As a supplier of rigid PCBs, I’ve had the privilege of being deeply involved in the intricate process of their manufacturing. In this blog, I’ll take you through the step-by-step journey of how rigid PCBs are made, sharing insights from my years of experience in the industry. Rigid PCB
Design Phase
The manufacturing process of rigid PCBs begins with the design phase. This is a crucial step as it lays the foundation for the entire production. A team of skilled designers uses specialized software, such as Altium Designer or Eagle, to create a detailed schematic of the PCB. The schematic includes all the components that will be placed on the board, their interconnections, and the overall layout.
During the design process, several factors need to be considered. Electrical performance is of utmost importance. Designers must ensure that the traces on the PCB can carry the required current without overheating or causing signal interference. They also need to take into account the impedance of the traces, which can affect the signal integrity, especially in high-speed applications.
Mechanical design is another key aspect. The size and shape of the PCB must be carefully determined to fit into the intended device. Holes for mounting the board and cutouts for components need to be accurately placed. Additionally, the design should allow for easy assembly and testing of the PCB.
Once the schematic is complete, it is converted into a Gerber file. This file contains all the information needed for the manufacturing process, including the copper layers, solder mask, and silkscreen. The Gerber file is then sent to the manufacturing facility, where the actual production begins.
Substrate Preparation
The next step in the manufacturing process is substrate preparation. The substrate is the base material of the PCB, and it provides mechanical support and electrical insulation. The most commonly used substrate material for rigid PCBs is FR-4, a fiberglass-reinforced epoxy laminate.
The FR-4 substrate comes in large sheets, which are cut into the appropriate size for the PCB. The cutting process is usually done using a CNC router or a laser cutter, ensuring precise dimensions. After cutting, the substrate is cleaned to remove any dust or debris that may have accumulated during the cutting process.
To enhance the adhesion of the copper layers to the substrate, a thin layer of copper foil is laminated onto both sides of the substrate. This is done using a hot press, which applies heat and pressure to bond the copper foil to the substrate. The copper foil thickness can vary depending on the application, with common thicknesses ranging from 18 to 70 micrometers.
Copper Etching
After the substrate is prepared, the copper layers need to be patterned to create the electrical traces. This is done through a process called copper etching. First, a photoresist is applied to the copper surface. The photoresist is a light-sensitive material that will protect the areas of the copper that will form the traces.
A photomask, which is a transparent film with the pattern of the traces, is placed over the photoresist. The board is then exposed to ultraviolet light, which hardens the photoresist in the areas that are not covered by the photomask. The unexposed photoresist is then removed using a developer solution, leaving behind the protected copper areas.
The board is then immersed in an etching solution, which dissolves the unprotected copper. This leaves behind the desired copper traces on the substrate. After etching, the remaining photoresist is removed, and the board is thoroughly cleaned to remove any etching residues.
Drilling
Once the copper traces are formed, holes need to be drilled in the PCB for component mounting and electrical connections. The drilling process is typically done using a CNC drilling machine, which can accurately drill holes of various sizes. The drill bits used are very small, with diameters ranging from 0.1 to 1.0 millimeters.
Before drilling, a drill file is generated based on the PCB design. This file contains the coordinates and sizes of all the holes that need to be drilled. The CNC drilling machine uses this file to precisely position the drill bits and drill the holes. After drilling, the holes are cleaned to remove any debris or burrs that may have been created during the drilling process.
Plating
After drilling, the holes need to be plated with copper to provide electrical conductivity between the different layers of the PCB. This is done through a process called plating. First, the board is immersed in a chemical bath that deposits a thin layer of copper on the walls of the holes. This initial layer of copper is called the electroless copper plating.
The board is then placed in an electroplating bath, where a thicker layer of copper is deposited on the electroless copper plating. The electroplating process uses an electric current to deposit the copper onto the board. The thickness of the copper plating can be controlled by adjusting the plating time and the current density.
Solder Mask Application
A solder mask is a layer of polymer that is applied to the PCB to protect the copper traces from oxidation and to prevent solder bridges during the soldering process. The solder mask is usually green, but other colors such as red, blue, or black can also be used.
The solder mask is applied using a screen printing or a photoimaging process. In the screen printing process, a stencil is used to apply the solder mask to the board. The stencil has openings in the areas where the solder mask should not be applied, such as the pads for component placement.
In the photoimaging process, a photoresist is applied to the board, and a photomask is used to expose the areas where the solder mask should be removed. The unexposed photoresist is then removed using a developer solution, leaving behind the desired solder mask pattern.
Silkscreen Printing
Silkscreen printing is used to add text, symbols, and markings to the PCB. This information is important for component identification, assembly, and testing. The silkscreen is usually white, but other colors can also be used.
The silkscreen printing process is similar to the solder mask application process. A stencil is used to apply the ink to the board, and the stencil has openings in the areas where the text and symbols should be printed. After printing, the ink is cured using heat or ultraviolet light.
Surface Finish
The final step in the manufacturing process is the surface finish. The surface finish is applied to the exposed copper pads to protect them from oxidation and to improve the solderability. There are several types of surface finishes available, including HASL (Hot Air Solder Leveling), ENIG (Electroless Nickel Immersion Gold), and OSP (Organic Solderability Preservative).
HASL is the most commonly used surface finish. It involves dipping the PCB in a bath of molten solder and then using hot air to level the solder on the pads. ENIG is a more expensive surface finish that provides better corrosion resistance and solderability. It involves depositing a layer of nickel and then a layer of gold on the copper pads. OSP is a relatively new surface finish that is environmentally friendly and provides good solderability. It involves applying a thin layer of organic material to the copper pads.
Quality Control
Throughout the manufacturing process, quality control is of utmost importance. At each stage, the PCBs are inspected to ensure that they meet the required specifications. Visual inspections are done to check for any defects such as scratches, cracks, or missing traces. Electrical tests are also performed to verify the functionality of the PCBs.
X-ray inspection is used to check the internal structure of the PCBs, especially for multi-layer boards. This helps to detect any hidden defects such as short circuits or open circuits. Automated optical inspection (AOI) is used to detect surface defects such as solder bridges or misaligned components.
Conclusion
The manufacturing process of rigid PCBs is a complex and precise process that requires a high level of expertise and advanced technology. From the design phase to the final surface finish, each step plays a crucial role in ensuring the quality and functionality of the PCBs.
Prototype PCB Assembly As a rigid PCB supplier, we are committed to providing our customers with high-quality PCBs that meet their specific requirements. We use the latest manufacturing techniques and equipment to ensure the accuracy and reliability of our products. If you are in need of rigid PCBs for your project, we would be more than happy to discuss your needs and provide you with a customized solution. Contact us to start a procurement discussion and let us help you bring your ideas to life.
References
- Printed Circuit Board Handbook, by Clyde F. Coombs Jr.
- PCB Design for Manufacturability, by Sanjay Gupta
- Fundamentals of Printed Circuit Boards, by Paul Hurley
Huaswin Electronics Technology Co., Ltd.
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