1、Institute of Environmental Sciences and Technology IEST-RP-PR003.1 Product Reliability Division Recommended Practice 003.1 HALT and HASS Arlington Place One 2340 S. Arlington Heights Road Arlington Heights, IL 60005-4516 Phone: (847) 981-0100 Fax: (847) 981-4130 E-mail: informationiest.org Web: www.
2、iest.org 2 IEST 2012 All rights reserved Institute of Environmental Sciences and Technology IEST-RP-PR003.1 This Recommended Practice is published by the Institute of Environmental Sciences and Technology to advance the technical and engineering sciences. Use of this document is entirely voluntary,
3、and determination of its applicability and suitability for any particular use is solely the responsibility of the user. Use of this Recommended Practice does not imply any warranty or endorsement by IEST. This Recommended Practice was prepared by and is under the jurisdiction of Working Group 003 of
4、 the IEST Prod-uct Reliability Division. Copyright 2012 by the Institute of Environmental Sciences and Technology First printing, September 2012 ISBN 978-1-937280-07-9 PROPOSAL FOR IMPROVEMENT: The Working Groups of the Institute of Environmental Sciences and Tech-nology are continually working on i
5、mprovements to their Recommended Practices and Reference Documents. Sug-gestions from users of these documents are welcome. If you have a suggestion regarding this document, please use the online Proposal for Improvement form found on the IEST website at www.iest.org. Institute of Environmental Scie
6、nces and Technology Arlington Place One 2340 S. Arlington Heights Road Arlington Heights, IL 60005-4516 Phone: (847) 981-0100 Fax: (847) 981-4130 E-mail: informationiest.org Web: www.iest.org IEST-RP-PR003.1 Institute of Environmental Sciences and Technology IEST 2012 All rights reserved 3 HALT and
7、HASS IEST-RP-PR003.1 CONTENTS SECTION 1 SCOPE 4 2 REFERENCES . 4 3 TERMS AND DEFINITIONS . 4 4 BACKGROUND AND PURPOSE 5 5 HALT . 5 6 HASS 14 7 DIFFERENCES BETWEEN HALT AND HASS . 15 8 EQUIPMENT USED FOR HALT AND HASS . 16 9 FIXTURING 17 10 OTHER CONSIDERATIONS . 19 11 SUBJECTS OF CONCERN . 21 12 ADD
8、ITIONAL RESOURCES . 22 13 ACKNOWLEDGEMENTS 22 FIGURE 1 EXAMPLE FOR DETERMINING HOW MANY SAMPLES TO TEST. 7 2 THERMAL STEP STRESS TESTING. . 8 3 COLD STEP STRESS TEST EXAMPLE 8 4 HOT STEP STRESS TEST EXAMPLE. . 9 5 RAPID THERMAL CYCLING TESTING. . 9 6 REPETITIVE SHOCK TABLE TEST SETUP EXAMPLE. . 10 7
9、 ELECTRODYNAMIC SHAKER TEST SETUP EXAMPLE. 10 8 APPLICABILITY OF SHAKER TYPE 10 9 VIBRATION STEP STRESS TESTING. 11 10 LEGACY ESS INPUT. 11 11 SKEWED-AXIS TEST FIXTURE. 12 12 COMBINED VIBRATION AND THERMAL STEP STRESS TESTING. 12 13 EXAMPLE FIXTURING FOR REPETITIVE SHOCK. . 17 14 EXAMPLE OF FIXTURIN
10、G FOR ELECTRODYNAMIC SHAKER. 18 15 EXAMPLE PRODUCT THERMAL RANGES. 19 TABLE 1 LEGACY ESS INPUT . 12 2 EXAMPLE OF HASS THERMAL LEVELS 14 3 DIFFERENCES BETWEEN HALT AND HASS . 15 4 IEST 2012 All rights reserved Institute of Environmental Sciences and Technology IEST-RP-PR003.1 Institute of Environment
11、al Sciences and Technology Product Reliability Division Recommended Practice 003.1 HALT and HASS IEST-RP-PR003.1 1 SCOPE 1.1 Scope This Recommended Practice (RP) defines and de-scribes HALT (Highly Accelerated Life Testing) and HASS (Highly Accelerated Stress Screening). This RP contains information
12、 on the philosophy behind the testing, generic examples of tests, the differences between standard testing equipment and equipment used for highly accelerated testing, fixturing consid-erations, alternative approaches, additional environ-ments, and lessons learned, along with other useful informatio
13、n. This style of testing takes a Qualitative approach (looking for the quality of the design and workmanship) rather than a Quantitative approach (being able to use the results to calculate length of life in service). This RP is not meant to take the place of a test specification but to be used in c
14、onjunction with a test specification or as general guidance. 2 REFERENCES The cited editions of the following documents are incorporated into this RP to the extent specified here-in. Users are encouraged to investigate the possibility of applying the most recent editions of the references. MIL-STD-8
15、10: Test Method Standard for Environ-mental Engineering Considerations and Laboratory Tests Military Standards Standardization Document Order Desk 700 Robbins Avenue Bldg #4, Section D Philadelphia, PA 19111, USA http:/dodssp.daps.dla.mil/ 3 TERMS AND DEFINITIONS acceleration The rate of change of v
16、elocity with respect to time. For vibration testing, acceleration is usually ex-pressed in gravitational units (g) but may also be ex-pressed as m/sec2. accelerometer A sensor for converting acceleration into an electrical signal; a transducer featuring instantaneous output proportional to the insta
17、ntaneous acceleration input. bathtub curve A plot of product failures versus time, which has three sections: The first shows decreasing “infant mortality” (early failures); the second, constant random failures; and the third, increasing wear-out failures. dwell The length of time during which a test
