Selecting via types should be straightforward, but it's one of the most common sources of unnecessary cost in multilayer PCB fabrication. We review over 200 via specifications per week, and approximately 40% of boards quoted with blind or buried vias could route cleanly with through-hole vias and better stackup planning.
Here's the real data from our production floor — cost multipliers, lead time impacts, and the decision thresholds that tell you exactly when to upgrade.
The Quick Decision Framework
Before diving into details, here's the one-minute version:
- Through-hole vias: Baseline cost. Use for 2-8 layer boards, BGA pitch ≥0.8mm, signals below 10 GHz
- Blind vias: +25-35% cost, +3-5 days lead time. Use when BGA fanout needs partial-depth routing on 6+ layer boards
- Buried vias: +40-60% cost, +5-7 days. Reserve for 10+ layer boards with extreme inner-layer density
- Microvias (HDI): 2-3x base cost for 1+N+1, +7-10 days. Required when BGA pitch < 0.65mm
- Backdrilling: +5-10% cost, +1-2 days. Often beats blind vias for signal integrity alone
Through-Hole Vias: Still King for Most Designs
The mechanical drilling process uses carbide bits from 0.2mm to 6.35mm. Standard vias use 0.25-0.35mm drill sizes. The key constraint is aspect ratio (board thickness / hole diameter) — stay below 8:1 for standard processing, 10:1 maximum.
For a 1.6mm board, minimum reliable drill is 0.2mm (8:1 ratio). Through-hole vias remain correct when:
- Board has ≤8 layers
- BGA pitch ≥0.8mm
- Frequencies below 10 GHz
- Routing density allows adequate channels between via pads
Meet all four? Through-hole vias at baseline cost.
Blind Vias: The 25-35% Premium Question
Blind vias connect an outer layer to inner layers without penetrating the full board. The premium (25-35% on an 8-layer board) covers sequential lamination, additional drilling, and extra inspection.
Real numbers: On a standard 8-layer board costing $16-20/unit at 100-piece quantity, blind vias bring it to $20-27/unit. Lead time extends from 7 days to 10-12 days.
When they're actually justified: BGA fanout on 6+ layer boards where inner ball rows can't escape through through-hole vias because those vias block channels on every layer.
When they're over-specified: A 6-layer board with 0.8mm BGA, <300 pins. At this count, dog-bone fanout with through-holes works fine. We see this pattern weekly — adding 25-35% cost for zero routing benefit.
Buried Vias: The Most Over-Specified Via Type
Buried vias connect inner layers exclusively. Cost premium: 40-60%. Lead time: +5-7 days.
Here's the insight most guides miss: in 60% of designs we receive with buried vias, they could be eliminated by adding 1-2 layers (which is often cheaper). A 12-layer board with through-hole vias costs ~30-40% more than a 10-layer baseline. A 10-layer board with buried vias costs 40-60% more. Do the math — the simpler approach is frequently cheaper AND faster.
Microvias: When Nothing Else Works
Microvias (≤150µm, laser-drilled, 1:1 max aspect ratio) are the HDI building block. They span one dielectric layer only.
Cost: 2-3x base for 1+N+1 builds, 3-5x for 2+N+2. On a $16-20 baseline board, HDI takes you to $35-80/unit.
Stacked vs staggered: Our IST testing shows staggered configurations achieve ~40% better thermal cycling reliability (700+ cycles vs 500+ for stacked at ΔT=150°C). Use staggered for automotive/industrial; stacked is acceptable for consumer electronics where space is critical.
Backdrilling: The Signal Integrity Fix Nobody Talks About
Backdrilling removes the unused stub of a through-hole via. A 40-mil stub resonates around 18 GHz, but insertion loss degradation starts well below that — 10 Gbps signals with 60-mil stubs show measurable eye closure.
The math that matters: Backdrilling adds 5-10% to cost versus 25-35% for blind vias. If your only motivation for blind vias is stub elimination (not routing density), backdrilling achieves the same SI improvement at roughly one-third the cost.
Standard depth tolerance: ±4 mil. For most 10-25 Gbps applications, this delivers residual stubs under 10 mil — perfectly adequate.
The Over-Engineering Problem
From reviewing hundreds of designs monthly, these patterns recur:
Blind vias on low-pin-count BGAs: 0.8mm pitch, <300 pins, 6-layer board. Through-hole vias work fine here.
Buried vias where extra layers are cheaper: 10-layer with buried (40-60% premium) vs 12-layer through-hole-only (30-40% premium). The simpler board often costs less.
HDI when blind vias suffice: One or two fine-pitch BGAs surrounded by standard 0.8mm components? Mechanical blind vias at 0.2mm often work, dropping cost from 2-3x to 1.25-1.35x.
Full Cost Reference Table
| Via Type | Cost Premium | Lead Time Added | Trigger Condition |
|---|---|---|---|
| Through-hole | Baseline | 0 days | Default for all designs |
| Blind | +25-35% | +3-5 days | BGA fanout, 6+ layers, pitch ≤0.8mm |
| Buried | +40-60% | +5-7 days | 10+ layers, extreme inner density |
| Microvia (1+N+1) | 2-3x | +7-10 days | BGA pitch ≤0.65mm |
| Microvia (2+N+2) | 3-5x | +10-15 days | BGA pitch ≤0.5mm, 800+ pins |
| Via-in-pad fill | +$0.50-1.50/board | Minimal | Fine-pitch BGA, thermal pads |
| Backdrilling | +5-10% | +1-2 days | SI improvement, >10 Gbps |
All costs reference an 8-layer FR-4, 100x100mm, 1.6mm board at 100-unit quantity.
For the complete guide including via reliability data (IST testing results), DFM rules by via type, and detailed fabrication documentation requirements, see the full article on our engineering blog.
If you're uncertain whether your design needs advanced via structures, we review designs daily — our engineering team regularly identifies 20-50% cost savings by simplifying over-specified via structures. Learn more about our capabilities.
Top comments (0)