Drift Parametric change in value from design set point e.g., Component changes in value as result of temperature or vibration.
Dwell Time The stabilization temperature time plus the soak temperature time.
Dynamic Test Voltage or Vibration or Shock Testing.
Eyring Mathematical model used to relate behavior of an item at one stress level to its behavior at another stress level. The Eyring equation model allows 2 variables whereas the Arrhenius equation model only allows 1 variable.
Extrinsic Effect A failure in the product due to causes outside of the product i.e., chamber vibration or temperature.
Failure The termination of the capability of a part or component to perform its function.
Failure Mechanism The specific cause of failure.
Failure Mode The specific cause of failure at the macroscopic level.
Failure Repetition The repetition of a failure in a product when the test is repeated.
Fatigue The mechanical failure of a part which has been subjected to repeated reverse bending cycles.
Fatigue Life The specific number of cycles to fail by repeated reverse stressing.
Field Failure A defect which is found in a system used in the field.
Fixed Resonance Vibration at a fixed frequency corresponding to the natural frequency of the unit under test. Dwell
Fixture A device which is used to attach a UUT to a ESS chamber floor or table for vibration or temperature cycling.
Flatpack A semiconductor device that has leads extending from each edge outward.
Flip Chip A chip that has bumped terminations spaced around the device and is intended for face down mounting.
Forced Vibration A forced oscillatory excitation on a system.
Grand Mean Effect The main variation in functionality of a product due to all sources of input in a stress test.
Gull Wing A common lead form and shape used to interconnect used to mount surface mount devices to CCA’s.
Hard Failure A failure in a component or system which is catastrophic and can no longer operate. If the component or system is subjected to an excessive stress environment, the environment may "kill" the system thereby causing a hard failure.
Harmonic A integral multiple value of the natural frequency of a system e.g., if Fn=60 Hz, then the harmonics are HFn's = 60, 120, 180, .. Hz.
Hermeticity Test A leak test to determine if the test package is sealed.
Intermittent A component failure which is not consistent and may last for a very short time. The intermittent failure does not fail at the same time and input level usually.
Infant Mortality Early failures due to latent defects resulting from manufacturing errors.
Intrinsic Effect A failure resulting from causes internal to the product (weakness in design).
Inverse Power Law An accelerated test model used to analyze the reduction of life of a product with increase stress.
IR Reflow Infrared reflow. A technique to melt solder using long wave length light.
Isolation The separation of vibration from structure such that the structure does not feel the vibration.
Isolator A device which does not allow vibration to be transmitted from the source to the support.
Jerk Rate of change of acceleration.
Junction Temp The maximum allowable temperature of a micro-electronic device. Operating at the Junction temperature will cause early failure. Operating near the Junction temperature will lower MTBF.
Laminar Flow Low speed air flow which is smooth and where air streams do not cross or mix. Reynolds number less than 2100. Not desired in HALT or HASS air flow tests.
Latent Defect A defect in a part or item that would eventually prevent it from meeting its functional requirement when operating within its specified environment and within its specified lifetime. This type flaw is not normally obvious and cannot be seen with the naked eye.
Level The amplitude of a test condition.
Level of Screen The amplitude of RVSS which a unit is subjected or the temperature differential of TCSS.
Low Pass Filter The filtering effect of a system which allows low frequency effects but does not allow high frequency effects. A CCA has this phenomenon.
Mass Participation Factor The oscillation of a part in a system that moves in a different direction than the direction of vibration excitation. The mass participation factor is the percentage of the mass and its vector.
Mfg Defect A flaw caused by in-process errors or uncontrolled conditions during assembly, test, inspection, or handling.
Mean The average value of a set of values.
Miner’s Law The physics of fatigue where each material has a particular curve for fatigue stress failure vs. number of reverse stress cycles to fail.
Mixed Mode Test 2 Interpretations. #1) Vibration of a product at the primary mode and various harmonics of the primary mode. #2) Vibration and temperature testing.
Mode The natural frequency of a system or harmonic of the natural frequency.
Modal Analysis An analysis to determine the natural frequencies of a system. The analysis may be a real test or a calculation.
Narrow Band Power spectral density having a peak value within a narrow band of frequency.
NAVMAT Naval Materials Command. An obsolete branch of the U.S. Navy which was formerly in charge of Navy systems quality and specifying ESS testing for Naval systems. Testing guideline levels were established for vibration and Temperature Cycling profiles for ESS (called NAVMAT levels). No longer used by any defense vendors. The start of ESS in commercial work was due to the efforts of NAVMAT in 1983. Many tech papers still refer to NAVMAT levels for comparison to new technology. The NAVMAT random vibration level was 6 GRMS for all items. NAVMAT was disestablished in the early 90's.
Mode General term for the natural frequency of a system. Most systems have several modes. The first mode (or natural frequency) usually is the most damaging to a system.
Modeling The science of failure prediction by modeling the product and the analyzing the weaknesses in the design. Node The part or point of a system which does not move during vibration excitation.
Omni-Axial Refers to 6 DoF vibration system where the vibration vectors are in every direction of the globe.
Operating Limit The level of vibration or temperature at which a system will no longer operate but which will operate again if the stress level is reduced. Part In most cases, a nonrepairable, throwaway, electrical/electronic item.
Patent Defect A flaw in a part or item that is obvious and can be detected by normal visual inspection e.g., broken lead wires, cracked casing, solder balls, workmanship errors, etc.
Peak to Peak The difference in values of the maxima and the minima in a curve.
Physics-of-Failure A failure analysis to determine the root cause of failure (failure mechanism)
Pickup Transducer (accelerometer, pressure, etc.)
