Ag-Pd纳米合金低温连接及其抗电化学迁移性能

纳米银焊膏能够实现低温连接、高温服役,同时具有优异的导电、导热性能,其缺点是非常容易发生电化学迁移。本文采用脉冲激光沉积成功制备了完全互溶的Ag-10%Pd纳米合金,并将其用于SiC芯片的封装互连,旨在提高纳米颗粒烧结层的抗电化学迁移能力,同时保持纳米颗粒的低温烧结特性。研究表明,采用Ag-10%Pd纳米合金烧结连接SiC芯片及镀银的直接覆铜基板(DBC),在250℃的温度下可以实现剪切强度为21.89 MPa的接头,达到了美国军标MIL-STD-883K的要求(7.8 MPa)。Ag-Pd纳米合金抗电化学迁移能力是同等条件下纯银的4.3倍。在Ag-Pd纳米合金中,银离子的析出受到PdO的阻碍,迁移产物呈云雾状分布,有效延长了电极的短路时间。脉冲激光沉积Ag-Pd纳米合金的烧结避免了传统银、钯颗粒直接混合方法后续高达850℃的合金化过程。Ag-Pd纳米合金作为封装互连材料是实现低温连接的有效保证,并有望为功率电子器件的高可靠性封装提供解决方案。     

SPS工艺对铜/金刚石复合材料性能的影响

采用SPS(放电等离子烧结)工艺制备了高体积分数铜/金刚石复合材料,研究了SPS中主要的工艺参数烧结温度、保温时间和烧结压强对复合材料相对密度和热导率的影响。结果表明:最佳的烧结温度为930℃;热导率和相对密度随保温时间延长有所提高,20min后趋于稳定;而随烧结压强由10MPa提高到70MPa,热导率约上升15%。经过优化工艺后,所制备的铜/金刚石复合材料最高热导率达到354.1W(m.K)–1,最高相对密度为98.4%。     

SPS制备亚微米多晶LaB6块体的EBSD研究

用氢直流电弧法制备LaH2纳米粉末,再采用放电等离子烧结（SPS）技术,在压力50MPa,烧结温度1400℃～1600℃条件下制备了LaB6亚微米多晶块体。采用EBSD技术,对LaB6样品表面的晶粒、晶界特征及晶粒取向等进行了测试分析。结果表明,SPS制备的LaB6晶粒尺寸为0．14μm～1．10μm,晶粒大小随烧结温度升高而增大。随烧结温度的升高,小角度晶界（微取向差在10°以内）的含量逐渐增加。取向分析表明,SPS烧结LaB6多晶块体形成了几种择优取向。     

磁控共溅射GaAs/SiO2细小纳米颗粒镶嵌材料的结构和非线性光学性质

应用磁控共溅射技术和后退火方法制备了GaAs/SiO2纳米颗粒镶嵌薄膜,并分别应用原子力显微镜、X射线衍射和卢瑟福背散射实验来观测薄膜的形貌、相结构和化学组分.结果表明GaAs纳米颗粒的平均直径很小(约为1.5～3.2nm),且均匀地分布于SiO2之中,薄膜中的GaAs和SiO2组分都符合化学计量关系.应用脉冲激光高斯光束对薄膜的光学非线性进行了Z扫描测试和分析.结果表明,薄膜的三阶光学非线性折射率系数和非线性吸收系数都由于量子限制效应而大大地增强,在非共振条件下,它们分别约为4×10-12m2/W和2×10-5m/W,在准共振的条件下,它们分别约为2×10-11m2/W和-1×10-4m/W.     

磁控共溅射GaAs/SiO2细小纳米颗粒镶嵌材料的结构和非线性光学性质

应用磁控共溅射技术和后退火方法制备了GaAs/SiO2纳米颗粒镶嵌薄膜,并分别应用原子力显微镜、X射线衍射和卢瑟福背散射实验来观测薄膜的形貌、相结构和化学组分.结果表明GaAs纳米颗粒的平均直径很小(约为1.5～3.2nm),且均匀地分布于SiO2之中,薄膜中的GaAs和SiO2组分都符合化学计量关系.应用脉冲激光高斯光束对薄膜的光学非线性进行了Z扫描测试和分析.结果表明,薄膜的三阶光学非线性折射率系数和非线性吸收系数都由于量子限制效应而大大地增强,在非共振条件下,它们分别约为4×10-12m2/W和2×10-5m/W,在准共振的条件下,它们分别约为2×10-11m2/W和-1×10-4m/W.     

