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2.1 Chassis and Enclosure Preparation

The chassisChassis and enclosure formpreparation is the stagemandatory onfoundation whichthat everydictates otherthe partsuccess of afinal boxassembly. buildFailure mustat perform.this Theirstage geometry,— finish,neglecting andto cleanlinessverify determine whether fasteners bite correctly, gaskets compress evenly, andelectrical grounding paths workor asremove intended.machining Treatmentsdebris — introduces catastrophic latent failures like anodize,intermittent powder coat, or plating add protectionshorts and aesthetics,thermal butfailures. theyPrep alsomust introduceeliminate risks—especiallyForeign whereObject conductivityDebris or sealing is non-negotiable. By treating preparation as a controlled process rather than a formality, factories avoid a cascade of squeaks, leaks,(FOD) and electricalensure ghostsstructural thatintegrity otherwiseagainst erodeall qualitydefined andtolerances speed.before sensitive electronic sub-assemblies are installed.

2.1.1 WhyIncoming thisVisual stepand mattersDimensional (the 60-second view)Integrity

BoxAll buildsurfaces livesand orcritical diesdimensions onmust be verified against the metal/plasticdesign you start with. Clean, square parts with good threads, true gasket lands,drawing and readyquality bondspecification pointsupon makereceipt.

the

A) wholeSurface line calm. Dirty, chipped, or warped parts? You’ll fight squeaks, leaks, stripped screws,Grading and EMCAcceptance

ghosts
  • Grade all day. Prep once, build fast.


    2.1.2 Finishes & materials—what to watchA (Customer-Facing): Bezels, lids, and primary label zones. Mandate: Color and gloss must be uniform; no scratches visible at aarm's glance)length under diffuse light.

  • Grade B (Internal/Hidden): Bracket interiors and hidden sides. Minor cosmetic blemishes are allowed, provided they do not compromise function (e.g., no exposed base metal).

Material/Finish

WhatCritical itInspection gives

Hot spots to inspectPoints

Powder coatCoat/Wet (steel/alum.)Paint

Thickness at threadsDurable, color/cosmetics

Maskmask lines on gasket/bond lands, orangeruns/sags, peel, chipchips at edges,sharp thickness at threads

Wet paint

Color uniformity

Runs/sags, cure, softness (print-through)edges.

Anodize (AL)Aluminum)

HardMust surface,verify color

Insulating—needs maskedif bond lands were masked, as anodize is insulating. Color variance; color variance lot-to-lot is common.

Chromate/AlodinePlating (Zinc/Nickel)

CorrosionCheck protection, conductive

Staining/blotches (cosmetic), chemical residue

Zinc/Ni plating

Conductivity, corrosion

Burn marks,for burn marks and thread growth (potential Go/No-Go (Go/No-Gotight tight)

Bare stainless

Corrosion resistance

Burrs, tea staining (cleaning), sharp edgesspots).

Molded plasticPlastic

Lightweight detail

Sink marksWarp/flatness, gate blush, warp/flatness at gasket grooves, bosssink marks, and integrity of mounting bosses.


B)
Dimensional

2.1.3 Incoming visual & dimensional (grade A/B surfaces)

Grade A (customer-facing): bezels, lids, label zones.

Grade B (internal): hidden sides, bracket interiors.

Starter acceptance (tune to your spec)

Verification
  • Color/glossFlatness: uniformMating onplanes Gradeand A;gasket nolands scratchesmust visiblebe at arm’s length under diffuse light.
  • Edge breaks: safeverified to touchbe within the drawing tolerance (no burrs/sharp).
  • Flatness of mating planes/gasket lands: withintypically 0.3–3 – 0.5 mm across spanthe (orspan). drawing).
  • Hole patterns: ± 0.2–0.5 mm to datum; slots free of powder buildup.
  • Standoff heights: within ±0.1–0.2 mm (critical boards).

Use feelers/calipersfeeler gauges and a flat plate for quick spot checks.

  • Tolerance Check: Standoff heights for critical boards must be within tight limits (e.g., ± 0.1 to 0.2 mm). Record any consistent dimensional trend by vendor/lot.


    • 2.1.42 Threads, insertsInserts, &and captiveGrounding hardwareLands

    The mechanical and electrical interfaces are defined by the fastener system and the bonding pads.

