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ECE 477: Digital Systems Senior Design Last Modified: 08-03-2017 Reliability and Safety Analysis Year: 2017 Semester: Spring Creation Date: 3/30/2017 Author: Sneh Patel Team: 13 Project: RA-1 Last Modified: August 3, 2017 Email: [email protected] Assignment Evaluation: Item Assignment-Specific Items Reliability Analysis MTTF Tables FMECA Analysis Schematic of Functional Blocks (Appendix A) FMECA Worksheet (Appendix B) Writing-Specific Items Spelling and Grammar Formatting and Citations Figures and Graphs Technical Writing Style Total Score 5: Excellent 4: Good Score (0-5) Weight Points 5 4 5 x2 x3 x2 10 12 10 5 x2 10 5 x3 15 5 4 5 5 x2 x1 x2 x3 10 4 10 15 96 3: Acceptable 2: Poor Notes 1: Very Poor 0: Not attempted Comments: Good work! The report is well written and meets most of the requirements. https://engineering.purdue.edu/ece477 Page 1 of 12 ECE 477: Digital Systems Senior Design Last Modified: 08-03-2017 1.0 Reliability Analysis The components that are most likely to fail here are the LD1117 Low Dropout Regulator [1], the V7805 2000R DC/DC converter [2], the SN74HC595 serial to parallel shift register [3], and the STM32F407VGT6 microcontroller [4]. The LD1117 Low Dropout regulator was selected because it generates a lot of heat. The V7805 2000R was selected because it is responsible for regulating the voltage and will also have a lot of current going through it. The SN74HC595 was selected because it will be connected to the output of the DC/DC converter and may fail if too much voltage or current is provided to it. The STM32F407VGT6 microcontroller was selected because it is the most complex chip on our circuit and has 100 I/O pins. The model we are using can be found in the Military Handbook MIL-Hdbk-217f[5]: λP = (C1 * πT + C2 * πE) * πQ * πL The mean time to failure (MMTF) in years is: MTTF = 106 / (24 * 365 * λP) The assumptions are: The quality factor (πQ) for commercial products is taken to be 10 The learning factor (πL) is taken to be 1 as the products are all 2 years old at least The environment factor (πE) is taken to be 2.0 V7805 2000R DC/DC converter: The V7805 2000R DC/DC converter [1] has about 100 to 300 bipolar transistors and therefore the die complexity rate was taken to be 0.02 according to the MIL-Hdbk-217f. As the V7805 2000R is a 3-pin IC and is a surface mount device, the packaging coefficient was taken to be 0.00092. The temperature factor was taken to be 3.3 as the worst-case temperature would be taken to be about 85 °C as it runs a lot cooler than a voltage regulator. According to the formulas found in the MIL-Hdbk-217f, the Failure rate per million hours was found to be 0.6784 and the mean time to failure in years was found to be 168 years. Parameter name Description Value Comments C1 Die complexity failure rate 0.02 πT Temperature coefficient 3.3 C2 Package Failure rate 0.00092 πE Environment Factor 2.0 πQ πL Quality Factor Learning Factor 10 1 Based on the MIL-Hdbk217f for devices with 100 to 300 bipolar transistors This is based on the worst case junction temperature of 85 °C Based on the equation provided in the MIL-Hdbk217f for an SMT with 3 pins MIL-Hdbk-217f value for mobile devices Commercial Part Used for devices older than https://engineering.purdue.edu/ece477 Page 2 of 12 ECE 477: Digital Systems Senior Design Last Modified: 08-03-2017 2 years in production λP MTTF Failure rate per million 0.6784 hours Mean Time to Failure 168.27 Approximately 168 years for one device to fail LD1117 Low Dropout Regulator: The LD1117 Low Dropout Regulator [2] has about 100 to 300 bipolar transistors and therefore the die complexity rate was taken to be 0.02 according to the MIL-Hdbk-217f. As the LD1117 is a 3-pin IC and is a surface mount device, the packaging coefficient was taken to be 0.00092. The temperature factor was taken to be 5.9 as the worst-case temperature would be 125 °C. According to the formulas found in the MIL-Hdbk-217f, the Failure rate per million hours was found to be 1.1784 and the mean time to failure in years was found to be 97 years. Parameter name Description Value Comments C1 Die complexity failure rate 0.02 πT Temperature coefficient 5.9 C2 Package Failure rate 0.00092 πE Environment Factor 2.0 πQ πL Quality Factor Learning Factor 10 1 Based on the MIL-Hdbk217f for devices with 100 to 300 bipolar transistors This is based on the worst case junction temperature of 125 °C Based on the equation provided in the MIL-Hdbk217f for an SMT with 3 pins