In addition to the combined cycle of high temperature, low temperature, high temperature and high humidity, the cold and hot shock is also a common test item in the reliability environmental test. The purpose of the cold and hot shock test is to find out the design and process defects of products through the violent temperature change beyond the natural environment [the temperature change rate is more than 20 ℃ /min, and even up to 30 ~ 40 ℃ /min], but there is often a situation that the temperature cycle is confused with the cold and hot shock. "Temperature cycle" refers to the process of high and low temperature changes, the rate of change of temperature can be specified and controlled; The temperature change rate of "cold and hot shock" is not specified (ramp time), which mainly requires reset time (recovery time). According to IEC specification, there are three test methods of temperature cycle [na, Nb, nc]. Cold and hot shock is one of the three [na] test items [rapid temperature change of specified conversion time; medium: air]. The main parameters of cold and hot shock are: high temperature and low temperature conditions, residence time, reset time, and cycle number. In high and low temperature conditions and residence time, the current new specification will require that the surface temperature of the test object, rather than the air temperature of the test area of the test equipment, be based on.
