Manufacturing Process of Heavy Copper Multilayer PCBs

Heavy Copper Multilayer PCBs require a specialized manufacturing process to handle thick copper layers while maintaining high precision and reliability. These PCBs are widely used in power electronics, automotive applications, and industrial systems where high current-carrying capacity and excellent thermal management are essential. This article provides an in-depth look at the key manufacturing steps involved in producing Heavy Copper Multilayer PCBs.

1. Material Selection and Preparation

The first step in the manufacturing process is selecting the right base materials. The most common materials used for Heavy Copper PCBs include:

• FR4: A widely used substrate that provides a balance between cost and performance.
• Polyimide: Offers high-temperature resistance and durability, often used in aerospace applications.
• Metal-Core PCBs (MCPCBs): Feature an aluminum or copper base for superior thermal conductivity.

Before processing, the copper-clad laminates are cleaned and treated to remove contaminants and oxidation.

2. Inner Layer Circuit Formation (Etching Process)

Unlike standard PCB fabrication, Heavy Copper PCBs require a special etching process to handle thick copper layers.

• Standard PCB etching involves a subtractive process using chemicals to remove unwanted copper.
• Heavy Copper PCBs require advanced etching techniques, such as step etching or differential etching, to maintain fine-line precision without excessive undercutting.
• To prevent over-etching, manufacturers adjust etching times and use specialized resist coatings to protect the copper during processing.

3. Layer Stacking and Lamination

After the inner layers are etched, the PCB undergoes multi-layer lamination to bond the individual layers together.

• Stacking: The etched inner layers, prepreg (insulating dielectric material), and copper foil layers are stacked.
• Heat & Pressure: The stack is placed into a lamination press, where it is subjected to high temperature and pressure to bond the layers.
• Cooling & Curing: Once bonded, the stack is cooled and cured to ensure stability.

4. Drilling and Plated-Through Holes (PTHs)

Once the layers are laminated, holes are drilled for component mounting and electrical connections. However, drilling through thick copper layers presents several challenges:

• Standard drill bits wear out quickly when cutting through heavy copper, requiring special carbide drills.
• Laser drilling is sometimes used for high-precision micro-vias in multilayer designs.
• After drilling, the holes undergo electroless copper plating to create conductive pathways between layers.

5. Copper Plating and Surface Finish

Heavy Copper PCBs require thicker copper plating to ensure strong electrical connections and durability.

• Electroplating Process: Copper is electrochemically deposited onto the drilled holes and traces, increasing the thickness.
• Advanced Plating Techniques: Pulse plating or step plating is used to ensure even deposition across thick copper traces.
• Surface Finishing: A final protective coating is applied to prevent oxidation and improve solderability. Common finishes include:
• HASL (Hot Air Solder Leveling) – Cost-effective but not ideal for very fine traces.
• ENIG (Electroless Nickel Immersion Gold) – Provides excellent corrosion resistance.
• OSP (Organic Solderability Preservative) – A budget-friendly option for short-term storage.

6. Testing and Quality Inspection

Before final shipment, Heavy Copper PCBs undergo rigorous quality control and testing to ensure they meet performance and reliability standards.

• Electrical Testing (E-Test): Verifies that there are no short circuits or open circuits.
• X-ray Inspection: Used to check internal layer alignment and plating thickness.
• Thermal Stress Testing: Ensures the PCB can withstand high temperatures and mechanical stress.

Conclusion

The manufacturing of Heavy Copper Multilayer PCBs is a complex process that involves specialized etching, plating, lamination, and drilling techniques. Proper material selection, precise process control, and rigorous quality testing are crucial to ensure high-performance and durable PCBs. As demand for high-power electronic systems continues to grow, advancements in fabrication technology will further improve the efficiency and reliability of Heavy Copper PCBs.