Micro-thermocompression Bonding Mechanism and Modeling for Electronics Devise Interconnection

研究了微电子封装用线键合和细铅键合的工艺机理。采用基于有限元技术的数值模型，模拟了热压键合过程中无超声振动的变形过程。分析了导线表面与引线框架界面接触的生长过程。如果接触界面是固定的，那么横向导线表面与折叠同时扩展到引线框架，产生周长键合。另一方面，如果接触界面可以滑动，则接触面积中心大大扩大，而侧丝面不延伸。由此可见，即使在中心处没有形成强金属键，当产生周界键时，界面接触面积也趋于固定而不滑动。为确保牢固的周长键合形成，要求线材减量大于0.5。这得到了实验结果的支持。界面接触面积主要受线材收缩量的控制。如果减小量保持不变，那么带凹槽的刀具增加的接触面积略大于平面刀具，尽管带凹槽的刀具降低了线材的变形率。我们进一步讨论了线键合的尺寸限制，考虑到周长键合机制。在铅键合方面，研究了焊垫厚度和硬度对界面变形的影响。其中，衬垫厚度效应在很大程度上改变了衬垫与引线、衬垫与衬底之间的界面变形和应力分布。这得到了实验数据的支持。此外，还对细金丝的室温固相微键合进行了试验。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。我们不能忽略粘接界面周围的弹性变形。模拟了弹性应力分布的减小过程。

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.