赝三元半导体致冷烧结材料致密性和强度的研究

研究了以高优值系数赝三元半导体致冷区熔生长晶体为原料,制作烧结体材料的工艺,确定出以颗粒度为74～297μm的晶体粉末,400MPa下冷压成型,在380℃～400℃条件下,经五小时烧结处理,获得高致密度和高强度的半导体致冷器用烧结体材料。     

热处理升温快慢对非晶硅中形成的纳米硅粒尺寸的影响

含氢非晶硅薄膜经过快速热退火处理后,我们用拉曼散射和X-射线衍射技术对样品进行分析.我们的实验结果表明:在非晶硅薄膜中形成的纳米硅晶粒的大小随着热退火过程中升温快慢而变化.在升温过程中,当单位时间内温度变化量较大时（～100℃/s）,则所形成纳米硅粒较小（～1.6～15nm）;若单位时间内温度变化量较低（～1℃/s）,则纳米硅粒较大（～23～46nm）。根据分形生长理论和计算机模拟,我们讨论了升温快慢与所形成的纳米硅颗粒大小的关系.     

微米银焊点的超快激光图形化沉积及其在芯片连接中的应用探索

集成电路(IC)芯片封装中小尺寸、细节距焊点采用的传统锡基钎料在服役过程中存在桥接、电迁移、金属间化合物等问题,在大电流、大功率密度的应用中受到限制。采用脉冲激光沉积(PLD)技术,在覆铜陶瓷(DBC)基板上图形化沉积了多孔微米银焊点,用于替代传统的钎料凸点,并将其应用于Si芯片与DBC基板的连接。结果表明:采用不锈钢作为掩模,可沉积出500μm及300μm特征尺寸的疏松多孔银焊点阵列,银焊点呈圆台形貌;在250℃温度、2 MPa压力下热压烧结10 min, Si芯片与DBC基板连接良好,连接后的银焊点边缘的孔隙率为42%左右,银焊点中心区域的孔隙率为22%; 500μm和300μm特征尺寸的银焊点的连接接头的剪切强度分别为14 MPa和12 MPa;接头断裂主要发生在银焊点与芯片或DBC基板的连接界面处。     

甲酸预处理对基于Cu/Ag混合纳米颗粒的Cu-Cu键合的影响北大核心CSCD

针对功率电子器件中电气互连的需求,提出了一种适用于功率电子器件封装的Cu-Cu键合工艺。采用纳米尺寸的Cu/Ag混合颗粒浆料作为Cu-Cu键合的中间层,并利用甲酸气体在最佳预处理温度180℃对Cu/Ag混合纳米颗粒浆料进行预处理,之后在260℃的键合温度、外加5 MPa压力的情况下完成Cu-Cu键合。通过测试发现,甲酸气体预处理后混合纳米颗粒浆料中Cu纳米颗粒表面的氧化物得到了有效还原,使得混合纳米颗粒烧结得更充分,键合后的截面变得更致密。此外,甲酸气体预处理后的断面上产生了明显的韧性形变,且Cu-Cu键合的剪切强度平均值达到65.6 MPa。结果表明,该种键合工艺可靠,为功率电子器件封装中高可靠的Cu-Cu键合提供了新的解决方案。     

纳米银导电墨水的制备及烧结北大核心

通过液相化学还原法制备了纳米银颗粒,纯化后通过X射线衍射（XRD）和能量色散谱（EDS）分析证明得到了结构完整、较为纯净的纳米银颗粒。将其制备为纳米银导电墨水,墨水的粒度分布窄、平均粒径约为25 nm、分散性好,表面张力为32.13 dyn/cm（1 dyn/cm=0.001 N/m）、黏度为4.66 mPa·s,符合喷墨打印对于墨水的要求。将墨水喷印在聚酰亚胺（PI）基材上,分别在125,150,175,200和225℃下烧结30 min,然后测量导电线路的电阻率,发现150℃下烧结电阻率为5.72×10-4Ω·cm,已满足电子电路印刷需求,随着烧结温度的提升,电阻率也不断下降,225℃下烧结,电阻率达1.53×10-5Ω·cm;同时对其烧结过程进行了分析,探究了导电线路中不导电组分的挥发及纳米银的熔融程度对电阻率的影响。     

