What Is PCB Production?
Printed circuit board (PCB) production requires precision and meticulous attention to detail to ensure top-notch performance. PCBs come in different complexities, from single-layer to multilayered designs, and the production steps vary once the first layer is made. Depending on the PCB's structure, the manufacturing process may involve more than twenty steps.
The number of steps needed correlates with the complexity of the PCB. Skipping a step or trying to cut corners could harm the circuit board's performance. However, when each step is done correctly, PCBs function as crucial electronic components, effectively carrying out their tasks in various devices.
Components of a PCB
Examining the structure of a circuit board unveils four essential components. These components are integral to the PCB production.
Substrate
Often referred to as a circuit board's "skeleton," the substrate is a foundational element made primarily from fiberglass. This material provides structure strength to the PCB, ensuring durability and resistance against breakage. The substrate is the bedrock upon which the entire circuit board is built.
Copper Layer
The copper layer is a pivotal component that plays a role similar to that of the nervous system in the human body. Whether in copper foil or a comprehensive copper coating, it primarily carries electrical signals from and to the circuit board. This layer acts as a conductor, facilitating communication between different circuit parts.
Solder Mask
The solder mask is a protective "skin" pasted on the PCB. Composed of a polymer layer, it shields the underlying copper from potential environmental hazards. This protective coating prevents unintended short circuits and enhances the overall durability of the circuit board, making it more resilient to external factors.
Silkscreen
Located on the component side, the silkscreen serves as an informative layer of the PCB, alternatively known as legend or nomenclature. It showcases essential details like logos, part numbers, symbols, component references, test points, and switch settings. This visual guide assists in the assembly process and provides valuable information for maintenance and troubleshooting purposes.
PCB Production Process
Circuit board manufacturing involves systematic steps to ensure precision and functionality. Let's explore the key stages of circuit board manufacturing:
Step One: PCB Designing
The initial step in PCB production involves creating a design using specialized software like Extended Gerber RS-274X). This phase is dedicated to developing a detailed plan as per the requirements. Extended Gerber is an essential software tool used in the PCB design process. It plays a crucial role in encoding the design and capturing critical information like copper layer number and solder mask requirements.
Designers utilize the software to carefully outline the circuit board's layout, ensuring it meets all necessary criteria. It acts as a digital drawing board, where every detail, from copper pathways to solder masks, is considered and encoded.
The goal is to produce a comprehensive blueprint that serves as a guide throughout the entire manufacturing process. This blueprint marks the starting point, determining how the final PCB will function and perform.
Step Two: Reviewing the Design
Once the design is completed, engineers conduct a comprehensive examination to identify potential errors. This checkpoint is essential for maintaining the integrity of the PCB.
Engineers carefully review each design component, scrutinizing details to catch any discrepancies or issues that could impact the functionality of the circuit board. They aim to ensure the design meets the required standards and specifications.
The process advances to PCB printing once the engineers thoroughly review the design and provide clearance. This approval signifies that the design has met the necessary criteria and is ready to move forward in the manufacturing journey.
Step Three: PCB Printing
We move from the digital world to a tangible form in the third step. After completing all necessary checks, a specialized plotter printer brings the PCB design to life. This printer performs a unique task—it produces a "film" that looks like a negative of an old photo, revealing the circuit board’s inner layers.
The plotter printer uses two distinct colored ink: black for marking traces of copper and the pathways for electrical signals. Clear ink denotes non-conducting areas, such as the board base.
This printed film essentially becomes a visual representation of what the final circuit board should look like. This printed portrayal is a crucial guide for the subsequent steps in the PCB production process, ensuring that the physical board mirrors the intended design.
Step Four: Copper Printing
The manufacturing process starts as the printed design is transferred onto laminate material, and a copper layer is applied. This copper is bonded to the laminate, forming the PCB structure. The subsequent etching process removes excess copper, revealing the intended pathways.
The laminate panel then undergoes a coating with a photoresist, exposing it to ultraviolet light. The resist, a layer of photo-reactive chemicals, hardens, precisely matching the blueprint's photos and the printed photoresist. The UV light goes through the translucent parts of the film, causing the photoresist to harden and outline the areas intended for copper pathways.
After preparation, the board is then washed in an alkaline solution. This helps remove residual photoresists, followed by pressure-washing to clear surface debris. Post-drying, only the resist atop the remaining copper should be present. A thorough examination by a technician ensures error-free PCBs.
