PCB Board Guide | Anything related to circuits

Although the manufacturing process of PCB is similar but copper-based PCB, which is a metal substrate, is more complex and requires more technology. Here we discuss the process. This article is provided by TechSparks, maybe you can go to the website to learn more interesting knowledge.

Step 1: Substrate Selection

The substrate serves as the foundational material in the PCB layer stack, providing the core rigidity. Various materials, including FR-4, metal Copper, and polyimide, are options for the substrate. The chosen material is precisely cut to size, and its thickness is selected based on the mechanical and thermal requirements of the PCB.

Step 2: Copper Cladding

To initiate the copper cladding process, the substrate undergoes thorough cleaning to eliminate any potential contaminants on its surface that might interfere with subsequent steps. A laminating layer, referred to as prepreg material, is then applied to bond the layers together seamlessly. Subsequently, a thin aluminum foil is added to establish the conductive layer of the PCB.

Step 3: Layer Stack-Up

The layer stack-up is the organized arrangement of layers within the PCB. Tailored to the PCB's complexity, anticipated thermal characteristics, and the nature of signals involved, the layer stack-up is meticulously selected. Subsequently, the layers are precisely aligned and bonded together using heat and pressure, creating a copper-clad structure with the substrate and core materials in place.

Step 4: Circuit Patterning

The subsequent phase involves translating the copper traces designed by an engineer onto the actual copper-clad material. This process primarily utilizes photoresist material and copper etching. Photoresist, a film that solidifies upon exposure to ultraviolet light, is applied to the copper-clad substrate. A mask, featuring the circuit pattern, is then placed over the photoresist. The two are subjected to an ultraviolet light source, effectively transferring the design onto the copper clad.

Step 5: Copper Etching

Following the transfer of the design onto the copper-clad material, the next step involves removing the undesired copper zones. This process creates conductive traces that establish connections between various components of the circuit. The copper-clad material is immersed in an etchant solution, corroding away the exposed copper, which is the unwanted part, and preserving the areas covered by the solder resist.

Step 6: Surface Finish

Once the etching process is complete, the remaining chemicals and photoresist on the surface are thoroughly washed away. Subsequently, the exposed copper surface undergoes a polishing procedure, ensuring it is clean and ready for the subsequent stages of production.

Step 7: Solder Mask Application

Following the etching process, a protective layer known as solder mask is applied to the surface of the etched copper clad. This layer not only adds a color—commonly green—to the PCB but also serves as a protective barrier.

Step 8: Silkscreen Printing

The silkscreen layer plays a crucial role in conveying essential information about the board. It includes text and graphics that are screen-printed onto the surface atop the solder mask. To achieve this, a fabric is saturated with photoresist material that cures upon exposure to ultraviolet radiation. For controlled curing, a transparent print containing details from the silkscreen layer—such as component designators, courtyard, component polarity, connector labels, PCB information, and additional designer-added details—is placed over the fabric with unexposed photoresist material. When exposed to ultraviolet light, all parts of the fabric are cured, except the regions covered by the silkscreen content. These covered portions can then be washed away, creating a stencil for the silkscreen layer. This stencil serves as a guide for applying ink to the board.

Step 9: Drill and Plating

In this crucial stage, holes are precision-drilled for mounting components, creating vias, and forming mounting holes. The process is automated, employing programmable CNC drilling machines that utilize drill data extracted from the PCB's gerber files. This data guides the machines in accurately locating the hole positions and dimensions. Once all holes are drilled, the next step involves plating them to ensure conductivity between layers and enhance the rigidity and shape of larger holes.

Step 10: Quality Control and Testing

Following the completion of PCB plating, the critical phase of testing ensues. The PCB undergoes assessment using an automated testing jig equipped with miniature needle probes to verify continuity across all tracks. If it successfully clears this step, the board proceeds to an automatic optical inspection stage where a computer vision system meticulously examines the board to ensure it meets the designated standards. As an added layer of assurance, a visual inspection is conducted by an individual at the end of the production line to prevent any defective boards from progressing further.