低介电损耗AlN陶瓷及BN—AlN基陶瓷材料研究

首先利用化学工艺制备出烧结助剂Y2O3均匀混合的AlN粉体及BN均匀包覆AlN的复合粉体。利用无压烧结制备出AlN陶瓷及BN—AlN基复相陶瓷。通过对陶瓷显微结构、热性能及微波介电性能的研究发现,通过化学工艺,将BN包覆到AlN粉体表面,制备出显微结构均匀的AlN-20％BN（质量比）复相陶,其热导率为78．1w／m·K,在Ka波段介电常数为7．2、介电损耗最小值为13×10^-4通过材料化学工艺,将烧结助剂Y2O3均匀添加到AlN基体中,制备出热导率为154．2w／m·K,在Ka波段介电常数为8．5、介电损耗最小值为9．3×10^-4的AlN陶瓷材料。     

Thermal behavior of silver nanoparticles for low-temperature interconnect applications

Low-temperature sintering behavior of Ag nanoparticles was investigated. The nano Ag particles used (∼20 nm) exhibited obvious sintering behavior at significantly lower temperatures (∼150°C) than the T_m (960°C) of silver. Coalescence of the nano Ag particles was observed by sintering the particles at 150°C, 200°C, and 250°C. The thermal profile of the nanoparticles was examined by a differential scanning calorimeter (DSC) and a thermogravimetric analyzer (TGA). Shrinkage of the Ag-nanoparticle compacts during the sintering process was observed by thermomechanical analysis (TMA). Sintering of the nanoparticle pellet led to a significant increase in density and electrical conductivity. The size of the sintered particles and the crystallite size of the particles increased with increasing sintering temperature.     

无铅银浆烧结工艺与导电性能研究

制备了无铅低温玻璃粉,将其与银粉和有机载体混合配制成无铅导电银浆并烧结。通过SEM和EDX观察浆料烧结银膜的形貌并进行成分分析,用四探针测试仪测量烧结银膜的电阻率,讨论了浆料成分配比、烧结时间、烧结温度等方面对银膜导电性能的影响。确定了无铅导电银浆的最佳配比为:质量分数w(银粉)72%,w(玻璃粉)3%和w(有机载体)25%,最佳烧结温度为580℃,最佳保温时间为5min。     

Thermal Conductivity of Bi<Subscript>0.5</Subscript>Sb<Subscript>1.5</Subscript>Te<Subscript>3</Subscript> Affected by Grain Size and Pores

A fine measurement system for measuring thermal conductivity was constructed. An accuracy of 1% was determined for the reference quartz with a value of 1.411 W/m K. Bi_0.5Sb_1.5Te₃ samples were prepared by mechanical alloying followed by hot-pressing. Grain sizes were varied in the range from 1 μm to 10 μm by controlling the sintering temperature in the temperature range from 623 K to 773 K. The thermal conductivity was 0.89 W/m K for the sample sintered at 623 K, while a grain size of 1.75 μm was measured by optical microscopy and scanning electron microscopy. The thermal conductivity increased on the sample sintered at 673 K because of grain growth and decreased on those sintered at the temperatures from 673 K to 773 K because the increase of pore size caused to decrease thermal conductivity. The increase of thermal conductivity for the samples sintered at temperatures above 773 K was affected by the increase of carrier concentration.     

稀土掺杂对99氧化铍陶瓷性能的影响

对99BeO分别掺入16种稀土氧化物,系统地研究不同稀土氧化物掺杂对99BeO陶瓷热导率和密度的影响,研究发现：掺入0．1％和0．5％的Tb4O7能够提升BeO陶瓷的热导率,分别达到288w／（m·K）和295W／（m·K）。掺入CeO2,Nd2O3能够提升99BeO陶瓷的密度,在1630℃时烧结时达到2．939和2．927g／cm^3。     

Room-Temperature Sintering Process of Ag Nanoparticle Paste

Recently, the authors developed a novel room-temperature wiring method using Ag nanoparticle paste. In this paper, the sintering mechanism of the Ag nanoparticle paste was clarified through examination of the adsorption stability and the removal of the dispersant from the Ag nanoparticles. The Ag nanoparticles in the paste are protected by dodecylamine as a dispersant. This paste possesses substantially long shelf life and thermo stability at room temperature. When the printed line of the Ag nanoparticle paste is dipped in a methanol bath, methanol effectively dissolves and removes the dispersant from the nanoparticles. Ag nanoparticles are sintered within a short period. The sintering of Ag nanoparticles is not uniform. Some Ag nanoparticles quickly grow and form a network by sintering (necking). The others maintain a nanometer scale. Large Ag particles and an Ag skeleton continue to grow by absorbing very small nanoparticles. In addition, the use of ethanol and isopropanol as the treatment agent is shown for the first time.     

