Regular non-conductive thermal paste should not affect your AMD Warranty as long as you clean it off vert gently with, at least, 90+% Alcohol with a clean swab or cloth or small brush like a toothbrush.
also make sure to clean the Motherboard socket of any Thermal paste that might have dripped from the processor.
If you used conductive Thermal paste then you really need to thoroughly clean all the thermal paste off the pins and motherboard to prevent a short that can damage your processor and motherboard socket.
If you used Conductive Thermal paste and it shorted out the Motherboard or Processor then both Warranties would be voided due to Customer Error.