Feasibility Ananlysis Of Cu Wires Bonding In Memory Packaging

For nearly half a century, the rapid development of semiconductorscience and technology has brought great changes to our daily lives, suchas computers, mobile phone, digital cameras. All of these are due to therapid development of semiconductor technology. Following Moore’s law,semiconductor technology moves towards smaller size, faster speed, lowerpower and lower cost..Following the above development direction, wafer size becomesbigger (from6inch to current12inch) and single die size becomes smaller,so cost of manufacturing per die becomes lower. But for Assembly House,there has been no big change of raw material. Since the price of gold wireis rising (Currently gold price over$1,700/Ounce), Assembly House mustfind out the solution of substitute gold wire to make cost down. Currentlymany Assembly House and material suppliers are committed to research onCu wire bonding process.Because of copper’s lower price, good electric conductivity, thermalconductivity and mechanical features, copper wire bonding process is ofhigh feasibility. But there are some challenges, for example, Copper is easyto oxidation and harder than gold wire. Easy to be oxidated will deterioratebonding ball quality and reduce bonding reliability, and bigger hardnesswill damage the Al bonding pad. So Assembly House should co-work withcustomer, material suppliers and equipment vendor to do research and findout the solution. The solution should make the Cu wire bonding successfulfrom not only in theory mode or trial run production but also in massproduction. With high quality and low cost Cu wire bonding process, theAssembly House will be more competitive in the market in the wholeindustrial chain. With the combination of theory analysis and experiments, this thesiswill focus on the feasibility study of Cu wire bonding process to substituteAu. Chapter I will briefly describes the wire bonding process flow ofmemory package and standard quality criteria of bonding process. ChapterII will compare the performance of Cu wire and Au wire and describe theadvantage and disadvantage of Cu wire bonding process. We are going todeal with the main challenges, such as easy to be oxidated and bighardness, and find out solutions to resolve them. Chapter III will focus onto get optimized production parameter, and during the study we will usethe industrial experiments design method. Chapter IV will introduce theCu wire bonding reliability capability and failure mode analysis mode.Chapter V forecasts the development trend of Cu wire bonding and mainlyintroduces one new control method to prevent Cu oxidation, and at last, wedraw a conclusion in chapter VI.With great support from equipment vendor and material supplier, wehave used industrial experiments design method and have obtained a largenumber of Cur wire bonding optimized parameters, such as N2flow rate,capillary velocity, bonding time, bonding force, US current and so on. Theabove experiment results will help Cu wire bonding process being realizedin mass production from theory assumption. But it only took one step inthe industrial application, due to so many package types, we still needmore research and experiment for copper wire bonding for differentpackaging types and multiple pins package application feasibilityevaluation, only in this way we can introduce copper wire bonding to massproduction.