Temperature, Humidity, Bias (THB) Test

Temperature, Humidity, Bias (THB) testing is a reliability test designed to accelerate metal corrosion, particularly that of the metallizations on the die surface of the device.

Aside from temperature and humidity which are enough to promote corrosion of metals in the presence of contaminants, bias is applied to the device to provide the potential differences needed to trigger the corrosion process, as well as to drive mobile contaminants to areas of concentration on the die.

THB testing employs the following stress conditions: 1000 hours at 85 deg C, 85% RH, with bias applied to the device. The bias applied is usually designed to simulate the bias conditions of the device in its real-life application, maximizing variations in the potential levels of the different metallization areas on the die as much as possible.

Surface-mount devices are also preconditioned prior to THB testing. During THB proper, intermediate readpoints at 48H, 96H, 168H, and 500H are often used. This gives look-ahead reliability data as the THB test progresses.

The main drawback of THB is its long duration, necessitating weeks before useable data are obtained. Because of this, an alternative test, the HAST, has been developed. HAST uses more severe stress conditions but can be completed in only 96 hours. Its shorter duration is an advantage that makes it a more popular stress test in the industry.

Fig. 1. Examples of Temperature/Humidity Chambers

Reliability Tests: Autoclave Test or PCT; Temperature Cycling; Thermal Shock; THB; HAST; HTOL; LTOL; HTS; Solder Heat Resistance Test (SHRT); Other Reliability Tests

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