硅基芯片金锡共晶焊工艺中金硅扩散机理研究

金锡合金焊料(Au⁸⁰Sn²⁰)具有良好的导热、导电性,广泛用于高可靠集成电路共晶贴片工艺。研究了硅基芯片AuSn共晶焊工艺中工艺参数对硅原子向AuSn焊料扩散的影响,当共晶温度从310 ℃增加到340 ℃时,AuSn焊料中硅原子质量百分比增加1个数量级。分析了硅原子向AuSn焊料的扩散机理,讨论了硅原子向焊料扩散后对产品可靠性的影响及控制措施。     

直拉法制备锑化铟单晶的表面杂质研究

制备高质量锑化铟(InSb)单晶是发展大规模红外焦平面器件以及新型高温红外探测器衬底材料的关键。而在用直拉法生长InSb的过程中,表面杂质的出现会严重影响成品率。利用X射线光电子能谱(X-ray Photoelectron Spectroscopy, XPS)技术研究了生产中InSb晶体表面杂质膜层的成分,分析了其主要来源及造成的影响,并采取相应工艺措施进行了改进。结果表明,InSb晶体表面杂质膜层的主要成分为In₂O₃、Sb₂O₃和Sb₂O₅三者的混合物以及碳沾污,其厚度不超过40 nm。通过对单晶炉处理和保护气氛的工艺优化,表面杂质大大减少,为获得高质量晶体奠定了基础。     

H2和H2O对双极器件抗辐射性能的影响规律和机制

为了深入研究H₂和H₂O进入氧化层后对双极器件辐射效应的影响机制,以栅控双极晶体管为研究载体,分别开展了不同浓度H₂浸泡中的辐照试验和温湿度试验后的总剂量辐照试验。试验结果表明,随着氢气浸泡浓度的增加,器件的抗辐射能力逐渐降低;而温湿度试验后,由于水汽的进入,器件在随后的辐照试验过程中辐射损伤呈增大趋势。在此基础上,利用栅控栅扫描法进行氧化层辐射感生缺陷的定量分离,发现H₂和H₂O进入器件氧化层后,均会造成辐射感生界面陷阱电荷Nit的增加,并在一定程度上降低辐射感生氧化物陷阱电荷Not的量,结合理论分析进一步给出了H₂和H₂O造成器件损伤增强的潜在机制。研究成果对于辐射环境用电子系统的抗辐射性能评价和应用具有参考意义。     

MOS栅氧的界面特性和辐照特性研究

通过交流电导法,对经过不同时间N₂O快速热处理(RTP)的MOS电容进行界面特性和辐照特性研究。通过电导电压曲线,分析N₂O RTP对Si-SiO₂界面陷阱电荷和氧化物陷阱电荷造成的影响。结论表明,MOS电容的Si-SiO₂界面陷阱密度随N₂O快速热处理时间先增加再降低;零偏压总剂量辐照使氧化层陷阱电荷显著增加,而Si-SiO₂界面陷阱电荷轻微减少。     

真空共晶设备的改进对共晶焊接质量的影响

共晶焊接质量对芯片的可靠性及寿命影响很大。在这方面,通过改进后的真空共晶设备比改进前更具有优势。分析了真空环境对共晶焊接的影响,在原有设备增加了分子泵的情况下,实现无空洞焊接。对甲酸气体保护下的In焊料焊接进行了分析,并结合实际经验给出合理的工艺曲线,证实了在真空室加入甲酸气体的保护下,可以把In焊料表面的氧化层去除,使焊料在浸润性方面具有明显的优势。     

烧结温度对AuSn焊料薄膜及封装激光器性能的影响

采用不同温度对Au80Sn20共晶合金焊料进行烧结实验,研究了AuSn焊料薄膜在烧结后的形貌、物相组成以及对封装激光器的性能影响等.焊料在烧结后形成ξ相Au5Sn和δ相AuSn两种金属间化合物,随着烧结温度的上升,两相晶粒均明显长大,而ξ相Au5Sn趋向于形成枝晶.较低温度下烧结的焊料表面粗糙度较高,不利于激光器管芯的贴装.高温过烧焊料薄膜的导电导热性能有少许提升,对封装激光器管芯的功率没有明显影响,但焊料薄膜中残余应力较高,使激射波长有所蓝移.该结果将为AuSn焊料的烧结参数优化和硬焊料封装激光器的性能分析提供参考和指导.     

