Liew Li-Anne, Read David T, Martin May L, Christenson Todd R, Geaney John T
National Institute of Standards and Technology, Applied Chemicals and Materials Division, Boulder, CO 80305, United States of America.
HT Micro Analytical Inc., Albuquerque, NM 87109, United States of America.
Eng Res Express. 2021 Jun;3(2). doi: 10.1088/2631-8695/abfb10. Epub 2021 May 5.
Photolithographically defined thin film Au dots were used as micro fiducial markers for digital image correlation (DIC), to enable two-dimensional strain measurement of 200 m-thick LIGA (Lithographie, Galvanformung, Abformung) nickel alloys. Due to the sensitivity of electrodeposited films' microstructure and properties on the processing conditions, characterization of LIGA mechanical properties continues to be necessary for microsystems commercialization. DIC offers advantages over laser-based strain measurement techniques but creating suitable speckle patterns on specimens with dimensions under a millimeter is challenging. The material surface roughness itself is often used as the speckle pattern, or micro- or nanoparticles are applied to the surface. But for materials with highly polished surfaces, such as commercial LIGA alloys, the surface roughness is not always suitable, while application of particles still poses technical challenges in uniformity and reproducibility. We fabricated freestanding tensile specimens, with gauge sections 700 m wide × 3 mm long × 200 m thick, from electrodeposited Ni-10% Co using a commercial LIGA process, and conducted microtensile tests at strain rate 0.001 s. Designing and fabricating arrays of randomly oriented 1.5 m-thick Au dots on the specimens provided a suitable way to obtain full-field surface strains over the entire gauge lengths and was reproducible from one specimen to another. Microfabricated fiducial markers therefore can be a useful surface-preparation approach for investigating micromechanical behavior, particularly plasticity and fracture, of LIGA films using DIC.
光刻定义的薄膜金点被用作数字图像相关（DIC）的微基准标记，以实现对200微米厚的LIGA（光刻、电铸、注塑）镍合金进行二维应变测量。由于电沉积膜的微观结构和性能对加工条件敏感，因此对于微系统商业化而言，继续表征LIGA的机械性能仍然很有必要。与基于激光的应变测量技术相比，DIC具有优势，但在尺寸小于一毫米的试样上创建合适的散斑图案具有挑战性。材料表面粗糙度本身通常用作散斑图案，或者将微米或纳米颗粒施加到表面上。但是对于具有高度抛光表面的材料，例如商用LIGA合金，表面粗糙度并不总是合适的，而颗粒的施加在均匀性和可重复性方面仍然存在技术挑战。我们使用商用LIGA工艺，由电沉积的Ni-10%Co制备了标距段为700微米宽×3毫米长×200微米厚的独立拉伸试样，并在应变率为0.001 s的条件下进行了微拉伸试验。在试样上设计并制造随机取向的1.5微米厚金点阵列，为在整个标距长度上获得全场表面应变提供了一种合适的方法，并且从一个试样到另一个试样具有可重复性。因此，微制造的基准标记可以成为一种有用的表面制备方法，用于使用DIC研究LIGA薄膜的微观力学行为，特别是塑性和断裂行为。
