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2.3 Mounting PCBAs, Displays and Modules

MountingThe PCBAs,installation displays,of andsensitive moduleselectronic components into the chassis is the moment when design intent becomes tangible—andpoint where smallelectrical oversightsintegrity canand ripplemechanical intostructure majordirectly failures.intersect. PrecisionThis process requires strict control over mechanical stress, ESD risks, thermal transfer, and front-panel alignment. Errors in alignment,mounting careintroduce inlatent ESDfailures, handling,making disciplined adherence to specified procedures mandatory for product function and consistencycosmetic in torque application decide whether boards sit flat, connectors last, and seals hold against dust, water, and interference. Optical elements like displays demand cleanliness and centered reveals to preserve the product’s appearance, while thermal and EMI interfaces require just the right compression to function as designed. Treating this stage as controlled, repeatable craftsmanship ensures that delicate electronics integrate seamlessly into durable assemblies.integrity.

2.3.1 WhatESD “good”and looksHandling likeProtocol (in one line)Mandates

BoardsESD sit flat, connectors mate with a click (not a bend), displays center in the window without dust or light leaks, seals compress evenly—and youcontamination stayedcontrol are mandatory during component installation.

A) ESD-safeSafe the whole time.


2.3.2 ESD-safe handling (non-negotiables)

Handling
  • Mandate: ESD mat +and wrist strap must be checked at the start of shift;every ionizershift. on for plastics/films.
  • Handle boards only by edges,the not components;edges; use ESDESD-safe totes/totes and racks (nocardboard cardboard)is prohibited).
  • Atmosphere: Humidity must be controlled between 40–40% – 60% RH. helps;Avoid avoidusing sweatermaterials weather(like specific plastics or films) that generate static near open displays/boards.
  • Cleanliness: Only ESD-safe gloves/gloves or finger cots; noare talcpermitted. Talc or silicone hand creamcreams are prohibited near lenses or labels due to the risk of cosmetic failure (smears, label fish-eyes,adhesion lens smears)failure).

B) Protective Film Management

  • Keep protective films on lenses and displays until the last safe moment;moment peelbefore sealing the enclosure.
  • Peel films low and slowslow, pulling away from the sensitive gasket lands.
    lands to prevent static charge buildup or damage to the sealing surfaces.

2.3.32 PCBA and Module Mounting Sequence

Installation must follow a specific, documented sequence to prevent cross-threading and bowing.

A) Alignment &and fixturing (make the hardware do the aiming)

Fixturing
  • Pre-Alignment: Use dowel/locator pins or zero-point nests to set the board andposition; displayvisual position—don’talignment “("eye-ball.”balling") is prohibited.
  • Blind Mates: For blind-mate connectors (mezzanines,backplanes, backplanes)mezzanines), add guide pins/funnelspins; neveror funnels to the chassis; rely on screwsguide pins, not screws, to pull parts into alignment.
  • Displays: use a window template/bezel gauge so the active area centers before adhesive touches.
  • Keep first clamp before first bend on any attached harness (19.4/19.5): clamp within 50–80 mm of the connector.


B)
Installation

2.3.4 PCBA mounting sequence (repeatable, gentle)

Protocol
  1. PrepPrep:: verifyVerify standoff height and flatness on the chassis (23.1).chassis. Confirm screws/torque from the map (23.2).map.
  2. Dry fitFit:: layLay the board on standoffs; checkconfirm hole alignment with a plastic pick—noforcing forcing.is prohibited.
  3. Start by handHand:: insertInsert all screws 2–3 turns by hand to avoidprevent cross-thread.threading.
  4. PatternTorque Pattern:: seatSeat screws lightly corner-to-corner, then final torque in a cross cross-pattern. sequence.
  5. ConnectVerification: The finished board must not be bowed (bow ≤ 0.5 mm across the card). The gap over all standoffs must be even.

C) Connector Engagement

  • Mezzanines / Board-to-Board: Press straight down using thumb pads near the connector; avoid pressing at the board edge, which causes bowing.
  • FFC/FPC (ZIF/LIF): mateOpen board-to-boardthe latch fully, insert the cable to the depth mark, and harnessclose connectorsthe squarely;latch evenly. Do not route the tail with a tight fold immediately at the latch.
  • Acceptance: After mating, listen/feel for the latch click;click; engage TPA/CPA where present.
  • Verify: board not bowed; gap over standoffs even; no harness strain on headers.

