**2. Micromachining techniques in electronics applications**

#### **2.1 Overview of micromachining techniques**

Mechanical micromachining techniques, such as micromilling, micro–Electrical Discharge Machining (EDM), and laser micromachining, are indispensable tools in the creation of miniaturized electronic components. These techniques offer precise material removal and intricate feature generation, making them essential for fabricating compact and high-performance devices. Micro milling involves the use of rotating cutting tools to remove material from a work piece, creating intricate geometries with high precision. This technique is instrumental in the creation of miniaturized electronic components due to its accuracy, repeatability, and versatility in handling various materials. Micro milling enables the production of micro-scale features such as grooves, channels, and complex 3D structures. These structures are critical in microelectronics, MEMS devices, and micro-optics. Micromilling's role in miniaturized electronic components extends to applications like microfluidics, where precisely machined channels facilitate controlled fluid flow for lab-on-a-chip systems Câmara et al. [39]. Micro Electrical Discharge Machining (EDM) employs controlled sparks between an electrode and the workpiece to erode material and create intricate shapes. This non-contact process is pivotal in generating micro-scale features that are challenging to achieve with conventional machining methods. Micro EDM is used to fabricate micro-scale molds, tooling, and dies. These components play a crucial role in micro-injection molding for the mass production of microfluidic devices, micro-optics, and precision electronic connectors. The technique's ability to work with electrically conductive materials allows the production of miniaturized parts with high accuracy Kumar et al. [40]. Laser micromachining employs high-energy laser pulses to ablate or melt material, allowing the creation of intricate patterns with minimal heat-affected zones. This non-contact technique is versatile and suitable for various materials, including ceramics, metals, and polymers. Laser micromachining role in miniaturized electronics spans micro-via drilling in printed circuit boards (PCBs), creation of micro-optical components, and patterning for flexible electronics. Its precision and non-contact nature ensure minimal mechanical stress on delicate structures, making it an ideal choice for manufacturing micro-scale electronic components Gattass Rafael et al. [41].

*Micromachining and Its Applications for Electronics DOI: http://dx.doi.org/10.5772/intechopen.113892*

## **2.2 Micro milling, principle and process**

## *2.2.1 Micro milling*

Micro milling is a versatile micro-cutting process for producing micro-level components in small and medium quantities. CNC controllers allow for precise control of the cutting tool, while CAD/CAM software is used to generate the tool paths necessary to machine complex microstructures. The size, geometry, and composition of micro tools are all important factors in micro milling. The size of the tool determines the minimum feature size that can be machined. The geometry of the tool affects the cutting forces, surface finish, and tool wear. The composition of the tool affects the tool wear resistance and toughness. Commercially micro milling tools ranging from 25 to 1000 μm are available. A typical micro milling machine has got ultra-high-speed low run-out spindles for achieving acceptable machining rates. These spindles being temperature-controlled result in lower thermal errors and better surface finish. These machines use polymer concrete in place of cast iron for achieving high dynamic stiffness as well as submicron resolutions glass scales for better control and minimum motion errors (**Figure 1**). The machining of THz

#### **Figure 1.**

*(a) Kern Micro milling, (b) different systems of micro milling machine, (c) polymeric concrete construction, and (d) centring microscope.*


#### **Table 1.**

*Features of a typical Micro milling machine.*

waveguide geometries requires a very high level of geometrical tolerances and surface quality which can only be achieved through micro-milling [4, 5]. The generated topography of the micro-milled surface inside the waveguide is mainly influenced by the tool, machining parameters, and strategy of cutting. Hence micro-milling represents a suitable technique to manufacture THz waveguide components. **Table 1** shows a typical micro milling machine, and its features. This machine was extensively used to make waveguides at W band of frequency where the waveguide size is 2.54 × 1.27 mm within linear tolerances of 10 μm, surface roughness of the order of 150nmRa and flatness of 0.3 μm. when this frequent raises to 1THz the waveguide size becomes 0.245 × 0.127 mm within linear tolerances of 1–2 μm, surface roughness of 40–50 nmRa and flatness also of the order of half the wavelength at such a higher frequency Bhardwaj et al. [1, 42–46].

