Packaging Substrate Applications of Ultra Low CTE Polyimide

We succeeded in development of a thick laminate polyimide sheet composed by ultra low CTE polyimide films which showed low CTE comparable to that of silicon. A key issue in realizing a reliable through-hole interconnection in the package substrate is a CTE gap in Z-direction between an ultra low CTE polyimide sheet (100ppm/K) and copper (17ppm/K). In this study, reliability in double-sided PCB test pieces fabricated on the sheet was evaluated by thermal cycling test. The ultra low CTE polyimide sheet showed an adequate reliability after 5000 thermal cycles between -55 degrees C and 125 degrees C. This result shows the possibility of the use of the sheet as a core material for advanced package substrates.