My company recently had a number of boards manufactured that use the use the LT8611 with the UDD package. We had about 100 failures. I was given five boards to evaluate. One had no failure when I tested it. The other four failed my testing. I performed resistance checks looking for shorts to ground and to adjacent pins. I could not find any faults. The solder looked very good to me.
Going further, I removed the LT8611 from one board and everything looked good under the device. I cleaned the board pads and re-flowed the device. The board then passed testing.
On the remaining three boards, I tried to re-flow the solder to the LT8611, but the device continued to fail. I then removed the LT8611 cleaned the board and then replaced the device. Still the LT8611 failed. I did not have spare LT8611, but the PC board was also laid out to accommodate an LT8610 MSOP package. On the three remaining boards, I replaced the LT8611 with a LT8610 and then all three boards functioned normally.
So, any ideas on what else to check? Seems like replacing the LT8611 is the fix, but it's relatively expensive for this board. I still have almost 100 boards to repair.
The LT8611 is U2 on the board and schematic below...
