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64 The PCB Magazine • September 2017 Introduction While 3D printing, as stereolithography (SLA), has been around since the early 1980s, it is has evolved considerably into many forms. For the purposes of this paper, fused filament deposition (FFD), also known as fused deposi- tion modeling (FDM), will be considered. Only recently has FDM printing been joined by elec- tronic printing to create 3D printed electron- ics. With this evolution in 3D printing, print- ed circuit structures (PCSs) can possess distinct advantages over printed circuit boards (PCBs). Many components that are present on a PCB can be integrated into a PCS. It has been shown that PCSs can contain fully embedded circu- ity such as antennas [1,2] , lumped components [3] , and even connectors [4] . Instead of creating a PCB to attach to an object, it would be possible to print the object with the circuitry as an inte- grated part of it. This printing method is made possible using a direct digital manufacturing (DDM) machine that combines the use of multiple tool heads in- cluding a micro-dispensing pump, a heated ex- trusion head, a pick-and-place head, and a mi- cro-milling, drilling, and polishing head. While PCBs require the use of many machines and re- quire masking, PCSs can be completely auto- mated, as total fabrication is done in-situ on a single machine [5,6] . Although PCSs do have ad- vantages, there are still several obstacles to over- come, namely speed of fabrication and strength of final parts. Fabrication Speeds FDM-style 3D printing is notorious for be- ing slow. This is mainly due to the low volu- metric extrusion rates of conventional desktop 3D printers. There are many factors that deter- mine extrusion rate. Some of these include noz- zle diameter, nozzle temperature, bed tempera- ture, X-Y movement speed, material, and even the extrusion motor. While these have an effect on the total amount of filament being extruded, the nozzle diameter is the main determiner of extrusion rate. Layer height, extrusion widths, and print speeds are all based on the nozzle di- ameter, therefore this is the facet of the printing process that stands to generate the most bene- fits from improving. The standard printing nozzle has a 0.4 mm inside diameter. This allows for print speeds of up to 80−100 mm/s, depending on machine and desired print quality. Nozzle size can be in- creased, however, while this can shorten the overall print time, a decrease in quality will be seen. These decreases in quality can be things such as a rougher surface finish, rounded cor- ners, and incorrect dimensions. Larger diame- ter nozzles are also limited when printing small objects as the small features can be problematic. While the quality-related downsides of select- ing a large diameter nozzle are not attractive, they can be dealt with. A method of printing called "spaghetti" printing was developed to greatly increase ex- trusion rates and decrease print times. This pro- 3D PRINTED ELECTRONICS FOR PRINTED CIRCUIT STRUCTURES Figure 1: ASTM D638 Type V tensile specimen, 0° infill. Figure 2: ASTM D638 Type V tensile specimen, 90° infill.