氮气流量对磁控溅射C掺杂TiO2薄膜光学性能的影响

采用磁控溅射法制备了C掺杂TiO₂薄膜,并研究了氮气引入溅射过程对薄膜光学性能的影响。利用X射线衍射仪、拉曼光谱仪、X射线光电子能谱仪、分光光度计和原子力显微镜分析了不同氮气流量下薄膜的微结构、元素价态、透光性能和表面形貌。结果表明,沉积的薄膜主要是非晶结构,拉曼光谱中存在少量锐钛矿相,且随着氮气流量增大,锐钛矿特征峰强度减弱,意味着晶粒出现细化。当氮气流量增大为4cm³/min时,C掺杂TiO₂薄膜内氮元素含量为3.54%,其光学带隙从3.29eV变化至3.55eV,可见光区的光学透过率明显提高。可见改变氮气流量可实现对C掺杂TiO₂薄膜光学带隙和光吸收率的有效调控。     

基于纳米锥结构的钙钛矿材料吸收特性研究

本文对ZnO结构太阳能电池钙钛矿(CaTiO₃)薄 膜层中嵌入的Ag粒子的等离子体增强进行了理论分析。由于引入了Ag颗粒,归因于Ag颗粒的 强表面等离子体吸收和Ag与CaTiO₃之间的协同作用,太阳能电池的吸收得以增强。在计算 分析中,Ag粒子的最佳半径为80 nm。优化的纳米结构的平均吸收效 率可以达到80％,比纯CaTiO₃薄膜层结构的平均吸收效率高24％。因此认为,本文设计研究的 Ag/CaTiO₃太阳能电池结构可能以低成本和简单的制造工艺成为未来工业制造领域的焦点 。     

TiO2基染料敏化太阳能电池的表面修饰及性能研究

采用水热法制备TiO₂浆料,用La(NO₃)₃溶 液浸泡TiO₂薄膜获得修饰电极。用X射线光电子能谱(XPS) 和扫描电子显微镜(SEM)对修饰电极的主要成分及形貌进行表征的结果显示,电极薄膜分为 上下两层,表 面包覆层粒径较大,为La₂O₃颗粒;下层颗粒粒径较小,为TiO₂颗粒。电流-电压测 试结果显示,与修饰 前相比,用La(NO₃)₃溶液浸泡30min获得的膜电极性能最优,使 开路电压和短路电流分别提高了6.8%和 18.5%。电化学阻抗谱(EIS)测试结果表明,相同偏压下,TiO₂/La ₂O₃电极界面复合电阻比TiO₂要大,说明 La₂O₃包覆层在一定程度上抑制了界面的电子复合,改善了电池的光电化学性能。     

In0.53Ga0.47As表面氮化和硫钝化对其Al/Al2O3/InGaAs MOS电容特性的影响

本文通过对比频散特性和滞回特性,计算界面态密度D_it和有效边界缺陷密度ΔN_bt,分析界面缺陷和漏电流等方法,系统的研究了In_0.53Ga_0.47As表面氮化和硫钝化对其Al/Al₂O₃/InGaAs结构MOS电容特性的影响。实验结果表明,这两种方法都能够在InGaAs表明形成一层界面钝化层。相比较于未处理的样品,经过氮气等离子体处理的样品表现出较好的界面特性,得到了最小的积累区频散、滞回电压,以及良好的I-V性能。经过(NH₄)₂S_x处理的样品则获得了最小的平带电压区频散以及最低的界面态密度Dit=2.6E11cm_-2eV_-1.     

Electrochemical Migration Characteristics of Eutectic Sn-Pb Solder Alloy in NaCl and Na<Subscript>2</Subscript>SO<Subscript>4</Subscript> Solutions

Anodic dissolution and the electrochemical migration characteristics of eutectic Sn-Pb solder alloy in deaerated 0.001% NaCl and Na₂SO₄ solutions were investigated using anodic polarization and water drop tests. Anodic polarization results revealed that a Pb-rich phase was preferentially ionized in deaerated 0.001% NaCl solution and an Sn-rich phase was predominantly ionized in deaerated 0.001% Na₂SO₄ solution, which coincides well with the composition of the dendrites formed during water drop tests. X-ray diffraction and photoelectron spectroscopy results showed that the surface oxide film formed on pure Sn in deaerated 0.001% NaCl solution is more stable than that formed on pure Sn in deaerated 0.001% Na₂SO₄ solution. The surface oxide film formed on pure Pb in deaerated 0.001% Na₂SO₄ solution is more stable than that formed on pure Sn in deaerated 0.001% NaCl solution. Therefore, the quality of the surface film of eutectic Sn-Pb solder in a chemical environment seems to be critical not only for corrosion resistance, but also for electrochemical migration resistance.     