18、 article is sub-jected to an environment (e.g., thermal or vibration). electrodynamic (ED) shaker A type of shaker that uses electrical energy to create dynamic motion. In physics, the technology used is referred to as the “voice coil principle.” environmental stress screening (ESS) The application
19、of forcing function to a product for the purpose of characterizing the environmental per-formance of the product. Failure Modes and Effects Analysis (FMEA) A methodology conducted during product develop-ment to identify and classify potential reliability problems, and to define a course of action to
20、 mitigate failures according to priority. fixture An intermediate structure used to attach a test unit to a test platform such as a vibration table. IEST-RP-PR003.1 Institute of Environmental Sciences and Technology IEST 2012 All rights reserved 5 Fourier transform; discrete Fourier transform (DFT)
21、The representation of a time-history by a harmonical-ly related series of sines and cosines. The digitally sampled time-history is represented by the DFT. g-level The acceleration time-history amplitude of a pyroshock as measured by an accelerometer calibrat-ed in gs. May also be expressed in m/sec2
22、. gRMSThe root-mean-square acceleration. Power Spectral Density (PSD) The limiting mean-square value per unit bandwidth (i.e., the limit of the mean-square value in a given rectangular bandwidth divided by the bandwidth). These bands are grouped into a plot of power level (in g2/Hz) vs. frequency (i
23、n Hz), over the frequency range of interest. The resulting plot gives an indica-tion of the power at each frequency. root-mean-square (RMS) The square root of the time-averaged squares of a series of measurements. transducer (sensor) A device that converts shock or vibration into an electrical signa
24、l that is proportional to the parameter of the experienced motion or force. NOTE: The term “transducer” is often used inter-changeably with the term “sensor” in industry. The term “sensing element” is used to describe the sens-ing mechanism inside the transducer or sensor. 4 BACKGROUND AND PURPOSE H
25、ALT (Highly Accelerated Life Testing) and HASS (Highly Accelerated Stress Screening) are two meth-ods for potentially improving reliability and quality of products. The information learned from HALT can show whether the design is acceptable or changes are needed to achieve a more robust design. This
26、 infor-mation can help a practitioner decide what corrective actions are required. HASS is a follow-up to HALT and is performed at the end of fabrication to help detect changes in process or components that would adversely affect reliability. Used together, lessons learned from HALT and HASS process
27、 can improve quality, reliability, performance, and safety; can reduce cost and warranty issues; and can result in increased satisfaction with the product. 5 HALT HALT is a process specifically designed to detect design weaknesses in products. HALT was developed from an understanding that reliabilit
28、y is improved by finding and eliminating failure modes. An efficient means for generating failures is required for optimal product development. HALT is a product develop-ment approach that can be applied with any reasona-ble environmental stress. HALT is not a pass/fail test, but rather a discovery
29、process utilizing equipment and exposures for determining the product sensitivity to anticipated, measured, or known field stresses, and a means to develop a product to the practical limit of the employed design technology. The concept is to purposely stress products to understand the mecha-nisms mo
30、st likely to cause failure during the product life cycle of transportation, storage, and use. This knowledge can result in design actions that lower the field risk, thus enabling effective business decisions for market success. In HALT, test durations are com-pressed by increasing stress levels. Fai
31、lures and their effects found during HALT can then be used to verify a Failure Modes and Effect Analysis (FMEA). There are numerous environmental testing alternatives to HALT, including development, qualification, ac-ceptance, statistical reliability, and reliability growth, each of which has specif
32、ic goals and methods. HALT is not a substitute for any of the tests listed here. Prac-titioners must understand each method to select the appropriate test program. It is beyond the scope of this RP to discuss each of these methods. Reliability Growth Testing (RGT) and HALT are similar, but are condu
33、cted differently. RGT applies the defined environmental requirements of the system for extended periods of time or at slightly exaggerat-ed levels, or both. It is the goal of RGT to estimate reliability, design margin, and the infant mortality period of a reliability bathtub curve. On the other hand
