3.2 Connector Types & Mating Sequences
Keying,Connectors polarity,sit at the intersection of mechanical precision and sequenceelectrical planning.
reliability, Connectorsmaking arethem whereone carefulof designthe meetsmost humanfailure-prone hands,yet critical interfaces in electronics manufacturing. Every housing, latch, and tinypin mistakesnot becomeonly carries current but also encodes a set of human-proofing rules—whether through keying, color logic, or staged contacts. Planning the mating sequence and handling details prevents silent killers like bent pins, blowncrushed fuses,seals, or mysteriousreversed intermittents. The trick is matching families and features—keying, latch styles, and CPA/TPA (connector/terminal position assurance)—so the only possible mate is the correct one. Sequencing matters just as much: ground first to stay ESD-safe, low-force signals before high-force power, and sealed circulars last so O-rings aren’t crushed early. Small formats like FFC/FPC (flat flexible cable/flexible printed circuit) with ZIF (zero-insertion-force) latches reward calm, repeatable motions,polarity, while mezzanine stacks need guides that do the aiming, not screws. A clear visual language—Pin-1cues marks,turn colors,complex harnesses into predictable assemblies. When connectors are chosen and simpleused tugwisely, checks—turnsdownstream varietysystems intostay routine,protected—from keepingEMC polaritycompliance obviousto IP sealing—and strainproduction offruns thewith board.fewer Done right, the right plugs click in, in the right order, and everything downstream—IP seals, EMC, and test—stays happy.interruptions.
3.2.1 The goal (in one line)
Make the right plugs click in the right order—with no bent pins, no reversed polarity, and no new strain on the board or harness.
3.2.2 Connector families at a glance (what you’ll actually see)
3.2.3 Keying & polarity (make wrong impossible)
- Mechanical keys win: pick families with asymmetric shrouds, clocked shells, or coded inserts (A/B/C).
- Color logic helps humans: red = power, black = ground, blue = comms (use your plant legend).
- Mark Pin-1 triangles on PCB silkscreen, connectors, and labels; mirror the same arrow on the harness tag (19.5).
- Use CPA/TPA wherever available; add a checkbox to the SWI: “CPA engaged ✓”.
3.2.4 Planning the mating sequence (order that prevents damage)
Plan once, print in the SWI with arrows and numbers:
- Ground/chassis first where possible (earth lugs, shield clamps) → safe ESD drain.
- Blind-mates with guides next (backplane/mezzanine) → geometry set early.
- Low-force signal connectors before high-force power → avoid board bow while aligning.
- Inside to outside, bottom to top, back to front → don’t block your own access.
- Sealed circulars last → so O-rings don’t sit compressed while you keep working.
- Harness strain relief then first bend (24.1) → clamp 50–80 mm from backshell before routing away.
Rule: push on the housing/shell, never on wires or the board edge. Support the PCB behind the header.
3.2.5 FFC/FPC specifics (tiny, picky, repeatable)
- Identify latch type (flip, slide, or front-flip).
- Open fully; insert tail to silk depth line; close evenly (two thumbs).
- No fold at the latch; add polyimide strip as a strain tab if spec’d.
- Tug test: gentle pull—shouldn’t move. If it does, re-insert; never “push deeper” with tools.
3.2.6 Mezzanines & blind-mates (alignment is everything)
- Use guide pins/funnels; align by pin, not by screws.
- Press near the connector body; even pressure until you feel the travel stop.
- Verify join line is parallel; no corner high. If one side’s proud, separate and re-try—don’t lever.
- Add standoffs first; torque after mate (23.3).
3.2.7 Circular & sealed connectors (IP + torque)
- Check key clocking before engaging threads; never force a cross-start.
- Inspect O-ring: clean, undamaged, lightly lubed if spec’d (23.5).
- Hand-tight → torque to spec (SWI lists N·m).
- Engage CPA or lock ring; confirm gland/cable OD range is correct.
3.2.8 Coax & RF (quiet hands)
- U.FL / MHF: align square; press until click; remove with a nylon tool from the collar, straight up.
- SMA/TNC: finger start to avoid cross-thread; torque wrench to spec; don’t twist the coax.
- Route coax with gentle radius (≥10× OD); avoid metal edges.
3.2.9 Power connectors & staged contacts
- Many power headers/modules have staggered pins (longer ground/pre-charge). Seat fully so staging works.
- For ring lugs: serrated washer on painted chassis; torque; verify <0.1 Ω to earth.
- Never tin stranded wire for screw clamps—use bootlace ferrules (20.2).
3.2.10 Verification that takes 10 seconds (and saves hours)
- Click & flush: latch clicked, housings flush all around; no daylight at join.
- TPA/CPA: fully seated (visual line flush).
- Tug test: firm pull on the housing—no movement.
- Label check: J/P number matches SWI; polarity marks align (Pin-1 to triangle).
- Strain: first clamp is in; no bend at the connector.
3.2.11 Acceptance cues (starter)
3.2.12 Common traps → smallest reliable fix
3.2.13 Pocket checklists
Before mating
- Right connector family & key by PN; variant verified
- Pin-1/triangle aligned; labels readable
- Board supported; access clear; first clamp hardware ready
During
- Push on housing/shell; no wire force
- Hear/feel click; seat flush; CPA/TPA engaged
- For circular: O-ring clean; torque to spec
- For FFC: latch open → insert to mark → latch evenly
After
- Tug test pass; no bend at joint; first clamp ≤80 mm
- Coax routed with gentle radius; no twist
- Photos/evidence attached if your flow requires (end-A/B)