Salt Spray Resistance Test of Conductive Foam: ASTM B117 Standard and Automotive-Grade Applications

Conductive Foam Under Corrosive Environments

In harsh environments such as new energy vehicles and rail transit systems, conductive foam (also called EMI shielding foam) must maintain stable electromagnetic shielding while withstanding prolonged exposure to salt spray corrosion. Salt-induced oxidation accelerates surface resistance growth—often increasing over 300%—ultimately leading to EMI shielding failure.

ASTM B117 Salt Spray Test Explained

ASTM B117 is the international benchmark for evaluating the corrosion resistance of conductive materials and coatings. The key test parameters include:

• Salt concentration: 5% NaCl solution

• pH range: 6.5–7.2 (neutral salt fog)

• Temperature: 35 °C ± 2 °C

• Spray mode: Continuous or cyclic

• Test duration: 24–1000 hours (automotive-grade ≥ 500 hours)

Evaluation criteria after testing:

• Surface corrosion level (presence of white or red rust)

• Coating and substrate integrity (delamination or cracking)

• Electrical performance changes (surface and vertical contact resistance)

Test Procedure and Key Control Points

Sample Preparation

• Cut specimens to 50 × 100 mm while keeping the conductive layer intact

• Clean off oil residues to ensure consistent corrosion behavior

• Record baseline resistance:

  • Surface resistance: ASTM D4935

  • Contact resistance: MIL-STD-202G

Test Execution

• Suspend samples vertically to prevent solution pooling

• Inspect spray nozzles every 24 hours

• Maintain salt fog deposition at 1–2 mL/80 cm²/h

Post-Test Evaluation

• Visual inspection: Check for corrosion under 10× magnification

• Electrical retest: Compare resistance variation before and after corrosion

• Structural analysis: Check for substrate swelling or delamination

Corrosion Resistance of Different Conductive Coatings

Studies show that silver-copper composite coatings enhance corrosion resistance by optimizing coating density and uniformity. In a new-energy vehicle battery-pack test, conventional Ni-Cu foam saw a 400% resistance increase after 300 hours, while the Ag-Cu composite foam rose only 120%, successfully meeting automotive-grade EMI reliability requirements.

For more insights into how shielding materials perform under electrochemical stress, see
👉 Hidden Corrosion of Conductive Silicone Rubber: How Micro-Scale Electrochemistry Undermines EMI Reliability

Optimization Strategies and Material Selection

• Material Choice: For automotive and high-humidity environments, choose Ag-Cu composite or Ni-Cu-Ag triple-layer coatings.

• Structural Design: Use fully wrapped foam structures to reduce edge exposure.

• Process Control: Add passivation steps to improve coating density and adhesion.

• Verification: Require ASTM B117 test reports including pre- and post-corrosion resistance data.

Salt-spray resistance is not simply a “pass/fail” test—it’s a quantitative indicator of long-term material stability. Through ASTM B117-compliant testing, engineers can predict EMI foam degradation in coastal, humid, or polluted environments—helping prevent corrosion-induced EMI failure and ensuring lasting performance.

Learn how SMT Gaskets｜Compact Yet Powerful EMI Protection for Electronic Devices complement corrosion-resistant foams in compact electronic assemblies.