Highly accelerated stress test

These molding compounds were also used to encapsulate electronic devices for reliability testing. In Figures 4, 5, and 6, stable bromine CEN outperformed "state-of-the-art" resins in the bias pressure cooker device test (BPC), high temperature storage device test (HTS), and the highly accelerated stress test (HAST). 

Figure 6 shows the performance of encapsulated devices under the highly accelerated stress test which utilizes the following conditions 145°C, 85% relative humidity, 37 psig, and electrical bias. The bias on this test is cycled specifically, the bias is initially off to allow for full moisture penetration and then turned on. These cycles are repeated throughout the test. The stable bromine CEN compound took 2500 hours to reach 50% failure rate, compared to the standard resin compound at 1900 hours. 

Figure 6. Highly Accelerated Stress Test - Device Test LF412 Dual Op Amp, 145 C, 85% RH, and Bias...

Highly Accelerated Stress Test per JEDEC-STD-22-AllO. ... 

Thomsen B, Tryson M (2009) Highly accelerated stress testing (HAST) of DEAP actuators. Proc SPIE 7287 102-113... 

Humidity testing is nearly always carried out at temperatures ranging from 351-100°C with relative humidity from nearly zero to 100 %. Occasionally, steam bombs are used so tests can be run above 100°C. In the last ten years, highly accelerated stress tests have been developed to enable materials to be tested at temperatures above 100°C, but at a noncondensing relative humidity, typically 85 %. The most common applications for these tests are in evaluating coatings, paper, adhesives, adhesion between mechanically or chemically bonded materials, and, in electronics, for evaluating the effectiveness of device encapsulation. 

Ballard (Li et al, 2006) used two different test protocols to evaluate platinum durability for 2500 h of continuous cell operation advanced automotive duty cycle (AADG) and highly accelerated stress test (HAST). AADG involved potential cycling between 0.6 V and open-circuit potential (vs RHE) using fully humidified reactants (hydrogen in the anode and air in the cathode) at 70 °G cell... 

Highly accelerated stress testing unlike the pressure cooker tests, this test uses unsaturated steam, varying from 50 to 100%, at temperatures of 105-150°C, the experimental data being extrapolated to any temperature-humidity conditions by using theoretical models based on the usual Arrhenius equation. 

Infant-mortality period. In the early period of failures, accelerated stress tests such as burn-in, power cycling, temperature cycling, and vibration as well as highly accelerated stress and life testing are used. These methods are used to screen out parts that are inherently not reliable and prevent the delivery of dead on arrival parts to a customer. While this consumes some early life of an assembly by stress screening, the remaining population begins the useful life period or the flat area of the bathtub. 

Data describing the reliability of joints assembled with anisotropically conductive adhesives are incomplete. Several papers have been published, but usually the sample size investigated is small, the accelerated stress tests are not standardized, and the results are highly dependent on device type (e.g., flexible circuit to rigid PWB, surface-mounted components, and flip-chip assembles). Further work is required in this area. 

They also need this information to create a test plan for both EMC and HALT (Highly Accelerated Life Testing) that will verify/validate the design, and to design the routine EMC testing and physical stress screening required in volume manufacture. 

Benjamin, T.G., Membrane and MEA accelerated stress test protocols, presented at High Temperature Membrane Working Group Meeting, Washington, DC, May 14,2007. 

Alloys containing only a few per cent of zinc may fail if the stresses are high and the environment sufficiently corrosive. Most types of brass, besides the plain copper/zinc alloys, appear to be susceptible to stress corrosion. An extensive investigation of the effect of additions to 70/30 brass was carried out by Wilson, Edmunds, Anderson and Peirce , who found that about 1% Si was markedly beneficial. Other additions were beneficial under some circumstances and none of the 36 additions tested accelerated stress-corrosion cracking. Further results are given in later papers ... 

After obtaining the prototypes, tests must be made to determine the utility. Generally these include a short time destructive test to determine the strength and to check out the basic design. Another test that is done is to use the product in the projected environment with stress levels increased in a rational manner to make for an accelerated life test. Other tests may include consumer acceptance tests to determine what instructions in proper use are required, tests for potential safety hazards, electrical tests, self-extinguishing tests, and any others that the product requires. In the case of high risk products, the test program is continued even after the product enters service. 

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