    A) Thread and Fastener Preparation

    • Thread Gauge Mandate: Thread gauges (Go/No-Go) must be used on a sample per lot and on all critical holes. Powder/Powder coat or paint shouldmust not choke threads.
    • Insert Integrity: chokePEMs threads.
    • PEM®/rivnuts/studs(self-clinching nuts): headand rivnuts must be fully seated flush,flush, noshow spin;even press marksmarks, even;and studsbe verified for perpendicularanti-spin (capability. Studs must be visually checked for perpendicularity using a sight with square).
    • Captive screws/hinge pins: retainers present; no wobble beyond spec; grease only where called out.square.
    • Debris controlControl:: no chips in blind holes—chase & vacuumProhibited:; avoid oilyOily taps that bleed into gaskets/labels.gasket lands. All blind holes must be chased and vacuumed to ensure zero internal chips (FOD risk).

    Quick

    B) torque proof: sample fastener to spec N·m without paint shear or insert spin.


    2.1.5Electrical Bonding &and EMC lands (conductivity on purpose)

    Lands
    • Paint-scrapeScrape Pads: Grounding pads: must be verified to be present, of the rightcorrect size, and uncloggedclear of paint or anodize;. edgesEdges must be crisp (no overspray).
    • Continuity checkCheck:: The shell-to-land <continuity 0.05–0.10must Ωbe checked with a low-ohm meter. Mandate: Resistance must be less than 0.05 – 0.10 Ω to the chassis safety ground reference point.
    • GasketEMC framesGaskets: (conductiveConductive foam/foam or finger stock):stock straight,gaskets seated,must be inspected for proper seating, alignment with fastener holes, and notabsence compressedof yet;compression fastenerdamage holesprior aligned.
    • Anodizeto islid insulating: ensure masked bond pads or installed bond studs exist per drawing.installation.


    2.1.63 Sealing, Function, and Cleanliness

    These steps prepare the enclosure for environmental protection and ensure the final functional usability of doors and access points.

    A) IP Readiness and Seal surfaces & IP readiness

    Surfaces
    • Gasket grooves/landsPreparation:: clean,Gasket nolands must be clean and free of powder beads,beads or nicks. no nicksMandate:. Wipe with lint-free +cloth and approved solvent.solvent (e.g., IPA).
    • Compression targetsTargets: Compression must be predictable. For first articles, confirm compression targets (starter):e.g., silicone foam 25–25% – 35% of thickness;thickness) o-ringsusing 15–25%—confirma withgauge gauge/or tape test on first article.test.
    • Drain paths/Paths: Drain paths or weep holes must be checked to be clear of paint clots or weld spatter.

    B) Final Mechanical Function

    • Door Alignment: clear;Hinge nolines paintmust clots.be straight, the lid must sit without rocking, and the reveal (gap) must be equal left and right.
    • FastenerLatch pitchFunction: vsLatches sealand spec:cams allmust holesengage present;smoothly. noCheck cross-thread risk when compressed.


    2.1.7 Cleaning & handling (keep it Class “box build clean”)

    • Gloves on Grade A handling;for ESD straprattle when PCBs are near.
    • Wipe sequence: blow off filtered air, then lint-free + IPA (or approved cleaner), then dry.
    • No silicone residues unless design calls for it (label fish-eye risk).
    • FOD control: parts trays with lids; FOD can at the cell; magnet sweep for steel chips weekly.
    • Protective films: peel with two hands, low angle, away from gasket lands; bag and trash immediately.

    2.1.8 Labels, adhesives & cosmetics setup

    • Label zones clean, flat, and warm (≥ 15–20 °C). Do —a tape-pullgentle onshake paint if adhesion is suspect.
    • Adhesive tapes (EMI/rubber feet): check primer or scuff area if spec’d; press time ≥ 3–5 s with roller; observe cure dwell if required.
    • Touch-up paint only on non-sealing, non-bond Grade B areas—and only if your cosmetic spec allows (document color code). Never on gasket lands or bond pads.

    2.1.9 Doors, hinges, latches & alignment

    • Hinge line straight; equalmust reveal left/right; lid sits without rocking.
    • Latch/cam engages smoothly; no metal-on-metal scrape where a glide is specified.
    • Rattle test: gentle shake—no loose captive screws or washerwashers. buzz.
    • Foam bumpers must be present where drawings call themspecified to prevent buzz.

    C)

    2.1.10Class Data"Box toBuild captureClean" (so problems are traceable)

    Mandates
    • Enclosure PN/RevHandling:, vendor lotGloves, finishare mandatory for handling Grade A surfaces. type/colorESD code, film thicknessstraps (ifare measured).required when PCBs or sub-assemblies are brought near.
    • Cleaning Sequence: Blow off with filtered air, wipe with lint-free cloth + IPA (or approved cleaner), and then dry.
    • Prohibited Residue: Prohibited: Silicone residues unless explicitly called out, due to the high risk of label adhesion failure ("fish-eye") and paint contamination.

