2.5 Seals, Gaskets & Waterproofing

IP rating practices and material handling.

Keeping water out isn’t just a test at the end—it’s a design choice that touches materials, surfaces, and the sequence of assembly. Seals work only when lands are clean and flat, the gasket type matches the environment, and compression is set by numbers, not “feel.” IP (ingress protection) ratings turn that into proof, from spray checks to dunk or pressure-decay, so confidence is measured instead of guessed. Adhesive-backed gaskets and FIPG (formed-in-place gasket) bring speed and complex shapes, but only if handling, cure, and storage are treated like real specs. Done well, sealing supports EMC (electromagnetic compatibility) and customer-facing cosmetics too—no leaks, no light gaps, no lifted corners. The aim is simple: choose the right gasket, apply the right squeeze, and prove it right where the work happens.

2.5.1 Why this matters (one sentence)

Water always finds the laziest path; your job is to make sure that path never reaches electronics—and to prove it on the line, not at the customer.

2.5.2 IP ratings in plain language (what you’re aiming for)

Rating	What it means (starter summary)	Typical proof on the line
IP54	Dust-protected, splash from any direction	Spray test; visual inspection of seals
IP65/66	Dust-tight; water jets (low/high pressure)	Hose spray at specified distance/angle; no ingress
IP67	Dust-tight; immersion 1 m / 30 min	Dunk test or pressure/vacuum decay check
IP69K	High-pressure, high-temp jets	Rotating lance test; gasket compression and fastener torque must be exact

Your official test method comes from the product spec. On the floor, use representative checks (spray/dunk/decay) sized for tact and risk.

2.5.3 Gasket families & where they fit

Type	Best for	Compression target	Notes
O-rings (solid elastomer)	Grooved, rigid joints (covers, glands)	15–25%	Great for lids & shafts; groove tolerances matter
Foam/foam-silicone (closed cell)	Door frames, large lids	25–35%	Easy to assemble; watch long-term compression set
Conductive foam/fingers	EMC seams + light IP	20–30%	Don’t crush flat; ensure clean bond pads
Mold-in-place (FIPG)	Complex paths, one surface	Bead height set by spec	Requires cure; repeatable with fixtures
Adhesive gaskets (PSA)	Windows, bezels	Full contact, rolled	Cleanliness rules; dwell/cure time matters
Gel/encapsulants	Cable entries, odd cavities	Fill to spec	Messy; plan cure & rework route
Cable glands & grommets	Cable pass-through	Per maker	Choose by cable Ø and IP rating; torque to spec

Material quick picks

Silicone: wide temp, UV-resistant; good for outdoor.
EPDM: great vs water/steam; avoid oils.
Neoprene/NBR: oil/fuel tolerant; check temp range.

Match chemistry to environment (cleaners, oils, UV).

2.5.4 Surface prep (seals love clean, flat, bare)

Clean: lint-free + approved solvent; no silicone residue.
Flatness: gasket lands within 0.3–0.5 mm across span (23.1).
Bare where needed: EMI bond pads unpainted; no powder beads in grooves.
No burrs: edges that touch seals must be smooth—install edge guards if harness routes nearby.

2.5.5 Compression—hit the number, not the feel

Foam gaskets: 25–35% of thickness after closure.
O-rings: 15–25% squeeze in the groove (don’t over-crush).
Conductive foam: 20–30%; just enough for contact.

How to check quickly

First article: place tape stack/feeler at corners → close → measure pullout thickness.
Look for uniform witness (light contact line) all around; no “holidays.”

2.5.6 Order of operations (so nothing fights the seal)

Prep lands (clean/inspect; bond pads exposed).
Install brackets/frames (square the geometry, 23.4).
Place gaskets (or dispense FIPG bead) and seat shields if shared fasteners exist.
Apply TIM & mount heat sinks (23.4) without smearing into seal paths.
Close the lid with a cross-pattern, two-pass torque (50% → 100%).
Verify compression and run the chosen water/decay check.