PIND Testing Particle Impact Noise Detection Test. An amplified acoustical test using electro-mechanical methods for detecting loose particles in the cavity of an electronic device. (Rarely used).
Pitch The nominal center to center distance from one conductor trace to another.
Planned Obsolescence Refers to a product that has an intrinsically designed wear out period e.g., PO=2 years. PrePreg Adhesive sheet used to cement Multilayer sheets together under temperature & high pressure.
Probabilistic Reliability Reliability analysis based on statistical considerations without consideration of the structural design features.
Process A function or series of functions to produce a desired goal e.g., a process to surface defects.
Profile The graph of the input or response curve (Input Profile e.g., Input PSD or temperature graph); (Response Profile e.g., Response PSD or Temperature graph).
Quasi-Random Oscillatory motion which is not sinusoidal and is not predictable. Only the energy level Vibration G^2/Hz is controllable over a wide band frequency spectrum. (nearly pure random).
Random on Random A spectrum which contains a random vibration spectra over another random vibration base which is usually at a lower level. Real Estate Surface area available for mounting components on a CCA.
Reliability Quality or survivability of a product over time.
Reliability Growth Improvement in reliability of a product by testing and correction of causes of defects.
Reluctance Thermal reluctance. Refers to slow changing temperature of a product due to its high mass. A high thermal reluctance part cannot keep pace with the chamber temperature changes. Returns Refers to return of products to the seller due to defects or failures.
Robustness Strength of a product. Ability to withstand stress.
Room Constant The value of noise in a room with a noise source. The room constant depends on the size and volume of the room. The smaller the room the higher the room constant noise level since the walls, ceiling and floor will reflect the noise. Screen Strength The amplitude of the input vibration level or the maximum Temperature difference of the TCSS profile. Defects surfaced are proportional to screen strength.
Shock Response A plot of the maximum response experienced by a 1 DoF vibration system (product) as a Spectra (SRS) function of its own natural frequency in response to an applied shock or random vibration (tab table. Usually G's vs. Frequency.
Sigma The statistical deviation from the mean.
Sine on Random A spectrum contains a large narrow band frequency spike (Sine) in the spectrum over a wide band random vibration spectrum.
Skew The amount of asymmetry in a statistical distribution.
Soak Time The time allowed for soaking up heat at a given temperature. Immediately after stabilization time
Soft Failure A temporary failure in a component or system. A non critical failure.
Spectrum The shape of a vibration input or response curve. G’s or PSD vs. Frequency.
Stabilization Time The time it takes for a part to attain 95% of steady state temperature. Starting from the time the input profile temperature begins its flat (constant) level.
Stress The effect on an item when force is applied. Stress causes tension, warping, bending, stretching, temperature rise, breaking, etc. The higher the stress, the closer to failure. All parts and materials have stress limits.
Step Stress An accelerated test in which the levels of stress are increased in a step wise fashion to cause failure or find the operating limit of a product.
Stress Relief Reduction of stress in bending or pulling by a simple curl or loop in a wire.
Stress Screening Application of stressful environment on a product to surface weaknesses and defects.
Stress-Strength Failure A failure caused when the applied stress exceeds the strength of a product.
Sub Assembly An electrical assembly that fits into a larger electrical assembly.
System A group of units interconnected or assembled to perform an overall electronic function.
Test A specific evaluation of a UUT under specified examination conditions which will lead to proof or disproof of its acceptance to perform in a given environment.
Taguchi Method A Statistical method of predicting the reliability of a system.
Technology Limit See Destruct Limit. Also called design limit.
Thermal Cycle The input profile which rises and falls in a specified time but which ends at the same temperature that it began.
Thermocouple (T/C). Dissimilar pair of metallic wires used to measure temperature.
Thermal Shock The rate of change of environmental chamber temperature. Low Shock, RR< 35°C/Minute; High shock, RR> 50°C/Minute; Very high shock, RR>100°C/Minute.
Time History Plot A graph or plot of the data for input or response for amplitude vs. time.
Time Constant The time it takes for an exponential function to attain 63% of its steady state value. The function will attain 95% of steady state in three time constants (3 x Tc). Normally referred to in temperature testing or electrical testing.
Top Assembly Highest level of an electrical assembly. All sub assemblies fit into the top assembly.
Tracked Resonance Nearly the same as Fixed Resonance Frequency with exception that the shaker is programmed.
Turbulent Air Flow High speed air flow where the stream lines mix and cross and where the flow is turbulent.
Frequency Cycles per second (Hertz, Hz). Natural frequency is the self generated oscillation of a part or system. Applied frequency is the applied oscillation to a part from an outside source.
Undershoot Similar to Overshoot except that it is the margin under the Th. Usually caused by insufficient dwell time. Upgrading Changing the design specification to a higher level due to design improvements.
Uprating Changing the design specification to a higher level due to ability to withstand higher test levels.
Via Hole A very small hole in circuit card assembly used for passing current from one side of the card to another. It is not used for mounting components. Usually soldered through.
Vibrator The pneumatic piston assembly that produces the random vibration in a pneumatic vibration system by fast acting repeated shocks.
Wearout The last phase of the lifetime of the product.
Weibull Weibull distribution. Various plots of failure (% defects found) data vs. time, MTBF, etc.
What-If experiments Accelerated stress experiments designed to find defects and weaknesses when the product is operated in “out of bounds” electrical conditions e.g., What-if the voltage is higher or lower than the spec during the stress test ?
White Noise Pure or nearly pure Power spectral density at a constant value with little or no change over a frequency spectrum.
Wide Band Power spectral density having a values within a wide band of frequency.
Yield Strength The strength of a material which after having been stressed to a specific value of stress will not return to its original shape or size.