2.1 Chassis & Enclosure Prep

Cleaning, inspection, and finishing checks.

Great box builds start with honest metal and plastic. The enclosure’s finish and geometry decide whether torque holds, gaskets seal, and shields conduct—or whether squeaks, leaks, and stripped threads steal the day. Coatings and treatments like powder coat, anodize, and plating each bring benefits and pitfalls, especially around bond pads for EMC (electromagnetic compatibility) and seal lands for IP (ingress protection). Cleanliness and handling matter just as much: lint, chips, or oily residues travel into labels, threads, and gasket grooves where they become slow, expensive problems. By defining what “good” looks like up front—flat, square, conductive where needed, and truly clean—the rest of assembly becomes predictable rather than a rescue mission.

2.1.1 Why this step matters (the 60-second view)

Box build lives or dies on the metal/plastic you start with. Clean, square parts with good threads, true gasket lands, and ready bond points make the whole line calm. Dirty, chipped, or warped parts? You’ll fight squeaks, leaks, stripped screws, and EMC ghosts all day. Prep once, build fast.

2.1.2 Finishes & materials—what to watch (at a glance)

Material/Finish	What it gives	Hot spots to inspect
Powder coat (steel/alum.)	Durable color/cosmetics	Mask lines on gasket/bond lands, orange peel, chip at edges, thickness at threads
Wet paint	Color uniformity	Runs/sags, cure, softness (print-through)
Anodize (AL)	Hard surface, color	Insulating—needs masked bond lands; color variance lot-to-lot
Chromate/Alodine	Corrosion protection, conductive	Staining/blotches (cosmetic), chemical residue
Zinc/Ni plating	Conductivity, corrosion	Burn marks, thread growth (Go/No-Go tight)
Bare stainless	Corrosion resistance	Burrs, tea staining (cleaning), sharp edges
Molded plastic	Lightweight detail	Sink marks, gate blush, warp/flatness at gasket grooves, boss integrity

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)

Color/gloss uniform on Grade A; no scratches visible at arm’s length under diffuse light.
Edge breaks: safe to touch (no burrs/sharp).
Flatness of mating planes/gasket lands: within 0.3–0.5 mm across span (or 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/calipers and a flat plate for quick checks. Record any trend by vendor/lot.

2.1.4 Threads, inserts & captive hardware

Thread gauges (Go/No-Go) on a sample per lot and all critical holes. Powder/paint should not choke threads.
PEM®/rivnuts/studs: head seated flush, no spin; press marks even; studs perpendicular (sight with square).
Captive screws/hinge pins: retainers present; no wobble beyond spec; grease only where called out.
Debris control: no chips in blind holes—chase & vacuum; avoid oily taps that bleed into gaskets/labels.

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

2.1.5 Bonding & EMC lands (conductivity on purpose)

Paint-scrape pads: present, the right size, and unclogged; edges crisp (no overspray).
Continuity check: shell-to-land < 0.05–0.10 Ω with a low-ohm meter.
Gasket frames (conductive foam/finger stock): straight, seated, and not compressed yet; fastener holes aligned.
Anodize is insulating: ensure masked bond pads or installed bond studs exist per drawing.

2.1.6 Seal surfaces & IP readiness

Gasket grooves/lands: clean, no powder beads, no nicks. Wipe with lint-free + approved solvent.
Compression targets (starter): silicone foam 25–35% of thickness; o-rings 15–25%—confirm with gauge/tape test on first article.
Drain paths/weep holes clear; no paint clots.
Fastener pitch vs seal spec: all holes present; no cross-thread risk when compressed.

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

Gloves on Grade A handling; ESD strap 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-pull on 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; equal 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 washer buzz.
Foam bumpers present where drawings call them to prevent buzz.

2.1.10 Data to capture (so problems are traceable)

Enclosure PN/Rev, vendor lot, finish type/color code, film thickness (if measured).
Thread/insert audit results, bond resistance readings, flatness/standoff spot checks.
Rework/touch-ups with photos and location. Store per lot in MES.

2.1.11 Rework rules (what’s okay, what’s not)

Allowed (record it):

Thread chase to clear coating; no re-tap to larger size without PE/QE sign-off.
Minor edge de-burr; tiny paint touch-up on Grade B faces.
Clean/buff small scuffs on Grade A if they become invisible at arm’s length.

Not allowed (scrap or MRB):

Paint or anodize on gasket/bond lands; powder lumps in threads that won’t chase clean.
Warped panels beyond flatness spec; spun inserts or leaning studs.
Through-finish corrosion, deep gouges on Grade A, or label zones that fail tape-pull.
Any change that alters EMC/IP function without engineering release.

2.1.12 Common traps → smallest reliable fix

Trap	Symptom	First move
Powder in threads	Screws bind/strip	Go/No-Go audit; chase & vacuum; reject repeat offenders
Paint on bond pads	High shell-to-earth Ω	Rework: scrape to bare per drawing; re-measure <0.1 Ω
Mask creep on gasket lands	IP leaks	Scrape/recoat not allowed → MRB; don’t “silicone it”
Hidden burrs	Harness jacket nicks	Edge-break pass; add edge guards where the route passes
Warped lids	Uneven gasket compression	Check flatness; shim only if drawing allows; else MRB
Touch-up on A-surface	Customer complaints	Limit touch-up to Grade B; escalate otherwise
Oily residues	Labels lift/fish-eye	Enforce cleaning SOP; solvent swap; adhesion test gate

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)

Bottom line: verify geometry, threads, seals, and bonds before the first screw goes in—and clean like you mean it. A prepared enclosure makes torque honest, gaskets seal, shields conduct, labels stick, and the whole box build flows without surprises.