Uniform Electric Growth Of Copper Pillar On Packaging Substrate And Application

With the rapid development of information technology,the transistor density and working frequency of chip increase,which puts forward higher requirements for the conductivity and thermal conductivity of the package substrate directly carrying the chip.In order to meet this challenge,a coreless packaging substrate made by copper pillar method was developed,which reduced the volume of the packaging substrate and had superior electrical and thermal conductivity.Electroplated copper pillar is a key step to realize the interconnection of any layer by copper pillar method.The uniformity of copper pillar directly affects the performance of the substrate.In order to ensure the uniformity of electroplating copper pillar,only 1.5～3 A/dm~2current density is generally used in the production of electroplating copper pillar,the production efficiency is low.It is an urgent need in the production of electroplated copper pillar to improve the current density and production efficiency while ensuring the uniformity of electroplated copper pillar.In this paper,the factors affecting the uniformity of electroplating were investigated by numerical simulation.The uniformity of high speed electroplating copper pillar was optimized from the additive concentration,spray flow,temperature and so on.The copper pillar with good uniformity and reliability was obtained at the current density of 10 A/dm~2.In addition,the roughness of electroless nickel plating copper seed layer and wire copper pillar was reduced from the aspects of surface treatment and plating conditions respectively,and the uniformity was improved.Methods and guidance are provided for improving the uniformity of electroplated copper pillar.The main research contents and results are as follows:1.The multi-physical field coupling method was adopted to establish a model for the factors affecting the uniformity of electroplating copper pillar.The process of electroplating copper pillar was analyzed.The influence rules of initial cathode roughness,cathode resistance uniformity,electroplating pattern and current density on the uniformity of electroplating copper pillar were discussed,which provided ideas and methods for the subsequent optimization of the uniformity of electroplating copper pillar.2.The electrochemical characteristics of high-speed electroplating additive inhibitor A and accelerator B were analyzed and applied to the production of high-speed electroplating copper pillar.After optimizing the electroplating conditions through single factor experiment and orthogonal experiment,copper pillar with qualified uniformity was obtained by electroplating under the current density of 10 A/dm~2,and the reliability of the copper pillar was verified.A uniform and reliable scheme for high speed electroplating copper pillar is provided.Specific production conditions are chloride ion concentration 75 mg/L,high-speed electroplating additive inhibitor A concentration 35 m L/L,accelerator B concentration 3 m L/L,temperature 30℃,spray flow 400 L/min.3.The roughness of plating copper seed layer and copper pillar line on the rough electroless nickel plating surface was reduced by surface treatment and optimization of plating conditions.It was found that improving the surface roughness and electrical conductivity of electroless nickel plating by electroless copper plating can effectively improve the uniformity of copper plating seed layer.The influence of the concentration of accelerant and inhibitor in electroplating solution on the roughness of copper pillar of electroplating line was investigated by orthogonal experiment.The conditions of electroplating copper pillar with low roughness were obtained as current density 1.8A/dm~2,inhibitor C concentration 25 m L/L,accelerant D concentration 0.5 m L/L and leveling agent E concentration 25 m L/L.