PCB Fabrication Guide PDF

Creative Tech 8- For THURSDAY Fe. 5, 2025 **Steps in PCB Fabrication** PCB (Printed Circuit Board) fabrication involves several precise steps to create the physical structure that supports and connects electronic components. Here's an overview of the typical process involved in PCB fabrication: *...

Creative Tech 8- For THURSDAY Fe. 5, 2025 **Steps in PCB Fabrication** PCB (Printed Circuit Board) fabrication involves several precise steps to create the physical structure that supports and connects electronic components. Here's an overview of the typical process involved in PCB fabrication: **1. Designing the PCB Layout** - **Schematic Design**: The circuit schematic is drawn using PCB design software (like Eagle, Altium, or KiCad). This defines the electronic connections and layout. - **Board Layout**: The design is translated into a physical layout that includes the placement of components, traces, vias, and pads on the PCB. **2. Creating the Gerber Files** - **Gerber Files**: These files are the standard output format used in PCB manufacturing. They contain all the necessary information, such as layer details, drill holes, and other production data. **3. Printing the Design onto a Copper Clad Board** - **Copper Clad Laminate**: A copper-clad board (usually FR4 material) is used as the base material for the PCB. - **UV Light Exposure**: The board is coated with a photosensitive layer (usually a photoresist). The Gerber files are transferred onto the PCB using UV light exposure to create a mask of the design. This process uses a photomask or direct imaging to transfer the layout pattern onto the board. **4. Etching the PCB** - **Etching**: The exposed areas of the copper are etched away using a chemical etchant, leaving the copper traces that form the electrical connections. - **Cleaning**: The board is thoroughly cleaned to remove any excess photoresist and etching chemicals. **5. Drilling Holes** - **Drilling**: Drill holes are created for components that require through-hole mounting, and vias for inter-layer connections. These holes are precisely drilled using CNC machines. **6. Plating** - **Copper Plating**: The drilled holes are then plated with copper to create conductive pathways between the layers of the PCB. - **Surface Finish**: After plating, a surface finish like HASL (Hot Air Solder Leveling) or ENIG (Electroless Nickel Immersion Gold) is applied to the board to protect the copper and prepare the board for soldering components. **7. Solder Mask Application** - **Solder Mask**: A green (or other color) solder mask is applied to the surface of the PCB, except for the areas where components will be soldered. The solder mask helps protect the copper traces and prevents solder bridges during assembly. **8. Silkscreen Printing** - **Silkscreen Layer**: A silkscreen layer is applied, typically in white, to mark component locations, text, and other important information on the PCB. **9. Cutting the PCB** - **Board Cutting**: The large PCB panel is then cut into individual boards using a router or saw. This is done according to the design\'s edge cuts. **10. Electrical Testing** - **Testing**: A final electrical test is performed to ensure that there are no short circuits or open circuits. This step can include automated optical inspection (AOI) or flying probe testing. **11. Final Inspection** - **Inspection**: The PCBs undergo a visual inspection to ensure quality standards are met, checking for defects like scratches, incorrect solder mask application, and more. **12. Packing and Shipping** - **Packaging**: Once the PCB passes all tests, it's packaged and shipped to the client or assembly facility where components will be soldered onto the board. Each of these steps involves precision and careful handling to ensure the final PCB works correctly in the end application. Transferring the PCB layout onto a copper-clad board is a crucial step in the PCB fabrication process. This step ensures that the designed circuit pattern is properly applied to the copper surface of the PCB. The process typically involves the following steps: **1. Prepare the Copper-Clad Board** - **Copper-Clad Board**: Start with a copper-clad laminate, which is a board with copper foil laminated on one or both sides. The laminate is usually made of an insulating material like FR4 (a composite of fiberglass and resin). - **Cleaning**: Clean the copper surface thoroughly to remove any dust, oils, or oxidation. This is done using a mild abrasive or cleaning solution, followed by rinsing with water and drying. **2. Apply Photoresist Layer** - **Photoresist Coating**: A light-sensitive material (photoresist) is applied to the surface of the copper-clad board. The photoresist can be either a liquid or dry film, and it will only harden where it is exposed to UV light. - For **dry film photoresist**, the material is applied to the surface of the board and pressed into place. - For **liquid photoresist**, it is spread evenly over the copper surface using a roller or brush. - **Curing**: The photoresist layer is then dried and cured to ensure it adheres tightly to the copper surface. This step is critical for ensuring a solid foundation for the pattern transfer. **3. Align and Expose the Board to UV Light** - **Masking**: The Gerber file of the PCB layout is used to create a photomask. This mask, typically made from a transparent film with black and clear areas, has the design pattern that will be transferred onto the copper surface. - **UV Exposure**: The copper-clad board with the photoresist layer is placed under a UV light source, with the photomask positioned directly on top of the board. UV light exposure hardens the photoresist in the areas that are not covered by the photomask (the areas where the traces are designed to appear). - **Positive Photoresist**: In a positive photoresist process, the areas exposed to UV light become soluble and will later be washed away. - **Negative Photoresist**: In a negative photoresist process, the areas exposed to UV light become hardened and resist further chemical etching. **4. Develop the Photoresist** - **Developing**: After UV exposure, the board is placed in a developer solution, which removes the unexposed (or exposed, depending on the resist type) photoresist, leaving behind the circuit pattern on the copper surface. - For positive photoresist, the exposed areas (where UV light hit) are washed away, leaving the copper traces. - For negative photoresist, the unexposed areas are washed away, and the remaining resist forms the pattern of the traces. **5. Etching the Board** - **Etching Process**: After developing, the copper areas that are exposed (i.e., not protected by photoresist) are subjected to a chemical etching process. An etching solution (usually a mixture of ferric chloride or ammonium persulfate) is used to dissolve the exposed copper, leaving the patterned traces protected by the photoresist intact. - **Washing and Drying**: After etching, the board is washed thoroughly to remove the etching solution and dried. **6. Stripping the Photoresist** - **Removing Photoresist**: After etching, the remaining photoresist is stripped away using a chemical stripper or solvent, leaving only the copper traces exposed on the board. - **Final Inspection**: The board is inspected to ensure the traces are clean, well-defined, and free of defects. **7. Optional: UV Inspection** - Some manufacturers may conduct a final UV inspection to ensure that the copper traces are accurate and there are no defects such as broken traces or insufficient copper. **Summary of the Key Steps:** 1. Clean the copper-clad board. 