Creep modeling of precision adhesive joints in opto-electronic devices

光电子器件由附着在基板上的光学元件组成；将这些部件固定到基板上的最常见方法是使用粘合剂。在内外部应力的影响下，粘合剂容易发生蠕变和应力松弛，这可能会导致光学元件位置的微小扰动，从而随着时间的推移影响性能。光学机械设计需要考虑精密胶粘剂的这种寿命终结(EOL)行为。缺乏针对这些机制进行设计的预测性模型，导致了经验法则设计标准和材料选择过程。 胶粘剂在固化过程中可能会受到残余应力，例如由于光学元件、胶粘剂和基板之间的热膨胀系数(CTE)不匹配。外部应力是由重力和振动等力引起的。在光学器件中，外部应力通常是最终材料强度的一小部分，通常不需要考虑蠕变断裂。然而，这些设备对非常微小的位置变化非常敏感，因此即使是低应力也会影响设备性能。 有限元分析(FEA)是光学机械设计中的一种强有力的工具，非常适合于模拟复杂产品几何形状在上述载荷作用下的应力状态。在商业有限元分析软件中有几种标准的蠕变模型，如有限元分析软件，然而，尚不清楚它们是否适用于感兴趣的材料，或适用于低应力蠕变行为。 斯佩尔特教授和渥太华州立大学合作研究的重点是测量候选胶粘剂的蠕变特性，然后开发和评估用于有限元软件的胶粘剂蠕变模型，以预测光电胶接接头的蠕变。

Opto-electronic devices consist of optical elements attached to a substrate; the most common method of fixing these components to the substrate is by means of adhesives. Adhesives are susceptible to creep and stress relaxation under the influence of internal and external stresses, which may lead to subtle perturbation of the position of optical components, thereby affecting performance over time. Opto-mechanical design needs to account for this end of life (EOL) behavior of precision adhesive bonds. There is a lack of predictive model for designing against these mechanisms, leading to rule-of-thumb design criteria and material selection processes. Adhesives may be subjected to residual stresses during the curing process, e.g. due to mismatch in coefficient of thermal expansion (CTE) between the optical elements, adhesive, and the substrate. External stresses arise from forces such as gravity and vibration. In optical devices, the external stresses are typically a fraction of the ultimate material strength and normally creep rupture is not a concern. However, the devices are sensitive to very small changes in position, and therefore even low stress can affect device performance. Finite element analysis (FEA) is a powerful tool in opto-mechanical design, and ideal for modeling stress state due to the above loading for complex product geometry. There are several standard creep models incorporated in commercial FEA software such as ANSYS; however, it is not clear they are applicable to the materials of interest, or to low stress creep behavior. The focus of the proposed collaborative research between Professor Spelt and JDSU Ottawa is to measure the creep properties of candidate adhesives and then develop and evaluate adhesive creep models to be used in FEA software for the prediction of creep in opto-electronic adhesive joints.