2. Reliability Engineering for Medical Devices Richard C. Fries Manager, Reliability Engineering Datex-Ohmeda Madison, Wisconsin

3. Definition of Reliability The probability, at a desired confidence level, that a device will perform a specified function, without failure, under stated conditions, for a specified period of time

4. More General Definition of Reliability A reliable product: one that does what the customer wants, when the customer wants to do it

5. Reliability Basics Reliability cannot be tested into a product It must be designed and manufactured into it Testing only indicates how much reliability is in the product

6. Purpose of the Reliability Group Determine the weaknesses in a design and correct them before the device goes to the field

7. Areas Covered by Reliability zElectrical zMechanical zSoftware zSystem

8. Electrical Reliability

9. Mechanical Reliability

10. Theoretical Software Reliability

11. Practical Software Reliability

12. System Reliability

13. Set the Reliability Goal zBased on similar equipment zUsed as the basis for a reliability budget

14. Parts Count Prediction zUses MIL-HDBK-217 zIndicates whether the design approximates the reliability goal zIndicates those areas of the design with high failure rates

15. Chemical Compatibility zTest plastics with typically used chemical agents (alcohol, anesthetic agents, cleaning agents) zCleaning agents are the worst

16. Component Testing zCycle/life testing of individual components zComparison of multiple vendors of components zDetermine applicability for the intended use

17. HALT zAcronym for Highly Accelerated Life Teing zUsed to find the weak links in the design and fabrication process zUsually performed during the design phase

18. HASS zAcronym for Highly Accelerated Stress Screen zUses the highest possible stresses as determined by HALT testing zPerformed on 100% of the units being manufactured

19. HALT Testing zPossible stresses that can be applied: xrandom vibration xrapid temperature transitions xvoltage margining xfrequency margining zThe product is stressed far beyond its specifications zThe test can be set up to find the destruct limits

20. Goal of HALT Testing zOverstress the product zQuickly induce failures zBy applying the stresses in a controlled, stepped fashion, while continuing monitoring for failures, the testing results in the exposure of the weakest points in the design zThis test does not demonstrate that a product will function in its intended environment zThis test, if successful, will expose weak points in the design

21. Goals of HALT Testing zThe goal is more effectively met by testing at the lowest possible subassembly, typically individual PC boards zCard cages are not usually used due to the dampening effect of the cage on vibration zCages also can block air flow, thus reducing stresses

22. Environmental Testing zOperating temperature/humidity zStorage temperature/humidity zEMC ySurges/transients yBrown-outs yCell phones zESD zAltitude

23. Environmental Testing zAutoclave zShock zVibration zShipping zTip testing zThreshold testing

24. Customer Misuse zExcess weight on tabletop zFluid spillage zCross connection of wires zPulling unit by non-pulling parts zWrong order of pressing keys z“Knowing” how to operate the unit without reading the manual

25. Making a Design Foolproof The biggest mistake engineers make when trying to make a design completely foolproof is underestimating the ingenuity of complete fools

26. High Performance Air Compressor

27. Prototype Front Panel for Ventilator

28. Plastic Structure

31. Manifold Port

32. Prototype Switch

33. Autoclave Testing

34. Critical Care Ventilator

36. Life Testing zOperate the device in its typical environment and application zUse appropriate on/off cycles zCan be used to verify the reliability goal or a specific period of time, such as the warranty period

37. Tracking Reliability Growth in the Field zCollect manufacturing data on how many units were manufactured by month zCollect field failure data, by month zDevelop a reliability growth chart

38. Reliability Growth Example

41. Failure Analysis zFailure: device does not operate according to its specification zDetermine root cause of the failure zSuggest methods to address the failure

42. The Reliability Group You make it, We’ll break it