HDI PCB (high density interconnect printed circuit board)
High density interconnect boards · IPC-2226A HDI Types I–VI and the 2 [C] 1 designation, build-up order (1+N+1, 2+N+2), laser microvias and dielectric thickness, minimum trace and space, layer count and evaluation limits
An HDI (high density interconnect) printed circuit board carries more wiring per unit area than a conventional board by adding thin build-up layers joined by laser-drilled microvias, blind and buried vias to a core or in a coreless stack, so that fine-pitch parts such as BGAs can be routed in less space. Ask three things first: which HDI construction type and build-up order the design needs, what microvia size and dielectric the fabricator can laser drill, and what trace, space and layer-count limits apply before engineering evaluation.
Rigid HDI printed boards with microvia build-up layers (sequential lamination, blind, buried, stacked or staggered microvias), from 1+N+1 to higher-order and coreless constructions. Conventional multilayer boards, PCB assembly (a separate product page), flexible and rigid-flex boards and IC substrates sold alone are outside this page except where compared.
CNFX editorial research · Sources checked October 12, 2026 · 4 sources
IPC-2226A, the IPC sectional design standard for HDI printed boards, sets design requirements for organic and inorganic HDI boards and recognises six industry design types. Its designation counts HDI layers on each side of a core [C] or passive substrate [P]: a board with two HDI layers on one side of the core and one on the other is 2 [C] 1. Type I is 1 [C] 0 or 1 [C] 1 with through vias connecting the outer layers; Type II is the same with buried vias in the core; Type III is ≥ 2 [C] ≥ 0; Type IV uses a passive substrate with no electrical connection; Type V is coreless construction using layer pairs; and Type VI covers alternate constructions. Blind vias may exist in all types. [1]
PCBWay, a board fabricator, describes HDI builds in a 1+N+1, 2+N+2 … 6+N+6 notation, with six or more orders requiring evaluation. One 14-layer second-order board it shows used two laser drilling steps and three pressings, with 0.10 mm laser holes and 75/75 µm track and spacing. [2]
Editorial calculation: in that notation a 10-layer 2+N+2 board has N = 10 − 2 − 2 = 6 core layers, and two HDI layers on each side of the core would be written 2 [C] 2 in the IPC-2226A designation. The layer count is an assumed example; state both the build-up and whether microvias are stacked or staggered when you request a quotation.
Give the fabricator the Gerber or ODB++ data with the stack-up, IPC-2226A type or build-up order, layer count and board thickness, laminate material, microvia sizes and whether they are stacked, staggered or filled, via-in-pad and resin or copper fill, minimum trace and space, impedance targets, copper weights, surface finish, IPC class, panel size, quantity and lead time.
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Check the fabricator's microvia and line limits
PCBWay's HDI capability table lists blind, buried and through vias; up to 60 layers with evaluation above 30; finished copper of 18 to 70 µm; minimum trace and spacing of 0.065 mm; board thickness of 0.1 to 8.0 mm with evaluation below 0.2 mm or above 6.5 mm; minimum mechanical drilling of 0.15 mm; standard minimum laser drilling of 4 mil, with 3 mil needing evaluation; maximum laser drilling of 8 mil, where the dielectric may not exceed 0.15 mm; and a maximum aspect ratio of 14:1. [2]
Editorial calculation: 4 mil is 4 × 0.0254 = 0.1016 mm, so a standard laser microvia is about 0.10 mm across, consistent with the 0.10 mm laser holes in the second-order example; 8 mil is about 0.20 mm. These are one fabricator's limits, not IPC values; IPC-2226A has its own tables of typical HDI feature sizes and minimum drill hole sizes, which should be checked in the purchased standard. [2][1]
