Blind vs buried vs through-hole via?

Through-hole: penetrates all layers, visible from both sides. Blind: connects outer layer to inner layer(s), visible from one side only. Buried: connects inner layers only, invisible from outside. Blind and buried vias enable HDI designs with higher routing density and better RF performance by eliminating via stubs.

Why use blind vias in RF?

Through-hole vias create stubs below the target layer that act as resonant antennas at high frequencies. A via stub of 1 mm resonates at approximately 37.5 GHz in FR-4. Blind vias eliminate the stub entirely, improving return loss and reducing radiation above 10 GHz. They also reduce parasitic capacitance by 30-50% compared to through-hole.

Manufacturing cost impact?

Blind vias require sequential lamination: inner layers are drilled and plated before outer layers are added. This adds 2-4 lamination cycles, increasing PCB cost by 30-100% depending on complexity. Laser-drilled microvias (typically 100-150 micrometer diameter) cost more than mechanical drilling but enable finer pitch. The RF performance benefit often justifies the cost in high-frequency designs.

RF Design

Blind Via

A Blind Via is a plated hole in a PCB that connects an outer (top or bottom) copper layer to one or more inner layers without penetrating the entire board thickness. By eliminating the via stub that exists in through-hole vias, blind vias reduce parasitic capacitance by 30-50% and prevent stub resonances that degrade signal integrity above 10 GHz. They are essential in HDI (High Density Interconnect) designs for mmWave, 5G, and high-speed digital applications.

Category: RF Design

Typical Diameter: 100-250 μm

Understanding Blind Vias

In a standard through-hole via, the barrel extends from top to bottom layer. If a signal transitions from layer 1 to layer 3 of an 8-layer board, the remaining barrel from layer 3 to layer 8 is an unterminated stub. This stub resonates at f = c/(4·L·√ε_r), causing a notch in the signal spectrum. At 28 GHz (5G mmWave), even a 0.5 mm stub creates significant degradation.

Blind vias are fabricated using sequential lamination: inner core layers are drilled and plated first, then outer layers are added and drilled. Laser drilling enables microvias as small as 75 μm diameter for ultra-fine-pitch BGA components.

Via Stub Resonance

Quarter-wave resonance:
f_res = c / (4·L_stub·√ε_r)

1 mm stub in FR-4 (ε_r=4.2):
f = 3×10⁸/(4×0.001×2.05) = 36.6 GHz
Blind via eliminates this resonance entirely

Via Type Comparison

Via Type	Layers	Stub	Cost	RF Performance
Through-hole	All	Yes	Lowest	Poor above 10 GHz
Back-drilled	All (stub removed)	Minimal	Medium	Good to 40 GHz
Blind	Outer to inner	None	High	Excellent
Buried	Inner to inner	None	High	Excellent
Microvia (laser)	1-2 layers	None	Highest	Best (75-150 μm)

Common Questions

Frequently Asked Questions

Blind vs buried vs through?

Through: all layers, has stub. Blind: outer to inner, no stub. Buried: inner to inner, invisible. Blind/buried enable HDI and eliminate stubs.

Why for RF?

Eliminates stub resonances above 10 GHz. Reduces parasitic capacitance 30-50%. Essential for mmWave and 5G designs.

Cost?

30-100% more than through-hole due to sequential lamination. Laser microvias cost more but enable finer pitch. RF performance justifies cost.

Related Terms

← Blind Spot Detection Block ACK →