Micro-thermocompression Bonding Mechanism and Modeling for Electronics Devise Interconnection

研究了微电子封装中的引线键合和细引线键合的工艺机理。建立了基于有限元技术的数值模型，模拟了无超声振动热压缩连接过程中的变形过程。分析了导线表面与引线框架界面接触的生长过程。如果触点界面是固定的，则侧线表面在折叠到引线框架的同时展开，产生周向接合。另一方面，如果接触界面可以滑动，接触区域的中心将大大扩展，侧向导线表面不会延伸。结果表明，界面接触面积趋于固定，但即使在中心处没有得到较强的金属结合，也不会在界面产生周边结合时滑动。为了确保形成较强的周边结合，需要大于0.5的线压下量。这一结论得到了实验结果的支持。界面接触面积主要由导线减少量决定。如果压下量保持不变，则带凹槽的刀具增加的接触面积略大于平板刀具，尽管凹槽刀具降低了金属丝变形的速度。在考虑周向键合机制的基础上，进一步讨论了引线键合的尺寸限制。对于引线键合，研究了焊盘厚度和硬度对界面变形的影响。尤其是焊盘厚度效应对焊盘与引线、焊盘与基板之间的界面变形和应力分布有很大影响。实验数据证实了这一点。此外，还尝试了微细金丝的固态微室温键合。超高真空条件和离子束激活的键合表面使这种键合成为可能。我们不能点燃粘结界面周围的弹性变形。对弹性应力分布的简化过程进行了模拟。

Process mechanism of wire bonding and fine lead bonding used in pakaging of microelectronics was studed. Deformation processes during these thermocompression bonding without ultrasonic vabration are simulated by a numerical model which is based on the finite element technique. The growth process of interfacial contact between wire surface and lead frame is also analyzed. If the contact interface is fixed then the lateral wire surface expands simultaneously with folding to the lead frame, producing the perimeter bond. On the other hand, if the contact interface can slide, the center of contact area largely expands and the lateral wire surface does not extends. It follows that the interfacial contact area tends to be fixed but not to slide when the perimeter bond is produced even if strong metallic bond is not achieved at the center. The wire reduction greater than 0.5 is required for ensuring the strong perimeter bond formation. This is supported by the experimental rsults.The interfacial contact area is governed mainly by the wire reduction. If the reduction is kept constant then the tool with a groove increases the contact area somewhat larger than the flat tool, although the groove tool decreases the rate of wire deformation. We further discuss the size limit of wire bonding, taking into account the perimeter bonding mechanism.With respect to lead bonding, effect of pad thickness and hardness on the interfacial deformation was investigated. In paticular, pad thickness effect largely change the interfacial deformation and the stress distribution on the interfaces between pad and lead andbetween pad and substrate. This was supported by experimental data.Moreover, solid state micro room temperature bonding of fine golid wire was tried. Ultra high vacume condition and the bonding surface activated by ion beam make this bonding possible. We cannot ignor the elastic deformation around bond interface. The reduceing process of elastic stress distribution was modeled.