TI TPS54360 and MCC SK810L-TP on Rigid-flex Circuit

Gideon Analytical Laboratories received several rigid-flex printed circuit boards (PCBs), which containedTexas Instruments TPS54360 DC-DC converter and Micro Commercial Components Schottky rectifier SK810L-TP. The TI TPS54360 is a 60 V, 3.5 A, step down regulator with an integrated high side MOSFET. The device survives load dump pulses up to 65V per ISO 7637. Current mode control provides simple external compensation and flexible component selection. The SK810L-TP is Rohs compliant, has high current availability, and is for surface mount application. These rigid-flex PCBs, in turn, were receiving data and power from a 54V buss, which then interfaced and drive LEDs and LCG via a flex circuit. The task was to pay particular attention to theTI TPS54360 DC-DC converter and the MCC SK810L-TP rectifier.

Gideon Analytical Laboratories handled this failure analysis problem like the bosses we are. The trace lines were cut on the PCB and the diode was tested on the board. It was shorted, as were all diodes. The TI converter was also tested on and off the board. The ground, Vcc, and SW were all shorted. Next, several converters were removed from the PCB and decapsulated. EOS was noticed under the SW and the Vcc traces. All of the converters had very similar issues. Burn marks were clear. The diodes had suffered the same EOS problem. For example, one of the diodes had a voltage spike in the termination ring above the P region. As sure as we are of opposites attracting, these devices failed because of overvoltage. The mystery of why theTI TPS54360 and MCC SK810L-TP on a Rigid-flex Circuits were failing was solved.

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