materials, manufacturing process, and assembly underscores its critical role in driving innovation in fields like consumer electronics, healthcare, aerospace, and more.

As technology advances, PCB designs will continue to evolve, offering even greater functionality and reliability for next-generation devices. Choosing a reliable partner like SQPCB ensures robust performance, precision craftsmanship, and scalable production to keep your business ahead in a competitive global market.