A PCB Manufacturer Must Have a Robust Inspection Process
The PCB fabrication process is complex, and each step must be executed precisely to prevent problems such as short circuits. This requires careful planning and the use of computer guidance and machine-driven tools.
To begin with, the designer must create a blueprint for the circuit board. This is done using CAD software.
Design
Printed circuit boards (PCBs) are the foundation of many modern electronic devices. They connect electrical components to each other using conductive metal layers, usually copper, that are etched into the substrate. These copper traces are then soldered to the component leads. These connections are crucial to the function of the board.
PCB design begins with creating a schematic diagram, a symbolic representation of the circuit’s components and their interconnections. This is followed by the placement of components on the circuit board, known as PCB manufacturer layout. The location of the components is based on the physical specifications and constraints of the end product, as well as signal integrity requirements.
The routing of conductive tracks is another critical aspect of the PCB design process. During this phase, the designer will create routes for the signals from each component to the next. The goal is to minimize the length of the traces, which will reduce signal delays. In addition, the designer will take into account factors like line impedance, dielectric layer thickness and routing copper thickness.
The next step is to verify the design using a DRC (design rule check). This software checks for errors, such as traces that touch each other, holes that are too skinny, or drill hits that were made with dull bits. Once the PCB design is verified, it is sent to the fabricator.
Fabrication
PCB fabrication is a complicated sequence of steps that combines machine precision with strict inspections. The resulting boards are then ready for component assembly. The PCB manufacturing journey begins with front-end engineering, where ECAD software translates schematics into electronic drawings that define the electrical connections between components.
Once the design is finalized, the fabrication process is underway. During this phase, designers perform what is known as a Design for Manufacturability (DFM) check to ensure that the circuit board fulfills at least the minimum tolerances required by manufacturing processes such as etching, drilling and plating. DFM considers various factors, including the availability of components and manufacturing lead times.
After the DFM check, designers send the PCB file to a fabrication house for printing. The fabrication house uses a plotter, a specialized laser printer that produces photo films of the PCB. The manufacturer then images the copper layer of the circuit board by exposing it to ultraviolet light through a mask that represents the desired circuit pattern. The areas of the film that are exposed to light harden, while the unexposed areas are washed away by a chemical solution.
Alternatively, the circuit board can be directly printed using a laser, bypassing the need for photo tools. This method is more precise but is more expensive because each layer of the circuit board must be printed separately.
Inspection
A PCB manufacturer must have a robust inspection process to ensure all products leave their factory without faults. Faulty products can result in money losses through warranty payments and returns, not to mention reputation damage. A flawed product may even cause injury or death if used in a medical device or vehicle component.
The simplest form of inspection is manual visual inspection (MVI), which involves a worker looking over the PCB with the naked eye or with magnification. This involves comparing the PCB to its design drawings and checking for common defects. This is an important step that can be carried out at multiple points throughout the manufacturing process, including assembly.
MVI is usually followed by a more detailed examination with the aid of a microscope, to detect any faults that the naked eye couldn’t see. This is especially important with smaller, more densely packed PCBs. EMSG, for example, inspects every single PCB under a microscope after it has been fabricated.
Other inspection methods are also available, depending on the type of PCB being manufactured. For example, double-sided PCBs require more internal inspection than single-sided boards. X-rays can be used for this, along with automated optical inspection (AOI) and ALT inspection. AOI is more accurate and faster than MVI, as it removes the possibility of human error. It can also check for metalized vias, ensuring that they are complete and free from nodules and voids.
Testing
Once the PCB is complete, it must undergo testing to ensure that it meets quality and functionality standards. This process includes conducting tests like In-Circuit Test, Flying Probe Test, and Functional Testing. It also involves analyzing test data and results to identify issues or defects in the manufacturing process. This is a vital PCB Assembly part of the PCB fabrication and assembly process, and it can help improve overall efficiency and reliability.
The types of electrical tests performed on the PCB include continuity testing, which verifies that all connections are functioning correctly by measuring resistance or conducting a voltage drop test. This type of testing helps to prevent any open or short circuits that could disrupt the performance of the circuit board.
Environmental testing is another crucial component of the PCB testing process, which simulates real-world conditions to evaluate the board’s durability and performance. This can include exposing the PCB to various temperatures, humidity, and mechanical stress.
Functional testing examines the PCB’s functionality and adherence to specifications, and may include a variety of tests like contamination testing (to check for surface contaminants that could lead to corrosion), impedance testing using a time-domain reflectometer, solderability testing (to verify that the holes are durable enough for dependable solder connections), peel testing (to determine the strength of the adhesive used on the board), and more.