How are multi-layer circuit boards made?

Multilayer printed circuit boards (PCBs) are one of the most prevalent circuit board types in contemporary electronic devices. They are constructed by stacking multiple single-sided or double-sided circuit substrates, with insulating dielectric materials sandwiched between each layer to form an integrated unit. Each tier features distinct circuit traces, and these layers are electrically interconnected via conductive vias and interlayer wiring.

Advantages of Multilayer PCBs vs. Single/Double-sided PCBs

Manufacturing Process of Multilayer PCBs (Concise English Points)
1. Inner-layer Core Preparation: Cut the copper-clad laminate into core boards, then conduct pattern transfer, etching, and stripping to form inner-layer circuit patterns.
2. AOI Inspection: Perform automated optical inspection on inner-layer boards to detect defects like residual copper, open circuits, or short circuits.
3. Layer Stacking & Lamination: Stack inner-layer boards with prepreg (bonding material) alternately, then press under high temperature and pressure to form an integrated multilayer core.
4. Drilling: Drill through vias, blind vias, or buried vias at designated positions to establish interlayer connections.
5. Plating: Conduct copper plating on via walls and board surfaces to ensure reliable electrical conductivity between layers.
6. Outer-layer Processing: Repeat pattern transfer, etching, and stripping steps on the outer layers to form external circuit traces.
7. Surface Finishing: Apply surface treatments such as HASL, ENIG, or immersion tin to protect copper and enhance solderability.
8. Final Testing & Shaping: Carry out electrical testing (e.g., flying probe test) and dimension cutting, then inspect for overall quality before packaging.

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