Step 5: Etching
Etching refines the PCB's inner layers (the core). The goal is to carefully eliminate extra copper through controlled exposure to specific chemicals, such as ferric chloride or cupric chloride solutions. These chemicals selectively dissolve the unprotected copper, leaving behind the desired circuit traces on the board.
The choice between ferric chloride and cupric chloride depends on factors such as the type of PCB, manufacturing preferences, and environmental considerations.
The duration of this step can vary, depending on the size and structure of the PCB. Larger boards or those that have complex designs might take a bit more time or require a particular solvent to remove all excess copper thoroughly.
Step Six: Aligning the Layers
Following the meticulous cleaning of each PCB layer, the next phase involves aligning the layers and optical inspection. Utilizing the holes created earlier, a technician carefully positions the layers on an optical punch machine, aligning them precisely. This alignment is crucial for the subsequent steps in PCB production.
Step Seven: Automated Optical Inspection (AOI)
After layer alignment, an automated optical inspection machine scrutinizes the PCB for defects. This step is paramount, as any errors detected at this stage cannot be rectified later. The AOI machine carefully checks the manufactured PCB against the Extended Gerber design. This crucial step acts as a quality checkpoint, making sure that the actual PCB matches the design specifications perfectly, ensuring a smooth and error-free manufacturing process.
Step Eight: PCB Layers Lamination
With defect-free layers confirmed, the PCBs enter the lamination process. The lamination involves two key steps: lay-up and pressing. The outer layers, covered in pre-soaked fiberglass with copper foil etchings, are meticulously stacked and pressed together. The lamination press applies heat and pressure, melting the epoxy in the pre-impregnated resin and fusing the layers into a cohesive structure.
Step Nine: Drilling Process
An X-ray machine precisely locates the spots prior to drilling. Registration holes are drilled to secure the stack of PCBs, followed by computer-guided drilling based on the initial design. After drilling, any excess copper at the edges is carefully filed down.
Step Ten: Plating the PCB
The drilled panel undergoes plating, where chemicals fuse the various PCB layers. Thorough cleaning precedes the bath in chemicals, coating the panel with a layer of copper that is only a few microns thick. The holes drilled earlier cause the fiberglass substrate to be exposed, and copper plating covers the hole walls.
Step Eleven: Imaging the Outer Layer
A new layer of photoresist is applied to the outer layer. After imaging, the outer layers are plated similarly to the interior layers. However, tin plating is introduced for added protection to the copper of the outside layer.
Step Twelve: Etching the Outer Layer
The tin guard is utilized during the final etching of the outer layer to protect valued copper. Unnecessary copper is removed using the copper solvent, as the tin shields the etching area. The reversal of ink colors from inner layers allows for effective protection and removal.
Steps Thirteen: AOI of the Outer Layer
The outer layer also undergoes AOI. This inspection makes sure that the outer layer adheres to design specifications and verifies the removal of excess copper, creating a fully functional printed circuit board.
Step Fourteen: Application of Solder Mask
After cleansing, each panel receives a solder mask film and an ink epoxy. Ultraviolet light indicates areas for solder mask removal. The cured mask provides additional protection to the copper from corrosion and oxidation.
Step Fifteen: Applying the Silkscreen & Surface Finish
Vital information, including company details and part numbers, is printed onto the board in the silkscreen application. The surface finish is then applied, preparing the PCB for the final cutting, testing, and inspection.
Step Sixteen: PCB Finishing
The PCB undergoes conductive materials plating selected based on design specifications and budget constraints. Finishes like immersion silver, hard gold, or electroless nickel immersion gold are applied to facilitate the mounting of electronic components and protect copper from oxidation.
Step Seventeen: Testing the Electrical Reliability
After coating and curing (if necessary), the PCB undergoes electrical testing. This involves testing the circuit for isolation and continuity, ensuring the board meets IPC-9252 standards. Additional tests, such as the "bed of nails" test, evaluate the PCB's durability under high-pressure contact.
If the PCB passes all tests, it proceeds to the next step: profiling and route out.
Step Eighteen: Route Out and Profiling
Profiling identifies the shape and size of individual PCBs, guiding the routing out process. CNC machines or routers create small pieces along the edges, allowing clean separation of the boards without damage.
