In modern electronics manufacturing, even the smallest design details can significantly impact product reliability and production efficiency. One often-overlooked aspect is the proper design of PCB fixing holes and assembly holes. While they may appear simple, these holes play critical roles in both mechanical stability and automated assembly processes.
For beginners entering the PCB design field, understanding the difference between fixing (mounting) holes and assembly (tooling) holes is essential. Poor hole design can lead to misalignment, assembly failures, or even product damage.
In this guide, we’ll break down everything you need to know about PCB fixing holes and assembly holes, including design principles, common mistakes, and 2026 manufacturing cost considerations, along with practical insights from KingsunPCB, a leading PCB manufacturer in China.
1. What Are PCB Fixing Holes?
PCB fixing holes, also known as mounting holes, are used to secure a printed circuit board to an enclosure, chassis, or mechanical structure.
Key Functions
- Provide mechanical stability
- Enable secure installation inside devices
- Prevent PCB movement during operation
- Support heavy components (transformers, connectors)
Common Applications
- Consumer electronics (smart devices, laptops)
- Industrial control systems
- Automotive electronics
- Power supply boards
2. Types of Fixing Holes
2.1 Plated Mounting Holes (PTH)
- Copper plating inside the hole
- Can be connected to ground (GND)
- Improve EMI shielding
2.2 Non-Plated Mounting Holes (NPTH)
- No copper plating
- Used purely for mechanical fastening
- Most common for screws and standoffs
2.3 Threaded Holes
- Designed for direct screw insertion
- Less common, usually requires secondary processing
3. Standard Sizes and Design Considerations
Typical mounting hole sizes follow metric screw standards:
| Screw Type | Hole Diameter (mm) |
| M2 | 2.2 – 2.4 mm |
| M2.5 | 2.7 – 2.9 mm |
| M3 | 3.2 – 3.4 mm |
Design Tips:
- Keep at least 1.5–2 mm clearance from copper traces
- Place holes near board corners for stability
- Use keep-out areas to avoid routing conflicts
- Consider mechanical stress distribution
4. What Are PCB Assembly Holes?
PCB assembly holes, often called tooling holes, are used during the manufacturing and SMT assembly process to ensure accurate positioning of the PCB.
Key Functions
- Align the PCB on assembly machines
- Ensure precise component placement
- Improve production consistency and yield
Types of Assembly Holes
1. Tooling Holes
- Used by assembly equipment for board alignment
- Typically located at fixed positions
2. Fiducial-Assisted Alignment
- While not holes themselves, fiducials often work with tooling holes
- Improve optical alignment in SMT processes
Standard Specifications
- Common diameter: 2.0 mm / 3.0 mm
- Usually non-plated (NPTH)
- Positioned symmetrically on the PCB
- Require tight tolerances (±0.05 mm)
Placement Guidelines:
- At least 3 tooling holes per panel
- Keep consistent distance from PCB edges
- Avoid interference with components or copper
5. PCB Fixing Holes vs Assembly Holes: Key Differences
| Feature | Fixing Holes | Assembly Holes |
| Purpose | Mechanical mounting | Manufacturing alignment |
| Usage Stage | End product | Production process |
| Tolerance | Moderate | High precision |
| Location | Corners/edges | Standardized positions |
| Plating | Optional | Usually non-plated |
Summary:
Fixing holes ensure your PCB stays in place during use, while assembly holes ensure your PCB is built correctly in the first place.
6. Design Guidelines for Beginners
Designing PCB holes correctly is crucial for both functionality and manufacturability.
6.1 Choose the Right Hole Type
- Use NPTH for standard mounting
- Use PTH if grounding or shielding is required
6.2 Optimize Hole Placement
- Place fixing holes at corners or symmetrical points
- Ensure assembly holes follow panelization standards
6.3 Maintain Proper Clearance
- Keep distance from traces and components
- Avoid placing holes under BGA or fine-pitch components
6.4 Follow Manufacturer Recommendations
Professional manufacturers like KingsunPCB provide DFM (Design for Manufacturability) guidelines to ensure optimal results.
7. Common Mistakes to Avoid
Beginners often make avoidable errors when designing PCB holes:
- Using incorrect hole sizes for screws
- Placing holes too close to traces
- Ignoring tolerance requirements
- Misaligning assembly holes
- Mixing plated and non-plated holes improperly
These mistakes can lead to:
- Assembly failures
- Increased production costs
- Reduced product reliability
8. How Fixing and Assembly Holes Affect PCB Manufacturing
8.1 Fabrication Impact
- Additional drilling increases complexity
- Tight tolerances require higher precision equipment
8.2 Assembly Efficiency
- Proper tooling holes improve SMT accuracy
- Reduce defects and rework rates
8.3 Cost Considerations (2026 Pricing)
In 2026, PCB manufacturing costs are influenced by hole design:
| Item | Typical Cost Impact |
| Standard NPTH holes | Minimal (included) |
| High-precision tooling holes | +5% to 10% |
| Plated mounting holes | +10% to 15% |
| Custom hole sizes/tolerances | +15% to 25% |
Estimated PCB Pricing (2026):
- Prototype PCB (2-layer): $5 – $30
- 4-layer PCB: $30 – $100
- Complex boards with tight tolerances: $100+
Working with experienced manufacturers like KingsunPCB helps optimize hole design to balance cost and performance.
9. Practical Design Example
Consider a simple rectangular PCB:
- 4 fixing holes placed at each corner (M3 size)
- 3 assembly holes positioned symmetrically
- Adequate clearance from traces and components
Design Strategy
- Ensure even mechanical stress distribution
- Maintain alignment during SMT assembly
- Avoid interference with functional areas
This approach improves both product durability and manufacturing yield.
10. FAQ
Q1: What is the difference between mounting holes and tooling holes?
Mounting holes are used in the final product for mechanical fixing, while tooling holes are used during manufacturing for alignment.
Q2: Are fixing holes always non-plated?
No. They can be plated if grounding or EMI shielding is required.
Q3: How many assembly holes are needed?
Typically 2–4 holes, depending on PCB size and panelization.
Q4: Can fixing holes be used as grounding points?
Yes, if designed as plated through holes connected to the ground plane.
11. Conclusion
PCB fixing holes and assembly holes may seem like minor design elements, but they play a crucial role in ensuring both mechanical stability and manufacturing accuracy.
For beginners, mastering these fundamentals can:
- Improve PCB reliability
- Reduce production errors
- Optimize manufacturing costs
By following proper design guidelines and working with experienced manufacturers like KingsunPCB, you can ensure your PCB designs are both production-ready and cost-efficient in 2026.