    • Starter torque (validate on your joint):

    M2: 0.2–0.3 N·m, M2.5: 0.35–0.6 N·m, M3: 0.6–1.0 N·m (23.2.5).


2.3.53 ConnectorsThermal you’llInterface meetManagement (andTIM)

how

Thermal notdissipation tooften breakrelies them)on precise application of TIM. Surfaces must be perfectly clean.

  • Mezzanines / board-to-boardPrep:: pressBoth surfaces must be cleaned with straightIPA downimmediately before TIM application.
  • Paste: Use a bead diameter gauge from the TIM kit. Apply the pattern per the Work Instruction (e.g., lines or X pattern). Torque the heat sink in a two-pass sequence (50% – 100%) using thumba padscross-pattern.
  • Pads: nearPeel theliners connector; neveronly at the boardmoment edge.of Use guide pins if available.
  • FFC/FPC (ZIF/LIF): open latch fully, insert to the line, close latch evenly; tug test (light) to confirm capture; route the tail with no fold at the latch.
  • Wire headers: support the board behind the header during mate; no harness pulling as a lever.
  • Coax (U.FL, etc.): align carefully, press until click; pop up with a nylon tool, not your nails.


2.3.6 Thermal interfaces while mounting (TIMs without mess)

  • Pads: peel liners last;placement; place with tweezers; avoid stretching;stretching nothe fingerprints.pad.
  • Paste: bead diameter gaugeCheck: from the TIM kit (22.3); apply pattern per SWI (lines/X), two-pass torque on heatsink (50% → 100%).
  • Checks:Verify light, even squeeze-out at edges; no paste on connectors;connectors; thermal sensors read sane after power-on.

2.3.74 Displays, Sealing, and Acceptance Cues

Installation of displays requires strict cosmetic and environmental sealing protocols.

A) Displays &and lightpipesSealing (centered, clean, sealed)

Prep

Protocol
  • Cleaning Prep: Clean the window and lens with the OEM-approved wipe. IPA is prohibited if the anti-glare coating is sensitive.
  • Mounting: Align the display using a window andtemplate; lens withtack the approved wipe (many anti-glare coatings hate IPA—use OEM wipe).
  • Stage gasket/adhesive and alignment template; keep dust down (ionizer + sticky mat).

Mount

  • Align with template; tack top edge first, then roll down—avoiddown to prevent air traps/bubbles.
  • Gasket Integrity: O-rings must be lightly oiled if specified; aim for 15% – 25% compression. Foam gaskets require 25% – 35% compression. Use a criss-cross torque sequence on multi-fastener sealed frames.
  • IfFinal using foam/EMI gasketCheck: around the display, confirm gap-free corners (no stretched miters).
  • Seat lightpipes fully; verify they don’t preload the PCB.

Finish

  • Peel the outer film only after a dust check under diffuse light.
  •  Run a light leak test (dim room, max backlight): nozero bright seams;seams uniformare bezel glow.permitted.


B)
Quick

2.3.8 Sealing (IPVerification and EMC) done right

  • O-rings: light oil if spec’d; compress 15–25%; use criss-cross torque.
  • Foam gaskets: aim 25–35% compression; do not crush—check with feeler/tape stack on first article.
  • EMI fingers/foam: require clean bond pads (23.1.5); verify continuity < 0.1 Ω across the seam.
  • Adhesive beads: steady bead diameter per SWI; no gaps/strings; keep off label zones. Cure per chemistry before test.

2.3.9 Quick verifications (catch issues now, not at test)

  • Flatness/bow: lay a straightedge; bow ≤ 0.5 mm across the card unless drawing says otherwise.
  • Earth bond: PSU tray or board lug to chassis < 0.1 Ω (22.1/23.1).
  • Connector seating: all latches engaged, TPA/CPA clicked; ZIF bars level.
  • Display fit: reveal uniform ±0.3 mm; flushness ±0.25 mm within bezel.
  • Seal path: continuous contact print (talc or witness tape) around the frame—no holidays.

