Molecular dynamics simulation study of sintering mechanism and thermal conductivity of nano-Ag particlesWU Peng,WANG Yiping,YANG Dongsheng,FENG Jiayun,TIAN Yanhong(State Key Laboratory of Advanced Welding and Joining,Harbin Institute of Technology,Harbin,150001,China).pp 1-7

Abstract:Nanosilver paste can achieve low-temperature sintering and high-temperature service,due to its special size effect and high specific surface area,which has a broad application prospect in the third-generation semiconductor packaging.However,the sintering mechanism of nanoparticles has not been clear and the thermal conductivity has decreased significantly after sintering,which needs to be further investigated.In this paper,the sintering process of silver nanoparticles was simulated by molecular dynamics simulation.The correctness of the potential function was verified by the calculation of thermal conductivity,firstly.And then the microstructural changes of silver nanoparticles were observed,the relationship between the sintering neck growth length and the sintering time was obtained,and the change of the phonon thermal conductivity at the sintering neck was also calculated.Finally,the experimental silver nanoparticles with the same characteristics as the simulation results were observed by the transmission electron microscope.The results showed that the fivefold twins were the stable structure of nanoparticles after sintering,the sintering neck length growth during nanoparticle sintering was a power function of time,and the microstructure at the sintering neck reduced the thermal conductivity of nanosilver by 4.42%.

Highlights:(1) Innovatively verify the correctness of potential function selection by calculating the size effect of thermal conductivity of silver materials.

(2) Calculate the thermal conductivity of complex microstructures of nanoparticles through molecular dynamics simulation.

Key words:MD simulation；nano-particle；thermal conductivity

Ultrafast laser microwelding and joint performance of silicon-sapphire heterogeneous structure for microfluidic device packagingHU Yifan,LIN Luchan,LI Zhuguo(Shanghai Key Laboratory of Materials Laser Processing and Modification,Shanghai Jiao Tong University,Shanghai,200240,China).pp 8-14

Abstract:In micro/nano sensor devices,integrated heterogeneous structures can determine the quality of devices packaging,and further affect their performance.For Silicon and sapphire,the heterogeneous joining technology that is flexible,environmentally friendly and suitable for large-scale materials integration is still lacking.In this paper,the welding feasibility of silicon-sapphire is explored by ultrafast laser transmission welding technology.When the gap between silicon and sapphire is less than 1 μm and the incident laser power is 7.5 W,sapphire and silicon at the heterogeneous junction can be fused with each other to form an interlocking area within width～ 3 μm.Meanwhile,defects such as pores and cracks that could normally be introduced at the junction area during brittle materials welding have also been effectively suppressed.The joint strength measured by shear test is up to 2.9 MPa.The welding of silicon and sapphire by ultrafast laser provides an alternative for the heterogeneous interconnection of hard and brittle materials with large difference.This microwelding technology has thus shown great potential in microfluidic device packaging.

Highlights:(1) An effective microwelding of wafer-level sapphire and Si is achieved by using picosecond laser transmission technology.

(2) By adjusting the gap between sapphire and Si,controllable energy deposition can be achieved in the heterogeneous structure to promote the interlock structure formation,and thus improving the joint strength.

Key words:ultrafast laser；sapphire；silicon；microwelding；interlock structure

Influence of the mesoscale porous structure features on the macroscale mechanical properties of sintered silver nanoparticlesLONG Xu1,CHONG Kainan2,SU Yutai1(1.Chongqing Science and Technology Innovation Center of Northwestern Polytechnical University,Chongqing,400000,China；2.Northwestern Polytechnical University,Xi ’an,710072,China).pp 15-20,27

Abstract:In order to investigate the influence of the mesoscale porous structure of sintered silver nanoparticles on the macroscale mechanical properties,representative volume elements (RVEs) with different porosities (0.1,0.2 and 0.3) are firstly generated by using the Gaussian filtering algorithm and the cutting quantile functions.The uniaxially tensile mechanical properties of the RVEs are obtained by applying periodic boundary conditions.A macroscale model of the lap joint made of sintered silver nanoparticles is then established using Abaqus software to simulate the shear test.The material properties of the sintered layer are consistent with the predicted elastoplastic stress-strain curves of the RVE.The findings reveal that as the porosity decreases,the elastic modulus and yield strength of the RVE model increase.However,it is worth noting that the stress at the final stage of the plastic deformation demonstrates a significant decreasing trend as strain increases,rendering the material more susceptible to damage.Furthermore,through a comparison of shear simulation results of the macroscale model,it can be observed that porosity variations have a notable impact on the shear deformation of sintered silver nanoparticles.Specifically,as the porosity increases,the likelihood of crack initiation and propagation in porous regions rises.This leads to the coalescence of cracks among multiple pores,consequently resulting in the reduction of shear strength of the sintered silver nanoparticles.

