The Processes of a Printed Circuit Board Manufacturer
The printed circuit board manufacturer follows a strict process in order to create a finished product. This includes testing the circuit board for functionality, ensuring it adheres to the original design specifications, and running quality assurance tests.
The PCB fabrication process begins with a base material, usually fiberglass. Then a copper layer is infused into it. This can be done through foil or a full-on copper coating.
Design
Before a PCB can be built, it must be designed. This is accomplished using a PCB circuit board design CAD tool. It is important to consider your fabrication partner’s capabilities in this stage, because they may have DFM (design for manufacturing) guidelines that can help you design the PCB to best fit their production process.
Printed circuit board design is broken down into two categories: schematic capture to create the circuitry connectivity in a diagram and PCB layout to design the physical structure of the board. The PCB fabrication and assembly process is very exact and demanding, so a good PCB designer must be able to translate a schematic into a layout that will withstand the rigorous manufacturing processes.
Once the layout is complete, engineers generate all of the drill files, rout files, image files, automatic optical inspection (“AOI”) files and test files needed to complete the various manufacturing steps on a panel. This is done by a computer-controlled machine that reads the design data from networked servers.
The next step is imaging and etching the inner layers of the board. The etching involves covering the necessary copper on the board with a special coating and then using a chemical to remove the copper from the areas that aren’t necessary for the printed circuit board manufacturer functioning of the circuit board. Then, the holes that connect the inner and outer layers are drilled. Those holes are called vias and must be precisely sized to ensure proper function.
Layout
The layout is the process of creating a physical design for a printed circuit board. The design is created in an electronic CAD system that is specialized for designing printed circuit boards. The resulting schematic is a detailed representation of the circuit board and includes logical models for the component pins that are connected to the copper interconnecting traces. The layout must meet the DFM requirements of the board to ensure that it can be manufactured without errors that could disrupt the functioning of the circuit board.
Once the layout is complete, it is exported into a format that the contract manufacturer can use to create the PCB. This is typically a Gerber file which encodes information including the layers of copper tracking, drill drawing and component notation. The bare board is then plated with copper and coated in a non-conductive solder mask. This protects the copper traces from accidental contacts with other components during assembly. The pads and lands which will require components to mount on the board are then plated with gold or nickel, both of which have superior solderability and corrosive resistance compared to lead based tin.
For smaller circuit boards, the copper is often etched back to expose the metal and then covered in solder resist. The traces, pads and lands are then silk screened with a legend to identify the components to be installed on the board. The screened text may include reference designators, switch settings and other information to help in the automated assembly of the components.
Fabrication
The fabrication process is where the PCB starts to take shape. First, the design blueprints are printed to a laminate, the body of the structure. Then, a layer of photo-reactive film is placed on top of the structure and hardened with ultraviolet light. This exposes the copper to be etched away and shows the design from the printed films.
After the etching is complete, the inner layers are aligned with registration holes drilled earlier. This helps keep the copper in alignment with the Printed Circuit Board Manufacturer Supplier pattern on the imaged film. Then, a computer-controlled machine punches holes through the inner layer to prepare it for the next step. This machine also inspects the hole and alignment to ensure that everything went correctly.
During this phase, the copper on the board is prepared for the manufacturing process. It’s either etched away or covered with a copper-clad laminate (FR-4 is the most common).
The last preparation step is to score the boards. This helps them separate cleanly when they’re done. The boards are then cleaned and polished to ensure they meet IPC-A-600 – Acceptable Quality Standard. Before the PCBs are plated, technicians perform a series of electrical tests on them. These tests help identify disconnections or shorts in the circuits. Then, they’re ready for the final steps in the production process. The finished product is sold to electronics manufacturers to use in their products.
Testing
In the production process, a printed circuit board is subject to numerous tests that can identify quality defects and catastrophic failures. These tests can also help a manufacturer fine-tune their production process to avoid such issues. These tests can include peel testing, solder float testing, and solderability testing. These tests can also identify potential problems such as component tolerances and part-to-part variation.
In-circuit test (ICT) is the preferred method for detecting errors in PCB assembly. This method allows a technician to verify that all components are properly placed on the board and that the board is functioning as designed. However, this method is not ideal for small-quantity production because it requires expensive test fixtures.
Flying probe testing, or fixtureless ICT, is a less expensive alternative to ICT. It uses a basic fixture to hold the board in place, and a software-controlled program moves test pins around the board. This can check multiple test points simultaneously, reducing the overall cost of the test.
Time Domain Reflectometry (TDR) testing can detect defects in a trace on a circuit board by sending an electrical pulse and measuring the time it takes for the signal to return. This method can spot a variety of flaws, including under and over-etching, lifted leads, and other defects. X-ray inspection is another unique test that can identify defects in the internal layers of a circuit board, such as missed connections or open solder joints.