**PCB Corrosion Testing: A Core Analysis of Manufacturing Processes and Applications**

PCB corrosion testing is a fundamental method for evaluating a product's corrosion resistance and ensuring its reliability, serving as a critical link in quality control within the electronics manufacturing industry. Through years of working in PCB technology, the author has observed that many companies hold misconceptions about corrosion testing standards. Common errors include confusing the applicable scenarios for salt spray testing versus temperature-humidity cycling testing, and failing to select testing standards based on the product's actual application environment. This often leads to test results that do not accurately reflect real-world usage conditions. Currently, the globally authoritative standards for PCB corrosion testing primarily include the IPC series, IEC series, AEC-Q200, among others. Different standards establish clear testing requirements tailored for various application scenarios (such as consumer electronics, automotive electronics, and outdoor equipment).

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**I. Classification of Core Authoritative Standards for PCB Corrosion Testing**

**1.1 International General Standards (Applicable to Most Electronic Products)**

*   **IPC-TM-650 (Test Methods Manual):** Developed by the Institute for Printed Circuits (IPC) in the United States, this is the most core testing standard in the PCB industry. It contains numerous corrosion-related test methods, such as Salt Spray, Temperature-Humidity Cycling, and Ionic Contamination testing.

*   **IEC 60068 (Environmental Testing):** Environmental testing standards developed by the International Electrotechnical Commission. Among these, IEC 60068-2-11 (Salt Spray Test) and IEC 60068-2-30 (Damp Heat, Cyclic Test) are commonly used for PCB corrosion assessment.

*   **ISO 9227 (Corrosion Tests in Artificial Atmospheres):** A salt spray testing standard developed by the International Organization for Standardization, suitable for evaluating PCB corrosion resistance in marine and industrial environments.

**1.2 Industry-Specific Standards (For Targeted Application Scenarios)**

*   **AEC-Q200 (Stress Test Qualification for Passive Components):** Formulated for automotive electronic PCBs, it includes corrosion-related tests like temperature-humidity cycling, thermal shock, and vibration, with more stringent requirements.

*   **MIL-STD-810 (Environmental Engineering Considerations and Laboratory Tests):** A corrosion testing standard for military electronic PCBs, encompassing multiple tests including salt fog, fungus, and sand/dust, suitable for harsh environments.

*   **IEC 60664 (Insulation Coordination for Equipment within Low-Voltage Systems):** Involves PCB insulation corrosion testing, specifying indicators such as insulation resistance and withstand voltage.

**1.3 Domestic Chinese Standards (Equivalent to International Standards)**

*   **GB/T 2423 (Environmental Testing for Electric and Electronic Products):** Equivalent to IEC 60068. Among them, GB/T 2423.17 (Salt Spray Test) and GB/T 2423.4 (Damp Heat, Cyclic Test) are commonly used standards by domestic PCB companies in China.

*   **GB/T 4677 (Test Methods for Printed Boards):** Equivalent to IPC-TM-650, containing various test methods related to PCB corrosion.

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**II. Key Corrosion Test Items: Standard Requirements and Test Methods**

**2.1 Salt Spray Test (Evaluating Resistance to Salt Fog Corrosion)**

**2.1.1 Standard Requirements**

*   **IEC 60068-2-11 / GB/T 2423.17:** Neutral Salt Spray (NSS), 5% NaCl solution, pH 6.5-7.2, temperature 35°C, test duration 24/48/96 hours.

*   **AEC-Q200 Clause 4.1:** Acidic Salt Spray (ASS), 5% NaCl solution, pH 3.1-3.3, temperature 35°C, test duration 96 hours.

*   **Acceptance Criteria:** After testing, the PCB surface should show no significant corrosion (e.g., copper foil blackening, pad detachment). Solder joint peel strength should be ≥1.5 N/mm, and insulation resistance should be ≥10^9 Ω.

**2.1.2 Test Method**

*   **Sample Preparation:** Select 3-5 representative PCBs, remove surface contaminants, and seal the edges (to avoid influence from side corrosion).

*   **Test Procedure:** Place samples in a salt spray chamber at a 15-30° tilt angle for continuous spraying. Record temperature and pH value during the test.

*   **Post-Treatment:** After testing, rinse samples with flowing clean water for 5 minutes, then dry at 80°C for 30 minutes.

*   **Evaluation:** Visually inspect for corrosion, and test electrical performance and solder joint strength.

**2.2 Temperature-Humidity Cycling Test (Evaluating Corrosion Resistance Under Alternating Temperature/Humidity)**

**2.2.1 Standard Requirements**

*   **IPC-TM-650 2.6.7:** Temperature range -40°C to 85°C, humidity 5% to 95%, cycle period 2 hours (1 hour high temperature, 1 hour low temperature), number of cycles 50/100/1000.

*   **AEC-Q200 Clause 4.2:** Temperature range -40°C to 125°C, humidity 5% to 95%, cycle period 4 hours, number of cycles 1000.

*   **Acceptance Criteria:** After testing, the PCB should exhibit no delamination, warping, or pad detachment. Impedance fluctuation should be ≤3%, with no open or short circuits.