2. Apply a photoresist layer (liquid or dry film). 3. Expose the board to UV light through a photomask to transfer the design pattern. 4. Develop the photoresist, removing the unwanted portions. 5. Etch the exposed copper areas to reveal the circuit traces. 6. Strip off the remaining photoresist. 7. Inspect the results for accuracy. This process is crucial for creating high-quality and precise copper traces on the PCB, and it requires a controlled environment and attention to detail to ensure proper transfer of the layout. **For: FRIDAY: Feb. 7, 2025** **What is Etching?** **Etching** is a critical step in the PCB (Printed Circuit Board) fabrication process, used to remove unwanted copper from the board and leave behind the copper traces that form the electrical connections in the PCB. Here\'s a more detailed look at the **etching process**: **1. Preparation for Etching** - **Board After Layout Transfer**: After the layout (design) has been transferred to the copper-clad board using photoresist (as described earlier), the next step is to remove the excess copper and reveal the desired trace pattern. - **Developed PCB**: By this stage, the PCB has undergone exposure to UV light and developing of the photoresist layer, which protects the areas of copper that will remain. The rest of the copper is now unprotected and ready for etching. **2. Etching Solution** - The PCB is exposed to an **etching solution** (usually a liquid chemical) that dissolves the unprotected copper areas. The most common etching chemicals are: - **Ferric Chloride (FeCl₃)**: This is a widely used etching solution, available in liquid form. Ferric chloride reacts with copper and dissolves it, leaving the copper traces intact. - **Ammonium Persulfate (NH₄)₂S₂O₈**: Another common etchant, used in some fabrication processes. - **Cupric Chloride (CuCl₂)**: Sometimes used, though less common than ferric chloride. - **Etching Process**: The board is placed in the etching solution, which dissolves the copper that is not covered by the photoresist. The photoresist protects the copper traces, preventing them from being etched away. **3. Etching Techniques** There are several methods used to apply the etching solution to the board: - **Immersion Etching**: The board is fully submerged in the etching solution. This is typically done in a shallow tank. The board is left in the solution for a few minutes until the unwanted copper is fully dissolved. - **Spray Etching**: In this technique, the etching solution is sprayed onto the board while it is held at an angle. The board is usually moved or rotated to ensure even coverage of the etching solution. - **Agitation**: The etching solution can be agitated (either by gently stirring or using a mechanical device) to help ensure uniform etching and prevent the build-up of copper particles on the board. **4. Etching Process Time** - **Time Control**: The etching time depends on the concentration of the etching solution and the temperature. Generally, it takes around 5--15 minutes for the etching solution to dissolve the copper in the unprotected areas. However, the time will vary depending on the etching method and the solution used. - **Visual Check**: You can observe the process to make sure the copper is being etched evenly and that the traces are clearly defined. It's important not to over-etch, as it can lead to the erosion of the copper traces or removal of the trace connections. **5. Rinsing the Board** - After etching, the board is removed from the etching solution and rinsed thoroughly with water to stop the etching process. It's also common to rinse the board in a dilute solution of baking soda or another neutralizing agent to ensure that any remaining etching chemicals are neutralized. **6. Inspecting the Results** - **Visual Inspection**: The etched PCB is inspected for any remaining copper or flaws in the traces. The goal is to have clear, precise traces without under-etching or over-etching. - **Test for Completeness**: Make sure that the etching process has removed all unwanted copper. The copper traces should be well-defined and not overly thin or broken. If there is any over-etching (where traces are too thin or eroded), the PCB may need to be reworked or replaced. **7. Removing the Photoresist** - After etching, the remaining photoresist layer, which has protected the copper traces, needs to be stripped away. This can be done using a chemical photoresist stripper or solvent. After this step, only the copper traces will remain on the PCB. **8. Cleaning and Drying** - The PCB is cleaned thoroughly to remove any leftover etching chemicals, photoresist residue, or any debris. The board is then dried completely before moving to the next steps, such as drilling holes or applying solder mask. **Etching Process Summary:** 1. **Expose the board to etching solution** (e.g., ferric chloride or ammonium persulfate). 2. **Dissolve the unwanted copper** areas not protected by the photoresist. 3. **Remove the board** from the solution once etching is complete, rinse and neutralize the chemicals. 4. **Inspect the traces** for accuracy, and ensure that copper traces are clean, sharp, and intact. 5. **Strip the remaining photoresist** layer, leaving only the etched copper traces. 6. **Clean and dry** the board to prepare for further processing. **Challenges in Etching** - **Over-etching**: This can happen if the PCB is left in the etching solution for too long, causing the traces to become too thin or even break. - **Under-etching**: If the PCB is not etched for long enough, unwanted copper may remain, or the traces may not be fully separated. - **Uneven Etching**: Sometimes, the etching process can be uneven, particularly if the board is not well agitated or the solution is not uniform, leading to inconsistent trace widths. By controlling the etching process, manufacturers can ensure the accurate and reliable formation of circuit traces on the PCB, allowing the board to function as intended in the final electronic device.