#### *2.2.2 Cutting mechanisms*

The material removal principles and process details of the micro-milling cutter are different from macro milling, and it can be characterized by small uncut chip thickness (UCT), specific cutting energy, tool run out noticeable size effect, and elastic recovery after machining. In micro-milling, the UCT is of the scale of the cutting-edge radius or the tool nose radius, also called the size effect (**Figure 2**) [11].

The unusual increase in the specific cutting energy as the depth of cut decreases below a critical value during micro-cutting operations using a geometrically defined tool is referred to as the size effect. It is among the principal issues in micro-milling which dominate cutting physics [12–17]. Three aspects of size-effect are as follows:

*Micromachining and Its Applications for Electronics DOI: http://dx.doi.org/10.5772/intechopen.113892*

**Figure 2.**

*Illustration showing the size effect in macro and micro-cutting [11].*


As shown in **Figure 3a**–**c**, whether an elastic deformation or recovery of the machined surface occurs in the chip formation stage during micro milling depends on the chip thickness and the material of the workpiece. If the chip thickness is small enough, the workpiece material will only undergo elastic deformation and will fully recover to its original shape after the cutting tool passes. This is typically the case in the elastic stage of micro milling, where the chip thickness is in the order of a nanometer. If the chip thickness is larger than the critical chip thickness, the workpiece material will undergo plastic deformation and will not fully recover to its original shape after the cutting tool passes. However, some recovery may still occur, especially if the workpiece material is soft and ductile. This is typically the case in the elastic-plastic stage of

#### **Figure 3.**

*Material removal in orthogonal micro-milling processes: (a) elastic deformation, (b) mixed elastic-plastic deformation region, and (c) complete chip formation region in the orthogonal micro-cutting process.*

micro milling, where the chip thickness is in the order of a few micrometers to millimeters. Overall, it is important to note that there is no clear-cut boundary between elastic deformation and recovery of the machined surface during micro milling. The two phenomena are often intertwined and depend on a number of factors. However, a general rule of thumb is that the chip thickness and the material of the workpiece are the most important factors affecting the recovery of the machined surface [10, 13].

In the case of micro milling of THz waveguides, the chip thickness is typically very small, and the workpiece material is often a soft metal such as aluminum or copper. This suggests that elastic recovery of the machined surface is likely to be significant. However, more research is needed to quantify the exact amount of elastic recovery and to determine its impact on the performance of THz waveguides.

#### *2.2.3 Material removal mechanism in micro-milling*

In micro milling, the uncut chip thickness (UCT) initially increases from zero to a maximum value approximately equal to feed per tooth, and then decreases from feed per tooth to zero as shown in **Figure 4a**. In side milling, the UCT reduces from maximum to zero as shown in **Figure 4b**. The minimum uncut chip thickness (MUCT) is the smallest chip thickness that can be removed without causing plastic deformation of the workpiece material. The MUCT is based on the geometrical relationship at the stagnant point, which is the point at which the material deforms or flows with minimum deformation or kinematic energy [14]. The MUCT varies from 1/4 to 1/3 of the cutting-edge radius, depending on micro-milling conditions, micro mills (tools), and workpiece material classes [10]. Malekian et al. [15] predicted the MUCT for Aluminum alloy (Al6061) as hm = re(1 − cosβ), where β is the friction angle between the workpiece and rake face. Son et al. [17] predicted the MUCT for Al, Brass, and OFHC as hm = re(1 − cos(π /4 − β/2)).

The MUCT is an important parameter in micro milling, as it affects the material removal behavior, fluctuations in the cutting force, and stability of cutting forces. By understanding and controlling the MUCT, it is possible to improve the quality of the machined surface. The MUCT is influenced by a number of factors, including the geometry of the cutting tool, the material of the workpiece, and the micro-milling conditions. It is important to note that the MUCT is not a constant value, but rather varies depending on the specific micro-milling operation [18].
