The PCB fabrication process involves the manufacturing of a printed circuit board (PCB) from the raw materials to the final product. Here's a general overview of the PCB fabrication process:
- Design Preparation: The process starts with the design of the PCB using computer-aided design (CAD) software. The design includes component placement, routing of traces, and defining the PCB layers.
- Material Selection: The appropriate base material for the PCB, often a fiberglass-reinforced epoxy laminate called FR-4, is selected. The thickness and copper foil weight is determined based on the design requirements.
- Preparing the Substrate: The base material is cleaned, and a layer of copper is applied to both sides. This copper layer acts as the conductive surface for the PCB.
- Imaging the PCB: A photoresist layer is applied to the copper surface. A photographic film or a laser plotter is used to transfer the PCB design onto the photoresist, creating a pattern of exposed and unexposed areas.
- Etching: The PCB is immersed in an etchant solution, such as ferric chloride or ammonium persulfate, which removes the exposed copper. This process selectively removes the copper, leaving the desired copper traces and pads on the PCB.
- Drilling: Precision holes are drilled into the PCB to accommodate through-hole components and provide electrical connections between layers. Computer-controlled drilling machines with high-speed spindles are used for accuracy.
- Copper Plating: To ensure electrical connectivity between layers, the drilled holes are plated with a thin layer of copper using an electroplating process. This process is called "through-hole plating" or "PTH" (plated through-hole).
- Outer Layer Imaging: The outer layers of the PCB are imaged with a photoresist layer. The resist is exposed to UV light using the PCB design film or laser plotter, defining the required circuit patterns.
- Outer Layer Etching: The exposed copper on the outer layers is etched away using an etchant solution, leaving behind the desired copper traces and pads.
- Solder Mask Application: A solder mask layer is applied to the PCB surface, covering all the copper traces except for the component pads. The solder mask protects the copper traces and prevents solder bridges during assembly.
- Silkscreen Printing: The PCB may undergo a silkscreen printing process to add component labels, symbols, and other markings. This is done using a special ink and a screen-printing technique.
- Surface Finish: The exposed copper surfaces are coated with a surface finish to protect them from oxidation and facilitate soldering. Common surface finishes include Hot Air Solder Leveling (HASL), Electroless Nickel Immersion Gold (ENIG), and Organic Solderability Preservative (OSP).
- Testing and Inspection: The fabricated PCBs undergo various tests and inspections to ensure their quality and functionality. This includes electrical testing, dimensional verification, and quality checks for solder mask coverage, solderability, and other critical parameters.
- PCB Separation: After fabrication and testing, the PCBs are separated from the manufacturing panel, also known as depanelization. Various methods, such as V-grooving, scoring, or routing, are used to separate the individual PCBs.
- Final Quality Control: The finished PCBs go through a final inspection to ensure they meet the required specifications and standards. Any necessary rework or repairs are performed before the PCBs are ready for use or assembly.
It's important to note that the specific details of the PCB fabrication process can vary depending on factors such as the complexity of the design, the number of layers, and the specific requirements of the customer or industry.
