Hitech’s 10 layer interconnection (ELIC) HDI pcb with electroless nickel immersion (ENIG) surface treatment which made of raw material FR4 370 HR, plug via-in-pad by resin and plate flat. ENIG becomes the most popular surface finish in the industry. It’s a double layer metallic coating, nickel acting as both a barrier to the copper and a surface to components are soldered. There is a layer of gold protects the nickel during storage. The advantages of ENIG high density boards are lead-free, flat surfaces, strong etc.