细间距倒装芯片互连过程中焊点界面金属间化合物的形成与演化

利用凸点间距为100μm,高度约为45μm,焊料成分为Sn-3.0Ag-0.5Cu(质量分数,%)(SAC305)的倒装芯片与树脂基板互连封装,研究芯片单侧凸点及芯片与BT基板焊点互连回流过程中界面金属间化合物(intermetalic compound,IMC)的形成和演化.结果表明,封装互连前,在芯片单侧镍焊盘界面上形成了长针状(Ni,Cu)₃Sn₄和薄层状Ni₃P,由于反应过程中焊料基体中Cu原子的大量消耗,没有形成典型的(Cu,Ni)₆Sn₅.封装互连过程中,由于大量Cu原子从铜界面扩散到镍界面,促使镍焊盘界面(Ni,Cu)₃Sn₄逐渐转化成(Cu,Ni)₆Sn₅,形貌由针状转变成短棒状,反应后(Cu,Ni)₆Sn₅成为主要IMC层;在铜焊盘界面上,形成了一层短棒状的(Cu,Ni)₆Sn₅,由于从镍焊盘界面扩散过来的Ni原子对Cu₃Sn生长的限制作用,反应后没有形成典型的Cu₃Sn.     

热时效过程中微米级SnAgCu焊点的界面金属间化合物形成及演变

研究微米级倒装组装焊点在150℃热时效过程中界面金属间化合物(intermetalic compound,IMC)的形成及演化.结果表明,在热时效300 h后,受铜焊盘界面扩散过来的Cu原子影响,镍焊盘界面(Ni,Cu)₃Sn₄全部转化成(Cu,Ni)₆Sn₅;在铜焊盘界面,热时效至100 h后,形成一层薄的Cu₃Sn,在随后的热时效过程中,由于Ni原子对Cu₃Sn生长的抑制作用,Cu₃Sn几乎没有生长.此外在时效100 h内,两侧界面(Cu,Ni)₆Sn₅生长速率增加较快,但随着时效时间的增加逐渐减慢.两侧界面(Cu,Ni)₆Sn₅顶端形貌随着时效时间的增加逐渐变平.     

铜/铝固态界面金属间化合物的生长行为

在573～773 K温度范围内对铜铝冷轧复合板进行退火处理。观察、分析了铜铝固态界面金属间化合物的演变行为,从扩散动力学的角度分析了界面相的形成机制和长大机制。结果表明:退火处理后试样界面反应层由靠近Al侧的Al_2Cu、靠近Cu侧的Al_4Cu_9以及处于二者之间的AlCu三层金属间化合物构成,其形成序列为Al_2Cu、Al_4Cu_9、AlCu;界面金属间化合物生长控制机制由前期的反应控制和后期的扩散控制两部分构成;退火温度越高,反应机制控制阶段终了时间越早。     

SAC305/Cu微焊点界面金属间化合物生长速率

界面金属间化合物(IMC)的生长速率是影响钎焊接头可靠性的重要因素. 文中研究了焊点尺寸、时效温度及镍镀层对SAC305/Cu微焊点界面IMC生长速率的影响. 结果表明,焊球尺寸为200,300,400和500 μm,时效温度为100,130,160 ℃条件下,界面IMC层厚度生长速率随时效时间平方根数值的升高而增长. 焊点尺寸由小变大,界面IMC层厚度更薄,IMC的生长速率也更小. 随着时效温度的升高,界面IMC生长速率增大. 镍镀层对界面IMC的生长速率有明显的抑制作用,即降低IMC生长速率,使其增厚变缓.     

轧制复合钢/铝界面金属间化合物生长动力学研究

研究了冷轧复合特种钢/铝合金复合带材的退火热处理工艺,探讨了退火温度和退火时间对复合界面金属间化合物生长的影响。结果表明,当退火温度达605℃时,金属间化合物开始在界面上生成,随退火温度和退火时间的增加,金属间化合物的厚度增大,且化合物层厚度随时间的变化复合抛物线规律,经线性拟合,得出化合物生长的激活能和化合物生长动力学曲线。     

轧制复合铝/不锈钢界面金属间化合物的生长动力学

对轧制复合铝合金/不锈钢双层复合材料进行不同温度和时间的退火,借助Zeiss Ax10金相显微镜、Quanta-200型扫描电镜、EDAX能谱仪和D-max X射线衍射仪对复合界面结合区进行金相组织观察、元素成分线扫描分析、界面化合物EDS分析及XRD物相鉴定,研究复合界面上金属间化合物的生长行为。结果表明:复合界面金属间化合物(IMC)主要为Fe2Al5相,当退火温度达773 K时,Fe2Al5已在界面上生成;随退火时间的延长,Fe2Al5的增厚符合抛物线法则;界面金属间化合物Fe2Al5的生长激活能为162.3 kJ/mol,并获得其生长动力学模型,通过此模型可对化合物层厚度进行初步计算。     

