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PCB board manufacturing process 2
Copper-clad laminate (CCL) is a substrate material that can be divided into rigid CCL and flexible CCL. CCL is a key material that determines the signal transmission speed, energy loss, and characteristic impedance in a circuit, and plays a role of interconnection, insulation, and support in a PCB.
Two steps in the PCB manufacturing process: CCL manufacturing
Copper-clad laminate (CCL) is a base material, divided into rigid and flexible CCLs. It's a key material determining signal transmission speed, energy loss, and characteristic impedance in circuits, playing roles of interconnection, insulation, and support in PCBs. The detailed CCL manufacturing process is: PP cutting → pre-stacking → combining → pressing → disassembling → cutting inspection → packaging → warehousing → shipping. As the core of the circuit board, dust on the CCL surface may cause short circuits or open circuits in the final circuit; therefore, a cleaning step is added in the PCB manufacturing process.
A printed circuit board is made by bonding copper foil to a CCL via a semi-cured sheet. Production starts with the core board in the middle, continuously stacked and then fixed.
The third step in the PCB manufacturing process: inner layer circuitry
After cleaning the CCL, we need to apply a photosensitive film to the surface of the PCB substrate to prepare for subsequent image transfer. This film has the characteristic of light curing. Therefore, we can use this film to form a protective film on the copper foil of the CCL.
To accurately position the PCB layout film stacking position, we need to insert the two PCB layout films and the double-layer CCL into the upper layer of the PCB layout film.
Precise placement of the PCB laminating film
After the above preparations are completed, the photosensitive film is exposed and cured to transfer the image of the base material to the photosensitive film. The film has transparent and opaque parts. When the photosensitive film passes through the photosensitive plate, the UV lamp cures the photosensitive film in the transparent areas. The cured part is the inner layer circuit we need, and the uncured part is removed with an alkaline solution.
After removing the photosensitive film, the hardened photoresist covers the copper we want to keep, and the CCL enters the next stage: removing the unwanted copper. Just as an alkaline solution removes the photoresist, stronger chemicals remove the excess copper. A copper etchant bath removes all exposed copper. Meanwhile, the required copper is fully protected under the hardened photoresist layer.
Not all copper boards are the same. Some heavier circuit boards require a greater amount of copper etchant and different exposure times. In addition, heavier copper boards require special attention to track spacing. Most standard PCBs rely on similar specifications.
The fourth step in the PCB construction process: AOI inspection
PCB testing includes various methods such as visual inspection, AOI optical inspection, electrical testing, and functional testing. AOI inspection is usually performed after SMT assembly, but to ensure the yield of the PCB, AOI testing is also needed after the inner layer circuit process is completed. This is because once the circuit board enters the lamination process, even if an error is found in the inner layer, it cannot be modified. Therefore, after the CCL enters the AOI inspection equipment, the equipment scans it and transmits the data of the defective images to the VRS, and then a specialist is responsible for repair.
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