1.2 Typical Products & Complexity Levels

Simple control units to high-end systems.

Box builds span from small control units to rack-scale systems, and “complexity” is rarely just parts on a BOM. It rises from how tightly things must fit, how many harnesses and shields must connect, what software and keys get loaded, and which safety or sealing claims must be proven. Treating these as adjustable dials makes planning concrete—turn one up (say, stricter IP ratings—IP means ingress protection) and the whole line design shifts. To keep that shift predictable, the material organizes real products into five practical levels and links each to fixtures, tests, and staffing that actually work on the floor. A quick scorecard turns what’s in the BOM and test plan into a level, surfacing needs like hipot (high-potential safety test), TIMs (thermal interface materials), or MES links (manufacturing execution system) before they surprise the schedule. The result is a shared language between design, manufacturing, and quality, so decisions on torque, routing, sealing, programming, and packing lead to smooth, repeatable builds.

1.2.1 What actually drives “complexity”

Not just part count. It’s a blend of:

• Assembly density (standoffs, fasteners, torque points, adhesives).
• Interconnect (harness count/length, shield bonds, RF).
• Software (programming, keys, calibration, variant options).
• Regulatory (earth/hipot/leakage, EMC gaskets, IP seals).
• Thermals & mechanics (TIMs, fans, airflow, tight cosmetics).
• Variant spread (SKUs, regional labels, accessories).
  
  

Use these as dials when scoping a new box.

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1.2.2 Five levels you’ll actually see (with examples)

Level	Typical product	What makes it simple/hard	Tester needed	Setup you want
L1 – Simple control unit	Small controller, sensor hub, wall thermostat	1–2 PCBAs, few fasteners, 1 harness or none, light labels	Continuity/power-on, basic I/O	Single bench or U-cell; paper SWI → later MES
L2 – Modular panel	DIN-rail panel, PSU tray, fan wall	Multiple subassemblies, torque map, 3–6 harnesses, earth test	Functional with loads, earth continuity	Small flow line; torque tools w/ presets; routing map
L3 – Connected device	Gateway, HMI, NVR, set-top	Programming, keys/MACs, storage, antennas, thermal pads	Scripted FCT, network check, soak	Fixtures for alignment, label station from MES, thermal/TIM kit
L4 – Rugged/IP system	Outdoor node, vehicle controller	Gaskets, 360° shield bonds, IP67 seals, heat spreaders	FCT + hipot/leakage, IP spray/dunk	Seal stations, gasket compression checks, 100% visual gates
L5 – High-end/rack system	1–4U server, cabinet/kiosk	Many modules, airflow management, variant kits, safety	Full FCT, burn-in, safety (earth/leakage), network	Conveyor/cell hybrid, kitting supermarket, serialized accessories

If it ships to the field solo and takes a screwdriver to open, it’s at least L2–L3.

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1.2.3 Effort by level (what to plan for)

Area	L1	L2	L3	L4	L5
Steps/unit	10–25	25–60	60–100	80–140	120–250
Torque points	2–6	6–20	10–30	20–40	40+
Harness touchpoints	0–2	3–8	5–12	8–15	15+
Programming ops	0	0–1	1–3	1–3	2–6
Safety tests	Rare	Earth	Earth	Earth + Hipot/Leakage	Earth + Hipot/Leakage
Cosmetic sensitivity	Low	Med	High	High (seals)	Very high (front panels)
Pack complexity	Low	Med	High	High	Very high (accessories/rails)

Numbers are guidance—use your BOM and test plan to size the cell.

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1.2.4 Complexity scorecard (10-minute estimate)

Give each item 0–2 points; sum for a rough Complexity Score.

• PCBAs ≥3 (1), ≥5 (2)
• Harness interfaces ≥6 (1), ≥10 (2)
• Programming/keys ≥1 (1), secure/provisioning (2)
• Gaskets/IP seals present (1), IP67/69K (2)
• Earth/hipot/leakage (1), plus RF/antenna tuning (2)
• TIMs: pads only (1), paste/shims map (2)
• Variant options ≥3 (1), ≥6 (2)
• Cosmetic grade B (1), grade A/retail (2)
  

Score → Level (rule of thumb)

0–3 → L1, 4–6 → L2, 7–9 → L3, 10–12 → L4, 13+ → L5.

Use this to pick fixtures, staffing, and test depth.

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1.2.5 Risks & first fixes by level

• L1: Risk: complacency (wrong labels, loose standoffs). Fix: one-page torque/label check; single fixture for alignment.
• L2: Risk: stripped threads/grounding misses. Fix: torque audit per shift; earth bond tile; star washer callouts.
• L3: Risk: key/memory mix-ups, thermals. Fix: scan-to-program, checksum verify; TIM kit with photo map; 5-min thermal sanity soak.
• L4: Risk: leaky seals and long shield pigtails. Fix: gasket compression gage; 360° backshells; IP spray sample per lot.
• L5: Risk: variant chaos and airflow mistakes. Fix: SKU scan unlocks SWI/labels; airflow arrows & tape-out in chassis; burn-in matrix.
  
  

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1.2.6 Staffing & line design patterns

• L1: 1–2 operators, one bench, torque driver + small tester.
• L2: 2–4 operators in U-cell; kitting cart; torque tools with presets; quick routing fixtures.
• L3: 3–6 operators; two fixtures (mech + test) in ping-pong; label/program station tied to MES; small burn-in rack.
• L4: 4–8 operators; seal station, leak/IP fixture; E-stop & hipot cage; dedicated visual gate.
• L5: Cell + conveyor; feeder lines for subassemblies; ICT/FCT + burn-in bays; pack cell with accessory supermarket.
  

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1.2.7 When to upgrade the process

• Change from L2→L3 when: programming & calibration show up, or test >5 min. → Add MES recipe push, image vault, and soak.
• L3→L4 when: IP claims or safety testing appears. → Add gasket gauges, hipot cage, 100% shield/earth checks.
• L4→L5 when: rack/cabinet scale or >6 variants. → Add product wheel, accessory kitting, separate pack line.
  

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1.2.8 Example mapping (three real-world flavors)

• Wall thermostat (L1→L2): snap-fit enclosure, 4 screws, one ribbon. Key risks: wrong faceplate label, cracked standoffs. Fixtures: bezel locator, torque driver 0.4–0.6 N·m.
• Outdoor gateway (L3→L4): PCBAs + LTE modem, GPS, IP67 gland, shielded harness. Risks: gasket nicks, antenna mis-seat. Needs: 360° shield clamp, IP spray, GNSS lock test, 700–1000 VDC hipot to chassis.
• 2U network appliance (L5): hot-swap fans/drives, rails, airflow baffles, dual PSUs. Risks: reversed fans, missing EMI fingers, thermal pads mis-placed. Needs: torque map, airflow verification, 30–60 min burn-in, label/IMEI/MAC control.
  
  

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1.2.9 Pocket checklist — scoping a new box build

• Count PCBAs/harness interfaces; assign a level (L1–L5) with the scorecard
• Identify tests: function, earth/hipot, IP, burn-in; estimate durations
• Note seals/TIMs and airflow features; plan gauges/fixtures
• Confirm programming/keys flow; tie to MES and label set by SKU scan
• Choose line pattern (bench/U-cell/conveyor) and staffing
• Define acceptance: torque, cosmetics, label map; first-article plan
  

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Bottom line: name the level, pick the fixtures and tests that match it, and gate the tricky bits—torque, routing, seals, programming—by scan. Do that, and whether you’re snapping a small controller or building a rack system, box build stays predictable.