Characterisation of embedded filters in advanced printed wiring boards

This paper describes the design, fabrication and test of a range of third order LC low pass Butterworth filters in MCM-L technology. There are seven filters in the range, each consisting of two inductors and one capacitor with cut-off frequencies ranging from 10 to 540 MHz. Inductance values range from 9.9 to 530 nH, and capacitance values vary from 14 to 723 pF. Air-core (by which we mean no magnetic material) spiral winding structures are designed to provide the inductive functions. A new FR4 type laminate material, which was developed by ISOLA, is used to form integrated parallel plate capacitor structures. The range of filters was successfully manufactured and electrically characterised using a HP4195A impedance analyser. Some environmental testing was also carried out on the embedded filters. These included thermal shock and humidity testing. There were no obvious changes in device performance after the environmental tests.