# EMS, system integration & rack-level test

Part ID: 4.02 · Layer 4 (Servers, racks & integration)

Electronics manufacturing services firms assemble, wire and burn-in the finished server or rack before it ships, standing between the ODM board build and the customer's data center floor.

EMS providers sit downstream of the board and tray builders (4.03, 4.04): they take built boards, populate chassis, route cabling, install the liquid-cooling loop hardware from layer 5, and run rack-level test and burn-in before a system leaves the factory. Several of the same companies that design and build the boards also run their own integration lines, while pure-play EMS firms take on integration and test work for OEMs that don't want to run factories themselves. AI racks make this step harder and more valuable: a liquid-cooled, multi-tray cabinet with a large number of internal cables and connectors has far more failure points to catch before shipment than a conventional 1U server, and a leak or a bad connection discovered in the field is expensive to fix. That raises the bar for test equipment and floor space, and it means integration capacity — not just chip supply — can gate how fast a rack generation ships. For investors, the signal to watch is which integrators win capacity commitments tied to a new rack generation, since qualification and yield on rack-level test tend to lag the underlying silicon ramp.

**AI delta:** AI rack complexity — liquid cooling, dense internal cabling, tight power budgets — raises the bar for pre-ship test and burn-in well past what a standard server requires.

## Companies

| Company | Role | Confidence | Ownership | Ticker | Note |
|---|---|---|---|---|---|
| Benchmark | manufacturer | inferred | public | BHE |  |
| Celestica | manufacturer | inferred | public | CLS |  |
| Compal | manufacturer | inferred | public | 2324.TW |  |
| Flex | manufacturer | inferred | public | FLEX |  |
| Foxconn (Hon Hai) | manufacturer | inferred | public | 2317.TW | US and Mexico rack-integration sites run by |
| Inventec | manufacturer | inferred | public | 2356.TW |  |
| Jabil | manufacturer | inferred | public | JBL |  |
| Kimball | manufacturer | inferred | public | KE |  |
| Plexus | manufacturer | inferred | public | PLXS |  |
| Quanta Computer | manufacturer | inferred | public | 2382.TW |  |
| Sanmina | manufacturer | inferred | public | SANM |  |
| Wistron | manufacturer | inferred | public | 3231.TW |  |

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