MIL-Hdbk-217f value for mobile devices Commercial Part Used for devices older than 2 years in production λP Failure rate per million 1.1784 hours Mean Time to Failure 96.678 MTTF Approximately 97 years for one device to fail SN74HC595 serial to parallel shift register: The SN74HC595 serial to parallel shift register [3] has less than 100 bipolar transistors and therefore the die complexity rate was taken to be 0.01 according to the MIL-Hdbk-217f. As the SN74HC595 is a 16-pin IC and is a surface mount device, the packaging coefficient was taken to be 0.0056. The temperature factor was taken to be 5.9 as the worst case temperature would be https://engineering.purdue.edu/ece477 Page 3 of 12 ECE 477: Digital Systems Senior Design Last Modified: 08-03-2017 125 °C. According to the formulas found in the MIL-Hdbk-217f, the Failure rate per million hours was found to be 0.702 and the mean time to failure in years was found to be 162.61 years. Parameter name Description Value Comments C1 Die complexity failure rate 0.01 πT Temperature coefficient 5.9 C2 Package Failure rate 0.0056 πE Environment Factor 2.0 πQ πL Quality Factor Learning Factor 10 1 Based on the MIL-Hdbk217f for devices with 0 to 100 bipolar transistors This is based on the worst case junction temperature of 125 °C Based on the equation provided in the MIL-Hdbk217f for an SMT with 16 pins MIL-Hdbk-217f value for mobile devices Commercial Part Used for devices older than 2 years in production λP Failure rate per million 0.702 hours Mean Time to Failure 162.61 MTTF Approximately 163 years for one device to fail STM32FVGT6 Microcontroller: The STM32F407VGT6 is a 32-bit microcontroller [4] and therefore the die complexity rate was taken to be 0.24 according to the MIL-Hdbk-217f. As the SN74HC595 is a 16-pin IC and is a surface mount device, the packaging coefficient was taken to be 0.0056. The temperature factor was taken to be 5.9 as the worst case temperature would be 85 °C. According to the formulas found in the MIL-Hdbk-217f, the Failure rate per million hours was found to be 9 and the mean time to failure in years was found to be 13 years. Parameter name Description Value Comments C1 Die complexity failure rate 0.24 πT Temperature coefficient 3.3 C2 Package Failure rate 0.054 Based on the MIL-Hdbk217f for devices with 0 to 100 bipolar transistors This is based on the worst case junction temperature of 85 °C Based on the equation provided in the MIL-Hdbk217f for an SMT with 100 pins https://engineering.purdue.edu/ece477 Page 4 of 12 ECE 477: Digital Systems Senior Design πE Environment Factor 2.0 πQ πL Quality Factor Learning Factor 10 1 λP Failure rate per million 9 hours Mean Time to Failure 12.684 MTTF Last Modified: 08-03-2017 MIL-Hdbk-217f value for mobile devices Commercial Part Used for devices older than 2 years in production Approximately 13 years for one device to fail 2.0 Failure Mode, Effects, and Criticality Analysis (FMECA) For this project, we identified three different criticality levels for part failure: low, medium, and high. A low criticality failure is associated with no harm to the user or the rest of the project. A low criticality failure is usually easily fixable. For example, an LED failure is classified as a low criticality failure. Low criticality errors should have failure rate of 10-6 or less. A medium criticality failure is one which causes no harm to the user but have the potential to damage the system. Heating up of the voltage regulator is an example of a medium criticality failure. These errors should have a failure rate that is limited to 10-7. A high criticality failure is defined as one that has the potential to harm users. These kinds of errors should have a failure rate of no more than 10-9. The different pieces of our robotic arm have been assembled together using nuts and bolts. Due to the mechanical movement of the arm, the nuts may get loose and result in the arm collapsing on the user. This is a potential high criticality failure. Our PCB harbors 4 major hardware components: RN4020 Bluetooth module, LCD, microcontroller, and power circuitry. We anticipate that the most common failures modes will be extreme current drawn by the servos, communication lag with the RN4020 module, and mechanical failure of the arm chassis. 