3.2 Connector Types and Mating Sequences

ConnectorsConnector sitmating atis the intersection of mechanical precision andfinal electrical reliability,step makingin themBox oneBuild ofassembly. Unlike crimping (which is permanent), mating is a high-risk, repeatable process. Failure to execute the most failure-prone yet critical interfaces in electronics manufacturing. Every housing, latch, and pin not only carries current but also encodes a set of human-proofing rules—whether through keying, color logic, or staged contacts. Planning thecorrect mating sequence and— handlingor detailsusing preventsthe silentwrong killersconnector liketype — leads to bent pins, crusheddamaged seals,sockets, orpoor reversedconductivity, polarity,and whilefield clearfailure. visualThe cuesprocess turnmust complexguarantee harnessesthat intomechanical predictablealignment, assemblies.electrical Whencontact, connectorsand final locking are chosen and used wisely, downstream systems stay protected—from EMC compliance to IP sealing—and production runs with fewer interruptions.

3.2.1 The goal (in one line)

Make the right plugs clickexecuted in the rightsequence order—withdefined noby bentthe pins,manufacturer. no

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reversed

3.2.1 polarity,Connector Classification and noSelection

new

Connectors strainare oncategorized by their function and mechanical engagement method. Selection is governed by the boardrequired ordurability, harness.vibration resistance, and environmental sealing.

A)

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3.2.2Common Connector families at a glance (what you’ll actually see)

Families

Family	Typical useUse	Keying/latchLatch	Notes for assemblyAssembly
Wire-to-board crimp housingsBoard (JST/Molex/Mini-Fit/Micro-Fit)	Power & I/O (Mini-Fit/Micro-Fit)	Polarized housing + latch; TPA/CPA on manyCPA.	Push on the housing (not wires); verify TPA/CPA; is fully engaged; partial mates are common—use tug test
Board-to-board / mezzanine	PCBA stacks	Mechanical keys; sometimes guide pins	Support both boards; press straight down; use guide posts; never “pull in” with screwstest.
FFC/FPC (ZIF/LIF)	Displays, compact links (ZIF/LIF).	ZIFLatch (flip/slide latchslide).	Open fully;latch fully; insert to depth mark; close evenly; no crease at exit.
Circular sealed (M8/M12/Bayonet)Sealed	Rugged/IP links (M8/M12).	Keyed shells; coupling nutnut.	Align key; hand-tight then torque to spec;spec; check O-ring/gasket; CPA if presentgasket.
D-sub / Micro-D	Legacy,Legacy rugged serialserial/parallel.	JackscrewsJackscrews.	Start threads by hand; torque evenly;evenly; avoid twisting the shell
RJ45/RJ12	Ethernet/telephony	Tab latch	Route to avoid tab stress; check link LEDs post-power
USB-A/C, HDMI	Consumer I/O	Form factor keyed	Straight insertion; no side load; protect during testshell.
Coax (U.FL/SMA)	RF / High frequency.	Snap-on or threadedthreaded.	Align carefully; clickclick/torque (U.FL)to / torque (SMA);spec; cap unused ports.
Blade/power modulesPower	High currentcurrent.	Polarized; staged pins.	Seat square; mindconfirm staggeredfull pinsseating so staging (ground first)
Ring/fork lugs	Earth/PE,works power studs	Washer/serrated bite	Torque to spec; record <0.1 Ω to chassis where requiredcorrectly.

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3.2.3

B) Keying &and polarityPolarity

(

• Mandate: Mechanical keys and asymmetric shrouds must be used to make wrong impossible)

insertion

• Mechanical keys win: pick families with asymmetric shrouds, clocked shells, or coded inserts (A/B/C).impossible.
• ColorPin-1 logicMarking: helpsPin-1 humans:triangles redmust =be power,marked blackon =the ground,PCB bluesilkscreen, =the commsconnector, (useand yourthe plantharness legend).
• Marklabel. Alignment of the Pin-1 trianglesmark to the triangle onis PCBa silkscreen,mandatory connectors,final and labels; mirror the same arrow on the harness tag (19.5).check.
• Secondary Lock:Use CPA/TPA (Connector/Terminal Position Assurance) devices must be used wherever available; addthe Work Instruction (WI) must include a checkboxmandatory tosign-off thestep: SWI: “"CPA engaged ✓”".
  

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3.2.42 PlanningMating theand matingUnmating sequence (order that prevents damage)Sequences

PlanThe once,order printof inengagement theis SWImandatory withto arrowsprevent physical damage (bent pins) and numbers:preserve connector durability.

A) General Mating Protocol

1. Ground/chassis firstAlignment: whereVisually possiblealign the connector body using the keying features. If using screw-lock mechanisms, engage the lead screw by hand (earth2–3 lugs, shield clamps) → safe ESD drain.turns).
2. Blind-mates with guidesSeating: nextApply (backplane/mezzanine) → geometry set early.
3. Low-force signalaxially and uniformly connectors before high-force power → avoid board bow while aligning.
4. Inside to outside, bottom to top, back to front → don’t block your own access.
5. Sealed circulars last → so O-rings don’t sit compressed while you keep working.
6. Harness strain relief then first bend (24.1) → clamp 50–80 mm from backshell before routing away.

Rule: push onalong the housing/shell,connector never on wires or the board edge.centerline. Support the PCB behind the header.header to prevent board bowing.

