【作者】 张威；

【导师】 王春青；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2008， 博士

【摘要】 光电子封装中激光器件与光导纤维之间的对准和定位是保证器件耦合效率和可靠性的关键技术。本文提出光纤自对准激光软钎焊的方法（Fiber Self-alignment by Laser Soldering,FSLS）,设想利用熔融钎料的表面张力所产生的回复力及回复转矩实现光纤在焊盘上的自动对准,由此方法产生的新工艺将使光电子封装制造成本下降。研究AuSn钎料与Au/Ti、Au/Ni/Cu两种焊盘及光纤Au/Ni镀层之间的界面组织在激光钎焊及老化过程中的演化规律,从而论证工艺的可行性;研究和阐明光纤自对准的基本原理,从理论上得出自对准的驱动力、分析材料与结构因素的影响规律并进行对准精度评价和误差估计。光纤定位激光软钎焊工艺试验研究表明:AuSn钎料合金在氩气保护下在小功率长时间条件下易于润湿铺展,形成良好的焊点。研究表明激光钎焊过程中AuSn钎料与Au/Ti焊盘界面反应的特点是:随着激光输入能量的增加,界面区域所生成的先共析ζ相的形状由扇贝状演变为粗大的棒状或树枝状。在老化过程中AuSn-Au/Ti界面生成的ζ相不断联合、长大;AuSn-Au/Ni界面生成的针状（Au,Ni）3Sn2不断溶解到钎料中直至消失,同时在界面形成了一层（Au,Ni）Sn;钎料内部共晶组织不断球化并粗化。激光钎焊条件下在AuSn-Au/Ni/Cu及AuSn-Au/Ni两界面处所形成的针状（Au,Ni）₃Sn₂在老化过程中逐渐平坦化,界面上形成了连续的（Au,Ni）Sn层,并随老化时间的延长而增厚;两个界面附近所形成的花状（Au,Ni）₃Sn₂在老化过程中向周围的δ相中不断溶解直至消失,同时δ相中的Ni含量增加。基于对光纤定位软钎焊焊点进行的合理假设建立焊点三维形态的数学模型,并对焊点形态的能量、体积以及边界条件进行合理描述,利用有限元法对焊点三维形态进行计算并分析材料及结构因素对焊点三维形态的影响规律,结果表明:随着钎料量的增加和焊盘尺寸的减小,钎料对光纤的包覆程度增大;随着焊盘长宽比的增加,焊点横截面曲线的弯曲程度增大。采用激光共聚焦扫描显微镜对焊点三维形态进行测量并与计算结果进行对比,结果表明焊点三维形态的试验测量结果与计算结果吻合良好,焊点三维形态计算方法及测量手段合理可靠。通过对光纤进行受力分析,从理论上得出自对准驱动力的解析式,根据公式可以得出自对准回复力及法向力主要受液态钎料对光纤润湿力的影响,而静压力可以忽略;利用有限元计算的方法得出不同形状焊盘的理论平衡位置,并得出材料与结构因素对自对准回复力及回复转矩的影响规律,结果表明:自对准回复力随着横向对准偏移成线性变化,回复转矩随着偏转角成线性变化;在一定范围内选择较大的钎料量、采用较大的焊盘长宽比、较大表面张力的钎料以及较小的钎料-焊盘接触角更有利于对横向对准偏移的自对准,在一定范围内选择较小的钎料量、采用较大的焊盘长宽比、较大表面张力的钎料和较小的钎料-光纤接触角更有利于对初始转角的自对准。光纤与焊盘间隙高度计算结果表明:只有钎料量超过临界值时,间隙高度才存在;间隙高度随着焊盘尺寸的减小、焊盘长宽比的减小以及钎料与光纤接触角的增加而增加。采用激光共聚焦显微镜对间隙高度测量,试验测量结果与计算结果吻合良好。更多还原