Thermal transient characteristics of die attach in high power LED PKG

The reliability of packaged electronics strongly depends on the die attach quality because any void or a small delamination may cause instant temperature increase in the die, leading sooner or later to failure in the operation. Die attach materials have a key role in the thermal management of high power LED packages by providing the low thermal resistance between the heat generating LED chips and the heat dissipating heat slug. In this paper, thermal transient characteristics of die attach in high power LED PKG have been studied based on the thermal transient analysis using the evaluation of the structure function of the heat flow path. With high power LED packages fabricated by die attach materials such as Ag paste, solder paste and Au/Sn eutectic bonding, we have demonstrated for characteristics such as cross-section analysis, shear test and visual inspection after shear test of die attach and how to detect die attach failures and to measure thermal resistance values of die attach in high power LED PKG. From the differential structure function of the thermal transient characteristics, we could know the result that die attach quality of Au/Sn eutectic bonding with the thermal resistance of about 3.5 K/W was much better than this of Ag paste and solder paste with the thermal resistance of about 11.5–14.2 K/W and 4.4–4.6 K/W, respectively. From this results, it is possible to fabricate high power LED with a small thermal resistance and a good die attach quality by applying Au/Sn eutectic bonding die attach with a high reliability and a good repeatability.     

Characterization of chip scale packaging materials

The mechanical stability of Chip Scale Packages (CSP) used in surface mount technology is of primary concern. The dominant issues are package warpage and solder fatigue in solder joints under cyclic loads. To address these issues, molding compound and die attach film were characterized with finite element method which employed a viscoelastic and viscoplastic constitutive model. The model was verified with experiments on package warpage, PCB warpage and solder joint reliability. After the correlation was observed, the effect of molding compound and die attach film on package warpage and solder joint reliability was investigated. It was found that package warpage tremendously affected solder joint reliability. Furthermore, a die attach film was developed based on results of the modeling. CSP with the developed die attach film are robust and capable of withstanding the thermal stresses, humidity and high temperatures encountered in typical package assembly and die attach processes. Also, a lead free solder is discussed based on the results of creep testing. This paper presents the viscoelastic and viscoplastic constitutive model and its verification, the optimum material properties, the experimental and simulated reliability and performance results of the u*BGA packages, and the lead free solder creep.     

铜颗粒增强对锡铅钎料蠕变寿命的影响

颗粒增强是提高合金性能的重要手段之一.增强体的不同含量对基体的性能会产生不同的影响.主要分析和讨论了铜的不同含量对铜颗粒增强的锡铅基复合钎料蠕变性能的影响.测定6种铜颗粒增强的锡铅基复合钎料的蠕变寿命.试验结果表明:在相同的条件下,复合钎料的蠕变寿命与锡铅钎料相比,均有不同程度的提高.当铜的质量分数约为1%时,复合钎料的蠕变性能最好,约为锡铅钎料的17倍.     

Power electronic assemblies: Thermo-mechanical degradations of gold-tin solder for attaching devices

The eutectic Au₈₀Sn₂₀ solder alloy has been applied in semiconductor assemblies and other industries for years. Due to some superior physical properties, Au/Sn alloy gradually becomes one of the best materials for soldering in electronic devices and components packaging but the voids growth in AuSn solder joints is one of the many critical factors governing the solder joint reliability. Voids may degrade the mechanical robustness of the die attach and consequently affect the reliability and thermal conducting performance of the assembly. Severe thermal cycles [− 55 °C/+175 °C] have highlighted degradations in AuSn die attach solder. The inspection of as-prepared die-attachments by X-ray and SEM (observation of cross-section) shows that the initial voids sizes were increased and a propagation of transverse cracks inside the joint between voids has appeared after ageing, it was featured also the existence of the IMC typical scallop-shape morphology with the phase structure of (Ni, Au)₃Sn₂ on as-reflowed joints. In this paper, we evaluate the origin of these degradations and ways to address them.     

