Influence of Cyclic Bending Tests on the Flexible Substrates’ Reliability

The paper deals with the reliability of the flexible substrates Pyralux® manufactured by DuPontTM. For this reason, the apparatus for cyclic bending tests of flexible substrates has been developed and fabricated. The main advantage of the developed cyclic bending test apparatus lies in the in situ measurement of the tested flexibles substrates’ resistivity during the bending tests. The testing as well as the resistivity measurement is controlled and processed by Matlab. This approach allows determining the specific number of cycles when the defects in the material are detectable via resistance changes. During the experimental part of this work, four kinds of all-polyimide flexible copper-clad laminates with different thicknesses of the copper (18, 25, 35, and 70 µm) have been tested and analyzed. The material defects in the form of cracks caused by the bending tests have been also proved by microscopic analysis. Based on the experiments described in this paper, the fatigue life of two kinds of materials has been determined.