2.3.10 Acceptance cuesCues

(starter

Final tolerances—tuneaudit tomust yourensure spec)that structural and electrical integrity is maintained.

Feature

AcceptAcceptance (Target)

RejectDefect (Reject)

PCBA seatingSeating

All screws torqued; noboard visibleflatness bow;maintained standoffs≤ fully0.5 bearingmm).

Bowed board, lifted corner, cross-thread, cracked bossboss, unseated standoff.

Mezzanine mate

Parallel join line; full latch engagement

One side high, intermittent function on tap

FFC/FPC

Tail at depth mark; latch level; no kink at exit.

Half-latched; tail skew; crease at the latch or tight fold.

Lightpipe/displayDisplay Fit

Centered in window; noreveal dust;uniform no± pressure0.3 marksmm.

Light leak seam; specksSpecks under lens; skewed revealreveal; pressure marks on display.

Seals (IP/EMI)

Compression even; corners tight; bond <0.1 Ω

Gasket gaps; crushed foam; high resistance

Harness strainStrain

First clamp ≤ 80 mm from backshell; no bend at solder cup.

Wire bending at solder cup; floating,harness un-clampedpulling on the connector header.

Earth Bond

PSU tray or board lug to chassis < 0.1 Ω .

High resistance or loose star washer.

Seals (IP/EMI)

Compression even; continuous contact verified.

Gasket gaps or crushed foam; high resistance across EMC seam.


Final

2.3.11 Common traps → smallest reliable fixChecklist

TrapMandate

SymptomCriteria

FirstVerification moveAction

ESD Control

UsingWrist screwsstrap tochecked; “pull”humidity misaligned40% parts– 60% RH; only ESD-safe gloves/cots.

StrippedVisual threads,confirmation warpedof boards

Addno guidestatic-generating pins/nests;materials loosen,near re-align,the hand-startworkstation.

Torque Sequence

BowedCritical PCBfasteners aftertorqued torquein a cross-pattern sequence.

Intermittents,Tool crackedlog vias

Verifycaptures standofftorque heights;value reduceper torque;critical add mid standofffastener.

PCBA Stress

ZIFBoard half-latchedflatness maintained (bow ≤ 0.5 mm); all mounting points secured.

Flicker/noFinal image

Open,visual re-insertaudit to mark,confirm closeuniform evenly,seating tugon teststandoffs.

Display Integrity

DustPanel centered; reveal uniform; zero dust/debris under lensthe lens.

CustomerCleanliness returns

Lateprotocol filmfollowed peel;(specific ionizerwipes); on;light lint-freeleak wipe;test clean room corner if neededpassed.

Thermal Bond

Over-compressedTIM gasketapplied with cross-pattern torque; surfaces cleaned with IPA.

IPPost-power-on failsthermal later

Torquesensor inreadings twoverified passes; verify 25–35% compression with tape gaugesane.

Seating Verification

EMIAll gasketlatches onengaged; paintTPA/CPA clicked; FFC/FPC seated to depth mark.

HighTactile bondand Ω

Exposevisual bondconfirmation pad;of clean;locking re-seat; measure <0.1 Ω

Harness preload on headers

Cracked solder joints

Add clamp; reroute; service loop per drawingmechanisms.


2.3.12 Pocket checklists

Before mounting

  • ESD checks green; ionizer on; gloves clean
  • Chassis threads/standoffs verified; bond pads clean
  • Fasteners & torque map at station; bits OK

PCBA install

  • Dry fit OK; screws hand-started; cross-pattern torque
  • Connectors mated square; TPA/CPA engaged
  • TIM pads/paste per kit; two-pass torque on heatsinks

Displays/modules

  • Window & lens clean; template in place
  • Gasket/adhesive applied without gaps; corners tight
  • Reveal/flush check; light-leak check; film peeled last

Sealing & finish

  • O-ring/foam compression in range; criss-cross pattern
  • EMI seam <0.1 Ω; earth lug <0.1 Ω
  • Harness clamps set; no bend at joints



With disciplined handling, guided alignment, and verified sealing, assemblies avoid stress cracks, light leaks, and noisy intermittents. The result is hardware that looks clean, functions reliably, and keeps its integrity long after it leaves the factory.


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