Highlights:(1) A numerical homogenization model based on the representative volume elements and periodic boundary conditions effectively predicts the elastoplastic properties of sintered silver nanoparticles with complex mesoscale porous features.

(2) Relationship between the mesoscale porous features and the macroscale mechanical response of sintered silver nanoparticles is revealed by the established the numerical models at both macro-and meso-scales.

Key words:sintered silver nanoparticles；porous structure；RVE；elastoplastic response

Joining mechanism and element distribution in laser microwelding of NiTi-Cu dissimilar alloysKE Wenchao1,ZHANG Kang2,ZHOU Naixun1,CHEN Wenchang1,CHEN Long1,PANG Bowen1,ZENG Zhi1(1.University of Electronic Science and Technology of China,Chengdu,611731,China；2.Military Representative Office of Army Aviation Equipment Department in Chengdu District,Chengdu,610000,China).pp 21-27

Abstract:To satisfy the thermo-driven requirements of NiTi shape memory alloys in different industrial applications,NiTi wire and Cu plate were welded by laser micro-welding technology.The microstructure and element distribution of the weld were experimentally studied using optical microscopy (OM)and energy dispersive spectrometer (EDS).Based on ANSYS Fluent software,a three-dimensional (3D) computational fluid dynamics (CFD) model for laser micro-welding of NiTi-Cu dissimilar alloys was established to analyze the evolutions of temperature and fluid flow fields and the element transport mechanism.The results indicate that the process of laser micro-welding can be mainly divided into 3 procedures,namely the "drilling" procedure of laser in NiTi wire,the preheating procedure of laser energy on Cu plate,and the "drilling" procedure of laser in Cu plate.The mixing of Ni,Ti,and Cu elements mainly occurs in the drilling process of laser in Cu plate,where the elements are mixing well under the driven of the metal vapor recoil pressure and Marangoni vortex.The Cu content in the molten pool is helpful to form low hardness Cu-Ti intermetallic compounds (IMCs),reducing the possibility of the formation of brittle Ni-Ti IMCs.The experimental and simulation results are in good agreement.The research provides important theoretical support for optimization of the laser micro-welding of NiTi-Cu dissimilar alloys.

Highlights:(1) 3D CFD model for laser micro-welding of NiTi-Cu dissimilar alloys was established.

(2) Molten pool flow behavior and element transport mechanism for laser micro-welding of dissimilar alloys were studied.

Key words:NiTi shape memory alloys；laser micro welding；dissimilar alloy；computational fluid dynamics；element distribution

Microstructural characteristics and properties of Cu@Ag NPs interconnect joints fabricated via ultrasound-assisted sinteringXIU Zijin,ZHANG Penghao,ZHANG Wenwu,WANG Xiuqi,JI Hongjun(Harbin Institute of Technology(Shenzhen),Shenzhen,518055,China).pp 28-34

Abstract:Silver-coated copper nanoparticles (Cu@Ag NPs),a two-phase core-shell structured material,were incorporated into solder paste,and ultrasound-assisted sintering technology was employed for the sintering process.Three sets of parameter experiments were designed to investigate the effects of sintering temperature,ultrasound time,and ultrasound power on the microstructure and mechanical properties of interconnect joints.The results demonstrate that in the sintered structure,silver and copper phases primarily existed as a replacement solid solution.With the introduction of ultrasound and an increase in sintering temperature,the density of the sintered structure increased significantly,ultimately achieving superior metallurgical bonding at temperatures ranging from 150 to 200 ℃,enabling low-temperature connections.As ultrasound time increased from 2 s to 8 s and ultrasound power increased from 50 W to 350 W,the resulting sintered structure gradually became denser and more uniform.However,excessive ultrasound energy led to noticeable plastic deformation and cracks within the sintered layer.When sintering temperature of 150℃ was applied along with an ultrasound time of 6 s and an ultrasound power of 250 W,a uniformly dense sintered structure with shear strength reaching up to 149.5 MPa was obtained.

