LED driver PT4115: how to avoid arc around IC pins?
Assuming the diode is still good, the layout of the board is really bad. 

That current sense line loops around the chip, crosses and runs parallel with the drive line. That's bad. The inductor is also a long way from the chip and Vin also crosses v-out..... . 

The PT4115 needs to be turned round 180 degrees with that part layout. But in truth the whole layout needs redone.

More like this...



See also "Layout considerations" on page 14 of the datasheet. 

Vital parts are:


  Minimize ground noise by connecting high-current ground returns,
  the input bypass-capacitor ground lead, and the
  output-filter ground lead to a single point (star ground
  configuration).
  
  The SW pin of the device is a fast switching node, so
  PCB tracks should be kept as short as possible.
  
  ...
  
  It is particularly important to mount the coil and the
  input decoupling capacitor as close to the device pins as
  possible to minimize parasitic resistance and inductance,
  which will degrade efficiency.