Manufacturing a Printed Circuit Board – Part II
In the previous post, we had discussed the various steps required to design a Printed Circuit Board (PCB). In this post, we will provide details on the manufacturing, assembly, and testing processes.
Manufacturing a PCB for an Industrial Application
The following points elaborate on the various steps to build and test a PCB before it is delivered to the client:
Create Traces on the Board: The board substrate is generally made from FR4 fiberglass. On top of this is a thin layer of copper foil. Earlier, chemicals would be used to create traces. However, with the advent of technology, laser etching has been found to be a more suitable option. Laser etching is performed to remove any unprotected copper, while keeping the traces in place.
Press and Form the Board: Dielectric materials such as porcelain, plastics, mica are used to create insulating layers. These layers should align with the copper traces. An adhesive is applied on the dielectric layers. The copper layer is heated so that it easily gets attached to the dielectric layer. These two layers are then joined using a press to form a solid board.
Drill Holes into the PCB: If the PCB is going to be assembled using PTH technology, then this step is required. The holes are drilled according to the specific locations provided on the diagram, and 3D model.
Place the Components: The components are placed in their designated areas as provided in the diagram. Components include connectors, integrated circuits, diodes, capacitors, and resistors.
Perform Wire Routing: Once all the components have been placed, the PCB undergoes wire routing. This ensures that specific terminals on the board are connected to each other according to the terminal nets or pre-routes.
Apply Solder Mask: This process is performed to protect the board from environmental contaminants. It also prevents solder bridges while protecting the copper from oxidation. Solder baths or reflow techniques are used to perform this procedure.
- Add a Surface Finish: This is usually a metal or organic coating applied onto the pad areas. Surface finishes are applied to the PCB to ensure solderability in the future, as well as giving the board a finished look. They also protect the PCB from external contaminants.
Testing: There are two primary tests that are performed on the PCB – quality control and electrical testing. Quality check is performed to inspect the PCB panel for cosmetic and physical defects. The panel is also compared with the diagram for dimensions and diameters accuracy. The second important test is electrical testing. Flying Probe test equipment is the equipment of choice to perform this task. Aspects like vias, circuit interconnects, test points, and component pads are checked carefully. The PCB is also tested for open circuits, holes without proper plating, and short circuits between nets.
PCBs are primarily designed for manufacturability. When the manufacturing process is performed with state-of-the-art equipment, durable materials, and adherence to quality standards, the finished PCB can provide numerous benefits to both the user and his application.