Temperature-humidity-bias

Fig. 6. Temperature—humidity—bias leakage testing of encapsulants at 85°C, 85% rh, and 180 V bias.

Figure 6 - Temperature Humidity Bias Testing of Silicone Gels. ...

Ling, H. C., and Jackson, A. M., Correlation of silver migration with temperature-humidity-bias (THB) failures in multilayer ceramic capacitors, lEEE-CHMT, 12, 130 (1989). 

Bias is frequently added for testing of electronic devices, printed wiring boards, and assemblies of electronic equipment. The 85°C, 85 % RH, bias test has been the predominant one in electronics for many years [8], While it sometimes misses failure mechanisms that later occur in the field, it also finds many weak points in new products. It is especially useful for quality control of seasoned devices for which long-term reliability is known to be high if the product passes this test. There are many commercial suppliers of temperature/humidity/bias test chambers and software is widely available to automate the operation, data collection, and data interpretation. Attention to data management is mandatory when hundreds of devices are tested simultaneously. This is frequently required in electronics to obtain sufficient data to make statistically valid predictions of lifetime and failure rate under use conditions. 

Temperature, Humidity, Bias. These tests are designed to promote corrosion on the PCB surface and conductive anodic filament growth, either of which can cause insulation resistance failures. 

Temperature, Humidity, Bias. The primary purpose of these tests is to identify surface insulation resistance (SIR) degradation due to corrosive materiak left on the board from the assembly process or due to galvanic couples set up in the assembly process. The usual test procedure is to use SIR comb patterns on the PCB, and to subject the assembly to 85°C/85 percent relative humidity/-20Vac for 1000 h.The bias voltage k dependent on the test device or test vehicle chosen. 

Sbar, N. L. and Kozakiewicz, R. P., New acceleration factors for temperature, humidity, bias testing, IEEE Trans. Electron Devices, ED-26 (1979) 56. 

As indicated previously, the insulation resistance is an extrinsic property of the material under investigation. This property will be affected by the test pattern chosen, temperature, humidity, bias voltage, and duration of test, as well as the contamination associated with previous processing steps. This contamination may result in electrochemical corrosion. 

Cycled temperature-humidity-bias life the test devices are subjected to a temperature cycle between 30 and 65°C, with a relative humidity of 90-98% and the operating voltage turned on and off at 5 min intervals. The specification requires a minimum of 63 cycles (total of 1008 h). 

Steady temperature-humidity-bias life (85°C/85% RH) the test specimens are stored for 1000 h or more at 85 2°C and a relative humidity of 85 5% with, depending on the device, a voltage applied either constantly or intermittently. Unbiased autoclave in the steam cooker test, the packaged devices are stored at 121°C under a saturated steam pressure of 0.103 MPa in a sealed autoclave. Depending to the intended application, the test conditions vary from 24 to 48 or 96 h of storage. The electrical measurements are performed at ambient temperature after the devices have been stored at room temperature for 48 h. Biased autoclave the test procedures are similar to the unbiased, except that a bias is applied through hermetic electrical connections. 

Steady temperature—humidity—bias life (85 °C/ 85% RH) the test specimens are stored for 1000 h or more at 85 2°C and a relative humidity of 85 5% with, depending on the device, a voltage applied either constantly or intermittently. 

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