Sn-9Zn-0.1S/Cu焊点液固界面金属间化合物的生长动力学

采用扫描电镜和光学显微镜观察研究了230~260℃焊接温度范围内Sn-9Zn-0.1S/Cu焊点界面金属间化合物的结构及生长动力学.结果表明,在该焊点界面形成的化合物可分为两层:靠铜侧的是厚且平直的γ-Cu₅Zn₈化合物层;靠焊料侧的则为另一薄且呈扇贝、粒状的CuZn化合物层.提高钎焊温度及延长反应时间基本不改变Sn-9Zn-0.1S/Cu焊点界面金属间化合物的结构和成分,但会使形成的界面金属间化合物层厚度增加.γ-Cu₅Zn₈金属间化合物层的厚度与反应时间的平方根呈线性关系,表明其生长由扩散机制控制.根据阿伦尼乌斯公式,Sn-9Zn-0.1S/Cu焊点界面γ-Cu₅Zn₈金属间化合物层反应活化能为22.09 kJ/mol.     

钛/不锈钢焊接界面金属间化合物的生成动力学

对TA2/316L焊接接头分别进行350～900 ℃、保温30～120 min的真空热处理,利用SEM、EDX及热力学、动力学等分析手段研究了热处理后界面反应物的生长过程及规律.结果表明,界面反应物呈层状出现,且随着热处理温度的升高,层状反应物由一层变为多层.动力学计算显示,在900℃以下对TA2/316L接头进行热处理,其界面金属间化合物呈线性增长,界面总金属间化合物生长动力学方程可表示为W=1.15×106exp(-50.93 kJ·mol-1/RT)t1/2.     

钛合金及金属间化合物中各组分的活度系数

根据Kohler三元溶体模型和Miedema二元系统生成热模型，建立了计算三元合金及金属间化合物各组分活度系数的方程，不仅能处理三元合金及金属间化合物体系，也能处理二元系，甚至可以近似处理多元系。计算了Ti-5Al-2．5Sn，Ti-6Al-4V，Ti-25V-15Cr-0．2Si及TiAl中各组分的活度系数并与有关实验值进行对比，发现根据本研究公式计算的结果比非对称计算公式获得的结果更符合实际。将计算结果应用于钛基复合材料的界面反应研究，可以预测到：SiC／Ti-6Al-4V基复合材料的界面反应较严重，SiC／Ti-25V-15Cr—0．2Si的界面反应较难进行，SiC／TiAl的界面反应程度最轻。     

基于蒙特卡罗方法的铝/钢熔钎焊界面金属间化合物层生长分析

针对铝/钢熔钎焊界面金属间化合物在SEM,EDS,XRD界面测试研究的基础上,确立了界面由Fe₂Al₅、FeAl₃等金属间化合物组成. 在此基础上采用蒙特卡罗方法,建立了铝/钢界面铝、铁扩散及Al-Fe化合物生长模型,并进行了数值分析和对比研究. 结果表明,所建立的模型能够很好地反映钢侧Fe₂Al₅的生长,铝侧FeAl₃离散存在,且金属间化合物层的厚度接近试验测量结果.     

热冲击条件下倒装组装微焊点的可靠性——裂纹生长机理

研究热冲击条件下细间距倒装微焊点的裂纹萌生及扩展,通过观察裂纹生长路径,并结合累积塑性应变能密度及应变在焊点上的分布,分析裂纹的生长机理. 结果表明,裂纹形成在微焊点外侧,位于镍焊盘界面IMC与焊料基体之间的界面上;随着循环次数的增加,裂纹进入镍焊盘附近的焊料基体中,沿着焊盘平行的方向扩展,累积塑性应变能密度及应变在微焊点上的分布与裂纹扩展方向一致. 对裂纹生长机理探讨可知,IMC与微焊点之间的界面处于双重应力集中状态,因此裂纹易在微焊点及IMC之间的界面上萌生;随着循环次数的增加,焊料基体的塑性变形增加,高塑性的焊料区域为裂纹扩展提供了条件.     

热冲击条件下倒装组装微焊点的可靠性--应力应变

采用有限元模拟法,研究倒装组装芯片在-55～125℃热冲击过程中微焊点所承受的应力和应变,对微互连焊点的裂纹生长情况进行分析.结果表明,芯片最外侧焊点具有最大的累积塑性应变能密度,为组装体中最易失效焊点;累积塑性应变能密度主要集中在芯片侧镍焊盘附近,在外侧最大,向内侧逐渐递减,这表明裂纹形成在芯片侧,沿着焊盘由外侧向内侧扩散,最终穿过整个焊点.试验结果与模拟分析相一致,进一步验证了模拟结果对裂纹生长的分析.     

