How To Conduct PCB CAM Engineering Work?

PCBs are a critical part in modern electronic devices, and their precise fabrication is essential for the functionality and reliability of these devices. PCB manufacturers employ a range of Computer-Aided Manufacturing (CAM) processes to ensure that the PCBs match the original design specifications. In this comprehensive guide, we will delve into the intricacies of PCB CAM tooling, covering the critical steps, considerations, and best practices involved in preparing a design for manufacturing.

PCB CAM: The Importance of Thorough Checks in the Engineering File Creation Process

When we receive artwork for a printed circuit board (PCB), our PCB engineering file creation process begins with thorough checks and adjustments to ensure the final product closely matches the original design. Our experienced team carefully examines every aspect of the design, and if any irregularities are detected, we take the necessary steps to clarify the designer’s intentions before moving forward, ensuring accuracy throughout the manufacturing process.

Since PCB designs sometimes include elements that are not feasible to manufacture, we offer a complimentary Design For Manufacturing (DFM) review with every order before releasing it for production. Leveraging our extensive experience with various design rule sets and software packages, we work to identify and address potential issues. Our engineering team typically spends around 3 hours meticulously reviewing, aligning, and adjusting each design during the PCB engineering file creation process to ensure your board adheres as closely as possible to the intended specifications, resulting in high-quality PCBs that meet or exceed expectations.

PCB CAM: CAM Review Overall Checklist for Bare Board Fabrication

Your checklist for CAM review in bare board fabrication is a comprehensive guide to ensure the manufacturability of printed circuit boards (PCBs). Here’s a breakdown of each item on the checklist:

1. Fabrication Print Review:
   • Verify that the fabrication drawing specifications match both the sales order and the Gerber files.
   • Ensure that all specifications in the fabrication drawing are achievable.
   • Check if the dimensions in the drawing correspond to the actual measurements in the digital file.
   • Look for any unclear or non-manufacturable instructions.
2. Alignment and File Verification:
   • Confirm the presence of all required digital files and ensure they are complete.
   • Align and orient all layers correctly.
3. Copper Layers:
   • Verify that the spacing between copper features meets the minimum requirement based on the desired copper weight.
   • Ensure that copper is not overlapping the board edge unless it is intentional.
   • Check for any dead-end trace fragments that may cause issues.
   • Delete any board outlines or extraneous information outside the board perimeter.
   • Scale up copper features to account for etch and plating processes.
   • Compare the drill file to the outer copper layers to ensure that plated holes have sufficient copper surrounding them.
   • If gold fingers are present, add traces to tie them to the buss bar for the electrolytic hard gold plating process.
   • On inner layers, remove non-functional copper pads around vias that do not connect to the layer.
4. Solder Mask:
   • Adjust solder mask swell to meet a 4mil – 5mil oversize mask clearance (2mil to 2.5mil per side of the copper feature).
   • Verify that there is enough spacing between copper features to reliably print mask dams.
   • Inspect the board for any potentially missing solder mask clearances and question clearances that don’t seem correct.
   • Delete any board outlines or extraneous information outside the board perimeter.
5. Silkscreen:
   • Verify that silk screen line width and character height meet the minimum requirements for legible printing.
   • Adjust or relocate silk screen elements that are too close to a solderable surface.
   • Delete any board outlines or extraneous information outside the board perimeter.
6. Drill File:
   • Confirm that drills are centered within their copper pads.
   • Check for any missing drill hits.
   • Delete duplicate drill hits.
   • Ensure that the customer-specified drill hole tolerance is achievable (IPC Class 2 Standard: +/- 3mil for Plated Through Holes (PTH) and +/-2mil for Non-Plated Through Holes (NPTH)).
   • Verify that the edge-to-edge spacing of drills meets the minimum requirements.
   • Compare the drill chart and drill map to the actual CNC drill file if supplied.

By following this checklist, you can help ensure that the PCB design is ready for manufacturing, minimizing potential issues during the fabrication process.

What does PCB CAM Engineer do？

Your additional checklist items for board outline, UL/Date Code/94V-0/RoHS markings, and checks for multilayer boards provide further detail on the CAM review and manufacturing process for PCBs. Here’s a breakdown of these items:

Board Outline

• Verify that the board outline matches the fabrication drawing and sales order.
• Determine the true edge of the outline using the center of the line used to draw it.
• If multiple outline layers are provided, use the .GM1 layer or another mechanical layer as the correct outline. Use the .GKO layer only if no other outline is provided.
• Add any cutouts or slots needed for routing to the mechanical board outline layer.
• Create a CNC route file for routing the board.

