With the continuous development of socio-economics and science and technology, product reliability requirements become an important part of product quality. To better understand this, you can refer to the terms for reliability testing below:
Accelerometer: A transducer that measures acceleration. Typically based on piezo-electronic technology, the device provides a voltage output proportional to the acceleration at the location and in the defined direction of the device. Typically several are attached to the UUT during and are used to monitor the UUT response to the vibration input from the table.
Air Control Thermocouple: A thermocouple that provides air temperature feedback to the chamber thermal control system. Depending on the control system settings, the air control thermocouple can act as a temperature safety limit controller, or as the control thermocouple for the system.
Alternating Low Level Vibration, Also referenced as “Modulated Vibration” or “Tickle Vibration”: A vibration test procedure that is typically introduced in HALT (Highly Accelerated Life Test) Vibration Step Stressing at input levels of 30 gRMS and higher. At the end of each vibration dwell and functional test, the vibration level is reduced to 5 gRMS and a complete functional test is conducted, without waiting for a dwell at that level. Then, the vibration level is increased to the next step level. Alternating low level vibration will help detect a failure mode that is precipitated at a higher gRMS level, but is not detectable at that level, and is also not detectable when the UUT is at rest. Low levels of vibration, however, can make the failure mode detectable. Certain types of cracked solder joints, including through-hole solder issues, can be identified this way.
Broadband Vibration: Vibration that contains energy over a broad frequency range (i.e. 10 Hz to 5 kHz or greater).
Corrective Action (CA): A change implemented in a design or process to eliminate a product weakness or flaw. Corrective actions may include changes in parts or material sources, product design, and production process changes.
Destruct Limit (DL): The stress level where a failure is identified and UUT functionality is not recovered when the stress is reduced. This type of failure is also known as a hard failure. Vibration step stressing will reveal the Vibration Destruct Limit (VDL), while cold thermal step stressing will reveal the Lower Destruct Limit (LDL) and hot thermal step stressing will reveal the Upper Destruct Limit (UDL).
ED (Electrodynamic) Shaker: A vibration system consisting of a table structure that is connected to a ferrous armature surrounded by a coil. This coil is separated by an air gap from a second coil in the body of the shaker system. Controlled current is passed through the coils to create an electromagnetic force between them that moves the table in a single axis. The UUT is mounted to the table structure. The spectral and real time content of the driving force is specifically controlled to meet a desired vibration profile.
Fast Fourier Transform (FFT): An algorithm for describing a real time signal in terms of its component frequencies. Used in vibration analysis to provide magnitude and frequency information about the frequency components of an acceleration signal.
Functional Test: A test of the UUT that measures functionality, UUT operation, and critical parameters to determine if UUT fails to perform to specifications or degradation has occurred within the UUT. This test may include internal diagnostics. Functional testing is to be performed throughout the thermal and vibration stresses of a HALT (Highly Accelerated Life Test) test.
gRMS: The RMS (Root Mean Square) level of an acceleration signal, normalized to the value of acceleration due to gravity. gRMS is measured across a specified frequency range, depending on the cutoff frequency of the filter on the acceleration level. gRMS can be measured both in the time domain, using analog RMS converter circuitry, and through sampling and FFT analysis, then calculating the square root of the area under the Power Spectral Density curve, cut off at the desired frequency (Figure gRMS is typically used as a measurement of the vibration energy present in a repetitive vibration signal. For vibration from an RS machine, the frequency cutoff used is typically 5 kHz.
HALT (Highly Accelerated Life Test), also referenced as “HALT test”: A process that utilizes a step stress approach to subject a UUT to thermal and vibration stresses of types and levels beyond what it may see in actual use, but which will rapidly induce failure modes, allowing them to be detected and corrected. The stresses applied include thermal extremes, extreme thermal ramp rates, 6DoF (Degrees of Freedom) RS (Repetitive Shock) vibration and combinations of these stresses.
HASS (Highly Accelerated Stress Screen): A production screen using the same accelerated techniques as HALT, but derated. Its purpose is to monitor the manufacturing process for deviations, by screening production units.
HASS Development: A process used to determine and define the appropriate HASS profile manufacturing test screen
HASS Profile: The temperature, vibration levels.
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