A conventional multilayer board connects its layers with mechanically drilled holes that pass through the whole panel. An HDI board drills the outer layers with a laser instead, so the connection only travels as far as it needs to. That releases the space a through-hole barrel would have occupied: more components fit in the same outline, the return path under a fine-pitch package gets shorter, and a board that would have needed extra layers stays thinner and lighter.
Stack-ups built here
- 1+N+1 — one microvia layer on each side of a mechanically drilled core, the usual first step up from a conventional multilayer board.
- 2+N+2 and 1+1+N+1+1 — two microvia layers per side, for fine-pitch BGA escape routing and denser connector fan-out.
- 3+N+3 — three microvia layers per side, where package pitch and pin count leave no other option.
- ELIC — every layer interconnected by microvias, without a mechanical core carrying through-holes.
Microvias are stacked directly on top of each other or staggered, and where a via sits inside a pad it is copper filled and capped so the pad stays flat for the paste deposit.
Microvias, drilling and plating
Microvias are laser drilled at 0.1 mm minimum, with mechanical drilling covering 0.15 mm and above at a 15:1 aspect ratio. The outer layers carry 0.075 mm line and space and copper from 0.5 oz to 20 oz, so a dense logic area and a power section can share one stack-up. After plating, the stack-up is imaged, laminated and inspected layer by layer; board profile, bow and twist and copper balance are checked against the same tolerances as the rigid line.
Materials and impedance
High-Tg FR-4 covers most HDI work, with halogen-free laminate where a customer's own approvals ask for it and Rogers, Arlon, Taconic or Nelco where the signal has to survive at high frequency. Impedance is held to ±10 % on 0.075 mm features, which is what makes dense HDI boards usable for high-speed buses as well as for miniaturised products; the same layer count in a multilayer PCB would need a larger board.
Where HDI boards are used
Consumer electronics, handheld and secure devices, security and camera systems, medical monitors and imaging, and automotive sensor and radar modules under IATF 16949:2016. Assembly runs on the same site — four SMT lines at six million chips per day down to 01005 parts, X-ray inspection and BGA rework — so the microvia under a BGA pad is inspected by the same team that placed the component.
Getting a quotation
Send the Gerber set with the intended stack-up, the finest pitch to be routed, impedance requirements and quantity. Prototypes come back in 1–3 days and medium volume in 4–10 days; process limits are listed on the capability page and the issued certificates on the certifications page.
HDI stack-ups that continue into assembly are quoted with sourcing and box build on the China PCB assembly page.