Step Nineteen: Visual Inspection and Quality Check
After scoring and breaking the boards apart, a final inspection is conducted. This comprehensive check verifies hole sizes, board dimensions, and cleanliness and ensures that finished boards meet design specifications.
Step Twenty: Packaging and Delivery
The last stage involves packaging the PCBs to protect them from dust and damage during shipping. Sealed containers preserve the boards' integrity and are then delivered to the customers. This marks the completion of the PCB production process.
Circuit Card Assembly
Circuit Card Assembly (CCA) is a vital stage in the PCB production process, where individual electronic components are strategically placed and soldered onto the printed circuit board. This assembly transforms the bare PCB into a functional circuit that can power various electronic devices. The CCA process involves meticulous attention to detail to ensure proper component placement and secure soldering connections.
Steps in Circuit Card Assembly
- Component Placement: Skilled technicians carefully position electronic components, such as resistors, capacitors, integrated circuits, and connectors, onto the designated areas of the printed circuit board. The accuracy of component placement is crucial for the circuit's functionality.
- Soldering: The components are securely attached to the PCB through soldering. Solder, a metal alloy with a low melting point, is heated to create a molten state. This molten solder forms a bond between the component leads and the copper pads on the PCB, creating a stable electrical connection.
- Reflow Soldering (if applicable): Reflow soldering is often used in modern CCA processes. This involves applying solder paste to the PCB before component placement. The entire assembly is then heated, causing the solder paste to melt and create reliable solder joints.
- Quality Inspection: After soldering, a thorough inspection is conducted to ensure the quality of the assembly. Automated Optical Inspection (AOI) systems may be employed to identify potential issues such as soldering defects, misplaced components, or short circuits.
- Functional Testing: After the visual inspection, functional testing is performed to verify that the assembled circuit operates according to design specifications. This testing phase is critical for identifying defects impacting the circuit's performance.
Importance of Circuit Card Assembly
- Precision and Accuracy: The success of the circuit card assembly relies on precise component placement and accurate soldering. Any errors in this process can lead to malfunctioning circuits.
- Reliability: A well-assembled circuit ensures the reliability of electronic devices. Proper soldering and thorough testing contribute to the longevity and performance of the final product.
- Efficiency: Automated assembly techniques, such as reflow soldering and AOI, enhance efficiency by reducing manual labor and ensuring consistent quality across multiple units.
Circuit card assembly is a pivotal stage that bridges the gap between the designed PCB and the fully functional electronic device. It demands technical expertise, advanced machinery, and stringent quality control measures to produce reliable, high-performance electronic products.
Understanding High-Density Interconnect (HDI)
High-density interconnect (HDI) is a printed circuit board (PCB) technology that enables designers to fit more functionality and features onto a single board while reducing the overall size of the PCB. HDI technology is instrumental in designing PCBs and printed wiring boards (PWBs), as it allows for high-density circuits to be completed and offers a means of routing signals between various parts of the board. Critical features of HDI PCB technology include:
- Microvias: HDI boards frequently have microvias with a diameter of 0.006 or less, which are smaller than conventional vias
- Blind and buried vias: HDI technology may also involve blind or buried vias, which are not visible on the board's surface.
- Higher circuitry density: Compared to conventional circuit boards, HDI boards have a higher circuitry density.
Design advantages of HDI technology include:
- Reduced size and weight: HDI technology reduces the size and weight of an assembly, making it easier to fit into smaller spaces.
- Increased functionality: HDI technology enables designers to integrate functionality into smaller form factors.
The manufacturing process for HDI PCBs involves several steps, including:
- Design: The design process consists of creating a layout for the board, including the components' placement and the signals' routing.
- Lamination: The board is laminated, which involves bonding layers of material together to create the final structure of the board.
- Drilling: Microvias and other vias are drilled into the board.
- Plating: The board is plated, which involves coating the surface with a conductive material to create the necessary electrical connections.
- Testing: The board is tested to ensure it meets the necessary electrical and mechanical specifications.
Final Thoughts
Printed circuit boards (PCBs) are a meticulous process that demands precision at every step. The complexity of the manufacturing process varies based on the PCB's design, with each stage playing a crucial role in determining the board's performance.
Essential components such as the substrate, copper layer, solder mask, and silkscreen collectively contribute to the PCB's structure, electrical pathways, protection, and informative layers. From designing with tools like Extended Gerber to High Density Interconnect (HDI) technology, the process ensures that the final product adheres to stringent design specifications.
