A printed circuit board comes in different types. It could be double-sided or single-sided. It could be flexible or rigid. It could also be multilayered or single layered. Whatever the type is, the manufacturing process is the same. After designing the board, manufacturers perform many processes before they ship the circuit board to the assembly team. In this article, you will learn about the steps in the PCB manufacturing process.
The manufacturing process begins with the selection of the inner layer or the laminate. The thickness varies and measures below half an inch. The number of inner layers depends on the design schematics. For a single layered design, the board consists of one inner layer. On the other hand, a multilayered board can contain up to 12 inner layers.
A board typically consists of a copper foil, its inner layers, and a prepreg. The most popular prepreg material is FR4. This FR4 material acts as glue between the copper foil and the inner layer.
Laminating the layers
The copper foil, inner layers and prepreg are heat-pressurized to create a laminate. After the process, the manufacturers produce a rigid board ready for the next steps.
The inner layers are coated with dry-film. This coating protects the inner layers from chemicals during the etch processing.
This step in the manufacturing of the printed circuit board comprises of five phases to complete. The first phase is the placing of the artwork or the layout of the circuit. This artwork is printed on a resist film that consists of two basic layers. One layer is negative while the other is positive. Both layers contain copper traces.
The second phase mainly involves exposing the layout to ultraviolet light. The negative layer allows the light to pass through and harden copper traces on the film.
The third phase focuses on removing the areas that are not hardened during the layout exposure. The fourth phase is etching the inner layer. It removes the film that does not contain the copper pattern. The last phase is about removing the resist film so that the copper patterns are completely exposed and usable.
To enhance the adhesion of the copper patterns, manufacturers often treat the circuit board with chemical solutions, giving the patterns a dark brown hue. Other chemicals may change the color of the copper patterns.
The standard method is automated optical inspection or AOI. This step inspects the printed circuit board for any error.
When the inspection team finds errors, they communicates such errors to the design team and other appropriate departments. If possible, they correct the errors accordingly and document such errors for future references.
Afterwards, the board is forwarded to the assembly team for component placement.
Drilling and deburring
The board is drilled with holes as per design requirements. For the through-the-hole assembly, it is a pre-requisite before the board is transferred to the assembly department. The deburring step removes raised edges after the drilling process.
Outer Layer Expose and Develop
The copper patterns are cured with tin strips, while the exposed panels are protected with other resist film. The final chemical curing involves etching the parts that are not cured with a tin strip. In this step, manufacturers are very careful since overexposure to the chemicals may strip off the copper patterns.
This step is labeling the board with the necessary nomenclature and other important legends. It also includes the prepping of the board for solder mask.
This step involves the placement of electronic components on the board. There are two known methods in the assembly stage. The first and oldest is through-the-hole assembly and the latest is the surface mounting assembly.
Through-the-hole assembly requires pre-drilling of holes on the board. This means, the board goes through an additional step of drilling before assembly. On the other hand, the surface mount technology uses the surface of the board to place the components. These are the general steps in manufacturing a printed circuit board.