**2.2.2 Test Method**

*   **Sample Preparation:** Solder representative components (e.g., 0402 resistors, QFP-packaged chips) onto the PCB and perform initial electrical tests.

*   **Test Procedure:** Set the temperature and humidity profile according to the standard, place samples in a programmable temperature-humidity chamber, and start the cycling test.

*   **Intermediate Inspection:** Every 100 cycles, remove samples for visual inspection and electrical testing.

*   **Final Evaluation:** After test completion, conduct a comprehensive inspection of PCB appearance, electrical performance, and reliability.

**2.3 Ionic Contamination Test (Evaluating Corrosion Risk from Surface Contaminants)**

**2.3.1 Standard Requirements**

*   **IPC-TM-650 2.3.25:** Use an isopropyl alcohol-water solution (volume ratio 75:25) for extraction. Ionic concentration should be ≤1.5 µg/cm² (NaCl equivalent).

*   **IEC 61189-2-602:** Ionic concentration should be ≤1.0 µg/cm² (for high-end PCBs).

*   **Acceptance Criteria:** Exceeding the ionic concentration limit indicates excessive residual contaminants on the PCB surface, which can easily lead to electrolytic corrosion.

**2.3.2 Test Method**

*   **Sample Preparation:** Select a test area on the PCB (area ≥10 cm²) and clean surface dust.

*   **Extraction Process:** Place the sample in the extraction solution and perform ultrasonic cleaning for 15 minutes at 40°C.

*   **Testing:** Use an ionic contamination tester to measure the conductivity of the extraction solution and convert it to ionic concentration.

*   **Handling:** After testing, the PCB must be re-cleaned to avoid residual contaminants.

**2.4 Chemical Resistance Test (Evaluating Resistance to Organic Solvents and Oil Contamination)**

**2.4.1 Standard Requirements**

*   **IPC-TM-650 2.6.4:** Immersion in specified chemical media (e.g., engine oil, brake fluid, ethanol) at 85°C for 1000 hours.

*   **AEC-Q200 Clause 4.4:** Immersion in automotive brake fluid or engine oil at 125°C for 500 hours.

*   **Acceptance Criteria:** After testing, the PCB surface should show no blistering, discoloration, or corrosion, with no degradation in electrical performance.

**2.4.2 Test Method**

*   **Sample Preparation:** Cut the PCB into 50mm x 50mm test coupons and perform initial appearance and electrical tests.

*   **Immersion Process:** Completely immerse test coupons in the chemical medium and place them in a constant temperature oven.

*   **Periodic Observation:** Remove and observe surface condition every 200 hours, recording any changes.

*   **Final Evaluation:** After test completion, clean the samples and inspect appearance, electrical performance, and adhesion.

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**III. Selection of Testing Standards for Different Application Scenarios**

**3.1 Consumer Electronics PCB (Mobile Phones, Computers, Smart Home Devices)**

*   **Core Tests:** Salt Spray Test (24 hours), Temperature-Humidity Cycling (50 cycles), Ionic Contamination Test.

*   **Recommended Standards:** IPC-TM-650, IEC 60068-2-11, GB/T 2423.17.

*   **Requirements:** Ionic concentration ≤1.5 µg/cm²; no significant corrosion after testing; defect rate ≤0.1%.

**3.2 Automotive Electronics PCB (BMS, Vehicle Cameras, Navigation Systems)**

*   **Core Tests:** Acidic Salt Spray Test (96 hours), Temperature-Humidity Cycling (1000 cycles), Thermal Shock Test, Chemical Resistance Test.

*   **Recommended Standards:** AEC-Q200, IATF 16949, IPC-TM-650.

*   **Requirements:** No delamination or pad detachment after testing; impedance fluctuation ≤3%; meeting a 10-year service life requirement.

**3.3 Outdoor Communication PCB (Base Stations, Routers, Surveillance Equipment)**

*   **Core Tests:** Salt Spray Test (48/96 hours), Temperature-Humidity Cycling (200 cycles), UV Aging Test.

*   **Recommended Standards:** IEC 60068-2-30, ISO 9227, GB/T 2423.4.

*   **Requirements:** No corrosion after salt spray testing; no solder mask cracking after UV aging; insulation resistance ≥10^9 Ω.

**3.4 Medical Device PCB (Monitors, Ventilators, Diagnostic Equipment)**

*   **Core Tests:** Temperature-Humidity Cycling (100 cycles), Ionic Contamination Test, Chemical Resistance Test.

*   **Recommended Standards:** ISO 13485, IPC-TM-650, IEC 60601.

*   **Requirements:** Ionic concentration ≤1.0 µg/cm²; no bacterial growth after testing (for implantable devices); stable electrical performance.

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**Conclusion**

The core principle of PCB corrosion testing is **"matching the standard to the application scenario."** Companies must select corresponding testing standards based on the product's actual application environment (e.g., salt fog, high temperature/humidity, chemical media) to avoid over-testing (increasing costs) or under-testing (leading to reliability risks). During the testing process, it is crucial to strictly adhere to standard requirements and control test parameters (temperature, humidity, solution concentration) to ensure test results are authentic and effective.