# Precision Manufacturing of Patterned Beryllium Bronze Leaf Springs via Chemical Etching
## 2 Principle and Process Flow
### Process Flow  
The process flow of this method consists of eight steps, namely, the pattern design, mask printing, pretreatment, pasting of photo-sensory membranes, exposure, development, etching and mold unloading, the details of which are as follows. (1) Pattern design. According to the actual demand of a particular type of measuring equipment, it is necessary to design the pattern of the leaf springs first and to then analyze and optimize the structural parameters of the pattern. [PERSON] et al. (2014) designed a four V-shaped suspending leaf spring pattern (shown in Figure 1) for their 3D contact-scanning probe [3,15]. (2) Mask printing. A high-precision mask is required to copy the designed pattern onto the beryllium bronze sheet. As a necessary intermediary, the precision of the mask directly determines the quality of the leaf springs. A professional film-printer of greater than 600 \(\times\) 600 dot per inch (DPI) was used to print the pattern onto the unsmooth surface of a piece of film. When printing, a part of the pattern should be transparent to allow ultraviolet light to pass through and the remaining part should be black. A printed mask is shown in Figure 2.  
(3) Pretreatment. Beryllium bronze is oxidized when exposed in air for a long period of time and forms an oxidation film on the surface. It is difficult for the oxidation film to be corroded by the solution of Na\({}_{2}\)S\({}_{2}\)O\({}_{8}\). Therefore, we have to clear the oxidation film using the following pretreatment procedures: select a piece of beryllium bronze with an appropriate size, polish it on both sides using fine waterproof abrasive paper (7000 #) with a griff size of far less than 0.5 \(\upmu\)m and wipe off the powders produced on the surface. We then need to place the polished beryllium bronze sheet into a solution (SanNy 3111,  
Figure 1: Four V-shaped leaf springs. 2017, Dunhua, Inc., Shenzhen, China) for approximately 30 s to clean the oxidation film thoroughly. Finally, we need to rinse the beryllium bronze sheet using clean water and dry it. Images of an original beryllium bronze sheet and polished (using SanNy 3111) and cleaned sheets, are shown in Figure 3, respectively. (4) Pasting photo-sensory membrane (No.2138, 2017, Hemera, Inc., Shenzhen, China) we used was composed of a polyester, photoresist and polyethylene layers in sequence, as shown in Figure 4. The polyester layer is used to support and protect the photosensitive layer from being diffused when exposed to oxygen, which can destroy the light sensitivity of the photoresist. The polyethylene layer is used to cover the other side of the photosensitive layer to prevent it from being polluted by dust or other types of particles. The photoresist layer is the main body of the photosensitive membrane and is mostly made of a negative photosensitive material. The polyethylene layer needs to be torn off before attaching the photosensitive membrane onto the beryllium bronze sheet. The total thickness of the polyester layer and photoresist layer is 38 \(\upmu\)m. Both sides of the beryllium bronze sheet need to be pasted with a photosensitive membrane and the photoresist layer should be attached to the sheet evenly and tightly with no bubbles. To affix the photoresist to the beryllium bronze sheet firmly, the beryllium bronze sheet with the photosensitive membrane needs to be pressed by two flat glasses and heated by a hot air blower. Figure 5 shows a beryllium bronze sheet pasted using a photo-sensory membrane. (5) Exposure. This process is used to place the prepared mask on the smooth surface of a beryllium bronze sheet with a photosensitive membrane and to make sure that the side with the printed pattern of the mask film is close to the beryllium bronze sheet. Both the beryllium bronze sheet and the mask film are clamped using two flat glasses. The next step is to expose the beryllium bronze sheet to a 365 nm  
Figure 3: Images of beryllium bronze sheet: (**a**) original, (**b**) polished, (**c**) and cleaned. Figure 2: Printed mask.