4.4.6: Testing (HALT)

What is HALT Testing

Highly accelerated life testing (HALT) techniques are important in uncovering many of the weak links of a new product. These discovery tests rapidly find weaknesses using accelerated stress conditions. The goal of HALT is to proactively find weaknesses and fix them, thereby increasing product reliability. Because of its accelerated nature, HALT is typically faster and less expensive than traditional testing techniques.

HALT is a test technique called test-to-fail, where a product is tested until failure. HALT does not help to determine or demonstrate the reliability value or failure probability in field. Many accelerated life tests are test-to-pass, meaning they are used to demonstrate the product life or reliability.

It is highly recommended to perform HALT in the initial phases of product development to uncover weak links in a product, so that there is better chance and more time to modify and improve the product.

HALT uses several stress factors (decided by a Reliability Test Engineer) and/or the combination of various factors. Commonly used stress factors for electronics and mechanical products are:

• temperature,
• vibration, and
• humidity.

Other factors can include voltage, current, power cycling and combinations of them.[1]

HALT procedures

Environmental stresses are applied in a HALT procedure, eventually reaching a level significantly beyond that expected during use.

The stresses used in HALT are typically:

• hot and cold temperatures,
• temperature cycles,
• random vibration,
• power margining, and
• power cycling.[1]

The system under test is in operation during HALT and is continuously monitored for failures. As stress-induced failures occur, the cause should be determined, and if possible, the problem should be repaired so that the test can continue to find other weaknesses.

HALT Test Chamber

A specialized environmental chamber is required for HALT.

A suitable chamber also has to be capable of applying pseudo-random vibration with a suitable profile in relation to frequency. The HALT chamber should be capable of applying random vibration energy from 2 to 10,000 Hz in 6 degrees of freedom and temperatures from -100 to +200°C. Sometimes HALT chambers are called repetitive shock chambers because pneumatic air hammers are used to produce vibration. Test fixtures must transmit vibration to the system under test.

The chamber should also be capable of rapid changes in temperature, 50°C per minute should be considered a minimum rate of change. Usually high power resistive heating elements are used for heating and liquid nitrogen (LN₂) is used for cooling.

The network system under test must be monitored so that if the equipment fails under test, the failure is detected.

Monitoring is typically performed with thermocouple sensors, vibration accelerometers, multi-meters, and data loggers.

Common causes of failures during HALT are:

• poor product design,
• workmanship, and
• poor manufacturing.

Failures to individual components such as resistors, capacitors, diodes, and printed circuit boards occur because of these type of issues. Failure types found during HALT testing are associated with the infant mortality region of the reliability bathtub curve as shown in Figure \(\PageIndex{1}\).