Photonic sintering of inkjet printed current collecting grids for organic solar cell applications

ITO-free organic solar cells with inkjet printed current collecting grids are demonstrated. For sintering those grids, thermal treatment and its faster alternative, photonic flash sintering, are applied and the characteristics of the resulting metal structures are compared with each other. The electrical potentials and resulting currents in the devices with different sintering conditions are calculated. The flash sintered current collecting grids exhibit clear advantages over thermally sintered grids in terms of geometry and conductivity. Similar conductivities are obtained after 5 s of flash sintering and 6 h of thermal sintering. This finding demonstrates the great potential of flash sintering for the roll-to-roll manufacturing of printed organic solar cells on flexible substrates.     

AlF_3-MgF_2-SiO_2系低温共烧氧氟玻璃陶瓷性能研究

制备了AlF3-MgF2-SiO2系低温共烧氧氟玻璃陶瓷材料,用XRD、SEM和阻抗分析仪等分析其烧结特性、显微结构、介电性能以及与Ag电极浆料共烧等性能。结果表明:该材料可以在900℃烧结致密化,烧成后的样品具有低的介电常数(6.2)和介质损耗(<0.002)、较低的热膨胀系数(7.4×10–6/K)、较高的弯曲强度(220 MPa)和热导率[2.4 W/(m.K)],能够与Ag电极浆料共烧,是一种很有应用前景的低温共烧陶瓷基板和无源集成介质材料。     

Thermoelectric Properties of Nanograined ZnO

Bulk ZnO with a grain size of 20 nm was successfully obtained by pulsed electric current sintering. The crystalline size was almost identical to that of the raw particles, because the sintering temperature was as low as 200°C. A pressure of 500 MPa effectively enhanced densification, leading to a relative density of >90% at 200°C. The small grain size led to a low thermal conductivity of 3 W/m K at room temperature, due to enhanced boundary scattering. The Seebeck coefficient was higher than that of micrograined ZnO with similar Ga doping (0.3 at.% Ga). However, the resistivity was increased by more than 1000 times. The temperature dependence of conductivity showed thermally activated conduction behavior, while that of micrograined ZnO exhibited metallic-like behavior. The thermoelectric properties suggest that a carrier trap in the nanograined ZnO hinders carrier transport. Surface modification of the ZnO nanoparticles by heat treatment in H₂ resulted in observable photoluminescence which was quenched in the starting nanoparticles, and led to a decrease in the resistivity of the sintered bulk, which indicates that control of surface defects on the nanoparticles is crucial for enhancement of the thermoelectric properties of nanograined ZnO.     

Are Sintered Silver Joints Ready for Use as Interconnect Material in Microelectronic Packaging?

Silver (Ag) has been under development for use as interconnect material for power electronics packaging since the late 1980s. Despite its long development history, high thermal and electrical conductivities, and lead-free composition, sintered Ag technology has limited market penetration. This review sets out to explore what is required to make this technology more viable. This review also covers the origin of sintered Ag, the different types and application methods of sintered Ag pastes and laminates, and the long-term reliability of sintered Ag joints. Sintered Ag pastes are classified according to whether pressure is required for sintering and further classified according to their filler sizes. This review discusses the main methods of applying Ag pastes/laminates as die-attach materials and the related processing conditions. The long-term reliability of sintered Ag joints depends on the density of the sintered joint, selection of metallization or plating schemes, types of substrates, substrate roughness, formulation of Ag pastes/laminates, joint configurations (i.e., joint thicknesses and die sizes), and testing conditions. This paper identifies four challenges that must be overcome for the proliferation of sintered Ag technology: changes in materials formulation, the successful navigation of the complex patent landscape, the availability of production and inspection equipment, and the health concerns of Ag nanoparticles. This paper is expected to be useful to materials suppliers and semiconductor companies that are considering this technology for their future packages.