UL/Date Code/94V-0/RoHS Markings:

• Add UL/Date Code/94V-0/RoHS markings to the board if requested by the customer.
• If no request is made, the default is to not add any additional markings.

Additional Checks on Multilayer Boards:

• Verify that a layer sequence is provided for multilayer boards.
• Ensure that the specified stack-up (controlled dielectric) can be met with materials on hand.
• For controlled impedance, verify the calculations and suggest changes to meet the target impedance.

Creating Arrays (Panels):

• Follow customer requirements for panelizing the design into an array for automated assembly.
• Add tooling rails, fiducials, tooling holes, scoring, and tab routing as needed for the array.
• Panelize the paste (stencil) layers as a courtesy for stencil manufacturing. Review these layers carefully, as no adjustments are made to them.

File Creation (Tooled / Working File):

• After all reviews and adjustments, create the finalized “working file” for manufacturing.
• Upload this working file to the server and send an email with a download link to the customer.

Electrical Testing and File Distribution:

• All boards undergo electrical testing based on an optimized netlist generated from the original file.
• If an IPC netlist is supplied, it is compared to the Gerber to ensure there are no discrepancies.
• Distribute the appropriate files to various manufacturing departments to prepare for production.

These steps ensure that the PCB design is thoroughly reviewed, adjusted as necessary, and prepared for manufacturing according to the customer’s specifications and industry standards. This comprehensive approach helps minimize errors and ensures the successful production of high-quality PCBs.These are just an introduction to the general content of CAM work. Next, we will discuss the CAM workflow and content in detail.

Detailed CAM Work Content

Check if the project is correct？

The normalization process for the Gerber files sent with each PCB order ensures that the files are standardized and compatible with the PCB panelization and manufacturing processes. Here are the basic steps involved in this normalization process:

1. Re-naming Gerber Files:
   • Rename the Gerber files to adhere to your company’s standard naming convention. This helps maintain consistency and clarity in file management.
2. Checking File Presence:
   • Verify that all necessary Gerber files are present. This includes files for different layers, solder mask, silkscreen, drill files, and any other relevant files required for manufacturing.
3. Importing into CAM Software:
   • Import Gerber files and NC drilling files into CAM (computer-aided manufacturing) software, such as: cam350, genesis2000, ucam，Incam, etc. This step is essential for further processing and analysis.
4. Reviewing Specifications:
   • Compare the PCB board’s specifications provided in the order with the data supplied in the Gerber files. Ensure that the specifications match to avoid discrepancies in the manufacturing process.
5. Checking Manufacturing Compatibility:
   • Evaluate the specifications and features in the Gerber files to ensure they are within the manufacturing capabilities of your PCB manufacturing process. This includes checking for design rule violations and manufacturability issues.

Create net and steel mesh files

Create net and steel mesh files, and optimize them. For example, copper layers belonging to the same net can be optimized and merged to reduce data size. Surface mount devices (SMDs) can be optimized by converting them into pads, and specific file attributes can be assigned to SMDs and ball grid array (BGA) components to streamline subsequent production processes.

To optimize production and streamline data for subsequent optimization by CAM engineers, it is necessary to perform a comprehensive inspection and optimization of the copper depicted in the image.

Define hole attributes and increase drill bit size.

A. Properly define hole attributes (via, plated through-hole (PTH), non-plated through-hole (NPTH)).

B. If the customer does not provide drill files, convert the separate drill drawing into drill data.

C. When creating slots, pay attention to their size, which is sometimes indicated in text boxes.

D. Consider the board’s specifications (e.g., solder mask thickness +0.15mm, gold immersion, gold plating, tin immersion +0.1mm, all NPTH holes +0.05mm).

E. Consider any special requirements from the customer.

F. Use the separate drill drawing to check for issues such as oversized, undersized, excessive, or insufficient holes, as well as hole misalignment.

G. Optimize the drill tape.

Modify inner layer films.

A. Negative inner layer:

Note:
a. All graphics displayed on the negative film are to be etched.
b. Size of isolation pads (0.15-0.30mm).
c. Opening size for solder mask pads (inner layer: larger than the hole by 0.2mm or more, outer layer: larger than the hole by 0.4mm or more, opening line: 0.25mm).
d. V-cut copper removal at the board edge (based on board thickness).
e. Ensure that the solder mask pads are completely isolated by the surrounding isolation pads.
f. Consider the need for shrinkage factor.

