Automated Process for PCB Manufacturing
The core process of PCB manufacturing includes key steps such as inner layer layout, lamination, drilling, plating, outer layer circuit formation, solder mask application, and surface treatment. The entire process is highly automated, ensuring the precision and reliability of the circuit boards.
Material Cutting
Large sheets of copper-clad laminate (e.g., FR-4) are cut into the required production dimensions.
Inner Layer Circuit Formation
First, the copper-clad laminate is cleaned, and a photosensitive film is laminated onto its surface. The designed circuit pattern is transferred onto the board via UV light exposure. The uncured photosensitive film is then washed away, and the unwanted copper foil is etched off using a strong alkaline solution, leaving the desired circuit traces.
Lamination
The prepared inner layer core sheets and prepreg (semi-cured epoxy resin sheets) are stacked alternately. Under high temperature and pressure in a vacuum press, the layers are bonded firmly. The prepreg melts and cures during heating, providing adhesion and insulation.
Drilling
High-precision CNC drilling machines or laser drilling equipment are used to create through-holes or blind/buried vias for interlayer electrical connections. X-ray positioning is often employed to align holes with inner layers and prevent drill bit deviation.
Electroless Copper Deposition (PTH – Plated Through-Hole)
Since the hole walls consist of non-conductive epoxy resin and glass fiber, a thin conductive copper layer (about 1 micron thick) is chemically deposited on the hole walls and the entire board surface to establish a conductive foundation for subsequent electroplating.
Outer Layer Circuit Transfer and Pattern Plating
A photosensitive film is applied again, exposed, and developed to transfer the outer layer circuit pattern using the "positive pattern" process. Electroplating follows, where copper is plated to a thickness of about 25 microns in the unprotected areas, followed by a protective tin layer over the circuit traces.
Etching and Film Stripping
The copper not protected by the tin layer is etched away, and the tin layer is subsequently removed, leaving the complete outer conductive circuit. This process is controlled precisely to minimize undercutting and ensure circuit accuracy.
Solder Mask and Silkscreen Printing
A solder mask ink (typically green or other colors) is applied to cover the board surface, leaving only the solder pads exposed to prevent short circuits during soldering. Component identifiers, polarity markers, and other information are then printed via silkscreening.
Surface Finish
To prevent oxidation of exposed copper and improve solderability, surface treatment processes such as HASL (Hot Air Solder Leveling), ENIG (Electroless Nickel Immersion Gold), immersion silver, or OSP (Organic Solderability Preservative) are commonly applied. For example, ENIG provides excellent flatness and long-term stability.
Profile Cutting and Testing
The final board shape is cut using milling or V-scoring, which is suitable for separating panelized boards. Finally, electrical continuity and the absence of short circuits are verified through flying probe testing or dedicated fixture testing.
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