Drill holes are the most precision-critical feature on a PCB. Every via, component lead, mounting screw, and connector pin passes through a drilled hole. Specifying the wrong drill size wastes money (oversized holes reduce routing space; undersized holes do not fit components) and risks reliability (tight aspect ratios challenge the plating process). This guide covers standard drill sizes, tolerances, aspect ratio limits, and practical recommendations for Indian PCB designers.
Table of Contents
- Standard Drill Sizes
- Via Drill Sizes
- Component Hole Sizes
- Mounting and Tooling Holes
- Tolerances and Accuracy
- Aspect Ratio Limits
- Cost Impact of Drill Choice
- Frequently Asked Questions
Standard Drill Sizes
PCB drills follow standard increments. Using standard sizes avoids tool changes during manufacturing:
| Drill (mm) | Drill (mil) | Common Use |
|---|---|---|
| 0.2 | 8 | Microvias, advanced HDI |
| 0.25 | 10 | Small vias, fine-pitch breakout |
| 0.3 | 12 | Standard vias (most common) |
| 0.4 | 16 | Large vias, power connections |
| 0.6 | 24 | Small component leads, test points |
| 0.8 | 31 | Standard component leads (resistors, caps) |
| 1.0 | 39 | IC DIP pins, large component leads |
| 1.1 | 43 | Pin headers (0.64mm square pins) |
| 1.5 | 59 | Large connectors, screw terminals |
| 3.2 | 126 | M3 mounting holes |
Via Drill Sizes
| Via Type | Drill | Pad | Annular Ring |
|---|---|---|---|
| Standard via | 0.3mm | 0.6mm | 0.15mm |
| Small via | 0.25mm | 0.5mm | 0.125mm |
| Micro via | 0.2mm | 0.45mm | 0.125mm |
| Power via | 0.4mm | 0.8mm | 0.2mm |
| Thermal via | 0.3mm | 0.6mm | 0.15mm |
The 0.3mm drill with 0.6mm pad is the universal default. Use it unless you have a specific reason to go smaller (routing density) or larger (current capacity).
Component Hole Sizes
Rule: hole diameter = lead diameter + 0.15-0.25mm. This provides adequate clearance for component insertion while ensuring good solder fill.
| Component | Lead Diameter | Recommended Hole |
|---|---|---|
| 1/4W axial resistor | 0.5-0.6mm | 0.8mm |
| Ceramic capacitor | 0.5mm | 0.8mm |
| Electrolytic capacitor | 0.5-0.8mm | 0.8-1.0mm |
| DIP IC pin | 0.5mm square | 0.8-1.0mm |
| Pin header (2.54mm) | 0.64mm square | 1.0-1.1mm |
| TO-220 leads | 0.8mm | 1.1-1.2mm |
| Screw terminal (5mm) | 1.0-1.3mm | 1.3-1.5mm |
Mounting and Tooling Holes
| Hole Type | Diameter | Plated | Notes |
|---|---|---|---|
| M2 screw | 2.2mm | Non-plated (NPTH) | For M2 screws |
| M2.5 screw | 2.7mm | NPTH | Standard standoff mounting |
| M3 screw | 3.2mm | NPTH | Most common PCB mounting |
| M4 screw | 4.3mm | NPTH | Heavy-duty mounting |
| Tooling hole | 2.4mm or 3.0mm | NPTH | Panel registration for assembly |
| Fiducial | 1.0mm pad (no hole) | N/A | Pick-and-place alignment |
Mounting holes should be non-plated (NPTH) unless you need electrical ground connection. Specify NPTH clearly in your drill file and fabrication drawing.
Tolerances and Accuracy
| Parameter | Standard | Advanced |
|---|---|---|
| Drill position accuracy | ±0.075mm | ±0.05mm |
| Drill diameter tolerance | ±0.05mm | ±0.025mm |
| Hole-to-hole distance | ±0.05mm | ±0.025mm |
| Hole-to-board-edge | ±0.1mm | ±0.075mm |
Aspect Ratio Limits
Aspect ratio = board thickness / drill diameter. Higher ratios are harder to plate reliably.
| Aspect Ratio | Capability | Example |
|---|---|---|
| 6:1 | Easy (all fabricators) | 1.6mm board, 0.3mm drill |
| 8:1 | Standard | 1.6mm board, 0.2mm drill |
| 10:1 | Advanced | 2.0mm board, 0.2mm drill |
| 12:1+ | HDI specialist | 2.4mm board, 0.2mm drill |
Stay within 8:1 for standard pricing. If you need smaller drills on thick boards, discuss with your fabricator before committing the design.
Cost Impact of Drill Choice
- Drills below 0.25mm require special micro-drill bits that wear faster — adds cost
- Drills above 6.35mm require routing instead of drilling — adds time
- Minimising the number of unique drill sizes reduces tool changes and speeds production
- Non-plated holes (NPTH) require a separate drilling step — specify only where needed
Frequently Asked Questions
How many unique drill sizes should I use?
Aim for 5-8 unique drill sizes per board. One for vias (0.3mm), one for standard components (0.8mm), one for headers (1.0mm), one for mounting holes (3.2mm), and a few others as needed. Each additional unique size adds a tool change during manufacturing.
What is the smallest drill available at JLCPCB?
JLCPCB supports 0.2mm minimum drill for through-hole vias at standard pricing. For 0.15mm drills, additional charges apply. PCBWay offers similar capabilities.
Should mounting holes be plated or non-plated?
Non-plated (NPTH) for most applications. Use plated mounting holes only when you need electrical ground connection through the screw — for example, grounding a metal enclosure to the PCB ground plane. Plated mounting holes with copper ring provide this connection.
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