Gold embrittlement in SnPb solder is a well-known failure mechanism in electronic assembly. Voiding in SMT solder joints &Gold plated components dislodging from the PCB are two well-known failure modesof Gold Embrittlement. BGA Test and Technology has developed a Robotic Process which uses SnPb alloy dynamic solder wave for gold removal.
QFN
IPC –J-STD-001 criterion. 4.5.1 Gold Removal

Gold Shall Be Removed: N1P2D3

  • From at least 95% of the surfaces to be soldered of theThrough-hole component leads with 2.54 μm ormore of gold thickness
  • From 95% of all surfaces to be soldered of Surface mount components regardless of gold thickness.
  • From the surfaces to be soldered of Solder terminals plated with 2.54 μm or more of gold thickness.
A double tinning process or dynamic solder wave may be used for gold removal prior to soldering the component in the assembly.

SMTA Publication http://www.smta.org/penang/presentations/s6_p3_chiu_alex.pdf