Highlights:The influence of ultrasound-assisted sintering parameters on the microstructure and shear strength of the sintered joint of Cu@Ag NPs was studied,and the reliable interconnection of Cu-Cu in a short time (6 s) and low temperature (150 ℃) was achieved.

Key words:nanoparticles；ultrasound-assisted sintering；joint properties；diffusion of interface

Interface microstructure and properties of nickel/copper foil reflow soldering and laser solderingSUN Qian,WANG Jiale,ZHOU Xingwen,WANG Xiaonan(Soochow University,Suzhou,215131,China).pp 35-40

Abstract:Under the background of replacing aluminum copper direct welding with nickel foil "bridge",heterogeneous connection of nickel copper foil is carried out using reflow soldering and semiconductor laser soldering.A comparative analysis was conducted on the formation mechanism of joint morphology,weld seam and interface microstructure,and their mechanical properties were evaluated.The research results showed that the weld defects were not detected for two welded joints.The microstructure of laser soldering welds was composed of Sn solid solution and Cu-Sn intermetallic compounds(IMCs) with equiaxed crystal morphology,while microstructure of reflow soldering welds was composed of Sn solid solution.The Cu-Sn and Ni-Sn interfaces of the two joints showed different morphologies,and the thickness of the Cu-Sn interface layer was greater than that of Ni-Sn interface.The microstructure at the Cu-Sn interface during reflow soldering was scallop-shaped,consisting of Cu solid solution →Cu3Sn IMCs→ Cu6Sn5IMCs.For laser soldering joints,the Cu-Sn interface consisted of various Cu-Sn IMCs.At the Ni-Sn interface,a continuous distribution of (Cu,Ni)6Sn5IMCs was presented in the reflow soldering welds,while the short rodshaped (Cu,Ni)3Sn4and strip shaped (Cu,Ni)6Sn5was showed in the laser soldering welds.The maximum shear force values of the two joints can reach over 320 N,far higher than actual production requirements.Based on this research results,it further demonstrated that laser soldering is a feasible technology to replace reflow soldering for the nickel/copper foil connection.

Highlights:(1) The formation mechanism of weld and interface microstructure of nickel/copper foil was compared and analyzed by reflow soldering and laser soldering.

(2) Laser soldering was proposed to achieve a high-quality connection for nickel/copper foil as a feasible technology,instead of reflow soldering.

Key words:reflow soldering；laser soldering；Sn solder；intermetallic compounds

Microstructural and properties of ultrafast laser selective micro-welding joints of sapphire and Invar alloysJIANG Qing1,XU Jiayi1,YANG Jin1,ZHAO Yixuan1,PAN Rui2,LI Peng3(1.Shanghai University of Engineering Science,Shanghai,201620,China；2.Beijing University of Technology,Beijing,100124,China；3.Shanghai Radio Equipment Research Institute,Shanghai,201109,China).pp 41-48,62

Abstract:The heterostructure joint of sapphire/Invar alloy was prepared using femtosecond laser selective welding technology,and the effects of laser power on the sealing performance,macro,micro-morphology,and shear strength of the joint were investigated.The interface welding defects,elemental distribution,and fracture behavior of the joint were characterized using scanning electron microscopy,energy dispersive spectroscopy,and laser scanning confocal microscope.The results showed that under ultrafast laser irradiation,sapphire and Invar alloy underwent melting,mixing,and diffusion processes through nonlinear absorption and linear absorption,respectively.This resulted in the formation of interlocking interfaces with intermingled features,indicating the presence of both metallurgical bonding and mechanical interlocking.The shear strength of the joint increases monotonically with the laser power,and the maximum shear strength is 145.3 MPa at a laser power of 10.19 W.The fracture of the sapphire/Invar alloy joint is mainly in the form of cleavage fracture,and both sides of the fracture contain the elements of Fe,Ni,Al,and O,which further suggests that the ultra-fast laser promotes metallurgical reactions of the two materials at the interface.

