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No claims to be in conformance with this standard may be made unless all requirements stated in the standard are met. This document is copyrighted by the EIA and may not be reproduced without permission. Organizations may obtain permission to reproduce a limited number of copies through entering into a license agreement. It employs severe conditions of temperature, humidity, and bias which accelerate the penetration of moisture through the external protective material encapsulant or seal or along the interface between the external protective material and the metallic conductors which pass through it.
Calibration records shall verify that the equipment avoids condensation on devices under test DUTs hotter than 50? C during ramp-up and ramp-down for conditions of maximum thermal mass loading and minimum zero DUT power dissipation.
Calibration records shall verify that, for steady state conditions and maximum thermal mass loading, test conditions are maintained within the tolerances specified in 3. Devices under stress shall be no closer than 3 cm from internal chamber surfaces, and must not be subjected to direct radiant heat from heaters. Boards on which devices are mounted should be oriented to minimize interference with vapor circulation.
NOTE: For interim readouts, devices should be returned to stress within the time specified in 4. For parts that require more than 24 hours to reach equilibrium at the specified HAST condition, the time should be extended to allow parts to reach equilibrium.
Stress temperatures above the effective glass transition temperature may lead to failure mechanisms unrelated to standard 85? NOTE — The priority of the above guidelines depends on mechanism and specific device characteristics. C higher than the chamber ambient temperature or, if the die temperature is not known when the heat dissipation of the DUT is less than mW.
If the heat dissipation of the DUT exceeds mW, then the die temperature should be calculated. If the die temperature exceeds the chamber ambient temperature by more than 5? C then the die temperature rise above the chamber ambient should be included in reports of test results since acceleration of failure mechanisms will be affected.
If the biasing configuration results in a temperature rise above the chamber ambient,? Tja, exceeding 10? C, then cycled bias, when optimized for a specific device type, will be more severe than continuous bias. Heating as a result of power dissipation tends to drive moisture away from the die and thereby hinders moisture-related failure mechanisms. Cycled bias permits moisture collection on the die during the off periods when device power dissipation does not occur. The die temperature, as calculated on the basis of the known thermal impedance and dissipation should be quoted with the results whenever it exceeds the chamber ambient by 5?
C or more. No Report? No 4 Procedure The test devices shall be mounted in a manner that exposes them to a specified condition of temperature and humidity with a specified electrical biasing condition. Exposure of devices to excessively hot, dry ambient or conditions that result in condensation on devices and electrical fixtures shall be avoided, particularly during ramp-up and ramp-down.
Condensation shall be avoided by ensuring that the test chamber dry bulb temperature exceeds the wetbulb temperature at all times, and that the rate of ramp up shall not be faster than a rate which ensures that the temperature of any DUT does not lag below the wet bulb temperature.
In a dry laboratory, the chamber ambient may initially be drier than this. C shall be long enough to avoid test artifacts due to rapid depressurization but shall not exceed 3 hours. The second part of ramp-down from a wet bulb temperature of ? C to room temperature shall occur with the chamber vented. There is no time restriction, and forced cooling of the vessel is permitted. Condensation on devices shall be avoided in both parts of the ramp down by ensuring that the test chamber dry bulb temperature exceeds the wet-bulb temperature at all times.
Ramp-down should maintain the moisture content of the molding compound encapsulating the die. Bias should be verified after devices are loaded, prior to the start of the test clock. Bias should also be verified after the test clock stops, but before devices are removed from the chamber.
Note: For intermediate readouts, devices shall be returned to stress within 96 hours of the end of ramp down. The rate of moisture loss from devices after removal from the chamber can be reduced by placing the devices in sealed moisture barrier bags without desiccant. Thus the test window can be extended to as much as hours, and the time to return to stress to as much as hours by enclosing the devices in moisture-proof bags. Contamination control is important in any highly-accelerated moisture stress test.
C above the chamber ambient.
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