Reliability of flexible thin-film embedded resistors and electrical characterization of thin-film embedded capacitors and inductors

The High Density Electronics Center (HiDEC) at the University of Arkansas is working with the Sheldahl MCM-L Consortium and Rensselaer Polytechnic Institute to develop low-cost embedded resistors, capacitors, and inductors in flexible polyimide film under a DARPA contract. The ability to remove discrete devices from the surface of PCB boards and MCMs and place them into a flexible film would be a breakthrough for MCM technology. Along with eventually using these films as free standing structures, comes advantages such as increased surface density, increased interconnect reliability, low weight, and low cost. The first part of this paper addresses the reliability of the resistor devices. This preliminary evaluation is focused on the processing of films consisting of polyimide layered with CrSi as a resistive material and copper for metallization. A test vehicle incorporating a full range of standard resistor values, with characterization and reliability structures, was used in this evaluation. Temperature, voltage, and moisture sensitivities were determined through temperature/bias, temperature/humidity, and thermal shock stresses. The mechanical dependability was evaluated using thermal shock cycling, and the power handling capability was determined from power cycling stress and power dissipation tests. The second part of the paper discusses the development and processing techniques used to make flexible thin film passive capacitors and inductors. The test vehicle was designed using a range of standard values of capacitors, inductors, and tuned circuits. Electrical characterization of the flexible thin film devices was performed up to 1.8 GHz. The extracted model parameters for the capacitors and inductors are reported.