Highlights:(1) Fabrication of sapphire/ Invar alloy femtosecond laser selective micro-welding joints was realized.

(2) The effect of laser power on the microstructure and properties of sapphire/ Invar alloy joints by femtosecond laser selective welding was studied.

Key words:femtosecond laser；sapphire；Invar alloys；micro-welding；selective welding

Application and reliability of Au-Sn electroplated layer on the CSP hermetical packagingLI Yafei1,WANG Yuxiang2,JI Xiaoliang2,WEN Zhiru1,MI Jia1,WANG Hongbing1,GUO Fu2(1.The 26th Institute of China Electronics Technology Group Corporation,Chongqing,404100,China；2.College of Materials Science and Engineering,Beijing University of Technology,Beijing,100124,China).pp 49-55

Abstract:Hermetical packaging in CSP component is increasingly investigated.In order to realize the hermetic interconnection between Kovar cap and ceramic substrate,the electroplating method was used and Au/Sn/Au sandwiched layers were fabricated on the HTCC substrate.Through the eutectic reaction between Au and Sn,a hermetic interconnection was realized.In this paper,the influence of Au/Sn/Au electroplated layer quality and soldering parameter on the packaging quality of Au-Sn eutectic solder was systematically investigated.It is found that the Au/Sn/Au electroplated layer thickness and interlayer bonding would directly determine the packaging results.During the soldering process,Sn electroplated layer firstly melted and a molten pool thus formed.The molten Sn then dissolved the surrounding Au electroplated layer and the Au-Sn eutectic reaction occurred.The shorter soldering time was better for the Au-Sn eutectic packaging.When the soldering temperature was 330 ℃ and holding time was set to 30 s,the (Au,Ni)Sn—ζ phase—(Au,Ni)Sn delaminated eutectic microstructures formed due to Au-Sn eutectic reaction and a reliable hermetical packaging between Kovar cap and HTCC substrate was eventually realized.

Highlights:(1) Through Au/Sn/Au electroplated layers,the reliable interconnection between Kovar cap and ceramic substrate in CSP component was realized based on the eutectic reaction between Au and Sn.

(2) The thickness difference between Au and Sn electroplated layers would pose a negative influence on the packaging results of Au-Sn eutectic solder.

(3) The soldering curve was optimized and the (Au,Ni)Sn—ζ phase —(Au,Ni)Sn delaminated eutectic microstructures formed at the interconnection interface when soldering temperature was 330 ℃.

Key words:Au-Sn solder；eutectic reaction；electrodeposition；CSP hermetical packaging

Impact of copper-plated carbon nanotubes on microstructure and properties of copper-based composite filmsZHAO Xinyu1,LIU Qiang1,CHENG Guowen1,LIN Tiesong2,HUANG Yongde1(1.Nanchang Hangkong University,Nanchang,330063,China；2.Harbin Institute of Technology,Harbin,150001,China).pp 56-62

Abstract:Solving the problem of carbon nanotube aggregation and improving the interface between carbon nanotubes and matrix materials are the key to improving the properties of carbon nanotube copper-based composite films.In this study,the influence of copper-plated carbon nanotubes on the microstructure and properties of composite films has been conducted by comparing the differences in microstructure and properties between carbon nanotube copper-based composite films and copper-plated carbon nanotube copper-based composite films.This analysis involve the application of the quantum tunneling effect,DLVO theory and relevant material mechanics theories.The results indicate that at a content of 1.0% (mass fraction) of uncoated carbon nanotubes and copper-plated carbon nanotubes,the electrical resistivity of carbon nanotube copperbased composite films and copper-plated carbon nanotube copper-based composite films are 25.17 μΩ·cm and 17.73 μΩ·cm respectively.The rate of change in resistance under different bending cycles has been found to be greater for the former than for the latter.After copper plating on carbon nanotubes,the changes in their size and surface structure suppress agglomeration,enhance their joining strength with the copper matrix,and ultimately enhance the properties of composite films.Considering the influence of reinforcing materials on the microstructure and properties of composite materials,the mechanism of the influence of copper-plated carbon nanotubes on the microstructure and properties of copper -based composite films has been obtained.These findings provide a theoretical basis for subsequent research on flexible printing electronic technology.

Highlights:(1) The inhibitory effect of copper plating layer on carbon nanotube aggregation in copper-based composite films has been studied.

