### 1. PCB File Inspection
Before any production work begins, the user’s provided files must undergo several routine checks to ensure the integrity and accuracy of the data.
– **File Integrity Check**: Verify that the provided disk file is complete and undamaged. Missing or corrupted files could lead to production delays.
– **Virus Scan**: Conduct a thorough virus scan on the files. If any viruses are detected, they must be eliminated to avoid potential damage to the production system or contamination of design data.
– **Gerber File Review**: If the user provides a Gerber file, ensure it includes the necessary D-code table or that it is appropriately encoded. The D-code table is essential for defining design rules and ensuring correct data processing for manufacturing.
### 2. Design Compatibility with Manufacturing Capabilities
Once the files are verified, it is crucial to assess whether the design aligns with the technological capabilities of the PCB manufacturing facility. This step ensures that the design can be physically produced without issues.
– **Spacing Compliance**: Review the spacings within the design, including:
– **Line-to-Line Spacing**
– **Line-to-Pad Spacing**
– **Pad-to-Pad Spacing**
Ensure that these spacings meet or exceed the minimum requirements dictated by the factory’s production process. Insufficient spacing may cause issues like short circuits or manufacturing defects during production.
– **Wire Width Verification**: Check the width of the traces or wires. It is essential that the trace width is greater than the minimum limit that the facility can reliably produce. Thin traces that are too narrow may not survive the manufacturing process or may cause electrical performance issues.
### Key Takeaways:
– **File integrity** and virus-free status are prerequisites before moving forward with any PCB design.
– **Design adherence to factory capabilities** is crucial to ensure the manufacturing process runs smoothly and the final product meets quality standards.
– **Spacing and trace width checks** are fundamental to ensuring the PCB can be produced reliably and function as intended.
By following this systematic approach, PCB manufacturers can minimize the risk of errors and ensure a smooth transition from design to production.
**PCB Manufacturing Process Guidelines**
1. **Check Via Hole Size**
Ensure the diameter of the via hole meets the smallest requirement based on the factory’s production capabilities. This will prevent manufacturing issues and ensure reliability in the final product.
2. **Verify PCB Pad Size and Aperture**
Check both the pad size and its internal aperture to ensure that the drilled pad edge maintains a sufficient width, minimizing potential issues with pad integrity and connectivity during production.
### 3. **Determining Process Requirements**
PCB process parameters should be established based on specific user requirements. Key considerations include:
**1. Negative Film Mirroring:**
Depending on the subsequent manufacturing steps, determine if the light-painted film (negative film) requires a mirrored image. The mirroring process ensures that the film’s drug-coated side (latex surface) is aligned with the film surface, minimizing errors. The film’s mirroring requirements depend on the process:
– For screen printing or dry film processes, the copper side of the substrate on the film side should be used.
– For diazo film exposure, the film is mirrored when copied, and the mirrored image should reflect the negative film without the copper side.
**2. Solder Mask Enlargement Parameters:**
Proper solder mask sizing is crucial to prevent exposure of underlying copper or misalignment with pads. Key rules include:
– The solder mask should not be too small to expose the pad edges.
– The solder mask should not cover the pad, as this could interfere with electrical connections.
To determine the appropriate enlargement:
– **Process Deviation**: The solder mask must account for any positional deviations in the factory’s solder mask process.
– **Wire Density**: If the board has high wire density, with pads placed close to traces, a smaller solder mask enlargement should be used to avoid excessive exposure. For low-density designs, larger solder mask expansion is permissible.
**3. Additional Process Considerations:**
– **Golden Finger or Printed Plug**: Determine if special processes, like the addition of process lines for these features, are necessary.
– **Electroplating**: Decide whether a conductive frame should be added based on the electroplating requirements.
– **Hot Air Leveling**: Evaluate if additional conductive process lines are needed for tin spraying processes.
– **Drilling**: Determine whether additional pad center holes are required for drilling.
– **Process Positioning**: Assess whether positioning holes are needed for later stages.
– **Board Shape**: Ensure that outline angles are defined based on the shape of the PCB.
– **Line Width Accuracy**: For high-precision boards requiring tight line width tolerances, determine if line width correction is necessary based on the factory’s production capabilities to account for side erosion effects.
### 4. **Converting CAD Files to Gerber Files**
For standardized management within the CAM process, CAD files must be converted to Gerber format. Ensure that process-specific parameters are considered during this conversion, as some of the manufacturing requirements may need to be implemented at this stage.
Most CAD software, except for Smart Work and Tango, can directly export to Gerber. These two programs can export to Protel format first, which can then be converted to Gerber.
### 5. **CAM Processing**
During CAM processing, various process treatments are applied based on the established manufacturing parameters. Special attention should be given to identifying any unusually small features in the user files that may require additional treatment or adjustments to prevent defects.
### 6. **Light Painting Output**
The processed CAM files are used to output light paintings (photomasks) for the manufacturing process. The imposition of the layout can be handled in the CAM system or during the output process. An advanced light drawing system may integrate CAM functions, such as line width correction, directly within the light painting process.
### 7. **Darkroom Treatment**
After light painting, the negatives must undergo development and fixation before they can be used in subsequent processes. Key factors in the darkroom include:
– **Development Time**: This affects optical density (or “blackness”) and contrast. Too little time results in insufficient density, while excessive development time increases fog.
– **Fixing Time**: Insufficient fixing time results in a less transparent background on the production plate.
– **Washing Time**: Inadequate washing can cause the base plate to yellow over time.
**Important:** Handle the negative film carefully to avoid scratching, which can compromise the quality of the production master.
