【作者】 张文武；

【导师】 刘向力； 计红军；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2023， 博士

【摘要】 金属纳米颗粒作为印刷电子导电墨水和微电子封装互连焊膏的核心原材料,其优异的导电导热与高温服役特性被广泛关注。其中,高成本纳米Ag易迁移性、低成本纳米Cu易氧化性等问题严重制约了它们的发展与应用,而银包铜(Cu@Ag)纳米颗粒不仅兼顾Cu/Ag的高导电导热,还能克服Ag易迁移与Cu易氧化的问题,使其成为印刷电子与封装互连中最具潜力的新材料之一。目前,关于Cu@Ag纳米颗粒的研究主要集中在催化、电池、生物医学等领域,针对常温/低温(<200℃)烧结Cu@Ag纳米颗粒的行为,Cu-Ag核-壳结构烧结界面演变规律,以及抗电迁移与剪切变形机理等问题尚不完全清楚。因此,厘清Cu@Ag纳米颗粒常温/低温烧结行为、电化学迁移机制与抗剪切变形机理等难题,对突破电子制造封装互连材料与技术的瓶颈具有重大意义。本文以声化学法合成与调控的Cu@Ag纳米颗粒作为核心材料,开发了高兼容性Cu@Ag纳米墨水/焊膏,研究了不同能场下(声、光、热、力)Cu@Ag纳米颗粒的室温/低温烧结行为,探索了其作为导电/互连材料时的电化迁移行为与抗剪切变形机理。本文对比分析了弱酸还原法与声化学法制备Cu纳米颗粒的反应机理,在声空化与射流作用下,Cu形核位点增多,并有效抑制聚乙烯吡咯烷酮(PVP)软模版生长,包覆层结构由支撑缠绕的PVP大分子链转变为静电吸附的抗坏血酸(Vc)小分子,烧结温度可大幅降低到200℃,为制备分散性优良、粒径更小、核壳结构更均匀的Cu@Ag纳米颗粒提供了一种新思路,最终制备出平均粒径约为52 nm的Cu@Ag核壳纳米颗粒,其高温抗氧化温度可达139℃和室温存储60天。论文研究了Cu@Ag纳米颗粒热烧结和脉冲光子室温烧结行为。在热烧结时,Ag壳“反润湿”产生了大量纳米Ag凸点(Ag nano bumps,Ag NBs),该Ag NBs能促进颗粒间的低温烧结互连,并在150℃下获得具有优异导电性(61μΩ·cm)与孔隙率(19.9%)的薄膜。采用脉冲光子烧结时,薄膜电阻率低至2.16μΩ·cm,孔隙率低至0.5%,表面粗糙度低至15.4 nm,这主要归因于高能光子与金属颗粒间的光热耦合作用,致使表面金属层超快升温与降温而产生超高过冷度环境,从而形成亚稳态过饱和Cu-Ag固溶体,最终大幅提升电极导电性与抗氧化性。此外,分析了纳米Cu的引入对Cu@Ag烧结电极的抗电化学迁移行为,分别对比了热烧结和光热烧结Cu@Ag电极抗电化学迁移机理。在低电场强度(E)下,热烧结的Cu@Ag电极可长时间(>2000 s)内不失效,随着E增加,电路总失效时间(t _A)缩短至36 s,相比烧结Ag的抗电化学迁移性能提升了4.6倍。在光子烧结时,随着脉冲光子能量(P_e)从0增加至8.04 J/m~2,t _A从91 s增加至411 s,相比热烧结Cu@Ag和Ag分别提升3.2和18.7倍,这主要是由于光子烧结产生的高固溶度(7.9 at.%)富Cu相固溶体和大量纳米孪晶组织对Ag的迁移有明显阻碍作用。论文分析了Cu@Ag纳米颗粒功率超声低温烧结行为与剪切强度变化规律。当热压烧结温度>250℃、保温时间>15 min、施加压力>10 MPa时,可实现互连强度达152 MPa,孔隙率低至2.3%,平均晶粒尺寸为157.8 nm,Cu颗粒析出相含量达13.9%,并阐明了Ag层反润湿、残留有机物软化与分解、Cu-Ag相互固溶、以及第二相Cu颗粒脱溶析出的烧结机理。当温度>150℃、2 s<超声时间<6s、超声功率>150 W时,互连强度达153 MPa,孔隙率低至0.5%,晶粒尺寸缩小至83.6 nm,Cu脱溶相含量下降至8.2%,小角度晶界占比上升至7.44%,界面局部位置产生变形,并发现富Ag相中存在大量Ag-Cu间隙固溶体。显然,在Cu-Ag高固溶、Cu脱溶相可控析出、晶粒细化、互连界面变形与溶蚀等多种作用机制下,超声烧结能在更低温度(150℃)和更高效率(6 s)下获得高质量的烧结组织。最后,对比了不同能场下Cu@Ag纳米颗粒的低温烧结行为,在超声或光子作用下,获得了具有高抗氧化、抗电化学迁移、抗剪切变形和高导电性的过饱和Cu-Ag纳米合金组织。更多还原

