# High-layer-count PCBs (HDI, backdrilled, 20–40 layers)

Part ID: 4.05 · Layer 4 (Servers, racks & integration)

The bare printed circuit boards themselves — high-density interconnect, backdrilled, 20 to 40 copper layers — that GPU and switch trays are built on.

This is the physical board substrate beneath the baseboards and switch trays (4.03, 4.04): a laminate stack of 20 to 40 signal and power layers, built with HDI microvias and backdrilling to keep high-speed signal integrity across the board. It sits downstream of the laminate and copper-foil suppliers (4.06) and upstream of everything that gets populated onto it. AI boards push layer count and manufacturing precision well past a standard server motherboard because scale-up interconnect, high pin-count sockets and dense power delivery all need more routing layers and tighter tolerances than a general-purpose board. That raises both the capital intensity of the fabrication step and the qualification burden, since a board with dozens of layers has far more opportunities for a manufacturing defect to show up only under load. For investors, this is a capacity-constrained, capital-heavy tier of the supply chain: the fabricators that can reliably hit the highest layer counts at volume are a shorter list than the board designers who spec them, and that gap tends to widen, not narrow, with each new rack generation.

**AI delta:** AI boards need far more routing layers and tighter fabrication tolerances than a standard server motherboard, because dense scale-up interconnect and high-pin-count sockets have to be routed across the same board.

## Companies

| Company | Role | Confidence | Ownership | Ticker | Note |
|---|---|---|---|---|---|
| AT&S | manufacturer | inferred | public | ATS.VI |  |
| Compeq | manufacturer | inferred | public | 2313.TW |  |
| Dongshan | manufacturer | inferred | public | 002384.SZ |  |
| Gold Circuit GCE | manufacturer | inferred | public | 2368.TW |  |
| Ibiden | manufacturer | inferred | public | 4062.T |  |
| ISU Petasys | manufacturer | inferred | public | 007660.KS |  |
| Kingboard | manufacturer | inferred | public | 0148.HK |  |
| Nan Ya PCB | manufacturer | inferred | public | 8046.TW |  |
| Shennan | manufacturer | inferred | public | 002916.SZ |  |
| Tripod | manufacturer | inferred | public | 3044.TW |  |
| TTM | manufacturer | inferred | public | TTMI |  |
| Unimicron | manufacturer | inferred | public | 3037.TW |  |
| Victory Giant | manufacturer | inferred | public | 300476.SZ |  |
| WUS | manufacturer | inferred | public | 002463.SZ |  |
| Zhen Ding | manufacturer | inferred | public | 4958.TW |  |

Confidence tags: disclosed = company/filing statement; reported = trade press or partner list; inferred = taxonomy lead.