Research On The Ball Bonding Process Of Rolling Copper Foil And Gold Wire

Wire bonding process is mainly applied to the electric interconnection betweenthe chip and the systems, and it occupies the important position in chipsmanufacturing and integrated circuits packaging. With the miniaturization ofintegrated circuits and highly-density packaging of integrated circuits, the higherrequirements of substrate material performance has been put forward. The electricalconductivity and thermal conductivity of copper is excellent and the chipperformance will be highly improved, if copper can be applied to the production ofbonding substrate.In this paper, the ball bonding process between T2copper foil and gold wirehas been studied. The influence degree and influence rules of the processparameters of bonding temperature, bonding pressure, ultrasonic power, ultrasonictime and bonding direction were investigated during orthogonal tests and controltests. During the experiments of process parameters, the better process window ofthis bonding process under the experiment conditions is bonding direction of45°and90°, bonding temperature from100℃to170℃, bonding pressure from170g to210g, ultrasonic power from185mw to195mw and205mw to215mw, ultrasonictime from160ms to180ms. The deformation rules of the gold ball under differentangles between ultrasonic vibration and rolling foil lines were analyzed during thesoftware of Abaqus. The parameter of bonding direction which represents theworking state of ultrasonic vibration is put forward for the influence of roll foillines on the copper foil surface. The bonding quality is evaluated by the circularity,area and shear force of bonding joints. The effects of bonding directions on bondingquality were higher than other parameters, shown by the results of the tests. The functions of roll foil lines made this process different to convention bon dingprocesses. The control tests of bonding temperature, bonding pressure, ultrasonicpower and ultrasonic time parameters were designed by the results of orthogonaltests and actual packaging features. The function rules researches of otherparameters were designed under the temperatures of25℃and200℃for itscomplex effects. It has shown in the tests that although the oxidization of copperfoil is more serious under200℃, however the bonding quality is better than thetemperature of25℃which has certificated the necessity of heat during the bondingprocess. The positive and negative effects of bonding temperature and ultrasonicpower are both obvious whose change would lead to the fluctuations of bondingqualities. Ultrasonic time and bonding pressure whose influence of bonding processis straightforward are factors which intensify the bonding effect. The results offinite element analysis shows that, the stress in the center of the bonding area werehigh enough to keep the deformation with the function of roll foil lines which solvethe problem of conventional bonding process.Through the summary of experimental results and finite element analysis, thebonding process is that the gold ball makes higher plastic deformation with thefunction of chopper and the assistances of thermal, ultrasonic vibration and bondingpressure on the copper foil. The stable bonding interface is obtained through theinsertion, extrusion and atomic diffusion of gold and copper. The metal bond isobtained by electronic sharing in the bonding interface which leads to the bondingat the atomic level. During the analysis of bonding interface, the bonding flaws arenot found which proved the positive effects of roll foil lines.