There is no such thing as a standard printed circuit board as each PCB has a single function for a particular product. Producing a PCB is a complex multi-step process. Here, we look at the most important steps in producing a multilayer PCB.
#1. Pre-Production Engineering
The customer supplied Gerber is used to produce a specific plate. Engineers compare orders/specifications with production capabilities to ensure compliance and also determine process steps and associated checks.
#2. Preparation of imaging tools
The plotter is the key step in PCB production, as it directly affects the quality of the final product.
#3. Print inner layers
Stage 1 consists of transferring the image using a film to the plate surface, using photosensitive dry film and ultraviolet light.
#4. Removing the unwanted copper from the panel using a tapping.
Once this copper has been removed, the rest of the dry sheet is removed, leaving only the copper circuit that matches the design.
#5. Automatic optical inspection of the inner layers (AOI)
Inspection of the circuit against the digital "images" to verify that it matches the design and that it is free of defects. This is accomplished through a board scan and to check for any abnormalities.
#6. Layer-up and bond
An oxide layer is applied to the inner layers which are then stacked together to provide insulation between the layers. A copper layer is added to the top and bottom of the stack.
Drill holes that will create connections between the multiple layers. This is a mechanical drilling process that must be optimized in order to get an exact record for each of the internal connections between layers. Drilling can also be done by laser.
#8. Plating and Copper deposition
The first step in the silver plating process is the chemical deposition of a very thin layer of copper on the inside walls of the holes. The plated silver provides a very fine deposit of copper that covers the whole walls and the entire panel.
#9. Outer layer imaging
The dry foil is removed from the circuit defined areas.
Additional plating is deposited in areas without dry foil / circuit. Once the copper has been plated, tin is applied to protect the copper.
#11. Final Etching
This is normally a three-step process. The first step is to remove the blue dry foil. The second step is to etch the exposed / unwanted copper while the deposited tin acts as a protector for the copper we want to keep. The third and last step is to chemically remove the tin deposit leaving the circuit.
#12.Automated optical inspection of the outer layers
Similar to the inner layers, the attacked panel is scanned to ensure that the circuit complies with the design and is free from defects.
#13. Solder mask application
The ink from the solder mask is applied to the entire surface of the PCB.
Various finishes are then applied to the exposed surface of the copper. This is done in order to protect the surface. Different finishes can include Nickel Immersion Gold, HASL, Immersion Silver, etc. Thickness and weld checks are performed.
This is the process of cutting panels manufactured to specified measurements and shapes based on customer design as defined in the data files.
It is used to check the integrity of tracks and connections. This ensures that there are no open circuits or short circuits in the finished board. There are two test methods, flying probe for small volumes and large volumes.
In the last step of the process, a team of precision sight inspectors give each plate a delicate added check. Visually checking the PCB against acceptance existing standards.
Note: Ensure that you liaise with a leading PCB manufacturer that has state-of-the-art equipment.