PCB board manufacturing consists of multiple steps, which may vary depending on design, number of layers, component layout, and complexity. The following are the main processes involved in PCB manufacturing:
circuit design
In order to design a fully functional circuit, it is necessary to first use computer-aided design (CAD) software systems to generate circuit designs. The design workflow begins with circuit development, layout definition, and CAD program generation. Allocate circuit components to different CAD layers based on expected functionality. In addition, the layout provides detailed instructions on component placement, routing, and component packaging types. The goal is to include as much data as possible for reference. From CAD tools, generator tools are used to develop control programs for manufacturing PCBs.
The use of the industry recognized light painting tool "Gerber" is the foundation for manufacturing PCBs in printed circuit board manufacturing equipment. A complete set of Gerber files must be sent to the PCB manufacturer, including the complete generated files for each layer.
Patterning
The patterning process can be completed through photolithography. In photolithography, a photosensitive material (also known as photoresist) is coated on a copper foil and then exposed to light. During the exposure process, a photomask is used to cover the patterns required for the manufacturing of printed circuit boards. Apply the solution to the exposed part of the PCB to dissolve the photosensitive material. Use another solution to etch away soluble photosensitive materials and unwanted copper foil. Then leave a pattern similar to the photomask on the copper foil. Finally, remove the residue through a cleaning solution. The basic process of PCB board manufacturing can be summarized as: exposure, development, etching, and peeling.
drilling
Recall that through holes are structures that connect different layers. This is achieved through the use of mechanical or laser drilling. The drilling process is often a bottleneck in PCB manufacturing services. The quality of drilling can be evaluated by the burr height, diameter, and roundness of the hole. These quality issues are mainly affected by the wear and degradation of drilling tools.
Through-hole filling
The inner wall of the through-hole should be plated with copper, which is a conductive material that can electrically connect different layers of the vertical structure. PCB manufacturers can choose between electrolytic or chemical plating methods. During the electroplating process, copper ions react in the chemical plating tank, and this chemical reaction is called the "reduction" process. Then transfer the copper plated material from the seed layer (or source) to the surface of the through-hole. During the electroplating process, the copper source is ionized by incorporating an electric field into the system.
Solder mask
As mentioned earlier, the solder mask layer is a thin protective polymer layer deposited on the FR-4 laminate, which helps to isolate conductive and insulating surfaces. The solder mask layer can be achieved through various direct and indirect deposition techniques. The application of solder mask varies depending on the classification and type of solder mask to be used. Thermosetting solder mask layer (also known as epoxy liquid) is screen printed onto the substrate and then thermally cured. Due to its faster curing time, UV solder mask layers are also widely popular. Due to its high precision and resolution, photosensitive solder mask is the most common type in the PCB manufacturing industry. The ideal solder mask should have strong adhesion, low refractive index, low coefficient of thermal expansion (CTE), and high thermal stability.
Surface Treatment
Through HASL OSP、ENIG、ENEPIG、 Surface treatments such as immersion in gold, silver, and tin protect exposed copper wires on PCB copper pads from external environmental influences. Here, we will discuss the most commonly used ones: HAP, OSP, and ENIG.
Hot air solder leveling (HASL): After using cured solder resist to manufacture PCBs, place the circuit board into a hot molten solder bath to form intermetallic compounds. According to the Restriction of Hazardous Substances Directive (RoHS), alternative surface treatment methods such as HASL are being adopted.
Organic Solderability Protective Agent (OSP): This is another commonly used surface treatment method, which is based on organic molecules forming a surface treatment film.
Chemical nickel gold plating (ENIG): The process flow of ENIG includes surface acid washing, etching, activator treatment, chemical nickel plating, and immersion gold plating. ENIG is definitely the most popular surface treatment method for manufacturing PCBs.
Screen printing
Screen printing is used to indicate some circuit board information, such as component placement, wiring, and other functions, which are useful during PCB manufacturing services. Templates containing specific patterns are installed on top of printed circuit boards. The opening on the template indicates the information to be transferred to the PCB, and then use a scraper. After removing the template, the pattern with information remains on the circuit board and is then baked to solidify the material.
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