Preparation And Characterization Of AIN Modified Polyimide Dielectric For Application In TSV Interposer

The 3D integration and packaging based on TSV interconnection has been paid much attention in recent years,especially for the emergence of the TSV interposer.This interposer provides a new solution for IC system integration,due to its’ low cost,high performance,low power,small-scale and high density.The polymers,such as polyimide(PI),have excellent insulation performance,good coverage and simple process,which has potential application as the dielectric of redistribution layer on TSV interposer.However,the polymers have the disadvantages of low thermal conductivity,large thermal expansion and swelling in organic liquid,which may lead to poor heat dissipation,thermal mismatch and large thermal stress.Therefore,it needs to be modified to have better comprehensive properties.Based on relevant literature,a novel integrated technology of utilizing nano-Al N to modify polyimide as dielectric of redistribution layer on TSV interposer was developed in this paper.This technology intends to improve the properties of polyimide in interposer by the inclusion of aluminum nitride(Al N).To meet the integration process requirements of TSV interposer,the Al N modification technology was stuied in this paper.Then the integration process was developed and the modification effects of Al N were fully characterized.Firstly,high energy ball milling was used to make Al N dispersed uniformily in polyimide matrix to achieve high efficiency mixing.Film coating and curing technology were optimized in the experiment.Based on the preparation technology of Al N modified polyimide composite,the unit technology such as coating,curing,polishing and electroplating were optimized and combined to develop the integrated fabrication flow of TSV interposer on Al N modified polyimide.The effects of nano-Al N content on the microstructure,thermal properties,mechanical properties,dielectric properties and water absorption of Al N modified polyimide composite film were fully investigated in this paper.The results showed that the nano-Al N was distributed uniformly in the composite film by this modification process,and the polyimide had been completely imidized.The thermal stability of composite film was enhanced and the thermal decomposition temperature was obviously improved.The coefficient of thermal expansion decreased significantly due to Al N.When the Al N content is 40 wt.%,the coefficient of thermal expansion is 2.39×10-5/°C.The micro hardness of the film was obviously improved and the bonding strength with Si substrate was hardly affected by the inclusion of Al N.The dielectric constant and loss were slightly increased by the addition of Al N.The water absorption of the film decreased significantly.So the polyimide film modified by Al N has better comprehensive properties.The TSV interposer which achieve high density packaging has strong demand for the heat dissipation capability of the surface dielectric layer.Because it is difficult to measure thermal conductivity of micro-scale films using traditional bulk thermal conductivity measuring equipment,a novel method to characterize the thermal conductivity of the thin films using infrared thermal imager was presented in this paper.The simulation results showed that this method could compare the thermal conductivity of insulating film with equal thickness.The MEMS technology was used to prepare the test samples,and the infrared thermal imager was used to analyze the temperature distribution of the film surface.The results showed that the thermal conductivity of the nano-Al N modified polyimide increased with the nano-Al N content increase.This technique provides an effective method to study the heat transfer properties of insulating materials in 3D packaging.