What Are the Different Types of PCB Vias, and When?

Detailed Explanation

A via is a plated hole that electrically connects copper on two or more layers of a PCB. The simplest and most common type, a through-hole via, is drilled mechanically straight through the entire board and plated along its length, connecting every layer it passes through whether or not a given layer actually needs that connection.

Blind vias connect an outer layer to one or more inner layers without passing all the way through the board; buried vias connect two or more inner layers only, with no connection to either outer surface and no visible trace of the via once the board is fully laminated. Both require fabrication to drill and plate those connections before the remaining layers are laminated on top — fundamentally more involved than drilling a single through-hole via after the whole stack-up is already built. Microvias are a further refinement: very small (often under 150 micron), typically laser-drilled vias used in High Density Interconnect (HDI) designs to connect adjacent layers only, enabling much finer routing pitch than mechanical drilling allows.

Practical Examples

A simple four-layer board with moderate routing density can usually rely entirely on through-hole vias — the extra fabrication complexity of blind or buried vias isn't justified by the routing problem they'd solve.

A dense fine-pitch BGA on a six-layer-or-more board is a different case: through-hole vias placed under or near the BGA's pads can block routing on multiple layers at once, while microvias or via-in-pad let signals escape the BGA's tight pitch without that blockage — the added fabrication cost is the trade-off for routing density that wouldn't otherwise be achievable.

Design Considerations

• Default to through-hole vias unless routing density specifically requires more — they're the cheapest and most reliably manufacturable option, and most designs never need anything else.
• Reserve blind, buried, and microvias for genuine routing-density problems, typically fine-pitch BGAs or very high layer counts, since each adds fabrication cost and lead time.
• Confirm your fab house's minimum via size and aspect ratio (depth-to-diameter) capability before specifying any via type — this varies meaningfully between manufacturers and directly limits what's achievable.
• Account for via type in your stack-up planning, since blind and buried vias are defined by which specific layers they connect, which has to be decided alongside the stack-up itself, not after.
• HDI and complex via structures: For high-density designs where microvias, via-in-pad, or buried vias are genuinely required, professional PCB layout services incorporate the stack-up and via strategy decisions that ensure these features are used correctly and are manufacturable.

Common Mistakes

• Specifying blind or buried vias as a default "best practice" without a routing-density problem that actually requires them, adding unnecessary fabrication cost.
• Placing through-hole vias directly under a fine-pitch BGA without checking whether they block routing on layers other than the one currently being worked on.
• Forgetting that via-in-pad requires fill and cap as a fabrication step, then being surprised by a quote or lead-time increase late in the project.
• Choosing a microvia aspect ratio or size the intended fab house can't actually manufacture reliably, discovered only after the design is sent for quoting.