Key being used to identify & allow door access and engine start has been developed to the possibility of integration into the cellular phone with the help of increased electronics and wireless communication skill. But even all electrical function can replace conventional ones, it still need mechanical key blade for the case of emergency situation. From that view, card type key would be more widely used in the future in the market due to the existence of emergency key blade. Making all required function work in slim size thickness is important success criteria for more widely use by increasing convenience of customer in carrying in the wallet. To overcome height limitation, integrated circuit type with a PLL IC/MCU, PCB coil antenna with thin battery was applied. Assessment of the various production methodology was done and RTM (resin transfer molding) method was selected. To make around 3mm thickness card type key, other conventional way that have been used up to now was not appropriate to overcome the constraints of the product to meet the functional requirement. This study shows main factors to be considered in product development of card type key for the case of RTM(Resin Transfer Molding) application and also important test result required for product development verification & validation. To fix complicated mold parameter for best condition, DOE (Design of Experiment) method was applied to reduce repetitive back& forth efforts. Making thickness be reduced from above 6 mm to 3 mm thickness level was possible by applying RTM method and this development result shows the possibility of making more slim cardkey in case challenged more.