Flip chip metallization for an electronic assembly

摘要

The specification describes techniques for applying under bump metallization (UBM) for solder bump interconnections (58) on IC chips (41) with Al bonding sites (54,55). The UBM of the invention comprises a copper layer (56) applied directly to the aluminum bonding sites (54,55). Reliable bonds are obtained if the Al surface is a nascent surface. Such a surface can be provided by back sputtering an aluminum bonding site (54), or by a freshly sputtered aluminum layer (55). The copper layer (56) is deposited on the nascent aluminum surface in e.g. a cluster tool without breaking vacuum. The UBM can be patterned using subtractive techniques.