【Abstract】 Metal nanoparticles(NPs)are the key raw materials for conductive nano-inks of printing electronics and interconnected nano-pastes in microelectronic packaging.Their characteristics with excellent electrical/thermal conductivity and high-temperature operation have been attracted widespread attention.Among them,the easy migration of nano-Ag and oxidation of nano-Cu were seriously restricted in the industrial development.However,Cu@Ag NPs also take into account the high electrical/thermal conductivity of Cu and Ag,and overcome the ease of Ag migration and Cu oxidation,making it one of the most potential new materials for printing electronics and packaging.Currently,the research on Cu@Ag NPs mainly focused on catalysis,battery,biomedicine,and other fields.The behavior of room/low temperature(<200°C)sintering,the evolution law of core-shell interface,the behavior of electrochemical migration(ECM),and the principium of shear deformation were still indistinct.Hence,it is of great importance to clarify the above problems to break through the development of interconnected materials in the field of electronic manufacturing and packaging.In this thesis,Cu@Ag NPs synthesized by sonochemical method were investigated as the fundamental material.A highly compatible Cu@Ag nano-ink/paste was obtained.The room/low temperature sintering behavior of Cu@Ag NPs under different energy fields of ultrasound,photon,heat,and pressure was investigated systematically,respectively.The behavior of ECM and the shear deformation were discussed in detail.The reaction behavior of Cu NPs prepared by weak reduction and sonochemistry was compared and analyzed.With the effect of acoustic cavitation and acoustic flow,Cu nucleation sites were greatly increased,and the soft template growth function of polyvinylpyrrolidone(PVP)was eliminated,and the structure of the cladding layer also transformed PVP molecular chains into the electrostatic adsorption of dehydroascorbic acid.And the theoretical sintering temperature of Cu NPs can be effectively reduced to 200°C.Eventually,these effects provided a novel idea for the preparation of Cu@Ag NPs with excellent dispersion,tiny size particle,and core-shell structure.Therefore,Cu@Ag NPs with an average size of 52 nm were obtained.It also exhibited high temperature antioxidation at 139°C and room temperature storage for up to 60 days.The sintering behavior of Cu@Ag NPs by pulse photon was expounded.During the process of heating,the“dewetting”behavior of Ag shell was found to form Ag nanobumps(Ag NBs).They could efficiently drive to sintering with the large radius of curvature,resulting in the conductive films with considerable conductivity(61μΩ·cm)and low porosity(19.9%)at 150°C.Compared with thermal sintering,the films prepared by high-energy photonic sintering have a resistivity as low as 2.16μΩ·cm,a porosity as low as 0.5%,and a surface roughness as 15.4 nm.It was mainly attributed to the optical thermal coupling of high-energy photon and metal particles,which made the surface metallic layer rapidly heating and cooling to produce an ultracold environment,thereby forming a supersaturated Cu-Ag solid solution,and then the conductivity was significantly improved.Additionally,the influence of nano-Cu on the ECM migration behavior of sintered Cu@Ag electrodes was analyzed,and the anti-ECM behaviors of Cu@Ag electrode after photonic and heat sintering were contrasted.At the low-electric intensity(E),the sintered Cu@Ag electrode could not be failed within 2000 s.With the increase of E,the total failure time(t _A)was shortened to 36 s,which was increased by 4.6 times compared to the sintered nano-Ag.During the photon sintering,when the photon energy(P_e)increased from 0 to 8.04 J/m~2,and t_a increased from 91 s to 411 s,which increased by 3.2 and 18.7 times compared to thermal sintered Cu@Ag and Ag,respectively.Because the process of photonic sintering generated a large amount of supersaturated Cu/Ag solid solution and nano twin,they created a significant hindrance to Ag migration.The effects of power ultrasonic sintering on the microstructure and shear strength of Cu@Ag NPs were comparatively studied.When the pressure temperature>250℃,the holding time>15 min,and the pressure>10 MPa,the shear strength could be 152 MPa,the porosity was 2.3%,the average grain size was 157.8 nm,and the content of Cu desolubilization phase reached 13.9%.The behaviors of dewetting of Ag shell,softening and decomposition of cladding layer,solid solution between Cu and Ag,and precipitation of second-phase Cu particles were proposed.However,when the sintering temperature>150℃,2 s<ultrasonic time<6 s,and ultrasonic power>150 W,the shear strength was also as high as 153 MPa,the porosity was as low as 0.5%,and the solid solubility of Ag/Cu-rich phase increases to 12.82%/3.45%,the average grain size shrunk to 83.6 nm,the content of Cu desolubilization phase decreased to 8.2%,and a large amount of Ag-Cu interstitial solid solution was found.Furthermore,the deformation and erosion at the interface also occurred.Therefore,under the combined action of such high solubility between Cu and Ag,controllable precipitation of Cu desolubilization particles,grain refinement,and local micro-deformation and erosion of interface,the ultrasonic sintered structure could achieve the ultrahigh strength at a lower temperature(150℃)and higher efficiency(6 s).Eventually,the low-temperature sintering behavior of Cu@Ag NPs under different energy fields was compared and summarized.And the supersaturated Cu-Ag nanoalloy structure with excellent oxidation resistance,ECM resistance,shear deformation resistance,and electrical conductivity was obtained under the action of ultrasound or photon.更多还原