The Nov-Dec 2013 issue of Chip Scale Review features an article written by Fernando Gonzalez et. al., regarding the advantages of Sono-Tek ultrasonic spray technology for use in precision C4 Flip Chip Fluxing. New coreless interposer designs require tighter control of flux deposition because of reduced surface area and the passives’ closer proximity to the contact pad. Sono-Tek has provided precision ultrasonic fluxing systems to PCB manufacturers worldwide for decades, and has shown promise in being able to aid semiconductor manufacturers in this new process challenge.

The entire article can be seen at http://www.chipscalereview.com/issues/1113/index.php
More information about Sono_Tek’s ultrasonic spray technology for flip chip C4 fluxing can be found at https://www.sono-tek.com/flip-chip-c4-fluxing/.