In the field of PCB (Printed Circuit Board) manufacturing, drilling is one of the most critical processes. It directly impacts the precision and quality of the final product, including parameters such as hole position accuracy, hole diameter tolerance, and hole wall roughness. Defects during drilling can severely affect the performance and reliability of the PCB. As such, it is essential to maintain strict quality control throughout this process. This article focuses on analyzing common drilling defects, including hole misalignment, pad explosion, short slot hole length, skewed holes, and rough holes, and proposes solutions to improve drilling quality.
1. Hole Misalignment (Hole Offset)
1.1 Defect Description
Off-center hole Centered hole
Hole misalignment is a common defect where the drilled hole deviates from its intended position. Misalignment can cause malfunctioning of the circuit and interfere with component placement, leading to overall poor performance.
1.2 Potential Causes
- Drill Bit Wear: Poor sharpening or uneven wear of the drill bit can lead to inaccurate positioning.
- High Drilling Speed: Excessive drill speed can result in positioning errors.
- Multiple Layers: Drilling too many layers at once can cause alignment issues due to inconsistencies between layers.
- Drill Machine Vibration: Excessive spindle vibration can lead to misalignment.
- Board Surface Contamination: Foreign particles on the PCB surface can hinder drill alignment.
- Inconsistent Drill Bit Mounting: Loose or uneven mounting of the drill bit can affect accuracy.
- Improper Board Handling: Inadequate board placement or handling, particularly with thin boards, can lead to misalignment.
1.3 Improvement Methods
- Control Drill Bit Wear: Ensure drill bits are properly sharpened and maintained.
- Reduce Drill Speed: Lower the drilling speed to improve precision.
- Minimize Layer Stack: Drill fewer layers at once to avoid misalignment.
- Recalibrate the Drilling Machine: Ensure that the drilling machine is properly calibrated to minimize vibration and misalignment.
- Clean the Board Surface: Clean the PCB surface thoroughly before drilling.
- Check Drill Bit Mounting: Ensure that the drill bit is securely and correctly mounted.
- Handle Thin Boards Properly: Use both hands to handle thin boards to ensure uniform placement.
2. Pad Explosion (Pad Delamination)
2.1 Defect Description
Hole edge burr, white halo, oil splashing
Pad explosion refers to the separation of the copper pad from the PCB during drilling, often caused by excessive force on the PCB surface. It can lead to a lack of proper electrical connections, rendering the PCB unusable.
2.2 Potential Causes
- Large Drill Hole Size: Drilling larger holes, such as those over 5mm, can cause excessive pressure on the PCB, leading to pad explosion.
- Fragile PCB Material: Materials like environmentally friendly laminates, CEM-3, and high Tg materials are more prone to pad explosion due to their brittleness.
- Worn-out Drill Bits: A worn drill bit can exert uneven pressure on the PCB during drilling.
- High Drill Speed: Excessive drilling speed can result in too much pressure on the pad, causing it to explode.
- Repeated Use of the Base Plate: Repeated use of the same base plate can weaken its effectiveness in protecting the PCB during drilling.
2.3 Improvement Methods
- Step Drilling: Use a smaller drill bit to make a preliminary hole before using the final desired drill size.
- Reduce Drill Speed: Lower the drilling speed to minimize pressure on the pad.
- Use New Drill Bits: Ensure drill bits are not worn out and are replaced regularly.
- Use Fresh Base Plates: Use fresh base plates or move the base plate periodically to prevent repeated drilling in the same areas.
3. Short Slot Holes and Skewed Holes
3.1 Slot Hole Definition
Slot holes can be classified into two types:
Short Slot Holes: When the ratio of length to width is ≤ 2.
Long Slot Holes: When the ratio of length to width is > 2.
3.2 Potential Causes
- Uneven Drill Bit Pressure: Uneven force on the drill bit when making slot holes can lead to skewed or short slot holes.
- Excessive Drilling Layers: High drilling speeds or too many layers can distort the hole shape.
- Incorrect Drill Bit Usage: Using the wrong drill bit, such as a standard drill bit for a slot hole, can cause deformation.
3.3 Improvement Methods
- Design Adjustments: Compensate for slot hole length and angle during the design phase.
- Reduce Drilling Layers: Minimize the number of layers being drilled at once.
- Use Correct Drill Bits: Always use the appropriate drill bit for slot holes according to design specifications.
4. Rough Holes
4.1 Types of Hole Roughness
There are three main types of hole roughness:
Fiber string
- Fibers in the Hole: The presence of fibers in the hole can be caused by low drill speed or worn-out drill bits.
- Rough Hole Walls: Uneven or rough walls can lead to poor soldering and component placement.
- Inner Layer Pad Pulling: This occurs when the copper pad from the inner layer is pulled away during drilling, leading to potential functionality issues.
4.2 Potential Causes
- Low Drill Speed: A low drilling speed can result in rough holes.
- Worn Drill Bits: Old or worn drill bits can cause uneven drilling.
- Thicker Copper Layers: Thicker copper layers on the inner and outer layers can cause more resistance, leading to rough holes.
- Inefficient Dust Extraction: Poor dust extraction can leave residue on the PCB, affecting the whole surface.
- Small Inner Layer Pads: Small pads on the inner layer can result in poor hole quality.
4.3 Improvement Methods
- Increase Drill Speed: Higher drill speeds can reduce roughness.
- Control Drill Bit Lifespan: Regularly monitor and replace drill bits before they become too worn.
- Adjust Drilling Layers: Reduce the number of layers drilled at once for thick copper boards.
- Use Sandpaper: After drilling, use sandpaper to smooth out rough holes.
- Improve Dust Extraction: Ensure the dust extraction system works properly to remove debris during drilling.
After PCB drilling, subsequent stages like SMT stencil printing demand tight dimensional accuracy and alignment.
At PCBYES, with over ten years of experience in PCB prototype and fabrication, we prioritize quality and precision in every aspect of PCB manufacturing. We understand the impact of drilling quality on the overall performance and reliability of PCBs. Our team of experienced engineers works diligently to meet the most demanding requirements, providing solutions that ensure your PCBs meet industry standards. Whether you need help with hole misalignment or pad explosion issues, PCBYES is committed to offering high-quality, cost-effective solutions for all your PCB and PCBA needs.