2.5.7 Cable entries: glands, grommets, vents

Glands: choose by cable OD range; tighten to maker torque; ensure strain relief is active; add 360° shield clamp ahead of the gland if EMC needs it.
Grommets: slit faces downstream; seat fully; no sharp edges in panel cutout.
Breather/vent membranes: equalize pressure (avoid “breathing” water); mount vertical; keep above splash line when possible.

2.5.8 Adhesive gaskets & FIPG (first-time right)

PSA gaskets (die-cut, with adhesive)

Wipe surfaces; prime if the spec calls it.
Align with a fixture/template; press with a roller for 3–5 s per section.
Respect dwell: initial tack now, full bond after 24 h (typical).

FIPG (formed-in-place)

Use meter-mix or syringe with nozzle gauge from the spec.
Bead size consistent; avoid gaps/overlaps; radius corners.
Skin/cure per chemistry before closure; log open time at the cell.

2.5.9 Storage & handling (gaskets are not immortal)

Store flat, bagged, out of UV/ozone; temp 15–25 °C.
Keep lot & date; many foams/adhesives have shelf life—scan at issue.
Don’t stretch or pre-compress before install; avoid creasing corners.
For lubed O-rings, use the right compatibility lube (silicone/fluorinated). Never flood PSA surfaces with oils.

2.5.10 Quick tests you can run on the line

Spray check (IP54/65/66 proxy): 5–10 min multi-angle; towel inside stays dry.
Dunk (IP67 proxy): 30 min at 1 m (or agreed depth/time for sampling).
Pressure/vacuum decay: plug ports, apply low pressure; stable reading = good (great for high mix).
Talc/witness tape: close on a dusted seal; open → continuous print = contact everywhere.

Tie the result to the unit SN (22.1/20.5).

2.5.11 Acceptance cues (fast eyes)

Feature	Accept	Reject
Gasket placement	Centered on land; corners tight	Overhangs into cavity; stretched/thin corners
Compression	Even around frame; within target %	Crushed flat spots; shiny “over-worked” foam
O-ring	No twists (“sit” is even)	Nicks, twist, or out-of-groove
FIPG/adhesive	Uniform bead/line; full contact	Gaps, bubbles, smeared bead onto label zones
Glands & grommets	Torque to spec; cable OD matches range	Undersized cable (no seal), torn grommet
Vent	Seated, clean; label over vent absent	Blocked/covered vent membrane

2.5.12 Common traps → smallest reliable fix

Trap	Symptom	First move
Powder coat on gasket land	Leaks, uneven compression	Scrape to bare per drawing; reject if land pitted
One-pass torque on big lids	Corner leaks	Two-pass cross pattern; verify compression
Wrong cable OD in gland	Drips at entry	Use correct insert; verify OD with calipers; re-torque
Over-tightened conductive foam	Lost EMC, early set	Target 20–30%; switch to thickness that lands in range
Paste/TIM on seal path	Seep/leak later	Clean immediately; protect with masks during TIM apply
PSA gasket lifted at corners	Water tracks	Re-roll with pressure; use primer; respect dwell time
Vent forgotten	Fogging, pump-in leaks	Add vent; ensure above splash line; keep film off it

2.5.13 Pocket checklists

Before install

Lands/grooves clean & bare where required; flatness OK
Correct gasket type/thickness pulled by PN; lot/shelf life valid
Glands/grommets sized to cable OD; vent present if spec’d

During

Gasket seated (no stretch); corners tight; no overlaps/gaps
FIPG/PSA bead continuous; cure/dwell timer started
Lid closed with cross-pattern; two-pass torque; witness marks

Verify

Compression within target (tape/feeler/witness)
Quick spray/dunk/decay check per plan; PASS logged to SN
Visual: no bead smears, no crushed foam, glands torqued

Rework rules (short)

Never reuse a torn or permanently compressed gasket
PSA gaskets: replace if lifted/contaminated
O-rings: replace if nicked/twisted; re-lube with approved grease

Bottom line: clean lands, the right gasket, the right squeeze, and a simple proof. Follow the install order, torque lids in two passes, pick glands by cable OD, and store seals like they matter. Do that, and your boxes shrug off rain, washdowns, and time.