基于钎料球重熔的MEMS微部件自组装及熔滴激光驱动行为

发布时间：2018-01-25 02:26

本文关键词： MEMS自组装钎料形态预测动态接触角激光重熔 MEMS三维封装　出处：《哈尔滨工业大学》2014年博士论文　论文类型：学位论文

【摘要】：基于微钎料熔滴表面张力的MEMS部件自组装技术能够自行实现对微机械部件的组装，形成具有高深宽比的三维复杂微结构，对微机械部件的制造具有重要意义。与此同时，微液滴的驱动行为则为MEMS微开关及微流体器件提供了关键技术，能够启发新型MEMS器件的研发。本文基于激光重熔工艺开发了一种新型的MEMS自组装技术，并搭建了高精度的自组装微操作平台；通过数值方法与试验相结合对影响自组装静平衡位置及精度的各因素进行了系统的研究；并基于计算流体力学方法对自组装的动态翻转过程、钎料同微部件之间的流固耦合机制进行了深入分析；同时，还首次对固体基板上微钎料熔滴的激光驱动行为进行了探索。自组装精度影响因素研究表明，自组装角度偏差小于2.5o；随着焊盘尺寸和长宽比的增大，自组装静平衡角度越小；同时，自组装中使用的钎料体积越小，静平衡角度越小，越利于自组装系统保持其静平衡位置；而在假设完全铺展润湿的前提下，钎料的表面张力及接触角变化对自组装静平衡位置几乎不会产生影响；在焊盘尺寸／钎料球直径一定时，其静平衡位置几乎相同，这一比值可定义为自组装尺寸因子η。对无铰链自组装结构的能量分析表明，系统具有减小固定和活动微部件之间间距的趋势（由此提出了“虚铰链”的概念），该趋势会逐渐随着活动微部件接近于静平衡位置而减小，当活动微部件达到静平衡位置时，间距闭合趋势消失。针对无铰链结构基于引线键合工艺，开发了一种新型的MEMS自组装限位结构，在引入该限位结构后，自组装角度偏差小于0.5o。基于数值研究方法探寻了微钎料熔滴的动态润湿行为，结果表明动态润湿角模型更适合于对快速润湿铺展过程进行拟合，随着润湿铺展时间的加大，会降低拟合准确性。在润湿铺展的初期快速铺展阶段，Rw(t)~tn（n=0.32~0.45）关系能很好的拟合润湿半径随时间的变化，但当钎料趋于平衡状态时，拟合出现偏差。进一步研究表明，钎料的润湿铺展过程可以通过两段Rw(t)~tn关系进行拟合，n值的差异意味着润湿铺展机制的转变。自组装动态过程的研究结果表明，自组装中钎料熔滴优先铺展翻转的活动微部件，之后才在固定微部件上快速铺展。翻转过程具有增大同一时刻下钎料熔滴在活动微部件上的动态接触角的趋势，增大润湿驱动力，使得活动微部件上熔滴润湿速率更快，，呈现出优先铺展的不对称现象。转矩分析表明，自组装动态过程中净转矩Mnet上下振荡，接触线的前进会加剧Mnet的复杂性。平衡位置附近，Mnet会一直保持在0值附近波动，且正负两边的波动接近对称。能量分析表明，自组装钎料熔滴及微部件动能相对于减少的钎料表面能而言十分微小，能量转换效率较低，大部分能量通过转化为内能的方式耗散。对影响自组装动态过程的各因素分析表明，随着钎料熔滴体积的减小，自组装翻转的速度也越快；钎料润湿铺展速度较慢时，自组装过程呈现出明显的“快-慢-快”的三阶段，这是钎料不对称铺展的结果。而钎料润湿铺展速度较快时，翻转作用对于润湿力的增强效应减弱，钎料熔滴呈现对称铺展的趋势。对于自组装翻转速度而言，当翻转速度较慢时，钎料熔滴自由表面能最低。翻转速度较快时，钎料熔滴自由表面能会出现升高的趋势，之后随着固定微部件上接触线的快速前进，又会急剧降低。最后，使用激光偏置局部加热方法在开放的固体基板上成功实现了微钎料熔滴的驱动，熔滴总是向着激光中心一侧（热端）移动，之后当激光束中心线同钎料熔滴对称中心重合时，熔滴停止前进。这同一般的液滴热致驱动方向（向冷端移动）正好相反。定性及定量分析结果表明微钎料熔滴驱动过程中，Marangoni对流及钎剂蒸汽反冲作用力会推动熔滴向偏离激光束中心一侧移动（冷端），减弱熔滴向激光束中心靠拢的趋势，钎料熔滴在基板上的热致润湿性变化才是驱动熔滴前进的主要机制。
[Abstract]:The MEMS component of micro solder droplet surface tension based on self assembly technology can automatically realize the assembly of micro mechanical components, formed with high aspect ratio of the complex three-dimensional micro structure, has important significance for manufacturing micro mechanical components. At the same time, the driving behavior of micro droplets is MEMS micro switch and microfluidic devices provide a key technology, research can inspire new MEMS devices. In this paper, laser remelting technology developed a new type of self-assembly technology based on MEMS, and built a self assembling high precision micro operation platform; through the combination of experiment and numerical methods on the factors influencing the accuracy of the static equilibrium position and self-assembly were studied; and the computational fluid dynamics method based on dynamic turning process of self-assembly between solder with the micro components coupling mechanism are analyzed; at the same time, but also for the first time on solid substrate The laser driving behavior of the droplet of the solder is explored.
Study on the factors affecting the accuracy of self-assembly showed that self-assembly angle deviation is less than 2.5o; with the pad size and length width ratio increases, the self-assembly of static balance angle is small; at the same time, since the volume of solder used in assembling the smaller static balance angle is smaller, more conducive to the self assembling system to maintain its equilibrium position; in the premise of fully wetting, surface tension and contact angle of the solder has influence on the static equilibrium position is almost not self assembly; in pad size / solder ball diameter, the static equilibrium position is almost the same, this ratio can be defined as self assembling size factor ETA.
