Military Standard
Standardized defense testing protocols outline environmental procedures to assess the resistance of electronic component parts to the damaging effects of high humidity and temperature. The military procedure known as mil-std-202 method 106 defines a cyclic moisture resistance test designed to evaluate the durability of small electrical components. This test simulates tropical exposure through repeated cycles of high humidity.
Procedure Cycle
The test consists of ten continuous twenty-four hour cycles that include periods of high humidity combined with rapid temperature transitions and low-temperature excursions. Throughout these cycles, the relative humidity is maintained between ninety and ninety-eight percent, while the temperature ranges from twenty-five to sixty-five degrees Celsius. In contrast to other moisture tests, mil-std-202 method 106 includes a sub-zero cold shock and a vibration step during the first nine cycles.
This additional mechanical and thermal stress forces moisture deeper into the internal structures of the device.
Moisture Trapping
The physical mechanism relied upon during this test is the cyclic condensation and subsequent trapping of liquid water within internal cavities of the component. When the temperature drops rapidly during the cooling phases, the air inside the component shrinks, drawing in moist external air that immediately condenses into liquid water. If the water cannot escape during the warmer phases, it accumulates and causes galvanic corrosion of fine internal wires and terminals.
For sensitive instrumentation, such as pressure transducers and board-mounted sensors, this test reveals whether the housing seals can prevent long-term degradation in high-humidity field applications.
Evaluation Criteria
Post-exposure analysis focuses on verifying the electrical functionality and structural integrity of the tested components. Following the completion of the mil-std-202 method 106 sequence, technicians perform insulation resistance and dielectric withstanding voltage measurements. If the insulation resistance falls below the specified threshold, the component is rejected as non-compliant.
