Quality/Reliability Terms

Thermal stresses mostly affect the life of a semiconductor device, among electrical, thermal, and mechanical stresses. The Arrhenius chemical reaction theorem has been proved to be useful for estimating the dependency of the response speed on thermal stress, and this theorem is used to expect the life of a semiconductor device.


For details, refer to the Review of Quality and Reliability Handbook.

Devices are checked for appearance and characteristics and defective ones are discarded, but this does not mean that all the remaining devices are fit to be shipped: There is still the possibility that some devices may contain potential defects that may lead to early failure.
Aging is a general term that refers to accelerated testing consisting in the application of stress to an extent that does not cause degradation or damage in normal devices, but accelerates degradation in devices with potential defects.

This is a failure mode that has become common as semiconductor devices are using increasingly fine patterns and as their wiring current density increases.
The wiring materials (mainly aluminum) have a polycrystal structure and their metallic atoms cause mass transfer, gaining momentum through collision with electrons.
As a result, short-circuiting is caused by break faults, hillocks, or spikes.

For details, refer to the Review of Quality and Reliability Handbook.

It is an accelerated test that repeats keeping at the high temperature and the low temperature without putting the bias at regular intervals.

For details, refer to the Review of Quality and Reliability Handbook.

Fit is used as a unit, which stands for Failure in time.
It describes the rate of failure in a given time period and can be expressed as 1 FIT = 1 x 10-9/hour.

A failure rate is an estimate value and varies depending on the operating conditions (voltage, duty, etc.) and environment (temperature, humidity, etc.) of the customer.

For details, refer to the Review of Quality and Reliability Handbook.

Screening refers to the elimination of devices with initial defects or accidental defects. Screening methods include appearance inspections performed without applying stress during the fabrication process, and accelerated testing (aging) following fabrication to remove only devices with potential defects through the application of stress to an extent that does not cause degradation or damage in normal devices.

For details, refer to the Review of Quality and Reliability Handbook.

Normal distribution is the type of distribution that is most frequently used for quality control.
This distribution curve is a symmetrical "bell-curve" with an average value at the center u, and contains +/-3σ (σ: standard deviation).



For details, refer to the Review of Quality and Reliability Handbook.

It is to impress voltage to a semiconductor device for a specific time at a high temperature of 100°C to 125°C in order to eliminate potential defects of the device.

When the failure rate is shown on the vertical axis and time on the horizontal axis, the curve of the failure rate looks like a bathtub. This is called as a bathtub curve.
The three failure stages are described below.

[Early failure stage]
This is the period where relatively early failures occur following the first operation of a semiconductor device, and is characterized by a gradual decline in the number of failures over time. This phenomenon is caused because products with latent failures cannot be completely eliminated during the sorting process. These latent failures reveal themselves in a short time after first use of the semiconductor device, due to temperature, voltage, and other stresses.

[Random failure stage]
Once the early failures have been eliminated, the failure rate stabilizes at an extremely low level, but latent failures may reveal themselves at random over a long time and thus their number does not decline to zero. Since failures occur at random, the failure rate is almost constant.

[Wear-out failure stage]
This is the period where the devices fail due to wear, fatigue, and so on, with the failure rate rising over time.

For details, refer to the Review of Quality and Reliability Handbook.

(2006/12)

Solder wettability refers to the adhesion characteristic of the solder used for connecting the pins and substrate in semiconductor devices.

Distribution of failure occurrence probability theorem devised by a scholar named Poisson, which serves as a basis of sampling inspection.

For details, refer to the Review of Quality and Reliability Handbook.

Weibull Distribution started using by scholar Weibull to indicate distribution of the rupture strength of steel. This is often used to analyze the life of a semiconductor device.

For details, refer to the Review of Quality and Reliability Handbook.

Indicates the minimum quality value (upper-limit failure rate) at which sampling inspection is aggressively judged to be acceptable.



For details, refer to the Review of Quality and Reliability Handbook.

Indicates compatibility of an electromagnetic environment.
If a current intermittently flows inside an operating electric system, noise is generated, affecting the other electric systems and causing them to malfunction.
This is considered as deterioration of the electromagnetic environment, and EMC is used to prevent this from happening.

As the causes of destruction of a semiconductor device due to static discharge, the following four models are proposed:

(1) Human model
Model of destruction that occurs if charge built up in a human body is discharged when the body touches the device
(2) Machine model
Model of destruction that occurs if metallic equipment having a capacitance higher and a discharging resistance lower than a human body comes in contact with the device
(3) Device charging model
Model of destruction that occurs when charge is released from the pin of the device if the package or lead frame of the device is charged by friction
(4) Electric field induction model
Model in which destruction of the oxide film occurs if a device having a MOS structure is exposed to a high electric field

For details, refer to the Review of Quality and Reliability Handbook.

Mean Time Between Failures of computers and equipment that are subject to repairs

Average interval of failure of components, etc., that are not subject to repairs