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Selection guide

What counts as HDI, in numbers.

A board is HDI when wiring density per unit area is higher than a conventional multilayer board can reach. In practice that means four things, and all four are measurable.

Microvia ≤ 150 µm
Trace / space ≤ 75 µm
Via pad down to 250 µm
Built by sequential lamination

Macro photograph of a printed circuit board showing an IC package, dense pad arrays and fine traces.
A populated board at macro range. Pad density and trace width are what separate an HDI stackup from a conventional one.
Conventional vs HDI

Where the two constructions actually differ.

Item Conventional HDI
Minimum via dia200–300 µm, mechanical drill75–150 µm, laser drill
Minimum trace / space100 / 100 µm (4/4 mil)50–75 / 50–75 µm (2–3 mil)
Via pad size500–600 µm200–350 µm
Layer-to-layer viaThrough-hole onlyMicrovia, blind, buried, stacked
BGA breakoutLimited — 0.8 mm pitch and above0.3–0.4 mm pitch feasible
Board thicknessTypically 1.0–2.0 mmThinner possible, 0.4–1.0 mm
Build-up structure

1+N+1 is the usual entry point, not the low end.

N is the core. Type I builds one microvia layer on each side of a 4-layer core and lands at 1+4+1 = 6 layers. Only the two buildup layers carry laser microvias; the core still uses mechanical through-holes. Two via types on one board is the norm, and the cheapest way to do it.

Cross-section of a Type I 1+4+1 HDI stackup: a four-layer core in the middle, one laser-drilled buildup layer on each face, and a mechanical through-hole passing through every layer.
Type I — 1+4+1 = 6 layers. Orange is a laser microvia and exists only inside a buildup layer; grey is a mechanical through-hole and passes through the whole board.
Type I1+N+1 · one buildup layer per side
0.65 mm BGA
Type II2+N+2 · two per side
0.5 mm BGA
Type III3+N+3 and up · copper-filled stacked vias
0.4 mm BGA
ELICEvery layer interconnect · no through-holes
0.3 mm BGA
Via choice

Stacked or staggered — this is where designs get expensive.

Stacked

Consecutive microvias line up. Copper fill is mandatory: without it the tower has nothing to stand on. Highest density, highest cost, and required for via-in-pad under fine-pitch BGA.

Staggered

Each via offsets from the one below. No copper fill needed. Cheaper, but it consumes routing area. For most boards this is the right default.

Put stacked vias only where density actually binds. Mixed via types on one board is normal, not a compromise.

Cost drivers

Four things move the price. Board size is the last of them.

HDI type, I→II→IIIabout +30–40% per added buildup layerStructure
Copper-filled viasabout +15–25%Structure
Trace / space 4/4 → 3/3 milabout +20–30%Design
Panel utilisation, volumeSmall boards utilise better; HDI is volume-sensitiveOrder

We do not publish unit prices. Fill the four rows in against your actual design and you will see where to stop — often it is cheaper to relax 3 mil back to 3.5 mil and buy another prototype round.

Not sure which type your board lands in? Send the Gerber and your BGA pitch. We will come back with the type, the step count, and the layers that will hurt.

Engineering reply within 12 hours

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