(2) The reinforcement mechanism of copper-plated carbon nanotubes in copper-based composite films has been studied.

Key words:carbon nanotubes；copper-plated carbon nanotubes；aggregation；joining strength

High-temperature anti-electrochemical migration behavior of Ag-In composite pasteZHANG Bowen,WANG Wei,FENG Haonan,ZHAO Zhiyuan,LU Xinyan,MEI Yunhui(Tiangong University,Tianjin,300387,China).pp 63-69

Abstract:Low temperature sintered nanosilver pastes have superior thermal,electrical and mechanical properties,making them one of the die-attach materials in wide band semiconductor devices.However,the oxidation and decomposition of sintered silver at high temperatures cause the occurrence of electrochemical migration,which may lead to short-circuit failure of electronic devices.Therefore,the competitive oxidation method is used,the electrochemical migration of sintered Ag is suppressed by adding In particles with higher oxygen affinity to the nano-Ag paste.The electrochemical migration lifetimes of sintered Ag-3In and Ag-5In pastes were significantly improved to 779 min and 804 min compared to sintered nano-Ag solder paste (382 min),which is about two times higher.Subsequently,the inhibition mechanism of In particles on the electrochemical migration of sintered silver in high temperature dry environment was analyzed.During the service process,In particles reacted with oxygen in preference to Ag particles to form In2O3,which inhibited the oxidation,decomposition and ionization of sintered Ag and significantly improved the electrochemical migration failure time of sintered silver.Meanwhile,the shear strength of sintered Ag-1In and Ag-3In pastes was improved by 30.92% and 32.37%,respectively,compared with that of sintered Ag paste.It was shown that the introduction of the appropriate proportion of In particles was effective in improving the shear strength of the die-attach samples while improving the electrochemical migration lifetime.

Highlights:(1) The electrochemical migration time of sintered Ag-3In and Ag-5In pastes is improved by about 1 times.

(2) In particles react with oxygen in preference to Ag particles thus inhibiting the electrochemical migration of sintered silver.(3) The shear strength of sintered Ag-1In and Ag-3In pastes is improved by 30.92% and 32.37% respectively.

Key words:electrochemical migration；nano-silver paste；anti-electromigration of Ag-In paste；packaging reliability

Size effect behavior of microstructure and mechanical properties in Sn-58Bi micro solder jointsWANG Xiaowei,WANG Fengjiang(Jiangsu University of Science and Technology,Zhenjiang,212000,China).pp 70-74,81

Abstract:The effect of reducing the size of reflow solder joints on the microstructure and morphology of Sn-58Bi solder joints was studied.The effect of reducing the size of solder joints at different aging times on the evolution of interfacial microstructure and shear properties of solder joints was also analyzed.The results showed that under the same cooling condition,the reduction of solder joint size resulted in a greater undercooling of solder joints during the solidification stage,the growth of β-Sn primary phases,and the differences in the grain size distribution of Sn and Bi phases within the solder joints.Due to the differences in the diffusion rates of Cu atoms,the reduction in the size of Sn-58Bi solder joint was beneficial to the growth of interfacial metallic compounds (IMCs) after reflowing.Meanwhile,under aging condition,the interfacial growth rate of IMC at the solder joint with size of 300 μm was greater than that with size of 400 μm and 760 μm.At the interface of solder joints,the joints with size of 300 μm needed a shorter time to grow from a scallop shape to a flatten shape.Due to constrain effect,the joint with size of 300 μm presented a higher shear strength compared with the joints with size of 400 μm and 760 μm.

Highlights:(1) The decrease on size of Sn-58Bi solder joints resulted in the change on grain size distribution due to differences in undercooling.

(2) Smaller Sn-58Bi solder joints presented higher shear strength due to significant mechanical constraints.

