Through Hole Pad and Drill Size Basics
Through hole packages combine component leads with plated through holes (PTH) in the PCB, so pad and drill dimensions must accommodate lead diameters while allowing reliable solder filling and mechanica l stresses. Use the chart below as a starting point, then adjust for manufacturing capabilities, thermal performance, and mechanical robustness. Always check your fabricator’s spec sheet for minimum annular ring, drill accuracy, and slot/polygon rules.
| Metric | Typical Range | Verified Detail | Source Type |
|---|---|---|---|
| Common drill sizes (Imperial) | 0.026" to 0.125" | Standard increments including 0.028", 0.031", 0.035", 0.040", 0.050", 0.060", 0.070", 0.080", 0.090", 0.100", 0.125" | IPC recommendations, common fab output |
| Common drill sizes (Metric) | 0.66 mm to 3.18 mm | 0.7 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm | IPC recommendations, common fab output |
| Annular ring (min) | 0.10 mm to 0.15 mm | Preferred ≥0.15 mm; ≥0.20 mm for high-reliability | Fabrication capability baseline |
| Pad diameter vs. drill | Pad diameter ≈ drill + 0.15–0.40 mm | Rule of thumb; verify with specific packages | Industry practice |
Common Through Hole Packages and Typical Sizes
Below are typical ranges for through-hole packages. Values are indicative and may vary by manufacturer; always confirm with the specific device datasheet and your PCB fabricator. When in doubt, prioritize annular ring and robust plating over minimal material use.
| Package | Pad Diameter Range (mm) | Recommended Drill (mm) | Annular Ring Target (mm) |
|---|---|---|---|
| DIP (dual in-line) | 0.8–1.2 | 0.7–1.0 | 0.15–0.20 |
| Axial resistors/capacitors | 0.8–1.3 | 0.7–1.0 | 0.15–0.20 |
| TO-220/TO-263 | 1.5–2.0 | 1.2–1.5 | 0.20–0.25 |
| Screw terminals / Power | 2.0–4.0 | 1.8–3.5 | 0.20–0.30 |
| Harting / D-sub connectors | 1.6–2.4 | 1.3–2.0 | 0.20–0.30 |
Design Guidelines for Robust Through Hole Pads
Conservative pad and drill choices reduce faults across temperature cycles, vibration, and cleaning processes. Keep solder mask defined (SMD) clearances in mind unless tenting or plugging is specified; avoid tight anti-pad clearances when routing near PTH. Evaluate thermal reliefs for high-current devices, and confirm drill aspect ratios with your fab to avoid voids or shallow plating.
Fabrication Tolerances to Remember
- Drill accuracy: ±0.05 mm typical; verify if tight-pin devices are used
- Aspect ratio limit: commonly 7:1 to 10:1; deeper boards may require smaller drills or adjusted pad sizes
- Annular ring: aim for ≥0.15 mm;
- Hole plating: standard PTH is 18–35 µm; consider thicker if high current or multiple reworks expected
Handling Tolerances and Mechanical Stress
Through hole connections endure bending, connector insertion force, and board flex, so mechanical robustness must complement electrical targets. Increase pad annular ring and add stitching vias or polygons where strain is likely. For connectors, follow IPC-2221 Class 2/3 land patterns and add courtyard clearances to prevent board cracks during mating/unmating.
DFM Checklist for Through Hole Land Patterns
Use this checklist when preparing your design for fabrication and assembly. Confirm drill capabilities, annular ring targets, and mask specifications with your supplier, especially for mixed technology panels.
- Verify drill sizes fall within fabricator capabilities; prefer standard increments
- Specify pad diameter = drill + 0.15–0.40 mm; add margin for high-stress connectors
- Set annular ring minimum ≥0.15 mm; increase for high-reliability or high-current
- Include clearances to mask openings, copper pours, and adjacent PTHs
- Confirm plating thickness and aspect ratio limits with your fab
Interpreting Datasheets and Footprint Libraries
Component datasheets often list maximum pin diameters and recommended mounting conditions, not ideal footprints. Use measurements as upper bounds; check mechanical stress and thermal requirements before locking dimensions. When footprints are sourced from vendor libraries, validate hole sizes and annular ring against your fab’s capabilities and expected rework policy.