Krishna G. Sachdev, Curt Fischer, Demian Riccardi, IBM Microelectronics Division, Hopewell Junction, New York
Removal of rosin flux residue from flip-chip solder interconnections and under-the-chip surfaces is necessary to ensure long-term reliability of devices and to prevent voids and adhesion problems in underfill material. Commonly employed cleaning methods are based on highly flammable, volatile solvents such as xylene, which require costly measures to protect the environment and worker safety. An environmentally friendly method of cleaning flux residue has been developed using nonaromatic organic solvent and aqueous alcohol solution for rinse.
In the fabrication of electronic devices, forming solder interconnections is an integral part of the module components assembly process. Typical examples include attachment of a semiconductor die to a substrate, solder ball and solder column attachment to backside metal (BSM) pads on a substrate, and a protective cap attachment to an assembled electronic module. Bonding techniques that employ solder bumps on semiconductor devices use a lead-tin (Pb/Sn) alloy of various compositions deposited by evaporation or plate-up processes. More recently, Pb-free solders, such as Sn/Ag/Cu, Bi/Sn, Sn/Ag, Sn/Cu, and Au/Sn alloys have been investigated by the industry to replace Pb-based solder alloys for electrically joining a semiconductor device to a chip carrier or a printed-circuit board (PCB). For high temperature melting solder interconnections, this involves connecting an array of solder bumps of various alloy compositions on the semiconductor chip to bonding pads on the substrate by heating the assembly to solder reflow temperature in the presence of rosin-based flux.
Julie MacShane, Managing Editor, SST at email: [email protected]