# Precision Manufacturing of Patterned Beryllium Bronze Leaf Springs via Chemical Etching
## 1 Introduction  
During the past two decades, a variety of micro-electromechanical systems (MEMS) have been fabricated through the rapid development of precision and ultra-precision machining technologies. [PERSON] et al. (1999) described two microthermal shear-stress sensors, in which high aspect ratio cavities of (200 \(\times\) 250) \(\upmu\)m (2) \(\times\) 400 \(\upmu\)m were fabricated using bulk silicon substrate etching and anodic bonding technology [1]. [PERSON] et al. (2013) developed micro hot-film shear-stress sensors using surface micromachining techniques and fabricated a micro silicon-nitride diaphragm and polycrystalline silicon heat-sensing element [2]. Therefore, micro/nano measurement equipment is required to assess the fabricating quality of micro devices. The leaf spring is often used as a key component of high-precision measuring instruments, or micro-actuators, when an elastic and recoverable micromotion is required, such as the cantilever beam used in atomic force microscopy (AFM). [PERSON] et al. (2010) and [PERSON] et al. (2014, 2016 and 2016) developed several probing systems for micro/nano CMMs [3, 4, 5]. Leaf springs are used to transfer the 3D displacements of the ball tip into the motions of a mirror in a vertical translation and horizontal rotation. The performance of the leaf spring directly determines the repeatability, stiffness and isotropy of the probe. Because the beryllium bronze sheet used as an elastic membrane has better repeatability and stiffness, it is a more suitable material for the fabrication of patterned leaf springs. The flatness and edge uniformity of a leaf springs mainly affect the probe's repeatability. The higher the flatness and uniformity, the better the repeatability. The size precision of a leaf springs mainly affects the probe's stiffness and isotropy. According to the Equation (1) or Equation (2) in Reference [3], we can obtain that the relative change of the stiffness or anisotropy is less than 0.5% when the four V-shaped leaf spring's width have an error of 10 \(\upmu\)m. Therefore, the target manufacturing accuracy of a leaf springs can be controlled in \(\pm\)10 \(\upmu\)m.  
A common method for fabricating beryllium bronze leaf springs is wire-electrode discharge machining (wire-EDM), which produces a better edge quality than laser cutting. However, we found that wire-EDM still cannot satisfy the high-precision manufacturing requirements of a leaf spring owing to the following disadvantages: (1) poor edge uniformity and a large offset, (2) processing heat and anisotropic stress causing a deformation of the fabricated leaf spring, (3) difficulty in fabricating leaf springs with complex patterns and (4) a high cost. Other methods can be used to process beryllium bronze. For example, [PERSON] et al. (2002) described a lithography technology for microstructure fabrication and fabricated micro-capillaries and a micro-valve [6]. [PERSON] et al. (2001) described an electrotyping technology, which they used to develop a copper lining for RF (Radio frequency) cavity sputtering [7]. [PERSON] et al. (2001) summarized the fabrication of 3D micro-optical resist structures (e.g., micro-lens arrays and blazed Fresnel lens structures) using hard optical and optoelectronic materials through ion beam and plasma jet etching technology [8]. Finally, [PERSON] et al. (2014) fabricated tetragonal tungsten bronze using RF magnetron sputtering [9]. Although high precision and a small size can be achieved through these methods, their practicality for the fabrication of leaf springs remains limited owing to high costs, low efficiency and difficult operations. Aiming at the shortcomings of above methods, a chemical etching method that can be used to fabricate a beryllium-bronze based leaf spring was adopted for this study. This method is based on the chemical reaction of copper (Cu) with sodium persulfate (Na\({}_{2}\)S\({}_{2}\)O\({}_{8}\), 2017, Taishan Chemical Factory Co., Ltd., Taishan, China).