Accelerated)Stress)Tes-ng)for) …

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 Introduc-on In the , 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 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.

2 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 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 What is HALT?

3 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.

4 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 HALT Program Process Flow Starts with approved plan Develop test procedures Step wise increase of stresses Inves-ga-on of failures End of test when either: Unit destroyed Planned limits are reached ASTR 2015, Sep 9 - 11, Cambridge, MA 6 APPROVED RELIABILITY PROGRAM PLAN DEVELOP TEST PROCEDURE START TEST MO NITO R UNIT UN DER TEST INCREASE STRES S LEVELS FAILURE DETECTED?

5 FAILURE ANALYSIS, UNIT REPAIR IF NECESSARY CONTINUE TEST TO CO MPLETE THIS LE VE L TE ST LIMITS REACHED? TEST COMPLETE DOCUMENT LESSONS LEARNED, SUBMIT REPORT NO NO YES YES UNIT REPAIRED? YES NO, UNIT IS DESTROYED 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 Effects of ESS and HALT ASTR 2015, Sep 9 - 11, Cambridge.

6 MA 8 Failure rate Time ESS HALT Lower Opera*ng Limit Product Spec Upper Opera*ng Limit Lower Destruct Limit Upper Destruct Limit Opera-ng Margin Destruct Margin Opera-ng Margin Destruct Margin Failure pdf Stresses Defini-ons: Product Limits ASTR 2015, Sep 9 - 11, Cambridge, MA 9 Airborne Environmental Profile ASTR 2015, Sep 9 - 11, Cambridge, MA 10 (Courtesy of Airbus Group) Accelera-on Model The most commonly used life- stress model for accelerated life tes-ng is the Arrhenius model R(T) = A exp (- Ea / kT) Where.

7 R(T) is the speed of the reac-on A is a constant, derived empirically from test results Ea 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 Ingredients for a HALT Stresses Specialized Chamber Courtesy of Cascade Engineering ASTR 2015, Sep 9 - 11, Cambridge, MA 12 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.

8 MA 13 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 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.

9 ASTR 2015, Sep 9 - 11, Cambridge, MA 15 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 Ingredients for a HALT Courtesy of Cascade Engineering ASTR 2015, Sep 9 - 11, Cambridge, MA 17 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 increments (.)

10 Thermal cycling: Hardware failure found, mi-gated with packaging change Reliability in- service is improved by a simple hardware change ASTR 2015, Sep 9 - 11, Cambridge, MA 18 Profile No. Low Temp ( C) High Temp ( C) Number of cycles 1 -45 90 3 2 -50 95 3 3 -55 100 3 4 -60 105 3 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.