High temperature reliability of lead-free solder joints in a flip chip assembly

The visco-plastic behaviour of solder joints of two models of a flip chip FC48D6.3C457DC mounted on a printed circuit board (PCB) via SnAgCu solder is investigated using Anand's model. While the bumps of one of the models are realistic with 6 μm thickness of intermetallic compound (IMC) at interconnects of solder and bond pads, the other are made up of conventional bumps without IMC at these interconnects. The solder bump profiles were created using a combination of analytical method and construction geometry. The assembled package on PCB was accelerated thermally cycled (ATC) using IEC standard 60749-25. It was found in the result of the simulation that IMC does not only impact solder joint reliability but also is a key factor of fatigue failure of solder joints. The IMC sandwiched between bond pad at chip side and solder bulk is the most critical and its interface with solder bulk is the most vulnerable site of damage. With reference to our results, it is proposed that non inclusion of IMC in solder joint models composed of Sn-based solder and metalized copper substrate is one of the major causes of the discrepancy on solder joint fatigue life predicted using finite element modelling and the one obtained through experimental investigation.     

Evolution of AuSnx intermetallic compounds in laser reflowed micro-solder joints

To investigate the effect of Au thickness on evolution of AuSnx IMCs,pads with 0.1,0.5 and 4.0 μm thickness of Au surface finish were utilized.Laser reflowed solder joints were aged in 125℃ isothermal ovens.Results indicated that little IMC formed at the interface of solder and pad with 0.1 μm thickness of Au.Even in condition of 744 hours aging,thickness of IMCs did not increase obviously.As for the joints with 0.5 μm thickness of Au,most of AuSn4 IMCs stayed at the interface and were in needle-like or dendritic morphology.With the increase of aging time,AuSn4 IMCs became flat and changed to a continuous layer.In the joints with 4.0 μm thickness of Au on pads,AuSn,AuSn2,AuSn4 IMCs and Au2Sn phase formed at the interface.As aging time was increased,more Sn rich IMCs formed at the interface,and evolved to AuSn4 IMCs in condition of long time aging.Thickness of AuSn4 IMCs reached about 30 μm.     

钢/铌焊接接头金属间化合物生长机制及调控研究现状

钢/铌焊接结构在航空航天工业具有广阔的应用前景,但是钢/铌焊接接头极易生成金属间化合物(IMC),显著降低接头性能,因此开展IMC生长机制及其调控措施的研究具有重要的理论和实际意义。简要介绍国内外IMC生长机制及其调控措施的研究现状,指出模拟法在IMC生长机制的研究中显现出巨大的优势和潜力,是未来IMC生长机制研究发展的方向。并指明能量-冶金联合调控是抑制接头IMC生长的有效解决方案。     

The numerical analysis of strain behavior at the solder joint and interface in a flip chip package

The aim of this study was to investigate the strain behaviors at the joint interface of a flip chip package during thermal cycling testing using a numerical method. Because the underfill and solder bump material properties exhibit a large non-linearity in the higher temperature range, the linear elastic assumption may lose accuracy during numerical analysis. This study compared the differences in interfacial stress or strain between the linear and non-linear material property assumptions. The viscoplasticity of the solder bump and temperature-dependent underfill properties were assumed in the non-linear analysis. The numerical results showed that the solder bump failure mechanism was a combination of fatigue and creep actions dominated by plastic shear strain. The tensile stress due to shrinkage and hardening in the solder joints in the low thermal cycle temperature dwell period could result in ablation at the joint interface.     

三元稀土硅化物Gd_2PdSi_3单晶生长(英文)

采用光悬浮区熔法以3 mm/h的生长速度制备Gd2PdSi3单晶。该化合物表现为同成分熔融,其熔点在1700°C左右。与Gd2PdSi3化学计量成分相比,制备的晶体中Pd含量略低,导致了熔区内Pd的富集以及实验过程中熔区温度的降低。采用标准成分给料棒制备的单晶内含有少量定向的GdSi沉淀,可以通过退火热处理减少其含量但并不能完全消除。采用给料棒成分微调的方法制备出不含GdSi沉淀的高质量Gd2PdSi3单晶。     

Solder joint reliability in flip chip package with surface treatment of ENIG under thermal shock test

This study investigated the microstructural evolution and evaluated the thermo-mechanical reliability of a Sn-3.0Ag-0.5Cu (in wt.%) flip chip package during a thermal shock test. The reliability of the flip chip bonded packages was evaluated by means of the thermal shock in the temperature range of 233 K to 398 K. After 250 thermal shock cycles, cracks finally occurred at the corner solder bump joint on the chip side interfacial regions. In that, the crack initiated at the solder region near the intermetallic compound (IMC) layers. For the interpretation of the failure mechanism of the package, finite element analyses were conducted. From the finite element analysis or computational simulation result, the distribution of the plastic work in the corner solder bump was found to be most considerable. This means that the corner solder bump has the highest potential for first crack initiation and growth, because the thermo-mechanical failure of the solder joints is mainly caused by the accumulation of the plastic work. This matched well with the experimental results.