Causes and Countermeasures for PCB Burr Formation

PCB manufacturing is a delicate and precise process that involves a variety of steps, each of which presents potential challenges. One of the common issues manufacturers face during PCB production is burr formation. Burrs are tiny protrusions, typically resulting from drilling, milling, or routing processes, which can compromise the quality, performance, and reliability of the finished product. Understanding why burrs form and implementing effective countermeasures is essential for achieving a burr-free and high-quality PCB.

Below, we delve into the specific causes of burrs and their corresponding solutions.

Causes of PCB Burr Formation

Via Hole Burrs
During the drilling of vias (plated through holes) or non-plated holes, burrs are commonly formed on the edges of the drilled holes. This happens due to inadequate cutting forces or a dull drill bit, which results in improper shearing of copper and substrate material. Additionally, the excessive speed or pressure applied during drilling can lead to tearing rather than cutting, creating uneven and jagged burrs along the edge of the hole.

Incorrect Milling or Routing Parameters
During the milling process, which defines the PCB outline, the use of incorrect cutting parameters such as high spindle speeds or inadequate feed rates may result in the formation of burrs. The incorrect combination of cutting forces leads to incomplete or uneven shearing of material, causing the edges of the board to become ragged or covered in burrs.

Dull or Worn-Out Cutting Tools
When drilling, routing, or milling, the condition of the tool is of utmost importance. Dull tools increase friction and generate excessive heat, which in turn causes material smearing rather than clean cutting. This often leads to the formation of burrs along the edge of the PCB, particularly in the copper layer.

CAM File Optimization Issues
Many burr-related issues can be traced back to how the Gerber production files are prepared by CAM engineers. If the toolpaths are not optimized, such as improper down-cut strategies (milling routes), burrs can form at the PCB outline. Specifically, failing to add optimized drill holes at sharp intersections or corners of the board outline can increase the chances of burr formation during milling. Inadequate planning for cross cuts or not adjusting tool entry and exit points can also lead to burrs. Moreover, CAM engineers need to add specific deburring drill holes and separate the tools used in different processes to ensure a clean cut.

Panelization Techniques: V-CUT Burrs
V-CUT is a commonly used panelization technique to separate individual boards. However, improper usage or poor quality control of V-CUT processes can create burrs at the edges, especially when the cutting angle or depth is not well controlled. V-CUTs create a score line for easy breaking, but due to the uneven forces applied during breaking, burrs may form along the edge of each PCB.

Clamping and Fixture Issues
Poor clamping or inadequate fixturing can cause the board to move or vibrate during drilling or milling, leading to the formation of burrs. If the PCB is not held securely, it may experience fluctuating cutting forces that result in rough edges.

Material Composition and Quality
Different types of laminate materials can influence the formation of burrs. For instance, harder materials may resist clean cutting and lead to burrs, while softer materials can deform, causing similar results. Improper handling of these materials during drilling or routing amplifies the problem.

Residual Stress in PCB Materials
Residual stress from earlier processes, such as lamination or heating, can influence how the material behaves during milling or drilling. If residual stress is present, the material may deform during cutting, leading to burr formation.

Countermeasures for Preventing PCB Burr Formation

Tool Maintenance and Replacement
Regular maintenance and timely replacement of drill bits and milling tools are crucial for reducing burrs. Implementing an ERP system to track tool usage and prompt replacement helps ensure that only sharp, high-quality tools are used in production. Particularly for special materials, fresh tools should be used to achieve cleaner cuts.

Optimize Drilling and Milling Parameters
Selecting appropriate spindle speeds, feed rates, and cutting depths is vital to achieve clean cuts. Slower drilling speeds with optimized feed rates can reduce tearing forces and improve the quality of the drilled holes. A balance between speed and feed rate ensures efficient shearing rather than tearing.

Second-Stage Drilling (Deburring Pass)
For vias and non-plated through holes (NPTH), implementing a second-stage drilling process can effectively remove burrs that form around the holes. For example, after the initial drilling, a smaller diameter bit can be used for a “deburring pass” to clean up the edges.

Improve CAM Optimization
CAM engineers must optimize the Gerber files to minimize burr formation. This includes adjusting the tool paths for smooth entry and exit, avoiding sharp intersections, and adding extra drill holes where the milling routes cross or meet at sharp angles. Tool segmentation should also be done thoughtfully to facilitate efficient cutting and deburring. Creating dedicated deburring drill holes in critical areas can help ensure the final product is burr-free.

Improve Clamping Techniques
Ensuring that PCBs are securely clamped during drilling and milling prevents unnecessary vibration or movement. Using vacuum tables or precision clamps can keep the board in place, ensuring more consistent pressure and preventing burr formation at the edges.

Reduced Use of V-CUT for Critical PCBs
If a customer specifies a high-quality finish with minimal burrs, consider reducing the use of V-CUT and using alternative panelization methods like tab-routing. If V-CUT is essential, use abrasive brushing or polishing to remove burrs after depaneling.

Material Considerations and ERP Integration
Using an ERP system to mark special material requirements is crucial for controlling burrs. Materials like aluminum or high-density laminates need specific handling instructions, such as the use of new cutting tools and lower milling speeds. Integrating these alerts into the ERP helps ensure that all personnel involved in the production process are aware of special handling requirements.

Post-Processing and Deburring
After milling or V-CUT, additional post-processing steps such as abrasive brushing, edge sanding, or manual polishing should be implemented to remove burrs. For one-stop PCB assembly (PCBA) services, ensuring burr-free boards is particularly critical to avoid issues during soldering or automated component placement.

Residual Stress Relief
Applying a residual stress relief treatment, such as thermal stress relief, prior to milling or drilling can minimize material deformation during cutting. By relieving internal stresses, the material is less likely to deform and form burrs.

Conclusion

PCB burrs are a major quality issue that can adversely impact the performance, appearance, and manufacturability of the final product. Burr formation can be attributed to multiple factors, including incorrect cutting parameters, tool wear, improper fixturing, suboptimal panelization techniques, and poorly optimized CAM files. By addressing these issues through preventive measures—such as tool maintenance, proper CAM optimization, ERP integration for material management, and careful clamping—burrs can be minimized, leading to higher quality and more reliable PCBs.

Implementing these strategies and keeping a close eye on the entire PCB manufacturing process is essential for producing clean, burr-free boards that meet customer expectations and are well-suited for assembly and further electronic integration.