34、, it is the function of HALT to ex-pose potential design weaknesses quickly, and HALT can be applied whether or not the system has defined environments. Defined environments can be used as the starting point for HALT. However, HALT envi-ronments are applied at levels that may greatly ex-ceed the def
35、ined environments, so correlated statisti-cal failure data cannot be obtained because of the low sample size and potentially high variation observed in times to failure. Damage models may require pa-rameter adjustment for accuracy. HALT entails a series of exposures (typically five) using various en
36、vironmental stresses. However, as a philosophy HALT is not limited to only these envi-ronments. HALT can expedite the ability to improve the robustness of the product design before the product reaches the production phase. Diligent fail-ure analysis and efficient feedback to the design team result i
37、n HALT being a valuable process. To be effective, HALT requires a commitment to the 6 IEST 2012 All rights reserved Institute of Environmental Sciences and Technology IEST-RP-PR003.1 process and the recognition that failures are desira-ble, with design decisions (often actions) required in response.
38、 These actions include replacing less ro-bust components, identifying material or intercon-nect deficiencies, exposing poor processes (though HASS is specifically used to identify these), and improving structures, among other things. Failures found during HALT should be analyzed to determine the fai
39、lure mechanism. Hardware and sys-tem failures should be evaluated to determine their root cause in light of materials, manufacturing pro-cesses, and design. Then informed decisions can be made that are consistent with business risk and tech-nology limitations. The philosophy is to continue making th
40、e product more resistant to environmental and usage stresses, and hence more durable. However, a point of dimin-ishing returns is reached if the product is determined to be sufficiently durable based on expected usage conditions and environmental extremes. The objec-tive is a strong and robust produ
41、ct, but not a product that is overdesigned. To maximize the efficiency of the HALT process, it is imperative to constantly monitor the unit under test (UUT) and to run functional tests while the unit is being stressed. Electronic monitoring with data ac-quisition, as well as visual observation by pe
42、rsonnel to detect deficiencies that might otherwise be missed, is critical. With each design change, the new configu-ration should be retested with either a reworked or a new unit. In some cases, changing out one compo-nent can result in failure of a different component. It should not be assumed tha
43、t the replacement of one component will rectify the overall design. Additional testing is required to verify the modified design. 5.1 Product limits during HALT Many product limits should be factored into the HALT process, including the following: a) SpecificationsThe environmental levels under whic
44、h the product is designed to function correctly. b) Upper and Lower Operating LimitsThe limits at which the product will stop operating correctly. For temperature and humidity there are upper and lower limits. For vibration there is only an upper limit. UOL (Upper Operating Limit) LOL (Lower Operati
45、ng Limit) VOL (Vibration Operating Limit) c) Upper and Lower Destruct LimitsThe limits at which the product has a complete and unrecoverable failure. Again, for temperature and humidity there are upper and lower limits. For vibration there is only an upper limit. UDL (Upper Destruct Limit) LDL (Lowe
46、r Destruct Limit) VDL (Vibration Destruct Limit) Depending on the product and its applicable environ-ments, other limits may also apply. These environ-ments include, for example, humidity, pressure, salt spray, and power cycling. All of these and other envi-ronments may be applicable to specific har
47、dware. The extreme limits to be used for the individual tests should be determined before testing commences, tak-ing into consideration hardware availability and time constraints for attaining the desired operating and de-struct limits. (The limits may be the same as the HALT chamber/vibration syste
48、m limits.) Knowing in advance the number of samples available for testing will aid in the decision-making process. It is also important to understand the temperature and vibration limits. Hu-midity is not always monitored or controlled during HALT, though monitoring humidity when not control-ling it
49、 can provide valuable additional data for failure analysis. Thus, a humidity limithigh, low, or bothmay also be chosen. Choosing predetermined limits (those falling outside of operating and destruct limits) is a matter of engineering judgment. In deciding whether to make improvements to the test item, any failure found within the range between the product specification and the operating limit is gener-ally considered to be a “must fix,” and any failure between the operating limit and the destruct limit is cons
