PCB Via Size Guide: Mechanical, Laser & Microvia Dimensions

Via selection is one of the earliest design decisions that constrains your entire PCB layout. Choose vias that are too large and you waste precious routing space—especially critical under fine-pitch BGAs. Choose vias that are too small and you push into HDI territory with associated cost premiums. Get the aspect ratio wrong and your board fails reliability testing.

This guide provides the complete specification framework for PCB via sizing—from standard 0.3mm mechanical vias through 0.075mm laser microvias—covering dimensional requirements, IPC standards, plating considerations, and the manufacturing capabilities that determine what’s actually producible.

Via Size Categories

Standard Mechanical Vias

Mechanical drilling uses carbide drill bits to create through-holes and is the most cost-effective via formation method.

Standard recommendation: 0.25–0.3mm drill diameter with 0.5–0.55mm pad for general-purpose designs. This provides reliable manufacturing with nearly all PCB fabricators worldwide.

Laser-Drilled Microvias

Laser drilling (UV or CO2) creates vias spanning 1–2 layers, enabling HDI construction:

Microvias are the foundation of HDI PCB design. They enable BGA breakout at 0.5mm pitch and below, where mechanical vias cannot physically fit between pads.

Buried Vias

Buried vias connect inner layers without extending to the outer surfaces:

Buried vias add manufacturing complexity and cost but enable higher routing density in thick multilayer boards. See our blind via vs buried via comparison for detailed tradeoff analysis.

Aspect Ratio: The Critical Design Constraint

Understanding Aspect Ratio Limits

The aspect ratio (board thickness ÷ drill diameter) determines how effectively the via barrel can be electroplated:

IPC-6012 Class 3 requires minimum 25 μm copper plating at the barrel center. For a 2.4mm thick 16-layer board, the minimum via drill to maintain 8:1 aspect ratio is:

Minimum drill = 2.4mm / 8 = 0.3mm

Aspect Ratio by Board Thickness

For thick boards requiring small vias, HDI stackup construction with blind/buried vias is the solution—breaking the via into shorter segments that each meet aspect ratio limits.

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Annular Ring Requirements

The annular ring is the copper ring surrounding the drilled hole on each layer. IPC standards define minimum widths:

Practical minimum: Design with 0.1mm (4 mil) annular ring on inner layers and 0.125mm (5 mil) on outer layers to account for drilling registration tolerance. For a 0.3mm drill:

• Minimum pad diameter (Class 2): 0.3 + 2×0.05 + drill tolerance = 0.45mm
• Recommended pad diameter: 0.3 + 2×0.125 = 0.55mm

Via Fill Options by Size

Copper-filled vias (IPC-4761 Type VII) provide the best thermal and electrical performance but become increasingly expensive above 0.2mm diameter. For thermal via applications, copper fill is strongly recommended regardless of via size.

Design Decision Matrix

Ready to optimize your via design? Upload your Gerbers for a free DFM review including via sizing verification.

Further Reading

• HDI PCB Design Guide: Stackup Rules, Via Structures & DFM Checklist
• Blind Via vs Buried Via: Design Rules, Cost Impact & When to Use Each
• PCB Thermal Via Design: Engineering Guide
• Via-in-Pad Design: Filled, Capped, and Plated Over