US Patent 9330946 Method and structure of die stacking using pre-applied underfill

Structures and processes for die stacking using an opaque or translucent pre-applied underfill material generally include selectively applying a low surface tension material to at least a portion of an alignment mark surface on a die; and applying the opaque or translucent underfill material to the die surface, wherein the underfill material does not wet or adhere to the low surface tension material such that the alignment mark surface is free of underfill material.