What Does a PCB Manufacturer Do?
PCBs are complex devices that are essential to everything from heart rate monitors to rockets. They consist of insulating layers with plated copper connections that are connected through drilled holes.
The PCB fabrication process begins with the designer who creates a blueprint using a program like Extended Gerber. This software converts the design into a file that the fabricator can use to create the actual printed circuit board.
Substrate
PCBs need a substrate to provide support for the conductive copper traces and circuits. The substrate is a laminated electrical insulator that connects to the rest of the board through holes plated on opposite layers. The best substrates don’t conduct electric currents and also have low moisture absorption. This helps prevent corrosion. PCB manufacturers use a variety of materials for their substrates, but the most common is FR-4, which is a fiberglass-epoxy laminate that is affordable, durable, and effective as an electrical insulator.
PCB substrates are organized into varying layers during manufacturing to create different types of PCBs. These layers vary in thickness, thermal properties, and dielectric constants. Depending on the type of circuit boards, the substrates may be rigid or flexible. Rigid-flex PCBs, for example, combine flexible and rigid materials to provide a balance of adaptability and structural integrity.
The maximum operating temperature (MOT) of a substrate is a measure of how high the material can be exposed to heat without damage or failure. The substrate manufacturer determines the MOT by testing the material’s characteristics at various temperatures.
The coefficient of thermal expansion (CTE) of a PCB substrate is important, especially for multilayer circuit boards. When the different layers of a PCB have different CTE values, they can expand at different rates, which can cause cracks and detachment. This is particularly a concern for high-speed traces that must have smaller linewidths to meet impedance requirements.
Conductive Layer
A key part of any PCB is the copper layer, which carries electrical signals to and from the board. Depending on the type of PCB, this may be in the form of a copper foil or a full-on copper PCB manufacturer coating. The conductive layer is crucial to ensuring that the circuit boards function properly, and the fabrication process is complex enough to guarantee that this step goes smoothly.
The next step involves printing the inner layers of the circuit board. Unlike architectural plans, which print out on a standard 8.5 x 11 sheet of paper, PCB designs are printed using a special plotter printer to create a film that looks much like the old transparencies used in school. The film is coated with clear ink to map out the lines of copper pathways, and black ink to mark areas that will be etched away later. The printer also creates a series of registration holes to help keep the layers lined up properly when they are added together.
Once the inner layers have been printed, the panels receive a wash to remove any residuals that remain on them. Next, they go through automated optical inspection to ensure that they meet the exact requirements of the original Gerber file that the PCB manufacturer received from the designer. This step helps to prevent accidental errors that could affect the performance of the finished product, such as improper electrical connections.
Components
PCBs are used in a wide variety of electronics and technology. They can range from simple single-sided boards to intricate multi-layer designs that integrate multiple functions into one unit. PCBs are made of a substrate with a conductive metal layer, usually copper, etched to create a circuit pattern on both sides. This layer is then populated with electronic components, typically soldered on the top surface of the board.
There are several different types of dielectrics that can be used to make a PCB. Polytetrafluoroethylene (commonly referred to as Teflon) is a common choice, but it’s not the only option. Other popular choices are FR-4, FR-1, CEM-3, and woven glass and epoxy. The choice of dielectric depends on the requirements of the circuit design.
The PCB fabrication process produces a variety of air emissions, including volatile organic compounds (VOCs). This type of pollution can PCBA Coating be controlled by using specialized equipment that captures and filters these chemicals. This type of technology is essential to reducing environmental impact and upholding the fabricator’s sustainability goals.
The PCB designer uses a computer software program to convert schematic diagrams into electrical drawings that define how the components will connect together. The software can also check the PCB design for errors such as traces that touch incorrectly or holes that are too skinny. The CM will have a set of DFM guidelines for their facility that the designer can consult to help adapt the design to the fabrication process.
Inspection
A thorough inspection process is essential for PCB manufacturing to ensure that products meet industry standards and consumer expectations. It also helps to save time and resources by avoiding costly rework and maintaining production efficiency. The inspection process includes general electrical testing and verification of the connectivity of conductive patterns, as well as pad plating, firmness, and clarity. It also checks for surface defects, solder bridges, and the quality of component placement. A robust inspection process also verifies that the components used in the circuit board comply with industry safety standards.
Automated optical inspection (AOI) uses high-resolution cameras and image processing software to automatically inspect PCBs for defects. It is highly effective at detecting issues such as solder bridges, surface defects, and component placement errors. However, AOI systems require significant up-front investment and expertise to calibrate the cameras and lighting, and program the inspection criteria. They are also unable to detect certain defects, such as internal layer problems and very fine cracks.
Visual inspection involves checking the circuit board for visible defects using a magnifying glass or a microscope. This is the most traditional and cheapest inspection method, but it can be difficult to spot some defects. This method is also prone to human subjective errors and lacks the ability to collect data for Statistical Process Control.
