## 2 Experimental Details  
### Laser-Induced Chemical Liquid Phase Deposition  
Electroless plating, known as chemical or auto-catalytic plating, is a non-galvanic plating method that involves several simultaneous reactions in a chemical solution, which occur without external electrical power. Unlike electro-plating, it can be applied to various substrates, such as glass or ceramics [19; 20]. For obtaining good electroless plating, the selection of deposition solution and process environment is very important.  
A commonly used electroless copper deposition method is based on a reduction reaction of copper ions. The main chemical reactions are shown in Equation (1) [21]:  
\[\left[\mathrm{Cu(L)}_{2}\right]^{2-}+2\mathrm{HCOH}+4\mathrm{OH}^{-}+\mathrm{ Energy}\rightarrow\mathrm{Cu}^{0}+2\mathrm{L}^{2-}+\mathrm{H}_{2}+\mathrm{H}_{2} \mathrm{O}+2\mathrm{HCOO}^{-} \tag{1}\]As can be seen from Equation (1), the electroless deposition reaction consists of four main elements: copper ions, ligand (L), reducing agent (HCOH), and OH-ions. Heat at 60 to 90 degrees Celsius is applied to this solution for several minutes or more to activate the chemical reduction reaction. However, in heating the entire solution in this way, it is impossible to form a selective circuit pattern unless an additional process is added. Therefore, local thermal energy can be applied to an arbitrary pattern by using a laser, thereby enabling the activation of a selective reduction reaction of copper ions within a short time [22].  
Figure 1 is a schematic diagram of the LCLD process used in this study. When a near-infrared laser with a wavelength of 1064 nm is irradiated on the upper surface of the glass, it reacts with the deposition solution on the lower surface after passing through the material because of the high transmittance of glass. Accordingly, the temperature of the deposition solution in the selective area irradiated with the laser increases instantaneously, thereby activating the reduction reaction. As a result, a very thin layer of copper begins to form. Additionally, it is possible to obtain a dense copper deposition layer by continuously irradiating a laser to apply thermal energy. At this time, if the energy is excessively high, the process is performed while destroying the thinly deposited copper, so the deposition layer is not formed in the middle part of the laser beam, and the deposition layer remains only in the peripheral part. Therefore, the process was mainly carried out in previous studies with very low energy and feed rates [12; 18]. However, even under high laser power conditions, a faster and more stable process will be possible if a condition that can activate the reduction reaction by the laser while diversifying the laser irradiation pattern to minimize direct damage to the copper deposition layer.  
Therefore, in this study, an LCLD solution was prepared based on a common electroless plating solution, as shown in Table 1. The possibility of process speed and quality improvement through various laser pattern changes was tested using this approach. CuSO4, which is generally readily available and has excellent reactivity, was used as the main reagent for supplying copper ions. As the ligand, ethylenediaminetetraacetic acid  
Figure 1: Principles of the LCLD process: (**1**) Laser irradiates from the top; (**2**) The copper ion reduction reaction occurs after heating up solution; (**3**) A thin layer of copper is deposited on the bottom of the glass; (**4**) The solution and the deposited Cu absorbs the laser energy and heats up the near area; (**5**) Dense copper layer is deposited on the bottom of the glass.  
(C\({}_{10}\)H\({}_{16}\)N\({}_{2}\)O\({}_{8}\); EDTA) was used, and formaldehyde was chosen as the reducing agent. For a stable chemical reaction, the pH was maintained at 12.6 during the process using NaOH, and a small amount of 2.2 dipyridyl reagent was added.