A novel production process for 10 μm microvias

This work investigates the capability of drilling and metallization of microvias of diameter less than 10 µm with aspect ratios of 1-10, using a fully additive process. The microvia has been produced using a sequential build up layer of urethane through which the via has been produced. The urethane layer is applied using spin-coating. Current process setting produces a 15 µm layer thickness. For thicker urethane, multiple layers are applied. Drilling of the via-hole through is made using 266 nm UV laser. The metallisation of the via-hole was made using a process called Covalent Bonded Metallisation (CBM). This process modifies the urethane surface by a grafting process where polymers are covalently bonded to the surface where metallisation is desired. A roughly 5 µm thin film of the used grafting solution is applied to the substrate surface. The grafting process is initiated by laser which draws the patterns where copper is desired. After laser drawing, the substrate is cleaned with deionized water. Next, the substrate is through a commercial chemical-copper process which builds copper only at the laser initiated patterns. Copper thicknesses of 1 µm is easily achievable. To increase the copper thickness, the substrate may be run into thick building chemical-copper process to achieve thicknesses up to 8 µm