Key words:Sn-58Bi solder joint；size effect；thermal aging

Thermal conductivity of flexible Cu-Ag composite thin films by laser direct writingYAO Yu1,GUO Wei2,LIU Tong2,ZHOU Xingwen3(1.Beijing Innowind Aerospace Equipment Company Limited,Beijing,100854,China；2.Beihang University,Beijing,100191,China；3.Soochow University,Suzhou,215000,China).pp 75-81

Abstract:With the increasing demand of flexible electronic products for efficient thermal management,the preparation of flexible thin films with high conductivity has attracted more and more attention in recent years.Cu and Cu-Ag thin films are prepared by laser direct writing technique on polyimide (PI)substrate.The phase analysis and structure characterization of the two films show that the copper nanoparticles and silver nanowires are sintered by partial melting of their surface under laser irradiation.By comparing the resistance changes of prepared copper and Cu-Ag thin films at different temperatures for 7 days,it is concluded that the introduced silver improves the overall oxidation resistance of the composites.The thermal diffusivity and thermal conductivity of the two composites are tested,and it is found that the thermal conductivity of Cu-Ag/PI is significantly improved,showing better thermal performance than Cu/PI.This work provides a quick,simple and economical method for the preparation of Cu/PI and Cu-Ag/PI composites with good thermal stability.

Highlights:(1) The flexible Cu-Ag films are fabricated using laser direct writing.

(2) The joining interface of Cu-Ag and the thermal conductivity of the film are studied.

Key words:laser direct writing；Cu thin film；Cu-Ag thin film；thermal conductivity

Research progress in low temperature bonding and patterning of metal nanomaterialsDU Rongbao1,2,ZOU Guisheng1,2,WANG Shuaiqi1,2,LIU Lei1,2(1.State Key Laboratory of Clean and Efficient Turbomachinery Power Equipment,Department of Mechanical Engineering,Tsinghua University,Beijing,100084,China；2.Key Laboratory for Advanced Materials Processing Technology,Ministry of Education,Beijing,100084,China).pp 82-96

Abstract:Utilizing the size effect of metal nanomaterials can significantly lower the bonding temperature and enhance the reliability of solder joints.Low temperature bonding metal nanomaterials,such as silver nano solder paste,have undergone extensive validation and mass production in the packaging of power devices,represented by third-generation semiconductors chips.However,when it comes to advanced packaging for integrated circuits that require patterned solder joints,the challenge lies in transferring power chip packaging technology to meet both low-temperature bonding and patterning bonding requirements,significantly increasing the technical complexity.This article begins by dissecting the fundamental scientific principles behind reducing bonding temperature through the utilization of metal nanomaterials.It then provides an extensive review of the current research status in low-temperature bonding with various nanomaterials.Finally,it focuses on summarizing patterning methods for bondable nanomaterials,offering technical insights for achieving precise spacing,high precision,and efficient graphical low-temperature bonding in advanced packaging.

Highlights:(1) The fundamental principles and theoretical research progress of achieving low-temperature bonding using metal nanomaterials are elucidated.

(2) An overview of the current research status on utilizing different forms of metal nanomaterials for low-temperature bonding is provided.

(3) The research progress in patterning various metal nanomaterials is systematically summarized.

Key words:advanced packaging；metal nanomaterials；low temperature bonding；patterning

Research progress on ultrafast laser processing of two-dimensional materialsGUO Linglan,ZHANG Honghao,ZHANG Xinquan,ZHU Limin,SHEN Daozhi(Shanghai Jiao Tong University,Shanghai,200240,China).pp 97-105

Abstract:Two-dimensional materials such as graphene,hexagonal boron nitride,transition metal dichalcogenides,and black phosphorus have attracted significant attention in the fields of science and industry due to their exceptional properties.These materials demonstrate great potential in applications like sensing,catalysis,and energy storage.Ultrafast laser processing technology,known for its high precision and wide material adaptability,plays a crucial role in the processing and device fabrication of two-dimensional materials,achieving non-destructive or low-damage processing.This technique demonstrates advantages in the reduction of graphene oxide,preparation,ablation,and patterned transfer of graphene.For transition metal dichalcogenides and other two-dimensional materials,ultrafast laser can also effectively induce phase transitions,exfoliation,thinning,and surface deposition.The interaction between ultrafast lasers and two-dimensional materials opens new opportunities in high-tech fields such as micronanoelectronics and optoelectronics,with future research focusing on reducing costs,improving the performance of quantum devices,and developing high-performance micronano devices.

Highlights:(1) This paper discusses the latest progress in ultrafast laser processing of two-dimensional materials from both domestic and international perspectives,focusing on the interaction between laser and matter.

