Manufacturing screening tests of contract end items consisting largely of electronic components should include temperature cycling and random vibration for maximum cost-effectiveness. The purpose of such tests is to stimulate the early occurrence of failures due to manufacturing defects in both parts and workmanship, for discovery and correction prior to delivery to the government. The specific requirements for such tests will be found in Navy instructions and contracts; this publication does not convey policy but is merely the guide to be followed whenever such policy is conveyed.

The tests may be conducted simultaneously or consecutively, depending upon the capabilities of the available test facilities. The equipment under test may or may not be energized and operating depending on considerations, however if not operating a full power on function test should be conducted upon test completion.

4.1 TEMPERATURE CYCLING

The temperature cycling screen should be conducted in accordance with the guidelines shown in Table 5.

Type of Equipment No. of Temperature Cycles    Simple (100 electronic parts)    Moderatley complex (500 electronic parts)    Complex (2000 electronic parts)    Very complex (4000 electronic parts) 1 3 6 10  Temperature Range     The suggested range is -65°F to 131°F, or as a minimum, a temperature of at least 160°F is recommended Temperature Rate of Change     The rate of change on internal parts should fall within 1°F and 40°F per minute. The higher rates provide the best screening. Temperature Soak Times     The next temperature ramp may be started when the internal parts have stabilized within 5°F of the specified temperature and the functional checks have been completed. Equipement Operation     Eqiupment should be energized and operated during temperature cycling, except the equipment should be turned off during chamber cool-down to permit internal parts to become cold. Equipment Monitoring     While it is desirable to continuously monitor the equipment during the temperature cycling, cost considerations may dictate otherwise. In such cases, periodic checks plus close monitoring of the final cycles is appropriate Failure Criteria     The last cycle shall be failure free. Each repair should be reviewed for the possibilities of introducing new defects into the hardware and additional temperature cycles added when appropriate. If repairs are complex or difficult to make and inspect, or many unscreened parts are used as replacements, additional cycles should be implemented as appropriate to the individual case.

Table 5. Guidelines for Temperature Cycling Acceptance Testing of Electronic Hardware

 

4.2 RANDOM VIBRATION

The random vibration screen should require that the equipment under test be hard-mounted to a shake table capable of reproducing random vibration having the power spectral density characteristics shown in Figure 5 (repeated herein). A pseudo-random or synthetic random vibration shaker capable of reproducing this power spectral density function will be an acceptable substitute for a true random vibration fixture.

The equipment under test should be oriented on the fixture such that the axis of vibration is perpendicular to the printed circuit boards. Where electronic components in the equipment under test are oriented in more than one plane, such equipment should be shaken sequentially in each of three orthogonal axes.

The duration of random vibration should be at least ten minutes if a single axis is sufficient. Where vibration in more than one axis is required, the duration of random vibration should be at least five minutes for each axis.