Locking: Confirm the primary mechanical lock engages. Listen/feel for the latch click; engage TPA/CPA where present.

Assurance: Apply final torque to jackscrews or coupling nuts as listed in the WI.

B) Flexible Circuit Mandates (FFC/FPC)

Flat Flexible Cables (FFC) and Flexible Printed Circuits (FPC) rely on Zero/Low Insertion Force (ZIF/LIF) connectors.

1. Latch

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   3.2.5 FFC/FPC specifics (tiny, picky, repeatable)

   • Identify latch type (flipOpen:, The locking bar must be opened slidefully.
   • Insertion:, orThe cable must be inserted straight, flat, and axially until the tail is fully seated at the front-flip).
   • Open fully; insert tail to silk depth line; close(silk mark).
   • Latch Close: The latch must be closed gently and evenly (twountil thumbs).it locks level with the housing.
   • Tug Test:No foldApply a light tug test to confirm capture; re-insert if it moves. Prohibited: Folding the FFC tail immediately at the latch;latch.

add

C) Mezzanine and Blind Mates

• Alignment: Use guide pins and funnels. polyimide stripProhibited: asRelying aon strainscrews tabto ifpull spec’d.parts into alignment.
• Tug test: gentle pull—shouldn’t move. If it does, re-insert; never “push deeper” with tools.
  

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3.2.6 Mezzanines & blind-mates (alignment is everything)

• Use guide pins/funnelsForce:; alignPress bystraight pin, not by screws.
• Pressdown near the connector body; even pressure until you feelverify 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)high).
  

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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.
  

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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.

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3.2.93 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).
  

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3.2.10Final Verification that takes 10 seconds (and savesIntegrity hours)Checks

Verification must confirm both mechanical retention and electrical potential.

A) Verification Test

• Click & flushFlush:: latchLatch clicked, housings flush all around;around (no daylight at join.the join).
• TPA/CPACPA:: fullyFully seated (visual line flush).
• Tug testTest:: A light, firm pull on the housing—no confirms the lock holds and prevents movement.
• Label checkCheck:: J/PVerify numberthe matchesharness SWI;Pin-1 polaritymark marksaligns with the Pin-1 triangle on the PCB.

B) Coax and Grounding Specifics

• Coax: For snap-on (U.FL), align perfectly and press until click. For threaded (Pin-1SMA/TNC), finger-start the threads to triangle)avoid cross-threading, then torque to spec (WI lists N·m). Prohibited: Twisting the coax jacket.
• StrainGround Lug:: firstFor clampring islugs in; no bend aton the connector.chassis, verify the connection has a low-ohm bond (
  < 0.1 Ω) after final torque, ensuring the serrated washer has successfully bitten through the finish.

Final

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3.2.11 Acceptance cues (starter)Checklist

FeatureMandate	AcceptCriteria	RejectVerification Action
Lock Engagement	Keying/orientationLatch clicked; shells fully home; TPA/CPA flush and engaged.	Tug TestKeys aligned;and Pin-1visual tocheck triangle;(no colorpartial code matches	Forced mate; mirrored plug; wrong color familymates).
FFC/FPC Seating	EngagementCable seated to the depth line; latch level; no crease at exit.	LatchVisual clicks;confirmation shellsthat fully home; CPA/TPA flush	Half-in;the latch riding;is CPAclosed notevenly engagedacross the width.
Threaded Mates	FFC/FPCJackscrews/coupling nuts torqued to spec N·m; threads finger-started.	Calibrated torque toolTail atused depthfor line;final latch level; no crease	Tail skew; one side high; kink at exitengagement.
Alignment Protection	Circular/IPBlind mate systems secured with guide pins/funnels.	ThreadsOperator smooth;supports torquethe toPCB spec;behind O-ringthe notheader pinched	Cross-thread;during under-torque; extruded O-ringseating.
CoaxCoax/RF Integrity	Click/Connector aligned perfectly; either click or torque correct;confirmed; no twist in cablethe cable.	Off-axisUse snap;a spunnylon coaxtool jacketfor unmating snap-on coax; never use fingernails.
Strain Relief	First clampStrain secured ≤80 mm from backshell; no bend at the cup.	FirstVisual clampconfirmation ≤80that mm;the nowire bendis at cup	Wirenot levered at header;the free-hangingtermination weightpoint.

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3.2.12 Common traps → smallest reliable fix

Trap	Symptom	Fix
Look-alike housings (same pitch, diff key)	Mis-mate, burnt boards	Use coded keys/colors; print J/P on labels; block in BOM
Partial insert on Micro-Fit/Mini-Fit	Heats under load	Tug test; require CPA; photo tile of “half-mate vs full-mate”
ZIF type confusion	Intermittent display	SWI shows latch type icon; train “open → insert → close”
Using screws to pull mezzanines together	Bowed board, cracked vias	Add guide pins; hand press square; then screw
Cross-threaded circulars	IP fail, broken shell	Hand start; torque wrench; add start-thread photo
Long shield pigtails	EMC fail	Bond at entry, 360° clamp; keep pigtail ≤10 mm

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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)

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A disciplined connector strategy—covering family selection, polarity marking, and sequence control—ensures reliable mating under real-world factory conditions. By following these practices, assemblies become faster, safer, and far less prone to costly rework or hidden field failures.