PCB manufacturing typically begins with the creation of the inner layer patterns, one of the most crucial steps in multilayer board production. First, the copper-clad laminate is cleaned and coated with a photosensitive material. Then, through exposure and development, the designed circuit pattern is transferred onto the copper layer. Etching then removes unwanted copper, forming a precise circuit structure. After the inner layers are completed, AOI (Automated Optical Inspection) is performed to check for defects such as broken lines, short circuits, or fine lines. This step is particularly important for multilayer boards because problems cannot be repaired once laminated.
After the inner layers are completed, lamination and drilling processes begin. Multilayer PCBs stack the inner layer core board and prepreg (PP sheet) according to the structure, pressing them together under high temperature and pressure to form a unified board, ensuring a strong bond between the layers. Mechanical drilling or laser drilling is then performed to create vias, blind vias, or buried vias for electrical connections. For high-density interconnect (HDI) boards, layer-by-layer lamination and microvia processes are also used to achieve even higher wiring density. After drilling, descaling and chemical copper plating are usually performed to make the hole walls conductive, laying the foundation for subsequent electroplating. Finally, there's the surface treatment and final product processing stage, which directly impacts soldering reliability and lifespan. The PCB undergoes pattern electroplating to thicken the copper layer, followed by outer layer etching to form the final circuitry. This is then covered with solder mask ink (green being the most common color) and silkscreened. Surface treatment processes include HASL hot air leveling, ENIG immersion gold, and OSP organic protective film, among others. Different processes are suitable for different applications; for example, immersion gold is more suitable for high-frequency and high-reliability products.
After these processes, electrical testing, visual inspection, and board separation are performed to ensure that each PCB meets design requirements before delivery.
