accelerated)stress)tes-ng)for) airborne,)high)reliability ... bechtold accelerated... ·...

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 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

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


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


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.


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


APPROVED RELIABILITY PROGRAM PLAN

DEVELOP TEST PROCEDURE

START TEST

MONITOR UNIT UNDER TEST

INCREASE STRESS LEVELS

FAILURE DETECTED?

FAILURE ANALYSIS, UNIT REPAIR IF NECESSARY

CONTINUE TEST TO COMPLETE THIS LEVEL

TEST 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


Effects of ESS and HALT


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


Airborne Environmental Profile


(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: 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


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


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.



•  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.



•  Fixturing •  Should not restrict airflow to components •  Should not concentrate heat •  Should not effect vibration response of

the product – unless that is your intent



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 0.1 increments (1.00, 1.10, 1.20, …)

•  Thermal cycling:

•  Hardware failure found, mi-gated with packaging change •  Reliability in-‐service is improved by a simple hardware change


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


Acknowledgements •  The author gratefully acknowledges the following contributors to this presenta-on:

Anapathur Ramesh (Boeing) William Nguyen (Boeing) Brel Roundy (Boeing)


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-‐217. 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-‐1413.1 and 1332 revision commilees and the SAE/Tech America G-‐41 Commilee.


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