Study On The Thermal Mechanical Characters Of The Packaging Body With Through Silicon Via

With many technology advantages(short interconnect path,small signal delay,large data transmission bandwidth,low heat transport thermal resistance and small packaging volume),3D through silicon via(TSV)packaging meets the semiconductor industry needs of miniaturization,multi-function and high reliability.Due to the thermal expansion coefficient mismatch of TSV heterostructure,the thermal mechanical reliability of the TSV packaging system is reduced.So the study on the thermal mechanical of the TSV and optimization design of the TSV is particularly important.This paper focused on the influence of the TSV structure characteristics and fabrication process factors on the thermal mechanical stability,analyzed the heat source,thermal resistance and thermal stress distribution characteristics in the TSV encapsulation structure,and studied the key factors on the heat transport capability of the TSV encapsulation body.With these analysis,some technology and structure design criterion for TSV was made.Some experiments were carried out for validating the simulation results.The improvement of the thermal mechanical reliability of the encapsulation body heat is meaningful for the further development and application of TSV.In this paper,the main research contents and innovation points are shown as follows:Firstly,by considering the influence of the TSV fabrication processes(drilling vias,filling vias),the ideal TSV model,inclined TSV model,scallops sidewall TSV model and void TSV model were built.The simulation analysis was about the typical load temperature and the key structure parameters on the thermal mechanical stability of the TSV structure.The geometrical structure of the TSV contains via diameter and aspect ratio,slope angle,scallop structure,the position of void and pitch.It has been gotten that the aspect ratio(AR)is greater than 8,which is beneficial to release the thermal stress of the TSV.And the AR shall not be smaller than 5.The pitch of the TSVs is the similar scale of its diameter with the same AR,such as,the pitch is more than 1.6 times of the diameter when AR=6.For the inclined TSV with AR?6,the inclination angle should be designed among 10.204 ~o--12.407 ~o.With the rising of the added temperature load TSV suffered the elastic deformation stage,plastic strengthen stage and elastic-plastic deformation stage.Secondly,the influence of the thermal stress and strain and changed structure induced by the 3D stacked processes on the thermal mechanical reliability of the ideal TSV was studied in detail.The initial stress and strain on the thermal mechanical reliability and fatigue life of the TSV was analyzed(The TSV port interface and its surrounding area was extended,and the fatigue life of TSV middle part was shortened).And then,the 3D stacked thermal load on the scallop(sawtooth wave)side wall TSV was studied.The influence of the scallops and sawtooth wave number on the thermal mechanical reliability(the thermal stress strain,strain energy and keep-out zone)of this 3D model was discussed.It can be concluded that the existence of the sawtooth wave will reduce the reliability of TSV,relatively smoother scallop's side wall can improve the reliability of the TSV.The 3D stacked processes on the TSV interconnected structure was discussed.The following 3D stacked process restricted the thermal deformation of the TSV and the additional redistribution layer and solder joint structure changed the deformation mechanism of the TSV.Next,the thermal mechanical characteristic of the 3D TSV packaging system was studied deeply.The thermal mechanical characteristic of the TSV interposer(the most simple and complete TSV micro-encapsulation)was discussed to improve the thermal condition of the TSV surrounding area and enhance the reliability of the TSV interconnection.Based on the TSV design criterions mentioned above,the TSV interposer model was established(concluding chip heat source,TSV and RDL interconnected wires).The influence of the interconnected forms between the TSV and heat source and the distribution of heat source on the thermal mechanical characteristic of the TSV was analyzed.The influence of the thermal conductivity,coefficient thermal expansion and Young's modulus of the RDL dielectric layer on the thermal mechanical reliability was discussed also.According to the simulation results,larger effective heat dissipation area brought better cooling effect,and the chip heat sources with scattered arrangement had better to be located at the center of the chip.The shorted interconnected length between the TSV-Cu and the heat source can improve the ability of heat transfer.When the RDL dielectric materials with higher thermal conductivity(enhanced to 10 times)and thermal expansion coefficient matched with Cu,the high temperature of sparse RDL interconnect area can reduced and the maximum thermal stress of TSV interposer also can be reduced(dropped 16.4%).Finally,the experiment was carried out to verify the simulation results.The developed in-situ measurement system based on sheet resistance was used to measure the thermal deformation of TSV.Based on the in-situ test of the TSV relative deformation and plastic deformation,the thermal deformation mechanism of TSV was discussed.TSV-Cu thermal deformation associated with the diameter and depth of TSV-Cu was divided into three stages:elastic stage,similar plastic reinforce stage and plastic deformation stage which matches well with the change trend of simulation results.According to the test results of TSV leakage current it could be obtained that the thermal mechanical reliability of the TSV with scallops side the sawtooth wave is better than the sawtooth wave and scallop TSV wall which is in agreement with the conclusion of the simulation results.Preparation of SiC whisker,nano particles and polyimide composites and measuring the material properties of the composite material has been carried out.The properties of the Polyimide with SiC whisker and nanoparticles composite material has been enhanced greatly,such as,higher thermal conductivity(larger than 10 times),smaller thermal expansion coefficient.With the simulated results above,the thermal mechanical reliability of TSV interposer with the composite materials can be improved greatly.