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- 04 Aug, 2025
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What Are PCB Drills and Why They Matter
PCB drills are precision tools used to create vias and plated through holes that connect multiple layers of a printed circuit board. These holes carry signals and allow mechanical assembly. As PCBs become more compact and complex, drills must maintain precise geometry at extremely high spindle speeds, often exceeding 100,000 RPM. Any loss in tip integrity can lead to defects such as nail heading, which compromises entry pad quality and hole performance.
Types of PCB Drills Prone to Nail Heading Issues:
- Micro Drills: Used for vias and plated through holes (PTHs), where tip integrity is critical to prevent pad damage.
- Depth-Controlled Drills: Designed for selective internal layer access, where precise entry is essential to avoid delamination or smear.
Smaller-diameter drills with reduced tip radii are particularly vulnerable to defects caused by tool wear, nail heading being one of the most common and critical issues.
Problem: Nail Heading at the Hole Entrance
Nail heading occurs when a worn or blunt drill tip fails to slice cleanly through the copper pad and instead compresses it. This compression forces part of the pad laterally or inward into the hole entrance, distorting the intended geometry. The resulting deformation often leads to:
- An apparent widening of the pad diameter at the entry point
- Misalignment between layers due to altered pad registration
- Reduced copper adhesion during plating, risking delamination or voids
This defect can compromise both structural reliability and compliance in high-density, multilayer PCBs.
How Rainbow TAC Coating Solves Nail Heading
Nail heading is a critical challenge in PCB drilling, often leading to entry pad distortion, copper smearing, and reduced hole quality. Rainbow-TAC, a high-performance ta-C coating applied via FCVA, addresses the root causes of nail heading with unmatched hardness, thermal stability, and adhesion.
Benefits and Solutions of Rainbow TAC Coating
| Benefit | Problem | Solution |
| Maintain Tip Sharpness and Geometry | Standard coatings dull quickly, leading to distorted hole entry and increased nail heading risk. | With a hardness rating of 5000 Hv, Rainbow-TAC maintains cutting-edge precision throughout extended tool life. |
| Reduces Heat-Induced Resin and Copper Deformation | Excessive friction softens resin, smearing copper into the pad and causing entry defects. | An ultra-low friction coefficient (<0.1) minimizes heat generation, stabilizing the cutting zone and preventing smear. |
| Resists Delamination at High RPMs | Conventional coatings often crack or flake under prolonged high-speed drilling stress. | Advanced FCVA deposition ensures a dense, crack-free film with superior adhesion to carbide, even under extreme rotational stress. |
Comparison: Rainbow TAC Coating vs. Traditional Coatings
| Coating Type | Hardness (GPa) | Friction Coefficient | Max Service Temperature (℃) | Resin Adhesion Tendency |
| Uncoated | 15~18 | 0.7-1.0 | 600 | Severe |
| Standard DLC | 20~30 | 0.1-0.2 | ≤300 | Minor |
| Rainbow-TAC | 50 | <0.1 | ≤500 | Minimal |
Conclusion
Rainbow-TAC significantly reduces nail heading in high-speed drilling operations. The coating preserves tool point geometry, controls thermal distortion, and extends drill lifespan, resulting in improved inner layer alignment and reduced rework. Upgrade your PCB drill bit coating to improve entry pad durability and overall hole quality.
Contact us today to learn how Rainbow-TAC can enhance your drilling performance.