The hinge of self-assembled structures of energy analysis shows that the system has reduced the spacing between the fixed and movable micro parts (the trend of "virtual hinge" concept), the trend will gradually decrease with the activities of micro components close to the equilibrium position, when the micro component reaches the equilibrium position, closed distance disappear according to the trend. No hinge wire bonding process based on the development of a new type of MEMS self-assembled limit'structure, in the introduction of the limit structure, self assembling angle deviation less than 0.5o.
Study on numerical method based on exploring the dynamic wetting behavior of micro solder droplet, the results show that the dynamic contact angle model is more suitable for fitting the fast wetting and spreading process, with the increase of wetting and spreading time, will reduce the fitting accuracy. Fast spreading in the early stage of wetting and spreading, Rw (T) ~tn (n=0.32~0.45) can good fitting wetting radius changes with time, but when the solder tends to equilibrium, the fitting deviation. Further study showed that the wetting and spreading process of solder using two Rw (T) by fitting ~tn relation, difference of n value means a change of the wetting and spreading mechanism.
That study of self-assembled dynamic process results in the self-assembly of solder droplet spreading flip priority moving micro parts, only after the fixed micro parts rapid spreading. The turning process with the increasing trend of dynamic contact of solder droplet in micro parts on the angle at the same time, increase the wetting driving force, the activity of micro parts of the droplet wetting rate faster, showing asymmetry priority spreading. Torque analysis showed that the self assembling net torque in the dynamic process of Mnet under oscillation, complexity of the contact line ahead will aggravate Mnet. Near the equilibrium position, Mnet will keep the values fluctuate around 0, and the positive and negative fluctuations on both sides of the nearly symmetric. The energy analysis shows that the self-assembly of solder droplet and micro components can reduce the surface energy of solder is very small relative to the energy conversion efficiency is low, most of the energy is transformed into energy consumption by the way Scattered.
The effect of self assembly factors of dynamic process analysis shows that, with the decrease of solder droplet size, self-assembly turning faster; wetting and spreading speed is slow, the self-assembly process showed significantly in the three phase of "fast slow fast", this is the solder spreading result. And asymmetry wetting and spreading speed, enhance the wetting force effect weakened for the reversal effects of solder droplet, symmetric spreading trend. For self assembling turning speed, when the turnover rate is relatively low, solder droplet surface free energy minimum. Turning speed is faster when the solder droplet free surface can appear increasing trend fast forward, then with the fixed micro parts contact lines, and sharply decreased.
Finally, the use of laser bias local heating method in solid substrate on the successful implementation of the open micro solder droplet, droplet always toward the laser center side (hot end mobile), when the laser beam center line with solder droplet symmetry coincide, droplet stop. This same general droplet heat the actuating direction (move to the cold end) on the contrary. The qualitative and quantitative analysis results show that the micro solder droplet driven process, Marangoni convection and flux of vapor recoil force will push the droplet to deviate from the laser beam center side (Leng Duan), weakened the droplet to move closer to the center of the laser beam, solder droplet on the substrate of thermally induced wettability change is the main driving mechanism of droplet advance.

【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TH-39

【参考文献】