Global Standards for the Microelectronics Industry

# Dictionary A

acceleration factor (*A*, AF)

For a given failure mechanism, the ratio of the time it takes for a certain fraction of the population to fail, following application of one stress or use condition, to the corresponding time at a more severe stress or use condition.

NOTE 1 Times are generally derived from modeled time-to-failure distributions (lognormal, Weibull, exponential, etc.).

NOTE 2 Acceleration factors can be calculated for temperature, electrical, mechanical, environmental, or other stresses that can affect the reliability of a device.

NOTE 3 Acceleration factors are a function of one or more of the basic stresses that can cause one or more failure mechanisms. For example, a plot of the natural log of the time-to-failure for a cumulative constant percentage failed (e.g., 50%) at multiple stress temperatures as a function of 1/kT, the reciprocal of the product of Boltzmann’s constant in electronvolts per kelvin and the absolute temperature in kelvins, is linear if one and only one failure mechanism is involved. The best-fit linear slope is equal to the apparent activation energy in electronvolts.

NOTE 4 The abbreviation AF is often used in place of the symbol A.

**References:**

JEP122E, 3/09

JEP143B.01, 6/08

JESD74A#, 2/07

JESD85#, 7/01

JESD91A#, 8/01

JESD94A, 7/08

acceleration factor, stress (*A*_{f})

The acceleration factor due to the presence of some stress (e.g., current density, electric field, humidity, temperature cycling).

**References:**

JEP122E, 3/09

JEP143B.01, 6/08

acceleration factor, temperature (*A*_{T})

The acceleration factor due to changes in temperature.

NOTE 1 This is the acceleration factor most often referenced. The Arrhenius equation for reliability is commonly used to calculate the acceleration factor that applies to the acceleration of time-to-failure distributions for microcircuits and other semiconductor devices:

*A*_{T} = *λ*_{T1}/ *λ*_{T2} = exp[(-*E*_{a}/*k*)(1/*T*_{1} - 1/*T*_{2})]

where

*E*_{a} is the activation energy (eV);

*k* is Boltzmann's constant (8.62 × 10^{-5} eV/K);

*T*_{1} is the absolute temperature of test 1 (K);

*T*_{2} is the absolute temperature of test 2 (K);

*λ*_{T1} is the observed failure rate at test temperature *T*_{1} (h^{-1});

*λ*_{T2} is the observed failure rate at the test temperature *T*_{2 n}(h^{-1}).

NOTE 2 Other acceleration factors can be calculated for electrical, mechanical, environmental, and other stresses that can affect the reliability of a device. Acceleration factors can be a function of one or more of the basic stresses. A plot of the reciprocal of absolute temperature, 1/T (K), versus the log of percent failed is linear for the lognormal distribution.

NOTE 3 *λ*_{s} = *λ _{t}* ∙

*A*

_{T}, where

*λ*

_{s}is the quoted (predicted) system failure rate at some system temperature

*T*

_{s}and

*λ*

_{t}is the observed failure rate at some test temperature

*T*

_{t}, and

*A*

_{T}is the temperature acceleration factor due to the change from

*T*

_{t}to

*T*

_{s}.

**References:**

JEP122E, 3/09

JEP143B.01, 6/08

JESD74A, 2/07

acceleration factor, voltage (*A*_{V})

The acceleration factor due to changes in voltage.

**References:**

JEP143B.01 6/08

JESD74A, 2/07

acceleration model

A mathematical formulation of the relationship between (1) the rate (speed) of a degradation mechanism or the time-to-failure and (2) the conditions or stresses that caused the degradation.

**References:**

JEP143B.01, 6/08

JEP148, 4/04

accept number

The maximum number of nonconforming components in the sample for which acceptance of the lot is allowed under the sampling plan.

**References:**

JESD16-A, 4/95

acceptance inspection

A sampling inspection or series of sampling inspections used to determine the suitability of a lot of material for shipment.

**References:**

JESD16-A, 4/95

access time

The time interval between the application of a specific input pulse and the availability of valid signals at an output.

**References:**

JESD100-B, 12/99

accumulator

A register in which one operand of an operation can be stored and subsequently replaced by the result of another operation. (Ref. IEC 824.)

**References:**

JESD100-B, 12/99

accuracy

The difference between the sample estimate and the population parameter being estimated.

**References:**

JEP132, 7/98

EIA-557-A, 7/95

acoustic data, A-mode

Acoustic data collected at the smallest X-Y-Z region defined by the limitations of the given acoustic microscope. An A-mode display contains amplitude and phase/polarity information as a function of time of flight at a single point in the X-Y plane.

**Example of A-mode display**

**References:**

J-STD-035, 5/99

acoustic data, B-mode

Acoustic data collected along an X-Z or Y-Z plane versus depth (Z) using a reflective acoustic microscope. A B-mode scan contains amplitude and phase/polarity information as a function of time of flight at each point along the scan line. A B-mode scan furnishes a two-dimensional (cross-sectional) description along a scan line (X or Y).

**Example of B-mode display (bottom half of picture on left)**

**References:**

J-STD-035, 5/99

acoustic data, C-mode

Acoustic data collected in an X-Y plane at depth Z using a reflective acoustic microscope. A C-mode scan contains amplitude and phase/polarity information at each point in the scan plane. A C-mode scan furnishes a two-dimensional (area) image of echoes arising from reflections at a particular depth (Z).

**Example of C-mode display**

**References:**

J-STD-035, 5/99

acoustic data, through-transmission mode

Acoustic data collected in an X-Y plane throughout the depth (Z) using a through-transmission acoustic microscope. A through-transmission mode scan contains only amplitude information at each point in the scan plane. A through-transmission scan furnishes a two-dimensional (area) image of transmitted ultrasound through the complete thickness/depth (Z) of the sample or component.

**Example of through-transmission display**

**References:**

J-STD-035, 5/99

activation energy (*E*_{a})

The excess free energy over the ground state that must be acquired by an atomic or molecular system in order that a particular process can occur.

NOTE The activation energy is used in the Arrhenius equation for the thermal acceleration of physical reactions. The term "activation energy" is not applicable when describing thermal acceleration of time-to-failure distributions.

**References:**

JEP122C, 3/06

JESD85, 7/01

JESD91A, 8/01

active desiccant

Desiccant that is either fresh (new) or has been baked according to the manufacturer's recommendations to renew it to original specifications.

**References:**

J-STD-033B, 10/05

active device

A device in which at least one circuit element is an active circuit element.

**References:**

JESD99B, 5/07

active-pulldown output

A bipolar (three-state or totem-pole) output whose source-current capability significantly exceeds its sink-current capability.

**References:**

JESD99B, 5/07