    2.1.4 Data Capture and Rework Control

    A) Traceability Data

    The following data must be captured and stored per lot in the MES system:

    • Enclosure PN/Rev, Vendor Lot, Finish Type/Color Code.
    • Thread/insert audit results, bond resistance readings, flatness/standoff spot checks.
    • Rework/touch-upsup actions with photos and location.location Store per lot in MES.
      logs.

    2.1.11

    B) Rework rulesRules (what’sMandate okay,vs. what’s not)

    Prohibition)

    Allowed (recordRecord it)It):

    • Minor edge deburr.
    • Thread chase to clear coating;coating no(must not re-tap to a larger size without PE/QEengineering sign-off.release).
    • Minor edge de-burr; tinyTiny paint touch-up on Grade B faces.faces, provided it is documented.
    • Clean/buff small scuffs on Grade A if they become invisible at arm’arm's length.

    Not allowedProhibited (scrapScrap or MRB):

    • Paint or anodize on gasket/gasket or bond lands; powder lumps in threads that won’t chase clean.lands.
    • Warped panels beyond flatness spec; spunspecification.
    • Spun inserts or studs leaning studs.out of perpendicularity.
    • Through-finish corrosion, deepDeep gouges on Grade A,A surfaces or label zones that fail a tape-pull.pull adhesion test.
    • Any change that alters the EMC/EMC or IP (Ingress Protection) function without engineering release.

    Final

    2.1.12 Common traps → smallest reliable fixChecklist

    TrapMandate

    SymptomCriteria

    FirstVerification moveAction

    Grounding Integrity

    PowderPaint/anodize inremoved; threadsbond resistance verified < 0.1Ω.

    ScrewsLow-ohm bind/strip

    Go/No-Gometer audit;audit chaseusing &a vacuum;star rejectwasher repeatat offendersthe bond point.

    Surface Flatness

    PaintMating onand bondgasket padslands verified to be within 0.3 mm tolerance.

    HighFeeler shell-to-earthgauge Ω

    Rework:check scrapeagainst toa baresurface per drawing; re-measure <0.1 Ω

    Mask creep on gasket lands

    IP leaks

    Scrape/recoat not allowed → MRB; don’t “silicone it”plate.

    Thread/Insert Health

    HiddenThreads burrsclear; captive inserts/studs are flush and anti-spin.

    HarnessGo/No-Go jacketthread nicks

    Edge-breakgauge pass;check; addtactile edgespin guardstest whereon the route passesinserts.

    Cleanliness/FOD

    WarpedSurfaces lidswiped with IPA; no chips/debris in blind holes.

    UnevenMagnet gasket compression

    Check flatness; shim only if drawing allows; else MRB

    Touch-up on A-surface

    Customer complaints

    Limit touch-up to Grade Bsweep; escalateconducted otherwiseweekly; blind holes vacuumed.

    Label Adhesion Zone

    OilySurfaces residuescleaned; zone free of silicone/oil residues.

    LabelsAdhesion lift/fish-eyeverified with a documented tape-pull test if necessary.

    Rework Restriction

    No paint touch-up or material addition on Gasket/Bond lands.

    EnforceRework cleaningaudit SOP;confirms solventonly swap;Grade adhesionB testareas gatetouched up; no warp or spun inserts allowed.


    2.1.13 Pocket checklists

    At receiving (lot level)

    • PN/Rev, finish, color match PO; protective films intact
    • Grade A scan under diffuse light; no obvious dents/scratches
    • Sample flatness & standoff height; record vendor/lot

    Pre-build (unit level)

    • Threads Go/No-Go (critical holes), chips vacuumed
    • Inserts/studs tight & square; captive hardware retained
    • Bond pads clean; shell-to-pad <0.1 Ω
    • Gasket lands/grooves clean; weep holes open
    • Grade A wiped; label zones pass tape-pull
    • Films removed cleanly; FOD bin used

    Before release to assembly

    • Doors/hinges align; reveals even; no rattle
    • Touch-ups (if any) logged; none on seals/bonds
    • Data captured (lot, audits, photos if exceptions)



    A disciplined approach to enclosure prep ensures that every box build begins on a stable foundation. By verifying threads, surfaces, and seals while keeping parts clean and controlled, assembly runs smoother, defects shrink, and the finished product meets its functional and cosmetic promise.


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