PCB fabrication refers to a series of steps that will produce the physical build of a printed circuit board. It takes an initial design file and generates a working board. The starting process is design preparation, which includes finalizing a board layout using CAD, or Computer-Aided Design, software. Layer count, trace width, and hole size are specifications that are quite critical in this process, considering multilayer boards can have up to 30 layers or more in advanced applications.
The fabrication of a PCB first involves the preparation of the board layers. Typically, this begins with the lamination of layers of copper onto a substrate material, usually FR4. For high-frequency boards, advanced substrates can be applied to improve durability and quality of signal. A photoresist layer is applied onto the copper layers of the board, and the exposure to UV light transfers the design pattern onto the board. Remaining areas that are unexposed are etched away to expose the copper traces beneath them. This process is repeated for each layer, and in multi-layer boards, layers are bonded to each other under intense heat and pressure; this process is known as lamination.
Other stages involve drilling, which involves the creation of via and component lead holes. Most of the time, the standard PCB has drilling that is performed at high accuracy down to 0.1mm to enable precise connectivity. In high-density boards, laser drilling in some cases uses microvias as small as 0.05mm, highly essential in compact designs. After drilling, the holes undergo plating to ensure electrical conductivity between layers; this is an aspect that advances the functionality of the board.
The board goes to the solder mask stage after drilling and plating. The solder mask layer is applied to insulate the copper traces but expose the pads for soldering of components. Following this process, the silkscreen application adds component labels and markings for assembly; both contribute to better usability of the board and increased accuracy of its assembly.
Surface finishing is one of the last processes, where the pads are electroplated with a protective coating, such as ENIG (Electroless Nickel Immersion Gold) or HASL (Hot Air Solder Leveling). This increases solderability and can prolong the life of the board. Finally, each PCB undergoes strict testing, which includes Automated Optical Inspection (AOI) and electrical tests to make sure that it functions to design specification. The best manufacturers continue to keep defect rates lower than 0.1%.
How does PCB fabrication work, one might ask? This is a complex process involving several stages aimed at transforming the digital design of a printed circuit board into a reliable and high-performance PCB that can be applied within a broad range of applications.
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