B. Positive inner layer:

Note:
a. Remove standalone pads (unless specified by customer requirements; typically remove during production).
b. Compensate for traces (add compensation value based on different copper foil thicknesses).
c. Optimize traces (distance between via PTH rings and distance between holes, traces, and pads).
d. Add teardrops.
e. Fill small gaps.
f. Remove inner copper foil (at board edges and V-cut areas).
g. Consider copper plating on process edges, avoiding V-cut lines and drill holes.
h. Consider the need for expansion/contraction factor.
i. Inner layer large copper areas near gold fingers should be removed inward by a depth of 0.5mm along the slanted edge of the gold finger.

Outer layer traces

Think before reading the article: Does the wiring in the picture below need to be optimized or is there any problem?

• Trace compensation.
• Remove NPTH pads.
• Optimize traces (hole ring size, spacing).
• Add teardrops (as required, generally not added).
• Remove copper from NPTH and non-solder mask PTH holes, and non-solder mask PTH holes should have smaller annular rings than the hole size.
• Copper clearance size.
• Fill small gaps and pinholes.
• V-cut and board edge copper removal.
• Inner layer gold fingers should be inwardly recessed in the gold finger area.
• Gold finger conductive wires, leads, dummy fingers.
• Consider any special requirements from the customer.
• Whether to add UL markings on the traces.
• Whether to move the etched text on the traces by 0.25mm.
•  Whether to add V-cut test pads.
• For V-cut boards, create NPTH holes.
• The gold finger conductive wires should form a path with the board edge.

Solder mask

a. Is the solder mask window large enough (0.05-0.08mm larger than the trace pad)?
b. Is there any exposed trace? Ensure the solder mask pad is at least 0.07mm away from the trace.
c. For NPTH and non-solder mask holes, add annular rings that are 0.15mm larger than the hole size.
d. Green solder mask bridges should be at least 0.075mm wide (for other colors, at least 0.1mm wide).
e. For holes with a diameter of 0.8mm that are not windowed, add annular rings that are 0.15mm smaller than the hole size.
f. Consider the solder mask curing cycle and ensure UL markings are not missed.
g. Create solder mask windows for gold finger openings and dummy finger openings.
h. Determine if solder mask windows should be created for test pads.
i. For V-cut boards, if the distance between the through-hole and the pad or BGA is less than 0.15mm, handle it accordingly.
j. Add annular rings for helper holes and explosion-proof holes.
k. Determine the nature of windowed through-holes and how to handle solder mask plugging.

Silkscreen

a. Check the width of characters and optimize the aspect ratio of characters.
b. Check the polarity of characters and optimize them.
c. Verify if there are engraved characters at the board edge and V-cut areas.

d. Ensure UL markings and cycles are added according to customer requirements, and confirm their placement relative to the forming lines, avoiding V-cut lines.
e. Ensure that the spacing between text and trace pads is at least 0.1mm on one side.

Forming drawing

a. Is all the data consistent with the Gerber files?

b. Are there any instances of multiple slots or missing slots?

c. Are the positioning holes placed at 1.0mm and whether NPTH holes are used?

d. Are all the standards complete and correct?

e. Is the remaining thickness after V-cut accurate?

f. Are the requirements for the beveled edge of the gold fingers correct?

Please review the forming drawing to ensure that these aspects are accurately represented and aligned with the intended specifications.

Final Inspection

After completing CAM production, meticulously compare the final output with the original manuscript to ensure accuracy. Verify the Gerber fabrication instructions and follow up with a thorough DFM analysis using software to assess compliance with specifications. Additionally, carefully inspect for any occurrences of excessive or missing pads.

In the image above, there is an inconsistency in the size of one of the holes within the same component footprint. If this hole size matches the specified hole chart, do you think it is necessary to confirm with the designer? For further discussion or any other questions, please feel free to contact our engineers. We highly encourage engaging in discussions.Discuss now

Conduct a comprehensive examination of the routing, solder mask, and character layers simultaneously to identify any anomalies or irregularities. This holistic approach ensures the detection of any abnormalities in the design.

Perform three rounds of network comparison checks using software to ensure the files are free from any network-related issues. This step is essential to maintain the integrity of the data. If any network issues are identified in the original Gerber files, promptly raise an RFQ to address and resolve the issues in a timely manner.

Export the gerber files for panelization, generate the required films, and meticulously complete the ERP data and production process documentation. This ensures accurate information for efficient manufacturing processes and facilitates smooth execution.

Conclusion

CAM engineers are highly experienced professionals whose job requires a great deal of expertise. At Highleap Electronics, we have a team of engineers with over ten years of experience, all of whom have worked with various types of Gerber files. With their extensive PCB manufacturing experience, they are capable of avoiding unnecessary errors and improving productivity.

CAM engineers often encounter numerous engineering issues. In this installment, we will only list a few of these problems. In the next issue, we will provide a detailed overview of common issues encountered in CAM engineering and offer optimization recommendations for design.