Vias are among the most critical features in multilayer PCBs, and drilling costs typically make up 30% to 40% of total PCB fabrication expenses.
Understanding PCB drilling dimensions is just as important for cost control as it is for circuit performance.
A standard via has two core parts: the inner drill hole, and the annular pad surrounding it.
The sizes of these two sections directly define the overall via dimensions and how the hole behaves in production.
In high-speed, high-density design, engineers naturally prefer smaller vias to free up routing space and reduce parasitic capacitance.
Smaller holes do benefit high-speed signals, but shrinking them too much drives up manufacturing cost and creates process risks.
Hole size is limited by real-world drilling and plating capabilities.
Smaller holes take longer to drill and are more prone to centering errors.
When hole depth exceeds six times the diameter, consistent copper plating on the hole wall becomes nearly impossible to achieve.
Balancing design goals and factory capabilities means following practical, proven guidelines.
Below are the key rules our engineering and production teams rely on for via size design in multilayer PCB via drilling.
Standard Via Size Recommendations
For general through-hole vias, the inner diameter should be at least 0.2mm (8mil), with an outer diameter of 0.4mm (16mil) or larger.
Tight layouts can go down to a 0.35mm (14mil) outer diameter as a strict minimum.
A widely used industry rule: outer via size roughly follows the formula ×2 ±2mil, based on the inner diameter.
For example:
- 8mil inner diameter: 8/14, 8/16 or 8/18mil
- 12mil inner diameter: 12/22, 12/24 or 12/26mil
BGA Via Design Rules
For BGAs at 0.65mm pitch and above, we recommend avoiding blind and buried vias whenever possible—they add significant cost.
If blind vias are necessary, stick to first-order structures (TOP–L2 or BOTTOM–L2).
Recommended dimensions for these vias are 0.1mm (4mil) inner diameter and 0.25mm (10mil) outer diameter.
Via Placement Best Practices
Never place vias directly on 0402 component pads.
While this theoretically reduces lead inductance, solder can flow into the hole during assembly, causing tombstoning and poor solder joints.
A spacing of 4–8mil between vias and pads works best in most designs.
Hole-to-hole spacing also needs careful attention.
Drilling too close together often leads to broken drill bits and damaged holes.
We suggest a minimum spacing of 0.5mm; spacing between 0.35mm and 0.4mm is high-risk, and anything below 0.3mm should be avoided entirely.
Via Tenting & Plugging Requirements
Most vias ≤0.5mm (except dedicated thermal vias) require plugging and ink covering, especially those with an inner diameter under 0.4mm.
This prevents solder wicking and short circuits during assembly.
For components with metal housings, avoid placing vias directly beneath them.
If vias are unavoidable, they must be plugged and covered to prevent shorts between the housing and plated holes.
From factory feedback, BGA vias placed too close to pads are a frequent engineering issue.
Uneven spacing between vias and BGA pads weakens solder reliability and can cause bridging.
We recommend centering vias between two BGA pads, and always plugging BGA-area vias to avoid solder ball shorts.
Reinforcement for Fixed Pads
For fixed pads such as headphone terminals, buttons, and FPC connectors, adding one or two evenly placed vias under the pad helps prevent copper foil peeling.
This simple step greatly improves mechanical stability under assembly stress.
Mastering PCB drilling dimensions helps balance design performance, manufacturability, and cost.
If you need custom guidance for your high-speed or high-density project, contact OPCBA for professional PCB drilling and via design support.
