[Source: High-tech LED's "LED Good Products" magazine February issue]
Foreword
Degradation of components and PCB material under most hot conditions is caused directly or indirectly by the adsorption of water vapor and water film by defective insulating materials, and by the wetness of the surface of metals and insulating materials. This phenomenon produces many types of degradation, including corrosion of metals, changes in material composition, and deterioration of electrical characteristics.
The alternating heat and humidity test, also known as the moisture resistance test, is an accelerated method for evaluating the ability of components and materials to withstand the effects of moisture degradation under typical tropical and subtropical high temperature and high humidity conditions. Under high-humidity conditions, the temperature cycle is used to provide a repeated alternating process of condensation and drying, so that the water vapor entering the sealed casing will have a "breathing" effect, and the influence of moisture will be more obvious, thereby accelerating the corrosion and enhancing the moisture resistance test. Effectiveness.
The test consists of a low temperature sub-circulation, because the stress caused by condensation of water vapor widens the crack, which accelerates the degradation that is not easily found in other cases. Thus, the degradation phenomenon can be revealed by measuring electrical characteristics (including breakdown voltage and insulation resistance) or performing a sealing test.
In the test, it is stipulated that a polarity voltage is applied to the insulator to study the possibility of electrolysis, since electrolysis can contribute to the dielectric breakdown that may occur. If necessary, in order to determine the ability of current-carrying components, especially thin wires and joints, to resist electrochemical corrosion, this test can also impose a certain electrical load on certain components or various types of molded PCB boards.
Regarding the moisture resistance test, "GJB 128A-1997 Semiconductor Discrete Device Test Method" is equivalent to the test method of "GJB 548B-2005 Microelectronic Device Test Method and Procedure", and no comparison is made here. The following only compares the three standards of GJB548B-2005, GJB 360B-2009, GJB1217A-2009, and gives the best test method.
Comparison of test process and test method
1. Pretreatment
(Table 1) GJB 548B-2005 does not specify the drying oven temperature, and can refer to the other two methods.
2, the initial measurement
For the latter two test methods, if a dry box is used, the initial measurement can be carried out within 8 hours of taking out the dry box by referring to GJB 548B-2005.
3, installation
The above three test methods can be used for mutual reference and complement each other.
4, the number of cycles
All four standards require that the test sample be subjected to 10 cycles of 24 hours each.
GJB 548B-2005 3.3 stipulates that in the first 9 cycles, if an accidental interruption occurs (such as a power interruption or equipment failure), the cycle can be redone and the test can continue. If an unexpected interruption occurs in the 10th cycle, in addition to requiring the cycle to be redone, an uninterrupted cycle is required, that is, the 10th cycle should be done twice. Any interruption for more than 24 hours requires a re-test from start to finish.
According to the provisions of this article, we can conclude that if a second accidental interruption occurs, the test should be repeated from beginning to end, or re-sampled and tested.
The other three standards do not specify interrupts. It is reasonable to refer to GJB 548B for implementation.
Unfinished: For more information, please refer to the February issue of Gaogong LED's "LED Good Products" magazine.
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