3.0 Sources Cited: [1] CUI INC, “NON-ISOLATED SWITCHING REGULATOR.” [Online]. Available: http://www.cui.com/product/resource/v78xx-2000.pdf. [Accessed: 31-Mar-2017]. [2] Microelectronics, ST. "Adjustable And Fixed Low Drop Positive Voltage Regulator". N.p., 2017. Web. 1 Apr. 2017. [3] TI,. "8 Bit Shift-Registers". Texas Instruments. N.p., 2017. Web. 1 Apr. 2017. [4] S. Microelectronics, "STM32F405xx STM32F407xx,". [Online]. Available: http://www.st.com/content/ccc/resource/technical/document/datasheet/ef/92/76/6d/bb/c2/ 4f/f7/DM00037051.pdf/files/DM00037051.pdf/jcr:content/translations/en.DM00037051. pdf. Accessed: Feb. 03, 2017. [5] DOD,. "Reliability Of Prediction Equipment". N.p., 2017. Web. 1 Apr. 2017. https://engineering.purdue.edu/ece477 Page 5 of 12 ECE 477 Digital Systems Senior Design Project Spring 2009 Appendix A: Schematic Functional Blocks . Fig 2. Header for motors Fig 3. Power input using barrel jack connector Fig 1. LCD Circuit -6- ECE 477 Digital Systems Senior Design Project Spring 2009 Fig 5. DC - DC converter with 5V output Fig 4. RN 4020 Bluetooth circuit Fig 6. LDO 5V to 3V -7- ECE 477 Digital Systems Senior Design Project Spring 2009 Fig 8. Programming header Fig 7. Microprocessor -8- ECE 477 Digital Systems Senior Design Project Spring 2009 Appendix B: FMECA Worksheet Subsystem A: LCD Circuit Failure Failure Mode No. A1 Wrong data appearing on the LCD display. A2 A3 Possible Causes Incorrect SPI settings, damaged shift register IC, No data appearing Damaged shift on the LCD register IC, incorrect display. SPI settings, damaged LCD display LCD display is Damaged LCD not powered. display Failure Effects Method of Detection Observation Low LCD does not display any data. Observation Low LCD backlight will not be on. Observation Low LCD has output that cannot be read or jibberish. Criticality Remarks Assuming shift register is working correctly. Subsystem B: Power Supply Failure Failure Mode No. B1 Short circuit Possible Causes If any of the connections are wrong or touching wires Failure Effects Short circuiting the entire PCB and burning the micro -9- Method of Detection Check using multimeter in resistance mode to check for short Criticality High Remarks ECE 477 Digital Systems Senior Design Project Spring 2009 B2 Incorrect Voltage Wrong values of capacitors and resistors in the power supply circuit Might result in overheating and even burning of some components Use multimeter Low to check voltage at all major junctions B3 Incorrect current rating Failure of the V7805 DC DC converter Use ammeter to check worst case scenario Med B4 Failure of any of the voltage regulators The V7805-2000R is rated for 2A. More current is drawn due to a high stall current on the servo motors Defective piece Unexpected behavior Test part before placing on the PCB Low Subsystem C: RN4020 Module Failure Failure Mode No. C1 RN4020 not able to communicate with the microcontroller. C2 RN4020 not able to communicate with the application. Possible Causes Damaged RN4020, incorrect communication settings. Damaged RN4020, incorrect communication settings. Failure Effects Loss of remote control setting, microcontroller could run in an infinite loop Loss of remote control setting. -10- Method of Detection Inspection of Tx, Rx on microcontroller. Inspection of Tx, Rx on RN4020. Criticality Low Low Remarks ECE 477 C3 Digital Systems Senior Design Project RN4020 sending wrong data to phone/ microcontroller. Incorrect communication settings. Loss of remote control setting. Observation Spring 2009 Low Assuming RN4020 is not damaged. Subsystem D: Microcontroller Failure Failure Mode No. D1 Microcontroller resetting unexpectedly D2 Microcontroller being unresponsive Possible Causes Failure Effects Damage to reset Unresponsive button or reset circuit, microcontroller, capacitors shorted constant resetting Damage to microcontroller, capacitors shorted Microcontroller heating up, product does not function at all Method of Detection Observation Criticality Medium Observation Medium Remarks Assuming the microcontroller is not constantly resetting Subsystem E: Servo Motors Failure Failure Mode No. E1 The servo not moving to correct position Possible Causes Incorrect microcontroller settings. Failure Effects Replay mode/Remote control mode will not function. -11- Method of Detection Observation Criticality Medium Remarks ECE 477 Digital Systems Senior Design Project Spring 2009 E2 Servo not moving at all Damage to servo, incorrect microcontroller settings. Replay mode/Remote control mode will not function. Observation Medium E3 Servo not sending data back Damage to servo, incorrect microcontroller settings. Record mode will not function. Observation Medium -12- Assuming no damage to servo motor.