Effects Of Electrothermal Coupling On The Growth Of Intermetallic Compounds Of Copper Pillar Bump

Miniaturization of electronic products is putting forward higher requirements for chip packaging.In order to follow its development,the use of bumps in bonding chips has become the mainstream trend of high-density packaging applications in industry.Copper pillar bumps are especially suitable for ultra-fine spacing interconnection systems because of their excellent heat transfer and electrical conductivity.Nevertheless,under the trend of miniaturization,the load imposed on a single copper column bump increase exponentially.Therefore,the study that what role thermoelectric coupling plays in the structure evolution of copper pillar bumps,the formation and growth of intermetallic compounds?IMC?and the formation and evolution of voids is of great significance in improving the reliability of three-dimensional packaging interconnection structures.The reliability of 50?m diameter copper pillar bumps themselves and with Cu/Sn interconnection samples were tested and analyzed.What's more,the reliability of copper pillar bumps interconnection under thermoelectric coupling is emphatically investigated.By setting up copper pillar bump interconnection samples,the structure evolution,intermetallic compound formation and growth,pore formation and evolution under different conditions of electric and thermal migration were studied.The mechanical/electrical properties of Copper-pillar bump interconnection samples were investigated.?1?Current density has a significant effect on the IMC at the interface of copper pillar bumps,mainly due to the directional migration of metal atoms driven by electronic wind,which affects the diffusion process.The polarity effect of IMC growth between cathode and anode bumps occurs due to electromigration.With the increase of current density,the polarity effect enhances.Because of the existence of Ni barrier layer,Cu cannot interact with Sn,IMC forms only with the diffusion of Ni and Sn.The main component of the IMC is Ni₃Sn₄ which is confirmed by EDS.The polarity effect is also reflected in the growth rate of IMC.The thickness order of Ni/Sn IMC of copper pillar bump is:anode>aging>cathode.?2?Temperature also has a crucial effect on the IMC at the interface of copper pillar bumps.Its mechanism is to enhance the diffusion process by increasing the mobility of metal atoms.The higher the temperature,the stronger the diffusion process of Ni/Sn,the thicker the IMC extremum,and the stronger the polarity effect.At 180°C,the solder on copper pillar begins to soften and flow downward along the side wall.Furthermore,it is found that the formation of Sn/Cu/Ni IMC on the side wall conforms to the diffusion reaction law of aging,with no polarity effect appearing.The reason may be that the electron wind only brings longitudinal kinetic energy.