Temperature-humidity-bias testing

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

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. 

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

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

High temperature/high humidity bias test and storage test, JIS C 7022, B-5 lEC PUB 68 Test C (heat test, MIL-STD-750, method 2031 ... 

HHBT High temperature High humidity Bias test done for example at 85 °C,... 

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. 

High temperature and high humidity bias test ... 

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. 

Electrical Properties. Electrical properties are important for the corrosion protection of chip-on-board (COB) encapsulated devices. Accelerated temperature, humidity, and bias (THB) are usually used to test the embedding materials. Conventional accelerating testing is done at 85°C, 85% relative humidity, and d-c bias voltage. Triple-track test devices with tantalum nitride (Ta2N), titanium—palladium—gold (Ti—Pd—Au) metallizations with 76... 

Accelerated solvent extraction (ASE), capillary chromatography sample preparation, 4 609, 610 Accelerated temperature, humidity, and bias (THB) tests, 10 9 Accelerated weathering tests, 19 584 Acceleration, exponents of dimensions in absolute, gravitational, and engineering systems, <5 584t Accelerators, 9 554-555 10 411, 713 22 61 23 861-862 for cement, 5 485... 

Figure 5 shows the performance of encapsulated devices under the high temperature storage device test. The conditions of this test are as follows storage in standard convection oven 0 200°C, no induced humidity, and no bias. Test results indicate that the encapsulant based on the stable bromine CEN took greater than 52 weeks to reach 50% failure that is, 50% of the initial number of devices have failed, in contrast to the standard high purity resin encapsulant which failed at 14 weeks. 

Figure 5. High Temperature Storage Device Test 200 C, No Induced Humidity, and No Bias...

Electrical-stability testing is essential for conductive adhesives used for electrical connections. Electrical conductivity can degrade at elevated temperatures, on aging with or without power, and on exposiue to humidity and temperature. The specific test method used depends on the application. One test used for die-attach adhesives specified in NASA MSFC-SPEC-592 (now inactive) involves a series of gold-plated Kovar tabs attached with conductive epoxy to metal pads on an interconnect substrate. In the test vehicle, a bias of 5 V and cmrent density of 139 3.9 A7cm (900 A/in ) are applied to a series of wire-connected tabs, and the resistance change is measured after exposure to 150 °C periodically up to 1,000 horns. The maximum allowable resistance change is 5%. 

Following particle deposition, the test specimens should be evaluated in a temperature/humidity environmental chamber. With electronic equipment, bias should be applied to the specimen as well, and the device or equipment assembly should imdeigo a foil series of functional tests. 

Since relative humidity plays such a key role in the corrosiveness of many environments, it is always desirable to monitor the interrelated humidity factors temperature, humidity, and dewpoint temperature. Since reliable commercial equipment is widely available, it will not be discussed further. Closely related to dewpoint is time-of-wetness (TOW), which is measured by monitoring the resistance between oppositely biased electrical conductors as a function of relative humidity. Bias can be applied through an external power source [72]. Alternatively, adjacent metal conductors can be selected to have substantially different corrosion potentials [73]. Above a critical level of relative hiunidity, the test specimen will adsorb a sufficient amoimt of moisture to produce a sharply lower resistance between conductors. The fraction of time of lowered resistance is commonly referred to as the time-of-wetness. It is one useful measure of the corrosivity of an environment. Such measurements were popular in the 1960s and 1970s. More recently, the preferred measurement, due to ease of use, is fraction of time the dewpoint is reached. A procedure for measuring time-of-wetness is contained in ASTM G 84, Standard Practice for Measurement of Time-of-Wetness on Surfaces Exposed to Wetting Conditions as in Atmospheric Corrosion Testing. 

To complete the selection trials applied to the conductive adhesives, MIL-STD-883 has issued a series of sequential environmental tests mainly aimed at devices used in the aerospace industry. The three tests are humidity-induced stress tests at elevated temperatures with and without bias, temperature-induced stress tests with and without bias, and a mechanical shock comprising acceleration 3000, 0.3 ms and constant acceleration 15,000 g (MIL-STD-883, Method 2001). The most severe tests are those involving both humidity and temperature, because they... 

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