Accelerated Stress Tes-ng for Airborne, High Reliability Applica-ons

Transcription

1 Accelerated Stress Tes-ng for Airborne, High Reliability Applica-ons Lori Bechtold Boeing Commercial Airplanes September, 2015 ASTR 2015, Sep 9-11, Cambridge, MA 1

2 Introduc-on In the U.S., high use of flight: 6 million people fly each day 31,000 commercial airplane flights per day Extensive safety program is cri-cal Reliability enhancement via Highly Accelerated Life Tes-ng (HALT) Supports design, test, cer-fica-on and fleet support Provides high reliability at entry into service and lowers maintenance costs Boeing Image ASTR 2015, Sep 9-11, Cambridge, MA 2

3 Airline Maintenance Costs Maintenance accounts for approximately 5% of airline s overall opera-ng costs Costs include schedule interrup-ons, maintenance technician labor, costs of spares, shipping costs Possible warrantee costs for the manufacturer Improvements in reliability are key to keeping airline opera-ons affordable ASTR 2015, Sep 9-11, Cambridge, MA 3

4 Reliability Enhancement Using HALT Highly Accelerated Life Tes-ng (HALT) Thermal Cycling, Power Cycling, Vibra-on Stresses Stress beyond qualifica-on limits Increases stepwise to drive weakness to failure Failure analysis provides product and process improvement Speeds reliability maturity, supports entry into service and lowers maintenance costs ASTR 2015, Sep 9-11, Cambridge, MA 4

5 What is HALT? Used to find product design weaknesses making the product more robust. HALT is done early during the design development process. Stresses are applied in steps to find a product's weaknesses, opera-onal design margins, and destruct limits. Stresses are higher than normal to obtain -me compression and accelerate aging. HALT is not a pass/fail test. It is pro- ac-ve! The stresses are increased un-l the product fails, rather than tes-ng to predefined limits. All HALT failures represent an opportunity for improvement and will probably show up in the field. Many failures are easy and inexpensive to fix. HALT typically takes 3-5 days. ASTR 2015, Sep 9-11, Cambridge, MA 5

6 HALT Program Process Flow APPROVED RELIABILITY PROGRAM PLAN DEVELOP TEST PROCEDURE START TEST Starts with approved plan Develop test procedures MONITOR UNIT UNDER TEST Step wise increase of stresses FAILURE ANALYSIS, UNIT REPAIR IF NECESSARY UNIT REPAIRED? NO, UNIT IS DESTROYED YES YES FAILURE DETECTED? NO CONTINUE TEST TO COMPLETE THIS LEVEL TEST LIMITS REACHED? NO INCREASE STRESS LEVELS Inves-ga-on of failures End of test when either: Unit destroyed Planned limits are reached YES TEST COMPLETE DOCUMENT LESSONS LEARNED, SUBMIT REPORT ASTR 2015, Sep 9-11, Cambridge, MA 6

7 HALT Supports ESS Planning Environmental Stress Screening (ESS) Thermal cycling and vibra-on stresses Drives manufacturing defects to fail in the test chamber rather than in service Lowers infant mortality failures When coupled with failure analysis, review and correc-ve ac-on, may improve overall reliability ASTR 2015, Sep 9-11, Cambridge, MA 7

8 Effects of ESS and HALT Failure rate ESS HALT Time ASTR 2015, Sep 9-11, Cambridge, MA 8

9 Defini-ons: Product Limits Lower Destruct Limit Lower Opera*ng Limit Product Spec Upper Opera*ng Limit Upper Destruct Limit Opera-ng Opera-ng Margin Margin Failure pdf Destruct Margin Destruct Margin Stresses ASTR 2015, Sep 9-11, Cambridge, MA 9

10 Airborne Environmental Profile (Courtesy of Airbus Group) ASTR 2015, Sep 9-11, Cambridge, MA 10

11 Accelera-on Model The most commonly used life- stress model for accelerated life tes-ng is the Arrhenius model R(T) = A exp (- E a / kt) Where: R(T) is the speed of the reac-on A is a constant, derived empirically from test results E a is the ac-va-on energy k is Boltzman s constant T is the temperature in degrees K ASTR 2015, Sep 9-11, Cambridge, MA 11

12 Ingredients for a HALT Stresses Specialized Chamber Courtesy of Cascade Engineering ASTR 2015, Sep 9-11, Cambridge, MA 12

13 Thermocouples and Accelerometers Multiple thermocouples should be used to monitor air temp around the product Thermocouples can be mounted inside unit or even attached to specific components, processors, power electronics Multiple accelerometers should be attached to different parts of the unit to measure differential energy response Accelerometers should be placed on dissimilar areas, such as on the rigid case and on an unsupported PCB ASTR 2015, Sep 9-11, Cambridge, MA 13

14 Ingredients for a HALT Functional Test and Monitoring Monitors the functionality of the product under test in real time. Should cover all unique signal paths. For a successful HALT failures must be caught as they happen. Work within the limitations of the product under test. ASTR 2015, Sep 9-11, Cambridge, MA 14

15 Ingredients for a HALT Fixturing Used to secure product during HALT. The HALT fixturing should be evaluated very carefully to ensure that it will not cause additional failures that wouldn t normally occur, or that it doesn t mask failure that may occur. ASTR 2015, Sep 9-11, Cambridge, MA 15

16 Ingredients for a HALT Fixturing Should not restrict airflow to components Should not concentrate heat Should not effect vibration response of the product unless that is your intent ASTR 2015, Sep 9-11, Cambridge, MA 16

17 Ingredients for a HALT Courtesy of Cascade Engineering ASTR 2015, Sep 9-11, Cambridge, MA 17

18 Example HALT A surface- mount technology electronics circuit card is selected for HALT tes-ng It will be included in the avionics suite in the EE- bay Vibra-on tes-ng will be random vibra-on, star-ng with qualifica-on level and increasing by 0.1 increments (1.00, 1.10, 1.20, ) Thermal cycling: Profile No. Low Temp ( C) Hardware failure found, mi-gated with packaging change Reliability in- service is improved by a simple hardware change High Temp ( C) Number of cycles ASTR 2015, Sep 9-11, Cambridge, MA 18

19 Conclusions HALT provides a las-ng value for highly reliable avionics Cost of in- service removals can be high, includes schedule interrup-ons, maintenance costs, costs of spares, shipping costs and possibly warrantee costs HALT is a cost effec-ve approach to improving reliability and providing value to the customer ASTR 2015, Sep 9-11, Cambridge, MA 19

20 Acknowledgements The author gratefully acknowledges the following contributors to this presenta-on: Anapathur Ramesh (Boeing) William Nguyen (Boeing) Brel Roundy (Boeing) ASTR 2015, Sep 9-11, Cambridge, MA 20

21 Lori Bechtold Author Biography Lori Bechtold is a reliability engineer with Boeing Commercial Airplanes in Sealle, WA. She holds a B.S. degree from the Massachusels Ins-tute of Technology (M.I.T.), and specializes in reliability analysis, physics of failure modeling and reliability industry standards development. Lori is the Principal Inves-gator of the AVSI Semiconductor Reliability project (AFE 83). She served on the DoD- led working group to revise MIL- HDBK She is chair of the VITA Standards Organiza-on Reliability Working Group, VITA 51. Lori is a member of the IEEE Reliability Society, par-cipated on the IEEE and 1332 revision commilees and the SAE/Tech America G- 41 Commilee. ASTR 2015, Sep 9-11, Cambridge, MA 21