(2) The paper analyzes the technical characteristics of ultrafast laser processing of different two-dimensional materials and elaborates on their related application developments.

Key words:ultrafast laser；two-dimensional materials；micro-nano processing；processing technology；nanomaterials

Research progress of laser direct writing technologies for the conductive metallic wire on dielectric surfaceCUI Mengya,HUANG Ting,XIAO Rongshi(Beijing University of Technology,Beijing,100124,China).pp 106-115

Abstract:Fabrication of conductive metallic wire on dielectric surface has a broad application in microelectronics,optoelectronics,electromechanical systems,etc.As a very promising alternative,laser direct writing is a maskless,efficient,and flexible approach that readily allows for free-form writing of a wide range of conductive metallic patterns on substrates,and hence has attracted an enormous amount of attention in the past several years.Laser direct writing can be achieved via photochemical or photothermal process,including photochemical reduction of metal ions,laser induced forward transfer,laser heating reduction of metal ions,etc.Herein,the laser direct writing strategies for fabrication of conductive metallic wires including the principle,characteristics and research progress have been reviewed in detail.Furthermore,remaining challenges and development trends are summarized and prospected.

Highlights:(1) Based on the interacting mechanism between laser and material,the advanced laser direct writing technologies of the conductive metallic wire on dielectric surface were systematically outlined.

(2) The research achievements of laser direct wiring manufacturing technologies in conductive metallic wires were listed.

(3) The challenges and the prospects in fabricating conductive metallic wires by laser direct writing were pointed out.

Key words:laser manufacturing；laser direct writing；conductive metallic wire

Research progress on low-temperature sintered silver and gold-based surface interconnectionsWANG Zhiwei,LIN Liting,LI Xin(Tianjin University,Tianjin,300072,China).pp 116-123

Abstract:Sintered silver has strong thermal conductivity,electrical conductivity,and mechanical qualities,allowing it to accomplish "low-temperature sintering,high-temperature applications" in high-temperature high-power electronic devices.However,the interconnections between sintered silver and gold-based surfaces continue to suffer from issues such as low shear strength and poor dependability.Therefore,firstly,the interconnection mechanism and performance of sintered silver and different interfaces are compared,focusing on summarizing the sintered silver-gold interconnection mechanism and key influencing factors.Then,the existing sintered silver-gold interconnection processes are summarized in terms of sintering process,gold-based interface preparation and reliability.Finally,through the review of the research results in the field of silver-gold interconnections,the future development direction of the silver-gold interconnections topic is prospected.

Highlights:(1) The influencing factors and mechanism of sintered silver-gold interconnections are analyzed.

(2)Methodsand research progress for improving sintered silver-gold interconnections are summarized.

Key words:sintered silver；interface interconnection；silver-gold joint；reliability

Research progress in high-performance power device packaging and power cycle reliabilityGUAN Ruofei1,JIA Qiang1,ZHAO Jin1,ZHANG Hongqiang2,WANG Yishu1,ZOU Guisheng3,GUO Fu1,4(1.Beijing University of Technology,Beijing,100124,China；2.Beihang University,Beijing,100191,China；3.Tsinghua University,Beijing,100084,China；4.Beijing Union University,Beijing,100101,China).pp 124-136

Abstract:The progress of semiconductor technology has made power devices face higher voltage,power density and junction temperature,which puts forward higher requirements for the reliability of power device packaging.How to improve and detect the reliability of power devices has become an important task in the development of power devices.Improving packaging reliability mainly focuses on optimizing packaging structure,improving die attach technology and wire bonding technology.Power cycling,as a reliability testing method closest to the actual operating conditions of power devices,has been widely studied in terms of testing techniques,monitoring methods,and failure mechanisms.This paper provides a review of research on the packaging structure,packaging technology,power cycling mechanism of power devices and attempts to summarize the methods for improving packaging reliability at home and abroad in recent years.This review also discusses the principles of power cycling test and the failure mechanisms of solder layers and bonding wires .Finally,the future development trend of power device packaging was prospected.

Highlights:(1) The research on improving the reliability of power device packaging was discussed from three aspects:packaging structure,die attach,and wire bonding.

(2) The research on control parameters,strategies,detection parameters,and failure criteria of power cycling test was summarized.

Key words:power device；packaging structure；power cycling test；die attach；wire bonding