Fabrication And Performances Of Polymer Based Interposer Reinforced With SiC Whiskers And Meshing Micro-structure

With the miniaturization development of IC,there is a higher demand for the performance of the chip,which contributing to the further development of the IC packaging.Traditional package was unable to meet the requirements of the chip in the transmission rate,size and reliability.So the three dimensional package has been proposed to achieve the connection of chip and PCB.Compared with the traditional package,the three dimensional package can greatly reduce the package size and increase the transmission efficiency,which significantly improving system performance.TSV is a typical representative of three dimensional package,the 2.5D package through interposer has the most practical potential recently.As the key part of the 2.5D package,the development of interposer has been received extensive attention.There are different kinds of interposers separated by the substrate materials.Among all the interposers,silicon based interposer with TSV has been used widely.However,the silicon based interposer still faces many challenges,such as isolation of the hole,filling the hole,wafer thinning,surface metallization and so on.In recent years,glass based interposer has been raised as a popular choice.Glass based interposer has the advantages of stable thermal performance and high resistivity.However,there exists some difficulties in preparation of the holes.In addition,the polymer based interposer with the advantages of low cost,simple technological process and high yield has been be taken seriously.Due to the limitations of polymers,the polymer based interposer has the following disadvantages: poor mechanical properties,great gap on the coefficient of thermal expansion with the chip and poor thermal conductivity.These disadvantages greatly limit its application range.According to the limitations of the above interposer,the modification of the interposer's substrate has been a research direction.The attempt of the orderly distributed metal network structure to strengthen the mechanical properties of the polymer based interposer achieved remarkable results.However,the bonding surface between metal and polymer is mostly smooth interface.When the interposer undertaking load,the reinforced structures and the polymer matrix are easily peeled and slipped,which leading to the invalidation of reinforcing effect.Another problem is the great mismatch of properties between metal and polymer.The mismatch may result in poor interface bonding.In this paper,two reinforcement mechanisms have been designed to reinforce the original metal grid reinforced polymer interposer.First one is the ordered reinforced mechanism,adding the ordered meshing micro-structures to the edge of the metal grid can realize mechanical interlock mechanism.The interface bonging performance can be improved by this way.Another is the random reinforced mechanism,replacing the pure polymer with whiskers reinforced polymer composites as the matrix of the interposer.The whiskers/polymer composites has better comprehensive performances,which can reduce the thermal expansion,thermal conductivity and stiffness between metal and polymer.The polymer interposer reinforced with ordered metal meshing micro-structures and random whiskers is called the complex reinforced polymer interposer.For the integrated manufacturing requirements of the interposer,the preparation of the whiskers reinforced polymer composites has been studied.The effect of whiskers content on the dispersion conditions has been analyzed.The effect of whiskers content on the properties of the composites film has been analyzed as well,the optimal ratio has been determinedThrough simulation,the effect of the micro-structure and the whiskers reinforced polymer composites on the properties of the interposer have been analyzed.The simulation results indicate that,the addition of the micro-structure has improved the mechanical and thermal properties of the interposer.For the same interposer model,the comprehensive performance has been improved with the increase of whiskers content.The properties of the interposer achieve an optimal value when the whiskers content reaches about 7%.With the increase of the whiskers content,the whiskers agglomeration becomes more obvious,which decreases the reinforcement effect.The preparation process of the whiskers reinforced polymer composites has been integrated with the existing MEMS micromachining process to form the manufacturing process flow of the complex reinforced polymer interposer,and a small batch of interposer samples have been fabricated.The original metal grid reinforced polymer interposer has also been prepared as a comparative sample.The mechanical properties,thermal properties and electrical properties of the interposers have been characterized respectively.Test results indicate that,the polymer interposer with complex reinforced mechanism has better comprehensive properties,the Young modulus and the thermal conductivity of increases for 35.89%and 65.60%,respectively,the coefficient of thermal expansion has been decreased for 21.17%.The resistance between the upper and lower surface of the interposer sample is good,and the vertical conductive metal cylinders have high yield,so the complex reinforced polymer interposer has obvious practical potential.