5.10 Seals, Gaskets, and Waterproofing

Environmental sealing is a mandatory requirement for products operating in corrosive, dusty, or humid environments. A seal's primary function is to achieve and maintain a certified Ingress Protection (IP) rating throughout the product's life. Failure to manage gasket compression, joint cleanliness, or fastener sequencing compromises the seal, leading to latent electrical failures and product corrosion.

5.10.1 IP Rating and Process Verification

The complexity of the sealing process must match the required IP rating. On the factory floor, process checks must be implemented to proxy the formal lab certification tests.

IP Rating Standards

The IP rating defines the assembly's resistance to solids (first digit) and liquids (second digit).

Quick Line Tests

• Talc/Witness Tape: The most effective setup check. Close the lid on a dusted seal; open it to verify a continuous print line around the entire gasket, indicating contact everywhere (no "holidays").
• Pressure/Vacuum Decay: Applying low pressure/vacuum and checking for a stable reading is excellent for high-mix lines.

5.10.2 Gasket Materials and Surface Preparation

Material selection and surface cleanliness are non-negotiable foundations for adhesion and function.

Material Selection and Compression Targets

Gaskets must be compressed to a specific percentage of their original height to achieve a reliable seal.

• Material Mandate: Match chemistry to the environment (e.g., Silicone for wide temp/UV; Neoprene/NBR for oil/fuel tolerance).

Surface Preparation Mandate

• Cleanliness: Gasket grooves and lands must be wiped using a lint-free cloth + approved solvent. Prohibited: Silicone residue, which prevents adhesion.
• Flatness: Gasket lands must be flat (e.g., within 0.3 – 0.5 mm across the span). Burrs and sharp edges that contact seals must be removed.
• Bonding: Conductive EMI bond pads must be unpainted; verify no powder beads are lodged in grooves.

5.10.3 Assembly Protocol and Torque Sequencing

Maintaining uniform compression across a long sealing seam requires precise management of the fastening sequence and torque.

Fastener Torque Sequence

• The Problem: Tightening fasteners sequentially (one after another) crushes the gasket unevenly, resulting in leaks.
• Mandate: Multi-point sealed enclosures must be tightened using a cross-pattern torque sequence (starting at the center and working outward, diagonally).
• Compression Torque: Fasteners must be driven to the minimum required torque necessary to achieve the target compression. Over-torquing is a Defect because it permanently destroys the material's ability to rebound.

Cable Entries and Grommets

• Cable Glands: Choose glands based on the cable OD range. Tighten to the manufacturer's specified torque to achieve the seal; ensure strain relief is active.
• Grommets: Must be fully seated. The panel cutout must be smooth; no sharp edges are permitted to touch the passing cable insulation.

Adhesive and FIPG Sealing

• PSA Gaskets (Adhesive): The surface must be cleaned; align the gasket with a template; apply pressure with a roller for 3 – 5 seconds per section. Respect dwell time; full bond takes time.
• FIPG (Formed-In-Place): Application must be automated (meter-mix or syringe) to guarantee consistent bead size. The material must be allowed to cure (skin) per chemistry before final enclosure closure.

Final Checklist