High temperature behaviour and reliability of Al-Ribbon for automotive applications

Abstract

Within the last years the bonding wire market is moving to ultra fine wires below 23 mum. Leading edge applications are now using 18 mum in mass production. This tendency is shown and predicted by the annual semiconductor industry roadmaps for IC/ASIC packaging. Special focus is on cost reduction and a continued decreasing of the package size. Contrary, the development in packaging of power devices is heading the opposite way to accommodate larger aluminium wires with multiple stitches. Currently the bonding process of thick aluminium wires is limited to 500 mum in industrial application. However, there is a need for the usage of aluminium wires with larger diameters to fulfil current and future interconnect requirements. In the past recent years aluminium ribbons were developed for power electronics application. Typical dimensions are 2000 times 200 mum or 1000 times 100 mum. In principle an aluminium ribbon offers the same advantages as an aluminium wire. In addition some of the disadvantages of thick wires are eliminated by ribbons. For instance a single 2000 times 200 mum ribbon could replace two 500 mum thick wires and transfer the same current load. A further advantage of a ribbon is the reduced thickness especially for thinner packages. Currently the automotive industry is looking for aluminium ribbon as replacement for aluminium thick wire in the next power electronic device generation. The reliability behaviour of aluminium thick wires is well known for many years whereas the reliability characteristics of ribbons have not yet been intensively investigated. This paper focuses on reliability of aluminium ribbons. Basic material properties for high purity as well as for corrosion resistive aluminium ribbons will be presented. This includes mechanical properties at various temperatures up to 250degC. Initial results for pressure cooker test will be shown. Ribbon bonding characteristics for DCB including high temperature storage test will be described.