Since the last time you finished your circuit design until the completed board is at your facility, the PCB fabrication process has a lot of high precision steps, high-quality control, and high-technology. Knowing this process of going through a digital design file and into a tangible printed circuit board gives an idea as to why selecting a potential pcb manufacturing company is important and how production underlies it.
Stage 1: Pre-Production and Stage Preparation of Design file
The process of making fabrications does not start at the factory floor rather it starts in the design review process. Once you have handed over Gerber files (PCB design industry standard format), it will be taken through a full Design for Manufacturability (DFM) check by the pcb fabrication service team. The focus of this critical review is to detect possible manufacturing problems such as small traces, inadequate spacing, dysfunctional positions of vias before the problems manifest into costly delays during production.
In this step, the manufacturer will check whether your design fits in their very specific capabilities in terms of number of layers, minimum trace width (usually 6 mils on regular designs), as well as trace separation (minimum 8 mils to avoid crosstalk). They produce production films and develop digital data that will manage the whole further manufacturing process.
Stage 2: Pattern Transfer and Inner Layer Imaging
In the case of multi-layer PCBs, inner layer imaging is the start of the process. Photoresist (new to copper-clad laminate sheets), which is light-sensitive, is applied to copper-clad laminate sheets, which are generally FR-4 (glass-reinforced epoxy laminate) in the industry. With specialized Laser Direct Imaging (LDI) technology, computer-controlled Lasers processively harden the photoresist forming the exact pattern of your circuit in your design files. What copper is to be left and removed is determined by this photomask.
Stage 3: Etching/Pattern Definitions
The open photoresist is then developed in an alkaline solution, which erases the areas that are not exposed, and brings forth the copper patterns. A process known as the etching of the copper is carried out to remove the bare copper using ether a chemical bath or a series of computerized conveyorized etching systems. The technique is subtractive and eliminates all the excess copper with just traces on the circuit that you have designed.
The unused photoresist is removed by caustic chemical processes and the use of high-pressure water. Automated Optical Inspection (AOI) system is a system where each layer is scanned with laser sensors and high-definition cameras which compare the actual board patterns with the one that was originally designed in Gerber format to detect any defect.
Stage 4: Multi-Die Overlay and Lamination
Multi-layer boards are also being stacked and registered on an individual basis, with the inner layers being processed. Copper layers are integrated, having prepreg sheets (partially cured epoxy-fiberglass composite) between them. The whole stack is inserted in a pressuring press and accuracy in heat, pressure, and timing is put in. This is whereby the layers are permanently fixed to form an individual, solid board. Dimensional test This is done after the lamination, to check the thickness of the layers and dielectric specifications.
Stage 5: Stage of Drilling and Via Creation
CNC drilling tools, which are computer operated drills, are used to create holes where component connections and vias (internal electrical connection of layers) are made. The latest equipments have tolerances of up to ± 0.002 inches, which is essential in the allowance of a good fit of components. Laser drilling is used in high-density designs involving micro-vias and the X-ray drilling has been used in buried via.
After the drilling, the edges are studied on delamination and internal alignment of the layers is checked using optical punch registration to achieve a variation of alignment to 0.005 inches.
Stage 6: Through-Hole Plating
Holes drilled should be made electrically conductive in order to connect internal layers. The board is then electrolessly deposited with copper- an auto-catalytic chemical method which is used to deposit a thin copper band on the walls of holes and the board surface. This is an important procedure which makes sure that an electroplated copper is applied later on. This copper should have minimum thickness of 0.0008 inches (20 microns) after all the plating is complete as per IPC Class 2 standards.
Further copper is applied both to the walls of holes and the board face with electroplating using computer controlled rectifiers. This is followed instantly by the plating of tin that helps to avoid corrosion of the copper during further etching and storage.
Stage 7: Outer lager Imaging, Plating and Etching
Photoresist application and the process of LDI imaging is done to the outer layer copper surfaces. The copper layer that is the last to be deposited is an electroplating on outer surfaces. Photoresist stripping is used to expose unwanted copper in order to be removed by tin plating to protect these surfaces. Last etch This last etch to eliminate all unmasked copper to get your circuit design only.
Stage 8: Solder Mask & Silkscreen Application
Solder mask is added and it is a protective polymer coating, which is found on all copper except on the component pads, and via surfaces where soldering will take place. This will be used to avoid solder bridges and oxidation. Silkscreen printing implements component reference designators and assembly indicators of polarity to assembly personnel.
Stage 9: Finishing of Surface
Surface finishes of the PCBs- they are generally HASL ( Hot Air Solder Leveling ), ENIG ( Electroless Nickel Immersion Gold ), or immersion tin, as you see the necessity. These surfaces block the oxidation of copper and increase its solderability.
Stage 10: Profiling, Testing and Quality Assurance
Finally, cut boards are either CNC routed or V-scored when panelizing a design. Flying probe testing (Electrical testing or fixture testing) can be used to test the functionality of the board. Last visualization using bright light will determine dimensional accuracy, silkscreen clarity and the overall quality.
Conclusion
The process involved in taking your Gerber files through pcb fabrication board development is hard engineering precision and chemical skill development coupled with strict quality standards on each step. By collaborating with an existing manufacturer of pcb fabrication, keep your designs to produce the most reliable and high quality circuit boards that can be instilled into practice. This realization would make you value the intricacy involved in this process, and make effective choices regarding whom to ask for pcb fabrication manufacturer.