# Fabrication of a Conductive Pattern on a Photo-Polymerized Structure Using Direct Laser Sintering
###### Abstract  
Three-dimensional (3D)-printed electronic technology is considered to have great potential as it can be utilized to make electronic products with complex 3D shapes. In this study, based on a 3D printer with single UV laser equipment, we continuously performed photo-polymerization (PP) and selective metal powder sintering to fabricate a conductive pattern. For this, 3D structures were printed at a low energy using a 355 nm DPSS laser with a galvanometer scanner, which are widely used in PP-type 3D printing, and then the selective sintering of metal powders was performed with a high energy. In order to obtain a high-conductivity pattern by laser sintering, a circuit pattern that could actually be operated was fabricated by experimenting with various condition changes from mixing the metal composite resin to the laser process. As a result, it was found that the optimal result was to irradiate a 0.8 W UV laser with a beam spot size of 50 \(\upmu\)m to 50 vol\(\%\) aluminum composite resin. At this time, an optimal conductive pattern with a resistance of 0.33 \(\Omega\)-cm\({}^{-1}\) was obtained by setting the pulse repetition rate, scan path interval, and scanning speed to 90 kHz, 10 \(\upmu\)m, and 50 mm/s, respectively. This suggested process may be of great help in the manufacturing of practical 3D sensors or functional products in the future. 3D printing; direct conductive patterning; laser sintering; photo-polymerization; metal 3D printing +
Footnote †: journal: Applied Sciences  
has been carried out in several studies using various methods such as local heat treatments. However, in this case, if the bonding force between the 3D-printed structure and the conductive ink is not sufficient, it may easily be peeled off by an external force or heat during the process [6; 7; 8]. Unlike conductive ink, if the 3D printing material itself has conductivity, it can have great advantages because it can increase the degree of freedom of circuit pattern shapes and adhesion to structures. The most widely known method is to utilize conductive filaments based on material extrusion (ME) systems. Conductive filaments are mainly manufactured based on materials with a high conductivity such as carbon fibers or metal fibers; thus, they can greatly contribute not only to imparting conductivity but also to improving structural strength. However, most of the conductive filaments that have been introduced so far have a relatively high electrical resistance (several \(\mathrm{k\Omega\cdot cm^{-1}}\)) because they must contain a certain amount of a binder for structural stability, so they are not suitable for practical circuit component manufacturing [9]. Similarly, there was a case where a single-walled carbon nanotube (CNT) was mixed with a photo-curable resin and applied to a photo-polymerization (PP) system [10]. However, if the CNT content was increased, it was easily agglomerated and the photo-curability was greatly reduced, so there was a limit on increasing the conductivity as with the ME method. In addition, there have been cases where copper wires were directly mounted onto a 3D-printed structure to achieve a very high conductivity, but because it was impossible to apply it to structurally complex shapes, there was a limitation on its application to the actual production of parts [11; 12]. Due to these limitations, many studies have attempted to fabricate conductive circuit components using chemical wet deposition methods. By using the deposition process, a high-purity metal material can be directly formed so that a high-conductivity pattern can be obtained regardless of the shape [13]. In particular, various studies have been conducted on metal seed formations and selective deposition processes based on three-dimensional molded interconnection device (3D-MID) technology, which is widely used in the existing commercial injection process.