A new Ni-W thin film metallization for solder interconnections and design method of metallization thickness

The demand for reliable thin-film metallization that can be repaired repeatedly by soldering has been increasing because multichip module on ceramic (MCM-C) has become widely used in workstations as well as main frame computers. This kind of metallization is also suitable for use with Pb-free solder with a high Sn content whereas a conventional metallization is consumed quickly by Sn. A Ni-W sputtered metallization satisfying this requirement has been developed by the authors. The reaction between Ni-W and Sn during soldering creates a Sn-Ni-W alloy layer. The diffusion of Sn into Ni-W and the formation of Sn-Ni-W is slower than any other thin-film metallization for solder interconnections ever applied to electronic devices, and this makes multiple solder repairs on a substrate possible. Furthermore, Ni-W is adequate for LSI metallization. Additionally, the film thickness appropriate to given amount of solder can be determined by adding the term for solder height to the frequency factor Do. This is especially important in designing fine connections for electronic devices.