Wire bonding technology is the earliest chip level interconnection technology, but it is still the most widely used one in integrated circuit (IC) assembly for its noticeable advantages over other interconnection technologies. Traditionally, gold wire has been the dominating wiring materials in wire bonding technique. Gold wire has many distinguished characteristics such as excellent ductility, conductivity and chemical stability. However, the biggest reliability issue of gold wire bonding is associated with intermetallic compound (IMC) generated at the gold wire-aluminum bonding pad interface. The rapid development of IC technology desires devices that are smaller, faster and cheaper; progressive high current or high power devices demand alterative interconnection materials which have...[ Read more ]

Wire bonding technology is the earliest chip level interconnection technology, but it is still the most widely used one in integrated circuit (IC) assembly for its noticeable advantages over other interconnection technologies. Traditionally, gold wire has been the dominating wiring materials in wire bonding technique. Gold wire has many distinguished characteristics such as excellent ductility, conductivity and chemical stability. However, the biggest reliability issue of gold wire bonding is associated with intermetallic compound (IMC) generated at the gold wire-aluminum bonding pad interface. The rapid development of IC technology desires devices that are smaller, faster and cheaper; progressive high current or high power devices demand alterative interconnection materials which have thermal properties and electrical conductivity that are superior to those of gold. With many distinguished advantages such as a higher conductivity, superior mechanical properties, less tendency of forming IMC and especially a much lower cost, copper have rapidly gain a foothold as the main potential material to replace gold for the wire bonding in electronic packaging. Although many integrated device manufacturers (IDMs) and fabless semiconductor companies are considering the application of copper bonding wire in at least some product designs, there are still deep reservations in the industry over the use of this material, particularly due to concerns over in-service product reliability. Corrosion issue is the biggest problem of copper wiring packages. To prevent the corrosion, epoxy molding compound (EMC) is required to have excellent properties to provide good protection to copper wiring packages. Thus the evaluation and selection of epoxy molding compound for copper wiring packages are very important.

In this study, the corrosion mechanism of copper wiring package is studies and discussed, EMC inherently absorbs moisture or water from the environment, substances contained in EMC may have a tendency to dissolve and ionize in the absorbed water and form an electrolyte, corrosion of copper wire will take place if placed in a suitable electrolyte. Due to its lower nobility compared with gold, copper wire has a higher possibility to be corroded under the same conditions, than means the requirement of epoxy molding compound is stricter when used in copper wiring packages.

Some EMC properties are correlated to the corrosion of copper wire in packages, and the effects of these properties on the corrosion of copper wiring packages are discussed in detail. To fully evaluate epoxy molding compounds, a series of systemic characterization methods are established in this study. EMC properties which affect the corrosion of copper wire are characterized. The criteria and methodology of EMC selection for copper wiring packages are proposed and demonstrated in this study. In addition, other optimization measures such like material and process amelioration which can improve the reliability of copper wiring packages are proposed and validated in this study. In conclusion, specific recommendations are made on reliability enhancement of copper wiring packages.