【Abstract】 In optoelectronic packaging, alignment and attachment between laser and optical fiber is the key technology to assure component coupling efficiency and reliability. In this paper, a new method of fiber self-alignment by laser soldering has been proposed which uses the restoring force and restoring torque to accomplish the self-alignment of fiber on the pad. The manufacturing cost of optoelectronic packaging can be reduced by using the new process produced by this method. The feasibility of the process was demonstrated by studying the evolution of intermetallic compounds (IMCs) at interface between AuSn solder and pad (Au/Ti pad and Au/Ni/Cu pad) as well as that between AuSn solder and fiber metallization (Au/Ni) during laser soldering and aging process. The basic principle of fiber self-alignment was studied and demonstrated, the driving force of self-alignment educed in theory, effects of material and structure factors analyzed, and alignment precision and error estimated.Research on fiber attachment by laser soldering process showed that AuSn solder alloy was prone to wetting, spreading and forming good solder joint at low laser power and long heating time in argon atmosphere. The characteristics of interfacial reaction between AuSn solder and Au/Ti pad during laser soldering process showed that with the increase of laser input energy the morphology of preeutecticζ-phase changed from scallop protrusions to large cudgel shape and dendritic shape. During aging process,ζ-phase formed at the interface of AuSn-Au/Ti began to coalesce and grow, while the needle-like (Au,Ni)3Sn2 formed at the interface of AuSn-Au/Ni began to dissolve into the solder and disappear, replacing by a layer of (Au,Ni)Sn at the interface, at the same time, the eutectic microstructure of solder began to spheroidize and coarsen. During aging process, the needle-like (Au,Ni)3Sn2 formed at the interface of AuSn-Au/Ni/Cu as well as AuSn-Au/Ni under the condition of laser soldering began to flatten gradually, and a continuous layer of (Au,Ni)Sn formed at the interface, the thickness of which increased with aging time; The flower-like (Au,Ni)3Sn2 formed near the interface of AuSn-Au/Ni/Cu as well as AuSn-Au/Ni began to dissolve into the ambientδ-phase and disappear during aging, at the same time, the content of Ni inδ-phase increased.Based on the reasonable hypothesis, the mathematical model of three dimensional (3-D) shape of solder joint in fiber attachment soldering was established, the energy, the volume and the boundary condition of solder joint shape was described in reason, 3-D shape of solder joint was calculated by employing finite element method (FEM), and the influence of material and structure factors on 3-D shape of solder joint was analyzed. The results showed that the extent of solder wetting on fiber increased with the increase of solder volume and the decrease of pad size; With the increase of aspect ratio of pad, the bending extent of curve at cross section increased. The 3-D shape of solder joint was measured by laser scanning confocal Microscope (LSCM) and the results were compared with those of calculated, the results showed that the measured results of 3-D shape of solder joint were in accordance with the calculated results, and the method of calculating and measuring of 3-D shape of solder joint was reasonable and credible.The formulation of self-alignment driving force was deduced theoretically by analyzing the force acting on fiber. Base on the formula, the restoring force and normal reaction force could be calculated which mainly depended on the wetting force acting on fiber by solder, and the hydrostatic pressure could be ignored. The theoretical equilibrium positions of pad with different shape were calculated by FEM, and the influences of material and structure factors on self-alignment restoring force and restoring torque were analyzed. The results showed that the self-alignment restoring force changed linearly with horizontal offset and the restoring torque changed linearly with yaw angle. Bigger solder volume within limits, bigger aspect ratio of pad, bigger surface tension of solder and smaller solder-pad contact angle were propitious to the self-alignment for horizontal offset, while smaller solder volume within limits, bigger aspect ratio of pad, bigger surface tension of solder and smaller solder-fiber contact angle were propitious to the self-alignment for yaw angle.Calculation results on stand-off height (SOH) between fiber and pad showed that the SOH existed when the solder volume exceeded the critical volume. SOH increased with the decrease of pad size, the decrease of aspect ratio and the increase of solder-fiber contact angle. SOH was measured by LSCM, and the measured results were in accordance with the calculated results.更多还原