Subtractive fabrication process

Solid Freeform Fabrication (SFF) technologies have in common the capability to build objects with comphcated 3D geometries, directly from Computer-Aided Design (CAD) files, without the necessity of tooling. SFF technologies also have in common the employment of an additive building process, in which a 3D object is built up by the repeated addition of layers of material. This is in contrast to more standard technologies which are characterized by the implementation of a subtractive fabrication process, e.g., CNC (Computer Numerical Control), where the 3D object is manufactured by calculated removal of material from a block of raw material. 

The process time depends on the complexity of the 3D microstructures therefore, it is commonly used for prototyping. An extensive review on stereolithography can be found in Reference 119. The latter method is a subtractive manufacturing process that uses a focused high-intensity laser beam to evaporate the material from the surface. Laser ablation is mostly used to fabricate microchannels in thermosetting polymers such as polyimide due to its physical properties. Microstructures of nanometer scale have been danonstrated, but the surface roughness and properties using laser... 

Unlike other subtractive machining processes, Generative Processes buUd parts by a layer-by-layer technique using form neutral substances like fluids, powders, foil-or wire-shaped materials by chemical and or physical reactions. In general the process, as shown in Fig. 79, results directly from a 3D model, which is sliced into thin cross-sections typically with a thickness of 0.1-0.4 mm. Depending on the kind of process, parts that may be difficult or even impossible to fabricate by conventional methods, can be produced out of polymers, metal, ceramic or composite materials [101]. A selection of RP-processes is described below, but due to the complexity of the processes readers are referred to the cited references. 

Fig. 19 (A) Background subtracted CVs on rGO/GC (al), graphite/GC (b 1) and GC electrode (cl) in 4 mM H2O2/PBS (0.1 M, pH 7), scan rate 50 mV s" (reprint with permission from ref. 78). (B) Electrochemical reduction of enzymatically produced hydroquinone (HQ) on the rGO/GC interface modified with anti-mouse IgG for the detection of mouse-IgG, revealed by interaction by anti-mouse IgG-HRP (reprint with permission from ref. 78). (C) Fabrication processes of the gold nanoparticle based graphene/chitosan bionanolabel with integrated HRP-modified carcinoembryonic antigen (HRP-anti-CEA) and measurements protocol, PB = Prussian Blue (reprint with permission from ref. 79).

Most priated circuit board (PCB) production uses the subtractive process (41). In the simplest version, a thin copper foil is laminated to a nonconductor, holes are fabricated, and the unwanted copper etched off. These siagle-sided boards do not require plating. Known as ptint-and-etch, this version is used for the most simple priated circuit boards. 

TFML interconnections are fabricated using a repetitional sequence of thin film processes to deposit and pattern the conductor and dielectric layers. A variety of individual processes and process sequences, including both additive and subtractive approaches, have been used. The subtractive process sequence shown in Figure 2 has been used at Honeywell for a variety of patterns (8 ) and is offered as an example. 

Microfabrication has emerged from microelectronics manufacturing and is using its proven processes and process sequences. Additionally, specific methods have been developed to fabricate mechanical, electrical, optical, or sensor structures, which are characteristics of microfabrication. In order to stay within the scope of this book, only top-down methods, that is, the manufacture of smaller structures with higher functionality from larger structures by the use of subtractive methods, will be discussed. Bottom-up methods, which create larger structures by ordered arrangement of small units (molecules, nanoparticles), are still in their infancy and mainly employed for biosensors. 

FIGURE 5.4.5 Process flow for the fabrication of polymer TFTs by inkjet printing. Steps 1 to 4 use a subtractive process for patterning of materials. The subtractive process prints an etch mask on a previously deposited film. Step 5 illustrates the additive inkjet printing process. The additive process simultaneously deposits and patterns the semiconductor material PQT-... 

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