February_EDFA_Digital

edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 23 NO. 1 24 • Design details not needed: This method can be applied without schematics or layout drawings. STEPS TO PERFORM IR-BASED DIRECT CURRENT INJECTION METHOD The process flow chart to perform IR-based direct current injection is shown in Fig. 2 and detailed here. It is preferred to perform the testing with an ambient temperature of nomore than 25°C toprotect components, but should not be less than 0°C. The steps below assume 25°C ambient temperature: 1. Visually examine the PCBA to exclude any obviously damaged components, soldering, or contamination issues. 2. Apply input power to confirm the issue of output power rails. 3. Use a digital multimeter to find shorted power rails. 4. Inject DC power to the shorted power rails via Vcc to GND. Limit current to 0.2 A, and slowly increase voltage from 0 V to rated power rail voltage while using an IR camera to monitor case temperature of components on PCBA. Make sure to also monitor the case temperature of components on the back side of the PCBA. Carefully pay attention to components with case temperatures of more than 40°C. Gradually increase voltage while allowing compo- nent temperature to stabilize but not exceed 50°C. If the case temperature starts to exceed 50°C, decrease the input voltage to prevent component damage. 5. If components do not exceed 40°C after reaching the 0.2 A current limitation, increase the current limit slowly to 0.5 A, then 1 A, 2 A, 5 A, etc. while monitor- ing the temperature of components on PCBA, until a component of more than 40°C is identified. 6. Continue to increase input power to let the sus- pected component reach 50 °C. Compare the results with a known good or golden sample if the tem- perature difference is more than 10°C on the same component, or if there’s no golden sample available, increase the temperature to 60°C or 70°C to confirm the problem. 7. Remove the shorted component from the PCBA for further analysis. 8. Repeat steps 2 to 7 to find other shorted components. TECHNIQUES TO ENSURE THE TEST IS NONDESTRUCTIVE The biggest challenge with performing the proposed IR-based method for short circuit localization is to make sure it’s nondestructive while achieving sufficient confi- dence to confirm faulty components. 1. Make sure to slowly increase injection power to prevent case temperature overshoot that can cause Fig. 2 Flow chart to conduct IR-based direct current injection.