Flip Chip Bonding

Flip chip developed for high interconnect density has grown to be a favorite for new product development (NPI). Flip chip bonding comes in two main forms: Controlled Collapse Chip Connection (C4) with pitch sizes from 150um to 250um and Cu Pillar with pitch sizes from 30um and 140um. Both forms of flip chip involving solder balls/ bumps and a thermocompression process (heat, time, force) to create a metallic bond with the substrate.

Flip-chip C4 technology, also known as Controlled Collapse Chip Connection, connects IC chips to a substrate using solder balls on the chip’s top-side bond pads, with pitch from 150um to 250um, and using eutectic (Sn63Pb37) or lead-free (SAC305) solder.

Flip-chip Cu-pillar technology uses small, vertical copper posts (Cu pillars) with a solder bump to create interconnects between a chip and a substrate enabling high frequency applications with 30um to 140um pitch, resulting in higher I/O counts, short interconnections and smaller form factor.

The non-conductive adhesive, commonly called “underfill,” is applied to the stand-off distance between the flip chip die and substrate after the die is connected, providing stress relief, robustness, and moisture protection.