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The Complete Guide

HDI PCBs fit more routing into less space.

High-density interconnect boards use microvias and thin build-up layers to escape fine-pitch BGAs and run high-speed signals that standard multilayer boards can't. This guide covers HDI types, microvia engineering, materials, cost, and DFM — so you specify the right stackup instead of overbuilding it.

Start with HDI types Get an HDI PCB quote
Type I · 1+N+1
One build-up layer
Single microvia layer each side. Entry-level HDI for moderate BGA density.
Type II · 2+N+2
Two build-up layers
Stacked or staggered microvias. Denser fan-out, higher layer count.
Any-Layer · ELIC
Every-layer interconnect
Microvias on all layers. Maximum density for HPC, mobile, and AI.

HDI scales by build-up layers — more microvia layers buy density, but multiply lamination cost.

01 — The Basics

What is an HDI PCB?

An HDI (high-density interconnect) PCB packs more wiring into a smaller area than a standard multilayer board. It does this with microvias — laser-drilled holes far smaller than mechanically drilled ones — plus thin build-up layers, finer traces, and via-in-pad construction. The result is the routing density needed to escape modern fine-pitch BGAs.

The defining feature is the microvia, typically 100 µm or smaller, laser-drilled and stacked or staggered across build-up layers. Where a standard board would need more layers or larger vias to break out a dense BGA, HDI breaks it out in fewer layers with tighter geometry — which is why it dominates smartphones, HPC, networking, and AI accelerator boards.

The trade-off is process: each build-up layer is a separate lamination and drilling cycle, so HDI costs more per layer and demands tighter DFM. The rest of this guide is about buying exactly the HDI level your design needs — no more.

Defining featureLaser microvias
Microvia size≤ 100–150 µm
Structure standardIPC-2226 Type I / II / III
Build-up styles1+N+1 · 2+N+2 · Any-Layer
Enablesfine-pitch BGA, high-speed
Used inmobile, HPC, AI, networking
03

Microvia engineering

Microvias are where HDI reliability is won or lost. Aspect ratio, stacked vs staggered geometry, and how the via-in-pad is filled all decide whether the board survives thermal cycling or fails in the field. These are the engineering details that separate a manufacturable HDI design from a yield problem.

Microvia aspect ratio for 99.5% yield
The geometry limit that keeps laser vias reliably plated.
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Stacked vs staggered microvias
Which geometry prevents BGA failure under thermal stress.
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Copper fill vs resin fill
Choosing the via-in-pad fill for reliability and flatness.
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Passing microvia thermal cycling
Qualifying stacked microvias against reliability standards.
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04

Routing & high-speed applications

HDI exists to solve routing problems standard boards can't: escaping fine-pitch BGAs, hitting PCIe 5.0 and DDR5 signal integrity, and embedding passives to save space. These guides cover the layout techniques that turn an HDI stackup into a working high-speed design.

Fine-pitch BGA fan-out routing
Escaping dense BGAs with microvia fan-out patterns.
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HDI for PCIe 5.0 & DDR5
Stackup and routing rules for high-speed interfaces.
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Embedded passive HDI design
Moving passives into the stackup to reclaim board space.
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05

Materials for HDI & high-speed

HDI build-up materials have to laminate cleanly in thin layers and hold signal integrity at speed. Matching the laminate to your data rate — from FR408HR to Megtron cores used in AI-server stackups — is what keeps loss and delamination in check.

Match HDI materials to signal speed
Choosing the laminate class for your data rate.
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Megtron 4: the core of NVIDIA stackups
Where the M4 core fits in high-speed HDI builds.
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FR408HR in AI-server hybrid stackups
The workhorse laminate behind many hybrid HDI builds.
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Megtron 6 material guide
Low-loss laminate specs for demanding high-speed HDI.
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06

Cost & DFM

Every build-up layer is a separate lamination and laser cycle, so HDI cost scales with structure — and small DFM misses turn into yield loss. The table shows how structure drives cost; the guides cover how to check DFM and cut sequential-lamination cost without dropping density you need.

HDI structure Microvia layers Relative cost Typical use
1+N+1 1 each side $$ Moderate BGA density, entry HDI
2+N+2 2 each side $$$ Dense fan-out, high-speed interfaces
Any-Layer / ELIC All layers $$$$ Mobile, HPC, AI accelerators
HDI vs standard PCB cost
What the density premium actually buys you.
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Cut sequential-lamination cost 30%
Structure choices that reduce build-up cost.
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HDI DFM checklist for layout
The manufacturability checks to run before release.
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07 — Common Questions

HDI PCB FAQ

What makes a PCB "HDI"?
An HDI PCB uses microvias (laser-drilled, typically ≤150 µm), build-up layers, and finer lines than a standard board, giving higher interconnect density. IPC-2226 defines the structure types. The practical trigger is a fine-pitch BGA or high-speed interface that a standard multilayer board can't route — see 7 signals you need HDI.
What is the difference between 1+N+1 and any-layer HDI?
1+N+1 has one microvia build-up layer on each side of the core; any-layer (ELIC) has microvias on every layer. More build-up layers mean higher density but more lamination cycles and cost. The stackup guide walks through the choice.
Are stacked or staggered microvias more reliable?
Both are used, but stacked microvias concentrate more thermal stress and need tighter process control, while staggered vias spread the stress. The right choice depends on density and reliability targets — covered in stacked vs staggered microvias.
How much more does an HDI PCB cost?
HDI costs more because each build-up layer is a separate lamination and laser-drill cycle. The premium scales with structure — 1+N+1 is modest, any-layer is the highest. Our HDI vs standard cost guide breaks down where the money goes.
Do I need HDI for PCIe 5.0 or DDR5?
Often yes — the fine-pitch BGAs and signal-integrity margins of PCIe 5.0 and DDR5 usually require HDI microvia fan-out and controlled stackups. See HDI for PCIe 5.0 & DDR5 for the routing and stackup rules.

Ready to build your HDI PCB?

QueenEMS manufactures 1+N+1 through any-layer HDI with laser microvias, via-in-pad, and controlled high-speed stackups — with DFM review before you release.

Get an HDI PCB quote