A residue-free locating agent is used to hold the solder balls on wafers. A production-scale reflow furnace containing a hydrogen activation function is used to reflow wafers in a non-flammable gas mixture of hydrogen in nitrogen. 100% ball attachment with good solder wetting and strong solder bonding is achieved. This technology eliminates residues and cleaning, thereby facilitating the industrial trend toward device miniaturization.
Photo courtesy of Air Products and Chemicals, Inc.