军用标准PIND试验方法发展与对比分析

封装腔体内部的可动粒子会引起半导体器件和电路的短路或间歇性功能失效,从而对其使用可靠性产生影响。粒子碰撞噪声检测(PIND)试验可有效剔除腔体内部含有可动粒子的器件,从而被纳入多项标准中作为一项无损筛选试验并得到广泛的应用。给出了腔体内部可动粒子的危害,详细研究了美国和中国军用标准PIND试验方法的发展历程及现状,对比了3种PIND试验标准不同版本试验参数的变化,分析了标准参数变化产生的影响,给出了筛选批接收的试验流程,对试验人员具有一定指导作用,提高了PIND筛选试验的准确性。     

SCSP中芯片黏结层在焊接时的可靠性

提出了一个细观力学模型,该模型同时考虑了热膨胀和蒸汽膨胀对叠层芯片尺寸封装(SCSP)中芯片黏结层变形的影响.当初始温度确定时,由该模型可求得给定温度下芯片黏结层内部的蒸汽压力和孔隙率,从而判断芯片黏结层在焊接回流时的可靠性.当温度从100℃升高到250℃时,芯片黏结层的饱和蒸汽压、等效弹性模量及孔隙率分别从0.10 ...     

Failure mechanism of lead-free solder joints in flip chip packages

The failure mechanisms of SnAgCu solder on Al/Ni(V)/Cu thin-film, underbump metallurgy (UBM) were investigated after multiple reflows and high-temperature storage using a ball shear test, fracture-surface analysis, and cross-sectional microstructure examination. The results were also compared with those of eutectic SnPb solder. The Al/Ni (V)/Cu thin-film UBM was found to be robust enough to resist multiple reflows and thermal aging at conditions used for normal production purposes in both SnAgCu and eutectic SnPb systems. It was found that, in the SnAgCu system, the failure mode changed with the number of reflows, relating to the consumption of the thin-film UBM because of the severe interfacial reaction between the solder and the UBM layer. After high-temperature storage, the solder joints failed inside the solder ball in a ductile manner in both SnAgCu and SnPb systems. Very fine Ag₃Sn particles were formed during multiple reflows in the SnAgCu system. They were found to be able to strengthen the bulk solder. The dispersion-strengthening effect of Ag₃Sn was lost after a short period of thermal aging, caused by the rapid coarsening of these fine particles.     

Effect of solder creep on the reliability of large area die attachment

High temperature solders have been widely used for power device die attachment. One typical solder is Pb92.5In5Ag2.5, which is a ternary eutectic alloy with a eutectic temperature of 310°C. Such a Pb-based solder has a low Young's modulus, a low yield strength, and a high strain prior to failure. So it can be used to attach large size silicon die to mismatched substrates. In this paper, stresses and strains have been studied on a large size power MOSFET attachment using the Pb92.5In5Ag2.5 solders. A commercial finite element analysis software is employed as the simulation tool. Three types of substrates, pure copper, copper–tungsten composite, and pure molybdenum are used in the study, where molybdenum has the closest coefficient of thermal expansion to silicon. In addition to the plastic deformation simulation of the solder, a creep model of the solder was incorporated due to the low melting temperature of the solder alloy. Firstly, stresses and strains are calculated during the cooling cycle after attachment. It is found that the creep strain is the dominant plastic strain at low cooling rate (10°C/min). Also, the maximum Von Mises stress in the Si chip is decreased from 174 to 62.7 MPa after adding creep strain. As expected, the maximum creep strain happens to the die-to-copper substrate attach. Simulation on temperature cycling is done from −55°C to +150°C. The peak Von Mises stress occurs at the low temperature extreme and holds steadily during the soaking period, indicating insignificant contribution from creep. The Von Mises stress at the high temperature extreme is much lower and decreases with holding time. Significant plastic deformation of the solder layer is observed in cooling cycles. For silicon to copper substrate attach, its plastic deformation increases with each cycle. For all three substrates used, considerable solder creep is observed at heating cycles. The creep strain is much larger than the rate-independent plastic strain in the solder alloy for all three types of substrates. It is concluded that solder creep is the dominant factor affecting long term reliability of power semiconductor die attachment.     

微波电路中In/Au合金焊点的失效分析

本文针对微波电路元件焊接脱落问题,分析了In/Au合金焊点的微观结构及成分, 研究了In/Au芯片焊接的失效模式.找出了焊点脱落的主要原因:温度控制不当引起焊点的过热吃金或焊料的氧化引起的浸润不良,导致焊点的结合强度不够,致使焊点脱落.根据分析提出了严格控制温度及焊接时使用氮气保护的改进意见,较好的解决了In/Au合金焊接脱落问题,支撑了微波电路的生产工艺.