Fine line LTCC-structures by Direct Gravure Printing (DGP) method

Electrical thick film circuits for ceramic and LTCC-substrates have, up to now, been printed mainly with screen printing. In conventional screen printing technology, the printing accuracy limit is about 150 mum in high volume production. By using advanced thick film technologies such as photo-imageable pastes, more, accurate lines down to tens of mum can be produced. However, these processes are more complicated and costly compared to the direct printing processes. To overcome these limitations, a new printing process, Direct Gravure Printing (DGP), has been developed. In DGP the paste is printed directly onto the LTCC green sheet from a patterned gravure printing plate. The printing plates needed in the DGP processes are made by electro-depositing Nickel or moulding silicone polymer over a resist patterned flat plate. By using correct printing parameters, 100% transfer of the printing paste from the gravure grooves to the substrate can be obtained. The printed line width can be down to at least 25 mum with good line and especially edge sharpness. In this paper the DGP process is introduced. To demonstrate the capability of it, a simple LTCC microwave test structure with transmission lines was designed, manufactured and measured. The design consisted of lines and gaps down to 20 mum wide. The attenuation of a DGP processed 85 mum wide stripline was measured to be lower compared to a 185 mum wide screen printed one at frequencies below 14 GHz. At these frequencies, the conductor losses are the dominating ones, which indicates the high quality of the DGP printed transmission line.