The laminate sets how many lamination cycles and reflows an HDI build survives. Isola's 370HR data sheet (Rev. C, 2021), a 180 °C Tg FR-4 epoxy system it describes as HDI-compatible and proven on sequential lamination designs, lists a decomposition temperature of 340 °C, time to delamination of 60 minutes at 260 °C and 30 minutes at 288 °C, Z-axis expansion of 45 ppm/°C below Tg and 230 ppm/°C above, 2.8% total Z expansion from 50 to 260 °C, and a relative thermal index of 130 °C. Its Dk falls from 4.24 at 100 MHz to 4.04 at 2 GHz and 3.92 at 10 GHz while Df rises from 0.0150 to 0.0210 and 0.0250; laminates run from 0.05 to 3.2 mm with ½ to 2 oz copper. [3]
Editorial calculation: 2.8% Z expansion across a 1.6 mm board is about 45 µm of growth from 50 to 260 °C (1.6 × 0.028), strain the plated vias and stacked microvias must carry at each reflow; ask the fabricator which laminate and how many lamination cycles its HDI order uses. [3]
A second fabricator's tables show how laser via limits tie to dielectric thickness. Sierra Circuits (ProtoExpress) lists, for standard HDI, a minimum dielectric of 3 mil (0.0762 mm), a minimum laser drill of 5 mil (0.127 mm), a minimum capture pad of 5 mil over drill size, a laser aspect ratio of 0.75:1 and a largest laser drill of 8 mil (0.2032 mm); its mechanically drilled vias go down to 5.9 mil with 7 mil minimum drill-to-copper and ±3 mil plated-hole tolerance. For advanced HDI it lists a 2 mil (0.0508 mm) minimum dielectric, a 4 mil laser drill with a 4 mil capture-pad allowance over drill, a 6 mil largest laser drill, the same 0.75:1 laser aspect ratio and up to 5 sequential lamination cycles. It cites quality reporting to IPC 6012 Class 1, 2, 3 and ES. [4]
Editorial calculation: at Sierra's 0.75:1 laser aspect ratio a 3 mil dielectric needs a laser via of at least 3 / 0.75 = 4 mil, and its standard 5 mil via with a 5 mil allowance needs a capture pad of at least 10 mil (0.254 mm); PCBWay's rule of no more than 0.15 mm (about 5.9 mil) dielectric under an 8 mil laser via works out to about 0.74:1, close to the same ratio. [4][2]
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Compare what suppliers offer
Suppliers linked to this page list HDI boards; each card links to the page reviewed.
Listings include HDI boards alongside high-layer-count, flexible, rigid-flex and metal-core boards, higher-order HDI for AI servers and data-centre equipment, and HDI fabrication with assembly services. Ask each for its build-up capability, laser via sizes, filling, line widths and IPC class.
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Trace the board build-up
This is a functional reference built from the sources cited; it is not one maker's specification.
Fill the specification fields with values for your design
An HDI board quotation needs values for your design. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the fabricator.
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
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Compiled and source-reviewed by the CNFX editorial team.
Published product pages show what a company offers, not tested performance. Confirm the legal seller, factory and scope for your order. How we source and review
· Page last updated 13 October 2026
Buyer questions
What are the HDI types in IPC-2226A?
Types I to VI: Type I and II with one HDI layer per side (II adds buried core vias), Type III with two or more, Type IV on a passive substrate, Type V coreless and Type VI alternate constructions. [1]
What does 2 [C] 1 mean?
In IPC-2226A it is a board with two HDI layers on one side of the core and one on the other. [1]
How small can a laser microvia be?
PCBWay lists 4 mil as its standard minimum, with 3 mil requiring evaluation; check your fabricator's own limits. [2]
Which laminate properties matter for HDI sequential lamination?
Thermal ones: Isola's 370HR lists Tg 180 °C, Td 340 °C, 60 minutes to delamination at 260 °C and 2.8% Z-axis expansion from 50 to 260 °C. [3]
What aspect ratio can a laser microvia have?
Sierra Circuits lists 0.75:1 for both its standard and advanced HDI, so a 3 mil dielectric needs at least a 4 mil laser via (editorial calculation). [4]
Sources and what still needs a direct check
Sources checked 2026-10-12. IPC-2226A is the IPC design standard for HDI boards, cited from IPC's free table-of-contents and scope sample; PCBWay and Sierra Circuits are board fabricators stating their own capabilities; Isola publishes data for its own laminate.
