Photo/Thermally Cured Low Dielectric Silicon Resins Via Incorporating Silacyclobutane And Benzocyclobutene Groups

The rising communication technology and VLSI circuit board are developing towards the direction of high frequency and high speed,which puts forward more and higher requirements for low-dielectric materials of substrates,interlayer and mold components.However,the matching processes of traditional PCB metal patterning and resin curing are more complex.At the same time,with the development of special application fields and special-shaped devices,low-dielectric carrier plates and interlayer media also are increasingly required to have profile-shaped customization capabilities.Consequently,low-dielectric resins with photocurable properties are compatible with photolithography and 3D printing technologies to achieve low dielectric and patterned integration.Based on this,using di/silacyclobutane and BCB as the basic construction units,novel organosilicon-benzocyclobutene light/heat curing resins with multiple main chain structures constructed by through polymerization methods such as siloxane polycondensation,olefin metathesis and hydrosilylation.This paper studied the influence of main chain structure on the photo/thermal curing properties,thermal stability,mechanical and dielectric properties of the resin,and clarified the internal relationship between structure and properties.The cured resin showed good properties.The main research contents are listed below:（1）The siloxane segment was introduced into the skeleton of polycarbosilane to construct a new class of siloxane-carbosilane hybridized organosilicon oligomers.A hydrolyzed prepolymer with the structure of DSCB and siloxane was synthesized from1,3-dimethyl-1,3-diisopropoxy-disilocyclobutane by by hydrolysis-polycondensation reaction.Then,4-Br-BCB was used as the capping agent to obtain the organosilicon-benzocyclobutene oligomers（PCOSs）via Grignard reaction,and the molecular weight of the oligomer was determined regulation.Due to the presence of photoactive/thermally active groups（DSCB/BCB）in the oligomer structure,siloxane-carbosilane hybridized resins can be prepared by step-by-step crosslinking under UV irradiation and high temperature.The results show that the T_5%of PCOS-1 resin reaches565℃,which is much higher than that of BCB-containing polycarbosilane resin（462℃）,due to the high chemical bond energy and high crosslinking density.However,the dielectric constants at 10 MHz also increased from 2.51 to 2.74.Because the Si-O-Si bond formed after hydrolysis has a relatively high polarizability,so it shows the increasing trend of dielectric constant,but it is still a low-dielectric material with excellent comprehensive properties.The negative photolithography of PCOSs film was carried out by UV irradiation,and the results show that the resin has photoinduced patterning ability.（2）The hydrolytic condensation polymerization of 1,1-dichlorosilacyclobutane（DCSCB）was conducted,followed by the terminating of benzocyclobutene groups（DMVB）,which generated the oligomers in the main chain consisting of alternating SCB units and siloxane segments and BCB as terminated groups.The molecular weights of oligomeric SBCOs were tailored by adjusting the feeding ratio of DCSCB to DMVB.Through UV/thermal double crosslinking,oligomers（SBCOs）were prepared.With the increase of DCSCB/DMVB ratio,the T_5%of of the cured SBCOs increased from 499℃to 529℃,and the hardness of elastic modulus also increased.However,dielectric constant showed a decreasing trend（from 2.78 to 2.63）as molecular weight decreased.The increase in the proportion of SCB groups helps to increase the crosslinking density of the resin.（3）In view of the hard-soft hybrid design strategy,1,1-dichlorosilyl cyclobutane（DCSCB）,dimethyldiethoxysilane（DEDMS）,and DMVB monomer were used as raw material,and the flexible dimethylsiloxane chain segment was introduced into the polymer framework by hydrolysis and polycondensation.The novel oligomers synthesized consisted of alternating SCB units and dimethylsiloxane segments（SEMBOs）.Oligomeric SEMBOs were further cured by UV/thermal double cross-linking to obtain new siloxane-carbosilane hybridized resins.The proportion of SCB units in the main chain decreased with increasing the amount of DEDMS incorporated,thereby effectively regulating the crosslinking density of the polymer.The results showed that the T_5%of of the cured SEMBOs decreased from 497℃to 461℃,and the mechanical properties also decreased,as the proportion of flexible segments increased.However,the dielectric constant（at 10 MHz）increased from 2.82 to 2.91.The introduction of the flexible dimethylsiloxane segment changes the crosslinking density,thereby effectively regulating the properties and improving the brittleness of the SBCO resins.（4）The oligomers（ADM-PBSC）were synthesized by using acyclic diene metathesis（ADMET）polymerization of 1,1-dibutenylsilacyclobutane with benzocyclobutene terminated groups.In such a way,a pure carbosilane backbone formed helps to reduce the low dielectric constant.The oligomers with silacyclobutene and benzocyclobutene groups thus enable UV and thermally curing to obtain the ADM-PBSC resins.The initial decomposition temperature of ADM-PBSC resin is 458℃.Meanwhile,the dielectric constant（at 10 MHz）is 2.49,and the dielectric loss is at the level of 10^-3.The results show that the introduction of BCB groups improves the crosslinking density of ADM-PBSC resin,which makes it have good comprehensive properties.（5）The UV/thermocurable organosilicon oligomer（SHPSCBs）was prepared from BCB-containing monomer（4-DMSBCB）of 1,1-dibutenylsilacyclobutane（DBSCB）and p-DMSP by hydrosilylation reaction.Thus,C-C bond with higher thermal stability is introduced into the main chain.Three oligomers with different molecular weights were synthesized by changing the incorporation amount of 4-DMSBCB.With the increase of the molecular weight,the T_5%of SHPSCBs resin increased from 413℃to452℃,and the elastic modulus inproved from 1.5 GPa to 2.4 GPa.However,the dielectric constant decreased from 2.59 to 2.48.